Fatigue life estimation of surface mount solder joints

A novel and direct method to measure the stress-strain properties of surface mount solder joints is proposed in this paper. The specimen used in the experiments is a quad flat pack (QFP)-solder-printed circuit board (PCB) assembly and the fabrication of solder joints makes use of conventional surface mount technology (SMT). Mechanical cycling and thermal shock testing can be conducted directly on the specimen after assembly. In this manner, the specimen represents practical SMT solder joints in electronic products as far as possible. It is shown that the joint strain and stiffness of chip modules are good evaluation indices to reveal the fatigue status of solder joints. It is further proposed that the criterion of 50% load drop should be used for defining the fatigue life of solder joints. Finally, it is recommended that the total displacement Δδ_2p be used to measure the strain-fatigue life relation for both leaded and leadless joints