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

• High anisotropy in β-Sn dominates different electromigration-induced failure mode.
• Excessive dissolution of cathode Cu occurs if electrons flow in forward direction.
• Voids initiate and propagate at cathode if electrons flow in reverse direction.
• Failure modes are well explained in viewpoint of atomic diffusion flux in β-Sn.

The effect of high diffusivity anisotropy in β-Sn grain on electromigration behavior of micro-bumps was clearly demonstrated using Sn-3.0Ag-0.5Cu solder interconnects with only two β-Sn grains. The orientation of β-Sn grain (θ is defined as the angle between the c-axis of β-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 θ β-Sn grain occur when electrons flow from a small angle θ β-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 θ β-Sn grain when electrons flow in the opposite direction. The EM-induced failure mechanism of the two β-Sn grain solder interconnects is well explained in viewpoint of atomic diffusion flux in β-Sn.