Reliability of SnAgCu solder balls in packaging

SnAgCu ternary alloy is a commonly used lead-free alternative for SnPb solder. However, subjects regarding its thermo-mechanical response, microstructural evolution, material degradation and deformation mechanisms need further investigation. In BGA solder balls it is seen that deformation and damage propagation is strongly dependent on the microstructure in bulk as well as the bump/pad interfaces. The initial microstructure and material properties are collected through E-SEM observations and nano-indentation experiments. Critical interfaces under certain loading conditions are evaluated by inspecting fracture surfaces of SnAgCu solder paste reflowed on different substrates. These experimental results are supported by thermal cycling of commercial BGA packages with SnAgCu solder balls. A finite element model of a SnAgCu solder ball with Cu/Ni/Au metallization is made in 2-D. A cycling mechanical load is applied. Important microstructural constituents are also placed in the finite element model, and interfacial failure is analyzed using a cohesive zone model.