Abstract: Thermal fatigue life of QFP devices under thermal conditions of 25-125℃ was studied by means of FEM analysis, which the experiment results of 186 times is close to the simulated result of 213 times.Tensile strength test and SEM analysis of the soldered joint fralture were carried out to elucidate the effect of thermal cycling on tensile strength and microstructure of QFP soldered joint.Results show that the crack in soldered joint germinates at the inner side of interfaces of solder and brass pad. With increasing of the thermal cycling times, the tensile strength of the soldered joint reduces gradually and the fracture mode of the joint belongs to the toughness fracture before thermal cycling through observing fractographs of the fracture of the joint by SEM.With increasing of the thermal cycling times, crystal grains are coarsened and the dimples will grow up too, so that the brittle fracture plays a leading role after 120 times thermal cycling, and the fracture mode of the joint belongs to brittle fracture after 186 times thermal cycling.