On the Mechanism of Electrodeposition in the Dimercaptothiadiazole/Copper Pyrophosphate System

Abstract

Cyclic voltammetric stripping results are presented which show that a dynamic equilibrium exists in the dimercaptothiadiazole (DMTD)/copper pyrophosphate system involving a species which accelerates the copper deposition rate, a decelerating species, Cu⁺² ions, and other bath constituents. The experimental data are well explained by assuming that the accelerator is the copper‐complexed DMTD monomer species, whereas deceleration is produced by the DMTD dimer. A model is presented which explains the additive effects in terms of a critical balance between the nucleation of new growth centers by the accelerating additive species and copper ammine complexes, and the limitations on growth imposed by the decelerating additive species which functions by blocking growth sites. Based on this model, which is supported by a‐c impedance data and morphological studies, the important deposit properties can be understood and predicted.