Abstract
This paper summarizes some non-destructive ultrasonic bond quality test methods. Systems described in the literature are mainly based on monitoring the deviation of the vibration amplitude during welding and the correlation between the bond strength with these deviations. Practical application of these principles can give discouraging results. A better understanding of the bond formation process should enable one to understand what causes the amplitude to deviate, and why this is strongly dependent on the ultrasonic bond system involved.