Hi Mumtaz,
Not having seen pictures, I am reduced to guessing. particularly since you
did not say how thick the flex circuit is.
But when you get copper cracking, it always means that the ductility and
strength of the Cu was insufficient for the loading conditions. Thus, there are 3
possibilities alone or in combination:
(1) the properties of the copper deposit are bad;
(2) the loads [thermal expansion, bending, etc] are too high;
(3) geometric stress concentrations create loading conditions too severe for
the available material properties.
A good root-cause-analysis can give you the answer of the causes, which then
allows you to improve the situation as needed.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com


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