Hexagonal Boron Nitride (hBN) and Cordierite in Epoxy Underfill Materials: Single Filler System

Abstract

As electronic devices become increasingly powerful and compact, the materials used for packaging must withstand high thermal and mechanical stress. Epoxy underfill materials are essential in providing thermal conductivity, mechanical reinforcement, and electrical insulation. However, differences in thermal expansion among silicon chips, solder joints, and substrates can cause failures over time. This research investigates the enhancement of epoxy composites through the addition of hexagonal boron nitride (hBN) and cordierite fillers to improve their mechanical, thermal, and dielectric properties. Composites were prepared with filler loadings ranging from 0 to 9 vol%, utilising mechanical stirring and ultrasonic dispersion, with diethyl toluene diamine (DETDA) serving as the hardener. The study evaluated properties such as viscosity, flexural strength, fracture toughness, thermal conductivity and coefficient of thermal expansion (CTE), thermal stability, and dielectric behavior. Testing was performed using a Universal Testing Machine (UTM), Scanning Electron Microscope (SEM), KD2 Pro thermal analyzer, Linseis L75 dilatometer, NDJ-9S viscometer, and an LCR meter. Results indicated that hBN fillers significantly increased thermal conductivity, reaching up to 0.340 W/m·K at 9 vol% loading, while cordierite fillers improved mechanical strength, achieving a maximum flexural strength of approximately 119.91 MPa. Higher filler contents led to increased viscosity, with hBN composites demonstrating notably higher viscosity than cordierite-based systems. These findings suggest that hBN is more suitable for thermal management, whereas cordierite offers better structural reinforcement. Overall, the study highlights the critical role of filler selection in customising epoxy composites for advanced electronic packaging applications.