Study on the electrochemical corrosion behavior and solderability of SnAgCuNi solder alloy

This study mainly focuses on the effects of different Ni content in Sn–Ag–Cu–Ni solder alloys on their electrochemical corrosion behavior and solderability. The results demonstrate that the addition of nickel significantly refines β-Sn grains, promotes the formation of the intermetallic compound (Cu,Ni)6Sn5 by partially substituting the Cu6Sn5 phase, and inhibits the lamellar growth of coarse Ag3Sn, thereby enhancing microstructural homogeneity. By combining electrochemical techniques with in-situ Raman spectroscopy, the role of nickel in influencing the composition and passivation behavior of corrosion products was elucidated. At low nickel contents (0.05–0.1 wt%), the formation of dense Sn(IV) oxide films reduces the passivation current density, inhibits chloride ion penetration, and decreases the depth of corrosion pits (from 21.4 μm to 15.7 μm). In contrast, higher nickel contents (0.25–0.5 wt%) exacerbate intergranular corrosion due to enhanced galvanic coupling between the nickel-rich (Cu,Ni)6Sn5 phase and the β-Sn matrix. Moreover, the formation of porous passivation films composed of Sn(OH)4 and Sn–Cl complexes leads to local film breakdown and promotes pitting propagation. Differential scanning calorimetry results indicate that while nickel has a negligible effect on the melting point of the alloy, it reduces the degree of solidification supercooling (from 14.7 °C to 11.5 °C), thereby improving solidification stability.