Superior Sinterability of Copper Oxalate-Coated Cu Particles in a Double Reductant System and Rapid Compression Sinter-Bonding Characteristics between Cu Finishes

High-speed die attachment by compression (2 MPa) sinter-bonding at 300 °C in air was accomplished using a paste containing bimodal-sized (average sizes: 2 μm and 340 nm) copper oxalate-coated Cu particles, yielding a Cu-to-Cu bonding owing to the formation of a Cu bond line that can provide mechanical durability at high temperatures and excellent thermal conductivity. The particles were fabricated by immersing Cu particles in an oxalic acid solution, and a double reductant recipe was adopted to minimize the oxidation of the Cu particles and Cu finishes. The copper oxalate coatings inhibited the oxidation of Cu particles until decomposition at 290 °C, and the in-situ decomposition induced the generation of active Cu atoms, which significantly elevated the sinterability. Therefore, a sufficient shear strength exceeding 20 MPa and a near-full-density bond-line structure were achieved after bonding for only 1 and 3 min, respectively. Furthermore, the bond line did not contain an organic residue, differently observed in a paste directly including carboxylic acid. Therefore, the suggested paste formulation demonstrates the feasibility of a rapid solid-state sinter-bonding technique using low-cost Cu particles.