The interfacial fracture energies of Cu/Cr/polyimide systems are deduced by subtracting work expenditure from the peel strength. Two methods were used to obtain the work expenditure: one based on the X-ray measurement of the plastic strain of peeled metal film and the other based on a theoretical analysis of the foundation model for the attached part of the metal film. These two methods yield reasonably consistent work expenditure in most cases, imparting validity to the experimental and theoretical methods used here. The interfacial fracture energies of the Cr/polyimide interface were shown w.r.t., the film thickness and rf plasma power density activating the polyimide surface. The phase angle of the interface crack between the Cu and polyimide is determined by using elasto-plastic finite element analysis and the path independence of the J-integral. The presence of the polyimide interlayer increased mode mixity, and the phase angles were virtually independent of the metal film thickness, which is consistent with the nearly constant interfacial fracture energy with Cu film thickness.