The Sn-58 Bi solder ribbon was prepared by the twin-roll rapid solidification technique

and the Cu/Sn-58 Bi/Cu linear solder joints were prepared.The interface IMC

element diffusion and microstructure evolution of solder joints were analyzed by EPMA and EDS after the current density of 1×10

4

A/cm

2

（25 ℃）.The results reveal that the morphology of the anode IMC layer is changed from scallop shape to zigzag shape

and the cathode IMC layer is changed from scallop shape to irregular one with the increase of thickness gradually.Bi is segregated toward the anode to form a Bi-rich layer

and Sn is segregated at the cathode.And the matrix eutectic structure（Bi+β-Sn）is coarsened.Based on linear fitting

the growth coefficient n of IMC layer of the anode and cathode are 0.263 and 0.442

respectively

and the growth mechanism is attributed to volume diffusion.