Best Practice: HCl + H2O2 PCB etching (Hydrogen peroxide & hydrochloric acid) – Page 1


VERY WELL VENTILATED environment!! I did it on my balcony. Do not do this in closed space. Chlorine gas is very nasty and partial pressure of Chlorine is SURPRISINGLY high! 24 % HCl fumes is on the brink of nasty. DO take this seriously. If you don’t care about your lungs, eyes and other exposed body parts: consider all metal fixtures and equipment around you. It WILL corrode from the fumes. And very quickly.
USE GLOVES!! Both are really cheap.
Start with small patches of copper.
MARK the containers. ALL of them. With permanent markers. So that you cannot oversee it. Even if only water is in them. Especially since you are (I am) doing that at home – your noodles might taste funny when you accidentally use that food container again….
DO NOT do it in your kitchen, near food, your son’s / daughter’s bedroom and so on. Best in a workshop or outside. Not your dinner table, not your couch. Chemistry can be bad sometimes.
READ the damn Materials Safety Datasheets (MSDS). Print them out, read them 10 times. Try and remember what it says. It is important. Really is. I mean… REALLY. And read them every time you start doing your thing. Especially when you do something new.





Just to be safe: Don’t try and drink the deionized water. You might die of hyposalinity if you drink enough of it  :)

The chemistry
(please, correct if I am wrong – I did not have the time to look everything up right today):

H2O2 (aq)+ 2 HCL (aq) + Cu -> 2 H2O + Cu2+(aq) + 2 Cl (aq)

While the H2O2 serves as oxidant, I guess.
As far as I remember, Cu is almost inert to low(er) HCl-concentrations (<30 %).
So I’ll be bold and guess that H2O2 could work as a pure initiator (ergo, really small amounts may suffice?).

See attached picture for some of the materials I used.

1x 10 L PP container with screw cap
1x PP funnel
2x PP beakers, 20 ml, with 2 ml markings
2x PP 0.5 L food containers
1x Polymer tweezers (I used steel, but it’ll dessolve 🙂 )
1x safety goggles (DO use these! Cheap to buy, very valuable when you want to scratch your itchy eye….)
1x big box of cheap disposable vinyl gloves (Nitrile are more versatile. Vinyl will dissolve in Acetone, but are good for Oxidizing agents like HCl. Since I don’t mind the acetone, I chose vinyl. Also I like the feel better. Don’t buy Latex. They rip and puncture easily, plus they are expensive)
1x 7.8 M HCl (^= 24 %)
1x 8.8 M H2O2 (^=40 %)
1x pack of NaOH (I just used baking soda)
1x Acetone
1x Distilled / deionized water (really, tap water is just fine. But I am a sucker for best practice)
1x roll of packing tape (I just used it to mask one side of the dual sided copper clad board)
1x tin shears (for your copper clad boards)
1x steel wool
Xx permanent markers (Just for the try-out)
Xx strips of your copper clad board, FR4 (don’t start with an entire board right away. I tried a strip first to get a feeling)
Xx Paper wipes


cut small strips of copper clad PCB board with large tin shears.
abrasively cleaned surface with steel wool
thoroughly cleaned with acetone and paper wipes
made markings with permanent markers: different widths / areas, geometric forms and layer thicknesses
masked / covered areas (backside) of PCB strip that were not to be etched
Added cold tap water into 1st PP container

added into 2nd PP container as follows:

1st try:

  • Room temperature (~20 °C)
  • HCl, 24 %, 10 ml
  • H2O2, 40 % ~2ml

2nd try:

  • Room temperature (~20 °C)
  • deionized water, 15 ml
  • HCl, 7.8 M 24 %, 10 ml
  • H2O2, 8.8 M 40 % ~2ml

Added cold tap water into 1st PP food container
Added following chemicals into 2nd PP food container

After each try, I neutralized the solution with NaOH (baking soda in that case) and diluted it a little with some tap water and put it into a small PET bottle. I marked the bottle with a label and will get rid of it at a local chemical waste disposal service some time soon.


1st try
Some 3 second etching.
Very fast. Very reactive.
Some over-etching apparent.
transparent green solution remains

2nd try:
Maybe 10 – 15 seconds of etching. But not as exothermic as the first try.
Reaction easier to control.
transparent green solution remains
over etching not apparent (at least from what I can tell… )
One “layer” of permanent marker seemed to be enough if no blank spots were left.
Thin lines were apparently not over-etched


1: reaction control
Control reaction speed. I will try:

  • controlling H2O2 addition
  • diluting (although I guess controlling reduction agent may be better – HCl is slow with Cu anyway)
  • pure water and control reactants (dripping in oxidant and reduction agent equally)

2.: Waste management
Find a way to easily neutralize the solution so that I can just safely pour it down the drain.
I’ll check on that. If anyone is interested, let me know

3.: Alternatives
I really do not want to bother with FeCl. It’s a mess.

I had in mind to try and do it galvanically. BUT: What do I do when a part of the board is “etched” away and there is a gap between two parts? I still need a physical, conducting connection between parts that are to be removed. Maybe there is some solution to this out there. Cannot think of anything, though. probably stupid idea. But I like the idea of an electro-chemical approach to the problem – no nasty chemicals, quick, controllable, broad error margin, safe, clean, etc….

I don’t have the space for milling. So not an option. Also high CAPEX and inefficient (not that I’ll be producing 10’000 boards a day. Probably I’ll make 10 my entire life 🙂

4.: learn to actually design a PCB  :-DD
Never did it. Let’s see what I do first. I ordered a LOT of SMD-stuff from China. So far I only played with through-hole and DIP on prototyping boards & breadboards.
My first project is an Atmega238 fast auto-ranging and not all too precise ohmmeter (I called the project SpeedyOHMalez here in the forum, hehe) for sorting resistors.

5.: Solder mask & silk screening
I ordered UV paint for the solder mask (nice red). I’ve read a little. I am curious to see how I manage to coat the board evenly.
Need a UV light (anyone in Switzerland has an unused one lying around?) and to study curing time, temperature resistance, etc.

Also I want to find out the best way to apply the “silk screen” on top of the solder mask. I saw a lot of actual silk screening.
Since I’ll only make one-offs for starters, I really don’t want to make an actual silk screen just for one design. I was thinking: Same process as the solder mask, just inverted, no? so: covering the entire board in (in this case white) UV curing paint, put laser printed mask over it (inverted) and wash the other stuff off. Not very material efficient… but it should work, no?

I will try and make a complete tutorial out of this as I progress (and when I find the time). I want it to be a little more than the usual “pour this into this” you can find everywhere. Any help, comment, addition, constructive criticism ….. etc…. is much appreciated. Especially if I got things wrong. I’d generally like to stick to HCl as oxidizing agent. It is readily available and cheap.
There are safety issues with this, sure. But I think ignorance is a great tragedy and people should be educated – that should also involve properly handling hazardous chemicals.



Best Practice: HCl + H2O2 PCB etching (Hydrogen peroxide & hydrochloric acid) – Page 1 was last modified: September 9th, 2017 by Jovan Stosic