Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for other than internal combustion engine – or...
Reexamination Certificate
1998-04-17
2001-04-24
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for other than internal combustion engine, or...
C277S933000
Reexamination Certificate
active
06220607
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to thermal interfaces. Specifically, the present invention is directed to thermally conductive media ideally suited for systems which cycle over a range of temperatures.
Conventional thermal interface media reduce the temperature gradient between two different surfaces in close proximity with one another. The surfaces are typically mating surfaces. Conventional interface media are positioned in the gaps or voids between the two surfaces so that the thermal resistance is lowered, thereby allowing the heat to flow away from the hotter surface. The efficient flow of heat may be impeded if any gaps or voids remain at the interface surfaces. Therefore, not only must the interface medium be thermally conductive, but it must also compensate for certain manufacturing tolerances inherent in the interface.
Thermal paste is a common interface medium that provides heat transfer as well as conformal properties. A typical thermal paste may contain a mixture of zinc oxide in mineral oil. Thermal conductivity is achieved by peculating oxide particles in a low conductivity oil matrix.
U.S. Pat. No. 5,198,189 to Booth et al. discloses, in pertinent part, a liquid metal matrix thermal paste in which non-reacting thermally conductive particles are dispersed in a metal matrix having a low melting temperature. The particles are silicon, molybdenum, tungsten or other materials which do not react with gallium at temperatures below approximately 100° C. The preferred liquid metals are described as gallium and indium eutectic, gallium and tin eutectic, and gallium, indium and tin ternary eutectic. The liquid metal matrix thermal paste is described as being used for cooling high power dissipation components in conjunction with a conventional fluid cooling system. The paste may be cleaned from surfaces by using metal wool containing tin or copper filaments.
The use of thermally conductive pastes, however, is problematic. The paste must be applied with precision. If applied in incorrect quantities, e.g., if too thick, the heat transfer performance degrades. In addition, unwanted material, such as machining chips, tends to collect in the paste so that even larger gaps are produced, which can also reduce heat transfer performance. This problem is exacerbated by the difficulty of removing the paste without leaving a residue.
Thermally conductive gaskets overcome the problem associated with removing the paste from the interface. U.S. Pat. No. 4,776,602 to Paul E. Gallo discloses a conventional thermally conductive gasket that includes a metallic core with an upper and lower face. The core is fabricated from tin plated stainless or low carbon steel. A thermally conductive expandable graphite material contacts with the upper face. A pair of compressible non-asbestos facing layers are disposed on opposing sides of the core and comprise of clay, rubber, and aramid fibers. Tangs are formed in the core to clinch together all the layers in the device.
U.S. Pat. No. 5,137,283 to Giarusso et al. discloses, in pertinent part, a thermally conductive gasket formed by encapsulating a thermally conductive low melting temperature material in a plastic skin. The low melting temperature material conforms to the shape of the interface so as to completely fill the voids once heated above the aforementioned melting temperature. This provides a gasket which is easily applied and removed from the interface, thereby affording a re-usable gasket.
U.S. Pat. No. 5,459,352 to Layton et al. discloses, in pertinent part, a liquid metal aluminum/copper thermal conductor to provide a path for conducting heat from a chip to a fluid medium. In one embodiment, the thermal conductor is described as being formed from a fibrous metal body coated with a liquid metal alloy. The liquid metal alloy may include gallium, indium, selenium, zinc, or mercury. However, conventional thermal gaskets have limited compressibility necessitating increased thickness to fill voids which reduces the heat transfer qualities of the same.
What is needed, therefore, is a highly conformal thermally conductive medium that is reusable.
SUMMARY OF THE INVENTION
The present invention provides a reusable thermally conductive medium for increasing the thermal transfer at an interface between two surfaces while having increased conformableness to the surfaces. The present invention does so by having a body with a first melting point and encapsulating a portion of the body with a phase-changing material having a second melting point. The first melting point is greater than the second melting point, and the phase-changing material is configured to be in a liquid phase at temperatures above the second melting point and a solid phase at temperatures below the same.
In the liquid phase, an adhesive force is present between the body and the phase-changing material due to capillary attraction. In a first embodiment, the phase-changing material is non-wetting to the two surfaces. This prevents separation of the phase-changing material from the body, and facilitates easy removal of the thermally conductive medium from the two surfaces. A good thermally conductive seal between the two surfaces is ensured by the conformability of the phase-changing material when in the liquid phase. The conformableness of the phase-changing material facilitates a reduction in gas pockets being present between the two surfaces and the thermally conductive medium. To achieve the conformableness the phasechanging material must be heated above the second melting point. Thereafter, improved thermal conductive may result even at temperatures below the second melting point, due to the reduction in gas pockets that has been achieved by phase-changing material conforming to the shape of the two surfaces adjacent to the thermally conductive medium. In a second embodiment, the phase-changing material wets one of the two surfaces. This allows fixedly securing the thermally conductive medium to one of the two surfaces and improves thermal conduction between the thermally conductive medium and the surface which the phase-changing material wets.
In an exemplary embodiment, the body is formed from a thermally conductive material such as a plurality of interwoven metal threads, defining a plurality of interstices therebetween. The phase-changing material is also composed of a metal. A sufficient quantity of the phase-changing material is present in the liquid phase to allow complete filling of the plurality of interstices. In this fashion, most of the gas pockets may be removed from the volume of the interface between the two surfaces. Although any metal may be employed in accordance with this invention, in the exemplary embodiment the body is formed from copper wool, and the phase-changing material is formed from indium which coats the surface of the plurality of metal threads.
An exemplary use of the disclosed invention is discussed in conjunction with an inductively coupled reactor chamber ideally suited for etching processes. The reactor chamber is defined by a side wall and a circular ceiling integrally formed with the side wall. A supply of process gases is in fluid communication with the reactor chamber via feed channels. The ceiling may have any cross-sectional shape desired, e.g., rectangular, arcuate, conical, truncated conical, cylindrical, or any combination of such shapes or curves of rotation. The ceiling includes inner and outer opposed surfaces, with the inner surface facing the reactor chamber. A pedestal is positioned within the chamber, spaced-apart from the inner surface. The pedestal supports a workpiece, typically a semiconductor wafer, during processing.
A temperature control apparatus is in thermal communication with the ceiling and faces the outer major surface. The temperature control apparatus includes a thermally conductive torus having opposed surfaces with a plurality of axial bores extending therebetween, and a cold plate resting against one of the opposed surfaces. A housing is disposed within the central throughway, and a coil an
Kumar Ananda H.
Narendrnath Kadthala R.
Schneider Gerhard M.
Weldon Edwin C.
Applied Materials Inc.
Knight Anthony
Schwing Karlena D.
Townsend and Townsend & Crew
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