WLCSP Solder Ball Interconnection Enhancement for High Temperature Stress Reliability

WLCSP package has been demonstrated as one of most adequate packaging solution in both high electrical performance products, such as RF device, and high voltage application products, such as PMIC device, by its characteristics of short interconnection path and low package cost. As electronic components are aggressively adopted for automotive application to realize the autonomous driving capability in coming future, this makes WLCSP a very suitable package by its merits mentioned above besides its very thin small form-factor. To fulfill automotive application requirement (i.e. 1500C HTS 2000 hours or 1750C HTS 1000 hours for Grade 0), high temperature stress performance of package becomes extremely critical and essential. In WLCSP package structure, the most vulnerable interconnection interface to high temperature stress is UBM/solder ball interface due to Cu/Sn intermetallic compound (IMC) formation with kirkendall voiding issue. Therefore, it becomes the objective of this study to investigate different UBM Cu layer condition and solder ball composition impact on high temperature stress reliability performance of UBM/solder ball interface, also to evaluate accelerated stress conditions to shorten the investigation cycle.