Abstract: Optimum simulation for QFP devices and effects of lead widths and lead pitches of QFP on the thermal fatigue life of soldered joints of QFP devices were studied by means of FEM method. Results indicate that the maximum strain value exists at the front of the outside soldered joint in all the soldered joints of QFP64, where is the weakest position at which cracks initiation take place easily and lead to failure owing to thermal fatigue finally. When the lead pitches are constant, the equivalent strain existing in soldered joints increases with the increasing of lead widths, the reliability of the soldered joints declines and the thermal fatigue life decreases.When the lead widths are unvaried, the equivalent strain existing in soldered joints doesn' t decrease at all times in which there exists a maximum value of the thermal fatigue life with the increase of lead pitches. While lead width is 0.15mm and lead pitch is 0.45mm of QFP64, the reliability of the soldered joint is highest and the device can be served for longest time.