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containers I can use for developing and etching

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Thunderchild

New Member
what sort of containers can i use for developing boards with caustic soda and etching with the hydrogene peroxide + muriatic acide mix. I'm thinking of storing the liquids for reuse so something that will actually contian these chemicals is required. what about food storage containers ? I can get ones with proper lids that way for when not in use.
 

jpanhalt

Well-Known Member
Most Helpful Member
You have two different types of chemicals to consider.

Caustic soda: Almost any common food storage plastic is OK with caustic soda (alkali). At the concentrations being used, glass is also OK, but it does slowly etch. The greatest problem with glass is breakage.

Etchant: Hydrogen peroxide and HCl evolve gas. You should not store the mixture in a closed container. Many users do not store it at all, because the peroxide decomposes and the HCl is so inexpensive. As for stability of containers, many plastics, like polypropylene, polyethylene, etc. are stable. Those plastics are common for food storage too. Glass is stable. Do not use nylon (uncommon).

If you search on chemical compatibility of plastics, you will find an overwhelming amount of information. It is far easier to start with the plastic you want to use and then see if it is stable. Most plastic items are marked with a recycling symbol that tells you its composition (e.g., LPE, PE, PP). You will find the same symbols used in the chemical compatibility charts. If you plan on heating it, that is another factor to consider. Some plastics become pretty floppy at temperatures as low as 50 to 60°C.

An important point to remember about the peroxide etchant is that it is both a strong acid and an oxidant. Its copper content will have little effect on the plastic or glass container. Of course, anything you use for storing it should not be reused for food.

John
 

Thunderchild

New Member
thanks john, thing is I won't be doing quantity etching at least not for a while so throwing it away will make it exspensive. the other thing is as far as i know the etching solution is very dangerous and cannot be simply poured down the drain, my plan was to regenerate it by bubling air through it, at least for as ling as I can before its saturated with copper. I was also considering using "electroplating" to remove the coper from the tank and so keep it fresh, eventually the coper can be recycled.

So how do I dispose of the etching solution so easily (bearing in mind I'm in the UK)
 
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3v0

Coop Build Coordinator
Forum Supporter
If you are only going to do a little etching think about using Sodium Persulphate.

I mix up just enough to etch the PCB I am working on and then let the used up solution dry back to crystals. After a few years you can find some place to take the used crystals or find a way to extract the copper.

No liquid to store. When it is in the liquid state it is easier to handle.

3v0
 
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jpanhalt

Well-Known Member
Most Helpful Member
If you are not doing quantity etching, then throwing the etchant away may be the least expensive alternative.

The two etchants you mention are similar, but differ in significant quantitative aspects. Consider: 1) hydrogen peroxide/HCl; and 2) cupric chloride/HCl.

#1 uses hydrogen peroxide as the source of oxidant. True, it does produce CuCl2 in the end, but the concentrations of CuCl2 are a lot lower than one has when beginning with cupric chloride etchant. It releases gas (mainly oxygen), but you cannot regenerate the peroxide by bubbling air through it. Bubbling air will regenerate CuCl2 (if any CuCl is present), but because its concentration is so low early on, you will need to add hydrogen peroxide and possibly HCl to reuse it. In time and with use, #1 can be converted to #2, but you need to review the typical concentrations of CuCl2 that are used, and you will quickly see that you would have to etch a lot of boards to reach those concentrations. You also need a way to control the "free acid" concentration by adding HCl, as HCl is consumed in the process. Typically, that is done by a titration method.

In #2, the CuCl2 takes the place of peroxide to oxidize the copper on the PCB. #2 does not evolve gas, can be easily regenerated, and lasts a long time (forever). You still have to consider the free acid and CuCl2 concentrations. The latter is easily done with a float hydrometer to measure its specific gravity. If you want to consider that method, it is simpler and quicker to just buy copper oxide (CuO) and make up a solution using one of the available recipes. BTW, it is what I now use, and I would be happy to post my recipe, if you decide to go in that direction.

If you are doing a few boards occasionally, do not want to use ferric chloride, and want to use the peroxide method, then I suggest discarding the etchant between periods of use.

Does the UK restrict sale of CuO? That would be another consideration in your choice of method.

John
 

Thunderchild

New Member
hm yes John thats an interesting point i forgot, I will start with one chemical and produce another in the end which is long life. if option one has a lifespan issue can I get to stage 2 by just dumping some copper into the initial solution ?
 

jpanhalt

Well-Known Member
Most Helpful Member
<snip> can I get to stage 2 by just dumping some copper into the initial solution ?

Yes, of course, but you need to calculate the amount of copper, peroxide, and HCl needed. My CuCl2 etch bath is approximately 2.50 to 3.00 molar in copper. That's 175 gm of copper per liter of solution (2.75 M). It is going to take a while for that to react. So, it is far easier just to start with CuO, if you can get it.

John
 
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jpanhalt

Well-Known Member
Most Helpful Member
That is why my final recommendation above was to use the HCl/peroxide and to discard it, when it is not going to be used for long periods. It is extremely cheap. You could also consider using persulfate by just using sulfuric acid (battery acid) instead of HCl.

The "peracid" etchants are all quite similar. The active agent in sodium persulfate used by 3V0 is the persulfate. The sodium essentially has nothing to do with it, except make it into a dry salt that you can buy. There are differences in the way each behaves (HCl is volatile, H2SO4 is not), but I wouldn't worry about that.

You have made the big decision, which is not to use ferric chloride. Cupric chloride is like a transition between that and the easy home brew methods using peroxide.

John
 

Thunderchild

New Member
well I'm after the home brew methods that are cheaper and reusable with minimal waste which is what I thought the peroxide and acid becomes, I'm happy to stick with it once I've gotten started
 

3v0

Coop Build Coordinator
Forum Supporter
I think you fill find that if you only etch a few boards it is a false economy. $25 or $30 bucks will get you enough SP to etch for a around 2 years. If you can find someone who has it bulk you may be able to get it for much less.
 
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