Study on Evaluation Method of Thermal Fatigue Life for BGA Solder Joints

摘要

The thermal fatigue strength of BGA solder joints is one of important properties for design. However, the traditional approach to estimate the fatigue life consumes much time and cost. As a method of evaluating the thermal fatigue lives more efficiently, the evaluation of S-N diagram by the combination of thermal fatigue tests and finite element analysis was described. To estimate the design margin, each fatigue data is transformed into normalized fatigue strength, because the distribution of normalized fatigue strength can be estimated by the small number of samples. As a result, it becomes possible to estimate the design margin with a given probability of failure and confidence level considering an effect of number of samples. Based on the obtained S-N curve with a design margin, distribution of fatigue lives for other types of BGA specimens can be also estimated without additional experiments. It is revealed that the proposed method is very useful for the reliability estimation of solder joints.