Homebrew PCBs

At 11:17 am (PDT) Tue Sep 12, 2006, Hector Garcia wrote:
>I found the original source in english
>http://www.qsl.net/iz7ath/web/02_brew/14_howto/02_clor/index.htm

Again we have reference to this canard that seems to
claim that Ferric Chloride in aqueous solution isn't acid.

If the pH is around 7 (neutral) there will be so little
Fe3+ ion in solution it will be literally almost drinking
water. (Ferrous Hydroxide flocculation with FeCl is
used to purify water for human consumption.)

At an etching strength, the solution could be as low as pH 2,
which is very acid. It gets that way either by having been
acidulated by the addition of hydrochloric acid (the preferred
course) or by the precipitation of ferrous hydroxide until
equilibrium is found (and a lot of its etching potential is
wasted as brown sludge).

I get the impression that some of our members don't
acidulate their ferric chloride bath... :-(

I also get the impression that some people don't understand
the word "regeneration" - it ought to imply a return to (or very
close to) the original state.

For example, this is what happens in photo-processing labs,
where consistent chemistry is vital for consistent results.
A developer bath is made up from a concentrate and then
topped-up during use with a _different_ concentrate which
attempts to compensate for both the exhaustion of the
original developer and the contaminants introduced by
the film that has been processed. A fixer is regenerated
by the _removal_ of silver or silver salts and the addition
of a top-up concentrate.

Many people here write about "regenerating" FeCl by
methods which make no attempt whatever to remove
the accumulated copper.

This is _not_ regeneration, though if it restores activity
it might be called "reactivation". (I believe ST surmised
that these treatments move the bath towards a
combined FeCl - CuCl chemistry.)

But if you are going to use CuCl etchant, why not go
there directly and forgo the brown sludge?

Similarly, if you are considering using HCl and H2O2 to
reactivate your etchant, why not use them _as_ your
etchant? It's quick, clean and one less chemical to store.


Regards, LenW