Adhesion behavior of CuCr alloy/polyimide films under 350 degrees C and 85 degrees C/85% RH environments

CuCr alloys with varying Cr content were sputter-deposited onto polyimide films and the metal/polyimaaide films were exposed to a 350 degrees C/N-2 environment for up to 10 h or to 85 degrees C/85% relative humidity (RH) (T/H) conditions for up to 840 h for reliability measurements. The Cr contents of the alloy layers (x) prepared were 0, 2.5, 8.5, 17, 25, 34, and 100 atomic %. Before exposure to hostile environments, the peel strength increased proportionally with the Cr content in the alloy layer up to x=17 and saturated around 550 J/m2, and failure occurred within the polyimide near the metal/polyimide interface, except for the specimen with no Cr (x=0). After exposure to 350 degrees C, the peel strength dropped for all specimens, but most drastically for the specimens with lower Cr contents (x=8.5) which failed along the Cr-oxide/polyimide interface. The general trend was the same in the case of the T/H treatment, where interfacial failure along the CuCr-oxide/polyimide interface was found far the specimens with lower Cr content (x less than or equal to 17). The extent of interfacial failure over the peeled metal surfaces was found to increase with the T/H treatment time and was inversely related to the peel strength.