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

Abstract

The orientations of Cu6Sn5 grains grown on (001), (011) and (301) Sn single crystals plated with Cu were investigated under electrical loading. After current stressing, anode Cu6Sn5 grains preferred the following orientation relationships with Sn: {-111}Sn//{01-10}Cu6Sn5, 〈0-11〉Sn//〈2-1-13〉Cu6Sn5. Four different Cu6Sn5 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 Cu6Sn5 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 Cu6Sn5 grains with a low angle between the coherent interfaces and the initial interface form preferentially during the electromigration process. In addition, cline Cu6Sn5 grain boundaries were observed. A thermodynamics model based on coherent interfacial energy was presented to explain the relations and the formation of cline Cu6Sn5 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.