The microstructure and chemistry of the interface between SAC305 solder and electroless Ni–P coating (ENIG) was examined using scanning and transmission electron microscope equipped with an energy dispersive X-ray spectrometer. Four layers have been distinguished after 5 min of interaction at 503 K. There were: NiP-amorphous layer corresponding to Ni–P coating, Ni 12 P 5 and Ni 2 SnP. The discontinuous Ni 2 SnP layer at SAC/ENIG interface was composed of fine crystalline particles. The last layer was formed mainly of (Ni,Cu) 3 Sn 4 with some amount of (Cu,Ni) 6 Sn 5 and Ag 4 Sn phases. The voids observed in the NiP-amorphous layer after processing can be considered as the potential source of the “black pad” failure.