At 5/1/2022 23:17 UTC Mike wrote:
I have never used the pool solution but it is good to know where to look for large volumes at less than sky high prices.
A quick google indicates that adding a little NCl table salt, to the mixture should cause the AgNO3
AgNO3 into AgCl and NaNO3. The AgCl precipitates out, but the ClNO3 is very soluble and therefore hard to get rid of. I couldn't find any information on how it might effect of the sodium nitrate on the etching process and the stuff is soluble in water you would probably have less trouble trying to remove the copper than the sodium.
If you really must use 35% peroxide - it's really dangerous stuff in inexperienced hands - you can just add a little of the copper chloride etching solution to the SMALL PORTION of peroxide plus silver that you intend to use and the silver will precipitate due to the chloride in the etching solution. Let it settle a bit, add a drop more etching solution, and if the drop doesn't cause more precipitate, then all the silver is precipitated. You'll still have some nitrate (not likely a problem at such low concentration), but no sodium (also not likely a problem). I would NEVER add anything to the main large volume of peroxide - NEVER. If it decides to react for some reason, the reaction could have pretty serious consequences. If I had a choice of pouring concentrated (37%) hydrochloric acid or concentrated (35%) peroxide over my hand and waiting say 15 seconds to wash it off, I'll take hydrochloric acid any day of the week. The hydrochloric acid will itch and the hand may be a bit irritated, but 35% peroxide will cause blisters that will almost surely REQUIRE medical treatment.
However... all that said, I don't recommend 35% peroxide. It's totally unnecessary.
The far and away best solution is to not buy the strong peroxide in the first place since the reason for peroxide in the first place is largely unnecessary once the initial etching solution has been made... and even when making the initial solution you don't need 35%. You just need a slight excess of chloride ions so that the CuCl formed when the circuit board is etched is kept in solution vs forming a brownish sludge. The excess chloride also allows for regeneration of the spent CuCl back to CuCl2 by bubbling air thru the solution after etching is completed. Bubbling air does the same thing as peroxide does, only slower... and it doesn't dilute the solution like peroxide does... and it's far safer than handling 35% peroxide. If you must do peroxide to rejuvenate, 3% or maybe 6% if you can find it at a decent price, is all you need.
Peroxide speeds up the etching process... at the risk of slight undercutting that could be a real problem if the traces are quite thin. Shouldn't be a problem with wide traces if the masking is good. But all in all, the amount of speeding up with moderate amounts of peroxide can be achieved easily by adding a bit of 3% drugstore peroxide. In the end the greatest effect of added peroxide - in moderate amounts - is a slight reduction in the amount of impatience. You can load the solution up with 35% and things will happen very quickly assuming an excess of chloride - that excess chloride being far more important - but WHY? For my taste, all you do is dilute the solution for next time if you add a lot of peroxide. I have weeks or even months until I need to etch again so a little aquarium pump gets the job of rejuvenating done 50 times over. And if you don't go crazy with excess HCl, there are no noticeable fumes from the rejuvenating/bubbling process, assuming a half full container and a small opening. All this talk about needing 35% H2O2 and dangerous fumes when bubbling is stuff people who know no better are causing for themselves unnecessarily.
JimH
