Predicting Cure Evolution and Thermal Endurance of a Highly Filled Epoxy Underfill for Advanced Packaging

ABSTRACT

Epoxy underfill materials are critical to advanced semiconductor packaging by enhancing mechanical integrity, redistributing thermomechanical stresses, and improving solder‐joint reliability in flip‐chip and other fine‐pitch interconnect architectures. Their performance is strongly influenced by cure evolution during processing and thermal stability during service, making quantitative evaluation important for process optimization and long‐term reliability assessment. The cure kinetics and thermal degradation behavior of a highly‐filled epoxy underfill were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and diffusion‐incorporated kinetic modeling. Isoconversional analysis showed that the apparent activation energy varied with conversion and increased sharply at high conversion, indicating multi‐step cure behavior and diffusion control. A two‐step modified Kamal–Sourour model incorporating diffusion control in the second step improved prediction of conversion after vitrification and was used to predict cure evolution under a designed oven cure schedule, which achieved nearly complete cure. Cryomilling improved TGA reproducibility without causing detectable chemical changes. Analysis following the ASTM E1641/E1877 protocols revealed a strong temperature dependence of estimated thermal endurance based on a 5% mass‐loss criterion under nitrogen. Together, the results provide a quantitative framework for predicting cure evolution under practical thermal schedules, evaluating late‐stage diffusion effects, and estimating degradation‐based thermal endurance for highly‐filled industrial thermosets.