Sinter bonding and formation of a near-full-density bondline at 250 °C via addition of submicrometer Cu particles to micrometer Ag-coated Cu particles

Pressure-assisted die bonding at 250 °C in air using a paste containing 2 µm Ag-coated Cu particles (Cu@Ag) and 350 nm Cu particles was demonstrated for power device bonding. At a Cu@Ag-to-Cu mixing ratio of 6:4, the sinter-bonded dies showed a considerable average shear strength that approached 25 MPa after only 5 min of bonding. Furthermore, a near-full-density bondline and excellent strength, greater than 30 MPa, were achieved after only 10 min. The remarkably rapid improvement in the strength and microstructure was attributed to the generation of pure Cu nanoparticles on the Cu surfaces by in situ reduction during heating for the bonding.