Highly thermally conductive flexible copper clad laminates based on sea-island structured boron nitride/polyimide composites

A facile strategy for effectively constructing in-plane and through-plane thermal conduction paths in polyimide (PI) and its flexible copper clad laminates (FCCLs) was reported by incorporation of hexagonal boron nitride (h-BN) in a controlled manner. The in-plane thermal conductivity pathways resulted from the micron h-BN sheets well mixed within the continuous PI matrix, while the through-plane ones were mainly constructed by the arrayed pillar-like or striped-like high concentration (65.2 wt%) h-BN nano-particles/thermoplastic polyimide (TPI) composites (acting as islands), which were distributed in the above micron PI/h-BN composite (acting as sea) and perpendicular to the direction of thickness. The specific sea-island architecture allowed the preparation of highly thermally conductive flexible PI film and its FCCLs at relatively lower total boron nitride loading. Balanced thermal conductivities and mechanical properties were achieved, for example, in the PI/h-BN composite film containing 30 wt% micron h-BN. The in-plane and through-plane thermal conductivities increased from 0.18 W m−1 K−1 and 0.15 W m−1 K−1 of neat PI film to 2.56 W m−1 K−1 and 0.57 W m−1 K−1, respectively. Meanwhile, the tensile strength and elongation at break can remain at 98.4 MPa and 8.7%. Interestingly, when the pillar-like high concentration h-BN nano-particles/PI composites were present, the in- and out-plane thermal conductivities of the composite films considerably increased to 5.03–6.32 and 1.27–1.29 W m−1 K−1, although the total BN content was only raised by ∼1 wt%. The results of the current work may open a new avenue for promoting the practical application of thermally conductive PI based FCCLs.