Hi Eric,
Intermetallic compounds are all brittle (that means they not much capability
to plastically deform); however, most are brittle and strong. Two exceptions
are Au/Sn and Ag/Sn IMCs, which are brittle and weak.  Sn62/Pb36/Ag2,
Sn96/Ag4 and
Sn95/Ag5  are not inherently brittle, the brittle IMC are evenly distributed
and surrounded by ductile Sn or Sn/Pb phases. It is when the concentration of
IMCs gets large, e.g. near a surface where they are formed, that drouble
arises.
And yes, the evidence  that the failure  in the TI case back in 1982 was
related to Sn/Ag IMC is very clear.

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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