Room temperature wedge-wedge ultrasonic bonding using aluminum coated copper wire

The purpose of our study is to evaluate the feasibility of room-temperature wedge-wedge bonding using commercially available 25 μm copper wires, coated with aluminum. Bonding quality, reliability and aging resistance of the wire bonds have been investigated using standard wire pull tests immediately after bonding and after accelerated life tests, including temperature storage at 125 °C and 150 °C for up to 2000 hours. Using focused ion beam (FIB-) preparation and high resolution electron microscopy (SEM, TEM combined with EDX x-ray analysis), results of microstructure investigations of the Al-coating / Cu wire interface as well as of the bonding interconnect formed between the coated wire and the gold metallization on LTCC substrate will be presented. These investigations provide background information regarding the binding mechanisms and material interactions, and contribute to assess and to avoid potential reliability risks. Due to the found advantageous bond processing behavior and increased reliability properties, our results indicate that room temperature wedge-wedge bonding of coated copper wires has a remarkable application potential, for instance in medical and other high reliability applications. It combines all known advantages of usual copper bonding like excellent contacting behavior, high reliability and favorable material price with the possibility of processing temperature damageable components and considerable improved storage capability. Therefore, room temperature bonding using coated copper wire can also reduce cycle time, manufacturing and material costs and will be conducive to new products.