The effect of orientation on thermal expansion behavior in polyimide films

Abstract

AbstractThe 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. © 1994 John Wiley & Sons, Inc.