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.