Preparation And Research Of Low Temperature Co-fired Ceramic Based On CMBSL Glass/AIN

To better adapt to the requirements for high frequency and rapid signal transmission of wireless communication technology,an increase in demand has been put forward for low insertion loss and good temperature stability of microwave devices.In addition,with the recent breakthrough in electronic information technology,electronic devices are also rapidly developing in the direction of lightweight,miniaturization,and portability,making it necessary to improve the degree of integration and modularization for electronic components.Thus,this will place higher demands on the performance of microelectronic packaging materials and technologies.However,smaller sizes and greater power of electronic devices would inevitably result in a rapid increase of heat accumulation in the devices,which will seriously reduce their operation stability and lifespan unless the excess heat is effectively removed in time,Applying materials with high thermal conductivity is one of the most efficient ways to solve the bottleneck problem of heat dissipation.Therefore,there is an urgent need to further develop LTCC materials with both excellent microwave dielectric performance and high thermal conductivity to meet the requirement for high-performance electronic packaging.In this thesis,CaO-MgO-B2O3-SiO2-Li2O(CMBSL)glass was prepared by the conventional quenching method,and LTCC composites were obtained by flow casting and low temperature sintering.The optimal sintering temperature and AIN content in the CMBSL/AlN composites were determined based on the effects of different AlN contents and sintering temperatures on the densities and thermal conductivities.To further enhance the thermal conductivity,h-BN ceramics were introduced and the effects of different h-BN contents on the properties of pressureless sintered CMBSL/AlN/h-BN composites were investigated.Due to the low densities of h-BN ceramics under pressureless sintering,using a hot-pressing sintering process,the properties of hot-pressing sintered CMBSL/AlN/h-BN composites at different h-BN contents were analyzed.The main findings are as follows:(1)The content of AlN in the CMBSL/AlN composite is selected as 40 wt%,the green sheets should be discharged at 600℃ and sintered at 875℃.The prepared CMBSL/AlN composite has a dense structure,a thermal conductivity of 4.75 W/(m·K),a thermal expansion coefficient of 7.35 ppm/K,a dielectric constant of 6.64 at 24 GHz,and the dielectric loss tangent tanδ=2.18 × 10-2.(2)Four new phases,CaAl2Si2O8,Ca2SiO4,LiAlSiO4 and CaMgSi2O6,were generated in the pressureless sintered CMBSL/AlN/h-BN composites,and the CaAl2Si2O8 crystal underwent selective orientation growth.The h-BN platelets were added to connect the AIN particles isolated by glass to build up the heat conduction path and enhance the thermal conductivity of the composites.The better performance of the pressureless sintered CMBSL/AlN/h-BN composite was obtained when the hBN content was 3 wt%,and the thermal conductivity reached 6.55 W/(m·K),the thermal expansion coefficient was 4.47 ppm/K,the dielectric constant was 5.76 at 24 GHz,and the dielectric loss tangent tanδ=7.02 × 10-4.(3)The same four crystalline phases of CaAl2Si2O8,Ca2SiO4,LiAlSiO4 and CaMgSi2O6 were also generated in the hot-pressing sintered CMBSL/AlN/h-BN composites,in which the LiAlSiO4 crystal underwent selective orientation growth under hot-pressing sintering.Hot-pressing sintering can not only make the h-BN ceramics sinter dense,but also can induce the h-BN ceramics to interconnect to form a thermally conductive network,thus enhancing the thermal conductivity of the composites.The better performance of the hot-pressing sintered CMBSL/AlN/h-BN composites was obtained when the h-BN content was 4 wt%,with a maximum thermal conductivity of 10.3 W/(m·K),a thermal expansion coefficient of 5.12 ppm/K,a dielectric constant of 5.96 at 24 GHz,and a dielectric loss tangent tanδ=4.77 × 10-4.In this thesis,the as-prepared CMBSL/AlN/h-BN composites have excellent thermal conductivity and dielectric properties.At the same time,the thermal expansion of the composites matches well with semiconductor materials such as silicon,which will have potential applications in the field of 5G communication and electronic packaging.