THE EFFECT OF ORIENTATION ON THERMAL-EXPANSION BEHAVIOR IN POLYIMIDE FILMS

The anisotropy of the thermal expansion of polyimide films was investigated. Out-of-plane or thickness direction coefficients of linear thermal expansion (CTE) were calculated from the difference between the coefficient of volumetric expansion (CVE) and the sum of the in-plane or film direction coefficients of linear thermal expansion for commercial and spin-coated PMDA//ODA and BPDA//PPD films and spin coated BTDA//ODA/MPD films. The CVEs were obtained from a pressure-volume-temperature (PVT) technique based on Bridgeman bellows. The CVE was shown to be essentially constant, independent of molecular orientation and thickness. A decrease in the in-plane CTEs therefore occurs at the expense of an increase in the out-of-plane CTE. In all cases the calculated out-of-plane CTE was higher than the measured in-plane CTE. The ratio of the out-of-plane CTE to the in-plane CTE was 1.2,3.8, and 49.3 for the spin-coated BTDA//ODA/MPD, PMDA//ODA, and BPDA//PPD films, respectively. (C) 1994 John Wiley & Sons, Inc.