Etching PCB with sulphuric acid, hydrochloric acid and peroxide
My ferric chloride has become a toxic, stagnant, sludge which does about as much etching as wind erosion. I needed a better solution (Get it? Solution?). I came accross two options which seemed to be re-cycleable or re-usable:
Sulphuric acid & hydrogen peroxide (AKA piranah solution)
Hydrochloric acid & hydrogen peroxide (which becomes Copper Chloride in Aqueous Hydrochloric Acid Solution, discovered here)
WEAR GOGGLES and gloves too if you have them, I'm no chemistry expert but I can tell you what I did to make my etchants without killing myself.
Before I say anymore I need to say that both of these are dangerous, burn skin, give off noxious fumes and can explode if stored in a sealed container due to gaseous build up. My soltuion to explosion was to use a container sealed with a cork which has a lot of free air space. Air compresses quite a lot, this will allow any hydrogen and oxygen (from the hydrogen peroxide which turns into water and gas over time) to compress a lot before exploding, this will give me ample time to open the top, hold my nose and let the presure equalize in a well ventialted area (like outisde on a windy day).
IMPORTANT EXPLOSION RELATED UPDATE: seems like more presure than I expected was building up, my simple cork safety valve was nearly popping when I came back to my big bottle only about 6 hours later so I plan to install a relief valve connecting it to a pipe going out of a vent. YOU DO THIS OR PERISH IN A RAIN OF CORKS, GLASS AND ACID. Oh also, the relief valve will be home made and I'll make a post about it.
Do not make the solutions highly concentrated, the sulphuric acid one will eat through metal, plastic and anything organic. From my research it seems glass seems is about the only thing which can withstand it. This is why it's called piranah solution: it'll eat through anything!
I did all these experiments outside, near a tap, on a windy day.
Now on to the recipies:
My piranah solution was about 10% sulphuric acid, 1 to 2% peroxide and 84% water. The peroxide I was using was only 6% in solution of distilled water, which is enough for this concoction. I also added some water myself to water down the acid which started out at a highly dangerous 97% solution ("do it like you oughta: add acid to water", doing it the other way around results in spitting, hissing acid explosions because the water heats up as you add acid. If there's only a small amount of water and a lot of acid, it heats up a lot, very quickly and boils).
At first my board wasn't etching very fast but I didn't want to add too much acid for fear of eating through the plastic etch resist (a toner transfer). After about an hour with nothing much happening I sloshed in some more acid (by sloshed I mean really carefully added it, slowly) then things sped up and it began to eat through the plastic a little bit as it completed the etch in about 15 minutes.
So the key to using piranah solution may be lots of peroxide and little acid. Although, with lots of peroxide, that could get quite explodey if stored in a sealed container.
To recycle this you can extract the copper from the acid using electrolysis, copper for the negative electrode and carbon rod for the positive electrode. The carbon will get into the solution and need filtering out. You should be left with sulphuric acid. I haven't tried this but I've seen it done. A platinum electrode works better but costs a bomb.
In the future I would not use this as the below method worked better and does not eat away at plastic.
My Copper Chloride in Aqueous Hydrochloric Acid Solution started out as hydrochloric acid and hydrogen peroxide mixed in similar quantities to the above method; 1.5% peroxide 7.5% acid, the remaining 91%: water. I didn't need to add any additional water to this solution as the acid and peroxide were only at 10% and 6% to start with (the rest is water). Using peroxide and hydrochloric acid of these concentrations it was 1 part peroxide to 3 parts acid.
I'm no expert but my reading tells me that once you begin to etch, copper ions disolve into the solution; if it turns brown you need more peroxide/oxygen and if it's green you're good to go. Mine is currently blue because I only etched one board. The initial solution olny took about 20 minutes to etch completely.
Once more copper is disolved I can rejuvinate it by bubbling air through it! (or adding a tiny bit more peroxide, you don't need much!)
Something unusual which I observed: the solution etched better if I aggitated the tank when the copper began to oxidize a lot (that's technical terms for; give it a nudge every so often).
Remember: both solutions give off toxic gasses so ventilation is essential.
If they turn blue it means you're etching copper!
