Mechanical Properties Of Solder Research Articles

Microstructure and mechanical properties of Sn-xGa alloys and solder joints

Though Ga is a promising addition used in third-generation lead-free solders for harsh-environment applications, its influences on βSn structure and mechanical properties of solder alloys/joints are still unknown. This study demonstrated that Ga additions in Sn-XGa (X = 0.5, 1.0, 2.0 in wt%) can moderately refine βSn grains but render the alloys more susceptible to recrystallization during cross-section and polishing. Sn-1.0Ga shows substantially elevated yield/tensile strengths (45.1 MPa/64.9 MPa) compared with pure Sn, attributed to the strong solid-solution strengthening effect of Ga, and it also possesses good tensile ductility of >25%. Compared with pure Sn and Sn-3.0Ag-0.5Cu (SAC305) solder joints on Cu, Sn-XGa/Cu solder joints show significantly reduced dissolution of Cu substrate that benefits in suppressing the formation of primary Cu6Sn5. Among Sn-XGa/Cu, Sn-2.0Ga/Cu joint exhibits high shear strength (69.4 MPa) comparable to that of SAC305/Cu joint (70.5 MPa), owing to the Ga solid-solution strengthening and the extra second-phase strengthening from Cu9Ga4.

A dual-phase crystal plasticity finite-element method for modeling the uniaxial deformation behaviors of thermally aged SAC305 solder

Because typical solder joints undergo thermal aging during use, models simulating the behaviors of solder under mechanical stress must accurately reflect the changes in properties caused by thermal aging effects. The uniaxial deformation of SAC305 (96.5Sn–3.0Ag–0.5Cu wt.%) solder under different aging conditions indicates that the mechanical properties of solder are weakened with aging. In this study, the nanoindentation method was used to evaluate the effect of aging on the mechanical properties of the β-Sn dendritic regions and eutectic regions of SAC305. Based on this evaluation, a dual-phase (DP) representative volume element (RVE) crystal plasticity finite-element method (CPFEM) model was developed to simulate the thermal aging effects of SAC305 solder. In situ tensile tests performed with scanning electron microscopy (SEM) showed that the tensile deformation was concentrated in the β-Sn dendritic regions of the solder. The DP CPFEM model was established based on the microstructures shown by electron backscatter diffraction (EBSD) analysis performed during the in situ tensile tests. This model was used to verify the accuracy of the DP CPFEM in simulating the deformation localization by comparison with the strain field distribution observed via SEM–digital image correlation (DIC) technology. The developed DP CPFEM model allows the prediction of the potential failure locations of a microscale solder joint.

Effects of alloying element on mechanical properties of Sn-Bi solder alloys: a review

PurposeThis paper aims to review recent reports on mechanical properties of Sn-Bi and Sn-Bi-X solders (where X is an additional alloying element), in terms of the tensile properties, hardness and shear strength. Then, the effects of alloying in Sn-Bi solder are compared in terms of the discussed mechanical properties. The fracture morphologies of tensile shear tested solders are also reviewed to correlate the microstructural changes with mechanical properties of Sn-Bi-X solder alloys.Design/methodology/approachA brief introduction on Sn-Bi solder and reasons to enhance the mechanical properties of Sn-Bi solder. The latest reports on Sn-Bi and Sn-Bi-X solders are combined in the form of tables and figures for each section. The presented data are discussed by comparing the testing method, technical setup, specimen dimension and alloying element weight percentage, which affect the mechanical properties of Sn-Bi solder.FindingsThe addition of alloying elements could enhance the tensile properties, hardness and/or shear strength of Sn-Bi solder for low-temperature solder application. Different weight percentage alloying elements affect differently on Sn-Bi solder mechanical properties.Originality/valueThis paper provides a compilation of latest report on tensile properties, hardness, shear strength and deformation of Sn-Bi and Sn-Bi-X solders and the latest trends and in-depth understanding of the effect of alloying elements in Sn-Bi solder mechanical properties.

Effect of Multiple Reflows on the Interfacial Reactions and Mechanical Properties of an Sn-0.5Cu-Al(Si) Solder and a Cu Substrate.

In this study, the interfacial reactions and mechanical properties of solder joints after multiple reflows were observed to evaluate the applicability of the developed materials for high-temperature soldering for automotive electronic components. The microstructural changes and mechanical properties of Sn-Cu solders regarding Al(Si) addition and the number of reflows were investigated to determine their reliability under high heat and strong vibrations. Using differential scanning calorimetry, the melting points were measured to be approximately 227, 230, and 231 °C for the SC07 solder, SC-0.01Al(Si), and SC-0.03Al(Si), respectively. The cross-sectional analysis results showed that the total intermetallic compounds (IMCs) of the SC-0.03Al(Si) solder grew the least after the as-reflow, as well as after 10 reflows. Electron probe microanalysis and transmission electron microscopy revealed that the Al-Cu and Cu-Al-Sn IMCs were present inside the solders, and their amounts increased with increasing Al(Si) content. In addition, the Cu6Sn5 IMCs inside the solder became more finely distributed with increasing Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder exhibited the highest shear strength at the beginning and after 10 reflows, and ductile fracturing was observed in all three solders. This study will facilitate the future application of lead-free solders, such as an Sn-Cu-Al(Si) solder, in automotive electrical components.

Damage based PoF model of solder joints under temperature cycling and electric coupling condition

To predict the life of solder joints under temperature cycling and electric coupling condition, this paper proposes a Physics of Failure (PoF) model based on the continuum damage mechanics (CDM). Firstly, considering the effect of current on solder's mechanical properties, the current-affected constitutive models of plastic fatigue and creep are constructed. Then, based on the mechanism of energy dissipation, a unified creep-plasticity damage evolution law is deduced, and the nonlinear accumulation damage model is developed. Choosing electric resistance as the indirect damage variable measure, the thermal-electric coupling PoF model is finally established by substituting the current-affected constitutive models into the damage evolution model. A thermal-electric coupling test is carried out to verify the accuracy of PoF model. The experimental results confirm that the proposed PoF model can effectively predict the life of solder joints under temperature cycling and electric coupling condition.

Structural and mechanical analyses of soldering materials containing Pb, Sn, Ag, Cu, Bi and Zn

In present work the microstructural and mechanical properties (such as shear stress, shear strain, deformation and creep behaviour) of solder joints of four different solders at temperatures of 100 °C and 150 °C was studied. The soldering materials included in this study were: Type A—Sn-36.00Pb-2.00Ag, Type B—Sn-3.80Ag-0.70Cu, Type C—Sn-3.30Ag-3.82Bi and Type D—Sn-8.00Zn-3.00Bi. Microstructure and mechanical properties of solders were studied by using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Universal Testing Machine. It has been observed that the mechanical properties of Type B are not significantly changed with increase in temperature as compared to other materials.

Microstructures and Mechanical Properties of Sn-58 wt.% Bi Solder with Ag-Decorated Multiwalled Carbon Nanotubes Under 85°C/85% Relative Humidity Environmental Conditions

The mechanical properties of Sn-58 wt.% Bi solder with different amounts (0 wt.%, 0.05 wt.%, 0.1 wt.%, and 0.2 wt.%) of Ag-decorated multiwalled carbon nanotube (MWCNT) nanoparticles under 85°C/85% relative humidity environmental conditions for 0 h to 1000 h was investigated. Sn-58 wt.% Bi solder is a lead-free option for use in solder joints due to its low melting temperature and good creep resistance; however, it is brittle and has reliability issues. Ag-decorated MWCNT nanoparticles were used to improve these weaknesses of Sn-58 wt.% Bi solder. A ball shear test was performed using a bond tester to investigate the solder's mechanical properties. The microstructures of the solder joints and fracture mode were analyzed using a field-emission scanning electron microscope. The results demonstrated that the addition of Ag-decorated MWCNT nanoparticles to Sn-58 wt.% Bi increased the shear strength and fracture energy by approximately 15% and 14%, respectively, compared with Sn-58 wt.% Bi alone. After a high-temperature, high-humidity test for 1000 h, the shear strength and fracture energy of Sn-58 wt.% Bi with 0.1 wt.% Ag-decorated MWCNT nanoparticles were 13% and 21% greater than for Sn-58 wt.% Bi alone.

Effect mechanism of Ag and Bi elements on the corrosion process in Sn–9Zn–1Ag and Sn–9Zn–3Bi solders

Sn–9Zn lead–free solder is widely used in low melting temperature welding field due to its low melting point (198.5 °C), good connection reliability, and low cost. However, its poor wettability and corrosion resistance weaken its performance. According to previous studies, addition of 1% Ag and 3% Bi to Sn–9Zn alloy, respectively, can optimize the wettability and mechanical properties of solder. Nonetheless, the effect of added elements on corrosion process has not been determined. In this study, the effect mechanism of Ag and Bi elements on the corrosion process in Sn–9Zn–1Ag and Sn–9Zn–3Bi solders was analyzed. The changes of the surface state of each solder in the corrosion process were detected by electrochemical polarization experiment. The microstructural compositions of solders in different corrosion stages were compared through the immersion test. The results indicated that compared to Sn–9Zn solder, Sn–9Zn–1Ag solder exhibited the existence of a finer Zn-rich phase, which improved the pitting corrosion resistance of solder by blocking the entry of corrosive solution. In passivation film forming process, Ag–Zn compounds were formed on the surface of Sn–9Zn–1Ag solder, which reduced the content of Zn-rich phase, leading to the decrease of the overall corrosion rate. After the formation of passivation film, Ag compounds were precipitated on the surface of passivation film of solder, which prevented further destruction of the passivation film. However, Sn–9Zn–3Bi solder produced a large number of loose structural corrosion products on the surface of the corroded sample, thus the substrate could not be effectively protected. Furthermore, Sn–9Zn–3Bi solder showed a larger Zn-rich phase, thus it was easier for the corrosive solution to enter the sample, resulting in severe corrosion in the interior of sample. In this study, the effect mechanism of Ag and Bi addition on the corrosion process of Sn–9Zn–1Ag and Sn–9Zn–3Bi solders was revealed, which provides a theoretical basis for the study on improving the corrosion resistance of Sn–9Zn solder.

A continuum damage mechanics-based unified creep and plasticity model for solder materials

A nonlinear continuum damage mechanics model is developed for both lead-rich and lead-free solder materials. A unified creep–plasticity constitutive relationship is adopted to simulate the inelastic behaviors; both isotropic and nonlinear kinematic hardening are considered. A traditional continuum damage evolution law is a function of actual damage parameter and effective accumulated plastic strain. In the current work, absolute temperature is introduced into the damage model to reflect the effect of temperature on the accumulated damage mechanism. The mechanical properties of solders, incorporating damage initiation and accumulation, were analyzed based on the model developed. Fatigue life under fully reversed cycling is investigated by monitoring the change in peak stresses, which decreases continuously, owing to damage accumulation. The numerical results were compared with experimental data. It was shown that the developed model can predict the whole damage accumulation process of different solder materials with reasonable accuracy.

A multi-disciplinary study of vibration based reliability of lead-free electronic interconnects

Vibration loading can have a significant impact on the reliability of electronic components. Due to the cyclic strain and stress in the materials making up the component these can cause damage and hence wear out failures. The recent move from lead to lead-free soldering by the electronics industry has necessitated the generation of material properties data that will allow accurate prediction of the lead-free solder’s performance under vibration conditions. To assess the reliability of lead-free solders under vibration loading, test equipment has been designed for small solder joints. Such test equipment must be able to extract solder mechanical properties and physics of failure fatigue lifetime parameters/models for numerical model and prediction of lifetime of real electronic components. This paper focuses on the design, analysis and development of this type of test facility.

Formation of Primary Intermetallic Compounds in Sn-Ag-Cu Alloys

Sn-Ag-Cu alloys are considered one of the most favorable lead-free solder systems. In slowly-cooled eutectic Sn-Ag-Cu alloys, sometimes large primary Ag3Sn or Cu6Sn5 intermetallic compounds (IMCs) form. These IMCs may affect the mechanical properties of solders. However, explanations for the formation of these IMCs are still not clear. This study deals with interrupted tests in order to clarify the nucleation of IMCs in the liquid phase. In this study, Sn-4.41Ag-0.63Cu and Sn-3.30Ag-1.47Cu alloys were prepared. According to the thermodynamic calculation, Pandat, the equilibrium solidification paths are described as follows: Sn-4.41Ag-0.63Cu :L → primary Ag3Sn → binary eutectic (Ag3Sn +Sn) → ternary eutectic; Sn-3.30Ag-1.47Cu :L → primary Cu6Sn5 → binary eutectic (Cu6Sn5 + Sn)→ ternary eutectic. The actual solidification process was different from the estimation from the equilibrium phase diagram. In the case of Sn-4.41Ag-0.63Cu, only Ag3Sn grew as a primary phase in the liquid, while in the case of Sn-3.30Ag-1.47Cu, not only primary Cu6Sn5 but also pseudo-primary Ag3Sn grew in the liquid. Ag3Sn may nucleate easily in the liquid phase, but Cu6Sn5 would not nucleate in the liquid.

Experimental investigations for reducing wall thickness in solder (20-80) lead alloy rapid casting solution of three dimensional printing

In this work, three dimensional printing (3DP) technology has been used as rapid shell casting to make the shell moulds. An effort has been made through experiments, to study the feasibility of decreasing the shell wall thickness from the recommended one (12 mm), in order to reduce the cost and time of production, as well as to evaluate the dimensional accuracy, mechanical properties of solder (20-80) lead alloys castings obtained, for assembly purpose. The study suggested that the shell thickness, having value less than the recommended one, is more suitable from the dimensional accuracy and an economic point of view. Further sound casting results are supported by microstructure analysis. The result indicates that at 1 mm shell thickness, slight variation in hardness of the casting is observed, but production cost and production time has been reduced by 45.75% and 43% respectively from recommended 12 mm.

A review of mechanical properties of lead-free solders for electronic packaging

The characterization of lead-free solders, especially after isothermal aging, is very important in order to accurately predict the reliability of solder joints. However, due to lack of experimental testing standards and the high homologous temperature of solder alloys (Th > 0.5Tm even at room temperature), there are very large discrepancies in both the tensile and creep properties provided in current databases for both lead-free and Sn–Pb solder alloys. Some recent researches show that the room temperature aging has significant effects on mechanical properties of solders. This paper is intended to review all available data in the field and give rise to the possible factors including room temperature effects which causes the large discrepancies of data. This review of the research literatures has documented the dramatic changes that occur in the constitutive and failure behavior of solder materials and solder joint interfaces during isothermal aging. However, these effects have been largely ignored in most previous studies involving solder material characterization or finite element predictions of solder joint reliability during thermal cycling. It is widely acknowledged that the large discrepancies in measured solder mechanical properties from one study to another arise due to differences in the microstructures of the tested samples. This problem is exacerbated by the aging issue, as it is clear that the microstructure and material behavior of the samples used in even a single investigation are moving targets that change rapidly even at room temperature. Furthermore, the effects of aging on solder behavior must be better understood so that more accurate viscoplastic constitutive equations can be developed for SnPb and SAC solders. Without such well-defined relationship, it is doubtful that finite element reliability predictions can ever reach their full potential.

Compression stress–strain and creep properties of the 52In–48Sn and 97In–3Ag low-temperature Pb-free solders

Lead (Pb)-free, low melting temperature solders are required for step-soldering processes used to assemble micro-electrical mechanical system (MEMS) and optoelectronic (OE) devices. Stress–strain and creep studies, which provide solder mechanical properties for unified creep-plasticity (UCP) predictive models, were performed on the Pb-free 97In–3Ag (wt.%) and 58In–42Sn solders and counterpart Pb-bearing 80In–15Pb–5Ag and 70In–15Sn–9.6Pb–5.4Cd alloys. Stress–strain tests were performed at 4.4 × 10−5 s−1 and 8.8 × 10−4 s−1. Stress–strain and creep tests were performed at −25, 25, 75, and 100°C or 125°C. The samples were evaluated in the as-fabricated and post-annealed conditions. The In–Ag solder had yield stress values of 0.5–8.5 MPa. The values of ΔH for steady-state creep were 99 ± 14 kJ/mol and 46 ± 11 kJ/mol, indicating that bulk diffusion controlled creep in the as-fabricated samples (former) and fast-diffusion controlled creep in the annealed samples (latter). The In–Sn yield stresses were 1.0–22 MPa and were not dependent on an annealed condition. The steady-state creep ΔH values were 55 ± 11 kJ/mol and 48 ± 13 kJ/mol for the as-fabricated and annealed samples, respectively, indicating the fast-diffusion controlled creep for the two conditions. The UCP constitutive models were derived for the In–Ag solder in the as-fabricated and annealed conditions.

Materials behaviour and the reliability in performance of solder joints

While the implementation of lead‐free solder technology has been the focus of much recent research, the challenge of joint structural integrity should not be overlooked. The paper summarises the significant variability in the mechanical properties of solders, both in terms of the prevailing testing conditions and between the alloys themselves. Using conventional routes to life prediction for an elementary creep situation, it demonstrates the critical importance of understanding the failure processes and utilising materials data that are appropriate.

Getting Ready for Lead‐free Solders*

This paper reviews the status of lead‐free solder development works. Some of the solder systems — Bi‐Sn, Bi‐Sn‐Fe, ln‐Sn, Sn, Sn‐Ag, Sn‐Ag‐Zn, Sn‐Ag‐Zn‐Cu, Sn‐Bi‐Ag, Sn‐Cu, Sn‐Cu‐Ag, Sn‐In‐Ag, Sn‐Sb, Sn‐Zn and Sn‐Zn‐ln — are discussed in more detail, while others are briefly commented on. In general, compared with eutectic Sn‐Pb solder, all the lead‐free solder alternatives investigated more or less exhibit some shortcomings, such as price, physical, metallurgical or mechanical properties. Relatively, Sn‐ln‐containing systems are more promising in terms of solder mechanical properties and soldering performance, although the price of ln may be a concern. Eutectic Sn‐Ag solder doped with Zn, Cu or Sb exhibits good mechanical strength and creep resistance, due to refined microstructure. The Bi‐Sn systems doped with other elements may have a niche in the low temperature soldering field. Eutectic Sn‐Cu has good potential due to its good fatigue resistance. The eutectic Sn‐Zn system modified with ln and/or Ag may be promising in terms of mechanical properties. Finding a lead‐free alternative for high temperature solders presents the biggest challenge to the industry.

Microstructural characterization of Cu-Sn-Ni Solder in microelectronic packaging

Microelectronic packaging has experienced exciting growth in the past years, and solder joints plays important roles in the reliability of package system. Lead-tin (Pb-Sn) alloys are the most prominent solders for the interconnection and packaging of modern electionic components and devices. However, there are environmental concern on the toxicity of Pb. These concerns have inspired a great deal of research to study the feasibility of lead-free replacement alloys. It is known that the presence of intermetallic is often an indication of good wetting in solder joints. Nevertheless, excessive intermetallic growth may be detrimental to joint reliablity. The purpose of this study is to investigate the growth evolution between unleaded Cu-Sn-Ni alloys and metallized layer. These results will help to characterize the effect of aging on the microstructural and mechanical properties of solder / metallized layer / substrate systems.

Solder joint reliability of indium-alloy interconnection

Recent high-density very large scale integrated (VLSI) interconnections in multichip modules require high-reliability solder interconnection to enable us to achieve small interconnect size andlarge number of input/output terminals, and to minimize soft errors in VLSIs induced by α-particle emission from solder. Lead-free solders such as indium (In)-alloy solders are a possible alternative to conventional lead-tin (Pb-Sn) solders. To realize reliable interconnections using In-alloy solders, fatigue behavior, finite element method (FEM) simulations, and dissolution and reaction between solder and metallization were studied with flip-chip interconnection models. We measured the fatigue life of solder joints and the mechanical properties of solders, and compared the results with a computer simulation based on the FEM. Indium-alloy solders have better mechanical properties for solder joints, and their flip-chip interconnection models showed a longer fatigue life than that of Pb-Sn solder in thermal shock tests between liquid nitrogen and room temperatures. The fatigue characteristics obtained by experiment agree with that given by FEM analysis. Dissolution tests show that Pt film is resistant to dissolution into In solder, indicating that Pt is an adequate barrier layer material for In solder. This test also shows that Au dissolution into the In-Sn solder raises its melting point; however, Ag addition to In-Sn solder prevents melting point rise. Experimental results show that In-alloy solders are suitable for fabricating reliable interconnections.

Dynamic Mechanical Testing of Solder and Solder Joints

Successful use of solder joints to attach surface mounted devices to printed wiring board substrates requires knowledge of the stress‐strain properties of solder as functions of temperature, time, and loading conditions. In addition, the relatively high operating temperature of solder in comparison to its absolute melting temperature introduces a requirement for an understanding of the influence of creep effects on the mechanical properties of solder under cyclical loading conditions. In the past, studies of these solder properties have been limited by the need to use relatively large bulk solder samples that may or may not be representative of actual solder joints in a printed wiring board‐chip carrier environment. A previously unreported test method for the evaluation of the dynamic mechanical properties of solder and solder joints has been developed. The method is based upon the use of a Rheometrics Dynamic Spectrometer, which has been shown to be capable of determining both the elastic and plastic responses of solder joints during cyclical loading under a variety of imposed strains, strain rates, and temperatures that are within the range of anticipated service conditions. In addition, stress relaxation properties of solder joints may be studied.