Abstract
Lead-free solder joints are the most widely used interconnects in electronic packaging industries. Usually solder joints in most of the electronic devices are exposed to an environment where variation of temperature exists, which indicates cyclic thermal loading to be a very common type of external loading. Moreover, due to difference in the coefficient of thermal expansion (CTE) among dissimilar contact materials, shear stress develops in junctions under thermal loading, which significantly deteriorates the overall reliability. Hence, characterization of lead-free solder materials under thermal loading is essential to predict the performance and deformation behavior of joints in practical applications. A significant portion of the studies in this field are concerned with thermal loading of lead-free solder interconnects, each of which has a very small diameter, in sub-millimeter range. Although the solder balls have very small dimensions, most of the analyses considered them as a bulk material with homogeneous and isotropic properties. However, with the decrease of specimen dimensions, size effects and material directionality play a significant role in deformation mechanisms. Since a very few grains exist in a small specimen, individual grain properties play a vital role on overall material response. Therefore, modeling from the grain structure and orientation point of view could be an effective and more accurate way to predict solder joint deformation behavior under thermal loading.
In this study, the effect of grain size and orientation of SAC305 is investigated for predicting anisotropic behavior of solder joints under thermal load. A simplified three-dimensional model of beach-ball configuration solder joint was generated and simulated using ABAQUS finite element (FE) software. Experimentally obtained directional properties such as elastic modulus and CTE were assigned to the computational geometry to create material anisotropy. The effects of material anisotropy were studied for varying grain size specimens, as well as for specimens with varying grain orientation.
