Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla@...>" <m.j.watts@...>
HI Steve,
The reason I asked was so that I wouldn't
be duplicating
otherwise available information. From the two replies
I've received,
it seems that the mixture I use is not widely known,
so here it is.
The basic mix: 1 part commercial grade hydrogen
peroxide (about 30% I
think), 1 part fuming hydrochloric acid, AND 6 - 8
parts water with
the H2O2 and Hcl separately added *slowly* to the
water. This
concentration gives a useful etching speed. Waste
products are copper
II chloride (soluble with a low pH) and water.
DO's:
- Ventilation when pouring the Hcl out of the bottle
- A *good* impervious resist with no pinholes
- Occasional agitation to release small bubbles from
the surface of
the board
- water at hand to wash yourself if you get acid or
peroxide on your
hands. The peroxide in particular will attack skin
very rapidly
and you'll feel it.
DON'Ts:
- *DO NOT* mix the undiluted acid and peroxide
together. The
mix will produce copious amounts of chlorine (none
will be
produced if the mixing directions above are
followed).
- be tempted to use a strong mix to make etching much
faster.
A strong mix will not only etch a board bare in a
matter of
seconds, it will boil as well (spatter factor).
- be tempted to top up the acid and/or peroxide if
the etching
crawls to dead slow. Make a fresh mix instead.
Too much acid gives the mix a green hue during etching
and too much
peroxide makes the copper appear shiny. Ideal is for
an oystery sheen
to cover the copper if the board is lifted out of the
mix and
drained. If the acid is becoming exhausted, insoluble
blue deposits
appear on the copper. A correct mix will give the
mixture a blue
colour, deepening as more copper is dissolved.
The basic action seems to be that the peroxide
oxidizes the
copper leaving the oxide easy for the acid to deal
with.
Finally, the waste salt can be usefully mixed with
sodium carbonate
(washing soda) or sodium bicarbonate (baking soda) to
make a useful
anti-fungal spray for fruit trees. The result is
copper carbonate
(low solubility) which needs to be washed several
times to remove the
soluble NaCl.
I started using this recipe about 30 years ago and
it is a
winner. No more awful stains or waiting for hours. I
can't claim
originality for it - I first saw it mentioned in a
letter in an
electronics periodical "Practical Electronics".
Regards,
Malcolm
On 11 Dec 2001, at 12:33, Tesla list wrote:
Original poster: "Steve Greenfield by way of Terry
Fritz
<twftesla@...>" <alienrelics@...>
I don't know, you should join and ask. ;')
I've used whatever Radio Shack sells and found at
best
it is adequate, at worst a waste of money and time.
I've also used some dry stuff I think was Ammonium
Persulfate that I was satisfied with.
A colleague told me he's used a weak Nitric Acid mix
to etch boards -very- quickly but you have to be
well
rested, have a lot of ventilation and really be
paying
attention. And your etch resist coating had better
be
complete.
Steve Greenfield
--- Tesla list <tesla@...> wrote:
Original poster: "Malcolm Watts by way of Terry
Fritz <twftesla@...>"
<m.j.watts@...>
Hi Steve,
What etching fluids are used by your
group members?
Regards,
Malcolm
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