Factors affecting the long term stability of Cu / Al ball bonds subjected to standard and extended HTS

This paper will present the findings of work performed on 20-micron diameter copper wire of five different wire types from three suppliers with gold wire added as a control. The test die was mounted on BT resin substrates. The bonding parameters were optimized for each wire used. Part of the optimization process involved monitoring the flatness of the bonded ball and the amount of aluminum remaining under the bond. The crystal structure of the bonded interconnects were examined using composite imaging techniques. Visual data such as ball size, thickness, and shape were collected. First and second bonds were subjected to destructive testing, such as ball shear and wire pull, throughout the preparation process. The samples were subjected to an industry-standard, high temperature stress test to determine the long-term stability of the interface of each wire type. Data will be presented on all tests performed and will provide useful information on the material and process set best suited for long term reliability.