Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-05-10
2002-10-15
Thompson, Gregory (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C165S086000, C165S185000, C174S016300, C257S722000, C361S709000, C361S690000
Reexamination Certificate
active
06466444
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to heat sinks and, more particularly, to heat sinks or cooling devices for cooling down an electronic device. More specifically, although not necessarily solely, the present invention relates to a heat sink for a microprocessor or a central processing unit (CPU) and, more particularly, to a very high speed CPU device.
BACKGROUND OF THE INVENTION
Heat sinks are generally used to transfer heat away from a device in order to prevent overheating of the device which may result in instantaneous or premature failure of the device. In the past, heat sinks are mainly important for power devices, such as power amplifiers, rectifiers or other power electronic devices, and are seldomly of concern to the traditional “low-powered” devices such as microprocessors or CPUs for computers, especially micro- or personal computers.
However, with the rapid advancement of microelectronics in the last decades coupled with the rush by component manufacturers to compete by squeezing an ever increasing number of circuitries on a single IC chip, integrated circuits (IC), and particularly microprocessors or CPUs, become more and more highly integrated with the separation between adjacent circuitries within a single IC chip becoming less and less. Such a rush for an ever higher integration density of circuitries on a single chip is especially phenomenal among microprocessor manufacturers who are under constant pressure to provide an increased number of features, and therefore component circuitries, on a single chip to attract consumers. At the same time, microprocessor manufacturers are also racing to turn out microprocessors having very high operating clock rates. In fact, microprocessors having clock rates of 1.7 GHz are available and the clock rates are still expected to increase further.
However, with the ultra high density of circuit integration together with the high operating clock rates, the heat generated by a single microprocessor becomes an important issue. Appropriate instantaneous cooling must be provided to remove undesirable heat from the microprocessor in order to prevent accumulation of the undesirable heat and to ensure that the microprocessor works below the maximum permissible temperature. Adequate cooling is necessary to ensure device reliability as well as protecting the device from sudden or premature failure or interruption. Metallic heat sinks which are thermally coupled to a microprocessor are usually used to dissipated the undesirable heat from the microprocessors.
Conventional heat sinks are either of the integral or the non-integral type. The non-integral type of heat sinks consists primarily of a number of discrete components which are assembled together by, for example, welding, fastening or riveting to form a complete heat sink. Such heat sinks are inefficient or unreliable because of the imperfect junction between the discrete components. Heat sinks of the integral type are usually formed and manufactured from a billet by either hot extrusion, forging, die casting, cutting or milling. Among these methods, the minimum thickness of heat dissipating fins is said to be about 1.5 mm for heat sinks formed by milling. The lower limit for all practical purposes of the gaps between adjacent fins is said to be about 2 mm while the height of the fins cannot exceed 10 times the gap. With these practical limitations, milled heat sinks are not suitable for use with state-of-the-art microprocessors. On the other hand, heat sinks formed by cutting and die casting have such poor production efficiency that it is not economically feasible to adopt them in large-scale industrial production. While heat sinks made by hot extrusion are relatively inexpensive, it is however well known that the thickness and pitch of the fins are inherently limited such that the heat dissipating characteristics of such heat sinks are unsatisfactory.
In general, the performance of a solid state heat sink is measured by the heat dissipation area which can be provided in a given envelope volume as well as the efficiency or easiness of the flow of cooling air across the heat dissipating members. The heat dissipating area per unit volume can be increased by reducing the thickness of the heat dissipating members while the easiness of flow of cooling air across the heat dissipating members can be improved by careful arrangement or alignment of the heat dissipating members in order to reduce the resistance to the flow of cooling air. Hence, it is desirable to provide improved solid state heat sinks having an increased heat dissipation area per given envelope volume of the heat sink with heat dissipation members arranged in a manner which will be less resistant to the flow of cooling air across the heat dissipation members.
A usual approach to increase the flow of cooling air across the heat dissipating members of a heat sink is by using electric fans which are mounted adjacent to a microprocessor to cause forced convection of cooling air streams. While an electric fan is sometimes effective to increase the thermal dissipating rate, over-reliance on an electric fan can be dangerous as an electric fan is known to be noisy and have a limited operation life and reliability. Any interruption of the fan may cause interruption or damage to the microprocessor which can be annoying and is undesirable. Furthermore, the use of an electric fan also increases the power requirements of the computer as a whole and is undesirable for lap-top or pocket computers. Hence, a highly efficient heat sink particularly suitable for microprocessors which will reduce, obviate or even eliminate the reliance on electric fans to ensure adequate heat dissipation is highly desirable. Accordingly, it is desirable to provide a highly efficient solid state heat sink so that sufficient heat dissipation from a high speed microprocessor can be achieved through the heat sink without relying on an electric fan, or alternatively, an electric fan is only used as a standby cooling device or for contingence only.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide a heat sink with an enhanced heat dissipation capability. In general, the preferred heat sink will have an enhanced heat dissipation area per given envelope volume and the heat dissipation members are arranged in a manner which are less resistant to the flow of cooling air. It is also an object of the present invention to provide a heat sink having highly efficient heat dissipation characteristics by obviating the drawbacks associated with non-integrally formed heat sinks. It is another object of the present invention to provide an integrally formed heat sink made by cold forging an appropriate heat conducting material which provides a very satisfactory heat dissipation characteristic. It is a further object of the present invention to provide a heat sink formed of a preferred alloy which demonstrates improved thermal dissipation characteristics after subjecting to formation by a cold forging process.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a heat sink including a base portion, said base portion includes a first surface for thermally coupling said heat sink with an electronic device, and a second surface on which a first and a second group of heat dissipating members are integrally formed and extend upwardly therefrom; said first group of heat dissipation members includes a plurality of fin-shaped members each having main heat dissipation surfaces surrounded by thin peripheral edges including a top edge, an inside edge and an outside edge, said thin peripheral top edges generally extend from the interior of said base portion towards the outside periphery of said base portion, said main heat dissipation surfaces on adjacent heat dissipation members are substantially opposing to each other, and said second group of heat dissipation members are disposed between said first group of heat dissipation members and the centre of said base portion.
Preferably, said second
Cheung Yunk Woon
Thompson Gregory
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