The time-varying effect of thiourea on the copper electroplating process with industrial copper concentrations

Electrorefining is the process of choice to purify several metals, among which is copper. A crucial process parameter in electrorefining, and electroplating in general, is the additive activity. Several additives are introduced to the electrolyte to ensure a morphological smooth copper deposit. Thiourea is a crucial but complex additive used in copper electrorefining, it is known to degenerate and both the reaction product as thiourea itself can complex with the copper ions. Unfortunately, time dependent additive studies and mechanistic knowledge of the effect of aged electrolyte on the cathodic part of the electrorefining process are scarce. In this work, operando Odd Random Phase Electrochemical Impedance Spectroscopy (ORP-EIS) is used to study the electrochemistry of a copper plating system containing industrial copper concentrations. The approach applied enables the investigation of the time-varying effect of additives, in this case thiourea and chlorides, assisting the electroplating of copper.