Microstructure and chemistry of the SAC/ENIG interconnections

► Formation of 4 layers after interaction of SAC305 solder with ENIG substrate. ► Layers 1-3: NiP-amorphous (corresponding to initial Ni-P coating), Ni12P5, Ni2SnP. ► Layer 4: (Ni,Cu)3Sn4 decorated by (Cu,Ni)6Sn5 phase and also small particles of Ag4Sn. ► New evidences: Ni12P5 instead of Ni3P, Ni2SnP growth from Ni12P5 not from Ni2P.