Hydroxyl‐Terminated Polyphenylene Oxide Improved Thermal and Dielectric Properties of Active Ester Cured SiO ₂ /Epoxy Composites for Advanced Electronic Packaging

Low‐dielectric epoxy‐based composites are crucial for advanced electronic packaging in the high‐speed digital communication field. An effective method to achieving low dielectric loss ( D _f ) is to construct active ester‐curing system. However, the introduction of large ester groups negatively affects the thermal stability of cured epoxy composite. Herein, hydroxyl‐terminated polyphenylene oxide (PPO) is incorporated into allyl bisphenol A‐based active ester‐cured SiO ₂ /epoxy composites, and their thermal and dielectric properties are evaluated. By incorporating 20 wt% of PPO, the SiO ₂ /epoxy composites achieve an ultralow D _f of 0.0022 at 1 kHz and a low coefficient of thermal expansion of 29.0 ppm °C ⁻¹ below T _g , while the glass transition temperature ( T _g ) is increased from 97.7 to 117 °C and the value of Young's modulus is enhanced from 8610 to 10 331 MPa. Moreover, the introduction of PPO in the SiO ₂ /epoxy composites significantly enhances the thermal and humid stability of the dielectric constant ( D _k ) and D _f owing to the ultralow water absorption of 0.12%. These results demonstrate that the combination of PPO and active ester in SiO ₂ /epoxy composites should be a potential strategy for designing advanced electronic packaging materials.