Ultrasonic features in wire bonding and thermosonic flip chip

Driving voltage and current signals of Piezoceramic Transducer (PZT) were measured directly by designing circuits from ultrasonic generator and using a data acquisition software system. Input impedance and power of PZT were investigated by using Root Mean Square (RMS) calculation. Vibration driven by high frequency was tested by laser Doppler vibrometer (PSV-400-M2). Thermosonic bonding features were observed by scanning electron microscope (JSM-6360LV). Results show that the input power of bonding is lower than that of no load. The input impedance of bonding is greater than that of no load. Nonlinear phase, plastic flow and expansion period, and strengthening process were shown in impedance and power curves. The ultrasonic power is proportion to vibration displacement driven by the power, and greater displacements driven by high-power result in welding failure phenomena, such as crack, break, and peel off in wedge bonding,. For thermosonic flip chip bonding, the high power decreases position precision of bonding or results in slippage and rotation phenomena of bumps. To improve reliability and precision of thermosonic bonding, the low ultrasonic power should be chosen.