Hi Sarah:

Mark's right about clogging, valve maintenance and probe location, etc.
Also please be noticed that the pH meter is notorious for giving bad
measurement.  The general practice is to avoid using pH as control variable.
In my opinion, etchant density is the most important control variable for
ammoniacal copper etching.  This plus temperature control you have used up
your degrees of freedom for this system.

Control Cu++ concentration and always maintain good ventilation are ways to
better etch performance.  Chloride, pH are there for references.  If you
want to introduce extra ammonia and/or oxygen gas to your system, you have
to be very careful.  Bad design would upset your whole system.

By the way, I do custom design and implementation of various control
systems.

Yu-Shan Han, Ph.D., P.E.
Lead One Technology, Inc.
Seattle, WA
(206) 368 - 8429

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Sarah Boutwell
Sent: Thursday, August 26, 1999 8:44 AM
To: [log in to unmask]
Subject: [TN] etching pH controllers


Hello everybody
I would like to add a pH control system to my ammoniacal copper etcher that
would open and close a vent based on the pH of the bath.  Does anyone know
of a company that supply me with something like that?
Thanks


Sarah Boutwell
Manufacturing Engineer
Johnson Matthey Advanced Circuits
[log in to unmask]
612-684-5079

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