WO2024071430A1

WO2024071430A1 - Spherical alumina particles, manufacturing method therefor, and resin composite composition containing same

Info

Publication number: WO2024071430A1
Application number: PCT/JP2023/035844
Authority: WO
Inventors: 竜太郎沼尾
Original assignee: 日鉄ケミカル＆マテリアル株式会社
Priority date: 2022-09-30
Filing date: 2023-10-02
Publication date: 2024-04-04

Abstract

Provided are: spherical alumina particles having a low metal Al concentration and small particle size; a manufacturing method therefor; and a resin composite composition containing the same.　The present invention provides: spherical alumina particles in which the metal Al concentration is equal to or less than 1000 ppm, the average particle size is 0.3-2.0 µm, the specific surface area is 2.5-5.0 m2/g, the circularity is equal to or greater than 0.80, and the rate of transformation to α-alumina is equal to or less than 5.0%; a manufacturing method therefor; and a resin composite composition containing the same.

Description

Spherical alumina particles, their production method, and resin composite composition containing the same

The present invention relates to spherical alumina particles, particularly spherical alumina particles with a reduced concentration of metallic Al, a method for producing the same, and a resin composite composition containing the same.

In recent years, the amount of heat generated by electronic components inside electronic devices has increased due to the increasing functionality and speed of electronic devices such as mobile phones. To ensure that electronic devices operate normally, it is important to efficiently dissipate the generated heat to the outside. Heat dissipation sheets and heat dissipation adhesives are widely used for heat dissipation. These are attached or applied between the heating element and the heat dissipation fins and then pressed together to eliminate the gap between the heating element and the heat dissipation fins, allowing heat to be dissipated efficiently. Furthermore, the semiconductors themselves inside electronic components also generate significant amounts of heat due to their high functionality and high speed, and there is a demand for the encapsulating material that protects the semiconductors to also have heat dissipation properties.

In general, heat dissipation sheets, heat dissipation adhesives, and semiconductor encapsulants are composed of thermally conductive inorganic fillers and resins. Thermally conductive inorganic fillers are made from inexpensive aluminum hydroxide and aluminum oxide (hereafter referred to as alumina), as well as materials such as silicon carbide, boron nitride, and aluminum nitride, which are expected to have high thermal conductivity. Alumina in particular is often used as a thermally conductive inorganic filler because it is inexpensive and chemically stable.

Heat-conductive inorganic fillers such as alumina are also required to be small in particle size and spherical. This is because semiconductor packages such as ICs and CPUs are becoming smaller and thinner, which is leading to thinner bonding wires with smaller diameters and narrower pitches. In other words, heat-conductive inorganic fillers such as alumina used in semiconductor packages are also required to be small in particle size and spherical in order to improve filling ability into narrow spaces inside semiconductors.

Patent No. 6771078 Patent No. 5036984 JP 2008-120673 A

Several methods are known for producing small spherical alumina particles, typically with a particle size of 2.0 μm or less.

The most common method for producing spherical alumina is the flame fusion method, which uses aluminum oxide as the raw material. The raw material aluminum oxide is sprayed into a flame, and the surface of the aluminum oxide is heated and melted to form spherical shapes. However, the molten particles may stick together and form large aggregated particles, and the desired small particle size may not be obtained.

Patent Document 1 discloses a method for suppressing the aggregation of aluminum oxide by adding silica particles to the raw aluminum oxide and then thermally spraying the mixture. However, with this method, it is inevitable that silica particles will be mixed into the spherical alumina particles that are ultimately obtained.

Patent Document 2 discloses a method of suppressing the aggregation of aluminum oxide by placing a collision plate at the tip of a thermal spray burner, colliding the raw aluminum oxide with the collision plate, and then performing the thermal spraying process.

Patent Document 3 discloses that the raw material, fine low-soda aluminum oxide, is passed through a device with a crushing and dispersing function, and immediately after being dispersed in a carrier gas, it is continuously introduced into a flame, resulting in spherical alumina with an average particle size of less than 1 μm and extremely low metal impurities. The spherical alumina obtained here is said to have a metal Al concentration of <0.010%. However, with this method, the crushed and dispersed particles re-agglomerate due to a small amount of moisture in the carrier gas, making it impossible to obtain spherical alumina with a small particle size. In addition, there is a concern that the alumina particles contain a large amount of hard alpha alumina, which may wear out the device when passed through the device with a crushing and dispersing function. In addition, the basic properties of the obtained spherical alumina, such as the specific surface area and circularity, are unclear.

In addition to the flame fusion method, the deflagration method (VMC method) is also known. Specifically, it is said that fine alumina particles, for example with a particle size of 2.0 μm or less, can be obtained by dispersing metallic aluminum powder in an oxygen stream, oxidizing it by igniting it, and using the heat of the reaction to turn the metal and oxide into vapor or liquid, which can then be cooled. However, since an explosive reaction is used, there is a risk of a dust explosion, and there is also a possibility that some of the metallic aluminum will not react, i.e., will not turn into alumina, and the metallic aluminum will remain. In particular, if the remaining metallic aluminum is contained in a semiconductor package, etc., it may lead to serious accidents such as short circuits in the semiconductor. Note that neither Patent Document 1 nor Patent Document 2 mentions or suggests anything about the remaining metallic aluminum.

The present invention was made in consideration of the above situation, and its purpose is to provide spherical alumina particles with a low metal Al concentration, a low alpha conversion rate, and a small particle size, a method for producing the same, and a resin composite composition containing the same.

The inventors have discovered that by spraying a raw material containing at least one of alumina, boehmite, and aluminum hydroxide having a specified particle size in a flame fusion method, it is possible to obtain small-sized spherical alumina particles with a low concentration of metallic aluminum while suppressing aggregation of the raw material particles.

Based on the above findings, the gist of the present invention is as follows:

[1] Spherical alumina particles having a metal Al concentration of 1000 ppm or less, an average particle size of 0.3 to 2.0 μm, a specific surface area of 2.5 to 5.0 m ² /g, a circularity of 0.80 or more, and a rate of alpha conversion of 5.0% or less.
[2] The spherical alumina particles according to [1], having a gelatinization rate of 1.0% or less.
[3] A raw material preparation step of preparing a raw material containing at least one of alumina, boehmite, and aluminum hydroxide and having a particle size of 0.2 to 2.0 um;
a surface treatment step of surface-treating the raw material with a silicon atom-containing surface treatment agent;
a spheroidizing step in which the surface-treated raw material is introduced into a flame to melt it, and then rapidly cooled to form spheroids;
The method for producing spherical alumina particles comprising the steps of:
[4] A resin composite composition comprising the spherical alumina particles according to [1] or [2].
[5] The resin composite composition according to [4], further comprising at least one inorganic filler selected from amorphous spherical silica particles, crystalline spherical silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, and carbon fibers.

The present invention provides small-diameter spherical alumina particles with a low metallic aluminum concentration, a very low alpha conversion rate, and a controlled specific surface area, as well as a resin composite composition containing the same. Because of their small particle size, they can be used in miniaturized and thinned semiconductor packages, and because of their low metallic aluminum concentration, the occurrence of serious accidents such as short circuits is suppressed. In addition, because the alpha conversion rate is very low, the shape of the alumina particle surface is very smooth, which has the advantage of increasing fluidity and reducing equipment wear. Furthermore, the spherical alumina particles can be easily manufactured by the manufacturing method that is one aspect of the present invention.

[Spherical alumina particles]
(Metal Al Concentration)
The spherical alumina particles, which are an embodiment of the present invention, have a metal Al concentration of 1000 ppm or less. Alumina is an oxide of metal Al, and can be produced by oxidizing and dehydrating metal Al or an aluminum compound containing it (such as aluminum hydroxide). In the process of producing alumina, the metal Al contained in the raw material may not be sufficiently oxidized and may remain as metal Al in the alumina product. In particular, the deflagration method (VMC method) uses an explosive reaction to oxidize metal Al, so there is a high possibility that the metal aluminum will not be oxidized evenly, that is, will not change to alumina, and metal aluminum will remain. Metal Al has a much higher electrical conductivity than alumina (aluminum oxide). In applications requiring high insulation, such as semiconductor packages, if metal Al is contained, serious accidents such as unexpected short circuits may occur. From this perspective, the lower the metal Al concentration, the more preferable. The spherical alumina particles, which are an embodiment of the present invention, have a metal Al concentration of 1000 ppm or less, which suppresses the occurrence of serious accidents such as short circuits. More preferably, the metal Al concentration may be 800 ppm or less or 700 ppm or less. The lower limit of the metal Al concentration is not particularly limited and may be 0 ppm, but since the burden of production management may be large and difficult, it may be several ppm, specifically 1 ppm or more, or 5 ppm or more. Depending on the actual application and the target allowable range of insulation properties, the lower limit of the metal Al concentration may be adjusted, for example, 10 ppm or more, 20 ppm or more, or 30 ppm or more.

The metal Al concentration is analyzed as follows: Approximately 1 g of spherical alumina particle sample is weighed out and placed in a beaker. 60 ml of 1 mol/L hydrochloric acid is added to the beaker and stirred at room temperature for 5 hours. After stirring, the supernatant of the sample solution is removed and the volume is adjusted to 100 ml, and the solution is analyzed for Al content using ICP-MS.

(Particle size)
The spherical alumina particles according to one embodiment of the present invention have an average particle size of 0.3 to 2.0 μm. If the particle size is less than 0.3 μm, the particles tend to aggregate, and the fluidity of the resin composition when used as a filler is significantly reduced, which is undesirable. If the particle size exceeds 2.0 μm, the particles may get caught in the narrow space between the mounting substrate and the chip in a semiconductor package that is becoming smaller and thinner, which may cause the fluidity of the liquid encapsulant to decrease, resulting in a decrease in moldability.

Here, the average particle size refers to the average particle size (D50), and means the median diameter D50 at 50% cumulative volume in the volume-based particle size distribution measured by the laser diffraction/scattering particle size distribution measurement method. The laser diffraction/scattering particle size distribution measurement method is a method in which a dispersion liquid in which spherical alumina particles are dispersed is irradiated with laser light, and the particle size distribution is determined from the intensity distribution pattern of the diffracted/scattered light emitted from the dispersion liquid. In the present invention, a laser diffraction/scattering particle size distribution measurement device "Mastersizer 3000" (manufactured by Malvern) is used. The average particle size of the raw material for spherical alumina particles can also be determined in a similar manner.

(Alpha conversion rate)
Here, the alpha-alumina ratio refers to the ratio of alpha-alumina crystals in the crystalline phase. The spherical alumina particles, which are one embodiment of the present invention, have an alpha-alumina ratio of 5.0% or less. It is known that alumina becomes crystalline, and alpha-alumina, θ-alumina, and δ-alumina are known as typical crystalline forms. The spherical alumina particles, which are one embodiment of the present invention, can be manufactured based on a thermal spraying method in which a raw material is put into a flame, melted, and then quenched, as will be described in detail later. In this case, the obtained alumina can have a high amorphous ratio, and spherical alumina particles with an alpha-alumina ratio of 5.0% or less can be easily obtained. By controlling the ratio within this range, the alumina particle surface becomes smooth, and the effect of maintaining high fluidity when mixed with a resin and the amount of hard alpha-alumina particles are small, so that the equipment wear resistance is low. On the other hand, if the alpha-alumina ratio is low, the amount of alpha-alumina contained in the alumina particles becomes too small, so that the thermal conductivity of the particles decreases, and the thermal conductivity of the resin composition may also decrease. The lower limit of the alpha-conversion rate is not particularly limited and may be 0.0%, but may be 0.1% or 0.2% from the viewpoint of the burden of production management and the thermal conductivity characteristics of the resin composition. The upper limit of the alpha-conversion rate may be 3.0%, 1.5%, 1.0%, 0.9%, or 0.8%.

The alpha-conversion rate of the alumina particle powder is measured using a powder X-ray diffractometer. The integrated area of the obtained diffraction peaks is calculated, and the ratio of the diffraction peak area derived from alpha-alumina to the total is analyzed using the Rietveld method. Specifically, an X-ray diffraction pattern is obtained using a Bruker D2PHASER in the 2θ range of 10° to 90°. The alpha-conversion rate is calculated from the obtained pattern using a Bruker DIFFRAC. TOPAS by the Rietveld method. When calculating, the analysis is performed assuming that only three types of crystal phases, alpha-alumina, delta-alumina, and theta-alumina, are present, and the alpha-alumina content is calculated.

(Specific surface area)
The spherical alumina particles of the present invention have a specific surface area, measured by the BET method, of 2.5 m ² /g or more and 5.0 m ² /g or less.

If the specific surface area of the spherical particles is less than 2.5 m ² /g, the particles are unlikely to form a close-packed structure, and the fluidity of the liquid encapsulant containing the particles may decrease. On the other hand, if the specific surface area of the spherical particles is more than 5.0 m ² /g, the particles may tend to aggregate more easily, and the fluidity of the liquid encapsulant may decrease. The preferred lower limit is 3.0 m ² /g. The preferred upper limit is 4.0 m ² /g.

The specific surface area of the spherical particles can also be measured by the BET method, and typically, the specific surface area is measured by the following procedure.
Approximately 5 g of a sample was weighed out and vacuum dried for 5 minutes at 250° C. Next, the sample was set in an automatic specific surface area measuring device (Macsorb, manufactured by Mountec Co., Ltd.), and the nitrogen gas adsorption amount was measured at a relative pressure P/P0 value of 0.291 at a measurement temperature of 77 K using pure nitrogen and a nitrogen-helium mixed gas (mixture ratio: nitrogen 30%, He 70%), and the BET specific surface area was calculated by the one-point method.

(Circularity)
In one embodiment of the present invention, the spherical alumina particles may have a circularity of 0.80 or more.
The higher the circularity of the spherical particles, the lower the viscosity of the resin composite composition containing the alumina particles and the more improved the moldability. The circularity may be 0.85 or more, 0.90 or more, or 0.93 or more. The upper limit of the circularity is theoretically 1.0, but may be 0.98 or less, or 0.95 or less from the viewpoint of production management.

Circularity can be measured using an electron microscope or optical microscope and an image analyzer. For example, Sysmex FPIA. These devices are used to measure the circularity of particles (perimeter of equivalent circle/perimeter of projected image of particle). The circularity of 100 or more particles is measured, and the average value is taken as the circularity of the powder.

(Converted powder resistivity)
The spherical alumina particles according to one embodiment of the present invention may have a reduced powder resistivity of 3.0×10 ⁹ Ω·cm or more. Alumina particles may be used in applications requiring high insulation, such as semiconductor packages, and the higher the reduced powder resistivity, the more preferable it is. In this respect, the reduced powder resistivity of the spherical alumina particles may be 3.1×10 ⁹ Ω·cm or more, 3.2×10 ⁹ Ω·cm or more, 4.0×10 ⁹ Ω·cm or more, or 5.0×10 ⁹ Ω·cm or more. The upper limit is not particularly limited, but may be 1.0×10 ¹¹ Ω·cm or less, or 1.0×10 ¹⁰ Ω·cm or less.

The converted powder resistivity of the alumina particle powder (hereinafter, simply referred to as "converted powder resistivity") is calculated by multiplying the powder resistivity by the Na ₂ O content of the particles. In other words, it is calculated by the formula: (converted powder resistivity) = (powder resistivity of alumina particle powder) x (Na ₂ O content of spherical alumina particles). The powder resistivity of the alumina particle powder is measured using a powder resistivity measurement system MCP-PD51. As a pretreatment for the measurement, the powder is heated and dried in air at 200°C for 5 hours. The dried powder is introduced into a powder resistivity measurement probe unit, and the sample is gradually pressurized using the attached hydraulic pump. When the load reaches 20 kN, the measurement is performed using a high resistivity meter.

( _Na2O content)
The spherical alumina particles, which are one embodiment of the present invention, may have a Na ₂ O content of 1000 ppm or less. When the spherical alumina particles contain Na ₂ O, Na ₂ O may act as an impurity in a resin composite composition containing the alumina particles, and the desired properties may not be obtained. In this respect, the lower the Na ₂ O content, the more preferable it is, and the upper limit of the Na ₂ O content may be 750 ppm or less or 500 ppm or less. The lower limit of the Na ₂ O content is not particularly limited and may be 0 ppm, but since the burden of production management may be large and difficult, it may be several ppm, specifically 1 ppm or more, or 5 ppm or more. The lower limit of the Na ₂ O content may be adjusted according to the actual application and the target properties, and may be, for example, 10 ppm or more, 20 ppm or more, or 30 ppm or more.

The Na ₂ O content of the spherical alumina particles is measured using an atomic absorption spectrometer. 0.5 g of a sample is placed in a pressure vessel, 10 ml of sulfuric acid (1+3) is added, the vessel is closed, and the vessel is heated at 230° C. for 16 hours in a heating and drying furnace. The heated solution is allowed to cool, and then the solution is diluted to 100 ml and measured using an atomic absorption spectrometer. Note that sulfuric acid (1+3) refers to a solution diluted by adding 3 parts of pure water to 1 part of concentrated sulfuric acid by volume.

(Liquidity)
The spherical alumina particles according to one embodiment of the present invention may be those whose fluidity is evaluated as good, i.e., ◯ (Good), by the following measurement method. The spherical alumina particles can be used as a filler for a resin composite composition, and it is preferable that the fluidity is within an appropriate range from the viewpoint of manufacturing control. The fluidity varies depending on the conditions of the matrix resin, etc., but the evaluation criteria for the fluidity in this specification are shown as a guideline.

The method for evaluating fluidity in this specification is as follows. First, 30 g of a spherical alumina particle sample is weighed out and placed in a bag. 70 g of AZ10-75 (alumina powder manufactured by Nippon Steel Chemical & Material Co., Ltd., average particle size 10 μm) is then weighed out and placed in the bag containing the spherical alumina particles. The bag is then tied and thoroughly mixed. 43.5 g of the mixed alumina particle powder is weighed out and placed in a 200 ml plastic container. 6.5 g of silicone resin CY52-276A liquid manufactured by Dow Toray is added thereto, and vacuum mixed using a Thinky vacuum mixer "Awatori Rentaro". The mixing conditions are 15 seconds of premixing and 90 seconds of vacuum mixing. After mixing, the plastic container containing the mixture is placed in a water bath adjusted to 25°C and cooled for 1 hour. 10 g of the compound (resin composite composition) prepared by mixing is placed on a plate with a smooth surface. There are no particular restrictions on the material of the plate, but an iron plate was used in this example. The plate with the compound placed on it is tilted 60 degrees from the horizontal to check the degree of flow of the compound. In this test, if the compound has flowed 15 cm or more after 5 hours of tilting, the fluidity is evaluated as O (Good), and if the compound has not flowed 15 cm or more, the fluidity is evaluated as × (Not Good).

[Method of producing spherical alumina particles]
In one embodiment of the present invention, there is provided a method for producing spherical alumina particles, which is a method for suitably producing the above-mentioned alumina particles and includes the following steps:
(1) a raw material preparation step of preparing a raw material containing at least one of alumina, boehmite, and aluminum hydroxide and having a particle size of 0.3 to 2.00 um; and
(2) a surface treatment step of surface-treating the raw material with a silicon atom-containing surface treatment agent; and
(3) A spheroidizing step in which the raw material is introduced into a flame to melt it, and then rapidly cooled to form spheroids.

The order of the steps may change, but we will first explain the spheronization step (3).

The spheroidization process (3) is a process in which the raw material is fed into a flame, melted, and then rapidly cooled to form spheroids. The raw material can be fed into the flame while suspended in a carrier gas. Air, oxygen, propane gas, etc. can be used as the carrier gas. The method of forming the flame is not particularly limited, but the flame can be formed by supplying a fuel (such as propane) that forms a flame to the burner via a route separate from the feed of the raw material, or by pre-mixing fuel and a combustion support gas (air or oxygen) and supplying it to the burner to form the flame, or by mixing the raw material, fuel, and a combustion support gas and supplying it to the burner to form the flame. It is preferable to form the flame in a heat-resistant furnace. It is preferable to form a flame in the upper part of the heat-resistant furnace, supply the raw material into the flame, and collect the alumina particle material formed as it settles due to gravity from below. By preventing the formation of a flame in the lower part of the heat-resistant furnace, the alumina particle material that settles to the lower part is rapidly cooled and granulated.

In the raw material preparation step (1), raw materials to be charged in the spheroidization step (3) are prepared. The raw materials are prepared so as to contain at least one of alumina, boehmite, and aluminum hydroxide and have a particle size of 0.2 to 2.0 μm.
Boehmite is alumina monohydrate, and is represented by the chemical formula _Al2O3.H2O , _and aluminum hydroxide is represented by the chemical formula Al(OH) ₃ . When either of these materials is fed into the flame in the spheroidization step ( ₃ ), the hydrated portion ( _H2O ) or hydroxyl group (OH) in the raw material is first released as water vapor ( _H2O ), _and alumina ( _Al2O3 ) particles are generated. At least the surface of the _alumina ( _Al2O3 ) particles melts and is spheroidized.
When alumina is used as the raw material, examples of the raw material include calcined alumina obtained by sintering aluminum hydroxide, alumina obtained by electrofusion of aluminum hydroxide, low soda alumina produced from aluminum hydroxide, and high purity alumina produced by ammonia-alum thermal decomposition method, aluminum alkoxide hydrolysis method, aluminum water discharge method, or other methods. Alumina obtained by calcining low soda aluminum hydroxide is more preferable from the viewpoints of productivity and cost.
Of the above raw materials, boehmite or aluminum hydroxide contains sufficient moisture (water of hydration or hydroxyl groups), and therefore, as described below, an increase in the particle size of the raw material is particularly effectively suppressed in the spheroidizing step, making it possible to efficiently obtain spherical alumina particles having an average particle size of less than 1 μm, and therefore these are more preferred.

A conventional method for producing spherical alumina involves throwing alumina particles into a flame to spheroidize them. However, during this spheroidization process, the alumina particles, whose surfaces have been melted, fuse together and agglomerate, which can lead to an increase in the particle size of the resulting particles and a decrease in circularity. However, this embodiment eliminates these problems.

First, since the raw material of this embodiment contains moisture (hydration water and hydroxyl groups), it takes time for water vapor (H ₂ O) to escape from the entrance of the flame to the middle of the flame. In other words, there is little opportunity (short time) for the surfaces of the alumina particles to melt in the flame, fuse together, and aggregate. As a result, the particle size of the alumina particles after passing through the flame is suppressed from excessively increasing beyond the particle size of the raw material (0.2 to 2.0 um).

Furthermore, the water vapor (H ₂ O) released from the raw material expands when heated in the flame, and acts to increase the distance between the remaining raw materials, i.e., between the alumina particles. In other words, the chances of the alumina particles fusing together are further reduced. As a result, the particle size of the alumina particles after passing through the flame is prevented from excessively increasing compared to the particle size of the raw material (0.2 to 2.0 um). In addition, since there is little contact between the particles, the spheroidization of each particle is also promoted.

Next, we will explain the surface treatment process (2).

In the surface treatment step (2), prior to the spheroidization step (3), the raw material obtained in the raw material preparation step (1) is surface-treated. As the surface treatment agent for the raw material, a silane compound (such as a silane coupling agent), a silazane, an Al coupling agent, etc. can be adopted. The amount of the surface treatment agent can be appropriately adjusted depending on the material of the raw material, etc., but preferably, by blending these surface treatment agents in an amount of 1 mass% or more with respect to the raw material, it is possible to make it difficult for the raw material powders to adsorb to each other, so that clogging due to adhesion to the burner or piping and variation in the supply amount can be effectively prevented. Furthermore, it is possible to effectively prevent coarsening due to aggregation of the raw material powders. On the other hand, if there is an excessive amount of the surface treatment agent, the treatment agents react with each other and the particles crosslink with each other via the surface treatment agent. There is a risk that the original dispersion effect cannot be obtained, and from the viewpoint of economy, it is not preferable to add an excessive amount of the treatment agent. The preferable upper limit of the blending amount of the surface treatment agent is 10 mass% with respect to the raw material.
Among the above surface treatment agents, silicon-containing compounds such as silane coupling agents, alkoxysilane compounds, and silazane compounds (also referred to as "silicon atom surface treatment agents") are preferred from the viewpoints of economy and reactivity. These silicon atom surface treatment agents can be made of known substances. Examples of silane coupling agents include vinyltrimethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane. Examples of alkoxysilane compounds include hexyltrimethoxysilane and octyltriethoxysilane. Examples of silazane compounds include hexamethyldisilazane and trimethylsilane. From the viewpoint of excellent reactivity, silazane compounds are more preferred. Hexamethyldisilazane and trimethylsilane are more preferred.

The surface treatment method includes the following first step (heating step) and second step (surface treatment step).
First process (heating process)
The raw powder containing any one of alumina, aluminum hydroxide, and boehmite is heated at a temperature of 100°C to 500°C for 30 minutes or more. The preferred heating conditions are 150°C or higher for 2 hours or 5 hours. By heating the raw powder in this step, excess moisture present on the surface of the powder particles can be removed, thereby increasing the reactivity of the treatment agent and the particle powder in the subsequent surface treatment step. If moisture adheres to the surface of the raw material, the moisture reacts with the surface treatment agent, and the surface treatment agent cannot react appropriately with the raw material. There is no particular restriction on the method of heating the raw material, but a method of drying the raw material powder using a commonly used electric drying furnace, tunnel kiln, shuttle kiln, etc. is preferred. The drying temperature is preferably 500°C or less in order to obtain the effect of suppressing the coarsening of particle size due to moisture generated from the raw material during spheroidization as described above. By heating at 500°C or higher, moisture is completely removed from the aluminum hydroxide or boehmite, and moisture is not generated during spheroidization. The lower limit of the drying temperature is preferably 100°C or higher in order to evaporate moisture. After heating, the product may be cooled before use in the next step, or it may not be cooled. Preferably, the product is not cooled before use in the next step, which is the surface treatment step.

Second process (surface treatment process)
The raw material powder heat-treated in the previous step is put into an arbitrary mixer and stirred. When stirring, it may be stirred at room temperature or heated. In order to increase the reactivity of the silane compound, it is preferable to heat the mixture to preferably 50°C or higher, more preferably 80°C or higher, and then stir. After stirring for about 30 seconds to 10 minutes, the surface treatment agent is sprayed while stirring. The types of surface treatment agents are as described above, and preferably include hexamethyldisilazane and trimethylsilane. The amount of the surface treatment agent to be sprayed is preferably 1 to 5 times the amount calculated from the minimum coverage area of the surface treatment agent, the specific surface area of the raw material powder being treated, and the input weight (see the formula below).

Amount of surface treatment agent to be sprayed = (specific surface area of raw material powder) x (feed weight of raw material powder) / (minimum coverage area of surface treatment agent)

The method for mixing the surface treatment agent is not important, but a method in which the surface treatment agent, such as the silane coupling agent, is mixed into the raw material powder using a commonly used mixer such as a ball mill, vibration mill, planetary grinder, jet mill, mechanical stirring blade mixer, or container rotary mixer is preferable. The raw materials may also be heated during mixing. The heating method is not important, but the outside of the mixing container may be covered with a jacket and heated with steam, heated water, oil, etc. Heating can increase the reactivity of the surface treatment agent, making it possible to efficiently surface treat the raw materials.

Furthermore, prior to the surface treatment step (2), the raw material may be passed through an apparatus having a crushing/dispersing function as an auxiliary.
In the case of the dry method, the device having the crushing and dispersion function includes a device that swirls in a high-speed airflow such as a jet mill to crush powder by collision, and a device that causes dust-containing gases to collide with each other in counterflows to crush powder by collision. In the case of the wet method, the device includes a high-pressure wet jet mill type crushing device that crushes slurry by collision, and an ultrasonic dispersion device that can irradiate strong ultrasonic waves into the slurry delivery pipe. When passing through the above device having the crushing and dispersion function, it is desirable to line the powder contact part of the device to prevent the alumina particles from coming into contact with the metal part of the device and wearing it. The material for the lining is not particularly limited, but examples include urethane, boron carbide, alumina, silicon carbide, and Teflon (registered trademark). However, since alumina particles are a very hard material, alumina lining is more preferable as the material for the lining.

The raw material in this embodiment may contain at least one of boehmite and aluminum hydroxide, which contain more surface OH groups than alumina and are therefore easier to treat and the effects of surface treatment are more likely to appear. In other words, the raw materials are more effectively dispersed, and as a result, spherical alumina particles with the desired small particle size and high circularity can be obtained more easily.

The raw material according to this embodiment may contain components other than boehmite or aluminum hydroxide, for example, alumina, as long as the effects of the present invention are not affected.

Furthermore, the raw material in this embodiment is adjusted to a particle size equal to or slightly smaller than the particle size of the alumina particles to be produced, i.e., 0.2 to 2.0 μm. Preferably, it may be 0.3 μm or more, or 1.9 μm or less. The particle size may be adjusted by crushing or classification to obtain the desired particle size. As described above, in the manufacturing method according to this embodiment, the particle size distribution of the raw material is generally inherited as the particle size distribution of the alumina particle material to be produced.

[Resin composite composition]
According to one embodiment of the present invention, the composite composition of the finally obtained spherical alumina particles and resin can be produced. The composition of the resin composite composition will be described in more detail below.

By using a slurry composition containing spherical alumina particles and a resin, it is possible to obtain resin composite compositions such as semiconductor encapsulants (particularly solid encapsulants) and interlayer insulating films. Furthermore, by curing these resin composite compositions, it is possible to obtain resin composites such as encapsulants (cured bodies) and substrates for semiconductor packages.

When producing the resin composite composition, for example, in addition to the spherical alumina particles and resin, a curing agent, a curing accelerator, a flame retardant, a silane coupling agent, etc. are mixed as necessary, and the mixture is compounded by a known method such as kneading. The mixture is then molded into pellets, films, etc., depending on the application.

When producing the resin composite composition, other inorganic fillers may be blended in addition to the spherical alumina particles and resin. Examples of the inorganic fillers include amorphous spherical silica particles, crystalline spherical silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, and carbon fibers. The blending ratio of the inorganic fillers can be adjusted appropriately depending on the application of the resin composite composition, but from the viewpoint of exerting the effect of the spherical alumina particles of the present invention, it is preferable that (blended weight of spherical alumina particles): (blended weight of other inorganic fillers) = 95:5 to 60:40.

Furthermore, when the resin composite composition is cured to produce a resin composite, for example, the resin composite composition is heated to melt it, processed into a shape according to the intended use, and then heated to a temperature higher than that at the time of melting to completely cure it. In this case, a known method such as a transfer molding method can be used.

For example, when manufacturing semiconductor-related materials such as packaging substrates and interlayer insulating films, known resins can be used as the resin for the resin composite composition, but it is preferable to use an epoxy resin. The epoxy resin is not particularly limited, but for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, naphthalene type epoxy resin, phenoxy type epoxy resin, etc. can be used. One of these can be used alone, or two or more types with different molecular weights can be used in combination. Among these, epoxy resins having two or more epoxy groups in one molecule are preferred from the viewpoints of curability, heat resistance, etc. Specifically, biphenyl type epoxy resins, phenol novolac type epoxy resins, orthocresol novolac type epoxy resins, epoxidized novolac resins of phenols and aldehydes, glycidyl ethers of bisphenol A, bisphenol F, bisphenol S, etc., glycidyl ester acid epoxy resins obtained by reacting polybasic acids such as phthalic acid and dimer acid with epochlorohydrin, linear aliphatic epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, alkyl-modified polyfunctional epoxy resins, β-naphthol novolac type epoxy resins, 1,6-dihydroxynaphthalene type epoxy resins, 2,7-dihydroxynaphthalene type epoxy resins, bishydroxybiphenyl type epoxy resins, and epoxy resins into which halogens such as bromine have been introduced to impart flame retardancy. Among these epoxy resins having two or more epoxy groups in one molecule, bisphenol A type epoxy resins are particularly preferred.

In addition, resins other than epoxy resins can be used in applications other than composite materials for semiconductor encapsulation, such as prepregs for printed circuit boards and various engineering plastics, as resin composite compositions. Specific examples of resins that can be used other than epoxy resins include silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides such as polyimide, polyamideimide, and polyetherimide; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

The curing agent used in the resin composite composition may be any known curing agent for curing the resin, for example, a phenol-based curing agent. As the phenol-based curing agent, phenol novolac resin, alkylphenol novolac resin, polyvinylphenols, etc., may be used alone or in combination of two or more kinds.

The amount of the phenolic hardener to be blended is preferably such that the equivalent ratio to the epoxy resin (phenolic hydroxyl group equivalent/epoxy group equivalent) is 0.1 or more and less than 1.0. This eliminates the residue of unreacted phenolic hardener and improves moisture absorption and heat resistance.

The amount of the spherical alumina particles of the present invention added to the resin composite composition is preferably large from the viewpoint of heat resistance and thermal expansion coefficient, but is usually 70% by mass to 95% by mass, preferably 80% by mass to 95% by mass, and more preferably 85% by mass to 95% by mass. This is because if the amount of spherical alumina particles is too small, it is difficult to obtain effects such as improving the strength of the sealing material and suppressing thermal expansion, and conversely, if the amount is too large, segregation due to aggregation of the spherical alumina particles is likely to occur in the composite material regardless of the surface treatment of the spherical alumina particles, and the viscosity of the composite material becomes too high, making it difficult to use as a sealing material. Note that when the above-mentioned "other filler" is used in combination, the preferred amount added to the resin composite composition is the total amount of the spherical alumina particles and the "other filler".

In addition to the resin, additives such as silane coupling agents, hardeners, colorants, hardening retarders, and other known additives can be used.

As for the silane coupling agent, any known coupling agent may be used, but it is preferable to use one that has an epoxy-based functional group.

A slurry composition containing spherical alumina particles and resin can be used to produce heat dissipation sheets, heat dissipation grease, etc.

When obtaining the heat dissipation sheet, the spherical alumina particles, resin, and additives are appropriately mixed and compounded using a known method such as kneading. The resulting composite is molded into a sheet using a known method.

For example, when manufacturing a heat dissipation sheet, known resins can be used as the resin for the resin composite composition, and specific examples include silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamide such as polyimide, polyamideimide, polyetherimide, polyester such as polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin. Of these, it is preferable to use silicone resin. There are no particular limitations on the silicone resin, but for example, peroxide curing type, addition curing type, condensation curing type, ultraviolet curing type, etc. can be used.

When obtaining the heat dissipating grease, the spherical alumina particles, resin, and additives are appropriately mixed and compounded using a known method such as kneading. Here, the resin used in the heat dissipating grease is also called the base oil.

For example, when manufacturing heat dissipating grease, known resins can be used in the resin composite composition, specifically silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamides such as polyimide, polyamideimide, and polyetherimide; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, mineral oil, synthetic hydrocarbon oil, ester oil, polyglycol oil, silicone oil, and fluorine oil.

In addition to the resin, additives such as silane coupling agents, colorants, thickeners, and other known additives can be used. The thickeners that can be used include known ones such as calcium soap, lithium soap, aluminum soap, calcium complex, aluminum complex, lithium complex, barium complex, bentonite, urea, PTFE, sodium terephthalamate, silica gel, and organic bentonite.

The present invention will be explained through the following examples and comparative examples. However, the present invention should not be interpreted as being limited to the following examples.

Example 1
The boehmite raw material (D50 = 0.4 μm) was heated in advance in a heating furnace at 150 ° C for 5 hours, and the heated raw material was charged into a Henschel mixer. After charging, hexamethyldisilazane was charged while stirring to perform surface treatment. The amount of hexamethyldisilazane added was 1.5 wt % based on the weight of the raw material. Then, oxygen was supplied as a carrier gas into a high-temperature flame formed by the combustion of LPG and oxygen, and melting and spheroidization treatment were performed to produce spherical alumina particles described in Example 1 of Table 1.

Example 2
The spherical alumina particles shown in Example 2 in Table 1 were produced in the same manner as in Example 1, except that alumina powder (D50=0.7 μm) was used as the raw material.

Example 3
The spherical alumina particles shown in Example 3 of Table 1 were produced in the same manner as in Example 1, except that boehmite raw material (D50 = 0.2 μm) was used as the raw material.

(Comparative Examples 1 to 7)
Under the conditions shown in Table 1, various raw materials (metallic aluminum powder, boehmite, or alumina) were supplied to a high-temperature flame formed by the combustion of LPG and oxygen using air as a carrier gas, and oxidation and spheroidization treatment were carried out to produce spherical alumina particles shown in the comparative examples in Table 1.

Example 4
The spherical alumina particles obtained in Example 1 and aluminum nitride particles (D50 = 30 μm) were mixed so that the ratio of the spherical alumina particles to the aluminum nitride particles was 90:10, to prepare a spherical alumina particle mixture A. Furthermore, the spherical alumina particle mixture A was mixed with Dow Toray's silicone resin CY52-276A liquid so that the amount of the spherical alumina particle mixture A added in the resin composite composition was 90 mass %, and the mixture was vacuum kneaded using a Thinky vacuum kneader "Awatori Rentaro" to obtain a resin composite composition. The kneading conditions were preliminary kneading for 15 seconds and vacuum kneading for 90 seconds.

Example 5
The spherical alumina particles obtained in Example 2 and boron nitride particles (D50 = 20 μm) were mixed so that the ratio of the spherical alumina particles to the boron nitride particles was 90:10, to prepare a spherical alumina particle mixture B. Furthermore, the spherical alumina particle mixture B was mixed with Dow Toray's silicone resin CY52-276A liquid so that the amount of the spherical alumina particle mixture B added in the resin composite composition was 90 mass %, and the mixture was vacuum kneaded using a Thinky vacuum kneader "Awatori Rentaro" to obtain a resin composite composition. The kneading conditions were preliminary kneading for 15 seconds and vacuum kneading for 90 seconds.

Table 1 shows the physical properties of the spherical alumina particles produced.

The measurement methods for each physical property are described below.

(Average particle size measured by laser diffraction scattering method)
The laser diffraction/scattering particle size distribution measurement method is a method in which a dispersion liquid in which spherical alumina particles are dispersed is irradiated with laser light, and the particle size distribution is obtained from the intensity distribution pattern of the diffracted/scattered light emitted from the dispersion liquid. In the present invention, a laser diffraction/scattering particle size distribution measurement device "Mastersizer 3000" (manufactured by Malvern) was used.

(Specific surface area)
The specific surface area is measured by the BET method. Typically, the specific surface area is measured by the following procedure.
Approximately 5 g of a sample was weighed out and vacuum dried for 5 minutes at 250° C. Next, the sample was set in an automatic specific surface area measuring device (Macsorb, manufactured by Mountec Co., Ltd.), and the nitrogen gas adsorption amount was measured at a relative pressure P/P0 value of 0.291 at a measurement temperature of 77 K using pure nitrogen and a nitrogen-helium mixed gas (mixture ratio: nitrogen 30%, He 70%), and the BET specific surface area was calculated by the one-point method.

(Circularity)
The circularity can be measured using an electron microscope or optical microscope and an image analyzer. For example, Sysmex FPIA. Using these devices, the circularity of the particles (perimeter of the equivalent circle/perimeter of the projected image of the particle) is measured. The circularity of 100 or more particles is measured, and the average value is taken as the circularity of the powder.

(Alpha conversion rate)
The alpha-conversion rate of the alumina particle powder is measured using a powder X-ray diffractometer. The integrated area of the obtained diffraction peaks is calculated, and the ratio of the diffraction peak area derived from alpha-alumina to the total is analyzed by the Rietveld method. Specifically, an X-ray diffraction pattern is obtained using a D2PHASER manufactured by Bruker Corporation in the range of 2θ from 10° to 90°. The alpha-conversion rate is calculated from the obtained pattern by the Rietveld method using a DIFFRAC.TOPAS manufactured by Bruker Corporation. During the calculation, analysis is performed assuming that only three types of crystal phases, alpha-alumina, delta-alumina, and θ-alumina, are present, and the content of alpha-alumina is calculated.

(Metal Al Concentration)
The amount of metallic Al remaining in the alumina particles is measured using the following procedure. Approximately 1 g of a spherical alumina particle sample is weighed out and placed in a beaker. 60 ml of 1 mol/L hydrochloric acid is added to the beaker and stirred at room temperature for 5 hours. After stirring, the supernatant of the sample solution is taken and the volume is adjusted to 100 ml, and the solution is analyzed for Al content using ICP-MS.

(Converted powder resistivity)
The converted powder resistivity of the alumina particle powder (hereinafter, simply referred to as "converted powder resistivity") was obtained by multiplying the powder resistivity by the Na ₂ O content of the particles. In other words, it was calculated by the formula: (converted powder resistivity) = (powder resistivity of alumina particle powder) x (Na ₂ O content of spherical alumina particles). The powder resistivity of the alumina particle powder was measured using a powder resistivity measurement system MCP-PD51. As a pretreatment for the measurement, the powder was heated and dried for 5 hours under a condition of 200°C in the atmosphere. The dried powder was introduced into a powder resistivity measurement probe unit, and the sample was gradually pressurized using an attached hydraulic pump. When the load reached 20 kN, the measurement was performed using a high resistivity meter.

(Na ₂ O Content of Particles)
The _Na2O content of the alumina particles was measured using an atomic absorption spectrometer. 0.5 g of a sample was placed in a pressure vessel, 10 ml of sulfuric acid (1+3) was added, and the vessel was then covered with a lid, and heated in a heating and drying oven at 230°C for 16 hours. The heated solution was allowed to cool, then the solution was diluted to 100 ml and measured with an atomic absorption spectrometer.

(Liquidity)
30 g of spherical alumina particle sample is weighed and placed in a bag. 70 g of AZ10-75 (alumina powder, average particle size 10 μm, manufactured by Nippon Steel Chemical & Material Co., Ltd.) is further weighed and placed in the bag containing the spherical alumina particles. The bag is then tied and thoroughly mixed. 43.5 g of the mixed alumina particle mixed powder is weighed and placed in a 200 ml plastic container. 6.5 g of silicone resin CY52-276A liquid manufactured by Dow Toray is added thereto, and vacuum mixed using a vacuum mixer "Awatori Rentaro" manufactured by Thinky. The mixing conditions are 15 seconds of premixing and 90 seconds of vacuum mixing. After mixing, the plastic container containing the kneaded material is placed in a water bath adjusted to 25 ° C. and cooled for 1 hour. 10 g of the compound (resin composite composition) prepared by kneading is placed on a plate with a smooth surface. There is no particular restriction on the material of the plate, but an iron plate was used in this embodiment. The plate on which the compound is placed is tilted 60 degrees from the horizontal to check the flowability of the compound. In this test, if the compound flows 15 cm or more after 5 hours from tilting, the fluidity is evaluated as O (Good), and if the compound does not flow 15 cm or more, the fluidity is evaluated as × (Not Good).

It was confirmed that spherical alumina particles with a low metallic aluminum concentration, a low alpha conversion rate, and small particle size could be obtained. It was also confirmed that a resin composite composition containing the spherical alumina particles could be obtained.

The spherical alumina particles of the present invention have a small particle size and can therefore be used in miniaturized and thinned semiconductor packages, and because they have a low metallic aluminum concentration, the occurrence of serious accidents such as short circuits is suppressed. Furthermore, the spherical alumina particles can be easily manufactured by the manufacturing method which is one aspect of the present invention. A resin composite composition containing the spherical alumina particles exhibits good fluidity and can be used for other purposes as well, without being limited to semiconductor encapsulation materials. Specifically, they can also be used as prepregs for printed circuit boards, various engineering plastics, etc.

Claims

The spherical alumina particles have a metallic Al concentration of 1000 ppm or less, an average particle size of 0.3 to 2.0 μm, a specific surface area of 2.5 to 5.0 m 2 /g, a circularity of 0.80 or more, and an alpha conversion rate of 5.0% or less.
The spherical alumina particles according to claim 1, having a gelatinization rate of less than 1.0%.
A raw material preparation step of preparing a raw material containing at least one of alumina, boehmite, and aluminum hydroxide and having a particle size of 0.2 to 2.0 um;
a surface treatment step of surface-treating the raw material with a silicon atom-containing surface treatment agent;
a spheroidizing step in which the surface-treated raw material is introduced into a flame to melt it, and then rapidly cooled to form spheroids;
The method for producing spherical alumina particles comprising the steps of:
A resin composite composition containing the spherical alumina particles according to claim 1 or 2.
The resin composite composition according to claim 4, further comprising at least one inorganic filler selected from amorphous spherical silica particles, crystalline spherical silica particles, titania particles, magnesia particles, aluminum nitride particles, boron nitride particles, barium titanate particles, calcium titanate particles, and carbon fibers.