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(k)) (<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(k), low dielectric loss (D(f)), 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(k) and D(f) 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.