Study On Transparency And Thermal Conductivity Of Polyimide Films Based On Different Monomers

Polyimide（PI）films have excellent mechanical,thermal and chemical corrosion resistance,and have broad application prospects in the field of electronics and microelectronics.The thermal conductivity of traditional polyimide film is about 0.2 W/m·K,and the transparency of PI film is poor.Low thermal conductivity restricts the application of polyimide in the field of microelectronics,and poor transparency also restricts its application in flexible display substrate.How to solve the above problems has become a research hotspot.In this study,the problems of poor light transmittance and thermal conductivity of polyimide are studied as follows:Firstly,some kinds of transparent PI films are prepared by two-step method by choosing different dianhydride monomers and diamine monomers,such as,4’-Oxydianiline（ODA）,4,4’-（Hexafluoroisopropylidene）diphthalic anhydride（6FDA）and o-Phenylenediamine（ODPA）.The properties of obtained PI films are characterized by UV,DMA,TMA,broadband dielectric spectroscopy and SEM.The transmittance at 400 nm of PI film synthesized by ODPA monomer is71%,and it shows good solubility in various solvents.The mass retention of the PI film synthesized by M-tolidine and 3,3’,4,4’-Biphenyl tetracarboxylic diandhydride（BPDA）reaches 63.7%at 800℃and the tensile strength is 147MPa.Based on the aboved results and analyzied structures and properties of PI films with different monomers,a colorless transparent polyimide film was designed with 6FDA and 4,4’-[bis（4,1-phenyleneoxy）]bis（HFBAPP）as monomers.Moreover,the innovative gradient vacuum and secondary film-forming process were used to further improve the light transmittance of the film.Results indicated that the transmittance of the film at 400 nm is 82%,the thermal expansion coefficient is 67 ppm/K,the breakdown strength is 200 k V/mm,the dielectric constant is less than 2.2,and the dielectric loss is less than 10^-2.The film is further modified to improve the dimensional stability of the film.When the amount of silica（Si O₂）reached 4%,the folding space between molecules in the film is effectively expanded,the coefficient of thermal expansion is reduced to 37 ppm/K,and the thermal dimensional stability of the film is improved.Secondly,a preparation method of PI films with high thermal conductivity was designed,in which the 1,4-Bis（4-aminophenoxy）benzene（TPE-Q）and BPDA are used as monomers to synthesize polyimide film and aluminum nitride（Al N）and boron nitride（BN）are used as thermal conductive fillers to modify the films.SEM show that Al N and BN particles modified by KH560 are well dispersed in the film.The properties of PI films with high thermal conductivity are characterized by infrared spectroscopy,broadband dielectric spectroscopy,thermal conductivity analyzer and SEM.The thermal conduction path inside the films is successfully constructed,and the obtained PI films show as high as 0.876W/m·K in thermal conductivity,180 k V/mm in the electrical breakdown strength and 100 MPa in the tensile strength..