In this paper, a microstructure-dependent creep model is developed that accounts for the hierarchal microstructure at multiple length scales. The model considers three distinguishable phases in the solder alloy at two different length scales: at the larger scale Sn dendrites of micrometer size are embedded in a homogeneous eutectic phase; at a much smaller length scale the eutectic phase consists of sub-micron size Ag_3Sn particles embedded in a homogeneous Sn matrix. The model predictions agree well with creep test data of RE doped SnAg solders.
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