This study investigates the metallurgical reaction and shear strength of Pb-free SnAg2.5Cu0.8Sb0.5 and SnAg3.0Cu0.5Sb0.2 solder bumps on Au/Ni(P) metallization pads. It is found that (Cu,Ni)6Sn5 intermetallic compound (IMC) formed at the interface between the Sn2.5Ag0.8Cu0.5Sb solder and the metallization pad; whereas (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 IMCs formed when the SnAg3.0Cu0.5Sb0.2 reacted with the Au/Ni(P) metallization pad. The difference in the Cu concentration in the two solders may be responsible for the different interfacial IMC formation. The shear strengths for the SnAg2.5Cu0.8Sb0.5, SnAg3.0Cu0.5Sb0.2, SnAg3.0Cu0.5, and SnAg4.0Cu0.5 solders were also measured. The shear strength test revealed that the SnAg2.5Cu0.8Sb0.5 solder has the highest shear strength, which may be due to the solid-solution strengthening of the Sb atoms.