The performance of hexagonal boron nitride (hBN) and cordierite: hybrid filler system in epoxy underfill materials

Abstract This study investigates the influence of varying hybrid filler ratios of hexagonal boron nitride (hBN) and cordierite on the performance of epoxy underfill composites, in line with the rising demands of microelectronic packaging. Composites were formulated with constant total hybrid filler loading of 9 vol.%, composites were formulated with hBN to cordierite ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 using mechanical stirring and ultrasonic dispersion with diethyl toluene diamine (DETDA) as the hardener. Key properties are assessed include viscosity, flexural strength, fracture toughness, thermal conductivity, coefficient of thermal expansion (CTE), thermal stability, and dielectric behaviour. Results showed a trade-off effect: increasing hBN content enhanced thermal conductivity up to 0.340 W m ⁻¹ ·K ⁻¹ but reduced flexural strength and fracture toughness. Meanwhile, increasing cordierite content improved dimensional stability and mechanical performance. Among the investigated compositions, the 25:75 hBN:cordierite hybrid system exhibited a favorable balance of mechanical, thermal, and dielectric properties, indicating its potential suitability for next generation underfill materials. This study demonstrates, that tailoring hBN and cordierite ratios offers a promising route toward multifunctional epoxy underfills that address the simultaneous demands of thermal management, mechanical reliability, and dielectric stability in next-generation microelectronic devices.