Hi Mark,
First, you need to determine the failure mode—do you have barrel failures or
innerlayer interconnect separation? In the latter case, there are different
possible failure modes—foil cracking, separation at some interface. That, will
tell you where the weak link is.
Second, examine the PCB histories for thermal excursions (HASL, assembly
process (particularly manual), testing) for very high temperatures.
Third, examine the design (choice of dielectric: Tg, CTE(z), and innerlayer
copper foil (E1 or E3), foil thickness).
Fourth, examine the PCB manufacturing process (drilling, smear removal, copper
plating (ductility, uniformity)).
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]
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