Sn–8Zn–3Bi solder paste was applied as a medium to joint Sn–3.2Ag–0.5Cu solder balls and Au/Ni/Cu metallized ball grid array substrates at 210 °C. The spallation behavior of Ag–Au–Cu–Zn compound was studied as the Sn–Ag–Cu/Sn–Zn–Bi joints were reflowed respectively for 5, 20 and 30 s. After reflow for 5 s, the cracks were formed between Ag–Au–Cu–Zn compounds and Ni metallization. With further reflow time of 20 s, the cracks were propagated. The crack formation and propagation between Ag–Au–Cu–Zn compounds and Ni metallization, and the instability of Ag–Au–Cu–Zn IMCs at Ni layer might lead to Ag–Au–Cu–Zn compound spallation as the molten solder might flow to the gap zones, exerting a lifting force to the Ag–Au–Cu–Zn compounds during soldering. As a result, the reasons for the crack formation were discussed.