Development of growth model on interfacial intermetallic compound at circular Cu/Sn3.5Ag interface

The growth model of the interfacial Cu₆Sn₅ compound at the circular Cu/Sn3.5Ag interface has been established in this work. The present developed growth model can predict well the interfacial Cu₆Sn₅ compound growth curve at the circular-interface. We found that the interfacial Cu₆Sn₅ compound growth rate at the circular-interface is slower than that at the planar-interface. The major factor for the slower interfacial Cu₆Sn₅ compound growth rate at the circular-interface attributes to the increase of the interfacial reaction area at the circular Cu₆Sn₅/solder interface with the annealing time. It causes a larger driving force for the interfacial Cu₆Sn₅ compound to dissolve into the solder matrix, which reduces the growth of the interfacial Cu₆Sn₅ compound layer. Moreover, the effect of the Ag concentration on the reaction mechanism for the circular reaction interface was also studied. For the Ag-rich Sn5Ag solder matrix, smaller Sn grain size (larger grain boundary density) was observed. The larger grain boundary density promotes more Cu dissolution from the interfacial Cu₆Sn₅ compound layer into the Sn5Ag solder matrix. Hence, the growth of the interfacial Cu₆Sn₅ compound layer in the Ag-rich Sn5Ag system is slightly slower than that of the Sn3.5Ag system.