Application of New Criteria for Predicting Crack Initiation From the Interface Corner in the Molded Underfill Flip-Chip Package Under Thermal Load

Cracking at corner points or edges of multi-material interfaces has long been a critical reliability concern for engineered components and structures. In particular, accurate prediction of failure risks due to interface crack and delamination in advanced electronic packages is highly demanded for improvement of the reliability and the integrated circuit (IC) product yield. This study proposes a new approach, which combines the asymptotic stress solution at the singularity with the maximum average tangential stress (MATS) and maximum tangential strain (MTSN) criteria, to predict the crack initiation angle and critical fracture conditions. The proposed approach is first validated against the experimental results for silicon/glass anode bonds subjected to biased three-point bending as reported in the literature, demonstrating its accuracy and reliability. Further, and more importantly, the validated criteria are applied to analyze the cracking behavior of a typical molded underfill flip-chip (MUF FC) package under both heating and cooling loads. The predicted crack initiation angles are close to the analytical results derived from the fracture mechanics parameters obtained by finite element analysis. The present study has moved the reliability assessment forward to establish a practical and reliable framework for predicting the crack initiation at the interface corner of the MUF FC package structure, which is also highly anticipated to be used in other advanced electronic packages.