Adane Kassa Solomon

An all SiC MOSFET high performance PV converter cell

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.

Built-in Reliability Design of Highly Integrated Solid-State Power Switches With Metal Bump Interconnects

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 this paper, special effort has been devoted to material selection and geometric shape of the bumps in the design for improving the thermomechanical reliability of a highly integrated bidirectional switch. Results from 3-D 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 thermomechanical 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.

Application driven integrated design of a half-bridge power switch

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.

Thermal design optimization of novel modular power converter assembly enabling higher performance, reliability and availability

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.

Highly integrated low-inductive power switches using double-etched substrates with through-hole viases

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.

Modular power converter integration based on non-conventional power switch assembly and interconnects

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.

High power density, low stray inductance, double sided cooled matrix-converter type switch

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.

Integrated matrix converter switch

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.

Integrated half-bridge switch using 70µm thin devices and hollow interconnects

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.

A highly integrated high-voltage bi-directional switch

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.