At 5/11/2022 08:52 UTC Morris Odell wrote:
l finally got to etch a board in the more concentrated solution and it works very well. Etching was noticeably faster. the solution started off a lovely emerald green and did get darker as the copper dissolved and the amount of Cu(1) in the solution increased. I wasn't using a very large volume of solution so I had to add some more to keep it going but if finished up very well. I've got it all back in the bottle now with the bubbler going and I expect it to all return to the nice green color.
Excellent! I'm guessing one of two things cause the need to add more solution... either the solution is a bit weak in copper, which would be cured by adding some more copper wire and bubbling... which may also need a bit more HCl. **OR** maybe the volume of the etching tank is a bit small. Either way it works well without any hint that you didn't feel good about it and that's what counts. Good to hear.
When it comes to a possible need for a bit more HCl, maybe test the acidity of the spent etchant in the tank by adding a few drops of it to a bit of dry baking soda (sodium bicarbonate). If it doesn't bubble you need a bit more HCl in the solution before etching next time.
Either way it's working and adding a bit more solution part way thru wasn't a problem.
My interpretation of how this all works is as follows:
The etching process coverts both the green Cu(2) and the solid elemental Cu into black Cu(1) which is then oxidised later back to Cu(2) but at a slower rate than the etch. This means that it's important to start off with enough Cu(2) in the solution to deal with all the copper you need to remove. The solution becomes progressively darker as the etch progresses and this might cause the etch to slow down as the amount of Cu(2) falls unless there is an excess present to begin with. I imagine that commercial operations use high volumes of solution and circulate it between the etch tank and a bubbling tank. Converting the black Cu(1) to green Cu(2) uses oxygen either from the air or from H2O2 and that will gradually make the solution more alkaline so small amounts of HCl need to added to counteract that and provide more Cl- ions to match the Cu dissolved into the solution from the PCB.
Exactly!
I'm retired now but I used to work at a place where there was a chemical lab that employed some every highly educated people with doctorates and years of experience. However the lab was there for other reasons and dealt with entirely different processes and functions than this. Nobody could help with an understanding of CuCl2 etching or even swimming pool chemistry until I found discussions here!
Morris
Ain't the Internet great?!!! Just take some of it with a grain of salt, aka NaCl. ;-)
JimH
