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

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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.)

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AKL3216 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 AKL32113 days 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.

raukorist771 month ago

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

HassaanA1 month 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. :)

Can this be used to etch sterling silver?
mwestern11 month 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 :)
Mulemom32 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?

davidbarcomb3 months ago

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

jmsheehan864 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!
JacquelineC14 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.

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Victor8o5 made it!4 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.

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mbarela824 months ago
I tried it today and it works perfectly!
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jairusmartin4 months ago

Works really good, significantly reduces waste.

Bartm15 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

synthdood6 months ago

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

http://www.instructables.com/id/DIY-PCB-using-Liquid-Photoresist/

Orngrimm6 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...

Newton8 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.
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The Real Elliot (author)  Newton7 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!
Thanks!

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.
dunnos7 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)  dunnos6 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!7 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.

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The Real Elliot (author)  Ares33x7 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-owen7 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.

Victor8o59 months ago

Hi, I've noticed that the mix I've made releases small bubbles, resembling champagne ones, even thought there isn't any copper inside and the last reaction took time hours ago is this safe?

The amount of bubbles seems to be very low, but it keeps going for hours.

As a precaution measure the lid is a bit loose to avoid pressure to build up inside.

pelrun Victor8o58 months ago

Hydrogen Peroxide decomposes to water and oxygen spontaneously; that'll be what you're seeing. So it's pretty safe.

It happens faster when exposed to light, which is why it's sold in dark bottles.

JLDohm9 months ago

If you want more concentrated H2O2, is is available as "Clear Hair Developer" in the drug store with the hair dyes. 10 Volume is 3%, on up to 40 volume which is 12%.

rizoma made it!9 months ago

Hi, thanks for the tutorial, I successfully etched my first board today, before that I was using a cnc from a friend avoiding etching cause the concerns of disposing the acid etc, so the idea of the recycling etch was really amazing. Even thou seems that most people don't get it, and just like this recipe for the fast first etching...

I just did a little test, it was great, I got 15% hcl and 3% h2o2 I started mixing by 1:1, no etching so after 5 minutes I added another part of h202 and the etching started, took less then 5 minutes. Great.
I used a little glass bottle for the enchant, but after reading some comments now I'm afraid it could explode for the pressure, but I don't won't to leave it open cause I'm afraid it would loose it's effect... any advice for storage and for the next pcb? I would like to do the best I can for re-use everything the best possible way. I want to use a acquarium pump too...
ps. I think I got just 25ml of total for this little board picture attached.

my1stPCB.jpgnasty.jpg
mykiscool9 months ago

I found one that just uses vinegar and peroxide. That's as cheap and safe as you could get!

www.youtube.com/watch?v=D8M5BIo0a9Y

Ananse159 months ago

What metals will I be able to etch with this solution? I usually work with brass, copper and nickel silver blanks.
Thanks!

dkamegawa10 months ago

Reporting results after first use: this thing is sick, in the best way. Money for roughly 1.5 litres of this stuff set me back the same as a small (250ml) bottle of FeCl3. Roughly twice as fast on the first use, and if it can be reused almost indefinitely, this means I won't have to buy more chloride ever again. Piece of advice for everyone, this thing's quite friendly for toner and should be awesome for serigraphy (haven't tried) but it's very destructive on sharpie lines; try to make at least 3 layers of marker beforehand, because this tends to wash away the ink rather fast.

mkeen851 year 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 year 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?

If you do go down that road (attempting to concentrate the Peroxide) be *very* careful as it will become extremely caustic (chemical burns for you) and once past 80-90% concentration, it becomes explosive. I made a mess in a college chem lab by neglecting to watch some hydrogen peroxide I was boiling down. Thankfully, nobody was hurt.

The Real Elliot (author)  mkeen8512 months 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.

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