Effect of Grain Boundary Misorientation on Electromigration in Lead-Free Solder Joints

Abstract

Reduction in microelectronic interconnect size gives rise to solder bumps consisting of few grains, approaching a single-or bicrystal grain morphology in C4 bumps. Single grain anisotropy, individual grain orientation, presence of easy diffusion paths along grain boundaries, and the increased current density in these small solder bumps aggravate electromigration. This reduces the reliability of the entire microelectronic system. This paper focuses on electromigration behavior in Pb-free solder, specifically the Sn-0.7 wt.%Cu alloy. We discuss the effects of texture, grain orientation, and grain boundary misorientation angle on electromigration (EM) and intermetallic compound formation in EM-tested C4 bumps. The detailed electron backscatter diffraction (EBSD) analysis used in this study reveals the greater influence of grain boundary misorientation on solder bump electromigration compared with the effect associated with individual grain orientation.

Effect of FeCoNiCrCu0.5 High-entropy-alloy Substrate on Sn Grain Size in Sn-3.0Ag-0.5Cu Solder

“…In recent studies, it was reported that coefficient of thermal expansion (CTE) mismatch between Sn grains caused crack propagation on grain boundaries 24 . Furthermore, Sn grain boundary, which was a channel for atomic diffusions, caused under-bump-metallization dissolution and serious major IMC formation in solder joints during electromigration 25 . Thus, the grain size distribution in a solder matrix on any substrate is critical.…”

Microstructure and Grain Orientation Evolution in SnPb/SnAgCu Interconnects Under Electrical Current Stressing at Cryogenic Temperature

“…The grain structure of the bump was transformed from β-Sn (tetrahedral structure) to α-Sn (face-centered cubic structure) after stressing at CT. The grain boundaries were high-energy storage regions in this polycrystalline bump, and the diffusion behavior of metal atoms in the face-centered cubic lattice performed isomorphism [36]. As a result, the Pb atoms of the bump gathered at grain boundaries by diffusing through the face-centered cubic lattices around the long grain boundary, and eventually formed the long-range distribution and accumulation of Pb elements shown in Figure 8c.…”

Suppressed Growth of (Fe, Cr, Co, Ni, Cu)Sn2 Intermetallic Compound at Interface between Sn-3.0Ag-0.5Cu Solder and FeCoNiCrCu0.5 Substrate during Solid-state Aging

“…Tasooji, et al . clearly showed that, because the diffusivity of Cu through the Sn grain boundary is much higher than that through the Sn lattice, significant atomic diffusion occurs through high-angle grain boundary during electromigration, causing considerable IMC formation in the solder and exhausting the substrate 13 . Conversely, Sn has an anisotropy coefficient of thermal expansion (CTE) caused by its body-center-tetragonal structure.…”