Ultra‐low loss polyphenylene oxide‐based composites with negative thermal expansion fillers

Abstract The mismatch of coefficient of thermal expansion (CTE) of components has created numerous reliability issues in electronic packages. Incorporating inorganic fillers into polymer matrices has been proven to be an effective way to reduce the CTE, but properly balancing CTE with other key properties of the composites is still a challenge. In the current work, negative thermal expansion Zr 2 WP 2 O 12 (ZWP) particles were prepared by a high‐temperature solid‐phase synthesis method. Polyphenylene oxide (PPO)‐based composites with different volume fractions (0, 10, 20, 30 vol%) of ZWP particles were prepared and their thermal expansion and dielectric properties were characterized. PPO/silica composites with the same volume fractions of silica were also prepared and characterized for comparison. With the content of filler increased from 0 to 30 vol%, the CTE of the PPO/ZWP composites reduced from 74.2 to 45.4 ppm/°C, which is more significant than that of the PPO/silica composites (48.0 ppm/°C with 30 vol% silica). Meanwhile, the dielectric loss of PPO/ZWP composites decreased significantly from 0.0024 (0 vol% ZWP) to 0.0018 (30 vol% ZWP) at 10 GHz, which is better than PPO/silica composites (0.0019 with 30 vol% Silica). The PPO/ZWP composites exhibit excellent comprehensive properties, which may be promising materials for high‐frequency applications in electronic packaging fields.