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

Abstract

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 °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 °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.