Hi Dave,
You give me too much credit, I do not the deformation work or specifically
deal with the underlying deformation mechanism(s) of solder; I am more in
league with John Hagge who took some of my work on flex circuits and copper
foil and utilized it for solder. While I need to be concerned about the
deformation mechanism(s), it is only insofar as they limit the applicability
of practical first-order reliability estimation models. For the underlying
deformation mechanisms the credit for the current understand and perhaps hope
for future improvements need to go to people like Grossmann, Frear, Solomon,
Fox, Knecht, Shine, etc. Lau also does not work on deformation mechanism(s);
he uses FEM, neglecting creep and stress relaxation, to determine localized
stresses and strains, and than applies Norris-Landzberg even though that
model was discredited by other workers at IBM (Shah, et. al.) and does not
account for the all-important dwell time that limits full stress relaxation
in most accelerated tests.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

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