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The Influence of Surface Defect Size on the Wire Bond Pull Strength for Automotive Lead Frame Materials
Philip W. Lees
David W. M. Williams
Barry Njoes
Technical Materials, Inc.
Lincoln, RI 02865
Abstract: Permanent interconnection between lead frames and automotive hybrid circuits or multi-chip modules is achieved through aluminum wire bonding from the circuit or module bond pads to the aluminum areas on the lead frame. Aluminum to aluminum wire bonding has proved to be a robust process yielding reliable products. The lead frame raw material stock is manufactured using the clad inlay process. Stripes of aluminum are clad into a high conductivity copper alloy. Selective plating to accommodate separable interfaces may be applied to the strip or on stamped parts. After stamping, the parts are insert molded, then forwarded to the OEM for electronics integration, wire bonding and final assembly. During all stages of manufacture, from initial cladding to wire bonding, the potential exists to damage the soft aluminum surface. In this study, clad aluminum surfaces were machined to generate a variety of "defects". These "damaged" surfaces were quantified in terms of width and depth. Wire bonding was attempted within, and across the "defects." Both bond pull strength and failure category were recorded. It was found that the aluminum-to-aluminum system is very tolerant of surface damage.
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