You can actually build up the concentration of CuCl over time, then
you don't need to replace your etchant at all.
I have a tank that takes 2 or 3 liters, and still the same CuCl after
several years. The only thing i do is add some H2O2 if it seems slow
or i feel it might need it.
Sometimes i also add HCl, usually when i see blue stuff forming or if
adding H2O2 does not change the color, or simply if i feel it might
need it.
As you can see, both very precise scientific processes ;-)
One could measure these things easily, i've done it a few times, but i
don't find it necessary to bother.
With this setup i can just drop in a board many months after i last
etched and it still works. The H2O2 will obviously all be long gone,
but the CuCl acts as an accumulator.
At any time there is a certain amount of "useful" CuCl in the tank,
and a certain amount of "used" Cu2Cl (i think) that has already done
it's etching.
The "useful" CuCl is bright green, the "used" Cu2Cl is brownish.
Now if you have enough CuCl in your tank you don't need to add HCl or
H2O2 each time. This is because those two chemicals just convert the
used CuCl to the unused state (one used molecule makes two new ones).
In this regeneration process the H2O2 gives the oxygen to the H from
HCl (making water), leaving the Cl free to regenerate the Cu2Cl into
two CuCl.
Obviously as long as there is Cu2Cl all H2O2 will be used to
regenerate immediately, none is wasted to the air. Of course there
must always some spare HCl or it will not work, but some HCl can
always remain in the etchant.
With this etchant the exact amounts are not critical, as long as there
is some CuCl, some Cu2Cl, some HCl it will always etch, and if H2O2 is
added it will always regenerate. There is a wide process window and it
is easy to avoid "running out" of any one chemical. Of course etching
time will not be optimal with this "gut feeling" etchant maintainance.
ST
On Tue, May 20, 2008 at 6:05 PM, Michel Baguet <bagmik@...> wrote:
> I'm using HCl for a years. 700cc of distilled water, 270cc of HCl highly concentrate (you can see smoke when the bottle is open) and 30cc of H202 at 30% concentration.
> The only problem with this etchant is that H2O2 decompose with heat and light and if you etch another board a few days later, you don't know what part of H2O2 is still in solution. So I put the board to etch in the tank and take it out to see the color of the copper. If there is still enough H2O2, it must turn brown immediately.
> If not, I add 10cc and son on but never more than 30cc (obvious !).
> But the cost of HCl, H2O and H2O2 is so cheap that I often replace the etchant, to always get accurate results with small traces. A 200cm² double sided board with 35µ copper take between 4 to 6 min. in bubble etch tank @ 45°C.
>