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'[OT]:PCB chemistry'
2001\03\27@055520 by Alan Gorham

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I saw a discussion that started last week about PCB fabrication.
One of the messages said that the useful life of Ferric Chloride could be extended
by performing electrolysis on the solution to recover etched copper.

I have tried this and it works. I think that the cathode should be copper and that the anode should be non-cuprous to prevent a simple transfer of copper from anode to cathode.
The outcome of all this is that it removes the issue of diposal of used Ferric Chloride at least for a while as it now lasts for ages.

Hope this is useful to someone!

Alan

Embedded Systems Engineer
Microtima Ltd
Ouseburn Mews
3-7 Stepney Bank
Newcastle upon Tyne
NE1 2PW

Tel: 0191 2304411
Fax: 0191 2304422

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2001\03\27@214139 by Jinx

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> Alan Gorham wrote :
>
> I saw a discussion that started last week about PCB fabrication.
> One of the messages said that the useful life of Ferric Chloride
> could be extended by performing electrolysis on the solution to
> recover etched copper.
>
> I have tried this and it works. I think that the cathode should be
> copper and that the anode should be non-cuprous to prevent a
> simple transfer of copper from anode to cathode

Do you have any figures for the V and A of the electroplating
tank ? My book deals with clean solutions of copper salts, not
those contaminated with iron. A table that shows electrode
potentials has -0.43V for Fe and +0.33V for copper. In a solution
of mixed salts isn't there going to be migration of metals out of
solution on to both electrodes ? And I think I'm correct that CuCl
is the insoluble sludge, which is going to be more difficult to
electrolyse than an aqueous solution

If so, I don't know the dissociation constant for CuCl (which will
be very low if it's insoluble) but perhaps getting the Cu out of the
liquid phase before it reacts with the Cl atoms may work better
than working on the sludge

One idea I had for this (if it works) is to copper-plate other metal
items. Decorative parts could be lacquered

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2001\03\27@222638 by Jinx

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> And I think I'm correct that CuCl is the insoluble sludge

I wasn't correct - CuCl is soluble. Perhaps the sludge is an
Fe-Cu-Cl-impurities complex, the Fe+++ may even have
been reduced to Fe++

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2001\03\28@110704 by Alan Gorham

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If anyone is thinking about trying the electrolysis trick on some of their
tired Ferric Chloride, then please go ahead.
I have not delved too deeply into the Chemistry of it but I have seen
results.

I etch my boards in a plastic tray about the same dimensions as A4 paper and
a depth of approx 2cm of Ferric Chloride. This gives an idea of the volume
of etchant I use.

My electrodes are a 10cm copper rod and a 10 cm steel rod.
The cathode is copper and the anode is steel. The electrodes are at 6 cm
separation and I simply hook them up to a 0-30V, 2A bench power supply.

At a current of 1A I can recover about 10g of copper in 20 minutes.
The etchant certainly seems to be noticeably more effective after this
recovery.

With regard to dangerous gases emitted: I perform the electrolysis in a fume
cabinet with the extractor running.

Since I am quite pleased with the results I have not looked too deeply into
any implications, so if anyone can say if there are good reasons to stop
then I will!!

Alan
{Original Message removed}

2001\03\28@110820 by Bill Westfield

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If you're going to go to a replenishable etchant, you might as well
go all the way to Cupric Chloride etchant, which has some other nice
features as well (such as TRANSPARENCY!)

See http://www.dnai.com/~rexa/Projects/CuCl_ech.html

I'm not sure why Iron chloride is so popular.  Perhaps because it IS/WAS
an industrial chemical already, easilly available in large quantities for
low prices?

BillW

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2001\03\28@122841 by M. Adam Davis

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While I could assume this is the case, I'd rather ask and know for sure:

You remove the rods from the tank when you are not performing
electrolysis, right?

Do you current-limit the supply, or does the solution limit the current
acceptably for you?

Do you clean the copper rod before each use (as it should tarnish
quickly in air)?

Have you copper plated anything just for fun?

Have you ever thought about getting a heavier layer of copper on your
PCBs by using an unetched pcb as your cathode?

-Adam

Alan Gorham wrote:
{Quote hidden}

> {Original Message removed}

2001\03\28@214238 by Gennette, Bruce

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A couple of answers for you -

Current limiting is built in to the concentration of the solution and
SEPARATION of the electrodes.
Voltage should be monitored across the electrodes and limited to around 2V
(no large bubbles forming on the electrodes).  You need to supply about 5V
'push' to get 2V 'flow' through the electrolyte.

Clean metal (rubbed with sand paper) is essential for electrical conduction
into/out of the electrolyte.

Without special additives the metal ions will *NOT* adhere properly to an
electrode, you just get a buildup of metal powder over the surface.  Electro
plating requires special (and often poisonous) solutions held at selected pH
and temperature to achieve proper plating.

So, no, you can't expect to be able to plate things with a simple cell,
especially not existing circuit boards.  You *CAN* get some success with
(dull) nickle plating if you want to protect steel, copper or brass, but
it's usually cheaper to buy parts already plated.

Bye.

{Original Message removed}

2001\03\28@233520 by Jinx

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> A couple of answers for you -

Thanks, what you said ties in with what my creaky old e-p
book says (voltage, adding acid). In e-p terms an etching
solution is well out-of-spec so I'm not expecting any sort of
professional results. More of an experiment - if it fails I
haven't lost anything, not especially fussed either way

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2001\03\29@040438 by Roman Black

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Alan Gorham wrote:
{Quote hidden}

Thanks Alan! Does the resistance change when the
copper is completely removed from solution? Maybe
you could build a automatic circuit (using a PIC??)
that removes all the copper then switches itself
off.
-Roman

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2001\03\29@080613 by Bob Ammerman

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> Thanks Alan! Does the resistance change when the
> copper is completely removed from solution? Maybe
> you could build a automatic circuit (using a PIC??)
> that removes all the copper then switches itself
> off.
> -Roman

Yeah, but then the etchant would immediately start working away on the
copper electrode!

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\03\29@082952 by Kevin Blain

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...and then goes into 'trickle charge' where a small current flows to keep
the copper on the electrode
...or a servo/motor pulls the electrode out
...and makes the tea....


Kevin
{Original Message removed}

2001\03\29@172941 by Alan Gorham

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Roman - How technical do you want to make it!!! :-)

All I do is whack the electrodes into the etchant, turn on the extractor fan
in the fume cupboard, go and have a cup of tea and then come back.

I WILL check for a change in resistance though!

Alan

{Original Message removed}

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