William,
the best way to ensure a stable process would be by avoiding the pH to drop. Consider keeping the machine as tight as possible with as little exhaustion as possible during the periods where it is not used or pump it out of the machine and into a sealed container. We have good experience with this way to maintain the pH during the weekends and holidays. 

I have tried adding 25% ammonia solution, but the effect on the pH was somewhat very limited. I have used approx. 0,5 - 1,0 v/v% - be cautious as to much water can lead to the formation of sludge. 
If you want to increase the pH on a regularly basis consider using gas. However I have no experience with this, but I believe there will be some severe restriction to avoid accidents with leakage. Consult your equipment manufacturer.

Good luck

 

 -----Oprindelig meddelelse-----
Fra:    May William D (Dean) CNIN [mailto:[log in to unmask]] 
Sendt:  19. maj 2003 16:56
Emne:   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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