PCB printing


Joined Jul 17, 2007
Instead of ferric chloride, I've been using muriatic acid (hydrochloric acid 31.45%, 20°Baume, 68.55% distilled water) mixed with hydrogen peroxide (3% solution, 97% distilled water). If your concentrations are higher, you should carefully dilute them before mixing. If you fail to dilute them, your chemical reaction may be quite violent when you immerse the circuit board, resulting in large amounts of heat and dangerous fumes.

You do have to use a plastic basin, wear rubber gloves, and do this outside with good ventilation, as you don't want to breathe any of the fumes. Even though I do this outside, I use a large-diameter fan on a low speed setting to ensure a constant flow of air to carry the fumes away.

I use roughly 2 parts of the hydrogen peroxide solution to 1 part of the muriatic acid solution.
Pour the hydrogen peroxide solution into the plastic basin, then slowly add the muriatic acid solution while gently stirring, being careful to not splash it.

Using a paper towel or rag to wipe the board during the etching process speeds it up a great deal. Wipe, turn over, repeat until fully etched. If you manage to splash the solution on anything, immediately flush it using plenty of water (I keep the garden hose handy.) As soon as the board is sufficiently etched, flush with plenty of fresh water. It's far faster, and much cheaper.

Don't try to save used etchant. If you put it in a sealed container, it will continue to produce heat and gas from the chemical reaction of dissolving the copper, possibly causing the container to burst forcefully.

Instead, dilute it further with water (roughly 10 parts or more water to 1 part used etchant), then pour it in the toilet and flush it several times.


Joined Jan 18, 2008
I have been wanting to use that method and will, as soon as I run out of ferric chloride. I just did a quick search ("hydrochloric acid")and could not find any recipes on this forum. Perhaps, you will share your recipe. That is, how much and what concentrations of HCl and hydrogen peroxide do you use? John


Joined Jul 17, 2007
For "muriatic acid", I simply use the dilution that's obtainable from swimming pool supply stores. I get hydrogen peroxide in the health & beauty section of a large discount store. I mix it roughly 1 part acid to 2 parts hydrogen peroxide.

Your mileage may vary.

The hydrogen peroxide corrodes the copper, and the acid eats the copper oxide.

The solution starts off being completely clear. As the copper is eaten away, the solution takes on a green tinge. If it tends towards a dark green and/or the board is turning black, you probably need more acid to eat the copper oxide.

The board being etched should rapidly turn brown. Wipe across the brown oxide gently; it'll be bright copper underneath. Turn over and wipe the other side. This also serves to agitate the bath, helping the acid to eat the copper oxide and the hydrogen peroxide to get at the freshly exposed copper.

It will take a great deal longer amount of time to etch the board if you don't wipe it.

A few cautions:
Don't use anything nylon in the bath, as it will turn into sticky mush. If the sticky mush gets on your board, it will not etch where the sticky mush came in contact.
Stainless steel tools will be instantly etched and dulled by the mixture.
Concrete will be etched by the mixture.
Don't allow the mixture to dry on any surface; as it dries the concentration goes up astronomically. If you don't beleive me, try letting the rubber gloves you wore dry out without rinsing them off. Don't plan on using them again in that case.


Joined Jan 18, 2008
The question I have seen most often is whether to use 30% or 3% hydrogen peroxide, and secondarily, what the concentration of the acid is. Some people recommend the 30%, but I believe the 3% is supposed to work and gives a milder reaction with the hydrochloric/muriatic acid.

I hate to give a recipe based only on what's on the Internet for something I have never done. Do you use the 3%, which is the common concentration used for hair and skin cleansing purposes? Is there a particular ratio that you follow? And last, since the usual safety advice is to add acids to water and not the other way around, do you add the acid directly to the peroxide, or do you dilute the acid first?

For me, it is just looking forward to getting rid of the ferric chloride, but I suspect others on this forum may have a more immediate use.



Joined Jul 17, 2007
I updated my post to include more complete information and cautions.
Muriatic acid = hydrochloric acid 20° Baume, 31.45% (68.55% distilled water)
Hydrogen peroxide 3% (97% distilled water)

Hydrogen peroxide is measured/poured into the plastic etching tub first.
Muriatic acid is added slowly while gently agitating.

There is a rise in temperature during etching, but I have not recorded it.

I would not recommend using a stronger solution of either the muriatic or hydrogen peroxide, as the temperature rise would likely increase considerably, possibly resulting in an unsafe situation (etching tub meltdown).


Joined Feb 13, 2008
Have you tried the presynsethized board? What should be the right concentration for the developer?


Joined Jan 18, 2008
For Injectorall:
0.5 M KOH (28 g/L)
0.5 M NaOH (20 g/L)(NaOH = lye)

I am not sure all brands of presensitized boards are the same. Of course, for small amounts of developer you can reduce the formulas proportionately. I typically use, 8.4 g of KOH in 300 mL of water, which is pretty close to 0.5M.

To remove the resist after etching, just put a teaspoon or so more of NaOH (lye) in 300 mL of the developer, and it will remove everything. If you use lye, be sure it is only lye and doesn't contain materials to make it bubble, etc. John