Evaluation of a Novel Polyimide for Use as a Low-Loss, Low Dielectric Constant Interlayer in Electronic Packaging Applications

摘要

Low molecular weight fluorinated polyimide oligomers have been synthesized with controlled molecular weight and thermally cured under an inert atmosphere to produce low dielectric constant materials. Prior to curing, several of the fully imidized oligomers exhibited excellent solubility and low solution viscosity in NMP at concentrations as high as 40-50 weight percent. The relatively low viscosity and high flow properties should lead to good planarity. After curing, ductile films were obtained which displayed a high glass transition temperature (Tg) of well over 300 °C with a significant elastic modulus above Tg. The cured films also demonstrated excellent solvent resistance. This was in contrast to previously reported fluorinated imide systems, which have desirable properties, but very poor solvent resistance. Additionally, preliminary observations suggested that the new polyimide materials may adhere well to copper, silicon and other polyimide films when cured on these substrates. Confirmation of low dielectric constant behavior was obtained from preliminary refractive index measurements of a film which gave a value of 1.584. The low estimated dielectric constant of the new fluorinated polyimide endorses its use as an interlayer dielectric in MCM-D applications. Circuit structures utilizing this material would display lower propagation delays, making them ideal for high-speed digital electronics.