Homebrew PCBs

On Thu, 12 Oct 2006 18:25:06 +0200, nixiebuilder <g_cw@...> wrote:

>
> It works great for the first board or two, then takes longer for the
> folowing boards.  How long does the stuff last before you have (to toss
> it) replenish it with fresh?  There was a small mention of using an
> aquarium pump and air stone to help keep it fresh, but will that help as
> agitation to speed up the process?   Also not to add more peroxide as it
> has too much water in it and will dilute the mix even more.  I'm using
> the 2/1 ration, peroxide to acid as suggested.  I'd like to get away
> from the Ferric chloride - the sink is turning a nice awful brown.
> Sorry for the long first post :)
> Charles


What you need to do is migrate to a proper CuCl.
Basically you keep your etchant going by adding small amounts of hydrogen  
peroxyde and hydrochloric acid.
There is no need to dispose of this etchant at all (apart from a small  
excess that builds up), since it can be regenerated.
You can use oxygen from the air instead of H2O2, but really considering  
the minimal cost the "instant chemical fix" with no fumes seems much  
better to me. The bubbler is still good to speed up etching though.
You'll need 25-35% H2O2 (you were probably using 3% medical now?), else as  
you say it adds lotsa unwanted water.

The basic idea is to add just enough to make it work, add very small  
amounts of H2O2 just to keep it a nice bright green color (as opposed to  
dark almost brown). If you get gas bubbles, you have too much H2O2. HCl  
levels should be kept at a minimum constant level so there's always some  
present for regeneration. You can measure it or go by eye (bluish deposit  
on copper and no etch progress at all even after adding H2O2 shows lack of  
HCl). The links section contains good guides about feeding and care of  
CuCl. Only thing to keep in mind is you can gradually go from your  
HCl+H2O2 to CuCl without needing any additional copper as long as you are  
prepared to add a small amount H2O2 each time for a while. (Because there  
will not be enough CuCl to finish a board without regeneration partway  
through).

ST