The vibration characteristics of capillary in wire bonder

Currently, ultrasonic wire bonders with precision capillary tips are widely used for bonding wires to IC chips and circuits. In the bonding process, a metallurgical bond is achieved through the proper transmittal of ultrasonic energy under pressure to the bond surface at a constant ultrasonic frequency (60 kHz and above depending on the wire materials used). However, bond quality and strength are affected significantly by the change of the vibration characteristics of the bonding capillary and system during the bonding process, which is not yet well understood. Research effort has been made to develop a noncontact, nonperturbative and low-cost monitoring device for vibration measurement, in order to improve bonding quality control. This paper reports the initial study on the understanding of the capillary vibration. The capillary vibration characteristics, such as natural frequencies and vibration modes, are first analyzed using the finite element method. The predicted displacement profile along the capillary tip was compared with measurements using a noncontact laser vibrometer, and good agreement between prediction and measurements was obtained.