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'Re (OT) Etchant (was :PCB exposure unit)'
1999\04\28@074301 by Jochen Feldhaar

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Hello all,

it seems to me that nobody really understands what the etchant does do with
the copper. The HCL "acido clorhidrico" is the mainly active substance, but
the etching process would be a slow affair. So you add H2O2, and heat the
soup to 40 degrees centigrade, and in about 2-4 minutes a very clearly
defined PCB will emerge like Aphrodite out of the bath (without the
foam...). The H2O2 has to be replaced periodically, as it tends to decay
into O2 and H2O.
The CuCl is another matter. After some time, the reaction of the HCl and
the Cu will produce a certain accumulated amount of CuCl in the solution,
but it really is a polluting and annoying fact. Also after use, the
solution may not be "recycled" down the sink, but is dangerous waste that
has to be given to certain collecting points for chemical waste. Big
companies prefer to recycle the copper out of the solution, regenerating
it, but this only makes sense in big quantities. So, the CuCl is not an
initial ingredient in the solution!

my 0.02 Euro worth (falling almost daily)

Jochen Feldhaar DH6FAZ
spam_OUTjfTakeThisOuTspamdetektor.de

1999\04\28@081213 by Benjamin Petersen

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>
> Hello all,
>
> it seems to me that nobody really understands what the
> etchant does do with
> the copper. The HCL "acido clorhidrico" is the mainly active
> substance, but
> the etching process would be a slow affair. So you add H2O2,
> and heat the
> soup to 40 degrees centigrade, and in about 2-4 minutes a very clearly
> defined PCB will emerge like Aphrodite out of the bath (without the
> foam...). The H2O2 has to be replaced periodically, as it
> tends to decay
> into O2 and H2O.

How can we then replace it ? As I see it we can only add things to the soup.

> The CuCl is another matter. After some time, the reaction of
> the HCl and
> the Cu will produce a certain accumulated amount of CuCl in
> the solution,

CuCl is CobberXXXX ?

So can I some how reuse the solution of HCL and H2O2 ?

Regards
 Benjamin Petersen

1999\04\28@081832 by Jochen Feldhaar

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Hello all,

reusing the solution is really going the reverse process of the etching
process, but adding energy to dissolve the CuCl into its 2 components. As
the H2O2 will decay into water, and generally water will either evaporate
or just dilute the solution, the amount of solution will increase slowly.
For 20 litres, we added about 1/4 litre all 2 weeks, so it is no big deal.

By the way, I think Stefan wanted to say 20 and 60 degrees Centigrade, and
not 200 and 600...

Jochen Feldhaar DH6FAZ
.....jfKILLspamspam@spam@detektor.de

1999\04\28@154944 by Leo van Loon

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I think I owe you all some explanation about the cupric cloride/hydrogen
peroxide/hydrochloric acid bath.

First a little bit of chemistry. Simplified reactions are:

etching                 Cu2+  + Cu   =  2Cu+

regeneration    Cu+  =  Cu2+ + e
peroxide                2e + 2H+ + H2O2  = 2 H2O
Hydrochloric acid is essential to provide the protons (H+).

Never use hydrogen peroxide/hydrochloric acid direct to etch. It goes very
slow and is very dangerous. Deadly chlorine gas can be formed. It is also
the main disadvantage of the bath, when too much H2O2 is added. Only
regenerate CuCl, cause cupric chloride etches much faster.

The colour of the bath is also an indicator for the acidity. The right
colour is (dark)green. When the colour becomes blueish, you should add
hydrochloric acid until the bath is green again.

The ingredients are in common commercial, relatively safe concentrations
(weight percentages). When you use lower concentrations in the regeneration
process, the solution is too much diluted.
Hydrogen peroxide is usually packed in bottles with a pressure relief valve
in the cap. Do not screw normal caps tight.

Etching is mainly dependant of stirring speed. Etching in a spraying machine
goes in less than a minute. Bubble stirring has the disadvantage, that
corrosive vapours ruin all the metal in the neighbourhood of your bath. This
is true for all etchants. Work outdoors or in a fume-cupboard.

Leo van Loon
SBB simpeltronics
Netherlands
tel +31 (0481) 450034
fax+31 (0481) 450051
mail sbb.simpeltronspamKILLspamtip.nl
url http://www.sbb-simpeltronics.nl
SBB simpeltronics ontwikkelt technische projecten voor basisschool en
basisvorming.
SBB simpeltronics develops technical projects for children in primary and
secondary education.


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