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In order to understand the effects of plastic deformation and the interfacial fracture energy on the peel strength, thickness of the metal layer and the pretreatment conditions of polyimide were varied in the Cu/Cr/polyimide system. The work expenditure during the peel test was estimated using the stress strain curves of metal films, X-ray measurements of the plastic strain in the peeled films, and the elastoplastic beam analysis. Results indicate that the peel strength is strongly affected by the film thickness and the pretreatment condition in a synergistic way, and that the measured peel strength is more a measure of the plastic deformation during the peel test than a measure of the true interfacial energy.

In the present work, CuCr alloys with varying Cr content were sputter deposited on polyimide films, and the metal/polyimide thin films were maintained under 85° C/85%R.H. (T/H) conditions for the reliability measurements. Results showed that the peel strength without T/H treatments increased proportionally with the Cr content in the CuCr alloy layer(x) up to 17 at. %, and then saturated. Among the samples studied, the peel strength decreased with hold time under T/H conditions for all the cases, but most drastically for the sample with x=8.5. The very poor peel strength of that sample (x=8.5) was attributed to the occurrence of interfacial failures which were thought to take place along Cr-oxide/polyimide interfaces.

Adhesion of Cu and Cr to polyimide was studied by 90° peel test, AES, and X-ray diffraction. The two necessary conditions of the high adhesion strength were the presence of Cr interlayer and the preactivation of the polymer surface by RF plasma treatment. The Cr is thought to react with activated polyimide to form carbide-like bonds which enhance the adhesion strength drastically. Correlations between the peel strength and C260/Cr527 Auger PHR from the peeled metal strip were good. Qualitatively, the peel strength is related to the amount of plastic deformation done on the metal strip during peeling.