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Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373
Proud Mary wrote ...
Yes, how stable is 'unstable?"
Sodium hydroxide will do wonders to the stability and create a hot, foamy soup of sodium sulfate and turn the dilute copper into a muddy copper hydroxide precipitate Highly recommended chemical reaction!
Apart from those "I wonder what happens if..." experiments, my experience is that the etching solution can be used for over a year when stored cool. Just don't forget to leave the container a little air gap or ther container will morph into a sphere while you're not looking. The dissolved copper sulfate does not seem to cause a dramatic catalytic effect, It would be interesting to have someone report the behaviour of a long-term stored but unused sodium persulfate solution.
Registered Member #3040
Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237
I know this threads a bit old but I think this info may be useful. I etch a fair number of boards and use Sodium persulfate etchant. I only make up a new batch about every 6 months or if the etching starts to get noticeably slow. In between uses I simply wrap the tank in cling-film to prevent evaporation while not being airtight enough to cause an "Overpressure issue" :-
That TQFP board was made with etchant several months old.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
just a thought, but has anyone here attempted an "inverted etch" process? the idea is to take your blank board with inverted (B/W) image and expose to UV light as normal then develop. The additional step is to dip the board in copper sulphate with a corner connected via polymorph-encased wire blob, and deposit the required thickness of copper. Then take the board and expose again to UV light and redevelop to remove all the remaining resist. Etch as normal, once all the copper has gone from the flat regions the board is done and should be rinsed and dried.
such a board could be very useful for high current applications and should be amenable to tinning with the tin solution to prevent corrosion..
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Sodium persulfate Etching
Highly recommended chemical reaction!
