Microstructure evolution and shear strength of full Cu3Sn- microporous copper composite joint by thermo-compression bonding

Purpose The purpose of this paper is to quickly manufacture full Cu 3 Sn-microporous copper composite joints for high-temperature power electronics applications and study the microstructure evolution and the shear strength of Cu 3 Sn at different bonding times. Design/methodology/approach In this paper, a novel structure of Cu/composite solder sheet/Cu was designed. The composite solder sheet was made of microporous copper filled with Sn. The composite joint was bonded by thermo-compression bonding under pressure of 0.6 MPa at 300°C. The microstructure evolution and the growth behavior of Cu 3 Sn at different bonding times were observed by electron microscope and metallographic microscope. The shear strength of the joint was measured by shear machine. Findings At initial bonding stage the copper atoms in the substrate and the copper atoms in the microporous copper dissolved into the liquid Sn. Then the scallop-liked Cu 6 Sn 5 phases formed at the interface of liquid Sn/microporous copper and liquid Sn/Cu substrates. During the liquid Sn changing to Cu 6 Sn 5 phases, Cu 3 Sn phases formed and grew at the interface of Cu 6 Sn 5 /Cu substrates and Cu 6 Sn 5 /microporous copper. After that the Cu 3 Sn phases continued to grow and the Cu 3 Sn-microporous copper composite joint with a thickness of 100 µm was successfully obtained. The growth rule of Cu 3 Sn was parabolic growth. The shear strength of the composite joints was about 155 MPa. Originality/value This paper presents a novel full Cu 3 Sn-microporous copper composite joint with high shear strength for high-temperature applications based on transient liquid phase bonding. The microstructure evolution and the growth behavior of Cu 3 Sn in the composite joints were studied. The shear strength and the fracture mechanism of the composite joints were studied.