A variation in microstructure and mechanical property (microhardness) was observed across the Cu/Sn/Ni solder joint. The microhardness of the Sn solder joint monotonically decreases away from the Cu side toward the Ni side. A coarser shear band occurred in the indentation marks of the solder matrix near the Ni side. The above findings imply that the solder matrix with a hypoeutectic microstructure near the Ni side has lower mechanical strength. The hypereutectic microstructure near the Cu side has higher mechanical strength. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3447865] All rights reserved.