Adam: I am impressed, for a guy who claims his chemistry is not that good, you are doing a better job than most...
Yes, you can use the ORP reading in an ammoniacal etcher as well as Cupric, and this would be a great way to monitor Cuprous. You can also do a titration with Iodine, but I have a sense that getting the sample, neutralizing and diluting it would probably allow most of the Cuprous to be converted to Cupric, so your titration would probably be meaningless.
For a review of this chemistry, and I am not sure you need it, you may want to check out our website, www.pcbfab.com
Rudy Sedlak
Adam Seychell <[log in to unmask]> wrote:
I am wondering if there is a simple test for cuprous ions in ammoniacal
chloride alkaline etching, and thus determine when to increases or
decrease the air ventilation intake of the etching machine. I am brewing
my own chemistry based on typical operating parameters of ammoniacal
chloride etchants.
Copper 2 ~ 2.5 Molar
Chloride 4.5 ~ 5 Molar
pH 8.0 ~ 8.6
Temp. 40 ~ 45 °C
I discovered just like with acid cupric chloride etching, that when the
cuprous content reaches to even small concentrations then the etch rate
is severely affected. In the lab, I tested as little as 5g/L of
dissolved copper in the cuprous state will slow etch rate, and at 10 g/L
it becomes virtually a stand still. For acid copper chloride etchants,
the loss of its bright green color is a quick indicator of cuprous ions
being present, and even 0.5 g/L will show beginnings of color change.
However in alkaline etching the cuprous ions do not appear visible or
change the solution color. I have heard about ORP (oxidation-reduction
potential) probes used in acid cupric chloride machines. Can these same
probes be used in ammoniacal chloride etchants ?
My chemistry is a bit poor, although I'm wondering if is possible to
make such a probe, using a standard reference electrode (e.g Ag/AgCl )
and a piece of copper wire as the indicator electrode.
Adam Seychell
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