Etching boards

[sgtrutters]

Hey,
I was just wondering what everyone's preferred method for etching is.  I've tried a few different ones and had mixed results.  Which chemical do you use, do you heat it or use it at room temperature, just heat it at the start or continually? Just trying to get some tips on what has worked for others for me to try.

[madbean]

1:1 hydrogen peroxide and Muriatic acid is what I use. And, you only need a little to do the job. Takes about 5 minutes of agitation to etch 1oz copper and does not require heat. But, you must use gloves, eye protection and a mask...the stuff smells pretty bad and it will irritate skin if it gets on you.

Also, you need to consider disposal. This etchant will go dark green as it gets loaded with copper. You can re-charge it by adding more peroxide and it will continue to etch although it will get weaker as you add more peroxide. Anyway, you cannot just pour the remains down the sink because it will destroy your pipes. Since I generally only use 2-3oz on the rare times I etch these days I usually dilute it with 10oz water in a water bottle and toss it. Anything more than that and you really need to take it to a chemical waste recycling center or neutralize it before disposal. I think you can neutralize with baking soda but I'm not sure. I actually really need to figure that out because I've had a 5 gallon tub of old etchant sitting in my garage for the last 8 years!

[sgtrutters]

Thanks madbean.  I have tried it but had mixed results and the gas it gives off was almost too much, even with a fan blowing it straight outside.     Also I don't think I ever mixed it 1:1 so maybe that's why I didn't get as good results.

[m-Kresol]

Please do not use this mixture. Sorry to contradict the Bean here, but this is my professional opinion. Depending on how you do it/where you get it, this can go sour quickly.

Muriatic acid (ie. dilute hydrochloric acid) and hydrogen peroxide will give chlorine gas and water (2 HCl + H2O2 --> Cl2 + 2 H2O). Chlorine gas is toxic and very reactive and should be handled only with proper ventilation equipment, which you won't find outside a lab. The amount obviously depends on the concentration of acid and peroxide and is possible that Brian used them more dilute than you did.

I recommend iron chloride solution (FeCl3) which you can get at various places. It's still corrosive and you need old clothes as it stains, but it's comparably harmless. It's les reactive, so it will take 15-25 min depending on your design etc, but IMHO this is the way to go. Safety first! (properly label everything and keep out of reach of kids. Obvious, but I had to say it, just because it's the right thing to do for me)

[madbean]

Well I certainly won't argue against safety and Felix makes an excellent point that there are less toxic ways to etch. And, those should be looked into with considerations about ventilation, disposal, etc. I'm just describing the process I ended up with because there was a time where I needed to etch HUGE numbers of boards in a very cost-effective way.

I will say, spot on about the odor/fumes produced by HP and Muriatic acid. It is very, very intense and you need ventilation, a mask, and positive air-flow to minimize your exposure. These days, I've been working off the same gallon of acid for almost 8 years (that's how infrequently I do it now) and it is substantially weakened. It still etches but there are very few offensive fumes from it. There is a "safer", less potent form of Muriatic acid you can buy and I've used it, too. I think it's more like 25-50% strength.

Point being, FeCl3 is a very good alternative to peruse. When I used that, I actually would use an old pot, heat up some water, then put the FeCl container in it for a few minutes to warm up. Then when agitating I hit it with a heat gun on low. It does speed up the etching a bit.

Towards the end of my etching days I also used a laminator to do transfers onto PNP blue. It still required an iron for some final adhesion but it did make doing full sheets a lot easier. These days I only do an occasional faceplate and a simple iron is enough to do the job.

[Bio77]

Hi Felix, fellow lab guy here.  I was wondering about Bean's 5 gallon problem from above.  In the US, copper sulfate is sold as a biocide for tree roots in sewer lines.  People put a pound or so down the toilet.  Would there be any difference if the 5 gallons of used etchant was diluted and treated similarly?

[m-Kresol]

I was wondering about Bean's 5 gallon problem from above.  In the US, copper sulfate is sold as a biocide for tree roots in sewer lines.  People put a pound or so down the toilet.  Would there be any difference if the 5 gallons of used etchant was diluted and treated similarly?

the procedure Brian described will give you CuCl2 in hydrochloric acid solution. CuCl2 is also rated as toxic to the environment similar to CuSO4, so I wouldn't just dump it anyways. But I just add my little bits of leftovers to our waste at work, so that's an advantage for me that you likely don't have.
I think Brian was more concerned about the acidity of the residual solution. Even when less reactive/dilute, the pH will be quite low (I'd guess around 1-2), which is corrosive for sure. In Austria, all new buildings use plastic pipes, I think, so there's no hazard for the pipes, but it's still not the right way to just dump chemical waste down the drain. If you only have a little bit from etching 1 pcb, it might be ok to dilute and dump, but if you plan on etching more than I'd just get a container, collect it and dispose accordingly every now and then.

There is a "safer", less potent form of Muriatic acid you can buy and I've used it, too. I think it's more like 25-50% strength.

concentrated HCl is 37 w% or 12 mol/L, so it should be lower.

I think you can neutralize with baking soda but I'm not sure. I actually really need to figure that out because I've had a 5 gallon tub of old etchant sitting in my garage for the last 8 years!

You can neutralize it with baking soda (NaHCO3), but it will take a lot of it and it will take time. Assuming you have full 5 gallons, it will take approx. 2 kg of soda (assuming 5% HCl concentration). The neutralization will give you carbonic acid (H2CO3) which is not stable and will decompose to CO2 and water. long story short, it will foam a lot and get warm too, so you can only add a portion at a time...

[alanp]

All of this is why I just get boards fabbed Much less hassle, and the fab house has to deal with all that chemical disposal, and not you.

Plus you can have a silkscreen then!

[rockola]

You can neutralize it with baking soda (NaHCO3), but it will take a lot of it and it will take time.

That reminds me: A friend of mine used to work for the Arm & Hammer company. His job involved coming up with new uses for baking soda, one of their major products. He was therefore in charge of ploughing through all the tips and tricks that innovative customers would mail in. He said that the most memorable one was when someone had sent in a letter saying that they'd used baking soda to embalm their cat. We now return to our regularly scheduled programming...

[sgtrutters]

Thanks for the tips everyone.  I have ended up finding some ferric chloride to try and hopefully get good results with. I have also though about getting them dabbed somewhere but I think it's better for me cost wise to etch them, at least for now.

[sarde]

You can neutralize it with baking soda (NaHCO3), but it will take a lot of it and it will take time.

That reminds me: A friend of mine used to work for the Arm & Hammer company. His job involved coming up with new uses for baking soda, one of their major products. He was therefore in charge of ploughing through all the tips and tricks that innovative customers would mail in. He said that the most memorable one was when someone had sent in a letter saying that they'd used baking soda to embalm their cat. We now return to our regularly scheduled programming...

My Daughter and I mummified a chicken for a science/history lesson when she was studying Egyptology. Lots of salt and baking soda!!! It's currently wrapped in bandages and kicking around the garage until such a time as I make a sarcophagus for the bird.