Fatigue Life Predicting of Lead-Free Soldered Joints of QFP Device
Anand model was used to establish the constitutive equation of SnAgCu solder, the stress-strain response of soldered joints was analyzed by finite element code. Results indicated that the stress concentrates on the sharp corner of interior part of outermost soldered joint, where is the weakest position at which cracks initiation take place easily and lead to failure owing to thermal fatigue finally. The Modified Coffin-Mason equation by Engel Maier was uti lized to predict the fatigue life of soldered joint, the value of strain and stress in the soldered joint of Cu/Ni/Au finishes was least, the value was middle in the joint of Cu/Ni and the value was largest in the joint of Cu, which will provide a theory guide for practical applications.