Could this be an
example of the 'phase separation' problem with the flame retarded resin
formula?
Hello
Prasad,
Thanks for the off line photo. It was the "thousand words".
Based on the etch profile of layer two, the construction appears to be
a "cap foil" construction, thus prepreg was used in the construction of the
outer layers which fits with my first thoughts. I cannot see any evidence of
the effect in the small area or core material that is in view. If the effect
is an intrinsic artifact of the material, I would expect to find it everywhere
and not just in the prepreg zone.
I confess that I have not seen
anything exactly like it before but I am still leaning towards my earlier
thoughts regarding contamination of some sort in and between prepreg layers
(perhaps it is simply moisture in the prepreg as polyimide is quite
hygroscopic).
I am not an expert is resin formulations and thus would
defer to Brian's comments which make sense to me but I believe that EDX
elemental mapping analysis would find bromine if it is in fact present and
dominant in the voided areas. You might send your photo to Steve Zeva to have
him post on his website and let others take a look and share their thoughts.
Best of luck in finding cause and resolution.
Joe ---------------------------------------------------
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