Enhancement of thermal conductivity and dimensional stability of polyimide/boron nitride films through mechanochemistry

Polyimide composites with high thermal conductivity and low coefficient of thermal expansion (CTE) at a low filler loading for maintaining their processability and flexibility are critical for high-power microelectronic devices. We proposed a mechanochemical approach that was induced by ball-milling to prepare high-thermal-conductivity polyimide/boron nitride (BN) films with low CTE. In the mechanochemical process, BN platelets were dispersed uniformly in poly(amic acid) solution along with partial BN exfoliation and covalent linkage with polymer chains under mechanical force, followed by in-plane orientation in polyimide matrix during film formation and thermal imidization, resulting in the formation of heat-transfer network in the composite. Therefore, a superhigh in-plane thermal conductivity of 14.7 W/(m·K) could be achieved at only 20 wt% BN and the CTE decreased simultaneously from 33.5 ppm/K of pure polyimide to ~20 ppm/K. This method is simple and efficient, and enables simultaneous BN platelets peeling and surface covalent modification in one step, which allows for excellent matrix dispersion and the fabrication of high-thermal-conductivity composites.