Residual stress and mechanical properties of submicron thin film on polymer substrate

Abstract

Thin films on polymer substrates have been used in the electronic packaging applications and employed as specimens for material tests to study the mechanical properties of thin films. Residual stress and mechanical properties of a thin film on a polymer substrate are considered in this research. Especially, initial residual stress reduction in the film is studied due to the mismatch strain distribution in the film and the substrate. Exact mismatch strains in the film and the substrate are obtained and the effect of mismatch strain distribution on the curvature-mismatch strain relationship is analyzed. F.E simulation is performed to see the stress and curvature distributions during temperature changes. Estimation of residual stress of film by mismatch strain in the film is suggested. Tensile test machine was set up to investigate material properties and behaviors of a submicron copper film on a Kapton substrate. Alignment, gripping and the specimen geometry effect on the tensile test result are considered. Dependency of mechanical properties on the thickness is studied. Residual stresses are accounted fot the yield stress of the film. In addition, mechanical behaviors during elongation, such as, crack formation, saturation, buckling and delamination are observed using microscope and AFM.