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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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bezo888 months ago

nice work. I tried this design and it did not work. I used 1 part vinegar and 1part hydrogen peroxide and salt. I was testing to see if it works and I left a small pcb and a few pieces of copper wire in the solution overnight and it did not dissolve , it just got rusty and nothing happened to the pcb.

The Real Elliot (author)  bezo887 months ago

I've heard the vinegar suggestion a lot. I'm not a fan, and I don't understand the point.

For the chemical reactions involved, you really just want an acid -- a source of hydrogen ions. HCl is about as simple an acid as you can hope for, in terms of availability & purity & strength. It's un-dangerous enough that it's the acid of choice for regulating swimming pool pH. Good enough for me.

With vinegar you don't really know what you've got, chemically. All sorts of flavor compounds and colors? Residual sugars? Yuck. No thanks, give me cheap and pure hydrochloric any day.

freedomdivine7 months ago

HI I use the Ferric for etching metal jewelry. I buy it at Radio Shack its pretty pricey! Could you please tell me if this would work just the same on my metal jewelry? Thank you so much.

The Real Elliot (author)  freedomdivine7 months ago

No idea -- depends on the metal.

But acid + peroxide are cheap. Why not try it out and report back? This is one of those frequently-asked questions: a bunch of people will be interested to know how your experiments go!

ProMaker8 months ago

Not sure why others are having trouble. I just tried this technique for the first time and it worked perfectly. 3% H2O2 from Walmart (32oz bottle $.99) Muriatic Acid/31.4% HCL from Lowes (1gal. $7.29). Mixed it in the garage although fuming was so little probably could have done it in the basement with no issues. Etched in a small glass jar at room temp. and applied agitation throughout. 2"x3" double sided 1oz board etched in about 4 mins. Solution started clear and ended a light emerald green.

PCB.jpg
bobh92868 months ago

I started using this method today. I had a board I wanted to etch so I followed these instructions to the T. The board I am making is 2" x 6" only has a circuit on one side but the board I got is plated on both. My first run at this was an ugly failure. With a brand new batch of the etchant it took over an hour to remove all the copper on the side with the circuit and this resulted in a very pitted circuit that is unusable. No big deal as always expect a first time failure :)

On my second run it still took a good 30 to 45 minutes to etch the circuit side of the board and there was still at least a third of the copper on the other side. At this point I pulled the board and just sanded the remainder of the plating off. The board looks nice and is ready to go.

My concern is the length of time this appears to be taking. In earlier posts and reply's I see comments that if it takes longer than 15 minutes or so to etch a board something else is wrong. What could this be?

1st Board.jpg2nd Board.jpg
pilgrimsc10 months ago
hello can you tell me if this would be good for etching carbon steel?
Thanks,
Stephen
I WENT TO BUY HYDROCHLORIC ACID FOR ETCHING BUT SHOPKEEPER IS ASKING ME " BRING WHICH FORMULA OF CHEMICAL"

PLEASE GUIDE ME WHAT CHEMICAL FORMULA I NEED TO ETCH ON STONE ....SUCH AS GRANITE, MARBLE, LIME STONE, ITALIAN MARBLE, SLATE OR SAND STONE ETC.,.
The shopkeeper is being a jerk. Ask him for "muriatic acid" or "brick cleaner" or "hydrochloric acid for cleaning bricks". The concentration strength for cleaning bricks is the one I used for etching PCBs.

However, ANY concentration will work! Some will just take longer than others!
thefeeb moeburn11 months ago
I wonder if this is the reason mine is taking so godawful long, then. I tried this last night and after an hour of soaking, I barely had an image. I bought a gallon of muriatic acid from Ace Hardware. Even with the basement window and doors open, it got thick with that acid fog. Could it be the brand? Seems the pros are outweighed by the cons in my case... frustrating.
moeburn thefeeb11 months ago
You also have to watch the temperature. This is a chemical reaction, and chemical reactions are highly affected by heat; in this case, if it is below 20°c, it will take days. If it is 20-25°c, it will take a few hours, and if it is 30-40°, it can take just a couple hours. So if its a little chilly where you live, and your windows are blowing cold air over your acid, then you need to place the acid bowl/container in a bowl of hot tap water to speed it up.
thefeeb moeburn11 months ago
Thanks for the quick response! I was using the Hydrogen Peroxide, but I wasn't heating it... which I was unsure about. I have kept Ferric Chloride heated, as all tutorials outline, but I hadn't seen anything about temperature in this tutorial (sorry if I missed it!), so you've given me more to troubleshoot, thanks!
Also- I'm pretty sure I've read that getting the transfer, which I'm also struggling with, is easier if you turn up the resolution/blacken the image to get more toner, correct? I bought a laminator specifically for transfers, but it's been pretty spotty. I just read one tutorial that underscores the importance of pre-heating the copper, as ironing it directly will cause condensation, contributing to spottiness/areas of poor transfer. I'm surprised at how much of an art this seemingly simple process is turning into! :)Big thanks again!!
moeburn thefeeb11 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.
ew005411 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 ziggalo11 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.
moeburn1 year 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?
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.


drdread1 year 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.
gphein1 year 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.
awrrwa1 year ago
Can I store the solution in HDPE/LDPE/PP plastic bottle?
The Real Elliot (author)  awrrwa1 year 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.

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