The Sn Whisker Growth Evolution of IC Packaging on the PC Board Assembly

The whisker concern has been still affecting greatly lead free RoHS conversion confidence in the lead frame package, particularly for high reliability product conversion. Although JEDEC has directed standard whisker testing condition and measurement method, but the practical whisker performance data in service life is still very scarce due to numerous extra factors involved from surface mounting and waving soldering. Most of literatures on Sn whiskers study are the test results based on component level in storage issue 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 and PCB characteristics, solder joint, and process effect. In the study, the 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 the PCB with OSP surface finish, followed by TCT (-55 to 85degC) 1000 cycle, THT (60degC/90%RH) 3000 hrs and ambient condition 3000 hrs to investigate whisker growth propensity. The practical whisker performance confirmed on the PCB beyond reflow simulation and component level was concluded to understand whether the whisker risk will be reduced or raised in term of matt Sn structure, lead frame base, reflow profile, solder paste wetting behavior. Furthermore, SnPb and SnBi plated 4 types of package as above were taken as control 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.