Christian Schaeffer

Double-sided cooling for high power IGBT modules using flip chip technology

A new technique for the packaging of IGBT modules has been developed. The components are sandwiched between two direct bond copper (DBC) substrates with aluminum nitride. Wire bonds are replaced with flip chip solder bumps, which allows cooling of components on both sides. Microchannel heat sinks are directly integrated in the package to decrease the thermal resistance of the module. Thus, a very compact module with high thermal performance is obtained. A prototype with two insulated gate bipolar transistors (IGBTs) and four diodes associated in parallel was realized and tested. In this paper, the innovative packaging technique is described, and results of thermal tests are presented.

Analytic modeling, optimization, and realization of cooling devices in silicon technology

A novel cooling device fully built in silicon technology is presented. The new concept developed in this work consists of micromachining the bottom side of the circuit wafer in order to embed heat sinking microchannels directly into the silicon material. These microchannels are then sealed, by a direct wafer bonding procedure, with another silicon wafer where microchannels and inlet-outlet nozzles are micromachined too. A cooling fluid (water) is then forced through the array of channel to convey heat outside the chip. Such a configuration presents advantages to provide a significant reduction of the cooler overall dimensions, to reduce the number of the involved materials and to be compatible with integrated circuit fabrication procedures, In this study analytical tools were used in order to get a global evaluation of all the thermal resistances characteristic of such devices. Using these adequate analytic models with appropriate approximations, a global optimization procedure was then applied and led to the definition of he optimum dimensions of the silicon micro heat sink. The realization procedure was then carried out in a clean room environment. First experimental characterization results obtained from the earlier prototypes demonstrated that the thermal properties of this silicon-based cooling device are satisfactory and can be reasonably compared to those of commercially available copper micro heat sinking components.

Silicon heat pipes used as thermal spreaders

An increase in power densities in electronic devices is a direct consequence of their miniaturization and performance improvements. We propose the use of flat miniature heat pipes with micro capillary grooves to spread heat flux across a heat sink. Models of the structure were developed to calculate heat transfer limitations and temperature drops. A brass/water prototype was fabricated to demonstrate the feasibility of heat spreading using this type of heat pipe. Simulation and experimental results obtained with the prototype are described. The dissipated power reached 110 W/cm/sup 2/ without heat transfer limitations. The results are then extended to the design of this type of heat pipe in silicon. Thermal performance was calculated. Simulation, experimental results and the fabrication process are presented.

Integrated single and two-phase micro heat sinks under IGBT chips

Experiments have been performed to assess the feasibility of single and two-phase micro heat exchangers applied to the cooling of insulated gate bipolar transistor (IGBT) power components. After a brief recall of the principal characteristics of such heat exchangers, prototypes that have been built and tested are described. Then, the experimental measurements are compared to the predictions of the thermal and hydraulic performance with water and the inert fluorocarbon liquid (FC72) as coolant fluids.

Integrated micro heat sink for power multichip module

Today, more and more compact converters with high current rates are required. The thermal environment is a key point to meet these requirements: the heat sink must be integrated as close as possible from heat sources. Liquid-cooled microchannel heat sinks are very efficient and well adapted to the cooling of power components. Thus, a high performance micro heat sink was made and tested under a power multichip module. First, the principle of the microchannel heat sink and a three-dimensional approach are presented. Then, the prototype and the results are described. Composed of eight IGBT chips, the prototype has a current rating as high as 1200 A.

Fully integrated gate drive supply Around Power switches

Main power switches such as metal oxide semiconductor field effect transistors or insulated gate bipolar transistors have reached very high performances from an electrical point of view. If their electrical characteristics are getting closer to physical limits, there is still a lot to do to improve their functionalities. The paper presents the monolithic integration of a gate drive power supply with the power switch to be driven. The operating principle is discussed to demonstrate that all needed components for this function can be integrated with the power switch. It is also demonstrated that the solution does not require any main power switch technological process modification-leading to a cost effective solution. Modeling and analysis comments are provided in order to clarify and to present operating principles and possible design constraints. Finally, the realization itself is presented. Prototypes are used to highlight the interest of such function.

Toward Generic Fully Integrated Gate Driver Power Supplies

An original method to power supply gate drivers has been developed. This solution takes advantage of power switches commutations to recharge a storage capacitor, and then to create the necessary floating power supply, useful for many power electronic converters. This low cost solution can be integrated, but it presents disadvantages: the storage capacitor must be adjusted with respect to ON state time duration, and permanent ON state operation is forbidden. Moreover, with the existing solution, low frequency operation is forbidden, because high value storage capacitor would be required. The proposed work presents an innovative solution to allow flexible or even permanent ON state time duration operation of a self-powered MOSFET, using few supplementary elements and non linear voltage regulation techniques. This solution exhibits fairly good efficiency levels (corresponding to a short increase of ON state losses) and presents a high ability for simple implementation and monolithic integration. Added to these new specifities, lower storage capacitor value can be used for this self powered driver power supply, allowing low frequency operation, low storage capacitor value, and high duty cycle operation, leading to a generic and versatile powering solution. This particular innovation also improves the integration of the storage capacitor, in same substrate as the main switch and its self powering circuits

Single- and two-phase heat exchangers for power electronic components

Abstract Experiments were performed to assess the feasibility of single-phase and two-phase micro heat sinks applied to the cooling of power components. After a brief recall of the principal characteristics of a power component (IGBT, Insulated Gate Bipolar Transistor), experimental measurements are described for multichip modules cooled by single-phase or two-phase heat sinks machined in a piece of copper. The former is composed of rectangular microchannels, the second is composed of circular minichannels. Both offer very high cooling capabilities. Then, a comparison of performance is presented.

Heat Pipe Integrated in Direct Bonded Copper (DBC) Technology for Cooling of Power Electronics Packaging

As the power densities of power components continue to grow, thermal issues are becoming extremely important and vital for the product quality. The primary causes of failures in electronic equipment are the excessive temperatures of the critical components, such as semiconductors and transformers. Power systems for space application are usually housed in completely sealed enclosures due to safety reasons. Since the cooling of these systems primarily relies on natural convection, the effective management of the heat removal from a sealed enclosure poses a major thermal-design challenge. In this context heat pipes are very effective heat transfer devices and can be used to raise the thermal conductive path in order to spread a concentrated heat source over a much larger surface area. As a result, the high heat flux at the heat source can be reduced to a much smaller and manageable level that can be dissipated through conventional cooling methods. The objective of this work, presented in this paper is to describe the feasibility of a cooling system with miniature heat pipes embedded in a direct bonded copper structure (DBC). The advantage of this kind of heat pipe is the integration of the electronic component layout directly on the heat pipe itself, which eliminates the existence of a thermal interface between the device and the cooling system

Fully integrated driver power supply for insulated gate transistors

Nowadays, MOSFET and IGBT driver supplies are a great source of interest, mainly for two reasons: the need for high side transistor isolated driver supplies (mid and high power) and massive, low cost, MOSFET applications (home appliance). In order to remove the external floating power supply, necessary to power supply the driver of an insulated gate transistor (especially when its source is floating or at high voltage levels), we purpose to detail, in this article, a solution that integrates, in the same substrate, few supplementary parts, and as consequence, allows to create the necessary floating power supply. The added circuit operational characteristics have already been outlined and a special focus will be made on its full integration. Firstly, the paper recalls how its specific operating mode impacts on the design of its components. Then the technological and electrical compatibilities among all parts, within the main switch, will be outlined. After that, simulation and practical results are shown, according to that with no complex process flow modification, a floating power supply for insulated gate transistor is created (for static and dynamic operations)