A different Etchtant (was Re: Homebrew PCB mailing list invitation)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

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-at-qwest-dot-net>" <alienrelics-at-yahoo-dot-com>
> 
> I don't know, you should join and ask. ;')
> 
> http://groups.yahoo-dot-com/group/Homebrew_PCBs/
> 
> 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-at-pupman-dot-com> wrote:
> > Original poster: "Malcolm Watts by way of Terry
> > Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> > 
> > Hi Steve,
> >            What etching fluids are used by your
> > group members?
> > 
> > Regards,
> > Malcolm
> > 
> > On 6 Dec 2001, at 8:03, Tesla list wrote:
> > 
> > > Original poster: "Steve Greenfield by way of Terry
> > Fritz
> > <twftesla-at-qwest-dot-net>" <alienrelics-at-yahoo-dot-com>
> > > 
> > > I've started a Yahoo Group on making, etching,
> > > soldering printed circuit boards yourself. 
> 
> 
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