Fracture of metal-polymer line structures. I. Semiflexible polyimide

The fracture characteristics of metal/polymer line structures formed by depositing Au/Cr lines on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline (PMDA-ODA), substrate have been investigated using a stretch deformation technique. The delamination behavior, fracture morphology, fracture energy, and energy dissipation rate have been determined as a function of line width and thickness. The metal dimension was found to influence the crack formation mode and morphology. The experimental studies were supplemented by finite-element analysis to evaluate the stress distribution and deformation energetics of the line structure, which takes into account the plastic deformation of the metal and the polymer. Results from this analysis show that the observed fracture characteristics can be attributed to the edge and thickness effects induced by metal confinement. Essentially, the deformation behavior is determined by the mechanical environment induced by metal confinement at the interface. Plastic deformation of both metal and polymer plays an important role in controlling the stress distributions as well as the deformation energetics. The fracture energy of the metal-polyimide interface determined by an overall energy balance method was consistent with that obtained from energy dissipation rate. The average value is 25 J/m2 for the Au/Cr/PMDA-ODA line structure.