On Mon, 05 Jan 2004 23:10:50 -0000, dkesterline <
desterline@...> wrote:
>
>> it also depends where you do your shopping, if muratic acid (HCl)
> is easy
>> to come
>> by where you are and you can get H2O2 somewhere is most likely the
> cheapest
>> method.
>>
> Muratic acid is widely used for cleaning masonary (bricks, block, etc)
> and controlling PH in swimming pools. Most any masonary supply house or
> pool chemical supplier should be able to sell you some in gallon jugs for
> less then $5.
>
> H2O2 (hydrogen peroxide) should be available though any beauty supply
> shop, though I'm not sure about the strength you need.
I fear it is pretty thinned (no more than 10%)
> Very weak peroxide is available in the Pharmacy for disinfectant. It's
> not very strong, but if the recipie calls for water dilution, it might be
> made to work.
>
> Since this is redily available, someone want to post a recipie? Maybe
> some "Care and feeding" guidelines about the regeneration proccess?
>
The problem with diluted H2O2 (like 2% medical) is that you need a lot
more. and the price is nearly the same as 35% stuff.
the huge amount of water will keep your etchant growing.
I bought 1 liter 35% at a chemist's shop for some 3 or 4 eur if i remember
correct.
I use a simplified CuCl process (as i think now - if wrong pease write).
it works the following:
for a start you make a 15% HCl solution (tap water is fine)
Then you put a pcb in it.
then you put H2O2 in it.
for the first pcb you may need more than usual.
start slow, you should see discoloration of the copper very quick.
if you see bubbles forming it is more than enugh, stop adding h2o2.
After some time the etchant will become green.
as long as it is a bright green it etches and everything is fine.
over time it gets darker, and darker, nearly brown.
then it has stopped etching.
if you add a few drops H2O2 you see immediately the conversion to bright
green again.
Add enough to get the whole amount bright green.
but mind, stirr or agitate the container you are using.
a few drops h2o2 can regenerate the whole container, you will see amazing
effect when stirring.
You will also see that localy near copper surfaces the etchant gets brown.
if you agitate the brown drifts away and is diluted/regenerated and
dissapears in the green again.
Well, that pretty much is it. just add H2O2 to keep it bright green.
If you add too much H2O2 the whole thing starts to "boil" at the copper
surface.
lots of bubbles and gas, clorine smell, no good at all.
but if you have good ventilation and need a board in 10 seconds (no joke,
bowl etching) this is a option.
The H2O2 is volatile.
After a etch when the board it out there is no new copper to be converted.
any H2O2 still present has no where to go and will disappear over (not too
long) time.
therefore it is good to add only enough for one etch.
While there is still copper left a certain (tiny) amount of H2O2 in the
etchant
is good. it immediately regenerates the brown etchant to green (Cu2Cl2 to
CuCl2 i was told).
But it can only work as long as Cu2Cl2 is produced. if there is no Cu2Cl2
is left it is a fully
regenerated etchant.
So you see the reason for not adding too much. it will only produce oxygen.
The echant stays in regenerated state in storage.
so the CuCl2 is not lost between etches.
It does also stay in used Cu2Cl2 condition. but air oxygen slowly
regenerates it.
If you add a bubbler (air pump) and let it run (hours to days) you can
actually regenerate
it only from air oxygen.
I don't do that because H2O2 is so cheap, it is faster etching with it, and
air bubbling adds problems (mist).
There are two effects i can't fully describe:
a) the "start up" why it works with plain HCl and H2O2 in the beginning.
(but it really does, you need no day - long preparation)
there is no CuCl2 present, it must directly convert it from copper, HCl and
oxygen.
b) the "blue" effect.
Only once until now the etchant suddenly formed a blue soft sludge on the
copper and
refused etchnig. adding H2O2 did not help.
Adding HCl did help, but i also needed some H2O2 again.
I assume all Cl atoms were already used up and it din new HCl to get them.
The catch is that the copper is not regenerated out the solution.
the number of CuCL2 molecules steadily increases.
If one Cu2Cl2 is regenerated 2 CuCl2 are produced.
the clor needed is taken from the HCl.
but with the hcl there is hydrogen. the hydrogen is taken by the oxygen
from the H2O2.
this leaves you with additional water.
I hope this simple chemistry is correct, it is all i could come up with.
the growth of the etchant is very low in fact, i would say nearly
insignificant if some
water vaporizes and some is taken out sticking to the boards.
the consumption of H2O2 is also very low, only a few drops for a smaller
board.
the HCl consumption is not more, you will etch quite a few boards before
the initial 15% are used up.
you see i had the "blue" effect only once until now...
to the handling:
it is a strong etchant.
i have fetched the pcb several times by now with bare hands and in only one
second
washed it immediately in water. nothing was to be seen on the hand.
i strongly recomment not doing that anyways...
Longer exposure is not tested, and i don't like being test rabbit.
You can not use any metals in the tanks etc., no stainless steel or so.
only plastic holds up well.
For me this etchant is ideal with toner transfer - as it is as easy and
fast.
the toner takes no harm in the etchant.
photoresist works too.
Most ohp markers (edding etc) don't work too well.
the best is the red staedtler ohp pen ink.
with that you can correct your artwork if the toner transfer left errors.
Feel free to ask any questions.
Stefan