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Probably
the main etchant used within the circuit board industry. Due to it's
very smelly nature it is only used in spray etching applications.
Normal copper etching reaction is:-
Initial
reaction, which results in a build up of cuprous ions,
Cu2+
+ CuO >> 2Cu+
Secondary
reaction, oxygen is absorbed from the air which re-oxidizes the cuprous
ions back to cupric ions,
2Cu+
+ 1/2O2 + H2O >>
2Cu2+ + 2OH
The
basic etching reaction is the same as cupric chloride etching but to
work the copper (II) ions require complexing with ammonium chloride and
ammonia.
Cu2+
+ 2(NH4)Cl + 4NH3 >> 2NH4+
+ Cu(NH3)4Cl2
To
work free ammonia is present, which always finds it's way past any
extraction equipment resulting in strong odours. Ammonia loss results in
sludging, as do excess water or excess copper. Its an almost trouble
free process when correctly run but can result in hours of machine
cleaning if not.
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