Thermal Characteristics Dependency of Epoxy Underfill on Crosslinker Molecular Structures and Hardener Concentration in Electronic Packaging

Abstract The reliability of electronic packaging is highly dependent on underfill materials, which provide protection against moisture, pollutants, and mechanical stress. However, ensuring long-term reliability remains challenging, particularly regarding the thermal stability and mechanical durability of underfills. The molecular structure and hardener concentration of underfill materials play a crucial role in their performance, yet their effects on thermal and mechanical properties remain insufficiently explored. This study is motivated by the need to enhance the reliability of electronic packaging by understanding how these structural variations influence underfill behavior in an anhydride-epoxy curing system. Fourier transform infrared (FTIR) spectroscopy confirmed complete curing through the disappearance of specific epoxy peaks. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that molecular structure affects thermal stability and flexibility, with a glass transition temperature (Tg) of –2 °C for the linear structure (EPM) and no detectable Tg for the aromatic structure (EHM). Hardness tests confirmed EHM is harder than EPM, while lapping analysis showed greater flexibility in EPM. The coefficient of thermal expansion (CTE) was lower for EHM, indicating higher dimensional stability under thermal cycling. These findings highlight that molecular structure and hardener concentration significantly impact underfill material properties, directly affecting electronic packaging reliability. This study provides valuable insights for optimizing underfill formulations to enhance the performance and durability of next-generation electronic devices.