Boards are multilayer that have been thru a plasma etchback process.  Some
of the pics show buried via innerlayers which were panel plated prior to
lamination.  Multiple etch lines indicate electroless copper deposition,
panel flash plating and a final pattern plate.
     We have witnessed these circular voids after drill, after plasma
etchback, after flash plating and in as received coupons.  We have one pic
that plainly shows a black circle BETWEEN the electroless etch line and the
etch line showing the demarcation between the flash and pattern plating.

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