Cohesive failure of the Cu/polyimide system

The cohesive failure which occurs in the inside of the polymer near the metal/polymer interface was studied in the Cu:Cr/polyimide and Cu/CuCr/polyimide systems. The interface energy was varied by pretreating the polyimide surface by varying rf plasma power density, or by varying the Cr content in the CuCr alloy layer, respectively, and peel tests were conducted. Then, peeled metal strips were analyzed by AES and XPS, and correlations were made among the peel strength, the amount of carbide-like Cr-C bonds near the interface, and the polyimide thickness on peeled metal films inferred from the AES depth profiling. Results indicate that the peel strength increased with the rf power density at a constant metal thickness and that the thickness of polyimide adhering to peeled metal films increased with the peel strength, which was related to the amount of carbide-like Cr-C bond near the interface affecting the interface energy. In the case of specimens with the same plasma treatment but various metal layer thickness, the thickness of polyimide on peeled metal films remained constant even though the peel strength increased with the metal layer thickness. (C) 2000 Elsevier Science S.A. All rights reserved.