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

Picture of 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...

Picture of Put the Lime in the Coconut...
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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.

Picture of Add PCB and you're Etching.
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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.

Picture of 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.

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ChipBits2 days ago

UK visitors - Everbuild brick & patio cleaner (<10% Hydrochloric Acid) from hardware shops and Care+ Hydrogen Peroxide (9%) local chemist. Slow but works.

What ratio did you mix the two. I've a 6% H2O2 and a mix of 9.9% HCL (brick cleaner alright). It's turning green but it isnt etching a thing (only cleaning off the sharpie I used to fix a track on the etching).

Mine was about 3 x HCL to 1 x H2O2 by volume. I've noticed a lot of variation here and people seem to prime it with spare copper to reach optimum speed. These % mixtures are mostly water & seems a lot of people either use air bubbling, agitation or heat to either evaporate off the water or accelerate the reaction. Still experimenting here too!

Ok, to get rid of the excess copper chloride, you generate hydrogen gas and pass it over heated fine ground crystals which will reduce the copper salt to metal and give HCl gas as a byproduct which can then be bubbled into water to give more hydrochloric acid. We use to do something similar to this in the lab using zinc and hydrochloric acid and then we would pass the hydrogen through a heavy glass tube with a few Bunsen burners underneath, copper product inside. We used this to repair copper wool that had turned green and clean pennies. Most of the pennies were just oxidized with oxygen so we got out just water. Of course zinc chloride isn't very life friendly either, so maybe electrolysis of water to make the hydrogen would be better. Of course heating hydrogen gas over an open flame in a glass tube isn't to be taken lightly, so maybe you should just place the extra into plastic bottle and seal it into a bucket of concrete and take that 10 miles off shore and dump it into international waters like most industrialized countries do now. Who knows? If you survive my suggestions, later.

crazypj11 days ago

I'll try the toner transfer method to make 'real' circuit boards, this was just a thick Sharpie I picked up to test things which is why it's so rough

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The Real Elliot (author)  crazypj10 days ago
Bah! That's not rough -- it looks pretty darn good. And if it gets the job done, it's more than good enough.

I do a lot of little circuits with Sharpie and etchant. It's great for quickie one-offs when it's not worth designing a whole layout, but you still need the strength and structural stability of a PCB.

It's a great trick to have in your bag, if it helps you get stuff done faster or better.
crazypj made it!11 days ago

I was astounded how well it worked. Did a very rough drawing to make a series/parallel capacitor bank using miniature 'ultra caps'.

Was real easy to solder

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TrumanF15 days ago

Elliot the first time I tried this is worked flawlessly. Now I used a small tupperware leftover tub and the boards etched in just a few minutes. I tried it again two nights ago, which was a few weeks later and tried using the still very green solution but I played heck trying to get it to etch. I added a bit more acid but it only seemed to work once I added a little more H2O2. The color didn't change much but the board started losing copper at a more normal rate. Since I bought a laminator and couldn't wait to try it out again last night I threw a couple of small boards in the day old solution and the same result. Just wouldn't etch. Left it in for an hour just to see what would happen and nothing. Added more acid and unfortunately I was out of H2O2. The solution was still nice Kool Aid green too. My wife is picking up some HP today at the store and hopefully when I add that the magic will happen once again. The container is only 4 inches square and maybe 1.5 " deep. You think I should use a larger tub?

GeraldB317 days ago

will it work on steel painted with cellulose i.e wanting to etch on a stencil on the side of a commercial vehicle

dkoebnick21 days ago

Can you store the etchant in the container (plastic) that you are using for etching? Can you use a cover on it when storing?

The Real Elliot (author)  dkoebnick19 days ago

Yeah totally. But.

Make sure that the cover is airtight or else you'll likely get HCl fumes leaking out.

I bought a tray from Ikea that I thought had an airtight lid because it had a silicone-y gasket. Apparently it wasn't airtight. The fuming wasn't drastic, but it rusted a USB cable that I kept in the same drawer over the course of a few months.

Since then, I still use the tray for etching because it's transparent and spillproof, but I also use a funnel and pour the etchant back into a plastic drink bottle (appropriately labelled) after each use. It's not that much hassle.

Chimera Dragonfang made it!1 month ago

Had way too much fun with a bunch of the brass scrap kicking around in my workshop.

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zann681 month ago

I tried this method today to do a Arduino RSSI Antenna Tracker board, worked Perfectly!! Way better than Ferric Chloride method. Plus side also you can see what it's doing - Will now only use this method! Thanks!!

AKL3217 months ago

What is the best way to wash off the hydrochloric acid and hydrogen peroxide after the etching is done? Water? Would ammonia or baking soda cause a dangerous reaction?

weish AKL3211 month ago

i would just use a large water bath in a non reactive container to wash the board, then add some baking soda before dumping it out. don't add ammonia though, there's chlorine compounds in there and ammonia could liberate the chlorine gas, which is nasty in even small amounts.

raukorist772 months ago

what did you use as a resist for the etching? considering using this for some copper tubing

HassaanA2 months ago

Thanks a lot The Real Elliot. This worked amazingly well. Etched my 6x6 inches pcb in just 3 to 4 mins, Ferric Chloride used to take more than 30 mins. That is a great etchant. Much more cleaner and easier to use as compared to FeCl3. :)

jenjen.dobson2 months ago
Can this be used to etch sterling silver?
mwestern13 months ago
It doesn't surprise me that the 1:1 solution was a bit more energetic.
With the 1:2 ratio of 10M HCl and 3% H2O2, the actual molar ratio is 4:1, with the equation requiring only 2:1, so you do already have a fair bit of acid left over.

Although I'm not a chemist either ;)

Also, a minor correction (as I see it) to one of your equations:
4CuCl + 4HCl + O2 -> 4CuCl + 2H2O
Since oxygen doesn't naturally occur as a single atom :)
Mulemom33 months ago

Will the starter etchant work on brass? I'm using ferric to etch brass, but it stops working after just a few uses. If I can make the etchant cheep, I'm ok with that, but if I can make it cheep AND use it forever, well that sounds perfect! Would it work better if I dissolved some copper wire in it?

davidbarcomb4 months ago

With all the positive comments below, I gotta try this solution.

jmsheehan865 months ago
Question. First off I'm new to pcb etching. Always used perf boards. Tried this solution and love it! First few boards I etched took minutes with a fresh solution. I had to make another solution and dropped a board in it. It took nearly 20-30 minutes to etch a small board. Tried to mix another solution like instructable says and same thing. Slow etch. Why? Should the board be dry after rubbing paper off or could paper from the laser etcher still be on there slowing etch time down? Also, light? Could light really slow it down that fast? Heating? Can that speed it up? And I know about agitating it. Thanks!
JacquelineC15 months ago

I started using this combination to etch copper for jewelry components. i like it very much. It works fast and due to the size and amount you get of the pool acid, you can etch many things at a time in many containers. The etching is also very crisp.

Victor8o5 made it!6 months ago

Thanks! I finally got a laser printer and now I can print my own circuits. Your instructable has been very useful, I probably couldn't had been able to find Ferric Chloride in my area.

I'm making a coupler for a savaged VFD so I can hook it to a breadboard for testing. I intend to make a retro alarm clock with it.

mbarela826 months ago
I tried it today and it works perfectly!
jairusmartin6 months ago

Works really good, significantly reduces waste.

Bartm17 months ago

HI, I made this solution as described and tested some boards with a little bit of the solution and it worked great, in fact the best! But however, I did not use any of the bulk solution as yet, so it was as it was mixed, but now a week and a half later I wanted to use the solution and it has depleted its etching properties. how can I re-generate this mixture back to what it was. I did use distilled water. Do you think or can I re-mix the proportions using the old solution from 1 part acid to 2 parts H2OO, i.o.w 33% H2OO with the old solution to make the 3 % to mix with the acid. maybe I need to just make a bubbler for it?

Thanks L

synthdood7 months ago

Hey cool! I never use ferric chloride anymore. I use the same technique in my Instructable check it out,

Orngrimm7 months ago

I got a goob ammount of crystaline CuCl2 (i think). If pics are needed, please say so, Can make them in the weekend.

If i want to etch with this, i only need HCl and bubble it up during etching if i did my chemistry correctly, right?
Sorry... Electronician here not a chemist...

Newton9 months ago
Tried this method this morning and it worked like a charm. Messed up the mask a bit but nothing that cant be fixed.
The Real Elliot (author)  Newton9 months ago

Not bad! And awesome for a first run.

Are you using toner transfer? If so, I'd say your iron is running a little hot b/c of the smudged-out pin holes. Try using more pressure (lean into the iron with your full body weight) and less temperature and see if it's easier to get consistent results.

If you're feeling really experimental, you can run a bunch of practice prints reducing the temperature each time until you get a transfer that's not smudgy. No need to waste copper board by etching each trial either -- just wipe away with acetone and try again. You should get the proper temperature dialed in within half an hour.

Thanks for the hints! Will indeed try that myself! I always was afraid of pressure... Because of this smudging... But yeah: Maybe a higher pressure + Lower temperature may just do the trick!

Tanks for the feedback. Definitely giving this another try. I think I got the wrong transfer paper as it took forever to transfer to the copper. But time will tell, I'll post another pic when the next one is done.
dunnos8 months ago

Haha, I just got my hands on some 30% H2O2 and i thought it would be funny to make it really acidic. I mixed one part 30% H2O2 with three parts HCl.

Put in my board (about 10cm by 10cm). It made a hissing sound, I couldn't see my board through all the bubbles. Took 20 seconds for the entire etch. I was just standing there looking at the mixture like: what ಠ_ಠ

The Real Elliot (author)  dunnos7 months ago

Yeah. You _can_ push the concentrations up a lot, but eventually there are tradeoffs. Mainly:

1) Fuming. Highly concentrated HCl solutions end up in the atmosphere, rusting your kitchen knives and/or any other exposed metal nearby. (Guess how I know?) It's just a lot more convenient to handle lower (2-4M) concentrations. Keep the lid tight when you're storing the etchant regardless.

2) Etching too fast. There's a thin line between etching all the exposed copper away, and etching more than you wanted. If you think of the copper layer on the board in 3D, while the topmost surface may be protected, the sides are vulnerable once the etch is done. This kind of over-etching is called "undercutting". And all things equal, undercutting is easier to avoid (the timing is less critical) with a slower-moving etch.

I aim for a 10-minute (or so) etch with continuous agitation.

Next time it would probably be best to just get a plate and poor it on top while sitting outside.

Ares33x made it!8 months ago

Easy instructions and works pretty well. Thank you for this easy to follow and knowledgeable instructable. The comments were quite helpful and enlightening. Here is some quick boards I've done and the container for it. Does anyone know the pressure this solution can build up to in a container? or can I leave in a semi-sealed tank?

Swishing the board around really helps even with the bubbler now, I was thinking of heating the solution a little and somehow getting either a pump or something to keep the liquid moving over the boards. Without swishing it around it just wouldn't etch or etched really slowly and unevenly because the oxidized layer. With swishing it's taken around 20-30 mins depending on how much copper I am removing.

Also noted that the poor bubbler stone was nice and blue when I bought it, after sitting there for half a day it was very light and then a day late is just whitish now.

The Real Elliot (author)  Ares33x8 months ago

Nice job, great results, well documented. Best comments evar! :)

Thanks for mentioning your experience with swirling / agitation. I absolutely should have highlighted that in the instructable. The etchant (any etchant) saturates pretty quickly in the immediate neighborhood of the part you're etching, and it'll slow down almost to a crawl unless you keep that layer mixing with the rest of the solution.

When you swirl it, you can sometimes even see little dark brown clouds of copper coming off the board and then dissolving into the rest of the solution.

The bubbler looks awesome. Let us know how that holds up in the long run. And be careful not to let the etchant back up into the pump!

A hint, if I may:

You etched away a _lot_ of copper. If you add a ground plane pour in your design, you can drastically reduce the amount of copper to remove, and you'll speed the time up a lot. Or heck, use up some of that free space on the board for art...

Anyway, like I said: awesome comment!

Yeah, I have done some ground plane boards but for these particular ones I was trying to do a single point ground as suggested in the datasheet for the fun of it, and to get the solution started. The large board however I would have take the approach but I have 12 gauge wire on a lot of the tracks (it's an adjustable current sink). But the art ideas is an interesting way save up some copper from being eaten away, never thought of that, thank you.

m-m-owen9 months ago

Followed directions using 200ml 3% hydrogen peroxide and 100ml 31.45% HCL (muriatic acid). Worked perfectly and exactly as described. Good stuff. Way cheaper than the ferric chloride I have been using and I dont have to heat it.

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