Robert,

Surprising you have this problem in GI mat'l.  Sure you do not have this in
GF mat'l ?.  That is to say your plating may be suspect.

Also, see if your etchback attack is more severe on prereg, so that the
plating looks like "ACCORDIAN".  This, even if your plating quality is good
(tensile elongation strengths), may cause barrel cracks.  This is very common
for plating cracks.

The root cause of differential etch-back lies somewhere else.  Are prepreg
and core from same supplier ?.  Is the prepreg completey cured ?

Good luck

Rush
Accurate Engg Inc.

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