IMPROVED APPROACHES FOR FEA ANALYSES OF PBGA PACKAGES SUBJECTED TO THERMAL CYCLING

摘要

The study of solder joint reliability is one of the priority issues in electronic packaging. Solder alloys experience a highly nonlinear material behavior when subject to thermal cycling. It is a time consuming and difficult task to study the behavior of solder joints using experimental approaches. Finite element analysis provides a more efficient way to better understand the behavior of solder joints when accurate material models are available. With the developments of FEA algorithms and computer resources, the analysis approaches used for electronic packaging assemblies have evolved from 2-dimensional to 3-dimensional analyses, with far fewer assumptions needed in the fully 3D case. In this paper, we compare different FEA approaches covering various 2D and 3D modeling techniques to understand their advantages and drawbacks, especially as related to simulation accuracy and efficiency. Several models for a typical BGA assembly were prepared and analyzed including traditional mesh continuity models (2D slice model, 3D slice model, and 3D quarter model), as well as advanced models that employ Multi-Point Constraints (MPCs) and submodeling (global/local models). The Anand viscoplastic model was used for the solder joint material behavior in all of the FEA approaches. For the 3D mesh continuity models, an optimal analysis approach has been proposed to achieve the best balance between the accuracy of the simulation result and numerical efficiency of the simulation. Mesh transitions were used to maintain mesh continuity between regions of different mesh densities. A best choice of load step size was also found to reduce overall simulation time. For the analysis using MPCs to to bond different meshes, two improved modeling strategies have been proposed including a suggested ratio of contacting elements and the use of multiple-MPC contact pairs to reduce overall mesh density of the FE model. An improved simulation simulation strategy using submodeling has also been developed to obtain the best compromise in the global and local models between the mesh quality and load step size. An improved geometric simplification of the solder joint for use with energy based fatigue criteria was developed. Finally, comparisons and suggestions were made for the best analysis approach when using FEA techniques to predict the behavior of solder joints in PBGA packages.