Reliability of In-48Sn solder/Au/Ni/Cu BGA packages during reflow process

The interfacial reactions and shear properties of In-48wt.%Sn/Au/Ni/Cu solder joints were investigated in terms of reflow conditions, i.e., reflow temperature and duration time. The thickness of an AuIn2 intermetallic compound (IMC) layer, formed at the solder/substrate interface, slightly increased with the duration time. The spalling of the AuIn2 intermetallics in the solder led to the formation of a Ni3(Sn,In)4 IMC layer between the solder and exposed Ni layer. The longer duration time resulted in the spalling and grain growth of Ni3(Sn,In)4 intermetallics. The higher reflow temperature accelerated the interfacial reactions between the solder and substrate. From the ball shear test results, the formation and growth of a continuous plate-shaped AuIn2 IMC layer increased the shear force of the solder joints, whereas the spalling and grain growth of cubic-shaped AuIn2 intermetallics significantly decreased the shear force. The formation and spalling of cubic-shaped Ni3(Sn,In)4 intermetallics increased the shear force, whereas the spalling and grain growth of polyhedron-shaped Ni3(Sn,In)4 intermetallics decreased the shear force. The crack propagated at the Au-rich/AuIn2/solder interface in the initial reflow stage, then toward the AuIn2 intermetallics dispersed in the solder matrix, and finally along the Ni3(Sn,In)4 intermetallics spalling off in the solder.