[marc] Re: Soldering Tips and Tricks from Smith-Kettlewell
- From: <jerry.berrier@xxxxxxxxx>
- To: <marc@xxxxxxxxxxxxx>
- Date: Sun, 14 Jan 2018 12:25:39 -0500
Not sure how many of these attachments will get through, but let's see what
happens.
-----Original Message-----
From: marc-bounce@xxxxxxxxxxxxx [mailto:marc-bounce@xxxxxxxxxxxxx] On Behalf
Of bobdruk
Sent: Sunday, January 14, 2018 12:18 PM
To: marc@xxxxxxxxxxxxx
Subject: [marc] Re: Soldering Tips and Tricks from Smith-Kettlewell
Jerry
Unable to open this link
Can you send it in any other form
Bob
Sent from my iPhone
On Jan 14, 2018, at 4:16 AM, <jerry.berrier@xxxxxxxxx>
<jerry.berrier@xxxxxxxxx> wrote:
I ran across some information in my old computer files that you may find
interesting. Here's a Dropbox link to it.
It includes lots of suggestion for soldering.
https://www.dropbox.com/s/zuufagc2rsuabfc/smithkettle.zip?dl=0
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***
This is a service of the Middlesex Amateur Radio Club; Newton Massachusetts.
Please join us every Thursday evening at 7PM EST for our weekly net. We can
be found at 147.360 MHz with no PL tone, or on Echolink at call sign W1LJO-R
node number 462341.
To post a message to this listserv please address it to MARC@xxxxxxxxxxxxx
***
SOLDERING KINKS
Dale E. Heltzer of St. Paul, MN, writes:
"One feature of the small-diameter solder compatible with the JA3TBW
solder guide (SKTF, Spring 1983) is that it easily kinks. As a remedy for
this problem, I wind it in empty dental-floss containers, always keeping
two to three inches protruding so as to allow pulling it out.
"There are two types of floss containers that I am aware of: the
relatively flat packs, and the tall types which contain cylindrical
bobbins. I find that the tall version is better suited to holding long
pieces of solder; the long shaft on which it is wound gives less
opportunity for 'cross-overs' while winding"
The editor suggests that you file a notch in the lid of the container,
so that the solder can be drawn out with a minimum of tension. When
flux-core solder is stretched, the tubular structure of the solder
elongates, but the flux core, which is brittle, does not. Thus, when
solder is put under tension, it is possible to create unintentional voids
in the flux.
A notch in the lid of the floss container takes care of this problem of
stretching the solder, and it's a pretty good idea. Thank you, Mr.
Heltzer.
Jean Le Borgne sent me a couple of his latest-model feeders for the
tubular solder guide (SKTF, Winter 1986). Now of 1/14-inch aluminum and
about 2 inches long, it's pretty slick. It has a No. 2-56 setscrew near
the top to clamp onto the solder, and it slides nicely onto the
stainless-steel tube above the collar. (A 2-56 nut is threaded all the way
to the head to make a poor man's thumbscrew.) Its purpose is to feed
solder without kinking as it enters the tube. He sets the sleeve so that
he can make three or four connections before loosening the setscrew for
"reloading."
He also modified the solder guide. With a file, he filed away a portion
of the tube at the bottom so as to expose the solder on one side. In this
way, the solder can more directly be involved with the top of the iron. He
turned the collar so that its setscrew is on the side of this filed-away
portion.
Jean also suggests that the resultant pointed guide is the answer to a
maiden's prayer for soldering PL-259 coax connectors. The pointed end of
the tub is placed in the holes in the side for soldering the shield to the
shell.
Mr. Le Borgne is generous enough to make these Cadillac solder guides
available to readers. For now, he says they are free. (I, being a normal
greed-head, would take you for 4 or 5 dollars.) To get your solder guide,
write to: Jean Le Borgne, 12022 Celine Street, El Monte, CA 91732.
Thanks, Jean.
Everybody's concerned with kinks in their solder. What kind of kinky
crowd have I got out there? (As they laugh in Morse Code telegraphy, HI
HI.)
- END -
[from the Smith-Kettlewell Technical File
Vol. 1, No. 1, 1980]
SOLDERING (Part I)
by Bill Gerrey
For the last three years, I have intended to write a book on soldering
and the techniques used by blind technicians. There are as many different
soldering systems as there are fabrication processes and materials. The
compilation of such material would be a monumental undertaking.
I justify this preliminary discussion by proposing that "we have to
start somewhere." Arbitrarily, that "somewhere" will be with my own
experience in soldering. You can rest assured that this is just the
beginning of a series of articles regarding soldering as it is being done
by blind and visually impaired people. (At some point, we will be
including information on soldering under a closed circuit TV system.) If
you don't like this article, wait for the next one.
I will not burden you with a long bibliography; there are very few
discussions of soldering that are high on science and low on popular myth.
One such reference is SOLDERING, ITS FUNDAMENTALS AND USAGE
by Kester Solder Co., Copyright 1961. This 84 page booklet describes the
fundamental scientific principles and the practical applications in a
readable style.
Solder does not just "stick" or adhere to the metals being soldered; it
alloys with them. Liquid solder is actually a solvent which forms a
solution with the surface metals being bonded. With the solder acting as a
solvent, the surface metal need not melt for this chemical interaction to
occur.
The solder of interest to us is a tin-lead alloy which melts at a much
lower temperature than do tin or lead individually. If this alloy is
composed of 63 per cent tin and 37 per cent lead, (said to be the "eutectic
alloy"), the melting point (183 dg. C, 361 dg. F) is the lowest possible
with any tin-lead combination. The eutectic alloy is unique in yet another
way--there is no "plastic" phase. The eutectic alloy turns directly into a
liquid when brought to the eutectic temperature, and reverts back to a
solid when allowed to cool below the eutectic temperature. (Eutectic
solder can be purchased; it has the advantage of having the lowest melting
point possible for a tin-lead composition solder. I find in using it that
it is extremely sensitive to minor vibration while solidifying, and it can
actually "run away" from the heated part of the work to solidify
elsewhere.)
The most often used compromise solder alloy has 60 per cent tin and 40 per
cent lead. This composition, like any other composition that deviates from
the 63/37 eutectic alloy, does not abruptly change from a solid to a
liquid; it goes through a "plastic" phase which is best described as gummy.
We can understand how this can happen by considering that 60/40 solder is
eutectic solder with extra lead added to it. When this composition cools
to about 374 dg. F, 189 dg. C, crystals rich in lead (about 84 per cent
lead) solidify and form little "dendrites" (branch-like structures).
High-lead crystals continue to form until all that is left is eutectic
alloy. At 361 dg. F, the eutectic temperature, the solder changes from the
"plastic" phase (containing the lead-rich precipitant) to the solid phase.
The plastic phase comes in handy, the solder doesn't run away from the
connection before it cools, and minor vibration, such as the natural tremor
in your hands, will not weaken the connection as often as it does with
eutectic solder.
In order for "soldering" to take place, the connection must be hot!
hot! hot!, about 550 dg. F, (288 dg. C). The solder must be completely
liquefied, and the alloying temperature must be reached where the solder
"dissolves" or forms an alloy with the metals being bonded. The formation
of this alloy on the surface of the metals is called "wetting" of the
surfaces by the molten solder. The joint which has been "wetted" properly
does not have globs, balls or other rounded sculptures of solder attached
to it. A properly soldered joint over which good wetting has occurred is
shaped just about like it was before it was soldered; it is covered with
solder, but the contours of the joint are still present. The solder will
not just terminate it edges in lumps, but will nicely "feather" down to the
bare metal at its extreme edges. The joint will look as if a very elastic
sheet has been draped over it and been tucked in nice and cozily.
We have an understanding of the metallurgic principles of soldering,
but unless the cleaning and soldering operations can be done in an
atmosphere of helium, we can't just mix tin, lead, and the surface metals
in the face of a blow torch and expect to get passable results. We will
proceed to the discussion of "flux."
Metals that are electrically active (in the molecular sense) love to
combine with oxygen to form oxides. No matter how well you clean the
surface of metals such as copper, oxides will form as soon as you stop
cleaning. Furthermore, the formation of oxides is tremendously enhanced by
the application of heat to the metal. These oxides prevent the metallurgic
process of soldering; the molten solder cannot contact the bare metal
surface to alloy with it (no wetting occurs). The oxides which rapidly
build up at the point of heat transfer (between the hot iron and the work)
insulate the iron from the work so that poor heat transfer occurs.
There are agents which remove the oxides as the work is being heated
and soldered. For those of you who are chemists, these compounds (which
are called "fluxes") perform a reducing action which separates the oxides
from the surface metal.
The flux residue, containing the oxides
floats to the top of the boiling solder and allows the metal-to-metal alloy
to form underneath.
Rosin, as used in soldering, is an inert polymer (complex chain of
molecules) which resists forming chemical bonds when at temperatures below
those required for soldering. When the rosin flux is heated, the polymers
break up, leaving active molecules to serve as the reducing agent. Upon
cooling, the rosin and oxide compounds and once again inert, and harmlessly
remain on the surface of the joint.
Rosin is about the only flux which is inert, the others are conductive
corrosive nasty substances which work wonders during soldering, but which
must be washed away with water or other polar solvents after use. Why have
to bathe your project? Use rosin flux. There are a few other rosin based
fluxes whose residues are inert, but they are not as chemically stable as
rosin at high temperatures. I use rosin flux myself.
In hand soldering operations, thin tubular solder is used, in the
center of which the flux has been premeasured and stored. In electronics
work which is on the scale of the projects described in this issue, solder
of about 0.050 inches in diameter is suitably sized (Ersin Multi-core
solder comes by the gauge number; No. 20 through 22 are suitable). I
prefer this size of solder because it is rigid enough to be used as a
"feeler", and is small enough in diameter to permit accurate gauging of the
volume applied.
The metals being soldered must be in contact with each other, so that
they will heat up together. In order for efficient soldering to be
accomplished the iron should be applied to the point of maximum heat
capacity, i.e., the largest piece of metal permitting the largest contact
area. (All the surfaces being bonded should be in contact with the iron if
possible.) Solder which is applied to the iron will not bond to the
connection; its flux will be used up cleaning the iron and not the work.
Solder should be applied at the point of contact of the work and the
soldering iron. Once solder has melted at this point of contact, the flux
will attack the oxides cooking away between the iron and the work, and at
the same time, molten metal will flow between the iron and the work,
causing very efficient heat transfer. After that, solder applied just
about anywhere on the connection will be involved in the formation of the
surface alloys, because the surface itself is hot enough to melt the
solder. When the connection is hot enough to melt the solder, you are just
about guaranteed to have made a "good" solder connection.
The essential properties of the soldering iron warrant discussion here.
The tip of the soldering iron must be made of a metal whose thermal
conductivity is high. In addition, the tip of the iron must be able to
accept and to retain a surface alloy of tin or solder (known as "tinning")
so as to afford the formation of a completely continuous metallic path
between the iron and the work, which is necessary for efficient heat
transfer. Finally the iron must be powerful and efficient enough to heat
up the localized area of interest faster than heat can be dissipated or
transferred away from the iron.
Because of its high thermal conductivity, copper is widely used as a
base metal in soldering tips. The use of bare copper tips is a
long-standing tradition. Bare copper is highly soluble in solder, however,
so that these tips actually wear away and require frequent reshaping and/or
replacing. Because of the high degree of maintenance required on bare
copper tips, another type of soldering iron tip has become popular; it is
relatively maintenance free. This type uses copper as a base metal, to
take advantage of the thermal conductivity of copper, and has a plating or
cladding of ferrous metal (iron or steel).
"Tinning" the iron specifically refers to applying a coat of solder or
tin to the tip. This process retards the buildup of oxides on the exposed
tip metal. It also assures that fresh solder, when applied to the point of
heat transfer on the joint, will be able to wet the soldering iron tip and
establish a complete continuity of metals from the iron to the work. Bare
copper tips can be tinned by applying fresh solder to them on a regular
basis. (Periodically, the copper tip must be filed down to a smooth new
finish and tinned again.) Tips which are clad with ferrous metals are
tinned by the manufacturer, because the cladding does not readily dissolve
in solder. After a coating of tin is alloyed with the tip by the
manufacturer, solder can alloy with the surface tin. Keeping fresh solder
on the tip will help prevent oxides from separating the tin from the
cladding. Once the factory tinning has become flawed, the tip must be
replaced.
A common fallacy is that the iron must be small enough not to damage
the work. (I made this mistake for years.) Used inappropriately,
low-powered irons do more damage than soldering. Their intended
application is in cases where a larger iron cannot be maneuvered into
position for soldering. In general purpose soldering, low-powered irons do
not heat up the localized area of the connection quickly, allowing
considerable heat to be transferred to and absorbed by components of the
work. In most cases, an iron of 50 watts or more can heat up the
connection quickly and efficiently, allowing soldering to be accomplished
without overheating the entire collection of circuit elements. The iron
must be "big enough", not "small enough."
You ask, "Is he, the author, ever going to get down to business?" Yes,
yes, let us descend from the ivory tower of conceptual cognition and get
our fingers warm.
The remainder of "Soldering" will focus on soldering with "instant
heat" soldering irons or guns, which have proven to be well suited for use
by blind technicians. The next article will discuss the techniques that I
use when soldering with a continuous-heat soldering iron, along with a
survey of readily available tools and accessories used in soldering.
A variety of soldering irons and soldering guns are available whose
features include "instant heat" capability; they warm up to soldering
temperature with a few seconds of being turned on. However, only a
particular type of these "instant heat" irons is of interest to us. We are
interested in the irons and guns whose tips have very low mass, and
consequently have low heat storage capacity. These not only heat up
quickly, they cool down quickly after being turned off.
Unlike conventional soldering iron designs in which a large heating
element heats the tip by thermal conduction, the irons to be described here
use high current electricity to heat a small low-mass tip. The tip itself
is the heating element. Within 60 seconds after the current through the
tip has been turned off, the tip is cool enough to be touched.
These instant-heat, fast-cooling irons have two major disadvantages in
comparison to conventional irons. The first is that the small surface area
of the tip, which is the heating element, does not permit efficient heat
dissipation in free air. If the current through the tip is left on while
the tip is not in good thermal contact with the metals being soldered, the
tip can reach an extremely high temperature which will quickly oxidize its
surface and ruin the tinning job. The second disadvantage is that because
very high current is necessary to heat the tip, a physically heavy
high-current power source must be incorporated into the handle of the iron
or gun. These disadvantages are something that can be lived with, and they
are more than offset by the convenience offered to the user who wants to
guide the iron into position with his fingers while the tip is cool to the
touch. For the hobbyist who occasionally rolls up his sleeves and solders
a project together, these irons eliminate the need for constant practice
necessary to safely use a continuously hot iron. Two kinds of these
"instant heat" fast-cooling irons are commercially available. Actually,
they differ only in size. First is the transformer type soldering gun, and
the second is a battery operated "cordless" soldering iron.
The tip of the transformer type soldering gun is a simple elongated
loop of wire. The body of the gun contains a power transformer to match
the high current load of the tip to the a.c. power line. These guns are
available from a couple of manufacturers; however, in my opinion the best
is the Weller Model 8200 dual-heat soldering gun (also marketed by Radio
Shack as the Archer Professional Dual-Heat Gun). Its bare copper tip is
cheap and simple; a piece of 12 gauge can be fashioned into a tip in a
pinch. The binding posts for the tip are good solid construction so that
the ends of the tip can be secured firmly (these binding posts need to be
tightened occasionally). The two position trigger switch provides two power
ratings, 100 and 140 watts; one for small jobs and one for larger work.
The main limitation of these guns is that the tip is too large to be used
on integrated circuits and other crowded assemblies.
With the advent of sealed rechargeable batteries, a junior member of
this family of instant heat irons has become available. These units are
said to be "cordless." Instead of using a power transformer to supply
current to the tip, a nickel-cadmium battery is incorporated into the
handle. For practical reasons (not the least of which is that the high tip
current must be controlled directly by a pushbutton switch), these cordless
irons are very low power and are only good for very small work. In my
opinion, the best of the cordless irons is available from Radio Shack as the
Archer Cordless Iron, stock No. 64-2075, $20.00.
They work fine for circuit board work (either printed circuits or
point-to-point wiring on perforated boards), but they are not husky enough
for soldering terminal lugs such as those found on plugs and jacks.
With a complement of two irons, a cordless iron and a transformer type
gun, those who wish to use instant-heat soldering irons can cover the full
range of electronic assembly work by using the appropriate tool.
Tinning these irons and preparing them for use is a simple matter if
you carefully monitor what is happening by holding on to the solder. Spool
off a couple of feet of solder and wrap about three inches of it around the
tip of the iron or gun. Hold on to the solder about an inch away from the
tip. Turn on the iron and wait for the solder to melt, which will
disconnect the iron from the solder in your hand. Immediately and
simultaneously release the button or trigger and give the iron a quick
little shake in a direction away from you. After a minute, feel the tip
and inspect your tinning job. The tip should feel smooth and perhaps a
little gummy from the flux. If the tip feels rough in spots or if it has a
glob or an "icicle" of solder that might get in your way during the first
connection, repeat the process.
Some thought should be given to the preparation of the work area.
Since splattering and dripping of the solder is inevitable, choose a work
surface on which marring is of no concern.
Because the instant heat guns and irons are characteristically heavy, a
collection of blocks, books, or heavy transformers against which your hand
can be braced may help slipping of the iron of the connection.
Your paraphernalia should include good solid holding devices which can
rigidly support the work. A small table vise with a swivel is good for
most applications. (More on this in Part II.)
In designing the layout for your projects, try to arrange for the
soldering to be done n accessible places. When stringing connecting wires
around your project, make them long enough so that they can be gotten out
of the way during soldering.
When fashioning the connection to be soldered, make sure that all the
metals to be joined are in contact with each other so that they will heat
up together. It has been said, in fact overstated, that the connection
should be mechanically self-supporting before soldering. This philosophy
can get you into trouble; if leads are wrapped around and around terminals
to make them mechanically rigid, the solder may not flow around all the
surfaces leaving portions of the connection unsoldered. Maximizing the
area of metal-to-metal contact will minimize the susceptibility of the
solder bond to shear stress, but the small weight and size of modern
electronic components has outdated the wrapping practice. Some specific
examples of good practice are:
When soldering a wire to a round terminal post, bend the wire
three-quarters of the way around the post.
When soldering a wire to a flat terminal lug with a hole through it,
pass the wire through the hole and bend it over so that it lays against the
flat surface of the lug.
When components are installed on a printed circuit board, lean the wire
over at an angle before soldering it. In the military code, the wire must
be bent right down against the printing on the board, but this makes
component replacement difficult.
When attaching components to terminals, always leave a distance of at
least one-eighth inch between the terminal and the component. This
practice will permit the attachment of a clip-on heat sink when
appropriate, and will prevent direct heat from the hot iron on the body of
the component.
Identify the item of largest heat capacity on the connection so that
the iron can be put in good contact with it. In the ideal situation, the
iron should be in good contact with all the metals being soldered; however,
this is not always possible. To be specific, when a wire is being soldered
to a terminal lug, you must at least apply heat to the lug. When a
comparatively heavy component lead is being soldered to a very small
terminal on a socket for an IC (integrated circuit), you must at least heat
the wire, because it is massive compared to the socket terminal and can
absorb much more heat energy.
Using the above guide lines, clamp a project in your vise and fashion a
connection to be soldered. Place your iron or gun against the work and
brace your hands as necessary so that you are in a comfortable holding
position. Check to see that the "barrel" of your iron does not run close
to wires or components that could be damaged by the heat. With your free
hand, hold the solder about three-quarters of an inch back from the end,
and place the end of the solder up against the connection and the tip of
the iron--never against the iron alone. Make sure that the three-quarter
inch piece of solder between your fingers and the connection is straight,
so that you know which direction to move in feeding the solder once it
melts. Turn on the iron and wait for the solder to melt.
When the melting occurs, the solder will "disappear" off the end of the
piece in your hand. Depending on the size of the connection, you must
supply one-eighth to one-half inch of solder onto the joint. When feeding
the solder after the initial melting, apply it to the connection and not to
the iron. After the desired quantity of solder has been applied, leave the
iron against the joint for one or two more seconds. Then, slide the iron
off the connection with a smooth deliberate motion. Sliding the iron off
the connection rather than jumping straight away from it will help to break
the surface tension of the liquid solder without leaving sharp "icicles" in
the direction of your departure.
Any or all of three indications can be monitored to affirm that good
wetting and soldering has taken place. First will be if you can get the
solder to melt when applied to the connection at a point that is not in
direct contact with the iron; this means that the entire connection has
reached soldering temperature. The second indication is that very small
motion of the iron or of the components will feel "squeaky"; the flux has
done its cleaning job and the solder-wet surfaces are "squeaky clean" like
dishes in soapy water. (My thanks to Dennis Bernier, Vice President of
Research and Development at Kester Solder Co. for explaining this effect to
me.) The third sign is that heat transfer to all the component leads
becomes very efficient; the temperature of the connecting leads will rise
sharply.
After the connection has been allowed to cool (and don't allow
components to move in relation to each other until the solder has
completely solidified), a systematic inspection of the joint is in order.
Five indications of a faulty joint should be looked for:
If no solder has made it on to the connection, the terminals and leads
will feel "rusty", i.e. they will have corroded from being heated without
the presence of flux and solder to protect them.
If good wetting has occurred, the connection will not have lost its
characteristic shape, but will feel smoothly covered with solder. If,
however, solder has melted but not wetted onto the connection, round pieces
can be picked off, because they have not formed any surface alloy with the
metals being joined.
Gently wiggling each of the connected components should cause no
rattling or relative motion with respect to the others. If they are
soldered together, the connection is one piece of metal.
If too much solder has been applied to the connection, heavy droplets
may be hanging down from the underside of the joint which could short
something out or break off and rattle around in the project until they
bridge two other connections. Turning the connection upside down and
reheating it can often take care of this problem.
Finally, it is often difficult to keep two connections from "bridging",
i.e. adjacent connections may become soldered together accidentally. This
can happen if too much solder is applied, or if adjacent connections are
inadvertently heated simultaneously by the iron. A small probe, such as a
braille stylus or small screwdriver, should be passed between closely
spaced terminals to check for bridges. If a bridge is found, reheat the
connections separately and clear the bridge with your probe as the solder
melts.
-- END --
[from the Smith-Kettlewell Technical File
Vol. 2, No. 1, Winter 1981]
SOLDERING (Part II)
by Bill Gerrey
In the previous discussion, we covered the
principles of forming a solder bond. These principles are summarized
below:
1. Molten solder acts as a solvent--it dissolves metal from the
pieces being joined, forming a bridge of alloys from one metal to the
other.
2. All the metals being joined must reach "alloying temperature"
in order to be soluble in molten solder. The metals must be in firm
contact with each other so that they all reach this alloying temperature.
3. (a) Heat transfer from the hot iron to the joint of the
metals must be extremely efficient to afford good soldering and to prevent
damage to connected components of the work. If the transfer of heat is
done inefficiently, a long time will elapse before the adjoining metals
reach the alloying temperature; during this time, considerable energy will
be absorbed by the components and damage may result.
(b) In order for heat to be efficiently transferred to the
metals from a hot iron, a complete metallic path must be established
between the iron and the work. In fact, the iron itself must be involved
in the continuity of alloys. The iron and the metals being joined must all
have their surfaces in solution with the molten solder; this is known as
"wetting."
4. Oxides on the metallic surfaces prevent wetting by the molten
solder; the solder cannot reach clean surface metal to alloy with it.
Furthermore, oxides build up very rapidly at high temperatures, insulating
the hot iron from the work. A chemical "reducing agent," known as flux,
must be applied to all the surfaces during soldering to strip these
surfaces bare of oxides, allowing the formation of pure metallic alloys.
Rosin Flux (used in electrical soldering) is a fairly active reducing
agent when heated, but remains inert at temperatures below soldering
temperatures. Its resistance to chemical interaction after the solder has
cooled makes it ideal for electrical work; its residue is non-corrosive.
5. Given ideal conditions, soldering is done in the following manner:
The tip of the hot iron is put in contact with all the adjoining metals.
Flux-core solder is put in contact with the work and the tip of the iron
which causes a column of molten solder to flow between the iron and the
work. After this initial melting of solder, the application of additional
solder should primarily be fed to the work pieces and not to the tip of the
iron. Solder which is fed to the iron alone and which subsequently runs
down into the work will generally not involve itself in bonding. Its flux
will be used up cleaning the iron and not the work; it will not be able to
get through the oxides and onto the bare metal surfaces. Feeding solder to
the work alone maximizes the effectiveness of the flux, and provides a good
indication as to whether or not the metals being joined have reached
soldering temperature.
Continuous-Heat Soldering Irons
Much of what follows is a clean break from theory; it is a highly
subjective discussion of techniques _I use when soldering with a
continuously hot iron. Many of the statements are refutable. Take each
stated technique as a seed from which you can "grow your own". Please
submit your suggested additions and improvements to this Editor, so that
they can be shared with the rest of us.
There are two basic classes of continuous-heat soldering irons, simple
garden variety constant-power irons, and "temperature-controlled" irons.
Constant-power units are comparatively inexpensive. Their heating
element is a simple power resistor which is energized continuously. Their
main disadvantage is that while they are not in contact with the work
piece, they must dissipate all their heat energy in free air, which means
that they reach fairly high temperatures between soldering operations.
Their tip temperature may approach 1,000 dg. F, (about 450 dg. C) while the
iron is in the rest stand. To protect the "tinned" surface of the tip from
oxidizing at these high temperatures, it is crucial that fresh solder be
always present on the tip.
Temperature-controlled irons are those that have
"thermostatically-controlled" mechanisms for sensing and maintaining the
temperature of the tip. With these units, the temperature is held to a
specific value, whether the iron is in use or at rest. Typically, these
irons are designed to maintain a tip temperature of 650 dg. F (about 350
dg. C).
The tip of a temperature-controlled iron is not subjected to heat
cycling over a wide range of temperatures, and the overall tip temperature
is lower (more than 300 dg. lower). These features give rise to a longer
tip life. In addition, the likelihood of solder joint reaching a very high
temperature, which can damage the flux, is minimized. Finally, the 30
percent reduction in tip temperature may be slightly less injurious to the
fingers, if the job is such that the tip must be frequently touched. (in
all fairness, it should be stated here that Dennis Bernier, Vice-President
of Research and Development at Kester Solder Company, prefers a
well-designed constant-power iron over temperature-controlled ones. He
argues that a well-designed constant-power iron is able to maintain a
fairly constant temperature, and that temperature-controlled irons can
often subject the work to electrical transients as they switch on and off.
He also recommends that when choosing a temperature-controlled iron,
obtaining one with a tip temperature of no lower than 700 dg. F is
preferable for efficient heating of the work.)
When choosing a soldering iron, pick one with a high power rating, so
that it can supply heat energy to the localized area of interest at a much
faster rate than energy can be conducted away from the connection by
components of the work. Small-sized, low-power irons are made for
specialized applications, such as miniaturized assemblies on which larger
irons cannot be maneuvered into position. (I used a 25 watt iron for
years, only to find out that components were absorbing enough heat energy
to be damaging, while I shifted from one foot to the other waiting for the
solder to melt). The iron should be as large as can practically be used,
given its physical size and configuration.
Unless they are a very small size, temperature-controlled irons are
designed to supply high levels of heat energy when they are called on to do
so. When the tip temperature drops below their specified value, a high
amount of energy will be supplied by the iron until the tip temperature is
restored to the rated value.
Constant-power irons, on the other hand, only have their given power
rating available for transferring heat energy to the work. Ideally, given
the size of electronic components used in most assemblies, an iron of 50
watts or more enables the user to make connections quickly and efficiently.
However, for the blind technician, irons of this rating may have
unfavorable physical characteristics; they are often very long, and their
heating element may be comparatively large in diameter. The blind
technician may wish to compromise on the power rating to obtain an iron of
smaller physical size. I recommend not using irons of less than about 35
watts.
Key Physical Parameters--by picking an iron with certain key physical
characteristics, you can optimize your accuracy and stability in performing
the task of soldering.
The length of the hot portion of the iron (from the handle to the tip)
should be as short as possible, so that your sense of the tip position can
be accurately predicted. The iron becomes an extension of your hand; the
position of your hand and the angle at which you hold the iron are valuable
pieces of information which you must use to predict the tip's location.
The shorter the iron is, the more meaningful will be this information.
By the same logic, the handle of the iron should be well enough
insulated from the heat to afford holding the handle at its extreme forward
end.
The diameter of the "barrel", which is the heating element, should be
as small as possible to minimizing the likelihood of its contacting nearby
wiring or your other hand.
It is my experience that a great advantage in stability can be gained
from choosing a tip which has flat contact faces. In contrast to this, the
tip style which has gained overwhelming popular acceptance is conical in
shape; it has no contact face. When holding a conical tip against the
work, the contact force must be exactly perpendicular to the surface of the
cone, otherwise the iron will tend to slip or "glance" off the connection.
In other words, holding a round tapered tip against a work piece is
difficult, and is subject to instability. I have found that by using a tip
with flat contact surfaces, "glancing" of the iron off the work is less of
a problem.
Replacement tips which have flat contact surfaces are available for
almost any make of iron. In general, three such tip styles are available
from soldering iron manufacturers--pyramid-shaped, chisel-shaped and
screwdriver-shaped tips. (Incidentally, all these styles have far better
heat conductivity than does a tip of conical shape.) Screwdriver tips are
the most suitable for electronic assembly, since they are usually thin
enough to fit between closely spaced terminals. Whichever style is chosen,
the handle of the iron should be marked adjacent to each flat surface, so
that the tip can be properly oriented with respect to the work. The handle
can be marked by filing notches into it, or by attaching narrow strips of
Dymo tape along it.
Care and Feeding of the Soldering Iron
A soldering iron is a very vulnerable instrument. Operating at
extremely high temperatures, the iron can supply enough heat energy to
promote a variety of "endothermic" chemical reactions, all of which are
detrimental to its effectiveness.
Since the surface metal of a soldering iron tip is chemically active,
it is prone to oxidation; and this tendency is greatly accelerated at high
temperatures.
During idle periods, the heat of the iron can carbonize any flux
residue present on the tip.
The iron may accidentally come in contact with foreign materials which
melt when subjected to its intense heat. Some notable examples are plastic
building materials, insulation on the wiring, painted surfaces, and
insufficiently damp cleaning sponges. If deposits of such foreign matter
melt off on to the tip of the iron, they quickly carbonize and cling
stubbornly to the tip.
Any soil on the tip acts as a heat insulator, and it renders the iron
incapable of effectively heating the work. The only protection the iron
can have against this soil is to be kept wet with solder. Since the
surface metal of the tip will be exposed to the atmosphere under these
conditions, oxidation of the tip metal itself will not occur. Any
carbonized residues will tend to "float" on top of the molten solder, thus
protecting the tip itself from contamination.
Therefore, a solution of molten solder must always be kept present on
the tip of a well cared for iron. The solder-wet tip can easily be wiped
clean on a damp cleaning sponge, but this procedure should be followed
soon after with the application of fresh solder to the tip.
In the normal sequence of making solder connections one after another,
the tip of the iron is kept reasonably wet automatically. However, an
occasional "slap-dash" application of solder to the tip assures that voids
in the surface solution do not go untreated; a good bath in fresh flux will
strip oxides and other contamination off the surface metal. Initially, of
course, new tips should be bathed in fresh solder before being used.
Special mention should be made here regarding the simplest of tips,
those which are made of bare copper. Copper is extremely soluble in
solder. Copper from these tips is actually dissolved into each solder
connection; these tips eventually become pitted and worn away. They can be
redressed by filing or sanding them down to a smooth new surface, at which
point they must be treated as a new tip. _Never attempt this redressing
procedure on steel or iron-clad tips (see "soldering", Part I).
"Tinning" specifically refers to applying a coat of fresh solder to the
tip. This can be done in two ways. If the iron is cold, Wrap about three
inches of solder around the tip and turn the iron on. (To some people,
these three inches may seem like an excessive amount of solder, but the
point is to assure that the entire surface of the tip is bathed in fresh
solder. Overdoing the amount harms nothing.) If the iron is to be
"tinned" while hot, solder must be "brushed" along the tip. To make sure
that the entire tip is being bathed in fresh solder, turn the iron slowly
while "brushing" the solder over the tip.
Finding the tip of a hot iron with a piece of solder is no easy task.
To aid in doing so, rest both hands against some familiar object, such as
your vise or the rest stand, so that you have some idea as to where the
iron and the piece of solder will intersect. I often extend the piece of
solder an inch or so beyond my projected point of intersection, thus
allowing the iron to "cut" the solder to the exact length.
Do the "tinning" procedure over an unimportant surface which is not
flammable. It is a good idea to "tin" the iron over a wet cleaning sponge,
but remember to retrieve the solder droplets from the sponge; they will be
larger than those left in the sponge after normal wiping, and you do not
want the iron to pick them up later.
The iron can be cleaned by wiping it on a wet cloth or a wet cellulose
sponge. Whichever you use, the item must contain nothing which will
contaminate the iron. For example, no cloth having components of polyester
are acceptable. Also, many general purpose cleaning sponges contain
chemicals which can soil the tip. Above all, the item used must be _wet
(dripping wet is acceptable). This is essential, since while the iron is
being wiped free of its protective excess solder, it is very vulnerable to
charring foreign matter.
Sponges designed for this purpose are available from soldering
equipment manufacturers. The best cleaning sponges are those which envelop
or surround the tip when it is being wiped. These sponges can either be
convoluted (being made up of lobes), or they can be comprised of a
"sandwich" of separate sponges standing on edge. With simple flat sponges,
several passes must be made (rotating the iron between each pass) to assure
that the tip has been wiped on all sides. This tends to cool the iron more
than is done by making a single pass through a sponge of complex
configuration. (For the blind technician, it is essential that all
droplets of excess solder be removed, since they can cause serious burns.
Dennis Bernier of Kester Solder Company pointed out to me that wiping the
tip on a simple flat sponge tends to transfer droplets to the unwiped side
of the tip, and does not assure that they will be removed.) Wipe the iron
immediately before soldering. After soldering has been accomplished,
return the iron to its rest stand; _Do _not wipe the tip free of solder at
this time.
Many accidents can happen to damage the iron. All of these accidents
are preventable if reasonable steps are taken.
The power cord of the iron should be kept off to one side at all times
to prevent the iron from coming in contact with it. In fact, all cables
should be kept well out of the way, even if they do not pose an immediate
electrical hazard. If the tip of the iron comes in contact with any such
cable, it will become contaminated with very stubborn soil.
Plastic handle tools should be kept clear of the rest stand to avoid
being grazed by the tip, resulting in its contamination.
Finally, the tip should not be banged into things which can mar its
surface. To avoid striking the tip on sharp corners and edges of the rest
stand, carefully note the position of the rest stand so that you can
approach it slowly and gracefully.
Handling the Iron
This covers a lot of territory--practice reaching, establishing
well-defined reference points and rest positions ("landmarks"), and
touching and holding the iron. The limitation of writing is that these
ideas cannot all be conveyed simultaneously. As with swimming, which can
be described as the integration of kicking, paddling, breathing, and
adopting a good posture, the components of this discussion must be taken
together when performing the task of soldering.
It goes without saying that the techniques to follow should be
practiced while the iron is cold. In addition, a practice iron which is
always cold may be worth having. A dummy iron can be made by thrusting a
pencil through a couple of bottle corks of appropriate size; the pencil
should protrude the same distance as does the hot portion of your iron, and
the corks should be of a size that roughly simulates the handle of your
iron. With this tool, you can take a practice run any time you want to.
Even for veterans like myself, an occasional need arises for a practice
shot. For example, when working in a nest of wiring or when working in a
small space, a practice run can lead the way to taking the best approach,
and may spare you an unpleasant surprise.
Holding Instruments-- Surgeons, jewelers, and people working in
micro-assembly all know how to hold their tools and to support their hands
to maximize control and stability. We will take the following lessons from
them. (My thanks to Dr. Irene Gilbert of University of California Medical
Center and to Dr. Brian Brown of Smith-Kettlewell Eye Institute for these
lessons in physiology.)
We possess one set of muscles capable of precise manipulation, the
thumb and fingers. The muscles have a large number of nerve fibres
dedicated to them, and a large part of the brain is devoted to controlling
them. In Dr. Gilbert's words, "The area of cortical neurons overseeing the
thumb alone is almost as large as the area overseeing the leg and foot.
Therefore, precise manipulation of instruments can best be done with the
thumb and fingers.
Coarse muscle systems which are not designed for fine work, namely
muscles controlling motion of the arm, should be taken out of play. Free
motion of the arm has a profoundly detrimental effect on the precision of
finger motion. The main muscles which operate the fingers are not actually
in the fingers, they are in the forearm. The fingers are controlled
through a complicated pulley system of tendons and ligaments in the wrist.
Precise control of the thumb and fingers cannot be attained through an
unstable pulley system.
Much of what is seen as hand and finger tremor is caused by failure to
stabilize the arm and wrist. People who do fine work learn quickly to
stabilize their wrists and forearms on solid objects. Dr. Gilbert
remarked, "I once made a plaster half shell of my forearm from elbow to
wrist and mounted it through a ball and socket onto a base. The shell
could pivot and rock, and yet hold my wrist and forearm steady, leaving my
fine hand and finger muscles to manipulate freely and precisely." At the
very least, your elbow should be braced against your body, and your wrist
or hand should be resting comfortably against some solid object. Bracing
your hand against the work piece is often sufficient; however, books,
blocks, or the spool of solder should be used as needed.
Holding the iron like a pencil is usually advocated in discussions on
soldering. With the side of your hand resting on the stabilizing object,
the iron is held between your thumb and first finger, with the middle
finger curled under the handle to provide a supporting cross-bar. I modify
this grip by uncurling the middle finger and placing it along the handle
under the index finger; this arrangement gives me better vertical position
information. I hold the solder between my thumb and middle finger of the
other hand, leaving the first finger free to touch and guide the iron where
necessary. To maximize control of it, the solder should be held about
three-quarters of an inch from the end.
Land-Marking-- In the performance of all tasks involving movement, the
sense of joint and muscle position (kinesthetic sense) is relied upon
heavily. When pianists and typists have reached perfection, they no longer
look at the keys. A skill is really learned when one can say, "I can do it
with my eyes closed."
In soldering without visual feedback, much about the position of the
iron can predicted using the kinesthetic sense, but the limits of this
biophysical system must be understood. "Can the sense of the position of
your hand ever achieve a resolution of one-tenth of an inch, which is
necessary for soldering integrated circuits?" This question must be
answered with another question, "Where is your starting point with respect
to the target?" The accuracy with which a movement can reliably be made is
a fixed proportion of the distance to be moved. Generally, it is about 5
percent of the distance to be moved, and so to achieve the accuracy
necessary to solder integrated circuit pins, the last movement should be
from a landmark about two inches away. I propose that a few reference
points and rest positions along the way to the target be identified, a
procedure I shall call "landmarking".
Note the position of main items associated with the project on which
you are working. While holding the iron in your hand, these items can be
located with the heel of your hand or with a couple of straying fingers.
By bringing the iron over to one of these cross reference points, the
distance to the target can be reduced to at least one-fifth the original
distance (from the rest stand). By staying in contact with these items
(using them as rest points to stabilize your hand), the iron can be very
precisely controlled with the thumb and fingers.
For the next stage, the iron can be used to do some of the
land-marking. There are usually a number of relatively inert items which
will not be harmed by bringing the barrel or the tip of the iron into brief
contact with them. The edge of the chassis, the handle of your vise, or
strategically placed C clamp, alligator clip, or clip-on heat sink are
examples worth noting. If you are as lazy as your Editor, you may use the
edge of the circuit board, a nearby terminal strip, or the body of a
Bakelite component for land-marking with the iron (naughty naughty). Make
sure that the tip of the iron is wiped free of solder before you do this,
or you will spill droplets of solder into the project. Remember, be gentle
with the tip at this time, since it will be vulnerable to damage without
its protective coating of excess solder.
The final landmark should be chosen so that you have a short hop to the
target. Regarding the choice of this landmark's position, Dr. Gilbert
suggests that the following information on current research be noted:
(1.) Movements made horizontally are more precise than those made
vertically.
(2.) One is more accurate in knowing a movement's direction than
the length of the movement.
During the final reach, the iron becomes your "cane". In this way, it
can indicate to you when it has come to rest on the target. Unlike the
"cane" traveler, the person wielding the soldering iron has control over
the features of his terrain. He can arrange for the target to have unique
features. Some examples of this are listed below:
If a component is being soldered into a printed circuit board (PC
board), leave the leads long, so that the target is "the only tree in the
forest". These long leads will be easy to find with the tip of the iron,
especially if you remember to cut the excess wire off components you have
previously soldered.
A wire being soldered to a terminal lug may be arranged so that its
end protrudes beyond the terminal, making this terminal easy to find with
the iron. After it has been soldered, cut off the excess wire.
When wiring integrated circuits on perforated board (point-to-point
wiring), lay a component lead across its intended IC pin; cut it off so
that it extends conspicuously beyond the center line of the IC (between the
two rows of pins). When approaching this connection with the soldering
iron, reach not for the IC pin but for the point at which the component
lead crosses the center line of the IC. In other words, fish for the
extended wire with the tip of the iron; when you have found it, follow it
over to the pin. After this connection has been soldered, cut the excess
wire off close to the pin and proceed to the next pin. Arrange the order
of your tasks so that the pins are soldered in consecutive sequence (it is
harder to hit the pin if it is between two previously soldered ones). (You
will have more space between pins and have less trouble with bridging them
if you use only one component lead per pin. Other components going to this
pin can be soldered to the lead of the first component.)
When soldering multi-pin components on which the pins are very
long, such as PC-mount potentiometers, and wire-wrap sockets, solder these
pins in sequence, and cut them off near the solder joint as you go.
Touching The Iron-- With some jobs, such as soldering components into a
PC board or removing defective components from a PC board, no convenient
system exists to give the target unique features by which it can be easily
found. In such cases, the iron can be guided into position by a free
finger of your other hand. Believe it or not, the hot iron can be touched.
In touching the iron, two overriding principles must be adhered to:
the tip must be wiped clean, and you must not make any quick, uncontrolled
movements.
Any fisherman knows not to make fast jerky movements around his tackle,
otherwise he may impale himself on a hook. The same philosophy should
prevail when handling a hot soldering iron. The more relaxed and even
your motions are, the less chance you have of coming into unexpected firm
contact with the barrel or tip of the iron. If the job is such that you
must touch the iron, do so with smooth, light, brushing motions. (Your
Editor considers that fear of such things is relative. I would much rather
solder than light a cigarette, which scares the Devil out of me.)
Tactile Feedback
When you have hit the target, several indications can be used to affirm
that it is the desired one. At this point you have a "cane" in each
hand--the iron is in one hand, and the solder (which awaits your arrival at
the target) serves as a "cane" in the other hand.
Using the iron as your "cane", the contour of the target should make
sense as you gently scan it with the iron.
The solder, which is being held against the connection by your other
hand, will vibrate when the iron touches the connection. At this point,
move the iron over to where you suspect the tip of the iron is resting on
the connection. If it melts, the iron is on target and you were right
about its position. Bring the solder back to a point which is not in
direct contact with the tip of the iron and feed the desired amount of
solder to the joint (from one-eighth to one-half inch depending on the size
of the connection and of the solder).
The solder may melt immediately when the iron touches the connection;
this is your indication that the iron and the solder touched the target in
the same place. Often, you will lose the connection with the solder. When
this happens, feel around with the solder until you apply it to the
connection which causes it to melt.
Another indication of hitting the desired target is that the wiring and
components associated with the connection will heat up. A spare finger of
the solder-feeding hand can be used to monitor this condition.
Indications that you have missed the target are:
Components associated with a different connection may heat up,
indicating that you have found their connection instead of the desired one.
The solder will refuse to melt when it scanned over the connection.
Scanning adjacent connections with the solder will reveal which one is
being mistakenly heated.
If you suspect that you have gotten on to the wrong connection,
there is a clue which may indicate to you whether or not this connection
has been previously soldered. If small motions of the iron feel "squeaky",
the surfaces against which the iron is in contact are wet with solder,
which probably signifies that the connection has been soldered before (if
the work materials have been previously "tinned", the iron may be squeaking
against individual items rather than a fully completed solder connection).
If small motions of the iron do not feel "squeaky", the items you have
contacted have never been soldered.
Tools and Accessories
General Comments-- When people refer to the "balance" of instruments,
they are actually referring to the ease and control with which these
instruments can be manipulated. Used in this sense, the term "balance"
implies that a favorable compromise in weight and distribution of mass was
made in the design. In general, the tools of the highest utility are those
which are light in weight, and which present a minimum of inertia. It
follows that smaller tools are easier to control than larger ones, because
characteristics unfavorable to manipulation become less significant.
For many years I used a large fancy jack knife whose handle contained a
pair of pliers. However, for many small jobs (such as stripping wire) it
was clumsy to hold and would frequently topple out of position. Since
then, I have come to prefer very small pen knives with no extraneous
gadgets in the handle.
The above principles can be expanded to include all hand tools used in
soldering. Short light-weight tools which can be held near their center of
gravity afford precision control and promote stability when holding them in
place.
With regard to vises and holding clamps, "low-profile systems are
preferable. Having the work close to the work bench puts you in a
comfortable position and greatly increases the number of objects against
which your wrist can be stabilized.
Soldering Irons
Two grades of constant-power irons are listed, as well as detailed
information on my favorite temperature-controlled iron made by Weller. On
the advice of David Plumlee of Independence, Missouri, the Wahl "isotip
Cordless Solder Gun" appears in this list even though it is an instant-heat
fast-cooling iron as discussed in "Soldering, Part I".
UNGAR THREE-PIECE SOLDERING IRON--This iron is almost universally
available in parts stores. The price is always less than $13.00.
776--handle with cork grip
64-2082--33 watt heating element (screw-on tip is used)
64-2083--45 watt heating element (screw-on tip is used)
PL151--plated screw-on screwdriver tip
Avoid the 64-2080 "Cool Grip" handle, which gets very warm near its
forward end.
HEXACON ELECTRIC CO. HIGH-GRADE INDUSTRIAL IRONS--Although I have
never used irons of this brand, they come very highly recommended by Dennis
Bernier of Kester Solder Company. He specifically suggests trying the
"hatchet-shaped" model.
Hexacon claims that their irons are much more efficient than those of
their competitors. A 1-1/4 inch insertion of the tip into the heating
element provides very tight coupling.
These irons cost about $16.00, with the exception of the little H14 Hornet
Iron for $8.50.
22H-35--35 watt hatchet-shaped
22A-35--35 watt straight iron, with about 3 inches from handle to
tip
23A-50--50 watt straight iron, with 3-1/2 inches from handle to tip
H14--20 watt (Hornet series), 2 inches from handle to tip
Available from Marshall Industries. *
WELLER "SOLDERING STATION" TEMPERATURE-CONTROLLED IRON--A permanent
magnet plunger operates a set of switch contacts which turns the heater on
and off. The magnet in this plunger is attracted to a feromagnetic
"temperature sensor" in the shank of the tip. The feromagnetic sensor in
the tip loses its magnetic properties when it reaches its "curie
temperature", at which point the magnetized plunger is no longer attracted
to it. Thus, when the tip is at its Curie temperature, the spring loaded
plunger moves back and disconnects power to the iron. When the tip's
sensor drops below its Curie temperature, the magnet jumps forward, causing
power to the heater to be restored.
Tips for three different temperatures are available. Units of 600,
700, and 800 degrees F. are denoted by suffixes 6, 7 and 8 respectively.
SCTPM--Weller "Soldering Station" comes with conical tip
PTA--1/16 inch screwdriver
PTB--3/32 inch screwdriver
PTC--3/8 inch screwdriver
PTD--3/16 inch screwdriver
PTH--1/32 inch screwdriver
PTL--5/64 inch screwdriver (long)
PTM--1/8 inch screwdriver (long).
(Note--PTB, PTD and PTL tips are only available as 700 degree units,
PTB-7, PTD-7, PTL-7. All others are available at three temperatures.)
(Note--tips for this iron are "ironclad" with a surface plating of
nickel to accept tinning by the manufacturer. If this tinned surface
becomes flawed, the tip must be replaced.)
This WTCPM Station is available from Fordham Radio at $60.00. Tips are
five
for $12.00. *
WAHL "ISOTIP CORDLESS SOLDER GUN"--Not only is this an instant-heat
device, but it has a hands-free solder-feeding system that enables the user
to deal out solder from the same hand as holds the gun. I have always had
poor success with these solder-feeders, since monitoring the melting of
solder cannot be done directly. However, David Plumlee advises me that by
attending to the temperature of leads going to the connection (with the
other hand), the time at which solder should be fed from the gun can be
accurately guessed. A very sharp rise in the temperature of these leads
after the initial feeding of solder will indicate that the solder has
melted. Perhaps the squeaky feel of solder-wet metals can serve as an
additional indicator.
7900--Wahl "Isotip cordless Solder Gun"
Available from Fordham for $40.00 and from Allied at $45.00. *
Cleaning Sponges
The cleaning sponges which come with the rest stand of most soldering
irons are of the simplest configuration, flat. While these are better than
using your apron, several passes must be made over them while the iron is
being rotated in your hand. This cools the iron, weakens the power cord,
and does not guarantee that the tip will be wiped free of dangerous
droplets of solder. Take the trouble to procure the following item:
AMERICAN BEAUTY "ONE PASS TIP CLEANER"--contains four 3-inch sponges
standing on edge in a holder. These sponges have beveled edges to permit
the tip of the iron to "dive" down between them.
480--American Beauty "One-Pass Tip Cleaner" with holder
480S--replacement set of four sponges.
Available from Marshall Industries and Allied Radio at about $5.00. *
However, the 480 and 480S are also marketed by Mouser * as catalog numbers:
Mouser 543-63040--complete set with holder (480)
Mouser 543-63041--replacement sponges (480S)
Soldering Aids
Kits from two companies are listed here--Radio Shack and X-acto. The
four tools in the Radio Shack "Solder Ease Kit" are double-ended tools,
with different shaped probes extending from either end of plastic handles.
However, by sawing through the plastic about 3/4 inch from either end,
these tools become manageable. The probes included with the X-acto kit fit
into a pin vise type handle, which allows them to be used with or without
their heavy handle.
Radio Shack 64-227--"4-piece Solder Ease Kit", $3.00
Mouser 590-6348--X-acto "Solder Aid Kit", $6.00
Tweezers and Heat Sinks
Forceps which can lock or clamp on to wire leads are very useful tools.
These devices can be clamped on to the leads of heat-sensitive components
in order to absorb the heat and prevent damage to the components. These
forceps can be used as "handles" by which wire leads are held in place
while soldering them.
My favorite tools of this kind are surgeons' forceps. Shaped like
scissors, they can be used as very small pliers to aid in forming wires
around connection terminals. They have mechanisms allowing them to be
locked into place. Being made of stainless steel, they cannot be
accidentally soldered into the project.
Spring-loaded heat sinks can serve many of the same purposes. Radio
Shack sells a very nice kit of aluminum heat sinks which contains one such
clamp mounted on a strong permanent magnet.
"Seizers" (two position locking forceps):
42H--6-inch straight nose, $10.25
43H--6-inch serrated curved nose, $10.50
Available from Fordham. *
Radio Shack 276-001--"Heat Sink Kit", $2.00.
Lab Jack
If supporting the wrist is so important, perhaps there are those of you
who would prefer to return the dictionary to the bookshelf and use a
sophisticated adjustable platform instead. A "lab Jack" is made up of two
platforms separated by a sturdy scissor-jack mechanism. By turning a
thumb-screw, the height of the upper platform can be adjusted as desired.
"Jiffy-Jack"--6-1/4 by 7-1/2 inches (platform size),
Cole-Parmer * No. 8056-20, about $60.
Vises and Holding Devices
A good strong vise is the best tool for rigidly supporting a work
piece. A vise takes on a new measure of convenience when it can be
swiveled to orient the work in a favorable position for soldering. It is
for this reason that products of the Panavise Company are surveyed in this
list. The bases listed provide great flexibility in positioning the vise
heads.
Besides traditional vises, fixtures specifically designed for holding
circuit boards have become very popular. Many such holders grip one edge
of the board between two strips or blocks. In order for this type to be
used, a section along the edge of the board must be left free of circuit
elements. Holders made by Panavise, on the other hand, hold opposing edges
of the board between two spring-loaded V-shaped channels. This arrangement
permits the greatest flexibility of board layout.
All board holders have provision to flip the board over, so the work
can be done from either side.
Panavise Products-- Any combination of the items below can be
assembled. My favorite items are the low-profile head (304), circuit board
holder (315), and the vacuum base (380). I rarely take the time to clean
off the bench and secure the vacuum base as intended, but the rubber pad on
the bottom of this base minimizes slipping while allowing me to position it
anywhere.
CAUTION!! The jaws of these vise heads are nylon, and readily melt
when touched by the iron. This must be avoided or the tip of the iron will
be contaminated.
300--original screw-down base
305--low-profile screw-down base
380--vacuum base
308--weighted base mount for screw-down units
311--bench clamp base
303--original regular vise head (jaws are 2-1/2 inches across)
304--low-profile vise head
366--wide opening head (up to 6-1/2 inches)
315--circuit board holder.
Available from Fordham and Jameco. * All items are from $15.00 to $17.00
with the exception of the circuit board holder and the vacuum base which are
$20.00.
"THIRD HAND"--This is the simplest of board holders. It consists of a
spring-loaded slot into which one edge of the board is fitted, and this
whole assembly is hinged to a bench clamp. Its one disadvantage is that it
puts the work out beyond the edge of the bench, making bracing of the
wrists very difficult. However, an "Extension Bench Clamp" can be
purchased which puts the unit 6 inches back from the edge of the bench.
PCB-3--"Third Hand", $5.00
PCB-X--"Extension Bench Clamp", $13.00.
Available from Jameco. *
"DELUXE SOLDER STATION"--Although companies like Panavise make outfits
which have everything on them, including the soldering iron rest stand, few
are worth the money. Here's one that is. (I have been unable to find out
just who the manufacturer is.)
This device has a low-profile cast iron base on which an upright bar is
mounted. At the top of this bar a sandwich-type board holder is assembled
with provisions for tilting and rotating (flipping) the board. Two sockets
with set screws are located at the rear corners of the base, and these are
intended to accept cold-rolled steel rods supporting the spool of solder
and the iron rest stand.
My first recommendation is that the upright member supporting the board
holder be shortened. It is secured to the base by a stove bolt up through
the bottom, and you can drill and tap this upright bar to be mounted again
after it has been shortened.
The sockets in the rear corners can be used to mount any number of
ingenious gadgets having a 1/4 inch peg to fit into them. Whether you wish
to attach a homemade hand rest, or fly your school colors from the work
bench, this stand gives you the versatility to do so.
ST10--"Deluxe Solder Station", $25.00.
Available from Fordham. *
Conclusion
The basic difference between a sighted person soldering and a blind
person soldering can be described in terms of feedback. There is no
argument that a blind person is operating "open loop" (without direct
feedback) part of the time. In reaching from one place to the next and in
ascertaining what is actually happening during the soldering process, the
blind person is forced to use discontinuous bits of information, whereas
his sighted counterpart has information which is continuous. The gaps--the
discontinuities in information can be made less significant. By shortening
the reach, the target can be hit fairly accurately without vision. By
attending to alternative or indirect cues, deductive reasoning can verify
facts which are not seen. These principles are not new, but they have
tragically remained unsaid.
Blind people have been soldering throughout this entire century. As
for myself, I was employed as a technician for three years building very
complex electronic equipment. Since then, I have wired the prototypes of
my own engineering.
Topics yet to be covered include: tinning stranded wire, soldering
various connectors, desoldering, and "resistance soldering".
* Address List of Suppliers
Cole-Parmer Instrument Company, 7025 N. Oak Park Avenue, Chicago, IL
60648; Phone: (800) 323-4340.
Fordham Radio, 855 Conklin Street, Farmingdale, NY 11735; Phone: (800)
645-9518.
Jameco Electronics, 1355 Shoreway Road, Belmont, CA 94002; Phone:
(415) 592-8057.
Marshall Industries, 788 Palomar Avenue, Sunnyvale, CA 94086; Phone:
(408) 732-1100.
Mouser Electronics, 11433 Woodside Avenue, Lakeside, CA 92040; Phone:
(714) 449-2222.
- end -
[from the Smith-Kettlewell Technical File
Vol. 2, No. 2, Spring 1981]
SOLDERING, PART III
_Tinning Stranded Wire_--I have learned from experience that neglecting
to tin stranded or braided wire before soldering it to a terminal is no
shortcut. If the bundle of strands is not soldered together beforehand, it
is very likely that a few individual strands will not be involved in
bonding to the terminal. This weakens the connection, and individual
strands may subsequently stray over to an adjacent terminal.
In order for all the strands to be pre-soldered together, the stripped
end of the wire must be bathed in fresh solder. As it is with tinning the
iron, there is hardly such a thing as applying too much solder. A generous
amount of solder can be wrapped around the end of the wire and heated. I
keep a roll of very thin solder on hand for this purpose--about 0.03 inches
in diameter. For small wire, above 22-gauge, I use a length of solder abut
two times as long as the stripped-back portion of the wire. I double this
amount when soldering larger wire, such as lamp cord or braid.
Don't be stingy with the length of wire from which you remove the
insulation; remember, you will have to find this stripped end with the tip
of a hot iron. Give yourself a good half inch of bare wire beyond the
insulation.
Twist the stripped end of the wire between your fingers to tightly
bundle the strands. Using the 2-to-1 rule, fold the solder back against
itself about an inch from the end, thus forming a long skinny hook of
solder. Slide the wire all the way into the hook and position the bend of
the hook just ahead of the insulation. Wrap the one-inch long piece of
solder in a neat coil around the bundle of strands, progressing toward the
end of the wire.
Finding the wire with the tip of the iron is no easy task. Hold the
wire in one hand, the iron in the other, and rest both hands against a
familiar referencing object. While bringing them closer and closer
together, gently rock one of them up and down so that they are sure to
connect as soon as they cross. When they have met, put the bundle of
strands on top of the tip of the iron and wait for the solder to melt.
Melting of the solder will be indicated by the disengaging of the wire from
the solder leading back to the spook and by the usual squeakiness of
solder-wet surfaces. At this time, slowly slide the iron out from under
the end of the wire, allowing the wire to slip downward and shake off its
excess solder. This will tend to splatter solder, so don't do it in the
direction of other people or the family pet.
Tinning braided conductor deserves special mention. Taken together,
the many strands in the braid present a large amount of surface metal with
which the solder can alloy. In addition, These strands are in firm contact
with each other; efficient heat transfer occurs between them. The result
is that braid acts like a wick in the molten solder. Bathing the end of
the braid in solder will cause a surprising amount of the braid to become
stiffly soldered together. If you wish to tin merely the end of the braid
without impairing its flexibility further back, one or two clip-on heat
sinks can be attached just behind the length being tinned. This causes an
abrupt decrease in temperature beyond which the solder cannot alloy with
the strands of the braid. Remember to reattach a heat sink to the braid
when soldering it to a terminal, since this "wicking" of the solder can
still occur.
- END -
[from the Smith-Kettlewell Technical File
Vol. 3, No. 1, Winter 1982]
SOLDERING (PART IV)
POPULAR RF CONNECTORS
Having been a ham for two decades, and having worked in a lab full of
test equipment on which many of these connectors are used, the editor has
accumulated a bag of tricks for installing RF connectors. Besides making
the job of installation easier, these tricks are intended to address two
objectives; one is to prevent damage to the cable in preparing it, and the
other is to give the blind technician positive assurance that the connector
is properly fitted and soldered to the cable.
RCA phone plugs shall not be called RF connectors (in my presence), and
are taken up in Part V, as is their cousin the Motorola plug.
Cable-mounted male connectors are the ones addressed in this
discussion. Cable-mounted female units are used less frequently, and the
principles used in working with them are exemplified in the discussion of
their male counterparts. Chassis-mounted females often have conventional
solder terminals and warrant no special mention.
The Standard UHF Connector (PL259)
The so-called "UHF" connector (whose name goes back to a time when F's
were not very H and were not at all U) has been widely accepted by radio
amateurs and CB equipment manufacturers. In a way, this is unfortunate,
since installation is time consuming, and proper soldering of the shield
braid is difficult. What's worse is that this connector is poorly
understood even by veterans of radio work who often invent short-cuts to
proper installation, making it imperative that knowledgeable people (such
as we) oversee the preparation of cables at antenna parties.
The male center-conductor pin is tubular so that the cable's center
conductor can be passed through it. The overall length of this pin is 5/8"
from its tip to the bottom of the well inside the connector shell.
In the connector shell directly behind the center-conductor pin is a
chamber whose inner diameter is just large enough to accept the braided
portion of the cable. This chamber is about 1/2" deep and has an inner
diameter of .350". Four holes around the perimeter of this chamber allow
access to the braid through the shell of the connector; it is intended that
the braid be soldered to the shell through these holes.
Further back, the inner diameter of the connector is large enough to
accept the plastic-covered portion of large coaxial cable such as RG8/U.
Internal threads at the rear of the connector are provided to accommodate
"reducing adaptors" to be used with small-size cable.
Preparation of Large Cable ((RG8/U, RG11/U)--About 3/4" from the end,
cut through the outer sheath, the shield braid, and the dielectric
insulator, and remove these pieces to expose the center conductor. Check
with a fingernail to see that none of the strands of the center conductor
were badly damaged by the knife. If obvious damage has been done, it will
save you future grief to start over.
Using the procedures outlined in "Soldering Part III", smooth out and
rebundle the strands of the center conductor and _generously_ wrap them in
solder. Using a heavy-duty soldering iron or gun, tin this conductor with
the end of the cable pointing slightly downward to prevent a bead of solder
from collecting at the base of the lead; such a bead of solder can prevent
insertion of the wire all the way into its tubular pin. Before continuing,
insert the lead into the tubular pin from the front end of the connector to
make sure that it fits after being tinned.
Cut through the outer sheath 5/8" back from its end (5/8" back from the
previous cut). Make no sawing motions with the knife that might cut into
the braid; gently press the knife through the sheath on all sides, being
careful not to nick the braid. Carefully remove this short length of outer
covering and assess the damage. If whiskers around the knife cut indicate
that a half dozen braid wires have been severed, it would be wise to start
over.
Essential to installation of the connector is that the braid be
completely tinned so as to make soldering inside the connector shell
possible. Furthermore, the braid must be smoothed down so as to make it
small enough to fit into its chamber. What makes tinning the braid
difficult is that the dielectric insulator melts at a comparatively low
temperature. Bringing the braid to soldering temperature is often _very_
injurious to the center insulation, and melting of the plastic can even
contaminate portions of the braid, making it unsolderable.
I find that a thin strip of paper wrapped around the center insulator
under the braid can protect the plastic from the heat. The braid can be
flared out temporarily while the paper is wrapped around the plastic
insulator beneath, then the braid can be closed over the paper. You may
wish to "train" the paper by first wrapping it around a pencil to make it
more manageable. The strip should be at least 1/2" wide and about an inch
long. One-half of the slip from a Chinese fortune cookie works very well;
no only is it precut to the right width, but this paper is very thin and
supple.
It is nearly impossible to keep the braid smoothed down enough to fit
into its intended space, and you will more than likely have to file the
tinned braid down to size before the connector can be installed. As long
as filing will have to be done anyhow, a piece of thin bare wire can be
used to tie the braid into place. (Without the extra paper insulator, this
trick can get you into trouble, since the wire will assure firm contact
between the hot braid and the dielectric insulator.) Loop the wire around
the end of the braid, and twist its ends together, tightening it just
enough to keep it in place around the braid.
To keep the tip of the iron from contacting the plastic outer sheath,
you may wish to wrap the cable in gummed paper or masking tape just behind
the exposed braid. Whatever you use, it should be of a material that will
not readily contaminate the tip of the iron.
Wrap a coil of solder around the exposed braid, using perhaps as much
as 6 inches of solder. Using a heavy duty iron or gun, proceed in tinning
the braid on all sides of the cable. By starting on the under side, you
will prevent large segments of the solder coil from dropping off as you go.
Each time you contact the braid, linger just long enough to feel the
squeakiness of clean solder wet metals, then draw the iron off the end of
the braid. After you have done this on all sides, let the cable cool for a
couple of minutes and then check you work for large globs or unmelted
pieces of solder. Approach these soldered globs specifically with the iron
and draw them off the end of the braid.
On the one hand, you must take long enough with this process to assure
that the braid is thoroughly tinned. On the other hand, the intense heat
inside the braid cannot help but damage the cable. You objective should be
to reach a good compromise.
The braid can now be filed to size. Wrap a piece of tape around the
center conductor to protect it from being marred by the file. File down
the jagged end of the braid until it is even with the end of the dielectric
insulator. File around the outside of you tinning job until it is smooth
and cylindrical. (For those of you who own a micrometer, the tinned braid
should measure 349/1000 of an inch.) Concentrate your efforts on the 1/2"
of braid nearest the end, since this is the portion which must fit into the
soldering chamber.
Testing for Proper Fit--Unfortunately, the adaptor threads inside the
back end of the connector make testing for a fit difficult. This threaded
portion of the connector is small enough in diameter to bite into the outer
sheath of large-size cable; screwing and unscrewing the connector during
the trial-and-error process of fitting is laborious and damaging to the
sheath. A slip-on test jig can be built by cutting off the rear-most 1.2"
of a connector, thus doing away with these internal threads. Slipping this
test jig onto the cable will quickly indicate if the tinned braid is too
large for the chamber, or if the tinned center conductor is too large for
the tubular pin.
Two indications as to whether or not the cable can be fully inserted
into a connector are:
(1) The center conductor can become a "measuring stick" if you cut
it to the exact length of 5/8". When the braid and dielectric insulator
hit bottom in the connector shell, the end of the center conductor will be
even with the end of the tubular pin. (You will recall that advice was
given to cut away 3/4" of material to expose this center conductor.
Depending on the shape of the end of the cable initially, you may need this
extra length to insure that a good clean 5/8" long piece of this lead is
available.)
(2) By tapping through the soldering holes with the point of a
braille stylus, you will be able to tell whether or not the braid is
present underneath. The surface beneath the holes should feel and sound
metallic when tapped, and the holes should be completely obstructed by the
braid. If the holes are only half covered, either the soldering chamber or
the tubular pin is unable to accept full insertion. If the surface beneath
the holes feels rubbery, the braid has been forced back by the entrance of
the chamber, and your stylus is contacting the center insulator.
Preparation of Small-Sized Cable--Slide a reducing adaptor of
appropriate size onto the cable. Carefully remove one inch of outer sheath
from the end of the cable. Position the adaptor so that its front end is
even with the end of the sheath and wrap tape around the cable directly
behind the adaptor to keep it from slipping backward. Fold the braid back
over the small end of the adaptor and tie it into position with a wire
loop. Wrap the braid in solder and tin it; this time, draw the iron in
front-to-back motions as if to smooth out the braid. Solder droplets will
appear to stick to the adaptor, but the fact that the metal of the adaptor
never reaches soldering temperature makes picking these droplets off
possible after the project has cooled.
about 1/16" ahead of the adaptor and braid, strip off the dielectric
insulator to expose the center conductor. Tin this lead, even if it is
solid wire, since this will make soldering easier.
File the braid to size and test its fit in the connector as before.
Installing and Soldering of the UHF Connector--The connector comes with
a screw-on ring to be used in securing it to its mating socket. _Be sure
that this ring has been passed down the cable before installing the
connector_. Screw the connector onto the cable and repeat the above tests
to ascertain that it is properly in place.
Especially with large-sized cable, the center conductor should be
soldered first to hold the connector in place. If this is not done,
bringing the body of the connector up to soldering temperature will soften
the outer sheath, thus allowing the connector to slip forward. Your
subsequent unseemly remarks will have the neighbors concerned for you.
Clamp the connector in a vise with the tubular pin pointing upward.
Some technicians heat the pin from the side and _hope_ that the conductor
inside reaches soldering temperature. For this to work, the lead must be
wet with solder; it helps if there is room in the pin to slip thin solder
in along side the conductor. These connectors, however, have a
spoon-shaped end on the tubular pin so that the iron can be brought into
contact with both the pin and the lead.
Hold a straight piece of thick solder vertically and position it on top
of the pin. You can either position the tip of a soldering gun at the
opening of the spoon, or you can slide a hot iron up the pin until the tip
finds the spoon. When the solder melt, feed a half inch of it straight
down into the pin. Very often, you will lose the pin with the solder. Let
the project cool off and try again. Solder spilled outside the pin can be
wiped off with the iron later; do this with the pin pointing downward.
Also, it is a good idea to check for spillage around the abase of the pin
with a stylus or other small prove. This spillage can be removed with a
knife.
The braid must now be soldered through the holes in the shell. If the
connector is to be used outdoors, soldering all four holes will help
protect the cable from moisture.
Orient the cable horizontally and clamp it in a vise about an inch
behind the connector. (Clamping the connector in a vise directly will make
heating it impossible.) Before securing the cable in a vise, turn it so
that a solder hole is facing upward. It is easy to lose track of which
holes you have soldered. You may wish to lay a strip of tape adjacent to
the first hole to serve as a reminder.
I use a gun for soldering the holes, since positioning the tip of a hot
iron can be tricky. In any case, holder the solder at an angle and insert
it into the hole. Place the tip of the iron on the hole, or if possible,
orient it so that a corner of the tip seats in the hole. The solder which
melts immediately (which disconnects the solder in your hand from the
connector) will serve to create a column of molten metal under the iron in
order to improve the efficiency of heat transfer.
Keep trying to find the edge of the hole with the solder. Spilling
solder elsewhere on the connector will not hurt anything,just try to see
that some of it spills into the hole. Do not leave the connector with the
iron until rocking of the iron feels squeaky; this is your _only_ true
indication that wetting of the connector has occurred.
After the connector has cooled, clear some of the larger droplets out
of the way with a knife blade and feel in the hole with a stylus. The hole
should either not be there, or should feel more like a "dent" than a hole.
As a final test, try unscrewing the connector from the cable. Even
with the center conductor soldered, the connector will rotate an eighth of
a turn if no adhesion to the braid has occurred.
With knives, picks, files, grinders, hatchets, and soldering irons,
remove enough spillage from the connector so that the outer ring can be
attached as intended.
Salvaging UHF Connectors--Don't! Even if you are successful in getting
the cable free of the connector, it is impossible to assure that little
whiskers of braid are not lurking in the shelter of the soldering chamber
ready to arc to the center pin when power is applied. I always buy more
units than I need in case something goes wrong in soldering them, or in
case I forget that pesky outer ring. _Always start over with new
connectors_.
BNC and N Connectors
These connectors are much different from the "UHF" units discussed
above. Their connection to the shield braid is solderless. The only
soldering to be done is in attaching a tiny male connecting pin to the
center conductor of the cable. Without effective holding clamps, attaching
this pin can be difficult.
These connectors come with several small parts whose dimensions are
specific to a given size of cable. A connector which has been purchased
for one size of cable cannot effectively be used on another. (A list of
connector numbers at the end of this article should aid in ordering
appropriate units for standard-sized cables.) Care must be taken so as not
to lose any of the small parts, since _all_ of them are necessary for
proper installation. A list of these parts is given below:
(1) A very tiny pin which tapers to a point is intended for
soldering to the cable's center conductor. A hole drilled axially into the
rear of this pin accepts the center lead of the cable; the diameter of this
lead closely fits the lead of its intended cable. Soldering is done
through a hole in the side of the pin.
(2) A tapered washer is intended to fit a matching counterbore
inside the shell of the connector. The braid, which is folded back against
the tapered washer, is sandwiched between the washer and the bottom of the
counterbore.
(3) A rubber ring fits around the cable behind the tapered washer
and is held in compression; it clamps the braid firmly between the washer
and the connector shell, and it grips the outer sheath of the cable to act
as a strain relief device.
(4) A thin metal washer behind the rubber ring prevents damage to
the rubber as it is being compressed.
(5) A threaded insert screws into the shell of the connector
behind all of the above pieces and is firmly tightened with a wrench to
compress the rubber ring.
The threaded insert, the thin flat washer, and the rubber ring are slid
onto the cable in that specific order. Next, strip off some of the outer
sheath to expose the braid. (The amount of braid to be exposed will depend
on the connector and the size of cable. Basically, the braid should flare
out and fold back to cover the front surface of the tapered washer.) After
the sheath is removed to expose the braid, slip the tapered washer over the
braid (with the tapered side toward the end of the cable; press this washer
back against the sheath and fold the braid back over it.
About 1/8" ahead of this braid assembly, remove the dielectric
insulator to expose the center conductor. Generously tin this lead and cut
it off to a length of 1/8" (beyond the end of its insulator).
The tiny center-conductor pin can be held in locking forceps, with one
of the forceps handles being held in a vise. You may wish to line the jaws
of the forceps with bits of braille paper so as not mar the pin with their
serrations, and to keep the forceps from acting as a heat sink. Orient the
pin horizontally with the solder hole facing upward.
In order to keep the cable in position, it can be held in another vise
located a few inches away from the pin. The center conductor should
comfortably rest in the pin, i.e., there should be no sideways force on
this lead which will cause it too cut through the softening dielectric
insulator as the connection is heated.
Hitting the tiny pin with a soldering iron, without touching the
dielectric insulator, is no easy task. You may wish to protect the
insulator by poking the center lead through a small bit of braille paper,
thus creating a barrier between the iron and the plastic. Hold a very
straight piece of solder vertically and insert its end into the soldering
hole in the side of the pin. Carefully follow the forceps over to the pin
with the tip of the iron and position the iron on the under-side of the
pin. Since the pin is machined to fit its center conductor, you do not
need to apply very much solder to the connection. This is fortunate for
us, since feeding the solder straight down into the small hole is often a
mater of luck. You will often lose the pin with the solder, whereupon you
let it cool off and try again. Perhaps 1/8" of solder should be fed to the
connection. Spillage onto the sides of the pin can be filed away after it
has been secured to the center lead.
List of Connectors
PL259--UHF connector for large cable, RG8/U and RG11/U.
UG-175/U--Reducing adaptor for RG58/U cable.
UG-176/U--Reducing adaptor for RG59/U cable.
UG-21/U--Type N connector for large sized cable, RG11/U.
UG-88/U--Type BNC connector for RG58/U cable.
UG-260/U--Type BNC connector for RG59/U cable.
Amphenol No. 69475--Type BNC connector for RG174/U and other miniature
coax.
- End -
[from the Smith-Kettlewell Technical File
Vol. 3, No. 2, Spring 1982]
SOLDERING, Part V
RCA and Motorola Plugs
By the late 1930's, there were consistent needs in consumer products
for low-cost "shielded" (coaxial) connectors for use at audio and low radio
frequencies. Two such connectors were developed to address these
needs--the RCA "phono plug" (now the standard for interconnecting hi-fi
components), and the "Motorola plug" (now the standard for automotive
receiving antennas). (Note that in traditional terminology, a distinction
is drawn between "shielded" and "coaxial" cables and plugs in discussions
of audio and r.f. signal lines, respectively. Since single-conductor
shielded cables such as those used on these plugs are coaxial, the
distinction will not be made in this article.)
These two connectors are very similar in concept. Both have a tubular
center-conductor pin into which the "hot lead" is soldered. Both have a
four-segment shield shell, to which the "cold connection" is made, which
snugly fits a matching shell on the socket. The shell of the RCA plug is a
bell-shaped affair which surrounds the shell of its socket; the shell of
the Motorola plug is a sleeve-like structure surrounding the cable which
fits into the shell of its matching socket. Having four segments and being
made of springy metal (usually a hard brass plated with tin), these plugs
can easily be adjusted to tightly fit their respective sockets, thus
eliminating the need for close-tolerance machining in their fabrication
("stamping" and "extruding" are the only fabrication processes necessary).
Noting the principles of soldering as noted in Part I of this series
(summarized at the beginning of Part II, Winter, 1981), rare is the
soldering job which requires as many wholesale violations of the rules as
must be done in installing these connectors. The procedures for installing
the plugs along with the rules to be broken are listed below:
(1) "To solder the tubular pin, pass the lead through the pin and
secure the connector in a vice [sic] so that the pin points upwards; heat
the side of the pin while feeding solder straight down into it."
Efficient heat transfer only occurs when there is a
continuity of alloys between the iron and the work, i.e., the iron should
be in a solution of solder along with all the work pieces. This cannot
happen with the iron on the outside of the pin and the soldering going on
inside the pin. Furthermore, in order for all pieces of work to heat up
together, they must be in firm physical contact. Since the wire is usually
much smaller than the inner diameter of the pin, firm contact is unlikely.
(2) "On the Motorola plug, the cable shield is folded back against
the outer sheath so as to contact the inside of the staves of the connector
shell; after insertion, all four segments of the shell are soldered to the
braid."
As with the center conductor pin, the iron is used to heat up
the outside of the plug while soldering takes place inside the shell. A
solution of solder cannot be established between the iron and the work,
since spillage of solder onto the outside of the shell would prevent its
fitting into the socket.
(3) "On the RCA plug, the cable shield is to be folded over the
top of the bell-shaped shell and soldered to it."
Where possible, all components of the work piece should be in
contact with the iron so as to heat up simultaneously. Where this is not
possible, the iron should at least be in contact with the item of largest
heat capacity, the largest piece of metal. Unfortunately, in the case of
the RCA plug, the iron will be resting on the thin braid wires and not on
the metal shell of the plug. By the time the shell is brought up to
soldering temperature, the braid wires will have been heated for a
considerable length of time, and they often conduct so much of this heat to
the cable that the center insulator becomes severely damaged.
The points discussed in this section describe how we can cheat the laws
of physics with "tricks of the trade".
Soldering Tubular Pins
Because these pins fit into spring contacts in their socket, it is
imperative that no spillage be allowed to change their size and shape,
which would damage any socket receiving them. One thing in our favor is
that these pins are often plated on the outside with a metal less soluble
in solder than the base metal (they are often plated with cadmium).
Therefore, solder is less likely to stick to the outside than it is to the
inside. When going into solution, solder loves to "wick" along, around,
and into highly-soluble materials via "capillary action". Therefore, we
can expect solder to guide itself in the direction of soluble surfaces; it
will gladly flow into and around the inside surface of the pin as soon as
the necessary soldering temperature has been reached, whereas it will just
tend to "bead" on the outside of the pin. (If solder is melted directly
under the iron, it will alloy with some of the plating.)
The diameter of the lead is very often much smaller than the inside
diameter of the pin; being very loose in the pin, it may at times not be in
direct contact with the inside of the pin. As the pin fills with solder,
it becomes a sort of "secondary soldering iron"; it is intended that heat
be conducted from the pin to the lead via the molten solder. However, two
roadblocks can foil this plan. First, you may not be able to spill enough
solder into the pin to make a good conductive puddle, or by the time you do
so, some of this solder may have melted through the cable insulation to
cause a short behind the plug. Second, the flux may have been used up
before the materials inside the pin have been deoxidized to any significant
depth. By generously pretinning the lead and by inserting a piece of thin
solder into the pin along with the lead, these problems are minimized.
With the above principles in mind, the following three methods can be
used to solder a wire into a tubular pin:
(1) A tinned lead is prepared whose length is just short of
reaching the end of the pin. If the lead diameter permits, slip a piece of
thin solder into the pin alongside this lead and cut it off at the end of
the pin. Clamp the connector in a vice so that the pin points straight
upward. Using fairly thick solder (perhaps .05" diameter), vertical orient
and position a straight piece of this solder directly on top of the hole in
the pin, positioning your hand so that you can feed about 5/8" of it
straight down into the pin. Being sure your iron is wiped free of residual
solder (you don't want it to deposit solder onto the side of the pin), find
the side of the pin with the iron and hold it there until the solder melts.
Heat transfer will be best if your iron has a screwdriver or chisel tip;
turn the iron until you feel its flat side rests squarely against the side
of the pin (getting your feedback through the handle of the iron).
Reciting perhaps 17 stanzas of your favorite verse, wait for the solder to
melt--then feed it straight down into the pin. If anything goes wrong--if
you cut the solder in half with the iron while looking for the pin, or if
you lose the pin while feeding the solder--let the project cool, clear away
any droplets from around the work and try again.
(2) Prepare a long section of well-tinned lead whose length is
sufficient to protrude about 3/4" beyond the end of the pin. This time, it
is essential that a piece of thin solder be inserted into the pin alongside
the lead, primarily to provide fresh flux for cleaning the pin's inner
surface. You needn't cut the solder off as it emerges from the end of the
pin, you can use this same solder in making the eventual connection. Clamp
the connector in a vice with the pin straight upward. Hold the solder off
to one side in preparation for feeding it to the protruding wire, not to
the pin. With the iron, find the point at which the wire emerges from the
pin; rest the iron so that it contacts both the wire and the end of the
pin. The solder in your hand will quickly be disconnect from the pin, at
which point you should fish for the wire above the iron. Feed perhaps an
inch of solder to the wire, taking care to avoid the pin.
The theory is that most of the solder will wick down the highly
solder-soluble wire into the pin. For this scheme to work, plenty of fresh
flux must be available to make the pin's inner surface soluble, otherwise
the solder will wick everywhere else. Of course, the wire must be small
enough in diameter to leave room for solder to run past it on its way into
the pin.
(3) The connector pin can be pretinned--actually filled with
solder--and the tinned conductor can then be run through the molten solder
as the pin is reheated. Clamp the connector in a vice with the pin
horizontal, or perhaps pointing slightly downward. Feed a straight piece
of thick solder (0.05") into the pin from the rear of the connector until
it reaches the end of the pin; hold on to it behind the connector in
preparation for feeding about an inch of it into the pin. Find the end of
the pin with the iron and press the solder forward until it is melted by
the iron, and proceed to fill the pin with solder. After withdrawing your
piece of solder from the rear of the plug, slide the iron sideways off the
pin and let the project cool.
Prepare a suitable length of well-tinned lead--its length is not
critical. Fish for the rear entrance of the pin with this lead and prepare
to drive it up to the hilt in the connector as you reheat the pin. Once
again, find the end of the pin with the iron and wait for the solder to
melt, which will be indicated by squeakiness and by the fact that the lead
can be moved forward. Slide the lead in as far as it will go; Remove the
iron and wait for the solder to solidify without jarring the cable. If the
lead is longer than the pin, you will feel it run into the iron--in which
case, follow it out with the iron, letting the iron be pushed away from the
end of the pin.
This last method may be more difficult with Motorola plugs, because the
shell is so long that the pin is difficult to find with the center lead.
With the continuity tester connected between the hot lead at the other end
of the cable and the connector pin, you can verify having hit the solidly
filled pin with the lead. The pin rarely stays completely filled when
being tinned, since some of the solder is bound to run out the forward end.
Therefore, you may feel a depression at the rear of the pin with the lead,
and you may even achieve partial insertion before the pin is reheated.
Beads and icicles of stray solder can be removed with a clean iron, a
knife, or a file. If the pin's plating did not take the solder, spillage
can easily be picked off with a fingernail. The important thing is that
the pin be round and of an appropriate diameter for its matching socket.
Spillage of solder around the base of the pin, the application of too
much solder, or over-heating of the project can all cause short-circuiting
of the plug and/or cable. After each and every step, it is wise to check
for shorts between the pin and the shell, and between the pin and the cable
shield.
Installing Motorola Plugs
In principle, braid is folded back over the outer sheath and tinned
before inserting the cable into the connector; this braid is to be soldered
to the four staves of the shell at the rear of the connector. Critical
dimensions are listed below:
(1) The tubular pin is about 11/16" in length; the center lead
should be prepared accordingly.
(2) In order for the shell to reach the full insertion of 5/8"
into the socket, its four springy staves should be free to expand against
the sides of the socket for this distance, making it necessary to solder
the braid behind this point. Allowing 1/8" for the insulator to which the
tubular pin is mounted, there should be a spacing of 1/2" between the
entrance of the pin and the point at which the braid is soldered. In other
words, the center insulator should extend at least one half inch beyond the
folded-back braid.
(3) This connector's shell is best suited for a braid whose
outside diameter is about 5/16". RG59/U with its braid folded back over
the outer sheath is about this size, while braid folded back on RG58/U is
too small. Where necessary, masking tape or other non-contaminating
material can be wrapped around the outer sheath of smaller cable so that
the braid can be formed around something of appropriate size. (Actually,
it is a good idea to wrap a layer of this tape around the outer sheath of
any cable, even RG59/U, to keep the intense heat of tinning and soldering
from melting the plastic, thus contaminating the braid and making it
unsolderable.)
Preparing and Tinning Braid--Of course in preparing the cable, a
decision will have to be made as to which method of soldering the tubular
pin you intend to use, since the appropriate length of exposed center
conductor varies among the three alternative methods discussed earlier.
Behind the exposed center lead, the following procedures should be carried
out:
(1) Strip off about 5/8" of outer sheath--after the braid has been
folded back, this will give you just over 1/2" of center insulator to act
as a spacer inside the plug.
(2) After folding the braid back over the outer sheath, wrap paper
or masking tape around the cable at the end of the sheath to protect it
from the intense heat of tinning and soldering. If cable diameter is
smaller than about 1/4", wrap enough tape around it to bring it up to size.
(3) Fold the braid back over the sheath and smooth it out in
preparation for tinning. You will probably have to unbraid about half of
it to accomplish this; do so carefully with a Braille stylus or other
instrument which is thin _but not sharp_. Sometimes braidwires get rather
sparse as they are expanded over the outside of the cable; in this case,
twist the cable between your fingers and wrap them around t he sheath near
its forward end.
(4) Wrap a couple of turns of thin solder around the braid
nearest the forward end, just over the end of the sheath. Gently wipe the
iron over the circumference of the braid's forward end; tinning will not
take long, since the expanded braid has very low heat capacity (you may
wish to wrap the center insulator in a bit of masking tape to prevent it
from being damaged by the iron when you miss the braid.) Let the project
cool and survey the damage. An occasional lump of solder will not hurt
anything, since these connectors do not need a "precision fit" between the
braid and the shell. Any loose braidwires behind the tinning job can
simply be folded up near the front of the braid and forgotten about.
Pre-Tinning the Motorola Plug--Tinning the inside of the shell is an
essential part of the installation of the plug. There is no other
efficient way of getting solder and fresh flux inside the shell and onto
the shield connection.
Tinning the inside of the shell of a Motorola plug is good fun--it is
one soldering job during which you cannot get lost. Clamp the tubular pin
horizontally in a vice and turn the plug so that the stave to be tinned is
at the bottom. Slip a piece of thin solder through a crack near the top of
the shell in preparation for feeding about an inch of it down on to the
bottom stave. Insert the tip of the iron into the shell and rest it on the
bottom stave near the open end. Feed solder to this save just ahead of the
tip of the iron, then slowly withdraw the iron from the shell. Turn the
plug so that this can be done to all four segments of the shell.
Soldering the Shield of the Motorola Plug--Slip the tinned plug over
the prepared cable and solder the tubular pin; this will help keep the
cable in position. (You can assure firm contact between the segments of
the shell and the braid by bending the staves inward so as to tightly fit
the cable. They can be bowed out again if the plug fits loosely in its
socket.) Now clamp the tubular pin horizontally in a vice and reheat the
staves one at a time. As the solder melts under the stave, you may feel it
give a little under the iron--but more importantly, you will feel a rise in
the temperature of the cable behind the plug. After doing this to all four
segment of the shell, let the project cool. (You need not do all four
segments at once, you can let the plug cool after each phase if you wish
to.)
The connector should not rotate freely with respect to the cable; even
with the center conductor soldered, there will be considerable freedom of
motion if the braid has not adhered to the inside of the shell.
Furthermore, you should not be able to lift individual staves away from the
cable.
Reheating parts of the plug can be done to correct problems unearthed
during testing. If reheating fails to attach segments of the shall to the
cable, there is a secret weapon we have to assure eventual soldering of the
shell. Lay a piece of thick solder in a crack between two staves and place
the iron on top of it just over the braid beneath. This will get some
action; You can have fun filing the plug back down to size and polishing it
off with emery cloth after this drastic measure has been taken.
Installing RCA Phono Plugs
In principle the braid is flared out so that the plug can be slipped
onto the center conductor and soldered, then the braid is closed over the
rear of the plug (about the top third of the "bell") and soldered there.
Critical dimensions are listed below:
(1) The length of the tubular pin varies considerably--from as
short of 1/2" to a length of one inch. Older units came in two sizes, long
and short. A nominal 5/8" will serve as a practical estimate.
(2) There should be at least 3/16" of insulation between the
flared-out braid and the exposed center conductor. The presence of this
insulation is absolutely necessary, since this portion of the center lead
passes through a small opening in the rear of the bell-shaped shell behind
the tubular pin.
(3) The flared-out braid wires only need to be about 3/8" long,
since soldering is done on the rear portion of the shell and not along the
four segments. However, I usually trim the braid wires 1/2" with the idea
that they can be trimmed or filed off the connector later.
Tinning the RCA Plug--A fair sized puddle should be created at the back
of the shell; when the braid is pressed against the connector with the
iron, it will sink into this puddle and soak up the molten solder like a
gauze. I tin the pin with its tubular pin held horizontally in a vice. I
touch the shell with the iron and the solder in two or three places around
the circumference of the shell (do this toward the rear and try to avoid
the segmented section). After the unit has cooled, I check for bare metal
with a fingernail--those portions wet with solder will be very smooth and
gummy with flux. I usually find a spot which needs redoing, whereupon I
turn the plug to make this point accessible and go after it again. Lumps
of solder are not very important at this stage, but if they offend you,
wipe them off with the iron after you have stripped its tip free of excess
solder on your cleaning sponge.
Soldering the Shell of the RCA Plug--Solder the tubular pin to the
center lead, making sure that the plug has been pressed back firmly against
the flared-out braid. (If the cable is large and stiff, you can hold it
vertically in the vice while soldering the pin. If the cable is small or
very flexible, hold the connector in the vice while making sure the cable
is being pushed up snugly underneath.)
Turn the connector over and clamp its tubular pin in the vice with the
segments of the shell resting on top of the vice jaws. Arrange some way of
holding the cable _straight up from the connector_. Having the cable held
vertically is very important, since letting it droop sideways will bring
the center insulator of the cable firmly up against the rear entrance of
the shell; as soon as the shell is heated, it will cut through the
insulator and short out the cable. Finally, firmly press and smooth the
braid down over the shell. You may even wish to tie the braid in place
with a piece of thin wire--this wire can be smoothed down with a file
afterward.
With the iron in one hand and the solder in the other, solder the braid
in a few places around the shell. You will not need to apply much solder,
since what you are mostly doing is providing the braid wires with fresh
flux. You will only need to do this in four or five places around the
shell, and you can take as long between solderings as you wish. You may
even wish to turn the connector in the vice in order to conveniently reach
all sides. If your vice has metal jaws, you can use them as a landmark by
which you can first find the connector shell and then hop up to the upper
rim of its bell-shaped structure. In doing so, be careful not to jostle
the braid wires out of position.
After the project has cooled, check to see that adhesion has been
accomplished on all sides. Any individual loose braid wires can be
"tacked" down with the iron, most likely without applying additional
solder.
With wire cutters, trim ragged edges of braid off the plug and file the
plug until it is round and smooth. _Do not file or trim away any material
at the back of the shell_, just around the sides.
Alternate Methods for Attaching The Basic Connectors
Now that you know the "right way" to attach these plugs, perhaps you'd
be interested in how most of us do it. Although not as elegant, the braid
is often attached by gathering it into a "pigtail" and soldering it to the
side of the shell--soldering is only done in one spot. furthermore, since
they are gathered together, individual braid wires are less likely to sever
when the cable is flexed. This trick can be used on Motorola connectors by
bringing the "pigtail" out the rear of the plug and lapping it over the end
of one of the staves. (It should be noted here that this is how such
connectors are attached to unshielded 2-wire cables, such as speaker lines
and other non-coaxial applications.) A detailed example using an RCA plug
is given below:
Generously tin the "pigtail" and one spot on the rim of the plug's
shell. Bend the "pigtail" so that it curves around the upper rim of the
shell, covering about 1/4 of the circumference. Grab the end of the
"pigtail" in locking forceps and hold it in position while bringing the
iron into contact with both items. Watch for the squeakiness of solder-wet
metals and for a rise in temperature of the cable. Remove the iron and
don't move. If it didn't stick, wrap thin solder (0.03") around the
"pigtail" where it is to contact the plug and try again.
There are two accepted ways of getting a "pigtail" of braid:
(1) For cables whose center conductor does not bend easily, the
braid can be unwoven--simply combed out with a non-pointed instrument such
a Braille stylus. Once the braid wires are separated, they can be gathered
together and twisted into a bundle.
(2) With careful surgery, the center conductor can be extracted
from the braid at the end of the outer sheath, thus giving you a braided
pigtail. Remove a generous length of the cable's outer sheath.
Surrounding the braid with three fingers, massage it backward until there
is a little "balloon" of it right against the end of the outer sheath.
Sharply double the cable over at this point (at the balloon of braid).
With a Braille stylus, gradually work a hole in the braid at the outside of
this bend. Gently shift all the braid wires over to the inside of the
bend, exposing the doubled-over center conductor. Being careful to miss
all the braid wires, slip your stylus through the loop of center conductor
and ease it out of its knitted sleeve of braid. Afterward, looks for
whiskers indicating severed braid wires at the base of the center
conductor; get hold of them and simply pull these wires out and discard
them. Finally, massage and pull the braid out into a nice thin pigtail.
Alternative Varieties of These Connectors
A wide variety of these plugs are available, especially in the case of
RCA phono units. Your Editor's favorite variations will be listed here.
In addition, although not honestly classifiable as "alternative designs",
certain critical variations in the shape of RCA plugs will be discussed.
Motorola Plug--H.H. Smith makes a unit (12WJ) which includes soldering
tabs at the rear end of tow of the staves. Although I am not absolutely
sure of their intended use, it appears that they are to be soldered to the
braid without its being folded back over the cable's outer sheath. In any
case, the tabs can be adjusted to accommodate any size of cable, or they
can be treated as solder lugs to which a pigtail is attached. These tabs
can be cut off and treated as described earlier.
Basic RCA Plug Differences--Although I have used plugs without this
feature, very often the bell-shaped shell of the plugs you buy will have a
"double cup", that is, behind the large-diameter segmented section of the
shell is a slightly smaller-diameter section (also having straight sides),
and the braid can be tied into position around this portion of the shell
with a piece of wire. (Actually, this small-diameter section is used to
hold the phenolic insulator of the tubular pin.) As far as ease of
soldering is concerned, I would not reject plugs which are not so shaped.
There are mean/nasty self-destructive plugs having sharp edges at the
rear entrance of the shell which will damage the cable after it has been
attached. A notable example is the Switchcraft 3501M, whose shell includes
a sharp-edged flared-out portion which they use for mounting this plug on
various adaptors and cable clamps. The sharp edges at the back of this
plug will quickly sever the braid wires as the cable is flexed. It is
important that you render any such connector toothless before approaching
it with the cable. This can easily be done with a file.
RCA Plugs with Cable Clamps--The basic disadvantage of all the above
units is that stresses on the cable are borne by its fragile wires and not
by its protective outer sheath. Plugs are available with wrap-around cable
clamps which grip the outside of the cable and keep it from severing the
wires as it is flexed.
The Switchcraft 3501MC is a basic plug with an attached crimp-on clamp.
This clamp has two stages, one for the outer sheath and one for the exposed
braid (although you will have less trouble if you use them both for the
outer sheath and solder a pigtail of shield to the shell of the plug).
Because it is not completely shielded, this unit is poorly suited for RF.
The Switchcraft 3502 is a very fancy unit with a screw-on cover. Its
design has two major disadvantages. Its ground connection device has no
hole through which a shield pigtail can be inserted for soldering; the
pigtail must be "tacked" on to the back of the cable clamp support. The
other is that its tubular pin extends a full 3/16" into the connector
housing, making short circuits between this pin and the cable shield all
too likely. A fine hacksaw can be used to cut this pin without affecting
its structural integrity; this will separate the connection points and will
give you room to fully grip the outer sheath in its clamp.
- End -
[from the Smith-Kettlewell Technical File
Vol. 5, No. 2, Spring 1984]
SOLDERING, PART VI
Multipin Connectors
This task is more demanding of your skills than any other. You can
rest assured that any such connector has been designed to be of minimum
size. Also, there will always be nearby wire insulation that you can
abraid with the iron. Nevertheless, I have learned tricks which
help--both in finding the pin and in avoiding others--some combination of
which may get you out of a jam.
There are literally hundreds of varieties of multipin connectors, any
of which you are likely to encounter. However, since the problems are
similar (even for doing small switches), I have chosen two examples for
this discussion. One is the DB25 connector (which has become the standard
for computer interface), and the other is the DIP (dual in-line plug) that
fits into IC sockets. If you can solder wires on to these, you can do
anything.
[At the end of this article, computer connectors are listed which
permit soldering of the pins onto there wires before insertion, thus making
this job much easier. However, these are specialty items, and your Radio
Shack store won't have them.]
The DB25 computer connector has two closely spaced offset row of pins;
13 on one row and 12 on the other. (Actually, these connectors come in
sizes of 9, 15, 25, 37, and 50 pins, the 25-pin animals being most common.)
The back ends of the pins (or sockets, since the females are similar) are
scoop-shaped; being tubular to start with, their ends are cut off at a
steep angle to leave "scoops" into which wires are laid and soldered. The
"inner diameter" of each scoop is just large enough to accommodate wire of
20 gauge, and they have no eyelets or holes through which the wires can be
hooked. In short, each wire must be held in its scoop, the pin then heated
with the iron, and solder deposited into the scoop to surround the wire.
The DIP plugs are made of standard flat IC pins mounted in a flat
insulator plate; the top ends of these pins protrude only 1/16 inch above
the insulator board, and these back ends are slotted to form little "forks"
into which the wires are soldered. (Up to 22-gauge wire can be
accommodated..) Each wire is laid in its fork so that its end reaches out
toward the side of the plug. It is then soldered to the fork, after which
the end of the wire is clipped off close to the pin.
It should be obvious from the above descriptions that good systems for
holding these items should be instituted. Vises and holding clamps are not
only required for the connectors, but also for the wires and cables. For
example, one relatively heavy vise would be used to hold the connector. A
smaller vise can be used to hold the cable (perhaps a foot back from the
connector), and a nearby alligator clip can be set up to hold the
individual wire, not more than an inch back from the connector. (These are
only suggestions, but something has to keep the little wires in contact
with their "scoops" or "forks.")
[Holding the individual wires will probably not be necessary in cases
where the traditional solder lugs, having holes through which the wires can
be mechanically secured before soldering, are present. In these cases,
bend the stripped and tinned end of each wire almost double to form a
"hook"; hook the lug with the wire and squeeze the hook closed with
needle-nosed pliers. As the wire now holds itself in place, no complex
array of clamps will be necessary. However, you will thank yourself later
if you hold the cable so that wires come straight back off the pins, rather
than at odd angles; they will be easier to trace in the future, and bridged
wires will be less likely.]
Clamping Arrangements
The vise for holding your connector should be able to swivel and tilt
in several directions. As the thicket of wires becomes significant, you
will want to position the connector so as to avoid marring previously done
wires with the iron. Also, depending on the connector's design, soldering
on female terminals may have to be done with the pins horizontal, so as to
keep solder from running through the terminal and ruining the socket. You
will often have to use your imagination in order even to grab a connector
in the vise. For example, there is not enough meat on a DIP plug to hold
securely. In this case, the plug can first be inserted into a good, deep
socket to form an assembly of significant substance to be clamped securely.
A good vise for holding the connector is the "Panavise" listed in the
"tools" section of Soldering, Part II (SKTF, Winter 1981). (Of particular
usefulness are a swivel-type base such as the No. 380 "Vacuum Base" and the
standard vise head, No. 303.)
Unfortunately, however, the jaws of the Panavise are plastic; they will
readily contaminate the tip of the iron if struck accidentally, and they
are easily marred by the iron. For this reason, it is advisable to line
the jaws with braille paper, leaving flaps of paper folded back over them
to protect the jaws from the iron.
I have used an extraordinary variety of arrangements for holding
individual wires behind their terminals. An alligator clip suspended from
a piece of coathanger makes an adjustable structure for this purpose. The
far end of the coathanger can be held in another clamp (such as your board
clamp). Some arrangement with locking forceps in a board clamp is also
effective. Actually, the wire being worked on can be fixed to one to one
which has already been done by biting them both in a small alligator clip.
Holding a wire parallel to its neighbor is a rather secure way of doing it.
[There are commercial holding devices which are built around alligator
clips. One such instrument is the Radio Shack 64-2093, known as the
"helping Hands." Mounted on a small cast iron base, ball joints are used
to support two alligator clips, one at each end of a horizontal boom. The
base of the "Helping Hands" is not very heavy, however, and building a new
base for it would be highly advisable.]
Any arrangement for holding the cable a foot away from this
paraphernalia will work. Very often, I will just sandwich it between a
couple of heavy books or transformers; tying the cable to a C-clamp on the
edge of the bench is ideal. However you do it, the idea is to keep the
cable from pulling back or twisting as you set up the clamping system for
the connector.
Preparing the Cable
Short leads cannot be formed or held so as to stay in position for
solder. Furthermore, arranging leads to your advantage cannot be done
without flexing the cable; short leads that were previously attached will
be stressed to the breaking point. Finally, if heat-shrinkable tubing is
threaded over each wire in anticipation of insulating the finished
connections, short leads will conduct enough heat to the tubing to shrink
it while soldering--it will no longer accommodate the terminal. Therefore,
the prepared ends should be at least 1-1/4 inches long.
After you have stripped and tinned the ends, inspect them for marred
and peeled insulation. Cut the stripped portion very consistently to
perhaps 3/16 inch in preparation for attaching the wires to their
respective terminals.
[Of course, the appropriate length of the stripped and tinned ends
depends entirely on the type of terminals on the connector. For example,
large solder lugs with holes in them demand that 1/4 inch of lead be
available to hook through them. Also, in the case of DIP plugs where you
are soldering to very tiny forks, you may wish to make the bare ends quite
long (perhaps 1/2 inch) so that you can use this wire as a landmark to
guide the iron. In any case you will find that consistency is your best
friend; errors are quickly spotted among a grove of otherwise uniform
terminals.]
Soldering--
Doing More Good Than Harm
Probably the single most significant tool to enhance the chances of
successful work on multipin connectors is the Japanese Solder Guide (the
JA3TBW Solder Guide, SKTF, Spring 1983). Invented by Mike Bhagwandas of
Kobe, Japan, it provides the user with a good means by which a desired
terminal can be found with absolute certainty. A brief description follows
(appropriate suppliers are listed at the end of this article).
The solder guide consists of a 3- or 4-inch piece of thin-walled
stainless steel tubing whose inner diameter is about 0.05 inches.
Flux-core solder of about 0.03 inches in diameter is fed through the tube
so that it just emerges from the "bottom" end; this bottom end is then
rested on the desired terminal. In operation, the tube is used to guide
the hot iron to the terminal, and solder is then fed to the work from the
"top" end of the tube.
A sort of "handle" can be provided near the center of the tube; this
can be made from a drilled-out braille stylus handle, or a simple shaft
collar can be secured to the tube with a setscrew.
Solder is fed down the tube with the thumb and first finger, while
other fingers are used to support the tube above the "handle." The iron is
brought to the lower section of the tube, whereupon it is slid down to
contact the work pieces.
Soldering can still be done the old way (without the tubular solder
guide) by using tactile feedback to verify that the right terminal has been
found with the iron. Without the tube, a system of nearby landmarks will
greatly enhance your chances of hitting the right point with the iron;
these landmarks might consist of, first, the vise, second, a nearby
alligator clip, etc. With the solder in one hand and the iron in the other
(the solder resting on the work), verification of hitting the terminal with
the iron will come by noting the vibration of the solder, then by watching
the solder melt.
_Bridged Connections_--Because the pins are close together, a common
error is the accidental bridging two adjacent ones. Shorts between pins
can occur in the following four ways:
I often lose the pin temporarily with the solder--either I knock it off
with the iron, or it melts before I have expected it to--and I must then
fish around with the solder to find the hot pin. In re-finding it, it is
easy to spill a little extra solder into the connector, usually on the pins
below. This is, however, one of the easiest mishaps to correct. If metals
onto which solder has been spilled never reach soldering temperature (they
usually will not if they receive no direct heat from the iron), solder
droplets will not firmly adhere to them. The droplets can be dislodged
later with a braille stylus or a probe-type soldering aid. Remember to
check for droplets if you suspect that spillage has occurred.
Icicles of solder often form if the iron is abruptly pulled away from a
connection--sliding it off the connection will usually break the surface
tension and prevent icicles. If you abruptly leave the pin in the
direction of an adjacent one, you can form an icicle which decreases the
distance between pins. On the other hand, there really is not room to talk
about sliding the iron off these closely spaced terminals. Therefore, go
ahead and jump off the pin--knowing that occasional icicles will
result--but do so in a benign direction (straight up, for example).
If wires are touching each other directly behind the pins, their
insulation will melt from transmitted heat, whereupon the insulation will
give away and allow the wires to touch each other. If this happens, they
can often be pried apart and reinsulated with tape (or tubing, if it has
been previously installed onto them).
The most sinister kind of bridge is the bonafide "solder bridge"; this
occurs when two adjacent pins are simultaneously heated, thus allowing a
bridge of solder to alloy with both of them. To clear this type of bridge,
the connections must be simultaneously reheated and a probe of some sort
passed between them. [Sometimes a knife or small "mill file" (a mill file
has teeth on its edge) can be used to destroy the bridge without reheating
the pins, but you risk breakage of the pins or wires with the inevitable
rough handling.]
There are four ways of detecting shorted terminals. These are the
indications you should look for:
Connector pins often exhibit some mobility in their socket block; they
can often be wiggled slightly. They should all wiggle separately--one at a
time. If two pins insist on moving together, they're bridged.
Some kind of probe that fits between the terminals can be used to
explore them--a stylus, a soldering aid, a dental tool filched from your
dentist, a jeweler's screwdriver, etc. Make sure that you can feel the
insulated material of the socket block at the base of the pins; then make
sure that you can bring the tool unimpeded all the way back to the
insulated portion of the wiring.
If little pieces of tubing have been installed onto the wires in
anticipation of insulating the pins (thus burying your pins, as my
supervisor used to say), a good indication of success is if the little
segments of tubing slide all the way down over the pins to the insulator
block. Once again, consistency will be your best friend; if you have cut
all the tubes to exactly the same length, unevenness at their back ends
will show you which ones to investigate.
Finally, the best (and most tedious) test of the connector is checking
with a continuity tester, gong pin by pin. Each pin can be checked for
shorts to all of its neighbors (four neighboring pins, in the case of the
DB25); each pin can be tested for continuity back to its wire at the other
end of the cable. (I don't always go through this rigor myself. However,
the electrical items of lowest reliability are connectors; if you really
want to know that these are not your problem when the stuff doesn't work,
check the connectors thoroughly.)
[For making the above continuity checks, special test probes that fit
the connector are very helpful. These can be made by ravaging a spare or
damaged unit of the opposite gender. First, remove any metal framework
with a hacksaw--then dissect the insulator block with a coping saw to get a
few sample terminals. Then, make test probes out of them, using
heat-shrinkable tubing or tape to cover all but the business end. The
probes can be plugged into the connector you are testing, and the tubing on
the outside will keep you from getting false alarms when fishing around
adjacent pins.]
_The Paper Dam_--This trick has indeed served me well; I first tried it
when I was called upon to wire connectors having 120 pins (a slice of my
early work history which I would just as soon forget). My first "dams"
were made from little strips of braille paper--this worked most of the
time, but starting a conflagration is possible. Other materials worked
better in the face of extreme temperatures.
My favorite material is "fish paper," an insulating material that is
not easily damaged by the heat. (GC Electronics of Rockford, Illinois
markets fish paper in a 10- by 24-inch rolled up sheet. Their name for it
is "Fyberoid," No. 560.) Another good source of fish paper is the scrap
heap; old TV sets and other consumer products are loaded with it. Though
bits of it look like scrap to someone else, I save every square inch.
Another material is Teflon, strips of which can be cut from liners of
broken tape cassettes. (Make sure that the plastic liner of your cassette
is Teflon; other soapy-feeling plastics which are not heat-resistant are
used in cheaper tapes.) You should be careful of Teflon, however; once it
does reach the temperature of its destruction, it gives off gases which are
highly toxic--keep a breeze going around the workbench.
You can test a material for suitability by bringing the barrel of your
iron into contact with it. If it melts or smokes, don't use it.
The principle of the dam is to isolate the terminal of interest from
its neighbors. It will not only prevent bridging, but it will do much to
keep you from marring previously done work in your attempt to find the
terminal with the iron. The dam, which is perhaps 1/4 or 3/8 on an inch
wide, is "woven," as you might say, through the terminals.
My usual configuration is an L-shaped affair with the bend of the L
being a small U-shaped gutter that accommodates the terminal being
soldered. (In terms of items you might recognize, its shape is rather like
a sewer trap.) Suppose, for example, you are soldering wires along the top
row of pins on a DB25 connector--also picture yourself facing the end of
the connector. Suppose also that one or more wires have been attached near
the end farthest away from you. One end of the dam would be sticking
straight up between your next terminal and the ones previously done. The
dam then courses under the terminal of interest, after which it lies flat
on top of the pins to come.
The dam then becomes your main source of landmarks. With the iron, you
can follow the horizontal surface of the dam until it drops down under the
terminal you want. Or, with the iron, you can first find the vertical fin
that prevents you from hitting previously done wiring--then follow this
vertical surface down to the pin. In any case, there is only pin to which
you have easy access, and it's the one you want.
A much simpler example is that of using a dam for doing a pin at the
end of a row. Although I seldom use one here, a simple vertical strip
between this and the other pins is sufficient.
If the pins are long (which they are not in the case of the DB25
connector), they alone will hold the dam in place. If they are short, some
way of holding the dam in position will have to be devised. The fish paper
dam can be held in place by a small bit of masking tape; lay the tape
across the horizontal leg of the dam and secure it the frame of the
connector. Teflon, on the other hand, resists adhesion to sticky surfaces,
and it is best held in position by a small loop of wire or an alligator
clip.
The kind of tape you use is very important. Don't put plastic tape
around where you can accidentally find it with the iron; it will soil the
tip and render the soldering iron inefficient. On the other hand, n
adhesive tape is impervious to the heat of the iron. However, I have had
good luck with paper tapes (such as masking tape), and you should apply it
with the understanding that it should not be used for resting the iron
against while soldering.
[In reviewing my procedure in preparation for writing this article, I
came across a DB25 connector of unknown brand whose insulator block is
easily melted by the iron--a sinister practical joke indeed. My only
recourse was to lay masking tape over the side of the connector with the
edge of the tape "lipping" down over the edge of the insulator block above
the pins. Heating the tape was unavoidable, but it was better than soiling
the tip of the iron and ruining the connector block.]
Additional Comments on the DIP Plug
Because of its construction (having very short pins to which wires are
soldered at right angles), I have found no way to isolate these pins from
one another while soldering. Success depends mainly on how stable the
clamping setup is--whether or not the wires tend to stay in position while
you work.
The wire of interest can serve as a good landmark for finding the pin.
If previously done wires are cut off close to the terminals, and if a
substantial length of your prepared lead is allowed to protrude past the
edge of the plug, this lead becomes the "only tree in the forest." The
iron can be used to find the lead while the solder is held against the pin
to detect vibration when doing so.
If you wish to take the trouble, there is a very secure system of
holding wires in position which I have recently tried. Insert the dip plug
through a piece of perforated board, then plug it into a good-quality
socket to hold it there. When stripping and tinning each lead, provide one
full inch of bare wire beyond the insulation. Before laying the wire in
its fork, poke it into a hole in the perforated board adjacent to its pin
and bend it over so as to hook it in position. Then stretch the wire
across the fork and tape it down against the board on the other side of the
socket. With this system, jostling the wire loose from the fork will be
unlikely.
After one row of pins has been completed, you will find that avoiding
this wiring while doing the second row is very difficult. This again is a
good application for masking tape; place masking tape across the completed
forest of wires to protect them from the iron.
Miscellaneous
This article has been very difficult to write--connectors are widely
different, there is no foolproof procedure to assure successful soldering.
All I can do is suggest hints and techniques which have been of use to me
in various circumstances.
As you develop your own methods, you will no doubt sacrifice
connectors. Always buy extra ones, knowing that spare parts from the old
ones may be useful as test probes, and in some cases may be used to replace
damaged terminals.
Where possible, do your soldering before inserting the terminals into
the socket block; there will be no nearby terminals with which you can
bridge connections, etc. A good example of this was the 120-pin connectors
I was called upon to solder in my work as a technician. After wiring them
(and having much trouble with the finished devices), I discovered that my
supervisor had inserted the terminals into the blocks--he was trying to be
helpful. Wherever those instruments are, the connectors are still a source
of trouble.
Pin Connections
It is customary to number connector pins, viewing them from the pins of
males or from the backs of female sockets. In addition, if a "key way"
exists (some mark around the perimeter of the connector), this key way will
generally appear between the lowest and highest numbers. For example, DIP
plugs will usually have a notch at one end; holding the plug with the notch
up and the male pins facing you, count them in a clockwise direction
starting with the pin to the right of the "key way." A 14-pin DIP plug
would have its key way placed between pins 1 and 14; the column of pins on
the right-hand side would be numbered 1 through 7, while the pins on the
left side would be 8 through 14 (7 and 8 near the bottom).
The DB-type computer connectors are numbered a bit differently. For
example, viewing a DB25 connector with the male pins facing you, orient the
rows of pins so that the row of 13 is on top. Then, pins 1 through 13 are
on the top row (counting from left to right); pins 14 through 25 are on the
bottom row (also counting from left to right).
The Amphenol "Poke-Home" Series
These units are shipped with the pins not being installed in their
socket blocks. As you can imagine, soldering these pins individually would
be much easier than soldering pre-assembled connectors. When soldering,
the forward ends of the connectors should be held in something which does
not act as a big heat sink (they should not be directly held in a metal
vise). Line the jaws of your vise with braille paper or fish paper before
grabbing the pins. Another idea is to hold the pins in something of less
heat capacity, such as gripping them in your locking forceps.
The numbering system is simple. For example, the male set (insulator
block and 25 pins) of a DB25 plug is an Amphenol No. 17-20250. The female
set is an Amphenol No. 17-10250. Connectors with a different number of
pins require the "25" figure to be changed. For example, a DB15 male would
have the number 17-20150, and a 9-pin male would bear the number 17-20090.
In like manner, a 37-pin female would bear the number 17-10370.
Several people make equivalents to the "poke-Home" series, and it is
always worth asking your supplier for this breed. However, a more common
version of the "Poke-Home" series has crimp-on pins, and an expensive
crimping tool is needed to attach them. Be sure you know what you're
getting.
Suppliers
_Solder Guide Parts_--6-inch lengths of hypodermic tubing, catalog No.
HTX-15, are available from Small Parts, Inc., 6901 North East 3rd Avenue,
Miami, FL 33138; (305) 751-0856.
Shaft collars are available as "set screw collars," catalog No. 889,
from the Player Piano Company, 704 East Douglas, Wichita, KS 67202; (316)
263-3241.
Amphenol Industrial Division, 1830 South 54th Avenue, Chicago, IL
60650; (312) 242-1000.
GC Electronics, 400 South Wyman STreet, Rockford, IL 61101; (815)
968-9661.
- END -
[from the Smith-Kettlewell Technical File
Vol. 5, No. 2, Spring 1984]
SOLDERING, PART VII
Resistance Soldering
The method of resistance soldering works by passing extremely high
current through work pieces (the connections being soldered, not the
components); the work pieces then become heated and act as their own
soldering iron. The tool consists of either a pair of electrodes, or a
single electrode associated with a ground-return clamp. These tools are
sources of electric current, not sources of heat.
The resistance-soldering tool does not heat up and stay hot. The only
heat energy it absorbs is transferred to it from the connection--and,
unlike conventional irons, this transfer of heat to the tool is not very
efficient, since the tool is not in a molecularly bonded solution of solder
with the work. Therefore, the tool generally gets cool enough to touch
very soon after a connection has been made. This has great appeal to some
blind users; they position the tool and the solder with their fingers, and
then they press a foot switch to initiate current flow.
You ask, "Why didn't you tell me that there was a perfectly safe way to
solder, before you wrote hundreds of pages on lethal hot irons?" (The
author has been criticized by three readers who are dyed-in-the-wool
proponents of resistance soldering.) My answer is that things are not
always as simple as they seem; there are major pitfalls which must be
reckoned with. In fact, my respect for resistance soldering as a viable
technique came not from my own experience, but from seeing some top-notch
work being in the laboratory of Rick Joy, a deaf-blind reader of SKTF.
Manufacturers' advertisements tout that, "This method allows
connections to be made more quickly, so that heat won't be transferred to
nearby components and to insulation which might otherwise melt!" "Quickly"
is an undisputed truth--and at least one manufacturer, American Beauty, is
honest enough to include the statement, "The eye is generally the best
judge of when to remove the tool." I'll "second" that statement! The only
limit to the temperature a connection can reach is its ability to dissipate
power--the temperature can go sky high _very_ quickly.
My first casual experiments with this method were disastrous. I would,
in my usual style, nonchalantly feel about the connection with the solder;
when it melted, I withdrew the solder and then withdrew the soldering tool.
More than once, I would find that an inch or so of insulation had vaporized
along adjoining wires--that's getting hot. (The literature suggests that
you can also use this equipment to anneal and to temper metal parts--that's
hot!)
American Beauty suggest that, before you use the equipment on actual
work, you try several power settings on similar scrap work pieces. All the
manufacturers recommend their equipment chiefly for assembly-line
soldering,where the equipment can be preset for one size of joint.
Recognize also that there are electrical risks involved with resistance
soldering. If, for some reason, good contact between wires at the joint is
not established, you can inadvertently put components in series between the
electrodes of the tool; this can test your smoke alarm systems and set your
neighbors to wondering what you're cooking in there. It pays to know a
little electrical theory and to use good judgment when you place the
electrodes on the work. (These devices are powered by low-voltage,
high-current transformers; the current supplied to the electrodes is
therefore AC.) Problems can sometimes be eliminated by heating only one
item of the work pieces. If you heat one item, pick the one of largest
heat capacity--the biggest piece of metal.
Finally, you can only solder pretinned wire if it has been
pretinned--otherwise, you might burn up a strand or two, and never have an
effective "soldering iron" (the soldering iron being comprised of the work
itself). Of course, this raises the question of the tool's effectiveness
in tinning stranded wire, a necessary operation in all electronics work.
Therefore, you might well consider keeping an "instant-heat, fast-cooling"
gun or "cordless" iron on the premises for just this task. (A discussion
of guns and cordless irons appeared in "Soldering--Part I," SKTF, Fall
1980.)
All in all, however, "resistance soldering" is a legitimate alternative
for the blind technician. Though the above remarks may seem skeptical,
most of the questions will find adequate answers in the discussion to
follow.
General Description of Tools
_Electrode Configurations_--Three common styles of tools are readily
available. They are described as follows:
The classic electrode configuration is a single rod, traditionally made
of carbon, but nowadays often made of an alloy of metals. Along with this
is a "ground-return clamp" which is attached to one of the work pieces a
little ways away from the connection. This configuration is very good for
large items of high heat capacity. Carbon has the advantage that it can
tolerate higher temperatures, while metal has greater tensile strength.
Another configuration is to have two electrodes, mounted in a "fork"
with a fixed spacing, which can be adjusted (by bending or grinding) to fit
a particular job. This style is often used in assembly-line settings. On
the other hand, PC-board connections are just standard enough to make this
the instrument of choice for doing this kind of work.
The style of most interest to us is the tweezer-type tool. This
consists of two pointed electrodes (made of some metal alloy which does not
take solder) mounted in a spring-loaded insulating handle. This device,
though limited in the size of work it can accommodate, can handle any of
the most commonly found electronic connections. (These can be gotten in
large enough sizes to solder 14-gauge wire, for example, or small enough
for wire of less than 50-gauge.)
All of the above configurations are available in extreme variations, if
you jump from manufacturer to another. For example, the Hot Tip company
makes very small single-electrode probes. Other companies make a
"plier-type" tool which has carbon blocks for jaws--you can temper steel
with those things. Yet another style is a panel containing
electrodes--this panel being mounted directly onto the power transformer.
_Power Transformer Types_--The power transformers are either
multi-tapped or variable types; they are good for 100 watts or greater.
Their on-off switch is usually something separate. Most often, you buy a
foot switch which has a piggyback AC plug and socket at the end of its
cable; the transformer plugs into this receptacle. On the other hand,
American Beauty sells a series of units which is controlled from a separate
connector on the "power unit;" This facilitates the option of having a
pushbutton on the handle of the soldering tool.
An embellishment is to add a timer which shuts the power off after a
preset period. The American Beauty literature cautions that this is not a
recommended feature where variations in the size of work pieces is
expected.
_Solder Preforms_--Resistance soldering equipment is often used with
preformed units of solder; they may be in the shape of balls, beads, or
tiny washers--with or without flux. These "solder preforms" are marvelous
for industrial applications on an assembly line; you just slip them over a
lead, place the tool on the work, and press the foot control.
Use of solder preforms takes away an important source of feedback for a
blind technician. Now that you are not holding onto the solder, how will
you know when it melts? It may be possible to depend on alternative cues.
(The following tips refer to "Tactile Feedback" as discussed in
"Soldering--Part II," SKTF, Winter 1981.)
Looking for a sharp rise in temperature of an adjoining component lead
may still work, but only if the one you are feeling is not one being
electrically hated by the tool. If you are sure that the lead you are
monitoring is not being directly heated by the tool, a sharp temperature
rise will probably mean that wetting of this lead has occurred.
The "squeakiness" of solder-wet metals (when subjected to slight
motion) will always tell the story. However, this squeakiness will not be
as apparent through the resistance-soldering tool as it is through the
conventional iron. This is true because the electrodes of the
resistance-soldering tool are never "wet" themselves.
Finally, solder preforms are usually minuscule in size; fitting them in
place is not easy. I prefer to hook the solder around a lead (3/4 of a
turn being enough for small socket pins in a PC board), and this puts me
back in the position of being able to monitor the solder flow directly.
_Selection of Equipment_--Everyone agrees that "trial and error" (or
perhaps having a "sales consultant" drop by) is the way to decide which
setup best suits your application. It's not quite as bad as all that--you
can make a good guess from the tools listed here.
If you're going to err, do it on the large side. For example, if you
are going to solder house wiring, get the largest tweezers you can find, a
single electrode of perhaps 1/4 inch diameter, and a power transformer of
250 watts. If you are interested in soldering point-to-point wiring on
perforated board, whether IC's are involved or not, tweezers whose
electrodes are pointed and whose diameters range from 0.04 to 0.08 inches
will do fine, and the power transformer need only be good for 100 watts.
A continuously variable transformer may be a convenience; then again,
it means that tried-and-true settings will be harder to repeat exactly.
The variable transformers are a nicety where fine control over a particular
industrial operation is being set up. You work may involve a variety of
work sizes; close monitoring of melting of the solder will be necessary
anyhow, so why not make do with a less expensive multi-tapped unit.
Basic Procedure
Stated more than once in the American Beauty book,"The Principles of
Resistance Soldering," initial setup of the equipment will necessitate a
trial-and-error process. It is for this reason that this paper cannot say
specific things like, "Set the PDQ-5 power supply to position 3, and so
forth." Students of this series of articles know enough about the
metallurgy of soldering to do educated experimentation on their own--say
yes. The basic steps are:
1. Set the transformer for a setting suitable for the job (based
on your experience and by making an educated guess.)
2. Place the solder on the work in such a way that you can
judiciously monitor its status; you will want to know, with certainty, when
it melts. Wrapping the connection with a measured amount is one method;
you can then monitor the solder by pulling on it slightly. Then again,
some people like to feed solder when the time comes (this takes less setup
time); in this case, keep it against the connection and press forward
gently.
3. Place the electrodes on the connection with the power off
(doing so with the power on will cause impressive arcing).
4. Close the power switch (be it a foot control or a pushbutton
on the soldering tool).
5. Watch that solder like a hawk; put enough tension on it so
that you will know _immediately_ when it melts. If a predetermined amount
has not been wrapped around the connection, apply an appropriate
amount--and be quick about it!
6. Simultaneously release the switch, remove the tool and the
solder.
7. Modify the transformer setting as necessary, based on the
similar previous connection.
If you can pass current through all the connecting work pieces (and if
they are all of reasonable size), everything will get hot enough to take
solder. However, this does increase the chance that you might pass current
through circuit elements and not through the connection--if the items are
not in firm contact, etc. You can heat the largest item at the joint and
make this your "soldering iron" (instead of the whole collection of items).
If you do the latter, wetting of all metals will not occur simultaneously;
firm contact between the pieces is again necessary in order to promote
rapid heat transfer to them all.
In choosing the "correct" heat setting, all of the literature
specifically says to "choose the highest setting which the operator can
control effectively." I prefer to interpret this statement loosely; if
taming the system down a bit means that I have enough time to make a
decision or two during the process, I'll do it that way. Remember, these
tools are intended to be sold to assembly-line shops; they want to keep the
times minimal.
I would think that turning up the heat would have diminishing returns.
Nowadays, the solder we use often contains "activated flux." According to
the Kester soldering manual, "activated fluxes," when compared to the most
basic rosin flux of yesteryear, have inferior breakdown characteristics in
the presence of excessive heat.
On the other hand, setting the heat too low carries its own set of
risks. As with any soldering, too small an iron or too little heat will
allow a damaging amount of heat to be imparted to connected components
before the joint reaches soldering temperature. Given the wrong
conditions--poor lead and electrode placement--these ill effects could be
magnified with resistance soldering. The energy to one item could be
terrific, enough to damage this component, but not enough to heat its
neighboring leads at the joint.
_Troubleshooting_--I love this section in books. "Make sure the power
setting is correct, and make sure all connections are secure." Of course
all that stuff works, or you wouldn't be reading the book.
American Beauty suggests that the electrodes could have gotten
dirty--coated with flux or with oxides. With their units (which have solid
alloy electrodes; i.e., no plating), they recommend that you clean them
with a strip of emery paper or a small wire brush. Not knowing all the
variations you may run into, as far as electrode materials are concerned, I
would have to advocate reading the instructions of your particular tool.
I have seen one interesting problem with a set of Hot-Tip tweezers
which were not working. The electrodes had bent so that the chucks that
held them were shorting ahead of the connection; installing heat-shrinkable
tubing around one of the chucks would prevent this from ever happening.
Tools
Sorry, my direct experience with these tools is so old that I would not
feel comfortable in recommending any one product specifically. I can
outline (basically restate) principles discussed earlier, so that you know
what to watch for. Meanwhile, price is not much of a factor; Everybody,
except for Teledyne Kinetics, wants from between $100 and $120 for a setup
(by the time you get a foot control and such).
Of the three users I have interviewed on the matter, two use
"tweezer-type" instruments. Tim Cranmer, on the other hand, has used a
single-electrode device to heat the posts of wire-wrap IC sockets, around
which he would wrap the wires being attached (just one turn around the
post), then wrapping solder around the post further up. There are a couple
of single-electrode units small enough to permit this, and they are listed
here. Remember, you can buy one power unit (and an accompanying foot
control if it is not included)--then pick an array of hand pieces,
including both tweezers and single-electrode holders. (Of course, all
single-electrode assemblies come with the necessary "ground clamp" which
serves as the return path.)
All of the advertisements are misleading when they speak of "precise
temperature control" and "no heat being transferred to adjacent
components." What they really mean is that, given a specific repeatable
situation, you can set up the equipment for--and get the operator used
to--a given solder connection, and make the connection efficiently enough
to protect nearby components.
They all refer to their adjustable power supplies as having something
to do with "temperature control," which is true, only indirectly. One
manufacturer called their power supply "a solid-state temperature
controller;" right away I jumped for joy. Could this mean that they sense
the temperature of the connection and thus control the temperature? Nah,
it's just a transformerless variable power unit which is small enough to
plug into the wall directly.
If the marketing jesters were forced to study engineering (thus
spending a short while in a "Control Systems" class), they would learn that
the only systems that you can really call "controlled" are ones which have
corrective feedback. "Open-loop" systems have adjustments; one can adjust
them so that, all things remaining constant, the resultant "control" over
their operation will be predictable. Open-loop systems, however, are not
_controlled_, in the true sense of the word.
What you need to do is, by experiment, set up the variable power supply
so that a solder connection can be made in a reasonable time--in a range of
perhaps 2 to 7 seconds. This "control" will change for every piece of work
you're doing.
American Beauty
(American Electric Heater Co.) *
For each hand piece, a "power rating" is listed. This indicates with
which power unit the tool is to be fitted. It does not indicate the power
delivered to the work; this cannot easily be determined, since every item
has its own current density and resistance.
Note that the foot control comes separately from the power unit.
Although this is not true of other manufacturers, the prices of the
eventual setup are still quite competitive.
Single-Electrode Hand Pieces:
10552--5/64-inch metal electrode (stainless steel), 15 to 100 watt
1051[?]--3/32-inch carbon, 15 to 100 watt
10572--1/8-inch carbon, 15 to 100 watt
10573--3/16-inch carbon, 15 to 250 watt
10511--(said to be "standard" for general electrical work) 1/4-inch carbon
85 to 350 watt
10510--adaptor to convert 10511 hand piece for 3/8-inch carbon, tip No.
10527
10522--bushing to convert 10511 to 3/16 carbon, tip No. 10525
Tweezer-Type Hand Pieces:
105133--"Microtweezer" uses 0.040 inch diameter "chromel" wire electrodes,
15 to 100 watt, electrodes replaced with 105134 tips
10541--opens to 3/8-inch, 0.078 inch diameter stainless-steel electrodes
(ground to a point), 15 to 100 watt
105127--opens to 1/2-inch, uses 1/8-inch diameter stainless-steel
electrodes (ground down to blunt point), 15 to 250 watt
[The editor would start with the 10541 tweezers, with the possible
addition of the 10552 and 10572 single-electrode hand pieces.]
Power Units
(add suffix of 220/240v for these voltages):
105-A1--Three taps, 15, 50, and 100 watt
105-A2--Four taps, 85, 130, 185, 250 watt
105-A3--Continuously variable, 0 to 100 watt
Foot Switch:
10519--Has standard AC plug and socket on end of cable
Hot-Tip: *
Single-Electrode Hand Piece:
P-40--Typically used with 5/32-inch diameter copper-clad carbon electrode,
for use with H-101A and H-202 power transformer
P-8--For use with above P-40, this is a 0.040 inch diameter tungsten
electrode which has been pressed into a 5/32-inch brass adapter
P-9--For use with the above P-40, this is a 0.060 tungsten electrode which
has been pressed into a 5/32-inch adapter
Tweezer-Type Hand Pieces:
T-10S--"Standard tool" uses 0.040 inch diameter tungsten (type TT-2) tips,
for use with H-101A power transformer
TC-10S--Same as T-10S but with extra cork insulation for high duty-cycle
applications
T-10SA--For use with TT2A "Nichrothol" which are easily shapable, use with
H-101A power transformer
T-10S4--Uses "rigid" 0.060 inch diameter tungsten tips (type TT4), for use
with H-202 power transformer
TT-10S4A--Used with easily shapable "Nichrothol" tips (type TT-4A), for
use with H-101A and H-202 power transformers
Power Transformers
(120v 50/60 cycles shown in U.S. catalogues):
(Note: The foot switch apparently comes with these power units.)
H-101A--Has 5-position rotary switch, can deliver up to 200 watts (50% duty
cycle); position 1 good for soldering 52-gauge wire, with position
5 good for soldering two 14-gauge wires.
H-202--Has 5-position rotary switch; starts with position 4 of H-101A,
capable of approximately twice the power.
[The editor would start with the T-10S tweezers, and possibly include
the P-40 probe. The H-101A transformer has enough power for anything I
would be doing.]
Teledyne Kinetics *
These are basically self-contained; there is no power transformer on
the bench. The RSC-1 ($85) has a solid-state variable supply that plugs
into the wall. The RS-1 is simpler ($60); they don't say how this one is
powered. Neither have foot controls. Rather, they seem to have a
pushbutton control. They don't say whether the pushbutton also controls
closing of the tweezer noses, but it sort of looks like that from the
pictures.
RS-1--Self-contained unit with tungsten electrodes
RSC-1--Heat is controlled from a solid-state, plug-in unit; has tungsten
electrodes
Triton *
This device is a unit out of which protrudes electrodes that look like
square long-nosed pliers. It has a trigger that serves two functions: a
slight pressure closes the points. Additional pressure turns on the power.
Square carbon tips are standard. However, small-diameter "special
metal tips" can be gotten which are mounted into appropriate adapters.
The power transformer has two taps, high and low.
Model J--Whole setup with carbon electrodes
TLT--Is just the "Pres-to-Heat" hand tool (I give you this, since you could
probably adapt it for use with other power supplies).
1-0397--Replaceable carbon tips
1-2177--1/16-inch metal electrode, two of which are required
1-2249--You need two of these adapters for above electrodes.
* Suppliers and Manufacturers
Marshall Industries, 788 Palomar Avenue, Sunnyvale, CA 94086; (408)
739-8720
Macdonald, 1736 Standard Street, Glendale, CA 91201; (800) 423-2453
(Outside California)
American Electrical Heater Co. (American Beauty), 6110 Cass Street,
Detroit, MI 48202; (313) 875-2505
Triton Manufacturing Co., Inc., East Haddam, CT 06423
Hot Tip, 6 Elm Avenue, Hudson, NH 03051; (603) 883-7708
Teledyne Kinetics, 410 S. Cedros Avenue, Solana Beach, CA 92075;
(619) 755-1187
- END -
A FEEDER SYSTEM FOR THE
JAPANESE TUBULAR SOLDER GUIDE
by Jean LeBorgne
Although the Japanese solder guide (see "The JA3TBW Solder Guide,"
SKTF, Spring 1983) is a great idea, I think this modification constitutes
an improvement. Before, I always had trouble feeding the solder; it would
buckle as it entered the tube, and I would even lose control of the guide
while attempting to feed solder.
I designed a feeder sleeve which holds the solder above the top end of
the tube, and which permits a controlled amount of solder to be fed. It is
made of a piece of aluminum bar stock with a hole drilled through its
length to accommodate the stainless-steel solder tube. At its upper end, a
hole is drilled and tapped for a setscrew which can be tightened down
against the solder. With this setscrew, the feeder sleeve can be set to
feed a predetermined length of solder, since the tube and the feeder sleeve
will only telescope as far as the shaft collar permits (the shaft collar
being part of the original Japanese guide). (This system is similar to a
"metered" syringe, which has stops on the plunger to regulate dosage.)
In operation, the solder is passed first through the feeder sleeve,
then the solder guide. The solder is positioned so that it is even with the
bottom of the tube. Next, the feeder tube is slid down onto the guide to a
point just above the shaft collar (perhaps leaving a space of 1/4 or 3/8
inch). The setscrew at the upper end of the sleeve is then tightened
against the solder so that it can be fed by pressing down on the sleeve.
Put the bottom end of the solder tube against the connection and heat the
materials with the iron, using the tube to guide your iron down onto the
connection. When the solder melts, the sleeve will telescope down to the
shaft collar.
To prevent the flux from "gluing" the solder in the tube, either
withdraw the tube from the feeder, or loosen the setscrew in the feeder and
feed solder forward through the system--immediately after removing the tool
from the connection.
My feeder sleeve is made from 1/2-inch aluminum bar stock, and is cut
to about 1 1/2 inches in length. Then, a hole is bored along its length
which is 0.080 in diameter (using a No. 46 drill). Near the top of the
guide, a hole is drilled and tapped to fit a No. 3-48 machine screw--this
is the setscrew which holds the solder. I did not have a proper thumb
screw, which would be preferred, so I simply threaded a nut along a 1/2
inch screw and tightened this against the head, thus giving me a handle for
my fingers.
[Editor's Comments: Very nice! Thank you, Mr. LeBorgne. Playing
around with different materials for the feeder might be fun. For example,
I'd like to try 3/8 inch Teflon bar stock,--something nice and
"soapy-feeling" (self-lubricating). Delrin plastic would work, but you
might contaminate your iron on it once in a while. I wish I could pass
these on to you, dear readers, but the machining costs are more than we
could bear. Nevertheless, we can pass along more of the original solder
guides for those who need them.]
- END -
THE VINTHER FINGERTIP SOLDERING IRON
by Bernie Vinther
_Abstract_--Using the soldering tip of a battery "cordless soldering
iron," this instrument is of the quick-heating fast-cooling type; it can be
guided into place while it is still cool, and then energized by pressing a
foot pedal. Moreover, an external transformer has been substituted for the
large handle and heavy battery of the cordless unit. The particular tip
assembly chosen happens to have an extension arrangement which provides a
ready-made handle. The result is that, even with its supply cable, the
finished soldering iron is of feather weight, it can be put into position
directly by feel (before it is energized), and it extends very little
beyond the fingertips--hence the descriptive term, "fingertip soldering
iron." [While seeming simple enough, it is cleverly implemented, and the
right tip had to be found, and the editor considers this to be a major
advance in soldering tools for the blind.]
"All right, gentlemen, push the pedal to the metal and let the
soldering begin!" Formerly being a sighted electronics technician, now as
a blind person I've been frustrated by whatever approach at soldering I
tried; I always seemed to leave something melted or burned, especially my
fingers. In trying to use various methods (described in Smith-Kettlewell
reports), locating the parts to e soldered with a hot iron and applying
the solder, the materials would accidentally be jostled out of position, or
things would become overheated while I was trying to feed the solder.
Therefore, I most often chose to use a "cordless soldering iron" (first
made by the Wahl Clipper Corporation, and then also marketed by Radio
Shack). This iron has the following advantages:
First, the tip is cool to start with, and heats up quickly when you're
ready to solder. Therefore, the tip can be guided into position with
fingers of your free hand, after which the iron is energized when you are
out of the way. You no longer need a system of landmarks to guide the iron
to the connection. After the connection is made, the button is released,
and the iron cools down by the time you are ready to make another.
Because it is only energized when you need it, there is no danger of
leaving a hot iron lying around where it could burn something or someone,
or present a fire hazard. There is no chance of leaving it one to oxidize
badly overnight, which would leave you a lot of cleaning work to do on it.
An important advantage over regular irons is the distance from your
fingers to the soldering point. The tips of standard irons are normally 3
inches or more beyond the tips of your fingers; this makes for a
"wand"--which is also hot--that is hard to control. The cordless iron at
least reduces this distance to about 2 inches, and the proposed iron
described here further reduces this length to 1 1/4 inches.
Also, the cost of a temperature-controlled iron is outrageous in
comparison. The ones used by the Smith-Kettlewell group cost over $120.
I found that I could overcome the frustrations of feeding the solder by
wrapping a small length of it around the tip of the cordless iron when it
is cold. The length of solder needed depends somewhat on the size of the
connection and the diameter of the solder. However, I usually use only 3/8
of an inch--perhaps as much as 1/2 inch--of 23 gauge solder; this is fine
for most applications. This eliminates the need for intricate
manipulations or complex solder-feeding systems that can plug up or move
the parts out of position.
Yet the cordless iron is not without disadvantages. First, it is not
very rugged, and its tip can be damaged by mishandling (a problem
accentuated by the fact that the battery and handle assembly are heavy).
Next, its primary way of dissipating heat is in the connection you are
soldering; therefore, it can overheat if left on too long. Pushing down on
the button in the handle often caused extra undesirable movement of the
hand--my hand would tend to move away from the connection at times.
Finally, it seemed that the battery would always run down, just when I was
almost finished with a project I was dying to try out. These many
frustrations were, however, more than overcome by the quick-heating
fast-cooling feature, and that the solder was applied without complicated
techniques or feeding systems.
All this led me to devise the following improvements, which even offset
some of the disadvantages.
Describing the Vinther Fingertip Iron
The Wahl Clipper Corporation makes a variety of tips for their
instrument. One of these is known as the "Tuner Extension Tip" (apparently
designed for making long reaches into TV tuners). Bearing the Wahl Part
No. 7556, * it is the same as the standard-length "fine" tip No. 7545,
except
that it is mounted on long stiff leads--about 3 1/2 inches long. Moreover,
being held apart by an insulator, the conductors are encased in
heat-shrinkable tubing. The resultant lead assembly resembles a piece of
flat 300-ohm "twin-lead" TV lead-in wire.
* This part has been discontinued. There is no replacement
according to Wahl Clipper (as of 3-25-96).
You might ask, "But what good is a 4-inch long extension to a soldering
iron tip? Weren't you just complaining about length a little while ago?"
The 4-inch long extension serves as the handle. The fact that it is
insulated means that it doesn't heat up very much, and you can easily get
to within 1 1/4 inch from the soldering point. Voila, we have a fingertip
version of the quick-heating fast-cooling iron.
Instead of running this thing with a heavy and expensive nicad battery
pack, why not choose an appropriate transformer? This would solve another
problem; the on-off button can be in the primary circuit of the
transformer, and I chose to make this a foot control on the floor. No
longer does the battery run down. No longer does pushing a button cause
accidental movement of your hand. Finally, being of such light weight, it
is much easier to be gentle with this fragile tip construction, and the
tips will last longer.
The battery in the Wahl cordless iron is a 2-cell unit, supplying 2.5
volts. I simply went down to my local supplier and got a 5-volt transformer
whose secondary [is] centertapped. (My transformer is only good for about
3 amps. Though the tip draws about 7.5 amps when cold and settles to about
6 amps as it reaches soldering temperature, its intermittent use has caused
me no problems. Nevertheless, a 6-amp transformer is specified here.)
The two-wire cord that supplies the tip should be as flexible as
possible. In hardware stores, rubber-covered "heater cord" is sometimes
available which is more flexible than standard plastic-covered "zip-cord."
Belden Wire Company does not regularly distribute non-shielded
rubber-covered two-wire cable. For now, the Belden zip-cord listed here is
22-gauge. While they rate this at 5 amps, intermittent use with this iron
should not cause a problem. [If you have any better suggestions, the
editor is interested in announcing them--be specific, with catalog numbers,
please!]
Also still somewhat in doubt is the best way to attach the 7556 tip to
the cable. The pins provided are steel, and do not take solder readily
(although, if you wrap them with several turns of flux-core solder and heat
them before making any connection, soldering them will be much easier).
These pins are 0.037 inches in diameter, and they are spaced at 1/4-inch
centers. A socket such as the inside portion of the Amphenol 6175 two-lead
"UHF" antenna connector might work. I found some automotive push-on
connectors which I was able to modify to do the job. As will be seen in
the section "Tip Construction," these male pins on the back are actually
crimped into copper tubing, which you can get at by removing a small
portion of the heat-shrinkable tubing of the tip assembly. This tubing can
easily be soldered to, and the wires of the cable could even be fitted into
the tube ends after the pins are extracted with healthy pliers.
A straight SPST foot switch in series with the primary will work.
However, as mentioned, this type of iron can get very hot if left on too
long where the work pieces are small--the heat capacity of the work not
being enough to dissipate the iron's energy. I thought, "Wouldn't it nice
if there were a way of operating the iron at reduced power?" I tried using
a sewing machine foot control which has a variable resistor inside it;
however, I soon found that the resistance of this control wasn't high
enough to make an appreciable difference.
Another way of reducing the power might be to build a double-ended
foot-control switch, one with a button at either end. Thus, by pushing down
on the "toe end" of the control, full power would be applied; by rocking
back on the "heel end" of it, it would be run at about half power, which
would be fine for maintaining the tip temperature. This could be done by
having a pushbutton operate the primary circuit directly at the toe end,
and by putting the pushbutton at the heel end in series with a 15-watt
120-volt lamp, or perhaps a 500-ohm 20-watt wirewound resistor.
At present, if I need to maintain the heat for a while, but not supply
full power, I merely push up and down on the switch about once a second,
and this seems to work fairly well.
One more improvement completes the design. The diameter of the
soldering point on this tip is 0.070 inches (before tinning). The spacing
between pins of IC sockets is often 0.075 inches; thus, the tip can
sometimes contact two pins at once, causing a solder bridge. The surface
of these tips cannot be ground down or harmed with abrasives in any way;
they are clad with iron and tinned at the factory for long life, and this
cladding must not be harmed. While visiting at Smith-Kettlewell, we found
that you can flatten the last eighth inch gently in a vise without cracking
the iron-clad coating. Don't mash any farther back than this eighth inch,
or you will damage the heating coil inside. This gives the tip a
screwdriver-shaped end whose thickness is perhaps 0.050 inches, which can
easily pass between pins of an IC socket. When you flatten the tip, orient
it in the vise so that the flat sides coincide with the flat faces of the
"handle," as we now shall call the lead extension assembly.
Tips on Using the Fingertip Iron
The way I use it, this iron permits soldering to be basically a
one-handed operation. As mentioned earlier, I wrap a little piece of
solder around the tip before I put it into position; pieces 1/8 or 1/2
inches long will do nicely for IC sockets, while longer pieces could be
used for larger terminals. To save time when I am doing a lot of
connections (one after another), I prepare precut lengths, form them into
little rings, and stack them on a nail; they can quickly be picked off the
nail and installed on the iron's tip as needed.
If you find short pieces of solder difficult to deal with, you may
prefer just wrapping a turn and a half around the tip, then nipping this
assembly free of the spool. The amount you use will actually depend
somewhat on the diameter of solder you have, as well as the size of
connection. The amounts advocated here are based on my experience with
23-gauge solder.
Caution! It is important to hold onto the metal body of the tip when
wrapping it with solder, not the handle or the ceramic insulator that the
leads go through to reach the tiny heating element inside. If you do not
hold on to the metal portion, mechanical damage to the heating element can
occur.
Being cool to the touch (most of the time), I place the iron on the
target using an index finger of either hand. [Editor's Warning: As with
the old soldering gun, cooling of the instrument takes at least more than
half a minute. If you are doing a series of connections, don't let your
zeal get you in a hurry; you can still get a serious burn if the tip has
not been allowed to cool. The iron, once a trusted friend, can turn on
you.] A wet cleaning sponge should be kept on hand to wipe off excess
solder after every few connections (this is not necessary each and every
time, as it is with a constantly hot iron which is always building up
oxides.) If you have a connection to do right away, wiping the tip on the
cleaning sponge will help cool it faster.
(At Smith-Kettlewell, we tried using the sponge as a storage place for
the soldering iron. This got us into trouble in two ways. First, the tip
is apparently not watertight, and I got a serious burn one time as steam
came out of it. Second, the frequent drastic heat cycling was hard on the
tips; we had repeated failures due to the metal portion of the tip breaking
loose from its ceramic insulator.)
Because soldering is not a one-handed operation, you can use fingers of
your free hand to hold parts in position. In fact, I often do not use a
vise or board holder; oftentimes I just hold the board still with the heels
or palms of my hands.
Once everything is in place, I step on the foot pedal, and in five
seconds or so, soldering takes place. You know when soldering occurs by
two indications. One is that, when the flux has done its cleaning job, a
typical "squeakiness" can be felt as you make small motions with the iron.
Since you have free fingers on your other hand, the other can be when you
feel the quick rise in temperature of a component which happens when
"wetting" of the metals has occurred.
Voila! What a breeze! Soldering is no longer a complicated process.
No more scorched parts or burned fingers. Because it's so easy to hold
things while you're using this system, it makes experimenting with projects
much easier; I can just "tack" parts temporarily in place without formally
mounting them in some way.
If you don't like the idea of applying the solder to the iron, you can
still use your favorite system of feeding solder with your free hand. [The
editor actually prefers feeding solder to the work for two reasons: First,
by letting it run off the iron, you stand some chance of using up the flux
before it has a chance to clean the work pieces--although I've seen this
system work like crazy for ol' Bernie. Second, however, I like to use the
solder as my "pyrometer," as you might call it; the solder's melting tells
me when the parts are hot enough to accept it. However, the squeakiness
and rapid heat transfer described above are good indications of success as
well, so do as you like.]
When working on old hand-wired equipment (such as an old ham receiver I
had), I found this soldering iron to be a real boon for getting into tight
places. The fattest part of its hot portion is less than a quarter inch in
diameter, and since it is cool to start with, it is easy to find free room
for this before turning it on. With a standard pencil iron, it is easy to
burn nearby components with its hot barrel.
Still, the constantly hot pencil iron has its place. As I mentioned
before, these "cordless" tips are very fragile in their construction. A
little fingertip tool will simply not do heavy jobs--on large items. For
unsoldering, these fragile tips cannot withstand prying, twisting, and
other such procedures for separating parts.
When working with CMOS circuits, I've tried grounding the centertap of
the transformer. So far, I have had no problem, neither due to static
charges nor due to the AC supply. (I have ruined CMOS devices by using the
battery iron only, since it wasn't grounded.) Grounding the centertap does
not actually ground the iron's tip; it is insulated from its heating
element. However, not enough static charge apparently builds up to damage
the CMOS devices.
As listed in the next section, there are other tips available which,
with a little mechanical engineering, could also be used. The smallest
unit has an almost needle-like soldering point on it. I don't like it,
though, because its tip is so fine that I can't put enough solder on it and
it slips off the connection more easily. One use for this tip is for
cleaning out plugged-up holes in PC boards; it is so fine that it can
actually reach right through them.
Tip Construction and Availability
One problem of these "Tuner Extension Tips" is their scarcity, even
among dealers of Wahl products. A good source for them is Fordham Radio
(see "Address List"), where they can be ordered under their Wahl number
7556.
Another disadvantage is their cost, about $7. In dissecting one, it
was found that they are actually made by adding the extension assembly to
the "fine" tip, Wahl No. 7545. If you have the right tools--a small
crimping tool and a heat gun to shrink tubing around the assembly--you
could precisely duplicate the 7556 from the 7545 (a cheaper tip which costs
from $3.25 to $4 and which can even be gotten from Jameco). With some
mechanical engineering, one could machine a lightweight handle with
screw-type binding posts so that the more common short types could be used
instead of this rare one.
The pins on the short-legged tip are fitted into 2 3/4-inch lengths of
copper tubing, which is then crimped down tightly onto them. Likewise,
steel pins are fitted into the far ends of the tubes and crimped in place,
leaving about 7/16 inch protruding. (The tubing used is 1/16 inch o.d.,
and 0.040 inch i.d.) A strip of fiber insulation--often called "fish
paper"--is placed between these conductors, whereupon they are wrapped with
"transformer tape" (which is fairly resistant to heat). (This fish paper
insulator may be the hardest thing to duplicate; it is 1/16 inch thick,
which is unusual. Bakelite would work, as would the fish paper salvaged
from burned-out units. Just about any tape would do; just apply it an inch
back from the forward end so that it won't get warm.) With the fish paper
strip being 3/16 inches wide, the conductors are then spaced at 1/4-inch
centers. Finally, heat-shrinkable tubing (capable of a "recovered size" of
5/8 inches) is slid up to within 1/2 inch of the soldering tip and secured,
leaving 1/8-inch long steel pins to protrude at the back end.
An exact replacement for the tubing has not been found in small
quantities. "Small Parts" has 1/16-inch o.d. copper tubing, but its inner
diameter is 0.035 inches. (The pins of the tip are 0.037 inches.)
However, their 3/32-inch tubing (being 0.066 inches i.d.) would probably
work. This is Small Parts number TRC-2, and comes in 12-inch or 36-inch
lengths.)
Other Wahl Tips
7566--"Micro" Tip, 0.020 inches
7545--"Fine" Tip, 0.070 inches (Often comes as standard equipment with
the cordless iron.)
7535--So-Called "Regular," 0.156
Vinther Iron Circuit
Belden No. 9712 two-wire zip-cord is used to power the Wahl 7556 tip.
One side of the tip goes to the centertap of the transformer's secondary;
this centertap is also grounded to the anti-static pad on your bench and/or
a wrist strap, where necessary. The other side of the tip goes through a
15-amp fuse to one end of the secondary. (This transformer should be
capable of delivering 2.5 volts at an intermittent current of 7.5 amps. A
suitable unit is the Stancor 6455, which has a 6-amp 5-volt centertapped
secondary, and a 107- or 117-volt primary.) One side of the primary goes
through an on-off toggle switch to one side of the mains. The other lead
of the primary goes through a foot switch to the other side of the mains.
(The foot switch should be normally open, and can be one such as the Line
Master 491S. Also, foot switches with a standard three-prong male/female
end on them could be used, such as the Line Master 491SC360; a three-prong
electrician plug from the transformer can just be plugged into the latter
type of foot switch.)
Address List
Fordham Radio: 855 Conklin Street, Farmingdale, NY 11735; (800)
645-9518.
Jameco Electronics: 1355 Shoreway Rd., Belmont, CA 94002; (415)
592-8097.
Small Parts, Inc.: 6901 N.E. Third Ave., Miami, FL 33138; (305)
751-0856.
- END -
[from the Smith-Kettle Technical File,
Vol. 9, No. 2, Spring 1988]
TEMPERATURE CONTROLLING THE VINTHER FINGERTIP IRON
by Al Alden and Bill Gerrey
_Abstract_--Based on the idea published here in the Winter 1987 issue,
the resultant soldering iron is a quick-heating, fast-cooling iron which
can be put into position when cold, then energized by operating a foot
pedal. Its very small size allows the user to hold it only 1 1/2 inch away
from the work, and it is of feather-weight. Like many quick-heating irons,
however, this low-mass soldering tip cannot, by itself, dissipate the power
it consumes, and the uncontrolled version was prone to overheat. This
controller promotes safer operation, and it is expected that the life of
the tips will increase.
This soldering iron uses the so-called "tuner extension tip" available
for cordless soldering irons of the Wahl Clipper Corp. This tip is intended
to fit into a handle containing a 2.5v rechargeable battery and a
pushbutton switch. Besides the limitations of battery operation, this
cordless instrument has two disadvantages: The battery makes the handle
heavy, and its shape does not permit the user to "choke up" near the
business end to be close to the work. Second, the operation of a
pushbutton puts muscles in tension which destabilize hand position.
Nevertheless, a lot of blind technicians liked the Wahl cordless iron.
Because its tip heats up rather quickly, you can place it against the work
pieces when it is cool. Bernie Vinther fits the tip with little solder
"preforms" (little one- or two-turn coils which he makes from rosin-core
wire solder). With the tip loaded with this bit of solder and put in place
before it is turned on, the problems of coordinating a lot of activities
with only two hands are eliminated.
The extension tip discovered by Bernie Vinther has about a four-inch
insulated portion that remains cool. By attaching a two-wire cable to the
conductors in this extension, the iron can then be powered by a source from
the mains (a 2 1/2 volt transformer was used in the original article). The
foot switch can be wired in such a way as to avoid carrying the tip
current; it was in the primary circuit of the transformer in the original
article.
The "tuner extension tip" (Wahl part No. 7556) * uses the same element
as
the standard-length "fine tip" (part No. 7545); this is nice to know, since
the former is nearly twice the price of the 7545. The extension is made by
crimping 3 1/3-inch long copper tubes onto the pins of the 7545, taping
these tubes to a fiber separator and encasing them in heat-shrinkable
tubing. Save the copper tubes and the separators from burned-out 7556's,
since you can reuse bits of them to extend the cheaper standard-length
tips.
* This part has been discontinued by Wahl Clipper. There is no
replacement (as of 3-25-96).
The editor has gotten a couple of suggestions about how to attach wires
to these tips. However, nothing seems to be free of intermittent contact;
the tip draws about 8 amps when first energized--4 amps when hot--so you
can imagine how "positive" these connections need to be. (Various push-on
connectors, including parts of tube sockets, have always intermittently
failed me, darn them.)
Pins of these tips are steel, and they don't take solder very well.
However, the copper tubes are easy to solder to, and that is what the
editor advocates currently. Peeling away half an inch of the
heat-shrinkable tubing at the back end of the 7556 reveals that pins--just
like those on the heating element--have been inserted into the tubes to
"adapt" them to the cordless handle. I pull these out with pliers; then I
solder the flexible cable to the tube ends and wrap the assembly with tape.
A serious disadvantage of the original design was that, if you lost
track of melting of the solder, the iron would frequently be left on too
long and overheating would occur. Our temperature controller completely
solves the problem of overheating; damage to the work is now infrequent,
and the tips (which are rather expensive at $7 each) should last longer.
Theory of Operation
The controller works by putting the tip's hating element into a
Wheatstone bridge and measuring its resistance. This resistance increases
as a function of temperature; it starts out being about 0.3 ohms when cold,
and gets up to perhaps 0.5 ohms when soldering temperature has been
reached. An integrator senses the difference between the voltage on the
tip and that of a "temperature-control potentiometer," and the output of
the integrator is then used to control the tip current.
A new component is used to vary the tip current; introduced by
Motorola, it is called a "sense FET." In principle, a power FET is
comprised of 3600 FET's in parallel. (All the channels are in parallel,
and all the gates are connected together.) However, if we then disconnect
two of the "sources" and bring them out to a separate pin, we can use an
external "sensing resistor" to monitor one eighteen-hundredth of the
current. Thus, instead of providing the whole mess with a source resistor,
which would put a lower limit on the total "on resistance" of the control
circuit, a resistor of comfortable value (100 ohms) can be used to sample a
small branch of the total current.
The sense FET chosen is the Motorola MTP10N10M. With a gate voltage of
10v (positive with respect to the source) and with a drain current of 10
amps, its "on-resistance" is a maximum of a quarter of an ohm--typically
0.175 ohms.
Its TO220 package has five pins. three of these (pins 1, 3, and 5,
respectively) are "Gate," "Drain," and "Source" terminals. As mentioned,
however, only 3,598 of the sources go to pin 5; two of the 3600 elements
have their sources both going to pin 2, the so-called "Mirror" terminal.
Pin 4, the so-called "Kelvin" terminal, is a way of looking at the source
voltage, but not on pin 5 which passes all that heavy current. Pin 4 is a
separate light-duty wire that goes to the 3,598 sources.
In operation, a "sampling" resistor (we used 100 ohms) goes between the
"Mirror" and "Kelvin" terminals. When the FET is operated, a voltage (E
equals I times R) reflects the fact that 1/1800th of the drain current is
flowing through that resistor.
_Conceptual Model of the Wheatstone Bridge Circuit_--(Don't build the
circuit in this paragraph, or it will leave your iron cold.) The negative
supply point of the bridge is grounded. One side of the bridge consists of
the following: A 10K resistor goes from the plus supply point to the top
of a 10K temperature-control pot. The bottom of this pot goes through 91K
to ground. The arm of the pot is the take-off point for this branch. As
for the other branch: The positive supply point goes through 100 ohms,
then through the iron to ground. The take-off point for this branch is the
junction of the iron and the 100 ohms.
In order to make that circuit work, all you need is a way of
multiplying the current that flows through the 100 ohms by 1800 times and
apply it to the iron. This is accomplished by supplying the iron with
current from another branch. The iron gets most of its current from the
"Source" terminal of the sense FET. The "Mirror" terminal, which is at the
positive supply point of the bridge, goes through that 100 ohms to the
"source" (or more correctly, to the "Kelvin" terminal). The result is that
the companion resistor in the iron's half of the bridge has a simulated
value of 100/1800 ohms (0.056 ohms). (Don't worry that this is less than
the "on-resistance" of the FET; remember, it is dissipating lots of power
and getting supplied from a higher source.)
"Control" is affected by pulling up on the supply to the bridge. When
the pedal is pressed, the integrator gently suggests, then emphatically
demands, that more and more power be supplied; it does so because this is
the only way of getting the heating element's resistance to climb. When the
iron's resistance causes its voltage to exceed that on the wiper of the
control pot, power to the bridge is reduced until cooling changes the
condition of balance, at which point the bridge gets more power.
Without a little help, it is possible that the integrator would not
have anything to compare initially, since its output powers the bridge.
Thus, a "boot-strapping" capacitor from the non-inverting input (and the
arm of the control) goes to the supply line that gets operated by the foot
pedal; this causes an immediate unbalance that brings the sequence of
events into play.
Finally, there are two 1meg resistors which are protective in nature.
Imagine, if you will, what could happen if you forgot to install the chip
and the gate drifted aimlessly into the region of conduction. The FET
might turn fully on and burn out the iron. Thus, the gate goes through 1
megohm to ground to prevent this. Likewise, if the wiper of the pot got
dirty and opened temporarily, the non-inverting input to the integrator
could drift high, causing the integrator to turn the FET fully on. Another
1meg resistor to ground prevents this latter disaster.
Construction Details
While it might be done differently--in a fancy enclosed box--our
controller was built onto a 6 by 8 by 2 inch chassis. As the sense FET is
called upon to dissipate over 16 watts, a heat sink is required. This
chassis has a couple of transformers on it and is naked aluminum; it serves
as part of the heat sink, while a small additional heat sink was affixed to
the outside for good measure.
Two DC voltages are required by the circuit. First, the iron is
supplied by a heavy 5-volt filament transformer working into a bridge
rectifier (and filtered by 40,000 microfarads). A light 12- to 30-volt DC
supply is needed for the op-amp. (Since the op-amp only draws 0.8mA, a 12-
or 18-volt battery could be used instead. Furthermore, the op-amp is only
powered when the foot switch is depressed, so a battery would last its
shelf life.) We chose to use a separate small transformer for the op-amp's
supply. It's not that having 5-volt and 12-volt secondaries on the same
unit is a rare combination--it used to be quite common. But if you come
across a filament transformer whose 5-volt winding is for a 10-amp
rectifier, it will have been made with the assumption that the 12-volt
filaments add up to a lot of power as well, and such a unit will be heavier
than it need be.
The two transformers were mounted on top of the chassis, along with the
40,000uF filter cap. The rear panel has a large bridge-rectifier module
mounted on it. there are two fuses, a line fuse and a 10-amp fuse for the
6-volt supply; these can be internally placed, or put on the back panel.
The front of the chassis is rather interesting. On the left front
corner is the female spring clip for a cabinet door latch, the part which
usually is mounted up under the middle cabinet shelf. If you reshape it a
bit, it makes a fine clamp for the "extension" part of the iron. Our clip
needed no shaping; it was one of the double-roller types, and it squeezes
the handle of the iron just fine. There is a wrong kind with rollers; some
of them have metal "bridges" that hold the rollers' axes, and these would
not permit the iron's handle to slip down in. The rollers, or simple
spring flippers, should be placed so as to face upward, beyond the top of
the chassis. When the iron is in place, it will lie on top of the chassis
parallel to the left edge.
Also on the front panel is the temperature-control pot and the on-off
switch. A grommet in the lower middle permits the cord for the iron to
emerge; this cord should not come out the back, as it would then be in the
path of the iron more often. On the lower right, opposite the iron stand,
is the jack for the foot pedal.
Since the foot pedal supplies power to the op-amp, it cannot be common
to ground. therefore, its jack must be insulated from the chassis. This
is more trouble than you would immediately think; the standard jack used
for such foot pedals is the tiny 1/16th inch size, which is generally too
short to accommodate insulating washers. This jack can be mounted on a
piece of plastic behind a large hole in the chassis, but it was decided
that this was more trouble than adding a control transistor which would
permit grounding the jack. The jack ended up at the lower right corner of
the front panel--out of the way.
Other than the 6v high-current supply, all circuitry was put on a piece
of perforated board measuring 1.8 by 4.5 inches. It was mounted up
underneath the top of the chassis--with one of its long edges butting
against a side panel. By placing it thus, the sense FET, which is in a
TO220 package, can be stood up on the board (near the long edge) and bolted
to the side of the chassis when the board is in place. The case of the
sense FET is hot--plus 6v--so standard insulating hardware for the TO220
package must be used to insulate it from the chassis, which is ground.
The same bolt that holds the sense FET to the chassis also secures a
heat sink to the outside panel; the insulating shoulder washer goes on the
outside of this heat sink, putting the heat sink at chassis ground and
leaving the head of the mounting bolt hot. Our heat sink ended up on the
left side--the same side as the makeshift iron stand. This was probably a
mistake, since that heat sink can get pretty warm
Rather than putting binding posts on the outside for connecting to the
iron, we fashioned binding posts on the circuit board. We did so using
1/2-inch 6-32 bolts with two sets of nuts, the top set being used to secure
the ends of the iron's cable.
Circuit for the Controlled Vinther Iron
The two transformers have their primary windings connected in parallel.
One side of this combination goes to the cold side ("neutral") of the AC
line, while the other primary leads go through a 1/2-amp slow-blow fuse,
then through the on-off switch to the hot side of the line. If a 3-wire
plug is used, the "ground" prong goes to the chassis and to circuit ground.
(The neutral side of the plug is the right-hand prong as they point at you
with the ground at the bottom.)
The 12-volt transformer's secondary feeds a small bridge rectifier
unit. The negative output of the bridge is grounded. The positive output
(marked with a slightly longer lead, usually) is bypassed to ground by a
47uF 25v electrolytic (negative end at ground). The output will be perhaps
16 to 18 volts.
The positive output of the 18v supply goes to the emitter of a 2N2907
PNP transistor. The base of this transistor goes through 10K to its
emitter; this base also goes through 10K to the tip of the foot-pedal jack.
The sleeve of this jack is grounded.
The collector of this transistor goes to pin 8 of an LM358 dual op-amp.
Pin 4 of this 358 is grounded. One op-amp is not used: pins 6 and 7 are
jumpered together, while pin 5 is grounded.
Between pins 1 and 2 of the 358 is a feedback capacitor of 0.01uF
(Mylar). Pin 2 (the inverting input) goes through 10K to the iron side of
the Wheatstone bridge (the non-grounded side of the iron). Pin 3 goes to
the arm of the temperature-control pot. For protection, pin 3 goes through
1 megohm to ground. Pin 3 also goes through the boot-strapping capacitor
of 0.1uF (disc or Mylar) to the collector of the 2N2907. Pin 1 of the 358,
the output of the integrator, goes to the gate (pin 1) of the sense FET.
For protection, this gate also goes through 1 megohm to ground.
The 5-volt transformer's secondary feeds a high-current bridge
rectifier. The negative output of this bridge is grounded. Its positive
output (usually marked by a cutout on its adjacent corner) is bypassed to
ground by a 40,000uF 10v electrolytic (negative terminal at ground; and for
your safety, be assured of correct polarity). Because of voltage drops in
the bridge, the output of this supply will be perhaps 6.5v, dropping to 4v
under full load.
The output of the 6v supply goes through a 10 amp fuse to the drain
(pin 3) of the sense FET. The FET's source (pin 5) goes through the iron
to ground.
The supply point of the Wheatstone bridge is the "Mirror" terminal (pin
2) of the sense FET. This pin 2 goes through 10K to the top of a 10K pot
(temperature control); the bottom of this pot goes through 91K to ground.
Between pins 2 and 4 of the sense FET (between the "Mirror and "Kelvin"
terminals) is a 100-ohm sampling resistor.
Temperature Setting
The temperature-control setting that everybody seems to like is with
the pot about two-thirds of the way up (60 to 70 percent). It should be
noted that when the control is in the first quarter of its rotation, the
control circuit starts to warm things up--then collapses. Pressing the
control again brings on a fresh start, but there is definitely a lower
limit to the successful operation of the circuit at low settings.
Acknowledgements
A lot of heads were together on this one. It should be said that a
co-worker, Manfred Mackeben, was after Smith-Kettlewell to design such an
iron for darn-near a decade. It took Bernie Vinther's vigilance to find
the extension tip that made this all possible. Al Alden's creative use of
the sense FET to simulate an impractically low resistance value is sheer
genius.
Parts List
Resistors (1/4-watt 5%):
1--100 ohm
3--10K
1--91K
2--1 megohm
1--10K panel-mount pot with non-precision taper
Capacitors:
1--0.01uF Mylar
1--0.1uF disc ceramic or Mylar
1--47uF 25v electrolytic
1--40,000uF 10v electrolytic (Digi-Key P6422, 47,000uF 16v)
Transformers:
1--AC mains to 5v 8- or 10-amp (such as the Signal A41-43-10 which has
two 5-amp secondaries which can be paralleled, or the Signal
241-8-10 with a 10-amp center-tapped 10v secondary)
1--AC mains to low-current 12v (such as the Signal 241-3-12, or the
Radio Shack 273-1385)
Semiconductors:
1--Low-current 50-PIV bridge rectifier (such as the Radio Shack
276-1161)
1--8- or 10-amp low-PIV bridge (such as the Jameco MDA900-3 12-amp
unit, or the Radio Shack 276-1181 8-amp one)
1--2N2907 PNP transistor
1--LM358 op-amp chip
1--Motorola MTP10N-10M sense FET
Miscellaneous:
1--1/2-amp slow-blow fuse
1--10-amp slow-blow fuse
2--Appropriate fuse holders
1--SPST on-off switch
1--1/16th inch open-circuit foot-pedal jack
1--General-purpose tape-recorder foot switch
1--7556 Wahl Clipper Co. "tuner Extension Tip" (available from Fordham
Radio in Farmingdale, NY.)
1--Small heat sink with insulated mounting kit for TO220 packages (Note
that the chassis box should be bare metal, so that it can be the
main heat sink.)
1--Suitable bare metal chassis or box
Sense FET Pin Arrangement
The MTP10N-10M comes in a TO220 package from which five leads emerge.
With the mounting surface toward you and the leads pointing up, the pins
are numbered 1 through 5 from left to right. When you get them, the pins
are bent in a rather bizarre way: 1, 3, and 5 are positioned rather far
forward (away from the mounting surface), while 2 and 4 have only slight
"dog legs" in them and appear further back.
Pin 1--Gate
2--"Mirror" (The sources of two "cells")
3--Drain (common to the case)
4--"Kelvin" (connected internally to the main Source junction)
5--Source
Address List
Digi-Key Corp., P.O. Box 677, Thief River Falls, MN 56701; (800)
344-5439
Fordham Radio, 855 Conklin Ave., Farmingdale, NY 11735; (800) 645-9518.
Signal Transformer Co., 500 Bayview Ave., Inwood, NY 11696; (516)
239-5777.
[from the Smith-Kettlewell Technical File,
Vol. 9, No. 3, Summer 1988]
THE JAMECO XY168 SOLDER STATION
by Tom Fowle
_Abstract_--This is a brief review of a newly available
temperature-controlled soldering iron. Like the Weller WTCPM, it is
traditional in that it is constantly powered (it is not like the Vinther
iron, which is placed on the work when cool). Nonetheless, for those of us
who prefer a hot iron, this unit appears to fulfill all the needed
functions of the popular Weller soldering station at half or less the usual
price.
A recent flier from Jameco Electronics announces a new soldering
station, sold as Jameco catalog number XY168. The unit is priced at $49.95
and is temperature controlled, being adjustable from 270 to 800 degrees
Fahrenheit. A unit having digital temperature readout is available for a
$40.00 boost in price; that model has not been bothered with as no
conceivable need for such a readout could be imagined.
The advertising claims that the temperature control switching is
accomplished by a thyristor so that switching occurs on zero-crossings of
the AC line voltage, therefore keeping spikes and transients at a minimum.
(People who work with unprotected CMOS devices have reason to worry about
such transients.) Temperature control and stability is claimed to be
within plus or minus 10 degrees F.
To the technician, the unit appears very much like the old familiar
Weller solder station. There is a base unit of a more-or-less cubical
design whose top holds the spring-like cage for storing the iron between
applications. The top surface also has a small parts tray, along with a
well to hold the cleaning sponge. The slightly sloping front panel has the
on/off slide switch--to the left of center--with a meter just above it
which reads out temperature to a resolution of 50 degrees or so. To the
lower right of the panel is a nice heavy 5-pin amphenol connector of the
type often used for microphones on radio equipment. This accepts the plug
on the end of the iron cord. This is a considerable improvement over the
Weller unit, which has a strange light-duty 3-prong plug (a high-failure
item).
There are two small LED's towards the top of the front panel, the left
one being power and the right one showing the on/off state of the heating
element. Just above, and to the left of the iron socket, is a small
pointer knob which adjusts the temperature. Setting this knob with its
pointer at about the 1:30 clock position gives approximately 750 degrees, a
good starting temperature.
The tips supplied are "clad"; although it is advisable that they be
tinned immediately when first turned on, they require less service than the
old-fashioned copper tips. Unlike copper tips, they should never be
touched with abrasives; once the factory coating is damaged, they should be
discarded.
The "Station" comes with a 1/16th inch tip, although other sizes are
available. They list the following tips:
Note: These dimensions are in inches. The tips are not strictly
conical, but are slightly blade-shaped. A flat spot on the handle
conveniently enables the blind user to orient the tip's flat side as
desired. These tips are $3.49 each.
1/8th--xy3
1/16th--xy2
3/64th--xy4
1/32--xy1
As shipped, the spring iron sand is not installed. It has a large wire
hook which fits down into a slot near the top rear of the station base. The
unit comes with a flat cleaning sponge which can be wetted and kept in the
to of the base. However, the author much prefers the American Beauty
"One-Pass Soldering-Iron Cleaner," (American Beauty No. 480). This is
available from Marshall Industries and Mouser Electronics.
The soldering station also comes with an allen wrench whose purpose we
have not yet divine.
In use, there seems to be no problem with this unit, especially to
those used to the Weller. The lack of the repeated click of the Weller
turning on and off is somewhat missed as a small comforting reassurance of
action, but this is of no importance. There is no reason why an audible
reader could not be hooked up to the temperature meter, but we have not
tried this because there is a warranty period to wait through, and we see
no big need for such a readout other than amusement.
In conclusion, this unit is a valuable addition to less-expensive
quality tools, and we hope its existence may convince some of you, who have
been reluctant to spend $100.00 on a soldering iron, to become familiar
with the joys of a temperature-controlled unit. With such a tool, the
rapidity of soldering and the lessened fear of severe burns brings the
process of soldering to the realm of comfortable everyday work--away from a
process one does with a quaver and a cringe.
Suppliers
Jameco Electronics: 1355 Shoreway Rd., Belmont, CA 94002; (415)
592-8097.
Marshall Industries: 9674 Telstar Avenue, El Monte, CA 91731; (800)
522-0084.
Mouser Electronics: 11433 Woodside Ave., Lakeside, CA 92040; (619)
449-2222.
THE G3JYT SOLDER GUIDE
by Frank Jeanmonod, G3JYT
Pinner, Mi.x.[?], England
I have used this guide successfully for many years; it works very well
on the pins of IC chips, as well as for soldering larger connections. (I
use a small Weller iron for the IC projects.)
The basis of this tool is a darning needle (which we call a "Bodkin").
The handle is made from a bit of 3/4-inch doweling. I drill a tiny hole in
one end and ram the Bodkin into the hole so that the pointed end protrudes
about 2 1/2 inches.
Though not sharp, the point is such that when the tool is braced
against the connection, the darning needle tends to stay in position.
These needles are stainless steel, so solder does not adhere to them.
I first wrap solder around the bodkin--2, 3, or 4 turns, depending on
the connection--after which I locate the joint with its pointed end. Then,
I slide the solder down the bodkin so that it contacts the work.
The bodkin is easy to find with hot soldering iron; I then slide the
iron down to the work.
[Editor's Comments: Well now, we have another good inventor in our
midst. This tool has one distinct advantage over the tubular guide (SKTF,
Spring 1983); this guide will never clog up. It has the disadvantage that
you can no longer monitor the melting of the solder, which is ordinarily
the cue that the connection is hot enough. However, you still get other
indications: Small motions of the iron against the work will feel (and
sound) "squeaky" when the flux has done its cleaning job. The smell of
flux will be apparent. The adjoining leads and components will exhibit a
sharp rise in temperature as the solder-wet pieces promote efficient heat
transfer. Bravo, and thank you, Mr. Jeanmonod.]
- END -
[from the Smith-Kettlewell Technical File,
Vol. 4, No. 2, Spring 1983]
THE JA3TBW SOLDER GUIDE
As mentioned in our "Hints and Kinks," SKTF, Spring 1982, Mike
Bhagwandas (JA3TBW) of Kobe, Japan, invented this guide. Since that time,
our lab has done considerable experimenting with its use as an aid to
soldering short-legged components which have poor "landmarking" into
printed boards. Blind subjects who have built our prototype "kit sets"
have found this instrument indispensable when soldering the IC sockets and
trim pots. So that you can enjoy the fruits of this research, we have
attached the described version to each copy of the magazine; please wear it
in good health.
The material we settled on is stainless steel, and we did so for the
following reasons:
1. It will never char and contaminate the iron.
2. If "acid" or "stainless steel" flux is not used, it is
unlikely that solder will adhere to the tube.
3. Stainless steel has poor heat conductivity.
4. The resultant device can be of small diameter; it is available
having a wall thickness of 0.009 inches.
5. This tubing is commonly available, sometimes being known as
"hypodermic tubing."
Specifically, we purchased "Hypoflex" seamless thin-walled stainless
steel tubing of Grade 304; its dimensions are 0.072 inches outside diameter
(o.d.), 0.009 inch wall thickness, giving us what they call a "theoretical
inside diameter" (t.i.d.) of 0.054 inches. Unfortunately, this product
only comes in bundles of 120 feet at 62 cents per foot. However, a similar
product can be gotten from "Small Parts," * in 6, 12, and 24 inch lengths.
They have two types available: Htx-15 Hypodermic Tubing with a 0.009 inch
wall, and HTX-15TW "Thin Wall" tubing with the same outside diameter of
0.072 inches and a wall thickness of 0.006 inches. The former is $2 per
foot; the latter is $1.20.
The size was chosen so as to accommodate solder of approximately 0.003
inches; the tube has plenty of room to spare for wrinkles in the solder to
pass freely through it.
Two brands of solder can readily be gotten with these dimensions. The
first is Kester, 604A33-1SN6066.03144, available from Marshall Industries.
* This Kester solder, which has a diameter of 0.031 inches, is also
available from Mouser Electronics * under their number 533-24-6040-27.
Finally, 0.028 inch "Multicore" solder is available as Ersin number SN60
22SWG. The Kester is preferable, since "Multicore" solder tends to contain
an overabundance of flux, thus causing gumminess and stickiness in the
tube.
The tubing has such a thin wall as to afford being "parted" with a
file, especially knife-shaped or three-cornered files. After sectioning
off a piece (4 inches being a popular length in our trials), square off the
ends with a file; then de-burr the inner edges with the tip of a file or
with a drill bit. (We have done all of this to the 4-inch piece you have
received.)
For unclogging these units when solder gets lodged inside, a No. 55
drill bit is a handy addition. This bit is 0.050 inches in diameter, and
will comfortably ream it out without galling.
One final note on making your own customized version: You may wish to
devise a handle so as to afford better control. We would be very
interested in the schemes you come up with along this line. A small "shaft
stop" with a set screw is included with your guide. Used as an adjustable
collar, the shaft stop can be secured to the tube just below your hand so
as to promote stability in holding the tube against the work. (The shaft
stop is available from Player Piano Company. * It has an inside dimension
of 0.098 inches, listed as their catalog number 889 at 20 cents each.)
In operation, solder is passed through the tube so as to just make
itself known at the business end, this end being rested on the connection.
Solder can be fed to the work with the thumb and forefinger, while some
arrangement of the remaining three fingers is chosen to support the tube.
Good stability will be promoted if the connection has a feature against
which the inner edge of the tube can be braced. For example, I bend socket
pins outward once they have passed through the board; I actually set the
tube over the intended pin, at which point I lean the tube out to the side
so as to permit the iron to reach the pin.
Once you are in position, find the lower half of the tube with the iron
and slide it down onto the connection, all the while pressing the solder
down against the work. I find this technique to be so easy that glee
overtakes me, giving me a tendency to apply too much solder. Remember in
using this technique that all the solder will be applied in the right
place, for a change, and very little of it will be used up exploring the
iron.
If left stationary in the tube after the connection is made, the solder
will seize up in the bottom end. This is not due to actual bonding with
the stainless steel, but is due to the flux solidifying, acting to glue the
solder in place. Reheating the end of the tube with the iron will often
loosen things up, otherwise your No. 55 drill bit can be used to ream the
tube clear.
The way to prevent adhesion is to create relative motion between the
tube and the solder while the flux is cooling. Some of us pull the tube
away from the connection and run the solder through so as to protrude 1/4
inch or so. Others withdraw the solder into the tube about 1/2 inch or so.
I spin the tube while it is cooling. All of this is done after the
connection has been soldered; you have plenty of time because the flux must
cool considerably before it solidifies.
Like anything, this takes a little practice; you will at first, by
applying far too much solder or by heating up adjacent connections with the
iron, inevitably bridge pins here and there. However, comparing my success
with and without this instrument would be ludicrous--there is no
comparison. Thanks to Mike, JA3TBW, there is a way to take the heat off
our target practice when the going gets tough.
* Address List of Suppliers
Marshall Industries, 788 Palomar Ave., Sunnyvale, CA 94086; phone (408)
732-1100.
Mouser Electronics, 11433 Woodside Ave., Lakeside, CA 92040; phone
(714) 449-2222.
Player Piano Company, 704 East Douglas, Wichita, KS 67202; phone (316)
263-3241.
Small Parts, Inc., 6901 N.E. Third Ave., Miami, FL 33138; phone (305)
751-0856.
[from the Smith-Kettlewell Technical File,
Vol. 4, No. 1, Winter 1982]
HINTS AND KINKS
The following was submitted by John Dascenzo, W3IPD, of Fairfield, PA:
"I have always had stability problems when using a soldering gun, in
positioning the point on the work and then pulling the trigger. No matter
how careful I am, the action of pulling the trigger frequently causes the
point to move. I found a simple solution for this problem.
"First, the trigger of the gun is tied permanently 'on' with a piece of
string (color of string not important). The gun is then plugged into a
foot switch.
"My foot switch is rather fancy. I placed a microswitch on the side of
a heavy metal block--about the size of a brick. It is arranged so that by
merely sliding my shoe slightly, the gun goes on. An AC receptacle for the
gun is also mounted on this block."
Thank you, John Dascenzo. Your point has good basis in physiology. If
we look back at "Soldering, Part II" (Winter '81), an analogy is drawn
between the wrist and a pulley system, with the tendons being "ropes" which
connect the fingers to their muscles in the forearm. Applying tension or
moving one of the fingers puts the wrist in a very unstable condition;
uncontrolled movement of the hand is the _likely_ result.
The following ideas were contributed by John Lizza of Carle Place, NY:
"Obviously, Nichrome wire in heating elements cannot be spliced by
soldering the broken ends. Repairs can be made by inserting the broken
ends into a crimp lug and crimping it tightly.
"I do automotive work, and it is often necessary to note small but
critical differences in the voltage on the electrical system (say from 13v
to a high of 15v while the battery is charging). However, my multimeter
only has scales of 0 to 50 volts and 0 to 5 volts.
"I get around this problem by connecting a zener diode (for example, a
12.4-volt unit) in series with my meter while setting its range to the
5-volt scale. In this way, the critical changes end up as a 2-volt range
at the bottom of my more sensitive scale.
"To check liquid levels--brake fluid, oil, water, etc.--use a straw or
a piece of tubing through which you are constantly blowing. You will know
immediately when the other end becomes obstructed by the fluid."
Thank you, John Lizza. Also, it seems I missed a major point in
describing his work on circuit boards with the hand in a plastic bag. He
points out that this technique really shines when checking for intermittent
and loose connections. Sorry.
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