Asymmetric Growth of Cu6sn5 Intermetallic Compound in Cu/Sn/Cu Interconnection System Under the Vertical Ultrasonic Vibration

Abstract

The asymmetric growth of Cu6Sn5 intermetallic compound (IMC) in a Cu/Sn/Cu interconnection system was studied during the transient liquid phase (TLP) soldering process with the assistance of the vertical ultrasonic vibration. Being different from the symmetrical growth during isothermal aging without ultrasonic waves (USW), highly asymmetrical growth of Cu6Sn5 at the upper and down Sn/Cu interfaces was observed with the vertical USW, i.e., Cu6Sn5 grains exhibited scallop-type morphology, and were discrete at the upper Sn/Cu interface (the side of ultrasonic action); while that at the lower Sn/Cu interface (the opposite side of ultrasonic action) exhibited column-type morphology, and were conterminous. Under the assistance of USW, the Cu6Sn5 grains were remarkably refined, the shear strength of joint was increased, and the fracture mode was changed from transgranular fracture to transgranular and intergranular fracture. This anomalous behaviour can be completely ascribed to the asymmetrical ultrasonic effects across the entire Sn the intermediate layer of Sn.

Keywords: Intermetallic compounds, TLP soldering, Ultrasonic waves, Grain morphology, Fracture path