[SI-LIST] Re: IPC-2152 trace current/temperature calculator
- From: "Arjun Bingipur" <arjun.bingipur@xxxxxxxxxxxxxx>
- To: "Jack Olson" <pcbjack@xxxxxxxxx>
- Date: Thu, 14 Jan 2010 15:59:30 -0000
Thanks Jack. Personally, I feel without the modifier charts, it would
have been a difficult task analysing the temperature curve on its own. I
was on it for a quite some time without much clarity. But with modifiers
and temperature curves together, it becomes so much simpler. It would
have helped if it was part of the the IPC spec.
Regards,
Arjun
________________________________
From: Jack Olson [mailto:pcbjack@xxxxxxxxx]
Sent: 14 January 2010 15:11
To: Arjun Bingipur
Cc: Doug Brooks; SI-LIST
Subject: Re: [SI-LIST] Re: IPC-2152 trace current/temperature calculator
No, I created those charts myself, using the data in the new spec (which
was obtained from the Lockheed Martin and Naval Surface Warfare Center,
Crane Division experiments)
The reason I created the "modifier" system is because the way the
document is laid out, you have to read all kinds of extra stuff
(including the Appendix!!!) just to get a decent result. The charts give
you a starting number, but then the text describes all kinds of things
that can influence the number. I tried to condense what was there into
an introductory approach to deriving a better answer than the historical
charts could have ever provided. It is the SIMPLEST, in other words.
I couldn't put too many charts in the article (and PCDesign magazine was
already complaining about the length!) so for example I showed how to
use the universal chart (based on 3oz copper) and modify the result for
any other copper
thickness to get a decent approximation, but of course you will NOT have
to do this if you have all of the temperature curve charts in the spec
itself, because it contains ALL the copper thicknesses for both internal
and external.
And maybe I don't have to say this, but there are other considerations
that may influence your result. For example, this data is provided for
traces in STILL AIR, and since most of our designs are in sealed
housings these numbers are good enough for us, but if you have designs
with good air flow, you may get better results with even smaller traces.
On the other side of the coin, if you use a specific distance to your
nearest plane but your nearest plane is chopped and split,
your results may vary. And finally, I didn't even address parallel
traces at ALL, and just about every design has those.
so...
To summarize I can only say
1) this is a better starting point than IPC has ever provided before
2) It is only an approximation, so add some derating "wiggle room"
3) You may need thermal simulation to prove your own results
4) get the spec, it contains much more than I could put into that little
article
(that's why I don't envy Doug the task of trying to make a calculator.
everything needs a disclaimer!)
http://pcdandf.com/cms/magazine/209/6850/
hope that helps,
Jack
.
On Thu, Jan 14, 2010 at 5:06 AM, Arjun Bingipur
<arjun.bingipur@xxxxxxxxxxxxxx> wrote:
Jack,
As per your document, If we are trying to obtain the final trace
width
using the new universal chart rather than the conservative
chart, we
need to be able to modify the values according to the modifier
charts.
But, having gone through IPC 2152, I do not find the modifier
chart
information. However, I'm currently having access only to the
IPC 2152 -
final Draft document, dated December 2008. Does the released IPC
2152
spec contain this information or am I missing anything here?
Regards,
Arjun
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Jack Olson
Sent: 13 January 2010 19:38
To: Doug Brooks
Cc: SI-LIST
Subject: [SI-LIST] Re: IPC-2152 trace current/temperature
calculator
Doug,
I apologize for using the word WRONG in my last post.
You have my sincere gratitude for the papers you have written
and the
tools you have developed and shared so unselfishly. I really
appreciate
those contributions and I intend to make good on my promise to
buy you a
lunch someday for letting me use your utilities for FREE for so
long
(smile)
While I agree that it would be very difficult to implement all
the new
data in IPC-2152 into a simple tool, the one thing that jumped
out at me
was the proximity to planes. Most of the other factors can't
influence
the result by more than a few percent. And I'm not a programmer
either,
but it seems like it would be easy to add the distance to
nearest plane,
even if you want to derate it somewhat for safety margin.
Although I'm
not a "thermal guy", I was on the IPC committee (did you see my
name on
page iii? twice? My mom did! Ha) anyway (sorry about that
shameless
puffery) I would cheerfully help you any way I can, if you ever
try to
implement more of it into your tool. I even have a few formulas
that
were interpolated (?) from the curves in an excel spreadsheet.
By the way, we were considering incorporating the fusing data on
your
(UltraCAD.com) site into the standard, but we didn't want to
delay the
publication. maybe next revision....
Finally, I totally agree with you that the historical chart has
withstood the test of time (because in most cases it is very
conservative), but what is need is a safer way to "push the
envelope" if
the designer needs to use smaller features.
Do you have any interest in developing a free thermal simulator
for us?
(grin)
thanks, Doug
Jack (aka "the new guy")
p.s. PLEASE accept my apology for implying that your calculator
is wrong
.
On Wed, Jan 13, 2010 at 1:13 PM, Doug Brooks
<dbrooks9@xxxxxxxxxxxxxxx>wrote:
> Thanks for the link to your paper. Its a good contribution.
Well done.
> I'll consider trying to implement some of it in the next
version of
> the calculator.
>
> But please understand that this is now the third version of
our
calculator.
> We have never ever suggested that it is *RIGHT* or *WRONG*. In
fact,
> given that there are almost an infinite number of combinations
of
> stackups layer dimensions trace dimensions and form factors
swiss
> cheese effects component placement component thermal effects
> environmental effects materials properties etc
>
> anyone would be a little foolish to suggests they even knew or
could
> know what *RIGHT* and *WRONG* really was.
>
> Also, note that we did not help write the standard, nor were
we a
> member of any subcommittee
>
> We don't even necessarily endorse the standard (and the IPC
doesn't
> necessarily endorse our calculator, at least as yet)
>
> The calculator merely makes using the standard (right or
wrong,
> somehow
> defined) easier.
>
> The calculator is actually based on 5, user selectable data
sources.
> These sources differ by as much as 40%. The new IPC-2152,
Vacuum, is
> the most conservative. The old IPC-D-275 is the most
aggressive. The
> old standard has been criticized through the years (with some
> justification) BUT nevertheless many people think that it HAS
> withstood the 50-year test of time! The data from another
study,
> reported in Design News in 1968, provides results that are in
between
> the other standards. The final decision of what results to use
are the
> system designer's responsibility, based on the risks he/she
> understands and is willing to take. We don't endorse any one
of the
data sources.
>
> The trace current/temperature calculations are one of four
> capabilities of the calculator. Others include an estimate of
fusing
> current (see an article on our web site), skin effect
calculations
> (including skin depth, crossover frequency, and frequency and
> temperature adjusted trace resistance, see an article on our
web
> site), and basic Ohm's Law calculations for traces. The trace
> current/temperature calculations and fusing current
calculations can
be automatically adjusted for skin effects.
>
> Again, we never suggest our calculators are *RIGHT* or
*WRONG*. Just
> that they make working with already established formulas and
> relationships easier. We developed them for our own use, and
make some
> of them available to others --- as is and as represented.
>
> Doug
>
>
>
>
> At 08:45 AM 1/13/2010, Jack Olson wrote:
>
>> Not to complain (kudos for developing the calculator!) but
since
>> proximity to planes has the most drastic effect over any of
the other
>> factors, and it is a fairly linear relationship, I'm curious
why you
>> didn't incorporate it.
>> (only one extra box!) of course, not knowing about splits and
"swiss
>> cheesiness" of the plane, maybe you were simply afraid?
(grin,
>> kiddin' ya) There is a graph in this article if you are
interested:
>> http://frontdoor.biz/PCBportal/HowTo2152.pdf
>>
>> Unless I'm misunderstanding your calculator, I think your
result will
>> be about 50% WRONG in most cases (since most boards have
planes these
>> days)
>>
>> just trying to help,
>> keep up the good work,
>> Jack
>>
>>
>>
>> > From: dbrooks9@xxxxxxxxxxxxxxx
>> > Subject: [SI-LIST] Re: IPC-2152 trace current/temperature
>> > calculator
>> > Date: Tue, 12 Jan 2010 22:38:19 -0700
>> >
>> > I don't know if you have read the standard. There are a
couple of >> pages
>> > that address thermal modeling, planes, alternative
dielectrics,
>> > etc,= in
>> a
>> > very general manner. There are no quantitative adjustments
included
>> > ( >> with
>> > the possible exception of how to treat parallel conductors
which is
>> > pr= etty straightforward, and pretty obvious.) There is a
Figure
>> > A-13 that rela >> tes
>> > to some estimated factor adjustments that can be used based
on the
>> > dist= ancebetween the conductor and a plane for 1 Oz traces
in .070
>> > thick
>> Polyim >> > ide Board (and a single curve for 2 Oz traces).
The
calculator
>> > does n >> ot
>> > incorporate these adjustments in its calculations. But
these
>> adjustments >> > caneasily be made to the calculated results if
desired.
Overall,
>> > the
>> gene >> > ralities included in the Standard apply equally well to the
>> > calculated resu= lts from the calculator.
>> > The Calculator is based o= n Conductor Sizing Charts
contained in
>> > the Appendix (from Figure A-17, p 35= to Figure A-86, p83).
>> >
>> > Doug
>> >
>>
>>
>>
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<http://www.ultracad.com/>
>
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