Sn Intermetallics Research Articles

Indentation size effect and micromechanics characterization of intermetallic compounds in the Au–Sn system

The indentation size effect and the micromechanics characterization of intermetallic compounds in the Au–Sn system have been investigated by nanoindentation, using continuous multi-cycle loading mode and load-control mode, respectively. An analytic model based on the enlarged plastic zone and the maximum allowable density of geometrically necessary dislocation was established to describe the relationship between the indentation hardness and depth. Our new model gives better predictions of the indentation hardness of Au5Sn, AuSn and AuSn2 for small indentation depths compared to the Nix–Gao model. Pop-in events in the load–displacement curves corresponding to the peaks in the normalized velocity–load curves represent the elastic–plastic or harden-yield transition during indentation. A viscoplastic creep equation was employed to evaluate the creep behavior of the Au–Sn intermetallics. The stress exponents (n) can be well defined into two stress regimes: the high stress regime (HSR) and the low stress regime (LSR). In the HSR, dislocation motion is the dominant creep mechanism with n>5, while in the LSR, grain boundary sliding dominates the creep of Au5Sn and AuSn2 with n≈2, and dislocation viscous glide dominates the creep of AuSn and AuSn4 with n around 3.

Electronic and magnetic structures and bonding properties of Ce2T2X (T = nd element; X = Mg, Cd, Pb or Sn) intermetallics from first principles

The electronic structure and chemical bonding properties of four families of Ce2T2X (T = nd element; X = Mg, Cd, Pb or Sn) intermetallics crystallizing in an ordered U3Si2 type structure are shown from density functional theory (DFT) calculations to present electronic and magnetic structure properties arising from their peculiar valence electron count (VEC). Trends of the magnetism are discussed in terms of the characteristics of the Ce(4f) states as well as the energetic position of the transition metal element d states.

Ab initio study of the cohesive properties, electronic structure and thermodynamic stability of the Ni–In and Ni–Sn intermetallics

A comprehensive study of the structural, cohesive and electronic properties of several stable, metastable and non-stable intermetallic phases (IPs) of the Ni–In and Ni–Sn systems have been performed by ab initio density-funcional-theory (DFT) methods. Using the projector augmented wave method we have performed systematic spin polarized calculations with the exchange and correlation functions of Perdew and Wang in the generalized gradient approximation (GGA), as well as those by Ceperley and Alder in the local-density-approximation (LDA). Structural properties, the energy-of-formation (EOF) from the elements and the cohesive properties of the various phases have been established by minimizing the internal structural parameters. We present trends at 0 K in the composition dependence of the molar volumen, bulk modulus and its pressure derivative, electronic density of states, magnetic moments and the EOF of several stable and metastable IPs reported in the Ni–In and Ni–Sn systems as well as various non-stable (hypothetical) compounds which are relevant in connection with the thermodynamic analysis of the Ni–In and Ni–Sn systems using Gibbs energy models and the so-called CALPHAD techniques. The results are compared with the available experimental data and with previously reported theoretical results. The present study of the thermodynamic and cohesive properties of Ni–In/Sn intermetallic phases should contribute to the understanding of the phase-stability systematics in the Ni–In–Sn system and the design of new soldering alloys.

Lithiation behavior of single-phase Cu–Sn intermetallics and effects on their negative-electrode properties

Single-phase Cu–Sn intermetallics were used to investigate their phase transformations during lithiation/delithiation, together with their negative-electrode properties. The stoichiometric Cu–Sn samples were prepared as thermodynamically warranted phases using a reduction-diffusion method with controlled potentials. Potentiostatic lithiation tests suggested that Cu3Sn directly changes into LixSn, while Cu6Sn5 becomes Li2CuSn before LixSn forms. We also revealed that separation from Li2CuSn into Cu and LixSn occurs at +0.11 to +0.10V vs. Li. Additionally, charging/discharging tests with cutoff potentials of +1.5V to +0.11V showed better cycling performance than that with +1.5V to +0.00V, probably due to the suppression of LixSn formation. Such a tendency can be expected in other Cu6Sn5 electrode materials.

Corrosion characterization of Cu–Sn intermetallics in 3.5 wt.% NaCl solution

The corrosion behavior of Cu–Sn intermetallics was investigated in 3.5wt.% NaCl solutions and compared to that of Cu and Sn by using galvanic corrosion and polarization methods. Polarization curves showed that an increase in the Cu content increased the corrosion current density and shifted both corrosion potential and breakdown potential towards more noble values. The corrosion products on the surface of Sn, Cu and Cu3Sn were Sn3O(OH)2Cl2, CuCl, and co-existing phases CuCl and Sn3O(OH)2Cl2, respectively. In addition, the SnO2, Sn3O(OH)2Cl2, Cu2O, and CuCl2·3Cu(OH)2 were observed in the Cu6Sn5 phase.

Magnetic and structural properties of Pd–Mn–Sn intermetallics compounds

Magnetic and structural properties of Heusler Pd0.5Mn0.5- x Sn x with x = 0.05, 0.10, 0.17, 0.20 and 0.25, have been studied by magnetisation and X-ray diffraction measurements at room and low temperatures. The crystal structure at room temperature is L21 cubic phase for x = 0.17, 0.20, 0.25 and B2 cubic phase for x = 0.10. Martensite structure 10M, was observed at room temperature for x = 0.05. X-ray measurements at low temperatures revealed a structural transformation from B2 to 14M for the x = 0.10 case. The lattice parameter of the L21 phase decreases linearly with the concentration, x. A ferromagnetic behaviour has been detected for L21 compounds, but the ferromagnetic exchange characteristic of each composition is of different strength. This gives rise to different Curie temperatures.

Thermo-electrochemical activation of Cu 3Sn negative electrode for lithium-ion batteries

A Cu 3Sn film electrode (thickness = ca. 3 μm) is prepared by DC magnetron sputtering deposition of Sn on Cu substrate and subsequent annealing at 300 °C for 30 h. At 25 °C, this Cu–Sn binary intermetallic compound is inactive for lithiation, but becomes active at elevated temperatures due to facilitation of Cu–Sn bond cleavage for the conversion-type lithiation. The lithiated product at 120 °C is the most Li-rich Li–Sn alloy (Li 17Sn 4). Upon de-lithiation, the Cu–Sn intermetallics of different compositions are generated by the reaction between the metallic Sn that is restored from Li 17Sn 4 and the idling metallic Cu. The nature of the resulting intermetallics is dependent on the de-lithiation temperature: Cu 10Sn 3 at 120 °C and Cu 6Sn 5 at 25 °C. Only the latter is active for lithiation in the subsequent room-temperature cycling. That is, Cu 3Sn is thermo-electrochemically activated to be Cu 6Sn 5 by lithiation at 120 °C and subsequent de-lithiation at 25 °C. The higher lithiation activity observed with the more Sn-rich phase (Cu 6Sn 5) compared to the initial one (Cu 3Sn) has been accounted for by the higher equilibrium lithiation potential (thermodynamic consideration) and smaller number of Cu–Sn bonds to be broken (kinetic consideration).

Congenerous and heterogeneous brazing of porous FeAl intermetallics

Congenerous and heterogeneous brazing of porous FeAl intermetallics has been successfully realised using Cu–10Sn green compact as brazing filler. Cu–Sn intermetallic phases combined with (Cu,Sn) solid solution were formed in the brazing line for congenerous brazing, while (Cu,Sn) solid solution was the main phase formed for heterogeneous brazing. Maximum tensile strengths for congenerous and heterogeneous brazing are 75·0 and 83·9 MPa which are about 81·5 and 91·2% of that of porous FeAl alloy (∼92·0 Mpa) respectively. The interface structure of the stainless steel and porous FeAl joint brazed at 940°C for 15 min is S–S+(Cu,Sn)/(Cu,Sn)/Cu9Al4+(Cu,Fe)+(Cu,Sn)/AlFe3+Al4Cu9+(Cu,Sn). In the porous FeAl and porous FeAl joint brazed with Cu–10Sn filler at 940°C, Cu–Sn intermetallics and (Cu,Sn) solid solution were the main phases in the joint line.

Effects of Zn-Containing Flux on Sn-3.5Ag Soldering with an Electroless Ni-P/Au Surface Finish: Microstructure and Wettability

The microstructure resulting from Sn-3.5Ag soldering on an electroless Ni-P/Au pad using flux containing Zn(II) stearate was investigated. The content of zinc compound in the flux was 0 wt.% (Z-0), 20 wt.% (Z-20) or 50 wt.% (Z-50). A study of the interfacial microstructure revealed that both Z-20 and Z-50 fluxes yielded a thinner P-rich layer at the interface than did the Z-0 flux. In addition, compared with the bulky Ni–Sn intermetallics of the Z-0 joint interface, refined interfacial intermetallic compounds (IMCs) were observed when using Zn-containing fluxes, Z-20 and Z-50. Based on qualitative analyses of both Z-20 and Z-50 joint interfaces, it was presumed that their intermetallic layers would consist of Ni, Zn, and Sn. Additionally, the Ni content in the IMC layer of the Z-50 joint was lower than that of the Z-20 joint. Electron probe microanalysis (EPMA) of the initial Z-50 joint interface revealed Zn in the interfacial reaction layer, suggesting that Zn participated in the reaction between solder and the surface finish at an early stage of soldering. Consequently, the supply of Zn from the flux diminished Ni diffusion into the molten solder during heating. This effect may have caused a thin P-rich layer to form at the joint interface.

Interfacial microstructure and bonding strength of Sn–3Ag–0.5Cu and Sn–3Ag–0.5Cu–0.5Ce– xZn solder BGA packages with immersion Ag surface finish

Although it has been verified that tin whiskers can be prevented by the addition of 0.5 wt.% Zn into a Sn–3Ag–0.5Cu–0.5Ce solder, no detailed studies have been conducted on interfacial reactions and mechanical properties of Sn–3Ag–0.5Cu–0.5Ce– xZn solder joints with an immersion Ag surface finish. The intermetallic compounds formed during the reflow and aging of Sn–3Ag–0.5Cu and Sn–3Ag–0.5Cu–0.5Ce– xZn solder ball grid array (BGA) packages were investigated. Because more heterogeneous nucleation sites, provided by CeSn 3 intermetallics and Zn atoms, formed in the Sn–3Ag–0.5Cu–0.5Ce– xZn solder matrix, and Cu and Zn have a stronger affinity than Cu and Sn, the Cu–Sn intermetallics growth in Sn–3Ag–0.5Cu–0.5Ce– xZn solder joints with Ag/Cu pads was suppressed. The 0.2% Zn addition for inhibiting rapid whisker growth in RE-doped Sn–Ag–Cu solder joints is more appropriate than 0.5 wt.% additions, as excess Zn addition causes poor oxidation resistance and inferior bonding strength.

Electromigration in WLCSP solder bumps

Electromigration in two different bumping technologies for WLCSPs has been investigated. The UBM and the structure of the pads on the PCBs were found to have a major influence on the failure mode. A Ni metallization layer serving as a diffusion barrier drastically reduces the intermetallic growth in the solder ball compared to samples assembled on Cu-OSP pads. In the former the principal failure mode is electrical open due to voiding at the Ni–solder interface. In the latter Cu diffuses into the solder at a high rate creating Cu–Sn intermetallics and eventually leading to an electrical open in the Cu track on the PCB being the principal failure mode. Additional experiments showed that the lifetime of the Cu-OSP mounted samples can be extended by using via-in-pad structures.

Nanoindentation of rare earth–Sn intermetallics in Pb-free solders

Incorporating rare earth (RE) elements into Sn-rich solder often results in the formation of RE–Sn intermetallics, which affect the deformation behavior of the solder. Little information is available on these constituent phases, and even less on their mechanical properties. In this paper, we report on Young's modulus and hardness of LaSn 3, CeSn 3 and YSn 3 intermetallic compounds formed in a Sn–Ag–Cu–2RE alloy, determined using nanoindentation. Nanoindentation on pure Sn was also performed for comparison. The Continuous Stiffness Method (CSM) was used during indentation to obtain the instantaneous Young's modulus as a function of depth. Scanning electron microscopy (SEM) was used to analyze the indentations after testing. The measured values of Young's modulus for LaSn 3, CeSn 3 and YSn 3 were 64 ± 3, 69 ± 3 and 98 ± 4 GPa, respectively. Values of hardness for LaSn 3, CeSn 3 and YSn 3 were 1.04 ± 0.16, 1.03 ± 0.03 and 3.47 ± 0.27, respectively. Comparison of these values with limited data in the literature was conducted and is discussed.

Morphology and chemical composition of Ag/Sn/Ag interconnections

The main goal of the present contribution was to describe morphology and chemical composition of the intermetallic phases, which were formed during diffusion soldering process of the silver using tin. The Ag(3)Sn intermetallics is the main constituent of the joint after diffusion soldering at 235 degrees C and 265 degrees C. A closer inspection of the Ag/Ag(3)Sn interface revealed also the small crystallites of the second intermetallic phase, Ag(5)Sn, which was not previously observed using scanning electron microscope. Both phases are characterized by high melting temperatures: 480 degrees C and 724 degrees C, respectively. Therefore, their presence guarantees high thermal stability of the interconnection, which can be even three times higher than the temperature used for soldering.

Effect of casting methods on the structure and properties of tin babbit

Dependence of the properties of babbit of grade B83 on the structure formed due to different methods of casting is determined. A novel advanced method of centrifugal casting of babbit B83 is suggested, which ensures crystallization of SnSb and Cu 3 Sn intermetallics from a turbulently moving melt. This not only removes segregation but also transfers the acute-angle SnSb intermetallic into a globular form.

Structural, elastic and electronic properties of intermetallics in the Pt–Sn system: A density functional investigation

Abstract The structural, elastic and electronic properties of intermetallics in the Pt–Sn binary system are investigated using first-principles calculations based on density functional theory (DFT). The polycrystalline elastic properties are deduced from the calculated single-crystal elastic constants. The elastic anisotropy of these intermetallics is analyzed based on the directional dependence of the Young’s modulus and its origin explained based on the electronic nature of the crystals. All the Pt–Sn intermetallics investigated are found to be mechanically stable, ductile and metallic, and some of them show high elastic anisotropy.

First-principles calculations on the electronic structure and cohesive properties of titanium stannides

First-principles calculations based on the density-functional theory were employed to investigate the electronic structure and cohesive properties of Ti–Sn alloys. Based on the calculated results, the lattice constants, bulk modulus and formation energies for the Ti–Sn intermetallics were compared with previous experimental and theoretical investigations. It was demonstrated that in term of the means volume and cohesive properties, the structure stability of Ti–Sn intermetallics increased with decreasing Ti composition, which was also supported by the analysis of densities of states. Furthermore, it was found that the difference in stability between the Ti–Sn intermetallics could be attributed to the bonding electron numbers at the upper region of the valence-band complex, which was cut by Fermi level. In addition, the electronic structure of the Ti–Sn intermetallics also showed a strong hybridization between Ti 3d and Sn 5p states, which played a dominant role in the bonding mechanism of Ti 3Sn and Ti 2Sn.

Phase stability and cohesive properties of Au–Sn intermetallics: A first-principles study

The total energies and cohesive properties of 29 Au–Sn intermetallics (stable, metastable, and virtual) are calculated from first-principles density-functional theory (DFT) employing ultrasoft pseudopotentials (USPP) and both local-density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation functional. Among the intermetallics considered, the ground-state structures are found to be AuSn, AuSn2, and AuSn4. Another phase Au5Sn, though present in the equilibrium diagram, lies slightly above the ground state convex hull. The formation energies of stable phases calculated using USPP–LDA and USPP–GGA are nearly the same. Except for AuSn, calorimetric data for enthalpies of formation show a good agreement with the calculated formation energies. Based on our first-principles results, it is argued that the structures of two metastable phases arecP52-type γ brass (isotypic with Al4Cu9) at Au–20.5 at.% Sn andhP1-type γ (isotypic with HgSn6–10) at Sn–8 at.% Au. For the intermetallics considered in this study, we provide optimized values of lattice parameters and Wyckoff positions. The experimental lattice parameters show a better agreement with those calculated using USPP–LDA than with USPP–GGA. The results presented here form the basis for creating a reliable thermodynamic database to facilitate calculations of stable and metastable phase diagrams of binary and multicomponent systems containing Au and Sn, relevant to electronic packaging and many other joining applications.

Characterization of Co–Sn intermetallic compounds in Sn–3.0Ag–0.5Cu–0.5Co lead-free solder alloy

The minor addition of Co into Sn–3.0Ag–0.5Cu lead-free solder alloy triggered the formation of Co–Sn intermetallic compounds. The Sn–3.0Ag–0.5Cu–0.5Co solder alloy was heated up to 300 °C or 400 °C and then cooled down to the room temperature at different rates. A new Co–Sn intermetallic phase, say, CoSn 3 containing small amount of Cu, were detected. Only CoSn 3 phase was formed in the solder alloy from 300 °C regardless of the cooling rate. However, during the solidification from 400 °C, the CoSn 2 + CoSn 3 cascade structures were illustrated after slow furnace cooling due to the peritectical reaction, i.e., CoSn 2 + L(Sn) → CoSn 3, while only CoSn 2 was observed after rapid quench. A novel DSC technique was employed herein to demonstrate the presence of this peritectical reaction. The mechanical properties of the individual phases of Co–Sn intermetallics were measured and compared with other sole phases in the solder alloy.

Magnetic properties and electronic structure of R 3T 4X 4 compounds (R = Pr, Nd; T = Cu, Ag; X = Ge, Sn)

Polycrystalline samples of R 3T 4X 4 (R = Pr, Nd; T = Cu, Ag; X = Ge, Sn) intermetallics were investigated by means of magnetometric and XPS methods. All these compounds crystallize in the orthorhombic Gd 3Cu 4Ge 4-type structure. They were found to be antiferromagnets, except Pr 3Ag 4Ge 4 which is a collinear ferromagnet. Analysis of the XPS valence band data indicates strong overlaps of the Pr 4f states with the Cu 3d states and the Nd 4f states with the Ag 4d states. Analysis of the R 3d states on the basis of the Gunnarsson–Schönhammer model gave the information on the hybridization of the 4f orbital with the conduction band. The results showed that the Pr-based compounds are characterized by larger values of the hybridization energy than the Nd-based compounds.

Magnetic properties of R 3Cu 4X 4 (R = Tb–Er; X = Si, Ge, Sn) compounds

dc magnetization and magnetic susceptibility measurements were performed on polycrystalline samples of R 3Cu 4X 4 (R = Tb–Er; T = Si, Ge, Sn) intermetallics which crystallize in the orthorhombic crystal structure of the Gd 3Cu 4Ge 4-type. All of the studied compounds are antiferromagnets showing complex behavior. For some of them additional transitions below Néel temperature are observed and few indicate metamagnetic transition at 2 K. Reciprocal magnetic susceptibilities of all the samples obey the Curie–Weiss law above the Néel temperatures with negative values of paramagnetic Curie temperatures and the effective magnetic moments of rare earth ions being close to the respective free R 3+ ion values.