Research On Preparation And Properties Of SrTiO₃ Filled PTFE Composite Dielectric Substrate

With the rapid development of the modern communication industry,the use of microwave composite dielectric substrate is gradually increasing.In order to achieve the miniaturization along with high integration and high reliability of communication devices,high dielectric constant and low dielectric loss become the main performance indicators that the substrates need to obtain.Polytetrafluoroethylene(PTFE)has excellent dielectric properties,strong corrosion resistance and ultra-low water absorption,making it very suitable for the research and development of high-frequency dielectric substrates.SrTiO₃ceramics have high dielectric constant and relatively low dielectric loss.And SrTiO₃can be used as a filling material to increase the dielectric constant of composite substrates and improve the thermodynamic properties of PTFE resins.Therefore,in this thesis,PTFE was used as resin matrix and SrTiO₃ was used as filled ceramics to try to prepare high dielectric constant composite dielectric substrate.In this thesis,the surface modification effect of SrTiO₃ powder by the type and amount of coupling agent was firstly studied in terms of the hydrophobicity of ceramics and the dielectric properties of substrate.On this basis,the effects of different particle sizes of ceramic powders on the microscopic morphology,dielectric properties and water absorption of the substrate were studied,and the optimal ratio of the substrate was explored.Finally,a small amount of short glass fiber was added to try to improve the thermal properties of the composite dielectric substrate.The specific research contents are as follows:1.Research on surface modification of ceramic powders SrTiO₃:phenyltrimethoxysilane(Z6124),methacryloyloxypropyltrimethoxysilane(KH570),and vinyltrimethoxysilane(A171),the three kinds of couplings were used to modify the micron-sized SrTiO₃.Among them,Z6124-modified SrTiO₃ powder has the best effect.When the content of Z6124 is 2 wt.%,the modified ceramic has the strongest hydrophobicity,while its contact angle reaches 149.6°.And the composite dielectric substrate has the best comprehensive performance under the same ceramic content.At 10GHz,the dielectric constant is 6.84,a dielectric loss is 0.0015 and the water absorption is0.1142%.2.Research on the effect of ceramic particle size and content on substrate properties:Using Z6124-modified SrTiO₃ powder as filler,the effects of ceramic particle size and content on the microscopic morphology,dielectric properties,water absorption,thermal expansion coefficient of the substrate were systematically studied.Compared with submicron-sized(D₅₀=0.8?m)SrTiO₃ ceramics,the composite substrates prepared by micron-sized(D₅₀=2?m)SrTiO₃ ceramics have better comprehensive properties.The composite dielectric substrate exhibits the best performance when the ceramic content is75 wt.%.At 10 GHz,the dielectric constant reaches 17.01,the dielectric loss is 0.0034,and the dielectric constant has excellent frequency stability,the water absorption rate is0.08%,and the thermal expansion coefficient is 17.84 ppm/?.3.Research on the ratio of SrTiO₃/E-GF/PTFE composite dielectric substrate:After exploring the optimal ratio of SrTiO₃ ceramics and PTFE,adding glass fiber to a certain extent can improve the thermal properties of the composite substrate,witch will also lead to a decrease in the dielectric constant of the composite substrate,and an increase in dielectric loss and water absorption.When the ratio of E-GF is 1 wt.%,the overall performance is the best.At 10 GHz,the dielectric constant of the composite dielectric substrate is 15.48,the dielectric loss is 0.0041,the water absorption rate is 0.13%,and the thermal expansion coefficient is 16.69 ppm/?.