Adhesion energy of Cu/polyimide interface in flexible printed circuits

The adhesion strength of interfaces was evaluated for two Cu/polyimide laminates, which had the same interface but different polyimide film thickness. A new technique was applied to evaluate the bond energy of the interface, where micro scale polyimide film blocks were scratched off from the interface-side surface of the copper film. Energy consumed during plastic deformation was successfully calculated with the help of a numerical simulation for crack extension. Contrary to the results of conventional peel tests which yielded 340 J/m2 and 580 J/m2, respectively for the two samples, the interfacial adhesion energy was obtained as 30 J/m2 and 25 J/m2 by the new technique.