Large-Scale Correlations in the Orientation of Grains in Lead-Free Solder Joints
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A large number of lead-free Sn-Ag-Cu controlled collapse chip connection (C4) solder joints (∼100 μm in diameter) in flip-chip microelectronic packages were studied by electron backscatter diffraction (EBSD) in order to describe the statistical distribution of grain size and coincident site lattice boundaries associated with 60 deg twins in the Sn phase, as a function of silver content. It is shown that lower silver content results in smaller grains, and a lower propensity for grains to exhibit twinning symmetries. Indirect measurements of the creep properties of these joints were also obtained as a function of silver content, showing that, in the strain rate and temperature conditions that are the most relevant to the microelectronic industry, solder joints with low silver content are more susceptible to creep deformation.