Low Df Polyimide with Photosensitivity for High Frequency Applications

We have investigated molecular motion and polarity of polyimide chain to developed novel low dielectric constant (Dk) and dissipation factor (Df) polyimides. We found that Df at 10-100 GHz corresponds molecular mobility at -150 to -50 ℃. To reduce the dielectric loss (=Df) at high frequency, restriction of molecular motion at low temperature was important. In addition, to reduce polar and flexible unit in the polyimide chain is also important to obtain low Dk and Df polyimide. We exploited these knowledge for development of low dielectric loss polyimide for RDL. As the result, we achieved 0.002 of loss tangent and 2.7 of dielectric constant respectively about novel polyimide. Those polyimides are patternable by alkaline wet etching with positive photo-resist development and by UV laser ablation method. We also have developed photo-definable low loss tangent polyimide by blending of photo active reagent. Lower insertion loss of microstrip line was observed by the novel low Df polyimide than by conventional photosensitive polyimide. Those low dielectric loss polyimides are suitable for insulator of FO-WLP, interposer and other RF applications for microelectronics.