Preferred orientation relationship between Cu_6Sn_5 scallop-type grains and Cu substrate in reactions between molten Sn-based solders and Cu

摘要

A strong crystallographic orientation relationship between the Cu_6Sn_5 scallop-type grains and their Cu substrate has been found by synchrotron micro-x-ray diffraction study. Even though the crystal structures of Cu_6Sn_5 (monoclinic) and Cu (face-centered-cubic) are very different, angular distributions of crystallographic directions between Cu_6Sn_5 and Cu revealed a strong orientation relationship. Both SnPb solder and pure Sn showed the same result, indicating that this is general behavior between Sn-based solders and Cu. The strong orientation relation suggests that Cu_6Sn_5 forms prior to Cu_3Sn in the wetting reactions. A total of six different orientation relationships were found. In all the cases, the [101] direction of Cu_6Sn_5 preferred to be parallel to the [110] direction of Cu with a misfit of 0.24%. Due to pseudohexagonal structure of the Cu_6Sn_5, the six relationships can be categorized into two groups. From the orientation distribution, one group was found to be less rigid then the other group.