Dynamics of an ultrasonic transducer used for wire bonding

The vibration displacement distributions along a transducer used in ultraso nic wire bonding were measured using a heterodyne interferometer, and many nodes and anti-nodes were found. A mechanical finite element method (FER?) was used to compute the resonant frequencies and vibration mode shapes. The displacement distributions of the dominant 2nd axial mode agreed well with the measured values. Undesirable nonaxial modes, including the higher orde r flexural and torsional modes, also were excited at frequencies very close to the working frequency (2nd axial mode) of the transducer. Hence, the me asured displacements were the resultant of all the allowable modes being ex cited. However, the excitation of these nonaxial modes were small enough no t to affect the formation of consistent and high quality wire bonds. Result s of the present study were used to determine a suitable location for insta lling a piezoelectric sensor to monitor the bond quality.