Abstract
Electroless plating of copper onto insulating substrates is a process widely used in the electronics industry for manufacture of printed wiring boards, and in decorative plating of plastic trim parts for automotive and consumer appliance applications. Plastic surfaces must be specially prepared to catalyze deposition from the electroless bath. The process most widely used for this purpose involves a palladium-tin catalyst. The successive processing steps involve a complex series of reactions including redox reactions, colloid formation, precipitation and redispersion. We have studied these processes in detail using Mossbauer spectroscopy of the Sn119 to follow the chemical state of the tin and Rutherford backscattering to determine thr elemcnts present on the surface. The results show that : (1) the Sn-Pd bath contains extremely fine (colloidal) particles of Pd-Sn Alloy, (2) these particles are adsorbed on the plastic surface during treatment in the sensitizing bath, and (3) during the rinse after catalysis, a layer of stannic hydroxide is deposited over the Sn-Pd alloy particles. This stannic hydroxide must normally be removed by a separate processing step. With this understanding of the chemistry, it is possible to redesign the process to provide improved efficiency.
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