Mechanical and microstructural enhancements of Ag microparticle-sintered joint by ultrasonic vibration
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Mechanical and microstructural enhancements of Ag microparticle-sintered joint by ultrasonic vibration Runhua Gao1,4,*
, Yu-An Shen2,4, Jiahui Li1,4, Siliang He3,4, and Hiroshi Nishikawa4
1
Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Department of Materials Science and Engineering, Feng Chia University, Taichung 407, Taiwan 3 School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin 541004, Guangxi, China 4 Joining and Welding Research Institute, Osaka University, Osaka 567-0047, Japan 2
Received: 28 August 2020
ABSTRACT
Accepted: 14 October 2020
Silver (Ag) microparticle sintering bonding is a promising die-attach method for power device packaging. In this study, an ultrasonic-assisted bonding method that bonds chestnut-burr-like Ag microparticles rapidly at low temperatures is reported. Robust joints with an average shear strength of 36.2 MPa were achieved under * 240 °C (actual) 7 MPa in 300 s. Based on characterization of sintered microstructures obtained with different ultrasonic time and power, effects of the ultrasonic vibration were studied. Two unique microstructures, microbridges and dense layers, were generated with the ultrasonic vibration. The former achieved microparticle sintering, and the latter changed fracture mode of the joints from brittle interfacial debonding to ductile fracture. The results indicate the microbridges and dense layers enhanced the joints within a certain range and are generated due to crystallization driven by localized plastic deformation and localized high temperatures.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
1 Introduction Wide bandgap (WBG) semiconductors have drawn attention for their potential in power electronics operated at temperatures above 500 °C [1, 2]. However, commercial die-attach materials, such as solders, as crucial parts connecting semiconductors to substrates, limited applications of WBG at harsh conditions due to their relatively low liquidus temperatures. The finding that decreases in particle size decrease the melting point of the particles and
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https://doi.org/10.1007/s10854-020-04684-x
promote diffusion and sintering provides an idea for finding suitable die-attach approaches [3, 4]: sintering of metallic nanoparticles. Sintered joints can be prepared at high temperatures by low-temperature processes and are the replacement of solder joints because the single-metal system prevents the formation of brittle intermetallic components [5–9]. Among metallic nanoparticles, silver (Ag) nanoparticles have attracted considerable interest, due to its excellent thermal and electrical conductivity, reliable mechanical performance, and outstanding oxidation
J Mater Sci: Mater Electron
resistance [10]. Chua and Siow sintered nano-Ag paste at 250 °C under a mixed atmosphere of N2-H2 for 1 hour to obtain an Ag-sintered joint with a shear strength of 20 MPa; the joints maintained
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