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

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.