Complexation Mechanism of a Novel Alkaline Cu(I) Electroplating System Investigated by UV–Visible Spectroscopy

Copper (Cu) electroplating has been rising once again due to the giant industrial demands for metal interconnectors in the integrated circuit and the current collector in the lithium-ion battery. If the current acidic Cu(II) electroplating were replaced by the alkaline Cu(I) electroplating, it would reduce electricity consumption by at least 50%, not to mention the environmental friendliness. The bottleneck for alkaline electroplating is the complexation to stabilize the Cu(I) cations in solution. To this end, we developed a novel alkaline Cu(I) electroplating system and studied the complexation mechanism by both ex situ and in situ UV-visible spectroscopy. The results demonstrated that succinimide (SM) is a stronger complexant than sulfite and forms a stable [Cu(SM)₂]⁻ ion, which was further stabilized by maltose. The sulfite acted as no longer a complexant but a reductant. Thus, a high-quality Cu-plating layer was obtained with excellent metallographic structure and mechanical performance. The work demonstrates the vital capability of UV-visible spectroscopy in investigations on the action mechanisms of electroplating additives.