Microstructure Characterization of Cu₆Sn₅-based Intermetallic Compounds at Solder Matrix and Relevant Solder Joints

The microstructures of intermetallic compounds at the interface and dispersed in the solder matrix were characterized in this paper. Two sorts of solders, Sn3.5Ag and Sn3.5Ag0.3Co were selected to examine the interfacial reaction with the Cu substrate. In the Sn3.5Ag0.3Co solder matrix, the ternary Sn-Cu-Co IMC was detected, which indicated that the additives exhibit high affinity with the Sn atoms. The IMC composition on the solder side is almost the same as the ones distributed within the solder matrix, which means that the formation of IMC at this side is related closely to the solder microstructure. On the other hand, much lower additive concentrations were observed on the Cu side (or Cu₃Sn phase after aging). The non-homogeneous characteristic of IMC was suggested owing to the non-uniform concentration distribution of additives, that is, the IMCs morphology at the interface seemed quite different. The faceted and elongated shape was observed at the solder side, while the nearly rounded shape seen at the Cu side