Abstract
This study was undertaken to investigate the effect of bonding pressure profiles and ultrasonic vibration triggering timing on the deformation of gold balls and bond intermetallic formation process in Au-Al thermosonic wire bonding. The following results were obtained.
Under the condition of ultrasonic vibration triggered after bonding pressure, which makes contact surface of a gold ball flat, small intermetallics are formed dispersively at the flat contact interface of a gold ball and an aluminum pad. They grow in the following two processes. One is the process forming slender islet intermetallics at the middle portion of the bond by micro frictional slip. The other is the process forming intermetallics shaped in arcs at the periphery of the bond by plastic deformation. A dynamic load leads to larger deformation and intermetallics area than a static load during bonding pressure.
Under the condition of ultrasonic vibration triggered before bonding pressure, intermetallics are initially formed at the small contact area of spherical surface. They grow rapidly into islet shapes by micro frictional slip and are increased in numbers orthogonally to the direction of ultrasonic vibration. Then, arc-shaped intermetallics are also formed rapidly at the periphery of the bond by plastic deformation. The ultrasonic vibration triggered before pressure causes larger deformation and bond area in a short time than the ultrasonic vibration triggered after pressure. It is effective for reducing bonding time.
