Fred Barlow

Power Conversion With SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

Extending the ZVS Operating Range of Dual Active Bridge High-Power DC-DC Converters

A switching control strategy to extend the soft-switching operating range of the dual active bridge (DAB) dc-dc converter under the zero-voltage-switching (ZVS) operating mode is proposed. The converter topology consists of two active bridges linked by a high-frequency transformer. One drawback of this strategy is that soft-switching is only possible in a restricted converter operating region. A novel pulse width modulation strategy to extend the conventional soft-switching operating mode region and its analysis are presented in this paper. Experimental results are given in order to validate the theoretical analysis and practical feasibility of the proposed strategy.

Development of a SiC JFET-Based Six-Pack Power Module for a Fully Integrated Inverter

In this paper, a fully integrated silicon carbide (SiC)-based six-pack power module is designed and developed. With 1200-V, 100-A module rating, each switching element is composed of four paralleled SiC junction gate field-effect transistors (JFETs) with two antiparallel SiC Schottky barrier diodes. The stability of the module assembly processes is confirmed with 1000 cycles of -40°C to +200°C thermal shock tests with 1.3°C/s temperature change. The static characteristics of the module are evaluated and the results show 55 mΩ on-state resistance of the phase leg at 200°C junction temperature. For switching performances, the experiments demonstrate that while utilizing a 650-V voltage and 60-A current, the module switching loss decreases as the junction temperature increases up to 150°C. The test setup over a large temperature range is also described. Meanwhile, the shoot-through influenced by the SiC JFET internal capacitance as well as package parasitic inductances are discussed. Additionally, a liquid cooled three-phase inverter with 22.9 cm × 22.4 cm × 7.1 cm volume and 3.53-kg weight, based on this power module, is designed and developed for electric vehicle and hybrid electric vehicle applications. A conversion efficiency of 98.5% is achieved at 10 kHz switching frequency at 5 kW output power. The inverter is evaluated with coolant temperature up to 95°C successfully.

An overview to integrated power module design for high power electronics packaging

Abstract In recent years, there has been an explosion in demand for smaller and lighter, more efficient, and less expensive power electronic supplies and converters. There are a number of reasons for this recent necessity, ranging from the need for smaller and cheaper power converters for consumer electronics (such as laptop computers and cellular phones) to the need for highly reliable power electronics for such items as satellite and military craft power systems, which are required to be highly efficient, light in weight, smaller in volume, and low cost. This paper discusses the concept of Integrated Power Modules (IPMs), in which the electronic control circuitry and the high power electronics of the converter are integrated into a single compact standardized module. The advantages and disadvantages of such an approach will be discussed in reference to the current industry standard for power electronics design and packaging. The researchers will then take the readers through the IPM design, including basic circuit topology layout, module fabrication processes, and finally thermal considerations.

Fabrication of microvias for multilayer LTCC substrates

Advances in screen printing and photoimageable paste technologies have allowed low-temperature cofired ceramic (LTCC) circuit densities to continue to increase; however, the size of vias for Z-axis interconnections in multilayer LTCC substrates have been a limiting process constraint. In order to effectively exploit the 50-100-/spl mu/m line/spacing capabilities of advanced screen printing and photoimageable techniques, microvia technologies need to achieve 100 /spl mu/m and under in diameter. Three main steps in fabrication of microvias include via formation, via metallization or via fill, and layer-to-layer alignment. The challenges associated with the processing and equipment for the fabrication of microvias are addressed in this paper. Microvias down to 50 /spl mu/m in diameter with spacings as small as 50 /spl mu/m are achieved in 50-254-/spl mu/m-thick LTCC tape layers through the use of a mechanical punching system, whereas the minimum size of 75-/spl mu/m via/spacing is obtained using a pulse laser-drilling system in the LTCC tape layers with the same thicknesses as those for the punching test. The quality of punched microvias and laser-drilled microvias will be presented as well. Layer-to-layer alignment is crucial to the connection of vias in adjacent LTCC tape layers. Through a stack and tack machine with a three-camera vision system and an adjustable precision stage, less than 25-/spl mu/m layer-to-layer misalignment is achieved across a 114.3/spl times/114.3 mm (4.5/spl times/4.5 in) design area. In a six-layer LTCC test substrate (152/spl times/152/spl times/0.762 mm), microvias of 50, 75, and 100 /spl mu/m in diameter are successfully fabricated without the use of via catch pads. The cross section of fired microvias filled with silver conductor pastes at various locations of this substrate demonstrates a minor layer-to-layer misalignment in both X and Y directions across the substrate.

Power Conversion with SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

18 kW three phase inverter system using hermetically sealed SiC phase-leg power modules

Power electronics play an important role in electricity utilization from generation to end customers. Thus, high-efficiency power electronics help to save energy and conserve energy resources. Research on silicon carbide (SiC) power electronics has shown their better efficiency compared to Si power electronics due to the significant reduction in both conduction and switching losses. Combined with their high-temperature capability, SiC power electronics are more reliable and compact. This paper focuses on the development of such a high efficiency, high temperature inverter based on SiC JFET and diode modules. It involves the work on high temperature packaging (>200 °C), inverter design and prototype development, device characterization, and inverter testing. A SiC inverter prototype with a power rating of 18 kW is developed and demonstrated. When tested at moderate load levels compared to the inverter rating, an efficiency of 98.2% is achieved by the initial prototype without optimization, which is higher than most Si inverters.

Ceramic Interconnect Technology Handbook

Ceramics were among the first materials used as substrates for mass-produced electronics, and they remain an important class of packaging and interconnect material today. Most available information about ceramic electronics is either outdated or focused on their materials science characteristics. The Ceramic Interconnect Technology Handbook goes beyond the traditional approach by first surveying the unique properties of ceramics and then discussing design, processing, fabrication, and integration, as well as packaging and interconnect technologies. Collecting contributions from an outstanding panel of experts, this book offers an up-to-date overview of modern ceramic electronics, from design and material selection to manufacturing and implementation. Beginning with an overview of the development, properties, advantages, and applications of ceramics, coverage spans electrical design, testing, simulation, thermomechanical design, screen printing, multilayer ceramics, photo-defined and photo-imaged films, copper interconnects for ceramic substrates, and integrated passive devices in ceramic substrates. It also offers a detailed review of the surface, thermal, mechanical, and electrical properties of various ceramics as well as the processing of high- and low-temperature cofired ceramic (HTCC and LTCC) substrates. Opening new vistas and avenues of advancement, the Ceramic Interconnect Technology Handbook is the only source for comprehensive discussion and analysis of nearly every facet of ceramic interconnect technology and applications.

Interfacial thermal resistance and temperature dependence of three adhesives for electronic packaging

The thermal resistance and its temperature dependence was measured for three industrial adhesives used for electronic packaging. Measurements were made by the laser-flash method from room temperature to 300/spl deg/C. The samples were in the form of sandwiches consisting of two platelets of silicon carbide-reinforced aluminum (AlSiC) bonded together with the adhesives. The total thermal resistance of the bond (the sum of the bulk thermal resistance of the adhesive and the resistances at the two interfaces) was calculated from the thermal response of the sandwich subjected on one side to a single laser-flash. The total thermal resistance was found to decrease with increasing temperature. The bulk thermal resistance of the adhesive, calculated from its thickness and independently determined thermal conductivity, was found to be relatively independent of temperature. The interfacial resistance at the AlSiC interfaces, depending on the adhesive, ranged from about 60 to 80% of the total resistance decreasing to about 50% of the total interfacial resistance at 300/spl deg/C. For two of the adhesives considered in this study, the interfacial thermal resistances for the AlSiC/adhesive interfaces were found to be considerably higher than those found in an earlier study of Si/adhesive interfaces.

Low cost flex substrates for miniaturized electronic assemblies

Abstract Electronic power converters have been designed, produced, and disseminated to the market in mass quantities utilizing a number of fabrication techniques; ranging from standard printed circuit board (PCB) technologies for low cost applications, to conventional thick film on ceramic, to direct bond copper (DBC) approaches for high power, higher cost applications. Each of these approaches holds a share of the power packaging market, but they all demonstrate a limitation to conventional two dimensional “flat board” strategy. PCBs, thick films, and DBCs are all technologies which restrict, for the most part, circuit and package designs to two dimensional boards. The one potential pathway into the third dimension is through the use of multilayers; an approach, which becomes increasingly difficult with each additional layer added beyond the first, and with the exception of high performance solutions is typically cost prohibitive for the majority of applications. This paper will demonstrate the feasibility and viability of flexible polymer substrates. Flex technology employs industry standard PCB and/or thick film processes, offers the lower cost, higher performance solutions inherent with the majority of polymer plastics, and as a final bonus, essentially frees the designer to more efficiently utilize all three dimensions of space. The researchers have demonstrated the feasibility of this low cost alternative solution through the fabrication and testing of integrated power modules, which utilize flexible polymer substrates in conjunction with both surface mount and bare dice. These DC/DC power converters transform 120 V/240 V inputs to 9 V, 7-W outputs, and illustrate through their unique geometrical design the miniaturization advantages of fully utilizing the three dimensional space offered by flex circuitry.