Solders development and application process for a micro chip-camera

Nowadays, micro components have to fulfill rising optical requirements for different scientific and industrial fields like astronomy, medicine or multimedia. For this purpose, advanced miniaturized chip-cameras are produced for the microsystems engineering market. The assembly and joining technologies play a very important role in the production of these micro components. Several challenges are associated with the joining of chip-cameras. In this study, the application of the soldering technology has been considered in order to face these challenges. Two joining technologies have been investigated: active soldering and transient liquid phase (TLP) bonding. Both soldering processes have shown a big potential for hybrid microsystems joining in previous studies. For both processes, soldering alloys and parameters have been conceived in order to fulfill the joining requirements of the micro camera components. For instance, the joining temperature represents a major challenge because the chip-camera consists of a plastic material, polymethyl methacrylate (PMMA). Therefore, particular attention has been directed to the soldering as well as to the coating temperature. The experimental investigations concerning the solders application through physical vapor deposition (PVD) have been supported by finite element method (FEM) simulations. The analysis of  the temperature distribution in the micro components during the coating process was the focus of  the calculations. Possible undesirable local overheated areas of the chip-camera components can be detected through simulation.

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A case study validation of a knowledge-based approach for the selection of requirements engineering techniques

Requirements engineering (RE) is a critical phase in the software engineering process and plays a vital role in ensuring the overall quality of a software product. Recent research has shown that industry increasingly recognizes the importance of good RE practices and the use of appropriate RE techniques. However, due to the large number of RE techniques, requirements engineers find it challenging to select suitable techniques for a particular project. Unfortunately, technique selection based on personal experience has limitations with regards to the scope, effectiveness and suitability of the RE techniques for the project at hand. In this paper, a Knowledge-based Approach for the Selection of Requirements Engineering Techniques (KASRET) is proposed that helps during RE techniques selection. This approach has three major features. First, a library of requirements techniques was developed which includes detailed knowledge about RE techniques. Second, KASRET integrates advantages of different knowledge representation schemata and reasoning mechanisms. Thus, KASRET provides mechanisms for the management of knowledge about requirements techniques and support for RE process development. Third, as a major decision support mechanism, an objective function evaluates the overall ability and cost of RE techniques, which is helpful for the selection of RE techniques. This paper makes not only a contribution to RE but also to research and application of knowledge management and decision support in process development. A case study using an industrial project shows the support of KASRET for RE techniques selection.

Superior Thermoelectric Performance of Textured Ca3Co4−xO9+δ Ceramic Nanoribbons

Calcium cobaltite Ca₃Co_4−xO_9+δ (CCO) is a promising p-type thermoelectric (TE) material for high-temperature applications in air. The grains of the material exhibit strong anisotropic properties, making texturing and nanostructuring mostly favored to improve thermoelectric performance. On the one hand multitude of interfaces are needed within the bulk material to create reflecting surfaces that can lower the thermal conductivity. On the other hand, low residual porosity is needed to improve the contact between grains and raise the electrical conductivity. In this study, CCO fibers with 100% flat cross sections in a stacked, compact form are electrospun. Then the grains within the nanoribbons in the plane of the fibers are grown. Finally, the nanoribbons are electrospun into a textured ceramic that features simultaneously a high electrical conductivity of 177 S cm⁻¹ and an immensely enhanced Seebeck coefficient of 200 µV K⁻¹ at 1073 K are assembled. The power factor of 4.68 µW cm⁻¹ K⁻² at 1073 K in air surpasses all previous CCO TE performances of nanofiber ceramics by a factor of two. Given the relatively high power factor combined with low thermal conductivity, a relatively large figure-of-merit of 0.3 at 873 K in the air for the textured nanoribbon ceramic is obtained.     

Mitigating Detrimental Effect of Self-Doping Near the Anode in Highly Efficient Organic Solar Cells

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been one of the most established hole transport layers (HTL) in organic solar cells (OSCs) for several decades. However, the presence of PSS⁻ ions is known to deteriorate device performance via a number of mechanisms including diffusion to the HTL-active layer interface and unwanted local chemical reactions. In this study, it is shown that PSS⁻ ions can also result in local p-doping in the high efficiency donor:non-fullerene acceptor blends – resulting in photocurrent loss. To address these issues, a facile and effective approach is reported to improve the OSC performance through a two-component hole transport layer (HTL) consisting of a self-assembled monolayer of 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) and PEDOT:PSS. The power conversion efficiency (PCE) of 17.1% using devices with PEDOT:PSS HTL improved to 17.7% when the PEDOT:PSS/2PACz two-component HTL is used. The improved performance is attributed to the overlaid 2PACz layer preventing the formation of an intermixed p-doped PSS⁻ ion rich region (≈5–10 nm) at the bulk heterojunction-HTL contact interface, resulting in decreased recombination losses and improved stability. Moreover, the 2PACz monolayer is also found to reduce electrical shunts that ultimately yield improved performance in large area devices with PCE enhanced from 12.3% to 13.3% in 1 cm² cells.     

Pseudo-T2 mapping for normalization of T2-weighted prostate MRI

Magnetic Resonance Materials in Physics, Biology and Medicine - Signal intensity normalization is necessary to reduce heterogeneity in T2-weighted (T2W) magnetic resonance imaging (MRI) for...     

Verformungsverhalten nanostrukturierter HPPMS‐Hartstoffschichten

Elastic‐Plastic Deformation Behavior of Nanostructured HPPMS Hard Coatings Nitride hard coatings deposited via HPPMS (High Power Pulsed Magnetron Sputtering) or HiPIMS (High Power Impulse Magnetron Sputtering) are widely used in tribological applications due to their promising wear and corrosion resistance. During the application, the coated tools or components may be exposed to significant mechanical loads. Therefore, investigations on deformation behavior of the coatings under mechanical loading are of great importance. The objective of the present study was a comprehensive investigation on deformation behavior of nitride hard coatings from the coating system M‐Al‐O‐N (M = Cr, V) using nanoindentation und nanoscratch tests. In this regard, both nanoscale multilayer (nanolaminate) and monolayer coatings were investigated. All the coatings were deposited using HPPMS technology. Contrary to the expectations regarding a brittle behavior of ceramic‐like coatings, the results depict a considerable plastic deformation of the investigated hard coatings. Furthermore, in addition to a high strength, the applied coatings show a high crack resistance under mechanical loading.     

An Approach to Synthesize Thick α- and γ-Al2O3 Coatings by High-Speed Physical Vapor Deposition

Crystalline α- and γ-Al₂O₃ exhibit in many applications high wear resistance, chemical resistance, and hot hardness, making them interesting materials for production engineering. To synthesize α-Al₂O₃ with high coating thickness of s ≥ 10 μm, chemical vapor deposition at temperatures T > 1000 °C is well established. However, there are almost no studies dealing with the synthesis of thick α-Al₂O₃ by physical vapor deposition (PVD) at high temperatures T > 700 °C. High-temperature deposition of thick coatings can be realized by means of the dense hollow cathode plasma, combined with the transport function of the plasma gas in high-speed (HS) PVD. Herein, crystalline α- and γ-Al₂O₃ films are deposited on cemented carbides at substrate temperatures T _s ≈ 570 °C and T _s ≈ 780 °C by HS-PVD. These coatings exhibit a thickness up to s = 20 μm. Moreover, phase analysis presents α-phases in coatings synthesized at substrate temperature of T _s ≈ 780 °C with significant higher hardness than films by T _s ≈ 570 °C. These release the potential of HS-PVD to synthesize α-Al₂O₃ coatings with high thickness. Thereby, a higher thickness of these coatings is beneficial for the wear protection of turning and die casting tools.     

The double-edged effects of explanation prompts

Explanation prompts usually foster conceptual understanding. However, it has been claimed within cognitive load theory that prompts can take cognitive load to the upper limit when learning complex contents. Under such circumstances, prompts focusing the learners’ attention on specific aspects (e.g., conceptual aspects such as elaborations on domain principles) might have some costs: Other important aspects (e.g., procedural aspects such as how to calculate) cannot be processed deeply. Thus, we expected that conceptually-oriented explanation prompts would foster the detailedness of explanations, the number of elaborations on domain principles, and conceptual knowledge. In addition, we tested the influence of such prompts on the number of calculations performed during learning and procedural knowledge. We conducted an experiment in which we employed conceptually-oriented explanation prompts in a complex e-learning module on tax law. Tax law university students (N = 40) worked on this e-learning module under two conditions: (a) conceptually-oriented explanation prompts, (b) no prompts. The prompts led to double-edged effects: positive effects on the detailedness of explanations and on the number of elaborations on domain principles, as well as on conceptual knowledge and simultaneously negative effects on the number of calculations performed during learning as well as on procedural knowledge.     

Outsourcing der Informationsverarbeitung im Mittelstand: Test eines multitheoretischen Kausalmodells

In this paper determinants of information systems (IS) outsourcing are deduced from transaction cost economic theory, resource-based theory and power theory. They are summarized in a theoretical framework which is tested using a sample of small and medium sized enterprises (SMEs) in Germany. The results show that internal performance and know-how deficits vis-à-vis external service providers are key determinants that explain why different IS functions are outsourced to varying degrees in SMEs. Moreover, the determinants of IS functions were found to partially differ between IS functions. Revised reprint of an article from WIRTSCHAFTSINFORMATIK 43(4)2001:339–350.