Grain Orientations And Anisotropic Properties Of Cu-Sn IMCs In Micro-Interconnection Solder Joints

Driven by the high-performance computing and the miniaturization of electronic devices, Through Silicon Vias (TSV) 3D packing technology becomes a key technology in chip interconnect. With the decreasing substrate size, the volume fraction of intermetallics (IMCs) in solder joints increased and grain number in the substrate decreased, which had an effect on the IMCs orientations in the interface. When the volume fraction of IMCs in the solder joints was high and the grains with certain orientations had a limited number, the property of solder joints would be affected dramatically. Hence it was of great significance to conduct in-depth investigation on the grain orientations of the IMCs in the solder joints both on polycrystalline copper and single crystalline copper.In this paper, the IMCs formed between Sn3.0Ag0.5Cu and Cu substrates were systematically investigated. Firstly,the morphologies of Cu₆Sn₅ grains formed between Sn3.0Ag0.5Cu and (001), (111) Cu single crystals, polycrystalline Cu under liquid-state conditions with different reflow temperatures, times, cooling rates and solid-state aging conditions with different aging times were systematically observed. The kinetics of Cu₆Sn₅ with different morphologies were also investigated. Furthermore, electron backscatter diffraction (EBSD) technology combined with orientation imaging microscopy (OIM) analysis method were employed to investigate the orientation relationships between Cu₆Sn₅ and Cu substrates. The Link between the morphologies and orientations of Cu₆Sn₅ was established. The formation mechanism of Cu₆Sn₅ with hollow structure was also elaborated. Finally, the elastic and plastic anisotropy of Cu₆Sn₅ were investigated by nanoindentation.The results showed that the morphologies of Cu₆Sn₅ were determined by the substrate orientations and process parameters. With the increasing of the reflow temperature, the morphology of Cu₆Sn₅ transforms from scallop-type to rooftop-type; the rooftop-type Cu₆Sn₅ grains formed on single crystal copper arranged regularly, the theory of adsorption of surface-active material can be used to explain the adsorption of Ag3Sn nano-particles on Cu–Sn intermetallic compounds;Cu₆Sn₅ grains on the polycrystalline copper substrates and the scallop-type Cu₆Sn₅ grains formed on the single crystalline copper under 250℃had a relationship that the angle between the {0001} planes and the Cu substrate plane was 30°～50°. The orientation relationships between Cu₆Sn₅ grains formed at 300℃and Cu single crystals were obtained as follows: {0001} planes of Cu₆Sn₅ were perpendicular to the Cu substrate, { 2110 } planes were parallel to the Cu substrate and the <0001> directions of Cu₆Sn₅ were parallel to the <110> directions of copper, these orientation relationships which were from the effects of aging,were caused by the decreasing the misfit between the IMCs and substrate。The formation mechanism of Cu₆Sn₅ with hollow structure could be explained by the Bravais Law. Elastic modulus of Cu₆Sn₅ single crystal has anisotropy, the elastic modulus on the <0001> directions was maximum; there were also plastic anisotropy of Cu₆Sn₅ existing on Cu substrates with different orientations. The average Schmid Factor of Cu₆Sn₅ grains on the (001) single crystalline copper had the strongest anisotropy property, while that of the polycrystalline copper had the weakest anisotropy.