A review: microstructure and properties of tin-silver-copper lead-free solder series for the applications of electronics

Purpose The research on lead-free solder alloys has increased in past decades due to awareness of the environmental impact of lead contents in soldering alloys. This has led to the introduction and development of different grades of lead-free solder alloys in the global market. Tin-silver-copper is a lead-free alloy which has been acknowledged by different consortia as a good alternative to conventional tin-lead alloy. The purpose of this paper is to provide comprehensive knowledge about the tin-silver-copper series. Design/methodology/approach The approach of this study reviews the microstructure and some other properties of tin-silver-copper series after the addition of indium, titanium, iron, zinc, zirconium, bismuth, nickel, antimony, gallium, aluminium, cerium, lanthanum, yttrium, erbium, praseodymium, neodymium, ytterbium, nanoparticles of nickel, cobalt, silicon carbide, aluminium oxide, zinc oxide, titanium dioxide, cerium oxide, zirconium oxide and titanium diboride, as well as carbon nanotubes, nickel-coated carbon nanotubes, single-walled carbon nanotubes and graphene-nano-sheets. Findings The current paper presents a comprehensive review of the tin-silver-copper solder series with possible solutions for improving their microstructure, melting point, mechanical properties and wettability through the addition of different elements/nanoparticles and other materials. Originality/value This paper summarises the useful findings of the tin-silver-copper series comprehensively. This information will assist in future work for the design and development of novel lead-free solder alloys

Analysis of microstructure and mechanical properties of bismuth-doped SAC305 lead-free solder alloy at high temperature

SAC305 lead-free solder alloy is widely used in the electronic industry. However, the problems associated with the growth formation of intermetallic compounds need further research, especially at high temperatures. This study investigates the doping of Bismuth into SAC305 in the various compositions of 1, 2, and 3 wt.%. The microstructure in terms of intermetallic compound particles and mechanical properties was examined after thermal aging at temperatures of 100 °C and 200 °C for 60 h. The microstructure examination was observed using scanning electron microscopy, and the chemical composition of each alloy was confirmed with an energy dispersive X-ray. Tensile tests were performed to find the mechanical properties such as yield strength and ultimate tensile strength. The intermetallic compound’s phase analysis was identified using X-ray diffraction, and differential scanning calorimetry was done to study the temperature curves for melting points. Results showed that the addition of Bismuth refined the microstructure by suppressing the growth of intermetallic compounds, which subsequently improved the mechanical properties. The thermal aging made the microstructure coarsen and degraded the mechanical properties. However, the most improved performance was observed with a Bismuth addition of 3 wt.% into SAC305. Furthermore, a decrease in the melting temperature was observed, especially at Bismuth compositions of 3 wt.%

A review: microstructure and properties of tin-silver-copper lead-free solder series for the applications of electronics

Purpose: The research on lead-free solder alloys has increased in past decades due to awareness of the environmental impact of lead contents in soldering alloys. This has led to the introduction and development of different grades of lead-free solder alloys in the global market. Tin-silver-copper is a lead-free alloy which has been acknowledged by different consortia as a good alternative to conventional tin-lead alloy. The purpose of this paper is to provide comprehensive knowledge about the tin-silver-copper series. Design/methodology/approach: The approach of this study reviews the microstructure and some other properties of tin-silver-copper series after the addition of indium, titanium, iron, zinc, zirconium, bismuth, nickel, antimony, gallium, aluminium, cerium, lanthanum, yttrium, erbium, praseodymium, neodymium, ytterbium, nanoparticles of nickel, cobalt, silicon carbide, aluminium oxide, zinc oxide, titanium dioxide, cerium oxide, zirconium oxide and titanium diboride, as well as carbon nanotubes, nickel-coated carbon nanotubes, single-walled carbon nanotubes and graphene-nano-sheets. Findings: The current paper presents a comprehensive review of the tin-silver-copper solder series with possible solutions for improving their microstructure, melting point, mechanical properties and wettability through the addition of different elements/nanoparticles and other materials. Originality/value: This paper summarises the useful findings of the tin-silver-copper series comprehensively. This information will assist in future work for the design and development of novel lead-free solder alloys. © 2019, Emerald Publishing Limited

Reliability Assessment Of Self-Alignment Assemblies Of Chip Component After Reflow Soldering Process

Reliability of surface mount components and interconnect are significant issues in electronic manufacturing. Although the reliability of devices has been broadly studied,here we are focusing on the reliability of the solder joint after the self-alignment phenomena during reflow soldering.In this study,the quality of the self-alignment assemblies was analyzed relate to the joint shear strength according to the JIS Z3 198-7 standard and the inspection according to IPC-A-610E standard.The results from reliability study indicate that the shear strength of the misalignment component of solder joints indeed depends on the degree of chip component misalignment.For shift mode configuration in the range of 0-300µm,the resulted chip assembly inspection after the reflow process was in line with the IPC-A-610E standard

An investigation into nano-particulates reinforced SAC305-based composite solders under electro- and thermo-migration conditions

With the rapid development in electronic packaging due to product miniaturisation, the size of solder joints is decreasing considerably, thus the failure of solder interconnects induced by electro-migration (EM) and thermo-migration (TM) became a reliability concern. The incorporation of foreign reinforcement can effectively improve properties of the solder alloys. However, this presents an imperative need for a further investigation to elaborate the underlying fundamentals associated with the reliability of reinforced solders. In this study, the Sn-Ag-Cu (SAC) based solder alloy powders as matrix were incorporated with Fullerene (FNS), TiC and Ni-coated graphene (NG) reinforcements to form composite solders through powder metallurgical method. These composite solders were then characterised in terms of their microstructure, physical property, solderability, followed by a systematic investigation of their performance under isothermal ageing, current stressing and large thermal gradient, respectively. The results showed that three types of reinforcements were successfully incorporated into the solder matrix; with all reinforcements added being embedded in the solder matrix or around the intermetallic compounds (IMC). The average loss of FNS and TiC particles in the solders was approximately 80% after the initial reflow, while this was only 40% for NG particles. It has been observed that β-Sn and Ag3Sn in the SAC solder alloys can be refined by adding appropriate amount of FNS and TiC, which is beneficial to the wettability with a reduced coefficient of thermal expansion (CTE) with the minimal influence on the melting point and electrical resistivity of solder alloys. For the SAC alloys without reinforcements, obvious extrusion of interfacial IMC at the anode was present after 360 hours of current (1.5×104 A/cm2) stressing, while the changes of surface profiles of all reinforced solders were unnoticeable. Under the current stressing regimes, a continuous increase of interfacial IMCs at the anode of the original SAC alloys was observed, but decreased at the cathode with stressing time. For the composite solders, both anode and cathode showed a continuous growth of interfacial IMCs; the growth rates of IMCs at the anode were greater than that at cathode. In addition, NG and TiC were found to be most effective to retard the growth of Cu3Sn IMC under current stressing. A gradient in hardness across the stressed SAC joints was present, where it was harder at anode. However, no such obvious gradient was found in SAC/FNS and SAC/NG solder joints. FNS and NG were proven to be beneficial to prolong the service life of solder joints up to approximately 7.6% and 10.4% improvements, respectively. Thermal stressing made the interfacial IMC in the original SAC joints to grow at the cold end considerably; causing serious damage at the hot end after 600 hours under temperature gradient of 1240K/cm stressing; a large number of IMCs, cracks and voids appeared in the SAC solder joints. However, a uniform increase of IMCs at both sides in the composite solders was observed without apparent damages at the interfaces under the same thermal stressing conditions, indicating an effective reduction of the elemental migration in the reinforced solders. Although there were also some voids and IMCs formed in the composite solder joints after a long-term thermal stressing, the integrity of the composite solder joints was enhanced compared with the SAC alloys. During thermal stressing, the dissolution rate of Cu atom into the SAC solder joints was estimated to be 3.1×10-6 g/h, while the values for SAC/FNS, SAC/NG and SAC/TiC were only 1.22×10-6 g/h, 1.09×10-6 g/h and 1.67×10-6 g/h, respectively

Thermo-mechanical reliability studies of lead-free solder interconnects

N/ASolder interconnections, also known as solder joints, are the weakest link in electronics packaging. Reliability of these miniature joints is of utmost interest - especially in safety-critical applications in the automotive, medical, aerospace, power grid and oil and drilling sectors. Studies have shown that these joints' critical thermal and mechanical loading culminate in accelerated creep, fatigue, and a combination of these joints' induced failures. The ball grid array (BGA) components being an integral part of many electronic modules functioning in mission-critical systems. This study investigates the response of solder joints in BGA to crucial reliability influencing parameters derived from creep, visco-plastic and fatigue damage of the joints. These are the plastic strain, shear strain, plastic shear strain, creep energy density, strain energy density, deformation, equivalent (Von-Mises) stress etc. The parameters' obtained magnitudes are inputted into established life prediction models – Coffin-Manson, Engelmaier, Solomon (Low cycle fatigue) and Syed (Accumulated creep energy density) – to determine several BGA assemblies' fatigue lives. The joints are subjected to thermal, mechanical and random vibration loadings. The finite element analysis (FEA) is employed in a commercial software package to model and simulate the responses of the solder joints of the representative assemblies' finite element models. As the magnitude and rate of degradation of solder joints in the BGA significantly depend on the composition of the solder alloys used to assembly the BGA on the printed circuit board, this research studies the response of various mainstream lead-free Sn-Ag-Cu (SAC) solders (SAC305, SAC387, SAC396 and SAC405) and benchmarked those with lead-based eutectic solder (Sn63Pb37). In the creep response study, the effects of thermal ageing and temperature cycling on these solder alloys' behaviours are explored. The results show superior creep properties for SAC405 and SAC396 lead-free solder alloys. The lead-free SAC405 solder joint is the most effective solder under thermal cycling condition, and the SAC396 solder joint is the most effective solder under isothermal ageing operation. The finding shows that SAC405 and SAC396 solders accumulated the minimum magnitudes of stress, strain rate, deformation rate and strain energy density than any other solder considered in this study. The hysteresis loops show that lead-free SAC405 has the lowest dissipated energy per cycle. Thus the highest fatigue life, followed by eutectic lead-based Sn63Pb37 solder. The solder with the highest dissipated energy per cycle was lead-free SAC305, SAC387 and SAC396 solder alloys. In the thermal fatigue life prediction research, four different lead-free (SAC305, SAC387, SAC396 and SAC405) and one eutectic lead-based (Sn63Pb37) solder alloys are defined against their thermal fatigue lives (TFLs) to predict their mean-time-to-failure for preventive maintenance advice. Five finite elements (FE) models of the assemblies of the BGAs with the different solder alloy compositions and properties are created with SolidWorks. The models are subjected to standard IEC 60749-25 temperature cycling in ANSYS 19.0 mechanical package environment. SAC405 joints have the highest predicted TFL of circa 13.2 years, while SAC387 joints have the least life of circa 1.4 years. The predicted lives are inversely proportional to the magnitude of the areas of stress-strain hysteresis loops of the solder joints. The prediction models are significantly consistent in predicted magnitudes across the solder joints irrespective of the damage parameters used. Several failure modes drive solder joints and damage mechanics from the research and understand an essential variation in the models' predicted values. This investigation presents a method of managing preventive maintenance time of BGA electronic components in mission-critical systems. It recommends developing a novel life prediction model based on a combination of the damage parameters for enhanced prediction. The FEA random vibration simulation test results showed that different solder alloys have a comparable performance during random vibration testing. The fatigue life result shows that SAC405 and SAC396 have the highest fatigue lives before being prone to failure. As a result of the FEA simulation outcomes with the application of Coffin-Manson's empirical formula, the author can predict the fatigue life of solder joint alloys to a higher degree of accuracy of average ~93% in an actual service environment such as the one experienced under-the-hood of an automobile and aerospace. Therefore, it is concluded that the combination of FEA simulation and empirical formulas employed in this study could be used in the computation and prediction of the fatigue life of solder joint alloys when subjected to random vibration. Based on the thermal and mechanical responses of lead-free SAC405 and SAC396 solder alloys, they are recommended as a suitable replacement of lead-based eutectic Sn63Pb37 solder alloy for improved device thermo-mechanical operations when subjected to random vibration (non-deterministic vibration). The FEA simulation studies' outcomes are validated using experimental and analytical-based reviews in published and peer-reviewed literature.N/

Pencirian Sifat mekanikal bahan dengan pendekatan analisis fraktal Integrasi sistem pemantauan kesihatan dengan aplikasi iot dalam teknologi sukan: satu kajian

Pemilihan bahan merupakan salah satu faktor utama dalam struktur binaan. Dalam kajian ini, satu kaedah alternatif telah dilaksanakan iaitu dengan menggunakan kaedah analisis fraktal. Penggunaan kaedah ini dapat menyumbang kepada penjimatan kos dan mengurangkan kadar kemalangan untuk mengenalpasti pencirian sifat mekanikal setiap bahan. Tujuan penyelidikan ini adalah mengkaji siri masa yang terhasil dari ujikaji penggunaan sensor filem piezo menggunakan analisis fraktal dan menyiasat sifat bahan mekanikal (nisbah poisson) berlainan dengan daya hentaman berbeza menggunakan dimensi fraktal. Terdapat empat jenis bahan terpilih iaitu loyang, tembaga, keluli lembut dan keluli tahan karat yang berbentuk bulat. Daya hentaman berbeza dihasilkan dengan menggunakan tukul hentaman dan seterusnya isyarat getaran diperoleh daripada sensor filem piezo. Dengan menggunakan perisian Matlab, analisis menggunakan kaedah fraktal dijalankan. Dimensi fraktal diperoleh daripada nilai kecerunan graf log-log plot dan dimensi fraktal dihitung bagi setiap daya hentaman yang dikenakan pada setiap spesimen. Kemudian, nilai dimensi fraktal dibandingkan dengan menggunakan CES Edupack2012 bagi pencirian sifat setiap bahan. Hasil kajian menunjukkan bahawa nilai dimensi fraktal meningkat dengan peningkatan daya impak atau hentaman manakala penurunan dalam nilai nisbah poisson berlaku apabila dimensi fraktal setiap bahan meningkat

A Finite Element approach to understanding constitutive elasto-plastic, visco-plastic behaviour in lead free micro-electronic BGA structures

This work investigates the non-linear elasto-plastic and visco-plastic behaviour of lead free solder material and soldered joints. Specifically, Finite Element (FE) tools were used to better understand the deformations within Ball Grid Array solder joints (BGA), and numerical and analytical methods were developed to quantify the identified constituent deformations. FE material models were based on the same empirical constitutive models (elastic, plastic and creep) used in analytical calculations. The current work recognises the large number of factors influencing material behaviour which has led to a wide range of published material properties for near eutectic SnAgCu alloys. The work discovered that the deformation within the BGA was more complex than is generally assumed in the literature. It was shown that shear deformation of the solder ball could account for less than 5% of total measured displacement in BGA samples. Shear displacement and rotation of the solder balls relative to the substrate are sensitive to the substrate orthotropic properties and substrate geometry (relative to solder volume and array pattern). The FE modelling was used to derive orthotropic FR4 properties independently using published data. An elastic modulus for Sn3.8Ag0.7Cu was measured using homologous temperatures below 0.3. Suggested values of Abaqus-specific creep parameters m and f (not found in literature) for Sn3.8Ag0.7Cu have been validated with published data. Basic verification against simple analytical calculations has given a better understanding of the components of overall specimen displacement that is normally missing from empirical validation alone. A combined approach of numerical and analytical modelling of BGAs, and mechanical tests, is recommended to harmonise published work, exploit new material data and for more informed analysis of new configurationsEPSRC-funded PhD studentshi