Enhancement of solder properties of Sn‐9Zn lead‐free solder alloy

The eutectic alloy Sn‐9Zn was considered as a potential alternative to lead‐tin solder alloys when compared with other solders. In this paper, ternary, quaternary and penternary additions of the elements Bi, Cu and In were added to the eutectic alloy as a trial to improve its properties. The results showed that, the penternary alloy has properties superior to those of the binary, ternary and quaternary alloys. The alloy of composition Sn‐9Zn‐1Bi‐2Cu‐2In has the most suitable properties as a candidate alloy for lead‐free solder. It has a lower melting point, 186°C, which is very close to that of Sn‐37Pb solder, a lower value of electrical resistivity, 16.5 μΩ.cm, compared with that of Sn‐37Pb (17 μΩ.cm), higher value of the Young's modulus, 47 GPa, compared with 45 GPa of Sn‐37Pb and a higher value of the Vickers hardness, 191 MPa, compared with 129 MPa of Sn‐37Pb eutectic alloy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of indium content and rapid solidification on microhardness and micro‐creep of Sn‐Zn eutectic lead free solder alloy

The Sn‐Zn alloys have been considered as lead‐free solders. In this paper, the effect of 0.0, 0.5, 1.0, 1.5 and 2.0 wt.% Indium as ternary additions on melting temperature, structure, microhardness and micro‐creep of the Sn‐9Zn lead‐free solders were investigated. It is shown that the alloying additions of Indium to the Sn‐Zn binary system result in a suppression of the melting point to 187.9 °C. From x‐ray diffraction analysis, a new intermetallic compound phase, designated β‐In₃Sn is detected. The formation of an intermetallic compound phase causes a pronounced increase in the electrical resistivity and mechanical strength. Also, an interesting connection between dynamic Young's modulus and the axial ratio (c/a) of the unit cell of the β‐Sn was found in which Young's modulus increases with increasing the axial ratio (c/a). The ternary Sn‐9Zn‐xIn exhibits creep resistance superior to Sn‐9Zn binary alloy. The better creep resistance of the ternary alloy is attributed to solid solution effect and precipitation of In₃Sn in the Sn matrix. The addition of small amounts of In is found to refine the effective grain size and consequently, improves hardness. The 89%Sn‐9%Zn‐2%In alloy is a lead‐free solder designed for possible drop‐in replacement of Pb‐Sn solders. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comments and reconciliation of the Ni–Bi‐system thermodynamic reassessments

The binary Ni‐Bi alloys as well as multicomponent materials comprising systems like Ni‐Bi‐Sn, Ni‐Bi‐Sb etc. are recently considered as prospective for design of lead‐free solders. For that reason various authors focused their attention to the Ni‐Bi system thermodynamics. The studies identified five phases in the above system. Two of them (i.e., (Ni) and liquid), were treated as disordered substitutional solutions. The phase NiBi₃ is stoichiometric and a standard two‐sublattice model was repeatedly applied to describe its Gibbs free energy, while for the nonstoichiometric NiBi phase, a three‐sublattice model was retained. The pure bismuth phase ((Bi)) is stoichiometric as well. The results are discussed and compared to literature thermochemical and topological data. In liquid state, strong repulsions between nickel and bismuth atoms are anticipated in the nickel rich‐side, but no data about a liquid phase miscibility gap is available yet. Therefore, the stability of the liquid phase has to be reassured, in spite of positive deviations from ideal behaviour. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Bi‐content on hardness and micro‐creep behavior of Sn‐3.5Ag rapidly solidified alloy

In the present paper, the influence of 1, 3, 5 and 10 % Bi (weight %) as ternary additions on structure, melting and mechanical properties of rapidly solidified Sn‐3.5Ag alloy has been investigated. The effect of Bi was discussed based on the experimental results. The experimental results showed that the alloys of Sn‐3.5Ag, Sn‐3.5Ag‐1Bi and Sn‐3.5Ag‐3Bi are composed of two phases; Ag₃Sn IMC embedded in Sn matrix phase, which indicated that the solubility of Bi phase in Sn‐matrix was extended to 3 % as a result of rapid solidification. Bi precipitation in Sn matrix was only observed in Sn‐3.5Ag‐5Bi and Sn‐3.5Ag‐10Bi alloys. Also, addition of Bi decreased continuously the melting point of the eutectic Sn‐3.5Ag alloy to 202.6 °C at 10 % Bi. Vickers hardness of Sn‐3.5Ag rapidly solidified alloy increased with increasing Bi content up to 3 % due to supersaturated solid solution strengthening hardening mechanism of Bi phase in Sn matrix, while the alloys contain 5 and 10 % Bi exhibited lower values of Vickers hardness. The lower values can be attributed to the precipitation of Bi as a secondary phase which may form strained regions due to the embrittlement of Bi atom. In addition, the effect of Bi addition on the micro‐creep behavior of Sn‐3.5Ag alloy as well as the creep rate have been described and has been calculated at room temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural Studies on Ni75(SnSi)25 and Ni75(SnBi)25 Alloys

Ternary alloys on the quasi-binary system Ni₃Sn(r) in equilibrium condition. It has been observed that these phases undergo transformations at high temperatures but upto 500 °C room temperature modifications are stable. The two phases do not have any appreciable solid solubility in either of them. The phase Ni₃Si(r) crystallizes in to Cu₃Au (Li₂) structure where as Ni₃Sn(r) is based on c.p.h. structure with a = 5.305 A°, c = 4.254 A°. No new ternary phase has been detected in Ni₃Sn Ni₃Si section. The investigated alloys of the Ni Sn Bi system contain 75 at.% Ni. All the ternary alloys show simultaneous occurrence of three phases, namely Ni₃Sn(r), NiBi and Ni(Sn) in equilibrium state. The phase NiBi has NiAs(B8) type of structure. Due to non-existence of isostructural phases in the two binary systems (Ni Sn and Ni Bi), single solid solution phases are not formed. Widely differing atomic sizes of nickel and bismuth atoms restrict the formation of solid solution of bismuth in nickel in contrast to Ni(Sn) where atomic size factor is favourable.     

Calorimetric and phase equilibria studies of the Ni–Sn–Bi system

The phase equilibria at 1273 K were investigated and an isothermal section of the Ni‐Sn‐Bi phase diagram was constructed. The phase boundaries are inclined to the Bi‐rich region that is agreement with phase equilibria at lower temperatures. The molar enthalpies of formation of liquid ternary Ni–Sn–Bi alloys have been determined at 833, 873 and 933 K by direct reaction calorimetry using pellets of 325 mesh powders of pure Ni, Sn and Bi. Measurements were performed with alloys containing from 0.05 to 0.10 mole fractions of nickel, and at ratios of tin and bismuth mole fractions X_Sn/X_Bi = 2.8, 1.2 and 0.43. The experimental calorimetric data were used to calculate a regular solutions parameter of the ternary liquid phase by means of two different thermodynamic data files. It was found that the Ni–Sn–Bi ternary liquid phase could be described as temperature independent ternary regular solution. The assessed values of the ternary interaction parameter are ‐280 J·mol^–1 and 56 000 J·mol^–1, depending on the binary parameters used. Enthalpies of formation of solid binary phases were measured, too. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the tin‐rich region of the Sn‐Zn‐Ti system

The tin‐rich region of the system Sn‐Zn‐Ti system has been studied by diffusion couples, differential scanning calorimetry and electron microprobe analyses. Ternary eutectic reaction occurs at 193.7°C near to the binary tin‐zinc eutectic point and titanium content less than 0.9 at.% Ti. Three ternary compounds with approximate formulae: Ti₈Sn₅Zn₂ to Ti₅Sn₃Zn, TiSn₄Zn₅ and Ti₂Sn₄Zn₃ have been observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microscopic Theory of Tensosensibility of Multi‐Layer Polycrystalline Films

The microscopic theory for the coefficient of longitudinal tensosensibility of multi‐layer polycrystalline metal films has been developed. The theory takes into consideration as the scattering of conductivity electrons on external and internal surfaces of separate layers and crystalline boundaries, so as the dependence of specular reflection coefficient and coefficient of transmission of crystalline boundaries and boundaries between separate layers on deformation. The experimental verification of the theory done on three‐layer film systems Cr/Co/Cr, Cr/Cu/Cr and Ni/Co/Cr given as the quality correspondence.     

Crystallisation and performance characteristics of high‐temperature annealed electroless Ni‐W‐P coatings

Electroless deposition of Ni–P based alloys is a well‐known commercial process that has numerous applications because of their excellent anticorrosive and wear properties. However, for some special occasions, like the components for gas making furnaces in chemical fertiliser industry, the coatings must be reinforced to withstand short‐term high temperatures between 600 °C and 700 °C as well as light erosive wear. Therefore, co‐deposition of high melting point metallic element, W, has been considered as a preferred choice. In the present study, two Ni–W–P alloy coatings were deposited on mild steel panels from different alkaline baths. The microstructures of the annealed coatings were characterised by quantitative XRD, XPS and SEM/EDS analysis techniques and their microhardness, friction and wear behaviour, corrosion mechanism as well as microstrain and residual stress are discussed in comparison with the as‐plated state. The results indicate that the hardness mainly depends on the volume fraction and crystallite size of Ni₃P phase; the uniform corrosion in sulfuric acid solution is closely related to the ratio of I_Ni/I_Ni3P as well as grain size. The wear mechanism of the high‐temperature annealed coating is dominated by abrasive wear, but the wear in the early stages started from mild adhesive wear caused by adhesion between the friction couples. Electroless deposited Ni‐W‐P alloys with high phosphorus present relatively good properties, including hardness, wear and corrosion resistance when 700 °C is applied for annealing process.     

Wet‐chemical synthesis and characterization of NiBi nano‐ and micro‐particles

Preparation and characterization of NiBi nano‐ and micro‐particles are presented. Firstly, predetermined compositions were obtained by simultaneous precipitation from solutions of Bi(NO₃)₃ and Ni(NO₃)₂. The precipitates were heated under oxygen flow and in air, and thereafter reduced to metals under hydrogen flow at 673 K. Correlation between the predetermined and the actual compositions of the products was found. Characterization of the precipitates was carried out employing X‐ray diffraction, scanning and transmission electron microscopy. Nickel‐bismuth intermetallic phase (NiBi) particles with nano‐ and micro‐dimensions were observed in the samples after reduction. The other possible Ni–Bi intermediate phase (NiBi₃) did not form at these conditions although its presence was expected according to the phase diagram. This finding might be useful for the implementation of Bi‐based solders where the growth of the compound NiBi₃ in the solder joints must be prevented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of diffusion couple technique for the determination of the Ti‐Bi‐Sn phase diagram

The system Ti‐Bi‐Sn has been investigated by solid/liquid diffusion couples at 500, 600, 700 and 800°C. A non‐negligible solubility of Sn into solid Bi is found. Diffusion layers of the recently revealed ternary compound Ti₃BiSn have been observed, thus its existence has been confirmed. Data about the homogeneity ranges of the binary end‐system compounds have been obtained. The assessed growth constants of the diffusion layers are comprised in the interval 10^‐12 –10^‐14 m².s^‐1. The phases participating in the hypothetical ternary eutectic reaction, probably are: (Bi), (Sn), Liquid and Ti₂Sn₃. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of annealing temperature and Au concentration on the electrical properties of multilayered a-Ge/Au films

Multilayered a-Ge/Au was investigated to realize low-temperature formation of poly-Ge films on insulator. Increasing Au layer thicknesses, peak intensity of crystalline Ge–Ge TO mode increased and amorphous Ge–Ge TO mode decreased. When Au composition ratio is high, the samples are crystallized under eutectic temperature. Annealing temperature at 673 K, all samples with Au layer are crystallized. Crystalline Ge has no strain evaluated by X-ray diffraction and Raman scattering spectroscopy. However, the Au is compressed or expanded in the films with various annealing temperature. It is thought that this phenomenon changes depending on the size of the space in the film. The behavior of electrical resistivity is changed at eutectic temperature.     

Effect of laser‐induced nanocrystallisation on the properties of electroless Ni‐P/Ni‐W‐P duplex coatings

This paper presents a comparative study of nanocrystallisation and the wear resistance of electroless plated Ni‐P/Ni‐W‐P duplex coatings with a single Ni‐W‐P coating before and after high‐ power diode laser treatment. Effects of the laser operating parameters on microstructures, in terms of crystallisation, porosity formation, phase transformation and grain growth, were investigated using scanning electron microscopy (SEM) with energy dispersive X‐ray spectroscopy (EDX) and quantitatively X‐ray Diffraction (XRD). Microhardness and wear behaviour of the coatings before and after laser treatment were evaluated by measurement of coating surface and cross‐section hardness as well as un‐lubricated friction and wear tests. The results revealed that in the case of laser treatment, the Ni‐P/Ni‐W‐P duplex coatings offered better wear resistance than the single Ni‐W‐P coating, while the as‐plated, single Ni‐W‐P coating showed better wear resistance than the Ni‐P/Ni‐W‐P duplex coatings. Adhesive wear mechanism prevails in the laser‐treated coatings when subjected to wear test against hardened steel material. The effects of microstructural characteristics in the coatings, in particularly the grain size of Ni₃P phase and the degree of crystallisation, on the adhesive wear behaviour have been investigated and found to be dominant besides the effect of hardness.     

Notes on some supposed transitions of the phase NiBi

X‐Ray, DSC and magnetic susceptibility measurements were performed with NiBi specimens in the interval from room temperature to 700 K. The hypothesis of solid‐state transitions in this phase was not confirmed. Thermal and magnetic effects are observed, but they are due to the existence of small amount of phases others than NiBi (i.e. unreacted Ni and Bi). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase diagram calculation on Sn-Zn-Ga solders

Sn-Zn eutectic system is one of the most promising lead-free solders with the advantages of low melting points, excellent mechanical properties and acceptable costs, whereas its poor wetting ability confines its applications in many substrates. In this paper, gallium (Ga) was added to the Sn-Zn eutectic system in order to improve its melting properties and wetting abilities. Piecing binary phase diagram method was employed to calculate the uncharted Sn-Zn-Ga ternary phase diagram and the eutectic point of this ternary system. Differential scanning calorimeter (DSC) method was used to exam the melting point of the solder system. The SnZn6Ga solder has a melting point of 174.4 °C, with wetting rate of 48.9%, while the melting point of Sn-Zn alloy is 198.5 °C and melting rate is only about 20%. In addition, the method of piecing binary phase diagrams proves to be feasible to clarify certain unknown ternary phase systems.     

High‐strength bimodal ultrafine Ti‐based alloys with enhanced ductility

Bulk Ti₆₅Fe₃₅ and (Ti₆₅Fe₃₅)_96.15‐xSn_3.85Nb_x (x = 0, 3, 5 and 7 at.%) alloys were prepared by cold crucible levitation melting, and tested in compression at room temperature. The Sn and Nb modified hypereutectic Ti‐Fe alloys exhibited improved mechanical properties under compression. (Ti₆₅Fe₃₅)_93.15Sn_3.85Nb₃ alloy displayed an ultimate compressive strength of 2.7 GPa and a compressive plastic strain of 15%. Electron microscope observations revealed Ti‐Fe(Sn,Nb) alloys having a bimodal microstructure with micrometer‐scale primary TiFe dendrites distributed in an ultrafine eutectic (β‐Ti+TiFe) matrix. The orientation relationship of β‐Ti with TiFe phases is TiFe (011)[100] ∥ β‐Ti (011)[100]. The improved mechanical properties are attributed to the morphology of the phase constituents and the larger lattice mismatches between β‐Ti and TiFe phases due to the additions of Sn and Nb.     

Untersuchungen zur Wechselwirkung von Ar-, O2- und H2-Niederdruckplasmen mit Metallschichten

By the interaction of the positiv column of a glow discharge (plasma gases: Ar, O₂, H₂) with the surface of metal films (Au, Ni, Sn) sputtering processes are observed. The sputter yields are larger than will be assumed from known yields of low energetic ions which are dominant in the investigated surface layer. Impulse interaction increases the sputter yields. This effect is reduced to a destruction of metal lattice caused by reconstruction of the surface layer and the inertion of gases during the intervals between the impulses. The sputter yields strongly depend on the plasma gases and the current density directed to the wall (i_W ∼10⁻⁵ A. cm⁻²) it is possible by decreasing the sputter yield to observer reactive processes and gas insertion in consequence of the plasma-wall interaction. Sustained upon electron diffraction of Ni- and Au-films and kinetic analysis of sputter yields a model is developed assuming a critical surface layer of 30–50 Å thickness during the plasma influence in “equilibrium” with a metal vapour-plasma gas phase above it.     

Determination of mechanical, electrical and thermal properties of the Sn―Bi―Zn ternary alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries. Sn―Zn―Bi eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb―Sn eutectic solder without increasing soldering temperature. This study investigates the effect of temperature gradient and growth rate on the mechanical, electrical and thermal properties of the Sn―Zn―Bi eutectic alloy. Sn-23 wt.% Bi-5 wt.% Zn alloy was directionally solidified upward with different growth rates (V = 8.3-478.6 μm/s) at a constant temperature gradient (G = 3.99 K/mm) and with different temperature gradients (G = 1.78-3.99 K/mm) at a constant growth rate (V = 8.3 μm/s) in the Bridgman-type growth apparatus. The microhardness (HV), tensile stress (σ_t) and compressive stress (σ_c) were measured from directionally solidified samples. The dependency of the HV, σ_t and σ_c for directionally solidified Sn-23 wt.% Bi-5 wt.% Zn alloy on the solidification parameters (G, V) were investigated and the relationships between them were obtained by using regression analysis. According to present results, HV, σ_t and σ_c of directionally solidified Sn-23 wt.% Bi-5 wt.% Zn alloy increase with increasing G and V. Variations of electrical resistivity (ρ) for cast samples with the temperature in the range of 300-420 K were also measured by using a standard dc four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (C_p) for same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.     

Structural properties of liquid Au–Si and Au–Ge alloys with deep eutectic region

Au–Si and Au–Ge alloys have a deep eutectic region around 19 at.% Si and 28 at.% Ge, respectively. The metallic glass was prepared by quenching around 25 at.% Si near the eutectic composition for the Au–Si alloys [2] which has stimulated many researchers to study on the structural properties of such liquid alloys. However their results were different from each other, which seems due to the experimental difficulties from heavy absorption of both X-ray and neutron beams by Au atom in diffraction experiments. X-ray diffraction measurements have been carried out for liquid Au–Si and Au–Ge alloys around the eutectic region by the transmission method using high-energy X-rays to investigate the atomic arrangements in the liquid state. From the temperature dependence of the observed structure factors, the partial pair correlation and the detailed atomic arrangements will be discussed by Reverse Monte Carlo analysis. The produced atomic arrangements around the eutectic region suggest a substitutional structure and also an increase in liquid density with decreasing temperature.     

Characteristics of the binary faceted eutectic: benzoic acid – salicylic acid system

The consistent symmetry relations computed from the heterogeneous nucleation data of the non‐ideal benzoic acid – salicylic acid eutectic system verifies the validity of nucleation theory. The kinetics of crystal growth from the molten state of the system follows the dislocation mechanism. Anomalous behaviour of both viscosity and activation energy for the eutectic melt confirms the essence of specific interactions animating molecular clusters rich in predominating eutectic phase. Micromorphology of the system obeys the Hunt‐Jackson model. The plot between a mechanical property and variable anisotropic growth velocity for the eutectic composite evidentially complies with the Weibull probability distribution curve. The curve is perused with two cut‐off points corresponding to a lower strength limit in the slow and fast growth regions and an upper strength limit in the moderate growth region. The latter aspect reveals the theoretical strength of the eutectic crystallites. The strength‐growth relationship explicated thereby is linear, optimum and linear respectively in the slow, moderate and fast growth regions of solidification. The moderate anisotropic growth (∼2.96 X 10^‐7m³s^‐1) is of greater interest by virtue of its attribute to unifying and organizing the crystallites parallel to each other in the growth direction. The eutectic composite material obtained by this process attains remarkable superiority in the mechanical properties over its isotropic growth in an ice bath (∼273 K), and its constituent phases. The co‐relation between excess thermodynamic functions indeed predicting the liquidus character and the microstructural parameters inevitably structuring the morphology is presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)