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In this paper, we propose a mixed robust method based on three-level and second-order experiment design, the quadric surface, and finite-element analysis to analyze and optimize thermal fatigue reliability of an FBGA package. According to structural characteristics of FBGA packages, six design variables are selected as optimized objects. The equivalent thermal fatigue strain of solder joints of FBGA packages is used as an objective function of thermal fatigue reliability optimization design. Three-level and second-order experiment design was carried out for six design variables, and the equivalent thermal strain of solder joints was calculated by finite-element analysis according to experiment design. Then a quadric surface model of six design variables and the equivalent thermal strain of solder joints was built, and variance analysis and accuracy verification were performed. From the model and significance analysis, the nonlinear relation between design variables and thermal strain of solder joints, and the interaction among design parameters were obtained. Finally, a thermal fatigue robust optimization model was built, and optimum structural parameters and equivalent thermal fatigue strain of solder joints were obtained. Equivalent thermal fatigue strain decreased from 0.01858200 to 0.00951976 and was reduced by 48.77%, as shown by comparing the thermal strains before and after optimization.
Wan et al. (Fri,) studied this question.