Re: copper etching

From: Uncle Al (UncleAl0_at_hate.spam.net)
Date: 12/28/04 

Date: Tue, 28 Dec 2004 11:30:46 -0800

Steve Turner wrote:
>
> On Tue, 28 Dec 2004 10:44:16 -0500, Marshall Dudley
> <mdudley@king-cart.com> wrote:
>
> >1. Acetic acid, slow and tends to dissolve the ink.
> >2. Hot H2SO4, tends to dissolve the ink and evolves some nasty gases.
> >3. As you indicate nitric acid, but evolves really nasty gases and can attack
> >the board.
>
> Attack of the resist is definitely a problem which must be considered.
> So is undercutting of the trace, particularly with thin traces. The
> etchant used must be aggressive enough to do the job in a reasonable
> time (<30 min.), without attacking the resist or the underlying
> polymer. There are lots of things that attack copper, but far fewer
> that satisfy all of these criteria. For people living in the U.S.,
> just go to Radio Shack and buy their etchant. It's cheap and it
> works. After going through the time and hassle of laying down an
> intricate resist pattern, why take chances with etching, which is
> potentially about the easiest and most foolproof step in the whole
> process?
>
> >The etchant of choice would most likely be sodium persulphate, inexpensive,
> >and more environmentally friendly than any of the others, including FeCl3.
>
> I've seen this allegation about FeCl3 a number of times. I don't
> understand it. Why should FeCl3 be environmentally unfriendly?

FeCl3 is the flocculant in sewage treatment. It is made by dissolving
scrap iron - evrything from crushed cars to locomotives - in HCl +
chlorine. Enviro-whiners hate working solutions. 

-- 
Uncle Al
http://www.mazepath.com/uncleal/
 (Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

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