INFLUENCE OF Ni ADDITION ON MICROSTRUCTURE AND SOLIDIFICATION BEHAVIOUR OF SAC305 LEAD-FREE SOLDERS

This study investigates the addition of Ni into SAC305 solder alloy with varying nickel content (0–4 wt.% Ni) using experimental techniques and computational thermodynamics. The experimental part employed various techniques (scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and differential scanning calorimetry). The microstructure of the investigated alloys consisted of primary β-Sn and an eutectic mixture containing β-Sn and two intermetallic compound particles (Ag3Sn and Cu6Sn5). Small Ni additions (up to 0.2 wt.%) refined the microstructure and significantly reduced the undercooling from 30°C (SAC305) to about 12°C. However, Ni additions exceeding 0.4 wt.% led to microstructural coarsening and formation of Ni3Sn4 phase. For the computational part, Thermo-Calc software was used to investigate the conditions of Cu6Sn5 and Ni3Sn4 phase formation. The experimental results were consistent with computations from Thermo-Calc. The results suggest that minor Ni additions (up to 0.2 wt.%) offer possibilities to refine the microstructure and reduce undercooling, potentially improving the properties of solders.