Effects of wire deformation behaviour on bondability: Study of Cu wire stitch bonding (2nd Report)

Summary

With regard to the fact that, during Cu wire stitch bonding of copper lead frames, the wire deformation strongly affects the bondability and strength of the bonds obtained, this paper describes an investigation of the wire deformation being varied through variation in the initial capillary tip load and capillary tip load during application of ultrasonic vibration as well as the bondability and bond strength then obtained. When stitch bonding with soft copper wire is performed by the two‐step load control method, which has a higher initial capillary tip load and a lower capillary tip load during the second stage, the range of action of the material being worked under ultrasonic vibration can be widened, the deformation during the working time of ultrasonic vibration can be suppressed, the ultrasonic energy can make a greater contribution to bonding, and a higher bond strength can be obtained. The results obtained in this study suggest that, during wire bonding by the two‐step load control method, the optimum capillary tip load is obtained. Within the presently adopted experimental range, the optimum values are a capillary tip load of 1.4 N before the application of ultrasonic vibration and a capillary tip load of 0.4 N during ultrasonic vibration.