Optimal Design of Thermal Cycling Reliability for Plastic Ball Grid Array Assembly Via Finite Element Method and Taguchi Method

Abstract

A finite element simulation analysis model was developed for a plastic ball grid array (PBGA) assembly to analyze its behavior under thermal cyclic loading conditions. The stress distribution in the SAC305 solder joints at different locations within the array was investigated by using ANAND constitutive equations. Subsequently, the thermal fatigue life of the key solder joints was quantified. The study also examined the influence of the solder joint diameter, substrate thickness, solder joint height, printed circuit board (PCB) thickness, and mold compound height on solder joint stress. Optimization of assembly parameters was achieved through the application of the Taguchi method. An extensive analysis was conducted using different assembly parameter combinations, employing the L9(34) orthogonal array design to explore the thermal cycling effects. The computed average Von Mises stress Δσ for the critical thin-layer elements of solder joints located in hazardous positions within the assembly was notably affected by variations in the solder joint height, substrate thickness, solder joint diameter, and mold compound height. This impact ranked in descending order of significance as solder joint height, substrate thickness, solder joint diameter, and mold compound height. The optimal parameter combination determined was a solder joint height of 0.70 mm, a solder joint diameter of 0.85 mm, a substrate thickness of 0.51 mm, and a mold compound height of 1.12 mm. Implementing this optimized configuration led to a significant 4.07% reduction in average stress Δσ for the critical thin-layer elements within hazardous solder joints. Moreover, the extension of the thermal fatigue life was notably improved, achieving an impressive 51.72% increase.