Electroless copper plating using systems containing a small amount of Ni2+ or Pd2+ as a mediator and hypophosphite as a reducing agent was investigated using several electrochemical techniques. Isothermal and component-dependent polarization, rate, Emix, split-cell, and ac impedance data suggested that the systems obey mixed potential theory and function as follows: a) the mediator is initially deposited from solution to the surface of the workpiece via hypophosphite reduction, b) oxidation of the hypophosphite at mediator sites supplies charge for Cu reduction, and c) Cu plating occurs over the entire workpiece. XPS analysis and depth profiling of the resulting deposits suggested that they are homogeneous in nature and that the mediator is uniformly distributed throughout. The chemical composition determined by the XPS analysis agrees well with the results obtained by atomic emission spectroscopy. In addition, the analysis showed no evidence of Cu oxide formation.
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