Dynamic characteristics of stacked piezoelectric transducers of ultrasonic wire bonders used in integrated circuit packaging

Currently ultrasonic wire bonders with precision capillary tips are widely used for bonding wires to integrated circuit (IC) chips and circuits. However, the quality and strength of a bond may be affected significantly by the change of vibration during the bonding process. It is therefore important to understand the dynamics of the bonding process as well as the vibration characteristics of the bonding system, so bonding quality may be monitored. This paper reports the study on the dynamic characteristics of the stacked piezoelectric transducers used in the ultrasonic wire bonding system. The vibration characteristics are first analysed using the finite element method with resonant frequency and vibration modes. The predicted impedance response is compared with the measurement using a high-pressure (HP) impedance analyser. The displacement profile along the transducer assembly, which includes a piezoelectric stack, clamping and horn sections, are also analysed. The effects of multilayer and polarization on the response of the transducer are discussed. It was found there is good agreement between the prediction and measurement, and bending and extension modes may be excited differently according to the polarization configuration used in the multilayer stack.