Synthesis of nanoparticles composed of silver and copper for metal–metal bonding

A metal–metal bonding technique is described that uses nanoparticles composed of silver and copper. Colloid solutions of nanoparticles with an Ag content of 0–100?mol% were prepared by simultaneous reduction of Ag⁺ and Cu²⁺ using hydrazine with polyvinylpyrrolidone and citric acid as stabilisers. The nanoparticles ranged in size from 34 to 149?nm depending on the Ag content. Copper discs were strongly bonded at 400°C for 5?min under 1.2?MPa pressure in hydrogen gas; the maximum shear strength was as high as 23.9?MPa. The dependence of shear strength on the Ag content was explained by a mismatch between the d-spacings of Cu metal and Ag metal.     

Cu@Sn@Ag core–shell particles preform for power device packaging under harsh environments

This paper presents a novel die attach material for power device packaging based on transient liquid phase (TLP) bonding. Through two-step electroless plating, the Cu@Sn@Ag particles were prepared, and realize interconnection with Cu Substrates after being compressed into preform. Due to the large specific surface area of the core–shell particles, the reflow time can be reduced to 15 min at a low temperature of 250 °C under a pressure of 3 MPa to form high-remelting-point intermetallic compounds (IMCs), which can withstand a high temperature of at least 475 °C. Due to the protection of the Ag coating, the Cu@Sn@Ag particles exhibited excellent oxidation resistance, and the bonding process can be carried out in the atmosphere. Then, the service reliability of the bondlines was evaluated in harsh environments, such as high temperature and humidity, high temperature storing, and thermal shock. The average resistivity of the bondlines was increased from 4.6?±?1.4 to 8.5?±?3.8 µΩ cm after being stored at high temperature (85 °C) and high humidity (85% RH) environment for 14 days. After storing at 300 °C for 15 days, the porosity of bondline increased from 6.8 to 10.8%, and the average shear strength decreased from 30.5?±?6.3 to 22.3?±?5.6 MPa. After thermal shock between ? 40 and 125 °C for 500 cycles, the bonding rate decreased from 99.9 to 84.2%. Moreover, the short-circuit time of electrochemical migration under 60 V voltage was extended to 145 s. The bondline based on the novel core–shell particles exhibited excellent performance as a die attach material under harsh environments.

     

Solidification and interfacial interactions in gold–tin system during eutectic or thermo-compression bonding for 200 mm MEMS wafer level hermetic packaging

In this work, Au–Sn eutectic bonding and Au–Sn thermo-compression bonding are studied for applications in hermetic packaging at wafer level. Eutectic bonding experiments were performed under vacuum or pure nitrogen at temperatures between 300 and 350 °C while thermo-compression bonding experiments were performed under vacuum at 270 °C. During these experiments, the solidification of electrodeposited Au–Sn alloy as well as the interaction of this alloy with W₂N layers are studied. Some supplementary specific brazing experiments were performed using commercial sheets of eutectic Au–Sn alloy in order to understand the mechanisms of interactions between the Au–Sn alloy and the W₂N layer and of solidification of the Au–Sn eutectic alloy. The melting and solidification process of eutectic Au–Sn alloy were studied by differential scanning calorimetry under different geometrical configurations such as commercial eutectic Au–Sn sheets alone, brazing joints performed by commercial eutectic Au–Sn alloy and samples made by thermo-compression bonding. Bonded wafers with good mechanical properties were characterized by cross-section scanning electron microscopy using energy dispersive X-ray mode. Some samples were characterized by transmission electron microscopy. The mechanical strength of the seal was checked by shear tests.     

Future challenges for MOVPE – an industrial perspective

This paper attempts to predict where the future challenges lie for MOVPE from an industrial perspective. These key challenges include the need to provide ever-increasing capacity and ever-reducing costs, the need to cope with increasing complexity and the tightening of tolerances, the need for device-level qualification, the shortening of product development cycles and the need to address environmental sustainability and recycling issues. The paper identifies two themes that the author believes are crucial to the resolution of these key challenges. The themes are those of modeling and simulation and monitoring and control.     

An alternative method for manufacturing high-strength CP Ti–SiC composites by accumulative roll bonding process

For the first time, the accumulative roll bonding (ARB) process was used as an effective alternative method for manufacturing Ti–SiC composites and compared with the monolithic ARBed Ti. High-strength monolithic commercially pure titanium (CP Ti) and CP Ti–SiC composites with effective uniform reinforcement distribution were fabricated by this process. The tensile test, Vickers hardness measurements and SEM observations were done for the characterization of materials. A significant increase in yield and tensile strength and a drastic decrease in elongation were observed by applying 8 cycles of ARB process. An unexpectedly slight decrease of yield and tensile strength along with elongation was observed after the sixth ARB cycle for the monolithic sample. It was attributed to the weakening of the bond between the titanium layers in the final cycles. Strength of the composite samples was higher than that of the monolithic sample and did not decrease in the final ARB cycles. This was caused by the significantly improved distribution of SiC particles in the titanium matrix.     

Epos – an instrument for the assessment of the ethical position in software development

Digital technology becomes more powerful, intelligent, pervasive and ubiquitous. Ethical aspects of this development have not yet drawn the appropriate attention of researchers and engineers. This paper presents an instrument that aims at measuring the individual ethical position with regard to the design and development of computer software. The development of the Epos tool was based on two data collections. The data of the first survey (n₁ = 147 participants) were used to select items and to determine the factorial structure of the questionnaire. Results show that the Epos instrument reliably assesses peoples’ ethical opinion with respect to five central components: (1) regulation, (2) data privacy, (3) domain specific knowledge, (4) societal responsibility and (5) company responsibility. In the second survey, we determined the stability of the instruments factor structure by assessing a sample of n₂?=?196 participants. A confirmatory factor analysis (CFA) supported the initial factor structure. Next steps and further implications are discussed regarding the final version of the questionnaire.     

Particle swarm optimization: an alternative in marine propeller optimization?

This article deals with improving and evaluating the performance of two evolutionary algorithm approaches for automated engineering design optimization. Here a marine propeller design with constraints on cavitation nuisance is the intended application. For this purpose, the particle swarm optimization (PSO) algorithm is adapted for multi-objective optimization and constraint handling for use in propeller design. Three PSO algorithms are developed and tested for the optimization of four commercial propeller designs for different ship types. The results are evaluated by interrogating the generation medians and the Pareto front development. The same propellers are also optimized utilizing the well established NSGA-II genetic algorithm to provide benchmark results. The authors' PSO algorithms deliver comparable results to NSGA-II, but converge earlier and enhance the solution in terms of constraints violation.     

Modelling precipitation sequences in power plant steels Part 1 – Kinetic theory

Abstract

The ability of steels to resist creep deformation depends on the presence in the microstructure of carbides and intermetallic compounds which precipitate during tempering or during elevated temperature service. The precipitation occurs in a sequence which leads towards thermodynamic equilibrium. The present paper deals with an extension of the Johnson-Mehl-Avrami theory for overall transformation kinetics. The modification permits the treatment of more than one precipitation reaction occurring simultaneously, afeature which isfound to be essential for representing the reactions observed experimentally in a wide range of secondary hardening steels.     

The success-index: an alternative approach to the h-index for evaluating an individual’s research output

Among the most recent bibliometric indicators for normalizing the differences among fields of science in terms of citation behaviour, Kosmulski (J Informetr 5(3):481?C485, 2011) proposed the NSP (number of successful paper) index. According to the authors, NSP deserves much attention for its great simplicity and immediate meaning??equivalent to those of the h-index??while it has the disadvantage of being prone to manipulation and not very efficient in terms of statistical significance. In the first part of the paper, we introduce the success-index, aimed at reducing the NSP-index??s limitations, although requiring more computing effort. Next, we present a detailed analysis of the success-index from the point of view of its operational properties and a comparison with the h-index??s ones. Particularly interesting is the examination of the success-index scale of measurement, which is much richer than the h-index??s. This makes success-index much more versatile for different types of analysis??e.g., (cross-field) comparisons of the scientific output of (1) individual researchers, (2) researchers with different seniority, (3) research institutions of different size, (4) scientific journals, etc.     

Transparent Raman-enhancing substrates for microbiological monitoring and in situ pollutant detection

Opaque Raman-enhancing substrates made of Ag nanoparticles on incompletely oxidized aluminum templates have been rendered transparent by an ion-drift process to complete the oxidation. The result shows that the transparent substrates exhibit high/uniform surface-enhanced Raman scattering (SERS) capability and good optical transmissivity, allowing for concurrent SERS characterization and high contrast transmission-mode optical imaging of S. aureus bacteria. We also demonstrate that the transparent substrates can used in conjunction with optical fibers as SERS sensors for in situ detection of malachite green down to 10(-9) M.     

Ni–Cu alloy for diffusion bonding cermet/steel in air

Microstructural and mechanical evaluation for joints obtained by static and dynamic diffusion bonding of a 90MnCrV8 high strength steel coated with WC–Co, using a Ni–Cu alloy as interlayer, are shown in the present work. In all joints different reacted zones generated during the bonding process can be distinguished by means of scanning electron microscopy and dispersive X-ray spectrometry. The maximum tensile strength obtained using dynamic diffusion bonding process confirms a very promising technology for industrial applications.     

A fuzzy‐neural approach for output projection in a semiconductor fabrication factory

Abstract

Output projection is a critical task for a semiconductor fabrication factory. There are two steps in output projection: predicting the output time for every job in the factory, and projecting the outputs into each period. For enhancing the effectiveness of output projection, a fuzzy‐neural approach is proposed in this study. Firstly, a fuzzy back propagation network (FBPN) is applied to generate fuzzy‐valued output time forecasts. Then, the fuzzy output projection function is proposed to project the outputs into each period. To evaluate the effectiveness of the proposed methodology and to make comparison with some traditional approaches, production simulation is also applied in this study to generate test data.     

3He in Aerogel – an Inhomogeneously Disordered Unconventional Superfluid

We have examined the superfluidity of ³ He in 98.2% porous silica aerogel with up to 34% ⁴ He at 21.6 bar. The mixture is phase-separated for ⁴ He fractions between 11% and 34%. The ⁴ He-rich, phase preferentially occupies the regions of highest silica density in the aerogel, thus modifying the distribution of the correlated disorder seen by superftuid ³ He. The ³ He T _c increases slightly with ⁴ He content while the superfluid fraction decreases rapidly. This behavior is inconsistent with that of ³ He in a homogeneously scattering medium and is analogous to that of a granular superconductor.     

Possibilities and sustainability of “biomass for power” solutions in the case of a coal-based power utility

This paper investigates the possibilities and the sustainability of “biomass for power” solutions on a real power system. The case example is JP Elektroprivreda BiH d.d.—Sarajevo (EPBiH), a typical conventional coal-based power utility operating in the region of South East Europe. Biomass use is one of the solutions considered in EPBiH as a means of increasing shares of renewable energy sources (RES) in final energy production and reducing CO₂ emissions. This ultimately is a requirement for all conventional coal-based power utilities on track to meet their greenhouse gas (GHG) cut targets by 2050. The paper offers a discussion of possible options as a function of sustainability principles, considering environmental, economic and social aspects of biomass use. In the case of EPBiH, the most beneficial would be waste woody biomass and energy crop co-firing on existing coal-based power plants, as suggested by biomass market analyses and associated technological studies. To assess the sustainability of the different biomass co-firing options, a multicriteria sustainability assessment (MSA) and single criteria analysis (SCA) were used. Four different options were considered, based on different ratios of biomass for co-firing: 0 wt%-reference case, and 5, 7 and 10 wt% of biomass. Both the MSA and the SCA confirmed that the option with the highest share of biomass is the most preferable one for the considered case. In addition to that, the CO₂ parameter proved to be a key sustainability indicator, effecting the most decision making with regard to preference of options from the point of sustainability. Following up on the results of the analyses, the long-term projection of biomass use in EPBiH has shown an increase in biomass utilization of up to 450,000 t/y in 2030 and beyond, with associated CO₂ cuts of up to 395,000 t/y. This resulted in a 4 % CO₂ cut achieved with biomass co-firing, compared to the 1990 CO₂ emission level. It should be noted that the proposed assessment model for biomass use may be applied to any conventional coal-based power utility as an option in contributing to meeting specific CO₂ cut targets, provided that the set of input data is available and reliable.     

Hydrophobic microbeads as an alternative pseudo-affinity adsorbent for recombinant human interferon-α via hydrophobic interactions

Hydrophobic interaction chromatography (HIC) is increasingly used for protein purification, separation and other biochemical applications. The aim of this study was to prepare hydrophobic microbeads and to investigate their recombinant human interferon-α (rHuIFN-α) adsorption capability. For this purpose, we had synthesized functional monomer, N-methacryloyl-l-phenylalanine (MAPA), to provide a hydrophobic functionality to the adsorbent. The poly(2-hydroxyethyl methacrylate-N-methacryloyl-l-phenylalanine) [poly(HEMA–MAPA)] microbeads were prepared by suspension copolymerization. microbeads were characterized using FTIR, swelling behavior, and SEM micrographs. Equilibrium swelling ratio of poly(HEMA–MAPA) and poly(HEMA) microbeads were 53.3% and 69.3%, respectively. The specific surface area and average pore diameters determined by BET apparatus were 17.4 m²/g and 47.3 Å for poly(HEMA) microbeads and 18.7 m²/g and 49.8 Å for poly(HEMA–MAPA) microbeads. Adsorption experiments were performed under different conditions. Maximum rHuIFN-α adsorption capacity was found to be 137.6 ± 6.7 mg/g by using poly(HEMA–MAPA) microbeads with a size range of 150–250 μm and containing 327 μmol MAPA/g microbeads. Compared with poly(HEMA–MAPA) microbeads, nonspecific rHuIFN-α adsorption onto plain poly(HEMA) microbeads was very low, about 4.2 ± 2.3 mg/g. To determine the effects of adsorption conditions on possible conformational changes of rHuIFN-α structure, fluorescence spectrophotometry was employed. Repeated adsorption–elution processes showed that these microbeads are suitable for repeatable rHuIFN-α adsorption.