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.)

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moeburn thefeeb9 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.
ew00549 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 ziggalo9 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.
moeburn10 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!
pfolwarski1 year 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?
drdread pfolwarski11 months ago
Sounds like you have hard water: calcium carbonate in your water. Try rinsing the board in distilled water instead.
The Real Elliot (author)  pfolwarski1 year 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.

drdread11 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.
gphein11 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.
awrrwa11 months ago
Can I store the solution in HDPE/LDPE/PP plastic bottle?
The Real Elliot (author)  awrrwa11 months ago
Absolutely. (Maybe.)

I'm not sure about LDPE, but normal soda bottles work just fine. I've used a ~1L Gatorade bottle for years. They have a nice seal in the cap, and I've never had it leak.

rafari1 year ago
thank you for the info!
vsams141 year ago
I'm interested in getting into pcb etching. Will this etchant work with a sharpie resist? In that last set of pictures, it looks like the design was drawn on with a sharpie but it's hard to know for sure. I want to be able to use my reprap 3d printer as a plotter with the sharpie and then use this solution, as it's a lot cheaper and safer than ferric chloride. Thanks!
bruce50001 year ago
hello off topic question / i live were i can not find ferric ore a hazmat / so im a hobbyist looking to darken carbon steel possibly blacken will these etchant you posted will it darken carbon steel like ferric? thank,s good information these one
baligena1 year ago
My enchant is light green but its not etching as quick as the first time I created it, 5 days ago. Why?
The Real Elliot (author)  baligena1 year ago
Yeah. It will slow down initially. (If anything, the peroxide-acid etchant is a little bit too strong.) The first few runs with a new batch will go in like 2-5 minutes. Later, it should take more like 10-15 min.

Make sure that you're constantly agitating the solution so that fresh etchant is always exposed to the copper, and be patient. On the other hand, if it's taking longer than 15 minutes, something's wrong.

Keep the solution sealed when not in use -- strong hydrochloric solutions like this tend to fume, making the solution weaker and corroding all metal in the surroundings.

If it's green, and not etching well, add a little acid. If brown, add a tiny bit of peroxide. That's all I've ever needed to do...

Good luck! And if you figure out what's going on, post back?
baligena1 year ago
How do I know the cupric chloride has been regenerated?
panic mode1 year ago
i've been using ferric chloride for years and it works for me. the thing i like the best is that it so low maintenance: pour it into plastic container, toss in the pcb, remove pcb when done, pour etchant back into it's bottle (including any sediment), done.
downside - it is not fast (etching time 10-20min depending on temperature and use) and it is not clear so one normally takes PCB out for inspection.
the good side - cheap, easy to get, lasts for years and hundreds of PCBs, no maintenance (no mixing, measuring, shaking, bubbling or whatever). when you think you had it for too long, drop it off at a recycling place and buy new bottle.
etching time can be reduced by using air bubbler or agitator and warming up the etchant before use. another thing i am doing more often is to just let someone else manufacture my PCBs. then you get through hole plating, solder mask and silkscreen...
The Real Elliot (author)  panic mode1 year ago
Ferric's a great, traditional etchant. If it works for you, and you don't like to try new things, then by all means carry on. My experience with Ferric is that once it's starting to form black precipitate, it's running so slowly that it's time to get rid of it. So like a bottle of Ferric from RS is good for 20-30 small boards over a year for me. So yeah, it's just fine.

(I'm curious how you get your Ferric solution to last for "years" and "hundreds of PCBs".)

In contrast, I've used the same batch of this stuff that I made for this Instructable up until I left the US in 2011. So say from 2007 to 2011. Probably not "hundreds" of boards, maybe like 80-100. And as far as I know, they're still using my batch at my old hackerspace.

Industry switched from Ferric to more-easily renewable etchants in the late 1990s and early 2000s for environmental and cost reasons. I see no reason for the hobbiest not to do the same.

You are right about precipitate, once it develops things do get slower. Many things affect the etching time or how long the acid lasts. For example I tend to leave large copper areas (as large as possible, remove only what is needed) rather than etch them away. With few tricks i was still getting great results (clean edges, no pitted surface). Etching time using old acid may not be breaking records. but can be reduced for example by using wider container (so the level is low and area is large) and lamp to warm it up, using slow agitator (sloshing acid over the board). I don't have exact count of the boards I made but there was many (well over 200). I never bothered to "rejuvenate" it. Btw. just few weeks ago I just replaced it for new one. I expect it last even longer since I do less and less prototyping / debugging, and usually just order the boards from the PCB shops. In the last two years or so, I also used mill to to make some of the prototype PCBs. Milling is ok but can be pain to find shorts (sometimes fine burr remains attached to one of edges, if the other end reaches other track we have a problem). it is important to check the board before soldering or trouble could be under the soldered component.
Does anyone know if this etchant will work on bronze and nickel silver?? Both are copper alloys, but I don't know what the other components will do when reacting to the etchant...
vace1171 year ago
I just tried this method with a 50/50 mixture of the acid and peroxide. I was using a pre-coated photoresist PCB.

For some reason this process did not work for me. Even after 20 minutes, not the board was still looking pinkish, b/c not all the copper has been removed yet. The photo resist layer started dissolving on minute 10 of the etching, so I could not use this method at all. Here is the end result:

Does anyone know a possible reason for why this didn't work? Is the photoresist coming off too easily? Is the copper being removed much slower than it should be?
The Real Elliot (author)  vace1171 year ago
With the photoresist stuff (that I've never used), aren't you supposed to treat that in some way first before etching? And did you expose it enough? Those pinholes look suspicious to me.

Did you use double-sided board? It looks like the top actually etched clean, but there's still some copper left on the back side. It's a lot easier on the etchant, and a lot quicker, if you mask off the back side of a double-sided board with tape or paint or anything, rather than etch it away. *And* then if you hook it up to your ground, you get a nice ground plane for free.
The board was exposed to light for 8 minutes, and developed in a Positive Developer solution for 5 minutes. Before etching the mask looked really good and sharp. The copper areas looked cleaned and fully exposed. The pinholes are there b/c the board was in the etching solution for 20 minutes already (which is probably way too long), and yet the copper in the exposed areas of the board was still not gone. I really have no idea why that would be, considering that people are reporting etching time of less than 5 minutes...

It is a double-sided board, with tracks on both sides.
The Real Elliot (author)  vace1171 year ago
Darn. And yeah, I agree about the pinholes probably being caused by the long bath time.

Etching time can vary a lot depending on the thickness of the copper on the board, of course, but 20 minutes for fresh etchant mix seems very long to me as well. That's why I was wondering if you somehow the positive developer stage didn't go right or something? Maybe it the resist didn't get fully removed? (Like I said, I have _no_ experience with that stuff, I've always been an iron-on or sharpie kind of guy.) Can you test this with some clean copper? Maybe remove the photo-resist film with sandpaper or use un-treated board to be sure?

And here's all the rest I can think of: (shotgun-style, hoping something will hit)

Temperature? You're not doing this outside on a cold day, right?

Double-sided etches need 2x the solution as single-sided, and it's a lot harder to etch the downward-facing part of the board if it's resting on the bottom of a tupperware.

And then there's agitation. Even with a fresh solution, if you're not constantly swirling the solution around in the tray, it'll locally saturate with copper and slow down the reaction in the neighborhood of the traces. As you swirl it around, you'll see small dark clouds of dissolving copper coming off the traces that eventually dissappear into solution. Professional etching machines use pumps, bubblers, or spray-and-drip methods to keep fresh etchant in contact with the copper. We're stuck with emphatic swirling.

smallik1 year ago
Diluted H2O2 in 1:8 proportion and HCL in 1:3 proportion and It is taking barely 20 seconds to etch. It is an awesome etchant. Thanks a lot buddy.
smallik1 year ago
Hello Friend,

I was only able to arrange laboratory grade 30% h202 and some extra strong Muriatic acid used for toilet cleaning here in India. With 2:1 proportion, It barely took seconds to etch out the pcb, But I am having a hard time preserving it.

I kept it in a plastic bottle, but the mixture heated up by itself and exploded, costing a bucketful of sweat cleaning up the mess(excluding to the expenses of the chemicals). Can you please help me with proper guidelines on how to preserve it? It is creating a significant amount of fume and that's the reason for the explosion. but I am worried diluting the solution will affect the etching process. Please help.
The Real Elliot (author)  smallik1 year ago
Hmm... 30% H2O2 is *very* strong. I've only used 3%. It only takes a tiny bit of extra O2 to oxidize the copper in solution. If all you've got it 30%, dilute it down 1:10 first?

Second, I don't know how strong "extra strong" HCl is, but be aware that stuff used for cleaning toilets often has extra additives, and you'll have no idea what's going on chemically.

Anyway, it sounds like you've gone waaay too far in both possible directions. You're aiming for a 3M HCl solution with a tiny bit of excess oxygen. Dilute out your H2O2, and figure out how much of the diluted H2O2 solution to add to the acid, based on how strong the acid is.

Eg: I used 10M HCl, so to get it down to around 3M, I needed to dilute it 1/3, or one part in three, or 1:2 with a (weak) peroxide solution.
Hec0311 year ago
This stuff is wicked cool. I love this etchant. It's taking me about 20 minutes to get it to fully clear the copper from the board, but my features and traces only leave behind about 1% of the copper on the board, so given the large amount of copper that has to be dissolved it's moving very fast. Putting a board is the best way to prime the solution. Don't bother with any other method. It's a waste of time. Just get your board ready mix the Acid and Peroxide 1 to 1 and put the board in. The rest takes care of itself. I do agitate the solution periodically and will leave it out over night so it can oxygenate but other than that, this stuff is perfect for a DIY project.
mbeeby1 year ago
I tried finding these chemicals locally at Tesco (UK).

Hydrochloric Acid in Harpic Power Plus Original toilet cleaner. 9g HCL per 100g = 9% (Brick cleaner from builder merchants states 5-10% HCL)

Hydrogen Peroxide in Bausch & Lamb EasySept contact lens solution. States 5% Hydrogen Peroxide.

I finally got round to trying these as an etchant and got zero results. I added HCL (Harpic) to H20" (EasySept) then my copperclad. Even after 10 minutes there was no visible reaction, despite all info saying the first etch is super quick.

I'm not sure what to do from here, other than just buy some Ferric Chloride!
I'm using laboratory grade Hydrochloric Acid with hydrogen peroxide to etch my boards. But instead of the deep green colour I see in the image above, my solution is turning light blue(like copper sulphate) after etching. I'm 100% sure it's pure HCl. Anyone has any idea what's going on and why?
Found the answer. If anyone has the same problem, add more HCl. It should turn to the lovely green colour.
alpeperker1 year ago
Can this also be used to etch Aluminium?
HCl will react with Aluminum on its own. Be careful however, it leaves an aluminum chloride that is a darker gray color. This can be easily polished off. The reaction with aluminum releases explosive hydrogen gas and lots of heat. Do this etching process outside. Add the acid slowly to ensure that you do not ignite the gas. It is also very quick. You should be able to dissolve, lets say, a soda can in under 30 mins. Be careful. Msg me if you want help or an explanation. I have done a bit of chemistry with HCl.
The Real Elliot (author)  E_MAN1 year ago
A really fun way to etch Aluminium is to make up a lye solution (say 1tsp in a cup) and cover. Aluminum will oxidize in water, but it's sped up a whole bunch in the presence of hydroxide ions, provided by the lye. This reaction is "fun" in two different ways:

First off, it's thermally unstable -- the reaction generates heat and wants to run faster as it heats up. If you're doing this with more than a little bit of lye, you should have it in a cooling bath to limit the reaction speed and temperature,

Second, the end results are aluminum oxide (and your aluminum etched away), and hydrogen gas, probably with a bunch of lye/water vapor mixed in -- steam if it's hot enough. So you've got a potentially runaway exothermic reaction and a flammable (explosive if contained) gas, in a steam with caustic lye. Fun times.

But this is my favorite way of filling up hydrogen balloons at parties. To be quasi-safe, the procedure goes like this: Use small amounts of lye -- I'll put 1 tbs in 500 ml of water, and that's probably on the high end. Keep the solution cool -- have the lye + aluminum reaction going on in something heat-proof, and have it submerged in another bucket with a lot of water to suck the excess heat away and keep the reaction under control.

So yeah. Long story short: if you want to etch aluminum, lye in water is great. Just keep the lye in small amounts, don't ignite the resulting hydrogen unless you want to, and keep it in a water bath with ice on hand if it gets crazy to keep the temperature and reaction speed under control.

In the end, pull the aluminum out with tongs or something and rinse it off. Dilute the lye/water/aluminum oxide mixture with a lot of water and toss it down the drain.

raypsi1 year ago
hey OT:
Ferric Chloride should be cheap it's the waste product from cleaning rust off of steel. They use HCl to do it.
I'd like to find out how to reclaim all that copper I will be etching away with HCl and H2O2

gr8 blog BTW
dumle291 year ago
would using 10% peroxide have any noticeable effect on the ratios?
Also, with a 2 peroxide to 1 MA (30%), it keeps produceing gas. (on the second day) So I have to leave the solution outside, with the cap half on.

Other than that, I must say it's a great solution. I 5 by 5 cm board in 2-3 minutes, in -1°C So yeah. I just hope I wont run in to any issues with reuseing it like others have had.
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