Effects of Ultrasonic Power and Time on Bonding Strength and Interfacial Atomic Diffusion During Thermosonic Flip–Chip Bonding

In this paper, bonding strength of thermosonic flip-chip (FC) bonding was tested by a Dage 4000 bonding tester, atomic diffusion of bonding interfaces was detected by a scanning transmission electron microscope, and deformation of the bumps was observed by X-ray inspection system. Experimental results show that moderate ultrasonic power (about 4 W) results in higher shear strength of FC interfaces, while excessively high ultrasonic power induces larger displacement of vibration to damage bonding performance. Appropriate ultrasonic bonding time (about 100 ms) leads to the optimal thickness of atomic diffusion at the interfaces (about 200 nm) and better bonding bump shear strength with an average of 75 g. Overlong ultrasonic bonding time obviously aggravates the deformation of the bumps, which reduces bonding precision, thickens the thickness of atomic diffusion at the interfaces and damages the bonding strength. So, optimized parameters of ultrasonic power of 4 W and ultrasonic bonding time of 100 ms are proposed to improve the quality and performance of FC bonding.