JP6909120B2 - Silicon Nitride Sintered Substrate, Electronic Equipment, and Silicon Nitride Sintered Substrate Manufacturing Method - Google Patents

Description

The present invention relates to a silicon nitride sintered body substrate, an electronic device provided with the silicon nitride sintered body substrate, and a method for manufacturing the silicon nitride sintered body substrate.

In recent years, the heat generation density of power modules has been increasing with the increase in density and output of electronic devices and semiconductor devices. An increase in the temperature of the power module causes a malfunction of the element or a crack of the insulating circuit board. Therefore, ceramic substrates such as alumina and aluminum nitride, which are materials having relatively high thermal conductivity, have been used for the insulating circuit board. However, alumina and aluminum nitride have a drawback of low mechanical strength. Therefore, thick copper, which is strongly subjected to thermal stress, cannot be directly bonded to the ceramic substrate, which has restricted the structure of the power module. Specifically, since it is necessary to solder-bond a heat sink made of copper or aluminum to the insulating circuit board, it is a problem that the power module becomes large. _{Therefore, silicon nitride (Si 3} N ₄ ) material is attracting attention as an insulating circuit board. Since the silicon nitride sintered body has about twice as high strength and fracture toughness as the alumina and aluminum nitride sintered bodies, it is possible to directly bond thick copper to the insulating circuit board, which makes it possible to reduce the size of the module. To contribute.

For example, Patent Document 1 discloses a method for producing a silicon nitride sintered substrate having excellent mechanical properties and high thermal conductivity. In the production method, a silicon nitride powder having an Al content of 0.1% by weight or less is mixed with Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb. After molding by adding a sintering aid of one or more elements selected from the above in the range of 1% by weight or more and 15% by weight or less, under nitrogen gas pressure of 1 atm or more and 500 atm or less. Bake at a temperature of 1700 ° C or higher and 2300 ° C or lower. The silicon nitride sintered substrate obtained by the production method is composed of 85% by weight or more and 99% by weight or less of β-type silicon nitride grains, and the balance is composed of oxide or oxynitride grain boundary phases. Further, one or more metal elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb in the grain boundary phase. Is contained in an amount of 0.5% by weight or more and 10% by weight or less. The Al atom content in the grain boundary phase is 1% by weight or less, the porosity is 5% or less, and the proportion of β-type silicon nitride grains having a minor axis diameter of 5 μm or more in terms of the microstructure of the sintered body. Is 10% by volume or more and 60% by volume or less. That is, Patent Document 1 describes that the silicon nitride sintered body substrate has both excellent mechanical properties and high thermal conductivity by adding a sintering aid.

Japanese Unexamined Patent Publication No. 9-30866

That is, it is known that in order to obtain a silicon nitride sintered substrate having high thermal conductivity, a rare earth compound or magnesium oxide is added as a sintering aid, and the thermal conductivity and mechanical strength can be improved by the mixing ratio and the amount of addition thereof. Has been done. However, in a silicon nitride sintered substrate manufactured by a conventional manufacturing method (in other words, a method that does not go through the manufacturing process of the present invention), the fracture toughness in the plane direction is compared with the fracture toughness in the vertical (thickness) direction of the substrate. Was obtained by the inventor (see Comparative Examples 1 to 4 in Table 2). That is, it can be seen that the conventional silicon nitride sintered substrate is vulnerable to a force load in the plane direction as compared with the vertical direction due to the presence of anisotropy in mechanical strength. When the fracture toughness in the plane direction is low as described above, for example, the metal plate is thermally expanded under a specific harsh environment by a thermal cycle test in which the metal plate is fixed to a silicon nitride sintered body substrate and then heated and cooled repeatedly. -It is conceivable that durability and reliability may decrease, such as cracks in the substrate surface without being able to withstand the accumulation of force load in the plane direction due to shrinkage.

In order to solve the above problems, the purpose of the present invention is to provide a silicon nitride sintered substrate having high fracture toughness in both the vertical direction and the planar direction and / or improving the isotropic property of the fracture toughness. An object of the present invention is to provide an electronic device provided with the silicon nitride sintered body substrate and a method for manufacturing the silicon nitride sintered body substrate.

The silicon nitride sintered body substrate of one embodiment of the present invention comprises a silicon nitride sintered body containing _{1 to 15% by weight of a sintering aid and Si 3} N _{4 constituting the balance, and is composed of β-Si. 3} has an X-ray diffraction peaks of N _{4, β-Si} 3 of _{N 4} (101) of the X-ray diffraction peaks of surface intensity _{I 101} and _{β-Si 3 N 4 (210} ) plane of the X-ray diffraction peaks of The strength ratio I ₁₀₁ / I _{210 to the strength I 210} is 0.7 to 1.1, and the fracture toughness value K _{C1 in} the first direction parallel to the substrate plane is 5.5 MPa · m ^1/2 or more. _{The fracture toughness value K C2 in} the second direction perpendicular to the substrate plane is 5.5 MPa · m ^1/2 or more.

That is, the silicon nitride sintered substrate of the present invention has _{an intensity ratio I 101} / I ₂₀₁ of 0.7 to 1.1 of the X-ray diffraction peak _{of β-Si 3} N _{4 in} the X-ray diffraction measurement. .. The strength ratio I ₁₀₁ / I ₂₀₁ of the silicon nitride sintered substrate was controlled in the range of 0.7 to 1.1, so that the fracture toughness of the silicon nitride sintered substrate in the first direction and the second direction was controlled. The values of K _C1 and K _C2 were both 5.5 MPa · m ^1/2 or more. Therefore, the silicon nitride sintered substrate of the present invention can have high fracture toughness isotropically in the plane direction as well as in the vertical direction.

According to the silicon nitride sintered body substrate of the present invention, in the above structure, the ratio _K C1 _{/ K C2} between the value _{K C2} and the value _{K C1} of the first fracture toughness the second fracture toughness 0.9 It may be ~ 1.1.

The silicon nitride sintered body substrate of another embodiment of the present invention comprises a silicon nitride sintered body containing _{1 to 15% by weight of a sintering aid and Si 3} N _{4 constituting the balance, and is composed of β-Si. 3} intensity ratio _I 101 _{/ I 210} between the N ₄ of (101) plane intensity _{I 210} of the X-ray diffraction peaks of the (210) plane of the intensity of X-ray diffraction peaks _{I 101} and _beta-Si 3 _{N 4} of 0. The ratio K _C1 / K _C2 of the fracture toughness value K _{C1 in} the first direction parallel to the substrate plane and the fracture toughness value K _{C2 in} the second direction perpendicular to the substrate plane is 0.9 to 1.1. It is characterized by being 1.1.

That is, the silicon nitride sintered substrate of the present invention has _{an intensity ratio I 101} / I ₂₁₀ of 0.7 to 1.1 of the X-ray diffraction peak _{of β-Si 3} N _{4 in} the X-ray diffraction measurement. .. The strength ratio I ₁₀₁ / I ₂₁₀ of the silicon nitride sintered substrate was controlled in the range of 0.7 to 1.1, so that the fracture toughness of the silicon nitride sintered substrate in the first direction and the second direction was controlled. The ratio of _{K C1} and K _{C2 to K C1} / K _C2 was 0.9 to 1.1. Therefore, in the silicon nitride sintered substrate of the present invention, it is suppressed that the fracture toughness in the first direction parallel to the substrate plane is relatively lower than that in the second direction perpendicular to the substrate plane, and the fracture toughness and the like are suppressed. The directionality was improved.

The silicon nitride sintered substrate of a further embodiment of the present invention may have a three-point bending strength of 750 MPa or more. Further, the silicon nitride sintered substrate of the present invention may have a thermal conductivity of 80 W / mK or more.

According to the silicon nitride sintered body substrate of the further embodiment of the present invention, the sintering aid is Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, It may be an oxide of one or more elements selected from the group consisting of Er and Yb. Further, according to the silicon nitride sintered body substrate of the present invention, the sintering aid, and 1.5 to 3.5 wt% of MgO, it may consist 1-4 wt% of _Y 2 _{O 3} Metropolitan ..

The method for producing a silicon nitride sintered substrate according to another embodiment of the present invention is as follows.
A step of mixing silicon nitride powder having a β-Si ₃ N ₄ content of 7% or less and a sintering aid powder at a predetermined blending ratio, and adding a solvent to the mixed powder to form a slurry.
A step of adjusting the viscosity of the slurry to 13000 cps or more, preferably 13000 to 18000 cps, and
A step of molding the slurry having the adjusted viscosity into a sheet molded product having a predetermined thickness, and
A step of sintering the sheet molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body substrate.
It is characterized by including.

That is, according to the method for producing a silicon nitride sintered substrate of the present invention, a _{silicon nitride powder containing 7% or less of β-Si 3} N ₄ is used as a raw material, and the viscosity of the slurry is 13000 cps or more, preferably 13000 cps or more. By forming the sheet molded body after adjusting it to the range of ~ 18000 cps, _{the intensity I 101} of the X-ray diffraction peak of the (101) plane of _{the β-Si 3} N _{4 (101) plane of the silicon nitride sintered body substrate according to the manufacturing method was obtained.} The intensity ratio I ₁₀₁ / I ₂₁₀ of the X-ray diffraction peak of the (210) plane of β-Si ₃ N _{4 to the intensity I 210} can be controlled to be closer to 1. _{As a result, the fracture toughness value K C1} in the first direction parallel to the substrate plane of the silicon nitride sintered body substrate is relatively lower than _{the fracture toughness value K C2 in} the second direction perpendicular to the first direction. It is possible to obtain a silicon nitride sintered substrate which is suppressed and has isotropic fracture toughness in both directions.

According to the production method of a further embodiment of the present invention, the slurry whose viscosity has been adjusted by the doctor blade method may be formed into a sheet having a predetermined thickness. Further, according to the production method of the present invention, the step of adjusting the viscosity of the slurry may include defoaming the slurry in a vacuum, and the viscosity of the slurry depends on the defoaming time.

According to the production method of a further embodiment of the present invention, the sintering aid is derived from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb. It may be an oxide of one or more elements selected from the group. Further, according to the silicon nitride sintered body substrate of the present invention, the sintering aid, and 1.5 to 3.5 wt% of MgO, it may consist 1-4 wt% of _Y 2 _{O 3} Metropolitan ..

According to the silicon nitride sintered body of the present invention and the method for producing the same, the mechanical strength of the silicon nitride sintered body in the vertical direction and the planar direction can be improved.

(A) SEM image of α-phase silicon nitride particles and (b) SEM image of β-phase silicon nitride particles. SEM image of silicon nitride sintered substrate. The flowchart which shows the manufacturing method of the silicon nitride sintered body of one Embodiment of this invention. The schematic diagram which shows an example of the molding process of this invention. In the present invention, it is a schematic diagram for demonstrating the method of measuring the fracture toughness value in the 1st direction and the 2nd direction. In Example 1 of the present invention, (a) an image of a cross section of a silicon nitride sintered body substrate after a fracture toughness test and (b) an X-ray diffraction peak related to the degree of orientation are shown. In Comparative Example 1 of the present invention, (a) an image of a cross section of a silicon nitride sintered body substrate after a fracture toughness test and (b) an X-ray diffraction peak related to the degree of orientation are shown. In Comparative Example 2 of the present invention, (a) an image of a cross section of a silicon nitride sintered body substrate after a fracture toughness test and (b) an X-ray diffraction peak related to the degree of orientation are shown.

The silicon nitride sintered substrate of the present embodiment is mainly used as a substrate for mounting electronic components by brazing (brazing or soldering) a metal plate such as a copper plate to the substrate surface. Will be done. That is, the silicon nitride sintered body substrate of the present embodiment, the metal plate brazed to at least one surface of the silicon nitride sintered body substrate, and the electronic components mounted on the metal plate can be used for various purposes. An electronic device is configured. In such an electronic device, since the temperature rises during operation, the metal plate repeats thermal expansion and contraction at high and low temperatures. Therefore, the silicon nitride sintered substrate of the present embodiment has a more isotropic predetermined mechanical strength (fracture toughness) in both the first direction parallel to the substrate plane and the second direction perpendicular to the substrate plane. It was configured to work. The fracture toughness value in each direction is generated from the apex of the indenter by forming a diagonally long indentation on the side end face of the substrate having a predetermined thickness and pushing the Vickers indenter, in the first direction and the second. It was determined by the length of the crack in each direction.

The silicon nitride sintered body substrate is composed of a silicon nitride sintered body containing 1 to 15% by weight of a sintering aid and Si ₃ N _{4 constituting the balance.} In the present embodiment, the sintering aid powder is strontium oxide (SrO), barium oxide (BaO), magnesium oxide (MgO), rare earth elements (Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho). , Er, Yb) oxides or combinations thereof and the like. In particular, by adding the Mg component together with the rare earth oxide as the sintering aid component, the liquid phase formation temperature at the time of sintering can be lowered and the sinterability can be improved. Further, the sintering aid is more preferably a _Y 2 _{O 3} of 1.5 to 3.5 wt% of MgO and 1-4 wt%. Past findings have shown that by using Mg and Y as the sintering aid components, the silicon nitride sintered body can be densified, and as a result, both relatively high thermal conductivity and mechanical strength can be achieved. There is. In the present embodiment, as a sintering agent, MgO and _Y 2 _{O 3} was employed. It should be noted that it has been obtained in the past that the compounding composition ratio of the sintering aid does not significantly affect the characteristics of the silicon nitride sintered body substrate if it is in the range of 1 to 15% by weight. Those skilled in the art can arbitrarily select the type and compounding ratio.

There are two types of crystal structures of the silicon nitride sintered body: α-phase type silicon nitride Si ₃ N ₄ (α-Si ₃ N ₄ ) and β-phase type silicon nitride (β-Si ₃ N _4). FIG. 1 (a) shows an SEM image of a powder composed of _{α-Si 3} N ₄ , and FIG. 1 (b) shows β- obtained by heating _{α-Si 3} N _{4 of FIG. 1 (a).} The SEM image of Si ₃ N _{4 is shown.} Further, FIG. 2 shows an SEM image of the silicon nitride sintered body substrate. In general, it is known that α-Si ₃ N ₄ irreversibly undergoes phase transformation to _{β-Si 3} N ₄ at a high temperature (near the sintering temperature of 1500 to 1700 ° C.). As shown in FIG. 1 (b), the β-Si ₃ N ₄ particles have an elongated columnar crystal structure. Then, as shown in FIG. 2, it is known that in a silicon nitride sintered body, high mechanical strength is exhibited by entwining columnar crystal particles of _{β-Si 3} N _{4 with each other.}

In the X-ray diffraction method using Cu-Kα rays, _{2θ and Miller index (hkl) of α-Si 3} N ₄ and β-Si ₃ N ₄ are given by the following tables, respectively.

In the present invention, _{the intensity I 101} of the X-ray diffraction peak on the (101) plane of β-Si ₃ N ₄ and the intensity of the X-ray diffraction peak on the (210) plane of _{β-Si 3} N _{4 of the silicon nitride sintered body.} I focused on _{I 210.} Then, the inventor _{hypothesized that I 101} and I ₂₁₀ could be indicators of the number of columnar crystal particles oriented in the vertical direction (the substrate thickness direction) and the horizontal direction (the substrate plane direction) of β-Si ₃ N _{4, respectively.} .. In other words, the intensity ratio I ₁₀₁ / I ₂₁₀ was associated with the vertical and horizontal orientation (ratio) of β-Si ₃ N _4. That is, the degree of orientation decreases as the number of horizontally oriented particles increases, the degree of orientation increases as the number of vertically oriented particles increases, and the degree of orientation approaches 1 when the columnar crystal structures are randomly or evenly arranged vertically and horizontally as a whole. Can be considered.

The silicon nitride sintered substrate of the present embodiment was controlled to have an _{orientation degree close to 1 (I 101} / I _210). That is, in the silicon nitride sintered substrate, _{the columnar crystal structure of β-Si 3} N ₄ is parallel to the first direction parallel to the substrate plane and the normal line of the substrate plane (vertical to the first direction). They are arranged statistically evenly or randomly in the vertical and horizontal directions as a whole, without being unevenly arranged in either one of the second directions. Then, in the silicon nitride sintered substrate of the present embodiment, the columnar crystals are controlled to be arranged vertically and horizontally randomly, so that the columnar crystals are more evenly entangled in both the first direction and the second direction, and the columnar crystals are entangled more evenly. As a result, the mechanical strength (fracture toughness) of the substrate was exhibited isotropically, and improved mechanical properties (fracture toughness) were obtained in both the first direction and the second direction.

Specifically, the silicon nitride sintered substrate of the present embodiment has an orientation degree (I ₁₀₁ / I ₂₁₀ ) of about 0.7 to 1.1. In the silicon nitride sintered substrate, the fracture toughness value K _{C1 in} the first direction parallel to the substrate plane is 5.5 MPa · m ^1/2 or more, and the fracture toughness in the second direction perpendicular to the substrate plane is The value of K _C2 is 5.5 MPa · m ^1/2 or more. Further, the ratio K _C1 / K _C2 of the fracture toughness value K _C1 in the first direction and the fracture toughness value K _{C2 in} the second direction is 0.9 to 1.1. Further, the silicon nitride sintered substrate of the present embodiment has a three-point bending strength of 750 MPa or more and a thermal conductivity of 80 W / mK or more. Then, in a state where the metal plate (copper plate) is brazed to the silicon nitride sintered body substrate having a predetermined size, the silicon nitride sintered body substrate cracks even if the thermal cycle from -40 degrees to 150 degrees is repeated 3000 times. Was confirmed not to occur.

Subsequently, a method for manufacturing the silicon nitride sintered substrate of the present embodiment will be described. As shown in FIG. 3, the method for manufacturing the silicon nitride sintered substrate of the present embodiment is a _{silicon nitride powder having a β-Si 3} N ₄ content (β conversion rate) of 7% or less and a sintering aid. A slurrying step of mixing powder with a predetermined compounding ratio and further adding a solvent or the like to form a slurry, a slurry viscosity adjusting step of adjusting the viscosity of the slurry to 13000 cps or more, preferably 13,000 to 18,000 cps, and a viscosity. Includes a molding step of molding the prepared slurry into a sheet molded body having a predetermined thickness, and a sintering step of sintering the sheet molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body substrate. Hereinafter, each step will be described in detail.

(1) Slurry forming step In the slurry forming step, silicon nitride, additives, and raw material powders of a sintering aid are put into a ball mill together with a binder, a solvent, and the like to form a slurry. As the silicon nitride powder, a raw material containing _{β-Si 3} N ₄ particles of 7% by mass or less of the whole was selected. In other words, the α phase ratio of the raw material silicon nitride powder is 93% or more. Further, the silicon nitride powder is preferably a high-purity silicon nitride powder produced by a direct nitriding method, an imide pyrolysis method, or the like and having a low oxygen content. As a method for adjusting the slurry used for molding, wet mixing using an organic solvent is desirable in order to suppress productivity and an increase in the amount of oxygen during mixing. As a specific example, a dispersant, toluene, and an organic solvent mixed with ethanol are added to the raw material powder, and the mixture is adjusted by a usual mixing and pulverizing method. Then, the mixed powder is uniformly mixed and the particle size is adjusted by a method such as a ball mill, a bead mill, or a vibration mill. As the material of the mill or media used in the mixing and crushing method, a resin material such as urethane or nylon or a ceramic material such as silicon nitride or zirconium oxide can be used. It is preferable to use a resin or silicon nitride. The amount of the dispersant or organic solvent added needs to be adjusted according to the type and the specific surface area of the raw material. When silicon nitride is used as a raw material, an amine-based or phosphorus-based surfactant is preferably used as the dispersant. The amount of the dispersant added needs to be appropriately changed depending on the specific surface area of the powder, but good dispersibility can be obtained if the amount is in the range of 0.2 to 3% by weight. The type of solvent, dispersant, etc. can be arbitrarily selected as long as the viscosity can be adjusted in the following steps.

(2) Slurry Viscosity Adjusting Step In the slurry viscosity adjusting step, the viscosity of the slurry is adjusted by defoaming the slurry after the slurry forming step in a vacuum and volatilizing the solvent of the slurry. The viscosity of the slurry depends on the defoaming and volatilization time, and the longer the slurry is placed in vacuum, the higher the viscosity of the slurry. Then, by periodically measuring the viscosity of the slurry placed in vacuum, the viscosity of the slurry is adjusted to 13000 cps or more, preferably 13,000 to 18,000 cps.

(3) Molding Step In the molding step, a high-viscosity slurry having a viscosity of 13000 cps or more is molded into a sheet molded product having a predetermined thickness by the doctor blade method. As shown in FIG. 4, when the carrier tape 3 moves forward together with the slurry 1 stored in the storage unit (dam) 2 by the feeder 5, the slurry 1 passes between the tip of the blade 4 and the carrier tape 3. At the time of passing, the tip of the blade 4 comes into contact with the slurry 1 and is pressurized, so that a long sheet molded body having a predetermined thickness is formed. The thickness of the sheet molded product can be appropriately changed depending on the required thickness of the sintered body, but is usually in the range of about 0.1 to 1.3 mm. The sheet molded body can be processed into a desired shape by a die press or a cutting machine.

In this molding step, it the ratio of the _β-Si 3 _{N 4} occupies the whole to the particle _α-Si 3 _{N 4} particles is large, and, by the slurry is highly viscous (more than 13,000 cps), after sintering It is possible to prevent the β-Si ₃ N ₄ particles from being biased in one direction (plane direction). In other words, the viscosity adjusting step _{makes it possible to control the degree of orientation (I 101} / I ₂₁₀ ) of the silicon nitride sintered body substrate to about 0.7 to 1.1, and the silicon nitride sintered body substrate machine. It can greatly contribute to the improvement of isotropic strength. In particular, in the slurry after adjusting the viscosity, _{the orientation of the α, β-Si 3} N ₄ particles is random (the degree of orientation is about 1), whereas the pressure molding by the doctor blade is the Si ₃ N ₄ particles. It is considered that it physically affects the degree of orientation of. _{For example, if the proportion of β-Si 3} N ₄ particles, which are columnar particles, is _{large in the slurry, the β-Si 3} N ₄ particles rotate and turn sideways during pressurization for molding such as the doctor blade method. Easy to fall down. In other words, as shown in FIG. 1, columnar β-Si ₃ N ₄ particles are more susceptible to external forces in terms of particle shape _{than elongated non-columnar α-Si 3} N _{4 particles.} It can be said that. Alternatively, when the slurry has a low viscosity, the Si ₃ N ₄ particles are likely to move (rotate) in the slurry, and the particles are likely to settle, so that the randomness of the orientation before molding is likely to be lost. As a result, in the silicon nitride sintered substrate that does not undergo the manufacturing method, it is considered that _{many β-Si 3} N ₄ are oriented in the plane direction of the substrate and the degree of orientation (I ₁₀₁ / I _{210) is low.} On the other hand, when the slurry viscosity is larger than 18,000 cps, the moldability is lowered and it becomes difficult to mold into a predetermined sheet shape. Therefore, the slurry viscosity is preferably adjusted in the range of 13,000 to 18,000 cps.

(4) Sintering Step The sheet molded product obtained in the molding process is fired at a high temperature for a predetermined time to sinter the sheet molded product to obtain a silicon nitride sintered body, which is the final object of the present manufacturing method. .. The firing process is performed in a firing furnace in a non-oxidizing (nitrogen) atmosphere in a temperature range of about 1750 to 2000 ° C. Further, in _{order to prevent volatilization of Si 3} N ₄ and a sintering aid (for example, MgO), it is preferable to perform pressure firing under a pressure of 5 atm or more.

_{By going through the steps described above, the degree of orientation (I 101} / I ₂₀₁ ) is closer to 1 as compared with the silicon nitride sintered body manufactured without going through the present manufacturing method (particularly, the slurry viscosity adjusting step). It has become possible to manufacture a silicon nitride sintered body substrate controlled in this manner. As a result, the silicon nitride sintered substrate produced by this production method can have high fracture toughness isotropically in both the vertical direction and the planar direction.

The steps described above are merely examples and do not limit the present invention. For example, after the mixing step, a calcining step of heating the mixed powder may be added separately. Alternatively, the method for forming the slurry is not limited to the doctor blade method, and the slurry may be pressure-molded on the sheet molded body by an extrusion molding method, a casting molding method, or the like. That is, even in other molding methods, it is considered that the β conversion rate of the silicon nitride powder and the viscosity of the slurry affect the degree of orientation in the sintered body, as in the doctor blade method.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

The silicon nitride sintered substrates according to Examples 1 to 4 and Comparative Examples 1 to 4 were produced and manufactured according to the following conditions and procedures. The conditions of Examples 1 to 4 and Comparative Examples 1 to 4 are different in the compounding composition, the β conversion rate of the silicon nitride powder, and a part or all of the slurry viscosity.

First, a high-purity silicon nitride powder produced by the direct nitriding method was prepared. The silicon nitride powder has an average particle size (D50) of about 1.0 μm and an oxygen content of about 0.8% by weight. In accordance with the blending composition ratio of each powder, MgO and Y ₂ O ₃ is a sintering aid powder were added in an appropriate amount relative to the silicon nitride powder. To 100 parts by weight of this mixed powder, 0.3 part by weight of a surfactant and about 50 parts by weight of a mixed solvent of toluene and ethanol were added, and pulverization and mixing was carried out using a silicon nitride ball stone. Then, add 18 parts by weight of polyvinyl butyral as a binder, 6 parts by weight of dioctyl adipate as a plasticizer, and about 20 parts by weight of a mixed solvent of toluene and ethanol, and use a ball mill until the binder is completely dissolved and mixed. After stirring and mixing, a slurry was prepared. Then, the slurry was left in a vacuum to defoam and volatilize to adjust the viscosity to a predetermined viscosity of 13000 cps or more. The viscosity of the slurry was measured by a TVC-7 viscometer manufactured by Toki Sangyo Co., Ltd. Specifically, the spindle was rotated in the slurry, and the viscosity was calculated from the resistance force.

Next, a sheet molded product was obtained from the produced slurry by the doctor blade method. The obtained sheet molded product was die-cut into a predetermined shape by die pressing, and the sheet molded product was heated to 500 ° C. for about 4 hours to remove organic components such as a binder.

Then, the sheet molded product was heated at 1860 ° C. for 4 hours in a nitrogen atmosphere of 9 atm to sinter the sheet molded product to obtain a silicon nitride sintered substrate having a plate thickness of 0.35 mm.

The characteristics of the silicon nitride sintered body according to Examples 1 to 4 and Comparative Examples 1 to 4 include orientation (I ₁₀₁ / I ₂₁₀ ), fracture toughness (MPa · m ^1/2 ), and thermal conductivity (W / mK). ), The three-point bending strength (MPa) was measured. Various measurements were performed under the following conditions.

-Orientation The X-ray diffraction intensity of each sample was measured by the powder X-ray diffraction method using Cu-Kα ray using the model Ultima IV manufactured by Rigaku Co., Ltd. In the X-ray diffraction pattern of the substrate plane obtained by X-ray incident on the substrate plane, as shown in Table 1, the peak intensity of 2θ of 33.6 degrees is I _{101 and} the peak intensity of 2θ is 36.0 degrees is I _210. The degree of orientation was evaluated from the peak intensity ratio I ₁₀₁ / I _210.

-Fracture toughness The fracture toughness of each sample was measured according to JIS-R1607 using a Vickers hardness tester HV-120 manufactured by Mitutoyo Co., Ltd. That is, the cross section of the substrate cut along the thickness direction of the substrate is mirror-polished, and as shown in FIG. The diagonal lengths a1 and a2 of the compaction formed near the center, and the crack lengths c1 and c2 generated from the apex of the compaction were measured, and the indentation load, the diagonal length of the compaction, and the compression were measured. _{The fracture toughness value K C} was determined from the crack length and elastic modulus. According to JIS-R1607, fracture toughness _{K C} is obtained by the following equation.
K _C = 0.026 x E ^1/2 x P ^1/2 x a / C ^3/2 (Equation 1)
C = ((c1 + c2) / 2) / 2 (Equation 2)
a = ((a1 + a2) / 2) / 2 (Equation 3)
E: Elastic modulus P: Pushing load a: Half of the average diagonal length of the compaction C: Half of the average of the crack length On the other hand, in the present embodiment, the fracture toughness value K _C is set in the first direction (board plane). _{The fracture toughness value K C1} in the direction parallel to (the direction parallel to the _{substrate plane) and the fracture toughness value K C2} in the second direction (the direction perpendicular to the substrate plane) were evaluated separately. _{Specifically, K C1} was calculated by setting the crack length generated in the direction parallel to the substrate plane as c1 and replacing Equation 2 with C = c1 / 2. _{Further, K C2} was calculated by assuming that the crack length generated in the direction perpendicular to C1 (the thickness direction of the substrate) was c2 and replacing Equation 2 with C = c2 / 2. The thickness of the test piece was 0.9 to 1.0 mm, and the pushing load P was 10 kgf.

-Thermal conductivity The laser flash method was adopted as the method for measuring the thermal conductivity. For the measurement, TC-9000 of ULVAC, Inc. was used. The size of the test piece was 25 mm square in width and 0.3 to 0.4 mm in thickness.

-The 3-point bending strength measuring device is a model AG-IS manufactured by Shimadzu Corporation, and the measuring conditions are a cross head speed of 0.5 mm / min, a distance between fulcrums of 30 mm, and a test piece size of 20 mm in width and thickness. It was set to 0.3 to 0.4 mm.

-Heat cycle test A copper plate was brazed to a silicon nitride sintered body sample, and the sample was heated and cooled under a predetermined heat cycle. In the thermodynamic cycle test, the process of maintaining at −40 ° C. for a predetermined time, heating from −40 ° C. to 150 ° C., maintaining at 150 ° C. for a predetermined time, and cooling to −40 ° C. was defined as one cycle. In this test, the thermal cycle was repeated 3000 times. Whether or not a crack was generated in the sample was determined by observing the cross section of the interface between the metal plate and the silicon nitride substrate at the corner of the metal plate by an electron microscope image. The thermodynamic cycle test can be an index showing a relative evaluation rather than an absolute evaluation between samples.

Table 2 shows the conditions and various measurement results of Examples 1 to 4 and Reference Examples 1 to 4.

The silicon nitride sintered substrate of Examples 1 to _{4 has} a content rate (β conversion rate) of β-Si ₃ N _{4 of Si 3} N ₄ powder of 7% or less and a slurry viscosity of 13000 to 13000 in the manufacturing process. Manufactured under the condition of 18000 cps. As a result, the silicon nitride sintered substrates of Examples 1 to 4 have a controlled degree of orientation (I ₁₀₁ / I ₂₁₀ ) between 0.7 and 1.1. Further, in the silicon nitride sintered body substrate of Examples 1 to 4, both the fracture toughness _{K C1, K C2} becomes 5.5 MPa ^{· m 1/2} or more, and, _{K C1} indicating the isotropic fracture toughness / K _C2 is in the range of 0.9 to 1.1.

On the other hand, the silicon nitride sintered substrate of Comparative Example 1 has a slurry viscosity of 15000 cps and a ratio of β-Si 3 N 4 of Si 3 N 4 powder of 8% in the manufacturing process. produced. Orientation of the Comparative Example 1 (I 101 / I 210) is 0.47, although K C2 is high and 6.6MPa · m 1/2, K C1 is 4.3 MPa · m 1/2. In the silicon nitride sintered substrate of Comparative Example 1, the fracture toughness has high longitudinal and horizontal anisotropy (K C1 / K C2 = 0.65) and the fracture toughness in the plane direction is low. Further, the silicon nitride sintered substrate of Comparative Example 2 is manufactured under the condition that the slurry viscosity is 15000 cps and the ratio of β-Si 3 N 4 of Si 3 N 4 powder is 26% in the manufacturing process. rice field. The degree of orientation of Comparative Example 2 (I 101 / I 210) is 0.27, although K C2 is high and 6.6MPa · m 1/2, K C1 is 3.4 MPa · m 1/2. In the silicon nitride sintered substrate of Comparative Example 2, the fracture toughness has high longitudinal and horizontal anisotropy (K C1 / K C2 = 0.52), and the fracture toughness in the plane direction is low. According to Comparative Examples 1 and 2, as the ratio of β-Si 3 N 4 of the Si 3 N 4 powder increased, the degree of orientation decreased and the fracture toughness K C2 in the second direction (thickness direction) did not change. However, it was found that the fracture toughness K C1 in the first direction (planar direction) was significantly reduced.

When Example 2 and Comparative Examples 1 and 2 are compared and examined, even if the slurry viscosity is 15000 cps, when the ratio of β-Si ₃ N _{4 of the Si 3} N ₄ powder becomes 8% or more, the degree of orientation suddenly increases. It was found to decrease, and as a result, K _{C1 was extremely decreased.} Although the cause of this has not been clarified, _{when the amount of β-Si 3} N ₄ in the slurry exceeds a certain amount, α-Si in the sheet molded body of _{β-Si 3} N ₄ particles oriented in the plane direction during firing is performed. It is considered that the influence on ₃ N _{4 particles becomes large.} That is, phase transformation and grain growth to a large number of _α-Si 3 _{N 4} particles _β-Si 3 _{N 4} particles _β-Si 3 _{N 4} particles oriented in the planar direction in the sheet molded article beyond a certain amount as a nucleus Therefore, it is considered that _{β-Si 3} N ₄ particles oriented in the plane direction become the majority.

The silicon nitride sintered substrate of Comparative Example 3 was manufactured under the conditions that the slurry viscosity was 10000 cps and the ratio of β-Si 3 N 4 of the Si 3 N 4 powder was 7% in the manufacturing process. The degree of orientation of Comparative Example 3 (I 101 / I 210) is 0.55, although K C2 is high and 6.2MPa · m 1/2, K C1 is 4.0 MPa · m 1/2. In the silicon nitride sintered substrate of Comparative Example 3, the fracture toughness has high longitudinal and horizontal anisotropy (K C1 / K C2 = 0.64) and the fracture toughness in the plane direction is low.

Further, the silicon nitride sintered substrate of Comparative Example 4 is manufactured under the condition that the slurry viscosity is 8000 cps and the ratio of β-Si 3 N 4 of the Si 3 N 4 powder is 4% in the manufacturing process. rice field. Orientation of the Comparative Example 4 (I 101 / I 210) is 0.64, K C2 is high and 6.3MPa · m 1/2, K C1 is 5.2 MPa · m 1/2. Compared with Comparative Example 3, the longitudinal and horizontal anisotropy of fracture toughness was improved. (K C1 / K C2 = 0.83).

Comparing Examples 1 to 4 with Comparative Examples 3 and ₄ , even if the ratio of β-Si ₃ N _{4 of the Si 3} N ₄ powder is 7% or less, the slurry viscosity becomes 8000 cps, which is smaller than 13000 cps. It was found that the degree of orientation decreased, and as a result, K _{C1 decreased.} As described above, it is considered that the reason for this is that when the slurry has a low viscosity, the Si ₃ N ₄ particles settle and rotate in the slurry during pressure molding and are easily oriented in the plane direction.

Further, when Examples 1 to 4 were compared, the degree of orientation closer to 1 was obtained in the range of the slurry viscosity of 16000 to 18000 cps. Further, comparing Examples 1 and 2, when the ratio of β-Si ₃ N _{4 of the Si 3} N ₄ powder was lowered, the degree of orientation tended to be closer to 1.

Further, according to Table 2, the silicon nitride sintered substrates of Examples 1 to 4 and Reference Examples 1 to 4 have a thermal conductivity of 80 W / mK or more and a three-point bending strength of 750 MPa or more. It was found that these properties do not depend on the conditions between each sample.

In order to facilitate a visual understanding of the differences between the examples and the comparative examples, the X-ray diffraction peaks of the (101) plane and the (210) plane and the substrate surface after the fracture toughness test are shown in FIGS. 6 to 8. The image of is shown exemplary. FIG. 6 relates to Example 1, and FIGS. 7 and 8 relate to Comparative Examples 1 and 2. According to FIGS. 6 to 8, it can be seen that _{I 210} is seemingly larger in Comparative Examples 1 and 2 than the _{degree of orientation (I 101} / I _{210) in Example 1.} Also, in the images of fracture toughness, it can be seen that in Comparative Examples 1 and 2, the cracks in the plane direction (lateral direction) are relatively large as compared with Example 1.

Further, a thermodynamic cycle test was conducted on Examples 1 to 4 and Comparative Examples 1 to 4. In Table 2, ◯ was shown for the sample in which no crack was confirmed after the completion of the 3000 thermal cycle test, and x was shown for the sample in which the crack was confirmed. As shown in Table 2, no cracks were found in the silicon nitride sintered substrate after the completion of the 3000 thermodynamic cycle tests in Examples 1 and 2. On the other hand, after the completion of the 3000 thermal cycle test, cracks were found in the silicon nitride sintered substrate in Comparative Examples 1 to 4.

That is, in the manufacturing process, the silicon nitride sintered substrate manufactured under the conditions that the ratio of β-Si ₃ N _{4 of the Si 3} N ₄ powder is 7% or less and the slurry viscosity is 13,000 to 18,000 cps (implemented). Examples 1 to 4) have a controlled degree of orientation in the range of 0.7 to 1.1. Then, when the relationship between the degree of orientation and the fracture toughness of the silicon nitride sintered substrate was verified, K _C1 and K _C2 were 5.5 MPa because the degree of orientation was controlled in the range of 0.7 to 1.1. · ^m to ^1/2 or more, _K C1 _{/ K C2} is the aspect ratio of the fracture toughness was found to be in the range of 0.9 to 1.1. Therefore, the silicon nitride sintered substrates of Examples 1 to 4 exhibit fracture toughness isotropically as the mechanical strength of the substrate, and have improved mechanical properties (fracture toughness) in both the first direction and the second direction. )was gotten.

The production method of the above embodiment is only an example, and the technical idea of the present invention can be applied to the production of a silicon nitride sintered body composed of other types of sintering aids and raw material powders having different compounding compositions. Needless to say, there is. That is, it is possible to benefit from the present invention with respect to a method for producing a silicon nitride sintered body having a composition other than the above examples, and if it is within the technical scope of the present invention, it can be arbitrarily replaced, omitted and / or. Can be added.

The present invention is not limited to the above-described examples, and can be carried out in various embodiments as long as it belongs to the technical scope of the present invention.

Claims (15)

It is composed of a silicon nitride sintered body containing 1 to 15% by weight of a sintering aid and Si ₃ N ₄ constituting the balance, and has an X-ray diffraction peak of _{β-Si 3} N _{4 and β-Si. 3} intensity ratio _I 101 _{/ I 210} between the N ₄ of (101) plane intensity _{I 210} of the X-ray diffraction peaks of the (210) plane of the intensity of X-ray diffraction peaks _{I 101} and _beta-Si 3 _{N 4} of 0. _{The fracture toughness value K C1 in} the first direction parallel to the substrate plane is 5.5 MPa · m ^1/2 or more, and the fracture toughness value K _{C2 in the second direction perpendicular to the substrate plane is 7 to 1.1.} A silicon nitride sintered substrate characterized by having a temperature of 5.5 MPa · m ^{1/2 or more.} According to claim 1, wherein the first ratio _K C1 _{/ K C2} between the value _{K C1} fracture toughness value _{K C2} of the second fracture toughness of is characterized in that from 0.9 to 1.1 Silicon nitride sintered body substrate. It is composed of a silicon nitride sintered body containing 1 to 15% by weight of a sintering aid and Si ₃ N ₄ constituting the balance, and the intensity of the X-ray diffraction peak of the (101) plane of _{β-Si 3} N ₄ the intensity ratio _I 101 _{/ I 210} between the I ₁₀₁ and _β-Si 3 _{N 4} in (210) of the X-ray diffraction peaks of surface intensity _{I 210} is 0.7 to 1.1, the parallel to the substrate plane 1 A silicon nitride sintered body characterized in that the ratio K _C1 / K _C2 of the fracture toughness value K _{C1 in} the direction and the fracture toughness value K _{C2 in the second direction perpendicular to the substrate plane is 0.9 to 1.1.} substrate. The silicon nitride sintered substrate according to any one of claims 1 to 3, wherein the three-point bending strength is 750 MPa or more. The silicon nitride sintered substrate according to any one of claims 1 to 4, wherein the silicon nitride sintered body has a thermal conductivity of 80 W / mK or more. The sintering aid is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb. The silicon nitride sintered substrate according to any one of claims 1 to 5, which is an oxide of an element. The sintering aid, and 1.5 to 3.5 wt% of MgO, according to any one of claims 1 6, characterized in that it consists of 1-4% by weight of _Y 2 _{O 3} Metropolitan Silicon nitride sintered body substrate. The silicon nitride sintered body substrate according to any one of claims 1 to 7.
A metal plate brazed to at least one surface of the silicon nitride sintered substrate,
An electronic device including an electronic component mounted on the metal plate. The electronic device according to claim 8, wherein the silicon nitride sintered substrate does not crack even when the thermal cycle from −40 ° C. to 150 ° C. is repeated 3000 times. 1-15% by weight of a sintering aid powder, constituting the remainder, the proportion of β-Si ₃ N ₄ is mixed with 7% or less of silicon nitride powder, forming a slurry by adding a solvent to the mixed powder And the process to do
A step of adjusting the viscosity of the slurry to 13000 cps or more, and
A step of molding the slurry having the adjusted viscosity into a sheet molded product having a predetermined thickness, and
A step of sintering the sheet molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body substrate.
Only including,
In the silicon nitride sintered substrate, the fracture toughness value K _{C1 in} the first direction parallel to the substrate plane is 5.5 MPa · m ^1/2 or more, and the fracture toughness value in the second direction is perpendicular to the substrate plane. or K _C2 is 5.5 MPa ^{· m 1/2} or more, or the ratio _K C1 _{/ K C2} between the value _{K C2} and the value _{K C1} of the first fracture toughness the second fracture toughness 0. A method for producing a silicon nitride sintered body substrate , which is 9 to 1.1. The production method according to claim 10, wherein the viscosity of the slurry is adjusted to 13,000 to 18,000 cps. The production method according to claim 10 or 11, wherein the slurry whose viscosity has been adjusted by the doctor blade method is formed into a sheet having a predetermined thickness. The step of adjusting the viscosity of the slurry includes defoaming the slurry in a vacuum and volatilizing the solvent of the slurry, so that the viscosity of the slurry depends on the time when the slurry is placed in a vacuum. The manufacturing method according to any one of claims 10 to 12, characterized in that. The sintering aid is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb. The production method according to any one of claims 10 to 13, which is an oxide of an element. The sintering aid, and 1.5 to 3.5 wt% of MgO, according to any one of claims 10 14, characterized in that it consists of 1-4% by weight of _Y 2 _{O 3} Metropolitan Manufacturing method.

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