Lead-free Solder Alloys Research Articles

Microstructural, thermal and mechanical properties of Co added Sn–0.7Cu lead-free solder alloy

This study investigated the effects of cobalt microalloying addition on the microstructural features, thermal characteristics and mechanical behavior of eutectic Sn–0.7wt%Cu lead-free solder alloys. The results show that minor cobalt addition of ~ 0.05 wt% causes significant grain refinement of β-Sn, facilitates the formation of fine fibers (Cu,Co)6Sn5 phases and preventing the formation of η′-Cu6Sn5 phases, whereas a large amount of Co (~ 0.5 wt%) additions accumulated in the (Cu,Co)6Sn5 IMCs and clearly changed into coarse fibers. The precipitation strengthening mechanisms of fine fibers (Cu,Co)6Sn5 in the β-Sn matrix increased the ultimate tensile strength (UTS) and Young’s modulus (Y) of the alloy from 30.5 MPa and 15 GPa to 44.6 MPa and 22.3 GPa, respectively, but the ductility decreased from 60 to 45.7%. The coarse fibers (Cu,Co)6Sn5 in eutectic alloys is of interest from not only increased UTS and Y to 38.7 MPa and 16.3 GPa but also maintaining the ductility at the same level, allowing for unique microstructure design. Furthermore, 0.05wt% of Co significantly reduce the onset, eutectic temperatures and undercooling, although pasty rang has been slightly raised, which may enhance the thermal characteristics. This presumably has important implications for the reliability of solders as well as their performance in electronic service.

Robust effects of In, Fe, and Co additions on microstructures, thermal, and mechanical properties of hypoeutectic Sn–Zn-based lead-free solder alloy

This study examines the influence of separate and dual minor alloying additions of indium (In) and ferrous/cobalt (Fe/Co) on the microstructure, thermal, and mechanical properties of hypoeutectic Sn–7wt.% Zn lead-free solder alloy. The results showed that the addition of In resulted in significant refinement in the microstructure and formation of new intermetallic compounds (IMCs) such as In–Sn phases which capable of extensively removing the unfavorable needle-like α-Zn phase. However, the additions of Fe/Co resulted in the creation of new coarsening flower-shaped IMCs identified as Zn–Co, Fe–Sn, and Co–Sn–Zn distributed uniformly which may have a marked effect on the mechanical and thermal properties of Sn–Zn solder alloy. Thermal analysis by a differential scanning calorimeter indicates slightly reduction in the onset temperature, melting temperature, and undercooling of the Sn–7wt.% Zn by the addition of In, while the pasty range enlarged as compared to Fe/Co additions. The tensile tests indicate that the Sn-Zn-In solder alloy exhibited a superior balance of ultimate tensile strength, yield strength, Young’s modulus, and elongation of 51.5 MPa, 44.4 MPa, 22.2GPa, and 44.5%, respectively, which are better than both those of the Sn–Zn and Sn–Zn–Fe/Co solder alloys. This can be attributed to the synergistic strengthening mechanism of refinement in the microstructure and precipitation of fine secondary particles.

Study on the effects of Ag addition on the mechanical properties and oxidation resistance of Sn–Zn lead-free solder alloy by high-throughput method

Study on the effects of Ag addition on the mechanical properties and oxidation resistance of Sn–Zn lead-free solder alloy by high-throughput method

Investigation of the Microstructure, Thermal Properties, and Mechanical Properties of Sn-Bi-Ag and Sn-Bi-Ag-Si Low Temperature Lead-Free Solder Alloys

In this study, we investigated the microstructure, mechanical properties, and thermal performance of Sn-xBi-1Ag (x = 35, 37, 45, and 47 wt.%) solders, with a particular focus on the effect of adding trace Si atoms. The impact of different Ag concentrations on the properties of Sn-xBi-Ag-0.5Si solders was also studied. The results indicated that as the amount of Bi added to Sn-xBi-1Ag solder alloys increased, the tensile strength, microhardness, melting temperature, and melting range decreased somewhat, but the wettability improved. The Cu6Sn5 layer between the soldering alloy and the Cu substrate became thinner upon increasing the Bi content. Adding microcrystalline Si atoms to the Sn-Bi-1Ag alloy improved the tensile strength and microhardness, but the melting point and melting range were not significantly changed. The wettability was optimized, and the diffusion layer formed with the Cu matrix was significantly thinner. By increasing the Ag content in the Sn-Bi-(1,3)Ag-0.5Si alloy, the tensile strength of the alloy was continuously strengthened, while the hardness decreased slightly and the melting point and melting range increased slightly. The wettability was greatly improved, and the Cu6Sn5 layer became thinner.

Electrochemical corrosion and electrochemical migration characteristics of SAC-1Bi-xMn solder alloys in NaCl solution

The effects of Ag and Mn content were investigated from the electrochemical corrosion (ECC) and electrochemical migration (ECM) point of view in the case of SAC0307–1Bi-xMn and SAC305 lead-free solder alloys in NaCl solution. On the one hand, long-term results showed that lower silver content showed higher corrosion resistance. On the other hand, the microstructure and elemental composition of the dendrites formed after the ECM test were investigated by transmission electron microscopy (TEM) and energy dispersive X-ray spectrometer (EDS) which demonstrated that micro-alloying elements (i.e. Mn) also contributed to the ECM processes. The ECM model of Mn was also established.

Effect of Strain Rate on Tensile Behavior of Sn-9Zn-xAg-ySb; {(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} Lead-Free Solder Alloys

Effect of Strain Rate on Tensile Behavior of Sn-9Zn-xAg-ySb; {(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} Lead-Free Solder Alloys

Computational Study of the Thermodynamic Properties of Some Lead-free Solder Alloys

Activities of the components of the binary lead-free solder alloys Cu-Sn, and Ag-Cu were computed using the molecular interaction volume model (MIVM). The theoretical data have been compared with the corresponding experimental values. For the validity of the model parameters, the excess Gibbs free energy of mixing of Cu-Sn, and Ag-Cu liquid alloys have been determined and compared with the corresponding experimental data available in the literature. Similarly, the activities of Sn in ternary liquid alloys Sn-Ag-Cu were computed and examined with the available experimental data at 1000 K. It has been observed that the calculated activities of the components of the binary and ternary solder alloys have nearly the same tendency as the experimental data.

Effect of Sb and In additives on thermal and electrical properties of Sn–9Zn–4Bi alternative lead-free solder alloy

Due to the threats of lead to human and environmental health with Tin (Sn)- lead (Pb) solder alloys, efforts to develop lead-free solders continue. To adapt to different soldering areas, especially electronics, the search for alloys that can replace Sn–Pb has increased. The better the solders are in terms of thermal and electrical properties at the junctions, the better the performance of the circuit. In this study, changes in thermal conductivity, electrical conductivity, and melting behavior of 0.5–2 mass percent (wt.%) antimony (Sb) and 0.5–1.5 mass percent (wt.%) indium (In) addition to Sn–9Zn–4Bi alloy were investigated. Measurements of thermal and electrical conductivity with temperature were made by linear heat flow and four-point probe methods, respectively. The melting temperatures (peak temperature) of the alloys produced vary between 477.70 and 484 K (K). When the transition temperature, which is important in solders, is compared to Sn–9Zn–4Bi-[x]Sb (x = 0.5–2 wt%) and Sn–9Zn–4Bi-yIn (y = 0.5–1.5 wt%) alloys, it is the alloy with the lowest value with 13.80 K and the addition of 1 wt% Sb. The thermal and electrical conductivity values increased with the contribution of Sb and In. In addition, temperature coefficients for thermal and electrical conductivity were calculated. Electron and phonon contributions to the thermal conductivity were determined from the Wiedemann-Franz law. It was determined that electron contribution was higher for each alloy.

Selective etching of lead-free solder alloys: A brief review

This review covers recent applications of wet etching on solder alloys. Detailed characterization cases are presented and discussed accordingly to highlight the process flow and applicability of conventional, deep etching, and selective etching techniques. A brief introduction of solder alloys and the concepts of each etching methods are described at the beginning of the review. The equipment setup and outcomes are presented for each characterization methods and discussed in parallel with the case studies from selected articles. Comparisons, results, and insights regarding each characterization methods are highlighted to observe the effectiveness, advantages, and future potential, especially on the selective electrochemical etching in solder joints characterization. The compilation of the latest literature, technical setup, and the main findings of the authors are the essential value of this review. It provides an in-depth understanding of conducting etchings on solder joints evaluations.

Mechanical performance of advanced multicomponent lead-free solder alloy under thermal aging

Reliability of lead-free solders, used in harsh conditions such as in automotive, is still a serious concern. Simultaneous additions of multiple alloying elements like Bismuth (Bi), Antimony (Sb), Nickel (Ni) etc. to conventional Sn-Ag-Cu (SAC) based solders have recently been investigated to improve their reliability. The additional elements can bring about the improvements through solid solution and precipitation strengthening. In this study, the effects of simultaneous additions of Bi, Sb and Ni to SAC 305 solder on the evolution of microstructure and mechanical properties of the solder under thermal aging at 125 °C for up to 1008 hours are investigated. Superior microstructural stability and improved mechanical strength of the multicomponent alloy at long aging time and its fracture behavior are discussed. • Simultaneous additions of Bi, Sb, and Ni improve the microstructural refinement for SAC solder • Bi, Sb and Ni suppress the grain growth of SAC solder during thermal aging • Bi, Sb and Ni remain strength of SAC solder during thermal aging • Toughness of multicomponent solder is higher than SAC solder • SAC305 shows more ductile fracture than multicomponent solder in tensile testing

Dependence of mechanical and thermal deformation behaviors on crystal size and direction of Cu3Sn intermetallic: A molecular dynamics study

The implementation of environment friendly technologies in microelectronic packaging industry has widened the essentialities of lead-free solder alloys. The Cu3Sn intermetallic compound is blameworthy for the adverse influences of the mechanical and thermal properties of the lead-free solder alloys. This study explored the effects of crystal size and direction on mechanical and thermal deformation behavior of Cu3Sn using the modified embedded atom method (MEAM) parameter in molecular dynamics simulation. The stress–strain characteristics were tracked down at 25 °C temperature and 1010 s−1 strain rate, and the thermal deformation manner was observed from −100 °C to 200 °C temperature, which came up with the thermal expansion coefficient (CTE). Investigations show that the tensile properties differ 43–63 % owing to anisotropy, whereas the CTE varies only less than 1 %. Meanwhile, the tensile properties and CTE plummet topmost 25 % and 58 % consecutively throughout the crystal size. However, the thermal expansion proclivity in different crystal size was quite indistinguishable at higher temperature.

A new approach for measuring the wetting angles of lead-free solder alloys from digital images

This study aims to detect quaternary lead-free solder alloys and measure their dynamic wetting angles with a new approach. The detection of the prepared alloy drop and measurement of its wetting angle are automatically performed by the developed application. A video obtained after experimental studies is filtered over its frames and enhanced a better form in the preprocessing stage. The peak of the half alloy drop is detected by obtaining lane histogram and its global minimum point is found in the segmentation stage. Left and right corner points in contact with the ground are detected by tracking pixel intensity values with the help of the global minimum point. The median point for both left half alloy drop and right half alloy drop is calculated. Thus, circles passing through three points for the left half and right half of the alloy drop are obtained to measure θleft,θrightandθmean wetting angles. In the postprocessing stage, these angles are measured at 0th, 5th, 10th, 15th, 30th, 60th, 90th, 120th, 150th, and 300th seconds after the alloy drop contacted the ground. Besides, measurement of these wetting angles is performed at each second. The obtained results showed that the graph of θmean versus time is an exponential decay graph. This result proves that the alloy drop spreads over the ground as time passes and the value of θmean decreases and is consistent with the observation made during the experiment.

Machine learning assisted design of high-strength Sn-3.8Ag-0.7Cu alloys with the co-additions of Bi and In

A Machine Learning (ML) integrated process was utilized to optimize the properties of Sn–Ag–Cu (SAC) alloys. Bi and In were selected as the key alloying elements to optimize the mechanical properties of SAC387 based alloys. A virtual sample space was constructed for SAC387-xBi-yIn alloys using a machine learning model based on Gradient Boosting Decision Tree (GBDT) algorism. A series of virtual samples were selected and experimentally validated. Sample SAC387-3.5 wt%Bi-2.8 wt%In demonstrated an outstanding mechanical property, yielding a significant improvement in tensile strength (85.8% improvement vs. SAC387, 106% improvement vs. SAC305) with an acceptable ductility (>20%). The synergistic effects of co-additions of Bi and In on the properties of SAC387 based alloys were elucidated. The experimental results show good consistency with the ML predictions, proving that ML can be used as a powerful tool for designing lead-free solder alloys with optimized properties.

Effect of temperature on vibration durability of lead-free solder joints

Safety critical electronics in automotive, avionic or military applications have to work reliably in a range of harsh conditions, including simultaneous mechanical and thermal loads (Gromala, 2021; Qi et al., 2009 [1, 2]). The durability of electronics, more specifically their board level interconnects, under vibration and thermal loads must be investigated and understood for interconnects assembled with lead-free solder alloys. In this study, isothermal vibration fatigue tests have been carried out at −40 °C, 25 °C and 125 °C. A novel test specimen, specifically designed for combined vibration and temperature cycling experiments, was used for this study. The test PCB contains leadless chip resistor (LCR) components, soldered using the SAC105 solder alloy (Sn98.5Ag1.0Cu0.5). Failed specimens at each temperature were subjected to destructive physical analysis (DPA) for root cause analysis (RCA) of the observed failures. Dynamic finite element analysis (FEA) was carried out and combined with the experimental results in order to generate fatigue strain-life (SN) curves. Two opposing effects of increasing temperature - viz. decrease of fatigue strength for high-cycle fatigue (HCF) and increase of fatigue ductility for low-cycle fatigue (LCF) - are hypothesized to be responsible for this non-monotonic behavior.

Modification Structure and their Effects on Physical Properties of Tin Based Lead Free Solder Alloys for Industrial Applications

Soldering properties such as melting temperature and wettability of tin-zinc alloy improved after adding different alloying elements such as indium, aluminum, cadmium and bismuth. Decreasing zinc content (Sn91Zn9) up to 4% (Sn96Zn4 alloy) increased corrosion resistance from -0.847 to -0.530 and decreased corrosion rate from 51.84 to 7.705 mpy. Microstructure of tin-zinc alloy changed with increasing hardness value of it after adding alloying elements. Tin-zinc alloys have lower melting temperature compared to Sn95Sb5, Sn96.5Ag3.5 and Sn99.3Cu0.7 alloys. The Sn90Zn4Bi6 alloy has beast solder properties for electronic industrial applications.

Boron Nitride Nanotubes Modified on a Lead-Free Solder Alloy for Microelectromechanical Packaging

In this study, we have investigated the role of boron nitride nanotubes (BNNTs) on the microstructural and interconnection reliability of a Sn–3.0 wt % Ag–0.5 wt % Cu (SAC305) lead-free solder alloy for microelectromechanical (MEMS) packaging. The BNNT was added in different fractions (0, 0.03, 0.1, 0.2, 0.4, and 0.6 wt %) to a SAC305 molten bath by manual mixing and melting to fabricate a BNNT-decorated SAC305 alloy (B-SAC). We evaluated the effects of BNNTs on the grain morphology, intermetallic compound (IMC) thickness, wetting, and spreading of the SAC305 matrix. The resultant B-SAC alloy was applied to join a 1608 chip to a flip-chip MEMS package, and the joint shear strength of the 1608 chip/Cu pad was studied. The results showed that the B-SAC alloy with 0.4 wt % BNNTs demonstrated finer grains and IMC thickness, a maximum spreading ratio (SR) of 94.08%, least zero-cross time of 0.5 s and surface tension of 224 mN/m, and the highest wetting force (6.95 mN) compared to the pristine SAC305 alloy due to the adsorption of BNNTs into the SAC305 matrix and increment in material fluidity. The joint shear strength of the 1608/Cu pad of the MEMS package also showed maximum improved shear strengthening and fracture energy in B-SAC alloys.

Effect of rotating magnetic field on the microstructure and properties of Sn-Ag-Sb lead-free solder alloys

PurposeThe purpose of this paper is to study the microstructure and properties of Sn-3.5Ag and Sn-3.5Ag-0.5Sb lead-free solder alloys with and without a rotating magnetic field (RMF).Design/methodology/approachOptical microscopy, scanning electron microscopy and X-ray diffraction were used to analyze the effect of an RMF on the microstructure of the solders. Differential scanning calorimetry was used to study the influence of the RMF on the thermal characteristics of the solders. The mechanical properties of the alloys were determined by tensile measurements at different strain rates.FindingsThe ß-Sn grains and intermetallic compounds for the Sn-3.5Ag and Sn-3.5Ag-0.5Sb lead-free solder alloys were refined under an RMF, and the morphology of the ß-Sn grains changed from dendritic to equiaxed. The pasty range was significantly reduced under an RMF. The ultimate tensile strength (UTS) of Sn-3.5Ag improved under the RMF, whereas the UTS of Sn-3.5Ag-0.5Sb decreased slightly. The addition of Sb to the Sn-3.5Ag alloy significantly enhanced the UTS and elongation (El.%) of the samples. The UTS of the solder increased with increasing strain rate.Originality/valueThe results revealed that the application of RMF in the molten alloy had a significant effect on its microstructure and mechanical properties. The thermal characteristics of the Sn-3.5Ag and Sn-3.5Ag-0.5Sb solder alloys were improved under the RMF. This research is expected to fill a knowledge gap regarding the behaviour of Sn-Ag solder alloys under RMF.

Tensile properties dependency on crystal size and direction of single crystal Ag3Sn intermetallic compound: a molecular dynamics study

The necessities of lead-free solder alloys have been expanded by the advent of eco-friendly technologies of microelectronic packaging industry. Mostly lead-free solder alloys are SAC, which is the alloy of tin, silver and copper metal. Ag3Sn, Cu3Sn and Cu6Sn5 inter-metallic compounds are formed during microelectronic packaging, which reduce the properties of SAC solder joints adversely. The present study explores direction dependent tensile properties of various sized single crystal anisotropic Ag3Sn. Molecular dynamics simulation platform LAMMPS is used to examine the elastic behavior of these crystals by modified embedded atom method (MEAM) potential parameters. The atomistic investigation is performed for four crystal sizes of 30×30×30, 60×60×60, 90×90×90 and 120×120×120 Å3 at a temperature of 298 K and a strain rate of 1010 s−1. A comprehensive insight from this work is that the tensile properties fluctuations due to direction are within 13–25% at any distinct crystal size, whereas fluctuations at any specific direction are within 5–17% for mentioned interest of crystal sizes. An optimum crystal size of 60×60×60 Å3, exhibits maximum tensile properties. However, the fracture initiation patterns are quite similar for all sizes and directions where the natures are investigated as ductile.

The Effect of Bi and Zn Additives on Sn-Ag-Cu Lead-Free Solder Alloys for Ag Reduction

This study aimed to investigate the effects of the addition of Bi and Zn on the mechanical properties of Sn-Ag-Cu lead-free alloy frequently used as a soldering material in the semiconductor packaging process. To reduce the Ag content of the commercial alloy SAC305 (Sn-3Ag-0.5Cu) by 1 wt.%, Bi and Zn were admixed in different ratios and the changes in mechanical and electrical properties were analyzed. Compared to the SAC305 alloy, electrical conductivity and elongation at break decreased while tensile strength increased following the addition of the two elements. In particular, upon the addition of 1 wt.% Bi, the tensile strength increased to a maximum of 43.7 MPa, whereas the tensile strength was 31.9 MPa in the alloy with 1 wt.% Zn. Differential thermal analysis and scanning electron microscopy revealed that the changes in physical properties can be ascribed to a reduction in the activation energy required for formation intermetallic compound when Bi was added, and the refinement of the structure due to a decrease in undercooling degree when Zn was added. When Bi and Zn were added at the same time, each characteristic for the change in the microstructure was applied in a complex manner, but the effect on the change of the physical properties worked independently.

Enhancing the tensile properties of Sn-Zn-Ag lead-free solder alloy by loading MgO nanoparticles and irradiation

Lead-free composite solders has attracted more attention as they are required in the microelectronics industry to assure good electrical connections and the best mechanical response between integrated circuit devices and the substrate. The mechanical mixing technique was used to prepare the plain (Sn-5.3 wt% Zn-1 wt% Ag, SZA531) and composite solder (SZA531/0.5 wt% MgO), while MgO nanoparticles were synthesized by sol-gel technique. The aim to investigate the effects of loading 0.5 wt% MgO NPs and [Formula: see text]-irradiation doses (0–2.0 MGy) on the tensile properties of plain solder at different strain rates (ε•). The microstructural properties revealed that MgO was pure, crystalline, and had a nanoparticle-like morphology with an average crystallite size of 9.61 nm. Plain and composite solders contained β-Sn, Zn, and Ag, as well as some intermetallic compounds, Ag3Sn and AgZn. Loading MgO refined [Formula: see text]-Sn and Ag3Sn, while AgZn particles were partially dissolved. The thermal analysis reported that the melting point slightly increased from 206.1°C with SZA531 to 208.7°C when loaded which confirms the good solderability of composite solder. The tensile properties revealed that ultimate tensile strength and the tensile toughness increased with increasing ε•, dose of γ-rays, and MgO loading, while ductility decreased. The strain rate sensitivity index ( m) decrease with increasing the dose and MgO loading because of the decrease in the resistance to necking. These results were interpreted based on Orowan strengthening and dislocation strengthening.