Search Results (44)

This study investigates the interfacial reactions of FeCoNiCr and FeCoNiMn medium-entropy alloys (MEAs) with Sn and Sn-3Ag-0.5Cu (SAC305) solders at 250 °C. The evolution of interfacial microstructures is analyzed over various aging periods. For comparison, the FeCoNiCrMn high-entropy alloy (HEA) is also examined. In the Sn/FeCoNiCr system, a faceted (Fe,Cr,Co)Sn₂ layer initially forms at the interface. Upon aging, the significant spalling of large (Fe,Cr,Co)Sn₂ particulates into the solder matrix occurs. Additionally, an extremely large, plate-like (Co,Ni)Sn₄ phase forms at a later stage. In contrast, the Sn/FeCoNiMn reaction produces a finer-grained (Fe,Co,Mn)Sn₂ phase dispersed in the solder, accompanied by the formation of the large (Co,Ni)Sn₄ phase. This observation suggests that Mn promotes the formation of finer intermetallic compounds (IMCs), while Cr facilitates the spalling of larger IMC particulates. The Sn/FeCoNiCrMn system exhibits stable interfacial behavior, with the (Fe,Cr,Co)Sn₂ layer showing no significant changes over time. The interfacial behavior and microstructure are primarily governed by the dissolution of the constituent elements and composition ratio of the HEAs, as well as their interactions with Sn. Similar trends are observed in the SAC305 solder reactions, where a larger amount of fine (Fe,Co,Cu)Sn₂ particles spall from the interface. This behavior is likely attributed to Cu doping, which enhances nucleation and stabilizes the IMC phases, promoting the formation of finer particles. The wettability of SAC305 solder on MEA/HEA substrates was further evaluated by contact angle measurements. These findings suggest that the presence of Mn in the substrate enhances the wettability of the solder. Full article

With the enhancement of environmental protection awareness and the implementation of related regulations, lead-free soldering materials are gradually replacing the traditional leaded soldering materials in the field of electronics manufacturing. Sn–Ag soldering materials have become a research hotspot because of their good mechanical properties, solderability, and thermal fatigue reliability, but their high cost limits their large-scale application. The low silver content of the Sn–Ag solder reduces the cost while maintaining an excellent performance. However, as the size of electronic components shrinks and the package density increases, the solder joint spacing decreases, the potential gradient increases, and electrochemical migration (ECM) becomes a key factor affecting the reliability of solder joints. In this study, the ECM failure process was simulated by the water droplet method, and the SEM and XPS analyses were utilized to investigate the ECM mechanism of Sn1.0Ag solder alloys, and the effects of different concentrations of NaCl solutions on their ECM were investigated. The results showed that the ECM of the Sn1.0Ag solder occurred in a 0.01 M NaCl solution, the dendritic composition was pure Sn, and the white precipitate was a mixture of Sn(OH)₂ and Sn(OH)₄. With the increase in the NaCl concentration, the corrosion resistance of the Sn1.0Ag solder alloy decreases and the ECM reaction intensifies, but with a high concentration of the NaCl solution, a large amount of precipitation hinders the migration of Sn ions, resulting in the generation of no dendrites. The present study provides new insights into the ECM behavior of a low-silver-content Sn–Ag solder system. Full article

As semiconductor packaging technologies face limitations, through-silicon via (TSV) technology has emerged as a key solution to extending Moore’s law by achieving high-density, high-performance microelectronics. TSV technology enables enhanced wiring density, signal speed, and power efficiency, and offers significant advantages over traditional wire-bonding techniques. However, achieving fine-pitch and high-density interconnects remains a challenge. Solder flip-chip microbumps have demonstrated their potential to improve interconnect reliability and performance. However, the environmental impact of lead-based solders necessitates a shift to lead-free alternatives. This review highlights the transition from Sn-Pb solders to lead-free options, such as Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Zn, and Bi- or In-based alloys, driven by regulatory and environmental considerations. Although lead-free solders address environmental concerns, their higher melting points pose challenges such as thermal stress and chip warping, which affect device reliability. To overcome these challenges, the development of low-melting-point solder alloys has gained momentum. This study examines advancements in low-temperature solder technologies and evaluates their potential for enhancing device reliability by mitigating thermal stress and ensuring long-term stability. Full article

Soldering with Sn alloys has always been the essential assembly step of microelectronics. The conductive Sn whiskers, which can spontaneously grow from soldering surfaces, mean a considerable reliability risk for microelectronics due to possible short circuit formation between the leads of the components. Since their discovery in 1951, thousands of research studies have been conducted to unravel their growth mechanisms and find effective prevention methods against them. Till 2006, the Sn whisker problem was solved and partially forgotten due to the very effective whisker suppression effect of Pb alloying into the solder materials. The lead-free change gave new impetus to the problem, which was further enhanced by the application of new material systems, growing reliability requirements, and accelerating miniaturization in the 21st century. Our review would like to give an overview of the Sn whisker’s history from the beginning till the latest results, focusing on the suppression solutions by the modification of the solder alloy compositions. Recently, promising results have been reached by alloying Bi and In, which are metals that are the focus of low-temperature soldering, and by composite solders. Full article

With the development of electronic packaging technology toward miniaturization, integration, and high reliability, the diameter and pitch of solder joints continue to shrink. Adjacent solder joints are highly susceptible to electrochemical migration (ECM) due to the synergistic effects of high-density electric fields, water vapor, and contaminants. Dust has become one of the non-negligible causal factors in ECM studies due to air pollution. In this study, 0.2 mM/L NaCl and Na₂SO₄ solutions were used to simulate soluble salt in dust, and the failure mechanism of an Sn-58Bi solder ECM in the soluble salt in dust was analyzed by a water-droplet experimental method. It was shown that the mean failure time of the ECM of an Sn-58Bi solder in an NaCl solution (53 s) was longer than that in an Na₂SO₄ solution (32 s) due to the difference in the anodic dissolution characteristics in the two soluble salt solutions. XPS analysis revealed that the dendrites produced by the ECM process were mainly composed of Sn, SnO, and SnO₂, and there were precipitation products—Sn(OH)₂ and Na₂SO₄—attached to the dendrites. The corrosion potential in the NaCl solution (−0.351 V) was higher than that in the Na₂SO₄ solution (−0.360 V), as shown by a polarization test, indicating that the Sn-58Bi solder had better corrosion resistance in the NaCl solution. Therefore, an Sn-58Bi solder has better resistance to electrochemical migration in an NaCl solution compared to an Na₂SO₄ solution. Full article

As electronic packaging technology advances towards miniaturization and integration, the issue of electromigration (EM) in lead-free solder joints has become a significant factor affecting solder joint reliability. In this study, a Sn-3.0Ag-0.5Cu (SAC305) alloy was used as the base, and different Bi content alloys, SAC305-xBi (x = 0, 0.5, 0.75, 1.0 wt.%), were prepared for tensile strength, hardness, and wetting tests. Copper wire was used to prepare EM test samples, which were subjected to EM tests at a current density of approximately 0.6 × 10⁴ A/cm² for varying durations. The interface microstructure of the SAC305-xBi alloys after the EM test was observed using an optical microscope. The results showed that the 0.5 wt.% Bi alloy exhibited the highest ultimate tensile strength and microhardness, improving by 33.3% and 11.8% compared to SAC305, respectively, with similar fracture strain. This alloy also displayed enhanced wettability. EM tests revealed the formation of Cu₆Sn₅ and Cu₃Sn intermetallic compounds (IMCs) at both the cathode and anode interfaces of the solder alloy. The addition of Bi inhibited the diffusion rate of Sn in Cu₆Sn₅, resulting in similar total IMC thickness at the anode interface across different Bi contents under the same test conditions. However, the total IMC thickness at the cathode interface decreased and stabilized with increasing EM time, with the SAC305-0.75Bi alloy demonstrating the best resistance to EM. Full article

The restriction of lead content in alloys for the production of solder, based on the Directive of the European Parliament and of the Council of the European Union of 8 June 2011, which is also known as RoHS (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment), had a very positive impact on research into lead-free solder alloys, as well as on the economic impact of the production of solders. It opened the door to issues relating to the mechanical properties of lead-free solders and the microhardness of formed joints, with the aim of increasing their quality and efforts to reduce production costs. In addition to the production efficiency increase, without the need for the manual removal of so-called slagging, the moderation of oxide formation on the melt surface, standing for an increase in the yield of the total amount of solder, represents one of the many factors influencing the production of lead-free alloys for tin-based soldering. This work deals with the issues of material selection for the production of lead-free solders. Temperature affects the formation of different phases when there is a change in the concentration of the elements involved because it can be a negative aspect for soldering. Therefore, it is necessary to have detailed knowledge on the entire process that takes place during temperature changes. Full article

Sn-Ag-Cu-Bi (SAC-Bi) alloys are gaining popularity as a potential replacement for current lead-free solder alloys in microelectronic packages. In this study, the tensile and viscoplastic behaviors of eight SAC-Bi alloys with 0, 1 wt.%, 2 wt.%, and 3 wt.% Bi content were investigated. The samples of these eight alloys were cast, aged at room temperature, 75 °C and 125 °C, and tensile-tested at rates of 0.1/s, 0.01/s, and 0.001/s in ambient and elevated temperature environments to facilitate the quantification of viscoplasticity using the Anand viscoplastic model. The Anand parameters of all eight alloys in the as-cast and aged conditions were determined. Tensile strength was found to increase with the addition of Bi. Additionally, alloys containing 2 and 3 wt.% Bi showed a 5 to 10% increase in tensile strength after isothermal aging of 90 days at 125 °C. On the contrary, the tensile strength of alloys with up to 1 wt.% Bi decreased by 22 to 48% after such aging. Using a Scanning Electron Microscope (SEM) and energy dispersive spectroscopy (EDS), the microstructure of the alloys was characterized. The aging-induced property changes in the samples were correlated to strengthening by Bi solute atoms for alloys with 1 wt.% Bi and the formation of Bi precipitation for alloys with 2 wt.% and 3 wt.% Bi. Full article

This study was conducted on SAC105 (Sn-1wt.%Ag-0.5wt.%Cu) lead-free solder modified with Bi and Sb. The wetting, melting point, and mechanical properties were analysed with the addition of 1~5 wt.%Bi and 1~5 wt.%Sb for SAC105 base alloy. The wetting characteristics were assessed by wetting time (zero cross time, ZCT) obtained from wetting balance tests. The mechanical properties were analysed by tensile tests. Considering two factors (Bi, Sb), a three-level (0, 1, 2 wt.%) design of experiment (DOE) method array was applied for Taguchi optimization. The results indicated that the solder wetting increased as Bi content increased, while it decreased with Sb. The ZCT decreased with increasing Bi content up to 4 wt.%, while it increased proportionally to Sb content. The melting point, measured using a differential scanning calorimeter (DSC), showed that the melting point tended to decrease according to Bi increase, while it increases depending on the Sb content. Increase in Bi and Sb levels resulted in enhanced tensile strength in the mechanical properties tests, with Bi having a more noticeable impact. The Taguchi optimized conditions for the Bi and Sb studies were found to be 2 wt.%Bi and 2 wt.%Sb. This led to an optimal set of 0.9 s of wetting time, a 222.55 °C melting point, a 55 MPa tensile strength, and a 50% elongation. Full article

Sn-3Ag-0.5Cu (SAC305)- and Sn-9Zn-based alloys (Sn-Zn-X, X = Al, In) are lead-free solders used in the fabrication of solder joints with Cu metallization. Electroplating is a facile technology used to fabricate Cu metallization. However, the addition of functional additive molecules in the plating solution may result in impurity residues in the Cu electroplated layer, causing damage to the solder joints. This study investigates the impurity effect on solder joints constructed by joining various solder alloys to the Cu electroplated layers. Functional additives are formulated to fabricate high-impurity and low-impurity Cu electroplated samples. The as-joined solder joint samples are thermally aged at 120 °C and 170 °C to explore the interfacial reactions between solder alloys and Cu. The results show that the impurity effect on the interfacial reactions between SAC305 and Cu is significant. Voids are massively formed at the SAC305/Cu interface incorporated with a high impurity content, and the Cu₆Sn₅ intermetallic compound (IMC) grows at a faster rate. In contrast, the growth of the Cu₅Zn₈ IMC formed in the SnZn-based solder joints is not significantly influenced by the impurity content in the Cu electroplated layers. Voids are not observed in the SnZn-based solder joints regardless of the impurity content, indicative of an insignificant impurity effect. The discrepancy of the impurity effect is rationalized by the differences in the IMC formation and associated atomic interdiffusion in the SAC305- and SnZn-based solder joints. Full article

Sn58Bi solder is considered a promising lead-free solder that meets the performance requirements, with the advantages of good wettability and low cost. However, the low melting point characteristic of Sn58Bi poses a serious threat to the high-temperature reliability of electronic products. In this study, Sn58Bi solder alloy based on nickel (Ni) functionalization was successfully synthesized, and the effect of a small amount of Ni on creep properties and hardness of Cu/Sn58Bi/Cu micro solder joints at different temperatures (25 °C, 50 °C, 75 °C, 100 °C) was investigated using a nanoindentation method. The results indicate that the nanoindentation depth of micro solder joints exhibits a non-monotonic trend with increasing Ni content at different temperatures, and the slope of the indentation stage curve decreases at 100 °C, showing that the micro solder joints undergo high levels of softening. According to the observation of indentation morphology, Ni doping can reduce the indentation area and accumulation around the indentation, especially at 75 °C and 100 °C. In addition, due to the severe creep phenomenon at 100 °C, the indentation hardness rapidly decreases. The indentation hardness values of micro solder joints of Cu/Sn58Bi/Cu, Cu/Sn58Bi-0.1Ni/Cu, and Cu/Sn58Bi-0.2Ni/Cu at 100 °C are 14.67 ± 2.00 MPa, 21.05 ± 2.00 MPa, and 20.13 ± 2.10 MPa, respectively. Nevertheless, under the same temperature test conditions, the addition of Ni elements can improve the high-temperature creep resistance and hardness of Cu/Sn58Bi/Cu micro solder joints. Full article

Sn-Cu-Ni lead-free solder alloy electrodeposited on copper substrate from a deep eutectic solvent (DES)-based electrolyte under direct current (DC) and pulsed current (PC) was subjected to a reflowing process at the industrial company MIBATRON S.R.L. (Otopeni, Romania). The alteration of the alloy’s composition and anti-corrosive properties upon exposure to the reflow process were investigated via Scanning Electron Microscopy (SEM-EDX), X-ray diffraction (XRD), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Corrosion studies conducted in sodium chloride solution revealed that the system obtained under the DC plating mode (Sn-Cu-Ni-DC) exhibited enhanced anti-corrosive properties compared to the system obtained under PC (Sn-Cu-Ni-PC) after reflowing. However, prior to reflowing, the opposite effect was observed, with Sn-Cu-Ni-PC showing improved anti-corrosive properties. These changes in anti-corrosive behavior were attributed to the modification of the alloy’s composition during the reflowing process. Full article

The incorporation and doping of elements represent a widely used approach to enhance the solidity, integrity, and characteristics of pb-free solder joints. The present study summarizes the incorporation of indium and its impact on the mechanical aspects of the SAC105 pb-free solder alloy. To refine the mechanical impact of the solder alloy, the evaluation of samples were categorized into three groups: as-cast, low-thermal aged (at 125 °C), and high-thermal aged (at 180 °C). The tensile deformation data were obtained via the universal tensile machine (UTM). Investigational findings demonstrated the enhancement in mechanical characteristics, including ultimate tensile and yield strength of the solder alloy. The addition of 1 wt.% of indium to SAC105 led to a notable increase in ultimate tensile strength, rising from 29.6 MPa to 35.31 MPa, which corresponds to an approximate 19.30% increase over the initial value. Full article

The Sn-Ag-Cu (SAC) alloy family is commonly used in lead-free solders employed in the electronics industry, for instance, SAC305, SAC387, SAC405, etc. However, the trend in manufacturing small electronic products and device miniaturization faces some disadvantages in terms of mechanical properties and their higher melting temperatures compared to Pb-Sn solders, prompting new research relating to the reinforcement of existing SAC solders. The current study presents structural features of nanocomposite (Sn-3.0Ag-0.5Cu)_100−x(nanoNi)_x solders with 0.5 wt.%, 1.0 wt.%, and 2.0 wt.% Ni. Structural analysis of the investigated samples were performed by means of X-ray diffraction in a liquid state and scanning electron microscopy (SEM). SEM showed the mutual substitution of Ni and Cu atoms in the Cu₆Sn₅ and Ni₃Sn₄ phases, respectively. The performed structural studies in liquid and solid states provided essential information concerning the structural transformations of liquid Sn-3.0Ag-0.5Cu alloys caused by minor additions of nanosized Ni powder. The melting point and degree of undercooling of the samples were investigated by DTA analysis. Full article

Phase equilibria and thermodynamic properties of the Au-Sb-Sn ternary system are important for the design of Au-based alloys as high-temperature lead-free solders to replace high-Pb solders. In this work, phase transition temperatures of five Sb-Sn alloys were measured using differential thermal analysis (DTA), and the temperatures of three invariant reactions were determined. Based on the measured experimental results in this work and the reported results, the Sb-Sn binary system was re-optimized using the CALPHAD method. The calculated results were in good agreement with available phase equilibria and thermodynamic data. This work was further combined with the previous assessments of the Au-Sn and Au-Sb binary systems and the present optimization of the Sb-Sn binary system to calculate the phase equilibria and thermodynamic properties of the Au-Sb-Sn ternary system, according to the reported experimental results, including thermodynamic properties and phase equilibria. The calculated liquidus projection, isothermal sections, vertical sections, as well as enthalpy of mixing and activity of Sn in liquid alloys are consistent well with the reported experimental results. A self-consistent set of thermodynamic parameters was obtained to accurately describe Gibbs energies of various phases in the Au-Sb-Sn ternary system, which would serve as a sound basis for developing a thermodynamic database of multicomponent Au-Sn-based alloy systems. Full article