Mechanical behavior of peeling for local load on polyimide sheet adhesively bonded to curved surface

Abstract

As electronic products become more multi-functional, there are expectations for a device structure in which soft resin sheets, such as flexible printed circuits, are adhesively bonded to curved parts. For these devices, the bonding strength when a local load is applied is an important evaluation item for ensuring reliability in actual use. In this study, in order to evaluate the peel resistance of a device in which a polyimide (PI sheet is bonded to a curved surface with a pressure sensitive adhesive (PSA), we applied a mechanical simulation considering both the viscoelasticity of the PSA and the fracture energy of the bonding interface. The mechanical behavior against the local load applied on the PI sheet surface was evaluated using this simulation. To verify the accuracy of this simulation, we fabricated a local load tester that can apply a load to a local area of φ8 mm and compared the mechanical behavior with the simulation results. Dynamic mechanical analysis of the PSA with a film thickness of 19 μm was performed by nanoindentation [1], and the parameter of a generalized Maxell model were estimated by fitting the relaxation elastic modulus E(t) to conduct a mechanical simulation. For the double cantilever beam (DCB) test to derive the interfacial fracture energy, soft PI sheets were reinforced with Al substrates. As a result of these analyses, it was confirmed that the relationship between load and displacement obtained by this simulation agrees well with the actual local load test. This technique is considered useful for predicting the bonding strength of complex-shaped devices made using soft adherends and adhesives.