Mechanism of galvanic metallization of CoS-activated insulating polymer surfaces

The mechanism of direct galvanic metallization of insulating polymer surfaces activated by CoS(β) particles is investigated by means of conventional electrochemical techniques and surface analysis. The results show that a necessary step to induce metal electrodeposition is the electrochemical reduction of CoS(β) occurring at potentials E<−0.25 V. It is demonstrated that a direct galvanic metallization can be carried out only by electrodeposition of metals and alloys with a plating zone overlapping the reduction zone of CoS. The electrochemical reduction of CoS is limited by the solid state transport of sulphide ions from the bulk to the surface of CoS(β) particles. The resulting thin Co film on the particle surface catalyzes the reduction of the depositing metal leading to the formation of a primary metal film of 10–40 nm thickness. This primary film, in turn, acts as a seed layer, onto which further deposition of a secondary metal layer of higher conductivity takes place. The formation of the primary metal film makes it possible to contact neighbouring CoS particles and hence, further lateral propagation of the metal layer. Experimental results suggest that the propagation rate of the metal layer is controlled by the kinetics of sulphide reduction.