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Thermosonic bonding of crossed strip Au bumps

Abstract Gold strip bumps for electronic packaging are bonded using the thermosonic process. The Au strip bumps on the chip and substrate are aligned in a crossed configuration, and ultrasound is applied longitudinally on the chip to form a solid state bond between the crossed strip Au bumps. Deformed bump shapes are calculated numerically, and the shear force and fractured surface profile are measured to evaluate the bond quality. The deformed Au bump shape is similar to a saddle, which provides larger contact surface area and greater friction force. The bond strength of crossed strip bumps reaches the yield strength of Au, which is much higher than that previously obtained for bonding between Au bumps and a planar pad.