<p>The ultrathin-Ni(P)-type electroless nickel (Ni-P)/electroless palladium (Pd-P)/immersion gold (Au) (ENEPIG) surface finish coating over Cu circuits has recently received a great deal of attention from microelectronics and communications communities as it possesses good solderability and acceptable signal transmission characteristics. In this study, the electromigration reliability of ultrathin-Ni(P)-type ENEPIG surface finish in eutectic Sn-Cu (Sn-0.7Cu) micro-joints was systematically evaluated via ANSYS simulation and metallographic analysis. Experimentally, we investigated the transitions in crystallographic microstructure (grain orientation and grain size) and electrical resistance of Sn-0.7Cu joints with different surface finish combinations, including ultrathin-Ni(P)-type ENEPIG/Sn-0.7Cu/organic solderability preservative (OSP) (Case I), ultrathin-Ni(P)-type ENEPIG/Sn-0.7Cu/ultrathin-Ni(P)-type ENEPIG (Case II), and ultrathin-Ni(P)-type ENEPIG/Sn-0.7Cu/ENEPIG (Case III). The results showed that the utilization of ultrathin-Ni(P)-type ENEPIG surface finish in micro-joints can effectively reduce the Cu pad consumption in comparison with the OSP/Sn-0.7Cu/OSP joint structure, while retaining excellent electrical conductivity in comparison with the ENEPIG/Sn-0.7Cu/ENEPIG structure. The improvement in pad consumption strongly depends on the microstructure modifications of beta-Sn and interfacial intermetallic compounds (IMCs), which can improve the electromigration reliability of micro-joints.</p> Graphical Abstract <p></p>