Effect Of Low/Trace Doping On High Frequency Dielectric Properties Of Polystyrene

The wide application of 5G communication technology promotes the development of communication electronic devices,mobile terminals and other products to the direction of high integration and high precision,which puts forward higher requirements for the performance of the medium materials used in printed circuit boards/integrated circuits（PCB/IC）.On the premise of good mechanical properties,thermodynamic properties,machining properties and service life,dielectric materials need to have lower dielectric constant and dielectric loss at high frequency,so as to ensure high speed and low loss of high-frequency transmission signals.As a kind of low dielectric material with high frequency application potential,organic polymer materials have been highly concerned and widely studied by scholars.For a long time,many organic polymers with excellent dielectric properties have been screened,designed and prepared.In addition,researchers have also explored and summarized the laws of various factors affecting the dielectric properties of materials,such as polymer element composition,main chain side chain structure,material porosity,and composite with other materials,etc.However,some laws found are often limited to specific material types or systems and are not universal enough.Moreover,the heating caused by a small increase in dielectric loss will be amplified at a high frequency,resulting in more serious energy loss per unit time.Therefore,in the process of preparation and processing of low dielectric materials,the influence of unintentionally introduced low/trace impurities or particles on their dielectric properties becomes non-negligible in the high frequency range.However,the research on the effect of these particles on the high frequency dielectric properties of polymers is relatively lacking,and further research is needed.Based on the above problems,this paper chooses polystyrene（PS）,one of the commonly used low dielectric organic polymers,as the matrix,in which artificially doped into low/trace impurity particles,through the split post dielectric resonator method of high accuracy measurement at 10 GHz frequency of impurity doped polystyrene dielectric constant and dielectric loss,The effects of impurity ion valence state,small molecule polarity and structure,filler characteristics and other factors on the high frequency dielectric properties were investigated.The main research ideas and contents are as follows:（1）The pure polystyrene particles are prepared by two different processing methods,one is direct hot pressing and the other is dissolved,dried and then hot pressing.Then,the high frequency dielectric properties of the two kinds of PS sheets were tested respectively,and the effects of dust and residual solvent inevitably introduced during different processing methods and processes on the dielectric constant and dielectric loss of polystyrene were analyzed,the reason for the change of dielectric properties was analyzed by density and the specific surface area calculated by nitrogen adsorption test.The results show that the density of the latter decreases,the specific surface area increases and the free volume of the molecular chain increases.Therefore,the dielectric constant of the sample at high frequency is 2.53.The dielectric loss was 0.89×10^-3.（2）Sodium chloride,copper chloride and ferric chloride were selected as fillers to be doped into polystyrene.Different kinds of metal ions represented charged impurity particles with different amount of charge.The influence of the change of metal ion content and the difference of different ion valence states on the high frequency dielectric properties of polystyrene was explored.Dimethyl sulfoxide and naphthalene were selected as fillers to be doped into polystyrene.These two organic molecules represented the residual small molecules in the material.The effects of organic molecule content,molecular polarity difference and different molecular structure on the high frequency dielectric properties of polystyrene were investigated.The dielectric performance test results show that,at high frequency,even if the content of impurity ions or small organic molecules is very low,the dielectric loss of the material will be greatly increased by high-valence ions,high-polar molecules and conjugated structures.（3）Solid silica and hollow glass microbeads with different particle sizes were doped into polystyrene as fillers,and the influence of filler content,particle size,structure and interface on high frequency dielectric properties was investigated.The effect of nano-sized silica doping on dielectric constant was verified by molecular dynamics simulation.In addition,the surface hydrophobic modification of three particle sizes of silica was also carried out to explore the effect of improving the high frequency dielectric properties of polystyrene.The results showed that doping the fillers with low content,large particle size,hollow structure and surface hydrophobic modification was beneficial to maintain the low dielectric constant and low dielectric loss of polystyrene.