Thanks Jim,

I added about 3 cm of thick fine-stranded copper wire to my 700 ml of solution and left it overnight with the air pump going. The next morning all the copper had dissolved but the solution was quite dark, indicating that the copper (1) had not been oxidized to copper (2). I added 10 ml of concentrated (pool chemical) HCl and there was some improvement after another night. I added another 10 ml of HCl and now it looks terrific. I tested a tiny sample with a few drops of 6% H2O2 and there was no change, which I think means that oxidation using bubbled air was complete. I'm going to try etching a small piece of board to see whether it? can stay oxidized but I won't have time to do that for another couple of days due to other commitments. It does seem that the fix was to make sure there was enough HCl present. I don't have a pH meter but I imagine that one would be quite useful.

Watch this space!

Morris

At 5/6/2022 04:43 UTC Morris Odell wrote:

Thanks Jim,

I added about 3 cm of thick fine-stranded copper wire to my 700 ml of solution and left it overnight with the air pump going. The next morning all the copper had dissolved but the solution was quite dark, indicating that the copper (1) had not been oxidized to copper (2).

To me this means you had some available Cu(2) to dissolve the copper wire, but not enough free HCl to allow 2 Cl ions for each Cu, therefore much of the dissolved copper was in the form of Cu(1)... dark brownish and insoluble.

When it comes to the concentration of copper in the solution, my recipe for making an initial solution calls for about 200 grams (7 ounces) of copper to make a liter of solution. That's about 14 feet of #10 copper wire... 22 feet of #12... 36 feet of #14... 56 feet of #16. That's the generally recommended concentration of copper in the working solution. The 3 cm was a really good test of the problem... no free HCl. Now you need gauge whether you have enough copper. You'll have to do that based on your memory of how much was used to make the solution in the first place.

I added 10 ml of concentrated (pool chemical) HCl and there was some improvement after another night. I added another 10 ml of HCl and now it looks terrific.

Exactly what you needed. Good job!

I tested a tiny sample with a few drops of 6% H2O2 and there was no change, which I think means that oxidation using bubbled air was complete.

Yes. But 10 ml (a bit over 1/3 oz) is a pretty small amount of HCl depending on the total volume of solution... and some of that already went to form CuCl2 so you still don't have much excess... meaning that after not too many etches you might quickly get back to a muddy brown solution you can't rejuvenate just by bubbling. I like to have about a liter (bit over a quart) of solution - although I don't use all of it when etching - and if my solution were acting like you describe I'd add at least one, maybe two, ounces of 37% HCl. That's for a liter of solution. More or less depending on how much solution you have. It shouldn't make for enough excess HCl that you have to worry about fumes.

I'm going to try etching a small piece of board to see whether it can stay oxidized but I won't have time to do that for another couple of days due to other commitments. It does seem that the fix was to make sure there was enough HCl present. I don't have a pH meter but I imagine that one would be quite useful.

The slight excess of HCl was the key in your case.

You don't need a pH meter. Just take a bit of dry baking soda... Arm & Hammer Bicarbonate of Soda is one brand... and add a few drops of solution to it. If it bubbles fairly vigorously you have excess acid (HCl). And if it doesn't have a strong smell you don't have too much HCl.

Yes... please let us know how a trial etch turns out.

JimH

JimH

I'm a lurker and don't post much.? But I'd love to see a write up on how you make your Cupric Chloride solution.? This has been an interesting thread.

Dave

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One of the basics is to use pool acid (hydrochloric/muriatic) and Hydrogen peroxide (drug store variety).

Mix one part of HCL to 6 (IIRC) parts of Hydrogen peroxide.

That etches well until the excess oxygen is used up, perhaps a month of just sitting around.

From there on, you need to bubble air through the mixture when etching.? Etching for me went from about 7 to 10 minutes with fresh peroxide, to about 20 to 30.? Others will be able to take this further.

Harvey

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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.

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.

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

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