Thermal conductive sheet

Abstract

To provide a thermal conductive sheet containing thermosetting resin capable of improving the thermal conductivity.SOLUTION: In a disclosed thermal conductive sheet 1, a thermal conductive material 10 contains: first particles 12, which are long, coarse particles; second particles 14, which are short, coarse particles, and third particles 16, which are short, minute particles at a predetermined ratio. Furthermore, this thermal conductive sheet 1 has a thermosetting resin 20 content limited to 6 wt% or less of the total mass of the sheet. This allows formation of a heat conduction path P inside the thermal conductive sheet 1, where the first particles 12, the second particles 14, and the third particles 16 are in contact with each other, resulting in the thermal conductivity being greatly improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet. [Background technology]

[0002] Electronic devices such as integrated circuits (ICs) are becoming increasingly dense in order to improve their performance. These high-density electronic devices generate a large amount of heat during use, so they are sometimes used in conjunction with thermally conductive sheets. One example of such a thermally conductive sheet is the ceramic sheet described in Patent Document 1. The ceramic sheet described in Patent Document 1 is a sintered body of ceramic particles formed into a sheet. Other examples of thermally conductive sheets are disclosed in Patent Documents 2 and 3. The thermally conductive sheets described in Patent Documents 2 and 3 have inorganic particles (thermally conductive material) dispersed within a binder resin formed into a sheet. A thermosetting resin or the like is used as the binder resin for this thermally conductive sheet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-158259 [Patent Document 2] Japanese Patent Publication No. 2022-097775 [Patent Document 3] Japanese Patent Application Publication No. 2022-191990 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the density of electronic devices has been further increased, and the demand for thermal conductivity of thermally conductive sheets has also increased. The technology disclosed herein has been made in response to such demands, and aims to improve the thermal conductivity of thermally conductive sheets containing thermosetting resins. [Means for solving the problem]

[0005] The thermally conductive sheet disclosed herein includes a thermally conductive material and a thermosetting resin. The thermally conductive material of the thermally conductive sheet includes at least first particles having an average aspect ratio of 1.5 or greater and an average particle diameter of 5 μm to 70 μm, second particles having an average aspect ratio of less than 1.5 and an average particle diameter of 10 μm to 80 μm, and third particles having an average aspect ratio of less than 1.5 and an average particle diameter of 0.1 μm to 10 μm. When the total mass of the thermally conductive material is 100 wt%, the content of the first particles is 1 wt% to 7 wt%, the content of the second particles is 20 wt% to 40 wt%, and the content of the third particles is 50 wt% to 75 wt%. Furthermore, when the total mass of the thermally conductive sheet is 100 wt%, the content of the thermosetting resin is 6 wt% or less.

[0006] The thermally conductive sheet having the above configuration has excellent thermal conductivity. While not intending to limit the technology disclosed herein, it is believed that this improved thermal conductivity is achieved through the following mechanism. First, the thermally conductive material of this thermally conductive sheet contains large, elongated particles (first particles), large, short particles (second particles), and small, short particles (third particles). The long, first particles of this thermally conductive material tend to be oriented in a certain direction. This forms a thermal conduction path along the orientation direction of the first particles. Next, the short, second particles tend to be arranged between the elongated, first particles. This forms a thermal conduction path that intersects with the orientation direction of the first particles. Finally, the minute, short, third particles penetrate into the gaps between other inorganic particles (first particles, second particles). This facilitates contact between other inorganic particles via the third particles, forming a wide variety of thermal conduction paths. As described above, the thermal conductive sheet disclosed herein easily forms thermal conduction paths where inorganic particles come into contact with each other, thereby achieving high thermal conductivity. However, if the content of thermosetting resin in the thermal conductive sheet is too high, a large amount of thermosetting resin may penetrate between the inorganic particles, potentially cutting off the thermal conduction paths. For this reason, the content of thermosetting resin in the thermal conductive sheet disclosed herein is set to 6 wt% or less relative to the total mass of the thermal conductive sheet. This allows for the production of a thermal conductive sheet with favorable thermal conduction paths and high thermal conductivity. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating a thermally conductive sheet according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the technology disclosed herein will be described below. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. In other words, the technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. Furthermore, the notation "A to B" indicating a numerical range in this specification means A or more and B or less.

[0009] [Thermal Conduction Sheet] First, one embodiment of the thermally conductive sheet disclosed herein will be described. Fig. 1 is a cross-sectional view schematically showing the thermally conductive sheet according to this embodiment. In Fig. 1, the symbol X represents the "width direction (of the thermally conductive sheet)" and the symbol Z represents the "thickness direction (of the thermally conductive sheet)." In addition, in this specification, the direction perpendicular to the plane of the paper in Fig. 1 is referred to as the "depth direction (of the thermally conductive sheet)."

[0010] As shown in FIG. 1, the thermally conductive sheet 1 is a sheet-like member having a first surface 1a and a second surface 1b opposite the first surface 1a. The thermally conductive sheet 1 transfers heat from a device (such as an electronic device) placed on the first surface 1a to the second surface 1b. The shape of the thermally conductive sheet 1 is not particularly limited, and common shapes such as a strip, a disk, or a frame can be used without any particular restrictions. The thickness of the thermally conductive sheet 1 is preferably 3 mm or less, more preferably 2.75 mm or less, even more preferably 2.5 mm or less, and particularly preferably 2.25 mm or less. As the thermally conductive sheet 1 becomes thinner, the thermal conductivity from the first surface 1a to the second surface 1b tends to improve. On the other hand, the lower limit of the thickness of the thermally conductive sheet 1 is preferably 0.1 mm or more, more preferably 0.2 mm or more, even more preferably 0.3 mm or more, and particularly preferably 0.4 mm or more. This allows for the provision of a thermally conductive sheet 1 with excellent durability. Furthermore, according to the technology disclosed herein, even a thick thermally conductive sheet 1 such as that described above can exhibit high thermal conductivity.

[0011] Next, the thermally conductive sheet 1 according to this embodiment includes a thermally conductive material 10 and a thermosetting resin 20. Each element will be specifically described below.

[0012] 1. Thermal conductive material The thermally conductive material 10 is a powder material containing a plurality of inorganic particles. The inorganic particles in the thermally conductive material 10 come into contact with each other, forming a thermal conduction path P within the thermally conductive sheet 1. Heat applied to the first surface 1a of the thermally conductive sheet 1 is then transferred to the second surface 1b via the thermal conduction path P. The inorganic particles in the thermally conductive material 10 need only have a certain level of thermal conductivity, and any conventionally known inorganic material can be used without particular limitation. Examples of materials for the thermally conductive material 10 include ceramic materials, metal materials (including alloys), and carbon-based materials. However, thermally conductive sheets for electronic devices may require insulation to prevent electrical leakage. In this case, it is preferable to use a ceramic material for the thermally conductive material 10. This allows for both insulation and thermal conductivity.

[0013] In this specification, "ceramic material" refers to an inorganic material whose main component is ceramic. Here, "main component" means that the ceramic content is 90 wt% or more (preferably 95 wt% or more, and particularly preferably 99 wt% or more) when the total mass of the inorganic components in the particle is 100 wt%. In addition, examples of ceramics include oxide ceramics, non-oxide ceramics, and glass ceramics.

[0014] Oxide-based ceramics are ceramic materials containing oxides of various metal elements. Examples of such oxide-based ceramics include alumina (Al2O3), zirconia (ZrO2), yttria (Y2O3), titanium oxide (TiO2), magnesia (MgO), silica (SiO2), calcia (CaO), ceria (CeO2), tin oxide (SnO2), ferrite (Fe2O3), spinel (MgAl2O4), zircon (ZrSiO4), barium titanate (BaTiO3), and forsterite (Mg2SiO4). The inorganic particles in the thermally conductive material 10 may also be composite metal oxides containing two or more of the above-mentioned oxide-based ceramics. Examples of such composite metal oxides include steatite (MgO·SiO2), cordierite (2MgO·2Al2O3·5SiO2), and mullite (3Al2O3·2SiO2).

[0015] Non-oxide ceramics are ceramic materials containing nitrides, carbides, borides, silicides, etc. of various metal elements. Examples of nitride ceramics include boron nitride (BN), aluminum nitride (AlN), titanium nitride (TiN), gallium nitride (GaN), carbon nitride (CNx), and sialon (Si3N4-Al2O3 solid solution; Sialon). Examples of carbide ceramics include tungsten carbide (WC), chromium carbide (CrC), vanadium carbide (VC), niobium carbide (NbC), molybdenum carbide (MoC), tantalum carbide (TaC), titanium carbide (TiC), zirconium carbide (ZrC), hafnium carbide (HfC), silicon carbide (SiC), and boron carbide (B4C). Examples of boride ceramics include molybdenum boride (MoB), chromium boride (CrB2), hafnium boride (HfB2), zirconium boride (ZrB2), tantalum boride (TaB2), titanium boride (TiB2), etc. Examples of silicide ceramics include zirconium oxide silicate, hafnium oxide silicate, titanium oxide silicate, lanthanum oxide silicate, yttrium oxide silicate, titanium oxide silicate, tantalum oxide silicate, tantalum oxynitride silicate, etc.

[0016] Glass ceramics are ceramic materials that contain amorphous materials (glass materials). Examples of such glass-ceramics include SiO2-B2O3-based glass, SiO2-RO (RO represents an oxide of a Group 2 element, such as MgO, CaO, SrO, or BaO; the same applies hereinafter), SiO2-RO-R2O (RO represents an oxide of an alkali metal element, such as Li2O, Na2O, KO, Rb2O, Cs2O, or Fr2O, particularly Li2O; the same applies hereinafter), SiO2-B2O3-R2O-based glass, SiO2-RO-ZnO-based glass, SiO2-RO-ZrO2-based glass, SiO2-RO-Al2O3-based glass, SiO2-RO-Bi2O3-based glass, SiO2-R2O-based glass, SiO2-ZnO-based glass, SiO2-ZrO2-based glass, SiO2-Al2O3-based glass, RO-R2O-based glass, and RO-ZnO-based glass. The glass ceramic may contain one or more components in addition to the main components indicated in the name. The inorganic particles in the thermally conductive material 10 may contain not only general amorphous glass but also crystallized glass containing crystals.

[0017] Here, the thermally conductive material 10 according to this embodiment includes first particles 12, second particles 14, and third particles 16. The thermally conductive material 10 including these three types of inorganic particles can form a suitable heat conduction path P within the thermally conductive sheet 1. Each of the inorganic particles will be described below.

[0018] (1) First particle The first particles 12 are elongated particles with an average aspect ratio of 1.5 or more. These first particles 12 can form heat conduction paths with excellent thermal conductivity along their longitudinal direction. The average aspect ratio of the first particles 12 is preferably 2 or more, more preferably 5 or more, even more preferably 6 or more, and particularly preferably 8 or more. This allows for the formation of more suitable heat conduction paths. On the other hand, the upper limit of the average aspect ratio of the first particles 12 is not particularly limited, and may be 20 or less, 17 or less, 15 or less, or 12 or less. In this specification, the "average aspect ratio" refers to the average value of the ratio of the longitudinal dimension to the transverse dimension of a predetermined number of inorganic particles. For example, the aspect ratio can be obtained by drawing the smallest rectangle circumscribing the inorganic particles in a cross-sectional SEM image of the thermal conductive sheet and calculating the ratio (A / B) of the longitudinal dimension A to the transverse dimension B of the rectangle. Then, the average aspect ratio can be obtained by calculating the arithmetic mean value of the aspect ratios of a predetermined number (for example, 75 or more) of inorganic particles.

[0019] The first particles 12 may be elongated particles, and the specific shape is not particularly limited. Examples of the elongated first particles 12 include a scale shape, an ellipse shape, a rod shape, a needle shape, a plate shape, and a peanut shape (i.e., the shape of a peanut shell). Among the shapes mentioned above, the first particles 12 are preferably plate-shaped particles. Plate-shaped particles have the advantage of easily ensuring a contact area with the second particles 14 and the third particles 16 described below.

[0020] Next, the average particle diameter of the first particles 12 is set to 5 μm or more. Experiments have confirmed that thermal conductivity significantly decreases when the first particles 12 are too small. This phenomenon is presumed to be due to the first particles 12 being insufficiently large, resulting in insufficient thermal conduction paths in the thickness direction. From the viewpoint of further improving the thermal conductivity of the thermal conductive sheet 1, the average particle diameter of the first particles 12 is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, and particularly preferably 40 μm or more. On the other hand, if the first particles 12 are too large, there is a risk of adverse effects such as a decrease in the orientation of the first particles 12 in the thickness direction and difficulty in forming a puddle. From this viewpoint, the upper limit of the average particle diameter of the first particles 12 is set to 70 μm or less. From the viewpoint of further improving the thermal conductivity of the thermal conductive sheet 1, the average particle diameter of the first particles 12 is preferably 65 μm or less, and particularly preferably 60 μm or less.

[0021] In this specification, the "average particle size" refers to the average particle size measured based on SEM image analysis. Specifically, the particle size of the inorganic particles in the thermal conductive material is obtained by drawing the smallest rectangle circumscribing the inorganic particles in a cross-sectional SEM image of the thermal conductive sheet 1 and calculating the median ((A+B) / 2) of the shortest dimension B and the longest dimension A of the rectangle. The average particle size can then be obtained by calculating the arithmetic mean value of the particle sizes of a predetermined number (e.g., 75 or more) of inorganic particles.

[0022] The material of the first particles 12 is not particularly limited, and the above-mentioned inorganic materials can be used without any particular limitation. However, among the above-mentioned materials, boron nitride (hexagonal boron nitride), aluminum nitride, aluminum oxide, zirconium oxide, etc. are particularly suitable as materials for the first particles 12. These inorganic materials are easy to form elongated particles and have excellent thermal conductivity.

[0023] As shown by reference numerals 12a and 12b in FIG. 1 , the elongated first particles 12 tend to be aligned parallel to one another in a specific direction. The degree of orientation of the first particles 12 is preferably 60 or less, more preferably 55 or less, even more preferably 50 or less, and particularly preferably 45 or less. As the degree of orientation decreases, the orientation direction of the first particles 12 tends to vary. This results in more diverse directions of the thermal conduction paths P, contributing to improved thermal conductivity. Meanwhile, the lower limit of the degree of orientation of the first particles 12 is not particularly limited and may be 10 or more, 15 or more, or 20 or more. In this specification, the "degree of orientation of the first particles" refers to the ratio (I(002) / I(100)) of the peak intensity of the (002) plane to the peak intensity of the (100) plane in an X-ray diffraction spectrum. The X-ray diffraction spectrum can be obtained by irradiating the thermal conductive sheet 1 with X-rays in the thickness direction Z.

[0024] In this specification, the term "first particles" does not necessarily refer to primary particles but also encompasses secondary particles formed by aggregation of primary particles. Specifically, the first particles may be secondary particles formed by aggregation of multiple primary particles and having an average aspect ratio of 1.5 or greater. The aggregation form of the secondary particles is not particularly limited. For example, even when primary particles having an average aspect ratio of less than 1.5 aggregate to form secondary particles having an average aspect ratio of 1.5 or greater, the first particles can still have excellent thermal conductivity in the longitudinal direction. Furthermore, the secondary particles may have a house-of-card structure formed by aggregation of plate-like primary particles. Furthermore, the first particles may be a mixture of multiple types of inorganic particles with different average aspect ratios or average particle sizes. For example, the first particles may be a mixture of inorganic particles having an average aspect ratio of 1.5 and inorganic particles having an average aspect ratio of 2.0.

[0025] (2)Second particle The second particles 14 are short particles with an average aspect ratio of less than 1.5. These short second particles 14 tend to be arranged between the long first particles 12. This allows the formation of heat conduction paths P in which the first particles 12 are connected to each other via the second particles 14. Specifically, as described above, long inorganic particles such as the first particles 12 tend to be oriented along a certain direction. In this case, the direction of the heat conduction path becomes biased, making it difficult to improve thermal conductivity. In contrast, in the thermal conduction sheet 1 according to this embodiment, short second particles 14 are arranged between the long first particles 12. This allows the formation of heat conduction paths in a direction intersecting the orientation direction of the first particles 12. The average aspect ratio of the second particles 14 is preferably 1.48 or less, more preferably 1.46 or less, even more preferably 1.44 or less, and particularly preferably 1.42 or less. As the average aspect ratio of the second particles 14 decreases, the second particles 14 are more likely to be arranged between the first particles 12. On the other hand, the lower limit of the average aspect ratio of the second particles 14 is not particularly limited, and may be 1 (the short side and long side of the particle are the same).

[0026] Next, the average particle diameter of the second particles 14 is set to 80 μm or less (preferably 75 μm or less, more preferably 70 μm or less, even more preferably 65 μm or less, and particularly preferably 60 μm or less). As the second particles 14 become smaller, the second particles 14 become more likely to be arranged between the first particles 12. On the other hand, if the second particles 14 become too small, even if the second particles 14 are arranged between the first particles 12, a suitable heat conduction path may not be formed. From this viewpoint, the lower limit of the average particle diameter of the second particles 14 is set to 10 μm or more (preferably 15 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, and particularly preferably 30 μm or more).

[0027] The material of the second particles 14 is also not particularly limited, and the above-mentioned inorganic materials can be used without any particular limitation. However, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, zirconium oxide, etc. are particularly preferred as the material of the second particles 14. These inorganic materials have particularly excellent thermal conductivity, and are therefore suitable as the material of the second particles 14.

[0028] Like the first particles, the second particles may also be secondary particles formed by aggregation of primary particles. For example, when short secondary particles are formed as a result of aggregation of long primary particles, the secondary particles can be used as the second particles. The second particles may also contain multiple types of inorganic particles with different average aspect ratios and average particle diameters. For example, the second particles may be a mixture of short particles with an average particle diameter of 10 μm and short particles with an average particle diameter of 20 μm.

[0029] (3) Third particle The third particles 16 are shorter particles that are smaller than the second particles 14. As described above, the second particles 14 penetrate between the first particles 12 to form heat conduction paths that intersect with the orientation direction of the first particles 12. However, if only the first particles 12 and the second particles 14, which are coarse particles, are present, gaps are likely to form between the inorganic particles. In contrast, the thermal conductive sheet 1 according to this embodiment contains third particles 16, which are shorter particles that are smaller than the second particles 14. These third particles 16 can easily penetrate into the gaps between the coarse inorganic particles (the first particles 12 and the second particles 14). This allows a wide-ranging network of heat conduction paths P to be formed within the thermal conductive sheet 1.

[0030] Specifically, the third particles 16 are short particles with an average aspect ratio of less than 1.5. This makes it easier for the third particles 16 to fill the gaps between other inorganic particles. The average aspect ratio of the third particles 16 is preferably 1.4 or less, more preferably 1.3 or less, and particularly preferably 1.2 or less. As the average aspect ratio of the third particles 16 decreases, the third particles 16 tend to fill the gaps between other inorganic particles more easily. On the other hand, the lower limit of the average aspect ratio of the third particles 16 is not particularly limited and may be 1 (the short side and long side of the particle are the same).

[0031] Next, the average particle diameter of the third particles 16 is set to 10 μm or less (preferably 9 μm or less, more preferably 8 μm or less, and preferably 7 μm or less). As the third particles 16 become smaller, the third particles 16 become more likely to enter the gaps between other inorganic particles. On the other hand, if the third particles 16 become too small, aggregation of the fine particles occurs, making it difficult to form the thermal conductive sheet 1. From this perspective, the lower limit of the average particle diameter of the third particles 16 is set to 0.1 μm or more (preferably 0.2 μm or more, more preferably 0.5 μm or more, even more preferably 0.7 μm or more, and particularly preferably 1 μm or more).

[0032] The material of the third particles 16 is also not particularly limited, and the above-mentioned inorganic materials can be used without any particular limitation. Aluminum oxide, aluminum nitride, silicon nitride, zirconium oxide, and the like are particularly preferred materials for the third particles 16. These inorganic materials are particularly suitable as materials for the third particles 16 because they can be easily formed into fine particles.

[0033] Like the first and second particles, the third particles may be secondary particles formed by aggregation of primary particles. However, the third particles are required to be fine particles that can enter the gaps between other inorganic particles. For this reason, the third particles are preferably primary particles.

[0034] The third particles may be a mixture of multiple types of inorganic particles with different average aspect ratios or average particle diameters. In particular, the third particles are preferably a mixture of two or more types of inorganic particles with different average particle diameters (see 16a and 16b in FIG. 1). This allows the third particles 16 to be arranged according to the size of the gaps between the other inorganic particles, thereby further improving the thermal conductivity of the thermal conductive sheet 1. For example, the third particles 16 are preferably a mixture of large particles 16a with an average particle diameter of 5 μm to 10 μm and small particles 16b with an average particle diameter of 0.1 μm to less than 5 μm. This further improves the thermal conductivity of the thermal conductive sheet 1. The mixing ratio of the large particles 16a to the small particles 16b in the third particles 16 is preferably 30:70 to 70:30 (preferably 35:65 to 65:35). This further improves the thermal conductivity of the thermal conductive sheet 1.

[0035] (4) Content of each particle Next, the thermally conductive material 10 contains the above-mentioned first particles 12 to third particles 16 in a specific ratio. This makes it possible to realize a thermally conductive sheet 1 having a suitable thermal conduction path P. This will be explained in detail below. Note that the "content of inorganic particles" explained below is the content when the total mass of the thermally conductive material 10 is taken as 100 wt%.

[0036] The content of the first particles 12 is set to 1 wt% or more (preferably 2 wt% or more, more preferably 3 wt% or more, and particularly preferably 5 wt% or more). As the content of the long first particles 12 increases, the thermal conductivity along the longitudinal direction of the first particles 12 tends to improve. On the other hand, if the number of first particles 12 becomes too large, the direction of the heat conduction path P becomes biased, making it difficult to improve the thermal conductivity. From this perspective, the content of the first particles 12 is set to 7 wt% or less (preferably 6.8 wt% or less, more preferably 6.4 wt% or less, even more preferably 6.2 wt% or less, and particularly preferably 6 wt% or less).

[0037] Next, the content of the second particles 14 is set to 20 wt% or more (preferably 22 wt% or more, more preferably 23 wt% or more, even more preferably 24 wt% or more, and particularly preferably 25 wt% or more). This allows a sufficient number of second particles 14 to be arranged between the long first particles 12. As a result, heat conduction paths P that intersect with the orientation direction of the first particles 12 are easily formed. On the other hand, if a large amount of relatively coarse second particles 14 is added, the gaps between the inorganic particles become larger. As a result, there is a risk of regions where the heat conduction paths P are not sufficiently formed. From this perspective, the content of the second particles 14 is set to 40 wt% or less (preferably 38 wt% or less, more preferably 37 wt% or less, even more preferably 36 wt% or less, and particularly preferably 35 wt% or less).

[0038] Next, the content of the third particles 16 is set to 50 wt% or more (preferably 52 wt% or more, more preferably 55 wt% or more, even more preferably 57 wt% or more, and particularly preferably 60 wt% or more). This allows a sufficient amount of the third particles to fill the gaps between the other inorganic particles (the first particles 12 and the second particles 14). As a result, a heat conduction path P can be formed in which the first particles 12, the second particles 14, and the third particles 16 are interconnected. On the other hand, if a large amount of the third particles 16 is added, the gaps between the inorganic particles rapidly decrease, resulting in an insufficient area to be filled with the thermosetting resin 20. As a result, molding the thermal conductive sheet 1 (preparing the clay) may become difficult. From this viewpoint, the content of the third particles 16 is set to 75 wt% or less (preferably 74 wt% or less, more preferably 73 wt% or less, even more preferably 72 wt% or less, and particularly preferably 70 wt% or less).

[0039] (5) Other inorganic particles Furthermore, the thermally conductive material 10 may contain inorganic particles other than the first particles 12 to the third particles 16, as long as the effects of the technology disclosed herein are not significantly impaired. An example of such inorganic particles is inorganic particles having an average aspect ratio of 1.5 or more and an average particle diameter of less than 5 μm. Such fine, elongated particles do not significantly impede the formation of the heat conduction paths P by the first particles 12 to the third particles 16 described above. However, from the viewpoint of more optimally exerting the thermal conductivity improving effect of the technology disclosed herein, the content of inorganic particles other than the first particles 12 to the third particles 16 is preferably 10 wt % or less, more preferably 5 wt % or less, even more preferably 1 wt % or less, and particularly preferably 0.1 wt % or less.

[0040] Furthermore, when the total mass of the thermally conductive sheet 1 is taken as 100 wt%, the total content of the thermally conductive material 10 is preferably 90 wt% or more, more preferably 92.5 wt% or more, and particularly preferably 95 wt% or more. This allows the thermally conductive path P made of inorganic particles to be suitably formed within the thermally conductive sheet 1. On the other hand, from the viewpoint of facilitating the molding of the thermally conductive sheet 1, the total content of the thermally conductive material 10 is preferably 99 wt% or less, more preferably 98 wt% or less, more preferably 97 wt% or less, and particularly preferably 96 wt% or less.

[0041] 2.Thermosetting resin 20 The thermosetting resin 20 is a resin component that hardens through polymerization, crosslinking, or other reactions upon heating. As shown in FIG. 1 , in this embodiment, the thermosetting resin 20 is formed into a sheet. The thermal conductive material 10 is dispersed within the sheet-shaped thermosetting resin 20. The thermosetting resin 20 is not limited to a specific resin, and any conventionally known thermosetting resin that can be used to form this type of thermal conductive sheet can be used without particular restrictions. Examples of the thermosetting resin 20 include acrylic resin, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, urea resin, melamine resin, urethane resin, and imide resin. These non-silicone thermosetting resins have the advantage of being less susceptible to oil bleeding. Among non-silicone thermosetting resins, acrylic resin is particularly suitable as the thermosetting resin 20 for the thermal conductive sheet 1 due to its excellent thermal conductivity.

[0042] As described above, in the thermally conductive sheet 1 according to this embodiment, the shape, particle size, and content of each particle are set so that the first particles 12, second particles 14, and third particles 16 form a suitable thermal conduction path P. However, even when a thermally conductive material 10 satisfying these conditions is used, if a large amount of thermosetting resin 20 enters the gaps between the inorganic particles, the thermal conduction path P may be severed, resulting in a significant decrease in thermal conductivity. From this perspective, the content of thermosetting resin 20 is set to 6 wt% or less (preferably 5.8 wt% or less, more preferably 5.5 wt% or less, even more preferably 5.2 wt% or less, and particularly preferably 5 wt% or less). From the viewpoint of thermal conductivity, the lower limit of the content of thermosetting resin 20 is not particularly limited and may be 1 wt% or more, 1.5 wt% or more, 2 wt% or more, or 2.5 wt% or more. On the other hand, if the amount of thermosetting resin 20 is too small, it may be difficult to form the thermal conductive sheet 1. From this perspective, the content of thermosetting resin 20 is preferably 3 wt% or more, more preferably 3.5 wt% or more, and particularly preferably 4 wt% or more. Note that the "content of thermosetting resin" here refers to the mass ratio when the total mass of the thermal conductive sheet 1 is 100 wt%.

[0043] 3. Other additives The thermal conductive sheet 1 according to this embodiment has been described above. The thermal conductive sheet 1 may contain conventionally known additives as long as they do not significantly impair the effects of the technology disclosed herein. Examples of such additives include dispersants, monomers, crosslinking initiators, and plasticizers. The content of these additives is not particularly limited as long as the effects of the technology disclosed herein are achieved. For example, the content of the additives relative to the total mass of the thermal conductive sheet 1 is preferably 1 wt% or less, more preferably 0.8 wt% or less, even more preferably 0.7 wt% or less, and particularly preferably 0.6 wt% or less.

[0044] As described above, the thermal conductive material 10 of the thermal conductive sheet 1 according to this embodiment includes first particles 12 having an average aspect ratio of 1.5 or greater and an average particle diameter of 5 μm to 70 μm, second particles 14 having an average aspect ratio of less than 1.5 and an average particle diameter of 10 μm to 80 μm, and third particles 16 having an average aspect ratio of less than 1.5 and an average particle diameter of 0.1 μm to 10 μm. In the thermal conductive material 10, the content of the first particles 12 is 1 wt% to 7 wt%, the content of the second particles 14 is 20 wt% to 40 wt%, and the content of the third particles 16 is 50 wt% to 75 wt%. This allows for the formation of a heat conduction path P within the thermal conductive sheet 1, in which multiple inorganic particles are in contact with each other. Furthermore, in the thermally conductive sheet 1 according to this embodiment, the content of the thermosetting resin 20 relative to the total weight of the sheet is 6 wt % or less. This prevents the thermal conduction path P from being cut by a large amount of thermosetting resin 20. As described above, the thermally conductive sheet 1 according to this embodiment can exhibit extremely high thermal conductivity.

[0045] For example, the thermally conductive sheet 1 according to this embodiment can achieve a thermal conductivity of 5 W / m·K or higher (preferably 5.4 W / m·K or higher, more preferably 5.6 W / m·K or higher, even more preferably 5.8 W / m·K or higher, and particularly preferably 6.0 W / m·K or higher). A thermally conductive sheet 1 having such a thermal conductivity is particularly suitable for use in cooling high-density electronic components that generate a large amount of heat. On the other hand, the upper limit of the thermal conductivity of the thermally conductive sheet 1 is not particularly limited, and may be 15 W / m·K or lower, 12.5 W / m·K or lower, or 10 W / m·K or lower.

[0046] 2. Manufacturing method of thermal conductive sheet Next, a method for manufacturing the thermally conductive sheet according to this embodiment will be described. This manufacturing method includes a preparation step, a preparation step, a molding step, and a thermal curing step. Note that the thermally conductive sheet disclosed herein is not limited to those manufactured by the following manufacturing method.

[0047] (1) Preparation process In this step, materials for the thermally conductive sheet 1 (thermal conductive material 10, thermosetting resin 20, etc.) are prepared. Details and compounding ratios of these materials have already been explained, so redundant explanations will be omitted.

[0048] (2) Preparation process In this process, a puddle is prepared by mixing the thermally conductive material 10 and the thermosetting resin 20. In this specification, the term "puddle" refers to a clay-like material in which the thermally conductive material and the thermosetting resin are mixed. To prepare the puddle in this process, the above-mentioned materials must be mixed in an appropriate ratio. For example, if the third particles 16 are present in excess or if the thermosetting resin 20 is insufficient, it becomes difficult to prepare a puddle suitable for forming a thermally conductive sheet. Furthermore, various conventional stirring and mixing devices, such as a planetary centrifugal mixer, a kneader, or a kneader, can be used to mix the materials.

[0049] (3) Molding process In this step, a green sheet is formed from the clay. The method for forming the green sheet is not particularly limited, and any conventionally known forming method can be used without any particular restriction. Examples of sheet forming methods include roll forming, press forming, extrusion forming, and doctor blade forming. Note that using these forming methods makes it easier for the first particles 12 to be oriented along the sheet surface. In this case, while the thermal conductivity in the surface directions (the width direction X and the depth direction) is improved, the thermal conductivity in the thickness direction Z is reduced. However, with the technology disclosed herein, the second particles 14 and the third particles 16 can form heat conduction paths P along a direction intersecting the orientation direction of the first particles 12 (i.e., the thickness direction Z). In other words, the technology disclosed herein is particularly suitable for use when manufacturing a thermally conductive sheet 1 using roll forming or the like. (4) Heat curing process In this step, the green sheet obtained in the molding step is heated, thereby curing the thermosetting resin 20 and producing the thermal conductive sheet 1. The heating conditions in this step (heating temperature, heating time, temperature rise rate, heating atmosphere, etc.) are not particularly limited and can be adjusted appropriately depending on the type of thermosetting resin 20, etc.

[0050] In the thermally conductive sheet 1 manufactured by the above-described procedure, the second particles 14 and the third particles 16 form thermal conduction paths P in a direction intersecting the orientation direction of the first particles 12. Therefore, a thermally conductive sheet 1 with excellent thermal conductivity along the thickness direction Z can be manufactured without precisely controlling the orientation direction of the long inorganic particles (first particles 12) in a molding process or the like. Therefore, the technology disclosed herein makes it possible to manufacture high-quality thermally conductive sheets with high productivity.

[0051] [Test example] Test examples relating to the present invention will be described below, but these test examples are not intended to limit the present invention.

[0052] 1. Creating a sample In this test, three types of inorganic particles, designated as first to third particles, were prepared as the thermal conductive material. The first particles were plate-shaped hexagonal boron nitride (BN) particles with an average aspect ratio of 10. The second particles were short aluminum nitride (AlN) particles with an average aspect ratio of 1.4. The third particles were short aluminum oxide (Al2O3) particles with an average aspect ratio of 1.1. In this test, an acrylic resin was used as the thermosetting resin. Next, the above-mentioned materials were mixed in a vacuum mixer (Thinky Corporation, Awatori Rentaro ARV-200) to prepare a clay. The prepared clay was then rolled into a sheet using a roll molding machine. In this test, the roll molding conditions were adjusted to form a sheet with a thickness of 1 mm. The formed sheet was then heated at 110°C for 20 minutes. This produced a thermal conductive sheet sample.

[0053] In this test, 22 types of thermally conductive sheets (Examples 1 to 7, Comparative Examples 1 to 12, and Reference Examples 1 to 3) were produced with different inorganic particle sizes, inorganic particle amounts, and thermosetting resin amounts. The detailed composition of each example is shown in Table 1.

[0054] 2.Evaluation Test (1) Making clay In this test, the kneading speed for preparing the clay was 1400 rpm, and the kneading time was 2 minutes. After this kneading process, the clay was visually evaluated for proper preparation. The results are shown in Table 1. In Table 1, "◎" indicates that the inorganic particles were sufficiently wetted with the acrylic resin and were cohesive. "◯" indicates that the inorganic particles were wetted with the acrylic resin but not cohesive. "X" indicates that the inorganic particles were not sufficiently wetted with the acrylic resin or that the organic content was too high, resulting in a paste-like texture.

[0055] (2) Thermal conductivity In this test, the thermal conductivity of each sample was measured. The procedure for measuring thermal conductivity is as follows: First, the thermal diffusivity a (mm 2 The thermal diffusivity was measured in accordance with JIS R1611:2010. Next, the density ρ (g / m 3 ) was calculated. Furthermore, the specific heat capacity c (J / (g K)) at 25°C was measured using a DSC measuring device in accordance with JIS K7123. The thermal conductivity (W / m K) in the thickness direction was calculated from the product of each measurement result (a × ρ × c). The results are shown in Table 1.

[0056] (3) Degree of orientation In this test, the degree of orientation of the first particles (hexagonal boron nitride) in the thermal conductive sheet was measured. First, a test piece with a length of 15 mm was cut from the thermal conductive sheet to be measured. Then, an X-ray diffraction spectrum of this test piece was obtained. Specifically, an X-ray diffraction analyzer (manufactured by Rigaku, model: SmartLab) was used to irradiate X-rays in the thickness direction of the test piece to obtain the X-ray diffraction spectrum. Next, the peak intensity of the (002) plane and the peak intensity of the (100) plane in this X-ray diffraction spectrum were measured. The peak intensity ratio of the (002) plane to the (100) plane (I(002) / I(100)) was then measured as the degree of orientation of the first particles. A lower degree of orientation indicates greater variation in the orientation direction of the first particles. The results are shown in Table 1.

[0057] [Table 1]

[0058] Comparison of Example 1 with Comparative Examples 1 to 6 revealed that a thermally conductive sheet with excellent thermal conductivity can be easily formed by using a thermally conductive material containing the first to third particles. Furthermore, comparison with other examples revealed that even more suitable thermal conductivity can be achieved by adjusting the particle size and content of the first to third particles. Furthermore, as shown in Comparative Example 12 and Reference Examples 1 to 3, it was found that the content of the thermosetting resin affects the thermal conductivity of the thermally conductive sheet.

[0059] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0060] The technology disclosed herein includes the following items 1 to 10. The following items 1 to 10 are not limited to the above-described embodiment.

[0061] [Item 1] A thermally conductive sheet including a thermally conductive material and a thermosetting resin, The thermally conductive material is First particles having an average aspect ratio of 1.5 or more and an average particle diameter of 5 μm or more and 70 μm or less; second particles having an average aspect ratio of less than 1.5 and an average particle size of 10 μm or more and 80 μm or less; Third particles having an average aspect ratio of less than 1.5 and an average particle size of 0.1 μm or more and 10 μm or less; At least When the total mass of the thermal conductive material is 100 wt%, the content of the first particles is 1 wt% or more and 7 wt% or less, the content of the second particles is 20 wt% or more and 40 wt% or less, and the content of the third particles is 50 wt% or more and 75 wt% or less, A thermally conductive sheet in which the content of the thermosetting resin is 6 wt % or less when the total mass of the thermally conductive sheet is 100 wt %.

[0062] [Item 2] Item 2. The thermally conductive sheet according to item 1, wherein the first particles include at least one selected from the group consisting of hexagonal boron nitride, aluminum nitride, aluminum oxide, and zirconium oxide.

[0063] [Item 3] 3. The thermally conductive sheet according to item 1 or 2, wherein the second particles include at least one selected from the group consisting of aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, and zirconium oxide.

[0064] [Item 3] 4. The thermally conductive sheet according to any one of items 1 to 3, wherein the third particles include at least one selected from the group consisting of aluminum oxide, aluminum nitride, silicon nitride, and zirconium oxide.

[0065] [Item 5] 5. The thermal conductive sheet according to any one of items 1 to 4, wherein in an X-ray diffraction spectrum obtained by irradiating the sheet with X-rays in the thickness direction of the sheet, the degree of orientation of the first particles, which is the ratio of the peak intensity of the (002) plane to the peak intensity of the (100) plane (I(002) / I(100)), is 60 or less.

[0066] [Item 6] 6. The thermal conductive sheet according to any one of items 1 to 5, wherein the third particles include large particles having an average particle diameter of 5 μm or more and 10 μm or less, and small particles having an average particle diameter of 0.1 μm or more and less than 5 μm.

[0067] [Item 7] Item 7. The thermally conductive sheet according to item 6, wherein the mixing ratio of the large particles to the small particles is 30:70 to 70:30.

[0068] [Item 8] 8. The thermal conductive sheet according to any one of items 1 to 7, wherein the thermosetting resin comprises at least one selected from the group consisting of an acrylic resin, an epoxy resin, a phenolic resin, a polyimide resin, an unsaturated polyester resin, a urea resin, a melamine resin, a urethane resin, and an imide resin.

[0069] [Item 9] 9. The thermally conductive sheet according to any one of items 1 to 8, wherein the thermal conductivity of the thermally conductive sheet is 5 W / m·K or more. [Explanation of symbols]

[0070] 1. Thermal conductive sheet 10 Thermal Conductive Materials 12 1st particle 14 2nd particle 16 Third particle 20 Thermosetting resin

Claims

1. A thermally conductive sheet including a thermally conductive material and a thermosetting resin, The thermally conductive material is first particles having an average aspect ratio of 1.5 or more and an average particle diameter of 5 μm or more and 70 μm or less; second particles having an average aspect ratio of less than 1.5 and an average particle diameter of 10 μm or more and 80 μm or less; third particles having an average aspect ratio of less than 1.5 and an average particle diameter of 0.1 μm or more and 10 μm or less; At least When the total mass of the thermal conductive material is 100 wt%, the content of the first particles is 1 wt% or more and 7 wt% or less, the content of the second particles is 20 wt% or more and 40 wt% or less, and the content of the third particles is 50 wt% or more and 75 wt% or less, A thermally conductive sheet, wherein the content of the thermosetting resin is 6 wt % or less when the total mass of the thermally conductive sheet is 100 wt %.

2. The thermal conductive sheet according to claim 1 , wherein the first particles include at least one selected from the group consisting of hexagonal boron nitride, aluminum nitride, aluminum oxide, and zirconium oxide.

3. The thermal conductive sheet according to claim 1 , wherein the second particles include at least one selected from the group consisting of aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, and zirconium oxide.

4. The thermal conductive sheet according to claim 1 , wherein the third particles include at least one selected from the group consisting of aluminum oxide, aluminum nitride, silicon nitride, and zirconium oxide.

5. 2. The thermal conduction sheet according to claim 1, wherein in an X-ray diffraction spectrum obtained by irradiating X-rays in the sheet thickness direction, the ratio (I(002) / I(100)) of the peak intensity of the (002) plane to the peak intensity of the (100) plane is 60 or less.

6. The thermal conductive sheet according to claim 1 , wherein the third particles include large particles having an average particle diameter of 5 μm or more and 10 μm or less, and small particles having an average particle diameter of 0.1 μm or more and less than 5 μm.

7. 7. The thermal conductive sheet according to claim 6, wherein the mixing ratio of the large particles to the small particles is 30:70 to 70:

30.

8. 2. The thermal conductive sheet according to claim 1, wherein the thermosetting resin comprises at least one selected from the group consisting of acrylic resin, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, urea resin, melamine resin, urethane resin, and imide resin.

9. The thermal conductive sheet according to claim 1 , wherein the thermal conductivity of the thermal conductive sheet is 5 W / m·K or more.

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