Inelastic deformation of polyimide-copper thin films

Thin-layered composites of polyimide-copper are tested in tension. The specimens are prepared using standard thin film preparation techniques. The stress relaxation behaviour of the two phases is measured and modelled in terms of a single activated rate process. The internal stress in the polyimide is measured and increases with tensile strain. The deformed samples are examined with laser-scanning confocal microscopy and standard optical microscopy. Microcracks in copper and shear bands in polyimide are observed and correlated qualitatively with the stress relaxation model.