Zn Lead-free Solder Research Articles

Effects of Bi Doping on Zn-Rich Phase Evolution and Physical and Chemical Properties of Sn-6.5Zn Lead-Free Solder Alloy

Effects of Bi Doping on Zn-Rich Phase Evolution and Physical and Chemical Properties of Sn-6.5Zn Lead-Free Solder Alloy

Interfacial reaction of Sn-1.5Ag-2.0Zn low-silver lead-free solder with oriented copper

High density packaging technology reduces the pad size and the number of grains contained in the pad. When the polycrystalline pad turns into a single crystal pad, the grain orientation has an important impact on the formation of the intermetallic compound (IMC) at the interface. The growth of IMC at the interface between the solder and the single-crystal copper substrate is investigated by selecting the prospective Sn-1.5Ag–2Zn as the solder alloy. Sn-1.5Ag-2.0Zn lead-free solder joints soldered with single crystal (111) copper substrate and polycrystalline red copper substrate are reflowed at 250 °C for 5 min. Samples are subsequently aged at 160 °C. The uneven scallop like Cu6Sn5 IMC layer grows rapidly when the alloy solder contacts with the copper substrate. The Cu6Sn5 grain size formed on the surface of single crystal copper is larger than that of polycrystalline copper. Single crystal copper has no grain boundary to block atomic diffusion, which affects grain nucleation and growth. The growth rate of Cu6Sn5 formed by alloy solder and the single crystal (111) copper solder joint after aging treatment at 160 °C for 20 h is about twice that of the polycrystalline copper solder joint. Then it grows slowly with the increase of aging treatment time. The thick layer Cu6Sn5 breaks due to crack diffusion after 600 h of aging treatment, and the thickness of IMC remains at 3.5 μm. Cu5Zn8 generated at the solder and polycrystalline copper solder joint during aging treatment acts as a barrier layer, preventing the solder from contacting the copper substrate and inhibiting the formation of Cu6Sn5. Cu5Zn8 is broken and decomposed after 300 h of aging treatment, and Cu6Sn5 grows rapidly after the barrier layer disappeared. The thickness of Cu6Sn5 is about 2.8 μm. The thickness of IMC of solder joint on single crystal copper is 0.7 μm more than that on polycrystalline copper. After aging treatment, the IMC formed at the interface between alloy solder and single crystal copper has better compactness and basically no pores, while there are obvious pores between IMC grains at the interface between alloy solder and polycrystalline copper, which can predict that the soldering quality of the interface between alloy solder and single crystal copper is better. This will provide application prospects for solder joint interface reliability research.

Robust effects of In, Fe, and Co additions on microstructures, thermal, and mechanical properties of hypoeutectic Sn–Zn-based lead-free solder alloy

This study examines the influence of separate and dual minor alloying additions of indium (In) and ferrous/cobalt (Fe/Co) on the microstructure, thermal, and mechanical properties of hypoeutectic Sn–7wt.% Zn lead-free solder alloy. The results showed that the addition of In resulted in significant refinement in the microstructure and formation of new intermetallic compounds (IMCs) such as In–Sn phases which capable of extensively removing the unfavorable needle-like α-Zn phase. However, the additions of Fe/Co resulted in the creation of new coarsening flower-shaped IMCs identified as Zn–Co, Fe–Sn, and Co–Sn–Zn distributed uniformly which may have a marked effect on the mechanical and thermal properties of Sn–Zn solder alloy. Thermal analysis by a differential scanning calorimeter indicates slightly reduction in the onset temperature, melting temperature, and undercooling of the Sn–7wt.% Zn by the addition of In, while the pasty range enlarged as compared to Fe/Co additions. The tensile tests indicate that the Sn-Zn-In solder alloy exhibited a superior balance of ultimate tensile strength, yield strength, Young’s modulus, and elongation of 51.5 MPa, 44.4 MPa, 22.2GPa, and 44.5%, respectively, which are better than both those of the Sn–Zn and Sn–Zn–Fe/Co solder alloys. This can be attributed to the synergistic strengthening mechanism of refinement in the microstructure and precipitation of fine secondary particles.

Study on the effects of Ag addition on the mechanical properties and oxidation resistance of Sn–Zn lead-free solder alloy by high-throughput method

Study on the effects of Ag addition on the mechanical properties and oxidation resistance of Sn–Zn lead-free solder alloy by high-throughput method

The Variations of Electron and Phonon Contributions to the Thermal Conductivity with Temperature in the Sn–Bi–In–Zn Alternative Lead-Free Solder Alloys

The goal of this paper is to measure the electrical and thermal conductivity variations with temperature in the unidirectional solidified quaternary Sn–Bi–In–Zn lead-free solder alloys for nine different compositions to determine the phonon thermal conductivity variation with temperature. The measurements of electrical and thermal conductivity variations with temperature were put into practice with the methods of four-point probe and longitudinal heat flow, respectively, and the electron and phonon thermal conductivity variations with temperature for the alloys were plotted. In addition, the temperature coefficient values for electrical and thermal conductivity were calculated.

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

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

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.

Influence of Zinc on the Surface Tension, Density and Molar Volume of (Ag-Sn)eut +Zn Liquid Alloys

The dilatometric and maximum bubble pressure methods were applied for the measurements of the density and surface tension of liquid (Ag-Sn)eut+Zn lead-free solders. The experiments were carried out in the temperature range from 515 to 1223 K for the alloys of the zinc concentration equaling 0.01, 0.02, 0.04, 0.05, 0.1 and 0.2 of the mole fraction. It was found that the temperature dependence of both the density and the surface tension could be thought as linear, so they were interpreted by straight line equations. The experimental data of the molar volume of the investigated alloys were described by the polynomial dependent on the composition and temperature.Calculations of the surface tension by Butler’s equation were conducted and confronted with the experimental data. Some significant deviations between the experimental and the calculated surface tension were observed. They reached almost 40 mNm-1. The observed changes of the density and surface tension caused by the zinc addition to the Ag-Sn eutectic were discussed with the consideration of the thermodynamic properties and the influence of a small quantity of impurities in a protective gas atmosphere.

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.

Effect of rapid solidification on microstructure, creep resistance and thermal properties of Sn-10 wt.% Sb- 3 wt.% X ( X= In, Ag, Bi and Zn) lead-free solder alloys

AbstractThe harmful effects of lead on the environment and human health, coupled with the threat of legislation, have prompted a serious search for lead-free solders for electronic packaging applications. The melt-spinning processes of ternary Sn-10 wt.%Sb-3 wt.%X (X=In, Ag, Bi and Zn) were analyzed using x-ray diffractometer (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Vickers hardness tester (HV). The investigation showed that, the addition of a small amount of the third element enhances the ductility of the Sn–10 wt.% Sb lead-free solder due to the formation of a fine, homogeneous ternary microstructure.. It is concluded that, the addition of 3.0 wt% Ag improves the grain size of the ternary microstructure. Moreover, SnSb intermetallic compound, precipitated finely from the solid tin solution near the grain boundaries with antimony. This fine precipitated intermetallic compound suppresses the coarsening of the ternary structure and thus enhances solder ductility. Structural and microstructural analysis revealed that the origin of change in mechanical behaviors was due to refined beta-Sn grains and formation of intermetallic compounds (IMCs) SnSb, InSn19, β-In3Sn and Ag3Sn. The results indicated that the melting point of Sn-10Sb-3 wt.% Ag and Sn-10 wt.%Sb- 3 wt.% Zn alloys reduced to 230 and 240 ˚C respectively. In particular, the zinc addition at 3 wt.% is the most effective in improving solder ductility. The good creep resistance of Sn-10 wt.% Sb-3 wt.% Zn lead-free solder correlated to a large β-Sn grain size and complete soluble of SnSb IMC particles in the β-Sn matrix.

The effect of undercooling on the microstructure and tensile properties of hypoeutectic Sn–6.5Zn–xCu Pb-free solders

Abstract Hypoeutectic Sn–6.5Zn alloy may be regarded as a better choice than eutectic Sn–9Zn lead-free solder in microelectronics industry. In this study, the properties of hypoeutectic Sn–6.5Zn lead-free solder were modified with minor additions of Cu. SEM investigations reveal that the plain Sn–6.5Zn solder exhibits large number of undesirable acicular structure of angular needle-like Zn particles at the solder matrix. The acicular-shape morphology of Zn was remarkably suppressed after Cu modification. Moreover, a new type of small flower-like γ-Cu5Zn8 intermetallic compound (IMC) was detected with 0.5 wt.% Cu added specimens. The flower-like morphology of γ-Cu5Zn8 IMC appears to cause a sharp increase in Young’s modulus, yield strength (YS) and ultimate tensile strength (UTS) of Cu modified solder. However, this effectiveness is reduced when 1.5 wt.% Cu addition starts to enhance the growth of coarse dendrite morphology of γ-Cu5Zn8 phase with enlarged β-Sn matrix. In addition, a 1.5 wt.% Cu addition was found to induce undesirable effects on the degree of undercooling, melting temperature and pasty range. Constitutive Garofalo model was assembled based on the experimental data of Sn–6.5Zn lead-free solders.

Present status of Sn–Zn lead-free solders bearing alloying elements

Recently, the Sn–Zn family of alloys, which possesses many attractive advantages such as relatively low melting point, cheap cost and the environmentally friendly component of Zn, has been widely used in electronic industry as one of the most potential replacements for the traditional Sn–Pb solders. However, there’re still some arguments on its shortcomings about the poor wettability and the weak oxidation resistance, which definitely limits its further application in lead-free electronic manufacturing. In order to overcome these disadvantages and further enhance the properties of Sn–Zn lead-free solders, alloying elements such as RE, Bi, Ag, Al, Ga, Cu, etc. were selected by lots of researchers as alloys addition into the solders. This paper summarizes the effects of alloying elements on the wettability, oxidation resistance, mechanical properties and microstructures of Sn–Zn lead-free solder alloys.

Corrosion measurement of Sn–Zn lead-free solders in 6 M KOH solution

The corrosion measurements of Sn–Zn alloys with varying Zn contents from 0wt.% to 12wt.% were investigated in a 6M KOH solution. The corrosion parameters of this series of materials, which include open circuit potential, galvanic corrosion current, corrosion potential, and corrosion current, were studied. The Sn–Zn alloys initially revealed an activity similar with that of pure Zn in this 6M KOH solution. The alloy activity became more inert when the corrosion analysis was prolonged. In addition, phase and morphological analyses results confirmed the formation of mixed corrosion products on the surface after polarisation.

Interfacial Reactions of Sn, Sn-3.0Ag-0.5Cu, and Sn-9Zn Lead-Free Solders with Fe-42Ni Substrates

Interfacial reactions between Sn, Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC), and Sn-9 wt.%Zn (SZ) lead-free solders and Fe-42 wt.%Ni (alloy 42) substrates at 240°C, 255°C, and 270°C were investigated in this study. FeSn2, (Fe,Ni, Cu)Sn2, and (Ni,Fe)5Zn21 phases were formed, respectively, at the interface in the Sn/alloy 42, SAC/alloy 42, and SZ/alloy 42 couples. As the reaction time and temperature were increased, the layered intermetallic compound (IMC) assumed two distinct structures, i.e., a thicker layer and a pillar-shaped IMC, in all couples. The IMC thickness of these couples increased with the increase of reaction time and temperature. The IMC thickness was also proportional to the square root of the reaction time. The interfacial reaction mechanism of these couples was diffusion controlled.

Interfacial reactions between electroplated Ni–Zn alloy films and lead-free solders

Because of the miniaturization trend in electronic devices in recent years, the issue of reliability of solder joints in these miniaturized devices becomes very critical. Studies have shown that a thin layer of Ni is effective in reducing the interfacial IMC growth between Cu and Sn-based solder. This is because the reaction kinetics of Ni–Sn compounds are much slower than that of Cu–Sn IMCs. In this study, zinc is incorporated into the nickel barrier film in the form of Ni–Zn alloy by electrodeposition. The effects of the presence of Zn on the interfacial reactions between nickel barrier film and Sn–3.8Ag–0.7Cu (SAC) and Sn–3.5Ag (SA) solders are investigated. Ni–Zn alloy films with 1.73 wt% Zn were prepared from ammoniacal diphosphate baths. Elemental composition of the alloy film was determined by energy dispersive X-ray spectroscopy while X-ray diffraction method was used to determine the phases present in the alloy film. Solders’ spreading rate was characterized with the use of optical microscope. Reflows were done for 1 and 12 cycles to investigate the effect of multiple reflows on the IMC growth and morphology. Results have shown that the IMC formed at the interface of SA/Ni and SAC/Ni was Ni3Sn4 and (Cu,Ni)5Sn6, respectively. (Ni,Cu)3Sn4 IMC was formed at the interface of SA/Ni–Zn alloy film. No spalling was detected at the SA/Ni–Zn solder joint. On the other hand, it has been observed that (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 layer with continuous non-uniform morphology were formed on the SAC/Ni–Zn alloy film after 1× reflow. As the number of reflow increased, (Cu,Ni)6Sn5 layer spalled from the interface leaving only (Ni,Cu)3Sn4 IMC at the interfacial region.

Microstructure and mechanical properties of Sn–Bi, Sn–Ag and Sn–Zn lead-free solder alloys

The aim of this paper is to develop a comparative evaluation of mechanical properties of as-cast Sn–Bi, Sn–Ag and Sn–Zn alloys as a function of the resulting microstructural arrays with a view to application as solder materials. The resulting microstructures, ultimate and yield tensile strengths and elongations of Sn–40wt.% Bi, Sn–3.5wt.% Ag and Sn–9wt.% Zn alloys were examined and compared with the corresponding results of the traditional Sn–40wt.% Pb solder alloy. Tensile tests were carried out using specimens selected from specific positions along the length of the directionally solidified castings and Hall–Petch type correlations have been proposed relating the resulting tensile properties of each alloy to a parametric scale of the microstructure. It was found that all Pb-free alloys examined comply with a compromise between compatible mechanical strength and environmental protection. The Sn–Bi alloy has the highest ultimate tensile strength of all alloys examined, while both Sn–Ag and Sn–Zn alloys are lighter and exhibited higher ductility than the Sn–Pb and Sn–Bi alloys.

Determination of thermal conductivities of Sn–Zn lead-free solder alloys with radial heat flow and Bridgman-type apparatus

The variations of thermal conductivities of solid phases versus temperature for pure Sn, pure Zn and Sn–9 wt.% Zn, Sn–14 wt.% Zn, Sn–50 wt.% Zn, Sn–80 wt.% Zn binary alloys were measured with a radial heat flow apparatus. The thermal conductivity ratios of liquid phase to solid phase for the pure Sn, pure Zn and eutectic Sn–9 wt.% Zn alloy at their melting temperature are found with a Bridgman-type directional solidification apparatus. Thus, the thermal conductivities of liquid phases for pure Sn, pure Zn and eutectic Sn–9 wt.% Zn binary alloy at their melting temperature were evaluated by using the values of solid phase thermal conductivities and the thermal conductivity ratios of liquid phase to solid phase.

Interfacial reactions of Pb-free solders with Au/Pd/Ni/brass multilayer substrates

The interfacial reactions of Sn, Sn–3.0wt% Ag–0.5wt% Cu (SAC), Sn–0.7wt% Cu (SC), Sn–58wt% Bi (SB) and Sn–9wt% Zn (SZ) lead-free solders with an Au/Pd/Ni/brass multilayer substrate were systematically investigated in this study. The results revealed that (Cu, Ni)6Sn5 and CuZn phases were formed at the interface in the Sn, SAC, and SC solders reacting with Au/Pd/Ni/brass systems. In the SB/Au/Pd/Ni/brass system, (Ni, Cu)3Sn4, (Cu, Ni)6Sn5 and CuZn phases were formed at the interface. The CuZn5, Pd2Zn9, Ni5Zn21 and Cu5Zn8 phases were formed in the SZ/Au/Pd/Ni/brass system.

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.

Mechanical properties of Sn–Zn lead-free solder alloys based on the microstructure array

The aim of this study is to develop a comparative experimental study interrelating mechanical properties, solidification thermal parameters and microstructure characteristics of a hypoeutectic Sn–4 wt.% Zn, a hypereutectic Sn–12 wt.% Zn and a eutectic Sn–9 wt.% Zn solder alloys. A water-cooled vertical upward unidirectional solidification system was used to obtain the samples. It was found that a more homogeneous distribution of the eutectic mixture, which occurs for smaller dendritic spacings in hypoeutectic and hypereutectic alloys, increases the ultimate tensile strength. The resulting microstructure of the eutectic Sn-9 wt.% Zn alloy has induced higher mechanical strength than those of the Sn–4 wt.% Zn and Sn–12 wt.% Zn alloys. It was found that the eutectic alloy experiences a microstructural transition from globular-to-needle-like Zn-rich morphologies which depend on the solidification growth rate. It is also shown that a globular-like Zn-rich morphology provides higher ultimate tensile strength than a needle-like Zn-rich eutectic morphology.