Improved sinter-bonding properties of silver-coated copper flake paste in air by the addition of sub-micrometer silver-coated copper particles

To promptly form a bondline with high thermal stability and thermal conductivity using a small amount of expensive Ag, dies were attached to Ag finishes by pressure-assisted sinter bonding at 300 °C using micrometer-sized Ag-coated Cu (Cu@Ag) flakes. Small Cu@Ag particles of 350 nm size were also added to the paste to increase the sinterability by increasing the contact points, which resulted in a bimodal paste. The dewetting of the Ag shells in Cu@Ag induced initial sintering, and the rearrangement of the 350 nm Cu@Ag particles as well as the bending of the Cu@Ag flakes under pressure effectively filled the voids between the particles. As a result, shear strengths of almost 20 MPa and 28.9 MPa were obtained after only 1 and 5 min of sinter bonding, respectively. In addition, a bondline with a unique near full density microstructure was achieved in the 5 min sinter-bonded sample.