Development Of Lead-free Solders Research Articles

Effects of TiC nanoparticle addition on microstructures and mechanical properties of Sn-58Bi solder joints

The Sn58Bi solder has gained significant attention in the electronic packaging industry owing to its low melting temperature and excellent mechanical properties. However, the brittleness of Sn58Bi solder presents challenges in practical applications. This study investigates the effect of adding titanium carbide (TiC) nanoparticles on the mechanical properties of Sn58Bi solder joints. The study examines the melting behavior, spreadability, microstructure, and mechanical properties of Sn58Bi-xTiC (x = 0, 0.05, 0.1, 0.2 wt%) composite solders. The results indicate that adding TiC nanoparticles has merely a minor effect on the melting point of the Sn58Bi solder. However, the presence of TiC nanoparticles refined the solder’s microstructure, reduced the thickness of the intermetallic compounds, and enhanced the spreadability and mechanical properties. The Sn58Bi-0.1TiC composite solder exhibits the most favorable properties, including a 28.6 % increase in fracture energy compared with that of Sn58Bi solder. Consequently, incorporating TiC nanoparticles enhances the performance of the Sn58Bi solder by improving its spreadability and reducing its brittleness. These results hold great potential for advancing the development of lead-free solders with improved reliability and performance in electronic applications. The findings of this study could pave the way for the practical and widespread use of Sn58Bi-xTiC composite solders, offering a viable alternative to lead-containing solders while maintaining excellent mechanical characteristics.

Effect of nano-phased bismuth–tin alloy surface coating on tribo-mechanical properties of basalt fiber reinforced composites

A novel method for coating basalt fiber with a eutectic bismuth–tin (Bi–Sn) mixture was developed. Bi-Sn nanoparticles were synthesized using a sol-gel process and deposited on basalt fiber by chemical vapor deposition, with the aim of evaluating the tribo-mechanical properties of the final epoxy-composite material. X-ray diffraction showed that the synthesized Bi–Sn alloy was highly polycrystalline with equal distribution of tetragonal and orthorhombic Bi–Sn polymorph phases with crystallite sizes between 17 and 55 nm. High-resolution electron microscopy revealed that the sample possesses highly fused, flake-stacked planar layers, with 50 nm-thick flakes of variable length. Elemental analysis determined that the alloy contains 57% Bi (at.wt%), and Raman spectroscopy confirmed the characteristic Bi–Sn fingerprint peaks of 148, 201, and 397 cm−1. Thermal analysis of the composites showed good thermal stability with only 4% mass loss at 700 °C. Furthermore, an increase in the Bi–Sn loading enhanced the tribo-tensile properties. It was found that at a Bi-Sn gravimetric loading of 0.2 g the composite yielded the highest ultimate tensile strength of 303 MPa compared to the reference (154 MPa), even as the Young's moduli showed a decrease in elasticity by up to 24.99%. Moreover, the tribology results showed a good friction coefficient (0.5), with a negligible wear rate (4.53 × 10−8 mm3/Nm) and relatively low wear volume (0.118 mm3). Thus, the proposed method resulted in alloy composites with improved tribo-mechanical properties, and has potential applicability in the development of lead-free solders.

Development of lead free solder for electronic components based on thermal analysis

In the post COVID-19 virus era, online teaching and work from home have develop a common trends so the demand of electronic component rapidly increases. The development of lead-free solder has grown rapidly because various environmental legislations have enforced laws to restrict the use of Lead (Pb), Mercury (Hg) and Cadmium (Cd), etc because this is hazardous materials. In electronic and electrical industries. Many lead-free solder composition such as Sn - Bi, Sn - Cu, Sn - Zn, Sn - Ag, Zn - Bi, Sn – Ag - Cu, Sn – Zn - Bi, Sn – Cu - Bi, Sn – Cu - Ni etc. have been developed as a replacement of Sn - Pb solder. Researcher are facing challenges due to rise in melting temperature in lead-free solder (LFS) and the formation of intermetallic compound. This review paper aimed to summarise the thermal properties of lead free solders (LFS) and analyse the effect of addition of various elements and reinforcement in Sn based lead free solder (LFS).

Microstructural evolution of the Sn-51Bi-0.9Sb-1.0Ag/Cu soldering interface during isothermal aging

Development of lead-free solders with a melting point lower than that of the most widely used Sn-3.0Ag-0.5Cu (SAC305) is crucial for coping with the welding defects of ultra-thin microchips. The Sn-58Bi solder with a low melting point of 138 °C is a promising one. However, some severe issues of this solder, such as the brittle failure of soldering interface and the serious coarsening of the intermetallic compound (IMC) in the solder/Cu matrix interface, have hindered its applications in microelectronic assembly industries. In this work, the morphologies and layer thicknesses of interfacial intermetallic compounds between the Sn-51Bi-0.9Sb-1.0Ag solder and Cu substrate during the isothermal aging at 125 °C have been investigated. The results show that the scallop-like intermetallic compound layers of different curvature radii are formed at the solder joint interfaces. The main phase composition of the IMC layer is Cu6Sn5. After the isothermal aging treatment, the IMC layer gradually becomes a flat layer. The IMC thickness of the Sn-51Bi-0.9Sb-1.0Ag/Cu soldering interface at the stable state is thinner by 33% compared to that of the Sn-58Bi/Cu interface. By fitting the experimental data, the growth rate constant of the IMC layer in the Sn-51Bi-0.9Sb-1.0Ag/Cu solder joint is 2.060 × 10–18 m2·s−1, while it is 7.302 × 10–18 m2·s−1 in the Sn-58Bi/Cu solder joint. The present study indicates that the addition of Sb and Ag elements can substantially suppress the IMC layer growth.

The Effect of Germanium Addition on the Lead-free Solder Alloys: A Short Review

The Restriction of Hazardous Substances (RoHS) has been enforced a law to restrict the use of hazardous materials in electronic and electrical industries. Hence, it leads to the development of lead-free solder among the electronic industry. SnAg, SnCu, SnAgCu, and SnZnBi solders are found to be alternatives to replace SnPb solder alloys. However, they still have many problems, such as large undercooling and large intermetallic compounds are still present in the solder alloys. Later, researchers come up with the idea of adding alloying elements to lead-free solders to further enhance the properties of lead-free solders. This review paper is aimed to analyze and summaries the effects of germanium (Ge) addition to lead-free solders focusing on its microstructure and thermal properties. The Ge has an almost similar crystal structure as pure tin (Sn), so it is expected that the properties of the lead-free solder could be enhanced by adding an appropriate amount of Ge. Nevertheless, Ge has a unique characteristic as it could act as an antioxidant agent in the lead-free solders.

Characteristics of eutectic and near-eutectic Zn–Al alloys as high-temperature lead-free solders

Lead-based alloys are conventionally used for soldering interconnections that are expected to perform at high temperatures. Because of the concerns of lead toxicity, the development of lead-free solders became important. Till now, none of the proposed alloys have the characteristics that can completely substitute the Pb-bearing solders for high-temperature soldering application. Recently, researchers studied many ternary and quaternary systems near Zn–Al binary eutectic composition and reported prospects in soldering applications. However, the bulk solder properties of the Zn–Al binary system near the eutectic composition is rare in the literature. In the present study, the microstructure and thermal, mechanical and electrical characteristics of eutectic and near-eutectic Zn–Al alloys are investigated as replacement of traditional lead-bearing high-temperature solders. Mechanical and electrical properties of Zn was enhanced by alloying with Al, without altering much of the thermal expansion co-efficient. Finally, the material properties of the prepared Zn–Al alloys and other Zn-based alloys are compared with the conventional Pb–Sn solders. Research shows, 7 wt% Al–Zn alloy has multiple times higher magnitude of ultimate tensile strength, Vicker’s microhardness and electrical conductivity than the traditional Pb–Sn high-temperature solders. The melting temperature of the alloys was a bit higher than the Pb–Sn solders. A suitable ternary element addition to the system can potentially replace the conventional Pb-based high-temperature solders.

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.

Thermodynamic Optimization of the Ag–Bi–Cu–Ni Quaternary System: Part I, Binary Subsystems

A comprehensive literature review and thermodynamic optimization of the phase diagrams and thermodynamic properties of the Ag–Bi, Ag–Cu, Ag–Ni, Bi–Cu, and Bi–Ni binary systems are presented. CALculation of PHAse Diagrams (CALPHAD)-type thermodynamic optimization was carried out to reproduce all available and reliable experimental phase equilibrium and thermodynamic data. The modified quasichemical model was used to model the liquid solution. The compound energy formalism was utilized to describe the Gibbs energies of all terminal solid solutions and intermetallic compounds. A self-consistent thermodynamic database for the Ag–Bi, Ag–Cu, Ag–Ni, Bi–Cu, and Bi–Ni binary subsystems of the Ag–Bi–Cu–Ni quaternary system was developed. This database can be used as a guide for research and development of lead-free solders.

Influence of Bismuth in Sn-Based Lead-Free Solder – A Short Review

Since the implementation of RoHS in avoidance to useof lead in electronic packaging, the development of lead-free solder has become priority. However, some of the potential candidates for lead-free solder have weaknesses such as slightly higher of melting point, excessive of intermetallic growth (IMC) and uncertainty service reliability that need to overcome. One of the common methods used to improve the characteristic and properties of the lead-free solder is by the addition of another alloying element. One of the promising alloying elements is bismuth (Bi). A few researchers have found out that Bi has a capability to improve the microstructure, reduce the melting temperature and controlled the IMC growth, yet, its advantageous is believed have not been thoroughly explored. Influence of (Bi) in lead-free solder alloys give interest to be studied and understand from different perspective due to its capability to improve the wettability and solder spread, and also reduce the melting temperatures of the solder. In this paper, a review on influence of Bi inSn-based lead-free solder and its advantageous were discussed.

Investigation of Multicomponent Lead-Free Solders

Abstract According to the directives (RoHS and WEEE) adopted by the European Union, lead has been banned from the manufacturing processes because of its health and environmental hazards. Therefore, the development of lead-free solders is one of the most important research areas of the electronic industry. This paper investigates multicomponent Sn-Ag-Cu based lead-free solders with different compositions. The properties of the six-component Innolot (SAC+BiSbNi) and two low-Ag containing alloys were compared with the widespread used SAC307 solder. Microstructure investigations and X-ray diffraction measurements were performed to analyze and identify the formed phases, furthermore, tensile tests and microhardness measurements were executed to determine the mechanical properties of the examined solders.

Cooling and Annealing Effect on Indentation Response of Lead-Free Solder

With the development of lead-free solders in the electronic packing industry, Sn–Ag–Cu solders are one of the most promising lead-free alloys to be applied due to their outstanding mechanical property and wettability. By performing indentation experiments, the effect of cooling rate on the mechanical properties of Sn–3.0Ag–0.5Cu (SAC305) solder is investigated in typical cooling conditions (i.e., furnace cooled and water quenched) and compared with the as-machined samples of bulk solder bars from the industry. Based on continuous stiffness measurement technique, Young’s modulus and hardness are reduced by 2.3–3.9[Formula: see text]GPa and 0.053–0.085[Formula: see text]GPa, respectively, after annealing treatment for the indentation depth between 1000[Formula: see text]nm and 1100[Formula: see text]nm in samples after cooling, however, the value of hardness is independent of cooling condition. By defining the contact stiffness to represent residual stress in solder samples after cooling and annealing process, an exponential-based Oliver–Pharr model is employed to fit the unloading responses of indentation. It is found that the smaller cooling rate induces less contact stiffness and thus less residual stress. Despite different cooling conditions, the contact stiffness of unannealed and annealed solder samples are 711.8–842.5[Formula: see text][Formula: see text]N/nm and 655.2–673.4[Formula: see text][Formula: see text]N/nm, respectively. Thus, annealing treatment of 210[Formula: see text]C for 6[Formula: see text]h can effectively alleviate residual stress to a similar level for SAC305 solder samples with different cooling conditions. This conclusion is supported by the alleviation of pile-up deformation in the residual indentation after annealing treatment.

Microstructural, mechanical, electrical, and thermal properties of the Bi-Sn-Ag ternary eutectic alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries. Bi-Sn-Ag 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. We investigated the effects of temperature gradient and growth rate on the mechanical, electrical and thermal properties of the Bi-Sn-Ag ternary eutectic alloy. Bi-47 wt%Sn-0.68 wt%Ag alloy was directionally solidified upward with different temperature gradients (G=2.33-5.66 K/mm) at a constant growth rate (V=13.25 μm/s) and with different growth rates (V=6.55-132.83 μm/s) at a constant temperature gradient (G=2.33 K/mm) in the growth apparatus. The microstructures (λ), microhardness (HV), tensile stress (σ), electrical resistivity (ρ), and thermal properties (ΔH, C p, T m) were measured on directionally solidified samples. The dependency of the λ, HV, σ, and ρ on G and V was investigated. According to the experimental results, λ values decrease with increasing G and V, but HV, λ, and ρ values increase with increasing G and V. Variations of electrical resistivity (ρ) for cast samples with the temperature in the range of 300-400 K were also measured by using a standard dc four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (C p) for the same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.

Influence of alloying elements on stability and electronic structures of Cu6Sn5(0 1 0) surface by first principles calculations

Due to the reliability problem and high melting point, the development of lead-free solders is hindered. Alloying is considered to be a promising approach to design new Sn-based solders. Cu6Sn5 plays an important role in the quality of microelectronic packaging that formed at the interface of solder and Cu substrate. In the present study, first principles calculations were employed to study the occupation properties of alloying elements (A=P, Zn, Ag, In, Sb, Ce, Pb, and Bi) and anti-site defects (Cu and Sn) in (010) surface of Cu6Sn5 and their influence on the electronic structures of Cu6Sn5(010) surface. Formation energies were calculated to evaluate the occupation preferences of alloying elements in considered eight sites of Cu6Sn5(010) surface. Different alloying elements show different occupation preferences. The occupations of alloying elements in Cu6Sn5 surface show negative formation energies comparing the positive formation energies in bulk Sn. Therefore, the alloying elements will easily occur in the Cu6Sn5 compound during soldering process. Electronic structures were studied to reveal the occupation mechanisms of alloying elements, and the interactions between them and Cu6Sn5 surface. Large values of density of states appear around the Fermi energy level for Ce contained system. In terms of the lowest work function, the electrons in Ce contained systems will be much easier to lose than that in other contained systems. Therefore, alloying of Ce will greatly affect the stability and electrical properties of solder joints in microelectronic packaging.

Development of lead-free solders in China during the past decade

Development of lead-free solders in China during the past decade

Characterization of Low-Melting-Point Sn-Bi-In Lead-Free Solders

Development of lead-free solders with low melting temperature is important for substitution of Pb-based solders to reduce direct risks to human health and the environment. In the present work, Sn-Bi-In solders were studied for different ratios of Bi and Sn to obtain solders with low melting temperature. The microstructure, thermal properties, wettability, mechanical properties, and reliability of joints with Cu have been investigated. The results show that the microstructures of the Sn-Bi-In solders were composed of β-Sn, Bi, and InBi phases. The intermetallic compound (IMC) layer was mainly composed of Cu6Sn5, and its thickness increased slightly as the Bi content was increased. The melting temperature of the solders was around 100°C to 104°C. However, when the Sn content exceeded 50 wt.%, the melting range became larger and the wettability became worse. The tensile strength of the solder alloys and solder joints declined with increasing Bi content. Two fracture modes (IMC layer fracture and solder/IMC mixed fracture) were found in solder joints. The fracture mechanism of solder joints was brittle fracture. In addition, cleavage steps on the fracture surface and coarse grains in the fracture structure were comparatively apparent for higher Bi content, resulting in decreased elongation for both solder alloys and solder joints.

Experimental Determination of Phase Equilibria in the Ag-Cu-Sb Ternary System

Phase equilibria of the Ag-Cu-Sb system were experimentally determined by electron probe microanalyzer and x-ray diffraction. Three isothermal sections of the Ag-Cu-Sb ternary system at 300, 500 and 600 °C were experimentally established, and no ternary compound was found in this system. Experimental results show that the liquid phase region increases with the temperature increase in region from 500 to 600 °C. The newly determined phase equilibria in this system will provide important information for the development of lead-free solders.

Microstructural Evaluation of Bi-Ag and Bi-Sb Lead-Free High-Temperature Solder Candidates on Copper Substrate with Multiple Reflow Number

An impetus has been provided towards the development of lead-free solders by worldwide environmental legislation that banned the use of lead in solders due to the lead toxicity.This study focus on Bi-Ag and Bi-Sb solder alloys, in compositions from 1.5 to 5 wt % Ag and Sb. The effects of Ag and Sb amount, and reflow number on the microstructure and morphology of solder bulk were analysed by optical microscope and scanning electron microscope-energy dispersive X-ray. Based on the results, the grain boundary grooving was observed in all samples except Bi-5Sb in all three reflows. Metallurgical and chemical reaction between interface and solders were found in Bi-5Sb solder alloys in different reflow numbers which lead to appearance of Cu3Sb intermetallic compound layer at the interface. Reflow numbers had a significant effect on the size of Cu-rich phase. Also it was observed that, with increasing reflow number Bi-Cu phase found in Bi-2.5Sb solder dissolves into the solder bulk.

Research and development of lead-free solder for microelectronics in consideration of the environmental and qualitative aspects

The paper deals with the research and development of lead-free solder for microelectronics in consideration of the environmental, economic, and qualitative aspects. The main aim of this paper is to study the influence of In additives to the complex properties of solder joints. The SnCu0.67In2.0 solder alloys were used for the research. They had been confronted with the most commonly used SnAg3.0Cu0.5 solder in the electronics industry in terms of melting temperatures, wetting properties, microstructures, and costs. Thermo-Calc software was used for phase’s composition prediction. The solder joint reliability was assessed to evaluate the thermal cycling test in the range from −40 to 150 °C. Altogether, 1,500 cycles were carried out. Solder joints were exposed to the thermal cycling due to practice requirement. Optical microscopy, scanning electron microscopy (EDX microanalysis), and shear strength test were used for the evolution of microstructure, structural integrity, and mechanical strength of thermal-cycled solder joints. Designed SnCu0.67In2.0 solder alloys reached the most suitable result for microelectronic.

Thermal Properties of Sn-0.7Cu/re-Al Composite Lead-Free Solder

Composite approach in lead-free solder development was perceived as an expectation in finding new robust solder. Accordingly, Sn-0.7Cu/re-Al composite lead-free solder with varying amount of recycled-Aluminum (0, 3.0, 3.5 and 4.0 wt.% re-Al) particulates produced from aluminum beverage cans were successfully fabricated via powder metallurgy techniques in this study. This paper focuses on the thermal properties focusing on the melting temperature of the new developed Sn-0.7Cu/re-Al lead-free composite solder. The melting temperature (Tm) of the new solders was determined using differential scanning calorimetry (DSC). The melting temperature of the composite solders has showed comparable results with the monolithic solders of Sn-0.7Cu lead-free solder.

Evolution of microstructure, thermal and creep properties of Ni-doped Sn–0.5Ag–0.7Cu low-Ag solder alloys for electronic applications

For development of lead-free solder for advance electrical components, the correlation of microstructure with thermal and creep properties of novel Ni-doped Sn–0.5Ag–0.7Cu (SAC (0507)) lead free solders has been investigated. Results showed that addition of 0.05Ni into the lead-free SAC (0507) solder led to the microstructural refinement, more uniform distribution of the Ag3Sn, (Cu,Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. However, the SAC (0507)–0.1Ni alloy has relatively high fraction of the primary β-Sn phase and the IMCs appeared coarse within the matrix compared with the other examined alloys. DSC results showed that the addition of Ni did not produce any significant effect on the melting behavior. Interestingly, 0.05wt.% Ni addition exhibited a drastically reduced undercooling to be 6.3°C. In terms of creep behavior, the SAC (0507)–0.05Ni gave the highest creep resistance due to the fine dispersion of IMCs. Furthermore, 0.05wt.% Ni addition can evidently increase the creep–rupture life, about 2.0 times greater than that of the baseline SAC (0507) and approximately 5.0 times better than that of SAC (0507)–0.1Ni solder. Meanwhile, the SAC (0507)–0.1Ni alloy shows lower creep resistance which is mainly attributable to smaller volume fraction of the precipitate phases. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.