Large-scale production of boron nitride nanosheets-based epoxy nanocomposites with ultrahigh through-plane thermal conductivity for electronic encapsulation

Recent advances in two-dimensional (2D) nanomaterials have generated great interest in the investigations of these materials for wide ranging applications in the micro- to nano-scale electronics, healthcare, and energy storage areas. In particular, 2D materialas such as boron nitride nanosheets (BNNS) have been studied extensively due to their unique material properties that include a large specific surface area, high thermal conductivity (-750 W/mK), and wide bandgap (-5.5 eV), along with the associated electrical insulation. In this paper, we prepared BNNS by liquid exfoliation of hexagonal boron nitride (h-BN). Liquid exfoliation is an enhanced method to achieve large-scale and low-cost production, which is more suitable for large volume applications. In this paper, we have combined low-energy ball milling and sonication methods to produce BNNS on a large scale. BNNS have a high in-plane thermal conductivity due to their 2D morphology but a lower through-plane thermal conductivity. Also, the thermal interface resistance between BNNS is also an important factor that impedes the through-plane thermal conductivity. Thus, we employed a vacuum filtration method to obtain thick BNNS cakes. These cakes have a high x-y/in-plane thermal conductivity and a low z/through plane thermal conductivity. After slicing the cake vertically, it is rolled over to covert the strong x-y plane thermal conductivity to the z-plane. The now high thermal conductivity z-plane allows for effective 3D electronic packaging. Following this, BNNS are infiltrated into epoxy resins to fabricate epoxy nanocomposites with a low filler loading. This paper presents detailed studies on the coefficient of thermal expansion (CTE), electrical resistivity, thermal stability, and thermomechanical properties of the synthesized BNNS-epoxy nanocomposites. This study reveals the promising applications of high performance, thermally conductive epoxy nanocomposites in advanced packaging technologies such as 2.5D/ 3D packaging.