Solder joints in the advanced electronic packaging such as 3D packaging are subjected to multi-load consisting of thermal cycling and other mechanical constraints. Since multi-loads may produce ratchet influencing thermal fatigue reliability, a method evaluating thermal fatigue life under multi-loadings should be developed. In this paper, three-point bending tests of the ball grid array (BGA) package were carried out. Experiments were performed with several average stress levels. Number of cycles to failure in experiments decreases as a function of the average stress. FEA qualification was carried out to estimate the fatigue life in three-point bending tests. Error of computational estimated life to the experimental result is big when the average stress is high. It implies that modified Manson-Coffin's law should be used for thermal fatigue life of solder joints under multi-loadings.
