Homebrew PCBs

Hi Denny,

As I had mentioned in my post a 50-50 mix was IMHO way too strong, and I had
realized that while I was combining - at this point I was still in a big
guessing game (I only wish I were a chemist sometimes, would have made some
of this make much more sense and I probably would have known the info
presented to me was off, and that even my 33/67 was off)....

<snip>
The mixture on the site I had read was 50% H2O2 to 50% muriatic acid.  THIS
MIX IS TOO STRONG.  I mixed at ~33% acid to 67% h2o2 and it was still strong
enough to etch a 4.5x7 board of mostly copper
</snip>

I also mentioned that I felt a smaller ratio would work just as well...

<snip>
I think a much weaker mix with a longer etch time is desireable,
I'd rather do a 1 to 4 or perhaps a 1 to 5 mix
</snip>

1 to 5 is a 20% ratio of acid to the remaining components of the mix - so
that isn't too far off from 15%.  I'm glad to hear about the even lower then
I figured mixture ratio.

I do see why I didn't find anything - I spell the acid Muriatic - which is
the only way I have ever known how to spell it (see msds:
http://www.aldenleeds.com/html/muriatic.html) - I now see that it can be
spelled differently by people (muratic) - searching thru the emails with
muratic as a spelling would have given the results you spoke of.

I honestly didn't know it combined to do cupric chloride etching - Thank you
for that extra piece of info, I wish I had known about it before, I could
have forgone some of the bad mixture ratio sites, and a search on cupric
chloride etching would have resulted in a lot more accurate info I believe
(plus, I wouldn't have posted a long note on something that had just been
gone over recently, oh well, my bad).

Also the previous sites I had read this on had talked about just a mixture
of the acid with h2o2, now that I've been able to read a bit more from some
of the links, as well as the now found previous discussion I understand more
and find myself with a ton of extra h2o2 rofl.

-Tony




> The basic jist is 15% Muratic (hydrochloric) acid and about 2% H2O2.
> This isn't the acid etching, it's Cupric Chloride. The free oxygen in
> the H2O2 breaks the hydrogen from the hydro-chloric acid, producing
> water and free chlorine. The free chlorine recombines with copper
> from the board and produces copper-chloride. There's more to it, but
> I'm not going to reprint it here. There's a lot of great technical
> details on previous posts and in the links section. Do note though
> that acid from the hardware store is about 30% to start with and
> various H2O2 supplies are different percentages too.
>
>
> -Denny