Studies On Preparation Techenology And Properites Of PTFE/Glass Fiber Composites Substrate

Polytetrafluoroethylene（PTFE）-based composite dielectric substrates are ideal microwave dielectric materials,which is widely used in wireless networks,satellite navigation,radar communications and other fields because of low dielectric constant and low dielectric loss.Scientists and experts in various countries have developed out a series of PTFE-based composite substrate materials by applying different reinforcing materials.The microwave composite substrate materials developed by Rogers Inc.of the United States are at the forefront of the world and the products are typical representatives.The research of high-performance PTFE composite substrate material has important military value and scientific significance.In this paper,PTFE is used as matrix,glass fiber mat（GFM）and glass fiber cloth（GFC）as reinforcing materials to prepare composite substrate with specific properties and PTFE/GFM composite substrates and PTFE/GFC composite substrates are studied.The main research contents are as follows:1.Research on glass fiber mat（GFM）-reinforced PTFE composite substrate:The influence of pre-firing process and lamination process on the dielectric properties and water absorption of the composite substrate and the influence of the impregnation on the performance of the composite substrate were systematically studied:a)Five different pre-firing processes were studied.It was found that pre-burning at 230°C and holding for 2 h exhausted the organic micro-molecules such as surfactants in the impregnated layers and most of the GFM adhesives could be discharged,which is beneficial for obtaining composite substrate with excellent performance.The microwave composite substrate by this pre-baking method has a lower dielectric loss of 0.0007,a dielectric constant of 2.13,a water absorption of 0.022%.Five lamination processes were studied.It was found that as the PTFE adheres more tightly to glass fibers with the increase of PTFE/GFM layers and the gap between them are reduced The increase odf interface leads to increase of dielectric loss and emperature coefficient of dielectric constant.When the number of layers was 8,the performance of composite substrate was excellent,the dielectric constant is 2.21,the loss is 0.0012,and the water absorption is 0.024%.（c）Five impregnation methods were used for the preparation of thin PTFE/GFM composite substrate.As the impregnation concentration are decreased,the thickness of substrate are decreased,the dielectric constant and dielectric loss are increased,and the dielectric constant of the composite substrate at 10 GHz is lower than 2.5,the dielectric loss is lower than 0.0018.2.Research on Glass Fiber Cloth（GFC）Reinforced PTFE Composite Substrate:（a）Preparation of a PTFE/GFC composite substrate with five types of PTFE concentrations were studied.the best dielectric properties were obtained when PTFE concentrationat 60%,which dielectric constant is 2.81,dielectric loss is 0.0033,and minimum water absorption is 0.051%.（b）Enhancing the performance of the composite substrate by superimposing different layers of PTFE films.It was found that the dielectric constant decreases from 2.29 to 2.23 and the dielectric loss increases from0.0013 to 0.0018 with the increase of PTFE films.（c）PTFE/GFC composite substrates were prepared by using different layer of numbers.It was found that as the number of PTFE/GFC increases,the gaps between PTFE and glass fibers decrease,the dielectric constant of the composite substrate decreases and the dielectric loss increases.when the number of layers is 9,the thickness is 0.87 mm,the gaps between PTFE and glass fibers are less and the performance is excellent.The dielectric constant is 2.21,the loss is0.001,and the water absorption is 0.013%.3.Research of PTFE/GFC/GFM composite substrate and SiO₂ doped PTFE/GFM composite substrate:（a）PTFE/GFC/GFM composite substrates with different layers of PTFE/GFC were studied.It is found that as the number of layers increases,the thickness of the composite substrate increases,the dielectric constant increases from2.21 to 2.25,the dielectric loss 0.0014 increases to 0.0024,and the water absorption changes from 0.009%to 0.014%.（b）The effect of different concentrations of coupling agent on the SiO₂-doped PTFE/GFM composite substrate was studied.It was found that when the coupling agent concentration reached 7.5%,the effect of impregnation was better,and there were only a small amount of precipitate in 40 minutes.The performance of the composite substrate is excellent.It has excellent dielectric constant of 2.33,dielectric loss of 0.0015.