JP7455184B1 - Silicon nitride thin plate and silicon nitride resin composite plate - Google Patents

Abstract

[Problem] To provide a silicon nitride thin plate and a silicon nitride resin composite plate with improved breakdown voltage and thermal conductivity. [Solution] A thin plate containing sintered β-type silicon nitride particles and having a plate thickness of 160 μm or less, the β-type silicon nitride particles include elongated β-type silicon nitride particles having a hexagonal column shape with a long axis and a short axis, the ratio of the long axis length to the plate thickness being 0.7 or more, and the inclination of the long axis from the normal line to the surface of the thin plate being 45 degrees or less. A silicon nitride resin composite plate includes this thin plate and a resin layer adhered to at least one of its surfaces. [Selected Figure] Figure 1

Description

The present invention relates to a silicon nitride thin plate and a composite plate of the silicon nitride thin plate and a resin layer.

Silicon nitride (Si ₃ N ₄ ) material is attracting attention as an insulating circuit board used in electronic equipment and semiconductor devices. Silicon nitride sintered bodies have higher strength and fracture toughness than alumina or silicon nitride sintered bodies, which makes it possible to bond thick copper directly to insulated circuit boards, contributing to the miniaturization of modules. Therefore, silicon nitride sintered bodies with improved mechanical strength and thermal conductivity are being developed.

For example, Patent Document 1 discloses that Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er are added to silicon nitride powder with an Al content of 0.1% by weight or less. , Yb, in an amount of 1% to 15% by weight as a sintering aid, and then molded under a nitrogen gas pressure of 1 atm to 500 atm. Discloses a method for producing a silicon nitride sintered substrate with improved mechanical properties and thermal conductivity by firing at a temperature of 1700° C. or higher and 2300° C. or lower.

Patent Document 2 discloses that silicon nitride powder containing 7% or less of β-type silicon nitride (β-Si ₃ N ₄ ) is used as a raw material, the viscosity of the slurry is adjusted to 13,000 cps or more, and then a sheet molded body is formed. Disclosed is a silicon nitride sintered substrate whose thermal conductivity and mechanical strength are improved by controlling the degree of orientation of β-type silicon nitride particles by firing, and a method for manufacturing the same.

Patent Document 3 discloses that when another member is pressure-bonded to a conventional silicon nitride substrate, a gap is created between the substrate surface and the other member due to microscopic irregularities on the substrate surface, which deteriorates heat dissipation and causes damage to the substrate during pressure-welding. In order to deal with the problem of easy cracking, a resin surface layer with a Vickers hardness of 200 or less and a thickness of 20 to 100 μm is formed on the surface of the silicon nitride substrate to prevent the formation of the gaps and improve heat dissipation. An insulating sheet that is less susceptible to cracking is disclosed.

Patent Document 4 discloses that in order to deal with the problem that in conventional electrically insulating heat conductive sheets in which inorganic particles are mixed in a matrix resin, the flexibility of the sheet is lost when the amount of inorganic particles is increased, the sheets are arranged side by side. It has a plurality of plate-shaped ceramic members (silicon nitride, etc.) and an embedding resin that embeds the plate-shaped ceramic members, and has flexibility, high electrical insulation, and thermal conductivity. An electrically insulating and thermally conductive sheet is disclosed.

Japanese Patent Application Publication No. 9-30866 JP 2019-52072 Publication JP2015-092600A JP2019-176060A

The silicon nitride sintered substrates manufactured in Patent Documents 1 and 2 have room for further improvement in dielectric breakdown voltage and thermal conductivity.

Patent Document 3 improves heat dissipation by allowing the resin to penetrate into microscopic irregularities on the surface of a silicon nitride substrate, and there is no idea of reducing thermal resistance by the microstructure of silicon nitride particles.

Patent Document 4 obtains flexibility and thermal conductivity by embedding a plurality of plate-shaped ceramic members in resin, and there is no idea of reducing thermal resistance by using the microstructure of silicon nitride particles.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a silicon nitride thin plate and a silicon nitride resin composite plate with increased dielectric breakdown voltage and thermal conductivity.

[1] A thin plate containing sintered β-type silicon nitride particles and having a thickness of 160 μm or less,
The β-type silicon nitride particles have a hexagonal column shape having a long axis and a short axis, and the ratio of the length in the long axis direction (hereinafter referred to as "long axis length") to the plate thickness is 1.01 or more. , and includes elongated β-type silicon nitride particles whose long axis has an inclination of 45 degrees or less from the normal to the surface of the thin plate,
A silicon nitride thin plate characterized in that an end of the long β-type silicon nitride particles protrudes from at least one surface of the thin plate.

[2] The silicon nitride thin plate according to [1] above, wherein the plate thickness is 120 μm or less.

[3] The silicon nitride thin plate according to [1] or [2], wherein the inclination is 35 degrees or less.

[4] The silicon nitride thin plate according to any one of [1] to [3] , wherein the long axis length/short axis length (aspect ratio) of the long β-type silicon nitride particles is 4 to 40 .

[5] Any one of [1] to [4] above, wherein the elongated β-type silicon nitride particles include those in which the ratio of the long axis length to the plate thickness is 1.01 to 1.34. The silicon nitride thin plate described in .

[6] The silicon nitride thin plate according to [5], wherein the ends of the long β-type silicon nitride particles protrude from both surfaces of the thin plate.

[7] The silicon nitride thin plate according to any one of [1] to [6] above, wherein the arithmetic mean height surface roughness Sa indicating the surface roughness of the thin plate is 0.7 μm or more.

[8] The silicon nitride thin plate according to any one of [1] to [7], wherein the surface of the thin plate is a sintered surface.

[9] The silicon nitride thin plate according to any one of [1] to [8] above, wherein the thin plate has a dielectric breakdown voltage of 45 kV/mm or more.

[10] A silicon nitride resin composite board comprising the thin plate according to any one of [1] to [9] above, and a resin layer that is in close contact with at least one surface of the thin plate.

[11] A circuit board using the silicon nitride resin composite board according to [10] above.

[12] A heat sink using the silicon nitride resin composite plate described in [10] above.

[13] An insulating board using the silicon nitride resin composite board according to [10] above.

According to the present invention, it is possible to provide a silicon nitride thin plate and a silicon nitride resin composite plate with increased dielectric breakdown voltage and thermal conductivity.

FIG. 1 is a secondary electron image of a vertically cut cross section of Example 1. FIG. 2 is a secondary electron image of a vertical section of Example 2. FIG. 3 is a secondary electron image of a vertical section of Example 5. FIG. 4 is a secondary electron image of a vertically cut cross section of Comparative Example 1. FIG. 5 is a side view of the silicon nitride resin composite board. FIG. 6 is a schematic diagram illustrating lamination when firing a silicon nitride thin plate.

<1> Silicon nitride thin plate A thin plate containing sintered β-type silicon nitride particles and having a thickness of 160 μm or less,
The β-type silicon nitride particles have a hexagonal column shape with a long axis and a short axis, the ratio of the long axis length to the plate thickness is 0.7 or more, and the length from the normal to the surface of the thin plate is 0.7 or more. It is characterized by containing elongated β-type silicon nitride particles whose axial inclination is 45 degrees or less.

When the thickness of the silicon nitride thin plate is 160 μm or less, long β-type silicon nitride particles are likely to be included in the thin plate. For example, when the plate thickness is 160 μm, the long axis length of the long β-type silicon nitride particles is 112 μm, and the ratio is 0.7.

It is preferable that the thickness of the silicon nitride thin plate is 120 μm or less (more preferably less than 120 μm) because the thin plate is more likely to contain long β-type silicon nitride particles. For example, when the plate thickness is 120 μm, the long axis length of the long β-type silicon nitride particles is 84 μm, and the ratio is 0.7.

The long axis length/short axis length (aspect ratio) of the long β-type silicon nitride particles is not particularly limited, but may be 4 to 40, for example.

The long β-type silicon nitride particles have a hexagonal columnar shape with a long axis and a short axis, the ratio of the long axis length to the plate thickness is 0.7 or more, and the length from the normal to the surface of the thin plate is 0.7 or more. By having an axis inclination of 45 degrees or less (preferably 35 degrees or less), the thin plate is oriented so that the vicinity of one surface and the vicinity of the other surface are connected briefly, and the following (a) and (b) are achieved. In this way, thermal conductivity and breakdown voltage are improved.

(a) The oriented long β-type silicon nitride particles efficiently transfer heat between the two surfaces, increasing the thermal conductivity in the thickness direction of the thin plate and improving heat dissipation when used as an insulating substrate. improves.
(a) In general, it is thought that at the interface where silicon nitride particles and the grain boundary phase are in contact, the irregularity of the crystal is disturbed and ion diffusion is accelerated, so that dielectric breakdown is likely to occur in the direction of application of the electric field. In contrast, in the present invention, the oriented elongated β-type silicon nitride particles reduce the number of interfaces between the silicon nitride particles and the grain boundary phase in the thickness direction, thereby improving the dielectric breakdown voltage.

Preferably, the ends of the elongated β-type silicon nitride particles are exposed or protrude from at least one surface of the thin plate. This is because the adhesion with the heat dissipating grease or resin layer formed on the surface is increased, and the thermal conductivity is further increased.

Preferably, the long β-type silicon nitride particles include particles in which the ratio of the long axis length to the plate thickness is 1 or more. This is because the effect of improving the thermal conductivity and dielectric breakdown voltage described above is enhanced.

Preferably, the ends of the elongated β-type silicon nitride particles are exposed or protrude from both surfaces of the thin plate. This is because the adhesion to the heat dissipating grease or resin layer formed on both surfaces is increased, and the thermal conductivity is further increased.

It is preferable that the arithmetic mean height Sa, which indicates the surface roughness of the thin plate, is 0.7 μm or more. This is because, as described above, the ends of the elongated silicon nitride particles are exposed or protrude from the surface of the thin plate.

It is preferable that the surface of the thin plate is a sintered surface. This is because it is preferable to leave the edges of the elongated silicon nitride particles exposed or protruding from the surface of the thin plate (without removing them by processing such as polishing or honing) as described above.

It is preferable that the dielectric breakdown voltage of the thin plate is 45 kV/mm or more.

<2> Silicon Nitride Resin Composite Board This board is characterized by comprising the thin plate of <1> above and a resin layer in contact with at least one surface of the thin plate.

The ends of the long β-type silicon nitride particles included in the thin plate are likely to be near the surface of the thin plate and close to the resin layer, so that the thermal conductivity is high. In particular, when the ends of the long β-type silicon nitride particles are exposed or protrude from at least one surface of the thin plate, the adhesion with the thermal paste or resin layer formed on the surface increases, and the thermal conductivity increases. It gets even higher.

Examples of the resin layer include the following.
(f) A resin layer formed by a liquid or gel-like resin that comes into contact with the surface of the thin plate and solidifies.The liquid or gel-like resin is applied to the surface of the thin plate and the exposed or protruding edges of the elongated silicon nitride particles. It is preferable because it adheres closely without any gaps. Examples of this resin include, but are not limited to, thermosetting resins, reaction-curing resins, photo-curing resins, etc., and specific examples include silicone resins, epoxy resins, etc.
(g) A resin layer that is solid before it comes into contact with the surface of the thin plate. This resin layer is not particularly limited, but a flexible thermally conductive resin sheet can be exemplified. This resin is not particularly limited, but examples include silicone resin and acrylic resin.

The resin layer preferably has high thermal conductivity filler such as metal powder or ceramic powder added to the resin to increase thermal conductivity. Examples of the metal powder include Cu powder and Al powder. Examples of the ceramic powder include aluminum nitride powder, silicon nitride powder, alumina powder, and silica powder.

The thickness of the resin layer is not particularly limited, but is preferably 5 to 200 μm, more preferably 5 to 100 μm.

Since it is not possible to measure the thermal conductivity in the thickness direction of a single thin plate using the flash method (the thickness of the thin plate is below the lower measurement limit of the same method), in this application, we will measure the thermal conductivity of a silicon nitride resin composite plate as described later. Thermal conductivity in the plate thickness direction was compared and evaluated between Examples and Comparative Examples.

<3> Applications Applications of the silicon nitride thin plate and silicon nitride resin composite board of the present invention are not particularly limited, but include, for example, semiconductor modules, LED packages, Peltier modules, printers, multifunction devices, semiconductor lasers, optical communications, high frequencies, etc. Examples of the circuit boards, heat sinks, insulating plates, high frequency windows, etc. that are used include.

<4> Method for manufacturing silicon nitride thin plate The method for manufacturing the silicon nitride thin plate described in <1> above will be described. The manufacturing method for silicon nitride thin plates does not use silicon nitride powder as a starting material, but rather uses silicon powder as a starting material, and uses reaction sintering, in which the formed silicon powder is heated in a nitrogen atmosphere and nitrided and densified at the same time. By law. In general, the reaction sintering method improves the thermal conductivity of the sintered body due to high raw material purity, but it is said that it is difficult to adjust the raw materials and firing conditions for densification. In addition, in the general reaction sintering method, silicon powder is converted into rod-shaped β-type silicon nitride particles, so it is difficult to control the orientation in the thickness direction, and it is known that the orientation tends to be random. There is.

The method for manufacturing silicon nitride thin plates mainly consists of 85 to 95 mol% of silicon nitride equivalent when silicon is completely nitrided to silicon nitride, 1 to 3 mol% of rare earth oxides, and 4 to 12 mol% of magnesium silicon nitride. A mixing step in which a silicon raw material powder, a rare earth oxide powder, and a silicon magnesium nitride powder are mixed in a molar ratio to produce a mixed powder, and a forming step in which the mixed powder is made into a slurry and formed into a sheet shape to produce a compact. , a nitriding step in which the compact is heated from a first temperature to a second temperature in a nitrogen atmosphere, and a densification step in which the compact is fired at a third temperature and for a predetermined time in a nitrogen atmosphere to obtain a silicon nitride thin plate. It is characterized by including a process. Each step will be explained in more detail below.

Prepare silicon powder as a starting material. The silicon powder, organic solvent, and dispersant are ground in a ball mill, and the particle size is adjusted so that the silicon powder has a specific surface area of 5.0 m ² /g or more and a D99.9 diameter of 8 to 9.5 μm. Here, in a particle size distribution curve with the horizontal axis as particle diameter (μm) and the vertical axis as frequency (%), the D50 diameter (median diameter) is the particle diameter with a frequency of 50%, and the D99.9 diameter is , is the particle size (corresponding to the mode of the distribution) with a frequency of 99.9%. The reason why the particle size is adjusted so that the specific surface area of the silicon powder is 5.0 m ² /g or more is that unless the specific surface area of the silicon powder is 5.0 m ² /g or more, the silicon powder will not be nitrided uniformly and This is because the subsequent substrate will be undulated. Also, the reason why the particle size is adjusted so that the D99.9 diameter is 8 to 9.5 μm is that if the D99.9 diameter is larger than 9.5 μm, nitriding will not progress sufficiently to the center of the coarse silicon powder. In addition, if the D99.9 diameter is smaller than 8 μm, the amount of oxygen in the silicon particles increases due to excessive pulverization, and the thermal conductivity of the substrate after firing decreases. This is because you end up doing it.

Further, as a sintering aid, rare earth oxide powder and silicon magnesium nitride powder are mixed to prepare a mixed powder. The specific surface area of the silicon magnesium nitride powder is preferably 9.0 m ² /g or more.

Next, 85 to 95 mol % silicon, 1 to 3 mol % rare earth oxide, and 4 to 12 mol % silicon magnesium nitride are mixed in a molar ratio. This mixed powder is sufficiently mixed in a ball mill, and then a binder, a plasticizer, and an organic solvent are added to form a slurry.

Next, the slurry is vacuum degassed and the viscosity is adjusted. The ratio of organic solvent contained in the degassed slurry is set to 35 wt % or less, and the viscosity of the slurry is set to 15,000 to 25,000 cps. Then, a sheet-like molded product with a thickness of 160 μm or less (preferably 100 μm or less) is produced using a doctor blade or the like.

The molded body is produced so that the inorganic filling rate is 47% or more. In order to make the inorganic filling rate of the compact 47% or more, the silicon powder must be pulverized so that the specific surface area is 9.0 m ² /g or less (that is, within the range of 5.0 to 9.0 m ² /g). It is preferable to adjust the particle size and keep the proportion of the organic solvent after defoaming to 35 wt% or less. When the specific surface area of the silicon powder is larger than 9.0 m ² /g, the proportion of fine silicon powder increases and agglomeration tends to occur, resulting in poor filling properties. Furthermore, if the proportion of the organic solvent contained in the slurry after defoaming exceeds 35 wt%, the amount of organic solvent that evaporates during sheet molding will increase, resulting in increased drying shrinkage and the formation of fine bubbles in the molded product. The method for measuring the inorganic filling rate is as follows. The sheet molded body used for the measurement has a residual organic solvent of 0.1 wt % or less. The volume and weight of the sheet molded body are measured, and the green density ρ _g (g/cm ³ ) of the molded body is measured. Thereafter, the sheet molded body used for the measurement is subjected to a binder removal treatment in the atmosphere at 500° C. for 3 hours. The organic fraction Pi (%) is determined by measuring the weight after the binder removal treatment, and the inorganic filling rate Fi (%) is calculated using the following formula.
Fi=ρ _g ×(1-Pi/100)/ρ _th ×100
Here, ρ _th is the theoretical density at the time of mill blending, and is a value calculated from the weight ratio of the inorganic components of the raw materials.

Next, the produced sheet-like molded body is subjected to debinding in a dry air atmosphere at about 500 to 800°C. After that, it is heated in a vacuum to about 1000° C. (first temperature) in a furnace, and then the temperature is raised from about 1000° C. to about 1350° C. (second temperature) in a nitrogen pressurized atmosphere. At this time, the molded body can be nitrided by gradually raising the temperature from the first temperature to the second temperature (for example, 1° C./min) in a nitrogen pressurized atmosphere. Then, the inside of the furnace is made into a higher pressure nitrogen atmosphere, and the temperature is raised from the second temperature to a third temperature of about 1750 to 2000°C (preferably 1900°C). After raising the temperature, the nitrided molded body is fired by holding the temperature at the third temperature for a long time (for example, about 8 hours), and the molded body is sufficiently densified to produce a silicon nitride thin plate. can do.

By going through the steps described above, it is possible to manufacture a silicon nitride thin plate in which β-type silicon nitride particles are preferentially oriented in the thickness direction of the substrate. In other words, in the manufacturing method, the amount of oxygen in the molded body is suppressed by using magnesium silicon nitride and by minimizing the amount of yttrium oxide added (in other words, the amount of rare earth oxide is 1 to 3 mol%). It can be considered that the reducibility in the process and densification step is increased. When the reducibility increases in this way, the silicon oxide film on the surface of the silicon powder is reduced, and SiO(g) is volatilized in the thickness direction. Furthermore, the reduction reaction of SiO (g) + CO (g) → Si (g) + CO ₂ (g) is promoted, and the generated Si (g) becomes 3Si (g) + 2N2 (g) in the porous body before densification. → It is thought that a reaction process of β-Si ₃ N ₄ is obtained, and β-Si ₃ N ₄ is precipitated in the thickness direction within the pores. Furthermore, when the heat treatment temperature increases, a silicon nitride substrate is obtained in which β-type silicon nitride particles are preferentially oriented in the thickness direction using β-Si ₃ N ₄ precipitated in the thickness direction within the pores as nuclei. It is thought that the extension of the β-type silicon nitride particles in the thickness direction increases the thermal conductivity and improves the heat dissipation performance of the insulating substrate.

Note that the steps described above are merely examples and do not limit the present invention. For example, the method for forming the slurry is not limited to the doctor blade method, and the slurry may be pressure-formed into a sheet molded body using an extrusion method, a casting method, or the like.

Next, examples embodying the present invention will be described in comparison with comparative examples. Note that the materials, quantities, and conditions of each part in the embodiments are merely illustrative, and can be changed as appropriate without departing from the gist of the invention.

Silicon nitride thin plates (approximately 0.085 mm thick) of Examples 1 to 4 and Comparative Examples 1 and 2 shown in Table 1, and silicon nitride thin plates (approximately 0.115 mm thick) of Example 5 and Comparative Example 3 shown in Table 2. ) was produced under the following conditions and procedures. The silicon compounding ratios in Tables 1 and 2 are based on silicon nitride as described above.

[1] Raw Materials/Mixing Silicon powder having predetermined powder characteristics and sintering aid powder were prepared. Put an appropriate amount of silicon powder into a resin pot, and use silicon nitride grinding media to mix the silicon powder, organic solvent, and dispersant until the specific surface area and D99.9 diameter of the silicon powder reach the specified values. Particle size was adjusted using a ball mill. Here, the blending composition ratio and the values of the D99.9 diameter, D50 diameter, and specific surface area of the silicon powder in each sample are as shown in Tables 1 and 2. After the particle size of the silicon powder was adjusted, a predetermined amount of sintering aid was added and mixed in a ball mill for 1 hour.

[2] Sheet Forming Thereafter, a binder (polyvinyl butyral), a plasticizer (dioctyl adipate), and an organic solvent (a mixed solvent of toluene and ethanol) were added to form a slurry. The obtained slurry was defoamed under vacuum to adjust its viscosity. The proportion of organic solvent contained in the slurry after vacuum defoaming was 35 wt% or less, and the viscosity of the slurry was 15,000 to 25,000 cps. The viscosity of the slurry was measured using a TVC-7 viscometer manufactured by Toki Sangyo Co., Ltd. Specifically, a spindle was rotated in the slurry, and the viscosity was calculated from the resistance force. Then, using a doctor blade at a molding speed of 220 mm/min or higher, sheet-like molded bodies having three types of thickness after drying: 0.1 mm, 0.14 mm, and 0.3 mm were produced. A plurality of sheets of each thickness were cut into a size of 140 mm x 140 mm. The 0.1 mm and 0.14 mm thick sheets are for making samples, and the 0.3 mm thick sheet is for the next lamination.

[2] Sheet Lamination As shown in FIG. 6, first, BN as a mold release agent was sprayed on both sides of a 0.3 mm thick sheet, and a 0.1 mm thick sheet was stacked on top of it. Furthermore, a 0.3 mm thick sheet with BN sprayed on both sides is placed on top of that, and a 0.1 mm sheet is placed on top of that, and so on until the thickness is 0. A block of 21 laminates was prepared by alternately stacking sheets of .3 mm and 0.1 mm, and arranging the 0.3 mm sheet at the top of the laminate.
In addition, a 0.14 mm sheet was used instead of a 0.1 mm sheet, and sheets with a thickness of 0.3 mm and 0.14 mm were similarly laminated alternately, and the 0.3 mm sheet was placed on the top layer of the laminate. A laminate of 21 sheets per block was also prepared by arranging the laminates.

[3] Heating, firing, separation, and cutting The laminate was debounded at 500°C in dry air, then placed in a furnace, heated to about 1000°C in vacuum, and heated in a nitrogen pressurized atmosphere of 0.2 MPa. The temperature was raised to 1350°C at a rate of 1°C/min. Then, in a nitrogen pressurized atmosphere of 0.9 MPa, the temperature was raised from 1350°C to 1900°C, and firing was performed at 1900°C for 8 hours. The fired laminate is separated to form a silicon nitride thin plate with a thickness of about 0.085 mm (based on the 0.1 mm thick sheet) and a thin silicon nitride plate with a thickness of about 0.1 mm (based on the 0.14 mm thick sheet). A 115 mm silicon nitride thin plate was obtained. The outer periphery of each silicon nitride thin plate was cut with a laser to obtain a sample of 110 mm x 110 mm. The sample surface is the sintered surface.

The following observations and measurements were performed on the prepared samples of Examples 1 to 5 and Comparative Examples 1 to 3.

(i) Observation and measurement of vertically cut cross sections Using thin plate pieces cut from each sample into 10 mm x 10 mm, the thin plate pieces were embedded in epoxy resin, and the vertical cross sections of the thin plates were observed. The observation surface was prepared by the following procedure. Flatten with #800 diamond abrasive paper, polish with diamond slurry in the order of 15 μm, 6 μm, and 1 μm until the polishing scratches caused in each previous step are removed, and finish polish with 50 nm alumina slurry to create a mirror surface. I got it. After mirror polishing, CF ₄ plasma etching and gold sputtering film formation were performed to obtain an observation surface. Then, using a scanning electron microscope JSM-IT700HR manufactured by JEOL Ltd., a secondary electron image of a randomly selected field of view was observed at a magnification of 800 times.
1 is a secondary electron image of Example 1, FIG. 2 is a secondary electron image of Example 2, FIG. 3 is a secondary electron image of Example 5, and FIG. 4 is a secondary electron image of Comparative Example 1. to show. In FIGS. 1 to 3, the plate thickness t of the sample measured from the secondary electron image and the long axis length L of the largest β-type silicon nitride particle are shown. The measurement results and the L/t calculation results are shown in Tables 1 and 2.

(ii) Arithmetic mean height Sa
For the thin plate surface (sintered surface) of each sample, the arithmetic mean height Sa, which is the surface roughness of a 500 μm x 500 μm area, was measured using a laser microscope VKX-150 manufactured by Keyence Corporation. The measurement conditions are as follows, and the measurement results are shown in Tables 1 and 2.
Objective lens magnification: ×20
Image correction: Automatic surface tilt correction Filter type: Gaussian S-filter: 2μm
F-Operation: None L-Filter: 0.2mm
Terminal effect correction: Yes

(iii) Dielectric breakdown voltage Each sample is cut into 20 mm x 20 mm thin plate pieces, and conductive copper foil adhesive tape with a diameter of 10.4 mm is pasted on both sides (sintered surface) of each thin plate piece as measurement electrodes. Using a partial discharge measuring device model "A006" manufactured by Fujikura Dia Cable Co., Ltd., an AC voltage (sine wave) was applied in a fluorinated inert liquid (Fluorinert FC-43, manufactured by 3M Japan Co., Ltd.). did. The shape of the electrodes on the upper and lower surfaces was 11 mm in diameter, the rate of increase of the AC voltage was 500 V/s, and the average dielectric breakdown voltage was measured for the three samples. The measurement results are shown in Tables 1 and 2.

(iv) Preparation and thermal conductivity of silicon nitride resin composite plate Kapton adhesive tape (Teraoka Seisakusho Co., Ltd., product number: 650S#12) was pasted as a resin layer on one side of each sample, and a silicon nitride thin plate as shown in Figure 5 was prepared. A resin composite board was produced.
Then, the silicon nitride resin composite board was placed so that the Kapton tape-adhesive surface was the upper surface (detector side), and the thermal conductivity in the board thickness direction was measured by the flash method. For the measurement, a thermal conductivity measuring device LFA467 manufactured by NETZSCH Geratebau GmbH was used. Each composite sample was cut into individual pieces of 10 mm x 10 mm, and a gold sputtered film was formed on both sides of each piece (the sintered surface and the resin surface) to suppress the transmission of flash light to uniformly distribute the pulsed light. For the purpose of absorption, graphene spray was used on both sides of each piece to blacken the surface. When calculating the thermal conductivity, the specific heat of the silicon nitride substrate obtained is 0.68 J/(g K), and the specific heat of Kapton is 1.1 J/(g K). Using the values of 3.22 g/cm ³ as the specific gravity and 1.42 g/cm ³ as the specific gravity of Kapton, the composite density and specific heat of each composite sample were calculated based on the volume ratio of the silicon nitride substrate and Kapton tape, and the following The thermal conductivity λ was calculated from the relationship of the formula.
λ=C _p ×ρ×α
Here, C _p represents the specific heat of the composite sample, ρ represents the density of the composite sample, and α represents the thermal diffusivity of the composite sample.
The measurement results are shown in Tables 1 and 2.

[evaluation]
The silicon nitride thin plates of Examples 1 to 5 have a hexagonal columnar shape having a long axis and a short axis among the countless β-type silicon nitride particles, and have an L/t ratio of 0.7 or more, and Contained were long β-type silicon nitride particles whose long axis had an inclination of 45 degrees or less from the normal to the surface of the thin plate.
Furthermore, the silicon nitride thin plates of Examples 1 to 5 contained some of the long β-type silicon nitride particles exposed or protruding from at least one surface of the thin plate.
Further, in the silicon nitride thin plate of Example 1, some of the long β-type silicon nitride particles have an L/t ratio of 1 or more, and the ends of the long β-type silicon nitride particles are attached to the thin plate. It protruded from both surfaces.
On the other hand, in the silicon nitride thin plates of Comparative Examples 1 to 3, β-type silicon nitride particles having a hexagonal column shape with a long axis and a short axis were included among the countless β-type silicon nitride particles. , the above-mentioned elongated β-type silicon nitride particles were not included.

The silicon nitride thin plates of Examples 1 to 4 have a higher dielectric breakdown voltage than the silicon nitride thin plates of Comparative Examples 1 and 2, and the silicon nitride thin plates of Example 5 have a higher dielectric breakdown voltage than the silicon nitride thin plates of Comparative Example 3. it was high.
Furthermore, the silicon nitride resin composite plates of Examples 1 to 4 have higher thermal conductivity than the silicon nitride resin composite plate of Comparative Example 1, and the silicon nitride resin composite plate of Example 5 has a higher thermal conductivity than the silicon nitride resin composite plate of Comparative Example 3. Thermal conductivity was higher than that of In particular, Examples 1 to 4 containing particles with an L/t ratio of 0.9 or more had a high improvement rate in thermal conductivity compared to Comparative Example 1.

It should be noted that the present invention is not limited to the embodiments described above, and can be modified and embodied as appropriate without departing from the gist of the invention.

Claims (13)

A thin plate containing sintered β-type silicon nitride particles and having a thickness of 160 μm or less,
The β-type silicon nitride particles have a hexagonal columnar shape having a long axis and a short axis, the ratio of the long axis length to the plate thickness is 1.01 or more, and the long axis from the normal to the surface of the thin plate is Contains long β-type silicon nitride particles having an inclination of 45 degrees or less,
A silicon nitride thin plate characterized in that an end of the long β-type silicon nitride particles protrudes from at least one surface of the thin plate. The silicon nitride thin plate according to claim 1, wherein said plate thickness is 120 μm or less. The silicon nitride thin plate according to claim 1, wherein the inclination is 35 degrees or less. The silicon nitride thin plate according to claim 1, wherein the long axis length/short axis length (aspect ratio) of the long β-type silicon nitride particles is 4 to 40. 2. The silicon nitride thin plate according to claim 1, wherein the long β-type silicon nitride particles have a ratio of major axis length to the plate thickness of 1.01 to 1.34 . 6. The silicon nitride thin sheet according to claim 5, wherein the ends of said elongated β-type silicon nitride particles protrude from both surfaces of said thin sheet. The silicon nitride thin plate according to claim 1, wherein an arithmetic mean height Sa indicating surface roughness of the thin plate is 0.7 μm or more. The silicon nitride thin plate according to claim 1, wherein the surface of the thin plate is a sintered surface. The silicon nitride thin plate according to claim 1, wherein the dielectric breakdown voltage of the thin plate is 45 kV/mm or more. A silicon nitride resin composite plate comprising the thin plate according to any one of claims 1 to 9 and a resin layer in close contact with at least one surface of the thin plate. A circuit board using the silicon nitride resin composite board according to claim 10. A heat sink using the silicon nitride resin composite plate according to claim 10. An insulating board using the silicon nitride resin composite board according to claim 10.

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