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 degrees 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.