Preparation And Performance Of Ternary Copolymerized Low-Dielectric Polyimide Films

Since the 21 st century,science and technology have made rapid progress,and electronic products are developing towards high-frequency signal transmission and high-speed digitization.Especially after entering the era of 5G communication,the high-speed transmission of signals at high frequencies has put forward higher requirements for the material of antennas,forming a structure mainly composed of flexible printed circuits(FPCs).Polyimide(PI)materials are widely used as insulation materials for integrated circuits.However,conventional polyimide materials have high dielectric constant and dielectric loss,which are not suitable for direct use as the substrate of FPC boards at 5G frequency.In order to obtain four kinds of polyimides with good dielectric and thermodynamic properties and good comprehensive properties,this paper selects different types of diamine dianhydride monomers,adopts two-step method,adjusts the monomer ratio in the polymerization process,and prepares ternary copolymer polyimide films,and analyzes their structure and properties.Based on the design idea of molecular structure,the paper selects p-phenylene bisphenyltrimellitate dianhydride(TAHQ)with ester bond structure as the dianhydride.Based on four different diamine systems,the dielectric and other comprehensive properties of PI films under different diamine ratios are studied by means of ternary copolymerization.Wherein,the polyimide is prepared and named ATOPI by using para aminophenyl ester of para ester diaminoaminobenzoic acid(APAB)and 4,4 ’-diaminodiphenyl ether(ODA),and the polyimide is prepared and named PCMPI by using diamine 4-(4-(4-heptylcyclohexyl)phenoxy)phenyl-1,3-diamine(PC7E)and para phenylenediamine(PDA)containing alkyl fatty chain;The first fluorine-containing polyimide was prepared with 2,2 ’-bis(trifluoromethyl)diaminobiphenyl(TFMB)and PDA and named PTMPI,and the second fluorine-containing polyimide was prepared with 2,2-bis [4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane(HFBAPP)and ODA and named HFOPI.Characterization of the composition and structure using Fourier transform infrared spectroscopy and X-ray diffraction;Conduct performance testing and analysis using instruments such as a separated resonant cavity network vector analyzer,universal material testing machine,thermal weight loss analyzer,thermal expansion analyzer,contact angle tester,etc.The results showed that the dielectric constant and dielectric loss of ATOPI films decreased when the proportion of APAB containing ester diamine increased,the lowest dielectric constant reached 2.63,and the dielectric loss reached 0.0019.At the same time,the coefficient of thermal expansion of ATOPI films also gradually decreased,and the tensile strength and elastic modulus increased.The introduction of ester diamine was conducive to reducing the water absorption of ATOPI films,and the lowest water absorption reached below 1%;As the proportion of diamine PC7 E containing alkyl fatty chain structure increases,the dielectric of PCMPI film gradually decreases,and the mechanical properties and dimensional stability of the film decrease to a certain extent,but both are within a controllable range.The dielectric constant and dielectric loss of two PI films were calculated by simulating the dipole moment changes of polymers in an alternating electric field,and the results showed a consistent trend with the measured values;The overall change trend of coefficient of thermal expansion obtained by explicit fitting is also basically consistent with the measured value.The dielectric constant and dielectric loss of the two fluorine-containing polyimides PTMPI/HFOPI show a downward trend when the proportion of fluorine-containing diamine increases.When the proportion of TFMB/HFBAPP reaches 45～50%,the dielectric constant reaches the lowest.At this time,the dielectric constant of PTMPI film is 2.65,and the dielectric loss is 0.0028;The dielectric constant of HFOPI film is 2.61,and the dielectric loss is 0.0024.However,as the proportion of fluorodiamine increases,the mechanical properties and dimensional stability slightly decrease.The simulated dielectric constant after correction is in good agreement with the measured value,the simulated dielectric loss is also in good agreement with the experimental value,and the coefficient of thermal expansion also has a basically consistent change trend with the experimental value.