Homebrew PCBs

"Howard" <howard_g7lqy@...> writes:
> I have found some Hydrogen Peroxide that is 6% (20 vol), and some
> Hydrochloric acid which is only 16% (5ltr brick cleaner in Jewsons)
> 
> Would these items be ok to use in a 2:1 mix, need about 3ltr to use
> in a megga uk heated\air bubble type etchant tank ?

If your peroxide is twice as strong, and your acid half as strong,
maybe you want half the peroxide and twice the acid?  I.e. one part
peroxide to two parts acid.  You can mix up a small batch, like a few
ounces, and see how it etches a sample board.

Remember: always add the acid to the peroxide, not the other way
around!

> I would like to convert the solution to a cupric chloride etchant
> what's the best way to do this ?

Add copper.  Etch whatever boards you want to etch, and when you're
done etching boards, put in some scrap copper.  I think I figured my 3
liter tank would need a half pound of copper to fully convert, but I
put in a quarter pound and it etches just fine.

What you don't want to do is let the unconverted acid-peroxide mix sit
there too long; eventually the peroxide breaks down to plain water and
it won't dissolve copper any more.  One of the advantages of CuCl is
that it *wants* to be oxygenated, so over time it gets *better*
whereas peroxide gets *worse*.

Alternately, start with a small batch, just enough to etch your pcb,
and each time you want to etch a pcb, add more acid and more peroxide.
Then you'll be converting the solution as you need it, rather than all
at the beginning.