Sn-1.0 Ag-0.5 Cu-0.06 Sm lead-free composite solders were prepared by mechanically mixing method. The effects of creep on the matrix microstructure and interface morphology as well as mechanical properties of Cu/Sn-1.0 Ag-0.5 Cu-0.06 Sm/Cu solder joints were investigated by SEM

EDS and bond strength tester. The results reveal that under the action of long-term high temperature creep

Ag

3

Sn and Cu

6

Sn

5

phases can be continuously precipitated in the matrix structure of the solder joints

which is merged

grown and aggregated. The morphology of the IMC layer continuously is grown from a scallop shape in the reflow state to a relatively flat and thick layer

and transformed from Cu

6

Sn

5

single phase to two phases of Cu

6

Sn

5

and Cu

3

Sn

resulting in decrease of 21.3% in the tensile strength of the solder joint compared with that of the reflux state.