Preparation Of Polyimide Material For Freeadhesive Flexible Copper Clad Laminate By Low Temperature Imidization

In recent years,with the vigorous development of 5G technology and the continuous change of consumer demand,the field of electronics and electrical appliances has put forward higher requirements for the performance of free-adhesive flexible copper clad laminates.Polyimide is a commonly used insulating base film of free-adhesive flexible copper clad lamins.The traditional polyimide film has a high dielectric constant,which does not meet the growing performance requirements.However,reducing the dielectric constant of the material by introducing fluorine-containing groups will lead to the deterioration of the adhesion between polyimide and copper foil.So how to balance the dielectric and adhesion properties has become one of the research directions.In the process of producing free-adhesive flexible copper clad laminate by using coating method,the imidization temperature of polyimide is too high.Therefore,the copper foil is easy to oxidize and leads to serious damage of flexible copper clad laminate.Factories use the oxygen-free ovens to avoid this issue,however,this method will increase the difficulty of the manufacturing process and greatly increase energy consumption.Besides the performance of the obtained free-adhesive flexible copper clad laminate is much lower than that of flexible copper clad laminate with adhesive.Thus,it is of great significance to prepare low dielectric and high adhesion polyimide material which can be used in free-adhesive copper clad laminate and realize its low-temperature imidization.In this paper,a kind of BTDA-ODPA-APB-BAPP polyimide with high adhesion was synthesized by the two-step method.Curing catalysts were used to reduce the imidization temperature.The effects of the type and content of catalyst and temperature control program during imidization on the properties of polyimide were investigated.Then BTDA-ODPA-APB-BAPP polyimide was blended with a fluorinated polyimide 6FDA-BTDA-6FAPB to study the effect of blending ratio on the comprehensive properties of polyimide.A series of 6FDA-6FODA-ODA fluorinated polyimides with low dielectric constant and high adhesion were synthesized by the two-step method,and the effects of different copolymerization ratios on the properties of fluorinated polyimides were studied.Finally,the fluorine-containing polyimide of 6FDA-6FODA-ODA and the non-fluoride polyimide of BTDA-ODPA-APB-BAPP were blended to explore the effect of components on the properties of polyimide,and the best conditions for the preparation of polyimide by imidization at low temperature.Infrared spectroscopy,universal testing machine,differential scanning calorimeter,and thermogravimetric analyzer were used to investigate the molecular structure,imidization degree,mechanical strength,thermal stability,and bonding properties of copper clad laminates.It is found that the imidization temperature of polyimide decreases with the introduction of curing catalysts.When isoquinoline is used as the catalyst,the basic imidization reaction of polyimide can be completed below 180°C.When the mass ratio of isoquinoline to dianhydride is 2:1 and the temperature control program is set at 170,180°C for 2 h,the comprehensive performance of polyimide is the best and the residual amount of catalyst is the least.The blending of fluorinated polyimide and non-fluorinated polyimide can make polyimide possess both high dielectric and adhesion properties.When the quantity ratio of matter of fluorinated polyimide to non-fluorinated polyimide is 1:4,the comprehensive performance of blending polyimide is the best and can realize the imidization under the action of the catalyst.The dielectric constant of the material is 2.98 and the peel strength is 1.07 N/mm.6FDA-6FODA-ODA series of polyimide films have good dielectric properties,and the dielectric constant is in the range of 2.23 to 2.80.The polyimide of 6FDA-6FODA-ODA（n（6FODA）:n（ODA）=8:2）was blended with BTDA-ODPA-APB-BAPP at the mass ratio of 1:4.When isoquinoline was used as the catalyst and the imidization condition was 170,180°C for 2 h,the polyimide material was obtained with the tensile strength of 147.17 MPa,T_5%is 503.61°C,T_10%is 570.54°C,peel strength of 1.12N/mm and dielectric constant of 2.56.It is a kind of low dielectric and high adhesion polyimide with excellent comprehensive properties that can prepare by low-temperature imidization.