Modeling and experimental studies on thermosonic flip-chip bonding

Thermosonic flip-chip bonding is a new, solderless technology for area-array connections. It is a simple, clean, and dry assembly process using a bonding mechanism similar to thermocompression bonding, but with lower bonding pressure and temperature due to the introduction of ultrasonic energy. Modeling and experimental studies have been conducted to assist the development of this new bonding technology. The finite-element models can characterize the tool vibration as a function of length and mass. The important function of the model is to estimate the energy level propagated into the bonding tool corresponding to different lengths and masses. To verify the accuracy of the model, vibration amplitudes along the tool have been measured using a laser interferometer. The measured amplitudes for tool length of 4.28 cm were used to estimate the damping coefficient (ζ), and the amplitudes for a tool length of 3.31 cm were used to verify the prediction accuracy of the model. The model was used to determine the guideline for selecting the tool length for a better yield. The model is critical to an understanding of the proposed new thermosonic flip-chip bonding process. The model can also be used to characterize thermosonic wire bonding and tape automated bonding (TAB) processes