Preparation of thermoplastic polyimide composite film and its application in adhesive-free copper-clad laminates

Flexible copper-clad laminate （FCCL） is a key substrate material in fields such as mobile devices, wearable electronics, and biosensors. The purpose of this research is to address the problems of traditional three-layer copper-clad laminates （3L-FCCL） relying on epoxy resin adhesives, which suffer from issues such as thick adhesive layers and insufficient heat resistance. Developed an adhesive-free double-sided copper-clad laminates （2L-FCCL） with excellent dimensional stability, heat resistance and high peel strength. In this research, zinc sulfide-thermoplastic polyimide （ZnS-TPI） was prepared by introducing ether bonds and asymmetric structures and zinc sulfide （ZnS） particles as fillers by quaternary copolymer-thermal method. The purchased high-modulus low-thermal expansion polyimide （PI） film was used as the base film, and then ZnS-TPI precursor solution was used as the coating material to prepare thermoplastic polyimide （TPI/PI/TPI） composite film by coating-thermal imide method. Finally, 2L-FCCL was prepared by pressing copper foil and TPI/PI/TPI composite film by hot pressing. The composite film showed excellent comprehensive properties, the thermal decomposition temperature was as high as 541.3 ℃, the coefficient of thermal expansion （CTE） of 18.9×10⁻⁶·K⁻¹. Additionally, the composite film exhibits good dielectric properties, with a dielectric constant of 3.55 and a dielectric loss of 0.008 4. Under optimized lamination conditions （350 ℃, 3×10⁶ Pa, 60 s）, the 2L-FCCL exhibited a peel strength of 1.35 N·mm⁻¹, indicated that the TPI/PI/TPI composite film is an excellent adhesive-free FCCL interlayer dielectric material. The research conclusion provides an effective strategy for the development of high-performance adhesive-free copper clad laminate.