Mechanical, dielectric and thermal properties of polyimide films with sandwich structure

With the development of high-frequency and high-speed flexible circuit boards, there are growing demands for low dielectric constant materials with high mechanical and electric breakdown strength. Herein, a novel sandwich structure is successfully fabricated using fluorinated graphene/polyimide (FG/PI) composite film as a dense outer surface layer and porous PI film as the middle layer. The middle porous layer lead to the ultra low dielectric constant. The presence of FG/PI layers resulted in the increase of mechanical and dielectric breakdown performance compared to that of porous PI. Especially, the three-layer FG/ PI film showed a tensile strength of 65.76 MPa, a tensile modulus of 2.96 GPa, a characteristic breakdown strength of 170.49 kV/mm, a dielectric constant of 1.92, and a dielectric loss of less than 0.003. Therefore, the sandwich structure PI film is a highly prospective candidate as flexible circuit substrates for electronics and microelectronics devices.