Stop using Ferric Chloride etchant! (A better etching solution.)

Ferric chloride is a traditional home-use circuit board etchant. It's easy enough to come by, and the Ferric by itself is no big environmental problem. However, once you've etched a board with it, you're left with a solution with a bunch of copper chloride in it. This dissolved copper is an environmental problem, and you can't just pour it down the drain (legally) -- you're supposed to take it to a hazardous waste facility. (For instance: How to Dispose of Ferric Chloride in this FAQ. )

Wouldn't it be nice if there were an etchant that you could re-use indefinitely so that you don't have to worry about disposing of the copper, and that could be made in lifetime supply for like $10.00 with ingredients bought at hardware and drugstores? (And it's prettier too.)

I got seven words for you: Copper Chloride in Aqueous Hydrochloric Acid Solution! (Exclamation point!)

But how're you going to get CCiAHAS? Conveniently enough, by starting out with a simple two-ingredient starter etchant, and doing a bunch of etching.

Step 1: Ingredients: The Starter Etchant

Picture of Ingredients: The Starter Etchant

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For the starter etchant itself, you only need two ingredients: hydrochloric acid and hydrogen peroxide.

(OK, actually three. But the third one's copper. See the chemistry section for an explanation.)

Hydrochloric (muriatic acid, "pool acid", etc.) is available at a hardware store. The acid I got is 31.45% (or 10M) and should run around $5 per gallon. Which is more than you'll ever, ever need.

The peroxide is normal 3% for mouthwash or cleaning cuts, and can be bought at a drug store for $2-3 for a big bottle.

You'll also need a non-metallic container that fits your PCB and two standardized measuring cups.

As long as you're in the hardware store, pick up some acetone if you don't already have some. It's useful for removing the etch resist. (That's for another instructable.)

I can't really get 30% hydrochloric acid, but can you use 10%, and then just make a 1:1 mixture, or something like that? My hydrogen peroxide is 3 %.

Thank you very much Elliot for this Instructable. I was able to get my solution (2 parts hydrogen peroxide 3% and 1 part Hydrochloric Acic 38%) and mixed in a very short time and began etching. My PCB turned out a dream in only a few minutes. I used a pyrex glass 1 litre jug as the mixing bowl with that sitting in a bowl of water to help cool the solution if things got too hot. No fuming at all, stripped the 4" x 3" pcb leaving just the circuit behind in just a few minutes. A couple of questions though as I am not that strong on my chemistry. 1st. The peroxide I used is from the supermarket medicine section and the solution turned brown when I added the acid. I am guessing there might be some kind of dye in the peroxide solution? 2nd question, in the prepratation for this I found some 12% hydrogen peroxide at the 'beauty section' and as it was a lot cheaper per volume than the 3% from the medical section I brought a bottle of that. It is a 'creme developer' and contains other chemicals. specifically CETEARYL ALCOHOL, SODIUM LAUREL SULPHATE, PHOSPHORIC ACID, ETHANOL, METHYLPARABEN I am worried about mixing this (diluted with water down to 3% peroxide) with acid. Has anyone else tried this sort of solution before? I could not find any straight hydrogen peroxide at 12% that was liquid like the 3% stuff from the medical section. Price difference is 4 bucks for 200ml at 3% vs 10 bucks for 1 litre 12%

I did this, and the results were amazing! Etched a test pattern in 2 minutes. The only difference was that I used 9% Hydrogen peroxide. The starter solution etches very fast and heats up a little bit, so I had to put the container with HCL+H2O2 into another container with cold water just to keep things cool :D P.S. The distance between the black marks in the second pic is 1 mm.

I will second the "things getting hot" comment.From my initial research, I was being cautious so I put my plastic mixing jug inside a larger heavy-duty plastic detergent bucket (picture 1). I also had a water hose, some extra containers, and other stuff on hand.I though I was going slow on the initial mixing, but there was still enough heat in the solution to start melting the inner jug. Visually, it looked like the bucket was collapsing sideways, melting, and shrinking. I immediately added a lot of cold water from the hose into the larger bucket, which stopped the melting process. Luckily, the inner jug retained the solution with no leaks. The second picture is the now cool but damaged jug.After the solution was cooled to ambient temps (around 70F on that day) I transferred the solution to a larger spare jug, then continued to combine the remaining 31% HCL, 12M (40% ?) H2O2, and copper wire. While the water in the large bucket looks blue (picture 3), it is because the blue solution in the new jug was making the clear water appear to be blue colored as well.Picture 4 is the final green solution after dissolving some of the copper wire, and another view of the melted jug. Notice the condensation on the inside of the large jug, which is the fumes from the solution condensing on the air cooled plastic wall.Picture 5 is the aquarium air hose used to bubble air through the darker green solution. Normally this was sitting in the heavy bucket seen in the rear, but I pulled the mixture out to take this picture.Picture 6 is the now emerald green solution after adding Oxygen from the air bubble hose. You can see more copper wire sitting in the solution, as I was continuing to test to color changes compared to the copper etching speed.Picture 7 is test of preparing a single sided PCB for etching. I had painted the entire PCB, and then used a laser to burn off the paint wherever the copper is to be removed. The paper shows the Gerber copper pattern, while the laser is still in the process of burning off the paint. I had to jump through hoops the generate a negative of the Gerber output for the Laser, as the black lines on the paper represents where the mask paint is to remain on the PCB. Note the left 75% represents one circuit, and the right 25% is another circuit, allowing the board to be split apart if desired (only one set of power and ground traces cross over the vertical "cutting line").Picture 8 is the first test of etching a board. The size of the etching tank didn't allow the entire board to fit, so the small circuit side was cut off before etching began. The three large holes used to attach the board to a plastic "stirring stick" using a zip tie. That allowed for manual agitation without having to reach directly into the heated solution. This board was left in the solution too long, so there is significant undercutting of the pattern. As a first test, I noted a number of process improvement to make (temperature control, move even agitation, improvements with work space lighting, etc.). However, there was enough copper left to make the board work by adding a few wire jumpers and bending some leads over missing pads so they connected with traces before soldering. The full design was double sided, but the missing top copper was only for jumpers, so wires were used to replace the missing top copper. This hand-etched PCB worked well enough to fix a some minor trace errors (flipped DB9 pin connections; incorrect pinouts in the CAD parts library) and prove the overall circuit worked before sending it out to a professional PCB fabrication house.Picture 9 is the first validation test of the professional board. The fixes based on the hand etched board resulted in this final PCB working correctly the first time.Picture 10 is a general setup shot prior to mixing the etchant solution. I using the 40% H2O2 solution, so the 2% solution went unused. I blocked out the one bottle since it would have been dangerous to add to the other chemicals, since it was used to clean the PCB copper prior to masking and etching.

Best to do your mixing in a glass/pyrex container, and then transfer it to the plastic storage after it has cooled. The last time I made enchant, I did it outdoors in the middle of an adjacent field, in glass, and with a face mask because you don't want to be breathing that hydrogen, and the chance of an errant spark/flame is less likely. When you're done making it, you can slowly funnel it into a plastic jug inside of a bucket (in case it tips over while you pour it). This stuff will make any metal in the room rust quickly if left open, or is stored in an improper container. I have my last batch stored in a yard/pool container with a flip top lid, along with the leftover acid I used to make it. One day I tossed a few scraps of stainless steel in the box for some reason or another. When I came back several months later, most of the stainless steel is rusted on the surface. There isn't much plating left. Before I started storing the acids outside in their own container, the vented caps would allow the acid into the air, and my tools were rusting like crazy from the open air.

You might try as Darrell_H suggested, putting the container in a bath. You might also want to make that bath a very icy one and give the etchant solution time to cool down to the temperature of the bath before putting the board in. In some cases this can slow chemical reactions and if nothing else it will help dissipate the heat faster.

wow. Neat

Will this work to etch aluminium? would i have to put some copper in it first?

I have used it to etch aluminum... It causes a thermal reaction and gets pretty warm and bubbly, and etched quickly. It was already used etchant. I'd do it outside of your going to try it, fumes a lot too.

For aluminum, the HCl that we're using here will work just fine just by itself. Look up "aluminum foil hydrochloric acid" on the web -- it's a well-known way of producing hydrogen gas, but the aluminum gets eaten up in the process. The downside of the reaction is that it creates heat, and speeds up (creating more heat) as it gets hotter. If you're reacting a lot of material, you're going to need to cool it or else you'll end up with runaway boiling hydrochloric acid in large quantites, which is about as fun as it sounds. I would call etching aluminum with HCl a strictly-outdoors activity, with lots of cool water in buckets on hand if things go wrong. Because of the hydrogen gas it produces, you want to make sure there are no open flames anywhere nearby. I'd experiment with diluted acid solutions first. OTOH, it's a great way to fill party balloons with hydrogen. :)

Great idea. I'll have to try that. Glad you relabeled your bottle. My first thought when I saw the photo was this... https://www.youtube.com/watch?v=xIMPbPDwj_g

nice work! How do you dispose the solution finally?

Let it dry up or neutralize with baking soda and take it to your local hazardous material center. You never want to pour down the sink or throw in the yard, the dissolved copper is highly toxic to fish and other animals.

Hello! The muriatic acid I have says to dilute the acid with water at a 20:1 ratio. Do I still do this prior to doing the hydrogen peroxide mixture at 2:1 or is the peroxide what dilutes the acid and I don't use any water at all? Any help would be greatly appreciated! Thank you!

Follow the intsructions in the instructable, not in the muriatic acid... So no, do not dilute

This looks great! Im a jeweler and I'm going to try it, but I'm wondering if this solution works on brass, just as ferric chloride does?

Works on brass, but the etchant gets gunky, so I use a separate container for brass

Could I Use high power electrolysis instead of an abrasive when etching? Theory being that running a current through the HCL will let it pick up the copper ions very easily- especially at high currents. This would allow makers to have super fine traces without the worry of brushing them off, or having them wilt off over time.

There are a million ways to skin a cat. (Gross!) I do 10 mil traces with toner transfer all the time now. I've run a couple boards at 6 mil, which is the design limit for a bunch of the cheaper overseas PCB factories. The etching is not the limiting factor -- it's getting the etch resist uniformly and reliably on such small features. I agitate the boards constantly in the tank -- meaning swishing the etchant around, not rubbing on them. I've never had problems with damaged traces. OTOH, if the electrical idea ends up a good replacement for swirling, I'm all for it. Tipping a tupperware back and forth is boring. So yeah. Try it out -- you might hit on an improvement. Let us know.

Would this solution etch a 4" x 9" piece of 360 brass plate?I'm trying to etch decorative markings onto the face of 360 brass.

The mixture is 2 parts peroxide, to one part acid. But always pour the acid into the peroxide. The initial reaction in my experience has been about a 20 degree temp increase.

I do a lot of custom circuit designing, and building. I started using this mixture over two years ago, I would never go back to ferric chloride again. I have a 3 gallon tank to do larger boards, and use an aquarium air pump to keep it fresh. When needed I top it off with a little acid, as in instructions. Mix it properly as it does get warm during the mix.

Could I mix copper II chloride with HCL and get the same result? I have a lot of copper 2 chloride the Blue Rock looking stuff laying around. if you're not sure I may just try it and see what happens.

1 finger is a single two is a double ! Ok my cup is 300 ml ! How much do I use? 25ml is a finger 50 is two . Six fingers is a Cup. Wagons do not travel in uk only on Television a long time ago. Nice is Nice but time has passed and that is the problem.

I understand your frustration that the US didn't move fully to metric system 30 years ago. Try living here and dealing with both systems side by side, all the time. If the loss of the Mars Climate Orbiter spacecraft mission (costing about $300 million USD) due to mixing up English and Metric units isn't enough to move us toward a metric only nation, I doubt any complaints in an instructable will have much impact. That said, adding fingers into the equation doesn't help much. Try the conversions listed here instead: https://en.wikipedia.org/wiki/Cup_(unit)

What really gets me is when reading a recipe for something and I ask the author "is that liquid oz or by weight?" and I get "WTF the difference?" in return. The measured substance not being water.Add to that UK ounces, US ounces and troy ounces (in jewelry).

Pretty Cool this is.

Everyone must be using 1/2 Oz boards because I mixed up a batch as stated, kept it heated to 74 deg F, and it took 4.5 HOURS to finish a 1" x 6" 3 Oz board! By finish it was a pretty green, and the next board took 6+ HOURS even with agitation and sponge wiping! Either I can't read or you all use micro thin copper. I did try a new batch with 1/2 Oz copper, and a 1" x 1" piece still took a half hour with constant agitation. Doesn't stain so that is nice, but I could have CARVED the boards with a jacknife in that time!

1) How much liquid did you make? A few shot glasses of liquid is no likely to have much etching capacity. Maybe you need more liquid volume? 2) Unless you live somewhere cold, 74F is only "room temperature", so will not have much effect. The solution needs to be warmer. My initial batch was about 1-2 liters in volume. Using some loose copper, the clear enchant went emerald green in about 20-30 minutes at around 65F (it was fall, and I was working outside). You could see the dark green haze of the removed copper as it went into solution. After mixing the solution, I used a "retired" crock pot to make a heated bath. The ceramic pot avoids problems with using the acid in a metallic pot. Once used this way, I will never use if for food again, and painted warnings to never use if for food (in case someone runs across the crock pot later, and I'm not there to stop them from cooking with it). At low heat the bath temperature was around 100F. Fumes are stronger as the temp goes up, so extra care not to breathe in the fumes is more important. I have seen commercial gear refer to temps in the 110F to 130F range, but at the high side of temps the material the equipment is made from is more has to be more durable to withstand the higher temps. I wanted to stay in the range of "hot tub" hot so if I needed to handle stuff during a problem/issue, I would not run the risk of a bad _thermal_ burn through my gloves. Besides the obvious goggles and gloves, I kept a large bucket of fresh water nearby to quickly dilute/cool issues that might come up. As the etching progressed, the color turned very dark green, which is the bath reaching it's ability to etch well. I used an aquarium air pump to bubble air through the solution overnight to add the oxygen to turn the solution back it emerald green. Adding extra acid/peroxide can recover the solution quicker if you don't have the time to air air, but it will increase the volume of solution. The air regeneration keeps the volume about the same over time (minus any H2O evaporation that occurs to slowly reduce the volume). I was using a single-sided 1 oz copper board, 4" x 7", removing about 90% of the copper cladding. Board was pushing the size the pot could hold (keeping the flat board covered in liquid in an oval pot), so I was agitating the board in the bath manually using a plastic stick attached to be board. I could see the end of the board on the far size from the handle and the top side compared to the bottom was etching faster. Since I could not get a really even agitation, the far end seemed to be getting more local fluid movement, and the top was probably more pronounced as lifting the board and down was probably caused more solution turbulance on top near the surface of the pot compared to the bottom. I have not yet had time to create a vertical bubble tank to see if the agitation can be made more even.IIRC, the first board took about 40 minutes, and a second board about 25 minutes. I was working in a garage with an air temp around 50F. I left the lid off for the first board, so the bath cooled down quite a bit during the etch. I left the lid on between agitations the second time, helping to keep the bath hotter. Fuming was more noticeable the second time around as well.

I forgot to add, after etching, I transfer the liquid into a thick walled, all plastic container that can be sealed. I air bubble the solution to regenerate it, with the lid sitting on top to help keep stuff from falling in while the air hose with an aquarium air stone is installed. Once the solution is ready for future use, I fully cap the container to seal it up. The ceramic crock pot is too heavy and cumbersome to handle without sloshing the bath, it cannot be sealed air-tight, and is to fragile (ie: breakage) for me to trust for secure long-term storage of a caustic liquid. The large plastic jugs used to sell pretzels in has worked well for me so far. I then store that inside an all-plastic cooler just in case the jug ever leaks. The cooler is also marked with "NEVER USE FOR FOOD" since some amount of liquid drips from the first jug during transfers are inevitable, and I don't want to be drinking diluted copper acid of any concentration off the outside of a beverage can in the future.

I'm glad it's not just me.

Thank you for this very useful 'recipe', it worked very well etching heavy (1.5mm) copper sheet using photocopy resist to create dog tags and other jewellery. My only addition to this instructable is- keep the coper flat when etching to get an even etch, I tried suspending a two sided piece in the solution, and although it worked fast, there was a tendency to leave heavy 'flow' marks on the surface- possibly something to do with the debris leaving the surface? Pieces left flat in the tank with some rocking agitation were fine.....I will check and see if there is an instructable on photocopy resist, and maybe add one?

This thread needs a professional chemist since you are suggesting using some pretty serious materials here. Concentrated acids, strong oxidants like hydrogen peroxide, and organic solvents like acetone are not to be handled lightly. (Background: I have a Ph.D. in inorganic chemistry and I work with these materials on a daily basis.)First, make sure to have proper personal protective equipment: goggles, nitrile gloves, and long sleeves that can easily be removed (think lab coat). Work in a well ventilated area with a sink/hose nearby. If you get the acid on yourself, wash it with water (that scene in Fight Club is wrong, don't neutralize and don't take advice from movies) for at least 15 minutes. Read the safety datasheets.Hydrogen peroxide is an oxidant. Acetone is a reductant (fuel, same thing). Don't mix them, they'll burn eventually and possibly rapidly. They can make explosive peroxides, which is a problem if they concentrate and crystallize out. If you do mix them, dilute with water 1000x. This advice goes for mixing hydrogen peroxide with methanol, ethanol, and isopropyl alcohol. Work with small volumes when possible, danger is increased with volume and concentration.When you are done, your solution will still be a solution of copper chloride in water. It's hazardous waste and needs to be disposed of properly in accordance with federal, state and local regulations.

Just an FYI: do NOT mix the hydrochloric acid, hydrogen peroxide, and the acetone together. Not that a person would do this...but it's possible someone might dispose of the stuff together or accidentally combine them. It can form acetone peroxide, an unstable (or, at least, very sensitive) explosive. Read about it on Wikipedia, that article explicitly referenced PCB etching with these chemicals. I'd encourage everyone to read it directly and not just take my word for it.

which article and which section is that?

You know Remediate the copper solution with yeast and bacteria from potted soil to absorb and use copper as an element. Since most copper hydroxide and salts are soluble in acids and lye you could use yogurt bacteria to neutralize it.

I am not that "chemistry" astute, other than that I still have in storage from High School. I etch brass and nickle sheets, would this etchant work with those metals too?

Great article - I especially like the fact that over time I could potentially recover the copper.I haven't done the calculations yet but I'm thinking of creating a 1:1 ratio of the mix as I plan to buy 12% H2O2 & 30% HCL & that way reducing the water dilution after a few etchings especially when needing to re-oxygenate the mix as I find bubbling air through the mix too cumbersome. I anticipate the initial reaction will create more gas than the 3%/31% mix

instead of hydrochloric acid you can use household vinegar

I haven't done PCB etching in years. Maybe when I retire... Just a thought on disposing of the solution. Since you want to keep the copper out of the environment, could you treat the solution as a plating bath and deposit the copper onto something, perhaps a piece of scrap PC board?

My first attempt failed. I used 200ml pool acid (30% HCl) and hydrogen peroxide (400ml 3% H2O2), and after 20 minutes it turned slightly green, and that was it. After 2 hours there is no sign that the copper is coming off of the PCB. I kept it warm and swished it around for the 1st hour, but it looks like nothing is happening to the board; I just left it outside for now - I'll check it in the morning. I need to get more H2O2 to try to tune the batch, but if that doesn't work, I'll have to go back to ferric chloride.

An hour with agitation is waay too long. Especially with fresh chemicals, it should go relatively fast, like ten minutes or so. You can tell it's etching when the shiny and coppery-colored metal goes in -- in a minute or so, it'll turn a matte pink color.Could anything be coating the copper? Try scrubbing the surface with a bit of sandpaper (finer grit is better for not leaving scratches, but if this is just a test...) beforehand?

I've just finished successfully etching my first board! Someone suggested that the peroxide I bought might be dud: even though I bought it new, if the bottle wasn't properly sealed and it had been on the shelf long enough, he said it could be useless - it had happened to him more than once. So I bought another bottle from a different shop, and hey presto! the board etched in a few minutes. I over did it a little bit, probably because I didn't agitate it evenly: I had to wait for a patch in the middle to dissolve. (Don't swirl: rock!) But it works, so from here it can only get better. I think my main lesson is to keep a few bottles of peroxide handy. BTW, before my 2nd attempt, I was also wondering if the "gloss" from the glossy paper might have coated the board with an invisible layer of plastic - it seemed possible - but I've now established that that is not the case. The paper works perfectly.

Hey fantastic! I'm glad to hear you got it working, and even more stoked that you found a way that things can go wrong. :)Peroxide has a shelf life, for sure. And as you note, a trip to the pharmacy and a couple of bucks can test that hypothesis.Re: agitation is key. The center pretty much always dissolves more slowly than the edges, no matter how you agitate (unless you're spraying, but that's another level of complexity altogether). If you let it sit for a second or two, then swirl, you can see brown/black dust coming off the board -- gives you a good idea of whether you're agitating well enough.Glad you got it working, and thanks for coming back with the report. Watch out for bad/expired peroxide, y'all!

You should add this to your Instructable as many people seem to be having this issue. :)By the way, great 'Ible. I want to try PCB etching one day so this might be just the right solution! ^^

Hi I am new to etching. Is the ink a special ink? Would like to know so that I buy from this ink. Thanks

Would this work with 9% H2O2 and 18% HCl?

Yup. I'd go one-to-one with those concentrations, though. Should be ballpark right. I

I am now confused. after reading so many comments I just want to do a PCB for a small electronic circuit. what my board is two inches by one inch . seven components four wires it is a light activated

this phone is stopping me from asking the question what is the amounts in Mililtres cups are not standard in UK