Ceramic plates, circuit boards, and power modules

Abstract

To provide a ceramic plate with excellent insulation reliability, and a circuit board equipped with such a ceramic plate. [Solution] The ceramic plate is 0.5~3.0cm 3 It is a flat plate shape with a volume of and contains silicon nitride as its main component. The volume resistivity R at any position on the ceramic plate is 1.0 × 10⁻⁶ in all cases. 15 The resistance is Ω·cm or greater. The circuit board comprises a ceramic plate and a conductive part bonded to the main surface of the ceramic plate.

Description

[Technical Field]

[0001] This disclosure relates to ceramic plates, circuit boards, and power modules. [Background technology]

[0002] In recent years, power modules for high-power control have been used in industrial equipment such as motors, and in products such as electric vehicles. Such power modules utilize circuit boards equipped with ceramic plates made of sintered bodies to efficiently dissipate heat generated from semiconductor elements and to suppress leakage current.

[0003] Ceramic plates composed of nitrides, carbides, borides, or silicides are known. For example, Patent Document 1 describes that silicon nitride sintered bodies with a high dielectric breakdown voltage are useful as circuit boards for electronic components such as power modules. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-166445 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Ceramic plates used in electronic components such as power modules are required to have excellent insulation reliability. On the other hand, ceramic plates composed of sintered bodies can have variations in resistance due to compositional imbalances, which can lead to a decrease in reliability. This disclosure provides a ceramic plate with excellent insulation reliability, a circuit board equipped with such a ceramic plate, and a power module equipped with such a circuit board. [Means for solving the problem]

[0006] One aspect of this disclosure provides the following ceramic plate. [1] A ceramic plate having a flat plate shape with a volume of 0.5 to 3.0 cm 3 , which contains silicon nitride as a main component and has a volume resistivity R at any position all being 1.0×10 Ω·cm or more. 15 Ceramic plate.

[0007] The ceramic plate of the above [1] has a sufficiently high volume resistivity R at any position. The above ceramic plate containing silicon nitride has a sufficiently suppressed variation in resistance value and excellent insulation reliability.

[0008] The silicon nitride plate of the above [1] may be any one of the following [2] to [7].

[0009] [2] When the maximum value and the minimum value of the volume resistivity R are R max and R min respectively, the ceramic plate according to [1], where R max / R min is 1.5 or less. [3] When the volume resistivity R at the center part is R1 and the volume resistivity R at the outer edge part is R2, the ceramic plate according to [1] or [2], where R2 / R1 is 1.5 or less [4] Having a main surface with an area of 10 to 80 cm 2 and a thickness of 0.01 to 0.1 cm. The ceramic plate according to any one of [1] to [3]. [5] The silicon nitride content is 85% by mass or more, and contains magnesium oxide, yttrium oxide and silicon oxide. [6] The silicon nitride content is 85% by mass or more, and contains magnesium oxide, yttrium oxide and silicon oxide, A ceramic plate according to any one of [1] to [5], wherein the total content of magnesium oxide, yttrium oxide, and silicon oxide is 6.5 to 9.0% by mass when converted to MgO, Y2O3, and SiO2, respectively. [7] The silicon nitride content is 85% by mass or more, It contains magnesium oxide, yttrium oxide, and silicon oxide. A ceramic plate according to any one of [1] to [6], wherein when magnesium oxide and yttrium oxide are converted to MgO and Y2O3, respectively, the ratio of Y2O3 to MgO is 2.5 to 4.0.

[0010] One aspect of this disclosure provides the following circuit board. [8] A circuit board comprising a ceramic plate as described in any one of [1] to [7] above, and a conductive portion bonded to the main surface of the ceramic plate.

[0011] The circuit board described in [8] above is highly reliable because it is equipped with a ceramic plate that has excellent insulating reliability.

[0012] One aspect of this disclosure provides the following power module: [9] A power module comprising the circuit board described in [8] above and a semiconductor element electrically connected to the conductor portion.

[0013] The power module described in [9] above is highly reliable because it is equipped with the above-mentioned circuit board. [Effects of the Invention]

[0014] This disclosure can provide a ceramic plate with excellent insulating reliability, a circuit board equipped with such a ceramic plate, and a power module equipped with such a circuit board. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view showing an example of a ceramic plate. [Figure 2] This is a perspective view showing an example of a circuit board. [Figure 3] This is a perspective view showing an example of a joint. [Figure 4] This is a perspective view showing an example of a power module. [Figure 5] This is a plan view of the ceramic plate of Example 1. [Figure 6] This is a plan view of the ceramic plate of Comparative Example 2. [Modes for carrying out the invention]

[0016] Hereinafter, several embodiments of the present disclosure will be described with reference to the drawings, where applicable. However, the following embodiments are illustrative examples for illustrating the present disclosure and are not intended to limit the present disclosure to the following. In the description, the same reference numerals will be used for identical elements or elements having the same function, and redundant explanations will be omitted where applicable. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Moreover, the dimensional ratios of each element are not limited to those shown.

[0017] In the following description, the symbol "~" used with numerical values ​​indicates a numerical range that includes upper and lower limits. For example, "X~Y" indicates a numerical range of "X or less and Y or less". Numerical ranges obtained by replacing the upper and / or lower limits of a numerical range with the numerical values ​​described in the examples are also included in this disclosure. Furthermore, numerical ranges obtained by replacing the upper and / or lower limits of one numerical range with the upper and / or lower limits of another numerical range are also included in this disclosure. In addition, content that applies the content described in one embodiment to other embodiments is also included in this disclosure. When multiple materials or components are exemplified, one of them may be used alone, or multiple may be used in combination.

[0018] The main component in the present disclosure refers to the component with the highest content. Components other than the main component are referred to as sub-components. The ceramic plate in the present disclosure is a sintered body, excluding a green sheet, powder, or slurry before sintering, and a formed body obtained by pressure molding. The relative density of the ceramic plate may be 95% or more, 97% or more, or 98% or more.

[0019] The volume resistivity R in the present disclosure, with the insulation resistance value being r [Ω], the thickness of the ceramic plate being d [m], and the effective area of the electrode contacting the ceramic plate being A [m 2 , can be calculated by the following formula (1). The insulation resistance value r can be measured in accordance with JIS C 2140:2009 "Solid Electrical Insulating Materials - Methods of Measuring Insulation Resistance". R = r × A / d (1)

[0020] The ceramic plate according to one embodiment is a flat plate-shaped ceramic plate having a volume of 0.5 to 3.0 cm 3 , containing silicon nitride as the main component, and the volume resistivity R measured at any position is all 1.0 × 10 15 Ω·cm or more. "The volume resistivity R measured at any position is all 1.0 × 10 15 Ω·cm or more" means that no matter at which position of the ceramic plate the insulation resistance value r is measured, the calculated volume resistivity R is 1.0 × 10 15 Ω·cm or more. The volume resistivity R of the ceramic plate may be 1.0 × 10 15 ~8.0 × 10 15 Ω·cm. From the perspective of further improving the insulation reliability, the volume resistivity R of the ceramic plate may be 1.5 × 10 15 Ω·cm or more, or 2.0 × 10 15 Ω·cm or more. The volume resistivity R of the ceramic plate may be 5.0 × 10 15 Ω·cm or less, 4.0 × 10 15 Ω·cm or less, or 3.5 × 10 15 Ω·cm or less.

[0021] Let the maximum value and the minimum value of the volume resistivity R measured at any position be R max and Rmin When R max / R min R may be 1.5 or less, 1.4 or less, 1.3 or less, or 1.2 or less. max / R min By bringing R closer to 1.0, the insulation reliability can be further improved. max / R min R may be greater than 1.0 and may be 1.1 or greater. max / R min This can be reduced by reducing the number of layers used when firing the molded body (green sheet) used in the manufacture of ceramic plates, or by reducing the size of the molded body. In addition, by increasing the uniformity of the raw material powder or slurry used in the manufacture of ceramic plates, R max / R min It can be made smaller.

[0022] The shape of the ceramic plate is not particularly limited as long as it is flat. Examples include a rectangular plate with a rectangular main surface, a square plate with a square main surface, a circular plate with a circular main surface, an elliptical plate with an elliptical main surface, a triangular plate with a triangular main surface, a polygonal plate with a polygonal main surface, and a flat plate with an irregular shape whose main surface does not conform to any particular shape. The ceramic plate may have one or more holes, or one or a notch.

[0023] The volume v of the ceramic plate is set to 0.6 cm³ from the viewpoint of maximizing its usefulness as an insulating material. 3 or more, or 0.7 cm 3 The above is sufficient. The volume v of the ceramic plate is 2.5 cm², from the viewpoint of further increasing the volume resistivity R. 3 Below, 2.0cm 3 Below, 1.5cm 3 The following, or 1.0 cm 3 It can be less than [amount].

[0024] The thickness d of the ceramic plate may be 0.01 cm or more, or 0.02 cm or more, from the viewpoint of increasing its usefulness as an insulating material. The thickness d of the ceramic plate may be 0.1 cm or less, 0.08 cm or less, or 0.05 cm or less, from the viewpoint of further increasing the volume resistivity R.

[0025] The surface area 'a' of the main surface of the ceramic plate is 10 to 80 cm². 2 It may be so. From the viewpoint of increasing its usefulness as an insulating material, the area a is 10 cm². 2 or more, or 20cm 2 The above is sufficient. From the viewpoint of further increasing the volume resistivity R, the area a is 80 cm². 2 Below, 50cm 2 Below, or 30cm 2 The following may apply: The main surface of the ceramic plate is the surface with the largest area and perpendicular to the thickness direction. The ceramic plate may have two main surfaces with the same area. In that case, each of the two main surfaces may have the area a described above. The shapes of the two main surfaces may be different from each other.

[0026] The silicon nitride content in the ceramic plate may be 85% by mass or more, 88% by mass or more, or 90% by mass or more. This allows for a well-balanced increase in various properties such as strength, heat resistance, wear resistance, and thermal conductivity. The silicon nitride content can be determined, for example, by X-ray diffraction.

[0027] The ceramic plate may contain oxides as a secondary component. The oxides may originate from sintering aids, or they may be a portion of silicon nitride that has been oxidized. The oxides may include magnesium oxide, yttrium oxide, and silicon oxide. When the magnesium oxide, yttrium oxide, and silicon oxide are converted to MgO, Y2O3, and SiO2, respectively, the total content of MgO, Y2O3, and SiO2 may be 6.5 to 9.0 mass%. This can further improve the insulation reliability of the ceramic plate. From the viewpoint of further improving the insulation reliability of the ceramic plate, the lower limit of the total content of MgO, Y2O3, and SiO2 may be 7.0 mass%, 7.5 mass%, or 8.0 mass%. From a similar viewpoint, the upper limit of the total content of MgO, Y2O3, and SiO2 may be 8.7 mass%.

[0028] When magnesium oxide and yttrium oxide are converted to MgO and Y2O3, respectively, the ratio of Y2O3 to MgO may be between 2.5 and 4.0. This can further improve the insulation reliability of the ceramic plate. From the viewpoint of further improving the insulation reliability of the ceramic plate, the lower limit of the ratio of Y2O3 to MgO may be 3.0 or 3.5. From a similar viewpoint, the upper limit of the ratio of Y2O3 to MgO may be 3.8.

[0029] Figure 1 shows an example of a ceramic plate according to this embodiment. The ceramic plate 10 in Figure 1 has a flat plate shape and comprises rectangular main surfaces 10A and 10B. The thickness d of the ceramic plate 10 may be within the range described above. The volume resistivity R of the ceramic plate 10 can be calculated using the insulation resistance value r measured between a pair of electrodes arranged on the main surfaces 10A and 10B so as to face each other.

[0030] The volume resistivity R1 at the center 12 of the ceramic plate 10 can be calculated using formula (1) above, using the insulation resistance value r1 between a pair of electrodes that cover the center C of the main surface 10A and the center of the main surface 10B and are arranged to face each other. The volume resistivity R1 at the outer edge 14 of the ceramic plate 10 can be calculated using formula (1) above, using the insulation resistance value r2 between a pair of electrodes that are arranged to face each other in the part of the main surface 10A (main surface 10B) that is closer to the outer edge E of the main surface 10A (main surface 10B) than to the center C. The insulation resistance value r2 may be measured at any of the four corners of the main surface 10A and the main surface 10B, or near the center of any of the four sides that make up the outer edge E. In other words, the insulation resistance value r2 may be measured in the part that is closer to the outer edge E than to the center C. The volume resistivity R2 can be calculated from the insulation resistance value r2 measured in this way.

[0031] The volume resistivity R1 and R2 may be within the range of the volume resistivity R described above. The ratio of volume resistivity R2 to volume resistivity R1 (R2 / R1) may be 1.5 or less, 1.4 or less, 1.3 or less, or 1.2 or less. In the ceramic plate 10, the oxide content tends to be higher in the part closer to the center C than in the part closer to the outer edge E because the sintering aid is more likely to remain there. Therefore, by reducing R2 / R1, the variation in volume resistivity R in the ceramic plate 10 can be sufficiently reduced. R2 / R1 may be 0.5 or more, 1.0 or more, or greater than 1.0. R2 / R1 can be reduced, for example, by reducing the number of layers when firing the molded body (green sheet) used in the manufacture of the ceramic plate, or by reducing the size of the molded body. R2 / R1 can also be adjusted by changing the composition of the sintering aid and the blending ratio of the sintering aid to the silicon nitride powder.

[0032] One or both of the main surfaces 10A and 10B of the ceramic plate 10 may have scribe lines composed of a plurality of laser holes. The laser holes can be formed by irradiating with laser light.

[0033] An example of a method for manufacturing a ceramic plate includes a preparation step of preparing a mixed raw material by mixing silicon nitride powder and a sintering aid powder, a molding step of producing a green sheet containing the mixed raw material, and a firing step of firing the green sheet.

[0034] The sintering aid powder may be prepared by blending, for example, magnesium oxide powder, yttrium oxide powder, and silicon dioxide powder. The composition of the ceramic plate can be adjusted by changing the blending ratio of each oxide powder, and the blending ratio of silicon nitride powder to the sintering aid powder.

[0035] In the molding process, a raw material slurry containing mixed raw materials, a binder, and a dispersant is prepared. The solid content in the raw material slurry is preferably 50-65% by mass, more preferably 55-60% by mass. This improves the uniformity of the raw material slurry and sufficiently reduces variations in the composition of the green sheet. The raw material slurry may be applied to a release film to a predetermined thickness by, for example, the doctor blade method, the calendering method, or the extrusion method. After that, the applied raw material slurry is dried and peeled off the release film to obtain a green sheet. The green sheet may be processed to a desired shape and size by, for example, cutting. The material and shape of multiple green sheets may be the same or different from one another.

[0036] The green sheet may be in a flat shape. The size of the green sheet should be adjusted so that the ceramic plate has the volume v, thickness d, and area a described above. The thickness of the green sheet should be about 1.3 to 1.6 times the thickness d of the ceramic plate. The area of ​​the green sheet should be about 1.5 to 1.8 times the area a of the ceramic plate. The volume of the green sheet should be about 2.2 to 2.5 times the volume v of the ceramic plate. When a green sheet of this size and shape is heated, firing proceeds smoothly and uniformly. This makes it easier to obtain a ceramic plate with excellent insulating reliability.

[0037] Multiple green sheets may be laminated and fired. The number of laminated sheets may be, for example, 50 to 100. By laminating and firing, it is possible to suppress excessive volatilization of the sintering aid from the green sheet (ceramic plate), which can lead to uneven composition between the surface and the interior. From the viewpoint of obtaining a ceramic plate with high uniformity of composition between the surface and the interior, when 50 to 100 green sheets having the above shape and size are laminated, the ceramic plate near the center of the laminate tends to have a more uniform composition than the ceramic plates at the top and bottom of the laminate. Such a ceramic plate has a small variation in volume resistivity R and excellent insulation reliability.

[0038] To prevent adjacent green sheets from sticking together vertically, a release agent may be applied to the main surface of each green sheet before lamination. Examples of release agents include ceramic powder such as boron nitride and graphite powder.

[0039] Before the firing process, a degreasing process may be performed to reduce organic matter by heating the green sheet or laminate. In the degreasing process, the green sheet or laminate is placed in a degreasing furnace and heated, for example, at 300°C to 700°C for 15 to 25 hours. This causes the binder and dispersant contained in the green sheet to volatilize, resulting in a degreased material with reduced organic matter. Performing the degreasing process makes it easier to obtain a ceramic plate with a sufficiently high volume resistivity R.

[0040] In the firing process, the green sheet (laminated or degreased) is fired. The firing process causes the powder in the green sheet to sinter, resulting in a ceramic plate containing silicon nitride as the main component. When a firing furnace is used in the firing process, the degreasing furnace used for degreasing and the firing furnace used for firing may be the same furnace or different furnaces.

[0041] The firing temperature in the firing process may be, for example, 1750°C to 1850°C. The heating time at this firing temperature may be, for example, 4 to 8 hours. The firing process may be carried out, for example, under a nitrogen gas atmosphere pressurized to 0.70 to 1.00 MPa. Under such an atmosphere, the formation of oxides due to firing is suppressed, and a ceramic plate with further reduced variations in insulation properties can be obtained.

[0042] When 50 to 100 green sheets having the above-described shape and size are stacked, degreased, and fired, the ceramic plates located near the center of the stack tend to have a higher uniformity of sintering aid distribution than the ceramic plates located at the top or bottom of the stack. Therefore, only the ceramic plates located near the center of the stack may have the above-described volume resistivity R. In other words, only some of the ceramic plates among the multiple ceramic plates have a volume resistivity R of 1.0 × 10⁻⁶ measured at an arbitrary position. 15 It may be greater than or equal to Ω·cm.

[0043] The applications of ceramic plates are not particularly limited. Because ceramic plates have excellent insulation reliability, they are useful, for example, as components of circuit boards and power modules.

[0044] A circuit board according to one embodiment comprises a ceramic plate and a conductive portion bonded to the main surface of the ceramic plate.

[0045] In the example shown in Figure 2, the circuit board 20 comprises a ceramic plate 10 and conductive portions 31 and 32 joined to its main surface 10A and main surface 10B, respectively. When the circuit board 20 is mounted on a semiconductor device, one of the conductive portions 31 and 32 may constitute part of an electrical circuit, or the other may function as a heat sink. Both conductive portions 31 and 32 may constitute part of an electrical circuit. The shapes of the conductive portions 31 and 32 may be the same or different. The circuit board 20 is highly reliable because it includes a ceramic plate 10 with excellent insulation reliability. In a modified example of the circuit board 20, conductive portions may be provided on only one of the main surface 10A and main surface 10B.

[0046] When manufacturing the circuit board 20, a joint 30 as shown in Figure 3 may be used. The joint 30 can be manufactured as follows: a brazing material is applied to all or part of the main surfaces 10A and 10B of the ceramic plate 10 shown in Figure 1. The brazing material may contain at least one of Ag and Cu as its main component and an active metal as a secondary component. A paste-like brazing material is applied to the entire main surfaces 10A and 10B of the ceramic plate 10 by a method such as a roll coater, screen printing, or transfer method.

[0047] A pair of metal plates 33 and 34 are stacked so as to cover the brazing material coating layer on the main surfaces 10A and 10B of the ceramic plate 10, and heated to 700-900°C in a heating furnace. The heating may be carried out while pressing the stack of ceramic plate 10 and metal plates 33 and 34 in the stacking direction. The metal plates 33 and 34 may be copper plates. The atmosphere inside the furnace may be an inert gas such as nitrogen, and the heating may be carried out under reduced pressure below atmospheric pressure or under vacuum. In this way, a joined body 30 is obtained in which the ceramic plate 10 and metal plates 33 and 34 are joined via the brazing material layer.

[0048] Next, a portion of the metal plates 33 and 34 in the bonded body 30 is removed by photolithography. Specifically, a photosensitive resist is printed on the surface of the metal plates 33 and 34. Then, a resist pattern having a predetermined shape is formed using an exposure apparatus. The resist may be negative or positive. Uncured resist is removed, for example, by washing. After forming the resist pattern, the portion of the metal plates 33 and 34 not covered by the resist pattern is removed by etching. After etching, the resist pattern is removed to obtain a circuit board 20 as shown in Figure 2. The circuit board 20 may be used, for example, as a component of a power module. The method for manufacturing the circuit board 20 is not limited to the above example.

[0049] A power module according to one embodiment comprises a circuit board and a semiconductor element electrically connected to a conductor. A power module is an electronic component for power conversion and control, and its performance and reliability are influenced by the circuit board used. The power module of this embodiment comprises a circuit board having a ceramic plate with excellent insulation reliability. Such a power module is highly reliable. Note that the application of the circuit board is not limited to power modules.

[0050] In the example shown in Figure 4, the power module 100 comprises a base plate 70 and a circuit board 20 joined to one side of the base plate 70 via solder 82. A conductor portion 32 on one side of the circuit board 20 is joined to the base plate 70 via solder 82. A semiconductor element 89 is attached to a conductor portion 31 on the other side of the circuit board 20 via solder 81. The semiconductor element 89 is connected to a predetermined location on the conductor portion 31 by a metal wire 84 such as an aluminum wire. In this way, the semiconductor element 89 and a part of the conductor portion 31 are electrically connected. To electrically connect the outside of the housing 86 to the conductor portion 31, a part 31a of the conductor portion 31 is connected to an electrode 83 that penetrates the housing 86 via solder 85.

[0051] A housing 86 is arranged on one main surface of the base plate 70, and is integrated with the main surface to house the circuit board 20 and semiconductor elements 89. The 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 20 and semiconductor elements 89. The resin may be, for example, a thermosetting resin or a photocuring resin.

[0052] Cooling fins 72, which form a heat dissipation section, are bonded to the other main surface of the base plate 70 via grease 74. Screws 73 for fixing the cooling fins 72 to the base plate 70 are attached to the end of the base plate 70. The base plate 70 and cooling fins 72 may be made of aluminum. The base plate 70 and cooling fins 72 function well as heat dissipation sections due to their high thermal conductivity. Since the power module 100 is equipped with a circuit board 20, it operates stably even when used in high-temperature environments and has high reliability.

[0053] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited in any way to the above embodiments. For example, the shape and structure of the ceramic plate, circuit board, and power module of the present disclosure are not limited to the illustrated structure and shape. For example, the ceramic plate and metal plate may have shapes other than a rectangular prism. Any surface treatment may be applied to the conductor portion of the circuit board. For example, a part of the surface of the conductor portion may be covered with a protective layer such as solder resist, and the other part of the surface of the conductor portion may be plated. [Examples]

[0054] The contents of this disclosure will be explained in more detail with reference to specific examples, but this disclosure is not limited to the following embodiments.

[0055] [Example 1] (Fabrication of ceramic plates) Silicon nitride powder and sintering aids, magnesium oxide powder, yttrium oxide powder, and silicon dioxide powder were prepared. The silicon nitride powder, magnesium oxide powder, yttrium oxide powder, and silicon dioxide powder were blended in a mass ratio of Si3N4:MgO:Y2O3:SiO2 = 91.35:1.58:6.00:1.07 to obtain a mixed raw material. A binder, dispersant, and dispersion medium were added to this mixed raw material to prepare a raw material slurry (solid content: 58.5% by mass). Next, the raw material slurry was applied onto a release film using the doctor blade method, and the application thickness was adjusted to 0.440 mm to produce a green sheet.

[0056] The prepared green sheets were cut to a length of 67 mm in the vertical direction and 57 mm in the horizontal direction, and 70 sheets were stacked to obtain a laminate. This laminate was placed on a boron nitride setter and placed in an electric furnace equipped with a carbon heater, and degreased by heating in air at 500°C for 10 hours. The resulting degreased material was fired at 1800°C for 6 hours in an atmosphere of nitrogen gas pressurized to 0.88 MPa to obtain a ceramic plate (silicon nitride plate) having a rectangular main surface as shown in Figure 5.

[0057] (Evaluation of volume resistivity) From the fired laminate, the 35th ceramic plate 10 from the top was removed. The size (length × width × thickness) of the removed ceramic plate 10 was measured using a ruler and calipers. The results are shown in Table 1. In Table 1, "length" is the length of the main surface 10A in the y direction in Figure 5, and "width" is the length of the main surface 10A in the x direction in Figure 5. As shown in Figure 5, electrodes TE (contact area with main surface 10A = 0.79 mm) were placed at the center 12 of the main surfaces on both sides of the ceramic plate 10. 2 The insulation resistance values ​​r1 were measured in accordance with JIS C 2140:2009 "Solid electrical insulating materials - Method for measuring insulation resistance" after attaching each component. The measurement was performed using the SM-8220 (product name) manufactured by HIOKI E.E. CORPORATION.

[0058] The electrode TE was removed from the central part 12 and attached to the outer edge 14 of the main surface on both sides of the ceramic plate 10. The insulation resistance value r2 was then measured using the same procedure. The attachment position of the TE was such that at one corner of the outer edge 14, the shortest distances SL1 and SL2 from the two sides intersecting at the corner to the outer edge of the TE were both 3 mm. The insulation resistance values ​​r1 and r2 were converted to volume resistivity, and these were defined as the volume resistivity R1 of the central part 12 and the volume resistivity R2 of the outer edge 14, respectively. The results are shown in Table 1.

[0059] Furthermore, the insulation resistance was measured at multiple arbitrary locations on the ceramic plate 10, and the volume resistivity was determined. As a result, the volume resistivity R1 shown in Table 1 was the minimum value (R min ) and the volume resistivity R2 is at its maximum value (Rmax ) was so. Therefore, R max / R min The value was 1.13.

[0060] [Comparative Example 1] A mixed raw material was obtained by blending silicon nitride powder, magnesium oxide powder, and yttrium oxide powder in a mass ratio of Si3N4:MgO:Y2O3 = 94.00:3.00:3.00. A ceramic plate was prepared in the same manner as in Example 1, except that this mixed raw material was used, and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0061] [Comparative Example 2] A green sheet was prepared in the same manner as in Example 1. The prepared green sheet was cut to a length of 250 mm in the vertical direction and 170 mm in the horizontal direction, and 70 sheets were stacked to obtain a laminate. This laminate was placed on a boron nitride setter and placed in an electric furnace equipped with a carbon heater, and degreased by heating in air at 500°C for 18 hours. The resulting degreased material was fired at 1800°C for 6 hours in an atmosphere of nitrogen gas pressurized to 0.88 MPa to obtain a ceramic plate (silicon nitride plate).

[0062] From the laminated structure after firing, the 35th ceramic plate from the top was removed. The size of the removed ceramic plate is shown in Table 1. Laser scribing was performed on the removed ceramic plate. As shown in Figure 6, on one main surface 90A of the ceramic plate 90, four scribe lines SCL were formed along the transverse direction (x direction), and two scribe lines SCL were formed along the vertical direction (y direction). This divided the main surface 90A into 5 × 3 = 15 regions. The size of each region was 40 mm × 30 mm. The ceramic plate 90 was divided along the scribe lines SCL to obtain 15 divided substrates.

[0063] Electrodes were attached to the centers of both main surfaces of the divided substrate originating from region CR, which includes the center of the main surface 90A, and the insulation resistance value r1' was measured in the same manner as in Example 1. Similarly, the insulation resistance value r2' of the divided substrate originating from region ER, which forms one of the four corners of the main surface 90A, was measured. The insulation resistance values ​​r1' and r2' were converted to volume resistivity, and these were defined as the volume resistivity R1 of the center and the volume resistivity R2 of the outer edge, respectively. The results are shown in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, the ceramic plate of Example 1 had a sufficiently high volume resistivity in both the central and outer edges. Furthermore, the variation in volume resistivity of the ceramic plate of Example 1 was sufficiently reduced. [Explanation of Symbols]

[0066] 10, 90... Ceramic plate, 10A, 10B, 90A... Main surface, 12... Center, 14... Outer edge, 20... Circuit board, 30... Joint, 31, 32... Conductor part, 33, 34... Metal plate, 70... Base plate, 72... Cooling fin, 73... Screw, 74... Grease, 80... Resin, 81, 82, 85... Solder, 83... Electrode, 84... Metal wire, 86... Housing, 89... Semiconductor element, 100... Power module.

Claims

1. 0.5–3.0 cm ３ A flat ceramic plate having the volume of, It contains silicon nitride as its main component. The volume resistivity R at any given position is 1.0 × 10⁻⁶ in all cases. １５ A ceramic plate with a thickness of Ω·cm or more.

2. The maximum and minimum values ​​of the volume resistivity R are given by R ｍａｘ and R ｍｉｎ When R ｍａｘ / R ｍｉｎ The ceramic plate according to claim 1, wherein the coefficient is 1.5 or less.

3. The ceramic plate according to claim 1, wherein when the volume resistivity R at the center is R1 and the volume resistivity R at the outer edge is R2, R2 / R1 is 1.5 or less.

4. Area: 10-80 cm² ２ It has a main surface which A ceramic plate according to any one of claims 1 to 3, wherein the thickness is 0.01 to 0.1 cm.

5. The silicon nitride content is 85% by mass or more. A ceramic plate according to any one of claims 1 to 3, comprising magnesium oxide, yttrium oxide, and silicon oxide.

6. The silicon nitride content is 85% by mass or more. It contains magnesium oxide, yttrium oxide, and silicon oxide. When the oxides of magnesium, yttrium, and silicon oxide are converted to MgO, Y ２ O ３ and SiO ２ respectively, the total content of MgO, Y ２ O ３ and SiO ２ is 6.5 to 9.0% by mass, and the ceramic plate according to any one of claims 1 to 3.

7. The silicon nitride content is 85% by mass or more. It contains magnesium oxide, yttrium oxide, and silicon oxide. Magnesium oxide and yttrium oxide are MgO and Y, respectively. ２ O ３ When converted to MgO, Y ２ O ３ A ceramic plate according to any one of claims 1 to 3, wherein the ratio is 2.5 to 4.

0.

8. A circuit board comprising a ceramic plate according to any one of claims 1 to 3, and a conductive portion bonded to the main surface of the ceramic plate.

9. A power module comprising a circuit board according to claim 8 and a semiconductor element electrically connected to the conductor portion.

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