We have recently seen "mousebites" on innerlayers caused by resin spots,
leaking through holes in the copper.  We saw this only on either reverse
treat, or double treat, but it could occur on regular copper as well....(this
customer uses almost no "plain" copper).

The resin leaked through the foil, caused a spot, which when it was on the
edge of a trace would not bond to the photoresist.  The photoresist would
lift, and allow etching on the inner part of the resin spot, and the resin
spot would be etched away, creating something that looked like a mousebite.

The customer started to inspect incoming foil/laminate with a black light,
which causes resin to fluoresce and makes it more easily visible, and
rejected anything with spots, and the problem went away.

Rudy Sedlak
RD Chemical Company

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