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This study explored the mismatch between the transition from mother tongue to English medium of instruction and teachers’ and students’ use of English. The study adopted a mixed method design. A questionnaire was administered to language as well as non-language teachers. Classroom observations were also conducted with non-language teachers who were supposed to use English as a medium of instruction. A group of students participated in focus group discussion, and another group participated in orally administered questions. Furthermore, grade 10 national exanimation results were analyzed. The findings revealed incongruity between the widely held perceptions about the English medium of instruction (teachers and students consider English as the language of science and technology, a language that facilitates future career development, and a language of success) and teachers' and students' use of English as a medium of instruction. The performance of students who made the transition in grade nine is significantly lower than those of others in almost all examination periods. There is an apparent difference in the performance of students who transitioned from a mother-tongue language to English as the medium of instruction at different levels. Generally, students who made the transition in grade seven were found to be superior in terms of achievement on grade ten national examinations to those who transitioned either in grade five or nine. The study uncovered teachers’ limited use of English as the medium of instruction and a lack of readiness among students to learn in English.

The future development of high-performance power electronics will rely increasingly on system-level integration, where semiconductor devices are co-packaged with other active and passive components (e.g., gate drivers, filter capacitors, and inductors) into a power module. In view of the widespread electrification of pivotal elements of the energy generation and distribution infrastructure (e.g., smart grids, electric aircraft, electric vehicles), modularity is also increasingly gaining importance as a means of enhancing overall system performance and reducing long-term maintenance costs. This paper focuses on the development of a highly integrated three-to-one phase matrix converter for avionic applications. It proposes an integration approach that enhances the volumetric and gravimetric power handling capability, with enhanced electromagnetic and electrothermal performance as compared to established solutions. Maintenance is also simplified by the modular assembly approach.

An application-oriented integration concept for a half-bridge switch assembly has been developed based on the latest generation 70- $\mu\hbox{m}$ -thin insulated gate bipolar transistors and diodes, which are rated at 600 V/200 A. This paper addresses the design and reliability of the assembly, with a fully bondwireless approach using cylindrical copper bumps. Advanced numerical structural simulation techniques are also applied to assess the influence of interconnect characteristics (material, size, and shape) and try to determine an optimum solution for reducing the stress and creep strain development in the solder joint. Preliminary experimental tests of the power module are also carried out at different switching frequency and loads to prove the validity of the proposed solution in terms of electromagnetic performance.

An alternative integration scheme for a half-bridge switch using 70 μm thin Si IGBTs and diodes is presented. This flat switch, which is designed for high-frequency application with high power density, exhibits high strength, high toughness, low parasitic inductance and high thermal conductivity. Such a novel assembly approach is suitable to optimize performance, reliability and availability of the power system in which it is used. The paper focuses on the thermal performance of this assembly at normal and extreme operating conditions, studied by means of FEM thermo-fluidynamic simulations of the module integrated with connectors and liquid cooler, and thermal measurement performed on an early prototype. Improved solutions are also investigated by the FE model.

This paper presents the work on an alternative integration scheme for a half-bridge switch using 70 μm thin Si IGBTs and diodes addressing higher strength, higher toughness and higher thermal conductivity. The switch is totally bond wireless, since bonded wires increase self-heating and introduce further thermomechanical degradation mechanisms. Moreover, this solution is equipped with double side liquid cooling, and plug-in edge connectors both on the driver and load sides, allowing high power density, good accessibility and modularity. Preliminary experimental results show good switching behavior.

The recent research exercises have targeted the transfer of the sandwich package benefits to application bespoke switch design, including flip-chip and device stacking topology [1]. This work presents the development of a highly integrated power switch, based on 70μm thin IGBTs and diodes rated at 600V/200A along with customized connectors to interface quickly the gate driver, the input, and the load side PCBs. This modular system has been designed with the aim to achieve high performance including the modularity and maintainability of power converter that can be worse in a system integrated into a single package.

In this study, enhancing student’s participation in practical analytical chemistry course at Haramaya University with various reasons was conducted. The data were collected from I year chemistry undergraduate students of class size 56 of which 23 were females and 33 were males. The class was arranged in to two groups for laboratory class and the experiment was conducted once per week in analytical laboratory. The research used mainly three kinds of data collection techniques namely questionnaire and laboratory report and demonstration result to gather the required qualitative and quantitative data for improving the participation of first year chemistry students. From the result, it was found that students were interested towards the practical analytical courses on the basis of condition such as, necessity of the chemistry with life, their participation in the laboratory, getting experience from the laboratory and performing the experiment in group. The results of the study support the notion that, students were more interested to a group work rather than individual work since they share idea, read their manual before coming to laboratory which contributed to their own participation in learning practical chemistry courses. The research has also shown that student’s activity through experimental demonstration in group increases student’s participations in the laboratory effectively by achieving better results than using laboratory report writing methods. The findings also revealed that some of the causes of students’ negative attitudes towards learning practical Chemistry were mainly due to problems in preparing a flow chart for the experiments by themselves and lack of exposure to well-equipped laboratory for conducting demonstrations. In view of the findings and conclusions drawn in the study, Chemistry laboratories should be adequately equipped to ensure a smooth running of the practical classes and students should be encouraged to participate on practical chemistry courses and appropriate motivation should be given so that they will develop positive attitude towards the practical sessions.

The future development of high-performance power electronics will rely increasingly on system-level integration, where semiconductor devices are co-packaged with other active and passive components (e.g., gate drivers, filter capacitors, and inductors) into a power module. In view of the widespread electrification of pivotal elements of the energy generation and distribution infrastructure (e.g., smart grids, electric aircraft, electric vehicles), modularity is also increasingly gaining importance as a means of enhancing overall system performance and reducing long-term maintenance costs. This paper focuses on the development of a highly integrated three-to-one phase matrix converter for avionic applications. It proposes an integration approach that enhances the volumetric and gravimetric power handling capability, with enhanced electromagnetic and electrothermal performance as compared to established solutions. Maintenance is also simplified by the modular assembly approach.

This work presents the development of a highly integrated power switch, based on 70μm thin IGBTs and diodes rated at 600 V. The integration relies on advanced ceramic substrate technology, featuring double-etched patterned copper tracks for a fully bond-wire-less double-sided cooling packaging solution; viases are also used in the ceramic substrates for vertical current conduction, which enables the introduction of a ground-plane structure within the switch, with greatly reduced overall values of parasitic inductance. The paper also proposes an outline of system-level integration solutions for ensuring that low-inductance characteristics at switch level are not lost when interconnecting to input filter and load.

A stacked substrate-chip-bump-chip-substrate assembly has been demonstrated in the construction of power switch modules with high power density and good electrical performance. In the present work, special effort has been devoted to material selection and geometric shape of the bumps in the design for improving the thermo-mechanical reliability of a highly integrated bi-directional switch. Results from Three-dimensional finite element simulation indicate that for all design cases the maximum von Mises stresses and creep strain accumulations occur in the solder joints used to join bumps on IGBTs during a realistic mission profile, but occur in the solder joints used to join bumps on DBC substrates during accelerated thermal cycling. The results from both the simulation and the accelerated thermal cycling experiments reveal that selection of Cu/Mo/Cu composite brick bumps in the stacked assembly can significantly improve the thermo-mechanical reliability of both the solder joints and the DBC substrates when compared to Cu cylinder bumps and Cu hollow cylinder bumps reported in previous work. Such results can be attributed to the effective reduction in the extent of mismatch of coefficients of thermal expansion between the different components in the assembly.

This work proposes the design and assembly of a very low inductance half-bridge power switch. It uses latest generation Infineon Technologies® 70μm thin IGBTs and diodes rated at 600 V/175 °C. The integration relies on state-of-the-art ceramic substrate technology, featuring double-etched patterned copper tracks enabling a fully bond-wire-less interconnection scheme; through-hole conducting viases are also present in the ceramic substrates for vertical current conduction, which enables the introduction of a ground-plane structure within the switch, with greatly reduced overall values of parasitic inductance. Moreover, the switch features double-sided cooling. The paper also proposes an outline of system-level integration solutions for ensuring that low-inductance characteristics at switch level are not lost when interconnecting to input filter and load.

Recent studies have pointed out the benefits of using Silicon Carbide (SiC) devices in photo-voltaic power conversion. In Particular, SiC Power MOSFET technology has greatly advanced over the last years and has presently reached sufficient maturity to stimulate a concrete interest in the development of power conversion circuits based entirely on this technology, in view of the clear potential advantages it offers over alternative SiC device technologies (e.g., JFET, BJT). This paper presents a thorough characterization of an all SiC MOSFET based single-phase bi-directional switched neutral-point-clamped (BSNPC) three level inverter, in which, for the first time, SiC Power MOSFETs of different voltage ratings (1200 and 600V) are used. A parametric experimental characterization of the power cell performance is carried out, separating the effects of output power, heat-sink temperature and switching frequency and load variations by means of bespoke heat-sink design. The effect of relying exclusively on the MOSFET body-diode for inductive load current freewheeling is critically assessed against usage of an external SiC Schottky diode. The experimental results are compared with a mixed approach design, where Silicon (Si) devices are used for the lower voltage switches and SiC MOSFETs are kept for the higher voltage ones, deriving a clear indication of the superior possibilities offered by SiC Power MOSFETs for improved efficiency, power density and reliability, key aspects of power electronics technology evolution.

This paper presents the design, assembly, functional test and preliminary technology assessment of highly integrated power switches for matrix converter application. The design is based on a built-in reliability approach and is verified experimentally by both functional and reliability tests. The assembly is based on a fully bond-wire-less double-sided cooling packaging solution, also featuring device stacking. As compared with standard solutions, the proposed integration approach brings along significant advancements in power density, as well as improvements in electro-magnetic and electro-thermal performance, by relying on a fully bond-wire-less double-sided cooled packaging concept.

An application oriented integration concept for half-bridge switch assembly has been developed based on the latest generation Infineon Technologies 70um thin IGBTs and diodes, rated at 200A/600V. This paper addresses the thermo-mechanical simulation to optimize the designed assembly along with three different cylinderical bump shapes for reducing the stress and creep strain development in the solder joints. The simulation results show that effect of the bump shape on thermal performance is negligible, however thin hollow cylinder type can reduce the creep strain accumulation in the solder joints as compared to solid and thick cylinder bumps. A preliminary experimental test was also carried out and the functionality of the assembly was demonstrated.

This paper presents the assembly of a half-bridge switch taking into account the actual current commutations encountered in power converter topologies. So, rather than optimizing the connection between an active switch (e.g., IGBT) and its anti-parallel freewheeling diodes, a novel approach is proposed which favors compact interconnection of the high-side transistor with the low-side diode and vice-versa. The result is a very low-inductive, double-sided cooled power switch, suitable for advanced integration of power conversion equipment.

This paper presents an advanced integration approach for vertical power semiconductor devices. Based on recently demonstrated surface bump technology, it advances previous work by implementing a flip-chip stacking concept, which results in an improved solution for space exploitation, device performance optimization and assembly process simplification. As a case study, the design of a high-voltage bidirectional switch is considered, for which a prototypal assembly is developed and preliminary functional tests are carried out.

In recent years, a bondwire-less integration approach has been demonstrated for vertical power devices [1]. It is based on the use of bumps (e.g. small blocks of copper) to connect the top of vertical power components. This enables a significant improvement in power density and performance compared with standard modules, the major benefits being a dramatic reduction of the stray inductance and the possibility for double-sided cooling. The approach of [1] was extended to stacked device integration in [2], which proposed a prototypal half-bridge switch design. In this paper, an approach is presented which advances the previous work by implementing a front-to-front device stacking concept, thus resulting in an improved utilization of space, optimized device performance and a more simplified assembly process. As a case study, the design and implementation of a high-voltage bi-directional switch is considered, and upon which preliminary functional tests are carried out.

This paper presents an original modular plug-in-type assembly approach for a single-phase inverter. The main focus here is, indicatively, on the power range 1–20 kW, but the methodology can be transferred to higher power levels too. At the core of the inverter lies a power-dense double-sided-cooled half-bridge power switch architecture with integrated cooler, which is interconnected to filter elements, gate driver, and control circuitry by means of compact flat connectors. The integration exercise targets, on the one hand, the optimization of the power switch performance and reliability, as well as the reduction of circuit parasitic elements; on the other, the production of a system compatible with maintenance and repairing, featuring minimized impact of single component failure on the system maintenance and repair cost, and, thus, on its availability. Preliminary experimental tests demonstrate the nominal functionality of the inverter.