Spallation of interfacial Ag-Au-Cu-Zn compounds in Sn-Ag-Cu/Sn-Zn-Bi joints during 210 °C reflow

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.