Lead-free Alloys Research Articles

Unveiling the shielding potential: Exploring photon and neutron attenuation in a novel lead-free XCr2Se4 chalcogenide Spinals alloys with MCNP 4C code

The study covers shielding properties of three promising lead-free XCr2Se4 alloys, where X represents Mn, Cu, or Ag, across a spectrum of energies between 0.02 MeV and 15 MeV. MCNP4C was employed to simulate the mass attenuation coefficient (MAC) for the three selected alloys. After being prepared using the conventional solid-state reaction method, the samples displayed densities ranging from 5.45 g cm−3to 6.22 g cm−3. The simulated results obtained from the MCNP4C are then benchmarked with data obtained using different software such as Phy-X, Py-MLBUF, EPIXS, and GRASP. Upon comparing the acquired results with the Phy-X data, a notable correlation was observed with a relative difference ranging from 0.11% to 8.57%. The accuracy of the simulated data was additionally validated through the Kolmogorov-Smirnov test. From the simulated MAC, different ionizing radiation shielding properties including linear attenuation coefficient (LAC), half-value layer (HVL), mean-free path (MFP), transmission factor (TF), radiation protection efficiency (RPE), and fast neutron removal cross section (FNRCS) were calculated to provide a comprehensive analysis of the samples' efficacy in dealing with different types of radiation. The LAC for neutrons at different energies is also examined. HVL analysis indicates the radiation-blocking capacity of the samples. The TF shows the alloys’ ability to either permit or restrain the transfer of radiation. Additionally, RPE and FNRCS give indication of the shielding potential of the studied samples. This study is important for nuclear physicians and researchers and serves as useful data for the development of superior shielding materials.

Theoretical exploration of thermodynamic characteristics in lead-free liquid alloys: Zn-Bi-In System

The calculations of Zn activities in the ternary liquid solder alloy Zn-Bi-In at 873 K were conducted through the application of the Molecular Interaction Volume Model (MIVM). The calculated values were compared to experimental data for three different cross-sectional examinations, namely for the bismuth-to-indium ratios (xBi: xIn) of 1:2, 1:1, and 2:1. Moreover, the integral excess free energy of these ternary liquid alloys was assessed using the same model parameters in order to test their validity. Then, the values were compared to the relevant experimental data reported in the literature that was already in existence. A satisfactory concordance has been observed between the theoretical predictions and the experimental findings.

A New Lead-Free Copper Alloy CuAl8Fe5Ni4Zn4Sn1 for Plain Bearings and Its Strengthening Mechanisms

CuAl8Fe5Ni4Zn4Sn1 (OF 2238) is a new lead-free copper alloy for plain-bearing applications that was first officially presented in a scientific journal in 2020. Soon after its invention, the use of the alloy for connecting rod bushings in heavy-duty internal combustion engines was promoted and validated with customers. The aim of this article is to describe the material properties of the new alloy in more detail than previously and explain how the advantageous properties of CuAl8Fe5Ni4Zn4Sn1 are generated. At the beginning of this article, the general development trends in the field of copper alloys for sliding applications are presented, into which the new alloy from this publication can be classified. In the main part of this publication, the authors go through the production chain of CuAl8Fe5Ni4Zn4Sn and show how the entire manufacturing process contributes to obtaining a material with a combination of high strength, ductility and sufficient toughness. This starts with fine microstructures after casting, followed by homogenisation and refinement during hot extrusion and work hardening chiefly during cold drawing. What is most surprising, however, is the finding that a strong hardening effect can be achieved in the new alloy by precipitation of fine κ-phase at temperatures of about 400 °C and air cooling without prior solution treatment. These results make it clear that there is great potential for further material developments to support material efficiency and even to expand the application limits.

Effect of Creep, Fatigue and Random Vibration on the Integrity of Solder Joints in BGA Package

This study employs Finite Element Analysis (FEA) to investigate the effects of creep, fatigue, and random vibration on the integrity of solder joints in BGA packages in electronic modules. Evaluating the response of lead-based Sn63Pb37 and lead-free SnAgCu alloy solders (SAC305, SAC387, SAC396, and SAC405) to induced loads - stress, strain, strain energy density, and displacement in the joints is obtained and studied better to understand the mechanism of the joints' degradation. SAC305 and SAC405 are modelled with linear stress-temperature relationships σ = 3.152T–68.167 and σ = 1.543T–34.983, respectively. The magnitude of the strain energy density in the joints is a key failure driver. SAC387 and SAC396 solder joints display lower values of strain energy density and thus have higher durability. Displacement analysis indicates that SAC305 and Sn63Pb37 are prone to deformation-induced failure. SAC387 exhibits the highest fatigue yield stress at 58 MPa, while SAC405 displays the lowest stress at 22 MPa. Analysis of the results of random vibration shows that Sn63Pb37 developed the highest stress at 34.62 MPa and is thus susceptible to stress-induced failure. The robust stress, strain, and strain energy responses of SAC405 and SAC396 provide key insights into improving the mechanical reliability of future electronic devices towards better sustainability.

Critical solder joint in insulated gate bipolar transistors (IGBT) power module for improved mechanical reliability

This investigation identifies the critical solder joint in a typical Insulated Gate Bipolar Transistor (IGBT) module and provided new knowledge on how operating thermal loads degrade IGBT-attach, Diode-attach, and Substrate solder joints in the device. SolidWorks software is used to create three realistic 3-D Finite Element (FE) models of the typical IGBT module used in this investigation. In-service operating power and IEC 60068–2-14 thermal cycles are implemented in ANSYS mechanical package to simulate the response of the three solder joints in the FE models to the load cycles. The solder in the joints is lead-free alloy of 96.5% tin, 3% silver, and 0.5% copper (SAC305) composition. The SAC305 material properties are modelled as time and temperature dependent with Anand's visco-plastic model employed as the constitutive model. Results show that the key degradation mechanism of solder joints in IGBT module are stress, plastic strain, and strain energy magnitudes. Accumulated plastic strain in the joints is found the predominant damage factor. Critical solder joint in the module depends on the load cycle the device experiences. IGBT-attach solder joint is critical in active power load cycle. Substrate solder joint degraded most in passive thermal cum combined passive thermal and active power load cycles.

Zinc and bismuth additives' impacts on the physical properties of lead-free alloys used in electronic appliances

Zinc and bismuth additives' impacts on the physical properties of lead-free alloys used in electronic appliances

Investigations on chip breakability in lead-free brass alloy CW511L using different chip breaking geometries

Brass is an alloy of copper and zinc, commonly alloyed with lead. Due to legal restrictions, the lead-content is decreasing nowadays. This leads to higher cutting forces and worse chip breakability. To face these challenges, adapted tool geometries were investigated. To decrease cutting forces, positive rake angles can be utilized. On the other hand, this will lead to worse chip breakability in single phase lead-free brass alloys. Therefore, chip breaking geometries are necessary. This paper investigates and compares different forms of chip breaking geometries to improve chip breakability when using highly positive rake angles in lead free brass alloy CW511L.

Development of a Friction Model for Cutting Simulations of Lead-Free CuZn-Alloys

The element lead is used as an alloying element in CuZn-alloys with mass contents of up to mPB = 4 % to improve machinability properties. Due to its toxicity, a variety of legislative initiatives aim to reduce the lead content in CuZn-alloys, which leads to critical machinability problems and a reduction in productivity of machining processes. In order to improve the machinability of lead-free CuZn alloys, it is imperative to analyze the influencing variables and mechanisms of chip formation in detail. In addition to the experimental analysis of the machining process, numerical modeling approaches can be used for this purpose. So far, no valid chip formation model for the description of the chip formation of lead-free CuZn-alloys has been established. Within the scope of this work, the foundation for the chip formation model is to be laid by developing a friction model for the meshing conditions in the machining process between lead-free brass and carbide. In addition to the material model, this model is the subsequent input variable for the chip formation model and thus enables the numerical simulation of machining processes with lead-free CuZn-alloys.

Theoretical Investigation of the Thermodynamic Properties of Lead-free Ternary Alloys Sn-Sb-Bi and their Subsystems

The concentration-dependent properties, like the constituents’ activities for the binary liquid alloys like Sb-Sn at 905 K, Bi-Sn at 600 K, and Bi-Sb at 1200 K, and the integral Gibbs free energy of mixing, ΔGXS, of the correspondent alloys were computed using the molecular interaction volume model (MIVM). Further, the model has been used to compute the activities of the component Sn in the ternary Sn-Sb-Bi system at 900K at the three cross-sections, i.e., Sb:Bi = 1:3, 1:1, and 3:1. The theoretical data have been analyzed with the corresponding experimental data accessible in the literature. An acceptable concurrence has been obtained, with some inconsistencies. The activities of the ternary alloys along the three cross-sections, i.e., Sb:Bi = 1:3, 1:1, and 3:1, show that the deviations change from positive to negative with increasing Sb content. The results confirm that MIVM is a good model for estimating the thermodynamic properties of binary and ternary systems.

The effect of high-pressure cutting fluid supply on the chip breakability of lead-free brass alloys

To improve machinability and in particular chip breakability, brass alloys are usually alloyed with small quantities of lead. Due to environmental and health concerns, the use of lead has been restricted in the last years. As lead-free brass alloys are progressively implemented in the industry, challenges arise due to their differing properties from traditional leaded brass alloys. One of the main challenges in automated continuous cutting processes is the worse chip breakability of lead-free brass alloys leading to longer and tangled chips. Hence, the impact of a high-pressure cutting fluid supply, as well as the impact of a chip-breaking geometry and the combined effect of both, has been investigated at different feeds. The three brass alloys CuZn37 (CW508L), CuZn38As (CW511L), and CuZn42 (CW510L) were studied at varying cutting fluid supply pressure levels and feed rates in a radial cutting operation. Cutting forces were measured, and chips were analyzed. No overall systematic impact of the cutting fluid supply pressure on the cutting forces was observed. In conclusion, increased pressure levels, a chip-breaking geometry, and an increased feed rate enhance the chip breakability of the investigated alloys.

Thermodynamic and Microstructural Analysis of Lead-Free Machining Aluminium Alloys with Indium and Bismuth Additions.

The present study comprises an investigation involving thermodynamic analysis, microstructural characterisation, and a comparative examination of the solidification sequence in two different aluminium alloys: EN AW 6026 and EN AW 1370. These alloys were modified through the addition of pure indium and a master alloy consisting of indium and bismuth. The aim of this experiment was to evaluate the potential suitability of indium, either alone or in combination with bismuth, as a substitute for toxic lead in free-machining aluminium alloys. Thermodynamic analysis was carried out using Thermo-Calc TCAL-6 software, supplemented by differential scanning calorimetry (DSC) experiments. The microstructure of these modified alloys was characterised using SEM-EDS analysis. The results provide valuable insights into the formation of different phases and eutectics within the alloys studied. The results represent an important contribution to the development of innovative, lead-free aluminium alloys suitable for machining processes, especially for use in automatic CNC cutting machines. One of the most important findings of this research is the promising suitability of indium as a viable alternative to lead. This potential stems from indium's ability to avoid interactions with other alloying elements and its tendency to solidify as homogeneously distributed particles with a low melting point. In contrast, the addition of bismuth does not improve the machinability of magnesium-containing aluminium alloys. This is primarily due to their interaction, which leads to the formation of the Mg3Bi2 phase, which solidifies as a eutectic with a high melting point. Consequently, the presence of bismuth appears to have a detrimental effect on the machining properties of the alloy when magnesium is present in the composition.

Power Law Creep Behavior Model of Third Generation Lead-Free Alloys Considering Isothermal Aging

Abstract In realistic applications, the solder joint is continually subjected to thermal-mechanical stress due to the difference in the coefficient of thermal expansion between the printed circuit board substrate and the electronic packaging components. Creep and fatigue processes were the most common causes of failure in electronic assemblies. Under isothermal aging, creep deformation becomes more prominent. The aged microstructure was recognized by intermetallic coarsening and the appearance of intergranular fracture generated by dynamic recrystallization in the bulk solder joint. In this study, the influence of Bi content on the creep behaviors of solder joints was investigated under various aging conditions. Three lead-free solder alloys, including SAC305, SAC-3Bi, and SAC-6Bi, are tested at room temperature. For each alloy, preliminary micro-indentation tests were conducted to define three stress levels for distinct aging conditions. After each test, displacement versus time data was gathered. A novel approach based on an empirical model was developed to systematically examine the development of the steady-state creep rate. A power dependency prediction model was developed to investigate the relationship between creep strain rate and stress levels. The steady-state creep rate of SAC305 is significantly higher than that of SAC-Bi alloys owing to the presence of bismuth (Bi) in the solid solution at room temperature. The creep properties showed less variation after 100 h of aging. SAC-Bi alloys showed less coarsening of the intermetallic compounds precipitates after aging than SAC305. In the SAC-Bi solder alloys, combinations of precipitate and solid solution hardening mechanisms were observed, while Ag3Sn particles were the dominant strengthening mechanism in the SAC305 alloy system.

Lower Temperature Soldering Using Supercooled Liquid Metal

Lead-free solder metal alloys can be formed into supercooled liquid metal microcapsules and used to create solid full metal interconnects at dramatically lower processing temperatures. These alloys can be made with or without bismuth. The technology encapsulates known and established RoHS compliant solder alloys inside a thin oxide/organic shell nanofilm that keeps the metal in a metastable supercooled liquid state at ambient temperatures. The thin oxide/organic shell can be mechanically broken or chemically dissolved to release the liquid metal that then rapidly solidifies all without requiring heat. The novel solder interconnect technology avoids thermal damage to components and materials, or quality issues caused by coefficient of thermal expansion mismatch.

Effect of temperature on the low cycle fatigue properties of BGA solder joints

Since the restriction of hazardous substances (RoHS) directive, lead-free soldering has been widely broad adopted. In many applications, lead-free alloys have been substituted for conventional SnPb (Tin-Lead) solder. Among lead-free alloys, SAC305(Sn-3.0Ag-0.5Cu) has gained the highest acceptance as a solder alloy. The fatigue performance of solder joints has become an essential reliability assessment criterion due to the transition to more reliable lead-free alloys from highly predictable lead-based alloys. This study examines the shear fatigue characteristics of sandwich test vehicles for SnPb and SAC305 at different temperatures using both Organic Solderability Preservative (OSP) and Electroless Nickel-Immersion Silver (ENIG) surface finishes. The fatigue experiments were performed using an Instron micromechanical tester at a constant strain rate, and microstructural analysis was carried out using Scanning Electron Microscopy (SEM) to identify the Intermetallic Compound (IMC) morphology and failure mode. The stress-strain (hysteresis) loops of SnPb and SAC305 were measured, and the fatigue life of the specimens was estimated using the strain-life equation at various temperatures. SAC305 was observed to have a better fatigue life than SnPb, particularly at higher strain levels or testing temperatures. The OSP surface finish demonstrated superior fatigue properties compared to the ENIG surface finish. Additionally, elevated testing temperatures were found to accelerate fatigue failure in solder joints. The Arrhenius model was utilized to develop a general empirical model that predicts the fatigue life of SAC305 and SnPb solder alloys with OSP and ENIG surface finishes as a function of the strain level and testing temperature.

Structural, mechanical and radiation shielding properties of lead and lead-free alloys doped with CuO nanoparticles for radiation protection

We examine four systems with different chemical compositions Pb-50Sn-0.5CuO, Pb-50Zn-0.5CuOx, Sn-50Bi-0.5CuO and Sn-50Zn-0.5CuO prepared by the melt-spun technique. To obtain the morphological features of the prepared alloys, a scanning electron microscope, SEM, was utilized. The prepared samples were analyzed by using an analytical XRD tool to verify the lattice distortion, different identification phases and crystallite size for the examined alloys. The mechanical investigations including basic parameters such as microhardness, elastic moduli, ultimate tensile strength and toughness were analyzed using the Vickers microhardness technique and tensile test machine. The results showed that Pb-free alloys doped with CuO NPs had proper mechanical properties and shielding capability for as-prepared systems. It may be due to refined microstructures that could obstruct the dislocation movement. The radiation shielding parameters of as-prepared alloys are studied at photon energies of 0.511, 0.662 and 1.275 MeV. The lead-free alloys’ doped CuO NPs can be superior shielding material than those of lead alloys. Therefore, the results indicated that the lead-free alloy compositions doped with CuO nanoparticles are recommended to exhibit maximum shielding efficiency. Hence, the Sn-50Bi-0.5CuO and Sn-50Zn-CuO alloys had excellent potential and could be applied as radiation shielding materials.

Ultra-low-temperature lead-free multicomponent alloy solder for application in heat-sensitive electronic components

This manuscript describes the development of a lead-free multicomponent solder alloy composed of Sn, Bi, In, Cu, and Zn for heat-sensitive electronic devices. The microstructure comprises a homogeneous distribution of CuZn particles embedded in a eutectic mixture of Sn (solid solution) and InBi with a melting temperature of 83.7 °C. The average thickness of the generated intermetallic compounds between solder/substrate (Cu) was < 4 µm with a wetting contact angle below 55°, which is acceptable in the electronic industries. Additionally, the solder's shear stress (12.94 ± 1.50 MPa) is lower than commercial counterparts; but it shows a much higher shear strain (0.53 ± 0.06 mm/mm). Thus, the developed system could have great potential for applications in ultra-low-temperature lead-free solders.

Investigation of microstructure, machinability, and mechanical properties of new-generation hybrid lead-free brass alloys

Abstract In this study, hybrid alloys were obtained by casting method with alloy elements and additive such as Si and MoS2, which can be used instead of lead, and compared with Ecobrass and free cutting brass samples used in the market in terms of microstructure, mechanical, and machinability properties. The microstructures of lead-free hybridized brass consists of alpha, beta, and intermetallic compound which were confirmed by the results of X-Ray Diffraction analysis and Scanning Electron Microscopy-Energy Dispersive Spectroscopy. The hardness values of the beta phase in the microstructure are between 180 and 220 Vickers hardness. It has been observed that increasing the amount of beta prime phase also increases the hardness. The machinability of samples was evaluated in terms of surface roughness and chip formation. Chips obtained from samples after machining process were categorized according to ISO 6385-G1 standard. Chip morphologies were examined under optic microscope and scanning electron microscope. The surface roughness value of samples with MoS2 additives was found to be the lowest due to its lubricity effect. Moreover, morphologies, distribution of phases, and intermetallic compounds in the microstructure are found to have a great impact on the machinability and ultimate tensile strength.

A comparative study on the machining performance of eco-friendly low-lead and lead-free brass alloys in replacement for leaded ones

A comparative study on the machining performance of eco-friendly low-lead and lead-free brass alloys in replacement for leaded ones

Structure formation and peculiarities of crystallisation of lead-free tin – zinc alloys obtained by rapid solidification

The results of the study of the microstructure of lead-free alloys of the tin – zinc system obtained by rapid solidification at a cooling rate of at least 105 K/s are presented. In tin and zinc alloys with concentrations of 1.2–2.0 wt. % Zn and 1.5 wt. % Sn, respectively, during rapidly cooling of the melt, the alloying element is captured. The formed solid solutions are supersaturated and at room temperature disintegrate according to the mechanism of formation and growth of nuclei of a new phase. The average size of zinc and tin precipitates after holding the foil for two days does not exceed 0.5 μm. Melts of compositions Sn – 4.4–15.0 wt. % Zn after rapidly cooling are supercooled and supersaturated by two components and experience spinodal decomposition (stratification) followed by the formation of supersaturated solid solutions based on tin and zinc, which disintegrate at room temperature. The average size of zinc precipitates in non-equilibrium eutectic does not exceed 2 μm. In rapid solidificated foils of alloys containing 50–80 wt. % Zn, a two-phase structure is formed from solid solutions based on tin and zinc. The average size of tin precipitates does not exceed 1 μm. As the crystallisation front moves away from the contact surface of the foil with the surface of the mold, the tin particles become larger and the specific surface of the interphase boundary decreases.

Latent heat induced deformation of PCB substrate: Measurement and simulation

The work evaluates the impact of latent heat (LH) absorbed or released by a solder alloy during melting or solidification, respectively, on changes of dimensions of materials surrounding of the solder alloy. Our sample comprises a small printed circuit board (PCB) with a blind via filled with lead-free alloy SAC305. Differential scanning calorimetry (DSC) was employed to obtain the amount of LH per mass and a thermomechanical analyzer was used to measure the thermally induced deformation. A plateau during melting and a peak during solidification were detected during the course of dimension change. The peak height reached 1.6 μm in the place of the heat source and 0.3 μm in the distance of 3 mm from the source. The data measured during solidification was compared to a numerical model based on the finite element method. An excellent quantitative agreement was observed which confirms that the transient expansion of PCB during cooling can be explained by the release of LH from the solder alloy during solidification. Our results have important implications for the design of PCB assemblies where the contribution of recalescence to thermal stress can lead to solder joint failure.