Fatigue Reliability Evaluation for Sn–Zn–Bi and Sn–Zn Lead-Free Solder Joints

Abstract

The use of Sn–Zn–Bi and Sn–Zn solders is increasing because of their low cost and low melting point. Therefore, it is important to ensure the fatigue strength of Sn–Zn–Bi and Sn–Zn solder joints. In this study, the mechanical fatigue strength of Sn–Zn–Bi and Sn–Zn solder joints was evaluated by using chip scale package (CSP) specimens. The influence of surface treatment on the fatigue strength was investigated by using specimens with Ni/Au or pre-flux on a Cu-pad. These specimens were aged at 85, 125 and 150 � C for 500 and 1000 h to investigate the influence of the appearance of intermetallic compounds at the joint interface. Through a series of isothermal mechanical shear fatigue tests and finite element method (FEM) analyses, it was found that the fatigue lives of Sn–Zn–Bi and Sn–Zn solder joints were greatly affected by the aging temperature. In particular, when Sn–Zn–Bi and Sn–Zn solder joints with Ni/Au plating of the Cu-pad were aged at a temperature above 125 � C, the fatigue strength decreased remarkably in comparison with the specimens without Ni/Au plating.