Thermo–vibration coupled reliability methodology of BGA solder joints considering the preload effect of heat sink bolts

With the ongoing trend toward high integration and miniaturization of electronic systems, ball grid array (BGA) packaging has become a dominant interconnection technology for high-performance devices due to its superior electrical and mechanical characteristics. Nevertheless, solder joints remain the most vulnerable elements within BGA assemblies, and their fatigue reliability critically determines the overall service stability of electronic products. In this work, the fatigue life of SAC305 lead-free solder joints in a BGA package is systematically investigated under thermo–vibration coupled loading conditions, explicitly accounting for the preload introduced by the heat sink assembly. A multi-physics reliability assessment framework is developed by integrating thermal cycling, random vibration excitation, and mechanical preload effects. Finite element simulations combined with a Palmgren-Miner-type linear summation approach are employed to characterize the temperature-dependent stress–strain responses and damage evolution of solder joints. The results demonstrate that the most critical solder joints are consistently located at the outer corner positions of the solder ball array, where severe stress concentration and accelerated damage accumulation occur under combined thermal cycling and high-temperature vibration. Based on the proposed coupled damage model, the fatigue life of the critical solder joint is predicted to be approximately 58.8 h. The present study provides a quantitative and physically interpretable methodology for reliability-oriented design and fatigue life prediction of lead-free BGA interconnects subjected to complex service environments.