Investigation On The Fabrication And Mechanism Of Thermally Conductive Bismaleimide Composites With Low Dielectric Constant

Polymers possess light-weight,high specific strength,excellent electric insulation,easy processability,good chemical stability and low cost,etc.,and have been applied in the field of microelectronic packaging.However,the intrinsic low thermally conductive coefficient ??0.20⁰.40 W/m K?of the polymeric matrix cannot meet the high-calorie heat dissipation requirements for higher power density,integration and miniaturization of microelectronic devices.Therefore,it is a scientific problem with importance to take account of thermally conductive polymer composites combining with outstanding thermal stabilities,low dielectric constant value & ideal mechanical properties by structure/function integration design,and to further develop and improve the thermally conductive mechanism of the polymer composites.Bismaleimide?BMI?resins present outstanding thermal stabilities/heat and humidity resistance,excellent dielectric properties,good radiation resistance & flame retardant,and designable chemical structure,etc.,and have been widely applied as copper-clad laminate?CCL?materials in printed circuit board?PCB?.However,cured pure BMI resin suffers from the brittleness and poor thermal conductivity,which cannot meet the higher requirement for CCL materials combining with light weitht,thin & small,and multi-functionalization.Therefore,the modification on the BMI matrix is to increase the thermal conductivities of BMI matrix,while maintaining its outstanding thermal stabilities and excellent dielectric properties.In our present work,thermally conductive BMI/diallylbisphenol A?DABA/BMI?composites with low dielectric constant value are successfully fabricated via casting molding method,herein,BMI as a polymeric matrix,DABA as a toughening agent and nano-boron nitride?n BN?fillers and silicon carbide particle/silicon carbide whisker?Si Cp/Si Cw?hybrid fillers as thermally conductive fillers,respectively.Furthermore,the combining method of ?-glycidoxypropyltrimethoxysilane/amine group polyhedral oligomeric silsesquioxane?KH-560/NH₂-POSS?is employed to functionalize the surface of the n BN fillers,and KH-560 is performed to functionalize the surface of the Si Cp/Si Cw hybrid fillers.The surface performance and component of two different thermally conductive fillers?n BN and Si C?are analyzed and characterized by static precipitation,relative wetting contact angle?RWCA?,X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared?FTIR?and thermogravimetric analyzer?TGA?.The effects of n BN and Si Cp/Si Cw contents on the thermal conductivities,dielectric & mechanical properties and thermal stabilities of the BMI composites are also investigated.In addition,phenyltrimethoxysilane?Ph TMs?and ?-aminopropyltriethoxysilane?KH-550?are performed to fabricate the terminal amine group hyperbranched phenyl polysiloxane?NH₂-HBPSi?,which is also performed to modify DABA/BMI resin matrix,and the mass fraction of NH₂-HBPSi affecting on the mechanical properties,dielectric properties,and the thermal stabilities of the NH₂-HBPSi/DABA/BMI resins are investigated.Finally,the mass fraction of thermally conductive fillers affecting on the thermal conductivities of the POSS-g-n BN/NH₂-HBPSi/DABA/BMI and f Si Cp/f Si Cw/NH₂-HBPSi/DABA/BMI is also analyzed.In summary,the main results are described as follows:I.Fabrication and properties investigation on the thermally conductive POSS-g-n BN/DABA/BMI nanocompositesPOSS molecule has grafted on the surface of the n BN fillers.The thermal conductivities of the POSS-g-n BN/DABA/BMI nanocomposites are increased with the increasing addition of POSS-g-n BN.The thermally conductive coefficient ? of the POSS-g-n BN/BMI nanocomposite with 30 wt% POSS-g-n BN is 0.607 W/m K,increased by 300% compared to that of pure DABA/BMI?0.228 W/m K?.The corresponding ? and tan? value of the POSS-g-n BN/DABA/BMI nanocomposite with 30 wt% POSS-g-n BN is 3.42 and 0.0085,respectively.Both the flexural strength and impact strength of the POSS-g-n BN/DABA/BMI nanocomposites are found to be optimal at 1 wt% POSS-g-n BN.Compared with those of pure DABA/BMI cured resin,the maximum flexural strength and impact strength of the POSS-g-n BN/DABA/BMI nanocomposite with 1 wt% POSS-g-n BN is improved to 141.7 MPa and 14.8 k J/m2,increased by 14.5% and 19.4%,respectively.The thermal stabilities of the POSS-g-n BN/DABA/BMI nanocomposites are increased with the increasing addition of POSS-g-n BN,but the Tg values are decreased.For a given n BN loading,the surface functionalization of n BN by KH-560/NH₂-POSS can further increase the thermal conductivities & mechanical properties,and decrease the ? and tan? values of the POSS-g-n BN/DABA/BMI nanocomposites.II.Fabrication and properties investigation on the thermally conductive f Si Cp/f Si Cw/DABA/BMI compositesKH-560 molecule has grafted on the surface of the Si C fillers.The Si Cw/Si Cp hybrid fillers are more favorable to improve the thermal conductivities of the f Si Cp/f Si Cw/DABA/BMI composites.The thermally conductive coefficient ? is improved from 0.228 W/m K for pure DABA/BMI to 1.125 W/m K for the f Si Cp/f Si Cw/DABA/BMI composite with 40 wt% f Si Cp/f Si Cw?mass fraction,1:3?hybrid fillers.The corresponding ? value of the f Si Cp/f Si Cw/DABA/BMI composite with 40 wt% f Si Cp/f Si Cw hybrid fillers is 4.12.The flexural strength and impact strength values of the f Si Cp/f Si Cw/DABA/BMI composites are found to be optimal at 10 wt% f Si Cp/f Si Cw hybrid fillers.Compared with those of pure DABA/BMI cured resin,the maximum flexural strength and impact strength of the f Si Cp/f Si Cw/DABA/BMI composite with 10 wt% f Si Cp/f Si Cw hybrid fillers is improved to 146.8 MPa and 15.3 k J/m2,increased by 18.6% and 26.6%,respectively.The thermal stabilities of the f Si Cp/f Si Cw/DABA/BMI composites are increased with the increasing addition of f Si Cp/f Si Cw hybrid fillers.For a given Si Cw/Si Cp loading,the surface functionalization of Si Cw/Si Cp by KH-560 can further increase the thermal conductivities & mechanical properties,and decrease the ? value.Compared to that of POSS-g-n BN/DABA/BMI nanocomposite with 30 wt% POSS-g-n BN,f Si Cp/f Si Cw/DABA/BMI composite with 40 wt% f Si Cp/f Si Cw hybrid fillers possesses relatively better thermal conductivities & mechanical properties and thermal stabilities,but relatively worse dielectric properties.III.Fabrication and properties investigation on modified BMI resins by terminal amine group hyperbranched phenyl polysiloxane?NH₂-HBPSi?The flexural strength values of the NH₂-HBPSi/DABA/BMI resins are increased firstly,but decreased with the excessive mass fraction of NH₂-HBPSi.However,the corresponding impact strength values of the NH₂-HBPSi/DABA/BMI resins are gradually increased.Compared with that of pure DABA/BMI,the maximum flexural strength of the NH₂-HBPSi/DABA/BMI resin with 10 wt% NH₂-HBPSi is improved to 159.9 MPa,increased by 29.2%.The maximum impact strength of the NH₂-HBPSi/DABA/BMI resin with 20 wt% NH₂-HBPSi is improved to 18.7 k J/m2,increased by 50.8%.The corresponding ? values of the NH₂-HBPSi/DABA/BMI resins are increased firstly,but decreased with the excessive mass fraction of NH₂-HBPSi.However,the corresponding tan? values are gradually decreased.The ? and tan? value of the NH₂-HBPSi/DABA/BMI resin with 20 wt% NH₂-HBPSi is 3.12 and 0.0098,respectively.The corresponding Tg values and thermal stabilities of the NH₂-HBPSi/DABA/BMI resins are increased with the increasing mass fraction of NH₂-HBPSi.For a given filler loading,with the addition of NH₂-HBPSi,the thermal conductivities of the POSS-g-n BN/NH₂-HBPSi/DABA/BMI and f Si Cp/f Si Cw/NH₂-HBPSi/DABA/BMI are both decreased,which are also lower than those of POSS-g-n BN/DABA/BMI and f Si Cp/f Si Cw/DABA/BMI composites.