Re: copper etching

From: Steve Turner (srturner1_at_spammers_die.net)
Date: 12/28/04 

Date: Tue, 28 Dec 2004 19:05:50 GMT

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?

Steve Turner