ISn is used on a lot of backplanes for telecoms use but I have always been
uneasy about it.

I understand that you don't get tin whiskers with immersion Sn because it is
not stressed as much as electroplated Sn.  But when you put a press fit
connector into it surely this stresses it?  Can this result in whiskers.

Neil

 -----Original Message-----
From:   Jeff Seeger [mailto:[log in to unmask]]
Sent:   28 October 2002 14:33
Subject:        Re: Press fit connectors...

[log in to unmask] wrote:
>
> snipped for brevity <
>
> Press fits were/are used primarily to permit wire wrapping of backplanes.

        Peter, I'll agree with "were", but for "are" I must dis-
        agree with you.  (That's a first!)

        I see pressfit in all manner of high performance elec-
        tronics, from CPCI and VME-64X through to mega-bandwidth
        network gear.  I believe it is popular in the complex
        spectrum because it spares a thermal excursion and is
        reworkable, both important on these .250" thick 20+ layer
        beasts, and as a non-soldered connection can be made in
        finer pitches.  2mm pitch is more than common and many
        more dense arrangements are showing up all the time.

        So from context you'll all know that I fall on the side
        of non-soldering, and take the -610 comment to regard
        single staked pins also.

        Meanwhile I've a new(ish) problem with pressfit.  Due to
        the hole size and construction contstraints, a number of
        fab shops want to move away from HASL to IAg or ISn for
        the surface finish.  I am suspicious both of the amount
        of insertion lubrication available in these finishes and
        also the long-term life when these are not dispersed in
        a soldering step.  Any commentary out there on this?

        Thanks and regards,
--

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

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