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.

Morris

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Morris,
I was curious why the stuff contained silver nitrate, looks like the sliver must form nano particles when used for disinfection purposes and the metallic silver likely reacts with the peroxide releasing its extra oxygen as part of its disinfection process.? There are numerous articles on Google.? Back to the question, the silver content is relative low so not likely to mess up the etching though I am not a chemist. ? ? Silver and for that matter most finely divided metals will cause the decomposition of hydrogen peroxide but so as long as the silver stays as a salt it's likely to be a non issue.?

I suspect that once you add the peroxide with silver nitrate? to your HCl the silver ions are going to react with the chloride and form an insoluble silver chloride precipitate that will settle out as sludge.
? ? ?

Have you been regenerating it by bubbling air through the solution? I've bee using it for years as well and have never found a need to add any hydrogen peroxide. I use a fish tank bubbler and bubble it for a couple of days or until it returns to a clear emerald green. Works as good as it did the day I originally made it.

You can also just bubble air through it. My understanding is that oxygen is the thing that hydrogen peroxide adds to the mix.

Have it far away from anything affected by the solution, though, as bubbling will atomize some of the mix.

--
Steven Greenfield AE7HD

At 5/1/2022 11:30 UTC 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.

If your solution needs a boost during etching, perhaps the volume of solution used is too small. Or perhaps I'm misunderstanding and all you're looking for is overall faster etching than you would get with a decently large volume that doesn't get appreciably weaker as etching progresses. If the latter, I'd tend to be more patient before resorting to a peroxide boost containing silver nitrate... which will react with the solution to give insoluble silver chloride which may be difficult to remove without boiling the solution for a while to clump the silver chloride, then filtering. It's not much silver, but it may look like a lot of precipitate if it remains suspended.

If you can buy 35% peroxide, you should also be able to get it without silver... tho maybe not in a pool store.

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.

If pharmacies keep it behind the counter, I'd guess you don't live in the USA. Here the typical peroxide that some use for wound cleaning (bad idea despite such use by many) is 3%. The 6% strength is better suited to bleaching hair... it's way too strong for application to skin and definitely to wounds... where it was never a very good idea anyhow.

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?

Silver will accumulate, but it will do so in the form of a precipitate that you will hope settles to the bottom of the container... but it might not... or at least slowly. Silver nitrate will react immediately with the chloride in the solution to form insoluble silver chloride, which I wouldn't want in my etch tank... just because it's going to be "messy" - at least for my definition of messy. It's will form a precipitate that probably won't settle readily unless the solution is boiled to "clump" the precipitate. If you can buy 35% peroxide, you should be able to also buy it without silver. Any pool stores selling the stuff you're describing are catering to folks who don't want chlorine in their pools and thus don't have problems with precipitation in their pools. Both peroxide and silver nitrate are powerful germicides. I'm wondering if this is used as the normal disinfectant, or as a shock treatment, but none of that is really important for your purposes.

Any advice from someone who knows more chemistry than I can remember from half a century ago would be most welcome.

I majored in chemistry the same half century ago that you mention... but having been retired a long time I've forgotten a lot of my more specific chemistry. From what I recall I'd tend to steer clear of silver in PCB etching solution... not because silver will plate onto the board as someone said... but because it will precipitate as silver chloride immediately - well before it has any real chance to plate out. And the precipitate has a pretty good chance of being annoying if it doesn't settle so you can get rid of it by decanting periodically. Boiling will make it settle far better, but that seems like a pain in the backside as well as likely to result in rapid loss of any remaining peroxide... with loss not being a big problem, but *rapid* loss could be if the solution suddenly foams up.

I've never had any problem etching using a proper strength well rejuvenated (by air bubbling) cupric chloride solution. Lots of air bubbling - even to great excess - also has the benefit of removing some of the water that gets added if you regularly add a bit of 3% peroxide... tho I've never thought that was necessary either. More than a touch of peroxide might even tend to cause some undercutting, which could matter if the traces are thin to begin with.

All in all I recommend at most very minimal added peroxide when etching and no added silver.

Good luck.

JimH

At 5/1/2022 13:13 UTC Nuno Yahoo wrote:

If you look for the reactivity series of metals, you'll find out that the silver in the silver nitrate will exchange places with the copper in the PCB.

The concept of the reactivity series isn't applicable because... long before the silver nitrate can contact the copper to plate out silver, the silver nitrate will react immediately with chloride in the etching solution to precipitate silver chloride. The solution will immediately turn cloudy and is likely to be slow to settle.

Since that silver will not be part of the PCB, but will be a fine elemental silver powder, will fall to the bottom along with the rest of the copper etched.

No... but if it could form fine elemental silver it would immediately, and very rapidly, catalyze the decomposition of the hydrogen peroxide in the solution. There would be a lot of foaming unless the amount of peroxide were very small.

If you're not after the silver, this isn't a concern. Actually speeds up the process.

Won't speed up anything because copper won't be removed by the silver in the first place. The silver nitrate will immediately react with chloride in the solution to form a precipitate of silver chloride, which won't react further because it's essentially insoluble.

The problem comes from the silver chloride that will form once the silver nitrate gets in contact with the chloride acid.
Silver chloride is a white solid substance that will create A BIG MESS everywhere. Sticks to everything and is a pain to clean.

Yes!... at least for some definition of a "BIG MESS." I'd guess big mess, but others might find it not so bad. Couldn't say until actually seeing it... but would rather not find out with my own solution. Even tho the silver concentration is low, for sure the precipitate will heavily cloud the solution. A little silver will look like quite a lot when precipitated as silver chloride.

Not sure if the amount mentioned is, or not, enough to be a problem. Maybe try first with a small sample?

For sure!

Seems to me that the AgNO3 concentration is really low. I would give it a try.

I wouldn't, but if tried the result at worse will just be annoying... requiring settling to remove the silver chloride... and perhaps boiling for some time to grow larger particles of precipitate that will settle faster. At best I can't imagine adding enough peroxide that I couldn't just avoid the precipitate by adding it in the form of 3% or 6% peroxide containing no silver.

JimH

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

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 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

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

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

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).

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

> 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 5/4/2022 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