Abstract: Aiming at the long-term storage reliability issues of PQFP packaged devices in aerospace applications, this study systematically investigates the optimization of solder joint process parameters and the evolution mechanism of IMCs. Through optical microscopy, mechanical property testing, and scanning electron microscopy analysis, the influence mechanisms of stand-off height and solder volume on solder joint quality were revealed: Increasing solder volume enhances wetting height (the theoretical optimal range is 0.05 ~ 0.0993 mm³), while greater stand-off height diminishes wetting effects. The combination of a 0.12 mm stencil and 0.05 mm stand-off height achieved the lowest bridging rate and optimal tensile strength. High-temperature accelerated aging experiments demonstrated that Cu₆Sn₅/Cu₃Sn IMCs on the Cu pad side evolved from a scalloped to planar morphology, while the Ni barrier layer reduced the thickness of (Cu,Ni)₆Sn₅ IMCs on the lead side. A kinetics model for IMC growth, based on Fick’s diffusion law, indicated parabolic growth behavior for bilateral IMC layers, with activation energies of 20.67 kJ/mol (Cu side) and 52.79 kJ/mol (Ni side). Using a critical IMC thickness of 3.5 μm as the failure criterion, the estimated service life of solder joints under 23 ℃ storage conditions reached 27.5 years. This research provides theoretical foundations and data support for the long-term reliability design and process optimization of aerospace electronic systems.