It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength-dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

SynopsisThe cure of a polyimide derived from pyromellitic dianhydride (PMDA) and oxydianiline (ODA) has been studied using infrared spectroscopy. A factorial experimental design, combined with regression analysis, was used to find the optimum curing conditions. It was shown that five micron films can be cured by heating a t 230-250°C for times of five minutes or longer, while samples cured initially a t 150°C did not cure completely when heated to higher temperatures.

Pyroelectric coefficients of a copolymer of vinylidene fluoride (95%) and tetrafluoroethylene (5%) have been measured, and were found to be significantly higher than those obtained for the poly(vinylidene fluoride) homopolymer. The effect of poling time and the nature of the (first cycle) thermally stimulated currents are also compared.

The addition of charge-transfer acceptors to a nematic liquid crystal at concentrations <0.1% has a profound effect on the voltage-transmission characteristics for dynamic scattering, reducing the threshold voltage by a factor of 2 for dc fields, but not appreciably altering the ac behavior. Charge-transfer bands in the visible may be introduced that depend on the concentration and nature of the acceptor molecule employed.

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