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

Guoqian Mu,Wenqing Qu,Yanhua Zhang,Hongshou Zhuang,Haiyun Zhu

doi:10.3390/met10091223

Abstract

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 °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 °C, and the thermal contact conductance is 83,541 W/(m2·K) with a holding time of 30 h at the bonding temperature of 100 °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 θ-CuGa2 phase, in addition to a small amount of residual copper, residual gallium and γ3-Cu9Ga4 phase. The interaction product of Cu and Ga is mainly θ-CuGa2 phase, with only a small amount of γ3-Cu9Ga4 phase occurring at the temperature of 100 °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.

Highlights

With the increasing power dissipation and shrinking feature sizes of high-power devices, the heat generated is gradually increasing
Research shows that the device failure rate doubles and the lifespan of the devices is halved for every 10 ◦ C rise in the joining temperature [1], and that more than 55% of the failures of electronic devices are caused by too-high temperatures [2]
This self-made interlayer can be used as a kind of thermal interface material to facilitate interfacial heat transfer

Summary

Introduction

With the increasing power dissipation and shrinking feature sizes of high-power devices (such as insulated gate bipolar translator, central processing unit, laser load devices, etc.), the heat generated is gradually increasing. High temperature has a bad impact on the performance of power devices. High requirements for heat dissipation are established [3], and some efficient heat sinks (such as heat pipe, microchannel, refrigeration chip, etc.) have been developed. The interfacial heat transfer between heat source and heat sink is becoming a severe bottleneck, currently limiting the further scaling of performance. The heat flux density through the interface is constantly increasing [4], so interfacial heat transfer enhancement is essential for the development of high-power devices. The common methods used currently are as follows: adding thermally conductive particles (i.e., metals, ceramics) to nonmetallic thermal interface materials (TIM) [5] and using low melting temperature alloy (LMTA) [5], etc. The thermal conductivity of nonmetallic materials is lower than that of metallic materials, and thermal

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Discussion

Conclusion