TW202440464A - Alumina powder and resin composition - Google Patents

Abstract

This alumina powder has, with respect to all crystal phases, a [delta]-type crystal phase proportion of at most 30 mass% and an [alpha]-type crystal phase proportion of at most 50 mass%, the circularity D50 at cumulative 50% from the low circularity side of the number-based cumulative circularity distribution being at least 0.90, and the particle diameter D90 at cumulative 90% from the fine particle side of the volume-based cumulative particle size distribution being less than 20 [mu]m.

Description

Alumina powder and resin composition

The present invention relates to an aluminum oxide powder and a resin composition using the same.

Heat generated by energizing electronic components can easily have an adverse effect on the performance of electronic components, so it is desirable to dissipate heat quickly. Therefore, for example, it is desirable that the material constituting the semiconductor sealing material surrounding the IC chip exhibits high thermal conductivity for heat dissipation. Thermally conductive components used for heat dissipation generally use a composite material including thermally conductive powder and resin as a material, and use thermally conductive aluminum oxide powder as a thermally conductive filler.

For example, Patent Document 1 discloses a spherical α-alumina powder characterized by an average sphericity of 0.93 or more and an α rate of the crystal form of 95% or more. By mixing the spherical α-alumina powder into a resin or rubber, etc., it can be mixed at a high density, and the ratio of the α crystal form is large, and the resulting composition exhibits excellent thermal conductivity. As a method for producing the above-mentioned α-alumina powder, Patent Document 1 discloses that: in a method of heat-treating metal aluminum powder or aluminum oxide powder with a flame to melt and soften it, and then cooling it while introducing it into a capture system to recover the aluminum oxide powder, the heat-treated product in the above-mentioned flame is passed through a region with a temperature of 800 to 500°C once before cooling, and after solidification, it is passed through a higher temperature region of 950 to 1500°C, thereby increasing the α rate.

In addition, as a spherical alumina powder suitable for a filler that has high flow properties even when highly filled in a resin, Patent Document 2 discloses: a spherical alumina powder having a ratio of the δ phase peak intensity detected at 2θ=45.6° to the θ phase peak intensity detected at 2θ=44.8° by X-ray diffraction (δ phase peak intensity/θ phase peak intensity) of 1.0 or more, an average sphericity of 0.90 or more, and an average particle size of 100 μm or less. Furthermore, Patent Document 2 discloses that after melting the aluminum oxide raw material, rapid cooling is performed with dry ice, thereby obtaining the above-mentioned spherical aluminum oxide powder that can impart higher flow properties to the resin composition even when highly filled in the resin. Prior Art Documents Patent Documents

Patent document 1: International Publication No. 2008/053536 Patent document 2: Japanese Patent Publication No. 2011-102215

[The problem the invention is trying to solve]

The technology of Patent Document 1 requires heat treatment after flame melting to improve the thermal conductivity of spherical alumina. In addition, the technology of Patent Document 2 requires rapid cooling after flame melting to improve fluidity. Both technologies require further treatment after flame melting. In addition, it is believed that further research is needed to ensure better thermal conductivity and better fluidity when mixed with resin.

The present invention is completed in view of the above situation, and its purpose is to provide an aluminum oxide powder that has high thermal conductivity, excellent fluidity when mixed with resin, and can be easily manufactured, and a resin composition containing the aluminum oxide powder. [Technical means for solving the problem]

Sample 1 of the present invention is an aluminum oxide powder, whose ratio of δ-type crystal phase to all crystal phases is 30% by mass or less, and α-type crystal phase ratio is 50% by mass or less, the roundness C50 of 50% accumulated from the low roundness side of the cumulative roundness distribution based on number is 0.90 or more, furthermore, the particle size D90 of 90% accumulated from the fine particle side of the cumulative particle size distribution based on volume is less than 20 μm.

Aspect 2 of the present invention is the aluminum oxide powder described in Aspect 1, and its cumulative roundness C5 of 5% from the low roundness side of the cumulative roundness distribution based on the number of particles is greater than 0.83.

Aspect 3 of the present invention is the aluminum oxide powder described in Aspect 1 or 2, wherein the particle size D50 of 50% of the particles in the cumulative particle size distribution based on volume is less than 10 μm.

Aspect 4 of the present invention is an aluminum oxide powder as described in any one of aspects 1 to 3, and its uranium content and thorium content are less than 10 mass ppb respectively.

Aspect 5 of the present invention is a resin composition, which contains aluminum oxide powder as described in any one of aspects 1 to 4. [Effect of the invention]

According to the present invention, there can be provided an alumina powder which has high thermal conductivity, excellent fluidity when mixed with a resin and can be easily manufactured, and a resin composition containing the alumina powder.

The inventors of the present invention have repeatedly conducted intensive research to obtain an alumina powder that has high thermal conductivity, excellent fluidity when mixed with a resin, and can be easily manufactured. As a result, it was found that as long as the ratio of the δ-type crystalline phase to the α-type crystalline phase relative to the total crystalline phase of the alumina powder is controlled, especially the ratio of the δ-type crystalline phase is suppressed to a certain level, and the roundness C50 of 50% accumulated from the low roundness side of the cumulative roundness distribution based on the number basis and the particle size D90 of 90% accumulated from the microparticle side of the cumulative particle size distribution based on the volume basis are set within a specific range. The alumina powder of this embodiment is described in detail below.

[Alumina powder] [Ratio of δ-type crystalline phase to α-type crystalline phase relative to all crystalline phases] The heat generated in electronic components has increased in recent years due to high integration, and resin compositions used in heat dissipation components are required to exhibit higher thermal conductivity. Previously, it was believed that in order to improve the thermal conductivity of alumina powder, it is better to increase the ratio of α-type crystalline phase in the crystal structure. However, in order to obtain alumina powder with higher thermal conductivity, the inventors of the present invention have conducted in-depth research on the relationship between the crystal structure and thermal conductivity of alumina powder. As a result, it was first discovered that in the crystal structure, the δ-type crystalline phase has a greater impact on the thermal conductivity of alumina powder than the α-type crystalline phase. To further improve the thermal conductivity of alumina powder, it is effective to suppress the ratio of the δ-type crystalline phase. It was also found that to achieve the required thermal conductivity, the ratio of the δ-type crystalline phase to the total crystalline phase needs to be set to 30% by mass or less. The ratio of the δ-type crystalline phase is preferably 25% by mass or less, more preferably 20% by mass or less, and further preferably 15% by mass or less. From the perspective of improving thermal conductivity, the smaller the ratio of the δ-type crystalline phase, the better, and it can be 1% by mass or more.

As described above, the alumina powder of the present embodiment has a thermal conductivity that can be improved by making the ratio of the δ-type crystalline phase to the total crystalline phase 30% by mass or less, and the ratio of the α-type crystalline phase, unlike the high α-ratio alumina powder of the prior art, 50% by mass or less. The ratio of the α-type crystalline phase can be further made 40% by mass or less, further made 30% by mass or less, and further made 20% by mass or less.

As long as the ratio of the α-type crystalline phase to the δ-type crystalline phase satisfies the above range, the ratio of crystalline phases other than the α-type crystalline phase and the δ-type crystalline phase, such as the θ-type crystalline phase and the κ-type crystalline phase, is arbitrary. Furthermore, from the viewpoint of further improving thermal conductivity, the (ratio of the δ-type crystalline phase/ratio of the θ-type crystalline phase) of the alumina powder of the present embodiment is preferably set to less than 0.5, for example.

The ratio of the δ-type crystal phase and the ratio of the α-type crystal phase to the total crystal phase are obtained by performing Rietveld analysis on the powder X-ray diffraction pattern of the aluminum oxide powder as shown in the examples described below. In addition, the Rietveld analysis can be performed not according to the method performed in the above examples, but using the patterns obtained by various powder X-ray diffraction devices using various radiation sources, and by various powder X-ray analysis software such as Rietan-FP, Rietan-2000, JADE, and JANA to calculate.

[C50 of the cumulative 50% circularity from the low circularity side of the cumulative circularity distribution based on the number basis] The circularity C50 of the aluminum oxide powder of this embodiment from the low circularity side of the cumulative circularity distribution based on the number basis is 0.90 or more. Since the aluminum oxide powder of this embodiment has a higher circularity as described above, it has a higher fluidity when mixed with the resin, has good kneading properties with the resin, and can also improve the fluidity of the resin composition (composite material) after kneading. Therefore, for example, in order to manufacture semiconductor sealing materials, when the molten resin composition (composite material) after kneading is injected into a mold having a substrate with an IC chip set inside, it is filled into a finer gap, which can suppress the generation of defects such as pores.

[Circularity C5 of 5% cumulatively from the low circularity side of the cumulative circularity distribution based on the number basis] The circularity C5 of 5% cumulatively from the low circularity side of the cumulative circularity distribution based on the number basis of the aluminum oxide powder of this embodiment is preferably 0.83 or more. The aluminum oxide powder of this embodiment suppresses the ratio of particles with low circularity, and it is preferred that the above circularity C5 is 0.83 or more, thereby further improving the fluidity when mixed with the above resin. The above circularity C5 may be less than 0.90.

The circularity C50 and the circularity C5 can be obtained by the method described in the embodiments described later.

[D90, the particle size at which 90% of the particles are accumulated from the side of the particles in the cumulative particle size distribution based on the volume basis] The particle size D90, the particle size at which 90% of the particles are accumulated from the side of the particles in the cumulative particle size distribution based on the volume basis of the alumina powder of this embodiment, does not reach 20 μm. In recent years, due to the miniaturization of semiconductors and the narrowing of wiring pitches, the heat dissipation filler contained in the heat dissipation component is required to have a smaller particle size. The alumina powder of this embodiment is most suitable as the above-mentioned heat dissipation filler with a smaller particle size. D90 is preferably less than 15 μm.

[D50 of the particle size at which 50% of the particles are accumulated from the particle side of the cumulative particle size distribution based on the volume basis] The particle size D50 of the alumina powder of this embodiment at which 50% of the particles are accumulated from the particle side of the cumulative particle size distribution based on the volume basis is preferably less than 10 μm. The particle size D90 of the alumina powder of this embodiment is smaller as described above, and the average particle size D50 of the alumina powder also satisfies the requirement of preferably less than 10 μm, thereby providing an alumina powder that is more suitable for the above-mentioned heat dissipation filler with a smaller particle size. D50 is more preferably less than 8 μm. The lower limit of D50 can be, for example, 0.5 μm or more.

The above-mentioned D90 and D50 can be obtained by the method described in the embodiments described later.

[Uranium content and thiobium content] The aluminum oxide powder of this embodiment preferably has a uranium content and a thiobium content of less than 10 mass ppb, respectively. The aluminum oxide powder of this embodiment can reduce the α-ray dosage by suppressing the uranium content and the thiobium content as described above, and can eliminate the operation errors caused by the α-rays in semiconductor applications. The uranium content and the thiobium content are preferably less than 5 mass ppb, respectively. The above-mentioned uranium content and the thiobium content can be measured by the method described in the embodiment described later.

The alumina powder of the present embodiment can be used well as a heat dissipation filler included in a semiconductor sealant, for example. As described above, in recent years, the miniaturization of semiconductors and the miniaturization of wiring pitches have been developing, and the alumina powder of the present embodiment is suitable for use as a heat dissipation filler with a smaller particle size included in a small semiconductor sealant, for example. Moreover, even when the ratio of the alumina powder as a heat dissipation filler included in the resin composition is increased, since the roundness of the alumina powder is higher and the fluidity of the resin composition containing the alumina powder is higher, the resin composition can be filled into a finer gap, for example, a small semiconductor sealant can be manufactured well. That is, by using the alumina powder of this embodiment as a main filler, it is possible to take into account both the improvement of the thermal conductivity of the semiconductor sealing material and the high fluidity required when manufacturing the semiconductor sealing material. Furthermore, since the uranium content and the thorium content of the alumina powder are preferably suppressed, the α-ray dose is small, and it is possible to prevent the semiconductor sealing material containing the alumina powder as a heat dissipation filler from being soft.

[Method for producing alumina powder] The method for producing the alumina powder of the present embodiment is not particularly limited as long as it can obtain an alumina powder having the above-mentioned crystal phase, roundness distribution, and particle size distribution. As an example of a method for producing the alumina powder of the present embodiment, it can be exemplified by the method shown below. First, a method for producing alumina raw material powder constituting the alumina powder is described. Specifically, a method for producing the alumina raw material powder by flame melting the raw material alumina is described. The alumina powder may be composed only of the alumina raw material powder produced by the following method, or may be obtained by mixing the alumina raw material powder produced by the following method with the alumina raw material powder produced by other methods in a manner that satisfies the specified crystal phase, roundness distribution and particle size distribution.

(Raw alumina for flame melting) Raw alumina for flame melting is produced by a known method. For example, the Bayer method, the ammonium alum method, the hydroxide method (AACH (Ammonium Aluminum Carbonate Hydroxide: aluminum ammonium bicarbonate) method), the solvent extraction method, the organic aluminum hydrolysis method (aluminum alkoxide method), etc. can be cited.

In the case of the Bayer process, raw alumina can be produced by calcining aluminum hydroxide obtained from alumina. In addition, the ammonium aluminate process, the AACH process, the solvent extraction process, and the aluminum alkoxide process can produce high-purity raw alumina with low uranium and thiobium contents, so it is preferred. If the raw alumina produced by these methods, in which the uranium content and the thiobium content are suppressed to less than 10 mass ppb, respectively, is used to produce alumina powder, it is possible to obtain alumina powder with suppressed uranium and thiobium contents, so it is preferred.

(Crushing of raw alumina for flame melting) The raw alumina for flame melting is crushed so that the flame melting can be performed to easily obtain raw alumina powder of the required size. The raw alumina can be crushed by a known method such as a vibration mill, a bead mill, a ball mill, a jet mill, etc., and can be crushed in either a dry state or a wet state.

In the above-mentioned pulverization, a surface protective agent is used. The surface protective agent not only protects the surface of the pulverized alumina powder, but also has the function of deactivating the surface of the alumina powder. By deactivating the surface, the agglomeration of the alumina powders can be reduced. It is suitable to use raw alumina with a high BET specific surface area that is easy to agglomerate, and obtain the target particle size of the alumina raw material powder after flame melting. As suitable surface protective agents, for example: monohydric alcohols such as methanol, ethanol, 1-propanol, and 2-propanol; glycols such as ethylene glycol, polyethylene glycol, propylene glycol, and polypropylene glycol; amines such as triethanolamine; higher fatty acids such as palmitic acid, stearic acid, and oleic acid, etc. Among these surface protective agents, one type can be used alone, or two or more types can be used in combination. Among them, diols are preferred, and one or more of ethylene glycol, polyethylene glycol, propylene glycol, and polypropylene glycol are particularly preferred.

Regarding polyethylene glycol and polypropylene glycol, which are preferably used as surface protective agents, there is no particular limitation on their molecular weight, but in view of ease of addition, liquids having an average molecular weight of about 200 to 600 are preferred.

When the raw material aluminum oxide is set to 100 parts by mass, in order to fully exert the effect of the surface protective agent, the addition amount of the surface protective agent is preferably set to 0.01 parts by mass or more. If the addition amount of the surface protective agent is too much, the effect of the surface protective agent will also be saturated, so it is preferably set to 10 parts by mass or less. The addition amount of the surface protective agent is more preferably 0.05 to 8 parts by mass, and further preferably 0.1 to 5 parts by mass.

The raw material alumina provided for flame melting is preferably an agglomerate of primary particles of alumina, and the particle size of the primary particles of alumina is preferably, for example, 1 to 100 nm. The particle size of the primary particles of the above-mentioned alumina can be obtained as the arithmetic mean of the circle equivalent diameter in the electron microscope photograph. In addition, the above-mentioned particle size can also be calculated based on the BET specific surface area. The raw material alumina provided for flame melting preferably has a higher BET specific surface area. By providing raw material alumina with a higher BET specific surface area for flame melting, it is possible to obtain an alumina raw material powder with less melt residue during flame melting and higher roundness. The BET specific surface area of the raw material aluminum oxide used for flame melting obtained by nitrogen adsorption method is preferably 40 to 500 m ² /g, more preferably 100 to 450 m ² /g.

(Flame melting) The flame melting method refers to a method of spraying raw aluminum oxide into a flame, causing it to dropletize, and then cooling and solidifying. According to the flame melting method, the particle size of the raw aluminum oxide can be roughly maintained to obtain an aluminum oxide raw powder. According to this embodiment, the raw aluminum oxide having a high BET specific surface area and being fine as described above is used, so that an aluminum oxide raw powder with no melting residue, fineness, and high roundness can be obtained.

After the flame melting, a cyclone separator or a filter bag can be used to capture the powder and grade it to obtain the aluminum oxide raw material powder with the desired particle size distribution.

The alumina powder of this embodiment can be formed by only the alumina raw material powder produced by the above method, or can be obtained by mixing the alumina raw material powder produced by the above method with the alumina raw material powder produced by other methods in a manner that satisfies the crystal phase, roundness distribution and particle size distribution specified in the alumina powder of this embodiment. According to this embodiment, even if heat treatment after flame melting or cooling control after flame melting is not performed as before, the specified alumina powder can be easily produced.

[Resin composition] By using the alumina powder of this embodiment as a filler for a resin composition, a resin composition (composite material) having high thermal conductivity can be obtained. The resin composition contains a resin and the alumina powder of this embodiment.

In order to ensure the thermal conductivity of the resin composition, the ratio (mixing ratio) of the aluminum oxide powder of this embodiment contained in the resin composition is preferably 60 mass % or more. On the other hand, from the perspective of ensuring the elasticity unique to the resin, the ratio of the aluminum oxide powder is preferably 97 mass % or less, and more preferably 92 mass % or less.

The resin used in the resin composition can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. The resin may be used alone or in combination of two or more.

Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride, and polytetrafluoroethylene, fluorine-based polymers such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers (ABS, Acrylonitrile Butadiene Styrene) resins, and polyphenylene ether copolymers (PPE, Polypheylene Terephthalate). ether) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimide, polyamide imide, polymethacrylic acid, polymethyl methacrylate and other polymethacrylates, polyacrylic acids, polycarbonate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether nitrile, polyether ketone, polyketone, liquid crystal polymer, silicone resin, ionomer, etc.

Examples of the thermoplastic elastomer include styrene-butadiene block copolymers or hydrogenated products thereof, styrene-isoprene block copolymers or hydrogenated products thereof, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, etc. Specific examples of the crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

From the viewpoint of obtaining properties such as processability, it is preferred to use a polyolefin resin, an acrylic resin, a polyimide resin, a polyamide resin, a polyamideimide resin, an epoxy resin, a phenolic resin, or a silicone resin.

Furthermore, in the resin compositions, one or more known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, anti-adhesive agents, antistatic agents, leveling agents, release agents, etc. may be appropriately formulated as needed within the scope that does not impair the effects of the invention.

The method for producing the resin composition is described. The resin composition can be obtained by mixing the aluminum oxide powder of the present embodiment with a resin using a commonly used known method. For example, when the resin is liquid (such as liquid epoxy resin, etc.), the resin composition can be obtained by mixing the liquid resin, aluminum oxide powder and a hardener, and then hardening them using heat or ultraviolet rays. As the hardener, mixing method and hardening method, known ones and known methods can be used. On the other hand, when the resin is solid (such as polyolefin resin or acrylic resin, etc.), after mixing the aluminum oxide powder with the resin, the target resin composition can be obtained by kneading them using a known method such as melt kneading.

The resin composition of the present embodiment may include: a formulation formed by mixing raw materials containing aluminum oxide powder and a resin, a mixture formed by mixing raw materials containing aluminum oxide powder and a resin, a molded product formed by molding the mixture, and a hardened product formed by hardening the mixture or the molded product.

The resin composition of the present embodiment can be used well as a heat dissipation component, such as a semiconductor sealing material. As described above, in recent years, the heat release of ICs due to the high integration of semiconductors has increased, but the thermal conductivity of the alumina powder and the resin composition containing the alumina powder of the present embodiment is relatively high, so even when they are used in high-integrated semiconductors, the generated heat can be well released. In addition, since it is preferred to suppress the uranium content and the thorium content of the alumina powder, the α-ray amount is less, thereby being able to suppress the soft error of the semiconductor sealing material containing the alumina powder, such as a heat dissipation filler. Example

The present invention is further specifically described below with reference to the following embodiments. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the above and the following purports, all of which are included in the technical scope of the present invention.

[Preparation of alumina raw material powder] Alumina raw material powder 1 and alumina raw material powder 2 described below were prepared as alumina raw material powder.

(Alumina raw material powder 1) γ-alumina obtained by the ammonium alumina method (the average particle size of the primary particles calculated from the value of the BET specific surface area below is 13 nm) was used as the raw material alumina. The BET specific surface area of the γ-alumina obtained by the nitrogen adsorption method was 120 m ² /g. 4 mass% of propylene glycol was added as a surface protective agent to the raw material alumina and mixed to obtain a powder for pulverization.

Next, a jet mill (Nippon Pneumatic Mfg. Co., Ltd., horizontal jet mill PJM-280SP) was used to process the powder at a feed rate of 30 kg/h and a surface pressure of 0.5 MPa at the air supply port during pulverization, thereby obtaining a flame melting powder (alumina raw material for flame melting) having an average secondary particle size of about 2 μm.

The obtained flame melting powder is put into a flame melting furnace to melt it to obtain a spheroidized alumina coarse powder. The gas atmosphere temperature in the flame melting furnace is set to 1250°C. The obtained alumina coarse powder is recovered by a cyclone separator and graded by a cyclone separator to obtain an alumina raw material powder 1 (particle size D50 is 5.5 μm). One of the SEM photographs of the alumina raw material powder 1 is shown in Figure 1. Furthermore, the physical properties of the alumina raw material powder 1 are the same as the physical properties of the alumina particles of Example 1 composed of the alumina raw material powder 1 shown in Table 1.

(Alumina raw material powder 2) Spherical alumina DSP-AN05 (particle size D50 is 5.2 μm) manufactured by Togoku R&S Co., Ltd. is used. An example of a SEM photograph of the alumina raw material powder 2 is shown in FIG2. In addition, the physical properties of the alumina raw material powder 2 are the same as the physical properties of the alumina particles of Comparative Example 1 composed of the alumina raw material powder 2 shown in Table 1.

[Preparation of Alumina Powder] The various alumina powders of Example 1, Example 2, and Comparative Examples 1 to 3 were obtained with the mixing ratio of the above-mentioned alumina raw material powder 1 and the alumina raw material powder 2 as shown in Table 1.

The content ratio of each crystalline phase, cumulative circularity, particle size, etc. of the obtained aluminum oxide powder were determined as follows.

[Content ratio of each crystalline phase in alumina powder] The existence ratio of α phase, θ phase and δ phase in alumina powder is determined as follows. First, alumina powder is subjected to powder X-ray diffraction measurement to obtain a powder X-ray diffraction pattern. The powder X-ray diffraction measurement is performed as follows. The powder X-ray diffraction pattern is obtained in the range of diffraction angle 2θ of 5° to 80° using a Bruker XRD device D8 Advance set in a BraggBrentano concentrated optical system with a CuKα radiation source.

The obtained powder X-ray diffraction pattern is subjected to Rietveld analysis to calculate the existence ratio (mass ratio) of the α phase, θ phase, and δ phase of the aluminum oxide powder. Rietveld analysis is a method of comparing the measured powder X-ray diffraction pattern with the simulated pattern from the crystal structure model and optimizing the crystal structure model in a way that minimizes the difference between the two. In the Rietveld analysis, the obtained powder X-ray diffraction pattern is assumed to be a mixture of three phases: α phase, θ phase, and δ phase. The powder X-ray analysis software TOPAS manufactured by Bruker is used to optimize the existence ratio of each crystal phase of α phase, θ phase, and δ phase. Furthermore, in the present embodiment, it was confirmed in a preliminary measurement that the crystalline phase of the aluminum oxide powder obtained above is roughly occupied by the α phase, the θ phase, and the δ phase. Therefore, as described above, the existence ratio is calculated based on the three phases of the α phase, the θ phase, and the δ phase.

[Cumulative circularity of aluminum oxide powder] According to the following steps, the cumulative circularity of the aluminum oxide powder of each embodiment and comparative example shown in Table 1 was calculated and evaluated.

First, each alumina powder was used to prepare a sample for cross-sectional observation. Specifically, each alumina powder was embedded in an epoxy resin, and after the epoxy resin was cured, Ar ion polishing was performed to prepare a sample for cross-sectional observation.

The obtained cross-sectional observation sample was fixed on the SEM sample stage to obtain SEM images. The SEM images were taken using a scanning electron microscope (Scanning Electron Microscope "S-4800" manufactured by Hitachi High-Technologies Co., Ltd.) at an accelerating voltage of 5.0 kV using a detector for reflected electron images.

The obtained SEM image is binarized using image processing software (e.g., free software ImageJ (https://fiji.sc/)), and the area of the particle enclosed by the outline (the "area" in the formula (1)) and the circumference of the particle (the "circumference" in the formula (1)) are calculated using the following formula (1). In addition, the circularity of one particle is calculated using the following formula (1). Circularity of one particle = 4 × π × area / (circumference ² )･･･(1)

Based on the above measurement and calculation results, the cumulative roundness distribution based on the number of pieces is produced, and the roundness C5, which is the cumulative 5% roundness from the low roundness side, and the roundness C50, which is the cumulative 50% roundness from the low roundness side, are calculated respectively.

[Particle size of alumina powder] The D90 (90% equivalent particle size based on the cumulative percentage of volume basis) and D50 (50% equivalent particle size based on the cumulative percentage of volume basis) of alumina powder are obtained by measuring the particle size distribution of alumina powder by laser diffraction method using "Microtrac MT3300EXII" manufactured by MicrotracBEL Co., Ltd. as a laser particle size distribution measuring device. The following powder dispersion is used as a sample for measurement. The powder dispersion is prepared by adding the powder to be measured to a 0.2 mass% sodium hexametaphosphate aqueous solution in such a way that the laser scattering intensity becomes appropriate, and then dispersing it for 5 minutes at 40 W of the built-in ultrasonic wave of the device. The refractive index of alumina is set to 1.76.

[BET specific surface area of alumina powder] Using "FlowsorbIII 2310" manufactured by Shimadzu Corporation as the specific surface area measuring device, the nitrogen adsorption BET specific surface area was determined by the nitrogen adsorption one-point method according to the method specified in JIS-Z8830 (2013). The measurement conditions were set as follows. Carrier gas: nitrogen/helium mixed gas Filling sample amount: 0.1 g Sample pretreatment conditions: 200℃ for 20 minutes Nitrogen adsorption temperature: liquid nitrogen temperature (below -196℃) Nitrogen desorption temperature: room temperature (about 20℃)

Using the aluminum oxide powder of Example 1, the contents of uranium and thorium, and the α-ray dose were determined as follows.

[Uranium and thorium content of alumina powder] The uranium and thorium content of the alumina powder of Example 1 was determined as follows. First, the alumina powder was placed in a mixed aqueous solution of sulfuric acid and phosphoric acid, and the alumina powder was heated to dissolve, thereby preparing an aqueous solution. Thereafter, the aqueous solution was brought into contact with a cyclohexane solution of tributyl phosphate, which is commonly used as an extractant for uranium, to extract the uranium contained in the aqueous solution. Thereafter, the uranium transferred to the aqueous phase again by back extraction with pure water was measured using ICP-MS by the intensity of U238 amu and Th232 amu. Furthermore, in the preparation of the calibration curve, a standard solution manufactured by SPEX was used. The above measurement results show that the uranium content of the aluminum oxide powder of Example 1 formed from the aluminum oxide raw material powder 1 from the ammonium alumina method is 2 ppb by mass, and the thorium content is less than 1 ppb by mass.

[α-radiation dose of alumina powder] The α-radiation dose of the alumina powder of Example 1 was measured using a measuring device model 1950 (manufactured by Alpha sciens). The measuring area of the sample was set to 1000 cm ² and the measuring time was set to 99 hours. The result was that the α-radiation dose of the alumina powder of Example 1 composed of the alumina raw material powder 1 from the ammonium aluminide method was 0.001 counts/(cm ² ･h).

[Table 1] Embodiment 1 Embodiment 2 Comparison Example 1 Comparison Example 2 Comparison Example 3 Ratio of each alumina raw material powder to alumina powder (volume ratio) Alumina raw material powder 1 100 80 0 50 20 Alumina raw powder 2 0 20 100 50 80 Physical properties of alumina powder granularity Particle size D50(μm) 5.5 5.6 5.2 5.4 5.3 Particle size D90(μm) 9.7 9.3 8.1 8.9 8.4 BET specific surface area (m ² /g) 0.56 0.55 0.58 0.51 0.53 Ratio of each crystalline phase (mass %) α phase 17 16 11 14 13 θ phase 73 59 11 41 25 Delta phase 10 25 78 45 62 Roundness Cumulative 5% roundness C5 0.85 0.84 0.71 0.81 0.73 Cumulative 50% roundness C50 0.91 0.91 0.9 0.91 0.91

[Determination of viscosity of resin composition] (Preparation of resin composition for viscosity measurement) First, a resin composition for viscosity measurement is prepared as follows. The alumina powder shown in Table 1 and spherical alumina AO-502 (particle size D50 is 0.52 μm) manufactured by Admatechs are adjusted in a ratio of 8:2 (mass ratio). Furthermore, the spherical alumina AO-502 is a filling alumina powder other than the alumina powder of this embodiment, and is used to realize highly filled alumina small particles assuming actual use. Prepare Resin 1 (53 type epoxy main agent manufactured by Sanqi Co., Ltd.) as a resin. Furthermore, the alumina powder, spherical alumina AO-502 and resin 1 shown in Table 1 were mixed in the manner of the mixing ratio (mass ratio) shown in Table 2, and mixed and kneaded using a rotation/revolution stirrer (ARV-310) manufactured by Thinky Co., Ltd., thereby obtaining a resin composition for viscosity measurement.

(Measurement of viscosity of resin composition for viscosity measurement) The viscosity of the obtained resin composition for viscosity measurement was measured using a dynamic viscoelasticity measuring device ("Rheosol-G3000" manufactured by UBM). The measurement was performed using a parallel plate with a diameter of 40 mm at a distance of 1 mm, a shear rate of 1 s ^-1 , and 100°C. The results are shown in Table 2. In this embodiment, the viscosity of the resin composition for viscosity measurement less than 6.0 Pa･s was evaluated as having good fluidity (○), and the viscosity of 6.0 Pa･s or more was evaluated as having poor fluidity (×).

[Table 2] Embodiment 1 Embodiment 2 Comparison Example 1 Comparison Example 2 Comparison Example 3 Resin composition for viscosity measurement (mass %) Alumina powder 70.4 70.4 70.4 70.4 70.4 AO-502 17.6 17.6 17.6 17.6 17.6 Resin 1 12 12 12 12 12 Viscosity(Pa･s) 4.0 4.7 8.1 6.4 7.7

[Measurement of thermal conductivity of resin composition] (Preparation of resin composition for thermal conductivity measurement) The alumina powder shown in Table 1 and spherical alumina AO-502 (particle size D50 is 0.52 μm) manufactured by Admatechs were adjusted in a ratio of 8:2 (mass ratio). The spherical alumina AO-502 is a filler alumina powder other than the alumina powder of this embodiment, and is used to realize highly filled alumina small particles assuming actual use. Resin 1 (53-type epoxy main agent manufactured by Sanqi Co., Ltd.) and Resin 2 (53-type epoxy hardener (manufactured by Sanqi Co., Ltd.)) were prepared as resins. Furthermore, the alumina powder, spherical alumina AO-502, resin 1 and resin 2 shown in Table 1 were prepared in the ratio (mass ratio) shown in Table 3, and mixed and kneaded using a rotation/revolution stirrer (ARV-310) manufactured by Thinky Co., Ltd., thereby obtaining a resin composition for thermal conductivity measurement.

(Determination of thermal conductivity of resin composition for thermal conductivity measurement) 2 g of the obtained resin composition for thermal conductivity measurement was placed in a mold with a diameter of 20 mm, and a pressure of 30 MPa was applied to form it, and the resin was left at room temperature for 24 hours to harden. Then, the hardened body was processed into a size of 10 mm square × 2 mm thick, and the surface was polished to obtain a test piece. The thermal conductivity of the test piece in the thickness direction was measured by the laser flash method using a xenon flash thermal conductivity analyzer (manufactured by NETZSCH, LFA467). The measurement was carried out in an atmospheric environment at 25°C. The results are shown in Table 3. In this embodiment, the thermal conductivity of 2.3 W/mK or more is evaluated as having higher thermal conductivity, and the thermal conductivity of less than 2.3 W/mK is evaluated as having lower thermal conductivity.

[Table 3] Embodiment 1 Embodiment 2 Comparison Example 1 Comparison Example 2 Comparison Example 3 Molded body for thermal conductivity measurement (mass %) Mixed Alumina Powder 72 72 72 72 72 AO-502 18 18 18 18 18 Resin 1 6.7 6.7 6.7 6.7 6.7 Resin 2 3.3 3.3 3.3 3.3 3.3 Thermal conductivity (W/mK) 2.7 2.4 1.9 2.2 2.1

According to Tables 1 to 3, the ratio of the crystalline phase, the cumulative circularity distribution, and the cumulative particle size distribution of the aluminum oxide powder of this embodiment, i.e., the aluminum oxide powder of Example 1 and Example 2, are within a specific range, so the fluidity is higher when mixed with the resin, and the thermal conductivity of the resin composition obtained by mixing with the resin is higher.

In contrast, the ratio of the δ-type crystalline phase in Examples 1 to 3 is higher, and the thermal conductivity of the resin composition obtained by mixing with the resin is lower.

According to the alumina powder of this embodiment, the uranium content and the thorium content are also small, and the α-ray dosage is sufficiently suppressed. Therefore, if the alumina powder of this embodiment is used as a thermal conductive filler, for example, a semiconductor sealing material with good heat dissipation and capable of preventing operation errors caused by α-rays can be realized.

This application claims priority based on Japanese Patent Application No. 2022-211968. Japanese Patent Application No. 2022-211968 is incorporated into this specification by reference.

FIG. 1 is an example of a SEM photograph of the aluminum oxide raw material powder 1 used in the embodiment. FIG. 2 is an example of a SEM photograph of the aluminum oxide raw material powder 2 used in the embodiment.

Claims (5)

An aluminum oxide powder, wherein the ratio of the δ-type crystal phase to the total crystal phase is 30% by mass or less, and the ratio of the α-type crystal phase is 50% by mass or less, The roundness C50 of 50% accumulated from the low roundness side of the cumulative roundness distribution based on the number basis is 0.90 or more, Furthermore, the particle size D90 of 90% accumulated from the fine particle side of the cumulative particle size distribution based on the volume basis is less than 20 μm. For the aluminum oxide powder of claim 1, the roundness C5 of the 5% accumulated from the low roundness side of the cumulative roundness distribution based on the number of pieces is greater than 0.83. For the aluminum oxide powder of claim 1 or 2, the particle size D50 of 50% of the particles in the cumulative particle size distribution based on volume is less than 10 μm. For the aluminum oxide powder in claim 1 or 2, the uranium content and the thorium content thereof are respectively less than 10 ppb by mass. A resin composition comprising the aluminum oxide powder according to claim 1 or 2.