JP2002128569A - High thermal conductive silicon nitride ceramic and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon nitride sintered body which enables the densification and grain growth of a sintered body by a low temperature sintering of <=1900 deg.C, and has a high thermal conductivity of >=100 W/mK. SOLUTION: When a high thermal conductive silicon nitride sintered body is manufactured so that the densification and grain growth of a sintered body are enabled by low temperature sintering of <=1900 deg.C, the silicon nitride powder wherein the sintering agent which contains at least silicon nitride magnesium (MgSiN2) is added, is molded. Subsequently, sintering the silicon nitride powder at a temperature of <=1900 deg.C, the densely sintered body which has a high thermal conductivity of >=100 W/mK, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to superior characteristics high thermal conductivity silicon nitride ceramics and a manufacturing method thereof, and more particularly, by using the silicon nitride magnesium (MgSiN ₂₎ as a sintering aid The present invention relates to a method for producing a highly thermally conductive silicon nitride sintered body by enabling densification and grain growth at a relatively low temperature, and a product thereof. The present invention provides a high thermal conductive silicon nitride sintered body suitable for use as a mechanical component material such as a heat engine, a heat exchanger, and a heat pipe, and an electric insulating material such as a semiconductor substrate and a printed wiring board, and a method for producing the same. Things.

[0002]

2. Description of the Related Art In general, regarding a material system used as a structural member, when considering a heat radiation material as a structural member, the most commonly used metal material is subjected to cooling or the like under a condition exceeding 500 ° C. It is impossible to use without it. Furthermore, these metal materials are inferior in corrosion resistance and oxidation resistance as compared with ceramics. Furthermore, since it is a conductor, it is difficult to use it as an insulating substrate material requiring high heat dissipation such as a power device. on the other hand,
Ceramic materials such as aluminum nitride sintered bodies and silicon carbide sintered bodies have both been used as heat dissipating substrate materials because of their high insulating properties and high thermal conductivity. However, these high thermal conductive ceramics have low strength and toughness, and lack mechanical reliability, so that their use has been very limited.

[0003] As for silicon nitride-based materials, silicon nitride sintered bodies are generally known as excellent structural ceramic materials having both high strength and high toughness. Furthermore, silicon nitride crystals also have high thermal conductivity due to the similarity in crystal structure with silicon carbide and aluminum nitride. However, in a polycrystal, that is, a silicon nitride sintered body, 1
In order to develop a high thermal conductivity of 00 W / mK or more, sintering in a high-temperature, high-pressure nitrogen, or hot-press sintering and heat treatment are combined as exemplified in the following Examples 1) to 4). A complicated and very expensive process such as a method was required. In the following examples 3) and 4),
A sintered body having an oriented structure is produced by a method combining seed crystal addition and a molding method such as sheet molding, and a high thermal conductivity of 120 to 140 W / mK in the orientation direction of the particles has been achieved. However, these sintered bodies show remarkable anisotropy of thermal conductivity, and exhibit only about half the thermal conductivity in the direction perpendicular to the orientation direction in the direction of high thermal conductivity.

Example 1) Silicon nitride having an average particle size of 0.5 μm
0.5-4 mol% Y in powder_Two O_Three And Nd_Two O_Three Etc.
The molar mixture was added as a sintering aid,
Thermal conductivity of sintered body sintered for 4 hours under nitrogen pressure of 00 atm
Was 100 to 120 W / mK (Journal
of the American Ceramic S
ociety, vol. 79, no. 11, pp. 28
78-82 (1996)).

Example 2) Hot press sintering of a powder obtained by adding 5 wt% of Y ₂ O ₃ to a silicon nitride powder having a specific surface area of 5 m ² / g under a uniaxial pressure of 1800 ° C. and 40 MPa in nitrogen of 1 atm. Further, the thermal conductivity of the sample heat-treated at 1850 ° C. for 16 hours was 110 W / mK in the direction perpendicular to the pressing direction of the hot press (Journal of
the American Ceramic Soci
ety, vol. 82, No. 11, pp. 3105-
12 (1999)).

Example 3) 5% by volume of rod-like silicon nitride particles (short axis diameter 1 μm, long axis diameter 10 μm) as a seed crystal in silicon nitride powder having a specific surface area of 10 m ² / g and 5 as a sintering aid
The slurry obtained by mixing wt% of Y ₂ O ₃ and an organic solvent and a binder was subjected to a doctor blade method to obtain a slurry.
It is molded to a thickness of about 100 μm, laminated, degreased, and densified by hot pressing.
Heat treatment was performed at 850 ° C. for 24 hours to obtain a silicon nitride sintered body having an oriented structure (Japanese Patent No. 28882575 (patent by the present applicant)). This sintered body has a particle orientation of about 120.
Although it has a high thermal conductivity of W / mK, the thermal conductivity in the direction perpendicular to the orientation direction of the particles is about 70 W / mK.

Example 4) Silicon nitride powder having an average particle size of about 0.5 μm and 5 wt% of rod-like silicon nitride particles (short axis diameter 1 μm, long axis diameter 10 μm) as seed crystals, and 0.5 mol% as a sintering aid Y ₂ O ₃ and 0.5 mol% Nd ₂ O
_3. Further, the slurry obtained by mixing the organic solvent and the binder was used to a thickness of about 100 μm using a doctor blade method.
m, laminated and degreased, densified by hot pressing, and further heat-treated at 2200 ° C. for 4 hours in nitrogen at 300 atm to obtain a silicon nitride sintered body having an oriented structure (Japan Journal of the Ceramic Society of Japan, 104 volumes,
December issue, pp. 1171-73 (1996)). This sintered body has a high thermal conductivity of about 140 W / mK in the grain orientation direction, but has a thermal conductivity of about 70 W / mK in a direction perpendicular to the grain orientation direction.

[0008]

As described above, conventionally, high thermal conductive silicon nitride sintered bodies have been manufactured by a high-cost process of performing sintering at a high temperature under a high nitrogen pressure or performing heat treatment after hot pressing. I was This is because (1) densification with a small amount of a sintering aid to reduce the low heat conduction glass phase remaining after sintering, (2) causing grain growth, This is because it is necessary to reduce oxygen inside the particles, which is a factor inhibiting heat conduction. Under these circumstances, the present inventors have conducted intensive studies in view of the above-mentioned conventional technology with the aim of developing a method for producing a high thermal conductive silicon nitride ceramic without using the above-mentioned high-cost process. As a result,
It has been found that the intended purpose can be achieved by adopting a method of adding a sintering aid containing at least silicon magnesium nitride (MgSiN ₂ ) to silicon nitride powder,
The present invention has been completed. An object of the present invention is to develop a new sintering aid capable of densification and grain growth at a low temperature in order to easily and at low cost produce a silicon nitride sintered body having high thermal conductivity. Further, the present invention provides a new method for producing a high thermal conductive silicon nitride ceramic which enables densification and grain growth at a low temperature by using a sintering aid containing at least silicon magnesium nitride (MgSiN ₂ ). It is the purpose. Still another object of the present invention is to provide a high thermal conductive silicon nitride sintered body having a high thermal conductivity of 100 W / mK or more, which is obtained by the above-mentioned production method.

[0009]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) A method for producing a high thermal conductive silicon nitride sintered body by allowing a sintered body to be densified and grown by low-temperature sintering at 1900 ° C. or lower, wherein silicon nitride powder contains at least silicon magnesium nitride (MgSiN _2). ) Is added and molded, then sintered at a temperature of 1900 ° C. or less to obtain a dense sintered body having a high thermal conductivity of 100 W / mK or more. For producing a high thermal conductive silicon nitride sintered body. (2) 10 obtained by the production method described in (1) above.
A high thermal conductive silicon nitride sintered body having a high thermal conductivity of 0 W / mK or more. (3) A highly thermally conductive silicon nitride sintered body obtained by using silicon magnesium nitride (MgSiN ₂ ) as a sintering aid, obtained by the production method described in (1) above.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has long been known that the addition of magnesium oxide (MgO) as a sintering aid to silicon nitride is very effective in lowering the sintering temperature. However, when MgO is added as a Mg source, low-temperature sintering is possible but grain growth is slow, and the oxygen content in the grain boundary glass phase is increased. It is difficult to achieve high thermal conductivity because it hardly occurs. The present inventors have proposed, as a Mg source instead of MgO,
As a result of searching for a non-oxide, it was found that MgSiN ₂ was stable even in an atmospheric process such as mixing and molding, and that densification and grain growth were possible at a relatively low temperature.
That is, by adding a sintering aid containing at least silicon magnesium nitride (MgSiN ₂ ) powder to silicon nitride powder, 100 W / mK at a sintering temperature of 1900 ° C. or less.
We succeeded in obtaining a dense sintered body having the above high thermal conductivity.

According to the present invention, a high thermal conductive silicon nitride sintered body is provided.
First, at least to silicon nitride raw material powder
Also silicon magnesium nitride (MgSiN_Two ) Including
Add the amount of sintering aid. This silicon magnesium nitride
For example, magnesium silicide metal powder (Mg
_Two Si) is heated to about 1400 ° C in a nitrogen atmosphere to synthesize
(The Ceramic Society of Japan, 105
Volume, pp. 934-939, 1997).
A powder obtained by pulverization is used. Silicon nitride raw material is α
Type, β-type crystal system may be used,
It is desirable to use fine powder having an average particle size of 1 μm or less.
New As a sintering aid, at least silicon nitride magnet
Cium (MgSiN_Two ) Is important to use
It is important to use other commonly used sintering aids, such as
For example, Sc_Two O_Three , Y_Two O_Three , Nd_Two O_Three , Yb_TwoO_Three 
Rare earth oxides such as HfO_Two , CeO_Two , ZrO_Two Etc.
One or more oxides can be added. The above sintering aid
The amount of the agent added depends on the method of densification (normal pressure sintering, gas pressure sintering,
Hot press, etc.), but hinders high thermal conductivity
To minimize residual glass phase as a factor
Grain growth is necessary for thermal conduction, but grain growth after densification
Means that the smaller the residual glass phase, the faster
It is desirable to keep it to the minimum possible density.
Is preferably 2 to 10 mol% as a sintering aid.

Next, in mixing these raw materials,
An ordinary machine used for mixing or kneading the powder, such as a planetary mill, a pot mill, and a trommel, can be used. This mixing may be either a wet type or a dry type, but is desirably performed in a wet type. In the wet mixing, a solvent such as water, methanol, ethanol, and toluene is used, and it is preferable to use an organic solvent to suppress oxidation of silicon nitride. When an organic solvent is used, mixing can be performed efficiently by using a dispersant such as cationic cellulose and polycarboxylic acid.

The mixed powder obtained by drying the solvent from the slurry mixed by the above method is molded into a predetermined shape using a mold. In some cases, cold isostatic pressing (CIP) is performed after the die forming to increase the forming density. In addition, an appropriate amount of an organic binder such as polyvinyl butyral is added to the slurry mixed by the above method, and a sheet-shaped formed body is directly produced by a sheet forming method such as a doctor blade method or an extrusion method. Can also.

Next, the molded body is first calcined at a temperature of 600 to 1000 ° C. in a nitrogen atmosphere to remove organic components by heating.
Sinter for 1 to 24 hours at 0 ° C. and 1 to 10 atm nitrogen. In the present invention, by using the above specific sintering aid, it is possible to densify the sintered body only by heating in nitrogen, but if necessary, it is possible to employ a hot press treatment or the like as appropriate. is there. According to the present invention, the sintered body can be densified (at a relative density of 98% or more) and a microstructure having an average grain size of 1 μm or more can be developed by low-temperature sintering at 1900 ° C. or less.

[0015]

The inventors of the present invention have conducted basic studies on increasing the thermal conductivity of silicon nitride. As a result, the improvement of the thermal conductivity of the silicon nitride sintered body requires the introduction of impurity oxygen inside the silicon nitride particles constituting the sintered body. Was found to be significantly reduced, and sufficient grain growth was required to reduce oxygen inside the particles. That is, even in a silicon nitride raw material having a high purity, about 0.5 wt% of impurity oxygen is contained inside the silicon nitride particles. After densification at high temperature, the fine raw material powder particles grow into large particles by a solution reprecipitation reaction via the liquid phase, but at this time, impurity oxygen inside the particles is left in the glass phase, and the oxygen content of the particles is reduced. Redeposit as less silicon nitride. Therefore, in order to increase the thermal conductivity, it is important to generate a liquid phase having a low oxygen content in order to enhance the effect of trapping oxygen, and to cause sufficient grain growth so that the average particle diameter becomes twice or more. . In the present invention, at least silicon magnesium nitride (M
By adding a sintering aid containing gSiN ₂ ), Mg required for lowering the sintering temperature can be added as a constituent element of the liquid phase without increasing the oxygen content in the liquid phase.
Since it is added as a nitride, the nitrogen concentration in the liquid phase is increased, and grain growth is promoted. As a result, a reduction in the sintering temperature and a high thermal conductivity are achieved at the same time.

[0016]

Next, the present invention will be specifically described based on examples, but the present invention is not limited to the examples. Example (1) Production of silicon nitride sintered body Magnesium silicide (MgSi ₂ ) was placed in a nitrogen stream at 140 ° C.
By heating at 0 ° C. for 5 minutes, a magnesium silicon nitride (MgSiN ₂ ) powder was synthesized. Average particle size 0.5
0.5 μ% of a dispersant in μm β-silicon nitride powder,
5mol% silicon magnesium nitride powder and 2-5m
ol% of ytterbium oxide (Yb ₂ O ₃ )
Using methanol as a dispersion medium, planetary mill mixing was performed for 2 hours using a silicon nitride pot and a silicon nitride ball. After evaporating the methanol using an evaporator,
Calcination was performed at 00 ° C. to remove organic components. The obtained powder was formed into a pellet having a diameter of 20 mm and a thickness of 5 mm using a mold, and further subjected to a CIP treatment at a pressure of 5 ton / cm ² .
The compact was placed in a crucible made of boron nitride (BN) and sintered at 1900 ° C. for 2 to 24 hours in pressurized nitrogen at 10 atm.

(2) Characteristics of Sintered Silicon Nitride The surface of the sintered body was ground to produce a disk-shaped test piece having a thickness of about 2 mm, and the thermal conductivity was measured by a laser flash method. . Table 1 summarizes the density and thermal conductivity of the thus obtained sintered body.

Comparative Example In the above example, magnesium oxide (MgO) having an average particle diameter of 0.2 μm was used instead of MgSiN ₂ for ₂ to 5 m.
Table 1 also shows the characteristics of the silicon nitride sintered body produced in exactly the same manner as in the example except that ol% was added.

[0019]

[Table 1]

As is clear from Table 1, the silicon nitride sintered body obtained by the method of the present invention is densified to a relative density of 98% or more and has a high thermal conductivity of 100 W / mK or more. As a result of measuring the average particle diameter from the cut surface of the sintered body, M
While the average particle diameter was about 1 μm when gO was added, the sintered body of the present invention to which MgSiN ₂ was added was 1.2 to 1.2 μm.
It has an average particle diameter of 3.8 μm, indicating that the addition of MgSiN ₂ is effective in promoting the grain growth.

[0021]

As described in detail above, the present invention relates to a method of manufacturing a silicon nitride powder containing at least silicon magnesium nitride (MgSi).
The present invention relates to a method for producing a silicon nitride ceramic having a high thermal conductivity, characterized by adding a sintering aid containing N ₂ ), molding and then sintering the same at a temperature of 1900 ° C. or less. ) It enables the densification and grain growth of the sintered body by low-temperature sintering at 1900 ° C or less, and 2) has the special effect of obtaining a silicon nitride sintered body with a high thermal conductivity of 100 W / ml or more. Can be

Claims (3)

[Claims] 1. A method for producing a sintered body having high thermal conductivity by enabling sintering at a low temperature of 1900 ° C. or lower to enable densification and grain growth of the sintered body. A sintering aid containing MgSiN ₂ ) is added, molded, and then sintered at a temperature of 1900 ° C. or less to obtain a dense sintered body having a high thermal conductivity of 100 W / mK or more. A method for producing a high thermal conductive silicon nitride sintered body, characterized in that: 2. A high thermal conductive silicon nitride sintered body having a high thermal conductivity of 100 W / mK or more, obtained by the production method according to claim 1. 3. A highly thermally conductive silicon nitride sintered body obtained by using the silicon magnesium nitride (MgSiN ₂ ) as a sintering aid, obtained by the production method according to claim 1.