Characteristic analysis of transducer drive current in ultrasonic wire bonding process

In the ultrasonic wire bonding process, the impedance change of transducer system was reflected by the current amplitude, the change of the system´s resonance frequency was represented by the change of the current´s frequency. The current signals contained much information about the bonding process and the resulted bond quality. The characteristics of current were depending on the tip states. Free, fixed, or damped tips led to different characteristics of current in some way. The bond formation process and the related physical process can be reflected by the current characteristics during bonding process. In this paper the current monitoring hardware system was set up for ultrasonic wire bonding, and the relevant software was designed. The reliable current signals had been acquired by data acquisition system and the bonding quality data was gathered by measuring the bonding shearing force. The current signals were analyzed by using the wavelet time-frequency method. Several characteristics were selected. The analysis results indicated that the frequency, the amplitude value and the change tendency of current signals are related to the bonding quality in certain extent. The fundamental resonance frequency deviation, very small current, and exceptional current changing tendency always mean failed bond.