Design and performance analysis of bidirectional vibration ultrasonic transducer for wire bonding

Ultrasonic frequency, amplitude and vibration mode are the key factors affecting the stability and reliability of ultrasonic wire bonding. Conventional wire bonding is realized by ultrasonic transducer (UT) with single frequency and longitudinal vibration. To optimize the bonding process and achieve high-performance bonding joints, we propose an UT that utilizes two longitudinal vibration and one bending vibration mode, which realized by the full PZT and regional polarization PZT. By employing a step-type flexible structure, the flanges for three vibration modes are optimized at the same node position. To drive the UT, the amplifier module circuit with 39.98 times amplification and 130 kHz bandwidth is designed. Under the 9 kg·cm torque for assembling UT, the longitudinal vibration frequencies of the UT are 71.2 kHz and 122.9 kHz, and the bending vibration frequency is 43.1 kHz. The self-developed amplifier module is designed to drive the UT for both single and coupled vibration, and the test results show that the amplitude of the bending vibration is 7.49 µm at a driving voltage of 20 V, and the amplitudes of the 1st longitudinal vibration and the 2nd longitudinal vibration are 5.72 µm and 4.44 µm, respectively, which satisfy the amplitude requirements for wire bonding. Furthermore, the coupled vibration trajectory of the UT forms a parallelogram, and the vibration area can be adjusted by changing the amplitude. Experimental results have shown that the bending mode is excited by regionally polarized PZT, achieving sufficient vibration in both x/y directions while ensuring a small and lightweight structure. This provides a potential application solution for the new bonding method of wire bonding.