WHISKER GROWTH ON SAC SOLDER JOINTS: MICROSTRUCTURE ANALYSIS

摘要

Sn whisker growth on electronics continues to be a widespread industrial concern. In this study, detailed metallurgical analyses were done on whiskers growing from solder joints formed on leaded components. The whiskers appeared after life testing for 10 days at 60°C and 20-30% RH with voltage cycling. Optical and Scanning Electron Microscopy (SEM) with EDX following by cross-sections through whiskers were performed. The analyses revealed that Sn whiskers originated not from the component lead plating as was expected, but from bulk SAC405 or SAC305 solder. A high precision metallographic technique using progressive polishing was developed to examine the details of whisker formation. This paper discusses the microstructural relationship between the whiskers, hillocks, and shell-like protrusions and the following factors: solder microstructure and its modification during oxidation and corrosion, Alloy 42 lead frame material, lead plating quality, component contamination and flux on solder.