The effect of a concentration gradient on interfacial reactions in microburaps of Ni/SnAg/Cu during liquid-state soldering

We report new findings in Ni/SnAg solder/Cu microbumps having a reduced solder thickness in the range of 40-10 mu m; the growth rate of the intermetallic compounds depends strongly on the solder thickness. In the Ni/40 mu m solder/Cu samples., the compound which grew on the Ni side grew slightly faster than that on the Cu side. However, the growth reverses as the solder thickness decreases below 20 pm due to the change in Cu and Ni concentration gradients in the solder. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.