Experimental and Simulation Investigations of Copper Reduction Mechanism with and without Addition of SPS

Rotating disk electrode and rotating ring-disk electrode were used to investigate the mechanism of copper reduction and the influence of convection on the effect of Bis-3-sodiumsulfopropyl disulfide (SPS), a widely used accelerator in copper via-filling and copper foil manufacturing. The experimental results show that the commonly accepted single electron transfer for copper reduction is dominating in the low overpotential range, whereas the double electron transfer is also involved in the high overpotential range. SPS was found to exhibit a weak inhibition effect even with Cl− ion in the solution under strong convection, and generate more intermediates in the solution with both Cl− ion and SPS than with Cl− ion alone. Based on the experimental observations, a reaction model for copper reduction considering competition between the single electron transfer and the double electron transfer, as well as desorption and runoff of generated Cu+-containing intermediates, was proposed and used for finite element method modeling. The simulation results enable quantitative description of the proportion of the two charge transfer reactions and the runoff of the intermediates, providing guidelines for selecting the additives and plating conditions in industrial manufacturing.