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August 2004

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Subject:
From:
Gabriela Bogdan <[log in to unmask]>
Reply To:
(Leadfree Electronics Assembly Forum)
Date:
Wed, 4 Aug 2004 15:59:27 +0200
Content-Type:
text/plain
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text/plain (115 lines)
God bless you, Mark!
Gaby
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, August 04, 2004 8:27 AM
Subject: [LF] AW: [LF] Tin Whiskers, Tin Finish and Accelerated Stress
Testing


> Dave,
> this is what we just observe with TC for FeNi42 components. Applying TC to
a component without having any solder paste applied, we observe pretty much
longer whiskers than in the real application conditions (assembled to a
board by soldering). We even found the same whisker length for SnPb plated
components and for Sn plated components after board assembly (both SnPb or
SnAgCu paste) submitted to TC.
> Thus we fear that in many cases we have identified conditions to grow
whiskers, but over rate the risk , since the correlation to field life
application is missing.
>
> We E3 / E4 have emphasized these circumstances again and again and
therefore claim for test conditions, which are as close to the application
conditions as possible and try to correlate test conditions to field life
conditions and identify acceleration factors, which we use as a basis for
the acceptance criteria rather than specifiying any arbitrarily chosen
numbers as acceptance criteria linked to arbitrarily chosen test conditions.
>
> The same situation counts for many of so called accelerated stress tests.
Everybody applies them since there is a standard available and usually the
crieria can be met, but nobody askes, whether these test conditions and
acceptance criteria really reflect reality and whether the correlation
factors are available or even true at all.
>
> One very famous axample is all the efforts we put in the correlation of
FEM simulated life time prediction to accelerated thermal cycling
conditions. Meanwhile we are pretty good in predicting # cycles to failure
in accordance to the thermal cycling test. But who can really say in how far
these test conditions reflect the application to which they are assigned to?
The majority of our customers does not even precisely know, what the field
life conditions of their products are, but nevertheless they request a
certain number of thermal cycles to pass under well defined conditions.
>
> This is the dilemma we are in whith established tests. And I fear will be
the dilemmy with whisker testing too, despite we are really willing to
correlate AST to field life conditions.
>
> regards,
> Marc
>
> -----Ursprüngliche Nachricht-----
> Von: Leadfree [mailto:[log in to unmask]] Im Auftrag von MA/NY DDave
> Gesendet: Montag, 2. August 2004 08:03
> An: [log in to unmask]
> Betreff: [LF] Tin Whiskers, Tin Finish and Accelerated Stress Testing
>
>
> Hi Philips-Pascal, Marc, Pratap, , and IPC LF Listservers,
>
> I replied earlier on an old note tread or stream from earlier in July
> (14July) and after reading some more, I wanted to ask at least one
question.
>
> From what I believe Pascal or maybe Infineon-MarcD wrote; as well as, the
article in the June 2004 IEEE Transactions on CP&MT, it seems like any AST
with Tin lead finishes will, has, (or may) produce greater failures (more
and longer whiskers) than in the real application environment. This would
also be true for any thermal shock type reliability or screening tests.
>
> This of course would make it more difficult to create life predictions via
using the AST thermal cycles engineers have been accustomed to, and might
lead some who were unaware to make erroneous conclusions.
>
>
> Any comments??
> Any cautions?
>
> Yours in Engineering, Dave
> Y i Engr, MA/NY DDave
>
> P.S If I could have found a link to the CP&MT article I would have sent
it. I guess IEEE protects it.
>
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