Microstructure Evolution and Growth Kinetics of Cu6sn5 Intermetallic Compound at Liquid-Solid Interfaces in Cu/Sn/Cu Interconnects Under Ultrasonic Waves

Abstract

The microstructure evolution and growth kinetics of Cu6Sn5 intermetallic compound (IMC) in a Cu/Sn/Cu interconnection structure during the ultrasonic-assisted transient liquid phase (TLP) soldering process were investigated. Being different from the symmetrical growth during isothermal aging without ultrasonic waves (USW), highly asymmetrical growth of Cu6Sn5 at the upper and lower Sn/Cu interfaces was observed with USW. Cu6Sn5 grains exhibited scallop-type morphology, and were discrete at the upper interface; while that at the lower Sn/Cu interface exhibited column-type morphology, and were conterminous at the lower interface. USW caused the mass migration of Cu atoms from the upper Cu surface toward the lower interface, resulting in sufficient Cu atomic flux for the fast formation of Cu6Sn5 at the lower interface, and many cavitation pits on the upper Cu surface. A growth model was established to explain the growth kinetics of the Cu6Sn5 IMC, indicating a reaction-controlled growth mechanism.

Keywords: Ultrasonic-assisted soldering, Interfacial reaction, Intermetallic joints, Microstructure evolution, Growth kinetics