Low-loss and high-speed transmission flexible printed circuits based on liquid crystal polymer films

Proposed are low-loss and high-speed transmission flexible printed circuits (FPCs) based on liquid crystal polymer (LCP) films. The transmission losses of FPC based on LCP and polyimide (PI) film were measured under various conditions. At 23°C with 60 %RH, the differential-mode loss of differential line based on LCP films was 0.52 dB/cm lower than that of the differential line based on PI films at 40 GHz. Moreover, the differences in the loss of LCP film, caused by changes in temperature and relative humidity, were smaller than those of the PI film. These results show that the transmission characteristics of the FPCs based on LCP films were more stable and lower than those of the FPCs based on PI films.