Electron beam and variable frequency microwave processing for rapid curing of polymer dielectrics

Variable frequency microwave (VFM) curing has been investigated as a rapid cure method for 3,3'.4,4'- Biphenyltetracarboxylic acid dianhydride / P-Phenylenediamine (BPDA/PPD) and two photosensitive polyimides In this study, films produced using VFM curing (cure time ranging from 600-1800 sec) are compared with film produced via a conventional thermal cure (cure time of 18000 sec) and a rapid hotplate cure (cure time ranging from 1200-3600 sec). Properties, including dielectric constant, residual stress, modulus, solvent resistance, tensile strength and coefficient of thermal expansion were measured for the films produced by each of the three techniques. The results of this study indicate that VFM curing can provide thin-film properties similar to those achieved via lengthy, (conventional) thermal curing. In addition, for the first time, low residual stress BPDA/PPD polyimide has been created via a rapid cure process. Hence, it can be concluded that VFM curing is a viable method for more rapid production of BPDA/PPD polyimide film. Electron beam irradiation was used to cross link polynorbornene, which was formulated so that no thermal crosslinking occurred. It was found that the electron beam exposure made the polymer solvent resistant, and improved surface planarity in a multilayer structure. Further, it was also shown that electron beam curing resulted in films with properties similar to those of thermally treated films.