Properties Of Lead-free Solder Alloys Research Articles

A Short Review on the Influence of Antimony Addition to the Microstructure and Thermal Properties of Lead-Free Solder Alloy

A Short Review on the Influence of Antimony Addition to the Microstructure and Thermal Properties of Lead-Free Solder Alloy

Electrochemical behaviour of lead-free Sn-In-Al solders alloys in 3.5 wt.% NaCl solution

The corrosion properties of lead-free solder alloy can not be ignored in the field of the electronic industry. However, there is no literature on the effect of aluminium on Sn-In binary solder alloys. This study looked at the corrosion of a lead-free solder alloy in a 3.5 wt.% NaCl simulated seawater environment. Three isopleths were created with varying aluminium content in the Sn-In-Al system while maintaining Sn and In radio constant (1:1). The vacuum sealing process was used to create the samples. The corrosion resistance of this lead-free solder ware was investigated at room temperature in a 3.5 wt.% NaCl solution. Corrosion resistance improves with Al content, according to the potentiodynamic polarization test. By lowering the current density (Icorr), the inclusion of aluminium refines the microstructure. It enhances the corrosion resistance of Sn-In-Al solder alloys, resulting in high resistance of the passive layer produced by lowering the current density (Icorr). Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDS) was used to analyze of surface morphology of the non-corroded and corroded Sn-In-Al solder alloys. Intermetallic compound (IMC) of non-corroded and corrosion products on the surface corroded solder alloys were studied using X-ray diffraction (XRD). According to XRD analysis, the composition of corrosion products altered as the aluminium content changed, forming phases such as Sn3O(OH)2Cl2, oxides, and chlorides of Sn.

Effective acquisition of elastoplastic and creep parameters of lead-free solder alloy from high-temperature micro-indentation eliminating the size effect

Effective acquisition of the related mechanical properties of lead-free solder alloys through micro-indentation tests is of great significance in the research on electronic interconnection design and reliability for the multi-functionalization and high integration of electronic products. The temperature-dependent elastoplastic and creep parameters of Sn–3.0Ag–0.5Cu (SAC) solder are systematically investigated by micro-indentation with plural indenters and the “rapid loading-holding-rapid unloading” test mode. Based on the depth dependence of indentation hardness from mechanism-based strain gradient plasticity and the stress independence of creep compliance for linear viscous assumption, the complete indentation load-depth curves eliminating the indentation size effect of SAC solder under different temperature and two pyramidal indenters with different equivalent semi-cone angles are reconstructed. Combining with the temperature-dependent elastic modulus measurements from cylindrical indentation, corrected load-depth curves for pyramidal indentation, and the concept of representative stress and representative plastic strain, the elastoplastic parameters eliminating the indentation size effect under different temperature are uniquely determined through numerical simulation and inversion analysis, as well as the corresponding creep parameters. The temperature dependence of elastoplastic and creep parameters of SAC solder is analyzed, and related deformation mechanism is discussed. Results of forward and inverse analyses indicate the effectiveness of proposed characterization method.

Solid-State Diffusion of Bi in Sn: Effects of Anisotropy, Temperature, and High Diffusivity Pathways

It has been determined that bismuth (Bi) stabilizes the mechanical properties of lead-free solder alloys over time and improves alloy reliability. This is caused by homogenization of the microstructure, driven by solid-state diffusion of Bi in the β-Sn matrix. It was previously determined that β-Sn grain orientation has little effect on the diffusivity at 125°C, and even low angle grain boundaries may convolute the relationship between orientation and diffusivity. In this work, several additional temperatures were considered, and similar effects of orientation on the diffusivity of Bi in Sn were observed. The simulation technique used to estimate diffusivity was applied to the previously discussed polycrystalline diffusion data, and temperature was found to strongly affect the ratio between lattice and polycrystalline diffusivity, due to the active nature of Sn-based systems. Finally, Harrison Type B kinetics were considered to study the effects of grain boundaries on the diffusivity of Bi in polycrystalline Sn.

Development of SnAgCu solders with Bi and In additions and microstructural characterization of joint interface

Properties of lead-free solder alloys and microstructural characterization of solder joints made from Sn1.0Ag0.5Cu1.0Bi and Sn0.9Ag0.5Cu0.9Bi1.0In (composition given in weight %) with Cu plate were widely studied in this work. The influence of Bi and In additions in these solder alloys was studied as well. The melting temperatures, diffluence and wetting properties, microstructures and costs were observed and evaluated. Thermo-Calc software was used for phase composition prediction. Altogether, 1500 cycles were carried out for the thermal cycling test in the range from +150 to −40 °C where the solder joints’ reliability was assessed due to practice requirement. Optical microscopy, scanning electron microscopy (EDX microanalysis) and shear strength test were used for the evolution of microstructure, structural integrity and mechanical strength of thermal-cycled solder joints. The reliability test results after temperature cycling indicate two lead-free solder alloys as the most convenient for soldering in the microelectronics industry.

An improved unified creep-plasticity model for SnAgCu solder under a wide range of strain rates

Based on the unified creep and plasticity theory, an improved constitutive model is proposed in this study to describe the uniaxial mechanical behaviour of Sn3.0Ag0.5Cu (SAC305) solder alloy subjected to a wide range of strain rates. In the usual service condition of electronic devices, the strain rates of solder material are far less than 1.0 s−1 at which the creep deformation is dominant, especially at higher working temperatures. However, the strain rate could range from 1.0 to 300 s−1 under drop impact in electronic packaging structures, which is drawing more attention due to lack of experimental data, especially on dynamic mechanical properties of lead-free solder alloys. In extreme impact conditions, the solder material may experience even higher strain rates. As different mechanisms dominate the respective regime of strain rates, the developed constitutive model is calibrated to be applicable to most of the strain rate regimes by properly considering the coupled effect of creep and plasticity. Moreover, the parameters in the proposed model are defined with clear physical meanings and reasonably determined by regression to the published experimental studies. Lastly, the developed model is compared with other constitutive models from the literature, including the power-law equation for creep deformation at low strain rates and the Johnson–Cook model for plastic deformation at high strain rates. It is concluded that the proposed model is more generalized and capable of predicting uniaxial mechanical behaviour of SAC305 solder at low, medium and high strain rates with reasonable accuracy.

High strain rate constitutive behavior of SAC105 and SAC305 leadfree solder during operation at high temperature

Industry migration to leadfree solders has resulted in a proliferation of a wide variety of solder alloy compositions. The most popular amongst these are the Sn–Ag–Cu family of alloys like SAC105 and SAC305. Electronics subjected to shock and vibration may experience strain rates of 1–100/s. Electronic product may often be exposed to high temperature during storage, operation and handling in addition to high strain rate transient dynamic loads during drop-impact, shock and vibration. Properties of leadfree solder alloys at high strain rates at low and high temperatures experienced by the solder joint during typical mechanical shock events are scarce. Previous studies have showed the effect of high strain rates and thermal aging on the mechanical properties of leadfree alloys including elastic modulus and the ultimate tensile strength. The ANAND viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components. In this study, SAC105 and SAC305 leadfree alloys have been tested at strain rates of 10, 35, 50 and 75/s at various operating temperatures of 50°C, 75°C, 100°C and 125°C. Full-field strain in the specimen have been measured using high speed imaging at frame rates up to 75,000fps in combination with digital image correlation. The cross-head velocity has been measured prior-to, during, and after deformation to ensure the constancy of cross-head velocity. Stress–strain curves have been plotted over a wide range of strain rates and temperatures. Experimental data for the pristine specimen has been fit to the ANAND's viscoplastic model.

Stress–Strain Behavior of SAC305 at High Strain Rates

Electronic products are subjected to high G-levels during mechanical shock and vibration. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. The second-level interconnects may be experience high strain rates and accrue damage during repetitive exposure to mechanical shock. Industry migration to lead-free solders has resulted in proliferation of a wide variety of solder alloy compositions. One of the popular tin-silver-copper alloys is Sn3Ag0.5Cu. The high strain rate properties of lead-free solder alloys are scarce. Typical material tests systems are not well suited for measurement of high strain rates typical of mechanical shock. Previously, high strain rates techniques such as the split Hopkinson pressure bar (SHPB) can be used for strain rates of 1000 s−1. However, measurement of materials at strain rates of 1–100 s−1 which are typical of mechanical shock is difficult to address. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1–100 s−1. High-speed cameras operating at 300,000 fps have been used in conjunction with digital image correlation (DIC) for the measurement of full-field strain during the test. Constancy of crosshead velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC305 solder. Constitutive model has been fit to the material data. Samples have been tested at various time under thermal aging at 25 °C and 125 °C. The constitutive model has been embedded into an explicit finite element framework for the purpose of life-prediction of lead-free interconnects. Test assemblies has been fabricated and tested under Joint Electron Device Engineering Council (JEDEC) JESD22-B111 specified condition for mechanical shock. Model predictions have been correlated with experimental data.

20306 温度サイクル負荷を受ける鉛フリーはんだ接合部の力学的特性

When we estimate the fatigue life, we have to conduct FE analysis using a constitutive model which can exhibit the mechanical properties of lead-free solder alloy. As such mechanical properties of lead-free solder joints under cyclic thermal loading, the stress strain curves, stress strain hysteresis loops and stress relaxation curves with these temperature dependencies and these rate dependencies are regarded. In addition, these solder joints under cyclic temperature load are stressed mainly in shear and the solder alloys have scale effect. Thus in this study, for FE analysis of solder joints under cyclic temperature load, we carried out tensile tests, tension-compressive tests and the stress-relaxation tests of lead-free solder alloy using the small sized shear specimen.

Integration of the NIST and SURDAT Databases on Physical Properties of Lead-Free Solder Alloys

The electronic SURDAT database published in 2007 (available freely from the website www.imim.pl/english ) is being integrated with the NIST database (available freely from www.boulder.nist.gov/div853/lead_free/solders.html ) to provide a single source for data on lead-free (Pb-free) soldering alloys. The NIST database was developed to support circuit board designers, and so it is focused primarily on mechanical properties. In contrast, the SURDAT database is focused primarily on thermophysical properties. Together, they will form a much more complete source for the properties of Pb-free solder alloys.

Modeling Material Properties of Lead-Free Solder Alloys

A full set of physical and thermophysical properties for lead-free solder (LFS) alloys have been calculated, including liquidus/solidus temperatures, fraction solid, density, coefficient of thermal expansion, thermal conductivity, Young’s modulus, viscosity, and liquid surface tension, all as a function of composition and temperature (extending into the liquid state). The results have been extensively validated against data available in the literature. A detailed comparison of the properties of two LFS alloys Sn-20In-2.8Ag and Sn-5.5Zn-4.5In-3.5Bi with Sn-37Pb has been made to show the utility and need for calculations that cover a wide range of properties, including the need to consider the effect of nonequilibrium cooling. The modeling of many of these properties follows well-established procedures previously used in JMatPro software for a range of structural alloys. This paper describes an additional procedure for the calculation of the liquid surface tension for multicomponent systems, based on the Butler equation. Future software developments are reviewed, including the addition of mechanical properties, but the present calculations can already make a useful contribution to the selection of appropriate new LFS alloys.

Investigation of microstructures and tensile properties of a Sn-Cu lead-free solder alloy

In recent years, the pollution of environment from lead (Pb) and Pb-containing compounds in microelectronic devices attracts more and more attentions in academia and industry, the lead-free solder alloys begin to replace the lead-based solders in packaging process of some devices and components. In this work, microstructures and mechanical properties of the lead-free solder alloy Sn99.3Cu0.7(Ni) are investigated. This paper will compare the mechanical properties of the lead-based with lead-free solder alloys (Sn99.3Cu0.7(Ni) and 63Sn37Pb). The tensile tests of lead-based and lead-free solder alloys (Sn99.3Cu0.7(Ni) and Sn63Pb37) were conducted at room and elevated temperature at constant strain rate; the relevant tensile properties of Sn99.3Cu0.7(Ni) and Sn63Pb37 were obtained. Specifically, the tensile strength of this lead-free solder- Sn99.3Cu0.7(Ni) in 25∘C, 50∘C, 75∘C, 100∘C, 125∘C was investigated; and it was found that tensile strength of the lead-free solder decreased with the increasing test temperature at constant strain rate, showing strong temperature dependence. The lead-free solder alloy Sn99.3Cu0.7(Ni) was found to have favorable mechanical properties and it may be able to replace the lead-based solder alloy such as Sn63Pb37 in the packaging processes in microelectronic industry.

Properties of lead-free solder alloys with rare earth element additions

Due to the inherent toxicity of lead (Pb), environmental regulations around the world have been targeted to eliminate the usage of Pb-bearing solders in electronic assemblies. This has prompted the development of “Pb-free” solders, and has enhanced the research activities in this field. In order to become a successful solder material, Pb-free alloys need to be reliable over long term use. Although many of these alloys possess higher strength than the traditional Sn–Pb ones, there still exist reliability problems such as electromigration and creep. Also, the solderability of many Pb-free alloys is inferior to that of Sn–Pb and any improvement or replacement will be welcomed by industry. In order to develop new Pb-free solders with better properties, trace amounts of rare earth (RE) elements were selected by some researchers as alloying additions into Sn-based solders. These solder alloys are mainly Sn–Ag, Sn–Cu, Sn–Zn and Sn–Ag–Cu. In general, the resulting RE-doped solders are found to have better performances than their original ones. The improvements include better wettability, creep strength and tensile strength. In particular, the increase in creep resistance in some RE-doped alloys gives creep rupture time increases by over four times for Sn–Ag and seven times for Sn–Cu and Sn–Ag–Cu. Like other Sn-based alloys, their creep rates are controlled by dislocation pipe diffusion in the Sn matrix. Also, it was found that the creep rate of these Sn-based alloys can be represented by a single empirical equation. With the addition of RE elements, solders for bonding on difficult substrates such as on semiconductors, diamond, and optical materials have also been developed. This report summarizes the effect of RE elements on the microstructure, mechanical properties, wetting behavior of certain Pb-free solder alloys. As an illustration of the advantage of RE doping, interfacial studies were carried out for electronic interconnections with RE-doped Pb-free alloys. It was found that the intermetallic compound (IMC) layer thickness and the amount of interfacial reaction were reduced in a Ball Grid Array (BGA) package. These results indicate that RE elements would play an important role in providing better electronic interconnections.