The interfacial reaction of Cu/Sn/Cu micro-solder joints aged for 0 h（post-weld state）and 400 hat 110℃ was investigated by means of electron backscatter diffraction（EBSD）.The results show that the microstructure of Cu/Sn/Cu micro-solder joint after interfacial reaction is composed of Cu

6

Sn

5

Cu

3

Sn and beta-Sn.After400 hisothermal aging

a large amount of beta-Sn is consumed.The morphology of Cu

6

Sn

5

is changed from scallop-like to polygon-like

and Cu

3

Sn still keep long strip-like structure.For orientation

the preferred orientation of Cu

6

Sn

5

（0001）surface is present after 400 hisothermal aging and

<

0001

>

crystal direction is parallel to RD direction.The interfacial type of Cu

6

Sn

5

after 400 haging was analyzed.The orientation difference angle is about 53°

45°

36°

presenting large angle grain boundaries.The analysis of microstructure and grain orientation shows that isothermal aging has a little effect on the orientation of microstructures morphology of solder joints

however it will affect greatly the transformation and growth of microstructures.