The effect of adding Bi to a eutectic Sn-3.5Ag solder alloy on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints was examined at the aging temperatures of 130 degrees C, 150 degrees C and 180 degrees C. At 150 degrees C and 180 degrees C, the growth rate of the Cu6Sn5 layer was significantly enhanced, but that of the Cu3Sn layer was rather reduced with increasing Bi content up to 12 wt.%. At 130 degrees C, however, both the eta and epsilon layers appeared to grow faster as the Bi content in the solder was increased to 12 wt.%. These results suggest that the accumulation of Bi ahead of the Cu6Sn5 layers can affect not only the interfacial reaction barrier but also the local thermodynamics at the interface between the Cu6Sn5 layer and the solder.