Enhancing Board-Level Drop Impact Reliability Through Epoxy-Based Underfill Modification

The growing demand for compact, high-performance electronics has driven the development of advanced packaging with finer pitches. However, this progress necessitates the improvement of mechanical properties to withstand the increasingly harsh conditions of diverse applications. In this study, we conducted board-level drop impact tests using a test kit to compare soldering with and without epoxy-based underfill. We explored the effects of underfill modification with three different hardeners: amine, thiol, and peroxide. Additionally, we employed finite element analysis to simulate Von-Mises stress and investigate failure mechanisms. Our results highlight the significant enhancement of board-level drop impact reliability when underfill is used. Among the various underfills, the thiol-modified underfill demonstrated the most remarkable improvement in impact resistance. Dispensing epoxy-based underfill with a thiol hardener increased the number of drops required to cause failure by over 70 times. Notably, cracks were observed at the wafer level package component side interface in the solder, and delamination was observed at the various interfaces with underfill. The finite element analysis revealed that delamination initiates at the interfaces with underfill and subsequently propagates into the solder, as maximum stress was concentrated at the underfill corner. Ultimately, cracks began to propagate into the solder joint from the edge, resulting in overall failure. This study underscores the potential of epoxy-based underfill modification, specifically with thiol, for enhancing board-level drop impact reliability in electronic packaging.