Relaxation modulus and thermal expansion coefficient of polyimide films coated on substrates

Abstract

A bending beam technique with the use of two substrates, silicon and gallium arsenide, has been successfully employed to simultaneously determine the biaxial relaxation modulus, Ef/(1 − νf), and thermal expansion coefficient, αf , of a rigid rod-like polyimide film, pyromellitic dianhydride-benzidine (PMDA-B) coated on a substrate. As measured, the two properties, especially αf , significantly increase with the increase of film thickness. At 150 °C, for example, the obtained Ef(1 − νf) increases from 6.0 to 8.2×109 N/m2, and αf from −0.33 to 2.42×10−6/°C for thicknesses ranging from 10 to 30 μm.