In the past I've used ferric chloride professionally as my
etchant (and left disposal of the etching solution to the work's
chemist) but now I'm doing things for myself safe disposal is going to
be my problem, searching on the web for an answer ammonium and sodium
persulphate come up as a suitable alternatives but not ones I've used.
Does anyone have experience of using persulphates as a D-I-Y PCB etchant
? Are they as good as ferric chloride, are there any problems with using
them & how easy is it to dispose of the spent solution ?

Last year, as an experiment, I marked up a small piece of double-sided
copperclad with Sharpie and similar marking pens. I then etched it in
a solution of sodium monopersulphate (cheaply available at pool-supply
stores - it's used as an oxygen shock) and hot tap water. A plastic
cup served as the container, and I agitated gently by hand.

It definitely etched! As I recall, 10-15 minutes was sufficient to
etch the unprotected areas down to bare fiberglass. The etch was easy
to monitor as the solution is clear to start with, and turns a clear
blue-green as the copper is etched. The different marking pens I'd
tried had different amounts of resistance to the etch... one or two
stood up fairly well, the others did not.

I haven't tried actually making a functional board with this etchant
yet, but may do so in the near future - I've refurbed an old HP
flatbed plotter, and converted the pen-holder to use Staedtler (sp?)
red-ink permanent marker pens which have a good reputation for etchant
resistance. Some form of improved solution-heating and
agitation/bubbling arrangment would probably be a good idea, to get a
quick and consistent etch.

Disposal can be quite easy. Mix up a solution of sodium carbonate
(washing soda, also sold at pool-supply stores as a mild alkali to
raise the pH of pool water) and titrate it into the used solution. The
dissolved copper will convert to copper carbonate, and precipitate
out... copper carbonate isn't very soluble in water. Strain the
solution through a paper filter (e.g. coffee filter) to separate the
carbonate from the remaining solution (which should be clear once
again if you added enough sodium carbonate).

I just dumped the copper-free solution into my swimming pool, and
discarded the filter in the trash. If you want to really immobalize
the copper carbonate, you could mix it into a batch of
plaster-of-paris or portland cement and let it harden up, and then
trash the resulting piece of rock.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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