Bill,
This will cost me a royalty fee, but "it depends" on what mitigating factors
you have either in your design, make-up of your final surface finish or
processing parameters. Some of factors are as follows:
* Pure tin is matte tin
* Pure tin is poisoned(97% Tin or less or another alloy additive that does
what lead did)
* Spacing or pitch is 0.5 mm or greater
* Minimize stresses during part/assembly processing and handling
* Have a Nickel barrier layer between Copper and Tin
* Bake parts/assembly after processing to relieve/reduce stress and/or
anneal
* Conformal Coat assembly. Acrylic will retard, but Polyurethane and the
more durable
  compounds are better.
Dewey


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kasprzak, Bill (sys)
USX
Sent: Thursday, February 03, 2005 7:28 AM
To: [log in to unmask]
Subject: [TN] So what about Tin Whiskers?


I've been watching the lead free drive move forward for a number of years
now.

So, I have to ask the lead-free pundits, what concerns should I have with
respect to tin whisker growth on SOIC's and other multi-leaded devices where
the lead finish is pure tin?

I know that at the solder joint area, there will not be any concerns about
tin whiskers, but what about between adjacent leads that are not soldered?

Any comments would be appreciated and welcomed.

Bill Kasprzak
Moog Inc., Systems Group, Process Engineer

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