KR20190001568A - Method for preparing silicon nitride sintered body, silicon nitride sintered body and heat radiation substrate using the same - Google Patents

Abstract

Provided are a method for manufacturing a silicon nitride sintered body, the silicon nitride sintered body and a heat radiation substrate using the same. The method for manufacturing a silicon nitride sintered body includes a step (S1) of preparing silicon nitride powder of which oxygen content is 1.5 mass% or less and a step (S2) of charging the silicon nitride powder in a sintering mold, and sintering the silicon nitride powder by continuously applying a pulse type direct current of 1-10 V and 500-40,000 A to a particle gap of raw material powder while pressurizing the powder with 70 MPa or higher.

Description

TECHNICAL FIELD The present invention relates to a silicon nitride sintered body, a silicon nitride sintered body and a heat dissipating substrate using the same,

The present invention relates to a method for producing a silicon nitride sintered body, a silicon nitride sintered body and a use thereof.

Silicon nitride (Si ₃ N ₄ ) has a hexagonal crystal structure and exists as α-silicon nitride (α-Si ₃ N ₄ ) and β-silicon nitride (β-Si ₃ N ₄ ). Silicon Nitride (Si ₃ N ₄ ) has a strong and stable three-dimensional structure due to covalent bonds, and is excellent in hardness, abrasion resistance, electrical insulation, mechanical strength and heat resistance. Therefore, it can be used as a material for engines, bearings, turbine blades, cutting tools . Since silicon nitride (Si ₃ N ₄ ) has a high theoretical thermal conductivity, it is employed as a heat dissipation substrate such as a power module.

As a main sintering method of the silicon nitride (Si ₃ N ₄ ) sintered body, an atmospheric pressure sintering method, a gas pressure sintering method, and a heat treatment press working method are used. Further, in the molding method, silicon nitride particles in the sintered body are randomly oriented because they are normally sintered after slip casting with α-Si ₃ N ₄ grains by equiaxed α-Si ₃ N ₄ particles or tape casting, and as a result, the thermal conductivity is extremely low .

On the other hand, in order to increase the thermal conductivity of silicon nitride (Si ₃ N ₄ ), a silicon nitride powder (α-silicon nitride particle), a seed crystal (seed crystal) β Silicon nitride (Si ₃ N ₄ ) having a thermal conductivity of 149 W / mK by orienting the c-axis direction of the? -Silicon nitride particles in the thickness direction of the substrate using a silicon nitride powder and a sintering auxiliary agent (Patent Example 2 of Document 1). However, just as was the β-Si ₃ N ₄ theoretical value of the thermal conductivity is also achieved with a thermal conductivity of about one-third of the theoretical value with the prior art about 450 W / mK in the c-axis direction.

Meanwhile, Spark Plasma Sintering (SPS) has been developed in Japan in the early 1960s as one of the ceramic sintering methods at present (Non-Patent Document 1: 'Ceramic Sintering by Spark Plasma Sintering (SPS) Phenomena and prospects'). In fact, it has been reported that a dense sintered body having a relative density of 99% at SPS sintering temperature of 1600 to 1700 ° C was produced by the SPS method without adding an amorphous nano silicon nitride Si ₃ N ₄ powder of 50 nm or less Non-Patent Document 2: Presented by Ryukoku University, Professor Oyanaki Mushi, "Research and Development Workshop of Metal Materials Research Institute, Tohoku University" Development and Application of New Materials by Electric Sintering Technology "Presentation of 20th Electric Sintering Society ').

However, development of a silicon nitride (Si ₃ N ₄ ) sintered body having a thermal conductivity close to the theoretical value, a simple and economical method of manufacturing the same, and a heat radiation substrate using a silicon nitride (Si ₃ N ₄ ) sintered body are still required.

Patent Document 1: JP-A-2015-063449

Non-Patent Document 1: "Development and Prospect of Ceramic Sintering by Spark Plasma Sintering (SPS)" (Masako Toki, Journal of Ceramic Society of Japan 49 (2014) No. 2, pages 91 to 96) Non-Patent Document 2: 'Research Workshop of Research Institute of Metallurgy Materials, Tohoku University' Development and Practical Application of New Materials by Electric Sintering Technology 'Presentation of 20th Electric Sintering Societies' (Ryukoku University, Professor Oyanaki Mushi)

The present inventors have focused on the oxygen content of the silicon nitride raw material powder and the SPS method to make a silicon nitride sintered body having a high thermal conductivity by adopting the improved SPS method with a small amount (substantially not containing) of the oxygen content, Silicon nitride sintered body obtained by the method and a heat radiation substrate using the same. The present invention is based on this finding.

Therefore, the present invention can propose the following embodiments.

[1] A method for producing a silicon nitride sintered body,

(S1) A silicon nitride powder having an oxygen content of 1.5% by mass or less is prepared,

(S2) The silicon nitride powder is charged into a sintering mold (sintering type) and pressurized to 70 MPa or higher, pulsed direct current of voltage of 1 V to 10 V and output current of 500 A or more and 40,000 A or less is continuously And sintering the silicon nitride powder.

[2] A method for producing a silicon nitride sintered body according to [1], wherein in the step (S1), silicon nitride powder having an oxygen content of 0.9 mass% or less is prepared.

[3] The production method of a silicon nitride sintered material according to [1] or [2], wherein in the step (S1), the average particle diameter (D ₅₀ ) of the silicon nitride powder is 0.8 탆 or less.

[4] The production method of the silicon nitride sintered body according to any one of [1] to [3], wherein the iron nitride concentration contained in the silicon nitride powder is 200 ppm or less in the step (S1).

[5] The method according to any one of [1] to [4], wherein the silicon nitride powder contains 90% or more of crystallized? -Silicon nitride and / or crystallized? -Silicon nitride in the step (S1) .

[6] The method for producing a silicon nitride sintered body according to any one of [1] to [5], wherein the sintering is performed at a temperature of 1650 ° C. or higher and 1750 ° C. or lower in the step (S 2).

[7] The silicon nitride sintered body has a true density of 3.10 g / cm 3 or more,

A process for producing a silicon nitride sintered body according to any one of [1] to [6], wherein the half width of the peak of the? -Silicon nitride (200) face of the XRD pattern is 0.154 or more and 0.160 or less.

[8] A silicon nitride sintered body formed by the manufacturing method according to any one of [1] to [7].

[9] A heat radiation substrate using the silicon nitride sintered body according to [8].

According to the present invention, a silicon nitride raw material powder substantially containing no oxygen atoms (molecules) is used as a raw material and further processed by the SPS method, whereby a silicon nitride sintered body having a high thermal conductivity and mechanical strength can be easily and economically It becomes possible to manufacture. Further, according to the embodiment of the present invention, a silicon nitride sintered body having a high thermal conductivity in the thickness direction of the silicon nitride sintered body can be manufactured simply and economically. Further, the silicon nitride sintered body according to the present invention is realized with extremely low thermal conductivity and an extremely small amount of oxygen. Therefore, for example, when the silicon nitride sintered body according to the present invention is employed as a heat dissipation substrate of a power module, heat generated from the power module can be efficiently discharged (heat dissipation). Therefore, the power module including the silicon nitride sintered body according to the present invention is excellent in heat dissipation efficiency and mechanical durability.

1 is a flowchart of a method of manufacturing a silicon nitride sintered body according to the present invention.

[Manufacturing method of silicon nitride sintered body]

Step (S1)

<Oxygen content>

As a raw material, a silicon nitride powder having an oxygen content of 1.5% by mass or less is prepared. Preferably, silicon nitride powder having an oxygen content of 0.9 mass% or less, more preferably 0.85 mass% or less (substantially no oxygen) is prepared. By not containing the oxygen content within the above-mentioned numerical range, preferably, silicon nitride is not influenced by oxygen atoms (molecules) and a high thermal conductivity can be achieved.

&Lt; average particle diameter &

The silicon nitride preferably has an average particle diameter (D ₅₀ ) of 0.8 μm or less, preferably 0.7 μm or less. The average particle diameter can be measured by measuring the volume distribution by Microtrac (for example, laser diffraction method). When the average particle diameter (D ₅₀ ) of the silicon nitride particles is within the above range, it is possible to obtain a silicon nitride sintered body in which many silicon nitride particles are densely formed without forming aggregates, Is high.

&Lt; Content concentration of other atoms &gt;

The concentration of atoms contained in the silicon nitride powder, for example, an iron source is 200 ppm or less, preferably 170 ppm or less. When the concentration is within the above range, deterioration of thermal conductivity and strength can be suppressed.

<Silicon nitride powder>

The silicon nitride powder is? -Silicon nitride and / or? -Silicon nitride. When β-silicon nitride and α-silicon nitride are mixed and used as the silicon nitride powder, the content of β-silicon nitride is not particularly limited and may be appropriately selected. The silicon nitride powder may be adjusted, or a commercially available product may be used.

Step (S2)

In the step (S2), the silicon nitride powder is filled in a sintering mold (sintering type) and a voltage of 1 V or more and less than 10 V, preferably less than 5 V, and an output current of 500 A or more and 40,000 A or less, preferably 1500 A or less, is continuously applied to sinter the silicon nitride powder. The sintered type is made of graphite (graphite).

<Pressure>

The silicon nitride powder filled in the sintered compact is pressurized to 70 MPa or higher, preferably 80 MPa or higher. When the pressing range is within the above range, a sintered body having a high thermal conductivity at a high density in a short time at a lower temperature can be obtained.

<Sintering Temperature>

The sintering is carried out at a sintering temperature of 1650 ° C to 1750 ° C, preferably 1700 ° C to 1750 ° C, while the temperature is raised. The sintering temperature may be continuously or intermittently heated, or may be maintained at a constant temperature for a specified time. When the sintering temperature is in the above-mentioned range, a sintered body having high density and high thermal conductivity can be obtained.

The sintering may be performed in two steps of a low temperature region and a high temperature region. Concretely, in the low temperature region, it is 1400 DEG C or higher and 1650 DEG C or lower, preferably 1500 DEG C or higher and 1600 DEG C or lower. The high-temperature region can have a temperature of 1600 DEG C or higher and 1800 DEG C or lower, preferably 1650 DEG C or higher and 1750 DEG C or lower. In a preferred form of the present invention, it is preferable to provide a time for maintaining the temperature in each of the low-temperature region and the high-temperature region. The holding time of the low temperature region is from 1 minute to 30 minutes, preferably from 5 minutes to 20 minutes. The holding time of the high temperature region is from 1 minute to 20 minutes, preferably from 5 minutes to 10 minutes.

<Sintering condition>

The sintering is preferably carried out in the absence of oxygen or under nitrogen gas filling.

Since the oxygen content is not contained in the above-mentioned numerical range, preferably, silicon nitride is not affected by oxygen atoms (molecules), and a high thermal conductivity can be achieved.

<Sintering agent>

In the present invention, a sintering auxiliary agent can be used. The sintering assistant is used to promote the crystal growth of the silicon nitride particles and to increase the relative density of the silicon nitride sintered body. Specific examples of the sintering aid may include alkaline earth metals, rare earth metals, transition metals and metals belonging to the group of typical metals, and oxides thereof. As a specific example of the sintering aid, it is possible to use one kind or a mixture of two or more kinds selected from the group consisting of Y ₂ O ₃ , MgO, CaO, HfO ₂ , SiO ₂ and the like.

The addition amount of the sintering auxiliary agent is 0% by mass or more and 15% by mass or less, preferably 2% by mass or more and 8% by mass or less with respect to the total mass of the silicon nitride particles.

[Sintered silicon nitride]

In the present invention, a silicon nitride sintered body can be proposed, and preferably, a silicon nitride sintered body obtained by the manufacturing method according to the present invention can be proposed.

Therefore, in the silicon nitride sintered body according to the present invention,

(S1) A silicon nitride powder having an oxygen content of 1.5% by mass or less is prepared,

(S2) The silicon nitride powder is charged into a sintering mold and pressurized to 70 MPa or higher while applying a voltage of 1 V or more and less than 10 V, preferably less than 5 V, and an output current of 500 A or more and 40,000 A or less, Or less, and continuously sintering the silicon nitride powder.

<True density>

The true density of the silicon nitride sintered body is 3.0 g / cm 3 or more, preferably 3.1 g / cm 3 or more. The true density can be measured by the Archimedes method.

<Relative density>

The relative density of the silicon nitride sintered body is 95% or more, preferably 97% or more. From this, it can be understood that the silicon nitride sintered body has a dense structure.

The relative density can be obtained as the relative density of the silicon nitride sintered body containing the? -Silicon nitride particles when the calculated density obtained from the composition of the raw material in the production method of the silicon nitride sintered body is the theoretical density. The relative density of the silicon nitride sintered body can be measured by the Archimedes method (JIS Z 8807).

<Half width>

The half width of the peak of the? -Silicon nitride (200) plane of the XRD pattern is 0.154 or more and 0.160 or less, preferably 0.154 or more and 0.157 or less. When the half width is within the above range, the crystallinity of the? -Silicon nitride sintered body is increased and the thermal conductivity can be increased. The conditions for XRD measurement are not particularly limited, but can usually be carried out in the range of 2? 10 ° to 90 °. In addition, the scan speed can be appropriately selected. The X-ray diffraction measurement can be performed using a CuK? Ray (for example, the wavelength of the source is 1.5406?).

This half-value width can be obtained from the width at half the peak height of the? -Silicon nitride (200) plane of the XRD pattern obtained by measuring the peak by XRD.

<Heat Diffusivity>

The thermal diffusivity (average value) mm 2 / s of the silicon nitride ceramics is 14 mm 2 / s or more and 20 mm 2 / s or less. According to the present invention, a silicon nitride sintered body having a high thermal diffusivity can be proposed. The thermal diffusivity (average value) mm 2 / s is a value measured by flashing a hot wire instantaneously from a xenon lamp and observing the heat conduction to the opposite surface of the sample as a time variation of the temperature of the back surface of the sample. For example, it can be measured by a Xe flash analyzer.

<Thermal Conductivity>

(Average value) W / mK of the silicon nitride sintered body is 20 W / mK or more, preferably 25 W / mK or more and 45 W / mK or less. According to the present invention, a silicon nitride sintered body having a high thermal diffusivity can be proposed. The thermal conductivity (average value) W / mK can be calculated from the measured thermal diffusivity of the sample and the specific heat and density of the sample.

[Usage]

The silicon nitride sintered body includes various heat dissipation substrates; Electric and electronic components such as power module substrates (for vehicles, for electric trains, for high power semiconductors), high frequency circuit boards, packages for LEDs, and submounts for optical pickups (for DVD and CD); Engine components such as engines for engines and gas turbines, rotors for turbo chargers, glow plugs for diesel engines, hot plugs; Heater tube, hot-water supply hot water pipe, protection pipe, blow pipe for degassing: heat and impact resistance member; Polishing cloth dressing plate; High frequency quenching jig, body assembly / engine manufacturing jig, press process jig; Insulating parts, insulating medical instruments and surgical instruments; Roller for plastic working; Silicon nitride heater (SN heater); Thermocouple protection tube; Nozzle, nozzle cover; Welding parts, jigs for welding processes, and the like.

&Quot; Example &

Hereinafter, an embodiment of the present invention will be described, but the scope of the present invention is not limited to these embodiments. It is needless to say that the present invention solves the problems of the present invention by reading the entirety of the present specification and further by the following embodiments, and those skilled in the art can easily carry out the present invention easily .

[Example 1]

A raw material powder was prepared under the conditions shown in Table 2, and spark plasma sintering (including arc plasma sintering) was performed.

As shown in Table 1, 5 wt% Y ₂ O ₃ powder and 2 wt% MgO powder (DENKA-SN9FWS: a crystalline phase: manufactured by Denka Co.) having an oxygen content of 0.85 wt% Were added and mixed using induction.

The mixed powder was charged into a graphite die, and the outside of the die was covered with a carbon insulating material and installed in an arc plasma sintering apparatus (tin-discharge plasma sintering apparatus DR. SINTER · LAB SPS-515: Sumitomo Coal Mining Co., Ltd.) The inside was filled with N ₂ of 1 atm, and then sintered by applying a voltage (3.45 to 3.6 V) and a current (1040 to 1090 A). The temperature was raised from room temperature to a sintering temperature of 1700 ° C. After reaching the sintering temperature, it was held for 5 minutes, and then the electricity was stopped and naturally cooled. Then, the graphite die was taken out from the apparatus to the outside and air-cooled (air-cooled). On the other hand, at the time of sintering, a pressure of 80 MPa was applied to the ceramics sintered body through the upper and lower electrode rods to obtain a ceramics sintered body.

The obtained sintered ceramics had a relative density of 97% or more, a thermal conductivity of 38.27 W / m 占 기재, and a half-width of the peak of the? -Silicon nitride (200) plane of the XRD pattern of 0.157 as shown in Table 3 .

[Example 2]

As shown in Table 1, a ceramics sintered body was obtained in the same manner as in Example 1 except that the silicon nitride raw material powder was a silicon nitride raw material powder (Combustion Synthesis product: CS-F1:? Crystal phase) having an oxygen content of 1.39 wt%.

The obtained sintered ceramics had a relative density of 97% or more, a thermal conductivity of 33.13 W / m 占 기재, and a half width of 0.154 as a peak of the? -Silicon nitride (200) face of the XRD pattern as shown in Table 3.

[Example 3]

A ceramics sintered body was obtained in the same manner as in Example 1 except that no sintering auxiliary agent was used at all and the sintering temperature was set to 1650 캜. The physical properties of the resulting sintered ceramics are shown in Table 3.

[Example 4]

A ceramics sintered body was obtained in the same manner as in Example 2 except that no sintering auxiliary agent was used at all. The physical properties of the resulting sintered ceramics are shown in Table 3.

[Example 5]

A ceramics sintered body was obtained in the same manner as in Example 1 except that no sintering auxiliary agent was used at all and the sintering temperature was maintained at 1900 캜 for 5 minutes. The properties of the obtained sintered ceramics are shown in Table 3 below.

[Comparative Example 1]

The mixed powder in Example 1 was formed into a compact by a uniaxial molding (Riken Mini Press, product of RIKEN SEIKI), and the compact was placed in a gas pressure firing furnace (Hi-Multi: manufactured by Fuji Electric Industries Co., Ltd.) N ₂ , maintaining the sintering temperature at 1500 캜 for 60 minutes, and maintaining the sintering temperature at 1900 캜 for 60 minutes, to obtain a ceramics sintered body. The physical properties of the obtained sintered ceramics are shown in Table 3.

[Comparative Example 2]

The sintering aid in Example 2 was not used at all, and the mixed powder in Example 2 was formed into a compact by uniaxial molding (Riken Mini Press, product of RIKEN SEIKI), and the compact was placed in a gas pressure baking furnace (High Multi: Fuji Electric Industry Co., ), A ceramics sintered body was obtained in the same manner as in Example 2 except that the inside of the apparatus was filled with N ₂ of about 10 atm, the sintering temperature was maintained at 1500 캜 for 60 minutes, and maintained at 1900 캜 for 60 minutes . The physical properties of the resulting sintered ceramics are shown in Table 3.

For the sintered ceramics of the examples and comparative examples, the relationship between the true density and the thermal conductivity was plotted as shown in Table 4.

Claims (9)

As a method for producing a silicon nitride sintered body,
(S1) A silicon nitride powder having an oxygen content of 1.5% by mass or less is prepared,
(S2) The silicon nitride powder is charged into a sintering mold, and a pulsed direct current having a voltage of 1 V or more and 10 V or less and an output current of 500 A or more and 40,000 A or less is continuously applied to the grain gaps of the raw material powder while being pressurized to 70 MPa or more, And sintering the powder. The method according to claim 1,
A silicon nitride powder having an oxygen content of 0.9 mass% or less is prepared in the step (S1). 3. The method according to claim 1 or 2,
Wherein the silicon nitride powder has an average particle diameter (D ₅₀ ) of 0.8 탆 or less in the step (S 1). 4. The method according to any one of claims 1 to 3,
Wherein the silicon nitride concentration in the silicon nitride powder in the step (S1) is 200 ppm or less. 5. The method according to any one of claims 1 to 4,
Wherein in the step (S1), the silicon nitride powder contains 90% or more of crystallized? -Silicon nitride and / or crystallized? -Silicon nitride. 6. The method according to any one of claims 1 to 5,
In the step (S2), the sintering is performed at a temperature of 1650 DEG C or more and 1750 DEG C or less. 7. The method according to any one of claims 1 to 6,
Wherein the silicon nitride sintered body has a true density of 3.10 g / cm 3 or more and a half width of a peak of the? -Silicon nitride (200) plane of the XRD pattern is 0.154 or more and 0.160 or less. A silicon nitride sintered body formed by the manufacturing method according to any one of claims 1 to 7. A heat radiation substrate using the silicon nitride sintered body according to claim 8.

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