Recently, preventing environmental pollutions, lead-free (Pb-free) solders are widely used instead of conventional lead-tin(Pb-Sn) eutectic solders. However, the mechanical properties of Pb-free solders have not been clarified. Intermetallic compounds are formed during reflow process between solder and electrical pads and gradually grow in service. Due to it's brittle manner, the reliability of solder joints are supposed to degenerate. By using the Cu-plates on which Cu or Ni or Ni+Au plating was deposited, and Pb-free solders (Sn-Ag-Cu solders), the specimen of solder joints were fabricated. After aging it in an isothermal chamber, tensile tests were performed and the relations between solder joint strength and aging period were considered. From SEM microscope observation and EDX microprobe analysis, the growth and components of the intermetallic compounds layer were also examined.