Mechanism of Activation of Polymer Surfaces by Mixed Stannous Chloride/Palladium Chloride Catalysts

Summary

Mixed stannous chloride/palladium chloride catalysts are often used to activate etched ABS surfaces prior to electroless nickel or copper deposition. Little is known of the nature or activation mechanism of the catalyst. The nature of the catalyst was investigated using nephelometry and electron diffraction. No evidence for the existence of colloidal metallic palladium was found. The active component of the catalyst is thought to be a complex chloride of tin (II) and palladium (II). The major species present on the ABS surface at each step of the pretreatment cycle were identified using electron diffraction. A mechanism of activation was proposed involving hydrolysis of an adsorbed chloride complex within the ABS surface. On subsequent treatment with ammonium bifluoride accelerator, a surface redox reaction is presumed to occur between the hydrolised species forming active palladium nuclei: Sn (II) + Pd (II) = Sn(IV) + Pd (0). The process variables were also investigated. It was found that immersion times in all pretreatment solutions including rinses had a direct influence on induction period.