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

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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.

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Keywords

Thermal properties, Polymers, Modeling and computational material science, Materials characterization and Composites

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