H. Greve, and F. P. McCluskey
CALCE/Department of Mechanical Engineering, Clark School of Engineering, University of Maryland, College Park, Maryland 20742
Low temperature transient liquid phase sintering (LT-TLPS) can be used to form high-temperature joints between metallic interfaces at low process temperatures. In this paper, process analyses and shear strength studies of paste-based approaches to LT-TLPS are presented. The process progression studies include DSC analyses and observations of intermetallic compound (IMC) formation by cross-sectioning. It was found that the sintering process reaches completion after sintering times of 15 min for process temperatures approximately 50oC above the melting point of the low temperature constituent. For the shear studies, test samples consisting of copper dice and copper substrates joined by sintering with a variety of sinter pastes with different ratios of copper and tin have been assessed. A fixture was designed for high temperature enabled shear tests at 25oC, 125oC, 250oC, 400oC, and 600oC. The influence of the ratio of the amount of high melting-point constituent to the amount of low melting-point constituent on the maximum application temperature of the sinter paste was analyzed. Ag20Sn and Cu50Sn pastes showed no reduction in shear strength up to 400oC, and Cu40Sn pastes showed high shear strengths up to 600oC. It was shown that LT-TLPS can be used to form high temperature stable joints at low temperatures without the need to apply pressure during processing.
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