Cu6Sn5 intermetallic compound anisotropy introduced by single crystal Sn under current stress

The orientations of Cu 6 Sn 5 grains grown on (001), (011) and (301) Sn single crystals plated with Cu were investigated under electrical loading. After current stressing, anode Cu 6 Sn 5 grains preferred the following orientation relationships with Sn: {-111} Sn //{01-10} Cu6Sn5 , 〈0-11〉 Sn //〈2-1-13〉 Cu6Sn5 . Four different Cu 6 Sn 5 orientations were found in anode of (001) Sn/Cu joints, where the coherent interface, {-111} Sn //{01-10} Cu6Sn5 , makes a 37.7° angle with the initial interface. Only two orientations were found in the (301) Sn/Cu joint, where the undiscovered orientations with coherent interfaces were nearly vertical to the initial interface. In (101) Sn/Cu joints, the Cu 6 Sn 5 grains with a 25.6° angle between coherent interfaces and the initial interface are much more numerous than with a high angle (60.8°). The results show that Cu 6 Sn 5 grains with a low angle between the coherent interfaces and the initial interface form preferentially during the electromigration process. In addition, cline Cu 6 Sn 5 grain boundaries were observed. A thermodynamics model based on coherent interfacial energy was presented to explain the relations and the formation of cline Cu 6 Sn 5 grain boundaries. It suggests that only when the angle between the coherent interface and the initial interface is lower than a threshold value will the relation form for the lower free energies.