Microstructure and chemistry of the SAC/ENIG interconnections

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, Ni12P5 and Ni2SnP. The discontinuous Ni2SnP layer at SAC/ENIG interface was composed of fine crystalline particles. The last layer was formed mainly of (Ni,Cu)3Sn4 with some amount of (Cu,Ni)6Sn5 and Ag4Sn phases. The voids observed in the NiP-amorphous layer after processing can be considered as the potential source of the “black pad” failure.