Study On Preparation And Properties Of Fluorine-containing Micro-branched Crosslinked Polyimide Films

Polyimide(PI)with imide ring and aromatic ring group is one of the most heat-resistant polymers.PI films have excellent thermal stability,mechanical strength,solvent resistance and dielectric insulation properties.In the microelectronics industry,the most important application of PI is as the interlayer dielectric insulator film material.Low dielectric constant can reduce the resistance-capacitance(RC)delay and crosstalk of signal,and low dielectric loss can reduce the thermal power consumption and weaken the device heating effect.With the advent of 5G era,large-scale antenna arrays and highly integrated chips have put forward higher requirements for the performance of interlayer dielectrics and packaging materials.The overall performance of PI film is excellent,but the dielectric constant of unmodified aromatic PI film is around 3.4(1MHz),making it increasingly difficult to meet the requirements of the electronics industry for low-dielectric materials.In our previous research,we proposed a design scheme to construct a micro-branched crosslinked structure in the PI molecular chain,and realized the simultaneous optimization of the dielectric constant and the coefficient of thermal expansion(CTE).In order to future reduce the dielectric constant of PI films,fluorine-containing monomers were introduced on the basis of constructing micro-branched crosslinked structure:the construction of microbranched structure can increase fractional free volume(FFV)and reduce the dielectric constant;the introduction of fluorine-containing groups can increase the FFV,reduce the molar polarizability and further reduce the dielectric constant,but it will lead to an increase of CTE;the construction of microbranched crosslinked structure can limit the movement of molecular segments and reduce CTE.The combination of fluorination and construction of microbranched crosslinked structure can further reduce the dielectric constant of PI films while regulating CTE and maintaining comprehensive performance,which provides a method for preparing intrinsic PI film with ultra-low dielectric constant.Based on the above plan,the main work of this research is carried out as follows.Firstly,PI films of four systems PMDA/ODA,PMDA/TFMB,6FDA/ODA,6FDA/TFMB were prepared by two kinds of dianhydride and two diamines.The effects of fluorine-containing monomer on mechanical properties,optical properties,hydrophobicity,and dielectric constant were discussed.In addition,PMDA/ODA/TFMB,PMDA/6FDA/ODA,6FDA/ODA/TFMB,PMDA/6FDA/TFMB were prepared by copolymerization,and the effects of chain stiffness and flexibility on mechanical properties and thermal dimensional stability were discussed.The results show that fluorination can improve the optical transmittance and hydrophobicity of PI films,and reduce the dielectric constant;the greater the stiffness of molecular chain is,the smaller the CTE is,and the greater the mechanical strength and modulus are.Further,in order to reduce the dielectric constant of fluorinated PI film and optimize CTE,four systems PMDA/ODA/TAPOB,PMDA/TFMB/TAPOB,6FDA/ODA/TAPOB,6FDA/TFMB/TAPOB were prepared using triamine monomer TAPOB as the crosslinking agent,focusing on the influence of TAPOB content on the dielectric constant,CTE and mechanical properties of PI film.The result show that the micro-branched structure can further reduce the dielectric constant of fluorinated PI films,and the existence of micro crosslinked structure improves the mechanical properties of fluorinated PI films,limits the movement of molecular chains at high temperature,and reduces CTE,providing a method for preparing intrinsic ultra-low dielectric constant PI film.