Characterization of PdSn catalysts for electroless metal deposition
by E. J. M. O'Sullivan, J. Horkans, J. R. White, J. M. Roldan
A set of electrochemical techniques has been developed to measure the component concentrations and the catalytic activity of the PdSn seeder solutions used to activate insulating substrates for the electroless deposition of Cu. The concentration of Sn(II) was calculated from the limiting current for Sn(II) oxidation, that of Sn(IV) from the difference between the Sn metal-deposition limiting current and the Sn(II) limiting current. The palladium concentration was determined by a stripping analysis after Pd deposition from an oxidized seeder solution. The catalytic activity of the PdSn catalyst was estimated by measuring its activity for the electro-oxidation of formaldehyde (the reducing agent used in the electroless Cu bath) or by the cyclic voltammetric response of a seeded electrode in an inert electrolyte. The cyclic voltammetric technique and transmission electron microscopy examination were used to evaluate various accelerating solutions used to increase the activity of the seeder.