Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
  • H01L33/64—Heat extraction or cooling elements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/50—Cooling arrangements
  • F21V29/51—Cooling arrangements using condensation or evaporation of a fluid, e.g. heat pipes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/50—Cooling arrangements
  • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
  • F21V29/83—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks the elements having apertures, ducts or channels, e.g. heat radiation holes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/85—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems characterised by the material
  • F21V29/86—Ceramics or glass
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
  • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
  • F28D15/046—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure characterised by the material or the construction of the capillary structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• the present invention is directed to a heat pipe that transports heat away from heat producing bodies, such as light emitting diodes (LEDs).
• LEDs light emitting diodes
• LEDs generate heat as well as light and the heat is desirably transported away from the LEDs because elevated LED-junction operating temperatures (e.g., above about 115 0 C) adversely affect light output.
• Heat can be transported away from the LEDs by mounting the LEDs on a substrate (heat sink) of sufficient thermal conductivity and appropriate surface area from which to dissipate the heat.
• substrate heat sink
• conventional metal and ceramic substrates often do not have sufficient thermal conductivity, especially when many LEDs are placed in a small area. Consequently, a supporting substrate with improved thermal conductivity suitable for use with LEDs is desired.
• a heat pipe is a heat transfer device that can transport large quantities of heat, significantly more than conventional metal and ceramic heat sinks, from one heat transfer location on the heat pipe to another heat transfer location on the heat pipe.
• the heat pipe is hollow and sealed closed, and contains a wick and a working fluid. Inside the heat pipe, the working fluid vaporizes at the hotter location and the working fluid vapor condenses at the cooler location. The condensed working fluid is impelled from the cooler location back to the hotter location by the capillary action of the wick.
• Heat pipes can take various shapes, with a flat heat pipe being disclosed in U.S. Patent Application Publication 2007/0295494 (Celsia Technologies Korea).
• This heat pipe includes two spaced-apart flat plates having therebetween a hollow vapor channel between two porous fluid channels that extend between two heat transfer locations.
• the plates are comprised of a board material which has sufficient rigidity that can protect the inner structure, such as aluminum, titanium, plastic, metalized plastic, graphite or other metal material and plastic combinations; preferably, a copper board having a high thermal conductivity can be used.
• the capillary wick is formed with a plane sheet type structure, which can be a synthetic fiber having a porous structure or a woven body manufactured by weaving wires.
• This flat heat pipe has been used to transport heat from LEDs in an LED lamp.
• An object of the present invention is to provide a novel heat pipe made entirely of ceramic that resists corrosion and on which electrical components such as LEDs can be mounted directly.
• a further object of the present invention is to provide a novel heat pipe with a body made of a non-porous ceramic, said body being sealed and having a ceramic wick inside the body that extends between two heat transfer locations spaced apart on an exterior surface of said body, a vapor transport channel inside the body that extends between said two heat transfer locations, and a working fluid that partially fills said vapor transport channel.
• a yet further object of the present invention is to provide a heat pipe where the body and wick together are a seamless monolithic structure made of the same ceramic material.
• Another object of the present invention is to provide a novel method of making this heat pipe that includes providing a body of a non-porous ceramic, providing a ceramic wick and a vapor transport channel inside said body, said wick and vapor transport channel extending between two heat transfer locations spaced apart on an exterior surface of said body, evacuating said body, providing a working fluid inside said body that partially fills the vapor transport channel, and sealing said body closed.
• Yet another object of the present invention is to provide a novel method of making this heat pipe where the body and wick are provided from the same ceramic material and are formed together as a seamless monolithic structure made of the same ceramic material.
• Figure 1 is a pictorial representation of an embodiment of the heat pipe of the present invention showing where LEDs may be located.
• Figure 2 is a cross-section through line II-II of the embodiment of Figure 1.
• Figure 3 is a corresponding cross-section of an alternative embodiment of the heat pipe of the present invention.
• a heat pipe 10 of the present invention includes a hollow sealed body 12 made of a non-porous ceramic, a central vapor transport channel 14 that extends between two heat transfer locations 16, 16' spaced apart on an exterior surface of the body 12, a ceramic wick 18 on the inside wall 7 of the body 12 and surrounding the vapor transport channel 14, the ceramic wick also extending between the two heat transfer locations 16, 16' and a working fluid 20 inside the body 12 that partially fills the vapor transport channel 14.
• a thermal load comprising heat-emitting bodies, such as LEDs 22, may be mounted directly on the ceramic body at one of the heat transfer locations 16' and the other heat transfer location 16 may be exposed to a cooler temperature so that operation of the heat pipe is conventional.
• non-porous ceramic means that the ceramic that forms the body of the heat pipe is sufficiently dense that it is impermeable with respect to the working fluid and vapor contained inside the heat pipe. It does not necessarily mean that the ceramic is 100% dense, i.e., has no pores.
• the wick 18 is porous and integral with the body 12, and formed in situ. That is, the body 12 and wick 18 together are a seamless monolithic structure made of the same ceramic material with the wick being formed inside the body when the body is formed. Alternatively, the wick can be formed outside the body and inserted into a hollow interior space in the body before it is sealed closed.
• the wick desirably is made entirely of porous ceramic with plural interconnected pores that generate a capillary action within the wick.
• the vapor transport channel 14 extends between the two heat transfer locations 16, 16' so that in operation the vaporized working fluid (vaporized by the heat from the LEDs 22 at heat transfer location 16') moves through the vapor channel to heat transfer location 16 where the vapor condenses.
• a continuous vapor transport channel be maintained through the heat pipe between the thermal load and the condensation zone(s) in order to allow vapor to move freely between the two regions.
• the pressure gradient inside the heat pipe impels the vapor from the 'hot spot' toward other locations where condensation can occur at a slightly lower temperature.
• the form of the open space is not limited to any particular geometry.
• Preferred vapor transport channel configurations include the single, central channel 14 as shown in Figure 2 or a series of smaller channels 25 spaced throughout the porous wick as shown in Figure 3. Although the vapor transport channels in the embodiments shown in Figures 2 and 3 extend linearly through the body, they need not run in a straight line. Curved or meandering channels are permitted provided that the vapor transport function is maintained.
• the wick 18 conveys the condensate back to the heat transfer location 16' by capillary action and the cycle is repeated.
• the working fluid 20 only partially fills the vapor transport channel(s) inside the heat pipe so there is open space for vapor transport between the heat transfer locations.
• the interior of the heat pipe preferably is evacuated before the working fluid is introduced in order to maximize the efficiency of the heat transfer as residual gas inside the heat pipe will interfere with the vapor transport within the device.
• Preferred working fluids include water, alcohols (e.g., methanol), ammonia and freons. The choice of working fluid will depend on the useful temperature range, environmental compatibility, and cost.
• the wick 18 is made entirely of a porous ceramic that is directly on an interior wall 7 of the body 12 and surrounds a single, central vapor transport channel 14.
• the porous ceramic has plural interconnected pores that extend continuously between the two heat transfer locations to provide a wicking action for moving the working fluid between the heat transfer locations.
• the wick 18' fills the interior of the heat pipe and a series of open vapor transport channels 25 are spaced throughout the ceramic wick and extend between the heat transfer locations.
• interconnected pores also includes elongated capillaries made after formation of the wick as well as pores in the wick material that appear during formation of the wick.
• the interconnected pores must sized and sufficiently interconnected such that the working fluid can be transferred by capillary action, i.e., 'wicked' from the condensate zone(s) to the region where the thermal load exists.
• the capillary action in combination with the vapor transport completes the working cycle of the heat pipe, i.e., heat is removed from the thermal load by vaporizing the working fluid, the heat is then removed from the vapor by condensation at a location remote from the thermal load, and the condensed working fluid is re-supplied to the thermal load region by the capillary action of the wick.
• a ceramic is defined herein as an article having a glazed or unglazed body of crystalline or partly crystalline structure, or of glass, which body is produced from essentially inorganic, non-metallic substances and either is formed from a molten mass which solidifies on cooling, or is formed and simultaneously or subsequently processed by the action of heat applied to the material, e.g., aluminum oxide, aluminum nitride, and silicon dioxide.
• the ceramic is aluminum oxide (alumina).
• the ceramic is a dielectric
• the surface of the body 12 is not electrically conductive so that LEDs and other electrical components can be mounted directly on the body at a heat transfer location and remain electrically isolated. Further, since the body and wick are ceramic and since there are no metal parts, the heat pipe resists corrosion and galvanic reactions associated with dissimilar metals.
• the ceramic heat pipe of the present invention can be manufactured by fabricating the body from a hollow circuit board made of an appropriate ceramic (e.g., glass or alumina).
• the body may be preformed from a green ceramic using conventional ceramic techniques, such as injection molding, extrusion, dry pressing, or slip casting.
• the body 12 also may be formed of ceramic parts that are joined together, as shown in Figure 3, with a suitable adhesive, e.g., a glass frit.
• the porous wick may be formed in situ inside the body or by inserting the porous wick inside the hollow interior of the body. After evacuating the interior of the heat pipe body and introduction of the working fluid, the body is sealed closed conventionally.
• the preferred method of forming the porous wick is an in situ sol-gel process.
• a sol-gel process uses organic precursors, which are first formed into a gel and then pyrolyzed or decomposed at high temperatures to form a porous ceramic material.
• the interior walls of the hollow interior of the body are coated with the organic gel precursor that is pyrolyzed to form the porous wick structure.
• the entire part is then fired to form a monolithic structure made up of the outer ceramic body that is dense and impermeable and the inner ceramic wick that is porous (this is shown in Figure 2) with interconnected pores that extend between the two heat transfer locations.
• Another method is to insert plural ceramic spheres into the hollow interior of the ceramic body to create a packed bed.
• the spheres are then fused together to the inner walls of the hollow interior of the body by heating to induce viscous sintering.
• the gaps between the spheres connect to produce the interconnected pores that extend through the wick between the two heat transfer locations.
• a still further method is to extrude the entire vessel from one ceramic material so that the final part contains an inner array of open channels as shown in Figure 3 that extend between the two heat transfer locations.
• This technology has been used to make autocatalyst support structures (introduced by Corning).
• a further step generates the interconnected pores in the ceramic wick.
• the interconnected pores can also be prepared by introducing fugitive material into a green ceramic that is to form the wick.
• a polymer e.g., latex or polystyrene spheres of controlled size
• graphite or other fugitive material
• the body and wick may be made from the same green ceramic material with the fugitive material inserted into the wick part.
• the fugitive material decomposes at an early part of a sintering cycle, prior to necking of the ceramic particles, consequently evolving gas and thus leaving interconnected pores that extend through the wick between the two heat transfer locations.
• the pores are too large and too stable to be eliminated during the final sintering step. This a technique that is known for making porous ceramic structures for high temperature or corrosive filtration.
• a yet further, and perhaps simpler, method is incomplete sintering.
• the body is formed from a first green ceramic part having either a first density or first particle size distribution
• the wick is formed by inserting a second green ceramic part into the hollow interior of the first green ceramic part, where the second green ceramic part has either a second density lower than the first density or second particle size distribution larger than the first particle size distribution.
• the assembly is sintered so that the first green ceramic part is completely sintered and the second green ceramic part is incompletely sintered. This will provide the interconnected pores in the second green ceramic part that extend through the wick between the two heat transfer locations.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Sustainable Development (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Power Engineering (AREA)
• Computer Hardware Design (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
• Cooling Or The Like Of Electrical Apparatus (AREA)
• Porous Artificial Stone Or Porous Ceramic Products (AREA)

Applications Claiming Priority (2)

Publications (2)

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Citations (5)

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• 2008
  • 2008-09-30 US US12/242,051 patent/US20100078151A1/en not_active Abandoned
• 2009
  • 2009-08-25 CN CN2009801384650A patent/CN102171819A/zh active Pending
  • 2009-08-25 KR KR1020117009691A patent/KR20110063844A/ko not_active Application Discontinuation
  • 2009-08-25 WO PCT/US2009/054846 patent/WO2010039358A2/en active Application Filing
  • 2009-08-25 EP EP09818180.3A patent/EP2332172A4/de not_active Withdrawn
  • 2009-08-25 CA CA2738072A patent/CA2738072A1/en not_active Abandoned
  • 2009-08-25 JP JP2011529054A patent/JP2012504339A/ja active Pending

Patent Citations (5)

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