Sintering Mechanism of Bimodal-Sized Cu Nanoparticle Paste for Power Electronics Packaging

The sintering process of Cu nanoparticles is challenging due to the oxidation of Cu and the formation of voids in the die-attach layer. In this work, a simple and cost-effective bimodal-sized Cu composite paste was prepared for a high-strength Cu-Cu joint. The joint microstructure and sintering properties were systematically investigated by adjusting the mass ratio of the particle dimensions from 80 nm to 300 nm and varying the sintering parameters. Die attachment by pressure (20 MPa)-assisted sintering in air at 250°C was rapidly achieved using bimodal-sized Cu particles. The joint sintered for 1 min exhibited shear strength of 85.63 MPa, while 5-min sintering was able to obtain a dense bondline structure, and the shear strength reached 102.46 MPa. The sintered layers in nitrogen had the highest thermal conductivity of 284 W/m K and low resistivity of 4.42 µΩ cm. These results confirm that bimodal-sized Cu composite paste can be considered as an inexpensive potential die-attach material for high-temperature electronics packaging.