Homebrew PCBs

On Thu, 2009-04-16 at 14:25 +1000, Adam Seychell wrote: 
> 
> Sodium and ammonium persulfates behave very similar, and you cannot 
> reuse either of them. Oxygen (from H2O2 or O2) regenerated cupric 
> chloride is the only practical reusable etchant for homebrew PCBs.
> 
> You can copper electroplate from just about any solution containing 
> copper ions, but the question is can you electroplate with thick
> smooth 
> ductile uniform deposits. With all the effort that goes into
> formulating 
> a copper plating solution, I highly suspect you won't find anything 
> useful from spent etchants.
> 

What a mess! My hope to find a usable and clean way to do PTH boards is
a proven waste of time for me. Much wanted the same and am sure not the
one with skills for it. 
I completely fooled myself with sodium persulfate. I really thought it
was reusable, fooled by very convincing speculation on the web. I just
wanted a reusable source os cooper anodes and a metallic resist
compatible etchant. I spent some time searching for a way to use
peroxy-sulfuric etchant for this. And then found sodium persulfate, and
it seem better for the purpose than peroxy-sulfuric.

Searching for patents on sodium persulfate only gives microetch uses.
'Printed Circuits Handbook' says persulfate based continuous
regenerative etchants are no longer used. Looking for all the posts in
this list for the matter only refers to a 'one use only' etchant.

What i had in mind was a copper electro winning system based on platinum
anode and copper/steel/titanium plates for cathode, it will deposit
copper and regenerate the persulfate 'from the sulfate' again. Will be
really great to be, and is written like that all over the web, but to
end with all the doubts the etchant reaction is: 
Na2(SO4)2 + Cu+ --> Na2SO4 + CuSO4 
Or like this?
Na2(SO4)2 + H20--> Na2SO4 + H2SO4 + H2O2
H2O2 + H2SO4 + Cu --> CuSO4 + 2H2O
basically both are right but the second ends with the speculation that
fooled me right?

Potassium persulfate is sold has a 'swimming pool oxy choke' (12eur/kg
here). And persulfates seems to be used as a solid source of oxygen on
chemistry (and explosives too).

>From the sodium persulfate microetch patents is said that is a slow
etchant and the presence of sodium sulphate lower the etch rate a lot
more. My use idea will end up having sodium persulfate, sodium sulphate,
sodium bisulphate and sulfuric acid all present. So very slow.

The other things was sodium persulfate is more compatible with metallic
resists than cupric chloride, it can be used with nickel (tin or
tin/lead with additives). And disregarding the quality of the plated
copper it also seemed a possible plating setup. 
But my questions was more about time and energy efficiency. After etch,
leting the copper cathodes there will saturate the bath in copper,
inverting the polarity with the board on circuit, it will plate copper
in the board (disregarding the plating quality). But to etch again will
be needed much recover time and energy (and platinum anode losses). I
really thought everyone that uses sodium persulfate use it like this and
the question was to know if this time and energy cost worth it.

I really want metallic resist because dry film covering the holes gives
much work and don't has the enough successful rate. Toner transfer or
direct printing, even if another plating step is required, is much more
pleasant. But i need a matching etch. 
'Printed Circuits Handbook' refers tin/nickel for cupric chloride, maybe
nickel works? Tin/lead is the cheapest but the matching peroxy-sulfuric
etch is not so cheap... 35% hydrogen peroxide is not easy to find (my
veterinarian sister says it is used to wash big animals foots but i had
no luck to find it anyway). But still using 35% hydrogen peroxide gives
much waste etchant, and a expensive etchant. 

But I really have to stop embracing what seems easy, if i ever want to
get a PTH system. But in a last breath of crazy ideas, there is any
other way to add oxygen to a sulphuric acid etchant? There is who says
hot concentrated sulphuric acid is usable as etchant but with really
toxic gases. But about bubbling oxygen gas? Nobody uses this, is just
expensive or not efficient? And water hydrolysis? The power and anode
(platinum) costs are acceptable?

Very thanks,
Simao