Wire Loss Monitoring in Ultrasonic Wedge Bonding Using the Kalman Filter Algorithm

Ultrasonic wedge bonding is an important step in the manufacture of integrated circuits (ICs). Due to the small size of IC chips, methods for maintaining the reliability of wedge bonding are necessary to avoid large amounts of material waste and low production efficiency. Wire loss or wire error is a typical bonding failure in the wire bond process. This paper presents a monitoring method that detects aluminum wire loss or wire error during the aluminum ultrasonic wedge bonding process. During the bonding process, the impedance from the ultrasonic transducer is measured, and then compared with a predetermined threshold to assess whether the wire has been lost. To improve monitoring accuracy and sensitivity, the Kalman filter with a forgetting factor is introduced during the ultrasonic wire bonding, and the influence of the forgetting factor on the rate of false positives and the speed of error detection is investigated. It is found that the forgetting factor can determine the rate of false positives and monitoring sensitivity. By optimizing the forgetting factor, the rate of false positives can be lowered to below 0.05%, and wire loss can be detected within five bonding times after the loss occurred. This novel method shows good monitoring accuracy and can be used in aluminum wedge bonding.