Pb-Sn-Sb-Ag Solder Thermal Fatigue of Hybrid Integrated Circuits

To solve the problem of the reliability of solder joints caused by changes of ambient temperature in a hybrid integrated circuit, a new type of solder with high reliability was developed to meet the welding requirements of the miniaturization and high-density hybrid integrated circuit. Melting point test, reflow profile, phase analysis and thermal cycle test were conducted under the reference of IPC-9701A on the newly developed Pb-Sn-Sb-Ag solder and the fact that the microstructure and mechanical properties of solder joints changed significant before and after thermal cycling was discovered. The results show that the liquid point of solder is 245℃, reflow peak temperature is 267℃, and there are three major phases in the solder joint, namely, Pb, Sb ₂Sn ₃, and Ag ₃Sn. The shear stress generated by thermal mismatch lead to micro cracks and the micro cracks extend further by the alternative temperature. The solder joints appear the fracture failure mode of whole peeling finally. The thickness of intermetallic compound and shear strength present approximate linear relationship gradually decreasing. Compared to the applied solders, the newly developed Pb-Sn-Sb-Ag solder has homogeneous microstructure and high reliability in -40-150℃ thermal cycling conditions.