Enhancing low-current-density brightness in acid sulfate copper plating via nicotinic acid-modified additives that preserve SPS activity

Dye-containing acid sulfate copper plating baths frequently suffer from severe dull deposits in the low-current-density (LCD) region due to the overpowering synergistic inhibition of polyether suppressors and dyes. To address this challenge, we developed a novel nicotinic acid-modified imidazole–epichlorohydrin complex (IEN1.5) designed to uniquely preserve the activity of the bis(3-sulfopropyl) disulfide (SPS) accelerator. Through a combination of electrochemical analyses, macroscopic plating tests, and DFT/MD simulations, we demonstrate that IEN1.5 physically interacts with SPS via specific non-covalent bonds rather than acting as a standalone, competing brightener. This original molecular strategy successfully breaks the severe LCD suppression, significantly enhancing deposit brightness and strengthening the Cu(111) crystallographic texture. Crucially, by preventing the detrimental over-coordination to Cu⁺ intermediates, IEN1.5 achieves unprecedented bath stability, reducing apparent SPS consumption to a mere 0.9% over 100 cyclic voltammetric stripping (CVS) cycles. These findings provide a highly original and robust mechanistic framework for designing stable, high-efficiency additive systems in advanced copper electrodeposition.