Mechanical Design and Reliability of Gold-Tin Eutectic Bonding for Silicon-based Thermal Management Devices

Thermal management of microprocessors and power electronics face major challenges including but not limited to a need for reliable and mechanically robust micro-cooler and micro-heat spreader devices. While the thermofluidic performances of the embedded microchannel with 3D manifold cooling and heat spreaders have received much attention (and carefully studied) for the past two decades, the challenges associated with the mechanical design and reliability have not been the focus of the research in thermal management community. Gold-tin eutectic bonding is proposed to attach silicon-based evaporator and condenser substrates in vapor chambers, as well as silicon microchannels substrate to silicon 3D manifold in high performance micro-coolers. The bonding interface in a silicon embedded microchannel to a silicon 3D manifold requires careful design to withstand pressures ~500 KPa, for target heat flux of ~1 kW/cm
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using single-phase water as working Evaporator and condenser bonding interface in a silicon-based vapor chamber must withstand water burst pressure of ~0.8 MPa when it is subjected to elevated temperature of 175 °C. In this study, a set of silicon microchannels in two substrates are fabricated using conventional microfabrication process, which then bonded using gold and tin multilayer composite structure (150 nm Au/75 nm Sn/150 nm Au) at 350 °C. Subsequently, the tensile stress is "directly" measured using carefully designed "test" samples, by means of applying direct tensile force to the sample. We measured tensile stress for 11 samples with contact areas ranging from 50 μm × 100 μm to 150 μm × 150 μm, the resulting stresses ranges from 2.0 to 5.5 MPa, with an average value of 3.2 MPa. Findings of this study will be largely beneficial in design and fabrication of silicon-based vapor chambers and high performance microchannel with 3D manifold coolers.