Phil,

You response tells me I am more or less on track with the chemistry. It
amazes me the fact that free acid concentration can vary across such high
range. It wouldn't be surprising then to hear conflicting arguments on what
is the best level of acid to use in CuCl2 etching.

What I hope to achieve is a 5 gallon immersion etching tank, for occasional
etching of single sided prototype PCB's. What you describe about the slow
regeneration with air bubbles is spot on to my observations. Yes, the
regeneration rate via air bubbles alone is many times slower than the rate
of copper being dissolved. Fortunately the tank will have limited use and so
it may continue being regenerated for a long time (e.g several hours) after
the PCB has finished etching. I believe the volume of solution should be
sufficient to hold the limited amount of copper(I) produced during the
relativly short etching period.

To test when regeneration is complete, I take a few drops of etchant and add
to 5 ml of water, if a cloudy precipitate forms then it indicates a
significant amount of copper(I) is present and regeneration must continue. I
have tested this on small scale, and it seems to give a good indiation, the
time for regeneration can be up to 3 or 4 hours. I guess the industry have
much cleaver more automated methods of keeping the solution regenerated with
chemical oxidizers.

Adam

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