The interfacial reactions between Sn-50 wt% Bi (Sn50Bi), Sn-57 wt% Bi (Sn57Bi) and Sn-65 wt% Bi (Sn65Bi) alloys with the Au substrate aged at 80, 100 and 120 degrees C for 12-350h are investigated in this study. The Au-Sn binary intermetallic compounds (IMCs) were observed at the interface, and the Au-Sn binary IMCs and ternary Au-Bi-Sn metastable (T) phase in the solder when the Sn-50Bi and Sn-65Bi couples. The Au-Sn binary IMCs and T phases were formed in the Sn-50Bi/Au couple aged at 100 degrees C and Sn-57Bi/Au couple aged at 120 degrees C for 100 h. However, this T phase was transferred into the AuSn(4) phase when the reaction was extended over 72 h. The increase in the Bi content in the Sn-Bi alloys could make the large (Bi) phase segregate in the solder/Au interface and decrease IMC growth. The IMC growth mechanism in all reaction couples is diffusion-controlled. The lowest reaction activity energy value could be found in the Sn-57Bi/Au couple due to its lowest liquidus temperature. (C) 2011 Elsevier B.V. All rights reserved.