Electromigration of gold and silver in single crystal tin

doi:10.1016/0022-3697(87)90060-6

Journal of Physics and Chemistry of Solids

Volume 48, Issue 8, 1987, Pages 693-696

https://doi.org/10.1016/0022-3697(87)90060-6 Get rights and content

Abstract

Measurements of electromigration have been performed for gold and silver in single crystal tin. The electromigration measurements of Ag in single crystal Sn along the c-axis give for Z_Ag^∗ a value of around −2.15±0.25. The temperature dependence of Z^∗_Ag is small, but there is a large Soret effect which may account for the considerable irreproducibility evinced by earlier measurements of Z_a^∗ in this system. The electromigration studies of Au in Sn show that the orientation of Sn has little effect on the Z_a^∗ values. The Z_a^∗ parameters are around −9.5 ± 0.33. The temperature gradient across the sample has less influence than that in the electroinigration of Ag in Sn.

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The electromigration reliability of Au/Pd(P)/Ni(P) surface finish in micro joints was investigated in this study. We found that the reaction of Pd(P) with molten Sn would yield a noticeable amount of (Pd,Ni)Sn₄ intermetallic compound (IMC) scattering in the Sn matrix after soldering reaction. Interestingly, upon electron current stressing, (Pd,Ni)Sn₄ was gradually driven to the anode interface, and a remarkable volume expansion was caused by the transition from a low Ni-containing (Pd_0.22Ni_0.78)Sn₄ (17 μm on thickness) into a high Ni-containing (Pd_0.04Ni_0.96)Sn₄ (56 μm on thickness) because of the substitution of Pd sublattice by a high fraction of Ni as a result of electromigration. This electromigration-induced unusual stoichiometric transition and massive IMC propagation has been rarely reported previously in the literature. The underlying mechanism associated with the electromigration phenomenon and mitigation strategies to the NiSn₄ formation were proposed in this study.
Dominant effect of high anisotropy in β-Sn grain on electromigration-induced failure mechanism in Sn-3.0Ag-0.5Cu interconnect
2016, Journal of Alloys and Compounds
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.
Electromigration in 3D-IC scale Cu/Sn/Cu solder joints
2016, Journal of Alloys and Compounds
Citation Excerpt :
The solid Sn exists in the β-type at temperatures above 13.2 °C and possesses a body-centered tetragonal (BCT) structure (space group: I41/amd) with lattice constant of a = b = 5.83 Å and c = 3.18 Å [2]. This anisotropic structure can produce different characteristics in relation with its crystallographic orientation (e.g., resistivity [3,4] and diffusivity [3,5]), thereby dominating the physical/chemical properties of the entire solder joint. This is especially true for miniaturized solder joints, which contain a very limited amount of Sn grains and grain boundaries.
The electromigration effect on the three-dimensional integrated circuits (3D-IC) scale solder joints with a Cu/Sn(25–50 μm)/Cu configuration was investigated using a field-emission scanning electron microscope (FE–SEM) combined with electron backscatter diffraction (EBSD) analysis system. Electron current stressing for a few days caused the pronounced accumulation of Cu₆Sn₅ in specific Sn grain boundaries (GBs). The EBSD analysis indicated that both the β-Sn crystallographic orientation and GB orientation play dominant roles in this accumulation. The dependencies of the Cu₆Sn₅ accumulation on the two above factors (i.e., Sn grain orientation and GB orientation) can be well rationalized via a proposed mathematic model based on the Huntington and Grone's electromigration theory with the Cu anisotropic diffusion data in a β-Sn lattice.
Real-time X-ray microscopy study of electromigration in microelectronic solder joints
2016, Scripta Materialia
Electromigration (EM) in microelectronic solder joints was investigated via transmission X-ray microscopy (TXM) in conjunction with three-dimensional computed microtomography (3D μ-CT). This nondestructive analysis provided visualization of the EM dynamics in the encapsulated solder joints and showed the linear dependence of the Cu pad depletion on the current stressing time. Quantitative analysis of the interstitial Cu diffusion in β-Sn based on Huntington's EM theory offered rationalization of this EM-induced degradation mechanism.
Role of diffusion anisotropy in β-Sn in microstructural evolution of Sn-3.0Ag-0.5Cu flip chip bumps undergoing electromigration
2015, Acta Materialia
The anisotropy of β-Sn grain is becoming the most crucial factor to dominate the electromigration (EM) behavior with the downsizing of solder bumps. When the c-axis of β-Sn grain is parallel to the electron flow direction, excessive dissolution of cathode Cu occurs due to the large diffusivity of Cu along the c-axis; when the c-axis of β-Sn grain is perpendicular to the electron flow direction, limited dissolution of cathode Cu occurs even in the current crowding regions. However, there is no evident dissolution of cathode Ni regardless of the orientation of β-Sn grains, due to the protection of a stable interfacial (Cu,Ni)₆Sn₅ intermetallic compound (IMC) layer and the extremely low solubility of Ni in β-Sn. Cu₆Sn₅-type protrusions selectively precipitated in specific Sn grains with small angle θ (between the c-axis of Sn grain and electron flow direction) but not in the neighbor grains with large angle θ or along the direction of c-axis of β-Sn. Sn hillocks are squeezed out to relieve the compressive stress generated by the formation of Cu₆Sn₅-type IMCs. The high diffusion anisotropy in β-Sn grains, which is calculated by a proposed model, accounts for the novel diffusion behavior of solute atoms, dissolution of cathode and consequent precipitation of IMCs in Ni/Sn-3.0Ag-0.5Cu/Cu flip chip solder joints.
Electromigration in thin-film solder joints
2014, Surface and Coatings Technology
Citation Excerpt :
Solid Sn possesses a body-centered tetragonal (BCT) structure (space group: I41/amd) with a lattice constant of a = b = 5.83 Å and c = 3.18 Å at temperatures above 13 °C [2], which is generally termed β-Sn or white Sn. Unlike the face-centered cubic (fcc) crystal structure of Pb, the anisotropic β-Sn can produce different physical/chemical characteristics in relation with the individual crystal axis, e.g., Young's modulus [3], resistivity [4], and diffusivity [1,4,5]. In terms of anisotropic diffusion behavior, the Cu diffusivity is approximately 2 × 10− 6 cm2/s at 25 °C along the Sn c-axis, which is 500 times faster than that along the a- or b-axis [5] and is approximately 1012 times the Sn self-diffusion rate [5].
Intermetallic compound (IMC) formation and growth are critical reliability issues with interconnected microelectronics, especially for small-scale solder joints in three-dimensional integrated circuits (3D IC) packaging. In this study, the growth behavior of IMCs in ultrathin 3D-IC solder joints under electromigration was investigated using a field-emission scanning electron microscope (FE-SEM) equipped with an electron backscatter diffraction (EBSD) analysis system. The joints consisted of a Cu/Sn/Cu configuration with a Sn thickness of ~ 30 μm. We determined a strong dependence of the IMC growth and Cu pad depletion on the β-Sn orientation upon electron current stressing. When the c-axis of the Sn grain was oriented in the direction of the electron flow, aggressive CuSn IMC growth and Cu pad depletion occurred at the anode and cathode, respectively. A mathematical analysis based on crystallography and electromigration theory was used to rationalize the strong dependences that were observed.

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^†: Present address: Department of Physics, St. Lawrence University, Canton, NY 13617, U.S.A.

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Electromigration of gold and silver in single crystal tin

Abstract

J. Phys. Chem. Solids

J. Phys. Chem. Solids

J. Phys. Chem. Solids

Phys. Status Solidi A

Phys. Status Solidi A