Ultrasonic power closed-loop control on wire bonder

Ultrasonic is one important factor of ultrasonic wire bonding process, which is widely used in semiconductor packaging industry. Control effect of ultrasonic power determines the quality and speed of wire bonding. Based on analysis of ultrasonic frequency characteristics and current response, this paper proposes a closed-loop control method of automatic frequency tracking and output current control, to improve the effectiveness of ultrasonic power, shorten the response time, and enhance the stability of ultrasonic generation. Automatic frequency tracking is based on phase lock method. Phase difference of voltage and current signals works as the feedback of the close-loop control of frequency to realize automatic frequency tracking and ensure that the ultrasonic transducer always works at resonance point. And output current control is working at constant current mode so that the vibration amplitude of ultrasonic can be better controlled by adjusting the ultrasonic current. The experimental results show that with the frequency automatic tracking method, the ultrasonic transducer system can achieve wider frequency bands, with faster phase locking and higher tracking precision. With close loop control, real-time tracking can be realized and less rise time and less overshoot of ultrasonic current can be achieved.