Development of Mold Compounds With Ultralow Coefficient of Thermal Expansion and High Glass Transition Temperature for Fan-Out Wafer-Level Packaging

Coefficient of thermal expansion (CTE) mismatch between an underfill encapsulant material and integrated circuit chips mounted on a substrate is the major reason for device failure in a fan-out wafer-level packaging (FOWLP) assembly. In this paper, a variety of moldable polymer composite systems with evenly dispersed dielectric nanoparticles or microparticles and minimal cure shrinkage for FOWLP assemblies have been investigated. Most importantly, a low CTE of 6.6 ppm/°C and a high glass transition temperature (T
_g
) above 300 °C were achieved through a processing methodology that exhibits fairly good repeatability. A special surfactant treatment of the particle surfaces has played a crucial role in further enhancing the thermomechanical properties, yield, and repeatability of the composite material.