I think I owe you all some explanation about the cupric cloride/hydrogen
peroxide/hydrochloric acid bath.

First a little bit of chemistry. Simplified reactions are:

etching                 Cu2+  + Cu   =  2Cu+

regeneration    Cu+  =  Cu2+ + e
peroxide                2e + 2H+ + H2O2  = 2 H2O
Hydrochloric acid is essential to provide the protons (H+).

Never use hydrogen peroxide/hydrochloric acid direct to etch. It goes very
slow and is very dangerous. Deadly chlorine gas can be formed. It is also
the main disadvantage of the bath, when too much H2O2 is added. Only
regenerate CuCl, cause cupric chloride etches much faster.

The colour of the bath is also an indicator for the acidity. The right
colour is (dark)green. When the colour becomes blueish, you should add
hydrochloric acid until the bath is green again.

The ingredients are in common commercial, relatively safe concentrations
(weight percentages). When you use lower concentrations in the regeneration
process, the solution is too much diluted.
Hydrogen peroxide is usually packed in bottles with a pressure relief valve
in the cap. Do not screw normal caps tight.

Etching is mainly dependant of stirring speed. Etching in a spraying machine
goes in less than a minute. Bubble stirring has the disadvantage, that
corrosive vapours ruin all the metal in the neighbourhood of your bath. This
is true for all etchants. Work outdoors or in a fume-cupboard.

Leo van Loon
SBB simpeltronics
Netherlands
tel +31 (0481) 450034
fax+31 (0481) 450051
mail sbb.simpeltron@tip.nl
url http://www.sbb-simpeltronics.nl
SBB simpeltronics ontwikkelt technische projecten voor basisschool en
basisvorming.
SBB simpeltronics develops technical projects for children in primary and
secondary education.


> >
> > Hello all,
> >
> > it seems to me that nobody really understands what the
> > etchant does do with
> > the copper. The HCL "acido clorhidrico" is the mainly active
> > substance, but
> > the etching process would be a slow affair. So you add H2O2,
> > and heat the
> > soup to 40 degrees centigrade, and in about 2-4 minutes a
> very clearly
> > defined PCB will emerge like Aphrodite out of the bath (without the
> > foam...). The H2O2 has to be replaced periodically, as it
> > tends to decay
> > into O2 and H2O.
>
> How can we then replace it ? As I see it we can only add
> things to the soup.
>
> > The CuCl is another matter. After some time, the reaction of
> > the HCl and
> > the Cu will produce a certain accumulated amount of CuCl in
> > the solution,
>
> CuCl is CobberXXXX ?
>
> So can I some how reuse the solution of HCL and H2O2 ?
>
> Regards
>   Benjamin Petersen
>