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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.

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

(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.

Hi I am new to etching. Is the ink a special ink? Would like to know so that I buy from this ink.<br>Thanks
<p>Everyone must be using 1/2 Oz boards because I mixed up a batch as stated, kept it heated to 74 deg F, and it took 4.5 HOURS to finish a 1&quot; x 6&quot; 3 Oz board! By finish it was a pretty green, and the next board took 6+ HOURS even with agitation and sponge wiping! Either I can't read or you all use micro thin copper. I did try a new batch with 1/2 Oz copper, and a 1&quot; x 1&quot; piece still took a half hour with constant agitation. Doesn't stain so that is nice, but I could have CARVED the boards with a jacknife in that time!</p>
<p>Would this work with 9% H2O2 and 18% HCl?</p>
Yup. I'd go one-to-one with those concentrations, though. Should be ballpark right.<br><br>I
1 finger is a single two is a double ! Ok my cup is 300 ml !<br>How much do I use? 25ml is a finger 50 is two .<br>Six fingers is a Cup.<br>Wagons do not travel in uk only on Television a long time ago.<br>Nice is Nice but time has passed and that is the problem.
I am now confused. after reading so many comments I just want to do a PCB for a small electronic circuit. <br>what my board is two inches by one inch . seven components four wires it is a light activated
this phone is stopping me from asking the question what is the amounts in Mililtres cups are not standard in UK
<p>As Sugarim say's it's about proportions.</p><p>IIRC, cups are used in American cookery and their use arouse during the 1930s recession (the method may hark back to the wagon-train times?), since one can make a recipe without the need of scales. I think that strictly, cups are based on fluid ozs, but in this context, it doesn't mater, you could use watering cans, shot glasses, clogs, or any container! One simply changes the cup size, or multiply the number of cups to scale up or down. Very smart!</p>
<p>Hi, laaaate reply, but here goes... you just need to get the proportions correct... As long as it's 1 part acid to 2 part peroxide, any amount will work. </p>
<p>Having been a long-term user of FeCl, I stopped making PCBs due to the issue of disposing of the waste. I will definitely use this method and start making boards again - Thank you! A great little article. Really useful, easy to read.</p><p>The secret to a good etch is a good mask, timing (watching) and a good quality copper clad board. I found fiberglass boards always gave better results than paxolin etc. Agitation improves speed and evenness of the etch, bubble etching is very good and in this case would help maintain the strength of the etchent.<br>As to the quality of the resist mask: Photo etching in my experience is best, but again the quality of the original photo mask is important. I know that there are many methods. The best quick method for 'neatness' and the ability to print from CAD that I found, was inkjet onto mat acetate, ink side presented to the board to ensure less fuzzy edges - the acetate will hold the pattern away from the board and allow light to erode the edges if you have ink uppermost; after that comes laser on laser safe acetate (multiple copies stacked). But the best for quality is the 'transfers and tape' method onto acetate (or directly onto copper), since they are very opaque and have good edges, they produce a sharp edge. Again, photo mask against the board before exposing if using acetate.</p><p>CNC printing with an XY plotter, using etch resist/or light resist pen is best method for speed/quality and the ability to draw from CAD. Photo resists are usually made 2x size, but of course require specialist projectors.</p><p>One last thing to help you make easy-to-use PCBs - Tin Plating crystals! Another nasty chemical, but a well cleaned board that has been tinned is a dream to solder! It comes as a powder, just add water! It lasts and lasts.</p><p>However.... Especially for multiple boards, you can't beat a professionally produced board complete with solder resist mask and ink layer. You may be surprised how cheap this can be. All you need to do is send them your PCB file. Maybe not as satisfying as creating your own masterpiece though.</p><p>May I make one comment about the article? - over use of the &quot;American Collective Noun&quot;! It's a pet project of mine, please use 'bunch' responsibly! Bunch of flowers/wires - Cool! Bunch of flour/wire/people/liquids/solids/cars/snow/etc. - not so cool ;) :p</p>
<p>Will this work to etch aluminium? would i have to put some copper in it first?</p>
<p>So will this work on knives and swords made out of damascus steel?</p>
<p>I made this today it works great. Have found that transparency film works great for toner transfer. If you use transparency film after you heat it for a few min let it cool all the way off then you can just peal the film off. I got in a rush the first time and pulled a few of the traces off. Lesson learned make sure that the pcb is cool to the touch before removing the film.</p>
<p>nice work! How do you dispose the solution finally?</p>
<p>This is very useful and I&quot;m going to try it for etching copper jewellery. What resist should I use? Will a Sharpie work?</p>
Sharpie is an OK resist, but not a great one. If you're going to try to etch deep, like you might for jewelery, something stronger might be a better choice.<br><br>Fingernail polish? What other thick / lacquery paints do you have on hand? Electrician's tape? <br><br>Or just experiment. :) <br><br>Some people bake Sharpie ink lightly to make sure it's totally dry beforehand, and that's supposed to help. I just wait 5-10 min or so.<br><br>Let us know how it goes?
<p>This is a great tutorial, I like that you explained the chemistry and gave a recap! I can't wait to try it! I'll be using it for sculpture similar to jewelry applications. </p>
<p>This may prove helpful. </p><p>http://www.chemcut.net/wp-content/uploads/2015/03/Chemcut_Bulletin_8_Cupri_Chloride_Proces_-Parameters.pdf</p>
<p>I did this, and the results were amazing! Etched a test pattern in 2 minutes. The only difference was that I used 9% Hydrogen peroxide. The starter solution etches very fast and heats up a little bit, so I had to put the container with HCL+H2O2 into another container with cold water just to keep things cool :D </p><p>P.S. The distance between the black marks in the second pic is 1 mm.</p>
<p>wow. Neat</p>
<p>Thank you very much!!!!!!!!!!!!!!!!!!!!!</p>
<p>I've got a chromed sink tube and want to get at the copper underneath before I start etching. Will this solution take the chrome off for me before I add my vinyl resist and do my etching?</p>
AFAIK, you want to be really careful with chrome. Fumes, toxicity, etc. And this etchant is aimed at copper -- whatever chrome you get off, you'll expose the copper beneath and it will pit like crazy.<br><br>I'd suggest another solution, but I don't know what. Sorry.
<p>Works great! Will be using it at TangibleTec.</p><p>www.tangibletec.com</p>
What etchant do u use sir ?? I used hcl + h2o2 but etching is not good
I used the HCl + H2O2 formula exactly as described in this instructable. I was sure to use the Muriatic acid that is 31.45% HCl and Hydrogen peroxide that 3%.<br><br>I also used Press N' Peel as my resist, as the kind of resist used can make a big difference in the outcome of the etch.
<p>I tried this etchent. I found it did not etch as fast as FeCl3, but worse, it etched my resist. So I will need to investigate different resist layers.</p>
Is this method just for making PCB or could one use this mixture for etching copper jewelry?
<p>It works great for copper jewelry too!</p>
<p>Hi Elliot, thanks for an awesome tutorial! I had a great time playing mad scientist in the kitchen (place with the best ventilation in my apartment). The solution slowed down drastically over the third try, but I was etching brass, so that could have been the reason. Adding peroxide and doing some sideways agitation did help... however, what helped even more was sprinkling a bit of salt over the pieces. It immediately removes the brownish coating on the surface, allowing the acid to eat at the metal again. </p><p>Also, over here, in India, for Indian readers, the place where you can find the acid is... and I was appalled... at your local grocery store, usually on the same shelf as club soda or cooking oil or other things that go into your mouth. It's called toilet cleaning acid... get the bottle that says &quot;pure acid&quot;. Most of the times, the bottles will have no indication of the percentage, or even what type of acid it really is, which is really not a good thing... but I digress. </p><p>Anyway, here's a crappy pic. I forgot to mirror the text (Darwin's Origin of Species) before transferring, but I sort of still like it. </p>
<p>Also, once done with etching, scrub the piece with a bit of baking soda to neutralize any further reactions. This is especially important if you're making jewelry.</p>
<p>&gt; Please, what is wrong here?</p><p>You haven't given me much to go on, but here goes:</p><p>1) How did you agitate the board while it was etching?</p><p>2) How did you clean the board before etching?</p><p>3) Does it have anything (oil, plastic film, ???) on it?</p><p>4) What strength is the acid exactly?</p><p>5) At what temperature?</p><p>6) How thick is the copper layer? (Although really &quot;hours&quot; is too long for anything that's remotely reasonable.)</p>
<p>I made up the recommended solution 1 pt acid to 2 parts peroxide. I tried to etch a small single sided board 53mm x 73mm it took hours to etch.</p><p>I was very surprised when you mention that a small board in the instructable took only a couple of minutes.</p><p>Please, what is wrong here?</p>
<p>Thanks for this. Off topic but your storage bottle reminded me of this... http://drunkard.com/images/scottie-hooched.jpg</p>
<p>I live in a place where it's impossible to get acids from a drug store. I can only find acids used in detergents or other cleansing material and so forth. So im wondering if there is any product at a normal market that could be used instead of hydrogen peroxide and hydrochloric acid?</p>
Search for vinegar/peroxide/table salt mix. It's about 100ml/100ml/10ml
Chemistry supply house? Hardware store? Or beauty supply store for the peroxide?<br><br>Hydrochloric acid is pretty common. It's used to balance the acidity of pools and to clean concrete. I don't know where you live, but I bet you'll find some.<br><br>The peroxide I used was really weak -- the kind that people often use as a mouthwash. But stronger peroxide mixtures are commonly used to bleach hair, for instance. <br><br>I'd avoid anything with additional additives. You just don't know what will happen. <br><br>(For instance: some people have substituted mostly-NaOH drain cleaners for NaOH, but then it's also got some aluminum flakes in it which make the reaction exothermic, and turn something potentially simple into a safety hazard.)<br><br>Look around more and get the pure stuff. <br>
<p>So I made a batch but am curious about my storage container. Its a glass jar with a glass lid an rubber seal that is closed with the clamp. Hopefully you know what I'm talking about. Will this be okay? I just don't want gasses to expand an compromise anything/break the jar. </p>
<p>So .. pool acid and mouthwash.<br>I read in the Ferric Chloride FAQ, that I need Washing soda &gt;&gt; is it enough of the materials you mentioned ?<br>And, how to test it with a paper ? normal paper and what's the sign that the mix is safe to pour?<br>Thank you,</p>
<p>Don't go substituting stuff! (Unless you really know what you're doing.) Hydrogen peroxide _is_ used by some folks as mouthwash, but that doesn't mean any other mouthwash will work.</p><p>Hmmm... washing soda. I'm guessing that's to neutralize the acid for disposal? If so, part of the point of this etchant is that you will not need to get rid of any of it for a reasonably long period of time (years? a decade?) because it's renewable. So you shouldn't need that.</p><p>And anyway, I'm not sure that knocking down the acid makes it safe to &quot;pour&quot;. You'll end up with a different copper compound, but it's the copper that's bad for water sources. </p><p>I think when people dispose of stuff this way, they neutralize it first and then let it dry out, and then take it somewhere where you can dispose of hazardous chemicals. But again, we're trying to avoid doing that in the first place.</p>
<p>If you have to be careful with the stainless steel sink, does this mean it well etch stainless steel like it does copper.</p>
<p>Thanks works great!!</p><p>I've made a mixture of: 1 cup H2O2 36%, 1 cup HCl 23%<br>and made a simple test pcb. I did nothing to start the process first try was slow but second try was much faster. Because there was already some copper in the mixture.<br>I was able to make a trace of 12mill =&gt; 0.3mm, my printer was the bottle neck.</p>
<p>made this etchant, it worked very quickly clean, no fumes excellent.</p>
<p>Thank you for your project, looks like a good system to me. Do you have a recommendation of what types of plastic I could use as containers for this project? I intend to use it to electroplate graphite painted 3d printed plastics such as PLA/ABS/HIPS/Nylon/TPE, can you think of any issues i might face with any those plastics?</p>
<p>Just one quick question, does the container need to be actively open when using the solution? The reason why I ask is I try to minimize any fumes I can (even when soldering). Like using a small glass pan with modified lid that locks everything air tight as it etches. I don't know if its like a fume pressure build up like smoke would cause, or more extreme like a 6th grade volcano kind of pressure. Thank you.</p>
<p>No problem closing it up as it etches. I always do that so that it doesn't spill while I'm agitating. (I etch in tupperware and slosh it around vigorously.)</p><p>Ziplock bags also make a nice etching tank. Board in, fill with etchant, close, and then lay it all flat in some kind of dish or tupperware in case you accidently break or open the bag. You can agitate the board by smooshing the bag (carefully) like a waterbed, and it's really easy to tell when it's done because you can press the bag up against the board like a window.</p><p>The other advantage of the tupperware + ziplock bag is that you can easily fill the tupper with warm water which will keep the etchant warm and speed up the reaction. </p><p>When you're done, snip off a corner from the bag and you've got a funnel to pour it back into your container.</p><p>Man, I should make an Instructable on that... </p>
For etching Cu try H3Cit + H2O2 with NaCl.
I think I used too much. All I did was create fumes are irriate my breathing. I'm going to toss the batch, air out my house and try again actually using you measurements. I've gotten too used to just winging it on the amounts of things I use.
<p>Too much what? </p><p>Just aim to get the acid down around 3M or 10%. So if you start with 10M / 34% acid, you need to add two parts water (or weak peroxide in our case). </p><p>Mixing a strong acid and water like this makes heat. If you toss water into the acid, you'll get hot acid and that might fume. Don't do that.</p><p>Measure out two cups of peroxide, pour into that one cup acid. Easy enough, but you need to measure and get the order right. </p><p>Open a window anyway, and if you're getting excessive / noticeable fumes rethink what you're doing.</p><p>And if you want to ditch a batch of the etchant before use (no copper dissolved in it yet), you can toss some baking soda into it to neutralize the acid and pour it down the drain with a lot of running water.</p>
can i use sulfuric acid 30% instead of muriatic acid?

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