Heat exchange – With impeller or conveyor moving exchange material – Mechanical gas pump
Reexamination Certificate
1998-04-02
2002-06-11
Leo, Leonard (Department: 3743)
Heat exchange
With impeller or conveyor moving exchange material
Mechanical gas pump
C165S080300, C165S185000, C174S016300, C257S722000, C257S719000, C361S697000, C361S704000
Reexamination Certificate
active
06401807
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to cooling devices, in particular, heat sinks for integrated circuit chips such as central processing units (CPU).
Cooling of electronic devices has become one of the major limiting factors in the performance of such devices. In particular, the central processing unit in a typical personal computer can generate up to 40 watts of heat in an area of less than 4 square inches. The performance of the chip is dictated to a large extent by its speed and the higher the speed, the more heat that is created. The more heat that is created, the slower Ad the chip runs and the shorter the life span of the chip.
Noise is also a major factor in the electronics area. Especially as electronic systems with CPU's are used more frequently inside the home, the desirability of a quiet system has become more prevalent. A typical method for cooling integrated circuit chips involves one or more air moving devices, e.g. fans, used to circulate cool air through the chip area or an attached heat sink. The more heat that is generated, the more air that has to be circulated. As larger and more rapidly moving fans are installed, the more noise that is generated.
Another aspect of computer systems involves the amount of space taken up by the electronic devices within the system. The tradeoff faced is that as a heat sink has a larger surface area, the more efficiently it will cool an attached device. It is highly desirable to provide a heat sink with a high surface area that can take up less space within a computer system and require a less powerful fan for circulating air therethrough to achieve the desired cooling.
Weight is also an issue with computer components. An extruded heat sink is a solid mass of aluminum and in many personal computer systems, in particular, those with an Intel Pentium Pro™ chip, the heat sink exceeds a quarter pound. As these processing chips change location from board mounts to cartridges, the weight becomes even more of a concern. For example, Intel limits the acceptable weight of a heat sink for its latest chip called Klamath to ½ pound (250 grams). This extra weight creates a need for extra mounting force using screws and in many cases extra support beams for the heat sink itself. Without the extra support and mounting force, these heavy heat sinks may dislodge themselves during shipping.
In the manufacture of personal computers, typically multiple fans are used which create noise. Also a heat sink is required for individual chips. The vast majority of these heat sinks are made from extruded aluminum. The aluminum is extruded into a design where thick fins run the length of the extrusion. The extrusion is designed to have a flat plane on the bottom which contacts the semiconductor device. To further increase the surface area of these fins, manufacturers typically “crosscut” through the thick fins in a costly machining process which creates separate pins along the extrusion. Each of these pins has at least four sides of surface area, twice as much as the straight thick fin previous to the crosscut. Extruded aluminum heat sinks face severe limitations. The height of the fin can only be a few times the gap of the distance between the fins because of the extrusion process, and the thickness of the fins is limited by the height because in typical extrusion processes the thickness at the base of the extrusion must be at least ⅕ of the height. Therefore, the higher the fin density for a given area, the shorter the fin height. The highest total surface area achievable for an extruded heat sink with crosscuts in a volume less than ½″ high and 4 sq. inches in area usually tops out at about 25 sq. inches. The amount of fins per inch is limited by the thickness and the height. This limitation on density of fins on an extrusion reduces the efficiency of the heat removal.
To make up for this limitation in density that extrusions have, an extrusion being used for a heat sink goes through many secondary operations after it is extruded. First, in many instances the base of the heat sink is machined for flatness in order to make smooth contact with the heat producing substrate it is attached to. Then the bars of extrusion which are typically 8 feet in length are cut down to a particular size, usually 2 inches for a typical semiconductor. The next step is the crosscutting step. After this, the heat sink is usually stamped in order to form mounting holes and locations and then it is anodized and deburred. In all, making an extrusion is an expensive and lengthy process.
U.S. Pat. No. 5,329,426 (Villani) is an example of a method that may be used to attach such an extrusion directly to a heat generating chip carrier. A spring is used to clip the solid heat sink to a pair of braces supporting the chip carrier package.
As the integrated circuit chips have become faster and hotter, the simple extruded heat sink was not sufficient. Manufacturers have added fans or other air-moving devices to these extruded heat sinks. The fan which generally includes its own housing, is screwed onto the top of the extrusion and forces air through the fins. The fan typically adds about an extra half inch to the total height of the extrusion. Due to the constraints within the typical computer system limiting the total height of the heat dissipation elements along the CPU to about one inch, the extruded heat sink portion is thus limited to a total of ½″ in fin height. To increase the cooling of the CPU, the fan speed has had to be increased to blow more air through the extrusion. The more air passing over a surface, the higher the thermal conductivity because air is pulling away the heat more quickly. Higher air flow is subject to diminishing returns, however, in that doubling the air velocity fails to double the thermal conductivity of the surface. Fans of the 40 mm. style, typically used for CPU heat sinks in a personal computer, spin at speeds as high as 10,000 RPM's. This high speed creates well over 30 dB's of noise. Reducing the fan speed will reduce the noise level, but also reduces the performance of the heat sink.
To overcome some of the limitations of extruded aluminum, some manufacturers have turned their attention to folded fin aluminum. A Taiwanese product made by TUV S.A. and called the CPU Cooler has been seen for sale in the United States. The CPU Cooler uses a strip of folded fin aluminum bonded onto a square thermally conductive base adjacent one edge thereof. On top of the base alongside the folded fin aluminum is a fan for directing air horizontally across the base and through the folded fins. The product recommends the use of thermal tape or thermal grease to adhere the thermally conductive base onto the top of a CPU.
U.S. Pat. No. 5,494,098 (Morosas) describes a heat sink with a fan mounted over folded fin aluminum. The process for making this heat sink involves a number of costly steps including brazing the folded fin to fix it to a solid block of aluminum and milling the top portions of the fixed fins to provide openings into the channels formed by the fins.
SUMMARY OF THE INVENTION
Embodiments of the present invention are directed to using clamping methods to secure folded fin to a thermally conductive plate to make a heat sink assembly and related fan assemblies. A sheet of aluminum or other heat conductive material is folded into a wave-like pattern forming an alternating series of ridges and troughs (grooves). The folded fin may be used for placement directly on a substrate to be cooled or on a separate conductive base plate to form a heat sink assembly. Where openings in the ridges of the folded fin heat sink are desired, a method for making such a folded fin heat sink involves providing a thermally conductive sheet with holes spaced periodically, folding the thermally conductive sheet to form the ridges and grooves such that the holes appear in the tops of the ridges and clamping the folded thermally conductive sheet to a thermally conductive surface.
The heat sink of an
Chapagain Bibek
Favini Peter B.
Wotring Blaine C.
Wyler Gregory T.
Bromberg & Sunstein LLP
Leo Leonard
Silent Systems, Inc.
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