Unveiling the synergistic inhibition of Cl⁻ copper plating: Pivotal roles of adsorption and desorption

Cl⁻ dissolved in electroplating solution is one of the most representative additives. Although the coordination structure of Cl⁻ and polyethylene glycol (PEG) has been investigated, the coordination structure was still highly puzzling. The synergistic effect of PEG and Cl⁻ in electroplating copper is analyzed and discussed by a series of design experiments and DFT. For the experiment, the through-hole of a printed circuit board (PCB) is electroplated with an acid plating solution, and the inhibition ability of complex and nucleation and growth process of Cu are studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). Theoretical analysis, the adsorption energy and Bader charge are computed by the first principles. Comparing experimental and theoretical results, the copper plating solution with Cl⁻ (PCC) shows better inhibition than that without Cl⁻ (PC), and the average thickness of coating in the hole (ATCH) of PCB are 22.33 μm and 57.76 μm and nucleation and growth process of Cu requires a smaller potential with Cl⁻ in the plating solutions. The energy curve shows that the adsorption energy of PCC* is higher than that of PC*. Due to the coordination of Cl⁻, the ability of Cu^2+/1+ in PCC* to obtain electrons is weakened, thereby suppressing the inability of Cu^2+/1+ to be reduced. This work not only illustrates clearly the inhibition ability of Cl⁻ and PEG but also highlights the crucial roles of charge capacity and energy barriers, which can help decipher the electroplating mechanism.