Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Simao Cardoso <simaocardoso@...> wrote:
> Electric regeneration of sodium persulphate etchant is really possible?
> You do it like this?
> http://www.electro-tech-online.com/general-electronics-chat/32177-new-pcb-etching-soultion.html#post668383
> 
> >From all etchant descriptions i ever read, this one really pleases me.
> But no more info anywhere. Any academic paper about this. Or any other
> information that can sustain the web post. From this group i got what
> convinced me to forget it. CuCl initiated with a peace of metal copper
> in acid and peroxide and regenerated with air, is the best thing around,
> but don't let me do things like i want to.
> So the regeneration of sodium persulfate is possible? It works like the
> post? Can you give me further info? 
> 

I have used the exact same post as basis for my experiment, and I have talked with the poster (contacted him directly).

I have found some patents on electrolytic production of persulfates:

http://www.freepatentsonline.com/2589982.pdf
http://www.freepatentsonline.com/4144144.pdf

Well to tell you the truth, I have tried it the first time. And it did not work as expected, but I do believe it should work. The solution afterwards was devoid of copper but had reduced etching power, it took a long time to etch. 

My first setup was basically partially spent sodium persulfate etching solution, a small platinum electrode and a piece of circuit board as the copper. The reason for the failure is the absence of sulfuric acid that needs to be there in the solution as a starter.

For the constant current power supply I use a small mc34063 switcher in constant current step down mode with a potmeter to adjust the current.

The platinum electrode can be gotten at this ebay shop for cheap. It is a bit small, but usable.

http://stores.ebay.com/teaybkk

This electrode specifically:

http://shop.ebay.com/160369927325

Today I will try out the second time but because I do not have any sulphuric acid nearby. Today I will get some battery acid and mix in some copper sulphate crystals in the mix to get the required SO4 ions as described in the patents and retry. 

As soon I know more I will post it here.

The reason I use sodium persulfate is because it has better under etching properties then CuCl and because it is almost acid free. HCl has corroded some tools nearby so I have stopped using it.

> 
> Big mail but full of info, no?
>

Thank you so much for the big post. I am looking into copper plating solder wire to create the solder filled eyelets at home.

The reason I do not go with trough hole plating baths is mostly the price and the space to maintain baths.

Greetings,

Bart