Electric power conversion systems – Current conversion – With cooling means
Reexamination Certificate
2003-03-04
2004-01-13
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
With cooling means
C361S145000, C361S147000, C361S689000, C361S069000
Reexamination Certificate
active
06678182
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an electrical bus with a means for dissipating heat from semiconductor components, and more particularly is a module comprising an electrically conductive porous metal heat sink that has semiconductor components attached to a surface thereof, the semiconductor components being directly and metallurgically attached via soldering to the heat sink. The invention also includes the method of manufacturing a porous metal heat sink for an electronic device.
BACKGROUND OF THE INVENTION
Many electronic components generate heat during operation. This characteristic becomes significant in instances in which an electronic device is used to generate, transfer, or convert electric power. An excellent example of this effect, cited in Applicants' related application (referenced above), is the inverter used in electric traction motors. Heavy electric vehicles, including locomotives, road and off-road vehicles, are driven by electrically powered traction motors which turn the wheels or tracks of the vehicle. These traction motors operate on AC power, but the electrical power supplied by the energy source of the vehicle is typically DC. This DC power must therefore be converted to AC power in an inverter. Further, the rotational speed of such traction motors is usually controlled by means of the frequency of the AC power. The electric power generation rectification/inversion/voltage control/frequency control system (hereinafter summarized as power converter) requires the use of multiple semiconductor devices, and integrated circuits to control the semiconductor devices, all of which generate a great deal of heat. Many other electrical applications require the use of semiconductor devices and integrated circuits to control them. They therefore also require some means of dissipating the heat generated.
To dissipate the heat produced in a power converter used in an electric vehicle, current art vehicles use either air-cooling systems or water cooled heat sinks, or both in combination. Similarly, other current art electronics applications require some method of heat dissipation, most often air-cooling. The current art methods of cooling give rise to several problems.
For any device to be air-cooled there must be adequate space around the device for air to flow in sufficient volume to remove the heat. In the specific instance of the power converter for the electric traction motor, since traction motor applications typically utilize three-phase AC power, six power semiconductor switch assemblies and six diodes must be employed. The electrical requirements of the motors require that a capacitor bank be present in the power converter, along with the power semiconductors and their accompanying diodes, sensors, switch driver circuitry, etc. The number of components required therefore mandates a significant space requirement. This space requirement is then further greatly exaggerated by the need for space to accommodate flow of air around the power converter components. This space requirement problem is common to all air-cooled electronic devices.
In direct contradiction to the need for open space for the flow of cooling air is the fact that all electrical devices function best in enclosed, non-ventilated environments. This kind of environment reduces the potential for contaminant buildup. Contaminant buildup can not only impede the desired heat transfer, but may also cause an electrical failure of the device. Therefore air-cooling can directly create a situation detrimental to the function of the electrical device.
Because of the problems caused by air-cooling, some current art devices utilize water-cooling, particularly in high power applications, to provide a more controlled environment. But a water-cooled heat sink system suitable for a power converter is generally not readily available in a vehicle. Thus, utilization of a power converter that is water-cooled leads to the necessity of including a water cooling system in a vehicle that would not otherwise require it. Still more space is therefore required. Moreover, due to the conductive nature of water, it is necessary to dielectrically isolate the power converter components from such a water-cooling system and this, in itself, results in less than satisfactory cooling of the semiconductor switches and diodes.
Further problems created by the use of current art cooling methods, in particular by the size requirements demanded by the current art cooling systems for power converters, are due to the fact that the power converter comprises a large unit contained in a compartment dedicated only to the power converter. This necessitates that lead wires for control and feedback systems must be fairly long, typically anywhere from 2 to 10 feet. Longer wires are by necessity heavier than shorter wires, both in terms of weight and electrical rating. Longer wires significantly increase the potential for distorted signals.
High power electric traction motors suitable for heavy vehicles are usually oil-cooled and such vehicles therefore require an oil-cooling system. Utilizing a dielectric fluid such as oil to cool the power converter allows the heat sink to be an integral part of the circuitry of the power converter. The oil-cooled heat sink can thus serve as an electrical power bus to which heat generating electronic components are directly mounted. The enhanced cooling capability achieved by oil cooling the electrical bus greatly enhances the electrical performance of these electronic components and therefore allows for a very compact, high performance power converter. The same oil-cooling system used to cool the traction motors can be used to cool the power converter. The space requirements are thus considerably less than current art air-cooled and water-cooled systems.
Accordingly, it is an object of the present invention to provide a module in which electronic components are attached to an electrically conductive heat sink in a way that gives rise to significantly reduced space requirements.
It is a further object of the present invention to provide a module in which electronic components are attached to an electrically conductive heat sink in a generally planar assembly, thereby reducing inductance.
It is another object of the present invention to incorporate the electrically conductive heat sink as an active part of the component circuitry.
It is still another object of the present invention to allow the electronic components to be metallurgically bonded to the electrically conductive heat sink.
The requirements of the electrically conductive heat sink, and the objects of the present invention are as follows:
1. The heat sink must comprise a plurality of pathways uniformly distributed throughout so as to allow uniform distribution and passage of the cooling fluid.
2. At least one surface of the heat sink must be made from a thermally and electrically conductive metal that is suitable for metallurgical bonding to the electronic components. Other elements of the heat sink can be constructed from metals offering optimum properties for fabricating an electrically conductive heat sink.
3. There must be a sufficient surface-area-to-volume relationship for the internal pathways to provide for the required convective transfer of heat from the heat sink to the heat exchange fluid.
4. All metallic components of the heat sink must be metallurgically bonded to each other to minimize resistance to conduction of heat and electricity throughout.
5. The bonding surface of the electrically conductive heat sink must be prepared to allow for metallurgical attachment of the electronic components.
SUMMARY OF THE INVENTION
The present invention is a module comprising an electrically conductive heat sink that has semiconductor components attached to the surface thereof, the semiconductor components being directly and metallurgically attached via soldering to one surface of the electrically conductive heat sink, and the method of manufacturing the heat sink with associated electronic components. One example of a
Arnold Kelly W.
Dorsch T. James
Evans Anthony C.
Joseph Craig
The Kline Law Firm
United Defense LP
Vu Bao Q.
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