Integrated microfluidic devices

Forced convective heat transfer across a pin fin micro heat sink

The extremely high rates of heat transfer obtained by employing microchannels makes them an attractive alternative to conventional methods of heat dissipation, especially in applications related to the cooling of microelectronics. A compilation and analysis of the results from investigations on fluid flow and heat transfer in micro- and mini-channels and microtubes in the literature is presented in this review, with a special emphasis on quantitative experimental results and theoretical predictions. Anomalies and deviations from the behavior expected for conventional channels, both in terms of the frictional and heat transfer characteristics, are discussed.

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A Comparative Analysis of Studies on Heat Transfer and Fluid Flow in Microchannels

Apparatus and methods according to the present invention preferably utilize electroosmotic pumps that are capable of generating high pressure and flow without moving mechanical parts and the associated generation of unacceptable electrical and acoustic noise, as well as the associated reduction in reliability. These electroosmotic pumps are preferably fabricated with materials and structures that improve performance, efficiency, and reduce weight and manufacturing cost relative to presently available micropumps. These electroosmotic pumps also preferably allow for recapture of evolved gases and deposited materials, which may provide for long-term closed-loop operation. Apparatus and methods according to the present invention also allow active regulation of the temperature of the device through electrical control of the flow through the pump and can utilize multiple cooling loops to allow independent regulation of the special and temporal characteristics of the device temperature profiles. Novel microchannel structures are also described.

Electroosmotic microchannel cooling system

Analysis of microchannel heat sink performance using nanofluids

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.

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

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

Today, more and more compact converters with high current are required. The thermal environment is a key point to meet these requirements: the heat sink must be integrated as closely as possible to 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, a prototype and results are described. Composed of eight insulated gate bipolar transistor chips, the prototype has a current rating as high as 1200 A.

Integrated micro heat sink for power multichip module

Thermal dissipation in power electronics systems is becoming an extremely important issue with the continuous growth of power density in their components. The primary cause of failure in this equipment is excessive temperatures in the critical components, such as semiconductors and transformers. This problem is particularly important in power electronic systems for space applications. These systems are usually housed in completely sealed enclosures for safety reasons. The effective management of heat removal from a sealed enclosure poses a major thermal-design challenge since the cooling of these systems primarily rely on natural convection. In this context, the presented paper treats the heat pipes as effective heat transfer devices that can be used to raise the thermal conductive path in order to spread a concentrated heat source over a larger surface area. As a result, the high heat flux at the heat source can be reduced to a smaller and manageable level that can be dissipated through conventional cooling methods. The objective of our work is to describe the feasibility of a cooling system with miniature heat pipes embedded in a direct bonded copper (DBC) structure. The advantage of this type of heat pipe is the possibility for implementation of the component layout on the heat pipe itself, which eliminates the existence of a thermal interface between the device and the cooling system

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

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.

C. Schaeffer

Papers

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

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

Integrated micro heat sink for power multichip module

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

Fully integrated gate drive supply Around Power switches