Homologous Bisphenol-A Modification Enables SiO₂/Epoxy Composites with Ultralow Thermal Expansion, High T_g, and Superior Thermal Shock Resistance for Power Device Packaging

Next-generation power device packaging demands epoxy (EP) composites that achieve a critical combination of low thermal expansion, high-temperature resistance, and thermal shock stability. High-performance EP composites were developed using a synergistic materials design strategy combining filler surface modification, filler gradation, and resin blending. Silica (SiO₂) was surface-modified with 2,2-bis(4-hydroxyphenyl) propane (Br5215), a bisphenol-A-based molecule structurally compatible with the epoxy matrix, forming a robust interfacial layer via covalent bonding and π–π interactions. This effectively suppresses filler agglomeration and enhances interfacial adhesion. In parallel, blending difunctional and trifunctional epoxy resins enabled simultaneous control of viscosity and cross-link density. Experimental results show that the glass transition temperature (T_g) of the B-SiO₂/EP composite reaches 205.6 °C. The coefficient of thermal expansion below T_g, denoted as α₁, is 25.81 × 10^–6/°C, representing a reduction of 70.1% compared to neat EP. After 1000 thermal shock cycles (−60 to 150 °C), the composite still maintains a T_g of 202.4 °C (only a 1.6% decrease) and an α₁ of 26.6 × 10^–6/°C (only a 3.2% increase), with no interfacial delamination from the copper substrate. This represents a significant improvement over neat EP (delamination after 200 cycles) and SiO₂/EP (delamination after 800 cycles). This study provides a practical strategy for developing high-reliability epoxy encapsulants for power device packaging.