The effect of 0.5 wt.% Ce additions on the electromigration of Sn9Zn BGA solder packages with Au/Ni(P)/Cu and Ag/Cu pads

It has previously been established that Sn-9Zn-0.5Ce alloy possesses mechanical properties superior to those of undoped Sn-9Zn alloy, and is free of the problem of rapid whisker growth. However, no detailed studies have been conducted on the electromigration behavior of Sn-9Zn-0.5Ce alloy. In this research, Sn-9Zn and Sn-9Zn-0.5Ce solder joints with Au/Ni(P)/Cu and Ag/Cu pads were stressed under a current density of 3.1 × 104 A/cm2 at room temperature for various periods of time. Due to finer grain sizes, the electromigration effects were more severe in Sn-9Zn-0.5Ce solder joints than in Sn-9Zn solder joints when joint temperature was around 80 °C. In addition, both solder joints (Sn-9Zn and Sn-9Zn-0.5Ce) with Au/Ni(P)/Cu pads possess longer current-stressing lifetimes than those with Ag/Cu pads because Ni is more resistant than Cu to migration driven by electron flow.