Ultrasonic-assisted connection of Cu/Cu structure using Sn58Bi solder enhanced by B4C nanoparticles

Abstract

In order to enhance the joint performance, the Cu/Sn58Bi-0.6B4C/Cu 3D structure was obtained by ultrasonic-assisted connection. The influence of ultrasound on the solder and its wettability, as well as the microstructure, interfacial IMC structure, and mechanical properties, was investigated. It is indicated that ultrasonic cavitation improves the crystal structure of the solder alloy by refining grain size and making the microstructure more uniform. The ultrasound also changes the preferred orientation of β-Sn and Bi phases, and increases the low-angle grain boundaries and local orientation differences for improved alloy strength. Additionally, the ultrasound promotes the molten solder spreading on the Cu substrate. The microstructure of the filler metal layer is improved by ultrasonic, and the Cu6Sn5 compounds floating in the solder matrix act as the strengthening phase. Cavitation bubbles erosion increases the contact area between the solder and Cu substrate. The audiogenic high temperature reduces the IMC thickness difference at both ends of the joint caused by the temperature gradient. Besides, the grain size in the solder matrix and interfacial IMC is refined with increased supercooling. The ultrasound strengthens joint shear strength significantly and improves the potential path for crack propagation. The appearance of dimples in the fracture alters its mode from being typically brittle to a mixed ductile and brittle fracture. The above enhancement will be further improved with the appropriate extension of ultrasonic time. We hope to strengthen joint performance by ultrasound, and provide reference for future research and application combining soldering with ultrasonic technology.