Hi Sarah,

I've used systems like the one you're setting up and have mixed feelings
about them.  On one hand they would appear to offer greater process control
and less variation in that they control the pH automatically, but I've found
that the systems are only as good as the maintenance you put in around them.
The systems are made up of a simple pH controller outputting signals to an
electric valve.  The valve gets clogged very easily rendering the system
worthless until it's recognized and fixed.  I'm sure you're aware of
ammoniacal etchant's propensity for clogging up vents and associated pipes
so you can imaging how quickly it goes to work on the automatic valves.  So,
when you install the system make sure to put very strict PM schedules in
place as well as routine process audits.  A separate pH meter reading is
still desireable to back up the automatic system.

With that said, you can buy the components for such a system from just about
anywhere.  One place would be Special Plastic Systems, Inc. (SPS).  They're
located in Alhambra, CA.  Phone number 800-423-4422.  I haven't done
business with them in quite some time but the parts involved in this set up
are pretty much off-the-shelf.  Just ask for an electric actuated valve (a
gate valve would be best as opposed to a ball valve if they make those) and
then get a pH controller with a suitable output (a Signet maybe or whatever
type you happen to like).

You may want to talk to your maintenance crew.  My guess is that they can
buy the parts from your local Grainger or McMaster supply house and set it
up pretty quickly.  I think the most important part is where you mount the
pH probe.  It has to have good solution flow around it.  I'm sure your
etcher already has one controlling the addition of fresh etchant so you
should utilize the same probe or set up another one in a similar manner.

Good luck.

Mark Mazzoli
Eng. Mgr.
Circuit Technologies, Inc.
3622 Clearview Pkwy.
Atlanta, GA 30340
770-458-1700
[log in to unmask]
----- Original Message -----
From: Sarah Boutwell <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 26, 1999 11:43 AM
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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