Dear Groovy

The mechanism for the wedge void defect you described is not solely limited to
the drilling process creating a mechanical separation. 

Another occurance of wedge voiding can be created in the microetch step that
follows deposition of a conductive material. Microetching is performed to
undercut the conductive material and improve dry film adhesion to the outer
layer.

The microetch, however, does not limit its' reaction to the surface copper.
Obviously, it also etches any copper that is present in the hole. Therefore, in
some direct plate systems, the process sequence is modified to perform
microetching prior to conditioning and thus eliminate the possibility of etching
off the tail of the nailhead subsequent to the conditioning and conductor
deposition steps. Otherwise, exposed glass that has not been conditioned will be
present and hence the chance for a wedge void. The other possibility is that the
copper supporting the conductive layer is removed which would also produce a
wedge void.

I assume your next question would be something to the effect of  "What about dry
film adhesion to the direct plate surface?" The answer is straightforward. If
you formulate the chemistry to not adhere to copper, very little of it will. Say
in the neighborhood of zero to several angstrom units, which can be easily
removed with mechanical scrubbing or other (non microetching) chemical methods.

It's difficult to describe the mechanisms of the process without slides, etc. I
hope this explains what I meant in my earlier message. If I can explain it any
better for you over the phone, please leave a message. I'll be on the road this
entire week, so it may take a while for me to get with you if you call. Thanks
for your interest!

Kevin H. Baranowski
Atotech USA
800 848 2826 X 4542