On the interface debond at the edge of a thin film on a thick substrate Original Research Article

The failure by debonding of 400 nm Al thin films on 152 μm-thick polyimide substrates has been studied in uniaxial tension experiments. To explain the edge debond of the Al film, the shear stress field along the film–substrate interface is determined. An analytical solution for the stress field exhibits a square root singularity near the free edges. The associated stress intensity factor is calculated in closed form by an asymptotic analysis. For a given loading, the stress intensity factor decreases with increasing length-to-thickness ratio of the film, and with decreasing film-to-substrate stiffness ratio. Governed by a single, dimensionless parameter, these trends are reported quantitatively in the form of a plot. Close correspondence is found for the interfacial shear stresses predicted by the presented method and by a finite element analysis.