Sn-Bi Alloys Research Articles

Measurements of Mixing Enthalpy for a Lead-Free Solder Bi-In-Sn System

Measurements of mixing enthalpy for a Bi-In-Sn system needs special attention as far as the lead-free solder applications are concerned. Lead-free solder is generally used for solder joints in electronic equipment. In this work, an MHTC 96 Line Evo (Setaram Instruments, France) drop-solution calorimeter was used to determine the integral enthalpy of mixing for a Bi-In-Sn system at 767 K, 813 K and 855 K using drop technique. The enthalpy of mixing was measured for three different cross sections of (Sn0.33Bi0.67)1−x Inx, (Sn0.50Bi0.50)1−x Inx and (Sn0.67Bi0.33)1−x Inx. Indium was dropped onto the Bi-Sn alloys over the entire composition of indium. Partial quantities of indium mixing were calculated from the integration of the heat flow curve using CALISTO software. Subsequently, integral molar quantities of mixing were calculated from the partial quantities. Mixing enthalpy was found to be almost temperature-independent in the Bi-In-Sn system. Iso-enthalpy curves for the integral mixing enthalpy were plotted at 813 K. The data from this study were analysed with a least-squares fit using the Redlich–Kister–Muggianu polynomial to determine the ternary interaction parameter.

Effect of porous Cu addition on the microstructure and properties of Sn58Bi solder joints

In this work, porous Cu (P-Cu) was added into Sn58Bi (SnBi) alloy to obtain a new SnBi@P-Cu composite solder. The microstructure, hardness, shear performance, and thermal conductivity of the solder were investigated in comparison with the eutectic SnBi. Experimental results shows that the addition of porous Cu in the composite solder joint increases the grain size of the β-Sn and the Bi-rich phases in the main area of the solder bulk. The hardness at such area is 292.6 MPa, which is similar with the average hardness of the eutectic SnBi. In some areas enclosed by the Cu pores in the composite solder joint, the solder bulk shows refined microstructure. The average hardness here is 349.3 MPa, which is higher than that of the others. The addition of porous Cu has limited effects on the shear strength of the solder joint. However, it leads to the failure mode transformation of the joint during the shear test. Compared with the eutectic SnBi solder, the thermal conductivity of the Sn58Bi@P-Cu composite solder increases from 22.96 W m−1 · K−1 to 25.90 W m−1 · K−1 due to the addition of the porous Cu.

Influence of Microstructure Length Scale on the Tensile Properties and Superplasticity of Cu-Doped Sn-34Bi TIM Alloy

Sn-Bi alloys are candidates for use as thermal interface materials, TIM. Such materials are often used to conduct heat away from a temperature sensitive device. Sn-Bi alloys are considered competitive in cost and cost volatility, being particularly interesting with doping of ternary elements. Among various attended pre-requisites, high manufacturability when utilizing rolling or pressing is a particular benefit. To take advantage of this property, Sn-Bi alloys should be designed to ensure high ductility, maximizing manufacturability. Suitable microstructures capable of improving the alloy's plasticity are very desirable. The present investigation aims to evaluate the effects of starting as-cast microstructures on the strength and ductility of the Sn-34 wt.%Bi-0.1 wt.%Cu alloy. Specimens with very different length scales of the dendritic array were subjected to tensile tests at three temperatures: − 50°C, 25°C and 60°C. It was demonstrated that the samples with more refined microstructure are related to slightly higher tensile properties at room temperature if compared to the results observed for the coarser microstructure specimens. On the other hand, much higher ductility was observed for specimens having more refined microstructure tested at 60°C. Strain was three times higher than those characterizing coarse related specimens. This disparity in ductility has been investigated. The principal mechanism of flow in superplasticity was found to be the grain boundary displacement. Various contributing factors were recognized for the Sn-Bi-Cu alloy sample with initial fine-dendritic form, which are: grain size lower than 10 μm, complete destruction of the dendritic array, significant rotation of grains during loading at 60°C and incidence of cavities.

Thermodynamic Calculation of Bi–Sn Alloy Phase Diagram Under Pressure with Advanced Density Measurements

Bi–Sn alloy phase diagram under pressure was re-calculated using the CALculation of PHAse Diagrams method by applying new density data. Theoretically, alloy phase diagram under pressure can be calculated with bulk thermodynamic database and thermophysical property data such as density and sonic velocity. In the recent study by Emuna et al. (J Alloys Compd 687:360–369, 2016), thermodynamic parameters were determined from literature values with additional modification to fit experimental data of phase boundaries. In this study, density of liquid Bi–Sn alloys was re-evaluated with an advanced density measurement technique: the constrained drop method. By applying the new density data, the Bi–Sn phase diagram under pressure could be calculated successfully without any modification of thermodynamic parameters.

Hybrid metal/thermoplastic composites for FDM-type additive manufacturing

Hybrid material systems, where two materials with similar melting temperatures are combined to form a new compound, represent a possible avenue to expand the materials palette available for 3-D printing platforms such as fused deposition modeling (FDM™). In general, the morphology of filler materials in thermoplastic composites is unchanged before and after combining with a polymer matrix. However, the processing of hybrid material systems in FDM™-type processing allows for the possibility of manipulating the morphology of the filler material. The work presented here demonstrates the development of three different hybrid (polymer–metal) blends for 3-D printing platforms based on FDM™ technology. Tin-bismuth (SnBi) alloy powder was combined with three thermoplastic materials: (1) acrylonitrile butadiene styrene (ABS), (2) polylactic acid, and (3) a polymer blend composed of ABS and styrene ethylene butylene styrene containing a maleic anhydride graft (SEBS-g-MA). A notable feature observed through the use of scanning electron microscopy (SEM) was the drawing of the spherical SnBi particles into wires, leading to an in situ reinforcement. The efficacy of a silane functionalization process was also noted, though the material processing temperatures were well above the melting temperature of the SnBi particles.

Microstructural evolution and change in macroscopic physical properties of microscale flip chip Cu/Sn58Bi/Cu joints under the coupling effect of electric current stressing and elastic stress

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Solidification structure evolution of immiscible Al–Bi–Sn alloys at different cooling rates

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Effect of Nanoparticles Addition on the Microstructure and Properties of Lead-Free Solders: A Review

With the development of microelectronic packaging and increasingly specific service environment of solder joints, much stricter requirements have been placed on the properties of lead-free solders. On account of small size effect and high surface energy, nanoparticles have been widely used to improve the microstructure and properties of lead-free solders. Therefore, the composite solders bearing nanoparticles have recently attracted wide attention. This article reviewed the recent research on SnAgCu, SnBi, and SnZn composite solder alloys and introduced the effect of nanoparticles on their microstructure, mechanical properties, wettability, and reliability. The mechanism of nanoparticles strengthening was analyzed and summarized. In addition, the shortcomings and future development trends of nanoparticle-reinforced lead-free solders were discussed, which is expected to provide some theoretical reference for the application of these composite solder in 3D IC package.

Compositionally Screened Eutectic Catalytic Coatings on Halide Perovskite Photocathodes for Photoassisted Selective CO2 Reduction

Selective CO2 reduction via photoelectrocatalysis is a creative approach to alleviating the energy crisis and environmental deterioration as well as to producing value-added chemicals. A considerable challenge is the development of electrocatalysts and photoelectrocatalytic systems to selectively and efficiently produce a target product. Here, we report an efficient and selective photocathode for converting CO2 to HCOOH in aqueous solution. A rational compositional screening strategy was first applied to pinpoint In0.4Bi0.6 from ternary In–Bi–Sn alloys as the most HCOOH-selective electrocatalyst composition among the electrocatalysts reported. A photocathode was then fabricated by coating the catalytic, protective, and conductive In0.4Bi0.6 alloy layer on a halide perovskite photovoltaic, effectively utilizing its low melting point eutectic molten state. The generated photovoltage assisted reduction of the overpotential by 680 mV while producing a stable current for nearly exclusive HCOOH production under...

Wetting of Cu and Cu-Sn IMCs by Sn-Bi Alloys over Wide Composition at 350°C

Wetting of Cu and Sn-Cu intermetallics (IMCs) by molten Sn-Bi alloys with different interfacial reactivity was studied by the sessile drop method. The pre-formed IMC substrate has a better wettability, also it can be a method to control the thickness of the IMC layer as well as preventing Bi segregation, which is a potential way for optimizing mechanical property of joints. The evolution of interfacial structures, both of Sn-Bi/Cu and Sn-Bi/IMCs, can be verified from a Sn-Bi-Cu ternary phase diagram, and Bi segregation at an interface of Sn-Bi/Cu results from the saturated precipitation from solid solution rather than diffusion from liquid. The reaction of Sn with Cu2O (oxide film), both in a Sn/Cu system and a Sn-Bi/IMCs system, is the key for the occurrence of spreading, and the difference of reactivity caused the different spreading characteristics.

Mechanical Alloying Effect on Structural, Thermal and Mechanical Properties of Sn-Bi Alloy

Mechanical Alloying Effect on Structural, Thermal and Mechanical Properties of Sn-Bi Alloy

A carbon-supported BiSn nanoparticles based novel sensor for sensitive electrochemical determination of Cd (II) ions

A novel sensor based on carbon supported BiSn alloy nanoparticles (BiSn@C) was prepared for the sensitive detection of Cd2+. The BiSn@C and Nafion modified glassy carbon electrode (GCE) exhibited improved electrochemical performance in Cd2+ detection, because of its large specific surface area, abundance of active sites, good electrical conductivity, and strong cation exchange ability. Under the optimum conditions, the fabricated sensor showed good linearity of its response from 0.01 μmol/L to 30 μmol/L for the detection of Cd2+ and a limit of detection (LOD) of 3 nmol/L, which is considerably lower than the limit specified for safe drinking water as guided by the World Health Organization. The Nafion/BiSn@C/GCE was successfully applied for determination for trace Cd2+ in river samples with satisfying recoveries using the standard addition method.

Preferred orientation of Bi and effect of Sn-Bi microstructure on mechanical and thermomechanical properties in eutectic Sn-Bi alloy

The grain sizes and grain orientations of Sn and Bi phases in Sn-58Bi alloy are investigated. We find that the grain size of Bi is larger than that of Sn. Tensile test and two-dimensional simulation reveal that the ductility and yield stress decrease upon Bi coarsening after 504 h of thermal aging at 80 ∘C, and that thermal stress is crowed on the Sn-Bi phase boundaries and is higher in Bi phase than that in Sn phase. Moreover, [0001] preferred orientation of Bi phase along the normal direction of the free surface of the casting model is observed.

The newly developed Sn–Bi–Zn alloy with a low melting point, improved ductility, and high ultimate tensile strength

A new Sn-45Bi-2.6Zn (wt%) alloy was developed to replace the eutectic Sn-58Bi alloy as a low-melting point solder alloy. A 112% increase in the tensile elongation (0.68 vs. 0.32 in strain) was obtained by increasing the Sn-to-Bi volume ratio by reducing the volume content of brittle Bi. A solidus temperature of 133 °C was calculated from the Sn–Bi–Zn ternary system. The calculation of phase diagram (CALPHAD) method was performed to help understand the melting behavior of Sn-45Bi-2.6Zn alloy.

Characterization of metallic-packaging fiber Bragg grating sensors with coated and bare fibers.

Metallic packaging of fiber Bragg grating (FBG) sensors is developed using the ultrasonic welding method. Both polyimide-coated fiber and bare fiber could be bonded well to aluminum alloy substrate using Sn-Bi alloy. Two kinds of metal-packaged FBG sensors, coated FBG and bare FBG, are characterized for studying the thermal sensitivity, strain response, short-term creep, and temporal temperature response. Both FBG sensors showed increasing sensitivity with temperature from -40°C to 80°C. The metal-packaged coated FBG sensor displayed relative strengths in strain stability, repeatability, creep, spectra shape, and temperature response when compared with the bare one. Moreover, the boundaries between optical fiber and metal alloy are intact, and cross-sectional scanning electron microscope micrographs clearly illustrated that metal alloy coated well with the coated and bare fiber.

Impact of Non-Reactive Ceria Nanoparticles on the Wettability and Reaction Kinetics Between Lead-Free Sn–58Bi and Cu Pad

Lead-free Sn–58Bi–xCeO2 (x in wt% = 0, 0.3, 0.6 and 0.9) composite solder was prepared via mechanical blending and melting route. The ceria nanoparticles (CeO2) were prepared from chemical precipitation method. Further, the variation in microstructure and phase composition, melting point, wetting and mechanical properties were studied through scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry, spreading ratio, contact angle and tensile testing, respectively. It was shown that Sn–58Bi–xCeO2 composite solders show 16.66 and 32.05% increase in spread ratio and wetting angle, respectively, due to the enhanced melt fluidity up to x = 0.6. The fraction of hard Bi-phase was also refined simultaneously. The tensile results showed a slight decrease in ultimate tensile strength and enhancement in ductility up to x = 0.3 and 0.6 except at x = 0.9. High temperature aging also demonstrated a reduced intermetallic compounds thickness when fraction of ceria nanoparticles in the matrix was up to x = 0.6. It is suggested that for optimum set of soldering properties, the concentration of the nanoparticles should be at 0.6 wt% in the monolithic Sn–58Bi alloy.

Analysis of experimental uncertainties in jet breakup length and jet diameter during molten fuel-coolant interaction

The jet breakup length is one of important phenomenological parameters to evaluate the corium debris bed coolability during the progress of severe accident in nuclear power plant, since the parameter is related to the determination of the liquid melt fraction in debris bed. Existing jet breakup length data reveal relatively large scattering and different trends, similar to the Saito or Epstein correlation, depending on cases. The scattering and separation of the data may be due to uncontrolled factors in the melt discharge condition and also inconsistent evaluation methods used for the jet breakup length.Through melt jet breakup experiments with low melting point metal alloy (Bi-Sn alloy), the influence of the estimation methods for the jet diameter (measured or calculated value) and the jet breakup length (position- or velocity-based value) was investigated. According to the comparison between the measured and calculated jet diameters, the experimental uncertainty was reduced by producing well-controlled melt jet. The concept of the jet breakup length was revisited in detail, emphasizing the shorter breakup length by the velocity-based method. The modification of the Saito correlation constant from 2.1 to 1.7 was suggested to fit the velocity-based breakup length. The importance of a well-defined data analysis process for non-dimensional jet breakup length was highlighted for the minimization of the experimental uncertainty.

Effect of Sn contents on thermodynamic, microstructure and mechanical properties in the Zn90–Bi10 and Bi88–Zn12 based ternary alloys

The thermal conductivity variations with temperature for Zn90 − x–Snx–Bi10 (x = 5,10, 40 and 85 wt%) and Bi88 − x–Snx–Zn12 (x = 1.39, 43.26 and 79.3 wt%) alloys were measured by using the linear heat flow method. From thermal conductivity–temperature plots, the coefficients of thermal conductivity for the Zn–Sn–Bi alloys were calculated. The microstructures of Zn–Sn–Bi alloys were observed using scanning electron microscopy (SEM). The existing phases into microstructure were identified energy dispersive X-ray (EDX) analysis. The melting temperatures, the enthalpy of fusion and specific heat change between the liquid and solid phases in the Zn–Sn–Bi alloys were determined from Differential Scanning Calorimetry (DSC) trace. The tensile strength and microhardness of the alloys were measured using a Shimadzu Universal Testing Instrument (Type AG-10 KNG) and Future-Tech FM-700 model microhardness device.

Effects of Different Mold Temperature on Dendrite Morphology of Sn-Bi Alloy in Directional Solidification

The directional solidification process of Sn–10 wt% Bi alloy with low melting point was observed by synchrotron X-ray imaging technology. The mold temperature was controlled, and the dynamic images of a series of alloy solidification behavior were obtained. The results show that columnar crystal grows in dendrite morphology. It is also found that dendrite morphology changes at different mold temperature. With the decrease of the mold temperature, the dendrite morphology begins to change from irregular to regular, and finally, the primary dendrites and the secondary dendrites are perpendicular to each other.

Effects of Ti addition on the microstructure, mechanical properties and electrical resistivity of eutectic Sn58Bi alloy

Titanium (Ti)-added tin-58 wt% bismuth (Sn58Bi) solder alloys were synthesized in this study. The microstructural evolution and mechanical property change of the eutectic Sn58Bi and Ti added Sn58Bi alloys were studied before and after thermal aging. Ti added Sn58Bi alloys exhibit a considerably refined microstructure compared with the eutectic Sn58Bi alloy because of the presence of the Ti2Sn3 and Ti6Sn5 intermetallic compounds (IMCs). The formation history of these Ti-Sn IMCs was studied based on a thermodynamic calculation. After thermal aging, the yield strength (YS) and ultimate tensile strength (UTS) of the eutectic Sn58Bi decreased, while the Ti added Sn58Bi alloys maintained the highest YS and UTS. Notably, the superior elongation of 0.5 wt% Ti added sample compared with that of the eutectic Sn58Bi alloy was obtained after 1008 h aging. The fracture morphology of the Ti added Sn58Bi alloys almost unchanged during aging due to the stable microstructure. In addition, the electrical resistivities of the eutectic Sn58Bi were tested, while the resistivities decreased in the Ti added Sn58Bi alloys at room temperature.