Ultrasound-assisted soldering process performance of Sn-Ag-Ti(Ce, Ga) active solders on thin film ZnO substrate

ZnO has been widely used in electronic industries as semiconductor and photovoltaic materials. In this study, directly soldering ZnO thin film (ZnO-TF) coated on solar glass was achieved with ultrasound-assisted soldering iron using Sn3.5Ag4Ti(Ce, Ga) active solder at 250 °C in air. Results show that the active solder can rapidly wet and spread on ZnO-TF with ultrasonic assistance. No distinct intermetallic compound layer can be detected at the interface. With certain ultrasonic parameters, the average shear strength of solder/film joints reaches 23.9 MPa. Shear fracture occurs at the interface of joints and partial solder remains on the surface of the ZnO-TF, meaning that there is a firm bonding between the active solder and the ZnO-TF. Element analysis on fracture surfaces reveals that Ti content in the remnant solder on the ZnO-TF is higher than that in the solder matrix. Combined analyses based on adhesion theory and thermodynamic calculation manifest that Ti tends to adsorb at the ZnO film and the redox reaction between Ti and ZnO takes place during ultrasound-assisted soldering process.