Homebrew PCBs

I can't actually give you the requested exact ratios since i built my
etchant bit by bit and do not know them.
However, i think you will have to do the same, since at least the H2O2
must be added gradually. At first there would not be enough Cu2Cl2 to
oxidise, so much of the H2O2 would dissipate.

The copper should be thin pieces, like sheets or stranded wire.
Electrode nuggets may take forever to dissolve.

A hydrometer is not for measuring humidity, that is a hygrometer and
many people are simply mistaken.

A hydrometer is used to measure fluid density, it is a glass tube,
with a weight at the bottom end and a scale at the top end. The higher
the hydrometer floats the denser the liquid is and you can read this
on the scale (the water line is the pointer). The ones sold to test
car battery acid cost only like 2 eur and are just about sufficient.

I recently bought a refractometer from china, for like 20eur. It is
also designed to measure car battery acid, but it tried it with
etchant and it seems to work. The refractometer is an optical
instrument where you place a drop of liquid on a prism and the
refraction coefficient is measured (Brechungsindex for you). You look
into it like in a telescope. It is very quick, accurate, and less
messy than the hydrometer in my opinion. But it does measure optical
density, not physical density, as long as the two correspond there is
no problem though. Also, of course, it is a measuring instrument and i
just had to have one, no matter what.

You only need the hydrometer to see how much copper there is in the
etchant. There's an ideal density range for this etchant where you get
the best speed.

Another analysis tool you should have is a way to determine the HCl
concentration in the etchant. This can be done by titration with NaOH
and methylorange as indicator. That's actually quite easy to do, but
not really needed that often.

Bubbling, yes you can use it for regeneration but that is dead slow.
H2O2 is more efficient. I just use bubbling to agitate the etchant so
it is quicker and more even. You definitely want some form of
agitation, CuCl is not the fastest etchant if you do not push the
chemical parameters into the ideal range.

ST

On Tue, Jan 6, 2009 at 10:02 AM, Markus Zingg
<homebrew-pcb@...> wrote:
> I would like to switch to cucl for a while cause having a solution that
> lasts virtually for ever seems to be very beneficial. Besides, I'm just
> before building a new etching tank and thought that this would be a good
> moment for a switch of the etchant too. Since english is not my native
> language, I always felt a bit unsure if I understood things correctly if
> you guys were talking about cucl in the past, and there were always some
> open ends. In particular the following things are not yet clear to me:
>
> So, one would i.e. need to build 3l HCL/H2O2 and put in half a pound of
> copper into it? Correct?
> How many HCL and H2O2 to get to a 3l solution to start with? I mean
> what's the ratio of HCL to H2O2?
> Any restrictions regarding the kind of copper? I do have copper left
> over that I use for the anodes in my through plating station. Would that do?
>
> Then, Stefan wrote " If you want to measure this, you can get a
> hydrometer. The ones sold for car battery acid checks will usually do. A
> refractometer should work as well."
>
> A hydrometer - when useing google - seems to be a device to measure
> humidity? Correct? What is a "refractometer", which of the two would be
> easier to get and where, and how would one measure what? Regarding the
> "air stone bubbler", I think I remember that one uses this to regenerate
> the solution. If so, does one have to do this every once in a while, or
> only during etching, or just before?
>
> I'm sorry if these are dumb questions, but since working with chemistry
> might be dangerous I want to be very sure I understand things correcly
> bevore I start to experiment.
>
> TIA
>
> Markus
>