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April 2003

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Thu, 17 Apr 2003 12:20:34 -0400
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Don't do it!  Unless you are going to retire within 6 month to a
year....(so you don't have to face the FA and all the answers required).
Scary!  After all the technical work dated since 1950, someone still
want to try.... With finer pitch devices, you will have more of problem
than before (shorter whisker will do the trick of failure rather than
the longer one when was needed in the old days....more difficult to find
and difficult to detect... When you take the assembly out, the whisker
will fall off from the shorting or leakage area....).  Conformal coat
everything and do not use pure tin....(annealing sometime will promote
the growth if you have minor ionics on the leads..).
Do you self a favour, stop it now!.
My 2 cents.
                                                                  jk

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Joseph
>Sent: Thursday, April 17, 2003 12:08 PM
>To: [log in to unmask]
>Subject: [TN] Tin Whiskers
>
>
>Some of our component suppliers have notified us that they
>will be changing some lead finishes to pure tin.  We suspect
>that this may be the beginning of a landslide, and as a
>high-rel supplier, we have to consider the risk of shorting
>from tin whiskers.
>
>Until about a decade ago, we used a lot of parts with tin
>finish, and never saw a whisker, at least that we know of.
>Whiskers appear to be rare, but the risk does not seem to be
>well understood, or at least quantifiable. Maybe they're lost
>within the noise of normal component failures.
>
>Technical literature has some anecdotes and a few interesting
>pictures, and there are suggestions on possible causes
>(stresses within the plating or from lead forming), and
>mitigations (e.g. matte tin is better than bright
>
>acid tin, conformal coat is good).  What we don't seem to have
>is anything that a reliability engineer could use to allow
>comparison of risks and benefits.
>
>One easy reaction would be to hot-solder dip the leads, but
>this will be expensive, and there is a finite probability of
>damage from the extra handling, ESD, moisture exposure, and
>the heat cycle.
>
>Maybe we could anneal the parts after plating or lead forming,
>or even the whole assembly after soldering.  Don't know what
>temperatures or bake times would be needed to anneal pure tin.
>
>I'm posting here instead of a lead-free forum because because
>this is going to affect us all, whether we use tin/lead solder
>or not.  And even with the dwindling membership, the jokes are better.
>
>Joe Kane
>BAE SYSTEMS Platform Solutions
>Johnson City, NY
>
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