Fracture of SnBi/Ni(P) interfaces

Fracture resistance of the interface between electroless Ni(P) and the eutectic SnBi solder alloy was examined in the as-reflowed and aged conditions, to investigate the potential role of Ni in inhibiting interfacial segregation of Bi in SnBi–Cu interconnect. In the as-reflowed condition, the fracture resistance of the SnBi/Ni(P) interface was about the same as that of the SnBi/Cu interface. Upon aging at 120 °C for 7 days the fracture resistance of the SnBi/Ni(P) interface was much higher than that of the SnBi/Cu interface. Such a difference was shown to result from the difference in fracture mechanism as the crack remained along the solder–intermetallic interface in the aged SnBi–Ni interconnect but propagated along the intermetallic–substrate interface in the aged SnBi–Cu interconnect. While fracture of the intermetallic–substrate interface in SnBi–Cu interconnect was due to Bi segregation onto that interface, no Bi was detected at the intermetallic-substrate interface in SnBi–Ni interconnects, implying that Ni(P) was effective in inhibiting the interfacial segregation of Bi.