Unveiling the potential and mechanisms of 3,3′-bicarbazole-based quaternary ammonium salts as levelers

It is important to introduce an effective leveler into electroplating bath to meet the desired requirement in the electronic industry. This work explored the impact of larger backbone structures of four 3,3′-bicarbazole quaternary ammonium salts on the performance of promising levelers in light of the ambiguous mechanism of action. For the first time, these four compounds have been functionalized and identified as promising levelers for copper electrodeposition in through holes. Electrochemical measurements, theoretical calculations, and dynamics simulations collectively revealed that among these levelers, BCz-BPD exhibits the tendency of optimal adsorption on the cathode with the strongest inhibition of copper deposition. Chronoamperometry tests were carried out to analyze the copper nucleation model during electroplating. By measuring the electrostatic potential, average local ionization energy, and planarity, the leveling mechanism of BCz-BPD leveler was analyzed. In order to confirm the high through-hole filling and excellent leveling performance of BCz-BPD in actual PCB plating, TP value measurement, SEM, and XRD tests were carried out sequentially. In addition, galvanostatic measurements were performed to study the interaction of BCz-BPD leveler with other kinds of additives.