Interfacial reactions and formation of intermetallic compound of Sn-ball/Sn-3.0Ag-0.5Cu-paste/Cu joints in flip-chip on BGA packaging

The interfacial reactions and formation of intermetallic compound of Sn-ball/Sn-3.0Ag-0.5Cu-paste/Cu joints in flip-chip on BGA packaging were studied by using a differential scanning calorimeter. Results show that a thin circular Cu6Sn5 layer forms first on the surface of Cu substrate due to the diffusion of Sn atoms dissolved in the soldering flux, subsequently the planar-like Cu6Sn5 layer forms and covers over the first layer, and many Ag3Sn particles form in the grain boundaries of Cu6Sn5. Then, a slight increase of the soldering temperature from 217°C to 218°C has a significant influence on the morphologies of the interfacial Cu6Sn5 and Ag3Sn, that is, the morphologies of Cu6Sn5 and Ag3Sn are changed into scallop-like and large plate-like, respectively. When the soldering temperature is increased to 221°C, a large amount of plate-like Ag3Sn phase dissolves into the molten solder and the small network-like Ag3Sn phase forms, and the grain size of Cu6Sn5 is increased. Furthermore, there is almost no trace of Ag3Sn at the interface layer of Cu6Sn5 at the soldering temperature of 227°C. The morphology changes of the interfacial Cu6Sn5 and Ag3Sn are attributed to the increase of interfacial energy and the eutectic reaction between Sn and Ag in the solder matrix, respectively.