Introduction: 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.
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.
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839 Comments
6 weeks ago
CAUTION: Sodium Hydroxide / Caustic Soda / Lye "Draino" can cause anaphylactic shock! I have been there and I don't look good blue! The instructions for the "simple titration procedure" uses Sodium Hydroxide - Caustic Soda / Lye is contained in Draino. I caught a couple breaths of it during a plumbing repair and hit the ground. My husband had to haul me out of the house, I came too, laying on the ground coughing my lungs out. Do not attempt this procedure without breathing apparatus!
Reply 6 weeks ago
Yeah. _Absolutely_ don't inhale lye dust. That sounds horrible. It burns your skin badly enough that I can't imagine what it would do in your lungs.
By the normal spoonful, it doesn't reach out and grab you, but I'd imagine that if you shook up a container, or otherwise pulverised it, you could get enough dust airborne to make for a bad time. Taking precaution against this is a good idea.
Anyway, if you have any concerns, just skip the titration step and you don't need lye in the first place. The mixture is not all that sensitive to the exact acid concentration anyway. I just had some on hand, and thought it'd be some fun chemistry. :)
(And note that a bunch of the drain openers have other stuff added in to make the lye act more violently against the crud in your drains -- mostly aluminum salts, so it gives off heat and hydrogen gas when it gets wet. I don't know if aluminum hydroxide messes up the titration or not. I'd use the pure stuff.)
2 years ago
The idea of replacing iron 3 chloride is good. But I've been making it a lot cheaper and easier for many years!
Add a little hydrochloric acid to the used 3-iron chloride solution in your etching vessel. Until the brown bottom sludge dissolves completely.
The color is now dark brown.
Pour the solution into a large plastic bottle. Cap the bottle and set it on its side so that the solution has a large surface area.
The oxygen in the air reacts with the solution and the color changes to light green. Open the bottle 3 or 4 times a day to let in fresh air with oxygen.
Depending on the surface and the temperature, you can etch again after 1-2 days.
This is much more effective than an air pump.
You never need to buy Eisen 3 Clorid again and never dispose of used solution! Just put it back in the bottle after etching and ventilate. If brown sludge forms in the bottle, add a little hydrochloric acid. One liter of hydrochloric acid 30% rich for 10 - 20 years!
Reply 6 months ago
Hello I'm a little confused are you saying that you can regenerate fecl3 solution used to etch steel by adding hcl in the same way cucl2 is being regenerated in the instructable
Reply 6 months ago
1. - No - FECL3 cannot be regenerated.
2.- FECL 3 does not etch copper!
Step 1: Cu + 2 FECL 3 ⟶ CUCL 2 + 2 FECL 2.
Step 2: CUCL 2 + Cu ⟶ 2 * cucl
That is the real etching!
Regeneration: Cucl + HCL + oxygen ⟶ CUCL 2
Reply 6 months ago
ah so initially i was intrested in etching steel for making pin badges but being abel to etch copper is still usefulll to me abut this is verry informative thankyou and am i correct in thinking that you can safely dispose of fecl3 by the following reaction
fecl3+naco3--> feco3 + nacl
feco3+ heat--> feo +co2
and would this leave you with only waste products that were safe for home disposal?
also would cucl3 etch steel?
zbyway thankyou foryour reply :-)
7 months ago
Warum so kompliziert machen???
Nehmen Sie einfach verbrauchtes Eisenchlorit - fügen Sie ein paar Tropfen Salzsäure hinzu. So lange, bis sich der braune Belag aufgelöst hat – fertig ist die Kupferchloridlösung.
Vergiss Peroxid! Das kostet unnützes Geld!
Die Lösung einfach in einer flachen Schale. Eine große Oberfläche ist sehr wichtig. Diese verwende ich seit vielen Jahren erfolgreich.
Beim braunen Belag bilden sich wieder einige Tropfen Salzsäure.
Ich arbeite seit vielen Jahren mit 1 Liter Säure und habe nie wieder Geld für die Ätzung bezahlt!
9 months ago
Great instructable! I have etched numerous boards using this, but I'm running into a big problem.
After leaving the solution set idle for about a week, it etches at a very, VERY slow pace, despite putting in chunks of copper boards in and stirring like mad just to agitate the solution after leaving it set. I have noticed that the bubbles in the initial mixture have disappeared too and it now looks like flat soda, if you understand what I mean.
I have it stored in a plastic container that I think is airtight.
My question is how do I regenerate it, or do you even regenerate its potency? The solution works well, but only if you constantly use it, I suppose.
Reply 7 months ago
I think I solved the problem - you were right The Real Elliot, it was a lack of oxygen! To solve it you either need to stir it like crazy so it regenerates oxygen or introduce oxygen to the system. I wonder if an aquarium pump would help with this???
Reply 9 months ago
Might be that it doesn't have enough oxygen? Toss in a capful of peroxide and see if that helps? Besides slowing down, an indication of needing more oxygen is that it gets dark or even brownish. A pretty emerald color is what you're aiming for.
If that doesn't do it for you, and especially if you've dissolved a bunch of copper already, it could be that the solution isn't acidic enough. In that case, a capful or two of additional acid should do it. You can calibrate it with lye, as mentioned, but in my experience neither excess oxygen nor acid hurt all that much.
I've gone periods of months without using mine, and it's just fine.
7 months ago on Introduction
I may have some Printplates ,but not made with acids . It glues at the walls of the room and is not for amateurs hands . It's dangerous for mens skin and eyes . Why exists no law for prohibiting this poison ? If you use it in your room , you must clean the walls .
10 months ago
May I ask what software you use to design single sided PCB's?
10 months ago on Step 5
Instead of 3% medical peroxide use chemical, food or cosmetology grades which are available at much higher purity levels (30% and up) and hence less unwanted water.
2 years ago
I've just tried this making 100ml of the etchant but I must have something wrong. I used 2 parts 6% Hydrogen Peroxide and 1 part 320g/l Hydrochloric Acid. The mix instantly went a dark orange/red colour but the solution shown here is clear until it starts etching some copper. I put two copper strips in it, one connect to +ve of a 12v battery and the other connected to the -ve. The solution changed to a dark yellow/green as it etched the copper. Can anyone suggest why I have this initial colour?
I tried etching some stainless steel with the battery connected to the work piece and a cotton bud soaked in the solution and it worked.
Reply 11 months ago
Hi, late answer but I am in Australia as well and had the same problm with a specific brand of HCl used for plumbing and sold in major harware stores. Turns out it is NOT pure HCl but some solution of FeCl that turns orange when H2O2 is added. I contacted the company at Eagle Farm but got no response to my questions about the product.
I purchased Bondall brand HCl and have had no issues since.
Reply 1 year ago
What was your container?
Reply 2 years ago
You did something wrong.
Either it was not pure hydrogen peroxide or there was a reaction with the etching vessel.
Give it a try with used iron 3 chloride - see my comment!
In addition, you should not apply any voltage to the copper!
Just put it in the solution.
I haven't tried any other materials than copper.
2 years ago
Better and easier!
In 100 ml of pharmacy 3% hydrogen peroxide, 30 g of citric acid and 5 g of table salt are dissolved. This solution should be sufficient for etching 100 cm2 of copper with a thickness of 35 microns. The etching time is 10 minutes.
Reply 1 year ago
Where do you buy citric acid? Certainly not at the hardware store or the grocery store.
Reply 1 year ago
You will find it easily in any major grocery store in the US, Canada, and most of Europe. It is used in candy making and other things and isn't really dangerous. If you have ever had any candies that have a sour tart taste, that is just a 50/50 mix of white sugar and citric acid on the outside. Though safe for us, it is widely used in many other industries. I have used it for a couple of decades in my jewelry business as a constantly heated pickling agent for brass/copper components after heat farming and/or soldering before the pieces move on to their cleaning and electroplating stages. I believe the longest I was able to keep one batch going by refreshing and pass filtering was about 7 years, and it was a 10-gallon tank. You can buy it on amazon and eBay as well. Though eBay tends to sell it in food-grade, but without explaining its food uses. People who do not know that they can get it most anywhere will think it is harder to find and not investigate the grossly overpricing of the listings.