Strong effect of Pd concentration on the soldering reaction between Ni and Sn–Pd alloys

The effect of Pd concentration on the soldering reaction between Ni and Sn–xPd alloys (x = 0–0.5 wt%) was investigated in this study. When the Pd concentration was low (x ≤ 0.05 wt%), the predominant reaction product was a layer of Ni₃Sn₄. In contrast, an additional (Pd,Ni)Sn₄ layer deposited over the Ni₃Sn₄ in the case of above 0.2 wt%. This microstructure evolution significantly weakened the strength of the interface, deteriorating the reliability of solder joints. A Pd–Ni–Sn isotherm simulated by the CALPHAD method was used to rationalize the above transition in the reaction product(s).