I would give some thought to both the final thickness of the copper lines and
the effect on the exposed base laminate.  Most folks are still using 1.4 mils
as their nominal thickness of 1 oz copper for impedance calculations, etc.
The reality is that today's foil is at least 10% thinner than that supplied by
the foil mfgrs, and maybe that doesn't get shops in trouble under normal
cleaning/microetch procedures, but eventually a few extra millionth's is gonna
be cause for some out-of-spec impedance.  (note:  fortunately, 1/2 oz foil is
usually delivered pretty close to 18 microns thickness, as people expect it to
be)

As far as the base laminate, my concern is the rinsing/contamination factor.
More process cycles to worry about leaving residue of some of the salts or
etchants after rinsing, which can be a cause of poor lamination or subsequent
failure in reflow/soldering/etc.

jimpaulus

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