Ceramic substrate, method of manufacturing ceramic substrate, and laminated substrate

Abstract

To provide a ceramic substrate with which a laminated substrate joined by uniform joining force in each part in an in-plane direction can be manufactured, a method of manufacturing a ceramic substrate, and a laminated substrate formed by joining a ceramic substrate and a metal plate.SOLUTION: There is provided a ceramic substrate 1 with a rectangular form in plan view, which has, on a surface 11 thereof, undulations that are ups and downs with intervals greater than roughness. In a longitudinal section of the ceramic substrate passing the midpoint X of two opposing sides along a thickness direction, a curve indicating the undulations has three or more extreme values. In the longitudinal section, a value obtained by dividing an amount of warpage by a length of a straight line connecting the midpoint of the two sides is 1 μm / mm or less, the amount of warpage being specified by a maximum distance of a normal of the straight line to the surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a ceramic substrate, a method for manufacturing a ceramic substrate, and a laminated substrate.

Background Art

[0002] In inverters that control high-power motors such as those for electric railways, power generation, and electric vehicles / hybrid electric vehicles, power modules such as IGBT modules are used (see Patent Document 1). This power module includes a ceramic insulating substrate having metal layers provided on both surfaces of a ceramic base material, and semiconductor elements joined on the metal layers of the ceramic insulating substrate. When joining the ceramic base material and the metal layer, at their outer peripheral portions, the bonding strength may become non-uniform due to being easily affected by the shape. In particular, when the ceramic base material is thick, since the rigidity of the ceramic base material increases, when the ceramic base material is deformed, it becomes difficult to correct the deformation of the ceramic base material even when a load is applied during bonding.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above circumstances, the present invention aims to provide a ceramic substrate, a method for manufacturing a ceramic substrate, and a laminated substrate formed by joining a ceramic substrate and a metal plate, which can manufacture a laminated substrate joined with a uniform bonding strength in each part in the in-plane direction.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a ceramic substrate having a rectangular shape in plan view is provided. This ceramic substrate has undulations on its surface, which are undulations with an interval larger than the roughness. In the longitudinal cross-section of the ceramic substrate along the thickness direction passing through the midpoints of two opposite sides, the curve showing the undulations has three or more extreme values. In the longitudinal cross-section, the value obtained by dividing the amount of warpage defined by the maximum distance from the surface of the normal line of the straight line connecting the midpoints of the two sides by the length of the straight line is 1 μm / mm or less.

[0006] According to such an aspect, a laminated substrate joined with a uniform bonding force in each part in the in-plane direction can be obtained.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described. Various characteristic matters shown in the following embodiments can be combined with each other. FIG. 1 is a perspective view showing one embodiment of the ceramic substrate of the present invention. FIG. 2 is a plan view (a) and a partial longitudinal cross-section (b) showing the ceramic substrate of FIG. 1. Note that FIG. 2 shows an exaggerated size in the thickness direction of the ceramic substrate.

[0009] The ceramic substrate 1 shown in Fig. 1 is rectangular in plan view. This ceramic substrate 1 has undulations on its surface 11, which are undulations with intervals larger than the roughness. And in the longitudinal section of the ceramic substrate 1 along the thickness direction passing through the midpoints A or B of two opposite sides, the curve showing the undulation (undulation curve) has three or more extreme values (indicated by thick arrows in Fig. 2(b)). For the ceramic substrate 1 having such undulations on the surface 11, when a load is applied during manufacturing the laminated substrate 4 (see Fig. 6) by bonding with the metal plate 2, it is possible to prevent the molten brazing material from staying at specific locations in the central portions of the ceramic substrate 1 and the metal plate 2, and smoothly move it to the outer peripheral portion. As a result, a laminated substrate 4 in which the ceramic substrate 1 and the metal plate 2 are joined with a uniform bonding force in each part in the in-plane direction can be obtained.

[0010] The undulation curve only needs to have three or more extreme values (inflection points), but preferably has four or more extreme values, and more preferably has five or more extreme values. Note that the upper limit value of the extreme values is not particularly limited, but is, for example, seven. By the number of extreme values in the undulation curve being within the above range, the movement of the molten brazing material is more likely to occur smoothly. It is preferable that the thickness of the outer peripheral portion of the ceramic substrate 1 is larger than the thickness of the central portion. Thereby, the load during manufacturing the laminated substrate 4 by bonding the ceramic substrate 1 and the metal plate 2 can be sufficiently applied to the outer peripheral portions of the ceramic substrate 1 and the metal plate 2. As a result, the entire opposing surfaces of the ceramic substrate 1 and the metal plate 2 can be brought closer to each other, and thus a laminated substrate 4 joined with a uniform bonding force in each part in the in-plane direction can be obtained.

[0011] Specifically, as shown in FIG. 1, when the thickness at the midpoint X of the diagonal line DL of the ceramic substrate 1 is T1 [mm] and the thickness at the point Y 2 mm from the end of the diagonal line DL is T2 [mm] (average value), it is preferably about 0.001 mm or more, more preferably about 0.003 mm or more and 0.07 mm or less, still more preferably about 0.005 mm or more and 0.03 mm or less, and even more preferably about 0.008 mm or more and 0.02 mm or less. Thereby, since the above load can be surely applied by the outer peripheral portions of the ceramic substrate 1 and the metal plate 2, it is easy to obtain the laminated substrate 4 joined with a uniform bonding force in each part in the in-plane direction.

[0012] Further, in the above longitudinal section, the value obtained by dividing the warpage amount W defined by the maximum distance from the normal line of the straight line A-A or B-B to the surface 11 of the ceramic substrate 1 by the length of the straight line A-A or B-B may be about 1 μm / mm or less, preferably about 0.85 μm / mm or less, and more preferably about 0.7 μm / mm or less. The lower limit of the warpage amount W is not particularly limited, but is about 0.15 μm / mm. In this case, it can be determined that the surface 11 of the ceramic substrate 1 has sufficiently small warpage or distortion at its central portion. Therefore, when the above load is applied to the ceramic substrate 1 and the metal plate 2, the central portions and the outer peripheral portions of their opposing surfaces can be sufficiently approximated.

[0013] When the ceramic substrate 1 has a long side and a short side, the longitudinal section defining the extreme value of the undulation curve and the warpage amount W is preferably a straight line A-A connecting the midpoints A of the two sides, that is, a straight line along the long side. When the extreme value of the undulation curve and the warpage amount W are within the above ranges in the longitudinal section along the long side, when the above load is applied to the ceramic substrate 1 and the metal plate 2, the central portions and the outer peripheral portions of their opposing surfaces can be more surely approximated. The properties of the surface 11 of the ceramic substrate 1 as described above can be measured, for example, by a three-dimensional shape measuring machine, or can also be measured by image capturing and image analysis of the longitudinal section of the ceramic substrate 1.

[0014] The surface roughness of the surface 11 of the ceramic substrate 1 is preferably about 0.1 μm or more and 0.3 μm or less, and more preferably about 0.15 μm or more and 0.25 μm or less. In this case, the adhesion with the bonding layer 3 (solder) for bonding the ceramic substrate 1 and the metal plate 2 can be sufficiently enhanced. In this specification, the surface roughness of the ceramic substrate 1 means the arithmetic mean roughness Ra measured in accordance with the method described in JIS B 0601:2013 "Geometrical Product Specifications (GPS) - Surface texture: Profile method - Terms, definitions and surface texture parameters".

[0015] The average thickness of the ceramic substrate 1 is preferably about 0.5 mm or more and 3 mm or less, more preferably about 0.75 mm or more and 2.5 mm or less, and even more preferably about 1 mm or more and 2 mm or less. Such a relatively thick ceramic substrate 1 is difficult to deform even when a load is applied during bonding with the metal plate 2, but due to having the thickness distribution and the properties of the surface 11 as described above, it can be bonded to the metal plate 2 with a high bonding force even at the outer peripheral portion. The length of one side (long side and short side) of the ceramic substrate 1 is preferably about 30 mm or more and 100 mm or less, more preferably about 35 mm or more and 90 mm or less, and even more preferably about 40 mm or more and 80 mm or less. In the ceramic substrate 1 of such a size, it is particularly easy to obtain a laminated substrate 4 bonded with a uniform bonding force in each part in the in-plane direction.

[0016] The ceramic substrate 1 can be composed of, for example, a nitride sintered body, a carbide sintered body, or an oxide sintered body. The ceramic substrate 1 is preferably composed of a nitride sintered body, and more preferably composed of an aluminum nitride sintered body or a silicon nitride sintered body. Such a ceramic substrate 1 has high flexural strength and thus excellent durability. Also, such a ceramic substrate 1 is excellent in thermal conductivity. The flexural strength of the ceramic substrate 1 can be 350 MPa or more, 380 MPa or more, 400 MPa or more, 420 MPa or more, or 450 MPa or more. In this specification, the flexural strength of the ceramic substrate 1 means a value measured by a three-point bending test in accordance with the description of JIS R 1601:2008 "Test Method for Room Temperature Bending Strength of Fine Ceramics". The thermal conductivity of the ceramic substrate 1 can be 150 W / m·K or more, or 180 W / m·K or more. In this specification, the thermal conductivity of the ceramic substrate 1 means a value measured by the laser flash method.

[0017] Such a ceramic substrate 1 can be manufactured, for example, as follows. Hereinafter, a method for manufacturing the ceramic substrate 1 (that is, an embodiment of the method for manufacturing the ceramic substrate of the present invention) will be described. FIG. 3 is a side view showing an example of a laminate and a holder used in the method for manufacturing a ceramic substrate. FIG. 4 is a perspective view showing an example of a configuration of a setter. FIG. 5 is a perspective view showing another configuration example of the setter.

[0018] As shown in FIG. 3, the method for manufacturing the ceramic substrate 1 includes a first step of sandwiching a laminate 100 including a plurality of ceramic green sheets 10 between two setters 20 having convex portions 21 such that the convex portions 21 face the laminate 100 side, and a second step of obtaining the ceramic substrate 1 from each ceramic green sheet 10 by heating the laminate 100. [First Step] In the first step, first, a plurality of ceramic green sheets 10 and the setter 20 are prepared. The ceramic green sheet 10 can be obtained, for example, by preparing a raw material slurry containing a ceramic powder, a sintering aid, a binder, and a dispersant, and molding this raw material slurry.

[0019] Examples of the ceramics include nitrides, carbides, oxides, etc. Specific examples of the ceramics include aluminum nitride, silicon nitride, silicon carbide, boron nitride, etc. Examples of the sintering aid include compounds of rare earth metals, compounds of alkali metals, compounds of alkaline earth metals, compounds of transition metals, etc. Specific examples of the sintering aid include yttrium oxide, lithium carbonate, sodium carbonate, magnesium oxide, calcium carbonate, and in addition, aluminum oxide, silicon dioxide, etc. These compounds are preferably used in combination of two or more kinds.

[0020] Examples of the binder include nitrocellulose, cellulose-based organic compounds such as methylcellulose, oxygen-containing organic compounds such as polyvinyl alcohol, polyethylene oxide, and polypropylene oxide, and acrylic resins obtained by polymerizing one or more monomers selected from the group consisting of acrylic acid esters, methacrylic acid esters, acrylic acid, and methacrylic acid. Examples of the dispersant include unsaturated fatty acids. The raw material slurry can be prepared by mixing the above raw materials using a mixing device such as a ball mill, a rod mill, or a mixer.

[0021] The raw material slurry is applied onto a release film with a predetermined thickness by, for example, a doctor blade method, a calendar method, an extrusion method, etc. Then, after drying the applied raw material slurry, it is peeled off from the release film. Thereby, the ceramic green sheet 10 is obtained. The ceramic green sheet 10 may be processed into a desired shape by, for example, cutting. Also, the constituent materials and shapes of the plurality of ceramic green sheets 10 may be the same as each other or different from each other.

[0022] As shown in FIG. 4, the setter 20 used in this embodiment has an overall rectangular parallelepiped shape, but has a shape in which the corners at a pair of opposing sides on the upper side are removed. Specifically, the front surface 201 and the rear surface 202 each have a hexagonal shape with a substantially constant width along the height direction from the lower side to the upper side and decreasing from the middle of the height direction. The size of the lower surface 203 is larger than the size of the upper surface 204. Specifically, the length of the lower surface 203 in the front-rear direction is substantially equal to the length of the upper surface 204 in the front-rear direction, and the length of the lower surface 203 in the left-right direction is larger than the length of the upper surface 204 in the left-right direction. The right side surface 205 and the left side surface 206 each have a height equal to the height of the portion where the widths of the front surface 201 and the rear surface 202 are substantially constant, and are connected to the upper surface 204 via a right inclined surface 207 or a left inclined surface 208.

[0023] In the setter 20 having such a configuration, the portions where the widths of the front surface 201 and the rear surface 202 decrease along the height direction constitute a convex portion 21. The height H of this convex portion 21 may be 10 μm or more, may be 20 μm or more, and may also be 30 μm or more. Further, the height H may be 100 μm or less, may be 75 μm or less, and may also be 50 μm or less. By setting the height H of the convex portion 21 of the setter 20 within the above range, it is easy to form the obtained ceramic substrate 1 to have the thickness distribution and the properties of the surface 11 as described above.

[0024] The setter 20 can be composed of at least one selected from the group consisting of, for example, boron nitride, silicon carbide, aluminum oxide, zirconium oxide, graphite, and silicon nitride. In particular, the setter 20 composed of boron nitride is preferably used because it has both heat resistance and good machinability. Note that, from the viewpoint of suppressing the adhesion between the setter 20 and the ceramic substrate 1 during firing, the constituent material of the setter 20 may be different from the constituent material of the ceramic substrate 1.

[0025] Next, a plurality of ceramic green sheets 10 are overlapped so that the main surfaces thereof are in contact with each other to obtain a laminate 100. Thereafter, the laminate 100 is sandwiched between a pair of setters 20 arranged to face each other in the laminating direction of the ceramic green sheet 10. At this time, the convex portions 21 (upper surface 204, right inclined surface 207, and left inclined surface 208) of the upper and lower setters 20 are brought into contact with the upper and lower surfaces of the laminate 100.

[0026] Furthermore, a weight 30 is placed on the upper setter 20 to produce a holding body 40. The weight 30 is made of, for example, a metal material (tungsten) having high stability even under high heat. The mass of the weight 30 per unit area (cm 2 ) of the laminate 100 (ceramic green sheet 10) is preferably about 10 g or more and 100 g or less, more preferably about 20 g or more and 80 g or less, and even more preferably about 30 g or more and 60 g or less. Thereby, sufficient compressive force can be applied to each ceramic green sheet 10. As a result, the obtained ceramic substrate 1 can more reliably have the thickness distribution and the properties of the surface 11 as described above.

[0027] There is no particular limitation on the number of ceramic green sheets 10. The constituent materials and thicknesses of the plurality of ceramic green sheets 10 may be the same as or different from each other. A release agent may be applied to the main surface of the ceramic green sheet 10 in order to suppress adhesion between adjacent ceramic green sheets 10 during firing. Also, a release agent may be applied to the surface of the setter 20 that faces the main surface of the ceramic green sheet 10. Examples of the components contained in the release agent include ceramic powders such as boron nitride, graphite powder, and binders.

[0028] [Second Step] In the second step, the laminate 100 is heated. First, a holder 40 including a laminate 100 is placed in a debinding furnace and heated, for example, in a non-oxidizing atmosphere (nitrogen atmosphere) at a temperature of 350°C or higher and 700°C or lower for 1 hour or longer and 10 hours or shorter. As a result, the binder and the dispersant contained in the ceramic green sheet 10 are volatilized, and the ceramic green sheet 10 shrinks. That is, the ceramic green sheet 10 is debound.

[0029] Next, the holder 40 including the debound laminate 100 is placed in a firing furnace and held, for example, in a non-oxidizing atmosphere (nitrogen atmosphere) at a temperature of 1600°C or higher and 1750°C or lower for 4 hours or longer and 10 hours or shorter to remove residual carbon, and then heated by raising the temperature to a sintering temperature of 1800°C or higher and 1900°C or lower. As a result, the ceramic green sheet 10 is fired to obtain a ceramic substrate 1. In addition, the heating temperature, time, and atmosphere during debinding and firing can be appropriately adjusted according to the composition of the ceramic green sheet 10.

[0030] Note that the debinding furnace used for debinding and the firing furnace used for firing may be the same furnace or different furnaces. In the latter case, the furnace to be used may be a batch furnace, but it is preferably a continuous furnace that continuously performs debinding and firing. In the case of a continuous furnace, the flow rate of the non-oxidizing gas flowing through the continuous furnace is preferably about 0.1 m / s or higher. In addition, the cooling rate when cooling from the firing temperature to 1500°C is preferably about 10°C / min or higher and 25°C / min or lower.

[0031] At this time, by changing at least one of the load weight (mass of the weight 30) applied to the laminate 100 and the number of ceramic green sheets 10 included in the laminate 100, it is preferable to adjust at least one of the number of extreme values of the undulation curve and the amount of warpage W of the obtained ceramic substrate 1. Also, the thickness distribution of the ceramic substrate 1 may be adjusted. According to such a configuration, a ceramic substrate 1 having a predetermined thickness distribution and the properties of the surface 11 can be obtained with a relatively simple configuration. In addition, when the setter 20 shown in FIG. 4 is used, it is easy to obtain the ceramic substrate 1 having a distribution of a predetermined thickness and the properties of the surface 11 in the long side direction.

[0032] As the setter, the setter 20' shown in FIG. 5 can also be used. The setter 20' shown in FIG. 5 has an overall rectangular parallelepiped shape, but has a shape in which all of the corners on the upper four sides are removed. The front surface 201', the rear surface 202', the right side surface 205', and the left side surface 206' are rectangular (rectangular) and have substantially equal sizes. In addition, the length of the lower surface 203' in the front-rear direction is larger than the length of the upper surface 204' in the front-rear direction, and the length of the lower surface 203' in the left-right direction is also larger than the length of the upper surface 204' in the left-right direction.

[0033] The right side surface 205' and the left side surface 206' are each connected to the upper surface 204' via a right inclined surface 207' or a left inclined surface 208', and the front surface 201' and the rear surface 202' are each connected to the upper surface 204' via a front inclined surface 209' or a rear inclined surface 210'. Therefore, the setter 20' shown in FIG. 5 has a convex portion 21' in the shape of a truncated square pyramid. When such a setter 20' is used, it is easy to obtain the ceramic substrate 1 having a distribution of a predetermined thickness and the properties of the surface 11 in the long side direction and the short side direction.

[0034] In addition, when increasing the number of ceramic green sheets 10, a setter having convex portions 21 or 21' protruding on both sides (upper and lower) in the thickness direction may be arranged in the middle of the lamination direction of the laminate 100. In this case, even if the number of ceramic green sheets 10 is increased, the ceramic substrate 1 having the thickness distribution and the properties of the surface 11 as described above can be favorably manufactured.

[0035] The laminated substrate of the present invention includes a ceramic substrate, a metal plate provided on at least one surface side of the ceramic substrate, and a bonding layer that bonds the ceramic substrate and the metal plate. FIG. 6 is a perspective view showing an embodiment of the laminated substrate of the present invention. The laminated substrate 4 shown in FIG. 6 includes a pair of metal plates 2 arranged to face each other, a ceramic substrate 1 interposed between the pair of metal plates 2, and a bonding layer 3 that bonds each metal plate 2 and the ceramic substrate 1. Examples of the metal plate 2 include a copper plate and an aluminum plate. In the configuration shown in FIG. 6, the ceramic substrate 1 and the metal plate 2 may have substantially the same shape and size, or may be different.

[0036] The bonding layer 3 is preferably formed of a brazing material. Examples of the brazing material include a composition containing 75 to 99 parts by mass of Ag, 1 to 25 parts by mass of Cu, 0.5 to 6 parts by mass of at least one active metal component selected from Ti and Zr, and 0.4 to 5 parts by mass of at least one element selected from In, Zn, Cd, and Sn. Also, the tap density of the Ag particles used in the brazing material is preferably about 3 g / cm 3 or more. When manufacturing the laminated substrate 4 (when bonding the ceramic substrate 1 and the metal plate 2), for example, while interposing a brazing material between the ceramic substrate 1 and the two metal plates 2, heat is applied while applying pressure.

[0037] The heating atmosphere preferably has a degree of vacuum of 1.0×10 -3 Pa or less. The heating temperature (bonding temperature) is preferably about 700°C or higher and 820°C or lower, more preferably about 720°C or higher and 810°C or lower, and even more preferably about 740°C or higher and 800°C or lower. The holding time at the above heating temperature is preferably about 10 minutes or more and 60 minutes or less, more preferably 20 minutes or more and 60 minutes or less, and even more preferably about 30 minutes or more and 50 minutes or less.

[0038] At this time, since the ceramic substrate 1 has the thickness distribution and the properties of the surface 11 as described above, it can be sufficiently joined to the metal plate 2 not only at the central portion but also at the outer peripheral portion. That is, a laminated substrate 4 joined with a uniform bonding force in each part in the in-plane direction can be obtained. In such a laminated substrate 4, one of the pair of metal plates 2 may be used as a heat dissipation material, and the other may be processed into a circuit pattern to produce a circuit board.

[0039] The circuit pattern may be formed, for example, by etching the metal plate 2 using an etching resist. Thereby, a circuit board capable of sufficiently suppressing leakage current or the like can be formed, or a heat dissipation plate can be formed. The etching resist is not particularly limited, and for example, an ultraviolet curable or thermosetting resist material can be used. Also, the method of applying the etching resist is not particularly limited, and for example, a screen printing method or the like can be adopted.

[0040] When etching a copper plate as the metal plate 2, examples of the etching solution include ferric chloride solution, cupric chloride solution, sulfuric acid, hydrogen peroxide water, etc., but ferric chloride solution or cupric chloride solution is preferred. On the laminated substrate 4 from which unnecessary metal portions have been removed by etching, residues such as the metal plate 2 and the bonding layer 3 adhere. These residues and the like are preferably removed using an aqueous ammonium halide solution, an inorganic acid such as sulfuric acid or nitric acid, hydrogen peroxide water, or the like. The peeling of the etching resist after circuit formation is preferably performed, for example, by immersion in an aqueous alkali solution.

[0041] As described above, the ceramic substrate, the method for manufacturing the ceramic substrate, and the laminated substrate of the present invention have been described, but these are not limited to the above-described embodiments. For example, when the metal plate 2 is joined only to one surface side of the ceramic substrate 1, only the one surface may have the properties as described above. Furthermore, it may be provided in each aspect described below.

[0042] (1) A ceramic substrate having a rectangular shape in plan view, having undulations with intervals larger than roughness on its surface, and in a longitudinal section of the ceramic substrate along the thickness direction passing through the midpoints of two opposite sides, the curve showing the undulations has three or more extreme values, and in the longitudinal section, the value obtained by dividing the warpage amount defined by the maximum distance from the normal line of the straight line connecting the midpoints of the two sides to the surface by the length of the straight line is 1 μm / mm or less. A ceramic substrate.

[0043] (2) The ceramic substrate according to (1) above, wherein the thickness of the outer peripheral portion of the ceramic substrate is larger than the thickness of the central portion.

[0044] (3) The ceramic substrate according to (1) or (2) above, wherein the ceramic substrate has a long side and a short side, and the straight line is a straight line along the long side.

[0045] (4) In the ceramic substrate according to any one of (1) to (3) above, when the thickness at the midpoint of the diagonal of the ceramic substrate is T1 [mm] and the thickness at a point 2 mm from the end of the diagonal is T2 [mm], T2 - T1 is 0.001 mm or more. A ceramic substrate.

[0046] (5) The ceramic substrate according to any one of (1) to (4) above, wherein the average thickness of the ceramic substrate is 0.5 mm or more and 3 mm or less.

[0047] (6) A method for manufacturing a ceramic substrate according to any one of (1) to (5) above, comprising a first step of sandwiching a laminate including a plurality of ceramic green sheets with two setters having convex portions such that the convex portions face the laminate side, and a second step of obtaining the ceramic substrate from each of the ceramic green sheets by heating the laminate.

[0048] (7) In the method for manufacturing a ceramic substrate according to (6) above, by changing at least one of the load applied to the laminate and the number of the ceramic green sheets included in the laminate, at least one of the number of extrema of the curve indicating the undulation and the magnitude of the warpage amount is adjusted. A method for manufacturing a ceramic substrate.

[0049] (8) A laminated substrate, comprising: the ceramic substrate according to any one of (1) to (5) above; a metal plate provided on at least one surface side of the ceramic substrate; and a bonding layer that bonds the ceramic substrate and the metal plate. Of course, this is not the limit.

[0050] Finally, although various embodiments according to the present disclosure have been described, these are presented as examples and are not intended to limit the scope of the invention. The novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. The embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Example

[0051] Hereinafter, the present invention will be described in more detail using the following examples and comparative examples, but the present invention is not limited to the following examples.

[0052] 1. Preparation of ceramic green sheet First, 3.5 parts by mass of yttrium oxide powder and 2.8 parts by mass of aluminum oxide powder were added to 100 parts by mass of aluminum nitride powder produced by direct nitridation, and mixed for 1 hour with a ball mill to obtain a raw material powder. Thereafter, 8 parts by mass of an acrylic resin binder, 2 parts by mass of glycerin, 4 parts by mass of stearic acid, 2 parts by mass of oleic acid, and 4 parts by mass of ion-exchanged water were added to 100 parts by mass of the raw material powder, and mixed for 1 minute with a Henschel mixer to prepare a raw material slurry. Next, this raw material slurry was formed into a sheet of a predetermined thickness using a single-screw extruder, and punched out using a press with a mold to obtain a ceramic green sheet. Note that boron nitride powder was applied to the ceramic green sheet as a release agent at an application amount of 1 mg / cm 2 .

[0053] 2. Fabrication of Ceramic Substrate (Example 1) First, 10 fabricated ceramic green sheets were laminated to form a laminate. Next, the laminate was sandwiched between two boron nitride setters shown in Fig. 4, and tungsten weights were arranged so that the mass per unit area (cm 2 ) was 40 g, and a holder as shown in Fig. 3 was assembled. Note that the height of the convex portion of each setter was 50 μm.

[0054] Next, this holder was supplied from one end of a pusher-conveyor type continuous furnace, held at 1730 °C for 6 hours in a nitrogen atmosphere, and then heated to a firing temperature of 1820 °C for debinding and firing to obtain a ceramic substrate composed of an aluminum nitride sintered body. Note that the heating rate from the holding temperature to the firing temperature and the heating rate from the holding temperature to the firing temperature were set to 5.0 °C / min. The size of the obtained ceramic substrate was approximately 50.0 mm in length × approximately 60.0 mm in width × approximately 1.0 mm in thickness.

[0055] (Example 2) A ceramic substrate was obtained in the same manner as in Example 1, except that the number of ceramic green sheets was changed to 15. (Example 3) A ceramic substrate was obtained in the same manner as in Example 1, except that the number of ceramic green sheets was changed to 30.

[0056] (Comparative Example 1) A ceramic substrate was obtained in the same manner as in Example 1, except that the number of ceramic green sheets was changed to 30 and a flat setter without convex portions was used. (Comparative Example 2) A ceramic substrate was obtained in the same manner as in Comparative Example 1, except that the weight was changed to a weight of 10 g per unit area (cm 2 ).

[0057] 3. Measurement and Evaluation 3-1. Measurement of Thickness The thickness T1 at the midpoint of the diagonal of the obtained ceramic substrate and the thickness T2 at a point 2 mm from the end of the diagonal were measured with a micrometer (Mitutoyo Corporation, model: SPM2-25MX). The measurement results are shown in Table 1. Regarding the thickness T2, two values (substantially equal) were adopted for one ceramic substrate, and Table 1 shows the average value of 2n values for the obtained n ceramic substrates.

[0058] 3-2. Measurement of Warpage The surface of the obtained ceramic substrate was measured using a three-dimensional shape measuring machine (KEYENCE Corporation, "VR-3000") to obtain the warpage amount W. The measurement results are shown in Table 1.

[0059] 3-3. Evaluation of Bonding State with Metal Plate An active metal brazing material containing 3.5 parts by mass of TiH2 powder (manufactured by Osaka Titanium Technologies Co., Ltd., "TSH-350") and 3 parts by mass of Sn powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., "Sn-HPN"; average particle diameter 3 μm) was applied to 100 parts by mass in total of 90 parts by mass of Ag powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., "Ag-HWQ"; average particle diameter 2.5 μm) and 10 parts by mass of Cu powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., "Cu-HWQ"; average particle diameter 3 μm) on the ceramic substrates obtained in each Example and Comparative Example. Thereafter, oxygen-free copper plates with a thickness of 0.8 mm were placed on each of the two surfaces of the ceramic substrate at 1.0×10 -3In a vacuum of less than Pa, heating was carried out at 800 °C for 30 minutes to bond a ceramic substrate and two oxygen-free copper plates. Thereby, a laminated substrate was obtained.

[0060] Next, an ultrasonic flaw detection image of the bonding layer was obtained for the obtained laminated substrate using an ultrasonic flaw detector (manufactured by Hitachi Power Solutions Co., Ltd., "FSP8VA FineSAT"). In the obtained ultrasonic flaw detection image, the bonding area ratio was determined by utilizing the fact that the location of poor bonding (where peeling occurred) between the ceramic substrate and the oxygen-free copper plate was represented by a black portion. The bonding area ratio means the ratio (area %) of the actually bonded area (in the ultrasonic flaw detection image, the area obtained by subtracting the area of the black portion from the area of the ceramic substrate: the bonding area) to the area to be bonded (that is, the area of the surface of the ceramic substrate). The results of this evaluation are shown in Table 1.

[0061]

Table 1

Explanation of Symbols

[0062] 1: Ceramic substrate 11: Surface 2: Metal plate 3: Bonding layer 4: Laminated substrate 10: Ceramic green sheet 100: Laminate 20: Sette 21: Convex portion 201: Front surface 202: Rear surface 203: Bottom surface 204: Top surface 205: Right side surface 206: Left side surface 207: Right inclined surface 208: Left inclined surface 20': Sette 21': Convex portion 201': Front surface 202': Rear surface 203': Bottom surface 204': Top surface 205': Right side surface 206': Left side surface 207': Right inclined surface 208': Left inclined surface 209': Front inclined surface 210': Rear inclined surface 30: Counterweight 40: Holder A: Midpoint B: Midpoint DL: Diagonal H: Height S1: Point T1: Thickness T2: Thickness W: Warpage amount X: Midpoint Y: Point

Claims

1. A ceramic substrate having a rectangular shape in plan view, having undulations with intervals larger than the roughness on its surface, in the longitudinal cross-section of the ceramic substrate along the thickness direction passing through the midpoints of two opposite sides, the curve showing the undulations has three or more extreme values, A ceramic substrate, wherein in the longitudinal cross-section, the value obtained by dividing the amount of warpage defined by the maximum distance from the normal line of the straight line connecting the midpoints of the two sides to the surface by the length of the straight line is 1 μm / mm or less.

2. The ceramic substrate according to claim 1, wherein the thickness of the outer peripheral portion of the ceramic substrate is larger than the thickness of the central portion.

3. The ceramic substrate according to claim 1, wherein the ceramic substrate has a long side and a short side, and the straight line is a straight line along the long side.

4. The ceramic substrate according to claim 1, wherein when the thickness at the midpoint of the diagonal of the ceramic substrate is T1 [mm] and the thickness at a point 2 mm from the end of the diagonal is T2 [mm], T2 - T1 is 0.001 mm or more.

5. The ceramic substrate according to claim 1, wherein the average thickness of the ceramic substrate is 0.5 mm or more and 3 mm or less.

6. A method for manufacturing a ceramic substrate according to any one of claims 1 to 5, comprising: a first step of sandwiching a laminate including a plurality of ceramic green sheets between two setters having convex portions such that the convex portions face the laminate side; a second step of obtaining the ceramic substrate from each of the ceramic green sheets by heating the laminate.

7. The method for manufacturing a ceramic substrate according to claim 6, wherein at least one of the load applied to the laminate and the number of the ceramic green sheets included in the laminate is changed to adjust at least one of the number of extreme values of the curve showing the undulations and the magnitude of the amount of warpage.

8. A laminated substrate, comprising: the ceramic substrate according to any one of claims 1 to 5; a metal plate provided on at least one surface side of the ceramic substrate; and a bonding layer for bonding the ceramic substrate and the metal plate.

Images