Paul Gould wrote:
> 
> In message Oscar Cammuse writes
> >
> >Does anyone have experience with Sn coatings on boards in lieu of solder
> >coatings and OSP coating?  What problems have you experienced?  Why is Sn
> >coatings not so acceptable?
> >
> We have used immersion tin coatings which are very thin and these have a very
> short shelf life of less than 2 weeks before solderability is unacceptable.
> --
> Paul Gould
> 
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Tin coatings are also known to cause " Tin Whiskers" a thin filament of 
tin metal that grows under stress put on coating and causes short to 
adjacent exposed electronic circuit elements. This has been discussed and 
explained in literature since 1976.

Ref. #1 'Filament Formation on Printed Wiring Boards' by Jennings, C. W., 
IPC Technical Review February 1976, pp 25-32.

Ref. #2  'Avoiding Electrolytic and Strain-induced Shorting Mechanism" A 
review by T.T. Hitch, Circuit Worlds, Vol. 16, No. 2, February 1990, pp. 
41-44.

Ref. #3  'Tin Whisker Growth Mechanism and Prevention" Chapter 6, Failure 
Modes and Mechanisms in Electronics Packaging by P. Viswanathan & P. 
Singh, (to be published 1997)
-- 
Pratap Singh
Tel./Fax: 512-255-6820
e-mail: [log in to unmask]

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