Ternary Sn-3.5Ag-xFe solders with varying amount of Fe; 0.1, 0.5, 1.0, and 2.0 wt. % were reacted with Cu UBM which was electroplated using SPS additive and characteristics of Kirkendall void formation at the solder joints were investigated. Results indicate that the propensity to form Kirkendall voids at the solder joint decreased with the Fe content. It showed that Fe dissolved in the Cu UBM and reduced the segregation of S atoms to the Cu3Sn/Cu interface, which suppressed the nucleation of Kirkendall voids at the interface.

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