Comparative Study of Intrachain Versus Interchain Cross-Linking on the Mechanical, Thermal and Dielectric Properties of Low-K Polyimide

Polyimide (PI) is widely used in high-frequency communication technology due to its exceptional comprehensive properties. However, traditional PI has a relatively elevated dielectric constant and dielectric loss (tan[[EQUATION]]), which hinders its compatibility with the requirements of fifth-generation communication technology. Herein, the different cross-linked structures were introduced in PI matrix and conducted a detailed discussion on the influence of cross-linking agent content and cross-linking structure type on the overall performance of PI films. In comparison to the dielectric constant of 2.9 of pure PI, PI with an interchain cross-linking structure containing 2 wt% 1,3,5-tris(4-aminophenyl)benzene (TAPB) (interchain-PI-2) exhibited the reduced dielectric constant of 2.55 at 1MHz. Compared with interchain-PI, the PI with intrachain cross-linking structure (intrachain-PI) has a lower dielectric constant. The PI films with intrachain cross-linking structure containing 2 wt% TAPB (intrachain-PI-2) exhibited the lowest dielectric constant of 2.35 and the minimum tanδ of 0.0075 at 1 MHz. It was due to the more entanglement junctions of intrachain-PI resulting in decreased carrier transport. The thermal expansion coefficients of both interchain-PI and intrachain-PI films were effectively reduced. Especially the CTE of interchain-PI-2 decreased by 8.5% as compared to that of pure PI. Moreover, in contrast to interchain-PI films, the intrachain-PI films maintained colorlessness and transparency as the cross-linking agent content increased. Both interchain-PI and intrachain-PI films showed excellent thermal stability and improved mechanical performance. This work systematically compared and analyzed the effects of two different cross-linked structures on the performance of PI films and provided a feasible way to obtain low-k PI films with excellent comprehensive performance for 5G applications.