hydrochloric acid and hydrogen peroxide

This method substitutes the oxidative Fe3+ ions with hydrogen peroxide. Sounds simple enough, and an over-simplified version of this reaction should end up looking something like this:

Cu + HCl + H2O2 =>CuCl +H2O

The hydrogen peroxide breaks down; creating free oxygen and an electron, which then oxidizes the copper, allowing it to break free into the solution and combining with chlorine. The oxygen in turn grabs a hold of the hydrogen in the area, creating water.

That’s the theory. In reality, you are going to deal with “half states”, intermediates of the reaction where the oxygen and chlorine escape without completing the reaction. Although these fumes are sparse, they still pose a significant threat to your respiratory system. DO THIS IN A WELL VENTILATED AREA. Oxygen is extremely reactive and will create O2 as well as ozone when it can’t find anything to bond to, ozone is explosive and also a (DUN-TADA!) super effective oxidizer; and though not explosive, chlorine will mess you up.

Also take into account that unlike ferric chloride,H2O2 will dissociate over time. Thus, only make batches that you are going to use on the spot, because a few minutes later it’s going to be unusable. The ratio depends on your concentrations: mine was liquid pool acid of 30% concentration and 40% mass concentration of hydrogen peroxide. If you want to get into the stoichiometry of things then feel free, but since having more of the one reactant will not change the outcome, you can just use rough guesstimation.

My mix consisted of 1/3 peroxide to 2/3 pool acid, which worked just fine. Unlike ferric chloride, this stuff is going to bubble and the gases released are going to be noxious. The solution? Wear a mask; use a fan; anything to get this stuff as far from your face as humanly possible. The problem is that if it’s just left stationary the reaction is going to stagnate, so you are going to have to agitate the mix until it is done. That means until the etching is done you will be between a rock and a hard place, having to juggle between having the gases in your face versus agitating the mix too far away to see if the etching is done. There is however a silver lining, this makes the reaction faster. But is the time saved worth it?

This solution easily neutralized afterwards but oh so deadly when it’s in use.The first time I used it the gases forced me outside, which was hell for a person like me who doesn’t spend much time in the sun. After about 5 minutesor so, the sides of the copper started to recede, and about 10 minutes after that the board was completely etched. Overall, it was a good result. It’s easy to use and even easier to make, but ferric chloride posses far less of a health risk.

Side note:

The mixture was not heated because there is a good deal of thermal energy released during the reaction, so it pretty much did that part itself. Also THIS STUFF HEATS UP, isn’t that cool? So bear in mind that a plastic container of sufficiently low quality will buckle or melt if high concentrations are used.

To neutralize the mix after use, simply add baking soda until it stops fizzing and you have yourself some sodium chloride (please don’t try to ingest this, it is contaminated with copper chloride, which is not good for you).