Ammonium, Potassium Persulfates all make good copper etches. They can even
have catalysts added which then allow them to be used with tin tin-lead
resists. When the salts are dissolved in water the Persulfate ion is
formed, which then goes on to oxidize copper to the cupric ion. Std
Reaction is :-
+(NH4)2S2O8 >> CuSO4
makeup is 100-200g/l of Persulfate salt, 20ml/l 96% Sulphuric Acid. A
mixed solution becomes exhausted in 3-5 days independent of usage.
acid must not be used as toxic chlorine gas would be liberated. Once done
the use of the wrong acid is never repeated.
etch is commonly used as a micro etch a sort of (chemical sandpaper) before plating