Homebrew PCBs

On Fri, 2009-07-10 at 20:09 +0200, Stefan Trethan wrote:
> How about electrolysis?
> 
> I experimented with etchant regeneration by electroplating before
> (carbon welding rod electrodes) and got copper plated from the CuCl,
> but there was also some gas created (probably hydrogen, oxygen, and
> chlorine).
> 

I don't think you get copper plated from the CuCl, just some removable
wet deposit around the cathode. But i want to say something about
chlorine gas use from HCl/CuCl electrolysis. I believe (but still not
convinced) that found a simple way of doing this. But only for bubbling
the resulting gas in to the CuCl etchant.

The idea is use the old saturated CuCl to produce chlorine and oxygen to
the new etchant while some copper gets deposited. Using a 'Hofmann
voltameter' type of container to separate the Chlorine/oxygen gas from
the hydrogen gas. See http://en.wikipedia.org/wiki/Hofmann_voltameter

This 'Hofmann voltameter' was to make water electrolysis where both
gases were collected in two different places. It can be made really
simple by just using the normal etching plastic container and just a
large vertical plastic tube inside the bath closed on top and with the
anode on bottom. One rubber tube will leave the chlorine/oxygen gas to
the etchant container. And the hydrogen gas will go to open air.

Using HCl or CuCl if water electrolysis occurs the oxygen will also be
on the anode. So no need of fine tune the voltage or current since both
gases are positive for the CuCl regeneration.

I use to buy 25% HCl in 1L. But one time i ask for a 5L container they
give me HCl in 37% because it was the only they have in 5L. That thing
was really gaseous. I believe that if i bubble air in 37% closed
container and the a tube leave the gas to the etchant i will get big
amount of chlorine in to the etchant. But electrolysis should work at
lower concentrations. 

Big pcb shops seems to use a copper electrowinning process for CuCl,
using a ion exchange membrane. And there is some processes to get
chlorine gas from HCl using a proton membrane, were the hydrogen is
mixed with air oxygen to get water. The only thing I found to be simple
to do was this 'Hofmann voltameter', from which i expect critics.