Electrochemical migration behavior and mechanism of PCB-ImAg and PCB-HASL under adsorbed thin liquid films

Abstract

The electrochemical migration (ECM) behavior and mechanism of immersion silver processing circuit board (PCB-ImAg) and hot air solder leveling circuit board (PCB-HASL) under the 0.1 mol/L Na2SO4 absorbed thin liquid films with different thicknesses were investigated using stereo microscopy and scanning electron microscopy (SEM). Meanwhile, the corrosion tendency and kinetics rule of metal plates after bias application were analyzed with the aid of electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP). Results showed that under different humidity conditions, the amount of migrating corrosion products of silver for PCB-ImAg was limited, while on PCB-HASL both copper dendrites and precipitates such as sulfate and metal oxides of copper/tin were found under a high humidity condition (exceeding 85%). SKP results indicated that the cathode plate of two kinds of PCB materials had a higher corrosion tendency after bias application. An ECM model involving multi-metal reactions was proposed and the differences of ECM behaviors for two kinds of PCB materials were compared.