Quality control and reliability of PQFP device solder joints

In view of the long-term storage reliability issues of PQFP devices in aerospace applications, the optimization of solder joint process parameters and the evolution mechanism of IMCs were systematically investigated. Through optical microscopy, mechanical property testing, and scanning electron microscopy analysis, the influence mechanisms of weld height and soldering alloy volume on solder joint quality were revealed. The results show that increasing soldering alloy volume enhances wetting height (the theoretical optimal range is 0.05 ~ 0.099 3 mm³), while greater weld height diminishes wetting effects. The combination of a 0.12 mm steel mesh and 0.05 mm weld height achieves the lowest bridging rate and optimal tensile strength. High-temperature accelerated aging experiments demonstrate that Cu₆Sn₅/Cu₃Sn IMCs on the Cu bonding pad side evolve from a scalloped to planar morphology, while the Ni barrier layer reduces the thickness of (Cu,Ni)₆Sn₅ IMCs on the lead side. A kinetics model for IMC growth, based on Fick’s diffusion law, indicates parabolic growth behavior for bilateral IMC layers, with activation energies of 20.67 kJ/mol (Cu side) and 52.79 kJ/mol (Ni side). By using a critical IMC thickness of 3.5 μm as the failure criterion, the estimated storage life of solder joints at 23 ℃ reaches 27.5 years. This research provides theoretical foundations and data support for the long-term reliability design and process optimization of aerospace electronic systems.