A Study on Evaluating the Risk of Underfill Delamination During Thermal Cycling by Finite Element Analysis

Thermal cycling (TC) is an important method to evaluate the reliability of electronic products. During the TC process, the solder joints have the risk of cracking due to fatigue stress, but the internal interfaces in the package will also be affected by the fatigue loads, presenting delamination at several interface areas. Due to the difficulty in experimental monitoring of delamination and the lack of effective simulation methods, the research on evaluating the risks of interface delamination has outstanding deficiencies during the TC process. This paper uses finite element analysis (FEA) to evaluate the risk of interface delamination of the underfill (UF) during TC. The viscoelastic property of UF is introduced in FEA. The stress and strain at the interface are carefully analyzed during TC, and the accumulated strain energy (ASE) at the risk position of the interface is calculated as the characteristics reflecting the damage of UF at the interface during TC. In addition, the influence of the coefficient of thermal expansion (CTE) of UF, the dwell time, and the stress-free temperature on ASE are systematically analyzed. This study provides a method for the qualitative and quantitative assessment of the risk of delamination for UF during TC.