QUESTION: Does the PWB community have any test data indicating that
 exposure to frequent, severe thremal transients will not cause such
 separations to propagate into the over-plating, causing failure of
 the interconnect?

The hesitancy to allow these separations at the outer foil/plating interface
was
not that it would propagate "around" the knee and onto the surface, but that
it would propagate into a crack into and through the plating at the knee.

I have seen some blind vias with cracks in the plating at the knees and I have
seen those that do not.  Whether they were propagations of separations such
as you describe, I don't remember.

Have you performed multiple thermal stress testing on samples that exhibit
this condition?  If you did this and did not get cracking, I would certainly
not
hesitate to use the boards.

I think if you check 6012, it has the same illustration of separation at the
knee
as that used in the military documents.

Susan Mansilla
Robisan Lab

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