Adam,
Ammoniacal etch needs to be air agitated or sprayed so that the cuprous ions
are oxidized back to cupric ions. Which actually do the etching. In the
presence of oxygen, the Cu(+1) should easily convert back to Cu(+2), and so
no need to measure it. In cupric chloride etchants, the ORP probe measures
the active chlorine in solution, which converts the Cu(+1) back to Cu(+2) so
it can etch the copper metal. Hope this helps.
Regards,
Denis Morrissey
Senior Manager- Wet Process Engineering
Tel: (631) 845-1041 EXT: 18
Fax: (631) 501-1270
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-----Original Message-----
From: Adam Seychell [mailto:[log in to unmask]]
Sent: Monday, June 12, 2006 7:03 PM
Subject: cuprous ions in ammoniacal chloride etching
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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