Abnormal spalling phenomena in the Sn-0.7Cu/Au/Ni/SUS304 interfacial reactions

The interfacial reactions in Sn-0.7wt%Cu/ENIG SUS304 couples at 240, 255, and 270 °C are examined in this study. The Ni-containing ternary Cu₆Sn₅ phase is formed at the Ni/liquid interface in the early reaction stage then it detaches massively from the SUS304 substrate and splits into two layers in the molten solder as the reaction time increases. This phase finally disintegrates and disappears. The square pillar-shaped FeSn₂ phase is found on top of the SUS304 substrate when the Cu₆Sn₅ layer detaches. The reaction phase formation, detachment, and split mechanisms are proposed. The spalling phenomenon is reviewed and discussed. The growth mechanism of the FeSn₂ phase obeys the parabolic law, and the activation energy is determined to be 112.5 KJ/mol.