Insulating thermal conductive filler

Abstract

To provide an insulating thermally conductive filler which can improve the shape of the filler surface and effectively improve thermal conductivity, and to provide a method for producing the same.SOLUTION: An insulating thermally conductive filler 5 of the present invention comprises the aggregation of multiple particles having an average particle size D50 of 10 μm to 40 μm. Alternatively, the insulating thermally conductive filler 5 of the present invention is characterized in that a plurality of humped projections 3 are provided on the filler surface, and the radius of curvature of the humped projections 3 is 5 μm to 20 μm. The insulating thermally conductive filler of the present invention is prepared by the sintering and agglomeration of multiple particles having an average particle size D50 of 10 μm to 40 μm. Alternatively, the insulating thermally conductive filler of the present invention is synthesized by a combustion synthesis method under a nitrogen atmosphere using Al particles with an average particle size D50 of 5 μm to 30 μm and a diluent composed of AlN with an average particle size D50 of 10 μm to 40 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to insulating and thermally conductive fillers such as AlN and a method for manufacturing the same.

Background Art

[0002] For example, aluminum nitride (hereinafter referred to as AlN) has high insulation and high thermal conductivity, and is thus applied as a high heat dissipation filler or the like. With the miniaturization and high functionality of semiconductor devices in recent years, the amount of heat generated from electronic components has tended to increase, and further improvement in the performance of heat dissipation members in electronic components and the like is required.

[0003] For example, in a composite material in which a plurality of types of fillers having different diameters are mixed, the thermal conductivity of the composite material can be improved by increasing the filling rate. Here, for the main filler having a large diameter, spherical powder described in Patent Document or granular powder having a plane is used, which has excellent filling properties.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When spherical powder is used for a sub-filler having a smaller diameter than the main filler and mixed with a spherical or planar main filler, the contact point between the main filler and the sub-filler becomes only one point.

[0006] Because there is only one contact point between the fillers, the heat transfer area between the fillers is small. Furthermore, in composite materials using spherical or planar main fillers, if subfillers are placed between the main fillers, for example, the distance between the main fillers increases by the size of the subfiller, thus increasing the distance between the fillers. As a result, the thermal resistance increases, and it was not possible to sufficiently increase the thermal conductivity of the composite material filled with main and subfillers.

[0007] Therefore, the present invention has been made in view of the above problems, and aims to provide an insulating thermal conductive filler that can improve the shape of the filler surface and effectively improve thermal conductivity, and a method for manufacturing the same. [Means for solving the problem]

[0008] The present invention relates to an insulating thermal conductive filler used for filling with a first spherical filler having an average particle diameter D50 of 10 μm to 30 μm and a second spherical filler having an average particle diameter D50 of 1 μm to 5 μm, wherein the insulating thermal conductive filler has an average particle diameter D50 larger than that of the first and second spherical fillers, and is composed of aggregates of multiple particles having an average particle diameter D50 of 10 μm to 40 μm, the surface of the insulating thermal conductive filler is provided with multiple knob-like protrusions, the surface of the knob-like protrusions is a rounded curved surface, the radius of curvature of the knob-like protrusions is 5 μm to 20 μm, the tap density of the insulating thermal conductive filler is 1.2 (g / cc) to 1.8 (g / cc), and the specific surface area of ​​the insulating thermal conductive filler is 0.08 (m²). 2 / g)~0.20(m 2 / g), and the insulating thermal conductive filler is AlN filler, and the AlN filler is AlN and grain boundary It is characterized by being composed of two phases, including the component Y4Al2O9.

[0009] In the present invention, it is preferable that 10 of the insulating thermal conductive fillers are extracted using SEM, and that 5 or more of the extracted insulating thermal conductive fillers are aggregated particles in which 3 to 100 particles with an average particle diameter of 10 μm to 40 μm are bound together.

[0010] The present invention relates to an insulating thermal conductive filler, characterized in that a plurality of knob-like protrusions are provided on the surface of the filler, the surface of the knob-like protrusions is curved, and the radius of curvature of the knob-like protrusions is 5 μm to 20 μm. In the present invention, the average particle size D50 of the insulating thermal conductive filler is preferably 60 μm to 150 μm. In the present invention, the tap density of the insulating thermal conductive filler is preferably 1.2 (g / cc) to 1.8 (g / cc). In this invention, the specific surface area of ​​the insulating thermal conductive filler is 0.08 (m²). 2 / g)~0.20(m 2 It is preferable that it be / g) In the present invention, the insulating thermal conductive filler is preferably an AlN filler.

[0011] The present invention relates to a method for manufacturing an insulating thermal conductive filler, characterized by sintering and agglomerating multiple particles having an average particle diameter D50 of 10 μm to 40 μm. The present invention is characterized by being synthesized by a combustion synthesis method under a nitrogen atmosphere, using Al particles with an average particle size D50 of 5 μm to 30 μm and a diluent consisting of AlN with an average particle size D50 of 10 μm to 40 μm. [Effects of the Invention]

[0012] According to the insulating thermal conductive filler of the present invention, it is possible to increase the number of contact points with other fillers, reduce the distance between fillers, and effectively improve the thermal conductivity of the composite material. [Brief explanation of the drawing]

[0013] [Figure 1] (a) and (b) are schematic diagrams showing the contact state between the main filler and the subfiller in the comparative example, and (c) is a schematic diagram showing the contact state between the main filler and the subfiller in this embodiment. [Figure 2] This is a particle size distribution diagram for this embodiment. [Figure 3] This is a SEM image of the AlN filler in this embodiment. [Figure 4] This is a SEM image of the AlN filler in the comparative example. [Figure 5] This is an X-ray diffraction chart of the AlN filler in this embodiment manufactured by the sintering method. [Figure 6] This is an X-ray diffraction chart of the AlN filler in this embodiment manufactured by the combustion synthesis method.

Modes for Carrying Out the Invention

[0014] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof. The notation "~" includes both the lower limit value and the upper limit value.

[0015] <Problems of Conventional Insulating Thermal Conductive Fillers> For example, insulating thermal conductive fillers are filled in heat dissipation materials such as heat dissipation sheets filled in resins or rubbers and heat dissipating adhesives filled in epoxy resins.

[0016] As the insulating thermal conductive filler, for example, the AlN filler has high insulation and high thermal conductivity and is used as a high heat dissipation filler. The larger the diameter of the filler, the more the thermal conductivity of the composite material (a mixture of a plurality of types of fillers with different particle diameters) can be improved. Therefore, for example, a large diameter of 60 to 150 μm is used for the main filler. The "main filler" refers to the filler having the largest mass ratio among the added fillers. Conventionally, spherical powders and granular powders having a planar shape with excellent filling properties have been used.

[0017] Figures 1(a) and 1(b) are comparative examples, and Figure 1(c) is a schematic diagram of the filler in this embodiment. Figures 1(a) to 1(c) show two main fillers 1 and one sub-filler 2. Note that "sub-filler" refers to fillers other than main filler 1, and has a smaller average particle size D50 than main filler 1.

[0018] As shown in Figure 1(a), when both the main filler 1 and sub-filler 2 are spherical, there is only one contact point between each main filler 1 and sub-filler 2. Similarly, as shown in Figure 1(b), when the main filler 1 is planar and the sub-filler 2 is spherical, there is also only one contact point between each main filler 1 and sub-filler 2.

[0019] As shown in Figures 1(a) and 1(b), there is only one contact point between the main filler 1 and the sub-filler 2, so the heat transfer area between the main filler 1 and the sub-filler 2 is very small.

[0020] Furthermore, as shown in Figures 1(a) and 1(b), when subfillers 2 are interposed between main fillers 1, the distance L1 between the main fillers 1 becomes the sum of the particle diameters of the main fillers 1 and the subfillers 2, thus increasing the distance L1. Therefore, in developing a main filler with a large average particle diameter D50, the inventors have invented an insulating thermal conductive filler that effectively improves thermal conductivity by improving the filler surface.

[0021] <Overview of the insulating thermal conductive filler of this embodiment> The insulating thermal conductive filler in this embodiment is characterized by being composed of aggregates of multiple particles having an average particle diameter D50 of 10 μm to 40 μm.

[0022] As shown in Figure 1(c), the insulating thermal conductive filler (hereinafter sometimes referred to as the main filler) 5 in this embodiment has a plurality of rounded, knob-like protrusions 3 on its surface. The plurality of knob-like protrusions 3 and the depressions 4 between each knob-like protrusion 3 give the filler surface a continuous curved, uneven shape.

[0023] Each of the knob-like protrusions 3 shown in Figure 1(c) consists of particles with an average particle diameter of 10 μm to 40 μm. The aggregation of these particles results in the filler surface having a curved, uneven shape, as shown in Figure 1(c).

[0024] Furthermore, in this embodiment, the surface of each knob-like protrusion 3 is rounded and curved, and the radius of curvature of the knob-like protrusion 3 is 5 μm to 20 μm. Since the insulating thermal conductive filler 5 of this embodiment is an aggregated particle formed by aggregating spherical particles with an average particle diameter D50 of 10 μm to 40 μm, each knob-like protrusion 3 has a rounded and smooth surface.

[0025] Furthermore, in this embodiment, it is preferable that 10 insulating thermal conductive fillers 5 are extracted using scanning electron microscope (SEM) images, and that 5 or more of the extracted insulating thermal conductive fillers 5 are aggregated particles in which 3 to 100 particles with an average particle diameter of 10 μm to 40 μm are bound together. In other words, the filler surface of the insulating thermal conductive filler 5 is provided with 3 to 100 knob-like protrusions 3 with a radius of curvature of 5 μm to 20 μm. By agglomerating 3 or more particles with an average particle diameter of 10 μm to 40 μm, it is possible to make the insulating thermal conductive filler 5 as a whole have a rounded shape. Furthermore, by agglomerating 100 or fewer particles with an average particle diameter of 10 μm to 40 μm, it is possible to prevent the insulating thermal conductive filler 5 from becoming excessively large, and as described later, the average particle diameter D50 can be appropriately kept within the range of 60 μm to 150 μm, while suppressing the increase in specific surface area and maintaining high packing efficiency.

[0026] As shown in the embodiment in Figure 1(c), the filler surface of the main filler 5 has a curved, smooth uneven shape, which increases the probability that there will be two or more contact points between each main filler 5 and the subfiller 2. This makes it possible to increase the heat transfer area between the main filler 5 and the subfiller 2.

[0027] Furthermore, as shown in Figure 1(c), in this embodiment, at least a portion of the subfiller 2 can be interposed in the recess 4 of the main filler 5, making the distance L2 between the main fillers 5 closer than the distance L1 between fillers in the comparative example shown in Figures 1(a) and 1(b). As a result, thermal resistance can be reduced.

[0028] On the other hand, in Figure 1(c), the filler surface of the insulating thermal conductive filler (main filler) 5 has an uneven shape. Therefore, when the insulating thermal conductive filler 5 is filled into the matrix (resin), friction with the matrix increases, which may reduce the filling efficiency. For this reason, in this embodiment, the surface of the knob-like protrusions 3 is made into a smooth uneven shape, and the entire outer circumference of the insulating thermal conductive filler 5 is rounded. This suppresses friction with the matrix and prevents a decrease in filling efficiency.

[0029] In this embodiment, the average particle size D50 of the insulating thermal conductive filler 5 is preferably 60 μm to 150 μm. The average particle size D50 can be measured, for example, with a laser diffraction particle size distribution analyzer (HORIBA LA-950). "D50" refers to the particle size at which the cumulative number of particles equals 50% of the total number of particles.

[0030] In this embodiment, the aspect ratio of the insulating thermal conductive filler 5 is preferably about 0.5 to 1, and more preferably about 0.7 to 1. The aspect ratio is the average aspect ratio obtained by observing with a SEM (Phenom ProX, manufactured by Phonom World) and measuring the aspect ratio (short axis / long axis) of 400 insulating thermal conductive fillers using analysis software (Particle Metric).

[0031] Furthermore, in this embodiment, the tap density of the insulating thermal conductive filler 5 is preferably 1.2 (g / cc) to 1.8 (g / cc), and more preferably 1.5 (g / cc) to 1.7 (g / cc). The tap density can be measured in accordance with JIS K 5101-12-2:2004.

[0032] Furthermore, in this embodiment, the specific surface area of ​​the insulating thermal conductive filler 5 is 0.08 (m²). 2 / g)~0.20(m 2 It is preferable that it be 0.10 (m 2 / g)~0.18(m 2 It is more preferable that the specific surface area is ( / g). The specific surface area can be determined by the BET method. For measuring the BET specific surface area, for example, BELSORP®-mini II (manufactured by Nippon Bell Co., Ltd.) can be used.

[0033] In this embodiment, as shown in the experiments described later, compared to the insulating thermal conductive filler of the comparative example with a planar shape, the tap density decreases and the specific surface area increases in this embodiment, which has many irregularities on its surface, but the amount of change is very small. Therefore, it is understood that the insulating thermal conductive filler 5 in this embodiment has a smooth irregular shape on its surface, and the influence of the surface shape on the filling properties is small.

[0034] The insulating and thermally conductive filler 5 in this embodiment is not limited to a specific material, but examples include aluminum nitride (AlN), silicon nitride (Si3N4), boron nitride (BN), aluminum oxide (Al2O3), magnesium oxide (MgO), zinc oxide (ZnO), titanium dioxide (TiO2), and silica (SiO2). Among these, AlN, which possesses both high insulating and thermally conductive properties, is preferred.

[0035] In this embodiment, the insulating thermal conductive filler 5 can be formed by sintering or direct nitriding. When the AlN filler of this embodiment is manufactured by sintering, its composition consists of two phases, including AlN and a grain boundary component (sintering aid) such as YAM (Y4Al2O9). When the AlN filler of this embodiment is manufactured by combustion synthesis, a type of direct nitriding, no sintering aid is used, and therefore it can be formed as a single phase of high-purity AlN.

[0036] <Regarding filling properties> The packing performance using the insulating thermal conductive filler of this embodiment will be described. The insulating thermal conductive filler of this embodiment is a main filler with an average particle diameter D50 of about 60 μm to 150 μm. In this embodiment, in addition to the main filler, several types of subfillers with different average particle diameters D50 are added. That is, for example, medium-diameter subfillers and small-diameter subfillers are added as subfillers. Although not limited, the average particle diameter D50 of the medium-diameter subfillers is about 10 μm to 30 μm. The average particle diameter D50 of the small-diameter subfillers is about 1 μm to 5 μm. Furthermore, although the shape of the medium-diameter and small-diameter subfillers is not limited, spherical particles are preferable from the viewpoint of packing performance.

[0037] In this embodiment, as the main filler, an insulating thermal conductive filler consisting of aggregated particles with an average particle diameter D50 of 10 μm to 40 μm, or an insulating thermal conductive filler having multiple knob-like protrusions on its surface, where the surface of the knob-like protrusions is curved and the radius of curvature of the knob-like protrusions is 5 μm to 20 μm, is used. This allows for multiple contact points with the subfiller, thereby reducing thermal resistance. At this time, from the viewpoint of reducing the number of particle interfaces that cause thermal resistance, it is preferable to fill with a medium-diameter subfiller with an average particle diameter D50 of 10 μm to 30 μm. That is, if only a small-diameter subfiller is used as the subfiller, the number of particle interfaces with the main filler increases. Therefore, in order to reduce the number of particle interfaces and more effectively improve thermal conductivity, multiple types of medium-diameter and small-diameter subfillers with different average particle diameters D50 are added as subfillers. In this embodiment, by using a main filler with an uneven surface, the distance between fillers is reduced, resulting in a more favorable heat transfer path.

[0038] Furthermore, because the main filler in this embodiment has an uneven surface, the surfaces of the multiple bump-like protrusions formed on the surface of the main filler are rounded to create a smooth uneven surface in order to suppress friction with the matrix and prevent a decrease in filling performance. This suppresses friction with the matrix and prevents a decrease in filling performance.

[0039] From the above, in this embodiment, the filler filling rate of the composite material filled with a main filler, a medium-diameter subfiller, and a small-diameter subfiller, each with a different average particle diameter D50, can be increased, and in particular, the filler filling rate can be increased to 70% or more. By increasing the filler filling rate to 70% or more, it is possible to dramatically improve the thermal conductivity. In this embodiment, a high filler filling rate similar to that obtained when spherical powder or granular powder with flat surfaces is used as the main filler, as in the comparative example, can be obtained, and thermal resistance can be effectively reduced, thereby dramatically improving the thermal conductivity.

[0040] <Method for manufacturing insulating thermal conductive filler according to this embodiment> The insulating thermal conductive filler in this embodiment can be formed through the following process: (1) by sintering, or (2) by direct nitriding. In the following description, the insulating thermal conductive filler will be described as an AlN filler.

[0041] In the sintering method, first, AlN particles with an average particle size D50 of 10 μm to 40 μm are prepared. Although AlN particles can be manufactured by existing methods, it is preferable to manufacture them by, for example, the combustion synthesis method. The AlN particles are preferably smooth particles with rounded surfaces, and in particular, spherical particles are preferred.

[0042] Next, multiple AlN particles and a sintering aid are mixed, the mixed powder is packed into a crucible, and sintering is carried out in a sintering furnace equipped with a carbon heater under a nitrogen atmosphere. The sintering temperature is preferably around 1650 to 2000°C, and the sintering time is preferably around 1 to 10 hours. The material of the sintering aid is not limited, but examples include Y2O3, CaO, CaCO3, SrCO3, BaCO3, La2O3, CeO2, PrO2, Nd2O3, Sm2O3, Gd2O3, Dy2O3, etc.

[0043] Furthermore, in this embodiment, since relatively large spherical AlN particles with a large average particle diameter D50 are used, the specific surface area is small and the oxygen content is low. Therefore, the yttrium aluminate phase necessary for bonding is not easily formed during sintering. For this reason, it is preferable to add Al2O3, which is not usually added as a sintering aid, in a mixing ratio close to the composition ratio of the yttrium aluminate phase necessary for bonding.

[0044] Since the mixed powder after sintering is in an aggregated state, it is preferable to lightly crush it using a mortar and pestle or a ball mill. This makes it possible to manufacture insulating thermal conductive fillers with a high yield, in which multiple particles with an average particle size D50 of 10 μm to 40 μm are aggregated, or insulating thermal conductive fillers in which multiple knob-like protrusions are provided on the surface of the filler, the surface of the knob-like protrusions is curved, and the radius of curvature of the knob-like protrusions is 5 μm to 20 μm.

[0045] In this embodiment, it is preferable to use a carbon heater and a carbon crucible for sintering the mixed powder. This is because the reduction sintering method, which is a common AlN sintering method, reduces grain boundaries and improves the thermal conductivity of the insulating thermal conductive filler. However, the use is not limited to a carbon heater and a carbon crucible.

[0046] In this embodiment, other methods for manufacturing the insulating thermal conductive filler, such as spark plasma sintering (SPS), which generates heat and sintersects due to particle interface resistance, can also be considered.

[0047] In this embodiment, the method is not limited to sintering; for example, the insulating thermal conductive filler can also be manufactured by direct nitriding. For direct nitriding, combustion synthesis is preferred. In the combustion synthesis method, by utilizing the heat of formation, it is possible to easily manufacture insulating, thermally conductive fillers with a smooth, uneven surface.

[0048] For example, it can be synthesized by combustion synthesis under a nitrogen atmosphere using Al particles with an average particle size D50 of 5 μm to 30 μm and a diluent consisting of AlN with an average particle size D50 of 10 μm to 40 μm. In this case, both diluents are particles with smooth surfaces, and spherical particles are particularly preferred. In this embodiment, the diluent can be produced by combustion synthesis.

[0049] The diluent is mixed with the raw material to suppress the welding of Al particles together. In this embodiment, the average particle size D50 of the diluent is about 10 μm to 40 μm, which is larger than the average particle size D50 of the Al particles. By using a diluent with such a large average particle size D50, aggregated particles can be produced in which multiple AlN particles are synthesized along the surface of the diluent into knob-like protrusions.

[0050] In the above-described embodiment, the powder is sintered as is for pre-sintering molding. However, methods such as sintering after compaction molding, creating an uneven shape beforehand by rolling granulation, or, as an application of this method, bonding spray-granulated powders together before sintering are also possible.

[0051] For example, a heat-plasticizing resin or the like can be used as a binder to bind the granulated powders together. Styrene-based polymers, acrylic polymers, vinyl acetate, etc., can be used as binders. Alternatively, a method can be considered in which agglomerated powder is attached to the core resin (binder) by a rolling granulation method and then sintered.

[0052] The insulating thermal conductive filler of this embodiment can be applied, for example, to an insulating high heat dissipation sheet. This high heat dissipation sheet is placed between a heat sink and an integrated circuit and is used in 5G communication servers, AI and automotive integrated circuits, and the like. [Examples]

[0053] The present invention will be described in detail below with reference to examples taken to clarify its effects. However, the present invention is not limited in any way by the following examples.

[0054] <Production of AlN filler using the sintering method> AlN filler was manufactured by sintering according to the following process. However, the manufacturing conditions shown below are just an example.

[0055] First, 90 wt% of approximately spherical AlN particles (AN-HF30LG-HTZ, manufactured by Combustion Synthesis Co., Ltd.) with an average particle size D50 of 30 μm were mixed with sintering aids: 5 wt% Y2O3, 3.5 wt% Al2O3, and 1.5 wt% CaO, using a ball mill.

[0056] Next, the mixed powder was packed into a carbon crucible, and then sintered in a firing furnace equipped with a carbon heater under a nitrogen atmosphere (at atmospheric pressure) at a temperature of 1800°C for 5 hours.

[0057] The mixed powder after sintering was lightly crushed using a mortar and pestle or a ball mill. The resulting AlN filler was classified using a sieve, and particle size distributions with average particle size D50 of 60, 80, and 100 μm were obtained (Figures 2(a) to 2(c)).

[0058] <SEM image of AlN filler in the example> Figure 3 shows an SEM (Phenom ProX, Phonom World) image of the AlN filler in this embodiment. The average particle size D50 of the AlN filler shown in Figure 3 was 80 μm. As shown in Figure 3, it was found that multiple nodule-like protrusions were formed on the filler surface. It was found that three or more nodule-like protrusions were aggregated on each AlN filler. The average particle size D50 of the nodule-like protrusions was approximately 30 μm, and the surface of the nodule-like protrusions was smooth and rounded, with a radius of curvature of approximately 15 μm. The radius of curvature can be determined from the particle outer circumference shape obtained from imaging methods such as SEM, laser microscope, and image-based particle size distribution analyzer, by connecting the start point, vertex, and end point of the unevenness with an approximate circular arc, and using the radius of the arc and the image scale.

[0059] Furthermore, observations were performed using a SEM (Phenom ProX, manufactured by Phonom World), and the aspect ratio (short axis / long axis) of 400 AlN fillers was measured using analysis software (Particle Metric). The average aspect ratio was found to be 0.7.

[0060] <Regarding the AlN filler used in the comparative example> In a comparative example, AlN fillers were produced by using a combustion synthesis method, reducing the amount of diluent added to approximately 5% to 50% by mass, and increasing the combustion temperature to generate crystalline particles with an average particle size of 50 μm to 300 μm. These particles were then crushed to produce AlN fillers in which the planar shape occupied a large area of ​​the particle surface, and these were used. Figure 4 shows an SEM image of the comparative example AlN filler. The average particle size D50 of the AlN filler shown in Figure 4 was 80 μm. Unlike the AlN filler in the comparative example shown in Figure 4, which had an uneven surface, the AlN filler in the example shown in Figure 3 had many flat surfaces.

[0061] <Tap density and specific surface area of ​​the examples and comparative examples> Table 1 below shows the relationship between particle size distribution range, tap density, and specific surface area for AlN filler. The average particle size D50 was measured using a laser diffraction particle size distribution analyzer (HORIBA LA-950). The specific surface area was determined by the BET method using BELSORP®-mini II (manufactured by Nippon Bell Co., Ltd.).

[0062] [Table 1]

[0063] The AlN fillers in the examples shown in Table 1 are AlN fillers having the particle size distribution shown in Figures 2(a) to 2(c), manufactured based on the sintering method described above.

[0064] In each example and comparative example, the particle size was adjusted to the range of particle size distribution shown in Table 1 to minimize the influence of particle size distribution, and then the tap density and specific surface area were measured.

[0065] As shown in Table 1, compared to the comparative example, which had many flat areas on the filler surface, the example, which had many uneven areas on the filler surface, showed a decrease in tap density and an increase in specific surface area. However, the amount of change was only slight compared to the comparative example. From this, it was found that the AlN filler in this example has an uneven surface shape that changes smoothly, and that the influence of this surface shape on filling performance can be minimized.

[0066] <Experiments on thermal conductivity> Next, the thermal conductivity and viscosity were measured for each sample shown in Table 2 below. As shown in Table 2, in the examples, AlN fillers with average particle diameters D50 of 60, 80, and 100 μm, as shown in Figures 2(a) to 2(c), were used as the main filler. In the comparative examples, planar AlN fillers with an average particle diameter D50 of 60 μm, planar AlN fillers with an average particle diameter D50 of 80 μm, and planar AlN fillers with an average particle diameter D50 of 100 μm were used as the main filler. All of these planar AlN fillers were manufactured by the manufacturing method described in <About the AlN fillers in the Comparative Examples> above. In both the examples and comparative examples, a small-diameter AlN filler with an average particle size D50 of 1 μm (AN-HF01LG-HT, manufactured by Nenshin Gosei Co., Ltd.) and a medium-diameter AlN filler with an average particle size D50 of 30 μm (AN-F30LG-HT, manufactured by Nenshin Gosei Co., Ltd.) were used as subfillers.

[0067] In the experiment, the main filler and subfiller were mixed in silicone oil (KF-96-20CS, manufactured by Shin-Etsu Chemical Co., Ltd.), and the amount of filler was fixed at either 70% by volume or 73% by volume. In both the examples and comparative examples, the small-diameter subfiller was fixed at 25% by mass of the total filler mass, and the medium-diameter subfiller at 15% by mass. Table 2 below shows the experimental results for thermal conductivity and viscosity in the examples and comparative examples.

[0068] [Table 2]

[0069] Thermal conductivity was measured using the ai-Phase method. Viscosity was measured at 25°C using a B-type viscometer.

[0070] As shown in Table 2, when comparing the examples with comparative examples that had the same average particle size D50 of the main filler, filler ratio, and filler filling amount, it was found that all examples had higher thermal conductivity than the corresponding comparative examples. Regarding viscosity, the examples showed values ​​similar to those of the comparative example filled with planar AlN filler, which has excellent filling properties, indicating high filling performance.

[0071] In this experiment, in addition to the main filler, a medium-diameter subfiller is added. As shown in Figure 1(c), when the medium-diameter subfiller is interposed between the main fillers, in this embodiment it enters the recessed parts of the uneven shape, resulting in multiple contact points and reducing the distance between fillers. This reduces thermal resistance and increases thermal conductivity.

[0072] On the other hand, in the comparative example, spherical medium-diameter subfillers are interposed between the planar AlN fillers, which are the main fillers, resulting in a wider gap between the main fillers than in this example, and thus a decrease in thermal conductivity. Thus, it was confirmed that, as in the example, using main fillers with a smooth, uneven surface can effectively increase thermal conductivity.

[0073] <About compositional analysis> Figures 5 and 6 show the X-ray diffraction charts of AlN filler produced by the sintering method described above and AlN filler produced by the combustion synthesis method.

[0074] In the combustion synthesis method, Al particles with an average particle size D50 of 15 μm and a diluent consisting of AlN with an average particle size D50 of 30 μm were used, and the synthesis was carried out under a nitrogen atmosphere at 0.9 MPa.

[0075] The resulting mixed powder after combustion synthesis was lightly crushed using a mortar and pestle or a ball mill. The crushed AlN filler was then classified using a sieve to obtain particle size distributions with average particle diameters D50 of 60, 80, and 100 μm. As shown in Figure 5, it was found that the sintering method produces a two-phase structure consisting of AlN and YAM (Y4Al2O9), which is a grain boundary component (sintering aid). On the other hand, as shown in Figure 6, the combustion synthesis method does not use sintering aids, so it was possible to obtain a high-purity composition that is a single-phase AlN and free of impurities.

[0076] Thus, compositional analysis using X-ray diffraction charts can predict whether the material was manufactured by sintering or combustion synthesis. [Industrial applicability]

[0077] The insulating thermal conductive filler of the present invention possesses both excellent thermal conductivity and high filling properties, can be manufactured inexpensively, and is useful as a high thermal conductive filler used in resin encapsulants and the like. [Explanation of Symbols]

[0078] 2 Subfillers 3. Nodular protrusions 4. Indentation 5. Insulating and thermally conductive filler (main filler)

Claims

1. An insulating thermal conductive filler having a larger average particle size D50 than the first and second spherical fillers, which is used for filling with a first spherical filler having an average particle size D50 of 10 μm to 30 μm and a second spherical filler having an average particle size D50 of 1 μm to 5 μm. Multiple particles with an average particle diameter D50 of 10 μm to 40 μm are aggregated together. The surface of the insulating thermal conductive filler is provided with a plurality of knob-like protrusions, the surface of the knob-like protrusions is rounded and curved, and the radius of curvature of the knob-like protrusions is 5 μm to 20 μm. The tap density of the insulating thermal conductive filler is 1.2 (g / cc) to 1.8 (g / cc), The specific surface area of ​​the insulating thermal conductive filler is 0.08 (m²). ２ / g) ~ 0.20 (m ２ / g) and The insulating thermal conductive filler is an AlN filler, and the AlN filler is composed of AlN and a grain boundary component Y ４ Al ２ It consists of two phases with O9, An insulating thermal conductive filler characterized by the following features.

2. The insulating thermal conductive filler according to claim 1, characterized in that 10 of the insulating thermal conductive fillers are extracted by SEM, and 5 or more of the extracted insulating thermal conductive fillers are aggregated particles in which 3 to 100 particles with an average particle diameter of 10 μm to 40 μm are bound together.

3. The insulating thermal conductive filler according to claim 1 or 2, characterized in that the average particle size D50 of the insulating thermal conductive filler is 60 μm to 150 μm.

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