Preparation And Properties Of Polyimide With Low Dielectric Permittivity

Polyimide(PI)has been widely used in microelectronics due to its excellent thermodynamic and dielectric properties.With the rapid development of electronic technology in recent years,the line spacing of integrated circuits is getting closer and closer,and the degree of integration is getting higher and higher.Higher requirements are put forward for IC line to line insulation materials,which need lower dielectric constant on the basis of maximizing the mechanical properties to reduce the signal hysteresis caused by too close line spacing.Due to the high dielectric constant of intrinsic polyimide,it can not meet the current high performance requirements.Therefore,it needs to be modified to reduce the dielectric constant of the material.In order to reduce the dielectric constant of PI,the three fluorine methyl and flexible ether bonds were introduced into the molecular chain.Two kinds of phthalic anhydride monomer with different structures were selected:hexafluorodicanine(6FDA)and diphenyl anhydran(BPAD)reacted with diamino diphenyl ether(ODA)respectively to prepare two polyimides(FPI and BPI).The monomer feed ratio,solid content,reaction temperature and reaction time were studied.The synthetic conditions with the maximum viscosity were selected.Then,PAA was synthesized under this condition,and two kinds of polyimide matrix materials with different structures were obtained by thermal imidization.The FTIR,solubility,dielectric constant,thermal stability,mechanical properties,contact angle and water resistance of FPI and BPI were tested.The results showed that FPI and BPI had better comprehensive properties,among which the dielectric constant was lower than that of commercial PI,FPI was 3.20;BPI was 3.31;the carbon residue rate was above 55%;tensile strength was135.3MPa,120.1MPa;elongation at break was 15.8%,21.3%;water absorption was 1.66%,1.39%.The Si-O bond can cut off the charge transfer in imide,weaken the conjugation and reduce the dielectric constant.In this paper,the PDMS was copolymerized with two PI monomers as the third monomer,and the influence of PDMS content on FPI and BPI was studied.The results showed that the dielectric constant of FPI and BPI decreased first and then rose with the increase of PDMS content.The lowest dielectric constant was 2.90 when 3%mole content of polysiloxane was introduced into FPI,and 2.92 when 4%mole content was introduced into BPI.The thermal stability of the two copolymers decreased with the increase of PDMS content;the tensile strength decreased with the increase of PDMS content;the elongation at break increased;the hydrophobicity gradually improved with the increase of PMDS content,which showed that the contact angle gradually increased and the water absorption decreased gradually.In order to further reduced the dielectric constant of PI and improved the decrease of tensile strength caused by PDMS,copolymers Si FPI-3 and Si BPI-4 were used as matrix respectively.Polyimide/porous silica composites were prepared with two kinds of substrates.And it was tested and characterized.It can be found that the introduction of porous structure in PI was effective to reduce the dielectric constant.When the content of porous silica was 6wt%,the dielectric constant of the two substrates was the lowest.With the increase of Si O₂content,the dielectric constant of Si FPI-3/Si O₂first decreased and then increased.When the content of porous silica was 6wt%,the dielectric constant of Si FPI-3/Si O₂was the lowest,which was2.33.The thermal property decreased slightly,and the tensile strength first increased and then decreased.When the content of porous silica was 4wt%,the tensile strength reached the maximum,which was 145.8MPa The dielectric constant of Si BPi-4/Si O₂first decreases and then increases.The dielectric constant of Pi-4/Si O₂was the lowest at 6wt%,which was 2.37.The thermal properties gradually improved,and the tensile strength first increased and then decreased.The tensile strength reached the maximum at 4wt%,which was 120.2MPa.The elongation at break gradually decreases,and the water absorption gradually decreases.