To design an effective and realistically applicable sinter bonding process for power devices, we proposed a two-step process using a 200 nm Cu-particle-based paste to form a bondline having high-temperature sustainability and superior thermal conductance. This process involved rapid pressure-assisted sinter bonding in air followed by pressureless annealing in a nitrogen atmosphere. In the case of a paste prepared with a mixture of 20 wt.% malic acid and 80 wt.% ethylene glycol, sinter bonding at 300 °C and 5 MPa for only 30 s resulted in a sufficient shear strength of 23.1 MPa. The shear strength was significantly enhanced to 69.6 MPa by the additional pressureless aging for 30 min. Therefore, the two-step sinter bonding process is expected to provide an outstanding production rate as a next-generation sinter bonding process.