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Solder Joint Thermal Fatigue Analysis of MCP
Keywords: MCP, solder joint reliability (SJR), thermal simulation
Solder joint reliability (SJR, lead free) is one of the major concerns for MCP product, the widely studied common failure mechanisms is low cycle thermal fatigue of solder joints. A three-dimensional finite element analysis model has been developed to study the solder joint reliability of MCP (133-FBGA) assembly during temperature cycle from -60¡ã degree to 150¡ã degree in this paper. According to widely accepted Darveaux¡¯ thermal fatigue theory, solder ball¡¯s lifetime is based on the solder crack, included crack initiation and crack growth, and can be predicted by the volume weighted average viscoplastic strain energy density. In this study, solder ball viscoplastic energy accumulated per temperature cycle from the simulation was applied to predict solder ball's lifetime in this FBGA product. Since solder is above half of its melting point at room temperature, solder ball creep behavior in the process are expected to dominate the deformation kinetics, so Anand model was selected to describe the 96.5Sn/3Ag/0.5Cu performance in Ansys material library. Because the macro/micro model is a good choice to consider the plastic deformation and to identify the most susceptible joint because of computation efficiency, to achieve accurate analysis, temperature change was loaded on the whole MCP model (the global model) firstly. After displacements gotten from the simulation result, the boundary interpolation was made on the corresponding nodes in the solder ball (the local model). Simulation can continue considering of more complicated solder joint structure in the local model, such as solder mask and Cu pattern. Finally plastic energy was calculated from the local model to predict the fatigue life time. From the experiment result, it shows that solder crack always extends along the area which IMC concentrates on the top side. Since the computed results were compared with experimental data, the simulation results were reliable. OSP finish/Nickel Au finish, were set up in the modeling respectively in this paper. The viscoplasic energy accumulated per cycle lead to different fatigue lifetime, according to the simulation and experimental result, Ni/Au pad finish has longer lifetime due to stronger structure.
Kelvin Chen, Engineer
Samsung Semiconductor (China) R&D Center
Suzhou, Jiangsu 215021,
P. R. China

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