Abstract: Microstructures of Sn₆₂Pb₃₆Ag₂ solders with different duration in molten state and cooling rate were investigated by metallographic analysis. Heterogeneous microstructure coarsening was found in the solder with slow cooling rate and/or longer duration. This phenomenon was attributed to the deviation of the composition of the composition of the solder from eutectic point due to depletion of tin resulted from the formation of intermetallic compounds such as Cu₆Sn₅ and Ag₃Sn. Heterogeneous microstructure coarsening can reduce the solderability of the solder.