We have an 18 layer PWB with blind vias that have their bottom between
layer 8 and 9. We have experienced laminate separation between layers 8
and 9 and separation at the copper plating knee betwwe the vendors
copper and the plated copper. It reminds me
resin smear between the board's external copper and the plated copper.
It is hard to tell if the separation is due to a crack from thermal
stress or whether it is due to smear.

        The available specifications due not seem to address this effect
Does any one know whether this copper separation is deleterious or
whether it is acceptable. There is one opinion that this is acceptable
because it resulted from fabrication of a board outer layer.
        There is another view that the resulting separation ends up in
the internal part of the board after lamination and is thus a separation
        in an internal layer. Does any one have an answer to these
questions?

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