In-situ experimental characterization of interfacial toughness of aluminum thin films on polyimide substrates

Interfacial delamination embodies a major issue as concerns the mechanical reliability of metal-on-polymer thin films. The interfacial toughness of a metal/polymer material system is a relevant constraint when dealing with the design of electronic devices, which feature stacks of several dissimilar materials. This evidence provides the motivations for the experimental measurement of metal/polymer adhesion. In this study, the interfacial delamination of Aluminum thin films on Polyimide substrates has been investigated combining in-situ light microscopy with a miniaturized 90° peel test setup. Being peel forces in the mN range, dedicated clamps have been designed in order to avoid the use of conventional sliding fixtures meanwhile ensuring proper 90° peel geometry when testing samples on a uniaxial tensile stage. Peel tests revealed a very sharp delamination front, with no evidences of interface heterogeneities. In-situ imaging allowed to interpret the trend of the force/displacement curve. Meaningful data for the computation of the fracture energy (~90 J/m2) were clearly distinguished from data affected by undesired dissipation phenomena competing with delamination, such as plastic deformation of the Aluminum film.