RELAXATION MODULUS AND THERMAL-EXPANSION COEFFICIENT OF POLYIMIDE FILMS COATED ON SUBSTRATES

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 - nu-f), and thermal expansion coefficient, alpha-f, of a rigid rod-like polyimide film, pyromellitic dianhydride-benzidine (PMDA-B) coated on a substrate. As measured, the two properties, especially alpha-f, significantly increase with the increase of film thickness. At 150-degrees-C, for example, the obtained E(f)(1 - nu-f) increases from 6.0 to 8.2 X 10(9) N/m2, and alpha-f from -0.33 to 2.42 x 10(-6)/degrees-C for thicknesses ranging from 10 to 30-mu-m.