Polyimide Films Containing Trifluoromethoxy Groups with High Comprehensive Performance for Flexible Circuitry Substrates

The outstanding overall performance of polyimide (PI) films is critical for their application in the microelectronic and optoelectronic industries. A series of novel PI films containing trifluoromethoxy groups were prepared from a 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/2,2′-bis (trifluoromethyl) biphenyl-4,4′-diamine (TFMB)/2,2′-bistrifluoromethoxy-biphenyl-4,4′-diamine (TFMOB) tri-copolymer in this paper. The comprehensive performances of the derived PI films could be modulated by the molar ratio of TFMOB/TFMB, and each performance of the PI films was explored in detail. All PI films exhibited excellent overall performance against PI-ref (PI films were prepared by PMDA and ODA in our lab, which referred to the raw materials of Kapton films), especially PI-30, which possessed the best performance, such as remarkable thermal stability (T_5% = 581 °C and T_g = 368 °C), outstanding mechanical properties (T_S = 195 MPa and T_M = 3.5 GPa), ultralow moisture absorption (M_a = 0.74%), lower dielectricity (D_k = 2.877 and D_f = 0.00815 at 10 GHz), and high optical transparency. In addition, PI-50 had the largest breaking elongation (E_b = 27.6%), PI-70 had the lowest dielectric loss (D_f = 0.00514), and PI-100 presented the lowest moisture absorption (M_a = 0.50%). Each PI film possessed its own unique advantages to meet the special demand. Subsequently, the PI-30 film was used as a colorless and transparent substrate for flexible circuits, which could withstand multiple bends and still maintained excellent electrical performance after 1,40,000 folding times. The high comprehensive performance makes these PI films favorable candidates for flexible circuit substrates, foldable screens, and solar panels in the optoelectronic engineering and microelectronics industries.