etching a copper board with ammonium persulfate

[nils]

Hi there.

I'm about to plan my next project. Iinspired by the Captain Coconut, I'm thinking to build something similar with my three favorites, being a Foxx Tone Machine, some kind of TS and a (univibed) Phase 45 (this combo rocks on my pedal board!).

So far I've built everything on stripboard, but I'm thinking about etching copper PCBs this time (for the first time). What I wanted to know: When I etch the board, can the dissolved ammonium persulfate be "recycled", i.e. can I put the rest into a glass bottle or something for future use? Or will it slowly eat through the glass and make me clean my kitchen? Or is the water-AP-solution useless after etching one (a few?) PCBs?

Thanks!

[markr04]

I use a little prescription bottle (would hold about 1 ounce of liquid). I fill it with the persulphate crystals and dump that in a little plastic/glass/non-metal bowl (never use this bowl to eat from again) which is just right for a 2"x3" PCB. You wanna use 3 or 4 parts water, so I fill that little prescription bottle with water 4 times and dump it into the bowl with the persulphate. Swish it around until the crystals are disolved. You can use this mixture for 2-3 PCBs, depending on how much copper you're removing from the boards. I bought the 1kg/2.2lb size of MGChemical brand about a year ago. I've etched 30-something boards and I'm not 1/2way through it yet!

Once the solution sits for 2-3 days, it begins to crystallize and lose its effectiveness. So, I'd say recycling is out. But mixing such a small amount makes recycling a non-issue really. I've got a lot of mileage out of this $17 container, and much more to go. BTW, it will not eat through glass. It's not had any effect on the plastics I've used either.

[markr04]

and...

Heating the solution and swishing it around really speeds up the process. Some people put hot water in another bowl and set the etching bowl down in it. I heat the solution directly. Either way will work, but I'd venture to say my way has more hazards associated with it.

[nils]

ok, thanks for clearing that up.

[Paul Perry (Frostwave)]

I've kept used ammonium persulphate for a couple of months, and reused it successfully. I saw a few bubbles (presumably of oxygen) on the side of the etching tank during this time so I guess there was a little decomposition, but it etched fine.
I was using one of those skinny vertical Plastic PCB etch tanks & a heater from a tropical fish tank (dont let any metal parts of the heater get into the solution!!!) plus an aquarium bubbler pump.
Eventually the solution goes blue (copper ions) but, it worked quite a while for me.

[nils]

thanks for the info.