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May 2003

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 19 May 2003 10:13:57 -0700
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Ed: We have always used anhydrous ammonia, liquid ammonia resulted in sludge
out problems. It is introduced to the bottom of the etch sump thru a
multi-leg gas sparge and controlled with a pH probe. A sp.gr.controller is
used to add the replenisher.
The key was making sure things stayed clean and not plugged or crusted over.

You can reduce the ammonia losses when not operating by closing down the
vents.

I would recommend you talk with your ethcant supplier's technical
engineering folks. They should be able to supply you with additional
information on design and equipment.

                                                                Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076
-----Original Message-----
From: May William D (Dean) CNIN [mailto:[log in to unmask]]
Sent: Monday, May 19, 2003 7:56 AM
To: [log in to unmask]
Subject: [TN] Controlling pH of ammonia etcher


Due to the start/stop nature of our pcb shop I am looking to control the pH
of an ammoniacal copper etcher using aqueous ammonia.  After the etcher has
not been used for a couple of days to a week the pH has dropped somewhat.

I would use a metering pump to add the ammonia to the sump of the etcher.
Are there any concerns I should be aware of before setting the aqua ammonia
up?  What grade of ammonia must I use so that I don't contaminate the
etchant?  Can you add ammonia too fast to cause a problem?  Can you add too
much over time?

Are there other ways to accomplish the goal?  Is there a proper way to
introduce anhydrous ammonia so that the solution can properly metabolize the
anhydrous into the solution?  It seems to me that contact time with the
anhydrous would need to be considered for it to do any good?

Thanks for your consideration!

Edward A. McAtee
Crane Division, Naval Surface Warfare Center (NSWC Crane)
Harnessing the Power of Technology for the Warfighter
Code 6086, Bldg. 38
300 Highway 361
Crane, IN 47522-5001
Ph:  812.854.3892
Fax:  812.854.1174
Email:  [log in to unmask]

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