Abstract: To address the issues of low reliability of ball grid array (BGA) solder joints under combined effect of mechanical loading from heat sinks and thermal cycling loads, with unclear influencing factors from heat sink mechanical loading, a finite element simulation was conducted to analyze the stress and strain of BGA packages under combined loads of MIL-STD-883 thermal cycling standards and bolt preload force. The Darveaux fatigue life prediction model was employed to calculate the fatigue life of critical solder joints. Furthermore, through orthogonal experimental design, a range analysis was conducted with fatigue life as the evaluation index to analyze the effect of heat sink application on the fatigue life of the solder joints. The research results have indicated that under the combined effect of thermal cycling and mechanical loading, maximum Von Mises stress and cumulative equivalent plastic strain concentrate at the corner solder joints of the outermost ring of the solder ball array, particularly at the junction between the top and side surfaces of the solder balls. Orthogonal experiments reveal that bolt preload force, bolt position, and substrate thickness significantly influence solder joint fatigue life, with bolt position being the most critical factor and substrate thickness having the least impact. In simulation, solder joints achieve the longest fatigue life and optimal reliability under conditions of bolt preload force at 35 N, bolt position at 70 mm, and substrate thickness of 1.6 mm.