Novel Photosensitive Dielectric Materials Based on Polynorbornene for Wafer Level Packaging Applications

摘要

New materials are necessary to meet the needs of the emerging Wafer Level Packaging (WLP) market in order to enable a variety of innovative package designs. Polynorbornenes, a new polymer family produced by BFGoodrich under the trade name Avatrel~(TM) Dielectric Polymers, have both the intrinsic properties and tailorability to fulfill the needs of WLP. The hydrocarbon nature of the polymer offers low moisture absorption values with 0.3 wt% at saturation and a dielectric constant between 2.4 and 2.7. Typical epoxies and polyimides can have moisture absorption of 2-3% and a dielectric constant greater than 3. Through extensive polymer and formulation optimization, novel photodefinable compositions have enabled high aspect imaging on films up to a 150 μm thick. Photodefinition is achieved through an I-line exposure of 500 to 2000 mJ/cm~2 and development with an environmentally friendly solvent. Dynamic Fourier transform infrared spectroscopy has allowed the optimization of the processing conditions by monitoring the extent of cure as a function of exposure energy, post exposure bake conditions, and curing conditions. The cured polymer has a high glass transition temperature greater than 250℃ while maintaining a low modulus of 450 MPa. In summary, recent developments have allowed quantum improvements in the processing capabilities of polynorbornene, while still maintaining its inherent advantages in electrical and physical properties.