Microstructure and mechanical property of thick Cu/AlN joints formed at low temperature

Abstract The bonding of thick Cu and AlN is necessary in power modules with the development of high‐frequency communication technology. In this work, 2 mm‐thick Cu was successfully bonded with AlN by using Sn9Zn solder with the assistance of ultrasonication at 230°C. Results showed that an AlN/Sn9Zn/Cu joint without crack was manufactured with a cooling rate of 7°C/min. Nonreactive wetting was realized between AlN and Sn9Zn, forming an amorphous transition layer. CuZn 2 and CuZn were formed at the Sn9Zn/Cu interface. A joint with the highest bonding strength of 30.07 MPa was obtained, in which the AlN/Sn9Zn interface was no longer the weakest location. This work provides a low‐temperature manufacturing method for thick Cu/AlN joints.