Effects of reflow and cooling conditions on interfacial reaction and IMC morphology of Sn-Cu/Ni solder joint

The interfacial reaction and morphology change of intermetallic compound (IMC) between eutectic Sn-Cu solder and Ni substrate under various reflow and cooling conditions were investigated. The reaction between the solder and Ni layer resulted in the formation of (Cu,Ni)6Sn5 IMC at the interface. Reflow and cooling conditions changed the morphology of the IMCs formed at the interface. At low temperatures (≤255 °C), only a needle-type (Cu,Ni)6Sn5 IMC with a hexagonal cross-section was formed. On the other hand, the morphology of the (Cu,Ni)6Sn5 IMC changed from needle-type to dodecahedron-type with increasing reflow temperature and time. The morphology of the (Cu,Ni)6Sn5 IMC was also affected by cooling condition. Even though the morphology of the IMC changed with the reflow and cooling conditions, these IMCs had a similar chemical composition.