--- In
Homebrew_PCBs@yahoogroups.com, "N2CUA" <n2cua@...> wrote:
> Is there any issues with mixing etching solutions
>
> From 30% HCL / 30% H2O2 to the right concentrations/ ratios
>
> And mix together and store that way ?
On Thu, May 9, 2013 at 10:28 AM, designer_craig <cs6061@...> wrote:
> ∗∗
>
> The HCL/H202 is just the starter, the real etchant is the Cupric Chloride
> (+2 oxidation state)you eventually end up with. Initially the HCL/H202 etch
> the copper off the board forming Cuprous ions (+1 oxidation state)in the
> solution. Then more H202 is added or O2 is bubbled through the solution to
> oxidizes the Cuprous ions back to Cuperic ions. As the quantity of copper
> in solution increases more HCL must be added to keep the chloride ions in
> balance with the ever increasing copper in solution. You actually make more
> etchant with every board etched. There has been extensive postings about
> this process and how to replenish and regenerate the etchant. My
> understanding is that 3% H202 adds too much water and dilutes your etchant.
> For best results use 30% if you can find it.
>
I use the 30% HCL ("muriatic acid") from Home Depot (~$12/gallon) and the
drug-store-variety 3% peroxide. I mix up only 2oz (~50ml) at a time for
boards up to 4x6 inches (the largest I ever do), and I use it ∗one shot∗
and then dispose of it (more on that later). This provides very consistent
results, and I don't have to wonder about shelf life or strength. I learned
this one-shot chemistry technique in photography. I'd guess I spend about
10 cents on each shot.
Responsible disposal is, of course, an issue. At first, instead of dumping
it down the drain, I dumped in into a five-gallon bucket filled with wood
shavings. My plan was to keep that bucket of shavings for as long as
possible before triple bagging them for the land fill. But then someone on
the list chewed my ass for creating more toxic waste. His alternative was
to neutralize the solution in such a way that the copper is bound-up in a
safe compound. I do not now recall his simple process (I haven't done any
etching since then), but searching this list for "peroxide" and "muriatic"
and "wood shavings" will turn up his postings and my bloody ass.
Best,
Todd
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K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
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QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design
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