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

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.