Revealing of ultrasonic wire bonding mechanisms via metal-glass bonding

Very complex phenomena and interface changes occur during the ultrasonic wire bonding process, which lead to an incomplete understanding of the process, especially for the friction and softening phases. In this work, the bonding process was real-time observed via metal-glass bonding to achieve a deeper understanding of these phenomena. Through the 2D high-speed observation, the emergence and changes of five areas including the contact area, friction area, stick area, microwelds area and oxides area were observed and quantified. The stick and microwelds area were observed to start from the central region and extend outwards. Normal force and ultrasonic power interactively influence these areas. The moving of oxides was captured and confirmed to be caused by both the material flow and vibration. The ultimate shear stress of microwelds was calculated to be 95.72 MPa with which the quantification of the observed microwelds area can be used to predict the bonding strength.