JP2008516413A - Thermal solution with sandwich structure - Google Patents

Abstract

  A thermal solution (10) for an electronic device disposed between a heat source (100) and the outer surface of the electronic device and / or other components of the electronic device, wherein the thermal solution (10) Heat is dissipated from the heat source (100) while the second component is shielded from the heat generated by the heat source (100).

Description

Field of Invention

  The present invention manages the heat generated from a heat source, such as a component of an electronic device, and can dissipate the heat generated from the heat source while mitigating the effects of heat on the device user and other device components. Regarding the solution.

  Electronic devices with the ability to operate at high processing speeds and high frequencies, small, more complex power requirements, and other technologically advanced devices such as integrated circuits and hard drives in microprocessors and electronic and electrical components Electronic devices, including high-capacity and response memory components, electromagnetic sources, high-power optical devices such as incandescent bulbs and other devices in digital projectors, Extreme temperatures may occur. However, microprocessors, integrated circuits, and other sophisticated electronic components typically operate efficiently only under a certain range of threshold temperatures. Excessive heat generated during the operation of these components is not only detrimental to their inherent performance, but also compromises overall system performance and reliability and can even cause system failure. Increasing the range of environmental conditions in which electronic systems are expected to operate, including extreme temperatures, also contributes to the adverse effects of excess heat.

  As the need to dissipate heat from microelectronic devices increases, thermal management becomes an increasingly important factor in the design of electronic products. Both the performance reliability and expected life of an electronic device are inversely proportional to the component temperature of the device. For example, by reducing the operating temperature of a device such as a normal silicon semiconductor, the processing speed, reliability, and expected life of the device can be improved. Therefore, to maximize component life and reliability, it is most important to control the operating temperature of the device within limits set by the designer.

  In addition, the need for smaller, more integrated electronics, such as laptop computers, cell phones, digital cameras and projectors, is increasing, as the heat source is closer to the outer surface of the device and closer to other components. Means that. Heating the outer surface of the device is uncomfortable and even dangerous for the user. Moreover, heat generated from certain parts in the device can adversely affect adjacent parts. One possible solution is to insulate the heat source, since this maintains the risk that the heat generated from the heat source will concentrate on the heat source and damage the heat source. Not a preferred solution.

  For example, in some laptop computers, the hard drive that can generate a large amount of heat is usually the so-called “palm rest” of the computer where the user puts his hand when typing, the area between the keyboard and the user Placed below. In thin laptops, heat generated from the hard drive can be transferred to the user's hand through the laptop case, causing discomfort and even pain. In fact, some laptops have measured palm rest temperatures above 40 ° C. Similarly, heat-generating components can heat the bottom of a laptop computer and cause the user to feel discomfort or even pain if the laptop is placed on the user's lap. This has become a serious problem for laptop computer and other portable device manufacturers who are constantly striving to make their devices smaller and more portable.

  A group of relatively light materials suitable for dissipating heat generated from a heat source, such as an electronic component, commonly referred to as graphite, but in particular materials based on natural graphite and flexible graphite as described below. It is. These materials are anisotropic and heat dissipation devices can be designed to preferentially move heat in selected directions. Graphite materials are much lighter than metals such as copper and aluminum, and graphite materials have many advantages over copper and aluminum when used in combination with metallic parts but for heat dissipation give.

  Graphite is formed from a hexagonal array of carbon atoms or a layer plane of a mesh. The layer planes of these hexagonally arranged carbon atoms are substantially flat and are oriented or arranged to be substantially parallel to each other and equally spaced. Substantially flat, parallel, equally spaced sheets or layers of carbon atoms, usually referred to as graphene layers or basal planes, are connected or bonded together and their groups are arranged in crystallites. ing. Highly ordered graphite consists of considerable size of crystallites, which are highly aligned or oriented with respect to each other and have a well-ordered carbon layer. That is, highly ordered graphite has a highly selective crystallite orientation. Graphite has an anisotropic structure and thus exhibits or has a number of highly directional properties such as thermal and electrical conductivity and fluid diffusivity.

  Briefly, graphite can be characterized as a carbon laminate structure, ie, a structure consisting of overlapping layers or flakes of carbon atoms joined together by a weak van der Waals force. When considering a graphite structure, two axes or directions are designated: a “c” axis or direction and an “a” axis or direction. For simplicity, the “c” axis or direction can be considered as a direction perpendicular to the carbon layer. The “a” axis or direction can be considered a direction parallel to the carbon layer or a direction perpendicular to the “c” direction. Graphite suitable for producing a flexible graphite sheet has a very high degree of orientation.

  As mentioned above, the only binding force that holds one parallel layer of carbon atoms is the weak van der Waals force. Treat natural graphite, sufficiently widen the spacing between the overlapping carbon layers or flakes, and expand greatly in the direction perpendicular to that layer, ie the “c” direction, to form an expanded or expanded graphite structure In this case, the thin layer properties of the carbon layer are substantially maintained.

  Largely expanded, more specifically, graphite flakes having a final thickness, i.e., "c" dimension expanded more than about 80 times the original "c" dimension, without the use of a binder. Cohesive or integrated sheets of expanded graphite, such as webs, papers, strips, tapes, foils, mats, etc. (typically referred to as “flexible graphite”) can be produced. Graphite particles whose final thickness, that is, the “c” direction dimension is expanded to about 80 times or more than the original “c” direction dimension, can be formed into an integrated flexible sheet without using a binder. It is believed that forming by compression is possible due to the mechanical interlocking force or cohesiveness achieved between the highly expanded graphite particles.

  In addition to flexibility, the sheet material has expanded graphite particles and a graphite layer oriented substantially parallel to the opposing surface of the sheet obtained by very large compression, such as roll pressing. As noted above, it has also been found that it has a high degree of anisotropy in terms of thermal and electrical conductivity and fluid diffusivity, comparable to the starting natural graphite. The sheet material produced in this way is excellent in flexibility, has good strength and is highly oriented.

  In brief, anisotropic graphite sheet materials that do not contain flexible binders, such as webs, paper, strips, tapes, foils, mats, etc., are manufactured under a predetermined load, In the absence of a binder, a graphite sheet having a “c” dimension that expands to about 80 times or more than the original particle is compressed or compressed, and is a substantially flat, flexible, integrated graphite sheet. Forming. Expanded graphite particles are generally worm-like in appearance or elongated, and after being compressed, maintain compression set and are aligned with the opposing major surfaces of the sheet. The density and thickness of the sheet material can be varied by controlling the degree of compression. The density of the sheet material is about 0.04 g / cm3 to 2.0 g / cm3. Flexible graphite sheet material exhibits a considerable degree of anisotropy because the graphite particles are oriented parallel to the opposing parallel major surfaces of the sheet, the degree of anisotropy rolling the sheet material Increased by pressing and increasing the orientation. In a roll pressed anisotropic sheet material, the thickness, ie, the direction perpendicular to the opposing parallel sheet surface, comprises the “c” direction and is along the length and width, ie, the opposing main The direction along or parallel to the surface comprises the “a” direction, and the thermal, electrical and fluid diffusivities of the sheets are very large and differ by orders of magnitude in the “c” and “a” directions.

  It has been proposed to use exfoliated sheets of graphite compressed particles (ie, flexible graphite) as heat sinks, thermal interfaces and heat sink components for dissipating heat generated from a heat source (eg, the United States). Patents 6,245,400, 6,482,520, 6,503,626, and 6,538,892) are referred to as "temperature at contact", ie outside the electronic device. The problem of the surface generating heat to the extent that the user feels uncomfortable or at risk and heating of adjacent components has not been adequately addressed.

  Moreover, due to the flexibility of the graphite material, it is difficult to form complex structures or shapes with the graphite material. Such complex shapes are desirable when the material is used, for example, as a fin that fits around a device component or in an irregular space or is attached to a graphite or metal heat sink base. Furthermore, since graphite cannot be soldered in place like metal fins, it is also a problem to attach graphite fins to a metal base.

  Another problem in using graphite in electronic components is the unreasonable fear that individual graphite particles or flakes may delaminate from the graphite heat dissipation component. Given the conductivity of graphite, this delamination may interfere with the operation of the part where the graphite material is located.

  Accordingly, there is a continuing need for improved designs of thermal solutions for electronic devices that give the weight and thermal advantages of graphite parts, formability, and other advantages over metal parts.

  The present invention provides a thermal solution that can dissipate heat from an electronic component while simultaneously shielding a user or an adjacent component from the effects of heat generated from the component. The thermal solution of the present invention is an anisotropic sheet of exfoliated graphite compressed particles sandwiched between non-graphitic materials, particularly metallic materials such as aluminum or copper. (Sometimes called “flexible graphite”). The term “flexible graphite” as used herein also includes sheets of pyrolytic graphite, either alone or as a laminate. The in-plane thermal conductivity of the flexible graphite sheet used as the thermal solution of the present invention is substantially higher than its in-plane thermal conductivity. That is, the thermal solution of the present invention has a relatively high thermal anisotropy ratio (on the order of 10 or higher). This thermal anisotropy ratio is a ratio of in-plane thermal conductivity and through-plane thermal conductivity.

  By sandwiching the flexible graphite material between the other materials, other advantages such as formability or formability and graphite encapsulation properties are obtained while maintaining the thermal properties of the graphite. For example, if the non-graphite outer layer comprises a plastic material, exfoliation of graphite is prevented. Other materials that can be used as the non-graphite outer layer include titanium nitride, boron nitride, and silicon carbide. Most preferably, however, the non-graphite outer layer comprises a metal-based material such as copper, aluminum, magnesium, titanium, etc., in particular aluminum. Aluminum is not as heat conductive as copper, but is preferred because it is lighter than copper.

  By using a metal-based outer layer, the resulting structure can be shaped and / or formed into a complex shape that meets special spatial requirements, taking advantage of the isotropic nature of the metal, and making the heat more efficient in the graphite core The graphite exfoliation can be suppressed while being dispersed. In fact, as will be apparent to those skilled in the art, the sandwiched outer layers need not be made of the same material, and different materials can be used to maximize optimum performance.

However, when forming a sandwich-like thermal solution, the nature of the material selected for the outer layer and the thickness of the three layers can have a significant impact on the thermal performance of the thermal solution. For example, both thermal conductivity (measured as W / m ° K) and thermal diffusivity, ie the rate at which heat diffuses through an object (measured as mm ² / sec), are more important due to the nature and thickness of these layers. May be affected. Thus, the material used for the non-graphite outer layer and the thickness of the individual layers making up the sandwich-like structure of the present invention is preferably the thermal function expressed as Fx for each of the outer layers combined with the graphite-based core: It should be chosen to be about -10 to about +7.

で表され、ここで、Ｙ_１は、外側層の一方に対するヤング率であり、Ｙ_２は、グラファイト系コアに対するヤング率であり、Ｔｈｉｃｋ_１は、ミリメートル（ｍｍ）で表した外側層の厚さであり、Ｔｈｉｃｋ_２は、グラファイト系コアの厚さであり、Ｔｃ_１は、外側層の熱伝導率であり、Ｔｃ_２は、グラファイト系コアの熱伝導率であり、ｄ_１は、外側層の密度であり、ｄ_２は、グラファイト系コアの密度である。 The thermal function of the outer layer / graphite core combination is:

Where Y ₁ is the Young's modulus for _one of the outer layers, Y ₂ is the Young's modulus for the graphite-based core, and Thick ₁ is the thickness of the outer layer in millimeters (mm). Thick ₂ is the thickness of the graphite-based core, Tc ₁ is the thermal conductivity of the outer layer, Tc ₂ is the thermal conductivity of the graphite-based core, and d ₁ is the outer layer's thermal conductivity. Density, and d ₂ is the density of the graphite-based core.

  If the thermal function of both outer layers and flexible graphite core is about -10 to about +7, it can optimize both the thermal conductivity and thermal diffusivity of the sandwich structure of the present invention to provide an effective thermal solution it can. That is, the temperature gradient represented by Δt from one position on the thermal solution to another is minimized. When Fx deviates from the preferred range, a relatively low Δt may be obtained, but such a phenomenon is not designed as if the Fx range of about −10 to about +7 is maintained. It seems to be just a coincidence.

  The sandwich structure of the present invention can be formed by various methods. For example, a graphite sheet or laminate of sheets is placed between the outer layers and the edges of the outer layers are melted together (eg for plastic materials) or welded or soldered together (eg for metals) Can do. Alternatively, the edges of the outer layer are folded together to form a sandwich structure, or an adhesive is applied to the surface of the outer layer and / or the graphite layer to adhere the outer layer together and / or to the graphite. be able to.

  The sandwich thermal solution of the present invention comprises two major surfaces, one of which is operated in contact with the surface of a heat source, for example a light source casing in a hard drive or digital projector. The area of the thermal solution should be larger than the contact area of the thermal solution on the heat source so that heat is dissipated from the heat source due to the in-plane thermal conductivity of the thermal solution. One of the main surfaces (which need not be the same main surface as the surface in contact with the heat source) also operates in contact with a heat dissipation device, such as a heat sink, so that the heat generated from the heat source is relatively low in the thermal solution. Due to the high in-plane thermal conductivity, it is most advantageous to diverge through the thermal solution and be directed to a heat sink where it is dissipated.

  Because the thermal conductivity through the thickness of the graphite is relatively low (in other words, the thermal anisotropy ratio is high), the heat generated from the heat source does not move easily through the thermal solution. Therefore, if a thermal solution is placed between the heat source and the outer surface of the device in which the heat source is located, or between the heat source and another part in the device in which the heat source is located, the thermal solution The solution reduces or eliminates heat flow from the heat source to the outer surface or other components. Since the thermal solution of the present invention is moldable, it can also be used in applications where space is limited or the thermal solution needs to be fitted around or close to the structure in the device.

  Furthermore, another advantage of using a flexible graphite / metal sandwich structure in the thermal solution of the present invention is that the product of the present invention may block electromagnetic and radio frequency (EMI / RF) interference. is there. The thermal solution of the present invention is believed to shield the components of the device in which the thermal solution is located from EMI / RF interference, in addition to its primary heat dissipation / shielding function.

  In another embodiment of the present invention, the thermal solution can have a thermal interface material, such as thermal grease, or is described in International Patent Application No. PCT / US02 / 40238, and / or A graphite-based thermal interface commercially available as an eGraf Hi-Therm (trade name) product from Advanced Energy Technology Inc. of Lakewood, Ohio is inserted between the thermal solution and the heat source, and the heat source and the thermal solution of the present invention are connected. Heat transfer between can be promoted. In addition, a compressible material, such as rubber or polyurethane foam pad, is placed on the side of the heat source opposite the thermal solution of the present invention, biasing the heat source relative to the thermal solution, and from the heat source to the thermal solution of the present invention. Heat transfer can be promoted.

  In addition, the thermal conductivity is relatively low to improve the mechanical robustness of the thermal solution and to further block or shield heat transfer from the heat source to the outer surface of the device or to other device components. A low material, such as a plastic material such as Mylar® or other resin or similar material, can be placed over the thermal solution.

  Accordingly, it is an object of the present invention to provide an improved thermal solution for dissipating heat from electronic device components while simultaneously shielding adjacent structures from heat.

  Yet another object of the present invention is to provide a thermal solution having a sufficiently high thermal anisotropy ratio to effectively dissipate heat while avoiding heat transfer to adjacent structures.

  Another object of the present invention is to provide a thermal solution having a thermal function of about −10 to about +7.

  Yet another object of the present invention is to provide a moldable thermal solution that can both dissipate heat and shut off heat in an environment where available space is limited.

  These and other objects, which will be apparent to those of ordinary skill in the art upon reading the following description, are systems for dissipating and shielding heat for electronic devices (eg, laptop computers), the systems comprising electronic devices And the thermal solution, the electronic device having a first part (eg a hard drive), the first part being on the outer surface of the electronic part (eg a laptop case) and / or the device Comprising a heat source for transferring heat to a second part (e.g. a laptop chipset), the thermal solution having two main surfaces, wherein one of the main surfaces is in contact with the first part Arranged to operate and the thermal solution is the first component and the outside of the electronic component from which the first component transfers heat Inserted between the face and / or the second part, the thermal solution comprising at least one sheet of flexible graphite sandwiched between outer layers, in particular metals, for example aluminum, Can be achieved by the system. The thermal solution preferably has an in-plane thermal conductivity of at least about 140 W / m ° K, more preferably at least about 200 W / m ° K, and a through-plane thermal conductivity of about 12 W / m ° K or less, more preferably Is about 10 W / m ° K or less.

により求められる、Ｆｘで表される熱関数が約−１０〜約＋７になるように選択され、式中、Ｙ_１は、外側層の一方に対するヤング率であり、Ｙ_２は、グラファイト系コアに対するヤング率であり、Ｔｈｉｃｋ_１は、ミリメートル（ｍｍ）で表した外側層の厚さであり、Ｔｈｉｃｋ_２は、グラファイト系コアの厚さであり、Ｔｃ_１は、外側層の熱伝導率であり、Ｔｃ_２は、グラファイト系コアの熱伝導率であり、ｄ_１は、外側層の密度であり、ｄ_２は、グラファイト系コアの密度である。 In a preferred embodiment of the present invention, the material used for the non-graphite outer layer and the thickness of the individual layers making up the sandwich structure of the present invention are preferably: :

Is selected such that the thermal function represented by Fx is about −10 to about +7, where Y ₁ is the Young's modulus for _one of the outer layers, and Y ₂ is for the graphite-based core Young's modulus, Thick ₁ is the thickness of the outer layer in millimeters (mm), Thick ₂ is the thickness of the graphite-based core, Tc ₁ is the thermal conductivity of the outer layer, Tc ₂ is the thermal conductivity of the graphite-based core, d ₁ is the density of the outer layer, and d ₂ is the density of the graphite-based core.

  The system of the present invention further includes a heat dissipation device, such as a heat sink, a heat pipe, a heat plate, or a combination thereof disposed not directly adjacent to the first component, and further the main surface of the thermal solution. Advantageously one of them operates in contact with the heat dissipation device.

  In another embodiment of the present invention, the thermal solution can have a protective coating thereon, such as plastic. Most preferably, the thermal conductivity of the protective coating is less than the through-plane thermal conductivity of at least one sheet of flexible graphite. A heat transfer material, such as a thermal interface material, can also be placed between the thermal solution and the first component. In addition, a biasing material, such as a compressible pad, can be placed to bias the thermal solution component and the thermal solution together.

  It is understood that both the above general description and the following detailed description provide embodiments of the present invention and provide an overview and framework for understanding the nature and characteristics of the claimed invention. Should. The accompanying drawings are included here to form a part of this specification for further understanding of the present invention. These drawings illustrate various embodiments of the invention and, together with the description, serve to disclose the principles and operations of the invention.

  As described above, the thermal solution of the present invention is a sandwich structure, the inner core of which is formed from a sheet composed of compressed particles of exfoliated graphite. Graphite is a crystalline form of carbon comprising atoms covalently bonded in flat layered planes and weakly bonded between the planes. By treating graphite particles, such as natural graphite flakes, with an intercalate of, for example, a solution of sulfuric acid and nitric acid, the crystal structure of the graphite reacts to form a compound of graphite and intercalate. The treated graphite particles are hereinafter referred to as “intercalated graphite particles”. Upon exposure to high temperature, the intercalate in the graphite decomposes and volatilizes, and the intercalated graphite particles are accordioned in the “c” direction, ie, perpendicular to the crystal plane of the graphite. Inflated with a size of about 80 times or more of its original volume. Since the exfoliated graphite particles have an elongated appearance, they are generally called worms. These worms can be compressed together to form flexible sheets, but these sheets can be shaped and cut into a variety of shapes, unlike the original graphite flakes.

に従う値を意味する。ここでｄ（００２）は、オングストローム単位で測定した結晶構造中にある炭素のグラファイト層間における間隔である。グラファイト層間の間隔ｄは標準的なＸ線回折技術により測定される。（００２）、（００４）および（００６）ミラー指数に対応する回折ピークの位置を測定し、標準的な最小二乗技術を使用し、これらのピークすべてに対する総誤差を最小にする間隔を導く。グラファイト化度の高い炭素質材料の例としては、様々な供給源から得られる天然グラファイト、ならびに他の炭素質材料、例えば化学蒸着、重合体の高温熱分解、または溶融した金属溶液からの結晶化、等により製造されたグラファイト、がある。天然グラファイトが最も好ましい。 Suitable graphite starting materials for use in the present invention are highly graphitized carbonaceous materials that can be intercalated with organic and inorganic acids and halogens and then expanded when heated. These highly graphitized carbonaceous materials most preferably have a degree of graphitization of about 1.0. The term “degree of graphitization” used in the present invention has the following formula:

Means the value according to Here, d (002) is an interval between carbon graphite layers in the crystal structure measured in angstrom units. The spacing d between the graphite layers is measured by standard X-ray diffraction techniques. The positions of the diffraction peaks corresponding to the (002), (004) and (006) Miller indices are measured and standard least square techniques are used to derive the interval that minimizes the total error for all of these peaks. Examples of highly graphitized carbonaceous materials include natural graphite from various sources, as well as other carbonaceous materials such as chemical vapor deposition, high temperature pyrolysis of polymers, or crystallization from molten metal solutions , Etc., manufactured by. Natural graphite is most preferred.

  The graphite starting material for the flexible sheet used in the present invention can contain non-graphite components as long as the crystal structure of the starting material maintains the required degree of graphitization and is peelable. In general, any carbon-containing material that has the required degree of graphitization and that can be peeled is suitable for use in the present invention. Such graphite is preferably at least 80% by weight in purity. More preferably, the graphite used in the present invention has a purity of at least about 94%. In the most preferred embodiment, the purity of the graphite used is at least about 98%.

  A general method for producing graphite sheets is described in US Pat. No. 3,404,061 to Shane et al., The disclosure of which is incorporated herein by reference. In a typical implementation of the method of Shane et al., Flakes are contained in a solution comprising, for example, a mixture of nitric acid and sulfuric acid, preferably at a level of about 20 to about 300 parts by weight (pph) of intercalating solution per 100 parts by weight of graphite flakes. By dispersing, natural graphite flakes are intercalated. The intercalation solution contains oxidizing agents and other intercalating agents known in the art. Examples include solutions containing oxidizing agents and oxidizing mixtures such as nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid, etc., or mixtures such as concentrated nitric acid And chlorates, chromic acid and phosphoric acid, sulfuric acid and nitric acid, or a mixture of strong organic acids, such as trifluoroacetic acid, and strong oxidizing agents soluble in organic acids. Alternatively, the oxidation of graphite can be caused by using an electric potential. Chemical species that can be introduced into graphite crystals using electrolytic oxidation include sulfuric acid as well as other acids.

  In a preferred embodiment, the intercalating agent is 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 periodic acid, And so on. Although less preferred, the intercalation solution is a metal halide, such as ferric chloride, and ferric chloride mixed with sulfuric acid, or a halide, such as a solution of bromine and sulfuric acid, or an organic solvent solution of bromine. As well as bromine.

  The amount of intercalation solution is about 20 to about 350 pph, more typically about 40 to about 160 pph. After the flakes are intercalated, any excess solution is drained from the flakes and the flakes are washed with water. Alternatively, the amount of intercalation solution can be limited to about 10 to about 40 pph, thereby allowing washing as disclosed in US Pat. No. 4,895,713, the disclosure of which is hereby incorporated by reference. The process can be eliminated.

  The particles of graphite flake treated with the intercalation solution react with the surface coating of the oxidative intercalation solution at a temperature between 25 ° C. and 125 ° C., if desired, for example by mixing, selected from alcohols, sugars, aldehydes and esters. Can be contacted with a reducing agent that can be used. Suitable specific organic reagents include hexadecanol, octadecanol, 1-octanol, 2-octanol, decyl alcohol, 1,10 decanediol, decylaldehyde, 1-propanol, 1,3-propanediol, Ethylene glycol, propylene glycol, dextrose, fructose, lactose, sucrose, potato starch, ethylene glycol monostearate, diethylene glycol, dibenzoate, propylene glycol monostearate, glycerol monostearate, dimethyl oxylate, diethyl oxylate, methyl formate And compounds derived from ethyl formate, ascorbic acid and lignin, such as sodium lignosulfate. The amount of organic reducing agent is preferably about 0.5-4% by weight of the graphite flake particles.

  Improvements can also be made by applying an expansion aid before, during or immediately after intercalation. These improvements include lowering the exfoliation temperature and increasing the expansion volume (also referred to as “warm volume”). The expansion aid herein is advantageously an organic material that is sufficiently soluble in the intercalation solution so that an improvement in expansion can be achieved. More particularly, this type of organic material, preferably containing only carbon, hydrogen and oxygen, may be used. Carboxylic acids have been found to be particularly effective. Suitable carboxylic acids useful as expansion aids have at least one carbon atom, preferably up to about 15 carbon atoms, and greatly improve one or more characteristics of exfoliation in an intercalation solution. Selected from aromatic, aliphatic or cycloaliphatic, linear or branched, saturated and unsaturated monocarboxylic acids, dicarboxylic acids and polycarboxylic acids which can be dissolved in effective amounts. Any suitable organic solvent can be used to improve the solubility of the organic expansion aid in the intercalation solution.

Representative examples of saturated aliphatic carboxylic acids are acids having the formula H (CH ₂ ) _n COOH, where n is a number from 0 to about 5, formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexane Acids, etc. Instead of carboxylic acids, acid anhydrides or reactive carboxylic acid derivatives such as alkyl esters can also be used. Representative examples of alkyl esters are methyl formate and ethyl formate. Sulfuric acid, nitric acid and other known aqueous intercalates have the ability to ultimately decompose formic acid into water and carbon dioxide. For this reason, it is advantageous to immerse the flakes in an aqueous intercalate after contacting formic acid and other sensitive expansion aids with the graphite flakes. Representative examples of dicarboxylic acids are aliphatic dicarboxylic acids having 2 to 12 carbon atoms, especially 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 acids such as phthalic acid or terephthalic acid. Representative examples of alkyl esters are dimethyl oxalate and diethyl oxalate. Typical examples of cycloaliphatic acids are cyclohexane carboxylic acids, and typical examples of aromatic carboxylic acids are benzoic acid, naphthoic acid, anthranilic acid, p-aminobenzoic acid, salicylic acid, o-, m- and p-tolyl. Acids, methoxy and ethoxybenzoic acid, acetoacetamide benzoic acid and acetamide benzoic acid, phenylacetic acid and naphthoic acid. Representative examples of hydroxy aromatic acids are hydroxybenzoic 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. Of the polycarboxylic acids, citric acid is particularly preferred.

  The intercalation solution is aqueous and contains an effective amount to enhance exfoliation, preferably about 1-10% expansion aid. In embodiments in which the expansion aid is contacted with the graphite flakes before or after immersion in the intercalation aqueous solution, the expansion aid is in an amount of about 0.2 to about 10% by weight of the graphite and typically the graphite flakes. And can be mixed by suitable means such as a V-blender.

  After the graphite flakes are intercalated and the intercalated graphite flakes are mixed with an organic reducing agent, the mixture is exposed to a temperature of 25-125 ° C. to promote the reaction of the reducing agent with the intercalating coating. The heating period is up to about 20 hours, with higher temperatures in the above range being shorter, for example at least about 10 minutes. At higher temperatures, it may be less than half an hour, for example on the order of 10-25 minutes.

  The graphite particles treated in this way are sometimes referred to as “intercalated graphite particles”. By exposure to high temperatures, for example at least about 160 ° C., in particular temperatures of about 700 ° C. to 1000 ° C. or more, the intercalated graphite particles are in the c-direction, ie with respect to the crystal planes of the constituent graphite particles. It expands to about 80 to 1000 times or more of its original volume in an accordion shape at right angles. Expanded or exfoliated graphite particles are generally called worms because they exhibit an elongated appearance. These worms can be compressed together to form flexible sheets, but these sheets can be shaped and cut into various shapes, unlike the original graphite flakes.

Flexible graphite sheets and foils are cohesive and have good handling strength, eg about 0.075 mm to 3.75 mm thick by roll press processing, typical density about 0.1 to 1.5 grams. Effectively compressed to cubic centimeter (g / cm ³ ). As disclosed in US Pat. No. 5,902,762 (included herein), about 1.5-30 wt% ceramic additive is mixed with the intercalated graphite flakes and finally The resin impregnation property of a flexible graphite product can be improved. These additives include ceramic fiber particles about 0.15 to 1.5 millimeters in length. The width of the particles is preferably about 0.04 to 0.004 mm. The ceramic fiber particles are non-reactive and non-sticky to graphite and are stable at temperatures up to about 1100 ° C, preferably above about 1400 ° C. Suitable ceramic fiber particles include chopped quartz glass fibers, carbon and graphite fibers, zirconia, boron nitride, silicon carbide and magnesia fibers, natural mineral fibers such as calcium metasilicate fibers, calcium aluminum silicate fibers, aluminum oxide fibers, Etc. are formed.

  The above-described method for intercalating and exfoliating graphite flakes can be achieved by subjecting the graphite flakes to a graphitization temperature, i.e., a temperature above about 3000 ° C., as described in International Patent Application No. PCT / US02 / 379949. Can be advantageously enhanced by pretreatment with and inclusion in the intercalate of the lubricity additive.

  Pre-treatment of graphite flakes, ie, annealing, significantly increases expansion (ie, increases expansion volume by 300% or more) when the flakes are subsequently subjected to intercalation and exfoliation. In fact, the increase in expansion is at least about 50% compared to a similar process that does not include an annealing step. The temperature used in the annealing process should not be much less than 3000 ° C., since the expansion is much smaller even at temperatures as low as 100 ° C.

  The annealing of the present invention is performed for a time sufficient to obtain flakes having a high degree of expansion by intercalation and subsequent exfoliation. Typically, the time required is 1 hour or more, preferably 1 to 3 hours, most advantageously in an inert environment. For maximum beneficial results, the annealed graphite flakes are intercalated in the presence of other treatments known in the art, ie, organic reducing agents, intercalation aids such as organic acids. It is also subjected to a treatment and a detergent wash following the intercalation treatment to increase the degree of swelling. In addition, the intercalation process may be repeated for maximum beneficial results.

  As the temperature used in the present invention is within the range of 3000 ° C. is at the upper end of the range found in the graphitization process, the annealing process of the present invention is known for induction furnaces or other graphitization in this field. Can be carried out in such devices that are recognized.

  Warms made using graphite that has been annealed prior to intercalation can be `` hardened '' in one piece and have been observed to adversely affect the homogeneity of the area weight. Additives that aid in the formation of “free flowing” worms are highly preferred. By adding a lubricity additive to the intercalation solution, the floor of the calendering area traditionally used to compress (or “calender”) the floor of a compression device (eg, graphite worm into a flexible graphite sheet). The worm can be more evenly distributed across the sheet, so that the resulting sheet has higher basis weight homogeneity and greater tensile strength.The lubricity additive is preferably a long chain hydrocarbon, more A hydrocarbon having at least about 10 carbons is preferred, and other organic compounds having long-chain hydrocarbon groups can be used even in the presence of other functional groups.

  More preferably, the lubricating additive is an oil, and especially mineral oil is most preferred, considering that mineral oil is less prone to unpleasant odors and odors, which is important for long term storage. It can be seen that the specific expansion aids described in detail above also meet the definition of a lubricity additive. If these materials are used as expansion aids, the intercalate may not need to contain another lubricity additive.

  The lubricity additive is present in the intercalate in an amount of at least about 1.4 pph, more preferably at least about 1.8 pph. The upper limit containing the lubricity additive is not as important as the lower limit, but the inclusion of the lubricity additive at a level above about 4 pph does not provide a measurable advantage.

  In some cases, the flexible graphite sheet is advantageously treated with a resin, and the absorbed resin, after curing, increases the moisture resistance and handling strength, i.e., rigidity, of the flexible graphite sheet and "fixes" the shape of the sheet. To do. " A suitable resin content is preferably at least about 5% by weight, more preferably about 10-35% by weight, and preferably up to about 60% by weight. Resins that have been found to be particularly useful in the practice of this invention include acrylic, epoxy and phenol based resin systems, fluoropolymers, or mixtures thereof. Suitable epoxy resin systems include those based on diglycidyl ether of bisphenol A (DGEBA) and other polyfunctional resin systems, and the phenolic resins that can be used include resole and novolac phenol systems. . If desired, the flexible graphite can be impregnated with fibers and / or salts in addition to or in place of the resin. Furthermore, reactive or non-reactive additives can be used in conjunction with the resin system to change properties (eg, tackiness, material flow, hydrophobicity, etc.). In order to maximize the thermal conductivity of the resin impregnated material, the resin can be cured at high temperature and pressure. More particularly, by curing at a temperature of at least about 90 ° C. and a pressure of at least about 7 megapascals (MPa), excellent thermal conductivity (in fact, in-plane higher than the in-plane thermal conductivity observed with copper). A graphite material having a thermal conductivity) is produced.

  Alternatively, the flexible graphite sheet of the present invention can utilize re-pulverized flexible graphite sheet particles instead of freshly expanded worms, as described in International Patent Application No. PCT / US02 / 16730. . The sheet may be a newly formed sheet material, recycled material, scrap sheet, or any other suitable source.

  In addition, the method of the present invention can also use a mixture of unused material and recycled material.

  The source material for the recycled material may be a sheet that has been compression molded as described above, or a cut portion of the sheet, or a sheet that has been compressed with, for example, a pre-calendering roll, but not resin impregnated. Further, the source material may be a resin or impregnated sheet or cut portion of a sheet that has not been cured, or a resin impregnated and cured portion of the sheet or sheet. The source material may be a flexible graphite proton exchange membrane (PEM) fuel cell component for circulation, such as a flow field plate or electrode. Each of the various sources of graphite can be used as is or mixed with natural graphite flakes.

  After obtaining the source material of the flexible graphite sheet, it can be pulverized by a known process or apparatus for producing particles such as a jet mill, an air mill, a blender, and the like. Preferably, the majority of the particles have a diameter that passes through a 20 US mesh, more preferably a major portion (greater than about 20%, most preferably greater than about 50%) does not pass through an 80 US mesh. Most preferably, the particles have a particle size of about 20 mesh or less. When flexible graphite is impregnated with resin, it may be preferable to cool it during pulverization to avoid thermal damage to the resin system during the pulverization step.

  The size of the milled particles can be selected so that the machinability and formability of the graphite product and the desired thermal properties are balanced. For example, small particles provide a graphite product that can be easily machined and / or molded, whereas large particles have a high anisotropy and thus a graphite product with high in-plane electrical and thermal conductivity. give.

  If the source material is resin impregnated, it is preferable to remove the resin from the particles. The resin removal will be described in detail below.

  After crushing the source material and removing all resin, the material is expanded again. Re-expansion uses the intercalation and exfoliation steps described above and the methods described in US Pat. No. 3,404,061 to Shane et al. And US Pat. No. 4,895,713 to Geleen et al. Can be done.

  Typically, after intercalation, particles are exfoliated by heating the intercalated particles in a furnace. During this exfoliation step, the intercalated natural graphite flakes can be added to the intercalated particles that are recycled. Preferably, during the re-expansion step, the particles are expanded to have a specific volume in the range of about 100 cc / g to about 350 cc / g or more. Finally, after the re-expansion step, the re-expanded particles can be compressed into a flexible sheet as described above.

  If the starting material is resin impregnated, the resin should preferably be at least partially removed from the particles. This removal step should be performed between the grinding step and the re-expansion step.

  In one embodiment, the removing step comprises heating the reground particles comprising the resin, for example over an air flame. More particularly, the impregnated resin is heated to a temperature of at least about 250 ° C. to remove the resin. Care should be taken during this heating process to avoid rapid ignition of the decomposition products of the resin, which should be done by heating carefully in air or in an inert atmosphere. Can do. Preferably, the heating should be in the range of about 400 ° C. to about 800 ° C. for at least about 10 to about 150 minutes or more.

  Furthermore, the resin removal step may increase the tensile strength of the product produced by the molding method as compared to a similar method that does not remove the resin. The resin removal step is advantageous because, during the expansion step (ie, intercalation and stripping), when the resin is mixed with the intercalation agent, toxic by-products can sometimes be formed.

  Thus, by removing the resin before the expansion step, a more excellent product can be obtained as in the above increase in strength characteristics. The increase in strength characteristics is partly the result of increased expansion. When resin is present in the particles, expansion is limited.

  In addition to strength properties and environmental issues, the resin may be removed prior to intercalation, as the resin may occasionally cause a runaway exothermic reaction with acid.

  From the above, it is preferable to remove most of the resin. More preferably, greater than about 75% of the resin is removed. Most preferably, more than 99% of the resin is removed.

  After pulverizing the flexible graphite sheet, it is formed into a desired shape and cured in a preferred embodiment (when resin impregnated). Alternatively, the sheet can be cured before grinding, but curing after grinding is preferred.

  If desired, the flexible graphite sheet used to form the thermal solution of the present invention can be used as a laminate with or without an adhesive between the laminate layers. The laminate stack structure can also include a non-graphite layer, but this requires the use of an adhesive, which can be detrimental because it can delay heat dissipation across the plane of the laminate stack structure. It is. Such non-graphite layers can include metals, plastics or other non-metallic materials such as fiberglass or ceramic.

  As described above, the exfoliated sheet of graphite compressed particles formed in this way is inherently anisotropic, i.e. the direction in which the thermal conductivity of the sheet penetrates the sheet, i.e. the "c" direction. On the other hand, it is larger in the in-plane direction, that is, in the “a” direction. In this way, the anisotropy of the graphite sheet directs heat in the planar direction of the present thermal solution (ie, in the “a” direction along the graphite sheet). Such sheets are generally at least 140 W / m ° K in the in-plane direction, more preferably at least about 200 W / m ° K, most preferably at least about 250 W / m ° K, and about 12 W / m in the through-plane direction. It has a thermal conductivity of no more than ° K, more preferably no more than about 10 W / m ° K, and most preferably no more than about 6 W / m ° K. Accordingly, the thermal solution has a thermal anisotropy ratio (ie, a ratio of in-plane thermal conductivity to through-plane thermal conductivity) of about 10 or more.

  Thermal conductivity values in the in-plane and through-plane directions of the laminate can be determined by changing the directional alignment of the graphene layer of the flexible graphite sheet used to form this thermal solution, including when used to form a laminate. Or by changing the directional alignment of the graphene layer of the laminate itself after the laminate is formed. In this way, the in-plane thermal conductivity of the thermal solution is increased while the through-plane thermal conductivity of the thermal solution is decreased, thereby increasing the thermal anisotropy ratio.

  One way in which this directional alignment of the graphene layers can be achieved is by applying pressure to the structured flexible graphite sheet, calendering the sheet (ie by applying a shear force), or die pressing or reciprocating platen pressing. (I.e., by compression), but calendering is more effective for directional alignment. For example, by calendering the sheet to 1.7 g / cc for a density of 1.1 g / cc, the in-plane thermal conductivity is increased from about 240 W / m ° K to about 450 W / m ° K or more. Through-thermal conductivity decreases proportionally, thus increasing the thermal anisotropy ratio of individual sheets and, in addition, all laminates formed therefrom.

  Alternatively, when forming a laminate, for example by applying pressure, the overall directional alignment of the graphene layers forming the laminate is increased, resulting in a density greater than the starting density of the flexible graphite sheet comprising the laminate. In fact, in this manner, a laminated product is obtained with a final density of at least about 1.4 g / cc, more preferably at least about 1.6 g / cc and up to about 2.0 g / cc. The pressure can be applied by conventional means such as pressing or calendaring. A pressure of at least about 60 megapascals (MPa) is preferred, and a pressure of at least about 550 MPa, more preferably at least about 700 MPa is required to achieve a density of up to 2.0 g / cc.

  Surprisingly, by increasing the directional alignment of the graphene layer, the density remains much less than that of pure copper, and the in-plane thermal conductivity of the graphite laminate is equal to that of pure copper. , Or higher conductivity can be increased. In addition, the resulting aligned laminates have increased strength over “unaligned” laminates.

  After forming the flexible graphite material as a single sheet or laminate, it is then sandwiched between two outer layers. Most preferably, the sandwich-structured graphite core has a thickness of about 0.05 to about 2 mm.

  As noted above, the outer layer can comprise a plastic material or ceramic, but is more preferably a metal, most preferably aluminum. In addition to aluminum, the selected outer layer can comprise copper, magnesium, titanium, titanium nitride, boron nitride and silicon carbide. Each of these outer layers should be about 10 mm or less in thickness, more preferably about 7.5 mm or less, and the sandwich structure of the present invention should be as thin as practical. Indeed, it is most preferred that the thickness of the outer layer is from about 0.02 mm to about 4 mm.

  As mentioned above, the sandwich structure can melt / weld / solder the outer layer together around the graphite core, or use an adhesive, or bend the outer layer around them or corrugate And thereby encapsulating the graphite material between the outer layers. In the most preferred embodiment, the outer layers are adhered to each other with an adhesive applied only where the two outer layers contact each other to avoid any reduction in heat transfer between the outer layer and the graphite core.

により求められる、Ｆｘで表される熱関数が約−１０〜約＋７になるように選択して形成され、式中、Ｙ_１は、外側層の一方に対するヤング率であり、Ｙ_２は、グラファイト系コアに対するヤング率であり、Ｔｈｉｃｋ_１は、ミリメートル（ｍｍ）で表した外側層の厚さであり、Ｔｈｉｃｋ_２は、グラファイト系コアの厚さであり、Ｔｃ_１は、外側層の熱伝導率であり、Ｔｃ_２は、グラファイト系コアの熱伝導率であり、ｄ_１は、外側層の密度であり、ｄ_２は、グラファイト系コアの密度である。 As described above, the sandwich thermal solution has the following formula for each of the outer layers combined with the outer layer material and the thickness of the three layers in combination with the graphite-based core:

And the heat function represented by Fx is selected to be about −10 to about +7, where Y ₁ is the Young's modulus for _one of the outer layers, and Y ₂ is graphite. Thick ₁ is the thickness of the outer layer in millimeters (mm), Thick ₂ is the thickness of the graphite core, and Tc ₁ is the thermal conductivity of the outer layer. , Tc ₂ is the thermal conductivity of the graphite-based core, d ₁ is the density of the outer layer, and d ₂ is the density of the graphite-based core.

  In this way, both the thermal conductivity and thermal diffusivity of the sandwich structure of the present invention can be optimized such that Δt is minimized and an effective thermal solution is obtained.

  Referring now to the drawings, in particular FIGS. 1 and 3, one embodiment of the thermal solution of the present invention is indicated generally by the number 10. As shown in FIG. 3, thermal solution 10 comprises a sandwich structure having major surfaces 10a and 10b and is composed of compressed particles of exfoliated graphite sandwiched between outer layers 30 and 40. The sheet 20 is included. One of the major surfaces 10a or 10b of the thermal solution 10 has a size arranged to operate in contact with a heat source indicated at 100, such as a laptop computer hard drive or a cell phone chipset, and the heat source 100 The heat generated from the heat is dissipated into the thermal solution 10. The thermal solution 10 dissipates heat from the heat source 100 because the area of the main surface 10 a or 10 b in contact with the heat source 100 is larger than the area in contact with the heat source 100.

  Furthermore, one of the major surfaces 10a or 10b of the thermal solution 10 can operate in contact with a heat dissipation device 110, such as a heat sink, heat pipe, or the like. The heat dissipation device 110 can contact the thermal solution 10 on the same major surface 10 a or 10 b as the heat source 100. Due to the anisotropy of the graphite core 20 of the thermal solution 10, the heat coming from the heat source 100 spreads to the heat dissipation device 110, thereby dissipating the generated heat. In this way, the thermal solution includes acting as a radiator that dissipates heat generated from the heat source 100 and dissipates heat to the heat dissipation device 110.

  However, due to the relatively high thermal anisotropy ratio of the thermal solution 10, heat passes through the surface of the thermal solution 10 from one of the major surfaces 10a or 10b operating in contact with the heat source 100 to the other. Not transmitted effectively. Accordingly, the thermal solution 10 is placed between the heat source 10 and the outer surface because heat is not effectively transferred to the outer surface of the device (eg, laptop computer or cell phone) in which the heat source 10 is placed. If so, the temperature of such an outer surface decreases (in some cases, it decreases by 10 ° C. or more).

  Similarly, even in a device (eg, a laptop computer or cell phone) in which the heat source 10 is located, heat is not effectively transferred to another component, so that the thermal solution 10 is connected between the heat source 10 and the other component. If placed in between, the temperature at which such other components are exposed is reduced.

  FIGS. 2a and 2b show examples of placing the thermal solution 10 in a laptop computer 120 to achieve the advantageous aspects of the design of the present invention. As can be seen from FIG. 2a, the laptop computer 120 has a number of components under its protective case, including one or more heat generating components indicated at 122. Further, the laptop computer 120 can have a heat dissipation device, such as a heat sink 124. Due to the limited space, the heat absorption source 124 cannot always be disposed adjacent to the heat generating component 122.

  However, in FIG. 2 b, the thermal solution 10 is placed in the laptop computer 120 so as to cover both the heat generating component 122 and the heat sink 124. As a result, heat can flow from the heat generating component 122 to the heat absorption source 124 to be dissipated. Moreover, because the thermal solution 10 has a relatively low through-plane thermal conductivity, heat does not flow effectively through the thermal solution 10 and prevents overheating of the environment shielded by the thermal solution 10. This may not be possible when more isotropic materials such as copper or platinum are used without a graphite based core.

  Furthermore, since the metallic outer layers 30 and 40 of the thermal solution 10 can be molded, the thermal solution 10 can be molded to follow the contours of the parts in the laptop computer 120, as shown in FIG. Therefore, it does not require much additional space.

  If desired, a protective coating can be applied to the thermal solution 10 to enhance the thermal shielding effect of the thermal solution 10. Suitable protective coatings can include any suitable material sufficient for the purposes described above, such as a thermoplastic material such as polyethylene, polyester or polyimide.

  The protective coating can be applied to the thermal solution 10 in several different ways. For example, after forming the thermal solutions 10, the material from which the protective coating is formed can be applied over the individual thermal solutions 10. For this purpose, the protective coating can be applied by various coating methods well known to those skilled in the art, such as spray coating, roller coating and hot laminating press processing. The protective coating can also be applied by mechanical mapping and lamination.

  In general, the coating method adheres the protective coating to the thermal solution 10 with sufficient strength for most applications. However, if desired or coated with a relatively low adhesion protective coating, such as Mylar® polyester material and Kapton polyimide material, both commercially available from EI du Pont de Nemours and Company of Wilmington, Delaware To do so, a layer of adhesive can be applied between the thermal solution 10 and the protective coating. Suitable adhesives are adhesives that can sufficiently adhere the protective coating to the thermal solution 10, such as acrylic or latex adhesives.

Example 1
The thermal properties of some embodiments of the sandwich structure of the present invention, the properties of some materials often used as thermal solutions for electronic devices, and the thermal conductivity (Tc) expressed as W / m ° K. ) And thermal diffusivity (Td) expressed as mm ² / sec. Each sample tested has a total thickness of 1.3 mm,
(1) Flexible graphite,
(2) Copper,
(3) Aluminum,
(4) Aluminum nitride,
(5) Sandwich structure formed from 0.5 mm of copper, 1.2 mm of flexible graphite of material (1), and 0.5 mm of copper,
(6) 0.5 mm aluminum, 1.2 mm flexible graphite of material (1), and sandwich structure formed from 0.5 mm aluminum, and (7) 0.5 mm aluminum nitride, flexible graphite of material (1) It consists of a sandwich structure formed from 2 mm and aluminum nitride 0.5 mm.
The results are shown in Table I.

Table I
Sample Thermal conductivity Thermal diffusivity
Graphite 240 230
Cu 368 108
Al 210 98
Aluminum nitride 35 12
Cu-graphite-Cu 345 278
Al-graphite-Al 383 324
Aluminum nitride-100 145
Graphite-aluminum nitride

Example 2
The thermal properties of various embodiments of the sandwich structure of the present invention, the properties of several materials often used as thermal solutions for electronic devices, and the thermal conductivity (Tc) expressed as W / m ° K. , And by measuring the thermal diffusivity (Td) expressed as mm2 / sec. Each sample tested has a total thickness of 1.5 mm,
(1) Aluminum,
(2) silicon,
(3) Flexible graphite,
(4) Sandwich structure formed from aluminum 0.1 mm, silicon 1.3 mm, and aluminum 0.1 mm,
(5) Sandwich structure formed from silicon 0.1 mm, aluminum 1.3 mm, and silicon 0.1 mm,
(6) 0.1 mm aluminum, 1.3 mm flexible graphite of material (3), and sandwich structure formed from 0.1 mm aluminum, and (7) 0.1 mm flexible graphite of material (3), 1.3 mm aluminum. And a sandwich structure formed from 0.1 mm of flexible graphite of material (3).
The results are shown in Table I.

Table II
Sample Thermal conductivity Thermal diffusivity
Al 210 98
Silicon 0.6 0.04
Graphite 240 230
Al-silicon-Al 1.8 0.23
Silicon-Al-silicon 0.8 0.05
Al-graphite-Al 383 324
Graphite-Al-graphite 260 245

Example 3
A series of sandwich thermal solutions were made using graphite materials with various thermal conductivities. In each case, the sandwich structure had a thickness of 1.55 mm, a width of 15 mm, and a length of 400 mm. A pressure of 200 tons was applied to these sandwich structures to eliminate air between layers. A 10 watt heat source is placed 20 mm from one of the edges of the sandwich structure, a first thermocouple is placed 20 mm from one of the edges opposite the sandwich structure, and a second thermocouple is placed on the first thermocouple. To 200 mm. Subsequently, the thermal conductivity and thermal diffusivity of each sample were calculated. The tested samples are
(1) A sandwich structure formed from 0.05 mm of aluminum, 1.45 mm of graphite having a thermal conductivity of 200 W / m ° K, and 0.05 mm of aluminum,
(2) Sandwich structure formed from 0.05 mm aluminum, 1.45 mm graphite having a thermal conductivity of 400 W / m ° K, and 0.05 mm aluminum,
(3) Sandwich structure formed from 0.05 mm of aluminum, 1.45 mm of graphite having a thermal conductivity of 500 W / m ° K, and 0.05 mm of aluminum,
(4) Sandwich structure formed from 0.05 mm of aluminum, 1.45 mm of graphite having a thermal conductivity of 800 W / m ° K, and 0.05 mm of aluminum,
(5) A sandwich structure formed from 0.05 mm of aluminum, 1.45 mm of graphite having a thermal conductivity of 1000 W / m ° K, and 0.05 mm of aluminum. The results are shown in Table III.

Table III
Sample Core Tc Outer layer Tc Sandwich structure Sandwich structure
Tc Td
1 200 240 360 312
2 400 240 550 355
3 500 240 600 380
4 800 240 760 400
5 1000 240 940 410

Example 4
To demonstrate how the thickness of the outer layer affects the thermal properties, a series of sandwich thermal solutions were made using various thicknesses of aluminum. In each case, the sandwich structure was 15 mm wide and 400 mm long. A pressure of 200 tons was applied to these sandwich structures to eliminate air between layers. A 10 watt heat source is placed 20 mm from one of the edges of the sandwich structure, a first thermocouple is placed 20 mm from one of the edges opposite the sandwich structure, and a second thermocouple is placed on the first thermocouple. To 200 mm. Subsequently, the thermal conductivity and thermal diffusivity of each sample were calculated. The tested samples are
(1) Sandwich structure formed from aluminum 0.1 mm, flexible graphite 1.45 mm having a thermal conductivity of 200 W / m ° K, and aluminum 0.1 mm,
(2) Sandwich structure formed from 1 mm of aluminum, 1.45 mm of flexible graphite with a thermal conductivity of 200 W / m ° K, and 1 mm of aluminum,
(3) A sandwich structure formed of 3 mm of aluminum, 1.45 mm of flexible graphite having a thermal conductivity of 200 W / m ° K, and 3 mm of aluminum. The results are shown in Table IV.

Table IV
Aluminum thickness Thermal conductivity Thermal diffusivity
0.1mm 380 312
1mm 300 280
3mm 260 220

Example 5
In order to demonstrate the effect of the thermal function on Δt, a series of sandwich-like thermal solutions were manufactured, with one of the outer layers having various thicknesses. In each case, the sandwich structure was 15 mm wide and 400 mm long. A pressure of 200 tons was applied to these sandwich structures to eliminate air between layers. A 10 watt heat source is placed 20 mm from one of the edges of the sandwich structure, a first thermocouple is placed 20 mm from one of the edges opposite the sandwich structure, and a second thermocouple is placed on the first thermocouple. To 200 mm. Subsequently, the thermal conductivity and thermal diffusivity of each sample were calculated. The samples were tested using 1.45 mm flexible graphite with a thermal conductivity of 200 W / m ° K sandwiched between aluminum layers. The results are shown in Table V.

Table V
Outer layer-1 outer layer-2 Δt
Thickness Fx Thickness Fx
0.05 4.51 0.05 4.51 4
0.05 4.51 4 8.90 9
0.05 4.51 0.15 5.61 6

  Thus, by using the present invention, the heat generated from the parts of the electronic device is shielded and dissipated, the heat of the device is dissipated, and the "temperature when touched" and the heat transfer to the adjacent parts Can be reduced. These functions cannot be achieved with traditional heat-dissipating materials such as copper or aluminum, and due to isotropic properties, the temperature when touched and the heat transfer to adjacent components is hardly reduced. . Insulating materials that can be used to reduce touching temperature and heat transfer to adjacent components do not dissipate heat and cause heat accumulation around the heat source component.

  Patents, patent applications and publications cited herein are hereby incorporated by reference.

  Obviously, the invention described above can be modified in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and as will be apparent to those skilled in the art, all such modifications are within the scope defined by the claims. It is.

1 is a perspective view showing a first embodiment of a thermal solution of the present invention arranged to bridge a heat source and an endothermic source. FIG. 2A is a perspective view of the laptop computer with its top plate removed, and FIG. 2B shows an embodiment of the thermal solution shown in FIG. 1 placed in-situ in the laptop computer of FIG. 2a. FIG. . FIG. 2 is a sectional end view of the thermal solution shown in FIG. 1.

Claims (22)

A system for dissipating and shielding heat for electronic devices,
An electronic device comprising an outer surface and a first part comprising a heat source;
A thermal solution comprising two major surfaces,
The thermal solution is arranged such that one of the major surfaces operates in contact with the first component and is inserted between the first component and the outer surface of the electronic component;
The system, wherein the thermal solution comprises at least one sheet of flexible graphite sandwiched between two outer layers.   The system of claim 1, wherein the outer layer comprises a material selected from the group consisting of plastic, metal, and composite materials, or combinations thereof.   The system of claim 2, wherein at least one of the outer layers comprises aluminum. For each of the outer layers in combination with the graphite core, the following formula:

(Where Y ₁ is the Young's modulus for one of the outer layers, Y ² is the Young's modulus for the graphite core, and Thick ₁ is the thickness of the outer layer in millimeters (mm)). Thick ₂ is the thickness of the graphite-based core, Tc ₁ is the thermal conductivity of the outer layer, Tc ₂ is the thermal conductivity of the graphite-based core, and d ₁ is (The density of the outer layer, d ₂ is the density of the graphite core)
The system of claim 1, wherein the thermal function expressed by Fx is about −10 to about +7.   The electronic device further comprises a heat dissipation device disposed at a location not directly adjacent to the first component, and further wherein one of the major surfaces of the thermal solution operates in contact with the heat dissipation device. The system according to 1.   The system of claim 5, wherein the heat dissipation device comprises a heat sink, a heat pipe, a heat plate, or any combination thereof.   The system of claim 1, wherein the thermal solution has an in-plane thermal conductivity of at least about 140 W / m ° K.   The system of claim 7, wherein the thermal solution has a through-plane thermal conductivity of about 12 W / m ° K or less.   The system of claim 1, wherein the thermal solution further comprises a protective coating on the thermal solution.   The system of claim 9, wherein the thermal conductivity of the protective coating is less than the through-plane thermal conductivity of at least one sheet of the flexible graphite.   The system of claim 1, wherein a heat transfer material is disposed between the thermal solution and the first part.   The system of claim 1, wherein the electronic device is a laptop computer and the outer surface comprises a portion of a case of the laptop computer. A system for dissipating and shielding heat for electronic devices,
Comprising a thermal solution comprising two major surfaces;
The system, wherein the thermal solution comprises at least one sheet of flexible graphite sandwiched between two outer layers.   The system of claim 13, wherein the outer layer comprises a material selected from the group consisting of plastic, metal, and composite materials, or combinations thereof.   The system of claim 14, wherein at least one of the outer layers comprises aluminum. For each of the outer layers in combination with the graphite core, the following formula:

(Where Y ₁ is the Young's modulus for one of the outer layers, Y ₂ is the Young's modulus for the graphite core, and Thick ₁ is the thickness of the outer layer in millimeters (mm)). Thick ₂ is the thickness of the graphite-based core, Tc ₁ is the thermal conductivity of the outer layer, Tc ₂ is the thermal conductivity of the graphite-based core, and d ₁ is (The density of the outer layer, d ₂ is the density of the graphite core)
The system of claim 13, wherein the thermal function expressed in Fx is about −10 to about +7.   The system of claim 13, wherein the thermal solution has an in-plane thermal conductivity of at least about 140 W / m ° K.   The system of claim 17, wherein the thermal solution has a through-plane thermal conductivity of about 12 W / m ° K or less.   The system of claim 13, wherein the thermal solution further comprises a protective coating on the thermal solution.   The system of claim 19, wherein the thermal conductivity of the protective coating is less than the through-plane thermal conductivity of the at least one sheet of flexible graphite.   The system of claim 13, wherein a heat transfer material is disposed between the thermal solution and the first part.   The system of claim 21, wherein the heat transfer material comprises a metal or a thermal interface.

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