ORGANOSOLUBLE, SEGMENTED RIGID-ROD POLYIMIDE FILMS .2. PROPERTIES FOR MICROELECTRONIC APPLICATIONS

The essential properties of polyimide films of importance in microelectronic applications are thermal and thermo-oxidative stability, dimensional stability, glass transition behaviour and the relative permittivity (dielectric constant epsilon'). A segmented rigid-rod polyimide was synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (PFMB) in order to develop new materials for microelectronic applications. The thermal and thermo-oxidative stability were investigated by determining the thermal degradation activation energy in air (210 kJ mol-1) and in nitrogen (303 kJ mol-1). The thermal stability was further studied through thermogravimetry-mass spectroscopy. The coefficient of thermal expansion, which indicates the dimensional stability, was measured via a tension mode of a thermomechanical analyser and doubly extrapolated to zero stresses, and was 6.98 x 10(-6)-degrees-C-1 for the BPDA-PFMB films. The glass transition temperature, measured thermomechanically, was found to be 287-degrees-C. The dielectric constant for the films, measured after ageing at 50% relative humidity for 48 h at 23-degrees-C, was between 2.8 and 2.9 in a frequency range from 0.1 kHz to 1 MHz. The temperature and frequency dependence of the dielectric behaviour is also discussed.