Etching of thick copper is difficult because conveyor speeds are so slow that
normal variation in the speed cause huge differences in the time in the
etchant. One way around this is to run the parts 2 or 3 times through the
etcher, with each pass being run where normal parts are run.  This controls the
amount taken off and provides relatively consistant line widths.  We
successfully etch 7 ounce copper layers with a 2 step process, we additionally
flip the layers top to bottom before the second etch to average out the top to
bottom differences.

Our etching is in a cupric (acid) etcher which does not degrade the
photoresist. When we try running photoresist in our alkaline (ammonium sulfate)
etcher we get only a single pass since the resist begins peeling up in the post
etch rinses.

Respectfully,  Rick Haynes


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Original text

From: sam mccorkel <[log in to unmask]>, on 2/27/97 2:42 PM:
I have 2 issues that I'd like to get some advise on.
1) Does anybody have advise on etching 4 oz copper? The traces are .024" and
we etch with ammoniacal etchant.
2) Is there any advise on laminating a 3 layer board with 4 oz base copper
on all layers? .062" finish thickness and the layup is at our discretion.

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