Interfacial reaction between molten Sn-Bi based solders and electroless Ni-P coatings for liquid solder interconnects

This paper reports on the interfacial reactions and lifetime of electroless Ni-P coatings in contact with molten Sn-Bi based solders. A layer of approximately 4 m thick electroless Ni-P in contact with the molten Sn-58Bi solder began to fail at 48 h at temperatures between 200 C and 240 C. Elemental additions to modify the solder, included 1–2wt.% of Al, Cr, Si, Zn, Ag, Au, Ru, Ti, Pt, Nb, and Cu. Of these, only Cu modified the interfacial intermetallic compound growth from Ni3Sn4 to (Cu,Ni)6Sn5, resulting in significantly decreased consumption rates of the Ni-P substrate in contact with the molten solder and increasing the lifetime of the Ni-P layer to between 430 and 716 h. Micro cracks were observed in all but the thinnest Ni-P layers, allowing the solder to penetrate.