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Composite Aluminum-Clad Copper Ribbon - Bond Behavior and Reliability Results
Keywords: Ribbon Bonding, Aluminum-Clad Copper, Reliability
Ultrasonic bonding is a very versatile joining technique with a wide applicability far beyond semiconductor packaging. Large diameter round Aluminum wire is widely used because of its flexibility and its robust bond process on a variety of surfaces. Aluminum ribbon bonding is an extension of large Aluminum wire bonding. Although the rectangular cross-section of a ribbon enables benefits in many applications, further improvements to fulfill anticipated future performance and functionality requirements may require changes to the interconnect material itself. An interconnect wire or ribbon needs to offer good properties regarding bond behavior and interconnect functionality. Aluminum offers a good compromise. It is a very good bonding material in terms of oxidation behavior and modulus, and has moderate electrical, thermal and mechanical properties. In contrast Copper is a much better interconnect material in terms of electrical, thermal and mechanical properties. However, its oxidation behavior and modulus make it much more difficult to bond with an ultrasonic process. A two-layer ribbon, consisting of a thin Aluminum and a thick Copper layer, creates a decoupling of the two functions, bonding and interconnecting, allowing robust bonding with the Aluminum layer, and maximized interconnect performance with the Copper layer. While such a double layer creates an additional interface, there is plenty of experience with Aluminum-clad Copper, as it has been used in different environments for decades, for example as lead frame material in automotive hybrid circuits. This paper gives an overview of the many potential benefits a composite ribbon, specifically an Aluminum-clad Copper ribbon, can offer. It analyzes and discusses specifics of the bond process, especially in comparison to the process for a regular Aluminum ribbon. Reliability data will be presented to demonstrate the improvement potential, and will be compared to data for regular Aluminum ribbon and large Aluminum wire.
Christoph Luechinger, Director of Strategic Development
Orthodyne Electronics
Irvine, CA
USA


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