Shape Prediction of Micro-Molten Solder and Its Application to Evaluating Fracture Life

The reliability of a solder joint in a semiconductor structure greatly depends on its solder shape. However, predicting the solder shape of miniaturized and lead-free joints is difficult because of its large deformation, topology change, and the difference in solder wettability. Therefore, we developed a new method for shape prediction based on the moving-particle semi-implicit (MPS) method. The MPS method is suitable for calculating incompressible flow and can easily express large deformation and topology changes. However, the original MPS method cannot sufficiently express the effect of solder wettability. Therefore, we enhanced the surface tension formulation of the MPS method, making it possible to express this effect. We applied this method to predicting the solder shapes of various semiconductor packages and found that the method is effective in predicting the solder shapes of miniaturized joints. Moreover, we evaluated the fracture life of a solder joint with the predicted solder shape by coupling the shape prediction method with our crack propagation analysis method. Crack initiation points and propagation paths are automatically calculated using this crack propagation analysis, and the fracture life is evaluated quantitatively by finite element analysis. We applied these combined methods to evaluating the fracture life of solder joints that had different shapes due to different wettability conditions. As a result, we found the differences in crack initiation points and evaluated crack propagation paths and fracture lives in different wettability conditions.