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Abstract: Anisotropic microstructure is becoming a critical issue in microbumps used in 3-D integrated circuit packaging. We report here an experimental approach for controlling the microstructure of η-Cu6Sn5 intermetallic compound in microbumps by using 〈111〉 oriented and nanotwinned Cu pads as the under-bump-metallization. By electroplating arrays of large numbers of 〈111〉 oriented and nanotwinned Cu pads and by electroplating the Sn2.3Ag solder on the pads, we form η-Cu6Sn5 in the reflow at 260°C for 1min. The η-Cu6Sn5 showed a highly preferential growth along the 〈0001〉 direction. As reflow time is extended, the preferred texture of η-Cu6Sn5 changed to { }. The results indicate that we can control the uniform microstructure of η-Cu6Sn5 intermetallic by controlling the microstructure of the Cu under-bump-metallization. [Copyright &y& Elsevier]