Nearly perfect Ag joints prepared by Ag stress-migration-bonding (SMB) process

Abstract

We introduce low temperature/pressure Ag-Ag direct bonding method for a high-temperature die-attachment structure, which joins SiC dummy chips and direct bonded copper (DBC) substrates. The process uses "nano-volcanic eruption of Ag" caused by stress migration at 250 °C. Neither joining paste nor solder is required. The bonding achieved a die-shear strength over 110 MPa. Only a pre-sputtered Ag thin layer on the surface of dummy chips and DBC substrates can realize bonding with a low pressure (1.0 MPa) provided by a simple bonding jig at 250 °C. The formed Ag joint has a joint layer thickness of less than 4 μm, whose density is similar to that of bulk silver. This feature realizes the ultra-high bonding strength as well as an ideal electric/thermal performance. The SMB technique is well compatible with the current die-attachment process for power-devices. This breakthrough achievement will bring a bright future to the development of next generation power devices with ultra-high performance and reliability.