Direct Ultrasonic Soldering of AlN Ceramics with Copper Substrate Using Zn–Al–Mg Solder

This research aims to develop the direct soldering of aluminum nitride (AlN) ceramics with a copper substrate using Zn–Al–Mg solder. The solder type, Zn5Al3Mg, has a close-to eutectic composition with a melting point of 359 °C. The microstructure of Zn–Al–Mg solder is composed of solid solution (Al), solid solution (Zn), an Mg2Zn11 phase and a minority MgZn2 phase. The tensile strength is from 82 to 169 MPa and depends on the magnesium content. The bond with AlN ceramics is formed due to the interaction of active Zn, Al and Mg metals with the substrate surface without forming a new transition phase. Zn and Al elements exert a substantial effect on bond formation with the Cu substrate. Magnesium does not contribute to bond formation with the Cu substrate. Two new phases, CuZn4-e and Cu33Al17/Cu9Al4/Cu5Zn8- γ, were observed, and form the transition zone of the joint. The maximum shear strength of the AlN/Cu joint fabricated using Zn5Al3Mg solder is 47 MPa. The maximum shear strength of the Cu/Cu joint fabricated using the same solder is 93 MPa.