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

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

开云体育

开云体育

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

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

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

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 5/4/2022 11:58 UTC Morris Odell wrote:

The 6% will do just fine, BUT... since it appears that your solution may be too dilute already, maybe you need to stop adding peroxide - which further dilutes it - and instead add some copper wire to it and let it bubble, bubble, bubble, adding some HCl to provide the Cl needed to turn that copper into CuCl2. With a stronger solution, with some excess Cl in the form of HCl, you shouldn't need peroxide.

Thanks for the tip, I'll do just that!

Realizing it may take some time... please try to remember to let us know the result. It might help a few others who may have strength/peroxide/whatever issues.

I'll hunt down and repost my recipe for making Cupric Chloride solution involving copper wire (or other source of pure copper), hydrochloric acid, peroxide, bubbling with air and patience. If anyone tries it and leaves out the patience, they're on their own. ;-) I'd rather not have to try to figure out how to adjust the result if my recipe isn't followed.

Once made, peroxide won't be required to produce good results when etching PCBs.

JimH

> The 6% will do just fine, BUT... since it appears that your solution may be too dilute already, maybe you need to stop adding peroxide - which further dilutes it - and instead add some copper wire to it and let it bubble, bubble, bubble, adding
> some HCl to provide the Cl needed to turn that copper into CuCl2. With a stronger solution, with some excess Cl in the form of HCl, you shouldn't need peroxide.

Thanks for the tip, I'll do just that!

Morris

At 5/3/2022 06:23 UTC Morris Odell wrote:

I do regenerate the solution by bubbling air through it from an aquarium pump but when I'm etching a board the solution gets darker faster than it can regenerate so I give it a little dose of H2O2 which brightens it up instantly. The dark color is due to the Cu(1) reaction product. Once it goes dark I leave the bubbling going overnight and it's as good as new in the morning. Maybe my solution is too dilute but If I use a lot of it it's hard to see how the etch is progressing.

If the solution goes dark due to Cu(1) during etching you either have a solution that is too dilute or you're using an insufficient volume of solution. I'd guess too dilute.

I'm in Australia where "safety" restrictions on chemical sales are inconsistent to put it mildly. You can buy big containers of concentrated HCl from pool shops but at hardware outlets it's kept under lock and key - go figure. You can get all sorts of inflammable solvents, poisonous pesticides and other chemicals from them with no problems. However the laboratory supply stores that were a fun part of my youth have all disappeared.

And the lab supply stores whose customers are commercial labs are reluctant to sell anything remotely dangerous to a home user, or else their prices are too high.

Anyway I might pass on the 35% H2O2 just because it's quite a nasty substance it it encounters something that will decompose it. The potential silver chloride problem is something I didn't know about either and I wouldn't relish having to clean it up. I guess the small bottles of 6% will have to do for my hobby purposes.

The 6% will do just fine, BUT... since it appears that your solution may be too dilute already, maybe you need to stop adding peroxide - which further dilutes it - and instead add some copper wire to it and let it bubble, bubble, bubble, adding some HCl to provide the Cl needed to turn that copper into CuCl2. With a stronger solution, with some excess Cl in the form of HCl, you shouldn't need peroxide.

JimH

On 3/5/22 4:23 pm, Morris Odell wrote:

Thanks to everyone who replied!
I do regenerate the solution by bubbling air through it from an aquarium pump but when I'm etching a board the solution gets darker faster than it can regenerate so I give it a little dose of H2O2 which brightens it up instantly. The dark color is due to the Cu(1) reaction product. Once it goes dark I leave the bubbling going overnight and it's as good as new in the morning.? Maybe my solution is too dilute but If I use a lot of it it's hard to see how the etch is progressing.
I'm in Australia where "safety" restrictions on chemical sales are inconsistent to put it mildly. You can buy big containers of concentrated HCl from pool shops but at hardware outlets it's kept under lock and key - go figure. You can get all sorts of inflammable solvents, poisonous pesticides and other chemicals from them with no problems. However the laboratory supply stores that were a fun part of my youth have all disappeared.
Anyway I might pass on the 35% H2O2 just because it's quite a nasty substance it it encounters something that will decompose it. The potential silver chloride problem is something I didn't know about either and I wouldn't relish having to clean it up. I guess the small bottles of 6% will have to do for my hobby purposes.

If it's a bit viscous, dilution with 1:1 water will speed things up.

HCl already has water in it, so that helps too.

Because of the success of air-ation, i've still got a 20L bottle of FeCl i got 20 yrs ago (i'm in australia).

Thanks to everyone who replied!

I do regenerate the solution by bubbling air through it from an aquarium pump but when I'm etching a board the solution gets darker faster than it can regenerate so I give it a little dose of H2O2 which brightens it up instantly. The dark color is due to the Cu(1) reaction product. Once it goes dark I leave the bubbling going overnight and it's as good as new in the morning.? Maybe my solution is too dilute but If I use a lot of it it's hard to see how the etch is progressing.

I'm in Australia where "safety" restrictions on chemical sales are inconsistent to put it mildly. You can buy big containers of concentrated HCl from pool shops but at hardware outlets it's kept under lock and key - go figure. You can get all sorts of inflammable solvents, poisonous pesticides and other chemicals from them with no problems. However the laboratory supply stores that were a fun part of my youth have all disappeared.

Anyway I might pass on the 35% H2O2 just because it's quite a nasty substance it it encounters something that will decompose it. The potential silver chloride problem is something I didn't know about either and I wouldn't relish having to clean it up. I guess the small bottles of 6% will have to do for my hobby purposes.

Morris

At 5/1/2022 23:14 UTC Norm Stewart wrote:

Obviously, I've kept it too long. Now to dispose of it safely.

As I remember this stuff didn't have any silver in it.

So just dump it in the toilet and follow it with plenty of water. Keep it off metal fixtures if it has any HCl or other acid with it. Or dump it in a hole in the ground. It will kill or blister stuff in contact with the concentrated liquid so dump it in a hole and cover it so no pets (etc) can touch it... but it will break down quickly and leave nothing but water and oxygen. Your local laws may say something else, but mine (USA) would let me do what I just said.

JimH

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

On 1/5/22 9:30 pm, Morris Odell wrote:

Hi all,
I've been using the regenerated copper chloride method for etching PCBs for years and have had very good results. One problem I do have though is getting adequate supplies of hydrogen peroxide which I use to give the solution a boost while etching a board. The local pharmacies only sell it in 100 ml bottles of 6% and even then they keep it behind the counter and give you the third degree when you ask for it. I thought I could get larger volumes from a hairdressing supply place but it turned out to mixed into a gel.
However I was at the swimming pool shop yesterday and was surprised to find 1 litre bottles of "chlorine free pool sanitizer" that contains 35% H2O2 and 0.33 g/L of silver nitrate which is 1.9 millimoles/litre. My question is, can this be used instead of pure H2O2? Should I be concerned that the AgNO3 would interfere with the etch or have a detrimental effect on the stock CuCl2 solution that I have built up over the years especially as it would accumulate?
Any advice from someone who knows more chemistry than I can remember from half a century ago would be most welcome.

I just add some HCl every few months to the FeCl, which is by now more like CuCl after 10 yrs of use. The FeCl started as a dilution 1:1 with water.

It uses a fish tank air pump to bubble air for agitation and oxidation.

Keep the tank covered when not in use to prevent corrosion of nearby metals.

At 5/1/2022 18:45 UTC Norm Stewart wrote:

Another peroxide question: how long can unopened peroxide be stored? Does it deteriorate? Some time ago I got a quart of 35%, then got sidetracked. Is it still usable?

Obviously depends on how long "some time ago" has been.

I used to work in a lab and unopened 35% peroxide should be plenty strong even after a year... though I never bought more than a month's supply at a time... simply because I didn't want that much of it on hand. For commercial lab use, rules in the USA require it to be stored in a heavy cabinet intended for storage of oxidizers.

It's potentially really nasty stuff that has no place in home PCB etching... except by folks who know very little about it and think more is better. It really isn't.

JimH