Zn Solder Research Articles

Application of ultrasonic assisted soldering method to hard-to-solder material

In this study, Pb-free solders were bonded to soda-lime glass and fused quartz plates using the ultrasonic assisted soldering (UAS) method. The solder–glass interfaces were observed and analyzed to clarify the effect of the elements in the solder and glass bonding behavior. As a result, the Sn–Zn solder was bonded to glass without the intermetallic compound (IMC) layer. However, the Sn–Ag–Cu solder was not able to bond to glass even though ultrasonication was performed during the soldering process. Chemical shifts for Zn 2p and O 1s spectra were observed at the interface by X-ray photoelectron spectroscopy (XPS) analysis, which is attributed to the chemical bonding between the substrates and elements in solder alloy. In conclusion, O in the substrate and Zn in the solder were important to form the bond between the glass and solder.

Investigation of Flux-Less Soldering of Metal Matrix Composite and Ceramics by Use of Zn Solder

The work was dealing with direct soldering of Al2O3 ceramics and a metal/ceramic composite (MMC) with Al matrix. The joints were fabricated by application of flux-less process by use of a hot plate at the assistance of ultrasound with frequency of 40 kHz. The experiments were performed by use of Zn6Al6Ag solder. Wetting was attained on both substrates. The joints of a good quality were fabricated. The soldering temperature was 420 °C. The microstructural studies of interface have revealed a transient zone of Al dissolving on the side of MMC and formation of Zn oxides on the side of ceramics, which were responsible for bond formation.

Effects of nanoparticles on the thermal, microstructural and mechanical properties of novel Sn3.5Ag0.5Zn composite solders

The effects of added nanoparticles (i.e., Al2O3 and TiO2) on the thermal, microstructural and mechanical properties of Sn3.5Ag0.5Zn nanocomposite solders have been investigated. Adding nanoparticles to the Sn3.5Ag0.5Zn solder increases the melting temperature by only 2.1–4.6 °C. It was also confirmed that the nanoparticles affect the microstructural and mechanical properties. The UTS, 0.2 YS, and microhardness of the Sn3.5Ag0.5Zn nanocomposite solder improved, which could be attributed to the refinement of the β-Sn grain size, the precipitation of Ag3(Sn, Zn) grains, and the second phase dispersion strengthening mechanism. The fracture mechanism of Sn3.5Ag0.5Zn nanocomposite solders was confirmed to be the ductile fracture mode. The cracks were initiated at the interfaces between β-Sn(Zn) grains and Ag(Zn, Sn) phases.

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.

Microstructural transformation and thermo-mechanical improvement of quinary Bi–Sn–In–Ga–Zn solder bumps on a flexible PET substrate

Novel Bi–Sn–In–Ga–Zn powders were fabricated using a gas atomization process. The addition of 5.0wt% Zn to a Bi–Sn–In–Ga alloy system resulted in the formation of a pure Zn state as a precipitate, which was mostly dispersed along the grain boundaries during solidification. From this reason, the refined microstructure, which was effective for easy adsorption of outer thermal energy and high surface free energy, could provide a lower onset melting temperature of 58.9°C and narrower melting range of 6.9°C compared to those of the quaternary solder powders used as a reference (61.6 and 7.6°C, respectively). The hardness of the quinary solder was also significantly increased (by 34.7%) by the addition of Zn. As a result, the quinary solder pastes reflowed at a low melting temperature of 110°C, which is well suited to the formation of solder joints on a flexible polyethylene terephthalate (PET) substrate.

Theoretical prediction of thermodynamic activities of liquid Au-Sn-X (X=Bi, Sb, Zn) solder systems

Molecular interaction volume model has been theoretically used to predict the thermodynamic activities of tin in Au-Sn-Bi and Au-Sn-Sb and the thermodynamic activity of zinc in Au-Sn-Zn at experimental temperatures 800K, 873K and 973K, respectively. On the premise of agreement between the predicted and experimental values, we predicted the activities of the remaining two components in each of the three systems. This prediction was extended from three cross-sections to five cross-sections, and to temperature range 400–600K, relevant for applications. Iso-activities were plotted. Results show that addition of tin reduces the tendency for chemical short range order in both Au-Sb and Au-Zn systems, while addition of gold and bismuth, respectively, reduce the tendency for chemical short range order in Sn-Sb and Au-Sn systems. Also, we found that, in the desired high-temperature region for applications, while a combination of chemical order and miscibility of components exist in both Au-Sn-Bi and Au-Sn-Zn systems, only chemical order exist in the Au-Sn-Sb system. Results, further show that increase in temperature reduces the phase separation tendency in Au-Sn-Bi system.

Comparative study on the wettability and interfacial structure in Sn–xZn/Cu and Sn/Cu–xZn system

Zn is the common used alloying element in Pb-free solder to depress the growth of interfacial intermetallic compound (IMC) in solder joints, but is also an oxidation preferred element to decrease the wettability of solder. This paper provides a potential replacement on the Zn-contained solder with small amount of Zn alloyed Cu substrate to avoid the deterioration on wettability but keep the depressing effect on growth of IMC through the comparative study on Sn–xZn/Cu and Sn/Cu–xZn. To systematically study the effect of Zn alloying, 0.2–0.8 wt% content of Zn was added into pure Sn solder and 2.29 and 4.89 wt% content of Zn was alloyed into Cu substrate. The wettability, interfacial reaction during soldering and interfacial IMC growth of Sn–xZn/Cu and Sn/Cu–xZn during isothermal aging were studied and compared with Sn/Cu system. Zn alloyed into Cu substrate exhibited a far better wettability than Zn alloyed into solder. Although there was no significant change on the composition, morphology and thickness of interfacial of IMC in Zn-contained system during soldering, Zn alloyed into Cu substrate or Sn solder obviously depressed the formation of Cu3Sn and the growth of IMC layers during isothermal aging compared with Sn/Cu system. The depressing effect and calculated activation energy on the growth of IMC increased with the content of Zn in Cu or in Sn, and can be attributed to the CuZn solid solution existed at the interface because it decreased the driving force on formation of Cu3Sn and the diffusion rate of Cu atoms. Compared Sn/Cu–xZn with Sn–xZn/Cu, Cu–4.89Zn substrate provided a similar depressing effect on IMC growth but an exceeding wettability compared with Sn–Zn solder, and can be offered as an alternative under bump metallurgy (UBM) in solder joints.

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.

Effects of coupled stressing and solid-state aging on the mechanical properties of graphene nanosheets reinforced Sn–58Bi–0.7Zn solder joint

With the addition of 0.075wt% graphene nanosheets (GNSs), the mechanical properties of coupled and aged solder joint were respectively investigated in this study. During the tensile tests, the weakening of the anode interface between intermetallic compounds (IMCs) and Bi layer significantly affected the ultimate tensile strength (UTS) of electromigration (EM) and thermal aging coupled solder joint. The formation of vacancies and stress concentration at the Cu–Sn–Zn/Cu–Zn interface in the aged solder joint was ascribed to the Bi segregation and GNSs. Nanoindentation results showed that the creep resistance of coupled solder joint was higher than that of the aged solder joint, which was because that the Bi layer, GNSs and cracks played a role of load transfer at the solder joint interface in coupled sample.

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.

Growth kinetics and mechanism of Pd2Zn9 at the interface of Pd substrate with molten Sn–9wt.%Zn solder

A uniform Pd2Zn9 layer was formed at the interface between liquid-state Sn–9wt.%Zn and Pd substrate. Detailed observation revealed a unique cruciform pattern formation of the Pd2Zn9 phase. The Pd2Zn9 layer ruptured at the edges, where no reaction phase was formed. The growth kinetics of Pd2Zn9 was systematically investigated at temperatures of 220–260 °C. In particular, a linear reaction-limited growth was found in the initial reaction stage. While growing to approximately 5 μm thick, the growth rate gradually decreased over the subsequent reaction and obeyed a parabolic relationship. The growth kinetics parameters and the corresponding activation energies were determined. Additionally, the microstructure in the Pd2Zn9 layer was characterized using focused ion beam microscopy. The Pd2Zn9 layer consisted of four distinct sublayers with different grain structures. The growth behavior of Pd2Zn9 was further discussed through a series of observations on microstructural evolutions at different reaction durations.

Development and characterization of Sn–1.3Ag–0.7Cu solder bearing Zn for electronic packaging

The effect of small amounts of Zn on microstructure, thermal behavior and mechanical properties of low silver-content Sn–1.3Ag–0.7Cu (SAC137) solder was investigated. Microstructural investigations of SAC137 solder revealed that both the intermetallic compounds of rod-like Cu6Sn5 and needle-like Ag3Sn particles are dispersed in β-Sn matrix, which are gradually diminished with increasing Zn content in plain solder. Moreover, addition of 0.75 wt% Zn promotes the nucleation of β-Sn grains and leads to formation of new (Cu,Ag)5Zn8 IMC particles. Although the strength and Young’s modulus of plain solder are increased with increasing Zn content, the elongation was firstly increased with 0.75 wt% Zn addition and then decreased after adding 1.5 % Zn. The higher mechanical strength was contributed by the fine β-Sn grains and precipitations strengthen effects of new (Cu,Ag)5Zn8 IMC particles. The presence of Zn in SAC137–0.75 wt% Zn solder seems to result in a complete reduction of brittle pro-eutectic Ag3Sn phase to maintain the ductility at the highest level. The new (Cu,Ag)5Zn8 IMC developed in Zn added specimens was found to enviably affect the thermal properties according to DSC analyses.

High-Temperature Die Attachment Using Sn-Plated Zn Solder for Power Electronics

Pure Zn is a Pb-free die-attach material considered suitable for application in high-temperature electronics such as widebandgap semiconductor devices, as it has both the requisite electrical/thermal conductivity and an excellent thermal shock resistance. The high melting point of Zn (419.5 °C), however, means that die-attachment using pure Zn would require higher bonding temperatures (>430 °C), whereas a lower temperature is more desirable for mass production. This paper, therefore, presents a bonding method based on using Sn-plated Zn solder (Sn/Zn/Sn structure) to achieve a lower bonding temperature than pure Zn die attachment. The resulting shear strength of this bonding exceeds 25 MPa at 350 °C for 30 min, which is attributed to a uniform and complete Ni–Zn IMC ( $\gamma $ -Ni5Zn21) reaction layer. Furthermore, this bonding strength is retained beyond 25 MPa without serious degradation, even after thermal shock testing within a temperature range of −50 °C–300 °C; and thus, the Sn-plated Zn solder proposed has great potential as a die-attach material for high-temperature applications such as power devices.

Low-temperature joining of Fe-based amorphous foil with aluminum by ultrasonic-assisted soldering with Sn-based fillers

Abstract Low temperature joining of amorphous alloys has big challenges to prevent them from crystallization. An ultrasonic-assisted soldering method was proposed to join the Fe-based amorphous alloys with the aluminum plates in air by using Sn-based solders. No obvious defects were observed and the joining ratio was more than 90%. At the interface of solder/aluminum, scallop α-Al solid solutions were formed and large fretting (pits) with a size of 50 μm on the aluminum plates was found due to ultrasonic vibrations. At the interface of solder/amorphous, Fe–Zn intermetallic compound (FeZn 13 ) was probably formed. Its formation activation energy was approximately 30.9 kJ/mol between the amorphous iron and the Sn–9Zn during the solid state diffusion, which was much lower compared with crystallized couples. The enhanced diffusion/reaction and the much low activation energy in this work are probably attributed to the amorphous state of the Fe-based foils. Adding nickel in the Sn–Zn solder can improve the hardness of the joints by formation of NiAl 3 intermetallic particles and depress the corrosion on the aluminum. Both the initially interfacial wetting and the microstructure refinement during solidification of the filler solder were improved by ultrasonic vibrations.

Analysis of the natural activities of radionuclides, heavy metals, and other poisonous elements in lead-free Sn–6.5Zn solders with different alloying elements

Problem statementSn–Zn solders are candidate alternatives to Sn–Pb-based solder alloys. With the increasing requirement for lead-free solders, the reliability of successor solders in microelectronics assemblies is in high demand. The elimination of radionuclides, heavy metals, and other poisonous elements in lead-free Sn–6.5Zn solders in the microelectronics industry is a worldwide goal. As a result, it is useful to identify the natural concentrations of radioactive nuclides, heavy metals and other poisonous trace elements (both macro- and micro-element contents), such as Au-196, Th-227, Ag-110M, Fe-59, Zn-65, Rb-89, Rh-106M, Bi-207, Cs-137, Eu-154, Sb-126, Eu-152, Co-56, Co-58, Co-60 and K-40. If this lead-free solder contains high concentrations of natural radioactive nuclides, then workers handling it might be exposed to significant levels of radiation. Therefore, it is important to determine the levels of radioactive nuclides in this solder to protect workers; these levels provide background for the safety rules and precautions that should be applied for those working in this field. ApproachThe levels of natural radionuclides (238U, 232Th, and 40K) and their daughter products contained in Sn–6.5Zn solders have been estimated via gamma-ray spectrometry using a 100% Hyper-Pure Germanium (HPGe) detector. ResultsThe mean activities due to radionuclides, heavy metals, and other poisonous elements were measured, and the results are summarised in tables. ConclusionThe results of this assessment obtained by gamma-ray spectroscopic analysis indicated the presence of high levels of natural radioactivity, heavy metals and other poisonous elements. This result implies that a comprehensive study should be conducted to protect workers from high doses of hazardous substances.

Effect of Ag on Sn–Cu and Sn–Zn lead free solders

Abstract Lead and lead-containing compounds are considered as toxic substances due to their detrimental effect on the environment. Sn-based soldering systems, like Sn-Cu and Sn-Zn are considered as the most promising candidates to replace the eutectic Sn-Pb solder compared to other solders because of their low melting temperature and favorable properties. Eutectic Sn-0.7 wt.% Cu and near eutectic composition Sn-8 wt.% Zn solders have been considered here for study. For the Sn-Cu system, besides the eutectic Sn-0.7 wt.% Cu composition, Sn-1Cu and Sn-2Cu were studied. Three compositions containing Ag: Sn-2Ag-0.7Cu, Sn-2.5Ag-0.7Cu and Sn-4.5Ag-0.7Cu were also developed. Ag was added to the eutectic Sn-0.7 wt.% Cu composition in order to reduce the melting temperature of the eutectic alloy and to enhance the mechanical properties. For the Sn-Zn system, besides the Sn-8 wt.% Zn near eutectic composition, Sn-8Zn-0.05Ag, Sn-8Zn-0.1Ag and Sn-8Zn-0.2Ag solder alloys were developed. The structure and morphology of the solder alloys were analyzed using a scanning electron microscope (SEM), filed emission scanning electron microscope (FESEM), electron diffraction X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Thermal analysis of the alloys was also done using a differential scanning calorimeter (DSC). Trace additions of Ag have been found to significantly reduce the melting temperature of the Sn-0.7 wt.% Cu and Sn-8 wt.% Zn alloys.