Zn Solder Alloy Research Articles

Effects of soldering temperature and preheating temperature on the properties of Sn–Zn solder alloys using wave soldering

Purpose This study aims to address the problem of low-temperature wave soldering in industry production with Sn-9Zn-2.5 Bi-1.5In alloys and develop qualified process parameters. Sn–Zn eutectic alloys are lead-free solders applied in consumer electronics due to their low melting point, high strength, and low cost. In the electronic assembly industry, Sn–Zn eutectic alloys have great potential for use. Design/methodology/approach This paper explored developing and implementing process parameters for low-temperature wave soldering of Sn–Zn alloys (SN-9ZN-2.5BI-1.5 In). A two-factor, three-level design of the experiments experiment was designed to simulate various conditions parameters encountered in Sn–Zn soldering, developed the nitrogen protection device of waving soldering and proposed the optimal process parameters to realize mass production of low-temperature wave soldering on Sn–Zn alloys. Findings The Sn-9Zn-2.5 Bi-1.5In alloy can overcome the Zn oxidation problem, achieve low-temperature wave soldering and meet IPC standards, but requires the development of nitrogen protection devices and the optimization of a series of process parameters. The design experiment reveals that preheating temperature, soldering temperature and flux affect failure phenomena. Finally, combined with the process test results, an effective method to support mass production. Research limitations/implications In term of overcome Zn’s oxidation characteristics, anti-oxidation wave welding device needs to be studied. Various process parameters need to be developed to achieve a welding process with lower temperature than that of lead solder(Sn–Pb) and lead-free SAC(Sn-0.3Ag-0.7Cu). The process window of Sn–Zn series alloy (Sn-9Zn-2.5 Bi-1.5In alloy) is narrow. A more stringent quality control chart is required to make mass production. Practical implications In this research, the soldering temperature of Sn-9Zn-2.5 Bi-1.5In is 5 °C and 25 °C lower than Sn–Pb and Sn-0.3Ag-0.7Cu(SAC0307). To the best of the authors’ knowledge, this work was the first time to apply Sn–Zn solder alloy under actual production conditions on wave soldering, which was of great significance for the study of wave soldering of the same kind of solder alloy. Social implications Low-temperature wave soldering can supported green manufacturing widely, offering a new path to achieve carbon emissions for many factories and also combat to international climate change. Originality/value There are many research papers on Sn–Zn alloys, but methods of achieving low-temperature wave soldering to meet IPC standards are infrequent. Especially the process control method that can be mass-produced is more challenging. In addition, the metal storage is very high and the cost is relatively low, which is of great help to provide enterprise competitiveness and can also support the development of green manufacturing, which has a good role in promoting the broader development of the Sn–Zn series.

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.

Effect of 0.3 wt% TiO2 nanoparticles on the thermal, structural, and mechanical properties of Sn3.8Ag0.7 Cu1.0Zn solder alloy

The Sn–3.8Ag-0.7Cu −1.0 wt% Zn (SACZ) plain solder alloy was reinforced by 0.3 wt% of TiO2 nanoparticles (NP). SEM, XRD, DSC, and stress-strain characterization techniques were used to examine the synthesized samples. The morphology of the samples is uniform and the grain size of the SACZ-TiO2 sample is refined compared to the plain solder. The TiO2 addition improved the crystallinity of the SACZ sample. Furthermore, the melting temperature of the prepared samples has the same value even if its pasty range is decreased by adding TiO2 NP. The mechanical properties of the examined samples were investigated at different temperatures and different strain rates. The activation energy (Q) of the SACZ-TiO2 is lower than that of the SACZ sample. The results of this study confirm that the 0.3 wt% TiO2 addition improves the physical properties of SACZ alloy.

Effect of Zn addition on alloy by 0.3, 0.6 and 0.9 wt.% on thermal properties, electrical conductivity and microstructure of eutectic Sn-3.5Ag alloy

In this work, the effects of 0.3, 0.6 and 0.9 wt.% Zn additives on the characteristic of Sn3.5Ag eutectic solder alloy, have been diluted to produce four micro alloys. Effects of 0.3 to 0.9 wt% Zn- additions on phase transformation and electrical resistivity of Sn-3.5Ag eutectic solder alloy have been investigated using Differential Scanning Calorimetry (DSC) and Keithley Source Meter (SMU), respectively. The addition of Zn reduced the melting point of the eutectic Sn–3.5Ag alloy and the pasty range (Tend - Tonset) for the Sn-3.5Ag-0.3Zn, Sn-3.5Ag-0.6Zn and Sn-3.5Ag-0.9Zn solder alloys are 8.34, 8.31 and 7.12 °C respectively, decreased from four micro alloys 8.34 °C to 7.12 °C. These results show that the Zn addition is beneficial to decrease the heat of fusion of the Sn-3.5Ag solder alloy This improvement is an indication for property enhancing the mechanical properties. It is showing that the solder alloy needs the lowest energy for melting and it is a useful for saving energy also the resistivity increases continuously with Zn content.

The Effect of Al Micro-Alloying on Corrosion and Thermal Properties of Sn-Zn Alloy

Electrochemical corrosion behavior of Sn–Zn solder alloys in 6 M potassium hydroxide solution was investigated by potentiodynamic polarization technique, aiming to investigate the role of Al additions. The effect of micro-alloying Al on the thermal properties was also studied by using DSC. The results reveal that the presence of Al content leads to increasing in corrosion potential yet reducing the corrosion current density and passivation current density, simultaneously. XRD analysis reveals the failure to produce new compound with Zn, limits the effect of adding Al towards the corrosion performance. Yet, significant improvement on thermal properties were seen, especially on the melting temperature and pasty range without modifying the eutectic melting behavior.

Achieving microstructure refinement and superior mechanical performance of Sn-2.0Ag-0.5Cu-2.0Zn (SACZ) solder alloy with rotary magnetic field

The investigation of a prospective lead-free solder alloy provides the essential data for microelectronic applications and estimation of solder joint reliability. In this study, we used the rotary magnetic field (RMF) as a novel approach to improve the mechanical performance and microstructure of Sn-2.0Ag-0.5Cu-2.0Zn (SACZ) lead-free solder alloy. The results revealed that both microstructure evolution and tensile characteristics enhanced by applying RMF. Microstructure studies showed that applying RMF reduced the grain size of β-Sn and IMCs. These modifications improved the tensile strength of the solder alloy. RMF improved Ultimate tensile strength (UTS), Yield stress (YS), Young modulus (E), and Elongation (El.%) of SACZ at room temperature by ~110%, 112%, 119%, and 108%, respectively. Besides, stress exponent, n, over the entire temperature and activation energy, Q, parameters calculated using the Garofalo hyperbolic sine law. n values were 5.9–8.3for SACZ alloy and 6.8–9.6 for SACZ-B alloy. Q values were ~ 51.8 kJ/mol for SACZ alloy and 79.2 kJ/mol for SACZ-B alloy close to pipe diffusion-controlled creep of tin. According to results, RMF is a promising approach to develop the microstructure evolution and mechanical characteristics of alloys. We hoped that the results would be useful for microelectronic applications.

Galvanic corrosion analysis of a Bi–Zn solder alloy coupled to Ni and Cu substrates

ABSTRACT Corrosion has become a frequent and significant issue in the electronics industry. For this reason, galvanic corrosion of soldered joints, i.e. when solder alloys are in contact with a metallic substrate, is so important. The present study aims to investigate the corrosion behaviour of the Bi-2.7wt-%Zn solder alloy when in contact with Cu and Ni substrates in a 0.06M NaCl solution. Polarisation curves show that Ni and Cu have nobler behaviour than the Bi–Zn alloy. However, although the Bi–Zn alloy exhibits active corrosion behaviour, the open circuit potential tends to shift toward more positive potentials over time. The galvanic current densities (i galv) of both Bi–Zn alloy/Ni and Cu couples are initially similar and three times higher than the corrosion current density of the Bi–Zn alloy. However, the couples show a decrease in i galv., with time and the couple formed with Ni has produced the lowest galvanic current density.

Interrelationship of thermal parameters, microstructure and microhardness of directionally solidified Bi–Zn solder alloys

Due to the health and environmental concerns associated with lead usage, the research on alternative lead-free alloys for replacing lead-based solders is a global demand. Despite numerous studies on Sn-based lead-free solders in recent years, there is not yet a standard solder alloy able to cover the spectrum of properties furnished by the classic Sn-Pb alloy. In this sense, particular lead-free alloys compositions have been suited for specific needs and the options have been broadening when elements other than tin are used as the base component, such as indium, gold and bismuth. The later element is well known in the hall of lead-free alloys as an alloying option rather than as a base component. This study aims to establish interrelations of solidification thermal parameters (growth and cooling rates), microstructure features (primary and secondary dendrite arm spacings – λ1 and λ2; eutectic spacing – λE and interphase spacing – λint) and hardness of Bi-Zn alloys (1.5wt% Zn-hypoeutectic, 2.7wt% Zn-eutectic, and 5wt% Zn-hypereutectic alloys) samples, which were directionally solidified in unsteady-state conditions under cooling rates similar to those of found in industrial soldering practice. Examination of the resulting microstructures by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) permitted the different phases morphologies to be characterized: Bi-rich trigonal dendrites and long Zn fibers, as primary phases of, hypoeutectic and hypereutectic alloys, respectively, immersed in a fiber-like eutectic mixture. The combined effects of macrosegregation, Zn alloying and representative scales of the phases forming the microstructure (λint, λ2 and λE) on hardness of the Bi-Zn alloys are evaluated and Hall–Petch type equations relating λint, λ2 and λE to hardness are proposed.

Effects of intermetallic-forming element additions on microstructure and corrosion behavior of Sn–Zn solder alloys

The corrosion behavior of ternary Sn–9Zn–0.1X (X=Ni, Cr, Cu and Ag) solder alloys were investigated by electrochemical techniques and surface characterization, aiming to explore the effects of intermetallic-forming elements on the corrosion resistance. Zn-rich precipitates in the modified alloys were suppressed and refined by formation of Zn-containing intermetallic compounds. As a result, the corrosion resistance improved markedly with addition of these elements, and the potency to suppress anodic dissolution increased in the order of Ag<Cu<Cr<Ni. Such improvement was discussed in terms of refined Zn-rich precipitates and enhanced passive film stability.

Effects of Wetting Behavior on Gallium Addition in In-Zn Solder Alloy

This paper reported the investigation on gallium, Ga addition into In-4.8Zn lead-free solder to improve its wettability performances. The effect of addition of Ga in In-4.8Zn solder alloy was studied. The results show with the addition of 0.5% Ga into the In-4.8Zn composition, the spreading area of In-4.8Zn-0.5Ga solder on copper increase between 35.71 and 43.75 %. Hence, as the spreading area increases, the contact angle decreased from between 22.09 to 39.71 %. Additionally, the addition of Ga as dopant increased the thickness of IMCs layer.

Improved microstructure and mechanical properties for Sn58Bi0.7Zn solder joint by addition of graphene nanosheets

The effects of graphene nanosheets (GNSs) on the microstructure and mechanical properties of Sn58Bi0.7Zn solder joint were investigated. Experimental results and finite element (FE) simulations showed that the best mechanical properties improvement came from the 0.076 wt.% GNS-doped Sn58Bi0.7Zn sample. It exhibited the highest creep resistant in all the as-prepared solder joints, and the average interphase spacing in solders was reduced by 32.52%, the stress exponent was increased by 13.70%. For the thermal aging samples, the ultimate tensile strength (UTS) of the solder joint was also increased by 2.04%. Moreover, the 0.114 wt.% GNS-doping significantly reduced the time exponent from 0.403 to 0.362 and decreased the thickness of total IMC layers by 56.31%. Based on the theories related to material performance and the restacking behavior of GNSs, the strengthening mechanism of GNSs in composite solder joint was analyzed and an optimum concentration of GNSs in Sn58Bi0.7Zn solder alloy was proposed.

Robust effects of Bi doping on microstructure development and mechanical properties of hypoeutectic Sn–6.5Zn solder alloy

Sn–9Zn lead-free solders possess remarkable potential as candidates for low temperature electronic applications. In this study, it is proposed to utilize the advantages of Bi alloying and reducing the amount of Zn to improve oxidation resistance and reliability of eutectic Sn–9Zn solder. The results indicate that hypoeutectic Sn–6.5Zn alloy composed of β-Sn-rich phase and α-Zn fiber. 1.0 wt Bi addition caused a strong inhibition of α-Zn fiber inside the alloy matrix. Moreover, the fiber spacing of α-Zn phase increased and its diameter decreased. With increasing Bi content to 3.0 wt, small bright of Bi particles are observed. The addition of Bi could effectively reduce the onset and eutectic temperatures, while the amount of undercooling <1.0 °C was recorded. The tensile strength of Bi-containing solders was enhanced to about 180 %, although the ductility was slightly decreased. The higher strength was contributed by solid solution effect and precipitations hardening of Bi atoms or particles, which can remarkably modify the microstructure, blocks the dislocation motion and increases the tensile strength of Bi-containing solders.

Low temperature In–Bi–Zn solder alloy on copper substrate

In this paper, characteristic of In–32.7Bi–0.5Zn lead-free solder system have been studied. DSC shows that, In–32.7Bi–0.5Zn system alloy give low melting temperature at 72.30 °C. Lowest melting temperature ensures that the solder melts, forms a joint with the substrates, and re-solidifies within the shortest possible process time. Further, the wettability between molten solder and copper substrate was measured at different reflow temperature. The contact angle for In–32.7Bi–0.5Zn solder alloys were decreasing 30.76° to 24.5° as the temperature increased from 100 to 140 °C. A significant increment of contact angle for In–32.7Bi–0.5Zn at 140 °C. The result of spreading area is inversed with the contact angle. Energy-dispersive X-ray analysis indicated two layer of intermetallic compound between the solder and the substrate; Cu5Zn8 and Cu11In9 compound.

Understanding corrosion mechanism of Sn–Zn alloys in NaCl solution via corrosion products characterization

The corrosion products formed on Sn–Zn solder alloys were systematically studied to elucidate the corrosion mechanism of Sn–Zn alloys in chloride‐containing solution. Sn–Zn alloys were subjected to immersion and polarization treatment in a 0.5 M NaCl solution. Ex situ analysis, including surface and cross‐section, of the corrosion products was carried out by scanning electron microscopy (FE‐SEM) and energy dispersive X‐ray spectroscopy (EDX). The corrosion products presented porous microstructure formed by a fine interlinked network. An increase of zinc content resulted in more pores and cracks of the corrosion products, indicating degradation of corrosion resistance. Intriguing is the finding that a gradient of chlorine concentration from the outer layer inwards the alloys through the Zn‐rich precipitates is observed, which demonstrates the migration of chloride ions inwards the alloys. Based on the results, a corrosion mechanism was proposed and discussed that explains the observations. Particular attention was paid to the anodic dissolution of Zn‐rich precipitates.

Ti addition to enhance corrosion resistance of Sn–Zn solder alloy by tailoring microstructure

The effect of trace addition of Ti on the corrosion behavior of Sn–9Zn (wt.%) solder alloy in NaCl solution was investigated using polarization and electrochemical impedance spectroscopy techniques. It is found that the corrosion resistance of Sn–9Zn alloy can be significantly enhanced by adding 0.05wt.% of Ti, evidenced by much lower corrosion current density, lower passive current density and higher impedance. Such enhancement results from the refinement of Zn-rich precipitates within the microstructure, which is conducive to forming a relatively more protective passive film on the surface of the modified alloy. This would be an important finding in the design of novel Sn–Zn solder alloys in electronic assemblies operating under aggressive conditions.

The role of Zn precipitates and Cl− anions in pitting corrosion of Sn–Zn solder alloys

Electrochemical corrosion behavior of Sn–Zn solder alloys in aerated and quiescent 0.5M NaCl solution was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques, aiming to assess the role of Zn precipitates and Cl− anions in pitting corrosion. The results reveal that increasing in Zn contents leads to increasing in pitting susceptibility, ascribed to the coarsening Zn precipitates with larger intergranular boundaries between Zn-rich precipitates and Sn matrix. The EIS results provide a quantitative description of the electrochemical interface behavior. The mechanism of pitting and the role of Cl− anions are discussed.

Evaluation of cooling rate on electrochemical behavior of Sn–0.3Ag–0.9Zn solder alloy in 3.5 wt% NaCl solution

The corrosion resistance of Sn–0.3Ag–0.9Zn alloy solidified under different cooling rates in 3.5 wt% NaCl solution was evaluated based on potentiodynamic polarization, electrochemical impedance spectroscopy and electrochemical noise. It is found that the corrosion resistance of this alloy improves with the increase of the applied cooling rate, which is attributed to the distinct microstructure. The furnace-cooled and air-cooled alloy with active Zn-rich phase and a microstructure formed by a coarser dendritic array associated with larger size of AgZn3 intermetallic compounds exhibit a worse corrosion resistance due to a serious galvanic corrosion. Besides, the Mott–Schottky measurement and the X-ray photoelectron spectroscopy were performed to analyze the semiconductor properties and composition of the passive film formed on the surface of the alloy. It confirms that the stability and protective ability of the passive films formed on furnace-cooled and air-cooled alloy are worse than that of water-cooled alloy due to their higher oxygen vacancy defects and concentration of unstable SnO. Furthermore, the major corrosion product on the surface of the Sn–0.3Ag–0.9Zn alloys is tin oxide chloride hydroxide.

Design of lead-free candidate alloys for low-temperature soldering applications based on the hypoeutectic Sn–6.5Zn alloy

The coupling effect of both minor alloying addition and reducing the amount of Zn phase have been proposed as an important strategy to improve the integrity and reliability of eutectic Sn–9Zn solder joints. In this work, the changes in microstructures, thermal behaviors and mechanical properties associated with the alloying of Ni and Sb to eutectic Sn–Zn after reducing the amount of Zn phase were explored. Thermal analysis confirmed that Ni and Sb additions being effective in reducing the amount of undercooling, while the melting temperature and pasty range remained at the hypoeutectic Sn–6.5Zn level. The resulting ultimate (UTS), yield tensile strength (YS) and elongation (El) of Sn–6.5Zn–0.5Ni and Sn–6.5Zn–0.5Sb alloys were experimentally determined and compared with the corresponding results of plain Sn–6.5Zn solder alloy. It was found that the Sn–6.5Zn–0.5Ni and Sn–6.5Zn–0.5Sb alloys examined comply with the compromise between high mechanical strength and ductility. Microstructural analysis revealed that the origin of change in mechanical properties was attributed to the enhanced solid solution effect of Sb and the flower shaped (Ni, Zn)3Sn4 intermetallics (IMC) phase produced by Ni addition. The Sn–6.5Zn–0.5Sb alloy has the highest UTS and appropriate ductility of all alloys examined. This finding indicates the capability of newly developed ternary solder alloys to serve a much wider array of value-added applications.

Creep deformation behavior of Sn–Zn solder alloys

Creep properties of three Sn–Zn solder alloys (Sn–9Zn, Sn–20Zn, and Sn–25Zn, wt%) were studied using the impression creep technique. Microstructural characteristics were examined using a scanning electron microscope. The alloys exhibited stress exponents of about 5.0. The activation energy for creep was calculated to be ~50–75 kJ/mol with a mean value of 66.3 kJ/mol. The likely creep mechanism was identified to be the low temperature viscous glide of dislocations.

Enhancing mechanical response of hypoeutectic Sn–6.5Zn solder alloy using Ni and Sb additions

In this paper, we report a convenient and informative procedure for improving the integrity and reliability of eutectic Sn–9Zn solder using minor alloying additions of Ni and Sb after reducing the amount of Zn phase. Results indicate that alloying of Ni or Sb into hypoeutectic Sn–6.5Zn resulted in slightly reduced the undercooling and pasty range with maintaining its melting temperature at the Sn–9Zn level. After 0.5% Sb addition, the enhanced solid solution effect and enlarged eutectic area with small needle-like α-Zn phase raised the creep resistance of hypoeutectic Sn–6.5Zn alloy, while the flower shaped (Ni,Zn)3Sn4 intermetallics (IMCs) and small spacing needle-like α-Zn phase produced by 0.5% Ni alloying results in small increase in its creep resistance. These results show that the creep strain rate of the entire alloys follows Garafalo hyperbolic sine equation, and the calculated creep stress exponent for three solders is reasonably close to other published data. Moreover, with the addition of Sb and Ni into Sn–6.5Zn solder, significant improvement in creep resistance of ∼270% and ∼182% is realized, respectively when compared with the hypoeutectic Sn–6.5Zn solder. This finding indicates the capability of newly developed ternary solder alloys to serve a much wider array of electronic applications.