Structural Designs of Transparent Polyimide Films with Low Dielectric Properties and Low Water Absorption: A Review.

The rapid development of communication networks (5G and 6G) that rely on high-speed devices requiring fast and high-quality intra- and inter-terminal signal transmission media has led to a steady increase in the need for high-performance, low-dielectric-constant (D) (<2.5) materials. Consequently, low-dielectric polymeric materials, particularly polyimides (PIs), are very attractive materials that are capable of meeting the requirements of high-performance terminal devices that transmit broadband high-frequency signals. However, such a PI needs to be properly designed with appropriate properties, including a low D, low dielectric loss (D), and low water absorptivity. PI materials are broadly used in various fields owing to their superior property/processibility combinations. This review summarizes the structural designs of PIs with low D and D values, low water-absorbing capacity, and high optical transparency intended for communication applications. Furthermore, we characterize structure-property relationships for various PI types and finally propose structural modifications required to obtain useful values of the abovementioned parameters.