[tinwhiskers] Re: [LF] FW: [SMART] Very useful RoHS review conference report
- From: "Fritz, Dennis D." <DENNIS.D.FRITZ@xxxxxxxx>
- To: <tinwhiskers@xxxxxxxxxxxxx>
- Date: Tue, 26 Jan 2010 18:08:05 -0500
Andrew.
I believe Enthone (Cookson) acquired at least the technology, if not the whole
company.
http://www.enthone.com/pwb/index.aspx#FinalFinishes(HASLAlternatives)
There is a small spelling difference as it seems to me Florida CirTech used the
name you give when they had the product for US distribution. I cannot vouch
for anything about whisker free, quoting from the from the 2005 JEDEC/IPC
mitigation guideline - JP002:
5.10.1 Immersion Tin
Immersion tin is a chemical displacement process that results in a relatively
thin (<40 micro-inches or 1 µm) and stress free tin film. Immersion tin's
primary purpose as a surface finish for PCB applications, is solderability
protection for the underlying copper basis metal.
As previously mentioned above, a potentially significant source for whisker
formation are stresses induced from the formation of Cu6Sn5 intermetallic
compounds (IMCs). While whisker formation is a concern, the primary concern is
migration of the IMCs through the deposit and subsequent oxidation at the
surface, thus rendering the deposit non-solderable. To this end it is
imperative that the specification for a minimum deposit thickness of 1 micron
be recommended. The thicker deposit improves shelf life, as a significant
layer through which the IMCs must travel before solderability is impaired. [55]
The use of annealing procedures of 150 °C for 1 hour is not practical for
printed circuit boards due to the potential negative impact of this temperature
on warp & twist characteristics.
Whiskers have been grown on immersion tin conductive features To date, these
whiskers have appeared at ambient conditions with time and not as a result of
exposure to heat, vacuum, pressure, humidity or bias voltage [55]. This would
seem to indicate that the primary source is Cu6Sn5 migration stress. Whisker
length has been reported to be significant in vias, with lengths measured at
150 microns, see Figure 4. Whiskers of much smaller length have been recorded
growing off the edge of surface mount (SMT) component pads, as well [55].
Figure 4: Whisker in an Immersion Tin Plated 0.46 microns (0.018 in) Diameter
Via Hole (picture in original)
Immersion tin is a suitable minimum risk selection that has been successfully
used by some companies in below gigahertz frequency applications. It is a
potentially viable lead-free finish option for some PCB applications.
From a mitigation viewpoint, there are several options that should be reviewed
if assembling a PWB with an Immersion Tin surface finish. The first option
should be to ensure that all surfaces plated with tin be soldered, including
vias. The consumption of the deposit as a function of soldering will all but
eliminate any potential for whisker growth [55]. Where it is not possible to
solder all vias, the use of hole-fill materials should be investigated. For
vias used as test points, the use of conductive hole-fill material that is
subsequently plated over with copper/immersion tin (considered at this stage a
round SMT pad) and then soldered, will help mitigate whisker formation but
still provide test point capability.
Denny Fritz
SAIC, Inc.
________________________________
From: tinwhiskers-bounce@xxxxxxxxxxxxx on behalf of Andrew Glass
Sent: Tue 1/26/2010 5:40 PM
To: Bob Landman
Subject: [tinwhiskers] Re: [LF] FW: [SMART] Very useful RoHS review conference
report
Hello Bob,
Really appreciate all the information Thanks.
Has anyone checked into OMICRON/TIN.
As a manufacturer of PCBoards I ran into this product
some years ago. The chemist said it will not whisker.
--
THANKS
Andrew Glass
AGCO Inc.
500 Rampart Range Road
Woodland Park Co. 80863
1-719-687-6875
FAX 1-719-687-6880
Andy@xxxxxxxxxx
Tuesday, January 26, 2010, 2:32:10 PM, you wrote:
> Sadly Nigel,
> The resulting RoHS legislation says otherwise. I don't think
> namecalling does any good. I'm of European heritage (mum was
> Canadian, fathers family was Romanian). The problem is a problem
> with humans in general, and politicians in particular (of all
> parties). To quote the Bard, the fault lies with ourselves.
> Clearly the science is presently on the side of lead. It appears
> thus far not to matter. No-one seems to offer a good explanation as
> to why that is so.
> Kindest regards,
> Bob Landman
> H&L Instruments
> On Jan 26, 2010, at 9:58 AM, Nigel Burtt <njb@xxxxxxxxxxxxxxxx> wrote:
>> Perhaps perjoratively referring to those disagreed with as "lefties"
>> and "loonies"
>> might be why the valid opinions are ignored should you ever care to
>> share them with people who can actually use the information to change
>> things.
>>
>> And as a point of fact, the right of the political spectrum in the EU
>> has always held the majority in the EP
>>
>> < http://en.wikipedia.org/wiki/File:EP_Groups_1979-2009.png >
>>
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