Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Thus far I have had great success with toner transfer and CuCl from my
very first etch. I did a bunch of PCBs 30 years using a resist pen
and FeCl, but these are the first boards I have made since then. I
have, however, noticed something that I have not seen reported in all
that I have read on the topic.

I am using 20% HCl and "40 volume" hair developer which is 12% H2O2
plus a bunch of stabilizers. When mixed 2 parts H2O2 to one part HCl,
the product is very reactive and can etch 1 oz. copper in 30 seconds -
1 minute depending on the amount of action on the board. However,
this etchant seems to degrade rapidly over 24 hours. It will still
etch the following day, but ∗very∗ slowly -- 30 minutes or more to
etch the same 1 oz. copper.

Oddly, I have never seen the equation for the generation of CuCl2 with
H2O2, but I believe it to be roughly the following:

2 HCl + Cu + H2O2 -> CuCl2 + 2 H2O

I say roughly because there is clearly a gas produced during the etch.
While this could be water vapor, I am not certain of it.

In any case, I believe what is going on is that I am only producing a
minimal amount of CuCl2, and something is causing the H2O2 to degrade
when it sits. At this point, I merely have a (diluted) acidic
solution with very low CuCl2 content. This would explain the vast
difference in etch times when the only variable is time (the time it
sat on the shelf). I suspect that if I had etched more copper before
the H2O2 degraded, I would have produced more CuCl2, and thus would
have had a much more concentrated solution for future CuCl2 etching.

I ∗have∗ seen some references to people mixing up very small
quantities of 35% H2O2 + HCl, and I wonder if they are only using the
HCl + H2O2 phase, and not actually bothering with the CuCl2 etch.

I think in the future I will be mixing up much smaller batches of HCl
+ H2O2 and then perhaps tossing in some scrap copper to produce CuCl2
while the H2O2 is still present.

Any ideas if I am correct of this? Am I merely re-discovering common
knowledge of this list? Are there many people who only use the first
phase due to its insanely fast etch times?

-p.