On Tue, May 13, 2014 at 3:54 PM, DJ Delorie
dj@... wrote:
> Note that H2O2 is photo-sensitive, and should be stored in a light-proof
> container. It will break down over time all by itself.
Indeed. I have read that storing in a refrigerator is even better,
and 35% solution should be stored in the freezer. A 35% solution
should remain liquid at typical home freezer temperatures. Supposedly
the hair developer contains something that reduces the rate of natural
degradation. I do not know what (if any) effect this has on PCB
etching.
> 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.
As an aside, where I am located 32 oz of 3% H2O2 (medical) costs $1.79
vs. $4.99 for 32 oz of 12% H2O2 (hair developer). As an oxygen
source, the hair developer is actually a somewhat cheaper. Not enough
to matter from a cost basis, but the more concentrated oxygen source
will result in your total etchant volume growing more slowly. Again,
this may or may not be an issue.
> When I made my etchant, after I used it for circuit boards, I put about
> half a pound of solid copper in it (3-4 liters of etchant) and let it
> slowly dissolve, which gave me enough CuCl for the next etch. It took a
> while but eventually worked. Once it's converted to a CuCl etchant, you
> can refresh it with plain old air.
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.
-p.