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, in which the thickness T2 of an outer periphery is greater than the thickness T1 of the central portion. In a longitudinal section of the ceramic substrate passing the midpoint X of two opposing sides along a thickness direction, a curl edge amount specified by a minimum distance from a point on a surface of the ceramic substrate at a position 3 mm inward from a lateral edge thereof along a direction orthogonal to the thickness direction to a straight line connecting the midpoint of the two sides is 30 μm or less.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] Power modules such as IGBT modules are used in inverters that control high-power motors such as those for electric railways, power generation, and electric vehicles / hybrid electric vehicles (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 joining 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 joining.

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 capable of manufacturing a laminated substrate joined with a uniform joining strength in each part in the in-plane direction, a method for manufacturing a ceramic substrate, and a laminated substrate formed by joining a ceramic substrate and a metal plate.

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. The thickness of the outer peripheral portion of this ceramic substrate is larger than the thickness of the central portion. In the longitudinal cross-section of the ceramic substrate along the thickness direction passing through the midpoints of two opposing sides, the curl edge amount defined by the minimum distance from the point on the surface of the ceramic substrate at a position 3 mm inside in the direction orthogonal to the thickness direction from the side end thereof to the straight line connecting the midpoints of the two sides is 30 μm or less.

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

Brief Description of Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes 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. And the thickness of the outer peripheral portion of the ceramic substrate 1 is larger than the thickness of the central portion. With such a configuration, when bonding the ceramic substrate 1 and the metal plate 2 to manufacture the laminated substrate 4 (see Fig. 6), the load 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 close 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.

[0010] 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 T2 - T1 being 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 to the outer peripheral portions of the ceramic substrate 1 and the metal plate 2, it is easy to obtain a laminated substrate 4 joined with a uniform bonding force in each part in the in-plane direction.

[0011] And in the ceramic substrate 1, as shown in Fig. 2, in the longitudinal section of the ceramic substrate 1 along the thickness direction passing through the midpoints A or B of the two opposing sides, from the point S1 on the surface 11 of the ceramic substrate 1 at a position 3 mm inside along the direction orthogonal to the thickness direction (the left - right direction in the figure) from the side end, the curl edge amount CE defined by the minimum distance to the straight line A - A or B - B connecting the midpoints A or B of the two sides is about 30 μm or less. In this case, it can be determined that the surface 11 of the ceramic substrate 1 has sufficiently small warping or distortion, etc. at its outer peripheral portion. Therefore, when the above load is applied to the ceramic substrate 1 and the metal plate 2, the outer peripheral portions of their opposing surfaces can be sufficiently brought close to each other.

[0012] The curl edge amount CE may be about 30 μm or less, preferably about 25 μm or less, more preferably about 20 μm or less, and even more preferably about 15 μm or less. The lower limit of the curl edge amount CE is not particularly limited, but is about 3 μm. In this case, the above effects can be further enhanced. In addition, since there are four points S1 on one ceramic substrate 1, four values can also be obtained for the minimum distance from these points S1 to the straight line connecting the midpoints A or B of the two sides. In this specification, the maximum value among these is defined as the curl edge amount CE.

[0013] Also, in the above longitudinal section, 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 is preferably about 60 μm or less, more preferably about 50 μm or less, and even more preferably about 40 μm or less. The lower limit of the warpage amount W is not particularly limited, but is about 10 μm. In this case, it can be determined that the surface 11 of the ceramic substrate 1 has sufficiently small warpage or distortion, etc. at its central portion. Therefore, when the above load is applied to the ceramic substrate 1 and the metal plate 2, the central portion and the outer peripheral portion of their opposing surfaces can be sufficiently approximated.

[0014] When the ceramic substrate 1 has a long side and a short side, the longitudinal section defining the warpage amount W is preferably the straight line A - A connecting the midpoints A of the two sides, that is, the straight line along the long side. When the warpage amount W is within the above range 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 portion and the outer peripheral portion of their opposing surfaces can be more reliably 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 photographing and image - analyzing the longitudinal section of the ceramic substrate 1.

[0015] 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) that bonds 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".

[0016] 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.

[0017] 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.

[0018] 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 the configuration of a setter. FIG. 5 is a perspective view showing another example of the configuration of a setter.

[0019] 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 heating the laminate 100 to obtain the ceramic substrate 1 from each ceramic green sheet 10. [First Step] In the first step, first, a plurality of ceramic green sheets 10 and a setter 20 are prepared. The ceramic green sheet 10 is 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.

[0020] 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.

[0021] 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.

[0022] The raw material slurry is applied to 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 or the like. 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.

[0023] 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 opposite 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 are each connected to the upper surface 204 via a right inclined surface 207 or a left inclined surface 208, and their heights are equal to the height of the portion where the widths of the front surface 201 and the rear surface 202 are substantially constant.

[0024] 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 the convex portions 21. The height H of the convex portion 21 may be 10 μm or more, may be 20 μm or more, or may be 30 μm or more. Also, the height H may be 100 μm or less, may be 75 μm or less, or may 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.

[0025] The setter 20 can be made 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 made of boron nitride has both heat resistance and good machinability, and thus is preferably used. 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.

[0026] 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 stacking 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.

[0027] Furthermore, a weight 30 is placed on the upper setter 20 to produce a holding body 40. The weight 30 is composed of, for example, a highly stable metal material (tungsten) or the like 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 is more surely provided with the thickness distribution and the properties of the surface 11 as described above.

[0028] 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.

[0029] [Second step] In the second step, the laminate 100 is heated. First, the holder 40 including the laminate 100 is placed in a degreasing 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 about 1 hour or more and 10 hours or less. As a result, the binder and dispersant contained in the ceramic green sheet 10 volatilize, and the ceramic green sheet 10 shrinks. That is, the ceramic green sheet 10 is degreased.

[0030] Next, the holder 40 including the degreased 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 about 4 hours or more and 10 hours or less 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, and the ceramic substrate 1 is obtained. In addition, the heating temperature, time, and atmosphere during degreasing and firing can be appropriately adjusted according to the composition of the ceramic green sheet 10.

[0031] Note that the degreasing furnace used for degreasing 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 performs degreasing and firing continuously. 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 more. In addition, the cooling rate when cooling from the firing temperature to 1500°C is preferably about 10°C / min or more and 25°C / min or less.

[0032] 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 contained in the laminate 100, it is preferable to adjust at least one of the thickness distribution of the obtained ceramic substrate 1 and the magnitude of the curl edge amount CE. Also, the magnitude of the warpage amount W may be adjusted. According to such a configuration, a ceramic substrate 1 having a predetermined thickness distribution and 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 properties of the surface 11 in the long side direction.

[0033] 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 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. Also, 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.

[0034] And 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 properties of the surface 11 in the long side direction and the short side direction.

[0035] In addition, when the number of ceramic green sheets 10 is increased, 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.

[0036] 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.

[0037] The bonding layer 3 is preferably formed of a brazing material. As the brazing material, for example, 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 is used. 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.

[0038] 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.

[0039] 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 fabricate a circuit board.

[0040] 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.

[0041] 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 solution of ammonium halide, 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.

[0042] The ceramic substrate, the method for manufacturing the ceramic substrate, and the laminated substrate of the present invention have been described above, 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.

[0043] (1) A ceramic substrate having a rectangular shape in plan view, wherein the thickness of the outer peripheral portion of the ceramic substrate is greater than the thickness of the central portion, and in the longitudinal cross-section of the ceramic substrate along the thickness direction passing through the midpoints of two opposing sides, the curl edge amount defined by the minimum distance from a point on the surface of the ceramic substrate at a position 3 mm inside along the direction orthogonal to the thickness direction from the side end thereof to the straight line connecting the midpoints of the two sides is 30 μm or less.

[0044] (2) The ceramic substrate according to (1) above, wherein in the longitudinal cross-section, the warpage amount defined by the maximum distance from the normal line of the straight line to the surface of the ceramic substrate is 60 μm or less.

[0045] (3) The ceramic substrate according to (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.

[0046] (4) The ceramic substrate according to any one of (1) to (3) above, 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.

[0047] (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.

[0048] (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.

[0049] (7) In the method for manufacturing a ceramic substrate according to (6) above, 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 thickness distribution of the ceramic substrate and the amount of the curled edge. A method for manufacturing a ceramic substrate.

[0050] (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 for bonding the ceramic substrate and the metal plate. Of course, this is not the limit.

[0051] 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

[0052] Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples.

[0053] 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 the mixture was mixed for 1 hour with a ball mill to obtain a raw material powder. Subsequently, 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 the mixture was mixed for 1 minute using a Henschel mixer to prepare a raw material slurry. Next, this raw material slurry was formed into a sheet with a predetermined thickness using a single-screw extruder and punched out using a press machine with a mold to obtain a ceramic green sheet. Note that boron nitride powder was applied to the ceramic green sheet as a mold release agent at a coating amount of 1 mg / cm 2 .

[0054] 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 to assemble a holder as shown in FIG. 3. Note that the height of the convex portion of each setter was 50 μm.

[0055] 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 was 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.

[0056] (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.

[0057] (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 ).

[0058] 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 (manufactured by 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.

[0059] 3-2. Measurement of Curl Edge Amount and Warpage Amount The surface of the obtained ceramic substrate was measured using a three-dimensional shape measuring machine (manufactured by KEYENCE Corporation, "VR-3000") to obtain the curl edge amount CE and the warpage amount W. The measurement results are shown in Table 1. Regarding the curl edge amount CE, the maximum value among four values for one ceramic substrate was adopted, and Table 1 shows the average value of n values for the obtained n ceramic substrates.

[0060] 3-3. Evaluation of Bonding State with Metal Plate On the ceramic substrates obtained in each of the examples and comparative examples, 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 Industry Co., Ltd., "Sn-HPN"; average particle diameter 3 μm) were added to a total of 100 parts by mass of 90 parts by mass of Ag powder (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., "Ag-HWQ"; average particle diameter 2.5 μm) and 10 parts by mass of Cu powder (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., "Cu-HWQ"; average particle diameter 3 μm), and an active metal brazing filler metal containing them was applied. Thereafter, oxygen-free copper plates with a thickness of 0.8 mm were placed on each of the two surfaces of the ceramic substrate, and heated at 800 °C for 30 minutes in a vacuum of 1.0×10 -3 Pa or less to join the ceramic substrate and the two oxygen-free copper plates. Thereby, a laminated substrate was obtained.

[0061] 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 portions where bonding failure (peeling occurred) between the ceramic substrate and the oxygen-free copper plate were represented by black portions. The bonding area ratio means the ratio (area %) of the actually bonded area (the area obtained by subtracting the area of the black portion from the area of the ceramic substrate in the ultrasonic flaw detection image: 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.

[0062]

Table 1

Explanation of Symbols

[0063] 1: Ceramic substrate 11: Surface 2: Metal plate 3: Bonding layer 4: Laminated substrate 10: Ceramic green sheet 100: Laminate 20: Setter 21: Convex part 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': Setter 21': Convex part 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: Weight stone 40: Holder A: Midpoint B: Midpoint CE: Curl edge amount DL: Diagonal line 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, wherein the thickness of the outer peripheral portion of the ceramic substrate is greater than the thickness of the central portion, in a longitudinal cross-section of the ceramic substrate along the thickness direction passing through the midpoints of two opposing sides, the curl edge amount defined by the minimum distance from a point on the surface of the ceramic substrate at a position 3 mm inside along the direction orthogonal to the thickness direction from the side end thereof to the straight line connecting the midpoints of the two sides is 30 μm or less. A ceramic substrate.

2. The ceramic substrate according to claim 1, in the longitudinal cross-section, the warpage amount defined by the maximum distance from the normal line of the straight line to the surface of the ceramic substrate is 60 μm or less. A ceramic substrate.

3. The ceramic substrate according to claim 2, wherein the ceramic substrate has a long side and a short side, and the straight line is a straight line along the long side. A ceramic substrate.

4. The ceramic substrate according to claim 1, 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.

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. A ceramic substrate.

6. A method for manufacturing a ceramic substrate according to any one of claims 1 to 5, 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. A method for manufacturing a ceramic substrate.

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 thickness distribution of the ceramic substrate and the magnitude of the curl edge amount. A method for manufacturing a ceramic substrate.

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

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