Preparation And Performance Study Of BN/SiO₂@MWCNTs/PVDF Composites

In the field of microelectronic packaging,as electronic components continue to develop in the direction of miniaturisation,integration and high power,the size of electronic products is dramatically reduced and the power density is increasing,thus causing heat dissipation problems that seriously affect product stability and service life.The production of materials with high thermal capacity and a certain degree of electrical insulation is an important way to solve the heat dissipation problem.The low thermal conductivity（0.1-0.5 Wm-1K-1）of polymeric materials limits their use in microelectronic packaging applications.However,the high content of thermally conductive fillers in composites with significantly improved thermal conductivity leads to serious deterioration of material processing and mechanical properties.How to construct more efficient thermally conductive networks in resin matrix while maintaining certain electrical insulation is of great significance for the development of high power density electronic devices.In this study,PVDF（Polyvinylidene fluoride,PVDF）with good processing and electrical insulation properties was used as the matrix,and multi-walled carbon nanotubes（MWCNTs）with a one-dimensional structure and two-dimensional boron nitride（BN）were used as the composite thermally conductive fillers.The PVDF-based thermally conductive composites were prepared by flow-delaying and electrostatic spinning methods using multi-walled carbon nanotubes（MWCNTs）and two-dimensional Boron Nitride（BN）as composite thermally conductive fillers,respectively.In addition,the MWCNTs were coated with an electrically insulating coating in order to inhibit the formation of conductive networks within the matrix.The composite introduction of 1D/2D fillers showed good synergistic effects in terms of thermal conductivity enhancement,and the pre-constructed thermal conductivity network using electrostatic spinning technology effectively enhanced the heat transfer efficiency.Firstly,the surface of MWCNTs was coated with silicon dioxide（SiO₂）using the sol-gel method to prepare SiO₂@MWCNTs core-shell structured thermally conductive fillers with both thermal and electrical insulation properties,and the MWCNTs were characterized by FTIR,SEM and TEM before and after the treatment.BN/SiO₂@MWCNTs/PVDF and E-BN/SiO₂@MWCNTs/PVDF composite films were prepared by the flow-delay method and electrostatic spinning method respectively,and the morphological structure,thermal conductivity,electrical properties and mechanical properties of the composite films were tested and characterized.The experimental results show that the thermal conductivity of the composites prepared by the flow casting method and the electrostatic spinning method are significantly improved compared to PVDF.The thermal conductivity of the composites tends to increase with the increase of the filler,and the thermal conductivity of the in-plane composites is higher than that of the out-plane composites when the filler content is the same.Compared to the flow-delay method,the composites prepared by the electrostatic spinning method achieved a more significant increase in thermal conductivity for the same filler content.At a BN content of 30 wt%and an SiO₂@MWCNTs content of 1%,the out-of-plane thermal conductivity and in-plane thermal conductivity of the BN/SiO₂@MWCNTs/PVDF composites prepared by the flow-delay method were0.4174 Wm-1K-1 and 0.8440 Wm-1K-1 respectively,an improvement of 176%and458%respectively compared to PVDF.The out-of-plane and in-plane thermal conductivities of the E-BN/SiO₂@MWCNTs/PVDF composites prepared by electrostatic spinning were 0.4693 Wm-1K-1 and 1.5642 Wm-1K-1 respectively,an increase of 209%and 931%compared to PVDF.With the introduction of thermally conductive fillers,the dielectric constants and dielectric losses of the composites were increased to varying degrees compared to PVDF.At 30 wt%BN content and 1%SiO₂@MWCNTs content,the BN/SiO₂@MWCNTs/PVDF composite prepared by the flow-delay method had a dielectric constant of 8.2 at100 Hz,a dielectric loss of 0.026,a volume resistivity of 5.7×1013Ω·m and a breakdown field strength of 63.30 k V/mm.The E-BN/SiO₂@MWCNTs/PVDF composite prepared by electrostatic spinning had a dielectric constant of 7.1 at100 Hz,a dielectric loss of 0.0236,a volume resistivity of 3.6×1013Ω·m and a breakdown field strength of 47.68 k V/mm.The tensile properties of the composites prepared by the cast method decreased with increasing BN content.at a BN content of 30 wt%and a temperature of 30℃,the energy storage modulus and loss modulus of the E-BN/SiO₂@MWCNTs/PVDF composites were 3452.4MPa and 137.2 MPa respectively.