Hi Roger,
Your comments regarding plating thickness and impact of thickness
non-uniformity are well taken.
However, you are off the mark regarding the relationship of thickness,
elongation and ductility of the copper deposit. Elongation tests are designed
to estimate material ductility; this works reasonably well for test specimen
with circular cross-sections or non-circular cross-sections with aspect
rations of no more than 5. For foil specimen--aspect ratio ~500--elongation
tests are notoriously bad in determining ductility. As long as the tests are
performed in exactly the same manner on very similar specimen they give
reasonable comparative information. The fact that foil elongation results are
thickness-dependent is wholly an artifact of an inadequate test method. It is
for these reasons that test methods ASTM E 796, "Standard Test Method for
Ductility Testing of Metallic Foil," and IPC-TM-650, Test Method 2.4.2.1,
"Flexural Fatigue and Ductility, Foil," were developed.

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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