Hi Jeffrey but the bussines of heavy copper is definatly not lab stuff at
present there are 9-10 shops world wide doing about 22-30 million in heavy
copper and many more just starting, the etch factor in this type of design
with the very thin base copper is  nothing,  as your only etching off the
1/8 -1/4 oz base copper the etcher is set at high speed and run
through.therefore the line resolution is a factor of dry film resolution and
plating factors. But the accuracy of 16 mils of dry film would blow your
socks off. And  it is correct the holes need to be drilled bigger to allow
for the extra plating, The 3 oz of plating in the hole is very strong and
the board can withstnd 10-20 solder cycles and many thermal cycles. Typicaly
3 oz is not considerd heavy copper it starts at 5-6 oz and goes to typicaly
15-20 oz . stripping is not to bad with a pre dip in KOH. start to think way
more outside the box , heavy copper rules.
robert Tarzwell

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