Sintering Mechanism of a Supersaturated Ag-Cu Nanoalloy Film for Power Electronic Packaging

Ag-Cu bimetallic nanoparticles, combining the advantages of both Ag and Cu, are a promising material for power electronic packaging. In this work, a supersaturated Ag-7.3 wt % Cu alloy nanoparticle film was developed by using pulsed laser deposition. Unlike Cu nanoparticles, the supersaturated Ag-Cu alloy nanoparticles can conduct bonding in air without the assistance of a reduction agent. The shear strength was >20 MPa when the bonding temperature reached 300 °C, which was above the die shear standard (MIL-STD-883 K, 7.8 MPa) and compatible with the typical die attach process. The Cu separating behavior was accompanied by the bonding process at 250-400 °C, which was discussed systematically. Neck formation was delayed to about 250 °C because of the hindering effect of the thin oxide shell of the Ag-Cu alloy. The necking networks provide volume diffusion paths despite the growth of surface oxide, resulting in compact densification. The bondline under the SiC die consisted of a porous Ag-Cu alloy matrix with a dispersed secondary phase of Cu₂O/CuO, which is supposed to have improved electrochemical migration resistance.