Study On The Microstructure Design And Thermal Conductivity Of Polyimide/Carbon Nitride Nanocomposite Film

Driven by the evolution of electronic packaging technology for high-dense integration of high-power,miniaturization and multi-function devices in modern electronics,more internal components are assembled in a smaller space.Considerable operating heat is accumulated severely compromising reliability,lifetime and even causing the component damage.How to achieve effective heat dissipation has become bottleneck restricting the development of electronic products.Polyimide film as an important part of electronic packaging system,plays a vital role in dissipating heat to cool chip.However,limited by the low thermal conductivity(approximately 0.2 W·M-1·K-1),polyimide film is far from meeting the demand in thermal management for electronic products.Considering the development of next generation electronics toward lighter,thinner,bendable,foldable and even wearable,the preparation of mechanically flexible polyimide film with high thermal conductivity has captured extensively attention in academia and industry.In this work,base on the design of carbon nitride-based composite fillers and its microstructure control,a series of thermally conductive polyimide films with electrical insulation were prepared.The thermal conductivity,electrical insulation and thermal expansion coefficient of polyimide composite films are systematically examined based on the microstructure.The main results are as follows:(1)CNNS is first used to improve the thermal conductivity of polyimide(PI)film.Based on the orientation of PI molecules during imidization and strong interaction with PI,CNNS realize in-plane self-orientation during solvent evaporation to form continuous thermal pathway in PI matrix.The thermal conductivity of PI/CNNS nanocomposite films reach 2.04 W·m-1.K-1 with relatively low CNNS loading(20 wt%)which is about eleven times of the corresponding pure PI(0.18 W·m-1·K-1).Meanwhile,the PI/CNNS nanocomposite films keep superior electrical insulation property and thermal stability.(2)After settling doping reduced graphene oxide with carbon nitride(rGO@CN)in polyimide film(PI)by a facile deciduous-like strategy,we obtain PI film with both high thermal conductivity and satisfied electrical insulation at low filler loading.By taking the advantage of thermally conductive channels provided by continuous rGO@CN layer,PI/rGO@CN composite film at 10 wt%filler loading exhibits a maximum thermal conductivity of 6.08 W·m-1·K-1 which is about 30-fold compared with that of pure PI film(0.2 W·m-1·K-1).Besides,the PI/rGO@CN composite film also maintains excellent electrical insulation,mechanical flexibility and thermal stability.Furthermore,the thermal conductivity of rGO@CN has been further explored by non-equilibrium molecular dynamics simulation.(3)A stitching strategy is adopted to fabricate an rGO/g-C3N4 film,where g-C3N4 works as linker to covalently connect adjacent rGO sheets for expanding the size of graphene and forming in-plane rGO-g-C3N4 heterostructure.The in-plane thermal conductivity of rGO/g-C3N4 film reaches 41.2 W·m-1·K-1 at g-C3N4 content of only 1 wt%,which increased by 17.3%compared to pristine rGO film.The interfaced thermal resistance between rGO and g-C3N4 is further examined by non-equilibrium molecular dynamics simulations.Furthermore,owning to the unique light absorption and welding ability of g-C3N4,the rGO/g-C3N4 film presents superior solar-thermal and electric-thermal responses to controllably regulate the chip temperature against overcooling.(4)From the second work,despite the substantial improvement in thermal conductivity of PI film after the introduction of rGO,the high cost limits rGO practical application and phonon scattering in the interlaminar space region still occurs.In this part,we employ low-cost glucose as the carbon source,and prepare unique plane heterostructural Cring-C3N4 as thermally conductive filler.On the one hand,the Cring introduction can improve the intrinsic thermal conductivity of g-C3N4.On the other hand,the existence of g-C3N4 can reduce the electric conduction of Cring.At the same time,the Cring-C3N4 can be arranged in the thickness direction in PI composite film due to its small lateral size.The through-plane thermal conductivity of PI film is 0.44 W·m-1·K-1 at low Cring-C3N4 loading of 15 wt%in which the through-plane thermal conductivity is about 1.37 times of the corresponding PI/CNNS nanocomposite film.