Abstract: The microstructure of Sn37Pb and Sn3Ag0.5Cu solder joints under as-reflowed and isothermal aged conditions were observed respectively.The shear strength of samples were also measured.The results suggested that despite the IMC layer of the Sn37Pb solder joints was thicker than the Sn3Ag0.5Cu solder joints, both of them were within the acceptable range.The Sn3Ag0.5Cu solder joints shows a bigger shear strength due to its special structure of β-Sn primary crystal coated by reticular eutectic.Besides, the shear strength of the two solder joints decreased after aging.Although lead-free solder is the inevitable trend to the development of electronic packaging industry instead of Sn37Pb solder, precision reflowing process still plays an important role to improve the quality of the solder joints.