WO2022210518A1

WO2022210518A1 - Aluminium nitride sintered body, production method for same, circuit board, and laminated substrate

Info

Publication number: WO2022210518A1
Application number: PCT/JP2022/014941
Authority: WO
Inventors: 江尹; 和久森; 勝博小宮
Original assignee: デンカ株式会社
Priority date: 2021-03-31
Filing date: 2022-03-28
Publication date: 2022-10-06
Also published as: JPWO2022210518A1; JP7429825B2

Abstract

One aspect of the present disclosure provides an aluminium nitride sintered body which comprises aluminium nitride particles and sintering additive particles, wherein the observed crack rate is less than 9.00% by area when a ten-cycle heat cycle test is carried out on a laminate body that has been produced by laminating the aluminium sintered body with a metal plate, and has then been exposed for five minutes to an environment of 350°C and then cooled for five minutes at 25°C, each cycle comprising exposing the laminate body to an environment of -78°C for five minutes and then returning to 25°C.

Description

Aluminum nitride sintered body, manufacturing method thereof, circuit board, and laminated board

The present disclosure relates to an aluminum nitride sintered body, a method for manufacturing the same, a circuit board, and a laminated substrate.

In recent years, industrial equipment such as motors and products such as electric vehicles use power modules for high power control. A circuit board or the like having a ceramic plate is used in such a power module in order to efficiently diffuse heat generated from a semiconductor element and to suppress leakage current. A ceramic sintered body used for such a ceramic plate is generally manufactured by forming a ceramic raw material powder into a predetermined shape to form a ceramic green body, and then sintering the ceramic green body.

As ceramic sintered bodies, those composed of nitrides, carbides, borides, silicides, etc. are known. Among them, the aluminum nitride sintered body is excellent in thermal conductivity and electrical insulation. Therefore, it is used as a heat sink material for electronic parts such as power modules. In order to improve suitability for these uses, Patent Document 1 discloses that a nitride selected from the group of Zr and Ti is used in an amount of 3 to 20 parts by mass in terms of oxide as a sintering aid, and an aluminum nitride sintered body is used. Techniques for increasing the thermal conductivity and mechanical strength of steel have been proposed.

JP 2018-184316 A

Electronic components such as power modules are expected to have even higher performance, and along with this, it is believed that the level of demand for the performance of various products used in electronic components will continue to rise. It is assumed that the amount of heat generated during use of electronic components will increase, and ceramic sintered bodies are also excellent in terms of withstanding the effects of differences in thermal expansion coefficients between constituent members of electronic components, that is, differences in the amount of deformation between constituent members. Bending strength is required. By using a ceramic sintered body with excellent bending strength, it may be possible to prolong the specified life of electronic components.

An object of the present disclosure is to provide an aluminum nitride sintered body with excellent bending strength and a method for producing the same. Another object of the present disclosure is to provide a laminated substrate and a circuit substrate which are equipped with the aluminum nitride sintered body and have excellent connection reliability.

One aspect of the present disclosure is an aluminum nitride sintered body comprising aluminum nitride particles and sintering aid particles, which is laminated with a metal plate to prepare a laminate and placed in an environment of 350° C. for 5 minutes. After exposure, the above laminate was cooled in an environment of 25 ° C. for 5 minutes, and after exposing it to an environment of -78 ° C. for 5 minutes, a heat cycle test of 10 cycles was performed, with one cycle of returning to 25 ° C. Provided is an aluminum nitride sintered body having an observed crack rate of less than 9.00 area % when the aluminum nitride sintered body is cracked.

The above-mentioned aluminum nitride sintered body can exhibit excellent bending strength because the occurrence of cracks is suppressed to a predetermined value or less when a heat cycle test is performed under specific conditions. The inventors of the present invention have found through studies that if there is variation in the surface properties of the aluminum nitride sintered plate (for example, the degree of unevenness on the main surface, etc.), when an external force is applied to the aluminum nitride sintered plate, the relative It was found that stress concentration occurs in the weak part, and there may be cases where the expected bending strength is not exhibited. Furthermore, cracks that occur when a heat cycle test is performed under specific conditions are caused by aluminum nitride. It was found that the above crack rate corresponds to the development of visible cracks from latent defects in the crystal plate, and is suitable for evaluating the surface properties of aluminum nitride sintered plates. The present disclosure has been made based on the above findings.

The aluminum nitride sintered body has a plate shape having a pair of main surfaces, and the difference between the maximum height roughness Ry and the arithmetic mean roughness Ra on the main surfaces may be 6.00 μm or less. When the difference between the maximum height roughness Ry and the arithmetic mean roughness Ra is within the above range, it is possible to suppress the variation in properties on the main surface and to more uniformly disperse the thermal stress, resulting in a more excellent It can exhibit bending strength.

The maximum height roughness Ry may be less than 10.00 μm.

In the cumulative frequency distribution curve of the particle size measured by electron microscope image analysis for the aluminum nitride particles, the particle size when the integrated value from the small particle size reaches 50% and 90% of the total is d50 and d90, respectively. , the value of d90-d50 may be less than 10.0 μm.

One aspect of the present disclosure provides a circuit board comprising the aluminum nitride sintered body described above and a conductor portion attached to the aluminum nitride sintered body.

Since the circuit board has the above-described aluminum nitride sintered body, even when the temperature during use is high, the circuit board can withstand deformation between members and exhibit excellent connection reliability.

One aspect of the present disclosure provides a laminated substrate comprising the aluminum nitride sintered body described above and a metal plate attached to the aluminum nitride sintered body.

Since the laminated substrate has the above-described aluminum nitride sintered body, even when the temperature during use is high, it can withstand deformation between members and can exhibit excellent connection reliability.

One aspect of the present disclosure is a firing step of obtaining a sintered body by firing a molded body composed of a mixture containing aluminum nitride and a sintering aid for 1 to 6 hours, and firing the sintered body at 1400 ° C. or higher and 1700 ° C. a step of obtaining an annealed product by heat treatment at a temperature of less than 1 hour or more; and a step of polishing the surface of the annealed product to obtain an aluminum nitride sintered body, the sintering aid The agent contains yttrium oxide and aluminum oxide, the mass ratio of the aluminum oxide to the yttrium oxide is less than 0.5, and the firing step includes heating at a temperature of 1700 ° C. or more and less than 1800 ° C. for 1 hour or more. , a step of obtaining a first fired body from the molded body, and a step of obtaining the sintered body from the first fired body by heating at a temperature of 1800 to 1900 ° C. for 1 hour or more. Provided is a method of manufacturing a body.

In the above method for producing an aluminum nitride sintered body, a sintering aid blended in a predetermined ratio is used, and the sintered body obtained by passing through at least two stages of predetermined firing processes is subjected to annealing treatment. As a result, the composite compound derived from the sintering aid formed between the particles of the aluminum nitride crystals is again liquefied to promote the growth of fine aluminum nitride particles on the surface of the sintered body, and the sintered body Defects such as grain boundaries and cracks occurring on the surface are repaired, unevenness on the main surface is reduced, and then the main surface of the sintered body obtained can be made more uniform by polishing. As a result, the aluminum nitride sintered body to be obtained can suppress the occurrence of stress concentration due to variations in the properties of the main surface when an external force is applied. That is, according to the manufacturing method described above, an aluminum nitride sintered body having excellent bending strength can be manufactured.

According to the present disclosure, an aluminum nitride sintered body with excellent bending strength and a method for producing the same can be provided. According to the present disclosure, it is also possible to provide a laminated substrate and a circuit substrate that are equipped with the aluminum nitride sintered body and have excellent connection reliability.

FIG. 1 is a perspective view showing an example of an aluminum nitride sintered plate. FIG. 2 is a perspective view showing an example of a laminated substrate. FIG. 3 is a perspective view showing an example of a circuit board. FIG. 4 is an SEM image showing the main surface of the annealed product and the main surface of the aluminum nitride sintered plate in the manufacturing process of the aluminum nitride sintered plate in Example 1. FIG. 5 is an SEM image showing the main surface of the sintered plate before polishing and the main surface of the aluminum nitride sintered plate in the manufacturing process of the aluminum nitride sintered plate in Comparative Example 1. FIG.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as the case may be. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents. In the description, the same reference numerals are used for the same elements or elements having the same functions, and duplicate descriptions are omitted depending on the case. In addition, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratio of each element is not limited to the illustrated ratio.

The materials exemplified in this specification can be used singly or in combination of two or more unless otherwise specified. The content of each component in the composition means the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. .

An embodiment of the aluminum nitride sintered body includes aluminum nitride particles and sintering aid particles. FIG. 1 is a perspective view showing an example of an aluminum nitride sintered plate. The aluminum nitride sintered plate 100 indicates a plate-shaped aluminum nitride sintered body having a pair of main surfaces, but its shape may be, for example, a sheet shape, and is usually a rectangular parallelepiped shape. . The sintering aid particles are particles containing a component derived from the sintering aid.

The aluminum nitride sintered plate 100 is laminated with a metal plate to prepare a laminate, exposed to a 350 ° C. environment for 5 minutes, and then cooled for 5 minutes in a 25 ° C. environment. When a heat cycle test of 10 cycles is performed, with exposure to an environment of -78 ° C for 5 minutes and then returning to 25 ° C as one cycle, the observed crack rate is less than 9.00 area%. . The crack rate is, for example, 8.00 area% or less, 6.00 area% or less, 5.00 area% or less, 4.00 area% or less, 3.00 area% or less, 2.00 area% or less, or It may be 1.00 area % or less. When the crack rate is within the above range, the bending strength is excellent. Although the lower limit of the crack rate is not particularly limited, it may be, for example, 0.01 area % or more. The crack rate may be adjusted within the above range, and may be, for example, 0.01 to 9.00 area %.

The crack rate in this specification can be determined by a heat cycle test under predetermined conditions. For the heat cycle test, a brazing material containing silver (Ag), copper (Cu) and an active metal (90 parts by weight of Ag, 10 parts by weight of Cu, 3 parts by weight of Sn, and 3.5 parts by weight of Ti) was used. A copper plate (thickness: 0.3 mm) was bonded to the aluminum nitride sintered plate 100 via a brazing material having a certain composition, so that the brazing material layer had a thickness of 15 μm. A measurement sample (laminate) prepared by bonding under the conditions of 1 hour and a degree of vacuum of 1×10 ⁻³ Pa is used. A crack rate is measured by a heat cycle test on the sample under predetermined conditions. A specific method of the heat cycle test is as described in Examples.

In the aluminum nitride sintered plate 100, from the viewpoint of further suppressing stress concentration and further improving bending strength, it is desirable that at least one of the opposing main surfaces is smoother, and both main surfaces are smooth. is more desirable. The aluminum nitride sintered plate 100 preferably has a small difference between the maximum height roughness Ry and the arithmetic mean roughness Ra on at least one main surface. The upper limit of the difference ((Ry-Ra) value) between the maximum height roughness Ry and the arithmetic mean roughness Ra on the main surface is, for example, 6.00 μm or less, 5.00 μm or less, 4.00 μm or less, 3 It may be 0.00 μm or less, 2.00 μm or less, or 1.00 μm or less. When the upper limit of the value of (Ry-Ra) is within the above range, it is possible to suppress the variation in properties on the main surface, disperse the thermal stress more uniformly, and improve the bending strength. can demonstrate. The lower limit of the value of (Ry-Ra) is not particularly limited, and may be, for example, more than 0.01 μm or 1.00 μm or more. The value of (Ry-Ra) may be adjusted within the range described above, and may be, for example, greater than 0.01 μm and 6.00 μm, or from 1.00 to 6.00 μm.

The upper limit of the maximum height roughness Ry of the aluminum nitride sintered plate 100 is, for example, less than 10.00 μm, 8.00 μm or less, 7.00 μm or less, 5.00 μm or less, 4.00 μm or less, 3.00 μm or less, or 2.00 μm or less. When the upper limit of Ry is within the above range, stress concentration can be further suppressed. The lower limit of Ry may be, for example, 0.30 μm or more, 0.60 μm or more, or 1.00 μm or more. When the lower limit of Ry is within the above range, the production of the aluminum nitride sintered plate 100 can be facilitated, and an increase in cost can be suppressed. The value of the maximum height roughness Ry of the aluminum nitride sintered plate 100 may be adjusted within the above range, for example, 0.30 to 8.00 μm, 0.60 to 8.00 μm, or 1.00 to 7 00 μm.

The maximum height roughness Ry and the arithmetic mean roughness Ra in this specification are described in JIS B 0601: 1994 "Product Geometric Characteristics Specifications (GPS)-Surface Texture: Contour Curve Method-Terms, Definitions and Surface Texture Parameters". It means the maximum height roughness Ry and the arithmetic mean roughness Ra, which can be measured by a line contact type measuring instrument. As for the line contact type, for example, "Surface Roughness Measuring Instrument Surftest SJ-301" (product name) manufactured by Mitutoyo Co., Ltd. can be used.

In the cumulative frequency distribution curve of particle diameters measured by electron microscope image analysis for aluminum nitride particles, the particle diameters when the integrated value from the small particle diameter reaches 50% and 90% of the total are d50 and d90, respectively. , it is preferable that the value of d90-d50 is small. The upper limit of the value of d90-d50 is, for example, less than 10.0 μm, 8.0 μm or less, 6.0 μm or less, 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less. good. When the upper limit of the value of d90-d50 is within the above range, there is little variation in the aluminum nitride particles, and it is possible to suppress the occurrence of large defects on the main surface of the aluminum nitride sintered plate 100, and the bending strength can be improved. The lower limit of the value of d90-d50 may be, for example, 0.1 μm or more, 0.5 μm or more, or 1.0 μm or more. When the lower limit of the value of d90-d50 is within the above range, the production of the aluminum nitride sintered plate 100 can be facilitated and an increase in cost can be suppressed.

The upper limit of d90 of aluminum nitride particles is, for example, 15.0 μm or less, 14.0 μm or less, 13.0 μm or less, 12.0 μm or less, 11.0 μm or less, 10.0 μm or less, 9.0 μm or less, 8.0 μm or less, or 7.0 μm or less. The fact that the upper limit of d90 is within the above range means that the formation of coarse particles in the aluminum nitride sintered plate 100 is suppressed, and that the structure of the sintered body is more uniform. That is, it is possible to suppress the occurrence of stress concentration when force is applied from the outside, and to further improve the bending strength of the sintered plate. The lower limit of d90 may be, for example, 4.0 μm or more, 4.5 μm or more, or 5.0 μm or more. When the lower limit of d90 is within the above range, it is possible to exhibit excellent bending strength and suppress deterioration of other properties such as thermal conductivity. When the lower limit of d90 is within the above range, it is possible to facilitate the production of the aluminum nitride sintered plate 100 and to suppress an increase in cost. d90 may be adjusted within the ranges described above, and may be, for example, 4.0 to 15.0 μm, or 5.0 to 15.0 μm.

　d50 and d90 in this specification mean values measured by the following method. First, a scanning electron microscope image (observed at a magnification of 2000) of a cross section horizontal to the thickness direction of the aluminum nitride sintered plate 100 is obtained. The object to be measured is a position that is dug down by 50 μm from the main surface of the aluminum nitride sintered plate 100 in the thickness direction. A region of 50 μm×50 μm is determined at an arbitrary position in the acquired image, and the particle size distribution of the aluminum nitride particles is created using image analysis software. Determine the particle diameter at which the cumulative frequency from the small particle diameter side in the cumulative frequency distribution curve of the particle diameter measured by electron microscope image analysis obtained as described above is 50% and the particle diameter at which the cumulative frequency is 90%. do. In the same image, the particle diameters are determined for five regions in the same manner as described above, and the arithmetic mean values are taken as the d50 and d90 of aluminum nitride, respectively. Incidentally, the shape of the aluminum nitride particles is usually not constant. Therefore, the particle diameter of aluminum nitride particles is defined as the distance between the two most distant points on the circumference of the particle to be measured. For image analysis software, for example, "GIMP2" (trade name) or "imageJ" (trade name) distributed under the GNU GPL can be used.

The upper limit of the thickness of the aluminum nitride sintered plate 100 may be, for example, 1.0 mm or less, 0.9 mm or less, 0.8 mm or less, or 0.7 mm or less. When the upper limit of the thickness is within the above range, the heat dissipation can be improved when used as a constituent member of the heat dissipation sheet. The lower limit of the thickness of the aluminum nitride sintered plate 100 may be, for example, 0.15 mm or more, or 0.20 mm or more. When the lower limit of the thickness is within the above range, the heat dissipation properties and thermal resistivity of the entire circuit board prepared using the aluminum nitride sintered plate can be improved. The thickness of the aluminum nitride sintered plate 100 may be adjusted within the above range, and may be, for example, 0.20-1.0 mm.

The aluminum nitride sintered plate 100 has excellent bending strength. The bending strength of the aluminum nitride sintered plate 100 can be, for example, 370 MPa or more, 390 MPa or more, 400 MPa or more, 450 MPa or more, or 500 MPa or more. Bending strength in this specification means a value measured according to the method described in JIS C 2141:1992 "Electrical insulating ceramic material test method". Specifically, it is measured according to the method described in the Examples of this specification.

Since the aluminum nitride sintered plate 100 has a uniform structure, the bending strength distribution is sufficiently suppressed. The aluminum nitride sintered plate 100 has a relatively large Weibull coefficient in the Weibull statistical analysis of its bending strength. The Weibull coefficient with respect to the bending strength of the aluminum nitride sintered plate 100 is, for example, 10.0 or more, 12.0 or more. It can be 13.0 or more, 14.0 or more, 15.0 or more, or 16.0 or more.

Weibull statistics are used to evaluate the distribution of flexural strength. Regarding the aluminum nitride sintered plate 100, when a Weibull plot is created in which the vertical axis is the fracture probability F (σ) and the horizontal axis is the bending strength σ (strength at break, bending strength), the slope m is the Weibull coefficient. is. A large Weibull modulus means that the bending strength distribution is narrow and close to normal distribution. The failure probability F(σ) in the Weibull plot is given by the following formula (1).
F(σ)=1−exp[−(σ/η) ^m ] (1)
In the above formula (1), η is a fitting parameter.

The aluminum nitride sintered body described above can be produced, for example, by the following method. One embodiment of a method for producing an aluminum nitride sintered body includes a firing step of obtaining a sintered body by firing a molded body composed of a mixture containing aluminum nitride and a sintering aid for 1 to 6 hours; A step of obtaining an annealed product by heat-treating the body at a temperature of 1400 ° C. or more and less than 1700 ° C. for 1 hour or more (hereinafter also referred to as an annealing step); and a step of obtaining a body (hereinafter also referred to as a polishing step).

"First, prepare the ingredients." As raw materials, for example, aluminum nitride, sintering aids, and, if necessary, additives are used. Additives include binders, plasticizers, dispersion media, release agents, and the like. Binders include, for example, methylcellulose-based binders having plasticity or surfactant effects, and acrylic acid ester-based binders having excellent thermal decomposability. Examples of plasticizers include glycerin and the like. Dispersion media include, for example, ion-exchanged water and ethanol.

Aluminum nitride is not particularly limited, and aluminum nitride powder produced by a known method such as a direct nitriding method in which metal aluminum is nitrided in a nitrogen atmosphere, and a reduction nitriding method in which aluminum oxide is reduced with carbon. Available.

The sintering aid contains yttrium oxide and aluminum oxide. The sintering aid may be particulate. The mass ratio of aluminum oxide to yttrium oxide (content of aluminum oxide/content of yttrium oxide) is less than 0.5. Thereby, aggregation of oxides in the aluminum nitride sintered plate can be suppressed. The mixing ratio of yttrium oxide and aluminum oxide can be adjusted within the range described above, thereby adjusting the oxide composition in the aluminum nitride sintered plate. Aluminum oxide and yttrium oxide form a liquid phase of a composite oxide during sintering to promote sintering. Thereby, the aluminum nitride sintered plate can be sufficiently densified.

The content of the sintering aid may be, for example, 1 to 10.0 parts by mass with respect to 100 parts by mass of aluminum nitride. By setting the content of the sintering agent within the above range, the density of the obtained aluminum nitride sintered body can be improved, and the bending strength can be further improved. By setting the content of the sintering aid within the above range, the thermal conductivity of the obtained aluminum nitride sintered body can be improved. The content of the sintering aid is a value calculated from the amount of the sintering aid in terms of oxide.

Also, the content of aluminum oxide may be, for example, 0.1 to 5.0 parts by mass with respect to 100 parts by mass of aluminum nitride. By setting the content of aluminum oxide to 0.1 parts by mass or more, the density of the obtained aluminum nitride sintered body can be further improved. In addition, by setting the content of aluminum oxide to 5.0 parts by mass or less, the relative content of aluminum nitride can be increased, and the decrease in thermal conductivity of the obtained aluminum nitride sintered body can be further suppressed. be able to.

The aluminum nitride, the sintering aid, and the additive added as necessary may be blended and mixed and used as a forming raw material. The forming raw material may be formed, for example, into a sheet by a known method such as a doctor blade method. The molded body obtained may be degreased. The degreasing method is not particularly limited, and for example, the compact may be heated to 300 to 700° C. in air or in a non-oxidizing atmosphere such as nitrogen. The heating time may be, for example, 1 to 10 hours.

The aluminum nitride sintered body can be obtained by firing the above compact. The baking step (hereinafter also referred to as the baking step) may be performed in an inert gas atmosphere. The inert gas may be nitrogen, for example. The firing step may be performed under atmospheric pressure.

In the firing step, a molded body composed of a mixture containing aluminum nitride and a sintering aid is fired for 1 to 6 hours to obtain a sintered body (the firing time is 1 to 6 hours). The firing step includes a step of obtaining a first fired body from the molded body by heating at a temperature of 1700 ° C. or more and less than 1800 ° C. for 1 hour or more (hereinafter also referred to as a first firing step), and a temperature of 1800 to 1900 ° C. and a step of obtaining the sintered body from the first sintered body by heating at for one hour or more (hereinafter also referred to as a second sintering step).

The term "firing time" as used herein refers to the time during which the temperature of the atmosphere in which the object to be fired, such as the molded article, is placed reaches the firing temperature and is maintained at that temperature.

The firing temperature in the first firing step can be selected depending on the composition of the sintering aid, and may be, for example, 1750°C or lower, 1730°C or lower, or 1720°C or lower. The rate of temperature increase until the firing temperature in the first firing step is reached may be relatively high, for example, 20° C./min or more, or 30° C./min or more. In the first sintering step, the sintering temperature is preferably maintained for a predetermined period of time. The firing time in the first firing step may be, for example, 1.0 hours or longer, 2.0 hours or longer, or 2.5 hours or longer.

From the viewpoint of improving the texture density of the resulting sintered body, the firing temperature in the second firing step may be, for example, less than 1850°C, less than 1840°C, or 1830°C or less. The rate of temperature increase until reaching the firing temperature in the second firing step may be, for example, 0.5° C./min or more, or 1.0° C./min or more. In the second sintering step, the sintering temperature is preferably maintained for a predetermined period of time. The firing time in the second firing step may be, for example, 1.0 hours or longer, 1.5 hours or longer, or 2.0 hours or longer.

The firing time of the firing step is 6.0 hours or less in total, but may be, for example, 5.0 hours or less or 4.0 hours or less. By setting the total firing time within the above range, it is possible to reduce the leakage of the sintering aid in the surface layer of the molded body or aluminum nitride sintered body to the outside of the molded body or aluminum nitride sintered plate. , the surface roughness can be reduced. The total firing time of the firing step may be, for example, 1.0 hours or more, 2.0 hours or more, or 3.0 hours or more. By setting the total firing time within the above range, the sintering aid is melted, the aluminum nitride particles are sufficiently dissolved, and the grain growth of the aluminum nitride particles can be performed in a more uniform environment. Therefore, an aluminum nitride sintered body having a more uniform particle size distribution can be prepared. The firing time of the firing step can be adjusted within the range described above, and may be, for example, 1.0 to 4.0 hours.

In the annealing step, on the main surface of the sintered body obtained in the firing step, the composite compound derived from the sintering aid formed between the grains of the aluminum nitride crystals is re-liquidized to form fine nitriding. By forming aluminum particles, repairing defects such as grain boundaries and cracks generated on the surface of the sintered body, reducing unevenness on the main surface, and then performing a subsequent polishing treatment, It is also possible to prepare an aluminum nitride sintered body with reduced unevenness on the main surface. Polishing is sometimes performed in the conventional method of manufacturing an aluminum nitride sintered body, but due to circumstances such as the presence of coarse particles of aluminum nitride on the surface, the unevenness before polishing is large, and it is necessary to increase the amount of polishing. If coarse particles of aluminum nitride shed from the surface during this process, large recesses may be formed. For this reason, it is not easy to smooth the surface in the conventional method of manufacturing an aluminum nitride sintered plate. In the production method of the present disclosure, the aluminum nitride particles are suppressed from being coarsened and homogenized in the sintering step, and the annealing step is performed to suppress an increase in the amount of polishing and further reduce the frequency of shedding. can prepare an aluminum nitride sintered body having a smoother and more homogeneous primary surface.

The heating temperature in the annealing process is 1400°C or more and less than 1700°C. The heating temperature in the annealing step may be, for example, 1650° C. or lower, or 1600° C. or lower. By setting the upper limit of the heating temperature within the above range, fine particles of aluminum nitride can be formed on the surface of the sintered body while suppressing coarsening of the aluminum nitride particles. The lower limit of the heating temperature in the annealing step may be, for example, 1400° C. or higher. By setting the lower limit of the heating temperature within the above range, the formation of fine particles of aluminum nitride on the surface of the sintered body can be promoted. The heating temperature in the annealing step may be adjusted within the range described above, and may be, for example, 1400-1600.degree.

The heating time in the annealing step is 1 hour or longer, but may be 2 hours or longer, for example. By setting the lower limit of the heating time within the above range, the liquid phase reaction can be promoted and the fine aluminum nitride particles can be precipitated more sufficiently. The upper limit of the heating time in the annealing step may be, for example, 6 hours or less. By setting the upper limit of the heating time within the above range, coarsening of the aluminum nitride particles on the main surface can be suppressed. The heating time in the annealing step may be adjusted within the above range, and may be, for example, 1 to 6 hours.

The polishing process can be performed by, for example, honing treatment. The honing treatment can be performed, for example, on the surface of the annealed object under conditions of polishing pressure: 0.15 to 0.35 MPa, polishing amount: 2 to 10 μm, and time: 1 to 5 minutes.

The aluminum nitride sintered plate obtained by the manufacturing method described above may be processed into a desired shape as necessary. The aluminum nitride sintered body may be processed into, for example, a plate having a pair of main surfaces to form an aluminum nitride sintered plate. A metal part such as a metal circuit or a metal plate may be attached to the aluminum nitride sintered body to form the substrate. The substrate may be, for example, a laminated substrate in which a main surface of a sintered aluminum nitride plate and a main surface of a metal plate such as a copper plate are bonded together. Moreover, it may be a circuit board having a circuit pattern formed by removing a part of a metal plate by etching or the like to form a conductor portion. Thus, the substrate of the present disclosure may be a laminate substrate or a circuit substrate. In the case of a plate shape, the lower limit of the thickness of the aluminum nitride sintered body may be, for example, 0.10 mm or more, 0.20 mm or more, or 0.25 mm or more. In the case of a plate shape, the upper limit of the thickness of the aluminum nitride sintered body may be, for example, 3.00 mm or less, 1.50 mm or less, or 1.00 mm or less. The thickness of the aluminum nitride sintered body can be adjusted within the above range, and may be, for example, 0.10-3.00 mm, or 0.25-1.00 mm. By setting the thickness of the aluminum nitride sintered body within the above range, both the heat dissipation characteristics and the thermal resistivity of the entire circuit board can be achieved at higher levels.

An embodiment of the laminated substrate comprises the aluminum nitride sintered plate described above and a metal plate attached to the aluminum nitride sintered plate. FIG. 2 is a perspective view showing an example of a laminated substrate. The laminated substrate 200 includes a pair of metal plates 110 arranged to face each other, and an aluminum nitride sintered plate 100 between the pair of metal plates 110 . Examples of the metal plate 110 include a copper plate. The shape and size of the aluminum nitride sintered plate 100 and the metal plate 110 may be the same or different. The metal plate 110 and the aluminum nitride sintered plate 100 may be joined with, for example, brazing material. One of the pair of metal plates 110 may be used as a heat dissipation material, and the other may be processed into a circuit pattern. The circuit pattern may be formed by etching the metal plate 110 using a resist. As a result, it is possible to form a circuit board capable of sufficiently suppressing leakage current or the like, or to form a heat dissipation board.

An embodiment of the circuit board includes the aluminum nitride sintered plate described above and a conductor portion attached to the aluminum nitride sintered plate. FIG. 3 is a perspective view showing an example of a circuit board. The circuit board 300 includes an aluminum nitride sintered plate 100 , a plurality of conductor portions 20 and a metal plate 110 . Conductor portion 20 is provided on one main surface 100A of aluminum nitride sintered plate 100 , and metal plate 110 is provided on the other surface of aluminum nitride sintered plate 100 . When the circuit board 300 is used for a power module, the metal plate 110 may function as a heat dissipation material.

The aluminum nitride sintered plate 100 in the laminated substrate 200 and the circuit board 300 is composed of an aluminum nitride sintered plate with excellent electrical insulation and thermal conductivity. Therefore, it has excellent reliability when used in various products such as power modules.

Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. For example, the shape and structure of the substrates of the present disclosure are not limited to those of FIGS. For example, circuit patterns may be formed on both main surfaces of the aluminum nitride sintered plate 100 . Also, instead of etching the metal plate 110, the conductor portion 20 may be formed by spraying metal powder and heat-treating it. Also, the descriptions of the above-described embodiments can be applied to each other.

Hereinafter, the present disclosure will be described in more detail using examples and comparative examples. It should be noted that the present disclosure is not limited to the following examples.

(Example 1)
(Production of aluminum nitride sintered plate)
To 100 parts by mass of aluminum nitride powder, 6.0 parts by mass of yttrium oxide powder as a sintering aid and 0.3 parts by mass of α-aluminum oxide were blended and mixed using a ball mill to obtain a mixed powder. For 100 parts by mass of the mixed powder, 6 parts by mass of cellulose ether binder (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: Metrose), 5 parts by mass of glycerin (manufactured by Kao Corporation, trade name: Excepar), and ion exchange 10 parts by mass of water was added and mixed for 1 minute using a Henschel mixer to obtain a molding raw material.

This molding raw material is molded with a screw type extruder to produce a sheet-like molded body (width: 80 mm, thickness: 0.8 mm), dried at 100 ° C. for 1 hour, and then cut into a length of 60 mm. x Width: 60 mm shaped compact was obtained. After applying boron nitride powder as a mold release agent to this compact, a plurality of the above compacts were laminated to adjust the mass of the laminate to 95 kg. A degreased body was obtained by heating the obtained laminate at 600° C. in the air for degreasing.

Next, the degreased body is placed in a heating furnace and heated from 25° C. to 1700° C. at a heating rate of 20° C./min under atmospheric pressure in a nitrogen gas atmosphere and held at 1700° C. for 2.5 hours. (first firing step). Next, the temperature was raised to 1820° C. at a temperature elevation rate of 1° C./min, and held at 1820° C. for 2 hours (second firing step). After that, the heating was stopped and allowed to cool in the heating furnace to obtain a sintered body.

An annealed product was obtained by heat-treating the sintered body at 1700°C for 2 hours in a nitrogen gas atmosphere (annealing step). Next, the surface of the annealed product is honed under the conditions of a polishing pressure of 0.15 to 0.35 MPa, a polishing amount of 2 to 10 μm, and a time of 1 to 5 minutes to obtain a thickness of 0.635 mm. of the aluminum nitride sintered plate was obtained (polishing step). For reference, FIG. 4 shows SEM images obtained by scanning electron microscope (SEM) of the main surface of the annealed product and the main surface of the aluminum nitride sintered plate. In FIG. 4, (a) shows the main surface of the annealed product, and (b) shows the main surface of the aluminum nitride sintered plate. As shown in FIG. 4(a), it can be confirmed that fine particles of aluminum nitride are formed on the surface of the annealed product. In addition, as shown in FIG. 4(b), no conspicuous shedding spots or the like were observed on the main surface of the aluminum nitride sintered plate after polishing.

<Heat cycle test for aluminum nitride sintered plate>
A heat cycle test was performed on the obtained aluminum nitride sintered plate (thickness: 0.635 mm). Specifically, first, a brazing material containing silver (Ag), copper (Cu), and an active metal (90 parts by mass of Ag, 10 parts by mass of Cu, 3 parts by mass of Sn, and 3.5 parts by mass of Ti A copper plate (thickness: 0.3 mm) was bonded to the aluminum nitride sintered plate through a brazing material having a composition of 830° C. for a bonding time of 15 μm. An aluminum nitride substrate (laminate) was prepared by bonding under the condition of vacuum degree: 1×10 ⁻³ Pa for 1 hour. The obtained laminate was exposed to a 350° C. environment for 5 minutes and then cooled to a 25° C. environment for 5 minutes. The laminate that has undergone the above pretreatment is first exposed to an environment in dry ice (-78 ° C.) for 5 minutes, and then returned to room temperature (25 ° C.) as one cycle. A cycle test was performed. After the test, the aluminum nitride substrate was etched with an aqueous solution of copper chloride, ammonium fluoride, and hydrogen peroxide to remove the metal plate and the brazing material from the laminate, and the aluminum nitride sintered plate was taken out. . An image of the main surface of the obtained aluminum nitride sintered plate on which the copper plate was laminated was taken with a scanner at a resolution of 600 dpi×600 dpi. After binarizing (threshold: 140) the obtained image with the image analysis software "GIMP2", the area of cracks generated in the horizontal direction on the main surface of the aluminum nitride sintered plate was measured. The ratio of cracks was calculated by dividing by the area of the main surface (total area). Table 1 shows the results.

<Measurement of physical properties of aluminum nitride sintered plate>
For the obtained aluminum nitride sintered plate, d50 (average particle diameter) and d90 of aluminum nitride (AlN) particles, arithmetic mean roughness Ra and maximum height roughness Ry on the main surface were measured. Table 1 shows the results.

<Evaluation of aluminum nitride sintered plate>
The bending strength and bending strength distribution (Weibull coefficient) of the obtained aluminum nitride sintered plate were measured. The bending strength of the aluminum nitride sintered plate was measured according to the method described in JIS C 2141:1992 "Electrical insulating ceramic material test method". In addition, a Weibull plot was created based on the bending strength obtained, and the Weibull coefficient was determined. Table 1 shows the results.

(Example 2)
An aluminum nitride sintered plate was prepared in the same manner as in Example 1, except that the annealing temperature in the annealing step was changed to 1400° C. and the annealing time was changed to 1 hour.

(Example 3)
An aluminum nitride sintered plate was prepared in the same manner as in Example 1, except that the annealing time in the annealing step was changed to 6 hours.

(Example 4)
An aluminum nitride sintered plate was prepared in the same manner as in Example 1, except that the annealing temperature in the annealing step was changed to 1500°C.

(Comparative example 1)
An aluminum nitride sintered plate was obtained in the same manner as in Example 1, except that the annealing temperature in the annealing step was changed to 1800° C. and the annealing time was changed to 8 hours. For reference, FIG. 5 shows SEM images obtained by a scanning electron microscope (SEM) of the main surface of the sintered body before polishing and the main surface of the aluminum nitride sintered plate. In FIG. 5, (a) shows the main surface of the sintered body before polishing, and (b) shows the main surface of the aluminum nitride sintered plate. As can be seen from FIGS. 5(a) and 5(b), depressions formed by shedding of aluminum nitride particles are observed on the main surface of the polished aluminum nitride sintered plate.

(Comparative example 2)
An aluminum nitride sintered plate was prepared in the same manner as in Comparative Example 1, except that the annealing step was not performed.

(Comparative Example 3)
An aluminum nitride sintered plate was prepared in the same manner as in Comparative Example 1, except that the annealing time in the annealing step was changed to 2 hours.

<Heat cycle test for aluminum nitride sintered plate>
A heat cycle test was performed in the same manner as in Example 1 for each of the aluminum nitride sintered plates obtained in Examples 2 to 4 and Comparative Examples 1 to 3. Table 1 shows the results.

<Measurement of physical properties of aluminum nitride sintered plate>
For each of the aluminum nitride sintered plates obtained in Examples 2 to 4 and Comparative Examples 1 to 3, in the same manner as in Example 1, d50 (average particle diameter) and d90 of aluminum nitride (AlN) particles, and , the arithmetic mean roughness Ra and the maximum height roughness Ry on the main surface were measured. Table 1 shows the results.

<Evaluation of aluminum nitride sintered plate>
For each of the aluminum nitride sintered plates obtained in Examples 2 to 4 and Comparative Examples 1 to 3, the bending strength of the aluminum nitride sintered plate and the distribution of bending strength (Weibull coefficient) was measured. Table 1 shows the results.

20... Conductor portion, 100... Aluminum nitride sintered plate, 110... Metal plate, 200... Laminated substrate, 300... Circuit board.

Claims

An aluminum nitride sintered body containing aluminum nitride particles and sintering aid particles,
A laminate was prepared by laminating with a metal plate, exposed to an environment of 350 ° C. for 5 minutes, cooled for 5 minutes in an environment of 25 ° C., and exposed to an environment of -78 ° C. for 5 minutes. , an aluminum nitride sintered body having an observed crack rate of less than 9.00 area % when subjected to a heat cycle test of 10 cycles, one cycle of which is an operation of returning to 25°C.
The aluminum nitride sintered body according to claim 1, which has a plate-like shape having a pair of main surfaces, and the difference between the maximum height roughness Ry and the arithmetic mean roughness Ra on the main surfaces is 6.0 µm or less.
The aluminum nitride sintered body according to claim 2, wherein the maximum height roughness Ry is less than 10.0 µm.
In the cumulative frequency distribution curve of the particle size measured by electron microscope image analysis for the aluminum nitride particles, the particle size when the integrated value from the small particle size reaches 50% and 90% of the total is d50 and d90, respectively. 4. The aluminum nitride sintered body according to any one of claims 1 to 3, wherein the value of d90-d50 is less than 10.0 µm.
A circuit board comprising the aluminum nitride sintered body according to any one of claims 1 to 4 and a conductor part attached to the aluminum nitride sintered body.
A laminated substrate comprising the aluminum nitride sintered body according to any one of claims 1 to 4 and a metal plate attached to the aluminum nitride sintered body.
a firing step of firing a molded body composed of a mixture containing aluminum nitride and a sintering aid for 1 to 6 hours to obtain a sintered body;
obtaining an annealed product by heat-treating the sintered body at a temperature of 1400° C. or more and less than 1700° C. for 1 hour or more;
and obtaining an aluminum nitride sintered body by polishing the surface of the annealed product,
The sintering aid contains yttrium oxide and aluminum oxide,
The mass ratio of the aluminum oxide to the yttrium oxide is less than 0.5,
The firing step includes
a step of obtaining a first fired body from the molded body by heating at a temperature of 1700° C. or more and less than 1800° C. for 1 hour or more;
and obtaining the sintered body from the first sintered body by heating at a temperature of 1800 to 1900° C. for 1 hour or longer.