Homebrew PCBs

>     From: "Stefan Trethan" stefan_trethan@...
>     Date: Wed May 3, 2006 0:44pm(PDT) 
> Subject: Re: Blue CuCl etchant...
> 
> On Wed, 03 May 2006 20:48:38 +0200, Steve
> <alienrelics@...> wrote:
> 
> > and I think the
> >
> > oxidized copper comes out of solution and sinks.
> 
> It doesn't, for me. copper coming out i mean.

Ferric Hydroxide sinks.  That's the brown, muddy 
stuff that forms when you etch boards with Ferric 
Chloride.  The Copper shouldn't percipitate out
and sink, unless something is seriously wrong, such
as WAY too much of the wrong kind of Copper Chloride
and not enough of the good kind.

> Something like that what you said is happening, yes.
> I'm not good at  
> chemistry but the oxygen in the H2O2 or air combines
> with the hydrogen  
>  from HCl and leaves Cl to make CuCl2 from Cu2Cl2
> (or something like that,  
> the green stuff from the brown stuff anyway).
> Because you could also regenerate CuCl with chlorine
> gas (if you are keen  
> on fatal accidents). So my thinking is the HCl and
> H2O2 is really only  
> delivering chlorine atoms.

You really don't want to bubble gaseous Chlorine
through a solution in anything short of an industrial
setting, with a medical and emergency response team
on hand.  

> The growth of CuCl is very slow, if you only do a
> couple of boards every  
> now and then almost not noticeable.
> You could try to reduce growth by electroplating the
> copper out, i tried  
> that a while ago with carbon electrodes and a wire
> to plate onto. It  
> works, but it is difficult to avoid chlorine bubbles
> forming on the  
> electrode (which is what is happening because you
> take the copper away  
>  from CuCl i assume). The chlorine should not build
> a gas, it should grab  
> hold of some copper from the brown stuff to form two
> green stuff, but  
> that's not always happening apparently. maybe
> something like the apparatus  
> used by fishkeepers to dissolve CO2 into water would
> help. 

Ack!  NO!  Fishkeepers don't dissolve CO2 into the
water.  That would kill the fish!  They bubble air
through the bubbler to dissolve Oxygen into the 
water.  Fish breathe Oxygen, and expel Carbon 
Dioxide.

> basically a  
> tube filled with marbles through which water is
> pumped, downwards. On the  
> bottom a very small stream of CO2 bubbles is
> introduced. 

Oxygen bubbles, usually provided by air.  Most of
the bubblers I've seen don't actively pump the water,
although I suppose some of the more efficient ones
could.  The smaller, cheaper ones just bubble air up
though the water, usually using a series of rocks 
to help break the bubbles up into smaller sizes to 
maximize the surface area of the bubbles to enhance
the dissolving of Oxygen into the water.

I think it's been proposed that a similar system 
could be used for etchants.  However, rocks probably
don't work so well, since they may tend to dissolve
when confronted by the Copper Chlorides and even 
some free Chlorine in the water.  Plastic spheres 
might work, though.

> As they rise  
> against the current and bump into the marbles the
> gas is dissolved. One  
> should be able to set this up with a electrode at
> the bottom fairly  
> easily, but since the growth is really so slow i
> never bothered to even  
> try.

As for electroplating the Copper out, I tried that 
once with some spent Ferric Chloride solution.  It 
mostly kind of worked, since I deposited Copper
crystals (Yes, metallic crystals of Copper, probably
because I was running the current density WAY too
high for a smooth plating, but, then again, I wasn't
really trying for a smooth plating.).  In my case, 
rather than using a Carbon electode (and risk 
producing Chlorine gas), I used an Iron electrode 
with the idea of producing Ferric Chloride.  I don't 
know that that happened (although I don't remember
producing any Chlorine gas bubbles), so from that 
aspect, the experiment was mostly a failure.  But, it 
did pull the Copper out of the solution, which I 
viewed as a plus, since that meant that I wasn't 
pouring Copper containing solutions down the drain 
[1].

[1] Copper solutions are lethal to almost all forms
of life.  Ferric Chloride isn't nearly as lethal, and
has actually been prescribed as a medicine at one
point in time.

In any case, I don't know that I could advise doing
any type of electroplating operation that could 
potentially release Chlorine gas.  That stuff can be
lethal, too!

> ST

Dave


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