Corrosion Reliability of Lead-Free Solder Systems Used in Electronics

The present work investigated the corrosion reliability of five Sn-Ag-Cu (SAC) based lead-free solder alloys. The first focus was placed on microstructural analysis of the intermetallic compounds (IMCs) formation in the ingots of SAC alloys and their influence on micro galvanic corrosion performance. The microstructural and phase analysis of solder alloys has been carried out using the scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Xray diffraction (XRD) methods. With the potentiostatic technique, the galvanic corrosion has been confirmed between cathodically active Bi phase and anodic (Sn, Sb) solid solution in InnoLot alloy, while the Ag3Sn phase was cathodically active in the other four alloys. In industrial application point of view, the electrochemical migration (ECM) has been reported as the critical issue. Therefore, in order to investigate the ECM susceptibility of five lead-free solder alloys, the study of the solder alloys has been conducted by water droplet (WD) tests on pure alloy ingot samples, and by accelerated humidity/temperature cycling tests on soldered surface insulation resistance (SIR) comb pattern. A ranking of susceptibility for five alloys has been confirmed by Weibull analysis (63.2% failure rate), leakage current level, and charge transfer over time. The paper theoretically illustrated the reason for the differences in corrosion reliability in the five alloys based on the composition and distribution of IMCs.