Werner,
We had this argument awhile back. The original question was about immersion
finishes -- tin and silver. Your warning was about (orders of magnitude
thicker) electroplated deposits on lead frames..........?!
Secondly, if silver IMC concentration is the same as for gold, how do people use
2 -- 5% silver-containing alloys?
Eric Yakobson
Werner Engelmaier <[log in to unmask]> on 03/28/2000 07:38:17 AM
To: [log in to unmask]
cc:
Subject: Re: [TN] Silver Embrittlement
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
ùand since forgot except for a few old-timers like me
ùwhat 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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