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

----- Original Message -----
From: "Phil" <phil1960us@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, September 27, 2004 9:21 PM
Subject: [Homebrew_PCBs] advice on CuCl etchant?


>I mixed up a batch of HCl and H2O2 and got good etching (which was
> mostly from the HCl). There were some bubbles but no chlorine gas. I
> etched 6 double sided boards that were on average 20x20 CM in the
> first session. The etchant turned the well described emerald green.
> 3 days later, I went to etch another board and got no (or r-e-a-l-l-y
> slow) progress. I bubbled it for about 18 hrs total (with 2 airstones
> - lots of bubbles). Still no etching.
>
> I got a hydrometer and the density is 1.075. This is well below the
> 1.17 recommended by
> <http://users.rcn.com/rexa/Projects/CuCl_ech.html>. From the HCl and
> H2O2 I put in, the s.g. should have been 1.029 so I assume that the
> difference, 0.046, is from the etched copper in the form of CuCl. It
> appears I have too weak a cucl solution by about 1/4 but I'm not 100%
> sure about the chemistry here. Everything I've read says that it
> doesn't take much copper at all so I'm a bit at a loss here. I need
> to get pH measuring capability but the density is clearly wrong.
>
> Any suggestions for fixing? The page mentioned above recommends CuCl
> salts which I have no idea where to get and probably shouldn't have to.
>
> I'm going to put a couple pieces of copper in over night to see if I
> can get more copper into solution but its not clear to me that will
> actually work.

Bubbling air takes a long time, adding some H2O2 would be quicker, but will
dilute the solution, so you might need to evaporate some water from it
first. Also, you might need to add some more HCl. I do this with FeCl3, to
regenerate it, so that I gradually end up with a mixture of FeCl3 and CuCl.
I've used the same solution for some months now by doing this, and it works
quite well. Only downside is that it's slower than fresh FeCl3.

Leon