Low alpha green compound development for CMOS 90 LQFP automotive product

Abstract

CMOS 90 wafers had been applied to BGA (Ball Grid Array) packages for many years. However, the application to lead package is not much. This paper introduced one application for CMOS 90 wafers to LQFP (Low profile Quad Flat Package). Simultaneously, it is for automotive application and need meet AEC Grade 1 reliability requirements [1]. Low alpha green compound is required for this package to reduce the SER (soft error rate) for electrical robustness. The package is 64 lead LQFP and silver is ring plated for the lead tips. At the beginning, the lead tip delamination was observed after TC (Temperature Cycle) through cross section analysis and SEM check. Pre mold plasma evaluation with Ar/H2 was also tried, but it couldn't remove the delamination. Then mechanical simulation was performed and confirmed that stresses are focused on the tips of the lead which will greatly affect the EMC adhesion. Finally, the compound was optimized by using the high adhesion type of coupling agent to improve the compound adhesion with silver and the lead tip delamination was successfully removed. As a result, the CMOS 90 LQFP package achieved the AEC Grade 1 reliability requirements and passed qualification for production.