Boron nitride particles, sheet-form base material, method for producing boron nitride particles, and module

Abstract

A boron nitride particle 1 comprises: a particle-shaped inner layer part 11 having a hollow part 10; and an outer layer part 12 covering the outside of the inner layer part 11. The inner layer part 11 contains boron nitride and has holes 11a communicating from the hollow part 10 to the outside. The outer layer part 12 covers the holes 11a.

Description

Boron nitride particles, sheet-like substrate, method for producing boron nitride particles, and module

[0001] This invention relates to boron nitride particles, a sheet-like substrate, a method for producing boron nitride particles, and a module.

[0002] In recent years, the frequencies used in communication equipment have tended to become extremely high. To suppress transmission loss in the high-frequency band, it is required to lower the relative permittivity and dielectric loss tangent of the insulating materials used in circuit boards.

[0003] For example, Patent Document 1 discloses the use of an inorganic filler containing at least one selected from the group consisting of boron nitride, titanium dioxide, and silicon dioxide, from the viewpoint of reducing the dielectric loss tangent of a film of a resin material such as a liquid crystal polymer or polyimide.

[0004] Among the inorganic fillers mentioned above, boron nitride is particularly noteworthy for its excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance. Therefore, attempts have been made to improve the thermal conductivity of resin materials with low thermal conductivity by mixing it as a filler. For example, Patent Document 2 discloses granular boron nitride with a hollow interior.

[0005] Japanese Patent Publication No. 2023-111313, International Publication No. 2024 / 034604

[0006] When granular boron nitride, as described in Patent Document 2, is mixed with a resin material as a filler, problems arise such as the resin material filling into the cavities of the granular boron nitride, making it impossible to maintain the hollow space and causing the filler to collapse. On the other hand, if it is possible to retain an inert gas such as air or nitrogen in the cavities of the granular boron nitride even when mixed with a resin material, it would be possible to create a substrate with high thermal conductivity and low dielectric properties by mixing only this filler with the resin material. However, such granular boron nitride or manufacturing methods are not disclosed in Patent Documents 1 and 2.

[0007] To date, in order to achieve both high thermal conductivity and low dielectric properties in resin materials, two types of fillers have been used: one that imparts high thermal conductivity and another that imparts low dielectric properties. However, in this configuration, the effects of high thermal conductivity and low dielectric properties of each filler are halved, so improvement is desired.

[0008] The present invention aims to solve the above problems and to provide boron nitride particles that impart low dielectric properties and high thermal conductivity to a resin material. The present invention also aims to provide a sheet-like substrate containing the boron nitride particles, a method for producing the boron nitride particles, and a module comprising a resin layer containing the boron nitride particles.

[0009] The boron nitride particles of the present invention comprise an inner layer having a hollow particle shape and an outer layer covering the outside of the inner layer, wherein the inner layer contains boron nitride and has pores communicating from the hollow to the outside, and the outer layer covers the pores.

[0010] The sheet-like substrate of the present invention is a sheet-like substrate composed of a resin, wherein the resin contains the boron nitride particles of the present invention.

[0011] The present invention provides a method for producing boron nitride particles, comprising the steps of: forming an inner layer containing boron nitride around a particle-shaped core; forming a hollow portion inside the inner layer by removing the core located inside the inner layer; and forming an outer layer that covers the outside of the inner layer having the hollow portion.

[0012] The module of the present invention comprises a substrate having a first main surface and a second main surface opposite to each other in the thickness direction, an electronic component mounted on the first main surface of the substrate, and a resin layer covering the electronic component and containing boron nitride particles of the present invention.

[0013] According to the present invention, boron nitride particles can be provided that impart low dielectric properties and high thermal conductivity to a resin material. Furthermore, according to the present invention, a sheet-like substrate containing the boron nitride particles, a method for producing the boron nitride particles, and a module comprising a resin layer containing the boron nitride particles can be provided.

[0014] Figure 1 is a schematic cross-sectional view showing an example of the boron nitride particles of the present invention. Figure 2A is a schematic cross-sectional view of a resin sheet containing the boron nitride particles of the present invention. Figure 2B is a schematic cross-sectional view of a conventional resin sheet containing boron nitride particles. Figure 3 is a schematic cross-sectional view showing another example of the boron nitride particles of the present invention. Figure 4A is a schematic cross-sectional view showing an example of a method for producing the boron nitride particles of the present invention. Figure 4B is a schematic cross-sectional view showing an example of a method for producing the boron nitride particles of the present invention. Figure 4C is a schematic cross-sectional view showing an example of a method for producing the boron nitride particles of the present invention. Figure 5 is a schematic perspective view showing an example of a sheet-like substrate of the present invention. Figure 6 is a schematic cross-sectional view showing an example of a module of the present invention. Figure 7 is a schematic cross-sectional view showing a modified example of the module of Figure 6. Figure 8 is a schematic cross-sectional view showing a modified example of the module of Figure 6. Figure 9 is a schematic cross-sectional view showing a modified example of the module of Figure 6. Figure 10 is a schematic cross-sectional view showing another example of a module of the present invention. Figure 11 is a schematic cross-sectional view showing a modified example of the module of Figure 10. Figure 12 is a schematic cross-sectional view showing a modified example of the module in Figure 11.

[0015] The boron nitride particles, sheet-like substrate, method for producing boron nitride particles, and module of the present invention will be described below. However, the present invention is not limited to the following configurations and may be modified as appropriate without departing from the spirit of the invention. Furthermore, a combination of several of the preferred configurations described below also constitutes the present invention.

[0016] In the following description, unless otherwise specified, each embodiment will simply be referred to as "boron nitride particles of the present invention," "sheet-like substrate of the present invention," "method for producing boron nitride particles of the present invention," or "module of the present invention."

[0017] The following diagrams are schematic representations, and their dimensions, aspect ratios, and scales may differ from those of the actual product. The same reference numerals are used for identical or equivalent parts in the diagrams. Furthermore, identical elements are denoted by the same reference numerals in each diagram, and redundant explanations are omitted.

[0018] [Boron Nitride Particles] Figure 1 is a schematic cross-sectional view showing an example of boron nitride particles of the present invention. The boron nitride particle 1 comprises an inner layer 11 having a hollow portion 10 and an outer layer 12 covering the outside of the inner layer 11.

[0019] The boron nitride particles 1 are entirely particle-shaped, and are spherical, for example, as shown in Figure 1. The particle shape of the boron nitride particles 1 is not particularly limited and may be flake-shaped, needle-shaped, cubic, rectangular parallelepiped other than cubic, polyhedral, cylindrical, etc. A spherical shape is preferred for the boron nitride particles 1.

[0020] The average particle size of the boron nitride particles 1 is not particularly limited, but can be appropriately selected depending on the application. For example, 1 μm to 100 μm is preferred, 5 μm to 70 μm is more preferred, and 20 μm to 40 μm is even more preferred.

[0021] In this specification, the average particle size of boron nitride particles, before mixing with the resin, is defined as the particle size (volume median diameter D) corresponding to 50% of the integrated value of the particle size distribution determined by laser diffraction and scattering. ５０ ) Furthermore, when contained in a resin, the average particle size is determined by the following procedure. First, the resin containing the boron nitride particles of the present invention is formed into a sheet by a casting method or the like, and the main surface of the sheet is polished to obtain a cross-section. In a scanning electron microscope image (SEM image) of the obtained cross-section at a magnification that allows 10 or more boron nitride particles to be confirmed, the area of ​​each boron nitride particle in the cross-section passing through the center of the particle is measured, the equivalent diameter of a circle is calculated, and the average value of these is taken as the average particle size of the boron nitride particles.

[0022] The inner layer 11 has a particle shape with a hollow portion 10, and is typically similar in shape to the boron nitride particle 1. In Figure 1, the inner layer 11 is spherical.

[0023] The inner layer 11 has holes 11a that communicate with the outside from the hollow portion 10. In this specification, the holes communicating with the outside from the hollow portion mean spaces through which a liquid fluid can flow from the hollow portion to the outside. The cross-section of the holes 11a may be not only the straight shape shown in Figure 1, but also a bent shape or a curved shape. Since the size of the holes 11a is very small compared to the size of the boron nitride particles 1, the inner layer 11 maintains its shape as a particle. The presence or absence of holes 11a can be confirmed, for example, by observing the above SEM image.

[0024] The inner layer 11 contains boron nitride. The inner layer 11 is mainly composed of boron nitride, preferably 95% by weight or more, and more preferably 99% by weight or more. The inner layer 11 may be composed of boron nitride alone.

[0025] Other components in the inner layer 11 besides boron nitride include, for example, components derived from the core used to form the hollow portion 10, which will be described later. If the core contains iron boride, other components in the inner layer 11 include iron boride, iron oxide, boron oxide, etc.

[0026] The average thickness of the inner layer is, for example, between 0.05 μm and 3 μm.

[0027] In this specification, the average thickness of the inner layer is calculated as follows: Observe the SEM image of the same sheet as described above, measure the thickness of the inner layer for 10 or more boron nitride particles, and take the average value as the average thickness of the inner layer.

[0028] The outer layer 12 covers the outside of the inner layer 11. The outer layer 12 does not have to cover the entire outside of the inner layer 11, but it is essential that it covers the holes 11a of the inner layer. Because the outer layer 12 covers the holes 11a of the inner layer, the hollow portion 10 of the boron nitride particle 1 becomes a closed space. In Figure 1, the outer layer 12 also has holes 12a, but because the positions of the holes in the inner layer and the outer layer are different, the hollow portion 10 of the boron nitride particle 1 becomes a closed space.

[0029] The outer layer 12 of the boron nitride particle 1 preferably contains boron nitride. When the inner layer 11 and outer layer 12 of the boron nitride particle 1 are formed by a method of growing boron nitride crystals, as described later, the inner layer 11 and outer layer 12 each have pores.

[0030] Preferably, the outer layer 12 covers the inner layer 11 in such a way as to maintain the hollow portion 10. "Maintaining the hollow portion" means that even when boron nitride particles are mixed with resin, the resin does not flow into the hollow portion, and the hollow portion maintains its space. The boron nitride particles 1 can maintain the hollow portion 10 because the outer layer 12 covers the pores 11a of the inner layer 11.

[0031] To determine whether the boron nitride particles of the present invention maintain their hollow portions, an SEM image of the same sheet as described above is observed. As shown in Figure 2A, the outer layer 12 of the boron nitride particles of the present invention covers the pores 11a of the inner layer 11, so even when mixed with the resin 15, the resin 15 does not flow into the hollow portions 10, and the hollow portions 10 maintain their space. Figure 2A is a schematic cross-sectional view of a resin sheet containing the boron nitride particles of the present invention.

[0032] On the other hand, when a sheet is similarly formed using conventional boron nitride particles as described in Patent Document 2, and a cross-sectional SEM image is observed, as shown in Figure 2B, the boron nitride particles described in Patent Document 2 do not have an outer layer, so the pores 11a communicating from the hollow portion 10 to the outside of the particle are exposed on the surface. As a result, the resin 15 flows into the hollow portion 10, and the hollow portion 10 cannot maintain its space. Figure 2B is a schematic cross-sectional view of a conventional resin sheet containing boron nitride particles.

[0033] Further, when these sheets are subjected to elemental analysis by energy dispersive X-ray spectroscopy (EDX), in the sheet containing boron nitride particles of the present invention (Fig. 2A), since the hollow part is a space, carbon is not detected in the hollow part. However, in the sheet containing boron nitride particles described in Patent Document 2 (Fig. 2B), carbon is detected because resin has flowed into the hollow part. When the hollow part contains air as described later, for example, a peak derived from resin is detected by Fourier transform infrared spectroscopy (FT-IR), so that boron nitride particles containing air in the hollow part and boron nitride particles containing resin in the hollow part can be distinguished.

[0034] The average thickness of the outer layer portion 12 is preferably the same as or greater than the average thickness of the inner layer portion 11. When the average thickness of the outer layer portion 12 is within the above range, the holes 11a of the inner layer portion 11 can be more reliably covered. The average thickness of the outer layer portion 12 is preferably 0.1 μm or more. The average thickness of the outer layer portion 12 is preferably, for example, 0.5 μm or less. When the average thickness of the outer layer portion 12 exceeds 0.5 μm, it takes time for film formation and the manufacturing cost increases, which is not preferable.

[0035] The outer layer portion 12 preferably covers 50% or more of the outer area of the inner layer portion 11.

[0036] The average thickness of the outer layer portion can be calculated by the same procedure as the average thickness of the inner layer portion.

[0037] The thermal conductivity of the material constituting the outer layer portion 12 is preferably the same as or greater than the thermal conductivity of boron nitride. When the thermal conductivity of the material constituting the outer layer portion 12 is within the above range, the thermal conductivity of the boron nitride particles 1 can be further enhanced. Examples of materials having a higher thermal conductivity than boron nitride include carbon-based materials and aluminum nitride.

[0038] The thermal conductivity of the material constituting the outer layer portion 12 is more preferably 1.0 W / m·K or more. The thermal conductivity of the material constituting the outer layer portion 12 is, for example, 3000 W / m·K or less. In this specification, the thermal conductivity of the material is a value obtained by measuring in a bulk state by a periodic heating method.

[0039] The hollow portion 10 may contain a gas. Examples of the gas contained in the hollow portion 10 include inert gases such as air and nitrogen.

[0040] FIG. 3 is a cross-sectional view schematically showing another example of the boron nitride particles of the present invention. As shown in FIG. 3, the outer layer portion 12A of the boron nitride particles 2 has no pores and preferably completely covers the inner layer portion 11. In the boron nitride particles 2, the outer layer portion 12A preferably contains carbon, aluminum nitride, etc., and more preferably contains carbon.

[0041] The boron nitride particles of the present invention have pores in the inner layer portion that communicate from the hollow portion to the outside, but since the outer layer portion covers the pores, even when mixed with a resin, the resin does not flow into the hollow portion, and the hollow portion can maintain a space. In the boron nitride particles of the present invention, since the gas such as air or inert gas contained in the hollow portion has a very low dielectric constant and dielectric loss tangent, by maintaining the space in the hollow portion, for example, when mixed with a resin, both low dielectric properties and high thermal conductivity can be imparted to the resin.

[0042] The use of the boron nitride particles of the present invention is not particularly limited. For example, in addition to being used as a filler for the sheet-like base material described later and a filler for the resin coating the electronic component, it can be blended into a thermal conductivity paste, a thermal conductivity adhesive, a resin composition for a thermal conductivity molded body, etc.

[0043] [Method for producing boron nitride particles] Hereinafter, with reference to FIGS. 1, FIGS. 3 and FIGS. 4A to 4C, the method for producing the boron nitride particles of the present invention will be described. The method for producing the boron nitride particles of the present invention includes a step of forming an inner layer portion containing boron nitride around the periphery of a core having a particle shape, and a step of removing the core inside the inner layer portion to form a hollow portion inside the inner layer portion, and a step of forming an outer layer portion covering the outside of the inner layer portion having the hollow portion.

[0044] (Process for forming the inner layer) In this process, an inner layer containing boron nitride is formed around the particle-shaped core. Figures 4A and 4B are schematic cross-sectional views showing an example of the method for producing boron nitride particles of the present invention. As shown in Figure 4A, the core 20 is, for example, spherical. The particle shape of the core 20 is not limited to a spherical shape, but since the shape of the boron nitride particles produced will be similar to the particle shape of the core 20, it is preferable to determine the particle shape of the core 20 according to the shape of the boron nitride particles to be produced.

[0045] The material of the core 20 is not particularly limited, but the following description will focus on the case where the core 20 contains iron boride. Iron borides include, for example, FeB, Fe ２ B, Fe ３ B, Fe ３．５ Examples include B. Iron borides include FeB and / or Fe ２ B is preferred. Iron boride can be obtained, for example, by heat-treating a raw material mixture containing iron oxide, boron oxide, and carbon to borize the iron in the iron oxide.

[0046] To form the inner layer 11, it is preferable to grow boron nitride crystals around the core 20. Specifically, boron nitride crystals (inner layer 11) are grown around the core 20 by heat treatment and nitriding of the core 20 containing iron boride under a nitrogen gas atmosphere. The atmospheric pressure is not particularly limited and may range from reduced pressure to increased pressure, and is usually at atmospheric pressure.

[0047] Heating is carried out at a temperature of 1750°C or higher and 2300°C or lower, preferably 2200°C or lower, for example, maintaining a temperature of 1800°C or higher and 2100°C or lower. In this way, by repeatedly reacting iron boride with nitrogen on the surface of the iron boride that melts and becomes a droplet due to heating, boron nitride crystals can be formed around the core. If the heating temperature is below 1750°C, the amount of boron nitride produced may be insufficient. If the heating temperature exceeds 2300°C, the iron boride may liquefy before boron nitride is produced. The heat treatment for nitriding may be carried out in a batch or continuous manner, or in a semi-batch manner where a nitrogen atmosphere is formed under a nitrogen gas stream.

[0048] The heating time generally ranges from 2 hours to 20 hours, preferably from 3 hours to 15 hours, such as about 5 hours or about 10 hours, depending on the heating temperature. If the heating time is less than 2 hours, the production amount of boron nitride may be insufficient. If the heating time exceeds 20 hours, impurities may be mixed in from the heat insulating material of the device for heating iron boride.

[0049] In this way, as shown in FIG. 4B, the inner layer portion 11 containing boron nitride can be formed around the core 20.

[0050] Nitridation can be carried out, for example, by heating a heat-resistant container (e.g., a crucible made of boron nitride) containing the core and maintaining the temperature of the core at a predetermined temperature for a predetermined heating time. To sufficiently react the boron and nitrogen in the iron boride contained in the core and to remove impurities and by-products during nitridation (e.g., CO, CO ２ , O ２ gas, etc.) to the outside of the system, the reaction may be carried out under a nitrogen stream.

[0051] After carrying out nitridation as described above, it is cooled to obtain particles with an inner layer portion formed around the core. The cooling may be carried out by any suitable method, for example, by allowing it to cool to room temperature. [[ID=******]]

[0052] The inner layer portion 11 formed by the above method has holes 11a that communicate from the core side to the outside, as shown in FIG. 4B.

[0053] In the above nitridation, it is preferable to use at least one selected from rare earth oxides and alkaline earth metal oxides as an auxiliary agent. Examples of the auxiliary agent include Y ２ O ３ , CeO ２ , La ２ O ３ , CaO, MgO, etc. are preferable. When using such an auxiliary agent, the oxygen contained in the auxiliary agent substantially lowers the melting temperature of the iron boride. As a result, it promotes the rapid melting of the iron boride to form droplets. As a result, it is presumed that the droplet-shaped iron boride can rapidly react with the nitrogen contained in the atmosphere, and as a result, the production of boron nitride can be promoted.

[0054] (Step to form a hollow space inside the inner layer) In this step, a hollow space is formed inside the inner layer by removing the core located inside the inner layer. Figure 4C is a schematic cross-sectional view showing an example of the method for producing boron nitride particles according to the present invention.

[0055] The core can be removed, for example, by using a liquid that dissolves the core. If the core contains iron boride, the iron boride can be removed by dissolving it in a liquid, for example, by washing the particles obtained in the above process (particles with an inner layer formed around the core) with an acid.

[0056] The acids used can be organic acids or inorganic acids, and examples of inorganic acids include hydrochloric acid, nitric acid, and sulfuric acid. The acid can be used for cleaning, for example, in the form of an aqueous solution. Since the inner layer 11 has holes 11a that communicate from the core 20 to the outside, the acid can flow from the holes 11a into the core 20 inside the inner layer 11 and dissolve the core 20.

[0057] By removing the core 20 located inside the inner layer 11, an inner layer 11 having a hollow portion 10 is obtained, as shown in Figure 4C.

[0058] The removal of core 20 may be performed by means other than acid, and by methods other than cleaning.

[0059] The method for producing boron nitride particles of the present invention may further include a step of cleaning the inner layer 11 having a hollow portion 10 after removing the core 20. In particular, if the core 20 is removed by cleaning with acid, it is preferable to remove any remaining acid by cleaning the inner layer 11 having a hollow portion 10 with water. The cleaning may be performed with a solvent other than water.

[0060] After cleaning, it is preferable to dry the inner layer 11 having the hollow portion 10 before proceeding to the next step.

[0061] (Step to form an outer layer that covers the outside of the inner layer having a hollow section) In this step, an outer layer is formed that covers the outside of the inner layer having a hollow section.

[0062] First, let's describe the case of forming the outer layer 12 of the boron nitride particle 1 shown in Figure 1. The outer layer 12 of the boron nitride particle 1 has pores 12a as described above. The outer layer 12 of the boron nitride particle 1 preferably contains boron nitride, and is preferably formed by growing boron nitride crystals on the outside of the inner layer 11.

[0063] The method for growing boron nitride crystals on the outside of the inner layer can be carried out in the same way as the method for growing boron nitride crystals around the core, as described in the "Step for forming the inner layer" above. In the method for growing boron nitride crystals, pores are formed in part of the boron nitride, but in the manufacturing method of the present invention, there is a step for forming a hollow space between the formation of the inner layer and the formation of the outer layer, so the growth of boron nitride crystals does not occur continuously between the inner and outer layers. Therefore, the positions where pores are formed differ between the inner and outer layers, and the outer layer is formed so as to cover the pores in the inner layer. Furthermore, since the growth of boron nitride crystals does not occur continuously between the inner and outer layers, the boundary between the inner and outer layers is clear.

[0064] Through the above process, boron nitride particles 1 shown in Figure 1 are obtained.

[0065] Next, we will describe the case in which the outer layer 12A of the boron nitride particle 2 shown in Figure 3 is formed. As described above, the outer layer 12A of the boron nitride particle 2 does not have pores 12a and preferably completely covers the inner layer 11. The outer layer 12A of the boron nitride particle 2 is preferably formed by coating the outside of the inner layer 11 with carbon.

[0066] A method for coating the outside of the inner layer 11 with carbon is, for example, the chemical vapor deposition (CVD) treatment described in Japanese Patent No. 5898628. By performing CVD treatment, a dense, poreless outer layer 12A can be formed, so that the inner layer 11 can be completely covered and the pores 11a can be completely hidden.

[0067] When the outer layer 12A is formed by CVD treatment, the carbon usually forms highly crystalline carbon, but this is not always the case.

[0068] Examples of organic substances that can be used as carbon sources in CVD treatment include benzene, toluene, xylene, ethylbenzene, nitrobenzene, diphenylmethane, naphthalene, phenol, and cresol. Other carbon sources include gaseous fuel, creosote oil, and mixtures thereof. Unsaturated hydrocarbons such as acetylene, ethylene, propylene, isopropylene, and butadiene can also be used.

[0069] The temperature for CVD processing is preferably between 800°C and 1200°C, and more preferably between 900°C and 1100°C. If the CVD processing temperature is below 800°C, the carbon deposition rate is too slow, resulting in a longer processing time and making it unsuitable for industrial production. A higher temperature for CVD processing results in a faster carbon deposition rate, but if the temperature is too high, the carbon may not grow into a film.

[0070] Through the above process, boron nitride particles 2 shown in Figure 3 are obtained.

[0071] [Sheet-like Substrate] Figure 5 is a schematic perspective view showing an example of the sheet-like substrate of the present invention. As shown in Figure 5, the sheet-like substrate 100 is composed of a resin 15, and the resin 15 contains boron nitride particles 1. In the sheet-like substrate 100, the boron nitride particles 1 are used as a filler. In Figure 5, boron nitride particles 1 are used, but boron nitride particles 2 may also be used. Furthermore, both boron nitride particles 1 and boron nitride particles 2 may be used.

[0072] The average particle size of boron nitride particles used in sheet-like substrates is preferably 1 μm to 40 μm. In order to increase the overall thermal conductivity of the sheet-like substrate, it is necessary to connect fillers in the resin to form heat conduction paths. However, if the average particle size of the boron nitride particles is less than 1 μm, a large number of filler contact surfaces are required to form heat conduction paths, and the sum of the thermal resistances at the filler contact surfaces becomes large, which can significantly reduce the thermal conductivity of the sheet-like substrate. In addition, if boron nitride particles are present at the via processing location, via processing may not be possible. Therefore, if the average particle size of the boron nitride particles exceeds 40 μm, the via processing location may be limited, and the defect rate of vias may increase.

[0073] The content of boron nitride particles in the sheet-like substrate is preferably 20% by volume or more and 40% by volume or less. If the content is less than 20% by volume, the effects of low dielectric strength and high thermal conductivity due to the addition of boron nitride particles cannot be fully obtained. On the other hand, if the content of boron nitride particles exceeds 40% by volume, adverse effects such as limitations on via processing locations and an increase in the via defect rate may increase.

[0074] In this specification, the content of boron nitride particles in a sheet-like substrate is determined as follows. First, the density of the boron nitride particles of the present invention is defined. In the boron nitride particles of the present invention, even when creating a sheet-like substrate, the resin does not enter the hollow parts of the boron nitride particles, so the apparent density including the volume of the hollow parts is defined as the density of the boron nitride particles. The density (apparent density) ρBN of the boron nitride particles of the present invention can be obtained in advance, for example, by the Le Chatelier specific gravity bottle method, the liquid weighing method, the liquid immersion method, etc. The density ρs of the sheet-like substrate containing the boron nitride particles of the present invention can be obtained by cutting the sheet-like substrate to an appropriate size, for example, by the pycnometer method. In addition, a known value is used for the density ρR of the resin. Using these values, the content R of boron nitride particles in the sheet-like substrate can be calculated from the following formula. R = (ρs - ρR) / (ρBN - ρR) × 100 (volume %) Note that the above formula cannot be used to calculate if ρBN and ρR are exactly equal, but since such cases are practically nonexistent, the content R is determined by the above formula.

[0075] For the sheet-like substrate, thermosetting resins or thermoplastic resins are preferred. Examples of thermosetting resins include maleimide compounds, cyanate resins, benzocyclobutene resins, and polycarbodiimide resins. Examples of thermoplastic resins include liquid crystal polymers. These resins may be used individually or in mixtures of two or more.

[0076] The sheet-like substrate of the present invention can be manufactured by known methods. For example, a resin dispersion containing a resin, boron nitride particles, and a solvent can be applied to a metal substrate by a casting method to form a resin layer, and then the resin layer can be obtained as a sheet-like substrate by peeling off the metal substrate. Alternatively, a laminate having a metal layer (metal substrate) and a resin layer (sheet-like substrate) can be obtained without peeling off the metal substrate.

[0077] [Module] Figure 6 is a schematic cross-sectional view showing an example of the module of the present invention. As shown in Figure 6, the module 200 comprises a substrate 210 having a first main surface 210a and a second main surface 210b that are opposite to each other in the thickness direction, an electronic component 220 mounted on the first main surface 210a of the substrate 210, and a resin layer 230 covering the electronic component 220 and containing boron nitride particles 1. In the module 200, the boron nitride particles 1 are used as a filler in the resin layer 230. In Figure 6, boron nitride particles 1 are used, but boron nitride particles 2 may also be used. Furthermore, both boron nitride particles 1 and boron nitride particles 2 may be used.

[0078] Module 200 improves the thermal conductivity of the resin layer 230 by including the boron nitride particles of the present invention in the resin layer 230. This improved thermal conductivity of the resin layer 230 enhances the thermal diffusion of heat generated from the electronic component 220, thereby improving cooling performance.

[0079] Examples of resins used in the resin layer 230 include the same resins as those exemplified above for use in the sheet-like substrate. In Figure 6, the resin layer 230 covers a portion of the first main surface 210a of the substrate 210.

[0080] In the following, in the cross-section of module 200 in Figure 6, the direction perpendicular to the thickness direction of the substrate 210 is defined as the width direction.

[0081] A circuit layer is formed on the first main surface 210a of the substrate 210 (not shown). The circuit layer includes lands for mounting electronic components 220 and wiring to connect to the lands. The electronic components 220 mounted on the substrate 210 are electrically connected to the lands of the circuit layer via solder bumps 221.

[0082] Between the electronic component 220 and the first main surface 210a of the substrate 210, an underfill 222 is formed by impregnating it with the same resin as the resin layer 230. In Figure 6, the underfill 222 and the resin layer 230 are formed from the same material, but the underfill 222 and the resin layer 230 may be formed from different resins. It is preferable that the underfill 222 and the resin layer 230 are formed from the same material because the underfill 222 and the resin layer 230 can be formed simultaneously.

[0083] If the underfill 222 is formed of a different resin than the resin layer 230, the material of the underfill 222 can be a known material.

[0084] Preferably, module 200 further comprises a metal layer 240 provided on the upper surface 230a of the resin layer 230 on the side opposite to the substrate 210. By further comprising the metal layer 240, which has high thermal conductivity, the thermal dissipation of heat generated from the electronic components 220 is improved, and the cooling performance is further enhanced. The metal layer 240 has the same width dimension as the resin layer 230.

[0085] The average particle size and content of boron nitride particles used in the resin layer are the same as those of the sheet-like substrate described above. The content of boron nitride particles in the resin layer can be determined by the same method as described above for the sheet-like substrate.

[0086] The electronic component 220 is not particularly limited and can include, for example, an IC, resistor, transformer, motor, etc. The electronic component 220 has a rectangular cross-sectional shape as shown in Figure 6. The shape of the electronic component 220 is not particularly limited.

[0087] As the metal used for the metal layer 240, metal materials with high thermal conductivity such as copper (Cu) and aluminum (Al) are preferred. However, since electrical conductivity, adhesion to the underlying resin layer, and corrosion resistance may be prioritized in some cases, metals with lower thermal conductivity than copper or aluminum may be used as needed.

[0088] Next, modules 201 and 202, which are modified versions of module 200, will be described below with reference to Figures 7 and 8. Here, only the differences from module 200 in Figure 6 will be explained.

[0089] Figures 7 and 8 are schematic cross-sectional views showing modified versions of the module in Figure 6. In module 201 shown in Figure 7 and module 202 shown in Figure 8, the widthwise dimensions of the metal layer 240 differ from those of module 200 in Figure 6. In module 201, as shown in Figure 7, the widthwise dimension of the metal layer 240 is the same as the widthwise dimension of the electronic component 220. In module 202, as shown in Figure 8, the widthwise dimension of the metal layer 240 is intermediate in length between the widthwise dimension of the electronic component 220 and the widthwise dimension of the resin layer 230.

[0090] The width dimension of the metal layer is preferably the same as or larger than the width dimension of the electronic component. This is because a larger width dimension of the metal layer improves thermal conductivity, thereby improving the thermal diffusion of heat generated from the electronic component and thus improving cooling performance. For this reason, when viewing the module of the present invention from the thickness direction of the substrate, it is preferable that the metal layer covers at least a portion of the electronic component, and more preferably that it completely covers it.

[0091] In modules 201 and 202, both the upper surface 230a of the resin layer 230 and the metal layer 240 are exposed when viewed from the thickness direction of the substrate 210. Because the resin layer 230 and the metal layer 240 have different gloss levels, they can serve as markers when mounting modules 201 and 202 onto a motherboard, thereby reducing mounting errors.

[0092] Figure 9 is a schematic cross-sectional view showing a modified version of the module in Figure 6. Here, only the differences from module 200 in Figure 6 will be explained. In module 203, as shown in Figure 9, two conductor portions 250 are provided from both ends of the metal layer 240, extending perpendicularly to the first main surface 210a of the substrate 210. The conductor portions 250 are along the side surface 230b of the resin layer 230 and are exposed. An electrode portion 260 is provided on the first main surface 210a of the substrate 210, and the conductor portion 250 connects the metal layer 240 and the electrode portion 260. In module 203, the heat generated from the electronic component 220 is dissipated via the conductor portion 250 and the electrode portion 260 through the substrate 210 on which the electronic component 220 is mounted. Therefore, the thermal diffusivity of the heat generated from the electronic component 220 is improved, and an improvement in cooling performance can be expected.

[0093] Module 203 has two conductor sections 250 and two electrode sections 260, but there may be one conductor section 250 and three or more electrode sections 260.

[0094] Examples of materials for the conductive portion 250 include the metal material used for the metal layer 240 described above. The material of the conductive portion 250 may be the same as or different from the material of the metal layer 240.

[0095] The electrode portion 260 is, for example, a land, a pad, etc. In Figure 9, the widthwise dimensions of the electrode portion 260 and the conductor portion 250 are the same, but from a manufacturing standpoint, it is preferable that the widthwise dimension of the electrode portion 260 is larger than the widthwise dimension of the conductor portion 250. The lengthwise dimension of the electrode portion 260 is not particularly limited, but it is preferable that it is larger than the lengthwise dimension of the conductor portion 250. Here, the lengthwise direction is the direction perpendicular to the thickness direction and the width direction.

[0096] Module 203 is equipped with a conductor portion 250 and an electrode portion 260, thereby connecting the metal layer 240 and the substrate 210. As a result, the thermal dissipation of heat generated from the electronic component 220 is improved, further enhancing the cooling performance.

[0097] Figure 10 is a schematic cross-sectional view showing another example of the module of the present invention. Here, only the differences from module 202 in Figure 8 will be explained. Also, for clarity, in the following explanation, the substrate on which the electronic components are mounted will be referred to as the module substrate. In module 204, as shown in Figure 10, the metal layer 240 is not located on the upper surface 230a of the resin layer 230, but rather is provided between the upper surface 230a of the resin layer 230 and the electronic component 220.

[0098] In module 204, the width dimension of the module substrate 210 is the same as the width dimension of the resin layer 230.

[0099] Module 204 can be mounted on the motherboard 300. Module 204 has its second main surface 210b mounted on the first main surface 300a of the motherboard 300. A heatsink 400 is provided on the second main surface 300b of the motherboard 300.

[0100] Module 204 has a metal layer 240 located inside the resin layer 230, and because the metal layer 240 is closer to the electronic component 220, the thermal conductivity of the metal layer 240 is improved. As a result, the thermal diffusion of heat generated from the electronic component 220 is improved, and the cooling performance is further enhanced.

[0101] Figure 11 is a schematic cross-sectional view showing a modified version of the module in Figure 10. Here, only the differences from module 204 in Figure 10 will be explained. In module 205, as shown in Figure 11, two conductor portions 250 are provided that extend perpendicularly to the first main surface 210a of the substrate 210, penetrating the resin layer 230 from the metal layer 240. The two conductor portions 250 are each located between the center and the end in the width direction of the metal layer 240. In module 205, an electrode portion 260 is provided on the first main surface 210a of the module substrate 210 and inside the resin layer 230. In module 205, the conductor portion 250 is provided inside the resin layer 230. The conductor portion 250 connects the metal layer 240 and the electrode portion 260.

[0102] In module 205, the conductor portion 250 is preferably a via conductor.

[0103] Each of the two conductor portions 250 may be connected to the end of the metal layer 240 in the width direction.

[0104] In module 205, the heat generated from the electronic component 220 is dissipated via the conductive portion 250 and electrode portion 260 through the substrate 210 on which the electronic component 220 is mounted. This improves the thermal diffusivity of the heat generated from the electronic component 220, and is expected to improve cooling performance. Furthermore, in module 205, the electronic component 220 is covered with a resin layer 230 and further surrounded by a metal layer 240 and two conductive portions 250. This improves the thermal diffusivity of the heat generated from the electronic component 220, resulting in even better cooling performance.

[0105] Figure 12 is a schematic cross-sectional view showing a modified version of the module in Figure 11. Here, only the differences from module 205 in Figure 11 will be explained. In module 206, as shown in Figure 12, the width dimension of the metal layer 240 is the same as the width dimension of the resin layer 230, and the end of the metal layer 240 is exposed on the side surface 230b of the resin layer 230. The two conductor portions 250 are each in contact with both ends of the metal layer 240 and extend along the side surface 230b of the resin layer 230 to the first main surface 210a of the module substrate 210. In module 206, the electrode portion 260 is provided outside the resin layer 230.

[0106] Modules 200, 201, 202, and 203 shown in Figures 6, 7, 8, and 9 can also be mounted and used on a motherboard equipped with a heatsink.

[0107] [Module Manufacturing Method] The manufacturing method of the module of the present invention is not particularly limited, but one example will be described below using the module 200 in Figure 6 as an example.

[0108] First, the substrate 210 and the electronic components 220 are prepared. A circuit layer including solder bumps 221 is provided on the first main surface 210a of the substrate 210 on which the electronic components 220 will be mounted. The electronic components 220 are placed on the solder bumps 221 and the electronic components 220 are covered with a resin containing boron nitride particles 1. At this time, the resin containing boron nitride particles 1 penetrates into the spaces between the solder bumps 221 due to capillary action. After that, a resin layer 230 is provided.

[0109] The metal layer 240 is provided on the upper surface 230a of the resin layer 230. The module 200 is thus obtained.

[0110] In the module 203 of Figure 9, which includes a conductor portion 250, when a circuit layer is provided on the first main surface 210a of the substrate 210 in the manufacturing method of the module 200 described above, an electrode portion 260 for connecting to the conductor portion 250 is also provided on the first main surface 210a of the substrate 210. Next, electronic components 220 are mounted, a resin layer 230 is provided, and a metal layer 240 is provided on the upper surface 230a of the resin layer 230. After that, the conductor portion 250 is provided.

[0111] The conductive portion 250 can be manufactured, for example, by screen printing a conductive material onto the side surface 230b of the resin layer 230 from the metal layer 240 to the electrode portion 260. The metal layer 240 and the conductive portion 250 may also be formed in a single process.

[0112] In module 204 of Figure 10, when providing the resin layer 230 using the manufacturing method of module 200 described above, first, the electronic component 220 is covered with resin up to the position where the metal layer 240 is to be provided. After providing the metal layer 240 on the surface of the resin, the resin layer 230 can be provided by further covering the metal layer 240 with resin. Next, a heat sink 400 is provided on the second main surface 300b of the motherboard 300, and module 205 is mounted on the first main surface 300a of the motherboard 300.

[0113] Module 205 in Figure 11 can be manufactured in the same manner as module 204, except that it differs in the following respects. When a circuit layer is provided on the first main surface 210a of the substrate 210, an electrode portion 260 for connecting to the conductor portion 250 is also provided on the first main surface 210a of the substrate 210. Next, the electronic components 220 are mounted and the electronic components 220 are covered with resin up to the position where the metal layer 240 is to be provided. A hole leading to the electrode portion 260 is made in the resin using a drill or laser, and after plating or the like is applied to the inner wall of the hole, a conductive material is filled in to provide a conductor portion 250 that penetrates the inside of the resin layer 230. After providing the metal layer 240 on top of the resin, the resin layer 230 can be provided by further covering the metal layer 240 with resin. The method of providing the conductor portion 250 is not particularly limited, and after covering the inside of the hole with a conductive material, plating or the like may be filled in.

[0114] Module 206 in Figure 12 can be manufactured in the same manner as module 204, except that it differs in the following respects. When the circuit layer is provided on the first main surface 210a of the substrate 210, the electrode portion 260 for connecting to the conductor portion 250 is also provided on the first main surface 210a of the substrate 210. After providing the resin layer 230, the conductor portion 250 is provided in the same manner as module 203 in Figure 9.

[0115] The following are examples that more specifically disclose the boron nitride particles and sheet-like substrate of the present invention. However, the present invention is not limited to these examples.

[0116] Example 1 The boron nitride particles 1 shown in Figure 1 were configured as follows, with the dimensions and material properties described below. A liquid crystal polymer containing 30 volume percent of these boron nitride particles was prepared, and a sheet was formed by casting. The dielectric constant, dielectric loss tangent, and thermal conductivity of the obtained sheet were simulated. The results are shown in Table 1. Average particle size of boron nitride particles: 10 μm Average thickness of the inner layer: 1.0 μm Average thickness of the outer layer: 0.5 μm Material constituting the inner layer: Boron nitride Material constituting the outer layer: Boron nitride

[0117] Comparative Example 1: A sheet was formed in the same manner as in Example 1, except that it did not contain boron nitride particles. The dielectric constant, dielectric loss tangent, and thermal conductivity of the obtained sheet were simulated. The results are shown in Table 1.

[0118] Comparative Example 2 A sheet was formed in the same manner as in Example 1, except that hollow boron nitride particles consisting only of the inner layer portion of Example 1 were used instead of the boron nitride particles of Example 1. The dielectric constant, dielectric loss tangent, and thermal conductivity of the obtained sheet were simulated. The results are shown in Table 1.

[0119]

[0120] Example 1, using the boron nitride particles of the present invention, showed lower dielectric constant and dielectric loss tangent compared to Comparative Examples 1 and 2. This is thought to be due to the boron nitride particles of the present invention maintaining a hollow structure even within the resin. Furthermore, the thermal conductivity of Example 1 was higher than that of Comparative Example 1 and similar to that of Comparative Example 2. These examples clearly demonstrate that the boron nitride particles of the present invention have the effect of imparting low dielectric properties and high thermal conductivity to resin materials.

[0121] 1, 2 Boron nitride particles 10 Hollow part 11 Inner layer part 11a Holes in the inner layer part 12, 12A Outer layer part 12a Holes in the outer layer part 15 Resin 20 Core 100 Sheet-like substrate 200, 201, 202, 203, 204, 205, 206 Module 210 Substrate (module substrate) 210a First main surface of the substrate 210b Second main surface of the substrate 220 Electronic components 221 Solder bump 222 Underfill 230 Resin layer 230a Top surface of the resin layer 230b Side surface of the resin layer 240 Metal layer 250 Conductor part 260 Electrode part 300 Motherboard 300a First main surface of the motherboard 300b Second main surface of the motherboard 400 Heat sink

Claims

1. A boron nitride particle comprising an inner layer having a hollow particle shape, and an outer layer covering the outside of the inner layer, wherein the inner layer contains boron nitride and has pores communicating from the hollow to the outside, and the outer layer covers the pores.

2. The boron nitride particle according to claim 1, wherein the outer layer covers the inner layer so as to maintain the hollow portion.

3. The boron nitride particles according to claim 1 or 2, wherein the average thickness of the outer layer is the same as or greater than the average thickness of the inner layer.

4. The boron nitride particle according to claim 3, wherein the average thickness of the outer layer is 0.1 μm or more.

5. Boron nitride particles according to any one of claims 1 to 4, wherein the thermal conductivity of the material constituting the outer layer is the same as or greater than the thermal conductivity of the boron nitride.

6. The boron nitride particles according to claim 5, wherein the thermal conductivity of the material constituting the outer layer is 1.0 W / m·K or higher.

7. The boron nitride particle according to any one of claims 1 to 6, wherein the outer layer contains boron nitride.

8. Boron nitride particle according to any one of claims 1 to 6, wherein the outer layer contains carbon.

9. A sheet-like substrate made of a resin, wherein the resin contains boron nitride particles according to any one of claims 1 to 8.

10. A method for producing boron nitride particles, comprising the steps of: forming an inner layer containing boron nitride around a particle-shaped core; forming a hollow portion inside the inner layer by removing the core located inside the inner layer; and forming an outer layer that covers the outside of the inner layer having the hollow portion.

11. The method for producing boron nitride particles according to claim 10, wherein the inner layer is formed by growing the boron nitride crystals.

12. A method for producing boron nitride particles according to claim 10 or 11, wherein the outer layer is formed by growing the boron nitride crystals on the outside of the inner layer.

13. A method for producing boron nitride particles according to claim 10 or 11, wherein the outer layer is formed by coating the outside of the inner layer with carbon.

14. A method for producing boron nitride particles according to any one of claims 10 to 13, further comprising the step of cleaning the inner layer having the hollow portion after removing the core.

15. A method for producing boron nitride particles according to any one of claims 10 to 14, wherein the core contains iron boride.

16. A module comprising: a substrate having a first main surface and a second main surface opposite to each other in the thickness direction; an electronic component mounted on the first main surface of the substrate; and a resin layer covering the electronic component and containing boron nitride particles as described in any one of claims 1 to 8.

17. The module according to claim 16, further comprising a metal layer provided on the upper surface of the resin layer opposite to the substrate, or between the upper surface of the resin layer and the electronic component.

18. The module according to claim 17, further comprising an electrode portion provided on the first main surface of the substrate and a conductor portion connecting the metal layer and the electrode portion.

19. The module according to claim 18, wherein the conductor portion is a via conductor provided inside the resin layer.

20. The module according to any one of claims 16 to 19, further comprising underfill filled between the substrate and the electronic component.

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