Low Dk/Df Polyimide Adhesives for Low Transmission Loss Substrates

Abstract

We developed solvent-soluble polyimides with good heat resistance and low dielectric constant (Dk)/dissipation factor (Df) characteristics by optimizing the composition ratio of the aliphatic, cycloaliphatic, and aromatic groups present in the polyimide back bone. We found that the adhesives prepared using our polyimides showed good adhesion to polyimide films and low profile copper foils and low Dk/Df. Furthermore, we developed a three-layer flexible copper clad laminate (3LFCCL) with our polyimde (PI) adhesives, low-pofile copper foils, and normal PI films. This 3LFCCL showed a transmission loss similar to that of liquid crystal polymer (LCP) FCCLs at frequencies less than 20 GHz. This result indicates that by using our PI adhesives, lower cost FCCLs can be prepared, which can then be used as high-frequency substrates.