PCB Etching Solution - Cupric Chloride




About: I'm an Engineer. I like hiking, flea markets, and electronics.


According to The Real Elliot's instructable titled Stop using Ferric Chloride etchant! (A better etching solution.), cupric chloride + hydrochloric acid is an excellent PCB (printed circuit board) etching solution. According to Adam Seychell's Etching with
Air Regenerated Acid Cupric Chloride
, more copper(II) ions enhance etching speed. The purpose of this instructable is to show how to prepare an etching solution with lots of copper(II) ions so that etching can proceed quickly starting with the first board etched.


A solution with copper(II) chloride will be made by electrochemically creating copper powder, oxidizing it into copper(II) oxide, reacting it with hydrochloric acid, and finally converting it into copper(II) chloride with hydrogen peroxide. This is a much faster way of making copper(II) oxide than letting copper metal corrode in hydrochloric acid.

Step 1: Cut & Soften Electrodes

1. Cut a square from scrap copper tubing, approximately 2.5" x 3.0" inches.
2. Unfold the square as best as possible, don't try to make it perfect yet.
3. Put the copper on a hot plate to oxidize and soften the copper.
4. When it turns black (oxidizes) turn the hot plate off and wait for the piece to cool.

Step 2: Pour Acid & Clean Copper

1. Pour about 11 oz. muriatic acid (25% hydrochloric acid) into a glass jar, its color should be clear.
2. Carefully place the cooled piece of oxizided copper into the jar, it will change the acid a yellow-green color.
3. Place the copper into a bowl of water to clean it, set the acid aside.

Step 3: Flatten, Cut, and Drill Copper

1. Since the copper is softer, flatten it with pliers.
2. Cut the copper into two electrodes, approximately 2.5" x 1" and 2.5" x 2".
3. Drill a hole into the top of each electrode.
4. Place leftover scraps aside.

Step 4: Select Electrolysis Source

Select either a resistor limited voltage source or a voltage limited current source for electrolysis. Below is an overview of both options:

1. Resistor Limited Voltage Source - Step 5:


This is a DC voltage source with a resistor in series to limit the current.

Pro: Simple, cheap, and easy to build.
Con: Lots of power loss. The resistor dissipates V*V/R watts electrodes have apprixmately 0.5 - 1.0 V drop.

2. Voltage Limited Current Source - Step 6:


This is a DC current source using switching techniques.

Pros: Higher efficiency. Preferred for electrochemistry.
Cons: Higher circuit cost and complexity.

Step 5: Resistor Limited Voltage Source

1. Get a suitable DC adapter greater than 1V 1A (ex. 12V).
2. Resistor Value = DC Voltage / Current Limit (ex. 12V / 0.5A = 24Ω).
3. Resistor Power = 2 * DC Voltage * Current Limit (ex. 2 * 12V * 0.5A = 12W).

Step 6: Voltage Limited Current Source

Here's my design for a switch-mode current source constructed out of general purpose parts. The most specialized part is the inductor, which is 560mH and saturates at 1.5A. It's variable from around 0.150 to 1.100 A. The large inductor value is chosen to minimize ripple. The switching frequency is around 100kHz. The link provides a schematic. All components were purchased on Mouser. The substrate (FR4 PCB) was purchased on E-bay. Soldering took a LONG time since traces had to be routed individually.

Step 7: Wiring the Electrodes

1. The smaller, corroding electrode goes through a red wire to the positive (+) terminal of the power source.
2. The larger, accumulating electrode goes through a white wire to the negative (-) terminal of the power source.
3. Immerse the electrodes into the muriatic acid used for cleaning as pictured.
4. Add hydrogen peroxide (3% pharmacy type) to the muriatic acid, turning it green.

Optional Steps:

5. Add scrap copper to the muriatic acid.
6. Block the jar top with a wad of dry paper towels to minimize acid release due to electrode bubbling.

Step 8: Copper Powder Formation

At regular intervals of 1 hour:

1. Clear off the accumulaled copper electrode by shaking it.
2. If the negative electrode corrodes too much, switch electrode polarities.

You can terminate the reaction at any time you want. I decided to run it for about 4-5 hours. Pictured are the electrodes during and after use.

Step 9: Separate & Wash

1. Pour the used electrolyte into a separate container (the drinking glass as pictured - DO NOT DRINK OR TELL WIFE).
2. Wash the remnants with water (the jar as pictured).
3. Add 1/2 tsp. of hydrogen peroxide to the used electrolyte, changing its color (do NOT stir with a metal spoon - use plastic).
4. Allow 30 minutes to settle.

Step 10: Oxidize Copper Powder & Scrap

1. Dispose of the water used to wash the copper powder & scrap mixture.
2. Place copper powder & scrap mixture onto the larger electrode plate.
3. Place electrodes & scrap onto the hot plate.
4. Oxidize the electrodes & pile with heat until blackening.
5. Allow everything to cool.

Step 11: Finalize Mixture

1.Recombine the electrolyte and oxidized copper, the solution will turn dark green-black.

In 15 minute increments:

1. Add 1/2 tsp. fulls of hydrogen peroxide (3% - general purpose type).
2. Stir the mixture with a plastic utensile (straw).

When the mixture is light green:

1. Filter it.
2. Store it.

In use, the mixture will become dark-black, recharge it by adding hydrogen peroxide.



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    23 Discussions


    6 years ago on Introduction

    I used some of the info on this intractable as well as some others. and had 99.9% success... HOWEVER... I did have a melt down too. I share this in hope that it may help you or someone who expects more from less.
    My tank and build.

    3 replies

    Reply 6 years ago on Introduction

    Thanks for the link. It may save some time if you're able to obtain the chemical compatibility table for a particular plastic. Most have them available. For example, try searching "HDPE hydrochloric acid chemical compatibility". It shows how well it stands up to hydrochloric acid (and others).

    Also, here's a nice document detailing how to test unknown plastics.


    Reply 1 year ago

    This is a useful link for chemical compatibility too: https://www.coleparmer.com/Chemical-Resistance


    Reply 6 years ago on Introduction

    Good stuff! thanks for the link. Im looking for all the fittings I need in either
    Polypropylene or PVDF/Kynar. whatever is cheapest and easy to get. I should be set!


    5 years ago on Introduction

    I don't understand all the extra steps here, this seems like a lot of work to save a day or two of waiting. All you have to do is put some HCl in a tank with some peroxide, add copper and bubble air through it with an aquarium pump until the copper is consumed and the solution turns a deep green (details on the chemistry can be found elsehwere). If you need etchant quickly, you can mix the HCl and peroxide and etch a board immediately. So what does electrolysis of copper followed by stove-top oxidation of the copper powder really save? Just get a setup with an aquarium bubbler, it's needed to regenerate the etchant anyway.

    2 replies

    Reply 2 years ago

    I agree with your thoughts on the extra steps here. However, the real gem of this instructable appears to be a simple recovery of metallic copper powder. In my case I was wondering about a simple fool proof way to recover copper from spent CuCl2. This seems to me to fit the bill nicely. Spent solution? pull excess copper by this method, set powder aside and smelt. Just my $.02


    Reply 2 years ago

    There's actually a sub-field of mining called "electrowinning" which focuses on extraction of metals from solutions via electrolysis. They typically use CuSO4 instead of HCl. You may also want to look into copper plating with CuCl2, there may be a way to add brighteners (not sure what exactly) that would allow the copper to form as a solid mass on the electrodes rather than as loosely adhered powder. There's actually a great book by Lowenheim from the 1978 called "Electroplating" which is voluminous about the process in general.


    3 years ago on Introduction

    For what it's worth, both Firefox and Chrome flag your link to Seychell's paper as a malware site. There appears to be a safe alternative here --



    5 years ago on Step 9

    "DO NOT DRINK OR TELL WIFE" - Best instruction on any instructable I have ever seen!


    5 years ago on Introduction

    What if...
    i can get my hands on really cheap and relatively pure (98%) copper oxide?
    Could i just go the shortcut and mix the CuO (Copper(II) Oxide) with the HCl (muriatic Acid) and add a bit of H2O2 (or use a bubbler to aeriate it)?

    2 replies

    Reply 5 years ago on Introduction

    That would probably work very well. I think they use a similar technique using sulfuric acid to extract copper ore in some mines.


    6 years ago on Introduction

    thank you for your process, ill definitely try it :)

    as a constant current source, I think we could use the el cheapo current limiting LED drivers. a 900mA 10V would be ok I think :)


    6 years ago on Introduction

    I just finished making a batch of this tonight. It's a brilliant, clear green. It eats aluminum foil like candy, I've never seen metal eaten so fast. I did a test etch on copper and it took a little longer than I'd hoped, but etch time isn't a huge problem I suppose, as long as I can do it reliably. Any suggestions for minimizing etch times?

    1 reply

    Reply 6 years ago on Introduction

    I haven't tested the hypothesis out, but supposedly, using an aquarium heater to warm the solution helps to increase its speed. Adam Seychell's link from the intro / purpose section provides some graphs of etch speed vs. temperature.


    6 years ago on Introduction

    Is the current limiting in step 4 just to protect the power supply, or is there some other reason to limit the current to a half an amp?

    The NTE resistors in that step remind me of lots of fun trips to the Electronics Barn, which was downstairs from Nu Tone Electronics in Bloomfield. Whatever I used to bring up to the counter the old man used to always tell me, give me five dollars ... I figured he wanted lunch money or something. Good times. I miss that place, I hear it is gone now.

    3 replies

    Reply 6 years ago on Introduction

    I used half an amp since those are the two resistors that I had on hand. I wanted to limit it to one amp, but I didn't have the right resistors to do so. I think you can safely get away with at least 2A, though I used current source from Step #6 supplying 1A.

    Anyway, here are two reasons to use a limiting resistor:

    1) At high currents, your electrolyte could get hot enough to boil, venting lots of HCl fumes. Also, at high currents, you get more hydrogen bubbles, which is not only a fire hazard, but also carries with it more HCl vapors.

    2) As you pointed out, protecting the supply. When it comes to power, if you use an adapter beyond its rated capacity, there's no guarantee that it'll work the way you expect it to. It could shut off, go out of regulation, or burn up.

    Lastly, if you use a high-current capable supply without limiting resistors, such as a modified computer power supply, or a car battery charter, you could supply the kind of currents capable of boiling the electrolyte.

    For example, when running 1A through it, the solution had between 0.570 and 0.780 V across the terminals, meaning that its resistance is 0.570 - 0.780 ohms. If you attach a 12V supply capable of supplying say... 30A (such as a modified computer power supply), you could get currents as high as 21A. This will certainly boil the electrolyte.


    Reply 6 years ago on Introduction

    Thank you for the informative reply. So any current under what boils the electrolyte is OK? Of course it is difficult to say exactly what that is as the electrode distance is going to vary from setup to setup. So pretty much whatever I'm comfortable with safety wise?

    I also wondered why you filled the bottom of your tank with bits of copper too. Just to get more copper suspended I imagine?

    I want to go with HCl and peroxide because I am sick and tired of FeCl getting copper loaded and stopping etching. I've gotten good etches out of FeCl, then the next time I go to use it the stuff stinks! lately Radio Shacks aren't even carrying the fluid, so I've tried to use the powder and I never got that to work good for me.

    This is my old etching setup:

    I'd prefer a bath solution that just kept on working, or one I could spike back to working strength. Lots of folks say this HCl and peroxide solution is the best way to go. I need to get back to etching, I'm tired of point to point wiring up circuits, I end up with messes like this:



    Reply 6 years ago on Introduction

    I think that's pretty much how it goes, so long as it doesn't boil or emit TOO much vapor from hydrogen bubbling.

    I added extra bits of copper so it would dissolve in the solution while the electrodes dissolve / accumulate copper powder.


    6 years ago on Introduction

    Thank you SO MUCH for this Instructable. I've had so many problems with PCB etching for so long I want to scream. Chemistry at home is so discouraged it's, well, discouraging. I will be making up a batch of this post-haste.