STRUCTURE AND PROPERTIES OF A PHOTOSENSITIVE POLYIMIDE - EFFECT OF PHOTOSENSITIVE GROUP

The photosensitive poly(p-phenylene biphenyltetracarboximide) (BPDA-PD A) precursor was synthesized by attaching photocross-linkable 2-(dimet hylamino)ethyl methacrylate (DMAEM) monomer to its poly(amic acid) thr ough acid/base complexation. The polyimide thin films were prepared by a conventional cast/softbake/thermal imidization process from the pho tosensitive precursors with various concentrations of DMAEM. The struc ture and properties of the polyimide films were investigated by small- angle and wide-angle x-ray scattering, refractive indices and birefrin gence analysis, residual stress and relaxation analysis, stress-strain analysis, and dynamic mechanical thermal analysis. In comparison with the polyimide film from the poly(amic acid), the films, which were im idized from the photosensitive precursors, exhibited a better molecula r order and microstructure; however, they exhibited less molecular ori entation in the film plane. Despite the enhancement in both the molecu lar order and microstructure, the film properties (i.e., mechanical pr operties, thermal expansion, residual stress, optical properties, diel ectric constant, and water sorption) degraded overall due to both the decrease in molecular in-plane orientation and the formation of microv oids caused by the bulky photosensitive group during thermal imidizati on. That is, on one hand, the PSPI precursor formation provides an adv antageous, direct pattern-ability to the BPDA-PDA precursor, and on th e other hand, it results in degraded properties to the resulting polyi mide film. (C) 1995 John Wiley & Sons, Inc.