Hi Werner! Sorry, but I disagree with your "nickel will NOT help" sentence.
We both agree  that a  nickel barrier won't help Neil avoid having a Ag
diffusion issue but a nickel barrier would eliminate the issue of
zincification. If Neil was able to process the components in a JIT type of
operation he would be able to manufacture good solder joints but the zinc
diffusion would result in a latent defective solder joints over time.

See you at IPC/SMTA  Assembly Expo!
Dave Hillman
Rockwell Collins
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Werner Engelmaier <[log in to unmask]> on 10/01/98 10:07:28 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
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To:   [log in to unmask]
cc:
Subject:  Re: [TN] Solderability Problems




Hi Neil,
Are you sure you have de-wetting? You may never have had any wetting in the
first place or you may have too much brittle and weak Au-Sn and/or Ag-Sn
intermetallic compounds (IMCs) near the interface, which with  upwards of 2
microns of Ag or Au, and particularly with 2 microns each of Ag AND Au, is
likely. You can tell the difference by analyzing the lead surface. If there
is
little or no Sn present, you never had wetting, if you have Sn and Ag/Au
present it is the IMCs.
The Ag does not reduce solderability, it is similar to Au in this respect.
With this much Au/Ag underplating with nickel will NOT help. The
Ni-underplate
only helps if the brass is not solderable by itself.

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]

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