JP2002293642A - Silicon nitride-based sintered compact having high thermal conductivity, method of producing the same, and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride-based sintered compact having a high strength and a high thermal conductivity. SOLUTION: The silicon nitride-based sintered compact is characterized in that the ratio of the area occupied by silicon nitride particles having minor axes of <=1.0 μm and aspect ratios of <=10 to the whole surface area of the whole silicon nitride particles is 50 to 100%, the oxygen content in the silicon nitride particles is <=0.1%, the amount of the sintering aid is <=0.05%, the thermal conductivity at room temperature is >=90 W/m.K and the three-point bending strength at room temperature is >=600 MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member for electronic parts such as a semiconductor substrate and a heat sink for a heating element, or a structural member such as a member for general machinery, a member for molten metal, or a member for a heat engine. The present invention relates to a high-strength, high-thermal-conductivity silicon nitride-based sintered body, a method for producing the same, and a circuit board formed using the silicon nitride-based sintered body.

[0002]

2. Description of the Related Art Conventionally, silicon nitride sintered bodies have excellent heat resistance, low thermal expansion, thermal shock resistance, and corrosion resistance to metals, in addition to mechanical properties such as high-temperature strength characteristics and wear resistance. It is used for various structural members such as members for gas turbines, members for engines, mechanical members for steelmaking, and melt-resistant members of molten metal. In addition, it is used as an electrical insulating material by utilizing high insulating properties.

[0003] In recent years, with the development of semiconductor elements having a large amount of heat, such as high-frequency transistors and power ICs, the demand for ceramic substrates having a high thermal conductivity to obtain good heat dissipation characteristics in addition to electrical insulation has increased. ing. As such a ceramic substrate, an aluminum nitride substrate is used, but there is a problem that mechanical strength and fracture toughness are low, and cracks are generated by fastening in a process of assembling the substrate unit. Further, in a circuit board in which a Si semiconductor element is mounted on an aluminum nitride substrate, since the thermal expansion difference between Si and the aluminum nitride substrate is large, cracks and cracks occur in the aluminum nitride substrate due to thermal cycling, and the mounting reliability is reduced. There's a problem.

Accordingly, a substrate made of a silicon nitride sintered body having high thermal conductivity, which is inferior in thermal conductivity to an aluminum nitride substrate but has a coefficient of thermal expansion close to that of Si and is excellent in mechanical strength, fracture toughness and thermal fatigue resistance, has attracted attention. And various proposals have been made.

[0005] For example, Japanese Patent Application Laid-Open No. 4-175268 discloses that silicon and aluminum are substantially composed of silicon nitride, where both Al and oxygen contained as impurities are not more than 3.5 wt% and the density is 3.15 Mg / m ³ ( A silicon nitride sintered body having a thermal conductivity of 3.15 g / cm ³ or more and 40 W / (m · K) or more is described.

[0006] Japanese Patent Application Laid-Open No. 9-30866 discloses that
85 to 99% by weight of β-type silicon nitride grains and the remainder are composed of an oxide or oxynitride grain boundary phase.
g, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, G
0.5 to 10% by weight of at least one element selected from d, Dy, Ho, Er and Yb, the content of Al element in the grain boundary phase is 1% by weight or less, and the porosity is 5
% Or less and a minor axis diameter of 5
A silicon nitride based sintered body in which the ratio of those having μm or more is 10 to 60% by volume is described.

[0007] Japanese Ceramics Association 1996 Annual Meeting Proceedings 1G11, 1G12, and
Japanese Patent Application Laid-Open No. 194842 discloses a method in which columnar silicon nitride particles or whiskers are previously added to a raw material powder, and a molded body in which the particles are two-dimensionally oriented is obtained using a doctor blade method or an extrusion molding method. There is described a silicon nitride sintered body in which anisotropy is given to heat conduction by firing to increase the heat conductivity in a specific direction.

Further, Japanese Patent Application Laid-Open No. 2001-19557 discloses a method for improving the thermal conductivity of silicon nitride to 100 W / (m · K) or more by containing 300 ppm or less of Al and 1 wt% or less of oxygen. Using silicon nitride raw material powder having a conversion ratio of 70 wt% or less, silicon nitride particles having a minor axis diameter of 2 μm or more are mixed so that the total content of oxygen, Al, Ca, and Fe is 1500 ppm or less. A method for producing a silicon nitride sintered body characterized by sintering while growing is described.

[0009]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 4-17 / 1994
In Japanese Patent No. 5268, a thermal conductivity of 40 W / (m · K) or more is obtained. However, a material having higher thermal conductivity and excellent mechanical strength is desired. Also, JP-A-9-30
According to the method described in Japanese Patent Application Laid-Open No. 866-866 and Japanese Patent Application Laid-Open No. 10-194842, a seed crystal or whisker serving as a growth nucleus is added in advance to obtain large columnar particles in a silicon nitride sintered body. And 10.1 MPa (1
Sintering in a nitrogen atmosphere of at least 100 atm) is indispensable. Therefore, special high-temperature and high-pressure equipment such as hot press or HIP is required, which leads to an increase in cost. In addition, since a molding process for obtaining a molded body in which silicon nitride particles are oriented is complicated, there is a problem that productivity is significantly reduced.

In the method described in Japanese Patent Application Laid-Open No. 2001-19557, oxygen, Al, Ca and Fe as impurities in silicon nitride particles in the obtained sintered body are used.
By reducing the amount, a silicon nitride sintered body having a high thermal conductivity of 100 W / (m · K) or more can be obtained. Furthermore, in the invention described in the publication, the silicon nitride powder has an α conversion ratio of X% and a particle size distribution of silicon nitride particles having a particle diameter of 2.5 times or more the cumulative average diameter in the silicon nitride powder. Assuming that the proportion in the powder is Y volume%, by having a particle size distribution satisfying 0 ≦ X ≦ 70, Y ≧ 0, and Y ≧ −0.05X + 1, the grain growth can be selectively performed in the sintering process. In this case, a high thermal conductivity of 100 W / (m · K) or more is achieved by constructing a structure composed of fine particles and coarse particles in the sintered body.

[0011] However, according to the examples described in the publication, a high thermal conductivity of 100 W / (m · K) or more is obtained, but since the coarse particles are generated in the sintered body, the strength is 600 MPa. And it becomes difficult to maintain high strength. Therefore, when the silicon nitride sintered body of the present invention is used as an insulating substrate, when assembling a semiconductor module, or when used under conditions in which thermal stress is repeatedly applied, mounting reliability such as cracking of the substrate is reduced. There is a disadvantage that it is inferior. Further, ZrO ₂ having an effect of reducing the amount of oxygen in the silicon nitride particles is 1 wt% to 3 wt%.
However, when a compact obtained by adding ZrO ₂ to a mixed powder composed of silicon nitride and a sintering aid is fired in a nitrogen atmosphere, Since the conductive ZrN precipitates between the silicon nitride particles and the grain boundary phase, a problem occurs in that the electrical insulation is significantly reduced,
The silicon nitride sintered body of the present invention cannot be used as a substrate for a semiconductor module.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object the purpose of high-cost and high-temperature sintering at 2000 ° C. or more and 10.1 MPa (100 atm) or more. It is an object of the present invention to provide a high heat conductive silicon nitride sintered body which does not require a method, has excellent mechanical strength, does not have anisotropy in the direction of heat conduction, and has an improved heat conductivity as compared with the prior art.

Another object of the present invention is to reduce the amount of a sintering aid and to control the sintering atmosphere through sintering by using a filler to define the particle size and shape in the sintered body. By reducing the amount of oxygen dissolved in the silicon nitride particles in the sintered body and the amount of sintering aid components, high density,
An object of the present invention is to provide a silicon nitride sintered body having high thermal conductivity and high strength and a method for producing the same. It is still another object of the present invention to provide a circuit board having good heat dissipation properties constituted by using the silicon nitride sintered body having high strength and high thermal conductivity.

[0014]

Means for Solving the Problems In order to achieve the above object, the present inventor has reduced the grain boundary phase which causes a decrease in thermal conductivity in a silicon nitride based sintered body, and further reduced the silicon nitride based sintered body. By defining the shape of the minor axis diameter and aspect ratio of the silicon nitride particles in the silicon nitride particles and reducing the solid solution amount of oxygen and the auxiliary component in the silicon nitride particles, 600MP
The present invention has been found that a high strength of at least a can be maintained and a thermal conductivity of at least 90 W / (m · K) can be stably obtained.

That is, in the silicon nitride sintered body of the present invention, the area ratio of silicon nitride particles having a minor axis diameter of 1.0 μm or less and an aspect ratio of 10 or less is determined in the silicon nitride sintered body. 50 to 10 of the area of all silicon nitride particles
It is a high thermal conductive silicon nitride based sintered material of 0%. Also,
In the silicon nitride sintered body of the present invention, the oxygen content in the silicon nitride particles is 0.1 wt% or less, and the sintering aid component content is 0.0
It is a silicon nitride based sintered body of 5 wt% or less.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A silicon nitride sintered body has a close relationship between its microstructure and thermal conductivity and strength, and the thermal conductivity increases with an increase in silicon nitride particles in the sintered body. On the other hand, as the size of the particles increases, the strength decreases because the size acting as the starting point of fracture increases. Therefore, in order to obtain a silicon nitride sintered body having high strength and high thermal conductivity, the size of the silicon nitride particles is made as small as possible,
It is important to improve the thermal conductivity of the silicon nitride particles themselves, which act as the main path of heat conduction.

When the amount of the sintering aid is reduced, the ratio of the grain boundary phase in the sintered body is reduced, and the strength is deteriorated accordingly. When the ratio of the grain boundary phase is small, the strength of the sintered body is largely controlled by the size and shape of the silicon nitride particles,
If the proportion of particles having a minor axis diameter of 1 μm or less is less than 50%, or if the aspect ratio of the particles exceeds 10, stress concentration will occur on these coarse particles, which will act as a fracture source, resulting in remarkable strength. Causes deterioration. Therefore, for a sintered body in which the amount of the sintering aid is 1.0 wt% or less, while maintaining a high strength of 600 MPa or more,
In order to obtain a thermal conductivity of 90 W / (m · K) or more, the short axis diameter is 1.0 μm or less and the aspect ratio is 10
It is indispensable that the area ratio of the following silicon nitride particles be 50 to 100% of the area of all the silicon nitride particles in the silicon nitride sintered body.

The silicon nitride-based sintered body is composed of a silicon nitride particle phase and its surrounding grain boundary phase. Since oxides are mainly added as a sintering aid, most of them are present as grain boundary phase components. I do. In order to achieve a thermal conductivity of at least 70 W / (m · K), it is important to reduce the amount of a grain boundary phase having a lower thermal conductivity than silicon nitride particles of the main phase. It is necessary to reduce the amount of the sintering aid component by minimizing the amount of the additive added to obtain a sintered body having a relative density of 85% or more. Here, when the sintering aid is based on MgO, its sinterability is superior to that when another oxide is used, so that the amount of the sintering aid can be further reduced.
In addition, even when silicon nitride powder containing a small amount of oxygen is used as a raw material, the amount of the grain boundary phase component can be reduced, thereby reducing the amount of the grain boundary phase and achieving high thermal conductivity of the sintered body. Is done. When a silicon nitride powder having a low oxygen content is used, the amount of SiO ₂ generated in the firing process is reduced and the sintering becomes difficult. However, by adding MgO to the sintering aid, a dense sintered body can be obtained. Obtainable. Therefore, it is possible to reduce the amount of the grain boundary phase, which is a low thermal conductive phase, and to significantly improve the thermal conductivity.

The oxygen contained in the silicon nitride particles in the sintered body causes scattering of phonon, which is a heat conduction medium, in this portion, and the thermal conductivity of the silicon nitride particles themselves, and furthermore, the thermal conductivity of the silicon nitride sintered body. Lower. Therefore, it is desirable that the amount of oxygen contained in the particles is as small as possible. Specifically, 90 W / (m
・ K) To obtain a sintered body having a thermal conductivity of 0.1 or more, 0.1
In order to obtain a sintered body having a thermal conductivity of at most 120 wt / (m · K), it is essential that the content be at most 0.05 wt%.

The sintering aid component contained in the silicon nitride particles in the sintered body also causes the scattering of phonon, which is a heat transfer medium, in this portion, similarly to the above-mentioned oxygen, and the silicon nitride particles themselves,
As a result, the thermal conductivity of the silicon nitride sintered body is reduced.
The amount of the sintering aid component that forms a solid solution in the silicon nitride particles differs for each component, and La, Gd, Y, etc., having a large ionic radius,
Hard to dissolve in the particles. On the other hand, Mg having a small ionic radius tends to form a solid solution in the particles. Therefore, when MgO is selected as the sintering aid, the amount of the grain boundary phase can be reduced while maintaining the densification. However, the amount of Mg dissolved in the particles increases, and as a result, it is difficult to achieve high thermal conductivity.

Therefore, it is desirable that the amount of the sintering aid component contained in the particles is as small as possible. The oxide selected as the sintering aid has a low solid solution in the particles and a small amount of addition. It is important to facilitate sintering. Specifically, in order to obtain a sintered body having a thermal conductivity of 90 W / (m · K) or more, the total amount of the sintering aid component is set to 1.0 wt% or less, and the ratio of MgO to the rare earth oxide ( MgO / RexO
y) is 1 or less, and the amount of Mg component in the particles is 0.1 wt.
% Or less, and other rare earth components are desirably 0.01 wt% or less. Furthermore, in order to obtain a sintered body having a thermal conductivity of 120 W / (m · K) or more, the content of Mg component in the particles is 0.05 wt% or less, and the content of other rare earth components is 0.01 wt%.
It is essential that:

The above-mentioned La, Gd, and Y are useful as sintering aids and are effective for densification of the silicon nitride raw material powder. Since these elements have low solid solubility in silicon nitride particles, which are elements constituting the silicon nitride sintered body, the thermal conductivity of the silicon nitride particles, and thus the silicon nitride sintered body, can be kept at a high level. .

Like La, Gd, and Y, the solid solubility in silicon nitride particles is small, and useful elements as sintering aids include Ce, Nd, Pm, Sm, Eu, Dy, Ho, Er, Tm,
At least one rare earth element selected from the group of Yb and Lu can be used.

The method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention is characterized in that the silicon nitride powder contains magnesium (Mg) and yttrium and / or a lanthanoid element.
After forming a raw material powder containing a total of 1.0% by weight or less of oxides of at least one kind, a temperature of 1800 ° C. to 2000 ° C., a nitrogen pressure of 0.9 MPa to 10 MPa, silicon nitride, boron nitride and It is characterized by using a mixed powder of magnesium oxide (MgO) and firing using a boron nitride crucible in a firing container. Here, silicon nitride, boron nitride and magnesium oxide (MgO) are indispensable as the filler component, but one or more oxide powders selected as the sintering aid components described above are used as the filler component. May be added.

Magnesium (M) added as a sintering aid
g) and the oxide of yttrium and / or lanthanoid group element is fired at 1.0 wt% or less, it is difficult to obtain a dense sintered body having a relative density exceeding 90 wt% by the conventional firing method. there were. However, according to the production method of the present invention, the densification becomes possible by adjusting the firing atmosphere. Specifically, when a mixed powder composed of silicon nitride, boron nitride, and magnesium oxide is used as a filling powder for adjusting the firing atmosphere, the main component Si ₃ N ₄ component is reduced during firing (1) Si The decomposition of the Si ₃ N ₄ component itself due to a reaction such as ₃ N ₄ (s) + 3SiO ₂ (L) → SiO (g) + 2N ₂ (g) can be suppressed.
Furthermore, in addition to this, the MgO component present in the flour is
Since the vapor pressure is high, it is easily vaporized in the firing process, is taken into the molded body, acts as an auxiliary component, and promotes the densification of the sintered body. That is, a dense sintered body can be obtained by a combined effect of suppressing the decomposition of the main phase and increasing the amount of the sintering aid component.
Here, when a crucible made of carbon (C) is used for the firing vessel, CO gas is generated in the crucible. (2) Si ₃ N ₄ (s) + CO (g) → 2SiC (s) + SiO (g) + 1 / 2O ₂ (g) + 2N ₂
The reaction (g) occurs on the surface of the sintered body, and the hindrance of densification and the precipitation of SiC on the surface of the sintered body cause a problem that the color tone is blackened. Therefore, in order to eliminate these adverse factors, it is desirable to use a firing container made of boron nitride. (S), (L) and (g) in the above reaction formulas (1) and (2) indicate a solid phase, a liquid phase and a gas phase, respectively.

From the viewpoint of grain growth, the MgO component present in the packing promotes uniform grain growth of silicon nitride particles. This is because the amount of liquid phase generated during the firing process can be minimized by reducing the amount of the sintering aid, and the behavior of abnormal grain growth during the grain growth process is suppressed, and fine particles are uniformly dispersed. It comes to have the microstructure which was made. In addition, when comparing the case where MgO is added in advance at the time of compounding the raw material powder and firing and the case where sintering is performed using a packing powder composed of a mixed powder of silicon nitride, boron nitride and magnesium oxide, the latter has low thermal conductivity. Although the phases have the same grain boundary phase amount, the Mg component which forms a solid solution in the silicon nitride particles can be reduced, and this effect can improve the thermal conductivity.

In the present invention, if the sintering temperature is lower than 1800 ° C., the densification is not promoted, and the density is reduced, whereby the strength is deteriorated. On the other hand, when the temperature exceeds 2000 ° C., the firing container and the heat insulating material are severely deteriorated, which causes a problem in productivity. If the nitrogen pressure is less than 0.5 MPa, the silicon nitride itself decomposes during firing, resulting in a decrease in the density of the sintered body, resulting in a decrease in strength. Further, when the pressure exceeds 10 MPa, the capacity inside the furnace is limited because of the high-pressure vessel, and the loading capacity of the sintered product in the firing furnace is limited. Occurs.
Therefore, the method for producing a silicon nitride-based sintered body of the present invention comprises a temperature of 1800 ° C. to 2000 ° C. and a nitrogen pressure of 0.5 MPa.
-10 MPa, silicon nitride in the filling for adjusting the firing atmosphere,
It is desirable to perform calcination using a mixed powder of boron nitride and magnesium oxide.

The silicon nitride sintered body produced by the above method has a thermal conductivity at room temperature of 90 W / (m · K) or more.
The three-point bending strength at room temperature is 600 MPa or more,
A sintered body with high strength and high thermal conductivity.

The substrate made of the silicon nitride sintered body of the present invention utilizes various characteristics such as a circuit board for a power semiconductor or a circuit board for a multi-chip module by utilizing the characteristics of high strength, high toughness and high thermal conductivity. It is suitable for electronic components such as a substrate, a heat transfer plate for a Peltier element, or a heat sink for various heating elements.

When the silicon nitride sintered body of the present invention is used as a circuit board for a semiconductor device, the occurrence of cracks in the substrate when subjected to repeated thermal cycles accompanying the operation of the semiconductor device is suppressed, and the thermal shock resistance is reduced. Properties and heat cycle resistance are remarkably improved, resulting in excellent reliability. Also,
Even when a semiconductor element for high output and high integration is mounted, deterioration of thermal resistance characteristics is small and excellent heat radiation characteristics are exhibited. In addition, the excellent mechanical properties allow not only the function as the original substrate material but also the structure itself to serve as a structural member, so that the structure of the substrate unit itself can be simplified.

Further, the silicon nitride sintered body of the present invention can be widely used for materials requiring heat resistance properties such as thermal shock and thermal fatigue, in addition to the above-mentioned electronic component members. Structural members include various heat exchanger parts and heat engine parts, heater tubes used in the field of melting metals such as aluminum and zinc, Stokes, die-cast sleeves, propellers for molten metal agitation, ladles, thermocouple protection tubes, etc. Applicable to Further, by applying the present invention to a sink roll, a support roll, a bearing, a shaft, or the like used in a hot-dip metal plating line for aluminum, zinc, or the like, a member having excellent crack resistance against rapid heating and cooling can be obtained. Also,
In the field of steel or non-ferrous processing, if it is used for rolling rolls, squeeze rolls, guide rollers, drawing dies, tool tips, etc., it has good heat dissipation properties when it comes into contact with the workpiece, so it can withstand heat fatigue and heat resistance. The impact resistance can be improved, thereby reducing abrasion and making it less likely to cause thermal stress cracking.

Further, the silicon nitride sintered body of the present invention
It can also be applied to sputter target members. For example, it is suitable for forming an electric insulating film used for an MR head, a GMR head, or a TMR head of a magnetic recording device, and for forming a wear-resistant film used for a thermal head of a thermal transfer printer. The film obtained by sputtering has inherently high thermal conductivity, a sufficiently high sputter rate, and a high electric breakdown voltage of the film.
For this reason, the electrically insulating coating for the MR head, GMR head, or TMR head formed with this sputter target has high heat conduction and high withstand voltage characteristics.
It is possible to increase the heat generation density of the element and reduce the thickness of the insulating film. In addition, the wear-resistant coating for a thermal head formed with this sputter target has not only good wear resistance due to the inherent characteristics of silicon nitride but also high thermal conductivity, so that thermal resistance can be reduced. Can be enhanced.

[0033]

Embodiments of the present invention will be described below. The present invention is not limited by the embodiments described below.

Example 1 Oxygen content is 0.3 to 1.5
wt.% silicon nitride (Si ₃ N) having an average particle size of 0.5 μm.
₄ ) Magnesium oxide (MgO) powder having an average particle diameter of 0.2 μm as a sintering aid, and an average particle diameter of 0.2 to 2.
A predetermined amount of one or two kinds of sintering aid powders selected from 0 μm rare earth oxide powders was added, an appropriate amount of a dispersant was added, and the mixture was ground and mixed in ethanol. Then, after vacuum drying, the mixture was granulated through a sieve with an opening of 150 μm, and was pressed with a press machine to have a diameter of 20 mm × a thickness of 10 mm and a diameter of 100 m
A disk-shaped molded body having a size of mx 15 mm was obtained by CIP molding under a pressure of 3 tons. Next, these compacts were inserted into a firing container made of boron nitride (BN), and
It was calcined for 5 hours in a nitrogen gas atmosphere at 0 ° C. and 9 atm. The packing powder for the firing atmosphere includes the above-mentioned silicon nitride powder: 50 parts by weight, boron nitride (BN) powder: 25 parts by weight, and Mg
O powder: 10 parts by weight of a mixed powder was used.

From the obtained silicon nitride sintered body, a diameter of 1
A test piece for measuring thermal conductivity and density of 0 mm × thickness 3 mm and a three-point bending test piece of 3 mm × 4 mm × 40 mm in length were collected. The density was determined from the results of dimensional measurement and weight measurement using a micrometer. The thermal conductivity was calculated by measuring the specific heat and the thermal diffusivity at room temperature by a laser flash method. The three-point bending strength is JIS R1 at room temperature.
The measurement was performed according to 606.

The evaluation of the minor axis diameter and the aspect ratio of the silicon nitride particles was carried out by using a scanning electron microscope (FE-SEM manufactured by Hitachi, Ltd.) for a microstructure obtained by mirror-polishing the sintered body and performing plasma etching using CF ₄ gas. S4500) direct observation magnification × 2000 times, observation visual field 200 μm ×
The minimum diameter and the maximum diameter were measured by an image analyzer using particles in 500 μm as evaluation targets. The particle diameter was determined from the minimum diameter, and the aspect ratio was determined from the calculation of the maximum diameter / minimum diameter. The area% of particles having a minor axis diameter of 1.0 μm or less was also determined by image analysis. FIG. 1 shows the microstructure of the silicon nitride sintered body according to the present invention.

With respect to the evaluation of the solid solution component in the silicon nitride particles, the silicon nitride sintered body was crushed in a grinding mortar, and the ground powder was sieved with a sieve having an opening of 100 μm.
The grain boundary phase was dissolved by a known method described in the Journal of the American Ceramics Society, July 1994, pp. 1857-1862, and only silicon nitride particles were extracted and dried. Oxygen analysis of the silicon nitride particles obtained by the above operation was performed using a nitrogen / oxygen simultaneous analyzer (LECO TC
436). The sintering aid component is HF + HN
The silicon nitride particles were dissolved using an O ₃ solution and H ₂ SO ₄ and evaluated by ICP analysis.

Tables 1 and 2 show the amounts of sintering aids, firing conditions and measurement results according to this example. The sample N
o. Sample Nos. 1 to 12 are examples of the present invention. 21-31
Is a comparative example. In addition, in the description items of the type of flour in Table 1,
SN-BN-MgO is a mixed powder of 50 parts by weight of silicon nitride powder, 25% by weight of boron nitride (BN) powder and 10 parts by weight of MgO powder, and SN-BN is 50 parts by weight of silicon nitride powder. , Boron nitride (BN) powder: represents a mixed powder of 25 parts by weight.

[0039]

[Table 1]

[0040]

[Table 2]

Sample Nos. According to the examples of the present invention shown in Tables 1 and 2 were used. From the results of 1 to 12, the silicon nitride particles in which the minor axis diameter of the silicon nitride particles is 1.0 μm or less are 50 to 10 with respect to the area of all the silicon nitride particles in the silicon nitride sintered body.
0 area%, and the aspect ratio of the silicon nitride particles having a minor axis diameter of 1.0 μm or less is 10 or less, and the oxygen content in the particles is 0.1 wt% or less and the sintering aid component amount Is 0.05 wt% or less, the three-point bending strength at room temperature is 600 MPa or more, the thermal conductivity at room temperature is 90 W / (m · K) or more,
A silicon nitride sintered body having both high strength and excellent heat dissipation was obtained. In addition, No. In No. 1, oxide powder as a sintering aid component was not added in advance, but by adding MgO powder to the filler component, the atmosphere during firing could be controlled and a dense sintered body was obtained. In addition, No. 2 is that the oxide powder as a sintering aid component is only MgO,
Further, by adding Y ₂ O ₃ powder, the atmosphere at the time of firing could be controlled, so that a dense sintered body was obtained, and a high strength and high heat conductive material was obtained. Therefore, the thermal conductivity of the prior art 1
Compared to a level of not less than 00 W / (m · K) and a bending strength of 400 MPa or more, while maintaining a high bending strength of 600 MPa or more, the thermal conductivity could be increased.

On the other hand, Comparative Sample No. 21-3
From the results of No. 1, the following findings were obtained. In No. 21 and No. 22, the compounding amount of the sintering aid exceeded 1.0 wt%, and the thermal conductivity of the silicon nitride sintered body was 90 W / (m ·
K). In addition, No. 23 and No. 2
No. 4, the ratio of the silicon nitride particles having a minor axis diameter of 1.0 μm or less was less than 50% to 40%, and the strength was 5%.
It dropped to 20 MPa. Silicon nitride particles having a minor axis diameter of 1.0 μm or less have an aspect ratio of more than 10 and a strength of 5
It dropped to 50 MPa. In addition, No. In No. 24, silicon nitride having an oxygen content of 2.0 wt% was used as a raw material powder.

In the case of No. 25, the oxygen content in the silicon nitride particles exceeded 0.1 wt%.
Further, since the component amount of the sintering aid exceeded 0.05 wt%, the thermal conductivity was 75 W / (m · K) and 5 W / (m · K), respectively.
It decreased to 5 W / (m · K). In Nos. 27 and 28, the amount of the auxiliary component in the silicon nitride particles was 0.1%.
It becomes more than 05 wt%, and the thermal conductivity is 70 W /
(MK) and 80 W / (mK). In addition, No. 25-No. 28, the oxygen content is 2.0 wt.
% Silicon nitride was used as a raw material powder.

In Nos. 29 and 30, the relative densities of the sintered bodies were 93.0% and 92.0%, respectively.
%, And accordingly, the respective strengths decrease to 58%
It became 0 MPa and 490 MPa. No. 3
In No. 1, the grain growth of the silicon nitride particles in the sintered body was suppressed, and accordingly, the thermal conductivity was reduced to 60 W / (m · K).

Example 2 Oxygen content is 1.0 wt%
Then, a magnesium oxide (MgO) powder having an average particle diameter of 0.2 μm and a Y ₂ O ₃ powder having an average particle diameter of 0.5 μm were added to a silicon nitride (Si 3 N 4) powder having an average particle diameter of 0.5 μm as a sintering aid. Mixed powders each containing 0.4 wt% as a sintering aid were prepared. Next, 2w of an amine-based dispersant was added.
The prepared mixed powder and a silicon nitride ball as a grinding medium were put into a resin pot of a ball mill filled with a toluene / butanol solution added with t%, and wet-mixed for 48 hours. Next, 15 parts by weight of a polyvinyl-based organic binder and 5 parts by weight of a plasticizer (dimethyl phthalate) were added to 100 parts by weight of the mixed powder in the pot, and then wet-mixed for 48 hours to obtain a slurry for forming a sheet. I got After adjusting the molding slurry, a green sheet was formed by a doctor blade method. Next, the formed green sheet was heated in air at 400 to 600 ° C. for 2 to 5 hours to add in advance and sufficiently degrease (remove) the organic binder component. Next, the degreased body is 0.9 MPa
In a nitrogen atmosphere of (9 atm), baking is performed at 1950 ° C. × 5 hours, and in order to further impart high thermal conductivity, baking is performed at 1950 ° C. × 20 hours in the same nitrogen atmosphere, and then cooled to room temperature. Then, the obtained silicon nitride-based sintered body sheet was machined to a length of 50 mm × width of 50 mm × thickness of 0.1 mm.
A 6 mm substrate for a semiconductor device was manufactured. The substrate surface properties were adjusted to Ra = 10 μm by dry sandblasting using # 400 alumina abrasive grains.

Using this silicon nitride sintered body substrate,
The circuit board shown in FIG. 2 was manufactured. In FIG. 2, the circuit board 1 is 50 mm long × 50 mm wide × 0.6 m thick.
A circuit board 3 made of copper is provided on a surface of a substrate 2 made of a silicon nitride sintered body having an m dimension, and a copper plate 4 is joined to a back surface of the substrate 2 with a brazing material 5. The substrates made of the silicon nitride sintered body used herein were the same as those of Tables 1 and 2 8 with a thermal conductivity of 108 W / (m · K) and a bending strength of 920 MPa.

The circuit board 1 was subjected to three-point bending strength evaluation and heat cycle test. As a result, the bending strength is as large as 600 MPa or more, and the frequency of occurrence of cracks caused by tightening cracks in the mounting process of the circuit board 1 and thermal stress in the soldering process is almost not observed, and the semiconductor device using the circuit board 1 It has been proved that the production yield can be greatly improved. In addition, the heat cycle test was performed by repeating a heating / cooling cycle in which cooling at −40 ° C. for 20 minutes, holding at room temperature for 10 minutes, and heating at 180 ° C. for 20 minutes were one cycle, and this was repeatedly applied. The number of cycles until cracks and the like occurred in the substrate portion was measured. As a result, even after 1000 cycles, there was no cracking of the silicon nitride-based sintered body substrate 2 or peeling of the copper circuit board 3 and it was confirmed that both the durability and the reliability were excellent. Also, even after 1000 cycles, the withstand voltage characteristics did not decrease.

[0048]

As described above, the silicon nitride sintered body of the present invention has a high thermal conductivity in addition to its inherent high strength / high toughness. Cracks are less likely to occur in the substrate due to repeated thermal cycles associated with the operation of the element, and the thermal shock resistance and the thermal cycle resistance can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a view showing an SEM observation image of a silicon nitride sintered body of an example of the present invention.

FIG. 2 is a sectional view showing a main part of a circuit board using the circuit board made of a silicon nitride sintered body of the example of the present invention.

[Explanation of symbols]

1: circuit board, 2: board, 3: copper circuit board, 4:
Copper plate,

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Claims (5)

[Claims] 1. An area ratio of silicon nitride particles having a minor axis diameter of 1.0 μm or less and an aspect ratio of 10 or less is 50 to 100 of an area of all silicon nitride particles in a silicon nitride sintered body. % Silicon nitride-based sintered body. 2. The amount of oxygen in the silicon nitride particles is 0.1 wt.
The silicon nitride sintered body according to claim 1, wherein the sintering aid component amount is 0.05 wt% or less. 3. The thermal conductivity at room temperature is 90 W / (m ·
The high thermal conductive silicon nitride sintered body according to claim 1 or 2, wherein the three-point bending strength at room temperature is at least 600 MPa. 4. Magnesium (Mg) is added to silicon nitride powder.
After forming a raw material powder to which a total of 1.0% by weight or less of one or more oxides of yttrium and / or lanthanoid group elements are added, the temperature is 1800 ° C. to 2000 ° C., the nitrogen pressure is 0.5 MPa to 10 MPa, and the firing atmosphere is adjusted. And baking a mixed powder of silicon nitride, boron nitride, and magnesium oxide as a filling material for the sintered body. 5. A circuit board comprising the high thermal conductive silicon nitride sintered body according to claim 1.