On Wed, Feb 20, 2013 at 4:08 AM, William Whyte <
olliewhy@...> wrote:
> ∗∗
>
>
Todd, What are your ratios, particuly the sodium chloride(salt) ?
Ollie,
I'm actually no longer using the salt additive, just the muriatic
(hydrochloric) acid and peroxide. I wish I could find my link, but I think
my original source used salt as a means of getting more chloride ions into
depleted etchant without adding more acid. I tried it a few times when I
was reusing the etchant and it did seem to shorten long etch times. Now
that I use the etchant one-shot---a small amount that is then discarded---I
don't need to refresh used etchant.
My formula for the one-shot version is the typical 1 part ≈35% muriatic
(hydrochloric) to 2 parts 3% hydrogen peroxide (the drug-store variety). I
warm it a bit to ≈100°F (38°C), but since I use only about 6oz (170ml) of
solution in a tray, it cools down fairly quickly. I use the foam trays that
meat comes packaged with.
I learned the one-shot method as an industrial photographer. Not reusing
film (and paper) developer, but using small amounts one-shot, allowed for
precise control that cannot really be had with reuse/replenishment schemes.
Precise repeatability is possible with one-shot. It's not with reuse.
Much of the need for repeatability, in my mind, is that we DIYers use some
pretty dubious methods of applying etchant resist to our boards--toner
transfer being the most common, it seems--I use it myself. This means using
materials that are not optimum for the purpose and applying them with
make-shift methods: cloths irons, etc. Combined with less-than-thorough
surface preparation of the copper clad, all this means our resist patterns
are fragile and cannot withstand long etch times with repeatable results.
It's not just that the resists are probably not-all-that chemically
resistant, but that their mechanical bond with the copper is weak and
uneven. Flaking of the resist, or undercutting of it in long etch times, is
an ongoing problem for many of us. Fast etch times and
repeatably-predictable results can minimize these problems. Both point to
one-shot etching.
Now in my online poking around in the last few days on these issues, I am
now persuaded that I need to be much-more careful in the disposal of my
etchant--especially since I'm tossing out several ounces at a time for each
board. To be perfectly honest, I used to just dump the stuff down the drain
with plenty of running water. Bad news! So what I'm going to try is to dump
it into a five-gallon bucket filled about 3/4 full of wood shavings. I have
a whole bale of the stuff left from when we had hamsters (a rant for
another occasion). Saw dust or even shredded paper might work just as well.
I'll dump the spent etchant into the bucket, maybe stir the shavings around
a bit (maybe not), and then keep the bucket open and outside (not
inside!!!) but out of the rain. Before long, each dumping will dry in the
bucket, sequestered (oh that word!) in the wood or paper fibers. I guess I
should put a warning sign on the bucket. At some point I'll have to
double-bag the shavings before tossing them in the land-fill garbage, but
as I'm thinking now it might take many years before that will be necessary.
It may never be necessary in my lifetime, so I'll have to leave disposal
instructions in my will (wink wink).
Best,
Todd
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