Homebrew PCBs

Hi Phil,

Is the solution a clear emerald green at the moment? If so I would guess 
that you are short of acid. If it is murky and more an olive-brown 
colour then it needs more oxygen.

Bubbling air through the solution can take a long time. Adding H2O2 is a 
lot faster. My etch tank is quite small (1.5 litre). It does not take 
long for the available oxygen to become exhausted. A teaspoon of 
100volume H2O2 is enough to get it etching well again. If the solution 
starts fizzing when you add the H2O2 and has a chlorine smell you have 
added too much.

Les


Phil wrote:

> 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.
> 
> 
> 
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