Localized corrosion and degradation of PCB-ImAg in sulfur-containing environments: a comparative study with PCB-Cu

Abstract

This study investigates the dynamic electrochemical corrosion behavior of copper-clad (PCB-Cu) and immersion silver (PCB-ImAg) circuit boards in a 0.1 mol/L NaHSO₃ solution. PCB-Cu exhibits continuous and rapid corrosion, characterized by the formation of porous copper sulfides and oxides, with its corrosion rate steadily increasing over time. In contrast, PCB-ImAg undergoes a complex, multi-stage degradation. Initially, a partially protective Ag₂S layer forms, showing an early positive shift in E_corr and a temporary reduction in I_corr, indicating film maturation. However, inherent microdefects in the immersion silver coating act as initiation sites, driving accelerated localized galvanic corrosion between silver and the exposed copper substrate. This leads to a progressive increase in overall corrosion rate, culminating in a distinct negative shift in E_corr and a drastic surge in I_corr at 168 h, signifying ultimate protective breakdown and accelerated corrosion. EIS, Raman, and XPS analyses confirm a dynamic film evolution, severe structural degradation, and the dominance of Cu₂S as a late-stage corrosion product, contributing to mechanical delamination. This work provides critical insights into the interplay of microstructural defects, film dynamics, and galvanic coupling governing PCB reliability in sulfur-rich environments.