Effects of Ni addition on the interfacial reactions between Sn-Cu solders and Ni substrate

This research investigates the effects of adding a small amount of Ni to solder. The interfacial reactions between Ni and the Sn-Cu solders at 250 C are examined. Two sets of Sn-0.7 wt% Cu-xNi solders and Sn-1.0 wt% Cu-xNi solders (x = 0.02, 0.05 and 0.1 wt%) were prepared. The results reveal that the interfacial reactions are very sensitive to Ni. With increasing Ni addition, the reaction phase grain, Cu6Sn5, becomes larger and its morphology changes from a rod-like shape into a faceted structure. The reaction progressions are accelerated in comparison with those without Ni addition. The solder spreading effect on the Cu6Sn5 morphology was also investigated. Cu6Sn5 exhibits a gradual change in microstructure from the center to the rim for the case when the solder ball spreads over a Ni substrate. However, the solder does not alter the Cu6Sn5 microstructure while reacting on a small Ni pad without spreading. This suggests that the Cu and Ni contents in the solder near the interface vary during the solder ball spreading process. (C) 2009 Published by Elsevier Ltd.