Synthesis and properties of a novel perfluorinated polyimide with high toughness, low dielectric constant and low dissipation factor†

Abstract

With the development of high-frequency communication technologies, polyimide (PI) materials with a low dielectric constant (D_k) and low dissipation factor (D_f) are urgently needed to reduce signal crosstalk and other transmission problems. The introduction of a trifluoromethyl group is a common strategy to reduce D_k and D_f, but the bulky trifluoromethyl group would diminish stacking density and consequently lead to inferior mechanical properties. Herein, a novel diamine monomer, 2,3,4,5,6-pentafluororo-3,5-bis(4-aminophenoxy)-1,1-biphenyl (5FBODA), was designed and synthesized using simple reactions. Subsequently, fluorinated diamine and dianhydride were copolymerized with 5FBODA to obtain a series of fluorinated polyimide (FPI) with excellent dielectric properties and good mechanical performances, particularly high elongation at break. The pentafluorophenyl side group showed an obvious electron-withdrawing effect and made the charge of the structure more balanced, which reduced the molecular polarization rate and charge concentration to some extent, significantly helping in reducing D_k at high frequency. As the 5FBODA content increased, the large lateral group restricted the movement of the main chain, constrained the dipole polarization, thereby effectively diminishing their D_f. Moreover, when 20–30% 5FBODA was added, the pentafluorophenyl side group increased the intermolecular forces, thereby enhancing the elongation at break while maintaining good thermal properties. These FPIs exhibited remarkable advantages for advanced microelectronic packaging applications, providing an innovative solution for the development of next-generation high-performance electronic materials.

Keywords: Wafer level packaging; Fluorinated polyimide; Low dielectric; High toughness.