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Reply To: | TechNet E-Mail Forum. |
Date: | Fri, 13 Aug 1999 09:29:47 EDT |
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Hi Phil,
Y.C. Koo gave you a good answer; however it is somewhat incomplete. Indeed,
Sn gets depleted from the solder leaving behind a weaker Pb-rich layer;
however, the depletion of Sn results from the formation of Sn-Ag
intermetallic compounds, which solder at least have been implicated in solder
joint failures similar to 'Au-embrittlement', but worse. Thus, even small
tensile forces on the via, the thermal expansion of the PCB is a likely
source, may break the connection. Heat transfer is almost eqyally as bad with
small physical separations and larger voids——and your original purpose of
heat transfer is defeated.
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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