Stress relaxation during thermal cycling in metal/polyimide layered films

The stress relaxation behavior during thermal cycling of metal/quartz and metal/polyimide/quartz layered structures has been investigated using a cantilever bending beam technique. The metals chosen for this study include Cu and Cr, two materials with contrasting mechanical and interfacial bonding properties. A finite element analysis, as well as an analytical calculation, has been carried out to deduce the stress distribution in the layered structures. Results indicate that the extent of stress relaxation strongly depends on the intrinsic mechanical property of the metal film with significantly higher stresses residing in the Cr film than in the Cu film. The interfacial polyimide layer has been found to serve as an effective buffering layer to reduce the residual stress in metal films. Observations from transmission electron microscopy suggest that the stress is partially released through the deformation of the polyimide near the metal/polyimide interface.