| With the rapid development of modern electronic information technology,the innovation of 5G communication technology brings more demands and challenges to the terminal electronic devices in the field of high-frequency high-speed signal transmission network in the future.In order to ensure the speed and efficiency of signal transmission,it is important to further reduce the dielectric constant and dielectric loss of dielectric materials.Polyimide(PI)low dielectric material has been used in printed circuit boards due to its excellent comprehensive properties such as thermal and mechanical properties.Hollow silica spheres are widely used in the fields of low dielectric materials and drug sustained-release carriers due to their advantages of low density,large air cavity and high stability.In this paper,soft template method and hard template method were used respectively to the two different particle size of silica hollow sphere: nanoscale silica hollow spheres(NHS)and micron grade silica hollow sphere(MHS),effects of the amount of CTAB 、 TEOS and ammonia on the morphology of hollow Si O2 microspheres were discussed.In addition,NHS and MHS were introduced into polyimide films,and the microstructure,dielectric,thermal,mechanical,moisture resistance and optical properties of the composite films were systematically studied.The main research work of this paper is as follows:(1)Nano-sized hollow silica spheres(NHS)were successfully prepared by soft template method.The results show that with the increase of alcohol/water volume ratio,silica particles form a hollow structure,the surface becomes smooth and the particle size becomes larger;With the increase of ammonia dosage,the hydrolysis rate increases,and silicon dioxide impurities are generated on the surface of silica hollow microspheres.With the increase of CTAB dosage,the particle size of silica hollow spheres gradually decreased.NHS/PI composite films were successfully prepared by the flow-casting method,and the effects of the amount of NHS on the dielectric,thermal,mechanical,moisture resistance and optical properties of the composite films were studied.When the NHS dosage was 1.0 wt %,the composite film obtained the lowest dielectric constant(3.13)and the dielectric loss decreased at 1 MHz frequency.The introduction of NHS also improved the thermal and mechanical properties.The addition of NHS was 1.0 wt %,the glass transition temperature was374.96 ℃ and the tensile strength was 115 MPa.The addition of NHS also leads to the decrease of moisture resistance and optical properties.(2)Micron hollow silica spheres were successfully prepared by combining hard template method and sol-gel method.The results show that with the increase of heating rate,the number of broken silica hollow microspheres increases;With the increase of cationic surfactant dosage,the number of nano-sized silica solid spheres increased and the particle size decreased.With the increase of the amount of silicon source,the wall thickness of silica hollow microsphere gradually thickens until a large number of free silica particles are produced.When ammonia was less than4 m L,silica hollow microspheres could not be formed.When ammonia was greater than 4m L,the hydrolysis rate increased,and the surface of silica hollow microspheres was rough with solid particles.The solid silica microspheres can be effectively removed by filtration.NHS/PI composite film was successfully prepared by the streaming-delay method,and based on NHS/PI composite film as a comparison.By comparing the two composite films with the same amount of addition,it is found that MHS can effectively further reduce its dielectric constant and improve its thermal and mechanical properties due to its larger cavity volume and better dispersion.When the MHS filler content is 2.0 wt %,the composite film has the lowest dielectric constant(2.79)and the dielectric loss decreases at 1 MHz frequency.The glass transition temperature is 388 ℃and the tensile strength is 85 MPa.46 figures;4 tables;93 references... |
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