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, E f /(1 - ν f ), and thermal expansion coefficient, α f , of a rigid rod-like polyimide film, pyromellitic dianhydride-benzidine (PMDA-B) coated on a substrate. As measured, the two properties, especially α f , significantly increase with the increase of film thickness. At 150 °C, for example, the obtained E f (1 - ν f ) increases from 6.0 to 8.2×10 9 N/m 2 , and α f from -0.33 to 2.42×10 -6 /°C for thicknesses ranging from 10 to 30 μm.