Enhanced mechanical performance of metallized Al2O3/Al joints using a Sn-alloy/Zn foil hybrid solder

This study developed a soldering process for joining Al to Cu-metallized ceramic substrates, aiming to overcome the formation of brittle intermetallic compounds in Sn-based solders, which usually lead to low joint strength. Zn foils coated with Sn-10Zn or Sn-20In solders were used as hybrid solders to bond Ni-plated Al components to Cu-metallized Al 2 O 3 substrates at 220 °C. With increasing soldering time, the solder on the Zn surface gradually transformed into NiZn 3 , and the formation mechanism of the NiZn 3 phase was analyzed from thermodynamic and kinetic perspectives. The shear strength of the joints increased with prolonged soldering times, reaching a maximum of 67 MPa for the Sn-10Zn/Zn solder at 240 min. In the Sn-10Zn joints, NiZn 3 formed a continuous transition layer that effectively reduced stress concentration. In contrast, the Sn-20In/Zn joints showed discontinuous NiZn 3 layers and significant interfacial stress, resulting in lower shear strength.