The Whisker Growth Investigation of IC Packaging on the PC Board Assembly

摘要

The whisker concern has been greatly affecting lead free RoHS conversion confidence in the lead frame packages, particularly for high end product conversion. Although plenty of related study in E4 and iNEMI have directed standard whisker testing conditions and measurement methods, the practical whisker performance data in service life is still very small due to numerous extra factors involved from surface mounting and waving soldering. Most of the literature on Tin (Sn) whiskers study are test results based at the component level in storage or reflow preconditioning to simulate backward and forward conversion in service life. However, for practical Sn-whisker issues, it is necessary to consider the entire structure, i.e., the component characteristics, solder joint, PCB and process effect. In this study, matt Sn plated packages with Cu and Alloy 42 based in PLCC, PDIP, LQFP and TSOP were subject to lead free surface mounting and wave soldering on PCBs with OSP surface finish, followed by TCT (-55 to 85°C) 1000 cycle, THT (60°C/90%RH) 3000hrs and ambient condition 3000hrs to investigate whisker growth propensity. Whisker growth on the PCB after reflow simulation and separate from the component level was examined to understand whether the whisker risk will be reduced or raised because of factors such as the matt Sn structure, lead frame base, reflow profile and solder paste wetting behavior. Furthermore, SnPb and SnBi plated 4 types of the same package types as above were used as controls for whisker growth comparison. Additionally, corrosion phenomenon due to higher temperature THT testing to correlate to whisker growth after the surface mounting condition will be explored with FIB analysis as well.