2009 Volume 3 Issue 4 Pages 667-678
The reliability of a micro-solder joint in a semiconductor structure depends on its solder shape. Therefore, many methods of predicting the molten-solder shape have been proposed. However, conventional methods cannot be used to accurately predict the shape of a miniaturized solder. In a miniaturized solder joint, molten solder greatly changes its shape during the reflow process, and even topology changes (e.g., merging with another solder in a neighboring joint or splitting into several pieces) might occur. Conventional methods cannot be used for expressing these phenomena. To predict a miniaturized solder shape, we developed a new shape-prediction method based on the moving-particle semi-implicit (MPS) method. In the MPS method, a continuum is expressed as an assembly of particles. In contrast to finite element analysis (FEA), our new method can easily express large deformation and topology changes because the continuum does not need to be divided into elements. Moreover, we evaluated the fracture life of a solder joint with the predicted solder shape by coupling our shape-prediction method with a crack-propagation analysis method that we also developed. The crack-propagation is used for automatically calculating a crack-initiation point and crack-propagation paths, and the fracture life is evaluated quantitatively. We applied this coupling method to evaluate fracture lives of various solder joints and found that a difference in solder shape caused a difference in crack-initiation points, crack-propagation paths, and fracture lives.
