A transfer-adsorption model for forward understanding the synergistic effects of additives in through-hole uniform copper thickening

Abstract

The additives in acidic copper electronic plating solution are of crucial importance in uniform thickening of through-hole (TH) for printed circuit board (PCB) fabrication. In this present study, we set up a transfer-adsorption model to forward understanding the synergistic effects of additives on TH uniform thickening based on the experimental facts of galvanostatic measurements, density functional theory calculations and chronocoulometric measurements. According to this model, during copper electronic plating, the suppressor of polyethylene glycol (PEG) adsorbs more at the mouth because of the replacement of PEG by the accelerator of bis-(sodium sulfopropyl)-disulfide (SPS) at the center of TH, the leveler of Janus Green B (JGB) adsorbs uniformly both at the mouth (where it works with PEG to weaken the adsorption of SPS) and center of TH (where it cooperates with SPS to promote the cupric ions electro-reduction), resulting in the copper layer thickness decreasing at mouth and increasing at center. Such complicated but effective synergistic effects of the three additives result in uniform thickening of TH. Copper electronic plating results further confirmed the reliability of the transfer-adsorption model in synergistic effects of copper electronic plating additives, and unveiled the interaction mechanism of additives for TH uniform thickening.