Deciphering the Role of Chromotrope 2R in Conformal Copper Electrodeposition and Microstructural Control for PCB Through-Hole Metallization

With the rapid development of 5G communication, artificial intelligence, and new energy vehicles, the metallization of through-holes (THs) in printed circuit boards (PCBs) has imposed stringent requirements on the uniformity and interconnection reliability of copper layers. In this study, a novel azo-based additive Chromotrope 2R (BSS2R) was developed, and combined with pulse electroplating to synergistically regulate the conformal filling of PCB THs and the microstructure of copper. Electrochemical tests showed that BSS2R could reduce cathodic polarization and accelerate Cu²⁺ reduction. Surface and crystallographic characterization confirmed that BSS2R could induce the formation of Cu(111) preferred orientation in the copper layer and increase grain size, and its concentration should be controlled within 20 mg/L to suppress the high-frequency skin effect. Density functional theory (DFT) calculations revealed that the sulfonic acid groups of BSS2R could form strong ionic coordination with Cu²⁺ and preferentially adsorb on Cu(111) crystal planes, driving the oriented growth of copper crystal planes. Pulse electroplating experiments verified the "adsorption pumping effect" of BSS2R, which could increase the throwing power (TP) of THs from 72.5% to 84.1%. This work provides theoretical support and practical technical solutions for the metallization of high-aspect-ratio THs in advanced PCB manufacturing.