Pb-Sn Eutectic Alloy Research Articles

Microscopic damage in eutectic SnPb alloy: First-principles calculations and experiments

This study aims to comprehensively elucidate the microscopic origins of damage in eutectic SnPb alloy through atomic-scale investigations, a crucial endeavor for enhancing the alloy’s properties and furthering the development of Pb-free solders. First-principles calculations based on density functional theory (DFT) were employed to examine the mechanical constants and defect formation energies of the Pb phase, the β-Sn phase, and potential Sn/Pb eutectic phases in the SnPb alloy. The Voigt-Reuss-Hill approximation was utilized to derive the mechanical parameters of the elastically stable structure in SnPb alloy, facilitating the prediction of its mechanical properties. The defect formation energy calculations revealed a higher difficulty in forming vacancy defects in the β-Sn phase compared to the Pb phase. This discrepancy can be attributed to the stronger interactions between Sn atoms, resulting in the formation of more stable Sn-Sn bonds, thereby impeding vacancy generation in the β-Sn phase. Furthermore, the Pb phase exhibited a tendency for Sn atoms to occupy octahedral interstitial sites, whereas in the β-Sn phase, Pb atoms tended to displace neighboring Sn atoms along the [110] orientation into adjacent interstitial sites and occupy their lattice positions. Experimental observations complemented these calculation findings, demonstrating significant Sn element presence, up to 27.22 at%, in the Pb-rich phase, with notable microvoid damage primarily concentrated within this region. This observation aligns with the conclusions drawn from first-principles calculations and unveils the microscopic origins of damage in eutectic SnPb alloys.

Pb Segregation in SnPb eutectic solder alloy induced by gamma irradiation

Pb segregated and formed a Pb segregation area in SnPb eutectic solder joint after 100 h of gamma irradiation. With the irradiation time increased to 150 h, Pb segregating stopped. The Pb segregation was attributed to the oxidation of β-Sn to SnO2 induced by the gamma irradiation. The Pb element content in the segregation area predicted by the segregation heat formulas is 53.5 %, which is consistent with the experimental result of 49.11 %. Density functional theory (DFT) calculation and Molecular dynamics (MD) simulation results were used to prove that the Pb segregation is caused by the oxidation of β-Sn.

Theoretical Analysis of the Thermodynamic, Structural, Surface and Transport Properties of PbSn Liquid Alloys at 1050 K

The thermodynamic, structural, surface and transport properties of PbSn eutectic alloys at 1050 K have been analyzed employing self association model. The model parameters have been evaluated on utilizing the experimental data of free energy of mixing of PbSn liquid alloys at 1050 K. For the validation of the model parameters, the calculated values of the excess free energy of mixing and activity of the components of PbSn liquid alloys have been compared with the experimentally measured data. Further, the estimated model parameters have been used to determine the thermodynamic functions i.e. the free energy of mixing, thermodynamic activity, entropy of mixing and heat (or enthalpy) of mixing, and the structural properties such as the concentration fluctuations and shortrange order parameter. The theoretical and experimental values are compared. A good agreement is observed. Again, the surface properties of PbSn liquid alloys at 1050 K have been investigated using the Butler model in the framework of self association model. The calculated values of surface tension of PbSn liquid alloys at 1050 K are in reasonable agreement with the data available in the literature. The transport properties like the diffusivity and viscosity of PbSn liquid alloys at 1050 K have been theoretically analyzed. For the computation of viscosity, the simple formula developed by Moelwin- Hughes has been used in conjunction with self association model. The present study reveals that PbSn eutectic liquid alloys at 1050 K are segregating in nature. Further, the model parameters are found to depend on temperature.Keywords: Gibbsfree energy; concentration fluctuations; short-range order parameter; surface tension; diffusivity; viscosity

Effect of Aging Temperature on the Fatigue Resistance and Shear Strength of SAC305 Solder Joints

The interconnection materials that are used in electronics assembly fabrication operating in harsh environmental conditions are frequently exposed to different types of mechanical stress and fatigue. Fatigue resistance does significantly affect the reliability of electronic assemblies. SAC alloys are commonly utilized in electronic assemblies’ fabrication operating in harsh conditions due to their superior mechanical and fatigue properties. Hence, this provokes the need to model and perform a detailed statistical analysis of their reliability behavior. SAC305 is commonly used as a lead-free alloy which is being utilized as a replacement of the eutectic SnPb alloy. The main goal of this study is to investigate the effect of aging temperature on the fatigue and mechanical behavior of SAC305 solder joints using accelerated shear-fatigue and shear tests. An Instron Microtester machine with a customized fixture was used to perform the tests. A two-factor test matrix for the fatigue test was constructed; where the stress amplitude has three levels (16, 20, and 24MPa) and the aging temperature has four levels (0, 50, 100, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150^{\circ }\text{C}$ </tex-math></inline-formula> ). Microstructural analysis was performed on samples aged at different temperatures using SEM microscopy to address the evolutions in the precipitates size and the intermetallic compound (IMC) layer. A stress-life equation and an Arrhenius model are used to develop a general reliability model as a function of aging temperature and stress amplitude. The relationship between the fatigue life and the inelastic work were analyzed using Morrow Energy equation. The results indicate a major reduction in the reliability and shear strength of the solder joints with increasing the aging temperature. Aging has been also found to have a more notable effect on the fatigue life when compared to shear strength.

Maximum shear stress-controlled uniaxial tensile deformation and fracture mechanisms and constitutive relations of Sn–Pb eutectic alloy at cryogenic temperatures

Sn–Pb eutectic alloy is widely applied to the deep-space electronics that work under cryogenic environments, but little is known about its responses to the mechanical loading at cryogenic temperatures. In this work, a comprehensive investigation about the deformation and fracture behaviors as well as constitutive relations of the eutectic alloy at cryogenic temperatures was conducted through uniaxial tensile experiments over a full temperature range from 293 K to 77 K, in-situ cryogenic tensile experiments and fractography. With the declining temperature, the tensile strength and quasi-static toughness increase substantially while the elongation is maintained at 25%–30%; Sn–Pb eutectic alloy achieves the optimal combinations of strength, ductility and toughness at 123 K, which is due to a number of deformation twins activated in the Sn matrix together with the compatible deformation between the Pb-rich phases and the Sn matrix. Multiple 45° shear bands induced by the maximum shear stress contribute to reconcile the deformation difference between the two phases, which reaches its minimum at around 123 K. A ductile shear fracture on the 45° shear planes with respect to the tensile axis occurs under the maximum shear stress at temperatures ranging from 293 K to 123 K, while the maximum normal stress leads to a brittle fracture on the 90° planes at 77 K. Moreover, the Anand model fails in fitting the constitutive relations of Sn–Pb eutectic alloy when the temperature declines to 233 K or lower. Instead, the Hollomon equation has been successfully applied to fit the constitutive relations at these invalid temperatures.

An examination of microstructural evolution in a Pb–Sn eutectic alloy processed by high-pressure torsion and subsequent self-annealing

Abstract The Pb–Sn alloy has a wide use in the electronic, energy storage and nuclear industries and a fine-grained Pb–Sn alloy may open up new possibilities for applications in these industries. In order to understand the behavior of grain refinement, a Pb-62% Sn eutectic alloy was processed by high-pressure torsion (HPT), stored at room temperature (RT) and then the microstructures of the alloy after HPT were repeatedly investigated during the course of self-annealing using electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is demonstrated that there is a large fraction of twin boundaries with a twin relationship of 62.8° in the microstructure of the initial as-cast condition. Due to the presence of the high imposed pressure, the mobility of Ʃ21 boundaries at 71° is greatly favoured during processing by HPT. After the high pressure is removed, the mobility of dislocation-twin boundaries near 62.8° is then favoured. Processing by HPT significantly increases the solubility of Sn in the Pb phase. The supersaturated state of Sn in Pb is not stable during self-annealing at RT and instead a decomposition of Sn from the Pb-rich phase is observed after storage for 16 days. The main mechanism for this decomposition is lattice diffusion.

Effect of Organic Plating Additives Concentration on Carbon Content and Donor Density of Electroplated Tin

Pure tin is widely used as a replacement of Pb-Sn eutectic alloy as finish and solder material. This study aims to determine how the increasing concentration of organic plating additives affects the carbon content and donor density of electroplated Sn. Pure tin was electroplated on an Al sheet in a Hull cell using a commercial plating solution. Plating was performed in electrolyte baths with primary additive concentration from 100 mL/L to 600 mL/L, and with secondary additive concentration from 8 mL/L to 48 mL/L. Current densities of 15, 8 and 3 A/dm2 were considered. The increased concentration of organic plating additives caused an increase in carbon content of the deposit from 5 wt.% C to 8 wt.%C. Mott-Schottky measurements showed increasing electron donor density of up to four orders of magnitude as a function of current density and carbon content. A higher current density during deposition causes the tin oxide film to reach the donor density saturation value at lower concentrations of organic plating additives. This suggests that current plays a role in the decomposition of organic additives, which results in the incorporation of carbon in the deposit.

Effect of Aging Treatment on Microstructural Evolution of Rapidly Solidified Eutectic Sn-Pb Alloy Powders

The microstructural stability of rapidly solidified eutectic Sn–Pb alloy solder powders was investigated through aging at room temperature (25 °C) and temperatures of 40 °C–120 °C. The coarsening behavior of the Pb-rich phase both at room and elevated temperatures was observed. The evident coarsening of the Pb-rich phase was detected upon storage after 40 days. At elevated temperatures, a similar sequence of Pb-rich phase coarsening was observed; however, it occurred substantially more quickly. Pb-rich coarsening rate kinetics at different temperatures were estimated using the Arrhenius equation. The apparent activation energy was 45.53 ± 4.23 KJ/mol, which indicates that grain boundary diffusion is a crucial mass transport mechanism controlling Pb-rich phase coarsening under annealing.

Manufacture of Continuous Metal Matrix Composite Strip Reinforced by Particulate Materials from the Semisolid Processing

Strip casting is a new method of producing metal matrix composites. Two-roll melt dragged processing (TRMD-ing) and single-roll melt dragged processing (SRMD-ing) methods were used to study the manufacture of 2-mm-thick composite strips by using PbSn (≈ 11.3 g/cm3) eutectic alloy matrix reinforced with iron (≈ 7.86 g/cm3) powder (≈ 70 μm) at a rate of 0.3 m/s. The metallic powder stored in the feed hopper (≈ 90 g) was pushed during the pouring operation of the cast alloy (≈ 4 kg) at 260 oC on the cooling slope to produce a mixture of metallic slurry and particles to feed the nozzle to be dragged by the lower roll. Various surface defects occurred during processing, such as the failure of the powder particle to be embedded in the matrix by SRMD-ing with and without stirrer into the nozzle, and the rolling up of the strip into the nozzle by TRMD-ing. Graphite nanoparticles formed inside the α-Pb grain revealed a complicate eutectic structure in both the processing methods. The colloidal graphite used to coat the crucible, cooling slope, and nozzle could act as a nucleation agent for preferential centre segregation in the α-Pb grain. This suggests that the graphite nanoparticles functioned as nucleation points in the lead-rich α phase. Thus, another type of composite was formed in the presence of graphite nanoparticles within the lead-rich α-phase surrounded by β-Sn. An electron probe microanalysis and scanning electronic microscopy were used to investigate the composition and distribution and identify the different phases. Several types of particulate reinforcements may be added to the matrix to obtain composites for mechanical, electronic, and magnetic applications using these technologies.

Thirty Years of Superplastic Ultrafine-Grained Materials: Examining the Legacy of Oscar Kaibyshev

The occurrence of superplasticity may be traced to the classic work of Pearson conducted in the U.K. in 1934 when an elongation of 1950% was reported in a Pb-Sn eutectic alloy. Subsequently, much attention in Russia was devoted to this scientific curiosity and this led to the first book on superplasticity written by Prof. A.A. Presnyakov and published in 1964. Later, in 1985, Oscar Kaibyshev established in Ufa the Institute of Problems of Superplasticity of Metals of the Russian Academy of Sciences and this was, and remains to this day, the only institute in the world devoted exclusively to studies of the phenomenon of superplastic flow and the development through superplastic forming of complex-shaped parts. An important development occurred in 1988 with the publication of a classic report by Kaibyshev and co-workers describing the potential for achieving low temperature superplasticity in a metallic Al-Cu-Zr alloy that had been specially processed by severe plastic deformation (SPD) to produce a remarkably small grain size of only 300 nm. This report formed the basis for the later development of SPD processing as a major tool for the production of exceptional grain refinement and as a procedure for achieving large superplastic elongations that cannot be achieved using more conventional processing. This report describes this early work, the subsequent developments and the modern status of superplastic flow in ultrafine-grained metals.

Modification in Bi-Ag Lead-Free Solder-Bearing Alloying Elements

The development of lead-free solder has an urgent task for material scientist due to health and environmental concerns over the lead content of traditional solders. The objective of this study is to examine Bi-Ag-rare earth (RE) element considered as one of the more attractive lead-free solders since it can easily replace Sn-Pb eutectic alloy with increasing soldering temperature while causes for high-temperature applications. In order to enhance the soldering properties of Bi-Ag alloys, a trace eare earth (RE) element of Ho added into Bi-Ag alloys. The results indicated that the addition of RE led to the refining of coarse Bi-Ag grains, in the microstructure. The tensile strength, Hv and creep resistance increased with a decrease in melting point and electrical resistance. This paper brief the influences of rare earth alloying element and rapid solidification on both of the microstructure, intermetallic compounds, creep resistance, melting behavior, electrical resistance and mechanical behavior.

Large-Grain Tin-Rich Perovskite Films for Efficient Solar Cells via Metal Alloying Technique.

Fast research progress on lead halide perovskite solar cells has been achieved in the past a few years. However, the presence of lead (Pb) in perovskite composition as a toxic element still remains a major issue for large-scale deployment. In this work, a novel and facile technique is presented to fabricate tin (Sn)-rich perovskite film using metal precursors and an alloying technique. Herein, the perovskite films are formed as a result of the reaction between Sn/Pb binary alloy metal precursors and methylammonium iodide (MAI) vapor in a chemical vapor deposition process carried out at 185 °C. It is found that in this approach the Pb/Sn precursors are first converted to (Pb/Sn)I2 and further reaction with MAI vapor leads to the formation of perovskite films. By using Pb-Sn eutectic alloy, perovskite films with large grain sizes up to 5 µm can be grown directly from liquid phase metal. Consequently, using an alloying technique and this unique growth mechanism, a less-toxic and efficient perovskite solar cell with a power conversion efficiency (PCE) of 14.04% is demonstrated, while pure Sn and Pb perovskite solar cells prepared in this manner yield PCEs of 4.62% and 14.21%, respectively. It is found that this alloying technique can open up a new direction to further explore different alloy systems (binary or ternary alloys) with even lower melting point.

The Influence of High Gravity in PbSn Eutectic Alloy

The study of materials processed in centrifuges improves the understanding of the acceleration influence in the convection behavior in materials processing. This work aims to study the influence of high gravity in PbSn eutectic alloy solidification using a small centrifuge designed and built in the Associate Laboratory of Sensors and Materials of the Brazilian Space Research Institute (LAS/INPE). The samples were analyzed by densitometry and scanning electron microscopy (SEM).

Influence of the melt cooling rate on the microstructure and texture of Sn–Bi and Sn–Pb eutectic alloys

The results of microstructure and texture studies into Sn–Bi and Sn–Pb eutectic alloys produced at melt cooling rates of 2 and 5 × 105 K/s are presented. Ultrafast quenching from the melt is found to initiate the formation of microcrystalline structure. The causes of the transition from the lamellar to the microcrystalline structural phase and the generation of nucleation texture are discussed.

Development and Characterization of Sn–Zn–Bi Lead Free Solder

Sn–Zn based lead free solder is a promising candidate to replace the Sn–Pb eutectic solder due to its low cost and melting temperature (198 °C) near to the Sn–Pb eutectic solder (183 °C). So far eutectic or near eutectic Sn–Pb alloys have been used as solder material but due to harmful effect on environment and human health Pb has to be eliminated from solder and prevent our environment from being polluted. Here the near eutectic composition of Sn-8 wt% Zn has been chosen. Apart from Sn-8 wt% Zn four different alloys containing different wt% of Bi were considered. They are Sn-8Zn-3Bi, Sn-8Zn-6Bi, Sn-8Zn-8Bi and Sn-8Zn-10Bi. The results of the differential scanning colorimetry (DSC) analysis show that addition of Bi to the near eutectic composition of Sn-8 wt% Zn lowers the melting temperature. The microstructure of the alloys were investigated using a scanning electron microscope and energy dispersive x-ray spectroscopy analysis. Tensile test shows that both tensile strength and elongation of the alloys reduce on addition of high wt% Bi to the Sn–8Zn solder alloy.

Structure, Electrical Resistivity, Oxidation and Corrosion Behavior of Tin-Lead Eutectic Alloy

The structure, electrical resistivity, oxidation and corrosion behaviors of the eutectic Sn-Pb alloy have been studied and analyzed using X-ray, Ohm’s law circuit, thermal gravimetric analysis (TGA) and chemical weight loss method, respectively. The results showed that, the alloy exhibited two phase mixtures of α-Pb and β-Sn. The I-V characteristic curve of this alloy was described and the room temperature electrical resistivity was calculated and found to be 24.6 ± 1 µΩ.cm. Also, the variation of electrical resistivity with temperature was described in the range from the room temperature to 91 oC and the temperature coefficient of resistivity (TCR) was also calculated. Furthermore, it was found that, the alloy exhibited a good oxidation and corrosion resistance for long run.

Heat Transfer During the Solidification of Eutectic PbSn Alloy Droplets in Drop Tubes

The study of heat transfer during the free fall of PbSn droplets is important to optimize the alloy solidification conditions in drop tubes. In this paper a model of heat transfer by conduction is applied in the solidification of PbSn eutectic alloys in a 3 m length drop tube installed at Associate Laboratory of Sensors and Materials of the Brazilian Space Research Institute (LAS/INPE). Drop tubes are one of the most suitable and low cost options to provide a microgravity environment on the ground.

Enhancement of interfacial reaction between solid iron and molten tin by mechanical actions

The influences of mechanical actions on interfacial reactions between an iron plate and molten tin were examined. Tensile and compressive stresses up to 100 MPa on the iron plate did not significantly change the thickness of the reaction layer and the corrosion depth of the plate. However, when the iron plate was subjected to repeated rubbing with tungsten and Pb–Sn eutectic alloy wires and when it was immersed in the rotating molten tin, the reaction layer thickness decreased and the corrosion depth of the iron plate increased. From these results, it was concluded that the corrosion of the iron plate in the molten tin was enhanced by repeated rubbing with the solder alloy on the plated iron layer and also by flow of molten solder alloy down the surface of the soldering tip in the soldering process.

Solution plasma synthesis of bimetallic nanoparticles

This paper describes the facile solution plasma synthesis of bimetallic nanoparticles, including solid solution alloys (Ni–Cu and Ni–Cr system), eutectic alloys of Sn–Pb, and intermetallic alloys (SnSb and Ni3Sn), by using metallic alloy wire as the cathode and Pt wire as the anode. In the typical process, the cathode was melted by the local-concentration of current, upon applying a DC voltage between the two electrodes immersed in the electrolyte. The solid solution alloys of Ni–Cu and Ni–Cr prepared in this study have a uniform distribution of composition. On the other hand, the uniformity in the composition of the eutectic Sn–Pb alloy depends on the microstructure of the electrode. The use of quenched electrode with small crystal grains favors the formation of Sn–Pb alloy nanoparticles, in which the Sn-rich and Pb-rich phases coexist in each particle. The formation of intermetallic SnSb and Ni3Sn alloy nanoparticles is accompanied by the formation of colloidal oxide. These results demonstrate that the solution plasma technique is applicable not only for the synthesis of pure metals but can also be used for the synthesis of various alloy nanoparticles.

Characterization of Solder Joint Reliability Using Cyclic Mechanical Fatigue Testing

This article summarizes the mechanics of two mechanical fatigue methods, cyclic bending fatigue and shear fatigue, in inducing failure in solder joints in package assemblies, and it presents the characteristics of fatigue failures resulting from these methods using example cases of Sn-Pb eutectic and Sn-rich Pb-free solder alloys. Numerical simulation suggests that both testing configurations induce fatigue failure by the crack-opening mode. In the case of bending fatigue, the strain induced by the bending displacement is found to be sensitive to chip geometry, and it induces fatigue cracks mainly at the solder matrix adjacent to the printed circuit board interface. In case of shear fatigue, the failure location is firmly fixed at the solder neck, created by solder mask, where an abrupt change in the solder geometry occurs. Both methods conclude that the Coffin–Manson model is the most appropriate model for the isothermal mechanical fatigue of solder alloys. An analysis of fatigue characteristics using the frame of the Coffin–Manson model produces several insightful results, such as the reason why Pb-free alloys show higher fatigue resistance than Sn-Pb alloys even if they are generally more brittle. Our analysis suggests that it is related to higher work hardening. All these results indicate that mechanical fatigue can be an extremely useful method for fast screening of defective package structures and also in gaining a better understanding of fatigue failure mechanism and prediction of reliability in solder joints.