Homebrew PCBs

grantfair2001 wrote:
> Hi Adam - my chemist friend (who, incidentally, grew up near Bondi
> beach) advised me some time ago to try this recipe. I did not get past
> trying some copper in muriatic acide, and, expecting a quick reaction
> and getting none, giving up. (He had no idea about the time frame
> required, and no suggestions about what to do next). Here is his
> recipe, FWIW:
> 
> "Dissolve 67 grams of copper in 100 gms muriatic acid solution (the
> 38% stuff). You could use an excess of copper to make sure all the HCl
> is consumed, but make sure you can remove the residual copper. Add 100
> gms muriatic acid and bubble the bejeezus out of it until it turns
> green. Add an additional 90 gms of muriatic acid solution and 606 gms
> of water and you should have about 900 mils of the recipe mentioned in
> the Rex Allers article."
> 
> I think he got the 38% figure for the HCl from the article, since the
> muriatic acid available in hardware stores here is 20 Baume, about 30%.
> 
> I don't know if that is helpful or not. He develops plastics for
> Dupont, so this is off the beaten track for him.


HCl won't react with Cu without oxygen present. The initial 67g 
Cu + 100g 38% HCl won't do anything. It also don't need to be 
that complicated or precise (see my the post of my latest test) .
 From what I recently learned, 1 liter of etchant can be prepared 
by placing approximately 140g +-15% of copper into a thermally 
insulated container (i.e. your cooler box) fitted with a sparger 
for producing fine air bubbles. Add 1 liter of 6.0 +-15% Molar 
HCl (or 20% wt or 220 g/L). Ideally the copper should be fully 
immersed, but not essential. Cover the container and bubble air 
through the solution until solution becomes deep green.
See pictures and description from by previous post for more info.

For horizontal etching you may need to have large bubbles as 
small bubbles may simply trap foam under the PCB and slow 
agitation. The fine bubbles then only be used for air 
regeneration. You can include a few air stones in addition to the 
PVC pipes for producing large bubbles for horizontal etching. I 
have never tried etching this way.

Adam