Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-01-10
2003-01-07
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S215000, C524S495000, C427S217000, C428S403000, C428S570000
Reexamination Certificate
active
06503964
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an improved method of manufacturing a composite material. More specifically, the present invention relates to a method of manufacturing a molded material, formed from a base matrix loaded with filler material, that results in a completed composition that has high thermally conductivity and reflects electromagnetic interference (EMI). In addition, the present invention relates to passively conducting heat away from heat generating objects by use of thermally conductive composite materials while further shielding the device from EMI.
In industry, there are various parts and components that generate heat during operation. For example, in the electronics and communications industries, it is well known that integrated circuit components generate heat during operation. Various types of electronic device packages containing integrated circuit chips, such as satellite dishes, are such devices that generate heat. Often these devices contain integrated circuit systems with a tightly packed configuration that requires all of the components to be installed in close proximity to one another. These integrated circuit devices, particularly the main processor chips, generate a great deal of heat during operation which must be removed to prevent adverse effects on operation of the system into which the device is installed. For example, the operational section of a satellite dish, containing many integrated circuit components, is highly susceptible to overheating which could destroy the device itself or cause the components within the device to malfunction.
There are a number of prior art methods to cool heat generating components and objects to avoid device failure and overheating, as discussed above. Since the space available within these devices is generally quite limited the heat must be conducted away from the heat-generating component for dissipation at the periphery of the device. In these cases, a heat-conducting device is commonly placed into communication with the heat generating surface at one end and a heat sink at the other to dissipate the heat therefrom. For example, heat pipes which are typically constructed from a metal casing that is charged with a conductive gas and serves primarily as a conductor with little heat-dissipating characteristic, are frequently used. However, they typically require the inclusion of a heat sink device in the cooling system. A heat sink typically includes a base member with a number of individual cooling members, such as fins, posts or pins, to assist in the dissipation of heat and may be incorporated into the case of the heat generating device. The geometry of the cooling members is designed to improve the amount of surface area of the heat sink that contacts the ambient air for optimal heat dissipation. The use of such fins, posts or other surface area increasing methods, in an optimal geometrical configuration greatly enhances heat dissipation compared to devices with no such additional cooling members, such as a flat heat spreader, such a heat sink may be used individually without the further assistance of a heat pipe.
To further enhance airflow and resultant heat dissipation, fans and devices have been used, either internally or externally. However, these external devices consume power and have numerous moving parts. As a result, heat sink assemblies with active devices are subject to failure and are much less reliable than a device that is solely passive in nature.
It has been discovered that more efficient cooling of electronics can be obtained through the use of passive devices that require no external power source and contain no moving parts. It is very common in the electronics industry to have many electronic devices grouped on a single circuit board, such as a motherboard, modem, or “processor card” such as the Celeron board manufactured by Intel Corporation. For example, video cards, which are capable of processing millions of polygons per second, are also susceptible to overheating and need efficient and effective cooling, as do the CPUs discussed above. Video cards typically have at least one chip thereon that runs extremely hot to necessitate a cooling system designed to operate within small clearances.
In the heat transfer industries, it has been well known to employ metallic materials for thermal conductivity applications, such as heat dissipation for cooling integrated circuit device packages. For these applications, such as device casings operating as heat sinks, the metallic material typically is tooled or machined from bulk metals into the desired configuration. However, such metallic conductive articles are typically very heavy, costly to machine and are susceptible to corrosion. Further, the use of metallic materials commonly creates electromagnetic interference (EMI), which often detracts from the performance of the device on which the heat sink is affixed. Finally, the geometries of machined metallic heat dissipating articles are very limited to the inherent limitations associated with the machining or tooling process. As a result, the requirement of use of metallic materials which are machined into the desired form, place severe limitations on heat sink and heat conductor design particular when it is known that certain geometries, simply by virtue of their design, would realize better efficiency but are not attainable due to the limitations in machining metallic articles. To compensate for these limitations, active cooling, such as by powered fans, must be employed to achieve the requisite cooling to prevent device failure.
It is widely known in the prior art that improving the overall geometry of a heat-dissipating article can greatly enhance the overall performance of the article even if the material employed is the same. Therefore, the need for improved heat sink geometries necessitated an alternative to the machining of bulk metallic materials. To meet this need, attempts have been made in the prior art to provide molded compositions that include conductive filler material therein to provide the necessary thermal conductivity. There compositions may include a polymer base matrixwith a conductive filler loaded therein. The ability to mold a conductive composite enabled the design of more complex part geometries to realize improved performance of the part.
However, a drawback in the thermally conductive molded polymer compositions, loaded with metallic reinforcing materials such as copper flakes, is that they inherently absorb EMI and radio frequency waves. As a result of their absorptive characteristics, these materials effectively operate as antennas, absorbing EMI that could potentially interfere with the operation of the device into which they have been incorporated. Further, attempting to insulate the composition to prevent EMI absorption would also interrupt the thermally conductive pathways and defeat the ability of the composition to transfer heat. As a result, the use of these conductive polymers in devices such as satellite components and receiver equipment is undesirable.
In view of the foregoing, there is a demand for a composite material that is highly thermally conductive and EMI reflective. There is a demand for a passive heat dissipation assembly with no moving parts that can provide heat dissipation without the use of active components. In addition, there is a demand for a composite material that can be molded or cast into complex product geometries. There is also a demand for such a moldable article that exhibits thermal conductivity as close as possible to purely metallic conductive materials while being an effective insulator against EMI absorption.
SUMMARY OF THE INVENTION
The present invention preserves the advantages of prior art thermally conductive plastic compositions namely net-shape moldability and thermal conductivity. In addition, it provides new advantages of EMI reflective properties not found in currently available compositions and overcomes many disadvantages of such currently available compositions.
The invention is
McCullough Kevin A.
Miller James D.
Sagal Mikhail
Smith Lyle James
Barlow Josephs & Holmes, Ltd.
Cool Options, Inc.
Yoon Tae H.
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