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| DUCTILITY OF POLYMER-SUPPORTED METAL FILMS WITH CURVED INTERFACES |
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Abstract Electronic components in modern flexible electronics are connected by interconnects, having typically the form of metal films on polymer substrates. Since the film/substrate system may sustain large deformation in practice, how to improve the ductility of polymer-supported metal films is a key issue for flexible electronics technology. Previous researches demonstrate that the interfacial bond strength can be improved by surface treatments of the substrate (such as acid/alkali soaking and sandblasting), but few consider how this would affect the ductility of the film/substrate system. We study experimentally the ductility of a polyimide-supported Cu film with rough interface (due to sandblasting) and show that, upon tensile loading along the direction of film surface, the crack density can be reduced by increasing substrate surface roughness. The distribution of tensile stresses in the film and their effects on film cracking (initiation and propagation) are subsequently studied using the method of finite elements. The rough interface is idealized as a perfect curved interface of sine wave form and two different films, one with flat surface and the other having curved surface (identical to that of the interface) are modeled. Obtained results show that a rough (curved) interface can reduce the tensile stresses along the film surface so as to restrain the cracking of the film. Finally, we employ the cohesive zone model to study the initiation and spreading of damage in the film and interfacial cracking of the curved interface. It is demonstrated that both the damage and length of interfacial crack are reduced due to interface roughening. Interface roughening provides a new route for improving the ductility of polymer-supported metal films.
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Received: 22 September 2009
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2011, Vol. 32 
