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Au-Ge Based Candidate Alloys for High-Temperature Lead-Free Solder Alternatives
Keywords: CALPHAD, Intermetallics, Thermal aging
The need for high-temperature solders is rapidly increasing to produce reliable electronics to which a high-density packaging technology and high-operating temperatures can be applied. High-temperature solders can eliminate wiring connectors and cooling system needed in conventional electronic system. For these reasons, they are currently being used for first level packaging applications. High-lead containing solders are at present state used as high-temperature solders. However, these high-lead content solders still hinder the recycling of electronic products. Thus, the establishment of high-temperature lead-free solders is an urgent priority in the electronics industry. Some of the indispensable requirements for the high-temperature solder selection are the melting temperature range and the ductility of the alloy to facilitate relaxation of thermal stresses. The selection of high-temperature solders is a challenge since a survey of the phase diagram reveals that there is no drop-in replacement. Zn-Al based alloys are being proposed as the cost-effective replacement. However, zinc is corrosive and aluminium possesses a high natural radius of curvature. Bismuth based alloys are also being considered but they have drawbacks such as low electric/thermal conductivity and brittleness. Au- (Ge, Si & Sn) based candidate alloys too are being proposed. Among them, Au-Si based alloys possess wetting constraints. Au-Sn based alloys consist of massive intermetallic compounds, making it viable only for small die applications. Thus, in this work focus has been on the development of Au-Ge based solder candidates. The promising Au-Ge based ternary alloys that were determined by the CALPHAD approach based on the solidification criterion were precisely produced using a hot-stage microscope. At high temperature, the microstructure of these promising solder candidates could significantly change and consequently their mechanical properties could be affected. Therefore, in this work, the high temperature stability of microstructures and mechanical properties of Au-Ge based solder candidates have been extensively reported.
Vivek Chidambaram, Ph.D. Student
Technical University of Denmark; Department of Mechanical Engineering
Kgs.Lyngby, Copenhagen DK-2800,

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