A Novel Approach Using Finite Element Modeling and Contact Area Parameter for Predicting Wire Bond Shear Strength Nondestructively

Wire bonding remains widely utilized in numerous products today due to its mature technology and cost-effectiveness. However, improper bonding parameters can result in damage to the metal layer at the bonding interface, leading to the formation of "craters." Therefore, it is worthwhile for continuous optimization of the bonding process. The presented work employs finite element modeling to investigate the thermo-compression ultrasonic bonding process, focusing on the impact of bonding parameters on the stress at the bond pad interface. It was observed that the main determinant of bonding strength is the peripheral ring area, where the FAB adheres to the bond pad. Furthermore, excessive bonding pressure was found to result in over compression and subsequent separation at the bonding interface. In the experiment, it was discovered that bonding force had the most significant influence on shear strength, followed by ultrasonic current, whereas bonding time exhibited a less pronounced effect. However, there was no significant difference in pull strength under different bonding process parameters. The optimized process parameters were determined to be 110 mA for ultrasonic current, 25 ms for bonding time, and 20 gf for bonding force. Finally, the mapping relationship between the bonding ball size parameter (bonding ring area S: the inner ring represents the capillary's inner diameter, while the outer ring represents the capillary's contact with the outermost boundary) and shear strength was determined: as S increases, the shear strength decreases. This indicates that this dimensional parameter has the potential to serve as a nondestructive indicator for predicting shear strength.