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March 2000

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 28 Mar 2000 10:38:17 EST
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Hi Steve,
My comment has nothing to do with Ag-containing solders, but with the effect 
of Ag-plating on component leads. Immersion Ag may be thin enough not to give 
you the necessary Ag concentration.
The experience I referred to goes back to about 1982. The industry found 
out—and since forgot except for a few old-timers like me—what silver can do 
to solder joints, when TI moved some of its PLCC production to Singapore. 
There somebody decided to Ag-plate the leads. At the first unfortunate 
recipient of this product, IBM-Austin, the PLCCs started to literally fall 
off the PCBs when slight bending, such during fixturing for functional 
testing, put even very small loads onto the solder joints. As a consequence 
of this scary news (nobody knew about the Ag yet and compliant leads were 
just invented and without history), 17 competing companies joined forces and 
formed the IEEE Compliant Lead Task Force.  
Silver, it turns out creates an even weaker intermetallic compound (IMC) with 
tin than does gold. The necessary IMC concentration necessary for this effect 
is about the same as for Au. 
Because of legal problems (the 2 companies with the lowest PLCC fatigue lives 
threatened to sue everybody involved in the IEEE CLTF), the results, except 
for some preliminary data, were never published.
If you go back into the TechNet archives, you will find some problems related 
to Ag (plating) being discussed.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com 

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