4.7 Article

Sintering mechanism of Ag-Pd nanoalloy film for power electronic packaging

Journal

APPLIED SURFACE SCIENCE
Volume 554, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.apsusc.2021.149579

Keywords

Pulsed laser deposition; Ag-Pd nanoalloy film; Power electronic packaging; Low temperature bonding; Sintering behavior

Funding

  1. National Key Research and Development Program of China [2017YFB1104900]
  2. National Natural Science Foundation of China [51775299, 52075287]
  3. High Performance Computing Platform of Beihang University

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This study successfully prepared a new material with high shear strength and excellent resistance to silver ionic migration by utilizing Ag-Pd nanoalloy as the die attach material. The research revealed the sintering mechanism of the alloy and confirmed the high reliability of Ag-Pd nanoalloy for low temperature bonding.
Silver electrochemical migration causing short-circuit could be mitigated by Ag-Pd alloy. The conventional mechanical mixed Ag and Pd nanoparticles requires high alloying temperature as high as 850 degrees C. In this work, Ag20Pd nanoalloy film is prepared using pulsed laser deposition under room temperature as die attach material. After low temperature bonding at 300 degrees C, the bondline keeps in Ag20Pd alloyed state with a shear strength of 23.5 MPa (higher than MIL-STD-883 K, 7.8 MPa). The Ag20Pd nanoalloy exhibits superior resistance to Ag ionic migration with short-circuit time tripled than pure Ag sintered layer. A Ag-rich layer appears on the surface of Ag-Pd nanoalloy, although the Ag-Pd is the typical isomorphous alloy system. Molecular dynamics simulation reveals that Ag atoms (214.0 kJ/mol) diffuse easier than that of Pd atoms (234.6 kJ/mol) on the nanoalloy surface layer, while showing similar mobility for inner nanoalloy. The Ag-rich layer consisting of dynamic exchanging atoms has a prewetting effect and contributes to the neck formation among nanoparticles. This work sheds light on the sintering mechanism of Ag-Pd nanoalloy, and it is confirmed that Ag-Pd nanoalloy is promising for low temperature bonding in terms of the high reliability power electronic.

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