Investigation on Automatic Regulation of Concentration in Electroless Copper Plating Bath

Studies on Electroless Plating of Copper (Part 3)

Abstract

An automatic regulating apparatus for pH and concentrations of copper and formaldehyde in electroless plating bath was manufactured for trial. The purpose of the apparatus was to maintain the concentrations of ingredients at constant during the deposition of copper.
The apparatus was used in the plating baths containing 0.02 and 0.03mol/l of copper ion and the deposition of copper for about 5hrs. was repeated 10 times.
In the bath containing 0.02mol/l of copper, the concentrations of copper ion and formaldehyde were maintained at 0.019-0.025 and 0.15-0.22mol/l, respectively, and pH was adjusted in the range of 12.0-12.3 during the operation.
The deposition rate of copper was likely to be increased with the number of repeating times of deposition. It would be due to the effects of HCO₂^- and SO₄^2- which were accumulated during the repeated depositions.
Accordingly, the addtion amount of the ingredients must be controlled, but the operating time may be changed in order to keep a constant thickness of the deposit for each time of deposition.