HI SJ,
David asked you good questions.
Given your second e-mail, there are a number of possibilities:
(1) interfacial cracks developed during transport mechanical shock
loading--this would occur is
     (a) not all solder balls were properly wetted--causes: insufficient
reflow temperature/ solderability
problems;
     (b) weak interfacial attachment [prime suspect: ENIG-'black pad'].
(2) no wetting has taken place [component warpage, PWB warpage during reflow]
or insufficient solder paste.
In order to get a more succinct advice, you need to determine the actual
failure mode and failure root cause(s).

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
E-mail: [log in to unmask], Website: www.engelmaier.com

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