The major failure mechanism of the solder bumps used in surface mount technology(SMT) is the thermally induced low cycle fatigue. To verify the solder joint reliability, the power cycling method and chamber cycling method have been commonly used. In this study, these two experimental techniques are examined and a new testing method modifying the power cycling method in such a way to perform it easily is developed. A tester is designed to perform the thermal cycling test by means of thermal conduction. This tester has a heating plate as a heater and $N_2$ gas and air as a coolant.
The specimen used in this study is BGA-type solder-printed circuit board. The size of solder ball reflowed between two circuit boards is 1mm(diameter). The solder joint specimens are prepared by the conventional SMT process. The strains of circuit boards are measured and compared with the results of FEM analysis. The temperature gradient and transient effect are measured. A thermal Fatigue testing is performed. In order to define the failure of solder joints, the bending moment of the circuit board is measured by the strain difference between two sides of a circuit board. A relationship between the decrease of the bending moment and the failure of the solder joint is found to exist, which can be usefully utilized in the future fatigue test for the tester made in this study.
