Micromechanical Modeling of SAC305: Homogenization and Effect of IMC Particles on Deformation Behavior

Lead-free solder joints are the most extensively used interconnects in electronic packaging industries. Most of the lead-free solder alloys (SAC) are composed of β-Sn, Ag, and Cu. To fabricate final products, SAC alloys undergo thermomechanical processes that result formation of intermetallic (IMC) compounds. The predominant intermetallic particles are Ag3Sn and Cu6Sn5, which are embedded in Sn matrix. The effects of IMC particles are very significant because they have very different crystal configurations with different anisotropic mechanical and thermal properties, compared to Sn matrix. Therefore, it is necessary to quantify the influence of intermetallics and tin matrix on overall properties of solder alloys. The outcome will lead to more accurate prediction of performance and deformation behavior of solder joints under various loading conditions in practical applications.The objective of this study is to develop a micromechanical model, that takes inputs pertaining to individual constituents' mechanical properties and volume fractions to produce outputs in the form of effective properties of bulk solder. Studies show that IMC particles work as reinforcement agents to strengthen the overall mechanical behavior. In this study, elastic moduli (E's) of Sn and Ag3Sn are calculated from stiffness matrix. Then a representative volume element (RVE) is considered which contains all of the constituents according to their volume fractions. Size, shape and volume fractions of IMCs are determined from Scanning Electron Microscope - Focused Ion Beam (SEM-FIB) technology. Effective properties of RVE are calculated using periodic boundary conditions (PBCs) in ABAQUS. Finally, a model of tensile specimens is developed in ABAQUS finite element software with effective mechanical properties, and a correlation is established between numerical predictions and experimental results.