--- In
Homebrew_PCBs@yahoogroups.com, garydeal <garydeal@...> wrote:
>
>
> This afternoon I finally got around to mixing up a small batch
>of
> the 1/3 HCl + 2/3 H2O2. I've read the positive reviews on that
>recipe
> here, but was really surprised/impressed at the results.
> My usual initial test is to cut a small strip of .005" brass
>and
> wave the end around in the solution, and it dissolved in record
>time. So,
> I set up a sheet with some photoresist (laminated dry-film), burned
>my
> favorite test file into the resist, developed it and popped it into
>the
> beaker. I hesitate to say that it took minutes to etch, it would
>make
> more sense to describe it as seconds. Since the test file has two
>parts
> panels, I dropped the second one in and it was nicely finished in
>short
> order. The guy that craves these parts is going to be really
>pleased, as
> am I.
>
> Question:
> The solution total was about 225 ml, and the brass sheet was
>etched
> one sided with an etch area of a couple of square inches. Afterward
>the
> solution was quite hot and bubbling like soda pop on the stove. I
>put it
> in a cold water bath to cool it down, but I have to wonder - is
>there the
> possibility of a runaway reaction and what is the result?
>
> Oh, and I'm sure this is common knowledge to the rest of you,
>but on
> say, a 1 oz and 2 oz board, what are the copper thicknesses?
>
> Thanks,
> -Gary
>
Your mixture is far too strong, you need to add more water (add acid
to water, not water to acid, though with regular muriatic the danger
isn't nearly as bad as adding water to lab grade sulfuric acid). The
40 volume H2O2 adds some water, but not enough, it seems. You don't
want the stuff etching so fast that you can't even get it out in time,
plus the fumes, heat, etc, might melt the container it's in.
Also, you want a bucket with a /lot/ of baking soda dissolved in it to
neutralize the etchant. During my one trial run with this process, I
discovered that sharpies and other permanent markers are useless as a
resist with this process, so you'd need to touch up with tough paint
on a fine brush. I'm sticking with FeCl3 so that if I /have/ an
accident I won't burn myself instantly.