Abstract: The reliability of SnAgCu solder joint of flip chip ball grid array packaging (FCBGA) device was analyzed by finite element method and Garofalo-Arrheninus steady-state constitutive equation under thermal shock. The results showed that the reliability of Sn3.9Ag0.6Cu solder joints was relatively high. By analyzing the mechanical constitutive behavior of SnAgCu solder joint, the maximum value of solder joint stress was found at the corner of the contact spot between the solder joint and the chip. The stress of SnAgCu solder joint changed periodically over time. The solder joint stress and creep of the solder joint Sn3.9Ag0.6Cu was the smallest, the Sn3.8Ag0.7Cu solder joint second, and the solder joint stress and creep of the Sn3.0Ag0.5Cu solder joint was the largest, which agreed with the actual test results of the FCBGA device. The fatigue life of solder joints was calculated by creep strain fatigue life prediction model. It was found that the fatigue life of Sn3.9Ag0.6Cu solder joint was higher than that of Sn3.0Ag0.5Cu and Sn3.8Ag0.7Cu solder joint.