Homebrew PCBs

Adam Seychell <a_seychell@...> writes:
> A pure CuCl2/HCl etchant can work with fairly wide range of copper 
> concentrations.

Your web page says 1.2 to 1.4 specific gravity, hence my "check my
math" posting - to get 3l (3kg) of water to 1.2 sg, you need 20% more
mass, or another 600g

> You can dump in 1 pound of copper pipe or old electrical cable , and
> let it bubble for a few days. Just keep the HCl additions so it
> stays acidic during this time. It goes green when finished.

Based on how the tank is acting, I think the acid is still OK - if I
put copper oxide (wire over a gas stove flame) in it, it eats the
oxide off pretty quickly.  It's also getting darker green over time,
as I etch more boards.  What I've been doing is adding H2O2 to bring
it back up to where it's supposed to be (i.e. to counteract
evaporation) when I etch boards.  I tried titration once, but didn't
have enough copper in it to act as an indicator then.

I did a board today and it took 40 minutes.  At least, I remembered to
go check it at 40 minutes and it was done ;-) I also positioned it so
that the air bubbles actually hit the board, not just went past it.

Actually, my problems over the weekend were due to *over* etching.
I'm still experimenting with the photomask.  So far I've learned to
match up line/space rules across a panel so that the etch times match.
Maybe I'll cut up the panel after exposure so I can etch them
individually.  Small traces with big spaces were etched away while
waiting for a board with small spaces to etch.  It never did, even
after 2 hours.  Maybe floating it over FeCl would result in a more
consistent etch.