Aluminum nitride plate, joined body, and power module

Abstract

To provide an aluminum nitride plate having excellent reliability.SOLUTION: The aluminum nitride plate includes aluminum nitride and an oxide having yttrium and aluminum as constituent elements. The surface strength of the central portion of the aluminum nitride plate measured at a compression speed of 0. 5mm / min using a universal tester is equal to or higher than 300MPa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an aluminum nitride plate, a joined body, and a power module. [Background technology]

[0002] In recent years, power modules for controlling large amounts of power have been used in industrial equipment such as motors and in products such as electric vehicles. These power modules use circuit boards with ceramic plates to efficiently diffuse heat generated from semiconductor elements and suppress leakage current. These circuit boards usually use plate-shaped ceramic sintered bodies.

[0003] Known ceramic sintered bodies are composed of nitrides, carbides, borides, silicides, etc. Among these, aluminum nitride sintered bodies have excellent thermal conductivity and electrical insulation properties. Therefore, aluminum nitride sintered bodies are useful for circuit boards of electronic components such as power modules. For example, Patent Document 1 proposes a technology for improving the volume resistivity by adjusting the composition of oxides contained in an aluminum nitride sintered body to fall within a predetermined range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 261452 Summary of the Invention [Problem to be solved by the invention]

[0005] The temperature of electronic components such as power modules changes significantly due to heat generated by semiconductor elements. Therefore, in a bonded structure in which an aluminum nitride plate and a metal plate are bonded, thermal warping may occur due to the difference in thermal expansion coefficients between the aluminum nitride plate and the metal plate. Therefore, if the aluminum nitride plate has low strength, there is a concern that it may be damaged or broken. Therefore, one aspect of the present disclosure provides an aluminum nitride plate having excellent reliability. Furthermore, a bonded structure and a power module having excellent reliability are provided by including such an aluminum nitride plate. [Means for solving the problem]

[0006] One aspect of the present disclosure provides the following aluminum nitride plate. [1] Aluminum nitride and an oxide having yttrium and aluminum as constituent elements, An aluminum nitride plate with a center surface strength of 300 MPa or more, measured using a universal testing machine at a compression speed of 0.5 mm / min. [2] The aluminum nitride plate according to [1], wherein the arithmetic mean roughness Ra of the main surface is 0.30 μm or less. [3] The content of the aluminum nitride is more than 95 mass%; The aluminum nitride plate according to [1] or [2], wherein the content of the oxide is 3 mass % or more. [4] The aluminum nitride plate according to any one of [1] to [3], wherein the oxide contains 3Y2O3·5Al2O3 and Y2O3·Al2O3, and the mass ratio of 3Y2O3·5Al2O3 to Y2O3·Al2O3 is 0.8 or more. [5] The aluminum nitride plate according to any one of [1] to [4], which has a thickness of less than 2.0 mm.

[0007] When a bonded body in which an aluminum nitride plate and a metal plate are bonded is used in a high-temperature environment, thermal warping occurs. The strain generated in the aluminum nitride plate at this time is usually greater in the central portion than in the edge portion. The aluminum nitride plate described in [1] above has sufficiently high surface strength in the central portion. In such an aluminum nitride plate, defects and cracks in the central portion are sufficiently reduced. Therefore, for example, breakage and destruction due to thermal warping are less likely to occur. Therefore, the aluminum nitride plate has excellent reliability.

[0008] The arithmetic mean roughness Ra of the main surface of the aluminum nitride plate [2] above is sufficiently small. This makes it even less susceptible to damage and fracture due to, for example, thermal warping, etc. Such an aluminum nitride plate has even greater reliability.

[0009] The central portion of the aluminum nitride plate of [3] and [4] above has sufficiently high surface strength. Such an aluminum nitride plate has even greater reliability. The aluminum nitride plate of [5] above is suitable for applications requiring miniaturization.

[0010] One aspect of the present disclosure provides the following conjugate: [6] A bonded body comprising the aluminum nitride plate according to any one of the above [1] to [5] and a metal plate bonded to the aluminum nitride plate.

[0011] The circuit board of [6] above includes an aluminum nitride plate that can sufficiently suppress the occurrence of cracks in the center when deformed by thermal warping, etc. Such a circuit board has excellent reliability in high-temperature environments.

[0012] One aspect of the present disclosure provides the following power module. [7] A power module comprising the aluminum nitride plate according to any one of the above [1] to [5] and a conductor part joined to the aluminum nitride plate.

[0013] The power module [7] above comprises the aluminum nitride plate described above and a conductor portion bonded to the aluminum nitride plate. This power module comprises an aluminum nitride plate that is resistant to damage and destruction due to, for example, thermal warping. Therefore, this power module operates stably even when used in a high-temperature environment and has excellent reliability. [Effects of the Invention]

[0014] According to one aspect of the present disclosure, it is possible to provide an aluminum nitride plate having excellent reliability, and by including such an aluminum nitride plate, it is possible to provide a joined body and a power module having excellent reliability. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a connection structure between a load cell used when measuring the surface strength of an aluminum nitride plate and a jig that is pressed against the aluminum nitride plate. [Figure 2] FIG. 2 is a diagram showing the positional relationship between a jig pressed against a main surface of an aluminum nitride plate and the aluminum nitride plate whose surface strength is to be measured. [Figure 3] FIG. 2 is a plan view showing the center of the main surface of the aluminum nitride plate against which the load ring is pressed. [Figure 4] 1 is a photograph showing an example of the appearance of an aluminum nitride plate after measuring its surface strength. [Figure 5] 1 is a graph showing an example of the relationship between stroke and test force when measuring the surface strength of an aluminum nitride plate. [Figure 6] FIG. 1 is a perspective view showing an example of a bonded body. [Figure 7] FIG. 1 is a perspective view showing a circuit board as an example of a joined body. [Figure 8] 1A and 1B are diagrams illustrating an example of a circuit board that has been thermally warped. [Figure 9] FIG. 1 is a cross-sectional view showing an example of a power module. [Figure 10] 1 is a graph showing the relationship between compression speed and surface strength. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present disclosure will be described, occasionally with reference to the drawings. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same reference numerals will be used for identical elements or elements having the same functions, and redundant descriptions will be omitted where appropriate. Positional relationships, such as up, down, left, and right, are based on the positional relationships relative to the orientation of the reference numerals shown in the drawings, unless otherwise specified. The dimensional ratios of each element are not limited to those shown. Numerical ranges indicated with the symbol "~" include the lower and upper limits. That is, a numerical range indicated as "A to B" means A or greater and B or less. Numerical ranges in which the upper or lower limit of each numerical range is replaced with the numerical value of any of the examples are also included in the present disclosure. When multiple numerical ranges are exemplified in stages, a numerical range in which the upper or lower limit of a first numerical range is replaced with the upper or lower limit of a second numerical range that is narrower than the first numerical range is also included in the present disclosure. Multiple exemplified substances and materials may be used singly or in combination of two or more arbitrarily selected types.

[0017] An aluminum nitride plate according to one embodiment contains aluminum nitride as a primary component and an oxide (composite oxide) having yttrium and aluminum as constituent elements as a secondary component. The aluminum nitride plate may be composed of an aluminum nitride sintered body. The surface strength of the center of the aluminum nitride plate is 300 MPa or more. The surface strength is measured using a universal testing machine at a compression speed of 0.5 mm / min.

[0018] The surface strength of the center of the aluminum nitride plate may be 330 MPa or more, 350 MPa or more, 370 MPa or more, or 380 MPa or more. An aluminum nitride plate having such surface strength has sufficiently excellent reliability against thermal warpage deformation. The surface strength of the center of the aluminum nitride plate may be 500 MPa or less, or 450 MPa or less. An example of the surface strength range may be 300 to 500 MPa.

[0019] A three-point or four-point bending test is known as a method for evaluating ceramic plates. However, the strength measured by the three-point or four-point bending test is highly dependent on the processing state of the edges of the ceramic plate. This makes it difficult to accurately evaluate the susceptibility to breakage and fracture at the center of the ceramic plate. On the other hand, the aluminum nitride plate of this embodiment has a surface strength of a predetermined value or more at the center of the aluminum nitride plate, which is less affected by the processing state of the edges. This allows for sufficient suppression of breakage and fracture due to thermal warping, etc.

[0020] The universal testing machine used to measure surface strength is not particularly limited, and commercially available machines can be used. For example, a Tensilon universal testing machine manufactured by A&D Co., Ltd. may be used. Surface strength is measured using a ring bending test jig based on ASTM C1499-19, "Standard Test Method for Monotonic Equiaxial Bending Strength of Advanced Ceramics at Ambient Temperature 1." The ring bending test jig has a support ring and a load ring that abut against the main surface of the aluminum nitride plate. The universal testing machine and the ring bending test jig may be connected using any structure.

[0021] The ring bending test jig shown in FIG. 1 comprises an upper jig 20 and a lower jig 30. In FIG. 1, the upper jig 20, which has a load ring 22, is mounted below a load cell 42 attached to a moving crosshead 40 of a universal testing machine, and the lower jig 30, which has a support ring 32, is mounted on the base 50 of the universal testing machine. The structure connecting the load cell 42 and the upper jig 20 comprises a guide 48 through which a load rod 44 connected to the load cell 42 is inserted, and a mounting plate 49 fixed to the guide 48 with screws 46 so as to be positioned below the guide 48. The mounting plate 49 has a holder that holds a hard ball 45 that abuts against the tip of the load rod 44. The upper jig 20 is fixed to the lower part of the mounting plate 49 with bolts (not shown). The hard ball 45 contacts the top surface of the upper jig 20, and the load from the load rod 44 is applied to the aluminum nitride plate whose surface strength is to be measured via the load ring 22 of the upper jig 20. The load applied to the aluminum nitride plate is detected by the load cell 42 via the upper jig 20, the hard ball 45 and the load rod.

[0022] As shown in Figure 2, the upper jig 20 has a main body 21 with an upper surface that contacts the rigid balls 45, and a cylindrical load ring 22 provided on the underside of the main body 21. The lower jig 30 has a cylindrical main body 31 and a cylindrical support ring 32 provided on the upper side of the main body 31. The load ring 22 and the support ring 32 are arranged opposite each other so that their centerlines coincide. The diameter D of the support ring 32 is S The diameter D of the support ring 32 is sufficient as long as it can stably support the aluminum nitride plate 10. S is the diameter D of the load ring 22 L It can be bigger than that.

[0023] When measuring the surface strength of the aluminum nitride plate 10, the aluminum nitride plate 10 is placed on the lower jig 30 fixed to the base 50 of the universal testing machine, and the upper jig 20 fixed to the mounting plate 49 is lowered. This causes the aluminum nitride plate 10 to be sandwiched between the load ring 22 and the support ring 32. The speed at which the upper jig 20 is lowered is adjusted, and the aluminum nitride plate 10 is compressed at a compression speed of 0.5 mm / min. By performing the measurement at this compression speed, the surface strength of the aluminum nitride plate 10 can be measured with high accuracy.

[0024] As shown in Figure 3, the lower surface of the load ring 22 abuts against the center 12 of the main surface 10a of the aluminum nitride plate 10. The aluminum nitride plate 10 is positioned so that the center line CL passing through the centers of the load ring 22 and the support ring 32 in Figure 2 passes through its center CE. The center CE is the geometric center of the aluminum nitride plate 10. The diameter D of the load ring 22 L The diameter of the center 12 where the load ring 22 abuts is preferably smaller than the shortest distance SP between the center 12 and the outer edge of the aluminum nitride plate 10. By using a load ring 22 of such a size, it is possible to measure surface strength with the influence of the structure of the end of the aluminum nitride plate 10 sufficiently reduced. The surface strength measured in this way has a high correlation with the susceptibility to breakage and destruction due to thermal warping, etc.

[0025] When the aluminum nitride plate 10 is continuously compressed at the above-mentioned compression speed, the center 12 of the aluminum nitride plate 10 breaks, as shown in the photograph in Figure 4. Figure 5 is a graph showing an example of the relationship between the stroke of the moving crosshead and the test force. This graph shows that the center 12 of the aluminum nitride plate 10 breaks when the test force reaches 940 N. The surface strength of the aluminum nitride plate 10 can be calculated from the breaking load (maximum test force, 940 N in Figure 5) when the center 12 breaks, using the following formula (I):

[0026]

number

[0027] In the above formula (I), σ f is the surface strength [MPa], F is the maximum test force [N], ν is the Poisson's ratio, h is the thickness of the aluminum nitride plate 10 [mm], D S is the diameter of the support ring [mm], D L indicates the diameter [mm] of the load ring, and D indicates the converted diameter [mm] of the aluminum nitride plate 10. ν is set to 0.22, and σ f When the aluminum nitride plate 10 has a square pillar shape, the converted diameter D can be calculated by multiplying the vertical length by the horizontal length by 0.54. When the aluminum nitride plate has a cylindrical shape, D is the diameter of the main surface.

[0028]

number

[0029] In the above formula (II), δ is the deflection [mm], E is the elastic modulus [MPa], and the other characters are the same as in formula (I). δ is calculated assuming that the elastic modulus E is 300,000 MPa.

[0030] The deflection δ of the aluminum nitride plate 10 may exceed 0.10 mm, and may be 0.11 mm or more, 0.12 mm or more, or 0.13 mm or more. This allows for sufficiently high reliability against not only thermal warpage deformation but also thermal shock.

[0031] The arithmetic mean roughness Ra of the main surface 10a of the aluminum nitride plate 10 may be 0.30 μm or less, 0.25 μm or less, or 0.20 μm or less. The arithmetic mean roughness Ra of the main surface of the aluminum nitride plate in this disclosure is measured on the main surface that contacts the load ring in accordance with JIS B 0601:2013. The arithmetic mean roughness Ra can be measured using a commercially available measuring device. The arithmetic mean roughness Ra of the main surface of the aluminum nitride plate may be adjusted by changing the firing temperature when producing the aluminum nitride plate, or by polishing the main surface. It can also be adjusted by changing the surface roughness at the green sheet stage.

[0032] The thickness h of the aluminum nitride plate 10 may be less than 2.0 mm, 1.5 mm or less, or 1.0 mm or less. Because the aluminum nitride plate 10 has sufficiently high surface strength, high reliability can be maintained even if the thickness h is reduced. By reducing the thickness h of the aluminum nitride plate 10, the circuit board including the aluminum nitride plate 10 can be made smaller. Such an aluminum nitride plate 10 is suitable for power modules, which require miniaturization.

[0033] The area of ​​the main surface 10a (upper and lower surfaces) of the aluminum nitride plate 10 is 1500 mm 2 Over 2000mm 2 or more, or 2500mm 2 This may be the case. This makes it possible to ensure a sufficient circuit area when used in a circuit board, for example. The shape of the aluminum nitride plate 10 is not particularly limited as long as it is plate-like. For example, it may be disk-shaped.

[0034] The aluminum nitride plate 10 is composed of an aluminum nitride sintered body. The content of the main component (aluminum nitride) in the aluminum nitride plate 10 may be more than 95% by mass or 96% by mass or more in order to increase thermal conductivity. The content of the main component in the aluminum nitride plate 10 may be 99% by mass or less, or 98% by mass or less in order to sufficiently increase density. In the present disclosure, the main component refers to the component contained in the aluminum nitride plate 10 with the largest content. Components other than the main component are referred to as minor components. Minor components are components different from the main component, and include oxides having yttrium and aluminum as constituent elements. Granular oxides may be dispersed in the grain boundaries of the granular aluminum nitride.

[0035] The oxide content in the aluminum nitride plate 10 may be 3% by mass or more, or 3.5% by mass or more, from the viewpoint of sufficiently increasing the density. The oxide content in the aluminum nitride sintered body may be less than 6% by mass or less than 5% by mass, from the viewpoint of increasing the thermal conductivity. The oxide content can be determined by removing components other than oxides from the aluminum nitride plate 10 by hydrolysis reaction.

[0036] The granular oxide contains 3Y2O3·5Al2O3 and Y2O3·Al2O3. 3Y2O3·5Al2O3 is a type of Y2O3-Al2O3-based compound, also known as YAG. Hereinafter, this component will also be referred to as "YAG" in this disclosure. The YAG content in the aluminum nitride plate 10 may be 0.5 to 2.5 mass% from the viewpoint of sufficiently increasing surface strength. The YAG content relative to the total oxide may be 35 mass% or more, 40 mass% or more, or 45 mass% or more from the viewpoint of increasing electrical insulation. The YAG content relative to the total oxide may be 65 mass% or less, or 60 mass% or less from the viewpoint of ease of sintering. An example of the YAG content relative to the total oxide is 35 to 65 mass%. This content can be adjusted by changing the composition of the sintering aid.

[0037] Y2O3·Al2O3 is also a type of Y2O3-Al2O3-based compound, and is a component also known as YAP. Hereinafter, in this disclosure, it may also be referred to as "YAP." The YAG content in the aluminum nitride plate 10 may be 0.5 to 2.5 mass% from the viewpoint of sufficiently increasing surface strength. The YAP content relative to the total oxides may be 65 mass% or less, or 60 mass% or less, from the viewpoint of increasing electrical insulation. The YAP content relative to the total oxides may be 35 mass% or more, or 40 mass% or more, from the viewpoint of ease of sintering. An example of the YAP content relative to the total oxides is 35 to 65 mass%. This content can be adjusted by changing the composition of the sintering aid. For example, the YAP content can be increased by decreasing the blending ratio of Al2O3.

[0038] The mass ratio of YAG to YAP may be 0.8 or more, or 0.9 or more. Increasing this mass ratio can further increase the surface strength. From the viewpoint of ease of firing, the mass ratio of YAG to YAP may be 2.0 or less, or 1.5 or less. An example of this mass ratio may be 0.8 to 2.0. It is presumed that as the mass ratio of YAG to YAP increases, the oxides become less likely to aggregate, which contributes to improving the surface strength. The mass ratio can be adjusted by changing the composition (type and blending ratio) of the sintering aid used as a raw material and the firing conditions.

[0039] The oxide composition in this disclosure can be determined by dissolving and removing the main component, aluminum nitride, from the aluminum nitride plate 10 through a hydrolysis reaction, and then subjecting the remaining oxide to X-ray diffraction. The hydrolysis reaction may be carried out using, for example, an aqueous sodium hydroxide solution. By dissolving and removing the main component, aluminum nitride, through a hydrolysis reaction, the aggregation state of the granular oxide can also be determined. For example, a MiniFlex (device name) manufactured by Rigaku Corporation can be used for X-ray diffraction.

[0040] The aluminum nitride plate 10 may contain granular oxides having yttrium and aluminum as constituent elements other than YAP and YAG. Examples of such oxides include 2Y2O3·Al2O3. This is also a type of Y2O3-Al2O3-based compound and is a component also known as YAM. Hereinafter, this may also be referred to as "YAM" in this disclosure. The YAM content may be lower than that of YAG and YAP. The YAM content relative to the total oxide content may be, for example, 5% by mass or less, or 1% by mass or less, and may be below the detection limit of X-ray diffraction.

[0041] The aluminum nitride plate 10 may contain components other than aluminum nitride and oxides having yttrium and aluminum as constituent elements. Such components include oxides such as aluminum oxide and yttrium oxide, nitrides other than aluminum nitride, and silicides. The content of components other than aluminum nitride and oxides having yttrium and aluminum as constituent elements may be less than 5 mass%, less than 3 mass%, or less than 1 mass% based on the aluminum nitride sintered body.

[0042] An example of a method for manufacturing the aluminum nitride plate 10 is described below. Examples of raw materials include aluminum nitride powder, a sintering aid, and, if necessary, additives. Examples of additives include binders, plasticizers, dispersion media, and mold release agents. Examples of binders include methylcellulose-based binders with plasticity or surfactant properties, and acrylic ester-based binders with excellent thermal decomposition properties. Examples of plasticizers include glycerin. Examples of dispersion media include ion-exchanged water and ethanol. The aluminum nitride powder is not particularly limited, and aluminum nitride powder manufactured by known methods such as a direct nitriding method in which metallic aluminum is nitrided in a nitrogen atmosphere and a reduction nitriding method in which aluminum oxide is reduced with carbon can be used.

[0043] As the sintering aid, for example, yttrium oxide is used. Aluminum oxide may be used as an oxide other than yttrium oxide. However, it is preferable that the amount of aluminum oxide used by mass is less than the amount of yttrium oxide used. For example, the mass ratio of yttrium oxide to aluminum oxide may be 1.5 or more, or 2.0 or more. This allows the surface strength of the aluminum nitride plate 10 to be sufficiently high.

[0044] Aluminum nitride powder, a sintering aid, and optional additives are blended and mixed to obtain a molding raw material. The molding raw material is formed into, for example, a sheet by a known method such as a doctor blade method. The obtained molded body may be degreased. The degreasing method is not particularly limited, and for example, the molded body may be heated to 300 to 700°C in air or a non-oxidizing atmosphere such as nitrogen. The heating time may be, for example, 1 to 10 hours.

[0045] The aluminum nitride plate 10 can be obtained by firing the above-mentioned molded body. Firing is performed by raising the temperature to 1720 to 1820°C in an inert gas atmosphere. The holding time at 1720 to 1820°C may be 1 to 5 hours. If the firing temperature is too high or the holding time is too long, abnormal grain growth is likely to occur, and the surface strength tends to decrease. On the other hand, if the firing temperature is too low or the holding time is too short, the densification of the aluminum nitride sintered body tends not to proceed sufficiently. Sintering may be performed under atmospheric pressure.

[0046] The aluminum nitride plate 10 obtained by the above-described manufacturing method may be processed into a desired shape as needed. For example, the main surface may be polished to adjust the arithmetic mean roughness Ra. A bonded body may be formed by bonding a conductor such as a metal plate to the aluminum nitride plate 10. The bonded body may be produced, for example, by bonding the main surface of the aluminum nitride plate 10 to the main surface of a metal plate such as a copper plate with a brazing material. The bonded body may also be a circuit board in which a circuit pattern serving as a conductor is formed by removing a portion of the metal plate bonded to the main surface of the aluminum nitride plate 10 by etching or the like. In this way, the bonded body may be a circuit board.

[0047] A bonded body according to one embodiment includes the aluminum nitride plate described above and a metal plate bonded to the aluminum nitride plate. The metal plate may be bonded to the aluminum nitride plate with a brazing material. The bonded body includes an aluminum nitride plate that is resistant to damage and fracture due to thermal warping or the like. Therefore, the bonded body has excellent reliability in high-temperature environments. Such a bonded body is useful, for example, as a circuit board for a power module exposed to a high-temperature environment. The bonded body in this disclosure includes one in which a metal member (such as a metal plate and a conductor) is bonded to an aluminum nitride plate. Therefore, a circuit board is an example of a bonded body.

[0048] FIG. 6 is a perspective view showing an example of a bonded body. The bonded body 60 includes a pair of metal plates 11 arranged to face each other, and an aluminum nitride plate 10 made of an aluminum nitride sintered body between the pair of metal plates 11 and 13. Examples of the metal plates 11 and 13 include copper plates. The aluminum nitride plate 10 and the metal plates 11 and 13 may have the same shape and size or may be different. The metal plates 11 and 13 and the aluminum nitride plate 10 may be bonded together, for example, with a brazing material. The metal plate 13 may be used as a heat dissipation material, and the metal plate 11 may be processed into a circuit pattern. The circuit pattern may be formed by etching the metal plate 11 using a resist. This allows for the production of a circuit board used in a power module or the like.

[0049] 7 is a perspective view showing a circuit board, which is an example of a bonded body. The circuit board 62 includes an aluminum nitride plate 10, a conductor 14, and a metal plate 13. The conductor 14 is bonded to one side of the aluminum nitride plate 10, and the metal plate 13 is bonded to the other side of the aluminum nitride plate 10. When the circuit board 62 is used in a power module, the conductor 14 may function as a terminal electrically connected to a semiconductor element. The metal plate 13 may function as a heat dissipation material.

[0050] FIG. 8 is a perspective view showing a circuit board 62A that has been thermally warped. The circuit board 62A may be obtained by placing the circuit board 62 of FIG. 7 in a high-temperature environment (for example, 100 to 150°C). As shown in FIG. 8, the circuit board 62A is deformed to a warped state. At this time, the aluminum nitride plate 10 is deformed so that the curvature of the central portion increases. Because the aluminum nitride plate 10 has high surface strength in the central portion, it is less likely to be damaged or broken due to thermal warping or the like. Therefore, the aluminum nitride plate 10 and the circuit board 62A including it have excellent reliability against thermal warping deformation.

[0051] An example of a manufacturing method for the bonded body 60 (circuit board 62) will be described. A paste-like brazing filler metal is applied to both main surfaces of the aluminum nitride plate 10 by a method such as a roll coater method, a screen printing method, or a transfer method. The brazing filler metal contains, for example, metal components such as silver and titanium, an organic solvent, and a binder. The viscosity of the brazing filler metal may be, for example, 5 to 20 Pa·s. The content of the organic solvent in the brazing filler metal may be, for example, 5 to 25 mass %, and the content of the binder may be, for example, 2 to 15 mass %.

[0052] A laminate is obtained by bonding the metal plates 11 and 13 to the main surfaces of the aluminum nitride plate 10 coated with the brazing material. The laminate is then heated in a heating furnace to sufficiently bond the aluminum nitride plate 10 to the metal plates 11 and 13, thereby obtaining a bonded body 60. The heating temperature may be, for example, 700 to 900°C. The atmosphere inside the furnace may be an inert gas such as nitrogen, and the heating may be performed under reduced pressure below atmospheric pressure or in vacuum. The heating furnace may be a continuous type that continuously produces multiple bonded bodies, or may be a type that produces one or more bonded bodies in a batchwise manner. Heating may be performed while pressing the laminate in the stacking direction. In this manner, the bonded body 60 can be obtained.

[0053] The circuit board 62 may be manufactured by removing a portion of the metal plate 11 in the bonded assembly 60 and forming a plurality of conductors 14. This process may be performed by, for example, photolithography. Specifically, a photosensitive resist is printed on the surface of the metal plate 11. Then, an exposure device is used to form a resist pattern having a predetermined shape. The resist may be negative or positive. Unnecessary resist is removed by, for example, washing.

[0054] After forming the resist pattern, an etching process is performed to remove the portions of the metal plate 11 that are not covered by the resist pattern. Then, the resist pattern is removed. In this manner, the circuit board 62 shown in FIG. 7 may be obtained. The manufacturing methods of the bonded body 60 and the circuit board 62 are not particularly limited. The circuit board 62 may be manufactured, for example, by a mounting method in which multiple metal plates that will become conductor portions are bonded to one main surface of an aluminum nitride plate. Furthermore, a plating process may be performed on at least one surface of the conductor portions 14 and the metal plate 13 of the circuit board 62.

[0055] A power module according to one embodiment includes the aluminum nitride plate described above and a conductor portion bonded to the aluminum nitride plate. The power module may include a circuit board 62. A power module is an electronic component for converting and controlling electric power, and its performance and reliability are affected by the circuit board used. Because the aluminum nitride plate and the conductor portion have different thermal expansion coefficients, thermal warping deformation occurs in high-temperature environments. The power module includes a circuit board having an aluminum nitride plate that is less susceptible to damage or destruction due to thermal warping, etc. Such a power module operates stably and has high reliability even when used in high-temperature environments. Note that the use of the aluminum nitride plate and the bonded body (circuit board) is not limited to power modules.

[0056] 9 is a cross-sectional view showing an example of a power module. The power module 100 includes a base plate 70 and a circuit board 62 joined to one surface of the base plate 70 via solder 82. A metal plate 13 on one surface of the circuit board 62 is joined to the base plate 70 via the solder 82.

[0057] A semiconductor element 90 is attached to at least one of the conductor portions 14 on the other side of the circuit board 62 via solder 81. The semiconductor element 90 is connected to predetermined locations of the conductor portions 14 with metal wires 84 such as aluminum wires. In this manner, the semiconductor element 90 and the conductor portions 14 are electrically connected. To electrically connect the outside of the housing 86 to the conductor portions 14, conductor portion 14a, which is one of the conductor portions 14, is connected via solder 85 to an electrode 83 that penetrates the housing 86.

[0058] A housing 86 is disposed on one main surface of the base plate 70, and is integrated with the main surface to house the circuit board 62. A housing space formed by the one main surface of the base plate 70 and the housing 86 is filled with resin 80. The resin 80 seals the circuit board 62 and the semiconductor element 90. The resin may be, for example, a thermosetting resin or a photocurable resin.

[0059] Cooling fins 72, which form a heat dissipation section, are joined to the other main surface of the base plate 70 via grease 74. Screws 73 are attached to the ends of the base plate 70 to secure the cooling fins 72 to the base plate 70. The base plate 70 and the cooling fins 72 may be made of aluminum. The base plate 70 and the cooling fins 72 have high thermal conductivity and therefore function well as a heat dissipation section. Since the power module 100 includes the circuit board 62, it operates stably even when used in a high-temperature environment and has high reliability.

[0060] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the shapes and structures of the aluminum nitride plate, bonded body, circuit board, and power module of the present disclosure are not limited to those shown in Figures 6, 7, and 9. For example, a circuit pattern may be formed on both main surfaces of the aluminum nitride plate 10. [Example]

[0061] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0062] [Example 1] (Production of aluminum nitride plate) Aluminum nitride powder and yttrium oxide powder were blended in a mass ratio of 97.0:3.0 and mixed using a ball mill to obtain a mixed powder. 6 parts by mass of a cellulose ether binder (manufactured by Shin-Etsu Chemical Co., Ltd., product name: Metrose), 5 parts by mass of glycerin (manufactured by Kao Corporation, product name: Exepar), and 10 parts by mass of ion-exchanged water were added to 100 parts by mass of the mixed powder, and mixed for 1 minute using a Henschel mixer to obtain a molding material. This molding material was molded using an extrusion molding machine to produce a sheet-shaped molded body.

[0063] After applying boron nitride powder as a release agent to the compact, 15 sheets were stacked and heated in air at 570°C for 5 hours for degreasing. The degreasing bodies were then placed in a heating furnace and heated to 1750°C (sintering temperature) in a nitrogen gas atmosphere (atmospheric pressure). After holding at 1750°C for 4 hours, they were allowed to cool in the furnace. In this way, aluminum nitride plates (sintered bodies) measuring 58mm x 49mm x 1.0mm in length x width x thickness were obtained. The arithmetic mean roughness (Ra) of the main surfaces of each aluminum nitride plate was measured using a surface roughness tester (product name: Surftest SJ-301) manufactured by Mitutoyo Corporation in accordance with JIS B 0601:2013.

[0064] (Evaluation of surface strength of aluminum nitride plate) Three aluminum nitride plates were randomly selected from the 15 obtained (n=3). A ring bending test was performed on each aluminum nitride plate using a Tensilon universal testing machine (model: RTG-1310) manufactured by A&D Co., Ltd. As shown in Figure 2, the aluminum nitride plate was sandwiched between an upper member having a load ring and a lower member having a support ring, and a load was applied to the center of the aluminum nitride plate at a compression speed of 0.5 mm / min to measure the fracture load (maximum test force: F). The surface strength σ of the aluminum nitride plate was calculated using the measured value and the above-mentioned formulas (I) and (II). f and deflection δ were calculated.

[0065] Since the aluminum nitride plate had a substantially rectangular parallelepiped shape, the converted diameter D was calculated by multiplying the vertical length by the horizontal length by 0.54. S is 25mm, the diameter of the load ring D L The thickness was 12.5 mm. δ was calculated assuming the modulus of elasticity E was 300,000 MPa. The minimum surface strength of the three aluminum nitride plates calculated using formula (I) is shown in Table 1. Table 1 also shows the arithmetic mean roughness Ra and deflection δ of the main surface of the aluminum nitride plate with the minimum surface strength. Deflection δ was calculated using formula (II).

[0066] (Composition analysis of minor components) A portion (30 g) of the aluminum nitride plate used for surface strength measurements was immersed in a sodium hydroxide solution (NaOH concentration: 10%) at approximately 20°C for 24 hours, dissolving the primary component, aluminum nitride, through hydrolysis. The aluminum nitride content in the aluminum nitride plate was determined, assuming that all aluminum nitride had dissolved. Powder X-ray diffraction analysis of the remaining granular secondary components was performed. A MiniFlex (product name) analyzer manufactured by Rigaku Corporation was used for the analysis. The secondary components were confirmed to contain 3Y2O3·5Al2O3 (YAG) and Y2O3·Al2O3 (YAP). In addition to these components, Al(OH)3 was detected. This Al(OH)3 is believed to have been produced during the hydrolysis reaction. The contents of aluminum oxide, yttrium oxide, and 2Y2O3·Al2O3 (YAM) in the secondary components were below the detection limit. In other words, no oxides other than YAP and YAG were detected. The contents of YAG and YAP relative to the total oxide, and the mass ratio of YAG to YAP were as shown in Table 1.

[0067] [Examples 2 and 3] Except for the firing temperature being as shown in Table 1, aluminum nitride plates were produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0068] [Comparative Example 1] Aluminum nitride powder, yttrium oxide powder, and aluminum oxide powder were blended in a mass ratio of 95.0:3.0:2.0 and mixed using a ball mill to obtain a mixed powder. An aluminum nitride plate was produced and evaluated in the same manner as in Example 1, except that this mixed powder was used and the firing temperature was set as shown in Table 1. The evaluation results are shown in Table 1.

[0069] Comparative Example 2 Except for the firing temperature being as shown in Table 1, aluminum nitride plates were produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0070] [Table 1]

[0071] As shown in Table 1, the aluminum nitride plates of Examples 1, 2, and 3 had a surface strength of 300 MPa or more at the center. The aluminum nitride plates of Examples 1, 2, and 3 were less susceptible to damage and fracture due to thermal warping than the aluminum nitride plates of Comparative Examples 1 and 2. Therefore, the aluminum nitride plates of Examples 1, 2, and 3 have superior reliability to the aluminum nitride plates of Comparative Examples 1 and 2.

[0072] <Influence of compression speed> The influence of compression speed on the evaluation of surface strength was investigated using the aluminum nitride plates of Example 1. Specifically, the breaking load (maximum test force: F) of each of three aluminum nitride plates was measured at compression speeds of 2.5 mm / min and 5 mm / min, and the surface strength was calculated using formula (I). The results are shown in Figure 10. As shown in Figure 10, it was confirmed that the variability in surface strength data could be reduced by setting the compression speed to 0.5 mm / min. [Industrial Applicability]

[0073] The present disclosure provides an aluminum nitride plate having excellent reliability, and also provides a joined body and a power module having excellent reliability by including such an aluminum nitride plate. [Explanation of symbols]

[0074] 10...aluminum nitride plate, 10a...main surface, 11, 13...metal plate, 12...center portion, 14, 14a...conductor portion, 20...upper jig, 21...main body portion, 22...load ring, 30...lower jig, 31...main body portion, 32...support ring, 40...moving crosshead, 42...load cell, 44...load rod, 45...hard ball, 46...screw, 48...guide, 49...mounting plate, 50...base portion, 60...joint body, 62, 62A...circuit board, 70...base plate, 72...cooling fin, 73...screw, 74...grease, 80...resin, 81, 82...solder, 83...electrode, 84...metal wire, 85...solder, 86...housing, 90...semiconductor element, 100...power module.

Claims

1. It includes aluminum nitride and an oxide having yttrium and aluminum as constituent elements, An aluminum nitride plate having a surface strength of 300 MPa or more at the center as measured at a compression speed of 0.5 mm / min using a universal testing machine.

2. 2. The aluminum nitride plate according to claim 1, wherein the arithmetic mean roughness Ra of the main surface is 0.30 μm or less.

3. The content of the aluminum nitride is more than 95 mass%; The aluminum nitride plate according to claim 1 or 2, wherein the content of the oxide is 3 mass % or more.

4. The oxide is 3Y ２ O ３ ・5Al ２ O ３ and Y ２ O ３ ・Al ２ O ３ Contains Y ２ O ３ ・Al ２ O ３ 3Y for ２ O ３ ・5Al ２ O ３ The aluminum nitride plate according to claim 1 or 2, wherein the mass ratio of

5. 3. The aluminum nitride plate according to claim 1, having a thickness of less than 2.0 mm.

6. A bonded body comprising the aluminum nitride plate according to claim 1 or 2 and a metal plate bonded to the aluminum nitride plate.

7. A power module comprising: a circuit board having the aluminum nitride plate according to claim 1 or 2; and a conductor portion joined to the aluminum nitride plate.

Images