Eutectic Sn 9Zn Solder Research Articles

Effect of Bismuth Addition on Physical Properties of Sn-Zn Lead-Free Solder Alloy

The aim of this work is to improve the properties of eutectic Sn-9Zn solder alloy by adding different amounts of bismuth to produce alternate lead-free solder alloys for use in electronic applications. Phase identification of the various solders was performed by x-ray diffraction analysis. Scanning electron microscopy was employed for morphological characterization of the prepared solder alloys. Spreading tests were used to measure the contact angle, and the electrical resistance was measured. Differential scanning calorimetry (DSC) thermographs were obtained for the alternate lead-free alloys. The results showed that Bi addition could clearly improve the wettability and physical properties of the Sn-9Zn base alloy by decreasing the melting point.

Glass-Cu joining by anodic bonding and soldering with eutectic Sn-9Zn solder

A new coupling technique for glass-metal joining was presented in this paper. Firstly, the glass and Al were successfully bonded by anodic bonding process, then the joining between Al and Cu was achieved by soldering with eutectic Sn-9Zn solder. The microstructures of glass/Al interface and solder joint were investigated by using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the interface evolution mechanism as well as the correlation between the glass/Cu joining strength and the interface morphology were discussed. The results showed that a sodium-depleted layer with a thickness of 546 nm was formed on the glass/Al interface at 400 °C/1000 V. Al-Sn-Zn solid solution, Cu5Zn8 and CuZn5 reaction layers were detected on Al/solder interface and Cu/solder interface respectively. As the soldering time increased, needle-like (Al)' phases and round (Al)'' phases were observed in sequence near Al/solder interface; at the same time, the thickness of Cu5Zn8 and CuZn5 layers increased accordingly. When the soldering time was 10 min, micro grooves on Al foil were observed, and CuZn5 IMCs spalled off and dispersed into liquid solder, which deteriorated the joint strength. During the soldering process, the whole interface evolution could be divided into four stages and was analyzed explicitly. Shear tests indicated the fracture mainly occurred at solder/Cu interface and a small amount of Al foil was torn off the glass substrate when soldering time exceeded 5 min. The shear strength increased at first and then reduced with the prolongation of soldering time, and the maximum strength was 12.7 MPa when the joint was achieved at 240 °C for 5 min.

Effect of nano Al2O3 additions on the interfacial behavior and mechanical properties of eutectic Sn-9Zn solder on low temperature wetting and soldering of 6061 aluminum alloys

In this study, an addition of Al2O3 nano-particles with a content in the range of 0–1 wt% to Sn-9Zn eutectic solder, were examined in order to understand the effects of Al2O3 additions as the particulate reinforcement to the melting point, wettability, microstructure, interface morphology and hardness as well as mechanical properties of soldering 6061 aluminum alloys. Here, an approach to prepare a composite solder by adding Al2O3 nano-particles to the molten Sn–9Zn solder alloy was developed. In the soldered joint using Sn–9Zn solders, there is a solution layer of Al8ZnSn4 located at the interface. Due to the addition of Al2O3 nano-particles, the scallop-shaped solid solution layer was changed into a flat layer, and its thickness was reduced. In the microstructure of the composite solder containing 1 wt% Al2O3 nano-particles, the fine acicular-shaped Sn-Zn eutectic structure and Al2O3 nano-particles were found to be distributed in the β-Sn matrix. These changes in the interfaces and the microstructure, leading to the improvement of wettability, mechanical properties and hardness of the composite solder.

Effects of Minute Addition of Ni on Microstructure and Mechanical Properties of Sn-Zn Eutectic Alloy

The current work explores the effects of a small addition of Ni on the microstructure and mechanical properties of Sn-Zn eutectic solder alloy (Sn-14.9 at.%Zn). In two sets of experiments, Ni is either added to the eutectic alloy or Zn in the eutectic alloy is replaced by an increasing amount of Ni. The study indicates that small additions of Ni in eutectic Sn-Zn solder (∼0.017 at.%) refines the eutectic microstructure together with the appearance of the small amount of primary Zn plates. Increasing the Ni content to 0.142 at.% and beyond, then an intermetallic phase ϒ-Ni5Zn21 with dendritic morphology appears in the microstructure along with dendrites of primary Sn. The scale of eutectic microstructure shows a decreasing trend till 0.902 at.%Ni with eutectic spacing of 1.98 ± 0.32 μm for this alloy. Further addition of Ni coarsens the microstructure. The replacement of Zn with Ni in the eutectic composition follows a similar trend with a lesser refinement of the microstructure. In both the scenarios, the addition of a small amount of Ni increases the eutectic temperatures till a critical concentration is reached beyond which one can observe a decrease in the eutectic point. The trend is similar for the solid solubility of Zn in Sn while the trend is opposite for the measured eutectic composition, which decreases at the initial stages of Ni addition. Through a detailed measurement of mechanical properties, the study establishes significant improvement of the strength of Sn-Zn solder with small additions of Ni in the alloy with a maximum hardness of 26 ± 1 HV and 0.2% proof stress of 72 ± 3 MPa at room temperature for the eutectic alloy with 0.902 at.%Ni.

The effects of Cu and Al on dry sliding wear properties of eutectic Sn-9Zn lead-free solder alloy

The present study investigates the influence of Cu and Al on microstructure and wear behavior of a eutectic Sn-9Zn solder alloy. The Sn-9Zn–X alloy was produced by adding various amounts of Cu and Al through investment casting method. The produced Sn-9Zn–X alloys were characterized by a scanning electron microscope, X-ray diffraction, and hardness measurements. In wear tests at 1 ms−1 sliding speed, 10 N load and 5 different sliding distances (400–2000 m) were used. The results show that as the amount of Cu and Al increased within Sn-9Zn alloy, the hardness of the alloy increased as well. Depending on the increase in hardness of the alloys produced by investment casting, it was observed that weight loss decreased during wear tests. Furthermore, the same proportion of added Al alloys’ hardness and weight loss were observed to be higher than the added Cu alloys. Furthermore, the Cu-added alloy exhibited higher hardness and lower weight loss than the Al-added alloy did.

Corrosion resistance of ternary Sn-9Zn-xIn solder joint in alkaline solution

Corrosion resistance performance of ternary tin-zinc-indium (Sn–9Zn-xIn) solders was compared with the binary tin-zinc (Sn–9Zn) solder in 6 M potassium hydroxide. Six different compositions of Sn–9Zn-xIn (x = 1, 2, 3, 4, 5 and 6 wt. %) were prepared. The corrosion resistance performance of the solders was investigated through potentiodynamic polarization. The addition of In introduces microstructure segregation to the eutectic Sn–9Zn solder. Pronounced influence of the microstructure alteration was seen to affect the passivation ability. Structural characterization proved that smoother corrosion products made of SnO, SnO2 and ZnO were formed on the surface after the addition of In. The presence of massive grooves produced by the preferential dissolution of the dominant enlarged Zn-rich phase limits the protection offered by the passivation film at the addition of over 4 wt. % of In. This becomes the crack initiation spot under tensile loading.

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.

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

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

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

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

Effect of nano Al 2O 3 additions on the microstructure, hardness and shear strength of eutectic Sn–9Zn solder on Au/Ni metallized Cu pads

Nano-sized, nonreacting, noncoarsening Al 2O 3 particles have been incorporated into eutectic Sn–Zn solder alloys to investigate the microstructure, hardness and shear strength on Au/Ni metallized Cu pads ball grid array substrate (BGA). In the plain Sn–Zn solder joint and solder joints containing Al 2O 3 nano-particles, a scallop-shaped AuZn 3 intermetallic compound layer was found at the interfaces. In the solder joints containing Al 2O 3 nano-particles, a fine acicular-shaped Zn-rich phase and Al 2O 3 nano-particles were found to be homogeneously distributed in the β-Sn matrix. The shear strengths and hardness of solder joints containing higher percentage of Al 2O 3 nano-particles exhibited consistently higher value than those of plain solder joint and solder joints containing lower percentage of Al 2O 3 nano-particles due to control the fine microstructure as well as homogeneous distribution of Al 2O 3 nano-particles acting as a second phase dispersion strengthening mechanism. The fracture surfaces of plain Sn–Zn solder joints exhibited a brittle fracture mode with smooth surfaces while Sn–Zn solder joints containing Al 2O 3 nano-particles showed a typical ductile failure with very rough dimpled surfaces.

Effects of rare earth element Nd on the solderability and microstructure of Sn–Zn lead-free solder

Effects of trace amount addition of rare earth Nd on the properties of eutectic Sn–Zn solder were studied in this paper. Results indicate that adding trace rare earth element Nd could remarkably improve the solderability and mechanical properties of Sn–9Zn solder joints. Especially when the content of Nd was 0.06 wt%, the wettability of the solder was improved significantly, and the shear force of Sn–9Zn–0.06Nd solder joint was enhanced by 19.6% as well as pull force increased by 26.6% compared to that of Sn–9Zn solder joint,respectively. It is also found that addition of rare earth Nd could refine the microstructure of the solder and some NdSn3 phase appeared in the solder matrix. Moreover, the IMCs thickness at the solder/Cu interface was reduced. NdSn3 phase appeared at the interface with excessive addition of Nd, which is the key reason that deteriorates the mechanical properties of soldered joint.

Elastic properties and thermal behavior of Sn–Zn based lead-free solder alloys

In this study, the effects of separate and dual additions of small amount of Cu, In and Ag on the microstructure and elastic properties as well as thermal behavior of the eutectic Sn–9Zn solder alloy were investigated. The elastic properties of the newly developed ternary and quaternary alloys have been investigated using sound wave velocity measurements at 4 MHz and T = 25 °C. In particular, the hardness, the attenuation coefficient, the bulk and shear moduli, Young's and Poisson's ratio have been established for a range of alloy compositions. Results showed that alloying of Cu, In and Ag resulted in reducing fusion heat, solidus temperature and broadening the pasty range. Moreover, the presence of additional elements in Sn–Zn alloy system allows many complex intermetallic (IMC) phases to form. Both the hardness and reduced modulus increase as the Poisson's ratio of the alloy decreases. The elastic properties can be correlated with the formation of the new IMC phases. By analyzing the quotient of shear modulus to bulk modulus, we can assume that the Sn–9Zn, Sn–9Zn–1.5Ag and Sn–9Zn–0.7Cu alloys are ductile solders whereas, the Sn–9Zn–1.5In and Sn–9Zn–1.5Ag–0.7Cu alloys are brittle in nature.

Effects of small addition of Ag and/or Cu on the microstructure and properties of Sn–9Zn lead-free solders

In the present study, the effects of separate and dual addition of small amount of Ag and Cu on the microstructure and mechanical properties of the eutectic Sn–9Zn solder alloy were investigated. Results indicate that alloying of Ag and/or Cu resulted in refine the coarse needle-like Zn-rich phase and formation of intermetallic compounds (IMCs) with the eutectic solder. Single addition of Ag led to formation of AgZn, Ag 5Zn 8 and ɛ-AgZn 3 IMCs, which results in significant increase in both ultimate tensile strength (UTS) and ductility, while, the flower shaped and rod shaped Cu 6Sn 5, γ-Cu 5Zn 8 and ɛ-CuZn 5 IMCs produced by Cu alloying, results in small increase in UTS and ductility. The dual addition of Ag and Cu suppressed the appearance of Ag 5Zn 8 IMCs due to the competition for Zn between Cu and Ag, which results in slight decrease in UTS and ductility of Sn–9Zn–1.5Ag solder. Worthy of notice is that all alloys demonstrated an increase in both UTS and yield stress with increasing strain rate and/or decreasing testing temperature, indicating that the tensile behavior of the four alloys often exhibits a strain rate and temperature dependence.

Reverse polarity effect from effective charge disparity during electromigration in eutectic Sn–Zn solder interconnect

Polarity effect on the interfacial reactions from high-density electric currents was investigated in a solder interconnect with a large disparity in the effective charge between the solder constituents. A reverse polarity effect was found where the intermetallic compound layer at the cathode grew significantly thicker than that at the anode under electric loading. Such an abnormal polarity effect was shown to result from electromigrations of Sn and Zn along opposite directions as dictated by the disparity in their effective charges. As Sn migrated to the anode under electron wind force, the resulting back stress drove Zn atoms to drift to the cathode. A kinetic analysis of the Zn mass transport explained the differential growth of the intermetallic compounds at the two electrodes, in good agreement with the experimental data.

Interfacial Reactions between Eutectic SnZn Solder and Bulk or Thin-Film Cu Substrates

Interfacial reactions between eutectic SnZn solder and bulk or thin-film Cu substrates are investigated and compared. The thicknesses of bulk and thin-film Cu substrates are 0.5 mm and 4,000 A, respectively. Different dominant reaction products and interfacial microstructures are observed in these two types of interfacial reactions. In the bulk Cu type, the Cu5Zn8 phase is the dominant reaction product under reflow and solid-state annealing. However, the CuZn5 phase becomes the dominant reaction product in the thin-film Cu type. The Cu5Zn8 phase in the bulk Cu type remains as a uniform microstructure after reflow. After solid-state annealing, however, the Cu5Zn8 phase fractures and the Cu6Sn5 and Cu3Sn phases are formed at the Cu5Zn8/Cu interface. The CuZn5 phase in the thin-film Cu type ripens after reflow and the phase morphology is transformed from a uniform layer into separated scallops. In situ observation of the interfacial microstructure after solid-state annealing reveals that prominent deformation occurs in the solder region close to the interface in the bulk Cu type. While in the thin-film Cu type, the CuZn5 grain is extruded out of the interface.

Effect of Cu addition on interfacial reaction between Sn–9Zn solder and Ag

The effect of Cu added eutectic Sn–9Zn solder reacting with the Ag substrate has been investigated in this study. Three Ag–Zn intermetallic compounds (IMCs), ∈–AgZn3, γ–Ag5Zn8, and ζ–AgZn, were formed on the Sn–9Zn/Ag interface at 260 °C. While Cu was gradually added to the Sn–9Zn alloy, microstructures of intermetallic compounds changed dramatically. The intermetallic compound microstructures became loose and Sn and Cu atoms in the Ag-Zn intermetallic compounds increased. If more than 3 wt% of Cu was added to the Sn-9Zn alloy, Ag-Sn intermetallic compounds were formed on the Ag surface and massive spalling of Ag–Zn IMC layers from the Ag surface occurred in a short reaction time.

Effect of small additions of alloying elements on the properties of Sn-Zn eutectic alloy

Sn-Zn alloys have been considered for use as lead-free solders. Their poor wetting and oxidation resistance properties are the main obstacles that prevent them from becoming commercially viable solders. The effects of alloying elements, such as lanthanum, titanium, aluminum, and chromium, on oxidation resistance, wetting properties, and tensile properties of eutectic Sn-Zn solder are described herein. Results show the addition of alloying Ti, Al, and Cr can improve the oxidation resistance of Sn-9Zn solder. La, Ti, and Cr do not have much effect on the wetting properties, whereas Al worsens the wetting. Differential scanning calorimetry investigations reveal the solidus temperature of these solders to be ∼200°C. Addition of Cr improves ductility while maintaining tensile strength.

Wetting Properties of and Interfacial Reactions in Lead-free Sn-Zn Based Solders on Cu and Cu Plated with an Electroless Ni-P/Au Layer

The wetting time, wetting force, contact angle and interfacial reaction of Sn-8.55Zn-0A5Al-XAg (mass%) and Sn-9Zn (mass%) lead-free solders on Cu and Cu/Ni-P/Au substrates have been investigated. The Ag content, X, of thesolders investigated was 0-3 mass%. The results indicate that the wettability of Sn-8.55Zn-0A5Al-XAg solders decreases with increasing Ag content. The Sn-8.55Zn-0.45Ai-XAg. solders containing low Ag content, less than 1mass%, exhibit better wettability than the eutectic Sn-9Zn solder. Furthermore, it was also found that the wettability of Sn-Zn based solders on Cu substrate is better than that on Cu/Ni-P/Au substrate, The when used on Cu and Cu/Ni-P/Au, Sn-9Zn solder forms Cu 5 Zn 8 and AuZn 3 respectively, while the Al-containing solders form Al 4 . 2 Cu 3 . 2 Zn 0 . 7 and Al 2 (Au, Zn). Further addition of Ag gave rise to AgZn 3 particles attached to the underlying intermetallic compound.

Effects of process parameters on the soldering behavior of the eutectic Sn-Zn solder on Cu substrate

The effects of process parameters such as flux, dipping temperature and the heat-treatment on the soldering behaviors of the eutectic solder (composition: 91Sn-9Zn) hot-dipped on Cu substrates were investigated. The most suitable flux as tested was oleic acid for the eutectic Sn-Zn solder system hot-dipped on Cu substrate for the solder coverage. The adhesion strength obtained increased from 9.6±0.6 MPa to 11.9±0.6 MPa when the dipping temperature increased from 250 °C to 300 °C. However, it decreased from 11.9±0.6 MPa to 5.2±2.2 MPa as the sample was heated at 150 °C for 1200 h. Planar γ-Cu5Zn8 isolate-shaped η-Cu6Sn5 intermetallic layers were found in the bulk sample after heating at 150 °C for 300 h but was not found in the as-cast sample. In the plate samples, scallop-shaped γ-Cu5Zn8/inverted trigonal-shaped η-Cu6Sn5 intermetallic layers were found after heating at 150 °C for 600 h. Some pores were found at the interface between γ-Cu5Zn8 intermetallic compound (IMC) and the solder alloy, which might come from the formation and growth of IMCs and decreased the adhesion strength. © 2000 Kluwer Academic Publishers