Sn-9Zn Solder Alloy Research Articles

The Effects of Gallium Additions on Microstructures and Thermal and Mechanical Properties of Sn-9Zn Solder Alloys

The effects of gallium additions on microstructures and thermal and mechanical properties of the Sn-9Zn solder alloys are investigated in this study. The results show that the melting temperature of the alloys decreases with the increase in the Ga concentration, while the pasty ranges of the alloys are simultaneously enlarged. By adding a 0.25–0.5 wt.% Ga element, the Sn-matrix region is slightly increased and the Zn-rich phase becomes slightly coarser; however, the overall microstructure is still very similar to that of the Sn-9Zn alloy. It is found that, when the Ga concentration is less than 0.50 wt.%, the ultimate tensile strength and elongation are maintained at the same values. The addition of a 0.25–0.50 wt.% Ga to the Sn-9Zn alloy also leads to small cup and cone fracture surfaces which exhibit near-complete ductile fracturing. With the addition being increased to 0.75 wt.%, larger cup and cone fractures are observed. The 1.00 wt.% Ga alloy has lower strength and ductility due to the coarser and nonuniform microstructures. However, the fracture surfaces of the 1.00 wt.% Ga alloy show partial cleavage and a partially dimpled fracture.

Creep deformation behavior of Sn–Zn solder alloys

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

Effects of 0.1 wt% Ni addition and rapid solidification process on Sn–9Zn solder

Effects of 0.1 wt% Ni addition and rapid solidification process on Sn–9Zn solder alloy were investigated. Characteristics of Sn–9Zn–0.1Ni alloy were analyzed compared with those of as-solidified Sn–9Zn alloy. Mechanical properties and interfacial microstructure of solder/Cu joints obtained using these solders were comparatively studied. By comparison with as-solidified Sn–9Zn alloy, the wettability of solder was obviously improved with 0.1 wt% Ni addition, and the melting behavior of the solder was promoted due to the rapid solidification process. The corrosion resistance of as-solidified and rapidly solidified Sn–9Zn–0.1Ni alloys was improved due to the formation of Ni–Zn intermetallic compound (IMC) and the refining of Zn-rich phases. Formation and growth of IMCs at the interface of Sn–9Zn–0.1Ni/Cu joints was significantly depressed. Rapid solidification process promoted the interfacial reaction during soldering and improved the bonding strength of joints.

Effects of phosphorus addition on the properties of Sn-9Zn lead-free solder alloy

This article explores the effects of phosphorus addition on the wettability between Sn-9Zn solder alloy and Cu substrates, the oxidation behavior and the corrosion behavior of Sn-9Zn solder alloy. Spreading test was used to characterize the wettability of Sn-9Zn-xP solder alloys to Cu substrates. The oxidation and corrosion behaviors of Sn-9Zn-xP solder alloys were determined by means of weight gaining, and secondary ion mass spectrometry was used to analyze the oxygen content. The role and mechanism of P in the solder alloys were also discussed. It is found that the addition of P can significantly improve the wettability of the solder alloys. Incorporating P into Sn-9Zn solder alloy obviously decreases the oxygen content and enhances the oxidation and corrosion resistance. Microstructure observations show that an appropriate amount of P can greatly refine coarse rod-like Zn-rich phases in Sn-9Zn solder alloy.

Influence of rapid solidification on microstructure, thermodynamic characteristic and the mechanical properties of solder/Cu joints of Sn–9Zn alloy

Rapidly solidified Sn–9Zn alloy foils were prepared by the melt-spinning method. The effects of rapid solidification process on the microstructure, thermodynamic characteristic, electrochemical corrosion properties and spreading properties of Sn–9Zn solder alloys were analyzed. The mechanical properties and fracture behaviors of the solder/Cu joints were also investigated. The results showed that the rapid solidification process could obviously refine the solidification structure of Sn–9Zn alloy and a fine netlike dendrite structure was formed due to the rapid branch of Sn phase. The Zn phase was distributed in Sn matrix in granular form. After rapid solidification, the pasty range decreased from 7K to 4K, the wettability was modestly improved, and the corrosion resistance of the rapid solidified alloy was improved significantly. The tensile shear strengths of the joints using the rapidly solidified solder were obviously higher than that of the joints using the as-solidified solders result from the formation of fine-grained intermetallic compound (IMC) with a needle pattern and more uniform IMC layer at the interface.

Effect of Micron Size Ni Particle Addition on Microstructure, Thermal and Mechanical Properties of Sn-9Zn Lead-Free Solder Alloy

This study had been carried out to investigate the effect of micron size Ni particle addition on the microstructure, melting behavior and mechanical properties of the ternary Sn-9Zn solder alloys. Different weight percentage, viz. 0.25, 0.5 and 1 of micron size Ni particle was added in the liquid Sn-9Zn alloy and then cast into the metal mold. Melting behavior was studied by Differential Thermal Analyzer (DTA). Microstructural investigation was conducted using Optical and Scanning Electron Microscope (SEM). Tensile properties were determined at a strain rate 3.00 mm.min-1. The results indicated that Ni addition increased both the melting point and solidification range of the Sn-9Zn solder alloy. The microstructures of newly developed ternary Sn-9Zn-xNi solder alloys consisted of fine needle-like α-Zn phase dispersed in the β-Sn matrix. It was found that small amount of Ni (0.25 wt. %) addition refined and dispersed the Zn needles throughout the matrix. Besides, enhanced precipitation of Zn in the β-Sn matrix was also observed. All these structural changes increased the hardness and tensile strength of Sn-9Zn alloy with the addition of Ni particle to a certain amount.

The microstructure and properties of as-cast Sn-Zn-Bi solder alloys

Research on the lead-free solders has attracted wide attention, mostly as the result of the implementation of the Directive on the Restriction of the Use of Hazardous Substances in Electrical and Electronic Equipment. The Sn-Zn solder alloys have been considered to be one of the most attractive lead-free solders due to its ability to easily replace Sn-Pb eutectic alloy without increasing the soldering temperature. Furthermore, the mechanical properties are comparable or even superior to those of Sn-Pb solder. However, other problems still persist. The solution to overcoming these drawbacks is to add a small amount of alloying elements (Bi, Ag, Cr, Cu, and Sb) to the Sn-Zn alloys. Microstructure, tensile strength, and hardness of the selected Sn-Zn-Bi ternary alloys have been investigated in this study. The SEM-EDS was used for the identification of co-existing phases in the samples. The specimens? microstructures are composed of three phases: Sn-rich solid solution as the matrix, Bi-phase and Zn-rich phase. The Bi precipitates are formed around the Sn-dendrit grains as well as around the Zn-rich phase. The amount of Bi segregation increases with the increase of Bi content. The Sn-Zn-Bi alloys exhibit the high tensile strength and hardness, but the values of these mechanical properties decrease with the increase of Bi content, as well as the reduction of Zn content. The results presented in this paper may offer further knowledge of the effects various parameters have on the properties of lead-free Sn-Zn-Bi solders.

Properties and microstructure of Sn-9Zn lead-free solder alloy bearing Pr

In the present work, effects of trace amount of Pr on the microstructure, wettability and mechanical properties of Sn-9Zn solder were studied. The range of Pr content in Sn-9Zn solder alloys varied from 0.01 to 0.25 wt%. Test results indicate that adding appropriate amount of Pr can evidently improve the wettability and mechanical properties of the Sn-9Zn solder alloy. The Sn-9Zn-0.08Pr solder shows the best comprehensive properties compared to other solders with different Pr content. At the same time, notable changes in microstructure were found compared with the Pr-free alloy. The needle-like Zn-rich phase in the Sn-9Zn solder was refined and became more uniform. Moreover, the thickness of the IMC layer at Sn-9Zn/Cu substrate was remarkably depressed with Pr addition.

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.

Depressing effect of 0.1 wt.% Cr addition into Sn–9Zn solder alloy on the intermetallic growth with Cu substrate during isothermal aging

In this paper, the effect of 0.1 wt.% Cr addition into Sn–9Zn lead-free solder alloys on the growth of intermetallic compound (IMC) with Cu substrate during soldering and subsequent isothermal aging was investigated. During soldering, it was found that 0.1 wt.% Cr addition did not contribute to forming the IMC, which was verified as the same phase structure as the IMC for Sn–9Zn/Cu. However, during solid-state isothermal aging, the IMC growth was remarkably depressed by 0.1 wt.% Cr addition in the Sn–9Zn solder, and this effect tended to be more prominent at higher aging temperature. The activation energy for IMC growth was determined as 21.2 kJ mol − 1 and 42.9 kJ mol − 1 for Sn–9Zn/Cu and Sn–9Zn–Cr/Cu, respectively. The reduced diffusion coefficient was confirmed for the 0.1Cr-containing solder/Cu. Energy-dispersive X-ray mapping and point analysis also showed ZnCr phase existing in solder matrix, which can reduce diffusion rate of Zn atoms.

Structure and Properties of Sn-9Zn Lead-Free Solder Alloy with Heat Treatment

The Sn-9Zn lead-free solder alloy was prepared by conventional casting technique then cold-rolled into long sheets of 1 mm thickness and 3 mm width. It was annealed at 80, 120 and 160°C for 60 min to investigate the effect of isochronal heat treatment on structure and mechanical properties of the cold rolled Sn-9Zn alloy. The results showed that, the crystallite size and lattice strain have opposite behavior with increasing annealing temperature due to recovery and recrystalization processes associated with the heat treatment process. Vickers micro-hardness number increases continuously from 155 to 180 MPa with increasing annealing temperature. Ultimate tensile strength (UTS) was also calculated. It was found that, it is equal to 61.4 MPa for the non annealed sample and slightly decreases to 60.5 and 58.2 MPa for samples annealed at 80 and 120°C, respectively. While, increases to 65.4 MPa for the sample annealed at 160°C. Also, ductility increases with increasing annealing temperature in opposite manor with the UTS. The new method for Micro-creep behavior as well as the creep rate calculated by this method has been characterized at room temperature.

Development of Sn–Zn lead-free solders bearing alloying elements

Sn–Zn solder alloys have been considered as one of the more attractive lead-free solders since it can easily replace Sn–Pb eutectic alloy without increasing the soldering temperature. However, there are still some problems to be resolved, such as the argument about the poor oxidation resistance and embrittlement behavior. In order to overcome these drawbacks, and further enhance the properties of Sn–Zn lead-free solder alloys, a small amount of alloying elements (rare earths, Bi, Ag, Al, Ga, In, Cr, Cu, Sb, Ni, Ge) added into Sn–Zn alloys were selected by many researchers. For example, a small amount of Al, P, Bi, Ga can improve the high-temperature oxidation resistance of Sn–Zn solders remarkably as well as Cr. This paper summarizes the effects of alloying elements on the wettability, oxidation resistance, melting behavior, mechanical properties, creep properties, microstructures and intermetallic compounds layer of Sn–Zn lead-free solders.

Effect of rare earth element additions on the impression creep of Sn–9Zn solder alloy

Creep behavior of the Sn–9Zn–RE alloys containing 0.1, 0.25 and 0.5 wt.% rare earth (RE) elements was studied by impression testing and compared to that of the eutectic Sn–9Zn alloy. The tests were carried out under constant punching stress in the range 40–135 MPa and at temperatures in the range 298–420 K. Results showed that for all loads and temperatures, Sn–9Zn–0.25RE had the lowest creep rate, and thus the highest creep resistance among all materials tested. This was attributed to the formation of Sn–RE second phase precipitates which act as the main strengthening agent in the RE-containing Sn–Zn alloys. RE contents higher than 0.25 wt.%, resulted in a lower creep resistance due to a reduction in the volume fraction of Zn-rich phase caused by the formation of Sn–Zn–RE intermetallics. The average stress exponents of 6.8, 6.9, 7.1, 6.8 and activation energies of 42.6, 40.6, 43.0 and 44.9 kJ mol−1 were obtained for Sn–9Zn, Sn–9Zn–0.1RE, Sn–9Zn–0.25RE, and Sn–9Zn–0.5RE, respectively. These activation energies were close to 46 kJ mol−1 for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about seven suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.

Thermodynamics of Oxidation on Pb-Free Solders at Elevated Temperature

Based on the available thermodynamic and phase equilibria data, the thermodynamic criteria for oxidation in tin-based lead-free solders under soldering condition was deduced. The dependence of Gibbs free energy on temperature in Pb-free solder oxidation reaction was calculated by applying MATLAB program. The characteristics of oxidation reaction of a varity of solder alloy systems such as Sn-Ag, Sn-Cu, Sn-Sb, Sn-Zn, Sn-Ag-Cu and Sn-Pb eutectic alloys at elevated temperature were analyzed. The results suggested that zinc preferentially oxidized in Sn-Zn solder alloys in the elevated temperature state, while tin preferentially oxidized in the other alloys. The oxidation potential of the Sn-Zn eutectic alloys was higher than that of the pure tin at elevated temperature, whereas the oxidation potentials of Sn-Ag, Sn-Cu, Sn-Sb and Sn-Ag-Cu eutectic alloys were approxiately equal to that of the pure tin. All tin-based Pb-free solder alloys more easily oxidized than the Sn-Pb solder alloys. Oxidizability of these alloys followed in a decreasing order: Sn-Zn＞Sn-Sb＞Sn-Cu＞Sn-Ag＞Sn-Ag-Cu＞Sn-Pb.

Effects of Ag and Al Additions on the Structure and Creep Properties of Sn-9Zn Solder Alloy

Creep behavior of the eutectic Sn-9Zn, Sn-9Zn-0.5Ag, and Sn-9Zn-0.5Al solder alloys was studied by impression testing under constant punching stress in the range of 60 MPa to 130 MPa and at temperatures in the range of 298 K to 370 K. Analysis of the data showed that, for all loads and temperatures, Sn-9Zn-0.5Al had the lowest creep rates and thus the highest creep resistance among all materials tested. The creep resistance of Sn-9Zn-0.5Ag was slightly lower than that of the Al-containing alloy. The enhanced creep behaviors of the ternary alloys are attributed to the presence of AgZn3 and very fine Zn particles, which act as the main strengthening agents in the Sn-9Zn-0.5Ag and Sn-9Zn-0.5Al alloys, respectively. Assuming a power-law relationship between the impression rate and stress, average stress exponents of 6.9, 7.1, and 7.2 and activation energies of 42.1 kJ mol−1, 42.9 kJ mol−1, and 43.0 kJ mol−1 were obtained for Sn-9Zn, Sn-9Zn-0.5Ag and Sn-9Zn-0.5Al, respectively. These activation energies are close to 46 kJ mol−1 for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about 7, suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.

Nanoindentation study of Zn-based Pb free solders used in fine pitch interconnect applications

Because of their hazardous nature, conventional Sn–Pb solders are slowly being replaced by Pb free solders. Sn–Zn solder alloys have been identified as a potential alternative because of their low melting point close to that of Sn–Pb solder. However, the high Sn content and reflow temperature will accelerate intermetallic compound (IMC) formation at the solder/substrate interface, which in turn controls the reliability of the solders joints. A detailed study of the growth morphology of IMCs in solder joints will enhance our ability to control their influence on the mechanical and physical properties. Knowledge of the mechanical properties of individual phases makes predictions of the mechanical behavior of an overall joint more straightforward. The small length scale of intermetallic phase formation may lead to a behavior different from bulk samples. One would like to measure the mechanical properties of the phases in interesting realistic geometries. However, even low-load microhardness testing results in indentations that span multiple phases within a real joint. In the present work, the micromechanical properties of Pb-free solder joints such as Sn–8 wt.% Zn–3 wt.% Bi/Au/Ni/Cu were probed using nanoindentation. Nanoindentation is a reliable technique in testing small volumes of materials and complex microstructures manifested in the fine pitch interconnects employed in the flip-chip technologies. The IMCs formed between Zn and Au, and Ni, Zn were characterized and their hardness, elastic modulus were investigated in the present work. The IMCs are found to be ɛ-AuZn 8; δ-NiZn 8 compounds and formation of these compounds are found to depend on reflow temperature and time. It is also found that the hardness and modulus of the δ-NiZn 8 is higher than that of the ɛ-AuZn 8 compound.

Solderability of Sn–9Zn–0.5Ag–1In lead-free solder on Cu substrate: Part 1. Thermal properties, microstructure, corrosion and oxidation resistance

The thermal properties, microstructure corrosion and oxidation resistance of the Sn–9Zn–0.5Ag–1In lead-free solder have been investigated by differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry, potentiostat and thermogravimetry. The Sn–9Zn–0.5Ag–1In solder alloy has a near-eutectic composition, it melts at 187.6 °C and the heat of fusion is determined as 71.3 J/g. The Sn–9Zn–0.5Ag–1In solder alloy with a corrosion potential of −1.09 V SCE and a current density of 9.90 × 10 −2 A/cm 2, shows a better corrosion resistance than that of the Sn–9Zn solder alloy. From the thermogravimetry analysis, the weight gain ratio of the Sn–9Zn solder alloy appears a parabolic relationship at 150 °C. The initial oxidation behavior of the Sn–9Zn–0.5Ag and Sn–9Zn–0.5Ag–1In solder alloys also shows a parabolic relationship but the weight gain ratio of them appears a negative linear one after aging at 150 °C for 2.5 and 5 h, respectively.

Electrochemical Behaviors of the Sn-9Zn-xAg Lead-Free Solders in a 3.5 wt % NaCl Solution

The electrochemical behaviors, microstructures, and corroded products of lead-free solders were investigated in this study. The 63Sn-37Pb and Sn-3.5Ag solder alloys were also tested for comparison. The Sn-3.5Ag solder alloy had a higher equilibrium potential than the ones of 63Sn-37Pb and Sn-9Zn The Ag addition enhanced the corrosion resistance of the Sn-9Zn solder alloy. Passivation behavior occurred in the solder alloys used in this study except the 63Sn-37Pb one. X-ray diffraction patterns showed that the Zn segregated in the Sn-9Zn solder alloy as solidified, but it dissolved when 0.5 wt % Ag was added to the solder alloy. The and were found in the Sn-9Zn-1.5Ag solder alloy but they were substituted by the when the Ag content in the solder alloy was above 2.5 wt %. However, they were the initial sites for pits formation. The corroded product of was observed in all solder alloys tested. In addition, the ZnO, and SnO were observed in the solder alloys. © 2004 The Electrochemical Society. All rights reserved.

Effect of Thermal Cycling on the Adhesion Strength of<tex>$hboxSn$</tex>–<tex>$hbox9Zn$</tex>–<tex>$hboxxAg$</tex>–<tex>$hboxCu$</tex>Interface

The effect of thermal cycling on the adhesion strength of the Sn-9Zn-xAg-Cu interface has been investigated by using pull-off tester, X-ray diffractometer, scanning electron microscope and energy dispersive spectrometer. The Sn-9Zn-xAg lead-free solders offer a better thermal cyclic resistance than the 63Sn-37Pb and Sn-9Zn solder alloys. The adhesion strength of the Sn-9Zn-Cu interface increases from 4.4 /spl plusmn/ 0.4 MPa to 13.8 /spl plusmn/ 0.9 MPa with increasing the thermal cycles from zero to three times but it decreases to 8.5 /spl plusmn/ 0.8 MPa for five cycles. The Sn-9Zn-xAg solder alloys (x=0.5, 2.5, and 3.5 wt%) have a similar tendency and the maximum adhesion strength of 21.41 /spl plusmn/ 1.5 MPa for the Sn-9Zn-2.5Ag solder alloy has been obtained after three thermal cycles. The adhesion strength of the Sn-9Zn-1.5Ag-Cu interface increases from 7.8 /spl plusmn/ 0.6 to 16.6 /spl plusmn/ 0.9 MPa with increasing the thermal cycles from 0 to 5 times.