Thermal conductive material and thermal pad including the same

Abstract

The present invention relates to a heat dissipation material having improved thermal conductivity by applying graphene with a relatively high carbon content of 80% by weight or more to coat the filler, thereby improving contact between the filler and the filler or between the filler and the resin, and a heat dissipation pad including the same.

Description

Technology Field

[0001] The present invention relates to a heat dissipation material and a heat dissipation pad including the same. Background Technology

[0003] As the miniaturization and high integration of electronic devices accelerate, the demand for Thermal Interface Materials (TIMs) capable of effectively dissipating heat generated from semiconductor chips, LEDs, and power modules is surging. These materials generally consist of thermally conductive fillers and polymer resins, and their thermal conductivity performance is determined by the type and packing density of the fillers. Inorganic materials such as alumina, boron nitride, magnesia, silicon carbide, aluminum nitride, and diamond powder are primarily used as fillers, and ensuring the thermal conductivity of the fillers and inter-particle connectivity serves as a key factor in enhancing thermal conductivity.

[0004] Conventionally, increasing the filler content was used to enhance thermal conductivity; however, this resulted in problems such as increased resin viscosity, reduced moldability, and mechanical brittleness. Furthermore, when the connectivity between fillers was low, discontinuous heat conduction paths were formed, which actually limited heat dissipation performance.

[0005] To overcome these limitations, research has been proposed to apply carbon-based nanomaterials to the surface of fillers to improve contact between fillers or between fillers and resins and to strengthen heat conduction pathways. However, most mainstream methods involve using graphene itself as a filler or directly adding it to the resin, and technology for uniformly coating the surface of fillers with pre-treated graphene has not yet been sufficiently developed. Prior art literature

[0007] U.S. Registered Patent 9716299 (July 25, 2017) U.S. Published Patent 2010-0128439 (May 27, 2010) The problem to be solved

[0008] The objective of the present invention is to provide a heat dissipation material and a heat dissipation pad containing the same, which is derived to solve the problem described above by applying graphene with a relatively high carbon content of 80 weight percent or more to improve the contact between the filler and the filler or between the filler and the resin to improve thermal conductivity. means of solving the problem

[0010] To achieve the above objective, a heat dissipation material according to one embodiment of the present invention comprises a filler made of an inorganic material and graphene coated on at least one region of the filler, wherein the graphene has a fixed carbon content of 80 to 95 weight% and a terminal functional group content of 5 to 20 weight%.

[0011] Here, the inorganic material may be one or more selected from alumina, boron nitride, magnesia, silicon carbide, aluminum nitride, and diamond powder.

[0012] And, the graphene can be coated in an amount of 0.03 to 0.5 parts by weight based on 100 parts by weight of filler.

[0013] In addition, the graphene may be one or more selected from graphene oxide, graphene reduction, expanded graphene, and carbon nanotubes.

[0014] A heat dissipation pad according to another embodiment of the present invention comprises 100 parts by weight of a polymer resin and 200 to 700 parts by weight of a heat dissipation material. Effects of the invention

[0016] According to one embodiment of the present invention, by applying graphene with a relatively high carbon content of 80% by weight or more to coat the filler, the contact between the filler and the filler or between the filler and the resin is improved, and the thermal conductivity can be improved. Brief explanation of the drawing

[0018] FIG. 1 is a cross-sectional view schematically showing a heat dissipation material according to one embodiment of the present invention. Figures 2 and 3 are photographs showing the results of Experimental Example 1. Specific details for implementing the invention

[0019] Hereinafter, embodiments of the present invention are described in detail. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various different forms, and these embodiments are provided merely to ensure that the disclosure of the present invention is complete and to more fully inform those skilled in the art of the contents of the present invention.

[0020] In this specification, when one element is described as being located 'above' or 'below' another element, this includes both the meaning that the one element is located directly 'above' or 'below' another element, and that an additional element may be interposed between the elements. In this specification, the terms 'above' or 'below' are relative concepts established from the observer's perspective, and as the observer's perspective changes, 'above' may mean 'below' and 'below' may mean 'above'.

[0021] In multiple drawings, the same reference numerals refer to substantially identical elements. Additionally, terms such as 'include' or 'have' are intended to specify the existence of the described feature, number, step, action, component, part, or combination thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0022] In describing the embodiments of the present invention, terms are defined considering the functions in the embodiments of the present invention, and these may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification.

[0024] Hereinafter, a heat dissipation material according to one embodiment of the present invention will be described in detail.

[0025] FIG. 1 is a cross-sectional view schematically showing a heat dissipation material according to one embodiment of the present invention.

[0026] Referring to FIG. 1, the heat dissipation material according to the present embodiment includes a filler and graphene.

[0027] The filler may be composed of inorganic materials and may include, for example, one or more selected from alumina (Al2O3), boron nitride (h-BN), magnesia (MgO), silicon carbide, aluminum nitride, and diamond powder.

[0028] It is preferable that the filler includes one or more shapes selected from spherical shapes of 5 to 80 μm and angular shapes to be more advantageous for coating, and for example, a mixture of spherical and angular shapes may be used. In addition, different sizes may be mixed, for example, spherical shapes with a diameter of 1 to 10 μm and angular shapes of 15 to 25 μm may be mixed in a weight ratio of 1:4 to 9.

[0029] Graphene can be coated on at least one region of the filler, for example, on at least one region of the filler surface. Such graphene can be coated in an amount of 0.03 to 0.5 parts by weight based on 100 parts by weight of filler. If the amount of graphene is less than 0.03 parts by weight, the graphene content is low, resulting in only partial coating of the filler surface. This can cause aggregation between fillers or uneven slurry dispersion, as well as a decrease in interfacial bonding strength and a negligible improvement in filling rate. If the amount exceeds 0.5 parts by weight, it can interfere with the inherent function of the filler and impair both dispersion stability and conductivity characteristics. When the above-mentioned range is satisfied, it is possible to achieve a thermal conductivity of 1.0 W / (mK) or higher.

[0030] For example, graphene can be coated in an amount of 0.03 to 0.4 parts by weight based on 100 parts by weight of filler when the filler diameter is in the range of 1 to 10 µm, 0.03 to 0.3 parts by weight based on 100 parts by weight of filler when the filler diameter is in the range of 10 to 20 µm, and 0.03 to 0.2 parts by weight based on 100 parts by weight of filler when the filler diameter is in the range of 20 to 30 µm.

[0031] In this embodiment, the graphene is one or more selected from graphene oxide, reduced graphene, expanded graphene, and carbon nanotubes, and may satisfy a diameter of 5 to 40 μm, for example, 5 to 20 μm. Such graphene may have a fixed carbon content of 80 to 95 wt%, for example, 82 to 90 wt%, and a terminal functional group content of 5 to 20 wt%, for example, 10 to 18 wt%.

[0032] Fixed carbon (FC) content is a key indicator of the structural and functional purity of graphene. A higher carbon content indicates fewer functional groups (-OH, -COOH) and better crystallinity, while a lower carbon content indicates more functional groups or oxides. If the fixed carbon content is less than 80 wt%, the impurity content increases, which may lead to reduced thermal conductivity, electrical conductivity, and mechanical stability. If it exceeds 95 wt%, the proportion of functional groups decreases, which reduces the bonding strength with the filler and may decrease coating efficiency.

[0033] Terminal functional groups refer to one or more polar groups selected from -OH, -COOH, -SO3H, and -NH2 located at the edges of graphene. They contribute to improving adhesion stability through electrostatic interactions, hydrogen bonding, or covalent bonding with the filler surface, and can play an important role in coating stability, dispersion stability, prevention of aggregation, and control of mixing viscosity, particularly in interfacial interactions with alumina. If the content of these terminal functional groups is less than 5 wt%, the electrostatic or chemical bonding with the filler surface is weakened due to the lack of functional groups, which may cause the coating to detach easily or not be uniformly distributed. If it exceeds 20 wt%, not only is the basic crystal structure of graphene damaged, but its intrinsic thermal and electrical properties may also deteriorate.

[0034] In the present invention, fixed carbon content refers to a value measured according to ASTM D3172 and means carbonaceous components excluding volatile components and ash, and terminal functional group content refers to a value quantitatively measured through XPS analysis or an elemental analyzer.

[0036] A heat dissipation pad according to another embodiment of the present invention comprises 100 parts by weight of a polymer resin and 200 to 700 parts by weight of a heat dissipation material. In this embodiment, as described above, by applying a heat dissipation material coated with graphene to a filler made of an inorganic material, it is possible to apply a larger amount of heat dissipation material than when using the filler alone, that is, a filler not coated with graphene, thereby improving heat dissipation performance.

[0037] As the polymer resin, one or more selected from silicone rubber, polyurethane, epoxy resin, polyimide, polycarbonate, polypropylene (PP), polyethylene (PE), and polyetheretherketone (PEEK) may be used.

[0038] If the content of the heat dissipation material is less than 200 parts by weight, the heat dissipation performance may be negligible, and if it exceeds 700 parts by weight, the flowability of the material during the mixing and molding process becomes extremely poor due to increased viscosity, as well as the possibility of filler aggregation increases, and the toughness and ductility may be reduced due to the relatively low resin content.

[0040] The present invention will be described in more detail below using examples. These examples are solely for the purpose of more specifically explaining the present invention, and it is obvious to those skilled in the art that the scope of the present invention is not limited by them.

[0042] Examples 1 to 8. Manufacturing of heat dissipation pads

[0043] A heat dissipation material was manufactured by coating graphene onto a filler under the conditions listed in Table 1. Then, a heat dissipation pad having a thickness of 200 μm was manufactured by adding the maximum amount to 100 parts by weight of silicone resin.

[0044] division Alumina Graphene coating content Maximum input amount Example 1 Spherical (1~10㎛) Coating (Graphene 0.25%) 350phr Example 2 Coating (Graphene 0.045%) 500phr Example 3 Coating (Graphene 0.045%) 700phr Example 4 Rectangular (1~10㎛) Coating (Graphene 0.03%) 500phr Example 5 Coating (Graphene 0.045%) 500phr Example 6 Coating (Graphene 0.06%) 500phr Example 7 Angular (15~25㎛) Coating (Graphene 0.045%) 350phr Example 8 Spherical (15~25㎛) Coating (Graphene 0.045%) 500phr

[0046] Examples 9 to 15. Manufacturing of heat dissipation pads

[0047] A heat dissipation material was prepared in the same manner as in Example 1, except that the conditions listed in Table 2 were applied. The graphene coating content was set to 0.03 parts by weight based on 100 parts by weight of filler.

[0048] division Alumina size, shape, and proportion (weight%) Maximum input amount Spherical (1~10㎛) Rectangular (1~10㎛) Spherical (15~25㎛) Angular (15~25㎛) Example 9 25 - 75 - 800phr Example 10 70 - 30 - 500phr Example 11 50 - 50 - 500phr Example 12 - 30 70 - 800phr Example 13 10 - - 90 350phr Example 14 10 - - 90 450phr Example 15 20 - - 80 450phr

[0050] Comparative Examples 1 and 2. Manufacturing of thermal pads

[0051] Comparative Example 1 manufactured a heat dissipation pad by adding 350 phr of graphene to 100 parts by weight of silicone resin, and Comparative Example 2 used an externally available semiconductor heat dissipation sheet.

[0052] In the case of Comparative Example 1, molding was impossible if graphene was added in excess of 350 phr, so it was added at 350 phr.

[0054] Experimental Example 1: Shape and Composition Analysis

[0055] Examples 2 and 5 according to the present invention were photographed using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively, and the results are shown in Figures 2 and 3.

[0056] Referring to FIGS. 2 and FIGS. 3, in Example 2 where the filler is spherical alumina, all elements are evenly distributed on the surface of the alumina, whereas in Example 5 where the filler is prismatic alumina, elements are concentrated in certain areas of the alumina. Therefore, since a more uniform distribution of elements is observed on the surface of spherical alumina than on prismatic alumina, it was found that the coating is more even when spherical alumina is used as the filler.

[0058] Experimental Example 2: Performance Evaluation

[0059] To evaluate the performance of the heat dissipation pad according to the present invention, an experiment was conducted as follows, and the results are shown in Table 3.

[0060] (1) Density

[0061] Measured according to the buoyancy method or the helium pycnometer method.

[0062] (2) Thermal diffusivity

[0063] Measured using the Laser Flash Method (LFA).

[0064] (3) Specific heat

[0065] Measured using Differential Scanning Calorimetry (DSC).

[0066] (4) Thermal conductivity

[0067] After LFA measurement, the thermal conductivity was calculated using Formula 1 below.

[0068] … … … … … … .Formula 1

[0069] In the above formula 1, k is thermal conductivity, α is thermal diffusivity, ρ is density, and C P is specific heat

[0070] division Density (g / cc) Thermal diffusivity mm 2 / s Specific heat J / g·K Thermal conductivity W / (mK) Comparative Example 1 2.232 0.480 0.931 0.998 Example 1 2.180 0.469 0.940 0.961 Example 2 2.368 0.53 0.907 1.140 Example 3 2.410 0.687 0.863 1.430 Example 4 2.462 0.467 0.914 1.052 Example 5 2.045 0.486 0.904 0.910 Example 6 2.065 0.482 0.902 0.902 Example 7 1.971 0.872 0.951 1.635 Example 8 2.437 0.581 0.901 1.276 Comparative Example 2 1.936 0.368 0.966 0.687 Example 9 2.708 0.566 0.861 1.320 Example 10 2.592 0.601 0.931 1.424 Example 11 2.616 0.582 0.905 1.387 Example 12 2.667 0.692 0.910 1.680 Example 13 1.977 0.895 0.948 1.678 Example 14 1.939 0.976 0.927 1.755 Example 15 2.095 0.974 0.927 1.861

[0071] Upon examining Examples 1 to 8, it was confirmed that the thermal conductivity was lower than that of Comparative Example 1, which was coated with an excess amount of graphene, and Examples 5 and 6, which were coated with 0.045 parts by weight of graphene while using 1-10 μm prismatic alumina as a filler. Additionally, under the same conditions, the thermal conductivity was higher when 15-25 μm spherical (Example 8) and prismatic (Example 7) fillers were applied compared to when 1-10 μm spherical and prismatic fillers were applied. Therefore, it was found that when prismatic alumina is applied as a filler, it is desirable to limit the amount of graphene coating to less than 0.045 parts by weight, and when spherical alumina is applied as a filler, it is desirable to limit the amount of graphene coating to less than 0.25 parts by weight. Looking at Examples 9 to 15, it was confirmed that all of Examples 9 to 15 had excellent thermal conductivity, and in particular, Example 15, in which spherical alumina of 1 to 10 μm and prismatic alumina of 15 to 25 μm were mixed and applied as fillers in a ratio of 1:4, was found to be the most excellent.

[0073] As explained above, the specific description of the present invention has been made through embodiments with reference to the attached drawings, but since the above-described embodiments are merely preferred examples of the present invention, the present invention should not be understood as being limited only to the above-described embodiments, and the scope of the rights of the present invention should be understood as the claims set forth below and equivalent concepts.

[0074] For example, the drawings are schematically illustrated with each component as the main subject to aid understanding, and the thickness, length, number, etc., of each illustrated component may differ from the actual product due to the process of drawing creation. Furthermore, the material, shape, dimensions, etc., of each component shown in the above embodiments are merely examples and are not specifically limited; various modifications are possible within a scope that does not substantially deviate from the effects of the present invention.

Claims

Claim 1 A heat dissipation material comprising: a filler; and graphene coated on at least one region of the filler; wherein the filler is a mixture of spherical shapes with a diameter of 1 to 10 μm and prismatic shapes with a diameter of 15 to 25 μm in a weight ratio of 1:4 to 9, and the graphene is coated in an amount of 0.03 to 0.5 parts by weight based on 100 parts by weight of the filler. Claim 2 A heat dissipation material according to claim 1, wherein the filler is composed of one or more inorganic materials selected from alumina, boron nitride, magnesia, silicon carbide, aluminum nitride, and diamond powder. Claim 3 delete Claim 4 A heat dissipation material according to claim 1, wherein the graphene is one or more selected from graphene oxide, graphene reduction, expanded graphene, and carbon nanotubes. Claim 5 The heat dissipation material according to claim 1, wherein the graphene has a fixed carbon content of 80 to 95 weight% and a terminal functional group content of 5 to 20 weight%. Claim 6 A heat dissipation pad comprising 100 parts by weight of a polymer resin; and 200 to 700 parts by weight of a heat dissipation material according to any one of claims 1, 2, 4, and 5 based on 100 parts by weight of the polymer resin.

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