Fun with Concentrated Hydrogen Peroxide and Pins

[Rag and Bone]

I had a surprising success with pins in HCl and concentrated 36% H2O2.

6oz. gold plated pins (low grade)
250ml HCl 31%
40ml H2O2 36%

Added HCl to pins in a beaker followed by H2O2. Immediate vigorous fizzing and bubbling. The fumes burnt my eyes despite the goggles. The pins where the H2O2 hit were stripped immediately. The solution turned dark within 30 seconds. The pins were stripped down to copper within a few minutes with just a few patches of gold remaining. I let the fumes die down and filtered out the gold. I was done in a half hour. The yield was pretty pathetic. I wasn't able to test the solution for dissolved gold (the stannous went bad).


In retrospect I used way too much H2O2. The concentrated stuff really packs a punch. I highly recommend it to the AP crowd.

Next time I'll try high grade pins with gradual additions of H2O2.

 

[geekzilla]

After watching Steves video on the AP process with gold fingers, I too began to wonder if a more concentrated HP solution would yield quicker results. Thanks for trying it out and posting your results.

Incidentally, I have found an online supplier for H202 that has flat rate shipping to anywhere in the US for $9.95 (they also sell HCl)! Here is the link:

http://www.pondepot.com/index.asp?PageAction=VIEWPROD&ProdID=3161

 

[Rag and Bone]

I just started using concentrated H2O2. The results have been very pleasing. I will never use the weak stuff again. Concentrated ends up being cheaper, less garbage (one jug rather than dozens of small ones), faster results, better penetration on persistent plating, smaller volumes of spent acid. I love it!

 

[Irons]

One has to be careful not to add too much Hydrogen Peroxide to HCl. When the solution starts boiling off Cl2 gas, it's time to back off. Chlorine is toxic and what boils off is wasted.

Once you see tiny bubbles rising to the surface, the H2O2 is doing its job, anything more is a waste of money.

 

[P_CARROLL]

Did any of the gold go into solution or was just the plating stripped off?

 

[Rag and Bone]

I suspect a good deal of it went into solution. The stannous went bad so I couldn't check. The gold that I did collect was extremely fine powder mixed with very fine red copper.I added the solution to some fingers in AP so it should come out in the wash. Like I said, I used way too much H2O2. It got me thinking though...

What if you mixed up some very strong AP and just flash stripped off the plating on pins, plated jewelry, cpus etc. ???

 

[lazersteve]

I have several gallons of 35% H2O2, but I still use the weaker 3% stuff in my AP. The main reason is for the extra water. The water allows the Copper II Chloride to become mobile in the solution and keeps the rejuvenation cycle going. The other main problem with the concentrated stuff is that you end up dissolving your gold along with the base metals due to the excessive amount of chlorine produced.

If you think about the etching reaction you will realize that the active ingredient is the copper II chloride, not the peroxide or the muriatic acid. With this in mind the water is necessary to allow the exchange of the copper metal ions in liquid form. If the solution becomes saturated due to lack of solvent (water), the copper won't convert to from the deactivated (and insoluble form) of copper I chloride back to the soluble desirable form (copper II chloride). If you find a lot of off white to gray colored sludge in your batches you are producing copper I chloride. It becomes discolored by the saturated etching solution which appear very dark brown in color and very thick.

Here's the overview of the chemistry:

Hydrogen Peroxide as a Replenisher

The Hydrogen Peroxide H202 system of replenishing has been unpopular in the PCB industry, for no outstanding reason, but not in the closely related Photo-Chemical Milling industry. Perhaps the real reason why it is not popular, is that a reliable control system, for both components required to replenish the system, Hydrogen Peroxide, and Hydrochloric Acid, has only recently become available. Previously, it was probable that those people who took on the challenge of devising their own control system would likely have chosen the least expensive, and easiest system to control replenishment system, which is the Chlorine system. The overall etch/replenishment reaction for Hydrogen Peroxide is:

H202 + Cu* + 2HCl -- CuCl2 + 2H20

The use of Hydrogen Peroxide also produces a purer Cupric Chloride, without Sodium Chloride (NaCl) impurities, but the Hydrochloric Acid level must be carefully monitored, as it is consumed in the regeneration part of the reaction. This replenishment method also suffers from the fact that over-replenishing with the Hydrogen Peroxide can generate free Chlorine gas.

The fact that the replenisher ingredients are supplied in water solutions, as well as the fact that the replenishment reaction produces water, limits the maximum Cupric Chloride content of the etch, but it is still possible to get to as high as 40* Be', depending on the concentration of the Peroxide and HCl replenishers.

..

Just like the Cupric Chloride etchant, the Copper that is already in solution in the etchant, dissolves the copper metal on the board.

Key things to remember to sort this explanation out:

1. The metal is dissolved by being "Oxidized", which means that it loses electrons, which changes it from the orange metal to a water-soluble blue compound.
2. The electrons are initially removed from the Copper on the panel by the copper that is already in solution. This seemingly unlikely idea can only happen because copper can exist in 3 forms:
1. Orange Metal - copper with a "correct amount of electrons"
2. Cupric salts, Cu++ (blue) -- copper missing two electrons. This is the blue, water-soluble form we are all familiar with.
3. Cuprous salts, Cu+ (white) -- copper missing one electron, or half way between form 1. and form 2. This form is usually insoluble, unless it is chelated, and is not often seen in a board shop in large amounts.

The actual etch reaction is:

Reaction 1.
Cu* reacts with Cu++ to give 2 Cu+

The cuprous salts are then (supposed to be) immediately oxidized (electrons removed) by the Oxygen in the air which is being pulled through the etcher. In the process, the spent Oxygen is converted to water. (See reaction 2.)

Reaction 2.
2 Cu+ + 0(air) + 2 H+ -- 2Cu++ + H20

I find the extra water is to an extent is helping, not harming. I think the optimal amount of water is just enough to hold the copper II chloride that you need to etch the proper amount of copper off of the scrap.


Steve

 

[Rag and Bone]

Wow. I completely misunderstood the AP process. I still don't fully understand it even after reading Lazersteves well written explanation (no surprise I failed Chem 101).

So, if copper II chloride is the active ingredient, will the AP process cease to work in the absence of copper?

 

[lazersteve]

Rag,

No. AP will still work on some base metals and even on gold due to the free chlorine that is formed when peroxide reacts with the muriatic.

Have you read the copper chloride document on my website?


Steve

 

[Art Corbit]

I guess I did something wrong. I put some pins and some chopped up board in HCL and Peroxide and got no reaction. No fizz only a small bubble now and then. However I was using the 3% peroxide you get at the drug store. I put about half as much Peroxide as I did HCL and still only a very light reaction. In the pins the acid is slowly turning yellow like the gold is dissolving. I didn't intend to do that. The acid on the boards is turning a light green.

Art

 

[Rag and Bone]

Art,
The reaction is slower with 3% H2O2. It can take days with fingers and longer with pins or cpus. Some pins don't dissolve very well in AP. It's good to do a small test batch to see if they will strip properly. To test, I put a couple pins in a petri dish with a small amount of AP.

What kind of boards are you working with?


I'm wary to give advice on the subject. Steve and others are more knowledgable. I have achieved good results with AP but I don't fully understand the chemistry behind it.

 

[Art Corbit]

The boards are out of phone systems. They are plated a lot heavier than the normal PC or card. I finally put everything in a crock pot and heated it up but now it looks like it is dissolving the gold and everything else. I wouldn't think HCL and Peroxid would dissolve Gold but maybe it will. I had to put about half as much Peroxid as I did the HCL to get any reaction at all. Then there was only a very few small bubbles. I have a lot of it to do so looks like I have got to make a trip to Tulsa to get some more Nitric. I sure thank you for your reply though.

Art

 

[Anonymous]

Art, I only add a little peroxide to get started then when the solution is dark green add some more it will turn to a emerald like much liter green right before your eyes and it will leave your gold alone if you do not add to much peroxide at a time.

 

[Art Corbit]

Mine wouldn't do anything untill I put a lot of peroxide in it. When I poured the HCL on it nothing at all happened. The caid stayed clear for several minutes and then you could see a real light color starting to apear. That was after I had alreadt added the Peroxide. I just went out and checked it and the gold is all gone but the copper is still there. I doubt if there is any way to drop the gold out of the HCL/Peroxide.

Art

 

[Anonymous]

Art,
I do not know how your gold could be insolution and the copper not, copper is used by some guys to precipated gold.

I have limited experience only a few months put I do the process with HCL and peroxide and never had my gold react and leave the copper.

If you do not throw anything away you have not lost any gold.

I am sure that someone with more knowledge will be alone to help you.

 

[Rag and Bone]

What color is the solution now?

 

[Art Corbit]

I still have the acid. If all else fails I guess I can pour it through some carbon. It really isn't enough to get upset about. I ran a small amount just to try the HCL/Peroxide method. I still don't understand why it wouldn't do much of anything untill I heated it. Then most of the copper still there and all the gold in solution really puzzled me. I'll try to find some way to get the gold out of solution. Needless to say I'm not very impressed with the HCL/Peroxide method.

Art

 

[Art Corbit]

The solution is green. The pins it was a yellow green.The boards was real dark green from the coating on the boards.

Art

 

[Rag and Bone]

I don't know what the problem was. If you are putting entire boards in the solution you can expect all sorts of complications.

 

[lazersteve]

Art,

You should keep your scrap types separated when processing with AP.

SMB will drop dissolved gold from AP.

Start with small batches and learn the process. I use it all the time and have excellent results with no heat.


Do you have some photos of the mix?

Steve