Low Permittivity and Dielectric Loss Polyimide with Patternability for High Frequency Applications

We have successfully developed novel low dielectric constant (Dk) and dissipation factor (Df) polyimides by following procedure. We investigated polyimides having various molecular mobility and polarity in polymer backbone to understand how to design low Dk and Df polyimide. We found that molecular mobility at -150 to -50°C was corresponded to Df from 10 to 100 GHz. To reduce Df at GHz order, it was important to reduce molecular mobility at low temperature around -50°C. In addition, to reduce polarity and flexibility in the polyimide backbone was also important to obtain low Df and Dk polyimide. We took advantage of these knowledge for development of low dielectric loss polyimide. As the result, we achieved 0.002 of dissipation factor and 2.7 of permittivity respectively. Those polyimides can be patterned by alkaline aqueous solution wet etching with positive-tone photoresist development and by UV laser ablation. We also have developed photo-definable low loss tangent polyimide by blending of photo active reagent. The novel polyimide showed lower insertion loss of microstrip line than conventional photosensitive polyimide. Those low Dk & Df polyimides can be exploited for insulator of redistribution layers which is essential for interposer, FO-WLP and other RF device.