Preparation And Properties Of Fluorinated Polyimide Materials With High Adhesion

In recent years,with the explosive growth of 5G technology,electronic devices were developing in the direction of miniaturization and high frequency,and the requirements for flexible printed circuit boards(PCB)were getting more higher.Two-layer flexible copper clad laminate(2L-FCCL)is the substrate material for PCBs,and its performance determines the application performance of PCBs.Fluorinated polyimide(FPI)has the characteristics of thinness,good thermal stability,low dielectric constant and excellent mechanical properties,which was expected to realize the application in high frequency communication substrate,especially in PCB substrate.However,FPI was chemically inert,had low bonding strength to other substrates,and the products were easy to peel off,which seriously limited the development of FPI in this field.The purpose of this paper is to explore FPI thin film materials with high adhesion and excellent overall performance.Firstly,four series of homopolymerized FPI were prepared by a two-step process,and we found that perfluorinated FPI and hemi-fluorinated FPI had their own advantages and disadvantages,and in order to find FPI films with better overall performance,three series of copolymerized FPI films were prepared by introducing three non-fluorinated dianhydrides BPDA,PMDA and BTDA into the reaction system based on A-series.After the tests of mechanical properties,optical properties,thermal properties and peel strength,two series of FPI films with excellent overall performance were finally found,namely 6FDA-BPDA-TFMB and 6FDA-PMDA-HFBAPP.In order to further investigate the effect of ether bonding on the structure and properties of FPI materials,two series of FPI films were prepared based on these two formulations,but the adhesion properties of the resulting materials still did not meet the design requirements.Therefore,DSX siloxane was introduced into these two FPI films for modification,and the effect of different content of DSX on the overall performance of FPI,especially the adhesion,was investigated,and FPI films with high adhesion and excellent overall performance were obtained.The results showed that the fluorine content had a great influence on the performance of FPI.Generally,the higher the fluorine content,the better the optical properties and hydrophobicity,but it will reduce the tensile strength,thermal stability and peel strength of FPI.In the perfluorinated FPI films prepared by 6FDA with TFMB,6FODA and HFBAPP,the fluorine-free dianhydride monomers BPDA,PMDA and BTDA were introduced to obtain FPI films with better overall performance,respectively.The two FPI materials with the best overall performance were 6FDA-BPDA-TFMB and 6FDA-PMDA-HFBAPP,which had tensile strengths of 90.20 MPa and 96.25 MPa,maximum transmittance of 90.47% and 87.59%,and thermal decomposition temperatures of 530.90 ℃ and 522.18 ℃,respectively,but the The peel strength did not reach the industrial requirements.The influence of the ether bond content on the performance of FPI was great.As the ether bond content increases,the molecular weight,elongation at break and peel strength of FPI increase,but its thermal stability,hydrophobicity and optical properties decrease,and changing the ether bond content alone did not enable FPI to meet the requirements of industrial production.The introduction of siloxane DSX into FPI can significantly improve the peel strength of FPI copper foil,where the addition of 10%content of DSX to 6FDA-PMDA-HFBAPP achieved an adhesion grade of 1 and peel strength with copper foil as high as 1.21 N/mm.However,the addition of DSX will reduce the comprehensive performance of FPI films,and with the increase of DSX content,the the tensile strength and thermal stability of FPI are significantly reduced,making it difficult to meet even the minimum requirements for industrial production.The use of release agent TPP allowed the highly adherent FPI to be easily peeled off from the glass sheet and also increases the thermal stability of FPI,but it also had some negative effects,such as making the tensile strength of FPI worse,the film became hard and brittle,and the practical value was reduced.