Dominant effect of high anisotropy in β-Sn grain on electromigration-induced failure mechanism in Sn-3.0Ag-0.5Cu interconnect

The effect of high diffusivity anisotropy in beta-Sn grain on electromigration behavior of micro-bumps was clearly demonstrated using Sn-3.0Ag-0.5Cu solder interconnects with only two beta-Sn grains. The orientation of beta-Sn grain (theta is defined as the angle between the c-axis of beta-Sn grain and the electron flow direction) is becoming the most crucial factor to dominate the different electromigration-induced failure modes: 1) the excessive dissolution of the cathode Cu, blocking at the grain boundary and massive precipitation of columnar Cu6Sn5 intermetallic compounds ( IMCs) in the small angle q beta-Sn grain occur when electrons flow from a small angle theta beta-Sn grain to a large one; 2) void formation and propagation occur at the cathode IMC/solder interface and no Cu6Sn5 IMCs precipitate within the large angle theta beta-Sn grain when electrons flow in the opposite direction. The EM-induced failure mechanism of the two beta-Sn grain solder interconnects is well explained in viewpoint of atomic diffusion flux in beta-Sn. (C) 2016 Elsevier B.V. All rights reserved.