On Sat, 20 Aug 2005 02:38:22 +0200, <
JanRwl@...> wrote:
> Can someone here PLEASE outline the procedure and chemistry to use for
> this
> etch-method? I have never seen ANYWHERE a list like,
> "1. Boil the bare blank in swamp-water;
> 2. Incant;
> 3. Swish the board around in a 30% CuCl solution over 80°C for 15
> minutes;
> 4, Etc. etc."
> With FeCl, you can omit steps 2. and 4., and the result is fine, but
> messy.
> Please?
I'll try.
Let's divide that into 3 parts:
Etching boards, maintainance, and first "brewing" of CuCl.
For normal etching, you'd need to do nothing much. You'd just put a board
in, and add H2O2 if the etchant is too dark in color. a few ml is enough
to oxidize it. The color is all you need to determine if it is ok or needs
something. Then you turn on the bubbler and simply wait until done.
Nothing needs to be done after etching.
The adding of hydrogen peroxide (H2O2) takes the hydrogen away from some
of the hydrochloric acid (HCl). That means the chlorine is freed and can
"take" one copper from Cu2Cl (the dark brown stuff) to form more CuCl
(light green), and water. CuCl is now prepared to take a second copper
again, thus etch the board. You can also introduce the oxygen from other
sources, like pumping air through it (takes long), or even chlorine gas
directly, but that's poisonous.
maintainance:
From time to time you might want to measure the molarity of the HCl in
there. That is, how many hydrochloric acid is still "free" (not carrying
copper) and can be used to form CuCl. Because every time you add H2O2 some
of the HCl is converted into CuCl. At some point, if all HCl is used up,
adding H2O2 will not bring on the expected brigtening of the etchant and
increase in etch speed. Also, the etchant will have a bluish color ad
deposit a blue sludge on boards. This is a sure indicator there is not
enough HCl, but you sould have added some by then.
To measure the HCl molarity, you need 4 things. A alkaline solution of
known molarity (NaOH), some indicator (like methylorange), and two
eyedroppers. You can get your NaOH solution by solving a weighed amount of
developer in water. It should be a 1 molar solution. How much you need to
weigh is said in one of the pages in the links section. When you have that
the procedure is simple. Put 10 drops of etchant in a small container, add
some water if you like, and one drop of indicator. It's now orange. Then
add the alkaline solution drop by drop, all the time swishing the
container to mix it. When it turns green stop and your number of alkaline
solution drops added is your molarity after dividing by 10.
I don't do that often, and usually only add HCl by feel. A wide range of
molarity will be ok. I keep it around 1. Still every few months i feel
like checking the molarity.
There's also the density to be measured. Adding the copper makes the
etchant more "heavy". In a away this is good - because you'll have more
CuCl do do the etching. But if it gets too much you need to remove some
etchant and add water. I have never encountered this, i guess the water in
the HCl and H2O2 added is enough. You can measure the density with a
hydrometer, which you can simply by in a car parts store, as a tool for
checking car battery acid. It comes in a neat huge "eyedropper" in which
the hydrometer swims.
First brewing:
Some tutorials call for adding copper in some form.
I have found you can start just as well with only HCl and H2O2, and water.
At first, you don't have any CuCl, but those two chemicals will etch all
by themself. You can make etchant up by diluting HCl to about 10% and
adding a swig of H2O2. Then put in the board and go by color.
At first there is none or little CuCl, so you have to add some H2O2 each
time you etch. As copper content increases you get more and more CuCl,
which does the etching and must only be re-oxidized from time to time. I'm
now at a stage where i need to add H2O2 maybe each third or fourth board.
Here you go.
ST