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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.

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.

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.

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.

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.

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.

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.

This paper aims to study the diffusion of Zn, Ni and Sn in the liquid state during the reflow ageing of the Sn-Zn solder above its melting point on an Ni/Cu substrate in relation to the formation of intermetallic compounds (IMCs).

The Sn-Zn solder is reflowed on Ni/Cu substrates and is aged at 503 K. The formation of IMCs and their composition is characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Diffusion coefficients and diffusion distances of Zn, Ni and Sn in the liquid state during reflow and ageing are theoretically calculated. Both experimental and theoretical behaviours for Ni and Zn diffusions are compared.

Calculations show a linear increment in the liquid-state diffusion coefficients of Ni, Zn and Sn in the solder matrix with a rise in temperature, but they remained constant during ageing. However, diffusion distances increased slowly with temperature but manifold with ageing time. The experimental results revealed segregation of Zn and Ni at the interface in the as-reflow aged specimens. The Zn was concentrated at the solder–substrate interface and it reacted with Ni diffusing from the substrate to form Ni-Sn-Zn IMCs. The rapid diffusion of Zn and Ni with the increase in ageing time increased their atomic concentrations in the IMCs against the reduction in Sn concentration owing to a comparatively slower diffusion.

The novelty of the paper is the detailed study of theoretical diffusion of Zn, Sn and Ni in the liquid state during reflow ageing of Sn-Zn above its melting points on a Ni/Cu substrate. This is compared with values obtained experimentally and related to the mechanisms of IMC formation.

This paper aims to compare the reflow and Zn diffusion behaviors in Sn-Zn and Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga (5E) solders during soldering on a Ni/Cu substrate under infrared (IR) reflow. The study proposes a model on the effect of various elements particularly Zn diffusion behavior in the solders on the formation of intermetallic compounds (IMCs).

The melting activities of two solders near their melting points on copper substrates are visualized in an IR reflow furnace. Reflowed solder joints were analyzed using scanning electron microscope and energy dispersive X-ray spectroscopy.

Reflow behaviors of the solders are similar. During melting, solder balls are first merged into each other and then reflow on the substrate from top to bottom. Both solders show a reduced amount of Zn in the solder. Theoretical calculations demonstrate a higher Zn diffusion in the 5E solder; however, the amount of Zn actually observed at the solder/substrate interface is lower than Sn-9Zn solder due to the formation of ZnAg3 in the solder. A thinner IMC layer is formed at the interface in the 5E solder than the Sn-Zn solder.

The present work compares the 5E solder only with Sn-Zn solder. Additional research work may be required to compare 5E solder with other solders like Sn-Ag, SnAgCu, etc. to further establish its practical applications.

The study ascertains the advantages of 5E solder over Sn-Zn solder for all practical applications.

The significance of this paper is the understanding of the relation between reflow behavior of solders and reactivity of different elements in the solder alloys and substrate to form various IMCs and their influence on the formation of IMC layer at solder/substrate interface. Emphasis is provided for the diffusion behavior of Zn during reflow and respective reaction mechanisms.

The purpose of this paper is a comparable evaluation of the influence of a particular element (Bi and Sb) added to Sn‐Ag‐Cu and Sn‐Zn alloys on their surface and interfacial tensions, as well as the wetting properties on the Cu substrate expressed by the wetting angle.

The authors applied the L₈ orthogonal Taguchi array to carry out the experiments and discussed the results using analysis of variance (ANOVA).

It was expected, on the base of previous studies, the decrease of the surface and interfacial tensions and thus improving wettability after the Bi and Sb addition to Sn‐Ag‐Cu and Sn‐Zn alloys. Unfortunately, the obtained results on the quinary Sn‐Ag‐Cu‐Bi‐Sb alloys and the quaternary Sn‐Zn‐Bi‐Sb alloys do not confirm these trends. The performed analyses suggest that the compositions of the quinary Sn‐Ag‐Cu‐Bi‐Sb alloys, as well as the quaternary Sn‐Zn‐Bi‐Sb alloys, do not have optimal compositions for practical application. The Cu, Bi and Sb elements in the case of the Sn‐Ag‐Cu‐Bi‐Sb alloys and the Zn, Bi and Sb elements in the case of the Sn‐Zn‐Bi‐Sb alloys show mutual interaction and, in consequence, there is no correlation between the tendency of the surface and interfacial tensions changes and the wettings of the Cu substrate.

It is suggested that further studies are necessary for the purpose of the practical application, but they should be limited mainly to the Sn‐Ag‐Cu‐Bi and the Sn‐Zn‐Bi alloys with the optimal compositions.

The performed analysis suggests that none of the investigated compositions of the quinary Sn‐Ag‐Cu‐Bi‐Sb alloys, as well as the quaternary Sn‐Zn‐Bi‐Sb alloys, have the optimal compositions for practical application.

The quickest way to determine which element of the alloy composition influences the surface tension and the wetting properties, and how, is to apply orthogonal analysis. After choosing the orthogonal array, the experiments were performed and analysis of variance (ANOVA) was used to perform the quantifiable analysis of the measured and calculated results of surface and interfacial tensions, as well as the wetting properties on the Cu substrate.

The purpose of this paper is to study the influence of silver on the high‐temperature oxidation behaviour of the Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga (x=0, 0.1, 0.3 and 0.5) solder alloys.

The weight gains of the studied solders are measured using thermal gravimetric analyzers (TGA) at temperatures of 250, 300, 350 and 400°C. The weight gains measured are used to compare the oxidation behaviour of the studied solders. The surfaces of the solders are also analyzed with Auger emission spectroscopy (AES) depth profiling and thin‐film X‐ray diffractometry (thin‐film XRD) to identify the elements present on the surface of the studied solders.

The TGA results show that the weight gains decrease with increasing silver content in the studied solders. It meant that increasing silver content could help improve the high‐temperature oxidation behaviour of the studied solder. AES and thin‐film XRD confirm that the formed oxide layers on the surface of the studied solder are Zn‐based oxide layers.

The findings of this paper will help provide an understanding of the effects of silver on Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solder.

This paper aims to investigate the effect different fluxes have on the mechanical properties of lead-free solders, specifically Sn-Zn-Bi solder alloy. The solder billets were soldered in between copper substrates and flux was applied. The mechanical tests carried out on the solder alloys were tensile and shear tests. They were experimented on with different fluxes, namely, water-soluble (paste), rosin mildly activated (RMA) and insoluble (RMA) flux. From these experiments, the ultimate tensile strength, shear strength, elongation, yield stress, Young’s modulus and the stress-strain curve are derived. The results showed that solder billets that were soldered onto copper substrates with water-soluble flux yielded the highest ultimate tensile strength and shear strength values of 9.9961 MPa and 118.836 MPa, respectively. Billets soldered using RMA flux had the highest values of elongation and Young’s modulus, 0.306 mm and 50,257.295 MPa, respectively. However, on viewing the failure of all the specimens under an optical microscope and scanning electron microscope (SEM), specimens soldered using water-soluble flux possessed the least deformities, depicting their higher level of mechanical properties, entailing their strength and ductility, deeming them as the most suitable flux for microelectronic applications.

The solder billets were soldered in between copper substrates and flux was applied. The mechanical tests carried out on the solder alloys were tensile and shear tests. They were experimented on with different fluxes, namely, water-soluble (paste), RMA and insoluble flux (RMA) flux. From these experiments, the ultimate tensile strength, shear strength, elongation, yield stress, Young’s modulus and the stress-strain curve are derived.

The results showed that solder billets that were soldered onto copper substrates with water-soluble flux yielded the highest ultimate tensile strength and shear strength values of 9.9961 MPa and 118.836 MPa, respectively.

This paper demonstrated that water-soluble fluxes gave the better strength and were most suitable for microelectronics applications.

To study the effect of Ag content on the melting temperature and wetting properties of Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga lead‐free Solders.

The solder alloys used in the experiment were Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga (x=0, 0.1, 0.3, 0.5, 1 and 1.5). In this study, the alloys were initially studied using differential scanning calorimetry to determine their melting temperatures. Afterward, the solderability of the solders was studied using wetting balance and contact angle methods. Moreover, the microstructures of the solders were also investigated with an optical microscope, scanning electron microscope, energy dispersive X‐ray, X‐ray diffraction and electron probe micro analysis.

A small increase in Ag content in the Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solders, from 0.1 to 1.0 wt%, has been found to lower their solidus temperature from 198.05°C to 190.20°C. A Ag content of 1.5 wt% increased the solidus temperature of the studied solder systems to 197.79°C. Furthermore, the study also found that the addition of silver lowered the wetting forces of the studied solders. The formation of multi‐intermetallic layers of Cu‐Zn and Ag‐Zn at the interface between the studied solders and copper might explain the reduction of the wetting forces.

The silver contents in the studied Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solders were limited to 0, 0.1, 0.3, 0.5, 1.0 and 1.5 wt%.

Useful literature for solder alloy designers and SMT engineers.

The paper provides the answers to the research question of what is the effect of silver content on the melting temperature and wetting properties of Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solders.

The purpose of this article is to establish why the wetting on PCBs with SnCu (HASL) and Snimm finishes in the presence of a flux is better than the wetting of those on a copper substrate. The practical aspect of the obtained results is the main goal of these investigations.

The authors applied the wetting balance method for the wetting measurements at 230 and 250°C, in nitrogen atmosphere, in the presence of the ORM0 type flux. The PCBs with the SnCu (HASL) and Snimm finishes were investigated in the state “as received”. To establish the wetting properties of the SnCu (HASL) and Snimm finishes on the PCBs, wetted by the investigated SnZnBiIn alloys, the SEM and EDX analyses were performed.

The authors obtained very good wetting results of the PCBs with the SnCu and Snimm finishes, wetted by the SnZn7Bi3In4 alloys. By applying the SEM and EDX methods, it was possible to establish that the barrier layer which was created during the HASL process between the copper and the SnCu solder is efficient enough to protect the copper against the influence of the Zn atoms from the SnZn7Bi3In4 solder. This is the reason for an improvement of the wetting properties. An immersion tin finish does not create such barrier layer with the copper. It results in a worse wetting than for the SnCu finishes but a better one than that for the copper. Immersion tin dissolves in the alloys during the soldering and this process delays the reaction between the copper and the Zn atoms from the SnZn7Bi3In4 solder.

It is suggested that further studies are necessary for the confirmation of the practical application, but they should be limited to the reliability of the solder joint performance.

The best wetting results of the PCBs with “tin finishes”, especially with SnCu, wetted by the SnZn7Bi3In4 alloy, at 230 and 250°C and in nitrogen atmosphere, suggest a possibility of a practical usage of the tin‐zinc‐bismuth‐indium alloys for soldering in electronics.

The wetting balance method combined with the SEM and EDX analyses were used as the quickest way to determine the mechanism of the better wettability properties in the case of the PCBs with the SnCu and Snimm finishes, wetted by the SnZn7Bi3In4 alloy, compared to those of the PCBs on the Cu substrate.

The purpose of this paper is to review and examine three of the most common corrosion characterization techniques specifically on Sn-Zn solders. The discussion will highlight the configurations and recent developments on each of the compiled characterization techniques of potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy (EIS).

The approach will incorporate a literature review of previous works related to the experimental setups and common parameters.

The potentiostatic polarization, potentiodynamic polarization and EIS were found to provide crucial and vital information on the corrosion properties of Sn-Zn solders. Accordingly, this solder relies heavily on the amount of Zn available because of the inability to produce the intermetallic compound in between the elements. Further, the excellent mechanical properties and low melting temperature of the Sn-Zn solder is undeniable, however, the limitations regarding corrosion resistance present opportunities in furthering research in this field to identify improvements. This is to ensure that the corrosion performance can be aligned with the outstanding mechanical properties. The review also identified and summarized the advantages, recent trends and important findings in this field.

The unique challenges and future research directions regarding corrosion measurement in Sn-Zn solders were shown to highlight the rarely discussed risks and problems in the reliability of lead-free soldering. Many prior reviews have been undertaken of the Sn-Zn system, but limited studies have investigated the corrosive properties. Therefore, this review focuses on the corrosive characterizations of the Sn-Zn alloy system.

The purpose of Part I of this paper is to investigate the influence of Bi additions on the surface tension, the interfacial tension, and the density of SnZn7Bi alloys (Bi=1 and 3 percent by mass) as a continuation of similar previous studies on Bi and Sb additions to the binary Sn‐Zn alloy. The main aim of Part I is to indicate that the lowering of the surface tension and interfacial tension is not sufficient for practical applications. However, knowledge of the interfacial tension between the soldering flux and the solder is necessary to convert the wetting force into the contact angle. This will be documented in Part II.

The maximum bubble method was applied for the surface tension and the Miyazaki method was applied for the surface tension and the interfacial tension, using the density values from the dilatometric technique. The experimental surface tension results are compared with the Butler's thermodynamic modeling results and are discussed by means of the analysis of variance (ANOVA).

On the basis of previous studies on Sn‐Zn‐Bi‐Sb alloys, the addition of Bi to SnZn7 slightly decreased the surface tension measured in an Ar+H₂ atmosphere, similarly to the Butler's modeling results. Also, a similar slight decrease of the surface tension from the Miyazaki method measured in air and in nitrogen was observed, as well as a more significant lowering of the interfacial tension with the use of a flux in nitrogen. There was also a slight influence of the temperature on the numerical values of the surface tensions and the interfacial tension. In the ANOVA, taking into account the Bi content, the temperature of measurements, the atmosphere and the flux, the flux used was shown as the most important, and also, to a lesser extent, the atmosphere.

It is intended (the purpose of Part II of this paper) to verify the positive influence of Bi additions in SnZn7 alloys on the surface tensions and the interfacial tensions via the contact angles from the interaction with Cu on printed circuit board with different lead‐free finishes.

It is suggested that further studies on more efficient fluxes are necessary for the practical application being in agreement with the ANOVA and the literature information.

A slight improvement of the wettability with the use of Bi additions in the SnZn7Bi alloys in the course of various experimental techniques is proven, similar to results reported in various references. The obtained results will enlarge the SURDAT database of lead‐free soldering materials.

To determine the endurance of stainless steels used for wave soldering container materials in molten lead‐free solders.

A dissolution test on stainless steel wires in molten lead‐free solders was performed. The effects of the composition of the stainless steel, test period, and composition of the lead‐free solder on the dissolution rate were investigated. Dissolution was measured by cross‐sectioning the wires and measuring the reduction in radius.

The Sn‐Ag lead‐free solder showed faster dissolution than did the conventional Sn‐Pb eutectic. A severe dissolution rate was also observed for the Sn‐Zn system.

Quantitative data for the reaction rate between stainless steels and molten lead‐free solder is useful for the design of soldering machines and in planning their maintainance.

This paper shows the effect of basic factors on the dissolution rate of stainless steels in molten solder. It can give a basic understanding to engineers of the effect of lead free solders on wave soldering process equipment.

This study aims to focus on the surface mount technology (SMT) mass production process of Sn-9Zn-2.5Bi-1.5In solder. It explores it with some components that will provide theoretical support for the industrial SMT application of Sn-Zn solder.

This study evaluates the properties of solder pastes and selects a more appropriate reflow parameter by comparing the microstructure of solder joints with different reflow soldering profile parameters. The aim is to provide an economical and reliable process for SMT production in the industry.

Solder paste wettability and solder ball testing in a nitrogen environment with an oxygen content of 3,000 ppm meet the requirements of industrial production. The printing performance of the solder paste is good and can achieve a printing rate of 100–160 mm/s. When soldering with a traditional stepped reflow soldering profile, air bubbles are generated on the surface of the solder joint, and there are many voids and defects in the solder joint. A linear reflow soldering profile reduces the residence time below the melting point of the solder paste (approximately 110 s). This reduces the time the zinc is oxidized, reducing solder joint defects. The joint strength of tin-zinc joints soldered with the optimized reflow parameters is close to that of Sn-58Bi and SAC305, with high joint strength.

This study attempts to industrialize the application of Sn-Zn solder and solves the problem that Sn-Zn solder paste is prone to be oxidized in the application and obtains the SMT process parameters suitable for Sn-9Zn-2.5Bi-1.5In solder.

The purpose of this paper is to investigate the growth behavior and mechanism of Sn whisker induced by RE addition in Sn‐Zn‐Ga‐Pr solder at ambient condition.

By means of aging treatment, FIB and SEM microstructure analysis, the whisker growth behavior was investigated.

It was found that the morphologies of tin whisker are changed during air exposure. After 60 days aging, the average length of the longest whiskers could reach up to 70 μm, some whiskers even can grow to a length of 100 μm. It was discussed that the oxidation of Pr‐Sn intermetallics provides driving force for whisker growth.

Tin whisker growth is a complex reliability issue for lead‐free solder. The current research can be helpful in re‐understanding the issue of tin whisker growth as well as an enriched understanding on the effects of REs on lead‐free solders.

The purpose of this study was to investigate the effects of aging time on the microstructure, mechanical properties and fracture morphology of Cu/Zn160%SAC0307/Al solder joints produced through solid-state bonding.

Zn particles with a size of 1 µm and Sn-0.3Ag-0.7Cu (SAC0307) particles ranging from 20 to 38 µm were used to achieve Cu/Al micro-connections using ultrasonic assistance at a temperature of 180 °C, followed by aging treatment at 150 °C to enhance the quality of Cu/Al joints. Scanning electron microscopy was used for observing and analyzing the solder seam, interface microstructure, and fracture morphology. The structural composition was determined using energy dispersive spectroscopy, while a PTR-1102 bonding tester was used to measure the average shear strength.

The results indicated that the intermetallic compounds formed at the interface between Cu substrates and solder metal primarily consisted of smooth Cu5Zn8. The Al-side interface mainly comprises an Al-Sn-Zn solid solution, with Zn-Sn-Cu phases forming between SAC0307 particles at 180 °C. During the aging process, atomic diffusion was accelerated, leading to improved connection quality. The shear strength of the joints initially increased before decreasing as aging time progressed; it peaked at 32.92 MPa after 24 h – an increase of 76.8% compared to as-received joints. After reaching stability at 96 h, there was still a notable increase in shear strength by 48.4% relative to as-received joints.

This study further explores the strengthening mechanisms associated with solid-state bonded Cu/SACZ/Al joints through aging processes. Joints created via solid-state bonding demonstrate superior reliability compared to traditional soldered connections. It is anticipated that insights gained from this research will contribute valuable knowledge toward developing low-temperature soldering methodologies for heterogeneous materials.

The purpose of this paper is to investigate the influence of Bi additions on the wetting properties of SnZn7Bi alloys (Bi=1 and 3 per cent by mass) on a copper substrate and printed circuit boards (PCBs) with lead‐free finishes (SnCu, immersion Sn, Ni/Au, organic solderability preservative) in the presence of fluxes. The practical implications of the results is the main purpose of these investigations.

A wetting balance method was used for wetting measurements at 230 and 250°C in nitrogen and air atmospheres in the presence of ORM0‐ or ROL0‐type fluxes. The PCBs were investigated ‘as received’ and after accelerated aging. The analysis of variance (ANOVA) analysis was performed in order to explain how the main factors of the experiments (the Bi content in the alloy (1 or 3 per cent), the test temperature and the test atmosphere) influenced the wetting ability of SnZn7Bi on Cu substrates.

As expected, a higher temperature and a higher Bi content in the alloy favoured the wetting of the copper substrate in the presence of the ORM0‐type flux in a nitrogen atmosphere. These results were confirmed by ANOVA analysis. Very good results were also obtained for the SnZn7Bi3 alloy's wettability on “tin coatings” on PCBs (SnCu and immersion Sn) both “as received” and after aging, in the presence of the ORM0‐type flux, for all the applied testing conditions (in both temperatures and N₂ and air atmospheres). The less active flux (ROL0) caused a worsening of the alloy's wettability properties; however, the PCBs with SnCu and immersion Sn finishes maintained their wettability, even after aging, at very good and good levels, respectively.

It is suggested that further studies are necessary for confirmation of the practical application, but they should be limited to the soldering of SnZnBi3 on PCBs with “tin coatings” and the quality of the solder joint performance.

The best SnZn7Bi3 wetting results on PCBs with “tin coatings” (SnCu and immersion Sn) at 230 and 250°C and in N₂ and air atmospheres suggest the possibility of a practical usage of the tin‐zinc‐bismuth alloys for soldering in electronics using both the ORM0‐type flux and the even less active ROL0‐type flux, which are currently used in industrial lead‐free soldering processes.

The wetting balance method, combined with ANOVA was used as the quickest way to determine the wettability properties of SnZn7Bi on Cu substrates. Wettability measurements were also performed on the SnZn7 and SnZn7Bi alloys with different lead‐free finishes, in different experimental conditions.

A variety of lead‐free solders are now commercially available. Of those suitable for mass soldering perhaps the ones closest to a direct, drop‐in, replacement for tin‐lead are the tin‐zinc‐bismuth alloys. For most tin‐based solders it is the tin which is the active element and dominates the all‐important interfacial reactions. As a result they have many properties in common. The addition of zinc, however, radically alters this picture. Zinc oxidation products are formed at the surfaces. Zinc intermetallic compounds are also formed in preference to tin‐compounds at the substrate interfaces. The nature and implications of these changes are outlined for the common basis materials.

This study aims to research properties of Cu/SAC0307 mixed solder balls/Al joints with different bonding temperature under ultrasonic-assisted.

A new method that 1 mm Zn particles and Sn-0.3Ag-0.7 (SAC0307) with a particle size of 25–38 mm were mixed to fill the joint and successfully achieved micro-joining of Cu/Al under ultrasonic-assisted.

The results indicated that when the bonding temperature was 180°C, there was only one layer of CuZn₅ intermetallic compounds (IMCs) at the Cu interface. However, when the bonding temperature was 190°C, 200°C and 210°C, the Cu interface IMCs had two layers: for one layer, the IMCs near the Cu substrate were Cu₅Zn₈ and for another layer, the IMCs near the solder were CuZn₅. In addition, the thickness of the Cu interfacial IMCs increased with the bonding temperature. In particular, the thickness of IMCs at the Cu interface of the Cu/Al joints soldered at 210°C was 4.6 µm, which increased by 139.6% compared with that of the Cu/Al joints soldered at 180°C. However, there was no IMC layer at the Al interface, but there might be a Zn–Al solid solution layer. The shear strength of Cu/Al joints soldered at 180°C was only 15.01 MPa, but as the soldering temperature continued to increase, the shear strength of the Cu/Al joints increased rapidly. When the soldering temperature was 200°C, the shear strength of the Cu/Al joints reached the maximum of 38.07 MPa, which was 153.6% higher than that at 180°C. When the soldering temperature was 180°C, the fracture of Cu/Al joints was mainly on the Al side. However, when soldering temperature was 190°C, 200°C and 210°C, the fracture of Cu/Al joints was mainly broken in the Zn particles layer.

A new method that 1 mm Zn particles and Sn-0.3Ag-0.7 (SAC0307) with a particle size of 25–38 mm were mixed to fill the Cu/Al joint at 210°C.

The purpose of this paper is to visualise the activities of three solders; Sn‐37Pb, Sn‐9Zn and Sn‐3.5Ag on Cu substrates during reflow near their melting points and to relate them with reflow reactions between solder and substrate.

Melting activities of three solders near their melting points on copper substrates are visualised in an infrared reflow furnace.

Solder balls demonstrate different ways of melting and reflowing behaviours in dissimilar times and temperature intervals. Melting of Sn‐9Zn solder balls is initiated simultaneously at the surface and joint between solder balls. This is followed by the melting at the joint between solder balls and the Cu substrate. During melting, solder balls are first merged into each other and then reflow on the substrate from top to bottom. Opposite to Sn‐9Zn, Sn‐3.5Ag solder balls start to melt at the surface and the joint between the solder and substrate, simultaneously. Balls are first reflowed from top to bottom and, in the process, liquid solder is merged. Unlike Sn‐9Zn and Sn‐3.5 Ag, melting of Sn‐37Pb solder balls is initially commenced at the surface only. This is followed by simultaneous melting at both joints. Variation in melting activities of these solders is found to be closely related to the coalescence mechanism of solder balls and the reflow reactions between the solders and the Cu substrate.

The elementary melting activities of different solders on Cu substrates is related with their reflow behaviours. This provides better understanding of solder behaviour and selection of good lead‐free solder for applications in the electronic industry.

This paper aims to investigate the effects of different ultrasonic-assisted loading degrees on the microstructure, mechanical properties and the fracture morphology of Cu/Zn+15%SAC0307+15%Cu/Al solder joints.

A new method in which 45 μm Zn particles were mixed with 15% 500 nm Cu particles and 15% 500 nm SAC0307 particles as solders (SACZ) and five different ultrasonic loading degrees were applied for realizing the soldering between Cu and Al at 240 °C and 8 MPa. Then, SEM was used to observe and analyze the soldering seam, interface microstructure and fracture morphology; the structural composition was determined by EDS; the phase of the soldering seam was characterized by XRD; and a PTR-1102 bonding tester was adopted to test the average shear strength.

The results manifest that Al–Zn solid solution is formed on the Al side of the Cu/SACZ/Al joints, while the interface IMC (Cu₅Zn₈) is formed on the Cu side of the Cu/SACZ/Al joints. When single ultrasonic was used in soldering, the interface IMC (Cu₅Zn₈) gradually thickens with the increase of ultrasonic degree. It is observed that the proportion of Zn or ZnO areas in solders decreases, and the proportion of Cu–Zn compound areas increases with the variation of ultrasonic degree. The maximum shear strength of joint reaches 46.01 MPa when the dual ultrasonic degree is 60°. The fracture position of the joint gradually shifts from the Al side interface to the solders and then to the Cu side interface.

The mechanism of ultrasonic action on micro-nanoparticles is further studied. By using different ultrasonic loading degrees to realize Cu/Al soldering, it is believed that the understandings gained in this study may offer some new insights for the development of low-temperature soldering methodology for heterogeneous materials.

Sn‐Zn based lead free solders with a melting temperature around 199°C are an attractive alternative to the conventional Sn‐Pb solder and the addition of bismuth improves its wetability. Whilst lead‐free soldering with Sn‐8Zn‐3Bi has already been used in the electronics assembly industry, it is necessary to study its low cycle fatigue properties since such data have not been reported up to now.

In this study, displacement‐controlled low cycle fatigue testing of Sn‐8Zn‐3Bi and Sn‐37Pb solder joints was done on lap shear samples. The test amplitude was varied whilst the frequency was kept constant at 0.2 Hz and failure was defined as a 50 per cent load reduction. Finite element (FE) modelling was used for analysis and the results were compared to the experimental data.

The microstructure of the Sn‐8Zn‐3Bi solder showed a mixed phase of small cellular‐shaped and coarser needle‐shaped areas. Au‐Zn intermetallic compounds were observed near the interface from the SEM‐EDS observation. The average lifetime for the Sn‐8Zn‐3Bi solder joints was 17 per cent longer compared to the Sn‐37Pb solder joints. The cross section observation indicated that the fatigue cracks propagated along the interface between the solder bulk and the Au/Ni layer. The locations of maximum equivalent stress from the FE simulation were found to be at the two opposite corners of the solder joints, coinciding with the experimental observations of crack initiation.

This is believed to be the first time, the low cycle fatigue properties of Sn‐8Zn‐3Bi solder have been reported.

To determine the Coffin‐Manson (CM) equation constants for fatigue life estimation of Sn‐8Zn‐3Bi solder joints, since Sn‐8Zn‐3Bi solder has a melting temperature of around 199°C which is close to that of the conventional Sn‐Pb solder which has previously been used in the electronics assembly industry.

Three dimensional finite element (FE) simulation analysis was used for comparison with the experimentally measured data and to determine the CM constants. Low cycle fatigue tests and FE simulations were carried out for these lead‐free solder joints, and eutectic Sn‐37Pb solder was used as a reference.

The CM equation for Sn‐8Zn‐3Bi solder joints was fitted to the lifetimes measured and the shear strains simulated. The constants were determined to be 0.0294 for C, the proportional constant, and for the fatigue exponent, β, −2.833.

The CM equation can now be used to predict the reliability of Sn‐8Zn‐3Bi solder joints in electronics assembly and the knowledge base for the properties of the Sn‐Zn solder system has been increased.

In the electronic assembly industry, low-temperature soldering holds great potential to be used in surface mounting technology. Tin–bismuth (Sn–Bi) eutectic alloys are lead-free solders applied in consumer electronics because of their low melting point, high strength and low cost. This paper aims to investigate how to address the problem of hot tear crack formation during Sn–Bi low-temperature solder (LTS) in the mass production of consumer electronics.

This paper explored the development of hot tear cracks during Sn–Bi soldering in the fabrication of flip chip ball grid arrays. Experiments were designed to simulate various conditions encountered in Sn–Bi soldering. Quantitative analysis was conducted on the number of hot tear cracks observed in different alloy compositions and solder volumes to explore the primary cause of hot tear cracks and possible methods to suppress crack formation.

Hot tear cracks existed in Sn–Bi solders with different bismuth (Bi) contents, but increasing the solder volume reduced the number of hot tear cracks. Experiments were designed to test the degree of chip transient thermal warpage with temperature change, and, according to the results, glue was dispensed in specific areas to reduce chip warpage deformation. Finally, the results of combined process experiments pointed to an effective method of low-temperature soldering to suppress hot tear cracks.

The study focuses on Sn–Bi solders only without other solder pastes such as SAC305 or Sn–Zn series.

With the growing popularity of smart electronics, especially in intelligent terminals, new energy vehicles electronics, solar photovoltaic and other field, there will be more and more demand for low- temperature, energy-saving, lead-free solders. Therefore, this study will help the industry to roll out LTS (Sn–Bi) solutions rapidly.

In the long term, lean and green manufacturing is expected to be essential for maintaining an advanced manufacturing industry across the world. Developing new LTSs and soldering processes is the most effective, direct solution for energy conservation and emission mitigation. With the growing popularity of smart electronics, especially in intelligent terminals, new energy vehicles and solar photovoltaics, there would be an increased demand for low-temperature, energy-saving, lead-free techniques.

Although there are many methods that can be used to suppress hot tear cracks, there is little research on how to control the hot tear cracks caused by the low-temperature soldering of Sn–Bi in laptop applications. The authors studied the hot tear cracks that developed during the world’s first mass production of 50 million personal laptops based on low-temperature Sn–Bi alloy solder pastes. By controlling the Bi content, redesigning the solder paste printing process (e.g. through a printer’s stencil) and adding dispensing processes, the authors obtained reliable and stable experimental data and conclusions.

Because of the complexity of relationship between surface tension and its decisive factors, such as temperature, concentration, electronic density, molar atomic volume and electro-negativity, a reasonable predicting model of surface tension of Sn-based solder alloys has not been developed yet. The paper aims to address the surface tension issue that has to be considered if the new lead free solder will be applied for electronics.

Using an artificial neural network (ANN) model with back-propagation (BP) algorithm, the surface tension for Sn-based binary solder alloys was simulated, and the comparison between the simulating results and data from experiments and literatures was analyzed as well. In addition, the relationship between surface tension and its decisive factors would be discussed based on the ANN and orthogonal design methods.

It is shown that the predicting model of surface tension of Sn-based solder alloys is constructed according to the BP–ANN theory, and the predicted value from the BP–ANN is in excellent agreement with the experimental results. The surface tension of Sn-based solders is determined by five factors, i.e. temperature, concentration, electronic density, molar atomic volume and electro-negativity. Among of the factors, molar atomic volume is major factor, and the order of degree of influence on surface tension is molar atomic volume > electro-negativity > electronic > density > concentration > temperature. Moreover, a simply reasonable equation is proposed to estimate the surface tension for Sn-based solders.

The five decisive factors of surface tension for Sn-based binary solder alloys have been analyzed theoretically, and a reasonable model of surface tension for Sn-based binary solder alloys is proposed as well. It is shown that ANN theory will be applied well to simulate the surface tension of Sn-based lead free solder.

The purpose of this paper is to publish on the review of the lead free solder for electronic packaging. This involved the basic principles of the solder, the lead solder and its legislation and the lead free solder with its mechanism. In addition, this paper also reviews on the lead free solder characteristics that focused on its wettability.

This paper approach on the review of the solder wettability on the surface. It reviews on the solder especially on the contact angle and surface tension that is covered under the wettability of the solder.

This paper also reviews on the lead free solder characteristics that focused on its wettability.

This paper summarized finding from other researchers. The authors collect and summarize the useful data from other papers or journals. It is to create an understanding for the reader by discussion from the others research papers findings.

This study aims to research properties of Cu/SAC0307 mixed solder balls/Cu joints with different Zn-particles content at low-temperature under ultrasonic assisted.

A new method that 1µm Zn particles and Sn-0.3Ag-0.7 (SAC0307) with a particle size of 25–38 µm were mixed to fill the joint and successfully achieved micro-joining of Cu/Cu under ultrasonic-assisted at low temperature.

The results showed that with a continuous increase in the Zn-particle content, the interfacial intermetallic compounds (IMCs) of the upper and lower interfaces of joints gradually changed from scallop-shaped Cu₆Sn₅ to wavy-shaped Cu₅Zn₈. Moreover, the IMC thickness of the upper/lower interface of joints first decreased and then increased with increasing Zn-particle content. The shear strengths of joints increased with Zn-particle content, the shear strength of joints went to a maximum of 29.76 MPa when the Zn-particle content was 40%, an increase of 62.6% compared to joints without Zn particles. However, as the Zn-particle content continued to increase, the shear strengths of the joints decreased. Additionally, when the Zn content increased to 50%, because the oxidation degree of Zn particles increased, the joints were mainly broken among Zn particles.

A new method that 1µm Zn particles and Sn-0.3Ag-0.7 (SAC0307) with a particle size of 25–38 µm were mixed to fill the Cu/Cu joint at 180°C.

This paper aims to investigate the creep behaviour of the recently developed Sn–8Zn–3Bi–xSb (x = 0, 0.5, 1.0 and 1.5) low temperature lead-free solder alloys.

An in-house compressive test rig was developed to perform creep tests under stresses of 20–40 MPa and temperature range 25°C–75 °C. Dorn power law and Garofalo hyperbolic sine law were used to model the secondary creep rate.

High coefficient of determination R² of 0.99 is achieved for both the models. It was found that the activation energy of Sn–8Zn–3Bi solder alloy can be significantly increased with addition of Sb, by 60% to 90 kJ/mol approximately, whereas the secondary creep exponent falls in the range 3–7. Improved creep resistance is attributed to solid solution strengthening introduced by micro-alloying. Creep mechanisms that govern the deformation of these newly developed lead-free solder alloys have also been proposed.

The findings are expected to fill the gap of knowledge on creep behaviour of these newly developed solder alloys, which are possible alternatives as lead-free interconnecting material in low temperature electronic assembly.

The aim of the present study was to gather and review all the important properties of the Sn–Ag–Cu (SAC) solder alloy. The SAC solder alloy has been proposed as the alternative solder to overcome the environmental concern of lead (Pb) solder. Many researchers have studied the SAC solder alloy and found that the properties such as melting temperature, wettability, microstructure and interfacial, together with mechanical properties, are better for the SAC solder than the tin – lead (SnPb) solders. Meanwhile, addition of various elements and nanoparticles seems to produce enhancement on the prior bulk solder alloy as well. These benefits suggest that the SAC solder alloy could be the next alternative solder for the electronic packaging industry. Although many studies have been conducted for this particular solder alloy, a compilation of all these properties regarding the SAC solder alloy is still not available for a review to say.

Soldering is identified as the metallurgical joining method in electronic packaging industry which uses filler metal, or well known as the solder, with a melting point < 425°C (Yoon et al., 2009; Ervina and Marini, 2012). The SAC solder has been developed by many methods and even alloying it with some elements to enhance its properties (Law et al., 2006; Tsao et al., 2010; Wang et al., 2002; Gain et al., 2011). The development toward miniaturization, meanwhile, requires much smaller solder joints and fine-pitch interconnections for microelectronic packaging in electronic devices which demand better solder joint reliability of SAC solder Although many studies have been done based on the SAC solder, a review based on the important characteristics and the fundamental factor involving the SAC solder is still not sufficient. Henceforth, this paper resolves in stating all its important properties based on the SAC solder including its alloying of elements and nanoparticles addition for further understanding.

Various Pb-free solders have been studied and investigated to overcome the health and environmental concern of the SnPb solder. In terms of the melting temperature, the SAC solder seems to possess a high melting temperature of 227°C than the Pb solder SnPb. Here, the melting temperature of this solder falls within the range of the average reflow temperature in the electronic packaging industry and would not really affect the process of connection. A good amendment here is, this melting temperature can actually be reduced by adding some element such as titanium and zinc. The addition of these elements tends to decrease the melting temperature of the SAC solder alloy to about 3°C. Adding nanoparticles, meanwhile, tend to increase the melting temperature slightly; nonetheless, this increment was not seemed to damage other devices due to the very slight increment and no drastic changes in the solidification temperature. Henceforth, this paper reviews all the properties of the Pb-free SAC solder system by how it is developed from overcoming environmental problem to achieving and sustaining as the viable candidate in the electronic packaging industry. The Pb-free SAC solder can be the alternative to all drawbacks that the traditional SnPb solder possesses and also an upcoming new invention for the future needs. Although many studies have been done in this particular solder, not much information is gathered in a review to give better understanding for SAC solder alloy. In that, this paper reviews and gathers the importance of this SAC solder in the electronic packaging industry and provides information for better knowledge.

This paper resolves in stating of all its important properties based on the SAC solder including its alloying of elements and nanoparticles addition for further understanding.

The interfacial structure is vitally important for achieving a good joint reliability during service. The purpose of this paper is to systematically explore the effects of Zn addition into the Sn-3.5Ag eutectic solder on the formation of intermetallic compound (IMC) layer at the interface between Sn-3.5Ag-xZn (x = 0, 0.9 and 3) solders and Cu pad.

To obtain useful information on the formation of interfacial structure and to determine an effective way to avoid the formation of brittle joints, a series of Sn-Ag lead-free solders with different Zn contents were prepared and soldered. To investigate the IMC layers between Sn-3.5Ag-xZn (x = 0, 0.9 and 3) lead-free solders and the Cu pads, three specimens of the Sn-3.5Ag-xZn/Cu were soldered at 250°C for one min.

It is found that the addition of Zn in the Sn-3.5Ag eutectic solder can prompt the formation of Cu₅Zn₈ IMCs, and restrain the formation of the Cu₆Sn₅ IMCs. Moreover, the addition of Zn in the Sn-3.5Ag eutectic solder will reduce the solubility of Cu in the liquid solder, which accelerates the growth of the formed IMCs. Consequently, the thickness of IMC layer increases with increasing the content of Zn.

This paper usefully demonstrates how the addition of Zn favoured the formation of the Cu₅Zn₈ phase and restrained the formation of the Cu₆Sn₅ phase. Moreover, the addition of Zn in the Sn-Ag eutectic solder would reduce the solubility of Cu in the liquid solder, which accelerates the growth of the formed IMCs. Consequently, the thickness of the IMC layer increased with increasing concentration of Zn.

Viscosity is an important basic physical property of liquid solders. However, because of the very complex nonlinear relationship between the viscosity of the liquid ternary Sn-based lead-free solder and its determinants, a theoretical model for the viscosity of the liquid Sn-based solder alloy has not been proposed. This paper aims to address the viscosity issues that must be considered when developing new lead-free solders.

A BP neural network model was established to predict the viscosity of the liquid alloy and the predicted values were compared with the corresponding experimental data in the literature data. At the same time, the BP neural network model is compared with the existing theoretical model. In addition, a mathematical model for estimating the melt viscosity of ternary tin-based lead-free solders was constructed using a polynomial fitting method.

A reasonable BP neural network model was established to predict the melt viscosity of ternary tin-based lead-free solders. The viscosity prediction of the BP neural network agrees well with the experimental results. Compared to the Seetharaman and the Moelwyn–Hughes models, the BP neural network model can predict the viscosity of liquid alloys without the need to calculate the relevant thermodynamic parameters. In addition, a simple equation for estimating the melt viscosity of a ternary tin-based lead-free solder has been proposed.

The study identified nine factors that affect the melt viscosity of ternary tin-based lead-free solders and used these factors as input parameters for BP neural network models. The BP neural network model is more convenient because it does not require the calculation of relevant thermodynamic parameters. In addition, a mathematical model for estimating the viscosity of a ternary Sn-based lead-free solder alloy has been proposed. The overall research shows that the BP neural network model can be well applied to the theoretical study of the viscosity of liquid solder alloys. Using a constructed BP neural network to predict the viscosity of a lead-free solder melt helps to study the liquid physical properties of lead-free solders that are widely used in electronic information.

The purpose of this paper is to investigate the effects of two different weight percentages of lanthanum on tin–zinc–antimony solder alloys. Two manufacturing techniques were used: the furnace melting method (FMM) and ball milling method (BMM). The alloys were characterized and mechanically tested.

Tin–zinc–antimony alloys with 0.5 and 1% lanthanum were prepared by FMM and BMM for 25, 30 and 35 h. The tensile, shear, hardness, wear and corrosion properties were characterized using optical microscopy, scanning electron microscopy and X-ray diffraction.

Ball-milled samples were harder and more resistant to wear than furnace-melted samples. Corrosion tests showed that ball-milled samples of both the 0.5 and 1% lanthanum tin-based solders showed higher corrosion than furnace-melted samples. The ball-milled samples exhibited a uniform particle distribution. The ductility of the milled samples was significantly higher than that of the furnace-melted ones. There was strong evidence of the presence of nanoparticles. X-ray diffraction revealed some amorphous phases, which have not been previously reported.

The quality of solder alloys prepared by FMM and BMM was compared. This comparison was not made in previous studies. In addition to the hardness, the wear and corrosion resistances were measured, which have not been previously reported. There seems to be evidence of the presence of nanoparticles in the solder, as suggested by the increase in the elongation. Tensile, elongation and shear tests were performed, and a theory was provided for the results obtained.

The purpose of this paper is to study the relationship between microstructure and mechanical properties of Sn‐4.0Bi‐3.7Ag‐0.9Zn (in wt%) solder, and the structural evolution of the soldered interfaces.

The solder was prepared by a vacuum arc furnace. Scanning electron microscopy (SEM) and X‐ray diffraction were used to identify the microstructure and composition. The melting temperature, microhardness and tensile strength were measured. Solder joints were prepared by reflowing at 250°C for 1 min in a vacuum oven and the soldered interfaces were observed by using SEM.

The microstructure of the slowly cooled Sn‐4.0Bi‐3.7Ag‐0.9Zn specimen is composed of bulk Ag₃Sn, AgZn intermetallic compounds (IMCs), Bi precipitates and a β‐Sn phase. The developed solder exhibits good comprehensive properties, such as low‐melting temperature, high microhardness and ultimate tensile strength. A complicated IMC layer forms at the interface with Cu pads and it turns into a thinner Ni₃Sn₄ layer with Ni/Cu substrates.

The paper shows how a high performance, lead‐free solder was developed.

Recently nanoparticles reinforced lead free solders are vastly developed in electronics packaging industry. Studies and investigations have been conducted to learn and investigate the types, properties, method, availability and importance of nanoparticles in this field.

Mechanical properties, melting temperature and microstructural conditions are taken into major considerations in any of the preparation on nanoparticles and being reviewed in this paper. Segregation of the types of nanoparticles being added together with their properties is summarized in this paper. High temperature reliability is crucial in providing a good viable solder and hence addition of nanoparticles have been seen to give a positive outcome in this particular property.

This paper reviews on the beneficial of the various nanoparticles addition in the solder. Briefed explanations and the factors are revealed in this review.

This paper reviews on the beneficial of the various nanoparticles addition in the solder.

Low-Ag SAC solder will lead to a series of problems, such as increased the melting range and declined the solderability and so on. These research studies do not have too much impact on the improvement of solders’ performance but were difficult to achieve satisfactory results. It is urgent to develop new soldering technology to avoid the bottleneck of lead-free solder. low-temperature-stirring soldering and ultrasonic-assisted soldering was developed in the authors’ early work, but slag inclusion and pore would gather and grow up to lead decreasing of the shear strength. In this paper, Cu/SAC0307 +Zn power/Cu joints with ultrasonic-assisted at low-temperature was successfully achieved.

45um Zn-powder and SAC0307 No.4 solder powder were mixed to fill the Cu-Cu joint, and the content of Zn-powder were 0 and 5%, 7.5% and 10%, 12.5% and 15% respectively. During the soldering process under ambient atmosphere %252C the heating platform provided a constant 220%253 F and the ultrasonic vibrator applied a constant pressure of 4 MPa to the copper substrate. The soldering process was completed after holding 70 s at 300 W.

The Zn particles made the IMC at the joint interface and in the soldering seam from scallop-type Cu₆Sn₅ to flat-type Cu₅Zn₈. The shear strength of joints without Zn was only 12.43 MPa, the shear strength of joints with 10% Zn reached a peak of 34.25 MPa, and the shear strength of joints containing 10% Zn was 63.71% higher than that of joints without zinc particles, and then the shear strength decreased. In addition, with the increase of zinc content, the fracture mode of the joint changed from the brittle fracture of the original layered tears to the mixed tough and brittle fracture.

A new method that Zn micron-size powders and SAC0307 micron-size powders was mixed to fill the joint, and successfully achieved micro-joining of Cu/Cu under ultrasonic-assisted without flux at low-temperature.

This study aims to investigate soldering of SiC ceramics by using Zn-Al-In-based solders and ultrasonic soldering. The focus was on the quality of soldered joints, examining the boundary of the solder/substrate joint and the strength of the fabricated joints. Moreover, the fractured surfaces of joints were assessed.

The Zn-5Al base, which is considered for eutectic solder, was used in experiments. When manufacturing this solder, In was also added to at 1 Wt.%. The soldering of SiC substrates on a hot plate with ultrasonic assistance was performed.

The solder at room temperature consists of a primary segregated solid solution (Zn) and the binary eutectics (Zn) + (Al) with a high Al content and binary lamellar eutectic with a high Zn and In content non-uniformly distributed on the grain boundaries. The average tensile strength of the Zn5Al1In solder was 52 MPa. The ceramic material was wetted during soldering via reaction between the solder and the SiC substrate, with the formation of Al-Si reaction products. The thickness of the reaction layer on the boundary was 0.5–1.1 µm. The average strength of the soldered joint was 59 MPa. The obtained results confirmed the high efficiency of ultrasonic soldering in air.

This work has characterised Zn5Al1In soldering alloy and examining soldering SiC ceramics by a flux-less ultrasonic process. The analyses were oriented to assess the strength and structure of the solder and the soldered joints. Based on the achieved results, it is possible to predict the suitability of the solder alloy for flux-free soldering of SiC ceramics.

This paper aims to study the effect of different Ni content on the microstructure and properties of Sn-0.7Cu alloy. Then, the spreading area, wetting angle, interface layer thickness and microstructure of the soldering interface was observed and analyzed at different soldering temperatures and times.

Sn-0.7Cu-xNi solder alloy was prepared by a high-frequency induction melting furnace. Then Sn-0.7Cu-xNi alloy was soldered on a Cu substrate at different soldering temperatures and times.

It was found that Ni made the intermetallic compounds in the Sn-0.7Cu solder alloy gradually aggregate and coarsen, and the microstructure was refined. The phase compositions of the solder alloy are mainly composed of the ß-Sn phase and a few intermetallic compounds, Cu₆Sn₅ + (Cu, Ni)₆Sn₅. The maximum value of 12.1 HV is reached when the Ni content is 0.1 Wt.%. When the Ni content is 0.5 Wt.%, the wettability of the solder alloy increases by about 15%, the interface thickness increases by about 8.9% and the scallop-like structure is the most refined. When the soldering time is 10 min and the soldering temperature is 280 °C, the wettability of Sn-0.7Cu-0.2Ni is the best.

It is groundbreaking to combine the change in soldering interface with the soldering industry. The effects of different soldering temperatures and times on the Sn-0.7Cu-xNi alloy were studied. Under the same conditions, Sn-0.7Cu-0.2Ni exhibits better wettability and more stable solder joint stability.

Laser soldering has attracted attention as an alternative soldering process for microsoldering due to its localized and noncontact heating, a rapid rise and fall in temperature, fluxless and easy automation compared to reflow soldering.

In this study, the metallurgical and mechanical properties of the Sn3.0Ag0.5Cu/Ni-P joints after laser and reflow soldering and isothermal aging were compared and analyzed.

In the as-soldered Sn3.0Ag0.5Cu/Ni-P joints, a small granular and loose (Cu,Ni)6Sn5 intermetallic compound (IMC) structure was formed by laser soldering regardless of the laser energy, and a long and needlelike (Cu,Ni)6Sn5 IMC structure was generated by reflow soldering. During aging at 150°C, the growth rate of the IMC layer was faster by laser soldering than by reflow soldering. The shear strength of as-soldered joints for reflow soldering was similar to that of laser soldering with 7.5 mJ, which sharply decreased from 0 to 100 h for both cases and then was maintained at a similar level with increasing aging time.

Laser soldering with certain energy is effective for reducing the thickness of IMCs, and ensuring the mechanical property of the joints was similar to reflow soldering.

The purpose of this paper is to investigate a Pb‐free solder alternative, specifically the effect of Bi on the microstructure and tensile strength of Sn‐3.7Ag solders casted under different cooling rates.

Sn‐3.7Ag solder paste was mechanically blended with different percentages of Bi particles (99.999 percent) to form composite solder pastes. The solder paste was cast under different cooling rates to form dog‐bone shape samples for tensile testing. The solder samples were subjected to tensile testing on an INSTRON 5543 tester with loading rate 10⁻³ s⁻¹. Both the as‐cast and tensile‐tested samples were mounted, ground and polished for microstructure and fracture surface analysis. Scanning electron microscopy/Energy dispersive X‐ray spectroscopy was used to characterize the microstructure, morphology, and composition.

The tensile strength of Sn‐3.7Ag solder increased with increased Bi addition. However, elongation decreased with increased Bi addition. The tensile strength of Sn‐3.7Ag‐xBi (x=0, 1, 2, 3, 4 wt%) solders increased with increased cooling rates when Bi is lower than 3 wt%. The reason for improved strength of Sn‐3.7Ag‐xBi solders is the result of the combination of the solid solution strengthening and precipitation strengthening effects of Bi.

Tensile testing Bi reinforced Sn‐3.7Ag solder formed under different cooling rates is new in the paper. With the additions of Bi to Sn‐3.7Ag, the solder strength has been increased, which may be beneficial to the electronics industry and other researchers seeking a better replacement for Sn−Pb solder.

This study aims to present a more accurate lifetime prediction model considering solder chemical composition.

Thermal cycling and standard creep tests as well as finite element simulation were used.

The study found lower error in the solder joint lifetime evaluation. The higher the Ag content is, the higher the lifetime is achieved.

It is confirmed.

This paper aims to cover the recent (2010-2016) techniques for carrying out hardness evaluation on lead-free solders. Details testing configuration/design were compiled and discussed accordingly to each of the measurement techniques: Vickers microhardness, Brinell microhardness and nanoindentation.

A brief introduction on lead-free solders and the concept of hardness testing has been described at the beginning of the review. Equipment setup, capabilities, test configuration and outcomes were presented for each technique and discussed in parallel along with the case studies from selected articles.

Comparison, outcomes and insight regarding each of the methods were highlighted to observe the recent trends, scientific challenges, limitations and probable breakthroughs of the particular hardness testing methods.

The compilation of latest reports, technical setup plus with the critics and perception from the authors are the main key value in this review. This provides an in-depth understanding and guidance for conducting hardness evaluation on lead-free solders.

This study aims to investigate the chromium (Cr) effects on the microstructural, mechanical and thermal properties of melt-spun Sn-3.5Ag alloy.

Ternary melt-spun Sn-Ag-Cr alloys were investigated using X-ray diffractions, scanning electron microscope, dynamic resonance technique, instron machine, Vickers hardness tester and differential scanning calorimetry.

The results revealed that the Ag₃Sn intermetallic compound (IMC) and ß-Sn have been refined because of the hard inclusions’ (Cr atoms) effects, causing lattice distortion increasing these alloys. The tensile results of Sn_96.4-Ag_3.5-Cr_0.1 alloy showed an improvement in Young’s modulus more than 100 per cent (42.16 GPa), ultimate tensile strength (UTS) by 9.4 per cent (23.9 MPa), compared with the eutectic Sn-Ag alloy due to the high concentration of Ag₃Sn and their uniform distribution. Shortage in the internal friction (Q⁻¹) of about 54 per cent (45.1) and increase in Vickers hardness of about 7.4 per cent (142.1 MPa) were also noted. Hexagonal Ag₃Sn formation led to low toughness values compared to the eutectic Sn-Ag alloy, which may have resulted from the mismatching among hexagonal Ag₃Sn phase with orthorhombic Ag₃Sn and ß-Sn phases. Mechanically, the values of Young’s modulus have been increased, with increasing chromium content, whereas the UTS and toughness values have been decreased. The opposite of this trend appeared in Sn_95.8-Ag_3.5-Cr_0.7 alloy, which may have been due to high lattice distortion (ƹ = 16.5 × 10⁻⁴) compared to the other alloys. Increase in the melting temperature T_m, ΔH, C_p and ΔT was because of Ag₃Sn IMC formation. The low toughness of Sn₉₆-Ag_3.5-Cr_0.5 and Sn_95.8-Ag_3.5-Cr_0.7 (109.56 J/m³ and 35.66 J/m³), relatively high melting temperature Tm (223.22°C and 222.65°C) and low thermal conductivity and thermal diffusivity (32.651 w.m⁻¹.k⁻¹ and 0.314 m²/s) make them undesirable in the soldering process. The high UTS, high E, high thermal conductivity and diffusivity, low creep rate and low electrical resistivity, which have occurred with “0.1 Wt.%” of Cr, make this alloy desirable and reliable for soldering applications and electronic assembly.

This study provides chromium effects on the structure of the eutectic Sn-Ag rapidly solidified by melt-spinning technique. In this paper, the authors compared the elastic modulus of the melt-spun compositions, which have been resulted from the Static method with that have been resulted from the Dynamic method. This paper presents new improvements in mechanical and thermal performance.

The purpose of this study is to investigate the addition of 0.05 Wt.% carbon nanotube (CNT) into the Sn-1.0Ag-0.5Cu (SAC) solder on the intermetallic (IMC) growth. Lead-based solders play an important role in a variety of applications in electronic industries. Due to the toxicity of the lead in the solder, lead-free solders were proposed to replace the lead-based solders. Sn-Ag-Cu solder family is one of the lead-free solders, which are proposed and considered as a potential replacement. Unfortunately, the Sn-Ag-Cu solder faces some reliability problems because of the formation of the thick intermetallic compounds. So the retardation of intermetallic growth is prime important.

The solder joint was aged under liquid state aging with soldering time from 1 to 60 min.

Two types of intermetallics, which are Cu₆Sn₅ and Cu₃Sn were observed under a scanning electron microscope. The morphology of Cu₆Sn₅ intermetallic transformed from scallop to planar type as the soldering time increases. The addition of carbon nanotube into the SAC solder has retarded the Cu₆Sn₅ intermetallic growth rate by increasing its activation energy from 97.86 to 101.45 kJ/mol. Furthermore, the activation energy for the Cu₃Sn growth has increased from 102.10 to 104.23 kJ/mol.

The increase in the activation energy indicates that the growth of the intermetallics was slower. This implies that the addition of carbon nanotube increases the reliability of the solder joint and are suitable for microelectronics applications.

The purpose of this paper is to investigate the effects of Sn-Ag-x leveling layers on the mechanical properties of SnBi solder joints. Four Sn-Ag-x (Sn-3.0Ag-0.5Cu, Sn-0.3Ag-0.7Cu, Sn-0.3Ag-0.7Cu-0.5 Bi-0.05Ni and Sn-3.0Ag-3.0 Bi-3.0In) leveling layers were coated on Cu pads to prepare SnBi/Sn-Ag-x/Cu solder joints. The microstructure, hardness, shear strength and fracture morphology of solder joints before and after aging were studied.

The interfacial brittleness of the SnBi low-temperature solder joint is a key problem affecting its reliability. The purpose of this study is to improve the mechanical properties of the SnBi solder joint.

Owing to the addition of the leveling layers, the grain size of the ß-Sn phase in the SnBi/Sn-Ag-x/Cu solder joint is significantly larger than that in the SnBi/Cu eutectic solder joint. Meanwhile, the hardness of the solder bulk in the SnBi/Cu solder joint shows a decrease trend because of the addition of the leveling layers. The SnBi/Cu solder joint shows obvious strength drop and interfacial brittle fracture after aging. Through the addition of the Sn-Ag-x layers, the brittle failure caused by aging is effectively suppressed. In addition, the Sn-Ag-x leveling layers improve the shear strength of the SnBi/Cu solder joint after aging. Among them, the SnBi/SACBN/Cu solder joint shows the highest shear strength.

This work suppresses the interfacial brittleness of the SnBi/Cu solder joint after isothermal aging by adding Sn-Ag-x leveling layers on the Cu pads. It provides a way to improve the mechanical performances of the SnBi solder joint.

The purpose of this paper is to investigate the effects of zinc (Zn) nanoparticles on the interfacial intermetallic compounds (IMCs) between Sn‐3.8Ag‐0.7Cu (SAC) solder and Cu substrate during multiple reflow.

The nanocomposite solders were prepared by manually mixing of SAC solder paste with varying amounts of Zn nanoparticles. The solder pastes were reflowed on a hotplate at 250°C for 45 s for up to six times. The actual Zn content after reflow was analyzed by inductively coupled plasma‐optical emission spectroscopy (ICP‐OES). The wetting behavior of the solders was characterized by analyzing the contact angles and spreading rates according to the Japanese Industrial Standard (JIS 23198‐3, 2003). The interfacial microstructure of the solder joints were investigated by field emission scanning electron microscope (FESEM) and energy dispersive X‐ray spectroscopy (EDAX).

It was found that upon the addition of 0.3 wt% Zn nanoparticles to the SAC solder, the growth of interfacial intermetallic compound (IMC) layers was retarded to a minimum value. Excessive amount of Zn nanoparticles (0.8 wt%) induced an additional IMC layer (Cu₅Zn₈) which increased the total IMC thickness and raising the reliability issue.

It is concluded that Zn nanoparticles undergo melting/reaction during reflow and impart their effect on the IMCs through alloying effects.

This study aims to investigate the NiO nano-reinforced solder joint characteristics of ultra-fine electronic package.

Lead-free Sn-Ag-Cu (SAC) solder paste was mixed with various percentages of NiO nanoparticles to prepare the new form of nano-reinforced solder paste. The solder paste was applied to assemble the ultra-fine capacitor using the reflow soldering process. A focussed ion beam, high resolution transmission electron microscopy system equipped with energy dispersive X-ray spectroscopy (EDS) was used in this study. In addition, X-ray inspection system, field emission scanning electron microscopy coupled with EDS, X-ray photoelectron spectroscopy (XPS) and nanoindenter were used to analyse the solder void, microstructure, hardness and fillet height of the solder joint.

The experimental results revealed that the highest fillet height was obtained with the content of 0.01 Wt.% of nano-reinforced NiO, which fulfilled the reliability requirements of the international IPC standard. However, the presence of the NiO in the lead-free solder paste only slightly influenced the changes of the intermetallic layer with the increment of weighted percentage. Moreover, the simulation method was applied to observe the distribution of NiO nanoparticles in the solder joint.

The findings are expected to provide a profound understanding of nano-reinforced solder joint’s characteristics of the ultra-fine package.

The purpose of this study is to investigate the effect of electromigration (EM) on solder alloy joint on copper with nickel surface finish. Sn-Bi solder alloy has been used in this research.

The EM process was completed with the duration of 0, 24, 48, 72 and 96 h under direct current (DC) of 1,000 mA. Tensile stress on the substrates was assessed after EM at a tension rate of 0.1 mm/min. Microscopy was used to observe the formation and size of voids and conduct an analysis between copper and nickel substrates.

Four types of intermetallic compounds (IMCs), namely, Cu-Sn, Cu3Sn, Cu6Sn5, and Sn-Bi, were detected between the Sn-Bi/Co solder joint. Voids appear to be at the anode and the cathode for 96 h of EM for Sn-Bi/Ni solder join; however, there seem to be more voids at the cathode.

EM is one of the crucial keys to produce a good integrated circuit (IC). When the current density is extremely high and will cause the metal ions to move into the electron direction flow, it will be characterised based on the ion flux density. In this research, the effect of EM on the Sn-Bi solder alloy joint on copper with nickel surface finish was studied.

The purpose of this paper is to present a novel high speed impact testing method for evaluating the effects of low temperatures on eutectic and lead‐free solder joints. Interfacial cracking failure of Sn‐based and Pb‐free solders at subzero temperatures is of significant concern for electronic assemblies that operate in harsh environments.

This paper presents a newly designed low temperature control system coupled with an Instron micro‐impact testing machine, which offers a package level test for solder bumps, and that is used at subzero temperature ranges as low as −40°C. This study examined the failure characteristics of 63Sn‐37Pb (Sn37Pb) and 96.5Sn‐3Ag‐0.5Cu (SAC305) solder joints at temperatures ranging from room temperature (R.T.) to −40°C, and at impact speeds of 1 m/s.

Three types of failure mode were identified: M1 interfacial fracture with no residual solder remaining on the pad (interfacial cracking); M2 interfacial fracture with residual solder persisting on the pad (mixed mode failure); and M3 solder ball fracture (bulk solder cracking). The experimental results indicated that the energy to peak load for both types of solders decreased significantly, by approximately 35 percent to 38 percent when the test temperature was reduced from R.T. to −40°C. In addition, the peak load of the Sn37Pb solder joint increased noticeably with a decreasing test temperature. However, the peak load of the SAC305 specimen remained virtually unchanged with a reduction in the temperature. The Sn37Pb solder joints failed in an M3 failure mode under all the considered testing temperatures. The SAC305 solder joints displayed both M1 and M2 failure modes at R.T.; however, they failed almost exclusively in M1 mode at the lowest test temperature of −40°C.

This paper presents a novel technique for evaluating high‐speed impact strength and energy absorbance of Sn‐based and Pb‐free solders at the chip level within a low temperature control system. To overcome the drawbacks experienced in other studies, this study focused specifically on cryo‐impact testing systems and the performed experimental steps to improve the accuracy of post‐test analysis.

The purpose of this paper is to investigate the effect of Sb (0, 0.2 and 2 wt.%) on wetting performance of lead-free solder of near eutectic Sn-Cu micro-alloyed with Ni and Ge.

The melting characteristic of the lead-free alloys was studied using differential scanning calorimetry. Wettability was examined using wetting balance test for two liquid fluxes, water based and alcohol based in two temperatures 265°C and 277°C. Also, contact angle was measured using sessile drop test.

It is shown that 0.2 wt.% Sb reduces the melting temperature and pasty range. Moreover, the addition of 0.2 wt.% Sb improves wetting behavior for alcohol-based flux. It is also demonstrated that the effect of Sb on meniscus height in wetting balance test and contact angle in sessile drop test follows the trend of wetting performance.

It is found that adding 0.2 wt.% Sb improves the wettability of Ni-Ge micro-alloyed Sn-Cu solder; however, higher concentration of Sb does not benefit the alloy.

The purpose of this paper is to study the effect of the addition of a small amount of Al (0.1 percent) on the properties of lead‐free solder type Sn‐4Ag‐0.5Cu (SAC 405).

The soldering properties of wettability and spreadability on a Cu substrate were studied, and the effect of Al on the growth of intermetallic compounds (IMCs) was observed. The shear strength of soldered joints was assessed. For comparison, soldering and strength tests were carried out on SAC 405 and SAC 405+ Al solders. Soldering was performed with an activated flux type ZnCl₂‐NH₄Cl, with non‐activated flux (rosin), and without flux in the air.

Experimental results show that Al addition slightly reduces the wettability and spreadability of SAC 405 solder. Also, the shear strength is moderately reduced, dropping by 8 MPa on average. Differential scanning calorimetry (DSC) analysis showed that the melting point of SAC 405+0.1%Al solder was increased to 221°C.

The positive effect of a small Al addition is due to the fact that it hinders the growth of IMCs formed on the contact surface with Cu substrate. The width of the transition zone of IMC was reduced by approximately 2 to 3 μm, depending on the soldering temperature.

Deformation studies on eutectic Sn‐Ag solder (Sn‐3.5Ag in wt percent) joints were carried out at a range of temperatures using a rheometric solids analyzer (RSA‐III). Various performance parameters were evaluated with this equipment by subjecting geometrically realistic solder joints to shear loading at various temperatures (25, 75, 100, 125, and 150°C) with a nominal joint thickness of ∼100 μm and 1×1 mm solder joint area. Mechanical properties such as shear stress versus simple shear‐strain relationships, peak shear stress as a function of rate of simple shear‐strain and testing temperature, and creep parameters were evaluated to gain a better understanding of the parameters contributing to thermomechanical fatigue.

This paper aims to investigate the effect of different beam distance by understanding laser beam influence on solder joint quality. The utilisation numerical-based simulations and experimental validation will help to minimise the formation of micro void in PTH that can lead to cracks and defects on passive devices.

The research uses a combination approach of numerical-based simulation using Finite Volume Method (FVM) and experimental validation to explore the impact of different laser beam distances on solder joint quality in PTH assemblies. The study visualises solder flow and identifies the optimal beam distance for placing a soldering workpiece and a suitable tolerance distance for inserting the solder wire.

The simulation results show the formation of micro void that occurs in PTH region with low volume fraction and unbalance heat concentration profile observed. The experimental results indicate that the focus point of the laser beam at a 99.0 mm distance yields the smallest beam size. Simulation visualisation demonstrates that the laser beam’s converging area at +4.6 mm from the focus point which provides optimal tolerance distances for placing the solder wire. The high-power laser diode exhibits maximum tolerance distance at 103.6 mm from the focus point where suitable beam distance for positioning of the soldering workpiece with 50% laser power. The simulation results align with the IPC-A-610 standard, ensuring optimal filling height, fillet shape with a 90° contact angle and defect-free.

This research provides implications for the industry by demonstrating the capability of the simulation approach to produce high-quality solder joints. The parameters, such as beam distance and power levels, offer practical guidelines for improving laser soldering processes in the manufacturing industry.

This study contributes to the field by combining high-power laser diode technology with numerical-based simulations to optimise the beam distance parameters for minimising micro void formation in the PTH region.