Hi Jeff! Yes, there are folks using immersion tin as a final pwa finish for
IPC Class 3 products. There are a number of different immersion tin
formulations available and I recommend that you thoroughly investigate them
to insure that they meet your use environment expectations. Collins has
completed a significant number of test data sets and we have qualified an
immersion tin for use in our avionics applications. I am in the middle of
finishing up the testing on interference and compliant pins - the initial
test results show that no abnormalities were found in terms of installation
forces, continuity etc. Collins published one paper on immersion tin
thermal cycling results (IPC APEX 2000 proceedings) and we plan on
publishing our pin data in the near future. We have satisfied ourselves
(based on our testing and vendor data) that we will not have a tin whisker
problem on the pwbs. But,  tin on components is a topic that the industry
(and ourselves) need to conduct additional investigations.

Dave Hillman
Rockwell Collins
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Jeff Seeger <[log in to unmask]>@IPC.ORG> on 05/09/2001 03:11:55 PM

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Subject:  Re: [TN] Sn whisker problem


,

        Would anyone be able to comment on relevance to Immersion
        White Tin as a surface finish on Class 3 hardware?

        Further, how about when not soldered (as in pressfit)?

        Lately I've had vendors reach for this finish in pressfit
        applications due to easier control of difficult finished
        hole size tolerances.  The NASA site seems to indicate
        *any* Sn is mil-prohibited as a final finish (still surfing).

        Thanks in advance, and thanks for a good technical thread!
--

      Jeff Seeger                         Applied CAD Knowledge Inc
      Chief Technical Officer                  Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                978 649 9800

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