Hi Rush,
1) Cracked cu barrels indicate either too thin copper and/or inadequate 
ductility for the thermal expansion experienced;
2) elongation is not a good way of assuring Cu ductility; to get real 
ductility values you need to use IPC-TM-2.4.2.1 or ASTM E-796;
3) you measured thin copper in failed vias;
4) that indicates localized plating conditions were different there than 
coupons—most likely plating current density;
5) QUESTION: Is failure location in same/similar [in terms of copper feature 
density at the surface] sections of PCB?
6) Solution Option #1: Equalize plating current density with thieving 
features.
#2: Plate whole PCB thicker.



Werner



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