Orientation transformation of Cu6Sn5 grains by Ag addition in Cu/Sn-xAg/Cu micro solder joints under temperature gradient

Cu6Sn5 intermetallic compound (IMC), which occupies most even full of solder joints bringing by the reduced size of interconnection and the multi-functional demand for devices, is a critical component contributing to the reliability of the electronic products. In this study, the orientation transformation of the cold end Cu6Sn5 grains in Cu/Sn-xAg/Cu micro solder joints under temperature gradient (TG) was investigated. It was found that the orientation transformation of the Cu6Sn5 grains significantly depended on the Ag content. With increasing Ag addition, the cold end Cu6Sn5 grains transformed from strong texture with [0001]//RD(TG) to weak texture with low Ag addition or no texture with high Ag addition. The results revealed that the Ag solid solution into the Cu6Sn5 phase and the Ag3Sn absorbates on the Cu6Sn5 grain surface or at the grain boundary contributed to the above orientation transformation. The combined effect of the Ag solid solution and Ag3Sn absorbates on orientation transformation was discussed from the viewpoints of the nucleation, growth and merging of Cu6Sn5 grains, which can provide guidelines for improving the reliability of micro joints for 3D packaging or high temperature applications. [GRAPHICAL ABSTRACT]