A Palladium Sulfide Catalyst for Electrolytic Plating

Abstract

During the manufacture of circuit boards, a palladium-tin colloid is adsorbed onto an epoxy substrate and serves as a catalyst for the subsequent electroless deposition of copper in nonconductive areas, viz., the drilled holes. This is normally followed by a thicker layer of electrolytically deposited copper. A simpler process has been developed which replaces the electroless step with a sulfide-containing solution which alters the adsorbed palladium-tin colloid and renders it resistant to acidic solutions and very effective for the subsequent electrolytic deposition of copper. Use of x-ray absorption spectroscopy techniques (x-ray absorption fine structures and x-ray absorption of near-edge structures) was conclusive in establishing that the altered catalytic film was a mixture of palladium sulfide, which remains stable for at least several months, and mixed valence sulfidized tin species, which begin to oxidize to stannic oxide within 24 h. Electrolytic copper plating characteristics are determined for this novel palladium sulfide activator and compared to those of a conventional palladium-tin catalyst. A "stepwise propagation with continuous conduction" model is proposed, based in part on the results of scanning tunneling microscopy which reveals PdS particles in intimate contact with each other.

Mechanism of Direct Copper Plating on Nonconducting Substrates

“…Bladon et al 2 proposed the model of "stepwise propagation with continuous conduction" for the modified process developed by the Shipley Company for improving the propagation speed of direct plating. They claimed that stable palladium sulfide particles with the diameter of 4.5 nm in contact with each other, are formed by immersion of the catalyzed substrate in a sulfide solution and cover the entire surface thereby providing electrical conduction.…”

Palladium(II)/allylpalladium(II) complexes with xanthate ligands: Single-source precursors for the generation of palladium sulfide nanocrystals

“…Platinum group metal chalcogenides find extensive applications in catalysis [1][2][3][4][5] and material science [6][7][8]. PdS, a semiconducting sulfide (E g = $2.0 eV), in particular, can be used as a catalyst for dehydrogenation [9] and dehydrodesulfurisation [10] of several thiophene derivatives.…”

Electrochemical study of the activating solution for electroless plating of polymers

“…The optimal composition of this solution should contain a mixture of SnCl 2 and SnCl 4 [4][5][6][7]. Palladium ions are reduced on the polymer surface by stannous ions to a palladium layer that serves as a catalyst for the subsequent electroless deposition of copper or nickel [8][9][10].…”