Greg,

In the case of the microvia drilled in deposited dielectric (don't know about
copper clad laminations), the permanganate in the electroless plate line
clears the via.   Actually, we at MacDermid have seen very, very little
residue with our dielectric when lased with either ESI Nd:YAG lasers, or
Lumonics CO2 lasers.   We usually see clear vias when the laser changes the
brown/black copper oxide exposed when the laser cuts through the screen
printed dielectric.   Actually,. we have had to put together daisy chains of
2,000 - 10,000 microvias and measure the resistance across them as daisy chans
of 200 together (ITRI Test Vehicle) weren't quite reliable enough to insure
process control of cleared vias.

Believe me, we have seen enough post separation and pink ring (of course only
on competitor's processes!) to be aware of either laser residue, or acid
attacked black oxide.   Call or e-mail me off line to discuss - or a bunch of
us microvia gurus will be at the Kirk Miller booth at Nepcon East on Wed and
Thurs to discuss.

Perhaps the best final answer will be if we get AOI worked out to
differentiate bare copper in the vias from the surrounding dielectric - but
that is work for another day.

Thanks

Denny Fritz
MacDermid, Inc
Waterbury, CT
203-575-5740

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