Homebrew PCBs

"Peter Johansson rockets4kids@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com> writes:
> On Tue, May 13, 2014 at 3:54 PM, DJ Delorie dj@... wrote:
>> You don't need a *lot* of H2O2 to etch, so a 3% solution is enough if
>> you use the 2:1 ratio.  The stronger H2O2 can be used a little at a time
>> to "freshen" the etchant just before you use it.
>
> If I am understanding the chemistry correctly, you do not need H2O2
> for CuCl2 etching proper, but rather to "regenerate" the CuCl to
> CuCl2.  Any extra H2O2 remaining after the CuCl to CuCl2 conversion
> will participate in the acid etch reaction.  This may or may not be an
> issue depending on your goals.

Right, initially you need the H2O2 because pure HCl will not etch
copper, you need a separate oxidizer.  CuCl doesn't need an oxidizer to
etch, but it does need oxygen to regenerate.

> Based on my experiences, using 12% H2O2 will convert raw copper to
> CuCl2 *quite* quickly.  Anyone looking to get started with CuCl2 in a
> hurry should definitely prefer more concentrated H2O2.

In my case, I was "done" with the etchant for a while.  It wasn't fully
fresh any more, and it was going to sit for a while.  The copper gave it
something useful to do while I was away, using only oxygen it had left
and whatever it got from contact with the air around it (i.e. not much).