Gerard:

Presume that you realize that there are three controllers on a Cupric etcher,
or should be, Baume', which controls water input, ORP, which controls the
oxidizer, usually Chlorate, or Peroxide, and Conductivity, which controls HCl.
And these three operate independently of each other.

This means that a given controller set could work smashingly on one control,
and poorly on another.   Further, given that many of the people putting
together controller sets do not make all the various different controls
themselves, and can change vendors on a given controller, you got a lot of
variables.

One vendor makes the most commonly used controller in the PCB industry, and
this controller is the only one that is different from the pack, as they use
colorimetry.  From what I have seen, this system is reasonably reliable, but
does not conrol as tightly, in widely varying process circumstances.

Good luck

Rudy Sedlak
RD Chemical Company

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