Quality Control in Ultrasonic Wire Bonding

This paper reviews methods of quality control for the ultrasonic wire bonding process. It also covers the basic principles of the process, a model for the bonding mechanism, and the criteria which determine bond quality. In practice, quality control in production is mainly by batch destructive testing and by ensuring consistent performance of the bonding machine by, for example, periodic calibration. A more desirable approach is that of in‐process monitoring and control of every joint made. Although in‐process techniques have been extensively studied, they are currently little used because of the lack of a universal system, doubts on reliability and access problems. The in‐process monitoring and control techniques which have been studied have concentrated on methods which involve the detection of variations in the mechanical impedance of the bond zone; these are reflected back into the excitation system of the equipment during bond formation. It is believed that further development of these techniques, coupled with simultaneous monitoring of associated parameters, e.g., bonding wire deformation, offers hope of improved process control.