Low Temperature Cu/Ga Solid-Liquid Inter-Diffusion Bonding Used for Interfacial Heat Transfer in High-Power Devices

Interfacial heat transfer is essential for the development of high-power devices with high heat flux. The metallurgical bonding of Cu substrates is successfully realized by using a self-made interlayer at 10 degrees C, without any flux, by Cu/Ga solid-liquid inter-diffusion bonding (SLID), which can be used for the joining of heat sinks and power devices. The microstructure and properties of the joints were investigated, and the mechanism of Cu/Ga SLID bonding was discussed. The results show that the average shear strength of the joints is 7.9 MPa, the heat-resistant temperature is 200 degrees C, and the thermal contact conductance is 83,541 W/(m(2)center dot K) with a holding time of 30 h at the bonding temperature of 100 degrees C. The fracture occurs on one side of the copper wire mesh which is caused by the residual gallium. The microstructure is mainly composed of uniform theta-CuGa2 phase, in addition to a small amount of residual copper, residual gallium and gamma(3)-Cu9Ga4 phase. The interaction product of Cu and Ga is mainly theta-CuGa2 phase, with only a small amount of gamma(3)-Cu9Ga4 phase occurring at the temperature of 100 degrees C for 20 h. The process of Cu/Ga SLID bonding can be divided into three stages as follows: the pressurization stage, the reaction diffusion stage and the isothermal solidification stage. This technology can meet our requirements of low temperature bonding, high reliability service and interfacial heat transfer enhancement.