Shear properties of low-temperature soldered joints of aluminum nitride metallized with Sn-1.0Ag-0.5Cu-Ti alloys

The wetting behavior of Sn-1.0Ag-0.5Cu-xTi (SAC-xTi, where x = 2, 4, 6) powder on the AlN surface was investigated. The SAC-xTi powder developed a high-quality tin-based metallization layer on the AlN surface when heated at 900 °C for 30 min. The pre-metallized AlN was successfully soldered to the Cu substrate using SAC solder paste at 250 °C. The wetting angle gradually increased with rising Ti content in SAC, achieving a minimum wetting angle of 8.2° with SAC-2Ti powder on the AlN surface. Additionally, there was observed a homogeneous and sequential flat pre-metallized layer on the surface of AlN. However, the layer becomes discontinuous as the Ti content increases, leading to the appearance of significant surface irregularities (bumps). Low-temperature preparation of Cu/SAC/pre-metallized AlN joints with the typical microstructures of: Cu/Cu₃Sn layer/Cu₆Sn₅ layer/β-Sn layer (containing Ag₃Sn and Cu₆Sn₅)/TiN layer/AlN. The pre-metallized layer significantly influenced the shear strength of the joints, which decreased with increasing Ti content. The shear strength of joints with pre-metallized layers formed using SAC-2Ti peaked at 24.27 MPa. As Ti content increased, the fracture paths gradually approached the AlN surface from the solder matrix.