KR20110050449A - Improved heat dissipation for low profile devices - Google Patents

Abstract

According to the present invention, there is provided a heat spreader for an electronic device, comprising: a first layer comprising at least one sheet formed of compressed particles of exfoliated graphite having two major surfaces; And a second layer comprising a metal foil having two major surfaces, the second layer having a surface structure on the first major surface of the metal foil layer, wherein the first major surface of the graphite layer and the The second major surface of the metal foil layer is in thermal connection with each other, and the surface structure on the first major surface of the metal foil provides a heat spreader that increases one or more of air flow turbulence and heat dissipation surface area.

Description

Improved heat dissipation for low profile devices {IMPROVED HEAT DISSIPATION FOR LOW PROFILE DEVICES}

SUMMARY OF THE INVENTION The present invention is a technique for improving heat dissipation in low profile devices such as flat panel displays, laptop computers, mobile phones, personal digital assistants, and the like. Is associated with. More specifically, the present invention relates to apparatus and methods for facilitating improved heat dissipation from low profile devices, in particular thin handheld devices, with limited space in the case of the device. The term "low profile device" as used herein refers to a ratio of the surface area of a major surface (ie, the length times the width of one of the major surfaces, measured in square inches) to an average thickness (inches) of about 10. By electronic device that is greater than or equal to 1 inch, more generally, greater than or equal to about 15: 1 inch (of course, a person of ordinary skill in the art would be able to Will be based on the same device and on a flat panel display or the like that does not include a stand).

While maintaining functionality, there is a need for smaller and lighter manufacturing of electronic devices such as flat panel displays and portable devices such as laptop computers, mobile phones, personal digital assistants. To date, this is a Sony OLED (organic light emitting diode) 11 "flat-panel television that is only 3 mm thick in some locations, an Apple Inc. MacBook Air laptop computer that is only 1.94 cm thick (closed), but also only 12.3 mm thick. Apple Inc.'s iPhone 3G personal digital assistant, and (closed) only 13.9 mm thick, devices such as Motorola, Inc.'s Motorazr V3 cell phone, and photovoltaic for generating electricity from solar energy. Photovoltaic solar panels are also designed to be as thin as possible.

One important obstacle to manufacturing smaller and thinner devices is heat management. While many device components can be effectively minimized, the power needed to deliver the features consumers want, expecting even basic mobile phones to include features such as games, digital cameras, and Internet access. When these power requirements are combined with a lack of space in the device, thermal management is often a limiting factor.

 In other words, without effective thermal management, device components can overheat quickly, which can result in intermittent or even catastrophic failure. In order to manufacture robust and long lasting devices, it is necessary to dissipate heat from heat generating device components such as chipsets without significantly increasing the space requirements.

In the wider field of large electronic devices, various thermal management techniques have been developed. Of course, "desktop" computers, large television sets, and some large laptop computers include fans to move air across the heat source to facilitate heat dissipation. In addition, heat spreaders, such as sheets formed of compressed particles of exfoliated natural graphite flakes, are due to their anisotropy (directional heat spreading), resulting in smaller devices. Has been used to obtain a great advantage in thermal diffusion.

For example, Reis et al. Disclose in US Pat. No. 7,365,988 a heat spreader formed of compressed particles of exfoliated graphite for use in flash LED light sources for cameras of portable devices such as cell phones. Graphite-based heat spreaders provide low operating temperatures at high power levels, improving the lighting and operating life of electronic components.

In US Pat. No. 7,292,441, Smalc et al. Disclose a thermal solution for a portable electronic device, such as a laptop computer, which is disposed between a heat source and an external case or other component of the device and generated by a heat source. The heat dissipation from the heat source is facilitated while shielding the outer case or the second part from the generated heat. Thermal solutions such as Smalc include sheets formed from compressed particles of exfoliated graphite.

In addition, US Pat. No. 7,385,819 to Shives et al. And US Pat. No. 7,306,847 to Capp et al., For improving heat dissipation in display devices, such as plasma display panels, liquid crystal display devices, and other types of display devices used today. A technique using a sheet formed of compressed particles of exfoliated graphite is disclosed.

Traditional heat spreading materials such as copper or aluminum have also been proposed, but this is undesirable because it adds significant weight to the device. In addition, metals such as copper or aluminum are isotropic, so that heat tends to flow easily through the thickness of the heat spreader, resulting in hot-spots on the heat spreader opposite the heat source. These hot spots have a negative effect on the touch temperature of the case of the device or adjacent temperature sensitive components.

Thus, preferred materials for use as heat spreaders for electronic devices consist of one or a plurality of sheets formed of compressed particles of exfoliated graphite flakes.

Natural graphite consists of layer planes of a network structure or hexagonal arrangement of carbon atoms when viewed in fine size. These layer planes of hexagonally arranged carbon atoms are oriented or ordered to be substantially flat, substantially parallel to each other, and at the same distance from each other. Sheets or layers of substantially flat and parallel equidistant carbon atoms, generally referred to as graphene layers or basal planes, are linked or bonded to one another and these groups are arranged in a crystalline state. Well aligned graphite consists of crystals of considerable size, which crystals are well aligned or oriented with one another and have a well aligned carbon layer. That is, well aligned graphite has a very desirable crystal orientation. It should be noted that graphite, obviously, has an anisotropic structure and exhibits or has many properties, such as high thermal conductivity and electrical conductivity and fluid diffusion.

In short, natural graphite is characterized by a laminated structure of carbon, ie the structure consists of an overlapping layer or laminae of carbon atoms bonded to each other by weak van der Waals forces. In view of the graphite structure, two axes or directions are generally mentioned, namely the "c" axis or direction and the "a" axis or direction. Simply, the "c" axis or direction may be considered a direction perpendicular to the carbon layer. The "a" axis or direction may be considered a direction parallel to the carbon layer or a direction perpendicular to the "c" direction. Graphite suitable for producing flexible graphite sheets has a very high orientation.

As mentioned above, the bonding force that holds the parallel layers of carbon atoms together is only a weak van der Waals force. Natural graphite is expanded or swollen graphite in which the space between the overlapping carbon layers or laminas is somewhat open to provide significant expansion in the direction perpendicular to the layer, ie the "c" direction, so that the layer properties of the carbon layer are substantially maintained. It can be chemically treated to form a structure.

Natural graphite flakes expanded chemically or thermally, more specifically to have a "c" direction dimension or final thickness that is at least about 80 times larger than the initial "c" direction dimension, may be used, for example, without the use of binders, for example, in web, paper, foil It may be formed from an adhesive sheet or an integrated sheet of expanded graphite, such as a foil, strip, tape, or the like. The formation of graphite particles expanded to have a "c" direction dimension or a final thickness about 80 times larger than the initial "c" direction dimension to form an integrally flexible sheet by compression without the use of any binding material is large. It is believed that this is possible due to the mechanical interlocking, or adhesion, achieved between the bulk expanded graphite particles.

In addition to flexibility, the sheet material has a large anisotropy in thermal and electrical conductivity due to the orientation of the expanded graphite particles substantially parallel to the opposite surface of the sheet due to compression, such as roller pressing, as described above. It is known to have. The sheet material thus produced has excellent flexibility, good strength and very high directivity.

In short, the process for producing flexible anisotropic expanded natural graphite sheet material, such as, for example, webs, paper, strips, tapes, foils, etc., is a substantially flat, flexible, cohesive graphite sheet. Compressing the expanded graphite particles having a "c" directional dimension that is at least about 80 times greater than the "c" directional dimension of the initial particles, under a predetermined load and, if necessary, without a binder to form. Expanded graphite particles, which are generally worm shaped in appearance, once compressed, remain compressed and aligned with the opposite major surface of the sheet. The properties of the product can be altered by the addition of additives or coatings and / or binders before the compression step. In this regard, see US Pat. No. 3,404,061 to Shane et al. The density and thickness of the sheet material can be varied by controlling the degree of compression. Higher horizontal strength and thermal conductivity are generally found in denser sheets. Typically the density of the sheet material is about 1.1 g / cc (g / cm ³ ) To within a range from about 1.8 g / cc or greater than or equal to 2.0 g / cc.

Natural graphite sheet materials prepared as described above typically exhibit a significant degree of anisotropy due to the alignment of the graphite particles parallel to the opposing and parallel major surfaces of the sheet, with the degree of anisotropy rollers sheet material at high density. Increases when pressing. In roller pressed anisotropic sheet materials, the thickness, ie the direction perpendicular to the opposing and parallel sheet surfaces, includes the "c" direction and is along the length and width, i.e. along the opposing major surfaces or parallel to the opposing major surfaces. The direction includes the "a" direction and the thermal properties of the sheet typically become very different in size with respect to the "c" and "a" directions.

However, even if excellent heat dissipation is obtained by the above-described graphite sheet, further heat dissipation improvement is required if a smaller and thinner device having improved and additional functions is to be developed. Thus, thermal management and / or dissipation of low profile electronic devices such as flat panel displays, laptop computers, mobile phones, personal digital assistants, etc., which maximize the inherent heat spreading capability of sheets formed from compressed particles of expanded graphite to improve heat dissipation. Mechanism for this is required.

In one aspect of the invention there is provided a heat spreader comprising a first layer comprising at least one sheet formed of compressed particles of exfoliated graphite having two major surfaces and a metal foil having two major surfaces. A second layer, comprising a second layer, having a surface structure on the first major surface of the metal foil layer, wherein at least about 25% of the surface area of the first major surface of the graphite layer is the second major layer of the metal foil layer. In thermal connection with the surface, the surface structure on the first major surface of the metal foil layer has a height no greater than about 10 times the thickness of the first layer and increases one or more of air flow turbulence and heat dissipation surface area.

The first layer of the heat spreader, ie the graphite layer, preferably has a thickness of about 0.05 mm to about 2.0 mm and a horizontal thermal conductivity of at least about 150 W / m-K. In one embodiment, the second layer of the heat spreader, ie the metal foil layer, has a thickness of about 0.025 mm to about 1.0 mm, and the metal foil layer is formed of aluminum, copper, steel, or a combination thereof.

In another embodiment, the present invention includes an electronic device, such as a low profile electronic device, comprising a heat spreader as described above and a mechanism for directing air across the surface structure of the second layer of the heat spreader.

Preferably, the mechanism for directing air across the surface structure of the second layer of the heat spreader is a fan, most preferably a fan comprising an air diffuser wherein the air diffuser is heat compared to a fan without an air diffuser. A fan that directs air flow across the heat spreader to enhance dissipation.

In yet another embodiment, the second major surface of the first layer of the heat spreader is in thermal connection with the surface of the heat source. In practice, preferably, the surface area of the second major surface of the first layer of the heat spreader is greater than the surface area of the portion of the heat source in thermal connection with the second major surface of the first layer of the heat spreader.

Other or further embodiments, features, and advantages of the present invention will become apparent to those skilled in the art from the following description in conjunction with the accompanying drawings.

1 is a side cross-sectional view of one embodiment of a heat spreader of the present invention.
FIG. 2 is a partially cutaway top perspective view of the heat spreader of FIG. 1, showing one embodiment for a second layered surface structure. FIG.
3 is a partially cut-away top perspective view of another embodiment of a heat spreader of the present invention, showing another embodiment of a surface structure on a second layer.
4 is a partially cut-away top perspective view of another embodiment of a heat spreader of the present invention, showing another embodiment of a surface structure on a second layer.
5 is a top perspective view of another embodiment of a heat spreader of the present invention, showing another embodiment of a surface structure on a second layer.
6 is a side cross-sectional view of another embodiment of a heat spreader of the present invention, showing another embodiment of a surface structure on a second layer.
7 is a top perspective view of another embodiment of a heat spreader of the present invention, showing another embodiment of a surface structure on a second layer.
8 is a top perspective view of another embodiment of a heat spreader of the present invention, showing another embodiment of a surface structure on a second layer.
9 is a plan view of one embodiment of a heat spreader of the present invention incorporating a fan and an air diffuser.
FIG. 10 is a partial side view of a cell phone with one embodiment of a heat spreader of the present invention incorporating a fan and an air diffuser.
Figure 11 is a partial side view of an FB-DIMM memory module, equipped with one embodiment of a heat spreader of the present invention.

Referring now to the drawings (not shown in the drawings for the sake of brevity, all members are shown by reference numerals), the invention provides, for example, portable electronic devices such as laptop computers, mobile phones, personal digital assistants, flat panel displays, Or thermal operation of a low profile electronic device, such as a photovoltaic solar panel, has one or more sheets formed of compressed particles of exfoliated graphite as the first layer 20 and a surface structure 32 thereon as the second layer 30. Substantially by the addition of a composite heat spreader, denoted by reference numeral 10, formed of a metal foil, the surface structure 32 providing an increased surface area and / or airflow turbulence for heat dissipation. It is based on the fact that it can be improved. The electronic device, indicated as 100, can operate at a substantially increased power level to provide improved functionality while operating at significantly lower operating temperatures.

Prior to describing how the present invention enhances current materials, it may be used as a natural graphite and flexible sheet to be used as the first layer 20 of the heat spreader 10 to form the product of the present invention. Give a brief description of the transformation.

Natural graphite is a crystalline structure of carbon that contains atoms covalently bonded in a flat layer plane with weak bonds between planes. By treating the natural graphite particles with, for example, an intercalant of a solution of sulfuric acid and nitric acid, the crystal structure of the graphite is reacted to form a compound of graphite and intercarant. The particles of treated graphite are then referred to as "particles of intercalated graphite". Upon exposure to high temperatures, the intercalant in the graphite decomposes and vaporizes so that the intercalated graphite particles are accordion-shaped in the "c" direction, ie perpendicular to the crystal plane of the graphite, approximately 80 times larger than their initial dimensions. Inflate. The expanded graphite particles are worm-shaped in appearance and are commonly referred to as worms. The worms may be compressed together in a flexible sheet that can be formed and cut into various forms, unlike the earlier graphite flakes.

Natural graphite starting materials suitable for use in the present invention include highly graphitic carbonaceous materials that can intercalate not only halides but also organic and inorganic acids and then expand when exposed to heat. . These highly graphite carbonaceous materials most preferably have a degree of graphitization of about 1.0. As used herein, the term “graphitization degree” refers to a value g according to g = [3.45-d (002)] / 0.095, where d (002) is the concentration of carbon in the crystal structure measured in Angstrom units. The distance between the graphite layers. The distance between the graphite layers is measured by standard X-ray diffraction techniques. The location of the diffraction peaks corresponding to the (002), (004) and (006) Miller indices is measured, and standard least squares techniques are used to derive the distance that minimizes the overall error for all these peaks. Examples of highly graphite carbonaceous materials include natural graphite from various sources.

The natural graphite starting material used in the present invention may contain a non-graphite component as long as the crystal structure of the starting material maintains the required degree of graphitization and the starting material can be peeled off. In general, carbon-containing materials capable of peeling and possessing the degree of graphitization required for the crystal structure are suitable for use in the present invention. Such graphite preferably has a purity of at least about 80% by weight. More preferably, the graphite used in the present invention will have a purity of at least about 94%. In the most preferred embodiment, the graphite used will have a purity of at least about 98%.

Conventional methods of making natural graphite sheets are disclosed in US Pat. No. 3,404,061 to Shane et al., The disclosure of which is incorporated herein by reference. In the practice of the method of the patent issued to Shane et al., Natural graphite flakes are advantageously in an amount of about 20 to about 300 parts by weight of intercalant per 100 parts by weight of graphite flakes (pph), for example in a solution containing a mixture of nitric acid and sulfuric acid. Intercalates by dispersing the flakes in solution level. In one preferred embodiment, the intercalation solution contains an intercalating agent that is different from the oxidizing agents known in the art. Examples are for example mixtures of concentrated nitric acid and chlorate, chromic acid and phosphoric acid, sulfuric acid and nitric acid, or mixtures of strong organic acids such as trifluoroacetic acid or nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate And solutions containing potassium dichromate, perchloric acid and the like and oxidizing agents such as strong oxidants and oxidizing mixtures which are soluble in organic acids. Alternatively, electrical potential can be used to cause oxidation of the graphite. Chemical species that can be introduced into graphite crystals using electrolyte oxidation include sulfuric acid as well as other acids.

In a preferred embodiment, the intercalating agent is a mixed solution of sulfuric acid, or sulfuric acid and phosphoric acid, and an oxidizing agent, ie nitric acid, perchloric acid, chromic acid, potassium permanganate, hydrogen peroxide, iodic acid or peroxoic acid and the like. Although less preferred, intercalation solutions are metal halides such as ferric chloride and ferric chloride mixed with sulfuric acid, or bromine as bromine solution and halides such as sulfuric acid or bromine in organic solvents. It may contain.

The amount of intercalation solution may range from about 20 to about 350 pph and more generally from about 40 to about 160 pph. After the flakes are intercalated, any excess solution flows out of the flakes and the flakes are washed. Alternatively, the amount of intercalation solution may be limited in the range of about 10 to about 40 pph, which may eliminate the washing step as disclosed and described in US Pat. No. 4,895,713, incorporated herein by reference.

The graphite flake particles treated with the intercalation solution are optionally selected by mixing with an organic reducing agent selected from alcohols, sugars, aldehydes and esters, which react with the surface film of the oxidative intercalating solution, for example, at temperatures ranging from 25 ° C. to 125 ° C. Can be contacted. Suitable specific organic agents include hexadecanol, octadecanol, 1-octanol, 2-octanol, decyl alcohol, 1,10 decandiol, decylaldehyde, 1-propanol, 1,3 propanediol, ethylene glycol, polypropylene Glycol, dextrose, fructose, lactose, sucrose, potato starch, ethylene glycol monostearate, diethylene glycol dibenzoate, propylene glycol monostearate, glycerol monostearate, dimethyl oxylate, diethyl oxylate, Ligrin derivatives such as methyl formate, ethyl formate, ascorbic acid and sodium lignosulfate. The amount of organic reducing agent is suitably about 0.5 to 4 weight percent of the graphite flake particles.

The use of inflation aids applied before, during or immediately after intercalation can also provide improvements. Among these improvements the peel temperature can be reduced and the expanded volume (also referred to as the "worm volume") can be increased. The expansion aid herein is advantageously an organic material that is sufficiently soluble in the intercalation solution to achieve expansion improvement. More narrowly, organic materials of this type containing carbon, hydrogen and oxygen may be used, preferably exclusively. Carboxylic acids are known to be particularly effective. Carboxylic acids useful as expansion aids include aromatic, aliphatic or cycloaliphatic, straight or branched, saturated and unsaturated monocarboxylic acids, dicarboxylic acids and one or more carbon atoms, preferably having up to about 15 carbon atoms and It may be selected from polycarboxylic acids and is soluble in the intercalation solution in an amount effective to provide an improvement in one or more aspects of exfoliation. Suitable organic solvents can be used to improve the solubility of organic expansion aids in intercalation.

Representative examples of saturated aliphatic carboxylic acids are acids such as the formula H (CH ₂ ) _n COOH and include formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, and the like, where n is a number from 0 to about 5 to be. Instead of carboxylic acids, reactive carboxylic acids such as anhydrides or alkyl esters may also be used. Representative examples of alkyl esters are methyl formate and ethyl formate. Sulfuric acid, nitric acid and other known water soluble intercalants can ultimately degrade formic acid into water and carbon dioxide. Because of this, formic acid and other sensitive swelling aids are advantageously contacted with graphite flakes prior to injecting the flakes into the aqueous intercalant. Representative dicarboxylic acids are aliphatic dicarboxylic acids having 2-12 carbon atoms, in particular oxalic acid, fumaric acid, malonic acid, maleic acid, succinic acid, glutaric acid, adipic acid, 1,5-pentanedicarboxylic acid, 1,6-hexanedicarboxylic acid, 1,10-decanedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid and aromatic dicarboxylic acid such as phthalic acid or terephthalic acid. Representative alkyl esters are dimethyl oxylate and diethyl oxylate. Representative alicyclic acids are cyclohexane carboxylic acids and representative aromatic carboxylic acids are benzoic acid, naphthoic acid, anthranilic acid, p-aminobenzoic acid, salicylic acid, o-, m-, and p-toryl acid, methoxy and o Oxy benzoic acid, acetoacetamidobenzoic acid and acetamidobenzoic acid, phenylacetic acid and naphthoic acid. Representative hydroxy aromatic acids are hydroxy benzoic acid, 3-hydroxy-1-naphthoic acid, 3-hydroxy-2-naphthoic acid, 4-hydroxy-2-naphthoic acid, 5-hydroxy-1-naphthoic acid, 5 -Hydroxy-2-naphthoic acid, 6-hydroxy-2-naphthoic acid and 7-hydroxy-2-naphthoic acid. Citric acid is typical among polycarboxylic acids.

The intercalation solution will be water soluble and preferably contains about 1 to 10% expansion aid, which amount is effective to enhance exfoliation. In embodiments in which the dilation aid is contacted with graphite flakes prior to or after infusion into the aqueous intercalation solution, the dilation aid is such as a V-blender in amounts generally ranging from about 0.2% to about 10% by weight with graphite. Can be mixed by appropriate means.

After intercalating the graphite flakes and then mixing the intercalated graphite flakes with the organic reducing agent, the mixture can be exposed to a temperature in the range of 25 ° C. to 125 ° C. to facilitate the reaction of the reducing agent with the intercalant coating. have. The heating period is about 20 hours or less, and shorter heating periods, for example at least about 10 minutes, for temperatures higher than the aforementioned ranges. A time of up to 30 minutes, for example on the order of 10 to 25 minutes can be used at higher temperatures.

As mentioned above, the graphite particles so treated may be referred to as “intercarated graphite particles”. When exposed to high temperatures, for example at temperatures above about 160 ° C. and especially at temperatures between about 700 ° C. and 1000 ° C. and higher, the particles of intercalated graphite are in the “c” direction, ie perpendicular to the crystal plane of the constituent graphite particles. In one direction it expands about 80-1000 times more than its initial volume in accordion form. Expanded, ie exfoliated, graphite particles are commonly referred to as worms because they are worm-shaped in appearance. The worms can be compressed together into a flexible sheet (referred to herein as a sheet formed of compressed particles of exfoliated graphite), which, unlike the initial graphite flakes, can be formed and cut in various forms.

For use in the present invention, the graphite sheet is cohesive with good processing strength, for example by a thickness of about 0.05 mm to 2.0 mm and about 1.1 to 1.8 g / cc or 2.0 g / cc by roller pressing. It is properly compressed to a higher typical density than that. If resin impregnation is desired, an intercar as disclosed in US Pat. No. 5,902,762 (incorporated herein) to provide improved resin infusion to the final flexible graphite product, with about 1.5 to 30% by weight of a ceramic additive. Mixed with the rated particle flakes.

The aforementioned method for intercalating and exfoliating graphite flakes and for forming sheets formed of compressed particles of exfoliated graphite flakes is described in International Patent Application PCT / US02 / 39749, the disclosure of which is incorporated herein by reference. As described above, it may be advantageously improved by pretreatment of graphite flakes at the graphitization temperature, ie, in the range of about 3000 ° C. or more, and by the inclusion of flexible additives in the intercarant.

Pretreatment, or annealing, of graphite flakes results in significantly increased expansion (ie, an increase in expansion volume of at least 300%) when the flakes are subsequently intercalated and peeled off. In fact, preferably, the increase in expansion is at least about 50% compared to similar processing without the annealing step. The temperature used in the annealing step should not be significantly lower than 3000 ° C., since temperatures below 100 ° C. cause substantially reduced expansion.

Annealing of the graphite flakes is carried out for a time sufficient to cause flakes with an improved degree of expansion upon intercalation and subsequent exfoliation. Generally the time required is at least 1 hour, preferably 1 to 3 hours and most advantageously proceeds in an inert atmosphere. For maximum beneficial results, annealed graphite flakes may be prepared by other processes known in the art to improve the degree of expansion, namely organic reducing agents, intercalation aids such as organic acids, and surfactant cleaning agents after intercalation. Will undergo intercalation in the presence of Moreover, for maximum benefit, the intercalation step may be repeated.

The annealing step is carried out in an induction furnace or other similar apparatus known and recognized in the field of graphitization, where the temperature used is in the 3000 ° C. range and the high range of temperatures that can occur in the graphitization process.

Worms produced using graphite after preliminary intercalation annealing were often observed to “clump”, adversely affecting impact area weight uniformity, so additives that assisted in the formation of “free flowing” worms were Very preferred. Adding a flexible additive to the intercalation solution, a compression device (such as a bed of a calendar station), commonly used to compress (or “calendering”) graphite worms into a flexible graphite sheet. A more uniform distribution of the worms across the bed of the is facilitated. The resulting sheet therefore has greater area weight uniformity and tensile strength. The flexible additive is preferably a long chain hydrocarbon, more preferably a hydrocarbon having about 10 carbons or more. While other functional groups are present, other organic compounds having long chain hydrocarbon groups can also be used.

More preferably, the flexible additive is an oil and is most preferred given the fact that mineral oil is less odor and odor, which is an important consideration especially for long term storage. Note that any of the aforementioned expansion aids meet the definition of the flexible additive. When these materials are used as expansion aids, there is no need to include a separate flexible additive in the intercalant.

The flexible additive is present in the intercarant in an amount of at least about 1.4 pph, more preferably at least about 1.8 pph. Although the upper limit of the content of the flexible additive is less important than the lower limit, the inclusion of the flexible additive to a degree of greater than about 4 pph does not have significant additional advantages.

The natural graphite sheet of the present invention can, if necessary, use flexible graphite particles rather than newly expanded worms, as disclosed in US Pat. No. 6,673,289, the disclosure of which is incorporated herein by reference. Such sheets may be newly formed sheet material, recycled sheet material, scrap sheet material, or other suitable source.

The treatment process of the present invention may also use a mixture of virgin and recycled materials.

One form of apparatus for continuously forming compressed natural graphite material is disclosed in US Pat. No. 6,706,400 to Mercuri et al., The contents of which are incorporated herein by reference.

In one embodiment, following a compression step (such as calendaring), when a resin is injected into a sheet formed of compressed particles of exfoliated graphite, the injected material is placed in a press where the resin is cured at high temperatures and pressures. . In addition, natural graphite sheets can be used in the form of laminates, which can be prepared by laminating individual graphite sheets together in a press.

The temperature used in the press must be sufficient to cause the graphite structure to be densified at curing pressure without adversely affecting the thermal properties of the structure. In general, this requires a temperature of at least about 90 ° C. or higher, and generally up to about 200 ° C. Most preferably, curing takes place at temperatures between about 150 ° C and 200 ° C. The pressure used for curing will be to some extent a function of the temperature used, but should be sufficient to ensure that the graphite structure is densified without adversely affecting the thermal properties of the structure. In general, for ease of manufacture, the minimum pressure necessary to densify the structure to the required degree will be used. Such pressures are generally about 7 Mpa (1 Mpa corresponds to about 1000 psi) or more and about 35 Mpa (corresponds to 5000 psi), and more widely used values are about 7 to 21 Mpa (1000 to 3000 psi). Curing times vary depending on the pressure, temperature and resin system used, but are generally between about 0.5 to 2 hours. After curing is complete, the material has a density of at least about 1.8 g / cc, generally about 1.8 g / cc to 2.0 g / cc.

Preferably, if the natural graphite sheet itself is provided as a laminate, the resin present in the injected sheet can act as an adhesive for the laminate. However, according to another embodiment of the present invention, the calendered and infused natural graphite sheet is coated with an adhesive prior to lamination and curing. Suitable adhesives include epoxy-, acrylic- and phenol-based resins. Phenolic resins that have been found to be particularly useful in the practice of the present invention include phenol-based resin systems including resole and novolak phenols.

Although forming sheets through calendering and molding is the most common method for forming graphite materials useful in the practice of the present invention, other forming methods may be used.

Referring now to the drawings, as described above, a heat spreader according to the present invention is denoted by reference numeral 10. The heat spreader 10 comprises a first layer comprising one or more sheets formed of compressed particles of exfoliated graphite, indicated by reference numeral 20, and a second layer comprising a metal foil, indicated by reference numeral 30. do. For use in the heat spreader 10 according to the invention, the graphite sheet has a mass of less than aluminum or copper, which in some circumstances is equal to or greater than the in-plane thermal conductivity of aluminum or copper. Can have More specifically, the sheet formed from the compressed particles of exfoliated graphite has a horizontal thermal conductivity of at least about 150 W / mK, more preferably at least 220 W / mK, and most preferably at least about 390 W / mK, and about 15 W / It has a through-plane thermal conductivity of less than mK, more preferably less than about 10 W / mK.

In addition, as described above, the sheet or sheets formed from the compressed particles of exfoliated graphite used as the first layer 20 of the heat spreader of the present invention is preferably between about 0.05 g / cc and about 2.0 g / cc. Has a density; More preferably the sheet has a density of about 1.4 g / cc to about 1.8 g / cc. The thickness of the (plural) graphite sheets should be between about 0.05 mm and about 2.0 mm. In a preferred embodiment, one or the plurality of sheets formed from the compressed particles of exfoliated graphite have a thickness between about 0.25 mm and about 1.0 mm.

The first layer 20 of the heat spreader 10 of the present invention, ie, a layer comprising one or more sheets formed of compressed particles of exfoliated graphite, has two major surfaces, indicated by reference numerals 20a and 20b. The second layer 30 comprises a metal foil (thus also having two major surfaces, denoted 30a and 30b); Preferably the metal foil is formed of aluminum, copper, steel or a combination thereof.

Preferably, one of the major surfaces 20a of the first layer 20 is in thermal connection with one of the major surfaces 30a of the second layer 30. The term “thermal connection” means that effective heat transfer is made between thermally connected products, in this embodiment between layers 20 and 30; This means that a measurable amount of heat applied to one of the products (ie layers) is transferred to the other product (ie layers). Indeed, in a preferred embodiment, at least 30% of the thermal energy applied to the first layer 20 is transferred to the second layer 30.

Preferably, at least about 25%, more preferably at least about 50%, of the surface area of one of the major surfaces 20a of the first layer 20 is at least one of the major surfaces of the second layer 30. Glued or attached or in contact. Most commonly, with the adhesive indicated by reference numeral 25 in FIG. 5, the adhesive is inserted between the first layer 20 and the second layer 30, so that the first layer 20 is attached to the second layer ( Or adheres to 30); In areas where such an adhesive is not provided, the major surface 20a of the first layer is preferably in direct contact with the major surface 30a of the second layer 30.

With an adhesive suitable for bonding the first layer 20 and the second layer 30 together, the first layer 20 and the second layer 30 are in thermal connection so as to form the heat spreader 10. Resins such as silicone-, epoxy-, acrylic-, and phenol-based resins. In addition, in one embodiment, the adhesive consists of a silicone adhesive filled with conductive particles to enhance thermal conductivity between the layers. In another preferred embodiment, phenolic resins such as resol and novolac phenol are used, in which a relatively thin film of the phenolic resin bonds the first layer 20 and the second layer 30 to each other to establish a thermal connection between these layers. Because it maximizes.

The second layer 30 may have a thickness of about 0.025 mm to about 1.0 mm. Preferably, the thickness of the second layer 30 is from about 0.05 mm to about 0.25 mm. The metal foil is thermally isotropic, and the thermal conductivity of aluminum and copper is relatively constant.

One advantage of using the heat spreader 10 formed as a composite of the first layer 20 and the second layer 30 is that the second layer 30 is non-continuous (i.e., the second layer ( The shape surface structure 32 on the second layer 30, which causes gaps or holes to exist in 30, allows the first layer 20 to maintain continuity, regardless of the number and properties of the surface structure 32. The continuity of the heat spreader 10 is maintained. Further, a first layer 20 comprising at least one sheet formed of compressed particles of exfoliated graphite having a thickness between 0.05 mm and 2.0 mm and a second layer comprising a metal foil having a thickness between 0.025 mm and 1.0 mm The heat spreader 10 comprising 30 will be considerably less weight than an equivalent heat spreader formed solely of metal foil. Furthermore, given a high horizontal thermal conductivity graphite sheet and an anisotropic graphite layer 20, the heat diffusion from the heat spreader 10 disclosed herein, and the prevention of hot spots, compared to a heat spreader made of metal only It will be considerably improved.

The second layer 30 also has a surface structure 32. More specifically, one of the major surfaces 30a of the second layer 30 is in thermal connection with the first layer 20; A surface structure 32 is provided on the second major surface 30b of the second layer to increase the surface area of the heat spreader 10 available for heat dissipation or to heat dissipation surface 12 of the heat spreader 10. Increasing ambient airflow turbulence, or both, improves heat dissipation.

Such surface structures 32 may take many forms, depending on the particular heat dissipation demands encountered, especially as shown in FIGS. 2-4. In one embodiment, the surface structure 32 may include one or a plurality of flaps formed by folding a second layer 30 (splitting) flaps (which is a first one). This may need to be done before mating the second layer 30 to the layer 20). Such flaps may be along the length of, or across the width of, the heat spreader 10 (not shown), or diagonally (as shown in FIG. 2), upon request of heat dissipation. Only within separate areas, such as not shown). The flaps may also be arranged along the edge of the heat spreader 10 to form an air flow conduit along the heat spreader 10, as shown in FIG. 5.

Alternatively, surface structure 32 may include a plurality of fins (described with reference to FIGS. 3 and 4) formed by pushing a punch or the like through second layer 30 (also It may need to be done before mating the first layer 20 and the second layer 30). These pins may be arranged linearly (FIG. 3) or in groups around the common punch hole (FIG. 4). In the embodiment shown in FIG. 4 this pin can be seen to provide the formation of a cheese grater. In another embodiment, the second layer 30 may be formed as a so-called folded fin structure, as shown in FIG. 6, wherein the metal foil forming the second layer 30 may be The folded and raised area in a corrugated pattern includes the surface structure 32. Another embodiment of the surface structure 32 may be simply a dimple, as shown in FIG. 7, within the second major surface 30b of the second layer 30, or as shown in FIG. 8. It may be a raised cone.

The height, number, shape, orientation, and grouping of the surface structure 32 may be determined by those skilled in the art, depending on factors such as heat source arrangement, air flow, heat dissipation requirements, and the like. It can be decided immediately. Preferably, the surface structure 32 has a height of 10 times or less, more preferably 5 times or less and most preferably 3 times or less of the thickness of the first layer 20. In most embodiments, the surface structure 32 has a height of about 10 mm or less, preferably between about 0.1 to 10 mm.

In addition to operating to increase the heat dissipation surface area of the heat spreader 10 and / or to improve air flow turbulence, the surface structure 32 exposes a portion of the graphite first layer 20 to provide a better It may also provide heat dissipation. In addition, the surface structure 32 may be arranged at a position corresponding to the heat source to facilitate heat dissipation.

In a highly preferred embodiment, the heat spreader 10 is disposed within the low profile electronic device 100 to facilitate heat dissipation from the heat generating components of the low profile electronic device 100. As described above, the device 100 includes a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a field emission display (FED), and a surface-conduction electron-emitter. display (SED), or a flat panel display such as a light emitting diode (LED) display. LCD displays may use, for example, LEDs, OLEDs, cold cathode fluorescent lamps (CCFLs) or flat fluorescent lamps (FFLs) for backlighting. Other low profile devices in which the heat spreader 10 of the present invention is particularly useful include portable or small devices such as laptop computers, mobile phones or personal digital assistants and photovoltaic solar panels.

Some components of device 100, such as chipsets, hard drives, and the like, generate heat during operation. Such parts will be referred to individually as heat sources 110 herein. In order for the device 100 to function as desired, it is important to dissipate heat from the (plural) heat sources 110 to prevent overheating. It is also important to ensure that the heat generated by the (plural) heat sources 110 does not affect other device 100 components such as batteries, displays, external casings and keypads of the device, which are (plural). Heat generated by the heat source 10 may be adversely affected or adversely affect the user of the device.

To do this, the second major surface 20b of the first layer 20 is in thermal connection with the surface of the one or more heat sources 110; In another embodiment, the second major surface 20b of the first layer 20 of the heat spreader 10 is in thermal connection with the surfaces of each of the plurality of heat sources 110 of the device 100. In another embodiment, the second surface 30b of the second layer 30 is in contact with the (plural) heat source 110. In each embodiment, heat from the (plural) heat sources 110 is transferred to the heat spreader 10 for dissipation. Preferably, the surface area of the second major surface 20b of the first layer 20 of the heat spreader 10 is equal to the surface area of the heat spreader 10 in order to increase the effective surface area of the heat source 110 for heat dissipation. It is larger than the surface area of the portion of the (plural) heat sources in thermal connection with the second major surface 20b of the first layer 20.

In another preferred embodiment, the heat spreader 10 may be mounted to a memory module for a low profile device. For example, as shown in FIG. 11, the heat spreader 10 is mounted to the FB-DIMM module 200, for example by a mounting clip 210, so that the heat spreader 10 is mounted on the FB-DIMM. The heat generated by the module 200 may be diffused and dissipated.

In another embodiment of the present invention, the first layer 20 of the heat spreader 10 is a protective coating on some or all of the surface of the first layer that is not in contact with the second layer 30 (as shown in FIG. 6). And 27, to block the possibility of graphite particles falling off or separating from the graphite first layer 20. The protective coating also advantageously and effectively insulates the first layer 20 to prevent electrical interference caused by insertion into an electrically conductive material (graphite) in the electronic device 100. Protective coatings may be used to prevent exfoliation of graphite materials and / or electrical insulation of graphite, such as thermoplastic materials such as polyethylene, polyester or polyimide, acrylic coatings, waxes and / or varnish materials. Any suitable material may be included. Indeed, if grounding is required, the protective coating may comprise a metal, such as aluminum, as opposed to electrical insulation.

As a preferred embodiment, referring now to FIG. 9, the apparatus 100 includes a second layer, most specifically, the surface structure 32, disposed across the heat spreader 10 to provide improved heat dissipation. It may also include a mechanism for directing air across surface 30b of 30. This mechanism can be one of a number of devices, such as fans, blowers, piezofans, diaphragms such as Nuventix's SynJet, and the like. Most generally, a device for directing air across the heat spreader 10 may include a fan 40.

The fan 40 is preferably a so-called "low profile" or "miniature" fan that can be used in the small space available within the portable electronic device 100 such as a laptop computer, a mobile phone, a personal digital assistant or the like. There are several definitions of what constitutes a low profile or small fan, but for the purposes of the present invention, the fan 40 has a footprint of about 450 mm ² or less, more preferably about 300 mm ² or less, ie It has a surface area of length and width and a height (or profile) of about 22 mm or less, more preferably about 15 mm or less. One mechanism useful as the fan 40 is the Micronel U16LM-9 with an installation area of 100 mm ² and a profile of 5 mm. This fan has a nominal speed of 6000 rpm. In large devices, the fan 40 will have a correspondingly large footprint and profile.

The use of the fan 40 creates an air flow around the heat spreader 10, in particular along the major surface 30b of the second layer 30 of the heat spreader 10, thereby facilitating dissipation. The fan 40, when used in conjunction with the surface structure 32 that can increase the surface area for dissipation of the heat spreader 10 and increase the airflow turbulence, can be used when the device 100 is used with the heat spreader 10. Can have significant advantages in heat dissipation from the (plural) heat sources 110.

In addition, it is highly desirable that the air flow exiting the fan 40 is directed onto the heat spreader 10 in a manner designed to most effectively dissipate heat from the (plural) heat sources 110 of the device 100. The most effective way of directing air flow is in the art, depending on the spatial dimensions of the electronic device 100 and the arrangement of the surface structure 32 on the second layer 30 of the heat spreader 10. It will be appreciated by those skilled in the art and can be readily determined, but in the most preferred embodiment the air flow from the fan 40 will be directed such that it is parallel to the length of the heat spreader 10; In the most preferred embodiment where the surface structure 32 is aligned in a (plural) straight line, the air flow from the fan 40 must be directed to the heat spreader 10 along a direction parallel to the surface structure 32.

In order to direct the air flow from the fan 40 in a desired manner, an air diffuser (sometimes referred to as a duct), denoted by the reference numeral 50, is combined with the heat spreader 10 as shown in FIG. Connected between the fans 40. The air diffuser 50 matches the exit angle of the air flow from the fan 40 with the arrangement of the surface structure 32 of the heat spreader 10, in particular the heat spreader 10. By "straightening" the air flow as the air flow from the fan 40 enters the heat spreader 10, the air flow can be used as effectively as possible in the heat dissipation from the device 100. Indeed, the use of an air diffuser 50 allows the fan 40 to run at low speeds (and thus save power and battery life) while allowing for equal heat dissipation or operating at the same speed without the diffuser 50. It has been found that greater heat dissipation can be achieved compared to the fan 40, or both of them are possible.

Referring now to the embodiment of FIG. 10, the heat spreader 10, together with the fan 40 and the air diffuser 50, allows the first layer 20 of the heat spreader 10 to be coupled with a heat source 110 such as a chipset. Disposed in a portable electronic device 100 such as a cellular phone so as to be in a thermoelectric connection. In addition, the heat spreader 10 is disposed between the heat source 110 and the second component 120, such as a part of the outer case or a battery of the mobile phone, to heat the second component 120 by the heat source 110. Shield from. The fan 40 generates an air flow directed by the air diffuser 50 across the surface structure 32 of the second layer 20 of the heat spreader 10, from the heat source 110 to the heat spreader 10. To dissipate the heat transferred.

Thus, a first layer 20 comprising at least one sheet formed of compressed particles of exfoliated graphite having two major surfaces 20a and 20b; And a second layer having a surface structure 32 on one of the major surfaces of the metal foil layer 30 as a second layer 30 comprising a metal foil having two major surfaces 30a and 30b. 30, the first major surface 20a of the graphite layer 20 and the second major surface 30a of the metal foil layer 30 and the first major surface 20a of the graphite layer 20 In thermal connection with each other, the surface structure 32 on the major surface 30b of the metal foil layer 30 includes raised fins to form airflow turbulence, increase heat dissipation surface area, or both. When using the heat spreader 10, in particular with the fan 40 and the air spreader 50, the heat from the (plural) heat source 110 of the low profile device 100 is better than ever seen. It can effectively dissipate in a manner.

All patents, patent applications and publications referenced in the present invention are incorporated by reference.

The foregoing description is intended to enable those skilled in the art to practice the invention. It is not intended to be exhaustive or to limit every possible change and modification that will become apparent to those skilled in the art from this specification. However, the scope of the present invention as defined by the following claims is intended to cover all such changes and modifications. The claims are intended to cover any arrangements and sequences of the elements and steps referred to that are effective to meet the objects of the present invention, unless the context specifically indicates otherwise.

Claims (20)

As a heat spreader,
(a) a first layer comprising at least one sheet formed of compressed particles of exfoliated graphite having two major surfaces; And
(b) a second layer comprising a metal foil having two major surfaces, the second layer having a surface structure on the first major surface of the metal foil layer;
At least about 25% of the surface area of the first major surface of the graphite layer adheres to, adheres to, or contacts the second major surface of the metal foil layer, and the surface structure on the first major surface of the metal foil layer is the first layer thickness. A ridge structure having a height of about 10 times or less, comprising a ridge structure that increases at least one of airflow turbulence and heat dissipation surface area,
Heat spreader.
The method of claim 1,
Wherein the first layer has a thickness of about 0.05 mm to about 2.0 mm,
Heat spreader.
The method of claim 1,
Wherein the first layer has a horizontal thermal conductivity of at least about 150 W / mK,
Heat spreader.
The method of claim 1,
The second layer has a thickness of about 0.025 mm to about 1.0 mm,
Heat spreader.
The method of claim 4, wherein
Wherein the metal foil comprises aluminum, copper, steel, or a combination thereof,
Heat spreader.
As an electronic device,
(a) a heat spreader,
(Iii) a first layer comprising at least one sheet formed of compressed particles of exfoliated graphite having two major surfaces; And
(Ii) a second layer comprising a metal foil having two major surfaces, the second layer having a surface structure on the first major surface of the second layer;
At least about 25% of the surface area of the first major surface of the first layer adheres to, adheres to, or contacts the second major surface of the second layer, and the surface structure on the first major surface of the second layer is A heat spreader having a height of about 10 times or less of the layer thickness and increasing one or more of air flow turbulence and heat dissipation surface area; And
(b) a mechanism for directing air across the surface structure of the second layer of the heat spreader;
Electronic devices.
The method of claim 6,
Wherein the first layer of the heat spreader has a thickness of about 0.05 mm to about 2.0 mm,
Electronic devices.
The method of claim 6,
Wherein the first layer of the heat spreader has a horizontal thermal conductivity of at least about 150 W / mK,
Electronic devices.
The method of claim 6,
The second layer of the heat spreader has a thickness of about 0.025 mm to about 1.0 mm,
Electronic devices.
10. The method of claim 9,
Wherein the metal foil of the heat spreader comprises aluminum, copper, steel, or a combination thereof,
Electronic devices.
The method of claim 6,
Wherein the mechanism for directing air across the surface structure of the second layer of heat spreader comprises a fan;
Electronic devices.
The method of claim 11,
The fan comprises an air diffuser,
Said air diffuser directs air flow across said heat spreader to improve heat dissipation as compared to a fan without air diffuser,
Electronic devices.
The method of claim 6,
The second major surface of the first layer of the heat spreader is in thermal connection with the surface of the heat source,
Electronic devices.
The method of claim 13,
The surface area of the second major surface of the first layer of the heat spreader is greater than the surface area of the heat source portion in thermal connection with the second major surface of the first layer of the heat spreader,
Electronic devices.
The method of claim 6,
A low profile electronic device,
Electronic devices.
As a photovoltaic solar panel,
A heat spreader, the heat spreader
(a) a first layer comprising at least one sheet formed of compressed particles of exfoliated graphite having two major surfaces; And
(b) a second layer comprising a metal foil having two major surfaces, the second layer having a surface structure on the first major surface of the second layer;
At least about 25% of the surface area of the first major surface of the first layer adheres to, adheres to, or contacts the second major surface of the second layer, and the surface structure on the first major surface of the second layer is Having a height of about 10 times or less of the layer thickness and increasing one or more of airflow turbulence and heat dissipation surface area,
Photovoltaic solar panels.
The method of claim 16,
Further comprising a mechanism for directing air across the surface structure of the second layer of heat spreader,
Photovoltaic Solar Panels.
The method of claim 16,
Wherein the first layer of the heat spreader has a thickness of about 0.05 mm to about 2.0 mm,
Photovoltaic Solar Panels.
The method of claim 16,
The second layer of the heat spreader has a thickness of about 0.025 mm to about 1.0 mm,
Photovoltaic Solar Panels.
The method of claim 17,
A mechanism for directing air flow across the surface structure of the second layer of heat spreader includes an air diffuser,
Wherein said air diffuser directs air flow across said heat spreader to improve heat dissipation as compared to without an air diffuser,
Photovoltaic Solar Panels.

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