RoHS Research Articles

Microstructural evaluation of interfacial intermetallic compounds between Sn58Bi and ENEPIG

BackgroundLow carbonization and Restriction of Hazardous Substances (RoHS) regulations have promoted the development of low-temperature lead-free solder. The solder and substrate are critical entities of joint connections. MethodsSn58Bi has been considered a promising low-temperature solder. Electroless nickel/electroless palladium/immersion gold (ENEPIG) is a good surface finish that prevents solder joints from oxidizing and extends the shelf life of the substrates. In this study, the interfacial reactions between the Sn58Bi solder and ENEPIG surface finish were systematically analyzed. Findings(Au,Pd,Ni)(Sn,Bi)4 was observed after reflow at 160 °C. Au and Pd dissolved into solder rapidly in the beginning. NiSn4 and Ni3Sn4 with small amounts of Au and Pd dissolution formed at the interface after aging. The morphology of NiSn4 evolved from block-like to needle-shaped and finally to a layered configuration as the aging temperature and time increase. Ni3Sn4 was observed between NiSn4 and substrate above 100 °C. This study established the growth mechanism of intermetallic compounds (IMCs) in the reaction between Sn58Bi and ENEPIG for low-carbon emitting processes.

Chemical management in electronics manufacturing: Protecting worker health and the environment

In the realm of electronics manufacturing, the management of chemicals is paramount to safeguarding both worker health and environmental sustainability. This review delves into the strategies and challenges associated with chemical management within this industry. The utilization of various chemicals in electronics manufacturing processes presents potential hazards to both workers and the environment. From cleaning agents to solvents and fluxes, these substances pose risks ranging from acute toxicity to long-term health effects and environmental contamination. Effective chemical management strategies are therefore indispensable. This review discusses the proactive measures implemented by electronics manufacturers to mitigate these risks. It explores the adoption of alternative, less hazardous chemicals and the implementation of engineering controls to minimize exposure. Additionally, stringent protocols for handling, storage, and disposal are essential components of comprehensive chemical management programs. Furthermore, regulatory frameworks play a pivotal role in shaping chemical management practices within the electronics manufacturing sector. Compliance with local and international regulations such as REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) and RoHS (Restriction of Hazardous Substances) is imperative to ensure the safety of workers and the environment. However, despite these efforts, challenges persist. Balancing the need for innovation and productivity with chemical safety requirements remains a significant challenge for manufacturers. Additionally, global supply chain complexities add another layer of complexity to chemical management efforts. Effective chemical management in electronics manufacturing demands a multi-faceted approach encompassing technological innovation, regulatory compliance, and a commitment to worker health and environmental stewardship. By addressing these challenges collaboratively, the industry can strive towards safer and more sustainable practices.

Evaluation of Metals in Printed Wiring Boards of Selected Discarded Mobile Phones in Nigeria

Obsolete mobile phones form a major component of the e-waste stream. The Printed wiring boards (PWBs) of mobile phones are packed with economic and toxic metals. Regulatory bodies such as Restriction of Hazardous Substances (RoHS) directives regulate the amount of these toxic metals in electrical and electronic equipment. This study is aimed at evaluating selected critical metals present in PWBs of three popular brands of discarded mobile phones used in Nigeria to understudy the behaviour of original equipment manufacturers (OEMs) regarding toxicity, economic potentials, and level of compliance with international initiatives by regulatory bodies to reduce the level of toxic metals in electronic equipment. PWBs obtained from 60 discarded mobile phones of 3 popular mobile phone brands used in Nigeria were chopped into smaller particles, extracted according to EPA 3050B method, and analysed using the Inductive Coupled Plasma-Optical Emission Spectrometry technique. It was observed that Mn, Fe, Zn, and Cu, had the highest concentration range across all brands studied. Notable toxic metals such as Pb, Cd, Cr, and As have mean and standard deviation values of 0.43±0.38 mg/kg, 0.62±0.160 mg/kg, 5.16±1.06 mg/kg, and 84.97±13.83 mg/kg respectively. Economic metals: Cu, Ag, and Au had mean and standard deviation values of 80.37±16.89 mg/kg, 2.12±0.43 mg/kg, and 0.95±0.19 mg/kg respectively. Results from the study indicate that PWBs of mobile phones are a perfect secondary source of a large variety of metals vital for the recycling industry. Also, the low levels of toxic metals suggest that some OEMs are already adopting the 'design-for-environment' option. Therefore, PWBs studied seem eco-friendly; however, need to be handled with care as there are still some toxic metals of concern not determined in this study.

A review of toxicity assessment procedures of solar photovoltaic modules

Environmental management of solar photovoltaic (PV) modules is attracting attention as a growing number of field-operated PV modules approach end of life (EoL). PV modules may contain small amounts of toxic metals, and the procedures for assessing and regulating the toxic metal content and release of such materials at EoL differ widely across nations. This paper provides an overview of the metal composition of PV modules and common procedures for toxicity assessment through extensive research and review of technical literature and legislative documents. This review focuses on three primary aspects: first, it explores the distribution of toxic elements within current and emerging PV module designs, with a specific focus on obtaining representative samples for proportional toxicity testing within different module laminate areas. Second, it examines a sampling standard and the diverse toxicity testing methods and regulations employed in various regions, encompassing standards like the Environmental Protection Agency (EPA) Test Method 1311 (Toxicity Characteristic Leaching Procedure, TCLP) in the U.S., Restriction of Hazardous Substances (RoHS) in Europe, and the Waste Extraction Test (WET) in California. Third, the review examines the sources of variability in toxicity testing outcomes, including techniques for securing homogeneous samples from non-uniform PV modules, selecting particle sizes representative of landfill conditions in extracted samples, determining appropriate leachate characteristics such as leaching agents and pH levels, and considering factors like test duration and temperatures. In summary, this review summarizes relevant regulations and offers a comprehensive overview of the strengths and limitations associated with several toxicity assessment procedures currently in practice.

Enablers for Adopting Restriction of Hazardous Substances Directives by Electronic Manufacturing Service Providers

The Electronic Manufacturing Service (EMS) industry contributes significantly to toxic waste generation due to its fabrication processes. Notably, adherence to the Restriction of Hazardous Substances (RoHS) Directive varies amongst EMS providers, despite its aim to reduce electronic waste. This study explores the factors influencing EMS providers’ decision to adopt the RoHS directive, utilizing the technology–organization–environment (TOE) and the human–organization–technology (HOT) fit, or the TOE-HOT fit framework. We validated our framework using partial least squares structural equation modeling (PLS-SEM), based on responses from 379 questionnaires from major EMS providers. The results demonstrated that expert resources, adequate resources, perceived industrial pressure, institutional pressure, and costs were positively associated with RoHS adoption. However, innovation, relative advantage, and verification ability were identified as significant barriers. In particular, innovation in the human dimension was the key determinant for RoHS adoption. Therefore, clear policy instruments and regulations may enhance RoHS adoption by EMS providers. These findings can guide environmental policy definitions in governmental laws and strategies, encouraging EMS providers and other firms to adopt RoHS standards.

Determination of Pb content in recycled plastic debris by laser-induced breakdown spectroscopy

During several last decades, the usage of plastics has risen steadily across the globe. However, many potentially toxic materials have been used especially in their earlier production. These materials include additions of heavy metals such as arsenic, cadmium, chromium (VI), mercury and lead. Recently, the levels of these heavy metals and other hazardous materials have become controlled by various directives (Registration, Evaluation, Authorization and Restriction of Chemicals - REACH1, Restriction of Hazardous Substances in Electrical and Electronic Equipment - RoHS2 and Waste from Electrical and Electronic Equipment - WEEE3). These restrictions apply also to plastic products made from recycled polymer waste. This post-consumer polymer waste is the most susceptible to an increased heavy metal content. Usually, lead is the heavy metal with the highest concentration.The heavy metal content level needs to be determined reliably and quickly, which is not the case presently. Companies need to wait for a traditional lengthy analysis, which also destroys the sample. Laser Induced Breakdown Spectroscopy (LIBS) provides a drastic improvement in time of measurement and high enough robustness in the sense of precision and accuracy to be considered for this application. This paper presents the capabilities of LIBS to reliably quantify the lead content in polymer post-consumer recycled materials. Using the methodology defined in this work, LIBS can be used directly in-situ to control levels of lead and other toxic substances. In this feasibility work, an accuracy of more than 90% with a relative precision higher than 86% was achieved for the quantification of lead content in standard samples provided by a recycling company using standard multivariate chemometric techniques.

End-of-life mobile phones parts contain toxic metals that make them hazardous, but can also serve as resource reserves for such metals

Abstract In this study, the concentration of some toxic metals in different parts of end-of-life mobile phones was assessed. Twenty end-of-life mobile phones of different brands and countries of origin, which were widely in use up to the year 2011, were collected from phone repair workshops in Lagos, Nigeria. The collected mobile phones were disassembled into the phone screens, printed wiring boards, plastic casings and batteries. Disassembled parts were individually milled and pulverized, and digested using HCl, HNO3 and H2O2. Flame atomic absorption spectrometry was used to quantify some toxic metals (Pb, Cd and Ni) in the digested samples, and the determined concentrations were compared with permissible limits. The average metals concentration in the disassembled parts followed the order: printed wiring boards > batteries > plastic casings > phone screens. The concentrations of Pb and Ni exceeded their toxicity threshold limit concentration in printed wiring boards, while Ni exceeded the limit concentration in batteries. Based on the maximum permissible concentration required by the Restriction of Hazardous Substances (RoHS) Directives, all Cd concentrations were below the limit concentration; Pb and Ni in printed wiring boards exceeded their limit concentrations, while Ni exceeded its permissible concentration in batteries. The results of this study indicate that printed wiring boards and batteries of end-of-life mobile phones are hazardous, and their improper disposal of could cause environmental and health problems. However, considering the very high concentrations of Pb and Ni, these mobile phone parts could serve as resource reserves for these metals.

Boosting the Photoluminescence Efficiency of InAs Nanocrystals Synthesized with Aminoarsine via a ZnSe Thick-Shell Overgrowth.

InAs-based nanocrystals can enable restriction of hazardous substances (RoHS) compliant optoelectronic devices, but their photoluminescence efficiency needs improvement.Wereport an optimized synthesis of InAs@ZnSe core@shell nanocrystals allowing to tune the ZnSe shell thickness up to seven mono-layers (ML) and to boost the emission, reaching a quantum yield of ≈70% at ≈900nm. It is demonstrated that a high quantum yield can be attained when the shell thickness is at least ≈3ML. Notably, the photoluminescence lifetimeshows only a minor variation as a function of shell thickness, whereas the Auger recombination time (a limiting aspect in technological applications when fast) slows down from 11 to 38ps when increasing the shell thickness from 1.5 to 7MLs. Chemical and structural analyses evidence that InAs@ZnSe nanocrystals do not exhibit any strain at the core-shell interface, likely due to the formation of an InZnSe interlayer. This is supported by atomistic modeling, which indicates the interlayer as being composed of In, Zn, Se and cation vacancies, alike to the In2 ZnSe4 crystal structure. The simulations reveal an electronic structure consistent with that of type-I heterostructures, in which localized trap states can be passivated by a thick shell (>3ML) and excitons are confined in the core.

Effect of temperature on the low cycle fatigue properties of BGA solder joints

Since the restriction of hazardous substances (RoHS) directive, lead-free soldering has been widely broad adopted. In many applications, lead-free alloys have been substituted for conventional SnPb (Tin-Lead) solder. Among lead-free alloys, SAC305(Sn-3.0Ag-0.5Cu) has gained the highest acceptance as a solder alloy. The fatigue performance of solder joints has become an essential reliability assessment criterion due to the transition to more reliable lead-free alloys from highly predictable lead-based alloys. This study examines the shear fatigue characteristics of sandwich test vehicles for SnPb and SAC305 at different temperatures using both Organic Solderability Preservative (OSP) and Electroless Nickel-Immersion Silver (ENIG) surface finishes. The fatigue experiments were performed using an Instron micromechanical tester at a constant strain rate, and microstructural analysis was carried out using Scanning Electron Microscopy (SEM) to identify the Intermetallic Compound (IMC) morphology and failure mode. The stress-strain (hysteresis) loops of SnPb and SAC305 were measured, and the fatigue life of the specimens was estimated using the strain-life equation at various temperatures. SAC305 was observed to have a better fatigue life than SnPb, particularly at higher strain levels or testing temperatures. The OSP surface finish demonstrated superior fatigue properties compared to the ENIG surface finish. Additionally, elevated testing temperatures were found to accelerate fatigue failure in solder joints. The Arrhenius model was utilized to develop a general empirical model that predicts the fatigue life of SAC305 and SnPb solder alloys with OSP and ENIG surface finishes as a function of the strain level and testing temperature.

Influence of Element Lead (Pb) Content in Tin Plating on Tin Whisker Initiation/Growth

The implementation of the Restriction of Hazardous Substances (RoHS) European Union (EU) Directive in 2005 resulted in the introduction of pure tin as an acceptable surface finish for printed circuit boards and component terminations. A drawback of pure tin surface finishes is the potential to form tin whiskers. Tin whiskers are a metallurgical phenomenon that is associated with tin rich/pure tin materials and has been a topic of intense industry interest. The acceptance and usage of pure tin by the electronics industry component fabricators is understandable as the pure tin surface finishes are inexpensive, are simple plating systems to operate and have reasonable solderability characteristics. However, high performance/harsh environment electronics typically have product life cycles that are measured in decades and therefore are much more susceptible to the potential long term threat of tin whiskers. The GEIA-STD-0005-2 “Standard for Mitigating the Effects of Tin Whiskers in Aerospace and High Performance Electronic Systems” established the definition of the term “Pb-free tin” as : “Pb-free Tin is defined to be pure tin or any tin alloy with <3% lead (Pb) content by weight. A functional definition of “pure tin” was necessary so that the electronics industry could establish tin whisker risk protocols against a known acceptable target value in terms of soldering materials and processes. An investigation was conducted to determine the influence of 1% - 5% elemental lead (Pb) content in tin plating on tin whisker initiation and growth. The investigation results were used in the revision of the GEIA-STD-0005-2 “Standard for Mitigating the Effects of Tin Whiskers in Aerospace and High Performance Electronic Systems” specification technical discussions.

Micro‐Particle Induced X‐ray Emission Study of Lead‐Free and Lead‐Based Solders and Interactions with Copper Wires

Pb‐free electrical solders, such as Cu–Sn alloys, work well for reflow soldering under tightly controlled conditions. Hand soldering, however, often results in poor quality joints compared to conventional Pb–Sn solders. To investigate this under realistic workshop conditions, micro‐particle induced X‐ray emission (micro‐PIXE) with 2 MeV protons has been employed. Commercial flux‐cored Cu–Sn and Pb–Sn solder wires are studied. Solder blobs under two cooling conditions as well as tinning Restriction of Hazardous Substances (RoHS)‐compliant and legacy component wires are investigated. The results show that the long heating and slow cooling of Cu–Sn solder blobs lead to formation of an acicular precipitate that can be ascribed to Cu6 Sn5. Pb–Sn solder under the same conditions shows phase separation with regions of high Sn and regions with high Pb. In the case of rapidly cooled blobs where a shiny surface is produced, no phase separation in either solder is observed. Tinning of RoHS‐compliant and legacy Cu component wires with the two solders produce significantly different interfacial depth profiles with varying degrees of grading, indicative of intermetallic phase formation.

Circular economy without chemicals controls? Evidence of recirculated toxic plasticizers in flexible PVC products

The global push towards a circular economy (CE) has led to increasing efforts to improve resource utilization efficiency, including plastics recycling. However, the presence of additives, especially those that are toxic, complicates plastics recycling in several ways. Without sufficient controls, the spread of hazardous additives via recycling activities represents a significant public health challenge, particularly among developing nations. This study demonstrates evidence of such uncontrolled recycling, based on an investigation of four household flexible PVC product groups available in Thailand. A versatile pyrolysis/thermal desorption gas chromatography-mass spectrometry (Py/TD-GC-MS) method was employed to simultaneously screen 18 target plasticizers in these products. Di-(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DINP) are the most frequently detected primary plasticizers. DEHP is dominant in vinyl boots, flooring sheets, and hoses, while DINP is dominant in cable sheaths, likely due to a spill-over effect from the EU Restriction of Hazardous Substances (RoHS) directive. Chlorinated paraffins (CPs) are secondary plasticizers that are also detected in most samples, except for boots. The other plasticizers detected include other ortho-phthalates and non-phthalates. These results provide insight into combinatory patterns of plasticizer ‘cocktails’, that comprise restricted, as-yet-unrestricted, and non-restricted plasticizers, embedded in the same individual samples, with a maximum of seven plasticizers found in a single cable sheath. These findings indicate the existence of potentially risky recycling practices that target embedded plasticizers to save cost, without due consideration of their inherent toxicity. Proper interventions are necessary to ensure that CE and chemical safety can be synergized.

Active Power Control of Retrofit LED Tube Lamps for Achieving Entitled Energy Savings in View of the EU Ban on Mercury

The performance of commercially available retrofit LED tubes intended for the replacement of linear fluorescent lamps is measured and analyzed with respect to “real-world” installed electronic ballasts, as ascertained through field recovery from installed bases, such as office buildings, parking garages, and industrial installations in western Europe from 2018 to 2020. Results show a wide variation in lamp power draw, which not only thwarts the energy-saving and climate protection aspects of the LED retrofit solution but also poses potential safety risks. Given the EU’s goals under the Restriction of Hazardous Substances (RoHS) directive to phase out mercury-containing fluorescent lighting, starting from September 2023, the situation is alarming. We show that this lamp power spread is due to the fundamental differences in impedance between fluorescent lamps and LEDs, in combination with the passive nature of the driver electronics that are currently employed in commercially available LED tube lamps. In response to this disparity, a novel driver topology including active power control (APC) is introduced, which shows that the power-spread problem can be avoided, and we offer a manufacturable solution. A prototype retrofit LED tube lamp incorporating this APC driver technology is shown to deliver safe and predictable energy savings, outlining a path toward guaranteeing the expected return-on-investment and positive environmental impact of the solid-state lighting replacement of mercury-containing linear fluorescent lamps.

Effect of the Microstructure of ZnO Thin Films Prepared by PLD on Their Performance as Toxic Gas Sensors

In 2008, the modified European Restriction of Hazardous Substances (RoHS) directive prohibited the use of hazardous substances such as lead, cadmium, and mercury. As such, an urgent need for lead-free components emerged in Europe. In this frame, we have decided to study the microstructure influence of zinc oxide thin films on the detection of hydrogen sulfide (H2S). Zinc oxide thin films were deposited by PLD on silicon substrates under different conditions to modify the microstructure. In order to compare our demonstrators to current commercial semiconductor gas sensors, measurements under H2S were also performed with sensors from Figaro and Winsen corporations. Gas sensors were therefore implemented by using commercial cases in view to test them with Simtronics gas detector DG477. The good sensitivity values measured at T = 400 °C under 100 ppm H2S, and response times as low as 30 s, definitely confirm that ZnO thin films could be developed for commercial sensors.

Highly efficient, ultrathin, Cd-free kesterite solar cells in superstrate configuration enabled by band level tuning via Ag incorporation

Kesterite, or Cu2ZnSn(S,Se)4 (CZTS) is promising in developing sustainable PV technology due to its earth-abundant, non-toxic composition. However, issues including instability of interface, high density of defects that fails to allow the short charge-collection length to meet its light absorption needs, use of Cd that fails to comply with the restriction of hazardous substances (RoSH), are promoting the development of alternative, eco-friendly device structure. Here, this study reports an important progress on this subject by adopting the superstrate configuration to kesterite, thus to realize advantageous light management and high defect tolerance in an ultrathin device. By incorporating Ag in kesterite to overcome the detrimental alignment at the pristine interface, a solar cell with PCE of 8.1% has been fabricated with ~ 200 nm absorber and ~ 15 nm TiO2 buffer, representing a PCE improvement of nearly three-fold from the baseline Cu2ZnSn(S,Se)4 device and breaking the 5% PCE limit for superstrate kesterite cells to date. Moreover, this enables the sole use of TiO2 as novel buffer material free of toxic Cd. Further analysis reveals the critical role of Ag in synergistically tailoring band offset and bandgap, along with largely reduced density of defects, leading to this substantial performance improvement.

Green market orientation and organizational performance in Taiwan’s electric and electronic industry: the mediating role of green supply chain management capability

PurposeGreen sustainability has become a critical challenge for businesses to execute green supply chain management (GSCM). Most of the literature on GSCM emphasizes regulations as drivers and few pieces of research are conducted from an internal organizational culture view. This study aims to use the cultural perspective of market orientation (MO) and draws on both the natural resource-based view (NRBV) and dynamic capability view (DCV) to explore the relationships among green market orientation (GMO), GSCM capability and organizational performance.Design/methodology/approachA total of 1,000 survey questionnaires were distributed to the Taiwanese electronics industry and 207 valid questionnaires were collected. Data was analyzed using structural equation modeling.FindingsThe results show that GMOs have a significant positive impact on GSCM capability, environmental performance and economic performance. Moreover, GSCM capability is positively related to environmental and economic performance. The results also show that GMOs have a significant indirect influence on environmental performance and economic performance through GSCM capability.Practical implicationsThe findings of this study suggest how Taiwan’s electrical and electronic manufacturers, while faced with pressure from competitors, customers and regulations (i.e. waste electrical and electronic equipment directive, Restriction of Hazardous Substances Directive and energy-using products directives), should efficiently and effectively implement GMO and enhance GSCM capability to improve organizational performance.Originality/valueThis study fills up the gap between MO and performance indistinct relationships. It has also integrated two perspectives, namely, NRBV and DCV, to explain GSCM capability as a mediator between GMO and organizational performance relationship and to examine the relationships among GMO, GSCM capability and organizational performance.

Institutional pressure, firm's green resources and green product innovation: evidence from Taiwan's electrical and electronics sector

PurposeIntegrating economic and green initiatives into firm strategies is a challenge for firms in various industries. The study aims to incorporate multiple views, i.e. green innovation theory (GIT), the green institutional perspective (GIP) and the natural-resource-based view (NRBV), to develop a comprehensive model to explore why and how firms implement green product innovation (GPI).Design/methodology/approachThe study explores the relationships among institutional pressure, the firm's green resources and GPI. The research also distinguishes two different types of GPI: exploratory GPI and exploitative GPI. A total of 270 valid questionnaires were collected from electrical and electronics manufacturers in Taiwan. The authors employed structural equation modeling (SEM) using analysis of moment structures (AMOS) 23.0 to test the hypotheses.FindingsThe results show that institutional pressure has a significant positive correlation with the firm's green resources. Furthermore, institutional pressure has a significantly positive influence on exploratory GPI and exploitative GPI, respectively. The firm's green resources also have a significantly positive effect on both exploratory GPI and exploitative GPI. In addition, institutional pressures have significantly positive indirect effect on both exploratory GPI and exploitative GPI.Research limitations/implicationsEconomic benefits and environmental sustainability are the most pressing issues faced by the electrical and electronics industry today. The study's investigation covers Taiwanese electrical and electronics manufacturers only, so the test of the research model has limited generalizability. The authors suggest that to expand the generalizability of the findings, future research should examine this model in the context of other regions such as Southeast Asia, Africa, South America, etc.Practical implicationsThe study has many interesting implications for both practitioners and policymakers. The authors' findings suggest that while Taiwanese electrical and electronics manufacturers face significant pressure from customers, competitors and regulation requirements (e.g. waste electrical and electronic equipment [WEEE], restriction of hazardous substances [RoHS] and energy using product [EuP] directives), firms in that sector should efficiently and effectively deploy their green resources and then perform proper GPI (e.g. exploratory GPI or exploitative GPI). These results also serve as a reminder to policymakers that balancing coercive (command-and-control) mechanisms with incentives and voluntary mechanisms is the best means by which to develop motivational and effective GPI policies.Originality/valueFirst and foremost, the paper divides GPI into exploratory GPI and exploitative GPI. Furthermore, the research incorporates two important schools of thought, i.e. the GIP and NRBV, thus providing a more holistic view by which to explore why and how companies adopt GPI.

High-temperature-tolerable superconducting Nb-alloy and its application to Pb- and Cd-free superconducting joints between NbTi and Nb3Sn wires

For more than 30 years, Pb–Bi alloy and Wood's metal (50% Bi, 26.7% Pb, 13.3% Sn, and 10% Cd) have been used as representative superconducting solder intermedia to establish superconducting joints between NbTi and Nb3Sn wires in high-field nuclear magnetic resonance magnet systems. However, the use of Pb and Cd has been severely restricted by environmental regulations, such as the Restriction of Hazardous Substances Directive. Herein, a novel method of forming a superconducting joint between NbTi and Nb3Sn wires without Pb and Cd has been proposed. This approach is based on metallurgical bonding processes using a superconducting Nb-alloy intermedium, whose fine microstructure is maintained even after exposure to temperatures higher than 650 °C. Further, fine crystal defects become sources of magnetic flux pinning centers. Among transition elements close to Nb, Hf is considered the most suitable additive for realizing high-temperature-tolerable (HTT) superconducting Nb-alloy intermedia. Utilizing the HTT characteristic of Nb–Hf, a superconducting joint between Nb3Sn filaments and one end of the Nb–Hf alloy core was created by forming a superconducting Nb3Sn layer at the interface through a chemical reaction. The other end of the Nb–Hf alloy core was cold-pressed with NbTi filaments, to connect their active new surfaces to each other in order to create a superconducting joint. Ultimately, a superconducting joint between NbTi and Nb3Sn wires was realized with a high critical magnetic field (Bc2) of more than 1 T. The formation of the superconducting joint was confirmed by current decay measurements. This method of forming a superconducting joint is promising for application in environmentally friendly nuclear magnetic resonance magnet systems.Graphical abstract

Metallurgical, physical, mechanical and oxidation behavior of lead-free chromium dissolved Sn–Cu–Bi solders

According to the European Union's (EU) legislation in 2006, the Restriction of Hazardous Substances (RoHS) led to eliminating Sn–Pb conventional solders from electronic assemblies. Despite this elimination, the use of lead-bearing solders in car electronics was persisted, and eventually, in 2014 the lead usage prohibition was introduced for the automotive industry. The reliability and safety issues are still arguable in this industry, notwithstanding the lead-free solders substitution. The Sn–Cu solder is one of the alternatives modified by alloying elements to improve its moderate mechanical properties. In order to fabricate a cost-effective solder that has simultaneously a good level of mechanical properties and oxidation behavior, the Cr along with Bi was added to the Sn–Cu base solder. In this research, a comparative study has been conducted on the Sn-0.8Cu-1.8Bi-xCr (x = 0, 0.01, 0.1 wt.%). The effect of adding these alloying elements on the physical and mechanical properties is studied compared to Sn-0.8Cu and Sn-0.8Cu-1.8Bi solders. The physical properties of synthesized solders such as microstructure, XRD, thermal properties, wettability, oxidation behavior, and density were investigated. Also, these experienced mechanical tests such as uniaxial tensile test, microhardness test, and fractography to evaluate the effect of Cr and Bi on mechanical properties. The results showed that the addition of the minor amount of Cr along with Bi can consequently improve the microstructure, add some kinds of new IMCs, modifies the oxidation behavior and the wettability. The mechanical properties of the base solder got better by the adding these alloying elements.

Tin Whisker Formation on Small Outline Transistors Assembled Using Bismuth-Containing Lead-Free Solder Alloys After Long-Term Ambient Temperature, High Humidity Storage Part 3: In-Depth Characterization and Mechanisms

With the introduction of environmental legislation such as the Restriction of Hazardous Substances (RoHS), lead (Pb)-free materials have made their way into the electronics manufacturing industry. One issue that has emerged is that Pb-free solder alloys can initiate and grow tin whiskers under specific conditions. These whiskers are thin, highly conductive filaments which have the potential to grow and can cause field failures in many applications. Most concerning with respect to tin whiskering are high reliability applications such as aerospace, automotive, and medical.
 Bismuth (Bi) is being considered for inclusion in solder alloys to replace the current industry standard (SAC 305) and provide improved thermomechanical and vibration reliability. In this paper, we discuss whisker formation of several Bi-bearing alloys after long-term (12,000 hours), ambient high humidity (25°C/85% RH) storage. Three alloys containing Bi, in addition to SAC 305 (Sn-3.0Ag-0.5Cu), were considered. These alloys were Violet (Sn-2.25Ag-0.5Cu-6.0Bi), Sunflower (Sn-0.7Cu-7.0Bi), and Senju (Sn-2.0Ag-0.7Cu-3.0Bi). The boards were fabricated with electroless nickel immersion gold (ENIG) and immersion tin (ImmSn) finishes and populated with parts having Cu and Fe42Ni alloy leads and chip parts, with half of assemblies cleaned and half cleaned and contaminated with low levels of NaCl.
 This paper is the third in a series of three in which we share more in-depth characterization of features of interest from the small outline transistor (SOT) inspection. Discussion regarding the role of Bi in the overall stress state of the joint will also be provided.