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

Picture of 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.

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Step 1: Ingredients: The Starter Etchant

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.)

Step 2: Put the Lime in the Coconut...

Measure out two quantities of hydrogen peroxide and pour it into your non-metalic container.

Measure out one quantity of hydrochloric acid and pour it in. ("Do like you oughta, add acid to water" to minimize the chance of an out-of-control exothermic reaction.)

Be careful with the acid. This stuff (at 10 molar) is strong. Mine fumed a bit when I took the cap off. Don't breathe it directly, and be sure you've opened the kitchen window.

The starter etchant you've just made, on the other hand, is not so bad -- around 3M HCl with a medium-strong oxidizer. I find it doesn't fume much at room temperature when I'm re-using a batch.

That said, you've got to be very careful to keep it away from metal -- especially your stainless-steel kitchen sink. It'll eat the stainless coating right off. Keep plenty of water flowing at all times when you've got any of this (even a drop) near the sink.

Step 3: Add PCB and you're Etching.

Toss the PCB into the solution and it'll take off.

If this is the first time you're using this batch of solution (and I presume it is), it'll etch super-fast. This small board took only 2 minutes. Yikes!

Since I use a deep container, I tend to swirl it around as it etches. This stuff is so active, though, that I'm not sure it's necessary.

Keep the window open for ventilation because the starter solution gives off a little chlorine gas. (The end-etchant gives off much, much less.)

Also, note how the etchant gets greener over time as it eats away the copper. This is good news.

What's happening is that you're dissolving the copper from the board and turning it into cupric chloride. In the long-run, the cupric chloride will be doing most of the etching (instead of requiring disposal). For now, just watch your solution turn light green. Next time you use it, the color will deepen.

Step 4: Chemistry Break

Picture of Chemistry Break
(Note: I'm an economist, not a chemist. Please leave a comment if you've got any corrections and/or additions to this stuff!)

I stumbled on this idea when I saw this website: Etching with Air Regenerated Acid Cupric Chloride by Adam Sechelle. Cupric chloride can be re-used indefinately by topping up the acid levels and adding oxygen (bubbled in from the atmosphere). Sounds cheap and environmentally friendly to boot.

The website's got a lot of good chemistry info on cupric chloride etching. His data on etching speeds is great, and his simple titration procedure for maintaining the acidity of the solution is pretty nice.

To make the cupric chloride solution, he dissolves a bunch of copper wire in hydrochloric acid, and mentions maybe using hydrogen peroxide to speed up the oxidation, but doesn't go into detail.

Which got me thinking. You didn't have any cupric chloride yet, but you can make it by dissolving copper. Dissolving copper is the name of the etching game. So we can make one etchant that makes another etchant that's infinitely re-chargeable. Elegant.

Turns out that hydrochloric/peroxide is a common home-brew etchant (and I've re-re-invented the wheel, again) but I guess that people got so used to throwing away their "spent" etchant that they don't think about re-using it. The whole point of this instructable is that you don't throw it away, but use the dissolved copper forevermore as your long-run etchant.

Here's what's going on chemically:

Before there's much copper dissolved in the solution, Cu + 2 HCl + H2O2 -> CuCl2+ 2H2O is the dominant net reaction. That is, the extra oxygen in solution from the peroxide is oxidizing the copper metal, in presence of the acid, to make copper (II) chloride. That's our starter etchant. The resulting CuCl2 shoud be a nice emerald green color.

After you've dissolved a lot of copper into the solution, and used up all the peroxide, the copper chloride does most of the etching for you: CuCl2 + Cu -> 2 CuCl. That's the end etchant.

Eventually you etch so much that you convert all the CuCl2 into CuCl, which doesn't dissolve copper (and is a yucky brown color). As long as you've got enough acid in the solution, you can simply add more oxygen to re-oxidize the copper(I), making more copper(II) chloride and water: 2 CuCl + 2 HCl + O -> 2 CuCl2 + H2O. And then you can etch again.

Bottom Line:

Two things to maintain: CuCl2 levels and acid levels.

CuCl2: After all the peroxide is used up, and the solution starts turning brownish, you'll have to add oxygen to regenerate the solution again: toss in a few more capfuls of peroxide or bubble air through the solution or swirl it around vigorously, or just pour it into an open container and wait. It's easy to tell when you're ready to etch again, because the solution turns green.

It's also impossible to add too much oxygen by adding air, so bubble/swirl to your heart's content. If you're using peroxide to add oxygen, be sparing -- a little goes a long way, and it's mostly water so you're diluting your etchant by adding it.

Acid: Note that HCl is being consumed in the starter etchant and the regeneration reactions. So we're going to have to add a bit more acid as time goes by. If you notice that it's harder to re-green your brown etchant, it's probably time to start thinking acid.

I've tried the titration described on Adam's site a couple times, and it's pretty easy but requires an accurate scale and pure lye (back to the hardware store...). It's easier to just toss in a capful of acid every few batches of boards, which seems to do the trick for me.

Step 5: Save the etchant for next round. You're done.

Once you're done etching, pour the etchant back into your storage bottle, rinse off the board, flux, drill, populate, and solder.

Some final notes here:

1) You can make quite a bit of this stuff very easily, and since you're re-using it, there's no real reason to skimp; put plenty of etchant in your "tank." When you use too little FeCl etchant, for instance, it can get saturated with copper and slow down which can result in long etching times and pitting or undercutting or worse. When I'm etching a board with copper chloride, I'll pour a couple extra inches of solution into the container. It's reusable anyway, and the extra exposure to oxygen just regenerates it. Live large.

2) Don't make too much. As you keep re-using the solution, you're going to need to add a little more acid and a little more peroxide every once in a while. If you've got a 750 milliliter container, start out with less than 500 milliliters of solution. Give yourself some room to grow over time. After all, the main point is to avoid having to dispose the copper in spent etchant.

3) If you've got too much volume of etchant (it will happen eventually) you can evaporate out the extra water by putting it in a shallow (non-metallic) pan or beaker or whatever and letting it sit for a while. This concentrates the copper in solution, giving you a stronger etchant. It'll also re-oxidize some of the copper for you, a bonus. Remember when you're adding the peroxide that you're actually adding 97% water.

4) The linked website suggests that the acid levels in the etchant are not critical as long as there's some acid in solution to do the CuCl2 regeneration. The amount of CuCl2 (vs CuCl) present is easy to diagnose by the color of the solution. Add oxygen to re-green, and add a bit of acid if that's not working. Worst case is that you may have to wait a few more minutes per etch with a sub-optimal bath. This isn't rocket surgery.

5) I do have an aquarium pump ($6 at fish store) that I've used to re-activate my solution. Sometimes I'd leave it on for a few hours while I'm at work if I've been etching a lot. But lately I've been lazy/impatient and tossed in a couple capfuls of peroxide. Both seem to work just fine.

6) The environmental benefit of etching with copper over ferric lies mostly in not having to dispose of the copper that comes off your boards every few times you etch. When and if you do end up with too much copper etchant, please treat it like the hazardous waste that it is -- look into your local hazardous chemical disposal options. There's no getting around the fact that copper salts are (for instance) poisonous to fish even in very dilute concentrations.

Step 6: Alternative (overly-complex) Method: Make Cupric Chloride Faster.

When I originally started trying to make Cupric Chloride etchant, I hadn't thought of just using the regular procedure of etching to get there. So I deliberately dissolved a bunch of copper from a wire.

I don't think it's a particularly good idea, but here's how I got to the end-stage etchant faster.

I mixed the acid/peroxide 1:1 instead of 1:2. The idea was to have a bunch of acid leftover for later regeneration. I don't think it's a good idea, and I wouldn't do it again. 1:2 is probably better, and results in more copper in solution faster with less fuming.

To control the fumes, I used the patent-pending (just kidding) Two-Pint-Glass Fume-Containment-Apparatus. Pour in the peroxide, add the copper, then put one glass on top of the other. Pour the acid down through a small gap between the two glasses and re-seal. Voila. No fumes. (See video. I think I did it with water as an example.)

I also kick-started the formation of cupric chloride by first making copper oxide, which turns to cupric chloride just in the presence of acid alone. This isn't necessary at all, but it was fun. Heat up a coil of copper wire on the stove to red-hot and you get a flakey coating of copper oxide.

Otherwise, it's basically the previous procedure, so just see the pics for notes. I wouldn't recommend it anyway. The less copper you dissolve, the less copper needs to be (eventually?) disposed of, and the acid/peroxide etchant is plenty easy to use.

The two-cup technique is cute. I still recommend it.

apappano1 month ago

On the chem page, Google is detecting malware on the original Adam Sechelle site. Here's a reposting of it:

May want to update the link until it gets fixed.

mkeen851 month ago

what is the minimum percentage HCL acid needed?

I can get 33% online, but is a bit pricey.

but i can get brick cleaner from local shop which is a lot cheaper but is only 10-15% HCL

The Real Elliot (author)  mkeen851 month ago

My recipe calls for 34ish% acid (10M) and 3% peroxide (97% water) mixed 1:2. This means the resulting acid is diluted by a third (one part in three total parts) and so is around 10%.

You're starting out with around 10% acid, so you can't really afford to add too much peroxide. If I were you, I'd experiment with straight 10% acid, and tossing in a few capfuls of peroxide at a time. Or maybe I'd go as far as a 1:1 mix of weaker acid and peroxide. Or maybe try to find some strong (10-15%) peroxide so that you don't have to water the mix down as much.

Either way, experiment. The worst that'll happen is that it doesn't work very quickly, but even with a weaker acid solution you should get etching. Post back with your results?

thanks i think i can get some 10% peroxide but would 30% hydrogen peroxide be over kill?

also once i have made the copper chloride could i boil it down then add more HCL to make it stronger?

The Real Elliot (author)  mkeen851 month ago

30% peroxide _is_ probably overkill. But then again, too much overkill is never enough!

On the other hand, boiling the acid is probably not a good idea. The stuff (at 3M) is nasty enough without being hot and spiiting.

If you need to increase the acid concentration, one way to go is to simply leave it sitting out in a shallow tray. The water evaporates. Done.

I bought some 31% Muriatic acid at Home Depot which was $4 (or somewhere around there) for a quart. I think they had it for pool supplies.

I'm not a chemist, but I would think that 15% would work, but your etching would take longer. You'd probably want to double down on HCl in the recipe above so you'd be adding the same amount of HCl as you should.

thanks I will try that.

akro1231 month ago

Thanks sooo much, this was my first time etching, and i didnt bring enough money to radioshack to buy the etch lol, this worked great!!

Sylentskye6 months ago
Is there a way to do this using vinegar and hydrogen peroxide (peracetic acid)? Would it be safer than using the muriatic acid? What ratio would you suggest to start with? (I have white distilled vinegar and both retail 3% and hair salon 30% hydrogen peroxide solutions available to me. Thanks!
The Real Elliot (author)  Sylentskye1 month ago

With vinegar (a weak acid) and 30% (strong!) peroxide, you're doing it all backwards. Instead you want essentially a strong acid with sufficient available oxygen.

Try the recommended recipe? It's worked for like a bazillion people.

It will technically work, but it might take days, or even weeks. It would be much safer than muriatic acid, but the only real danger of muriatic acid is that the fumes will hurt your lungs, and will rust any metal objects in the room.

If you are going to use vinegar, hydrogen peroxide is a great idea to add oxygen to speed up the acid reaction. Change the vinegar often; it will quickly become full of copper acetate, leaving little room for the vinegar to do its work. Add heat; put the reaction in a bowl of hot water or over an electric blanket or central air vent; just a few degrees Celsius can mean the difference between days and hours.
bezo882 months ago

nice work. I tried this design and it did not work. I used 1 part vinegar and 1part hydrogen peroxide and salt. I was testing to see if it works and I left a small pcb and a few pieces of copper wire in the solution overnight and it did not dissolve , it just got rusty and nothing happened to the pcb.

The Real Elliot (author)  bezo881 month ago

I've heard the vinegar suggestion a lot. I'm not a fan, and I don't understand the point.

For the chemical reactions involved, you really just want an acid -- a source of hydrogen ions. HCl is about as simple an acid as you can hope for, in terms of availability & purity & strength. It's un-dangerous enough that it's the acid of choice for regulating swimming pool pH. Good enough for me.

With vinegar you don't really know what you've got, chemically. All sorts of flavor compounds and colors? Residual sugars? Yuck. No thanks, give me cheap and pure hydrochloric any day.

freedomdivine2 months ago

HI I use the Ferric for etching metal jewelry. I buy it at Radio Shack its pretty pricey! Could you please tell me if this would work just the same on my metal jewelry? Thank you so much.

The Real Elliot (author)  freedomdivine1 month ago

No idea -- depends on the metal.

But acid + peroxide are cheap. Why not try it out and report back? This is one of those frequently-asked questions: a bunch of people will be interested to know how your experiments go!

ProMaker2 months ago

Not sure why others are having trouble. I just tried this technique for the first time and it worked perfectly. 3% H2O2 from Walmart (32oz bottle $.99) Muriatic Acid/31.4% HCL from Lowes (1gal. $7.29). Mixed it in the garage although fuming was so little probably could have done it in the basement with no issues. Etched in a small glass jar at room temp. and applied agitation throughout. 2"x3" double sided 1oz board etched in about 4 mins. Solution started clear and ended a light emerald green.

bobh92862 months ago

I started using this method today. I had a board I wanted to etch so I followed these instructions to the T. The board I am making is 2" x 6" only has a circuit on one side but the board I got is plated on both. My first run at this was an ugly failure. With a brand new batch of the etchant it took over an hour to remove all the copper on the side with the circuit and this resulted in a very pitted circuit that is unusable. No big deal as always expect a first time failure :)

On my second run it still took a good 30 to 45 minutes to etch the circuit side of the board and there was still at least a third of the copper on the other side. At this point I pulled the board and just sanded the remainder of the plating off. The board looks nice and is ready to go.

My concern is the length of time this appears to be taking. In earlier posts and reply's I see comments that if it takes longer than 15 minutes or so to etch a board something else is wrong. What could this be?

1st Board.jpg2nd Board.jpg
fschonholz3 months ago
So ... I have been experimenting with your technique and it is cool. As a first time etcher ... this made it easy. I have been having an issue with the "mask" (not sure what it is called technically) to etch. I used shappies and nail polish. The shappies have been useless. The nail polish has been a hit and miss, as some of the nail polish stays, some gets eaten away and some half way.

I build guitars and wan tot do one with an aluminum front that is decorated. I want the decorations to be etched out.

The question is, what should I used to "draw" the decoration that I do not want the acid to act on? and what should I use to protect the back of the plate I want to etch so only the front is etched?

Thank you!

Thank you for the assistance. I actually found the way to do it using nail polish ... just needed to find the right nail polish.

If I want to etched in the design, I paint the full surface with nail polish and then scrub out the design. If I want to etch out, then I draw the design with a market and then pain it with nail polish.

You can find the results here:

It is a bit rough for a first try; but just an excuse to do more :)

I have always used the toner transfer method, print what you want on photo paper. Lay the paper with the print upside down (toner facing the copper), use an old iron to melt the toner on it by putting it on the paper for a minute. Lay the board with the paper on it in a bowl of water (the paper should stick to the board, before you lay it in the water). Rub of the paper, and you have a very nice etch resist. Only works on laser printers.

nov8 fschonholz3 months ago

I found the best and most precise way is to take a vector file of the design you want to a print shop and have them make a decal. It’s pretty durable. It costs more than a Sharpie but saves on frustration. For the back of the piece I usually use electrical tape. But just recently I started using wax. Just melt it down and pour it on the back of your piece. It's cheaper in the long run and is re-useable. When you are finished I found the best way to remove the wax is to put the piece in hot water to soften, then peel it off.

pilgrimsc5 months ago
hello can you tell me if this would be good for etching carbon steel?
DEEPAKP13117 months ago

The shopkeeper is being a jerk. Ask him for "muriatic acid" or "brick cleaner" or "hydrochloric acid for cleaning bricks". The concentration strength for cleaning bricks is the one I used for etching PCBs.

However, ANY concentration will work! Some will just take longer than others!
thefeeb moeburn6 months ago
I wonder if this is the reason mine is taking so godawful long, then. I tried this last night and after an hour of soaking, I barely had an image. I bought a gallon of muriatic acid from Ace Hardware. Even with the basement window and doors open, it got thick with that acid fog. Could it be the brand? Seems the pros are outweighed by the cons in my case... frustrating.
moeburn thefeeb6 months ago
You also have to watch the temperature. This is a chemical reaction, and chemical reactions are highly affected by heat; in this case, if it is below 20°c, it will take days. If it is 20-25°c, it will take a few hours, and if it is 30-40°, it can take just a couple hours. So if its a little chilly where you live, and your windows are blowing cold air over your acid, then you need to place the acid bowl/container in a bowl of hot tap water to speed it up.
thefeeb moeburn5 months ago
Thanks for the quick response! I was using the Hydrogen Peroxide, but I wasn't heating it... which I was unsure about. I have kept Ferric Chloride heated, as all tutorials outline, but I hadn't seen anything about temperature in this tutorial (sorry if I missed it!), so you've given me more to troubleshoot, thanks!
Also- I'm pretty sure I've read that getting the transfer, which I'm also struggling with, is easier if you turn up the resolution/blacken the image to get more toner, correct? I bought a laminator specifically for transfers, but it's been pretty spotty. I just read one tutorial that underscores the importance of pre-heating the copper, as ironing it directly will cause condensation, contributing to spottiness/areas of poor transfer. I'm surprised at how much of an art this seemingly simple process is turning into! :)Big thanks again!!
moeburn thefeeb6 months ago
Oh, and add hydrogen peroxide! Hydrogen peroxide provides the much needed oxygen to speed up the acid reaction, and can mean the difference between days and minutes.
ew00546 months ago
It helps to have a pan of hot water underneath and partially-submerge your etching tank into the hot water to transfer the heat. Use two tupper containers of the same size so they nest easily, preventing spillover.
ziggalo4 years ago
 Why do you need to have water running?
ew0054 ziggalo6 months ago
Just pour it in the toilet and flush. It will be diluted well below safe limits. If you feel better, pour it into a bucket of water to dilute it further, than flush.

Actually, it is reusable. Save it in a covered tank and just add acid as needed (when the solution turns from green to brown).
prevent it from etching the sink. it'll wash away small drops before they can eat at the metal.
Pour acid over my metal kitchen sink? Not a chance!

I wonder, what percentage of people actually do this in their kitchen? If I was going to do it in the house at all I'd do it at the bathroom sink. Even then I'd run the water to protect the metal around the drain hole but at least the body of the sink is porcelain.
moeburn7 months ago
WARNING! Hydrochloric acid releases fumes! These fumes aren't just dangerous to your health, they're dangerous to your metal tools! Keep a lid on any bath containing hydrochloric acid at all times, or make sure you keep the bath in a sealed room with nothing valuable inside!

I used the hydrochloric acid etching method, in a tupperware container without a lid, in my shed. After 3 etching sessions, I noticed that every single metal tool in my shed was completely covered in rust. Most were totally ruined. The hydrochloric acid fumes had oxidized them. That was 10 years ago. I am still cleaning the rust off some of those tools to this day.

Protect your tools from the hydrochloric acid fumes!
pfolwarski10 months ago
I am having an issue with CuCl couperous chloride precipitating out when I try to dry my sample. I am using copper chloride for gain size testing under a microscope. The etchant works and I rise with water, then put it under a blowdryer to dry the sample. When I put it under the blow dryer (even on cool setting) a white precipatate forms (im assuming it is couperous chloride CuCl). I have tried using NaCl rise after etching and it sort of helps.

Have you ever had this white residue ( I dont know if it could be contamination)? Is my solution possibly too strong / weak?
Sounds like you have hard water: calcium carbonate in your water. Try rinsing the board in distilled water instead.
The Real Elliot (author)  pfolwarski10 months ago
No idea, but copper salts are usually blue or green or blue-green. If it's truly white, it may be something else?

So what's going on? You rinse off the board after etching and there's still some residue? The etchant is soluble enough in water that there really shouldn't be anything left.

drdread7 months ago
I tried this out with my two sons (ages 11 & 13) this morning, and it worked beautifully. No more ferric chloride for us! The only challenge I had was finding a small quantity of muriatic acid. The smallest quantity I could find was 2 gallons at the local pool supply store. Still, at $11 for 2 gallons, it wasn't much to pay. Next up is to hit the aquarium store for the $6 air pump so I don't have to keep adding h2o2.

Thanks much to Real Elliott for bringing this method to my attention. I love the idea of being able to re-use the etchant, and the kids were tickled by watching the solution turn green.

Some responses to questions posted before me:
1) gphein: I did the etching outside on my driveway, and brought a mason jar of water with me. Just pulling the board from the etching tank and dropping it in the jar stopped the etching instantly. Then rinsing in the kitchen sink is OK because there's so little acid left on the boar.
2) awrrwa: Any plastic container with a 2 or a 5 in the triangle will work great.
3) pfolwarski: this sounds like "hard water" i.e. heavy calcium carbonate (limestone) content in your water. Try dunking the board in distilled water from the grocery store instead of your tap water.
gphein7 months ago
This is great post. One thing isn't clear, though. What is the best way to rinse the board (i.e. neutralize the solution on it) after its acid bath? Rinsing in the kitchen sink (as suggested in the one of the photos in step 5 or 6) seems like a bad idea as does rinsing, well, anywhere.
awrrwa8 months ago
Can I store the solution in HDPE/LDPE/PP plastic bottle?

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