Ceramic Substrate

Abstract

To provide a ceramic substrate which can suppress warpage while suppressing cost.SOLUTION: A ceramic substrate includes an insulation base material composed of planar ceramic, a first brazing material layer provided on a first main surface of the insulation base material, a second brazing material layer provided on a second main surface of the insulation base material, a first metal layer which is fixed to the first main surface side of the insulation base material through the first brazing material layer and is composed of metal, and a second metal layer which is fixed to the second main surface side of the insulation base material through the second brazing material layer and is composed of metal. A difference between the thickness of the first brazing material layer at an arbitrary place and the thickness of the second brazing material layer at a place on the rear side of the arbitrary place is 4.0 μm or less, and the insulation base material is smaller in thickness than the first metal layer and the second metal layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ceramic substrate. [Background technology]

[0002] Conventionally, ceramic substrates having a ceramic base material with high heat resistance have been used as substrates for mounting electric circuit components that generate a large amount of heat, such as power modules. In the method for manufacturing a metal-ceramic bonding substrate described in Patent Document 1, a paste-like brazing material is applied to both sides of a ceramic base material formed into a flat plate shape by screen printing or the like, and metal plates are fixed to both sides of the base material by this brazing material. Then, a part of the metal plate is removed by etching to form a circuit pattern.

[0003] The applicant has also proposed a ceramic circuit board in which the amount of warping at room temperature is reduced to 100 μm or less per 50 mm by subjecting a bonded assembly, which includes a metal circuit plate and a metal heat sink plate provided on the front and back surfaces of the ceramic substrate, respectively, via a brazing material, to a cooling treatment at -110°C or less, as described in Patent Document 2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-159926 [Patent Document 2] JP 2003-309210 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the method described in Patent Document 2, the warping of the ceramic substrate can be suppressed, but the cost of the step of cooling to -110°C or less increases. For this reason, the present inventors have studied the cause of the warping and found that the difference in thickness of the brazing material applied to one side and the other side of each part of the ceramic base material is involved in the occurrence of the warping, which led to the invention. In other words, the object of the present invention is to provide a ceramic substrate that can suppress the warping while suppressing the cost. [Means for solving the problem]

[0006] The present invention aims to solve the above problems, Rectangular Flat Silicon Nitride Substrate And the above Silicon Nitride Substrate a first brazing material layer provided on the first main surface of the Silicon Nitride Substrate a second brazing material layer provided on the second main surface of the first brazing material layer and the first brazing material layer Silicon Nitride Substrate is fixed to the first main surface side of , Electric circuit components are installed The first metal layer and the second brazing material layer are interposed therebetween. Silicon Nitride Substrate is fixed to the second main surface side of , and dissipates heat generated in the electric circuit components. a second metal layer; In the ceramic substrate, the first metal layer and the second metal layer are copper plates, and the difference in thickness between the first metal layer and the second metal layer is 0.02 mm or less; The first brazing material layer and the second brazing material layer are Contains no silver The thickness at any point is 11.2 μm or more 20.4 μm or less There was, The difference between the thickness of the first brazing material layer at an arbitrary point and the thickness of the second brazing material layer at a point on the back side of the arbitrary point is 4.0 μm or less. The screen printing method is used to form the The above Silicon Nitride Substrate has a thickness smaller than that of the first metal layer and the second metal layer; The amount of warping per 100 mm along each side is 0.03 mm or less A ceramic substrate is provided. Effect of the Invention

[0007] According to the ceramic substrate, divided ceramic substrates, and method for manufacturing a ceramic substrate according to the present invention, it is possible to suppress warping while suppressing costs. [Brief description of the drawings]

[0008] [Figure 1] 1A to 1C show an example of the configuration of a ceramic substrate according to an embodiment of the present invention, where (a) is a plan view showing the front surface, (b) is a side view, and (c) is a plan view showing the back surface. [Diagram 2] The figure shows the state in which electrical circuit components are mounted on the front surface of one of the separated ceramic substrates, and a heat sink is attached to the back surface as a heat dissipation component, (a) being a plan view and (b) being a side view. [Diagram 3] FIG. 1 is a schematic diagram illustrating an example of the configuration of a screen printing device. [Figure 4] FIG. 2 is a plan view showing a screen used in the screen printing apparatus. [Diagram 5] FIG. 11 is an explanatory diagram showing a state in which a plurality of insulating base materials are dried in a thermostatic chamber. [Figure 6] 1A is a plan view showing the front surface of a ceramic substrate before etching, FIG. 1B is a side view of the substrate, and FIG. 1C is a plan view of the back surface of the substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Embodiment Mode] 1 shows an example of the configuration of a ceramic substrate according to an embodiment of the present invention, where (a) is a plan view showing the front surface, (b) is a side view, and (c) is a plan view showing the back surface. The ceramic substrate 1 includes an insulating base material 2 made of a flat ceramic plate, a first brazing material layer 31 provided on a first main surface 2a of the insulating base material 2, a second brazing material layer 32 provided on a second main surface 2b of the insulating base material 2, a first metal layer 41 made of a metal fixed to the first main surface 2a of the insulating base material 2 via the first brazing material layer 31, and a second brazing material layer 32 provided on the second main surface 2b of the insulating base material 2 via the second brazing material layer 32. It also includes a second metal layer 42 made of a metal and fixed to the main surface 2b.

[0010] In this embodiment, the ceramic substrate 1 is an aggregate substrate, more specifically, a ceramic aggregate circuit substrate. The ceramic substrate 1 is cut along the dashed lines shown in Fig. 1(a) and (b) and divided into a plurality of ceramic divided substrates 11-14. Each of the plurality of ceramic divided substrates 11-14 has electric circuit components mounted on the front side and heat dissipation components attached to the back side. In this embodiment, the ceramic substrate 1 is divided into four ceramic divided substrates 11-14, but the number of divisions of the ceramic substrate is not limited to four, and may be two, three, or five or more.

[0011] The first metal layer 41 and the second metal layer 42 are made of metal plates formed to have a uniform thickness. The metal plates are preferably ones having low electrical resistance and high thermal conductivity. In the present embodiment, the first metal layer 41 and the second metal layer 42 are made of copper plates, but the first metal layer 41 and the second metal layer 42 may be made of aluminum plates. However, in order to prevent warping due to differences in thermal expansion coefficients, it is preferable that the first metal layer 41 and the second metal layer 42 are made of the same type of metal.

[0012] The first metal layer 41 is a circuit board on which electric circuit components are mounted. The second metal layer 42 is a heat sink that dissipates heat generated by the electric circuit components mounted on the first metal layer 41. In order to suppress warping of the ceramic substrate 1, it is desirable that the thickness of the first metal layer 41 and the thickness of the second metal layer 42 are approximately the same, and in this embodiment, the difference between the thickness of the first metal layer 41 and the thickness of the second metal layer 42 is 0.02 mm or less. More specifically, the difference between the maximum thickness at each portion of the first metal layer 41 and the minimum thickness at each portion of the second metal layer 42, and the difference between the minimum thickness at each portion of the first metal layer 41 and the maximum thickness at each portion of the second metal layer 42 are both 0.02 mm or less.

[0013] FIG. 2 shows a state in which the first to third electric circuit components 51-53 are mounted on the front side of one divided ceramic divided substrate 11 and a heat sink 50 is attached as a heat dissipation component on the back side, (a) being a plan view showing the front side and (b) being a side view. The first to third electric circuit components 51-53 are power modules such as transistors and diodes, and are heat generating components. The heat sink 50 has a flat base plate 501 and a plurality of protruding pieces 502 provided so as to protrude from the base plate 501, and dissipates heat generated in the first to third electric circuit components 51-53 and conducted from the insulating base material 2 to the second metal layer 42 into the air. The types, shapes, and quantities of the electric circuit components mounted on the ceramic divided substrates 11-14 are not limited to those exemplified in FIG. 2, and can be appropriately changed and implemented. The number of electric circuit components mounted on each of the ceramic divided substrates 11-14 is not particularly limited as long as it is one or more. In addition, while FIG. 2 shows an example in which the heat sink 50 is attached to the back surface side, the heat sink 50 does not have to be attached to the back surface side, and electrical circuit components may also be mounted on the back surface side.

[0014] The insulating substrate 2 is, for example, a silicon nitride substrate formed by forming a slurry of a mixture of silicon powder, a sintering aid, and an organic binder into a flat plate of a constant thickness by a doctor blade method, cutting the slurry, degreasing and nitriding the slurry, and sintering the slurry. In the example shown in FIG. 1, the insulating substrate 2 is rectangular, and the length L1 in the long side direction is longer than the length L2 in the short side direction. The first brazing material layer 31 and the second brazing material layer 32 are formed by applying a brazing material, which is a mixture of copper powder and silver powder, together with a binder and a solvent, to the first main surface 2a and the second main surface 2b of the insulating substrate 2 by a screen printing method. In addition, when the raw material of the insulating substrate 2 is silicon nitride powder instead of silicon powder, the nitriding process may be omitted. In addition, the first brazing material layer 31 and the second brazing material layer 32 may not contain silver powder.

[0015] Next, a method for manufacturing the ceramic substrate 1 will be described. This manufacturing method is a method for continuously manufacturing a plurality of ceramic substrates 1, for example, 100 to 200 lots, and includes a first brazing material layer forming step of applying a brazing material to the first main surface 2a of a plurality of insulating base materials 2 to form a first brazing material layer 31, a second brazing material layer forming step of applying a brazing material to the second main surface 2b of a plurality of insulating base materials 2 to form a second brazing material layer 32, and a metal layer forming step of overlaying metal plates on the first brazing material layer 31 and the second brazing material layer 32, respectively, brazing and etching them, and forming a first metal layer 41 and a second metal layer 42. The second brazing material layer forming step is performed after the first brazing material layer forming step is performed on all of the plurality of insulating base materials 2 corresponding to the number of lots, and the metal layer forming step is performed after the second brazing material layer forming step is performed on all of the plurality of insulating base materials 2 corresponding to the number of lots.

[0016] 3 is a schematic diagram showing an example of the configuration of a screen printing apparatus 6 for screen-printing the brazing material in the first brazing material layer forming process and the second brazing material layer forming process. FIG. 4 is a plan view showing a screen 7 used in the screen printing apparatus 6. The screen printing apparatus 6 has a mounting table 61 on which the insulating base material 2 is mounted, a squeegee unit 62, a moving mechanism 63 for moving the squeegee unit 62 along the long side direction of the insulating base material 2, and a support member 64 for supporting the screen 7 immovably relative to the mounting table 61. In the first brazing material layer forming process, the insulating base material 2 is mounted on the mounting table 61 with the first main surface 2a facing vertically upward, and in the second brazing material layer forming process, the insulating base material 2 is mounted on the mounting table 61 with the second main surface 2b facing vertically upward.

[0017] The moving mechanism 63 includes, for example, an electric motor 631, a ball screw 632, and a guide rail 633, and moves the squeegee unit 62 linearly between an original position shown by a solid line in FIG. 3 and a moving end position shown by a two-dot chain line. The squeegee unit 62 includes a unit case 620, a first squeegee 621 for the forward path, a second squeegee 622 for the return path, a first lifting rod 623 connected to the first squeegee 621, and a second lifting rod 624 connected to the second squeegee 622. The unit case 620 moves above the screen 7 by the rotation of the ball screw 632. The first lifting rod 623 and the second lifting rod 624 move vertically relative to the unit case 620 by, for example, hydraulic pressure or air pressure.

[0018] The screen 7 has a frame 71 and a flat screen mask 72 fixed to the frame 71. The screen mask 72 has a mesh portion 73 in which a plurality of transmission holes 730 are formed to allow the paste brazing material 30 to pass therethrough, and a non-mesh portion 74 in which no transmission holes 730 are formed. The mesh portion 73 is provided in a rectangular shape at a position including the center of the inside of the frame 71, and the non-mesh portion 74 is formed so as to surround the outside of the mesh portion 73. Note that in FIG. 3, the screen mask 72 is shown by cutting away a part of the frame 71.

[0019] The mesh portion 73 is formed by weaving together a plurality of warp threads 731 stretched parallel to the long side direction of the insulating substrate 2 and a plurality of weft threads 732 stretched parallel to the short side direction of the insulating substrate 2 in a lattice pattern, and a portion surrounded by two warp threads 731 and two weft threads 732 forms a transmission hole 730. A length L3 of the mesh portion 73 in the direction along the movement direction of the squeegee unit 62 is slightly shorter than a length L1 in the long side direction of the insulating substrate 2, and a length L4 of the mesh portion 73 in a direction perpendicular to the movement direction of the squeegee unit 62 is slightly shorter than a length L2 in the short side direction of the insulating substrate 2.

[0020] When the first lift rod 623 descends, the first squeegee 621 comes into contact with the screen mask 72, and when the first lift rod 623 ascends, the first squeegee 621 moves away from the screen mask 72. Similarly, when the second lift rod 624 descends, the second squeegee 622 comes into contact with the screen mask 72, and when the second lift rod 624 ascends, the second squeegee 622 moves away from the screen mask 72. The first squeegee 621 and the second squeegee 622 are long plate-shaped extending in a direction perpendicular to the moving direction of the squeegee unit 62, and are formed such that the length in the extending direction is longer than the length L4 of the mesh portion 73 in the same direction.

[0021] At the start of the first brazing material layer forming process and the second brazing material layer forming process, as shown in Fig. 3 and Fig. 4, the brazing material 30 is piled on the non-mesh portion 74 on the original position side of the squeegee unit 62 from the mesh portion 73, and the first squeegee 621 moves on the mesh portion 73 toward the moving end of the squeegee unit 62 while pushing the brazing material 30 from the through hole 730 toward the insulating base material 2. When the squeegee unit 62 moves to the moving end, the first squeegee 621 rises and the second squeegee 622 descends, and the second squeegee 622 moves on the mesh portion 73 while pushing the brazing material 30 from the through hole 730 toward the insulating base material 2. By this single reciprocating movement of the squeegee unit 62, the brazing material 30 is applied to the insulating base material 2 in a thickness corresponding to the thickness of the mesh portion 73. In addition, the brazing material 30 may be applied to one insulating substrate 2 by multiple reciprocating movements of the squeegee unit 62, or the brazing material 30 may be applied by a one-way movement of the squeegee unit 62 on either the outbound or return path.

[0022] In the first brazing material layer forming process and the second brazing material layer forming process, the brazing material 30 is applied by screen printing, in which the brazing material 30 is pushed toward the insulating base material 2 by the first squeegee 621 and the second squeegee 622 while the brazing material 30 is replenished on the screen 7 multiple times. For example, when screen printing is performed continuously on 200 insulating base materials 2 in the first brazing material layer forming process or the second brazing material layer forming process, the brazing material 30 is replenished a total of 19 times every time screen printing is performed on 10 insulating base materials 2. In this way, in the first brazing material layer forming process and the second brazing material layer forming process, after the brazing material 30 is replenished, the brazing material 30 is applied to multiple insulating base materials 2 (10 in the above example) by the screen printing method until the next replenishment of the brazing material 30.

[0023] In the first brazing material layer forming process, the brazing material 30 is applied to the first main surface 2a of the insulating base material 2, and then the brazing material 30 is dried and solidified in a thermostatic chamber. Similarly, in the second brazing material layer forming process, the brazing material 30 is applied to the second main surface 2b of the insulating base material 2, and then the brazing material 30 is dried and solidified in a thermostatic chamber. In the metal layer forming process, metal plates are placed on the first brazing material layer 31 and the second brazing material layer 32 on which the brazing material 30 has solidified, and the insulating base material 2 is sandwiched between these two metal plates and heated to about 800°C with a load applied, thereby performing brazing. Then, parts of each of these metal plates are removed by etching to form the first metal layer 41 and the second metal layer 42. Note that etching may be omitted by processing the first metal layer 41 and the second metal layer 42 into a predetermined shape in advance.

[0024] FIG. 5 is an explanatory diagram showing a state in which a plurality of insulating base materials 2 are dried in a thermostatic chamber 81 after the first brazing material layer forming process. The plurality of insulating base materials 2 are placed on a tray 82 so that a space is formed on the first main surface 2a side, and the trays 82 are stacked in order from the bottom according to the order in which the brazing material 30 was applied in the first brazing material layer forming process. This makes it possible to manage the order of the insulating base materials 2 to which the brazing material 30 was applied in the first brazing material layer forming process. In the second brazing material layer forming process, the brazing material 30 is applied to the second main surfaces 2b of the plurality of insulating base materials 2 in the order in which the brazing material 30 was applied in the first brazing material layer forming process. In other words, the insulating base material 2 to which the brazing material 30 was applied in the nth order (n is a natural number equal to or less than the number of lots) in the first brazing material layer forming process is also applied with the brazing material 30 in the nth order in the second brazing material layer forming process. This is a measure to equalize the thickness T1 (see Figure 1(b)) of the first brazing material layer 31 and the thickness T2 (see Figure 1(b)) of the second brazing material layer 32 for each insulating substrate 2.

[0025] When screen printing is performed as described above, the inventors have confirmed that the thickness of the applied brazing material 30 is thin immediately after the brazing material 30 is replenished on the screen 7, and gradually becomes thicker each time the screen printing is repeated, and that the degree of change in the thickness of the brazing material 30 varies depending on the location of the mesh portion 73. This is thought to be due to an increase in viscosity caused by the volatilization of the volatile components of the binder of the brazing material 30. When the viscosity of the brazing material 30 increases, the brazing material 30 becomes more likely to adhere to the insulating base material 2, and the first brazing material layer 31 and the second brazing material layer 32 tend to become thicker. In other words, the thickness of the brazing material 30 at each location on the insulating base material 2 applied in the first brazing material layer forming process and the second brazing material layer forming process is correlated with the number of times screen printing is performed after the brazing material 30 is replenished.

[0026] The inventors have also confirmed that the greater the difference between the thickness of the first brazing material layer 31 and the thickness of the second brazing material layer 32, the greater the warpage that occurs in the ceramic substrate 1. This is believed to be because the first brazing material layer 31 and the second brazing material layer 32 shrink during cooling after heating in the metal layer forming process, and therefore, for example, if the thickness of the first brazing material layer 31 is greater than that of the second brazing material layer 32, the insulating base material 2 curves so that the first main surface 2a side is concave due to the contraction force of the first brazing material layer 31, and conversely, if the thickness of the second brazing material layer 32 is greater than the thickness of the first brazing material layer 31, the insulating base material 2 curves so that the second main surface 2b side is concave due to the contraction force of the second brazing material layer 32.

[0027] For this reason, in this embodiment, for each insulating base material 2, the number of times indicating the number of screen printings performed after the brazing material 30 is supplied in the first brazing material layer forming process is made to match the number of times indicating the number of screen printings performed after the brazing material 30 is supplied in the second brazing material layer forming process. In other words, for the insulating base material 2 that has been screen printed for the third time after the brazing material 30 is supplied in the first brazing material layer forming process, screen printing is similarly performed for the third time after the brazing material 30 is supplied in the second brazing material layer forming process. This makes it possible to reduce the difference in thickness between the first brazing material layer 31 and the second brazing material layer 32 in the ceramic substrate 1, and to suppress the amount of warping of the insulating base material 2.

[0028] In this embodiment, the difference between the thickness of the first brazing material layer 31 and the thickness of the second brazing material layer 32 at any point on the ceramic substrate 1 is 4.0 μm or less. In addition, when the thicker of the first brazing material layer 31 and the second brazing material layer 32 at any point on the ceramic substrate 1 is Ta and the thinner of them is Tb, the relational expression (Ta-Tb) / Ta≦0.2 is satisfied. As a result, the ceramic substrate 1 has a warpage of the insulating base material 2 of 0.03 mm or less per 100 mm along each side of the insulating base material 2. Here, the warpage refers to the maximum value at room temperature (20° C.) of the amount of deviation in the thickness direction of the ceramic substrate 1 with respect to the line segment connecting both ends of the measurement target range.

[0029] (Example) Next, a more specific example of the ceramic substrate 1 will be described. Fig. 6 shows the ceramic substrate 10 in a state before etching in the metal layer forming step, with (a) being a plan view showing the front surface, (b) being a side view, and (c) being a plan view showing the back surface. In this ceramic substrate 10, a first metal plate 401 is brazed to a first main surface 2a of an insulating base material 2 by a first brazing material layer 31, and a second metal plate 402 is brazed to a second main surface 2b of the insulating base material 2 by a second brazing material layer 32.

[0030] The first metal plate 401 is etched to remove unnecessary portions to become the first metal layer 41, and the second metal plate 402 is etched to remove unnecessary portions to become the second metal layer 42. In this etching, an etching resist pattern of a predetermined shape is formed on the first metal plate 401 and the second metal plate 402, and a part of the first metal plate 401 and the second metal plate 402 is removed by a chemical solution. Thereafter, the first brazing material layer 31 and the second brazing material layer 32 are removed from the parts where the first metal plate 401 and the second metal plate 402 have been removed by using a chemical solution for removing the brazing material.

[0031] The insulating base material 2 has a long side length L1 of 190.5 mm, a short side length L2 of 138.0 mm, and a thickness T0 of 0.32 mm. The first metal plate 401 and the second metal plate 402 are rectangular flat plates with long side lengths L11 and L21 of 188.4 mm, short side lengths L12 and L22 of 133.6 mm, and thicknesses T10 and T20 of 0.8 mm. The first brazing material layer 31 and the second brazing material layer 32 are formed to be the same size as the first metal plate 401 and the second metal plate 402.

[0032] FIG. 6(a) shows first to ninth measurement points 311-319 of the thickness of the first brazing material layer 31, and FIG. 6(c) shows first to ninth measurement points 321-329 of the thickness of the second brazing material layer 32. The first measurement point 321 of the second brazing material layer 32 is located behind the first measurement point 311 of the first brazing material layer 31. Similarly, the second to ninth measurement points 322-329 of the second brazing material layer 32 are located behind the second to ninth measurement points 312-319 of the first brazing material layer 31. Arrows A1 and A2 shown in FIGS. 6(a) and 6(c) indicate the direction of forward movement of the squeegee unit 62 when performing screen printing in the first brazing material layer forming process and the second brazing material layer forming process.

[0033] 6(a) and 6(c), the first measurement points 311, 321, the third measurement points 313, 323, the seventh measurement points 317, 327, and the ninth measurement points 319, 329 are located at the corners of the first metal plate 401 and the second metal plate 402. The fifth measurement points 315, 325 are located at the centers of the first metal plate 401 and the second metal plate 402. The second measurement points 312, 322 and the eighth measurement points 318, 328 are located at the centers of the long sides of the first metal plate 401 and the second metal plate 402. The fourth measurement points 314, 324 and the sixth measurement points 316, 326 are located at the centers of the short sides of the first metal plate 401 and the second metal plate 402.

[0034] Table 1 shows the thickness of the first brazing layer 31 at each measurement point 311-319, the thickness of the second brazing layer 32 at each measurement point 321-329, and the difference between the thicknesses (the difference between the thickness of the first brazing layer 31 and the thickness of the second brazing layer 32) when the number of times of screen printing in the first brazing layer forming process and the number of times of screen printing in the second brazing layer forming process are the same. As shown in Table 1, in this embodiment, the absolute value of the difference between the thickness of the first brazing layer 31 and the thickness of the second brazing layer 32 is 4.0 μm or less at all measurement points 311-319 and 321-329. In addition, when the thicker of the thicknesses of the first brazing layer 31 and the second brazing layer 32 is Ta and the thinner of the thicknesses is Tb, the relational expression (Ta-Tb) / Ta≦0.2 is satisfied.

[0035] [Table 1]

[0036] Table 2 shows the thicknesses of the first brazing layer 31 at each of the measurement points 311-319, the thicknesses of the second brazing layer 32 at each of the measurement points 321-329, and the difference between the respective thicknesses in a comparative example in which the number of times of screen printing in the first brazing layer formation step and the number of times of screen printing in the second brazing layer formation step were not the same. In this comparative example, the absolute value of the difference between the thicknesses of the first brazing layer 31 and the second brazing layer 32 exceeds 4.0 μm in some of the measurement points 311-319. In addition, the value of (Ta-Tb) / Ta is greater than 0.2 in some of the measurement points 311-319.

[0037] [Table 2]

[0038] In this comparative example, the warpage of the insulating base material 2 was larger than that in the example, and the amount of warpage per 100 mm in the direction along each side of the insulating base material 2 was greater than 0.03 mm. In other words, it was confirmed that by matching the number of times of screen printing in the first brazing material layer forming process and the number of times of screen printing in the second brazing material layer forming process, it is possible to reduce the difference in thickness between the first brazing material layer 31 and the second brazing material layer 32, and to make the amount of warpage per 100 mm in the direction along each side of the insulating base material 2 0.03 mm or less.

[0039] (Functions and Effects of the Embodiments) According to the embodiment described above, by making the difference between the thickness of the first brazing material layer 31 and the thickness of the second brazing material layer 32 4.0 μm or less, it is possible to suppress warping of the ceramic substrate 1. In addition, by making the number of times of screen printing in the first brazing material layer forming process and the number of times of screen printing in the second brazing material layer forming process equal to each other, it is possible to reduce the difference between the thickness of the first brazing material layer 31 and the thickness of the second brazing material layer 32 at each measurement point without adding a process. As a result, according to the embodiment, it is possible to suppress warping while suppressing costs.

[0040] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiment will be described by using the reference numerals and the like in the embodiment. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiment.

[0041] [1] A ceramic substrate (1) comprising: an insulating base material (2) made of a flat ceramic; a first brazing material layer (31) provided on a first main surface (2a) of the insulating base material (2); a second brazing material layer (32) provided on a second main surface (2b) of the insulating base material (2); a first metal layer (41) made of a metal and fixed to the first main surface (2a) of the insulating base material (2) via the first brazing material layer (31); and a second metal layer (42) made of a metal and fixed to the second main surface (2b) of the insulating base material (2) via the second brazing material layer (32), wherein the difference between the thickness of the first brazing material layer (31) and the thickness of the second brazing material layer (32) at any point is 4.0 μm or less.

[0042] [2] The ceramic substrate (1) according to the above item [1], wherein, when the thicker of the thicknesses of the first brazing material layer (31) and the second brazing material layer (32) at any given point is Ta and the thinner of the thicknesses of the first brazing material layer (31) and the second brazing material layer (32) at any given point is Tb, the thickness satisfies the relational expression (Ta-Tb) / Ta≦0.2.

[0043] [3] The ceramic substrate (1) according to the above [1] or [2], wherein one of the first metal layer (41) and the second metal layer (42) is a circuit board on which electric circuit components (51-53) are mounted, and the other is a heat sink that dissipates heat, and the difference between a thickness of the first metal layer (41) and a thickness of the second metal layer (42) is 0.02 mm or less.

[0044] [4] The ceramic substrate (1) according to any one of [1] to [3] above, wherein the insulating base material (2) is rectangular and the amount of warping of the insulating base material (2) per 100 mm in a direction along each side of the insulating base material (2) is 0.03 mm or less.

[0045] [5] A method for manufacturing a ceramic substrate, which continuously manufactures a plurality of ceramic substrates (1) according to any one of the above [1] to [4], comprising: a first brazing material layer forming step of applying a brazing material (30) to the first main surfaces (2a) of the plurality of insulating base materials (2) to form the first brazing material layer (31); a second brazing material layer forming step of applying a brazing material (30) to the second main surfaces (2b) of the plurality of insulating base materials (2) to form the second brazing material layer (32); and a metal layer forming step of overlapping and brazing metal plates (401, 402) on the first brazing material layer (31) and the second brazing material layer (32), respectively, to form the first metal layer (41) and the second metal layer (42). a brazing material layer forming step of 2, the brazing material (30) is applied by screen printing in which the brazing material (30) is extruded toward the insulating base material (2) by a squeegee while being replenished on a screen (7) a plurality of times, and after the brazing material (30) is replenished, the brazing material (30) is applied to a plurality of the insulating base materials (2) during the period until the next replenishment of the brazing material (30), and a number of times indicating the number of screen printings after the brazing material (30) is replenished in the first brazing material layer forming step is made to match a number of times indicating the number of screen printings after the brazing material (30) is replenished in the second brazing material layer forming step for each of the insulating base materials (2).

[0046] Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the embodiments described above. It should be noted that not all of the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

[0047] In addition, the present invention can be modified appropriately without departing from the spirit of the present invention. For example, in the above embodiment, the ceramic substrate 1 is an aggregate substrate and is divided into a plurality of ceramic divided substrates 11 to 14. However, the present invention is not limited to this, and can be applied to a ceramic substrate that is not an aggregate substrate. [Explanation of symbols]

[0048] 1...Ceramic substrate 2...Insulating substrate 2a...First main surface 2b...Second main surface 30: brazing material; 31: first brazing material layer 32: Second brazing material layer 401: First metal plate 402: second metal plate 41: first metal layer 42... second metal layer 621... first squeegee 622...Second squeegee 7...Screen

Claims

1. A rectangular, flat silicon nitride substrate; a first brazing material layer provided on a first main surface of the silicon nitride substrate; a second brazing material layer provided on a second main surface of the silicon nitride substrate; a first metal layer that is fixed to the first main surface side of the silicon nitride substrate via the first brazing material layer and on which an electric circuit component is mounted; a second metal layer that is fixed to the second main surface side of the silicon nitride substrate via the second brazing material layer and dissipates heat generated by the electric circuit component, the first metal layer and the second metal layer are copper plates, and the difference in thickness between them is 0.02 mm or less; The first brazing material layer and the second brazing material layer do not contain silver, have a thickness of 11.2 μm or more and 20.4 μm or less at any location, and are formed by a screen printing method so that the difference between the thickness of the first brazing material layer at any location and the thickness of the second brazing material layer at a location on the back side of the arbitrary location is 4.0 μm or less; the silicon nitride substrate is thinner than the first metal layer and the second metal layer, and has a warp amount of 0.03 mm or less per 100 mm in a direction along each side; Ceramic substrate.

2. The first brazing material layer is formed by X-th screen printing after the brazing material is replenished, and the second brazing material layer is formed by X-th screen printing after the brazing material is replenished. The ceramic substrate according to claim 1 .

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