EP1029352A1 - Appareil de gestion thermique a caloduc - Google Patents

Appareil de gestion thermique a caloduc

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Publication number
EP1029352A1
EP1029352A1 EP98957652A EP98957652A EP1029352A1 EP 1029352 A1 EP1029352 A1 EP 1029352A1 EP 98957652 A EP98957652 A EP 98957652A EP 98957652 A EP98957652 A EP 98957652A EP 1029352 A1 EP1029352 A1 EP 1029352A1
Authority
EP
European Patent Office
Prior art keywords
resin
thermal
carbon fiber
heat sink
thermal management
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98957652A
Other languages
German (de)
English (en)
Inventor
Kevin J. Levesque
James D. Miller
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BP Corp North America Inc
Original Assignee
BP Corp North America Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BP Corp North America Inc filed Critical BP Corp North America Inc
Publication of EP1029352A1 publication Critical patent/EP1029352A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • H01L23/3737—Organic materials with or without a thermoconductive filler
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/42—Fillings or auxiliary members in containers or encapsulations selected or arranged to facilitate heating or cooling
    • H01L23/427—Cooling by change of state, e.g. use of heat pipes
    • 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

  • This application claims the benefit of U.S. Provisional Application No. 60/065,418 filed November 13, 1997.
  • This invention relates to a heat pipe apparatus for thermal management, and more particularly to improved thermal management devices comprising a heat pipe and molded heat sink components. Still more particularly, the invention relates to a thermal management apparatus comprising a heat pipe component in thermal communication with a heat sink component wherein the heat sink component comprises a moldable, thermally conductive, filled polymer and preferably an injection moldable, thermally conductive, filled liquid crystal polymer.
  • the thermal management apparatus will be formed as a unitary structure by an insert molding operation.
  • Thermal management has long been the subject of extensive study and research. Early practice relied on the use of heat sinks, including carriers and housings, constructed of metals and alloys selected for their high thermal conductivity, and such devices continue to find wide use. More recent innovations and modifications in materials have included, for example, combinations of metal housings with metal-coated diamond chips or wafers, intended to take advantage of the fact that diamonds have the highest thermal conductivity known.
  • the obvious shortcomings of devices based on diamond particularly including the practical considerations imposed by the limited size of diamond components, as well as high cost, led to the development of metal matrix composites containing diamond particles as a filler to increase thermal conductivity.
  • Other solutions for thermal management problems designed particularly for use with high power density devices include liquid- cooled heat sink structures and chip module housings that rely on liquid nitrogen as the coolant.
  • thermal management devices have been constructed of metal, primarily because of the requirement for excellent heat transfer characteristics in combination with good mechanical properties.
  • CTE coefficient of thermal expansion
  • Matching CTE properties of heat sink materials with those of semiconductors requires the use of dense alloys that are difficult to machine and adds significantly to the weight of the device. Compensating for large differences in CTE is also practiced, but this requires complex designs that are difficult to fabricate.
  • effective dissipation of the heat by convection is a function of surface area. As thermal loads increase it becomes necessary to employ convective heat exchange components with still larger surface areas, again adding weight and impacting design flexibility.
  • Lower density materials have been suggested as metal replacements in thermal management. Particularly attractive are structures comprising carbon or crystalline graphite; both materials are highly thermally conductive, have substantially lower densities than the metals they replace and may be made into structures with a low and even negative CTE. Although light weight graphite structures and carbon-carbon composites are known and accepted for use in heat sink and other thermal management applications, fabricating complex structures from these materials is generally difficult and thus such components may be more costly than those constructed from metal.
  • Thermoplastic resins with good molding properties are readily available as are castable and moldable thermoset resins.
  • resins generally have a high thermal expansion coefficient and are poor conductors of heat. Few are capable of withstanding thermal cycling over a wide range of temperatures without undergoing failure through creep or warping or, in the case of rigid thermoset resins, cracking or similar failure due to thermomechanical stress.
  • Adding fillers to resins as a method for reducing CTE and thereby improving dimensional stability is well known and widely used in the resin formulating arts and may also be found useful for improving thermal conductivity.
  • Paniculate materials including conductive carbon or graphite fillers, spherical particles of various metals, glass or carbon black, non-spherical metal or ceramic particles, stainless steel filaments, aluminum fibers and the like are disclosed in the art and characterized as particularly useful where improved thermal conductivity is desired. However, where resins, containing these fillers have been employed for thermal management purposes only modest improvement has been realized. Commonly, filled thermoset resins used commercially in the electronics industry have thermal conductivities on the order of 2 to 4 W/mK, while injection moldable filled thermoplastic formulations are disclosed with thermal conductivities in the 4 to 9 W/mK range.
  • thermal conductivity of even the most conductive of the filled resin formulations disclosed in the art falls below 10 W/mK, while most commercially-available filled resins comprising such highly conductive fillers as metallic filaments and the like are still much lower in thermal conductivity, generally as low as 2 to 3 W/mK. Filled resins, and particularly filled thermoplastic resins, thus have found limited acceptance and are generally better suited for use where thermal loads are low and where minimizing the size of the heat exchange device is not an important design factor.
  • heat pipes as means for efficiently and rapidly transferring heat away from a heat source such as a microprocessor semiconductor component for further dissipation.
  • a heat pipe will be a hollow metal tube partially filled with a fluid, although alternative forms include heat pipes comprising a solid heat conducting material may also be employed in these structures.
  • the evaporator or heat input zone of the heat pipe will be thermally coupled either directly to the semiconductor structure being cooled or, more commonly, to an interposed heat sink in thermal communication with the device. Heat removed to the condenser or heat dissipation zone of the heat pipe will be dissipated into the surroundings by means of thermally coupled cooling fins or a second heat sink element such as a thermal plate or the like.
  • thermal transfer between the components is important for effective and efficient operation and the metal fins and heat sink elements are therefore generally swaged, soldered or brazed to the heat pipe.
  • the components may be held in mechanical contact by fasteners, clamping devices or the like, and thermally conductive adhesives have also been employed for these purposes.
  • thermal grease has been employed to fill airgaps and provide continuous contact region between the contacting surfaces of the parts. See U.S. 5,598,320.
  • Hinged computing devices have also been disclosed wherein a heat pipe serves as the pintle or hinge pin to transfer heat to the display housing through the gudgeon receiving the pintle. See U.S. 5,621,613.
  • heat pipe panels having internal micro heat pipes by forming channels within a substrate followed by enclosing the channels.
  • heat panels of vapor deposited tungsten or tungsten-rhenium alloy having internal tubular passageways forming micro heat pipes have been disclosed. See U.S. 5,598,632.
  • heat pipes may greatly improve the efficiency of heat removal, it will be understood that the removed heat will then be dissipated, normally into the surroundings, generally requiring the use of heat sinks, such as thermal panels or the like.
  • heat sinks such as thermal panels or the like.
  • these latter components most often have taken the form of a rigid metal structure such as a thermal plate placed in thermal communication with the environment, for example, as an external feature or structural component of the case of portable electronic devices. Requirements imposed by the thermal management device are thus seen to continue to impact and restrict design flexibility, as well as to increase the overall weight of the device.
  • thermal management apparatus comprising heat dissipating means formed of thermally conductive, lower density, readily molded structural materials suitable for use as the case component of an electronic device would be a useful advance in the thermal management art.
  • the improved thermal management apparatus of this invention comprises a heat pipe in thermal communication with a molded, thermally conductive heat sink comprising a filled, thermally- conductive resin.
  • the resin can be thermoplastic or thermoset.
  • thermoplastic resins which are suitable for this invention include liquid crystal polymers (LCPs), aliphatic polyamides, polyphthalamides, acrylonitrile butadiene styrene resins (ABS), and polyaryl ether resins such as PPO and PPS resins.
  • LCPs liquid crystal polymers
  • ABS acrylonitrile butadiene styrene resins
  • PPS polyaryl ether resins
  • Several thermoset resins, including epoxy resins, cyanate resins, thermoset polyesters and phenolic resins are also suitable for use in the present invention.
  • Thermoset resins are particularly useful when transfer molding is used to maufacture the molded heat sink. Other molding techniques such as compression and injection molding can also be used.
  • the heat sink component is injection molded from a thermally- conductive, filled liquid crystal polymer.
  • the heat pipe will be positioned in the molded heat sink to place selected portions of said heat pipe in thermal communication with the heat sink, preferably by insert molding to afford an integral unitary construction having excellent thermal transfer characteristics and without the need for thermal grease or the like.
  • the heat sink component is compression molded from a thermally-conductive, filled epoxy resin.
  • thermally conductive molding compounds particularly well-suited for constructing components having complex designs that are highly desirable and useful in thermal management, particularly for electrical and electronic devices.
  • the thermal management devices of this invention will comprise at least one heat pipe, together with one or more molded thermoplastic or thermoset heat sink components.
  • a heat sink includes any structure to which heat is transferred.
  • thermoplastic and thermoset formulations suitable for these purposes will be thermally conductive, preferably having a thermal conductivity greater than about 15 W/mK and as great as 600 W/mK or more, readily moldable at temperatures that will not cause damage to the heat pipe, and with high melt flow at the molding temperature. Still more preferred will be thermoplastic formulations which may be described as having high tensile modulus values, generally greater than 7 x 10 ⁇ psi, approaching the stiffness and rigidity of lighter metals including magnesium and aluminum.
  • thermoset formulation suitable for use in this invention will comprise a thermoset resin, such as an epoxy resin, filled with discontinuous pitch-based carbon fiber.
  • thermoset resins are well known and described in the art and are characterized by having low viscosity in the uncured state which facilitates wet out of the carbon fibers.
  • thermoplastic formulation suitable for use in the practice of this invention will comprise a liquid crystal polymer (LCP) resin filled with discontinuous pitch-based carbon fiber.
  • LCP liquid crystal polymer
  • LCP resins are well known and described in the art. Those further characterized as thermotropic liquid crystal polymers (LCP) exhibit optical anisotropy when molten, together with a remarkably low melt viscosity at melt fabrication temperatures. When further compounded with high levels of filler, even to levels as great as 75 wt% based on weight of resin and filler, such LCP resins maintain good melt processing character and moldability.
  • LCP thermotropic liquid crystal polymers
  • the preferred LCP resins are aromatic polyesters derived from monomers selected from one or more aromatic dicarboxylic acids and one or more aromatic diols, together with one or more aromatic hydroxycarboxylic acids.
  • aromatic dicarboxylic acids useful in forming the LCP resins useful in the practice of this invention are aromatic dicarboxylic acids such as terephthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-triphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid, diphenylether-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, diphenoxybutane-4,4'-dicarboxylic acid, diphenylethane- 4,4'-dicarboxylic acid, isophthalic acid, diphenyl ether-3,3'-dicarboxylic acid, diphenoxyethane-3,3'- dicarboxylic acid, diphenyle
  • Aromatic diols which may be found useful in forming the LCP resins include hydroquinone, resorcinol, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxytriphenyl, 2,6-naphthalene diol, 4,4'- dihydroxydiphenyl ether, bis(4-hydroxyphenoxy)ethane, 3,3'-dihydroxydiphenyl, 3,3'- dihydroxydiphenyl ether, 1,6-naphthalenediol, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4- hydroxyphenyl)methane, etc., and alkyl, alkoxyl or halogen derivatives of the aforementioned aromatic diols, such as chlorohydroquinone, methylhydroquinone, 1 -butylhydroquinone, phenylhydroquinone, methoxyhydroquinone, phenoxyhydroquinone, 4-chlororesorcinol
  • Aromatic hydroxycarboxylic acids which may be found useful in forming the LCP resins include 4- hydroxybenzoic acid, 3-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 6-hydroxy- 1 -naphthoic acid, etc., and alkyl, alkoxyl or halogen derivatives of the aromatic hydroxycarboxylic acids such as 3- methyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, 2,6-dimethyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoic acid, 3,5-dimethoxy-4-hydroxybenzoic acid, 6-hydroxy-5-methyl- 2-naphthoic acid, 6-hydroxy-5-methoxy-2-naphthoic acid, 3-chloro-4-hydroxybenzoic acid, 2-chloro- 4-hydroxybenzoic acid, 2,3-dichloro-4-hydroxybenzoic acid, 3,5-dichloro-4-hydroxybenzoic acid, 2,5- dichloro-4
  • LCP resins comprising thio-containing analogs of these monomers, e.g. aromatic thiol-carboxylic acids, dithiols and aromatic thiol phenols, as well as the amide analogs derived from hydroxylamines and aromatic diamines, are also known in the art, and these resins may also be found useful in the practice of this invention.
  • the polymers useful in the practice of this invention will be those LCP resins that are anisotropic in the melt. Those skilled in the art will understand that whether the polymer will be anisotropic in the melt will be determined by the particular components selected, the composition ratios in the polymer and the sequence distribution and will thus, select monomers and composition parameters according to experience and following knowledge and practice common in the LCP resin art.
  • the LCP resins especially preferred for use in the practice of this invention will contain at least about 10 mol%, preferably from about 10 to about 90 mol% of repetitive units containing a naphthalene moiety such as, for example, a 6-hydroxy-2-naphthoyl, 2,6-dioxynaphthalene or 2,6- dicarboxynaphthalene moiety or the like.
  • Particularly useful are polyesters containing from about 10- 90 mol%, preferably about 65-85 mol%, more preferably 70-80 mol% of such naphthalene units together with about 90-10 mol%, preferably 20-30 mol% hydroxybenzoic acid-derived units.
  • Polyesters containing from about 30 to about 70 mol%, preferably about 40 to about 60 mol% of hydroxybenzoic acid units, from about 20 to about 30 mol% of 2,6-naphthalene diol-derived units and from about 20 to about 30 mol% terephthalic acid-derived units may also be found useful.
  • the molecular weight of the LCP resins employed in the practice of this invention will be at least approx. 0.1 dl/g, preferably will lie in the range of from about 0.1 to about 10.0 dl/g when dissolved at 60°C. in pentafluorophenol at a concentration of 0.1 wt%.
  • LCP resins and methods for their preparation are well known and widely described in the art, and a number of suitable LCP resins are readily available from commercial sources. Particularly suitable are the LCP resins sold by Amoco Polymers, Inc. as Xydar® LCP resins.
  • Thermally conductive fillers suitable for use in the practice of -this invention include aluminum nitride, boron nitride, alumina, graphite, pyrolytic graphite, aluminum, copper and other metallic particles, diamond, silicon carbide, and preferably, carbon fibers.
  • Carbon fibers suitable for use in the practice of this invention include highly-graphitized carbon fiber having a high thermal conductivity and a low or negative coefficient of thermal expansion produced from pitch.
  • carbon fibers is intended to include graphitized, partially graphitized and ungraphitized carbon reinforcing fibers or a mixture thereof.
  • the preferred carbon fibers will be pitch-based carbon fiber having a thermal conductivity greater than about 600 W/mK, preferably greater than about 900 W/mK, and still more preferably greater than 1000 W/mK. Fiber with even greater thermal conductivities, as high as 1300 W/mK up to the thermal conductivity of single crystal graphite, 1800 W/mK and higher will also be suitable.
  • Thermally- conductive formulations may also be obtained using pitch-based carbon fiber having a thermal conductivity as low as 300 W/mK.
  • Pitch-based carbon fiber with thermal conductivities falling in the range of from 600 W/mK greater than 1100 W/mK, a density of from 2.16 to above 2.2 g/cc and a very high tensile modulus, from 110x10 ⁇ psi to greater than 120x10 ⁇ psi, is readily obtainable from commercial sources.
  • Commercial carbon fiber is ordinarily supplied in the form of continuous carbon fiber tow or yarn comprising a plurality, usually from 1000 to 20,000 or more, of carbon filaments 5 to 20 microns in diameter with the axially-aligned filaments providing strength in the fiber direction of the tow.
  • the fiber may either be chopped tow, generally greater than 1/4" in length, ordinarily from about 1/4" to about 3/4" in length, or a carbon particulate with a length of from about 25 to 1000 microns, preferably from about 50 to about 200 microns obtained by milling or granulating carbon fiber.
  • thermoplastic resins including LCP resin, and carbon fiber may be readily combined and compounded generally by following processes and procedures commonly employed in the resin compounding art.
  • discontinuous carbon fiber may be dry mixed or similarly combined with the dry resin in any convenient form using any suitable, conventional mixing means and then fed to a compounding extruder, thereby producing a filled extrudate which may be chopped for use in further fabrication steps.
  • thermoplastic resins together with the requisite quantity of carbon fiber in the form of continuous carbon fiber tow may be fed to a single screw extruder and extruded as a strand or pultruded, chopped to form pellets and collected.
  • Thermoset resins and carbon fiber may be readily combined and compounded by dry blending or compounded by way of mixers, extruders, stirrers, roll-mills, and impregnation devices such as prepreg machines. In addition, dipping, spraying or other coating processes may also be used.
  • the fiber damage and breakage will be minimized and the articles will then contain substantially greater length fibers, ranging from 100 microns to as great as 1/4", i.e., the original length of the chopped tow fiber, with a correspondingly higher aspect ratio, generally above about 10.
  • the filled resin formulations useful in the practice of the invention will comprise from about 20 to about 80 wt%, preferably from about 45 to about 80 wt% and still more preferably from about 60 to about 75 wt% carbon fiber and, correspondingly, from about 80 to about 20 wt%, more preferably from about 55 to about 20 wt% and most preferred from about 40 to about 25 wt%resin.
  • the formulations may further include such plasticizers and processing aids, as well as thermal stabilizers, oxidation inhibitors, flame retardants, additional fillers including reinforcing fillers and fiber, dyes, pigments and the like as are conventionally employed in the compounding arts for use with such molding resins. It will be readily recognized that the utility of the filled molding compounds of this invention lies in the substantial thermal conductivity exhibited by the material. These additional components, as well as the amounts employed, will thus be selected to avoid or at least minimize any reduction in the thermal conductivity of the formulation.
  • the filled resin will preferably be injection molded with the heat pipe using an insert molding operation to provide a unitary structure.
  • Insert molding processes typically include providing an insert within the mold and injecting the plastic material about the insert or desired portions of the insert to complete the component.
  • a heat pipe is inserted within the mold and the filled LCP resin is then injected to surround the desired portion of the heat pipe, filling the mold to form the heat sink.
  • the filled LCP resin upon cooling, forms a molded heat sink component having a near interference fit at all points of contact with the surface of the heat pipe thereby affording excellent heat transfer between the components.
  • the heat pipe is subject to being damaged when subjected to high temperatures or pressures.
  • Heat pipes are intended to operate in particular environments and within a particular range of temperatures depending in part upon the working fluid, the materials of construction and the design.
  • the end seal of heat pipe may be designed to rupture when subjected to temperatures significantly above the design upper limit. Further, subjecting a heat pipe to high external pressure or other severe mechanical stress may cause the pipe to bend or distort and become inoperable.
  • Highly filled polymers are generally difficult to injection mold and form a viscous melt that flows with difficulty, requiring high injection pressures together with stock temperatures well above the polymer melt temperature in order to fill the mold cavity.
  • Filled LCP resins such as those employed in the practice of this invention generally will have a low melt viscosity, and will permit molding using relatively low melt temperatures in the range 400-700° F (200-370° C), well within the design limit for many heat pipes. Moreover, excessive injection pressures are not required to fill the mold thereby avoiding damage to the heat pipe through mechanical stress.
  • thermoformable any of a variety of conventional molding equipment and processes adaptable for use in insert molding operations may be employed to mold the filled LCP resin with the heat pipe to form unitary thermal management devices according to the invention.
  • thermoplastic resins other than LCP resins are generally known in the art, and such resins, when filled with high modulus carbon fiber to provide thermally conductive resins that are injection moldable, may also be found suitable for the purposes of this invention.
  • aliphatic polyamides including those widely available commercially such as nylon 6, nylon 6,6, nylon 4,6, nylon 11 and the like; polyphthalamides, including the commercially available polymers of one or more aliphatic diamines such as hexamethylene diamine, 2- methylpentamethylene diamine and the like with terephthalic acid compounds as well as copolymers thereof with additional dicarboxylic acid compounds such as isophthalic acid, adipic acid, naphthalene dicarboxylic acid and the like; polyarylate resins including polyethylene terephthalate (PET) resins, polybutylene terephthalate (PBT) resins and the like; arylene polycarbonate resins including poly(bisphenol A carbonate); the well known polyaryl ether resins such as PPO resins, including the thioether analogs thereof such as PPS resins and the like and the corresponding sulfone- and ketone- linked polyaryl ethers such as polyether sulfones
  • thermoplastics when filled with thermally conductive fillers particularly including carbon fiber as described herein above, may be suitably thermally-conductive for many thermal management applications.
  • thermally conductive fillers particularly including carbon fiber as described herein above, may be suitably thermally-conductive for many thermal management applications.
  • it is necessary to employ a high level of carbon fiber loading generally at least as great as 45 wt%, preferably from 50 to 80 wt%.
  • most such thermoplastic materials may become quite difficult to mold, requiring pressures and elevated temperatures not as well suited for insert molding operations using heat and pressure sensitive inserts such as heat pipes or the like.
  • thermoset resins are also known and many are used commercially as thermally conductive potting, encapsulating, adhesive and coating materials as well as sheet molding compounds, bulk molding compounds or the like, particularly for thermal management in electronic applications.
  • Conventional thermoset resins including epoxy resins, cyanate resins, novolacs, resoles and similar thermosetting phenolic resins, thermoset polyesters, and the like may usefully be combined with chopped carbon fiber tow or milled or granulated carbon fiber as described herein above to provide thermoset molding resins and materials with thermal conductivity suitable for use in thermal management devices.
  • Such formulations may be formed and fabricated by conventional means, ordinarily by use of compression molding or transfer molding processes, or by use of a B- staged resin composition in a thermoforming step or the like.
  • filled resin articles may be produced with high thermal conductivities, from 2-5 W/mK to as high as 80-100 W/mK or more depending upon the level of filler employed, together with the dimensional stability at elevated temperatures that generally is recognized to be characteristic of most thermoset materials.
  • Filled elastomers that may be thermoformed and cured to provide tough, flexible parts are also known in the art, and these also may be made thermally conductive through use of suitable fillers.
  • Performance Products with published specifications including a tensile modulus of about 130x10" psi, a density of 2.21 g/cc, and a thermal conductivity of 1100 W/mK.
  • P-120 Carbon fiber obtained as Thornel® carbon fiber P-120 from Amoco Polymers, Inc. with published specifications including a tensile modulus of 120xl0 6 psi, a density of 2.17 g/cc, and a thermal conductivity of 900 W/mK.
  • E600X Carbon fiber obtained as Thornel® carbon fiber E-600X from Amoco Polymers, Inc. with published specifications including a tensile modulus of 120x10 ⁇ psi, a density of about 2.14 g/cc, and a thermal conductivity of 600 W/mK.
  • Radel A Polyether sulfone resin obtained as Radel® A3800 polyaryl ether sulfone from
  • PPA-1 Polyphfhalamide resin obtained as Amodel® polyphthalamide resin from Amoco Polymers, Inc.
  • LCP Liquid crystal polymer obtained as Xydar® SRT 900 resin from Amoco Polymers
  • Thermal conductivities were obtained from measurement of power/heat input and temperature differentials along multiple paths and determination of cross-sectional heat flow under steady-state conditions. Calibration of the device was made using aluminum or copper panels of known thermal conductivity. Thermal conductivity is calculated using the Fourier Conduction Law
  • Example 1 Chopped K-l 100 carbon fiber tow with a nominal length of 1/4" was dry mixed with Xydar LCP resin pellets and extrusion compounded and chopped to provide pellets of filled resin containing 45 wt% target levels of carbon fiber. Test specimens (6"x6"xl/16") were prepared by injection molding the dried resin pellets using a HPM 75 ton injection molding machine. Properties are summarized in Table I.
  • Example 2-5 The procedures of Example 1 were substantially followed in providing a series of filled Xydar resins at levels of 10, 45 and 60 wt% carbon fiber. The pellets were injection molded as in Example 1 to provide flat panels and 4"x4"xl/8" test specimens. Thermal conductivities are summarized in the following Table I.
  • Fiber Content nominal wt% fiber. It will be apparent that formulations comprising less than about 20 wt% carbon fiber are lacking in thermal conductivity. Although there is some variation, the filled materials may be molded to be anisotropic with respect to thermal properties, or substantially isotropic in the plane of the molded article. It appears that for most systems, there is some fiber alignment along the fiber plane, with the greater degree of alignment occurring most often in the flow direction. However, the properties normal to the flow plane indicate that little three-dimensional fiber orientation occurs for most injection moldings.
  • compositions according to the invention may also be manufactured using other thermoplastic resins to provide thermally-conductive parts.
  • Examples 6 and 7 Continuous K-1100X carbon fiber was compounded with Radel polyether sulfone by feeding continuous fiber together with the polysulfone resin to a Killion 1.5" single screw extruder, extruding the compounded resin into strand, and chopping the strand to form filled polysulfone pellets. The feed rates were controlled to provide strand with 18 wt% and with 33 wt% target levels of carbon fiber. The pellets were then dried and compression molded to provide 4" by 4" by 1/8" coupons for use as test specimens. Properties are summarized in Table II.
  • Example 8 Pultruded rod was prepared from nylon 6,6 resin by feeding the resin and continuous
  • Kl lOOx carbon fiber to the extruder at a feed rate controlled to provide rod having 60 wt% target level of carbon fiber.
  • the pultruded rod was chopped to give 1/2" pellets.
  • Test plaques were injection molded from dried pellets using an HPM 75 ton injection molding machine. Properties are summarized in Table II.
  • Examples 9 10 and 11 Chopped E-600X carbon fiber tow with a nominal length of 1/4" was dry mixed with PPA-1 resin pellets and extrusion compounded and chopped to provide pellets of filled resin containing 10, 50 and 70 wt% target levels of carbon fiber. Test specimens were prepared by injection molding the dried resin pellets as previously described. Properties are summarized in Table II. Table II
  • Fiber content 2 (wt%) 18 33 (60) 10 (9.6) 50 (44) 70
  • compositions according to the invention may also be compression molded to provide thermally- conductive parts.
  • Example 12 A composition consisting of 50 wt% Radel polyether sulfone and 50 wt% chopped K-l 100 carbon fiber tow with a nominal length of 1/4" was prepared by solution impregnation. The mixture was compression molded to provide thermal property test specimens. The in-plane (or x and y direction) thermal conductivities were 90.4 W/mK and 102.9 W/mK. The coefficient of thermal expansion was 4.0 ppm/°F.
  • Example 13 A dry blend consisting of 50 wt% Radel polyether sulfone powder and 50 wt% chopped K-l 100 carbon fiber tow with a nominal length of 1" was compression molded to provide thermal property test specimens. The in-plane (or x direction) thermal conductivity was 67.8 W/mK. Some wetting-out difficulties were observed.
  • Example 14 A dry blend consisting of 50 wt% Radel polyether sulfone powder and 50 wt% P- 120 carbon fiber milled or granulated to give 200 micron particles was compression molded to provide thermal property test specimens. The in-plane (or x direction) thermal conductivity was 37.0 W/mK. Some wetting-out difficulties were observed.
  • Thermoset resins such as the common epoxy potting resins may also be filled with carbon fiber, molded and cured to give thermally-conductive parts.
  • Example 15 A filled epoxy composition consisting of 70 wt% epoxy resin and 30 wt% P-120 carbon fiber milled or granulated to give 200 micron particles was prepared by combining the liquid resin and the particulate and hand mixing, then pouring into a mold and allowing the plaque to cure, providing a thermal property test specimen. The in-plane (or x direction) thermal conductivity was 15 W/mK. Insert Molded Thermal Devices
  • Example 16 A thermal device comprising a 3 mm x 160 mm heat pipe and an injection molded heat sink was constructed, using the 60 wt% carbon fiber-filled LCP resin formulation of Example 5.
  • the mold cavity measuring 12mm x 12 mm x 96 mm, was fixtured to center and support the heat pipe inserted into the mold cavity.
  • the closed mold was then injected with filled LCP resin formulation, using an HPM 75 ton injection molding machine as previously described. After ejecting the cooled molding, the centering fixture was removed to provide a heat pipe embedded at the condenser portion to a length of 51 mm in the injection-molded resin.
  • the block was then milled to form a plurality of fins 1mm in thickness and 4-5 mm in height, centered on and disposed normally to the axis of the heat pipe and spaced 1 mm apart along the embedded length.
  • the overall weight of the heat sink was 12 grams.
  • the source end of the heat pipe was imbedded to a length of 14 mm in a heat transfer block.
  • the heat transfer block was electrically heated at a constant power input of 5.5 watts. Temperature of the source and the ambient temperature were measured by thermocouples, the rise in the temperature for constant power input being inverse to the ability of the structure to dissipate heat.
  • the die/source temperature was 71° C, while the ambient temperature was 23° C, giving a thermal resistance of 8.6° C/watt.
  • Comparative Example A 3 x 160 mm heat pipe was attached at the condenser end and with an embedded length of 95 mm to a commercial cast magnesium finned heat sink measuring 13 mm x 20 mm x 140 mm in length, having a weight of 26 grams.
  • Thermal adhesive was applied to the contacting surfaces between the heat sink and the heat pipe.
  • the source end was embedded to a length of 14 mm in a heat transfer block, and heated as in Example 16.
  • the die/source temperature was 71° C, and the ambient temperature was 25° C, giving a thermal resistance value of 8.3 °C/watt. It will thus be seen that the injection molded heat sink provides substantially the same degree of heat dissipation as the larger and considerably heavier cast magnesium heat sink of the prior art.
  • thermal management devices represent a substantial advance in the art and provide significantly improved materials for use in thermal management applications.
  • the thermally conductive resin formulations used in forming the devices of this invention are readily fabricated using conventional processing means, and are generally tough materials having excellent mechanical properties and good dimensional stability. These improved thermally conductive resin molding compounds may find wide application for use in fabricating thermal management components. It will thus be seen that the thermal management devices of the invention may be described as comprising a heat pipe together with a molded heat sink, wherein the heat sink component is preferably insert molded with the heat pipe to form a thermal management device having an integral unitary construction.
  • the thermally conductive heat sink component may be further characterized as molded from filled thermoplastic or thermoset molding compounds having, depending upon the amount of conductive filler in the formulation, a thermal conductivity greater than about 5 W/mK, preferably greater than about 10 W/mK, and more preferably from about 80 to as great as 600 W/mK and still more preferably from about 100 to about 450 W/mK, together with an unusually low coefficient of thermal expansion, again depending upon the type and level of conductive filler, of generally less than 10 ppm/°C.
  • the filled thermoplastic injection molding compounds employed in the more preferred embodiments of the invention may be further described as comprising from about 80 to about 20 wt%, preferably about 50 to about 20 wt% of a thermoplastic LCP resin and about 20 to about 80 wt%, preferably about 50 to about 80 wt% carbon fiber, said carbon fiber having a thermal conductivity greater than about 600 W/mK, preferably greater than about 750 W/mK, more preferably greater than about 900 W/mK, and still more preferably greater than 1000 W/mK.
  • the filled resin formulations may further comprise such plasticizers, processing aids, stabilizers and the like as are conventionally used in the resin compounding and molding resin arts.
  • the formulations are particularly suited for use producing thermal management devices for electrical and electronic use, where the art has lacked suitable, readily-fabricated materials with high thermal conductivity.
  • thermal management devices may be designed employing a plurality of heat pipe components embedded in heat sink, including heat spreader or thermal plane, components in- an insert molding operation.
  • the use of further or post-molding operations are also contemplated, including overmolding the thermal management device, optionally including attached electrical or electronic components, for example to provide an attached, hermetically sealed housing.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
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Abstract

Appareil de gestion thermique qui comporte un caloduc en communication thermique avec un puits de chaleur moulé. Dans un mode de réalisation préféré, le puits de chaleur comporte un polymère à cristaux liquides ou une résine thermodurcie thermiquement conducteurs comportant une charge. De préférence, ledit appareil est formé en tant que structure d'une seule pièce par une opération de surmoulage.
EP98957652A 1997-11-13 1998-11-09 Appareil de gestion thermique a caloduc Withdrawn EP1029352A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US6541897P 1997-11-13 1997-11-13
US65418P 1997-11-13
PCT/US1998/023711 WO1999026286A1 (fr) 1997-11-13 1998-11-09 Appareil de gestion thermique a caloduc

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EP1029352A1 true EP1029352A1 (fr) 2000-08-23

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EP98957652A Withdrawn EP1029352A1 (fr) 1997-11-13 1998-11-09 Appareil de gestion thermique a caloduc

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EP (1) EP1029352A1 (fr)
JP (1) JP2001523892A (fr)
CA (1) CA2309630A1 (fr)
WO (1) WO1999026286A1 (fr)

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JP2001523892A (ja) 2001-11-27
CA2309630A1 (fr) 1999-05-27

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