Ceramic substrate, circuit substrate and method for manufacturing the same, and power module

Abstract

Provided is a ceramic substrate having excellent reliability as a component and a circuit substrate. The ceramic substrate has a first region and a second region having different surface roughnesses on a main surface. The ratio of the surface roughness Ra2 of the second region to the surface roughness Ra1 of the first region is 1.5 or more. The circuit substrate includes the ceramic substrate and a conductor portion joined to at least a portion of the first region.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a ceramic substrate, a circuit substrate and a manufacturing method thereof, and a power module. BACKGROUND

[0002] In the fields of automobiles, electrified railways, industrial equipment, and power generation, power modules that control large currents are used. An insulating substrate mounted on a power module uses a ceramic substrate. In such uses, a ceramic substrate is required to have not only insulation but also good heat dissipation characteristics. For example, in Patent Literature 1, as a ceramic substrate, a ceramic substrate of a material in which aluminum nitride, aluminum oxide, silicon nitride, or silicon carbide is a main component is proposed.

[0003] In addition, in Patent Literature 2, a technology is proposed in which the surface roughness Ra of a ceramic substrate used in a semiconductor module is set to 0.1 to 5 μm, and a resin layer is made to enter into microscopic irregularities of the surface of the ceramic substrate to improve the adhesion of the resin layer.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2017-212316

[0007] Patent Literature 2: Japanese Patent Application Publication No. 2016-181715 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] A power module is an important product that controls various devices, and is therefore required to stably function. A ceramic substrate used as a component in such a power module and other various uses is required to have high reliability. On the other hand, since various products such as power modules are used in various fields, along with this, further improvement in reliability is required for each component.

[0010] Therefore, in the present disclosure, a ceramic substrate having excellent reliability as a component is provided. In addition, a circuit substrate and a manufacturing method thereof having excellent reliability as a component are provided. In addition, in the present disclosure, a power module having excellent reliability by having such a circuit substrate is provided.

[0011] MEANS FOR SOLVING THE PROBLEMS

[0012] One aspect of the present disclosure relates to a ceramic substrate having a first region and a second region having surface roughness different from each other on at least one main surface. Such a ceramic substrate can adjust adhesion or joint properties to a component according to the kind of the component in contact with the main surface. Such a ceramic substrate has excellent reliability as a component.

[0013] The ratio of the surface roughness Ra2 of the above-mentioned second region to the surface roughness Ra1 of the above-mentioned first region can be 1.5 or more. Thus, by having the main surface with a surface roughness that greatly differs, the adhesion or the joining property to the member can be sufficiently adjusted according to the kind of the member that contacts the main surface. Such a ceramic substrate has more excellent reliability as a member.

[0014] The above-mentioned second region has a surface roughness Ra2 that is larger than that of the above-mentioned first region, and at least a part of the above-mentioned second region can be bonded with a resin. Since the second region has a surface roughness Ra2 that is larger than the surface roughness Ra1 of the first region, the adhesion to the resin can be improved by the anchoring effect.

[0015] The above-mentioned first region has a surface roughness Ra1 that is smaller than that of the above-mentioned second region, and a conductor portion can be joined to at least a part of the first region. Since the first region has a surface roughness Ra1 that is smaller than the surface roughness Ra2, the conductor portion can be sufficiently firmly joined by using, for example, a solder or the like.

[0016] The above-mentioned ceramic substrate can contain a ceramic component, and a metal oxide having Y and Mg as constituent elements that is different from the ceramic component, and the mass ratio of Y to Mg in the metal oxide, when converted to Y2O3 and MgO, respectively, is 0.3 to 3. If it is such a ceramic substrate, the surface roughness of the main surface can be adjusted with high freedom by etching. Therefore, for example, in a composite substrate of a ceramic substrate and a metal substrate, when the metal substrate is removed by etching to form a conductor portion, the surface roughness of the main surface can be adjusted at the same time.

[0017] The area ratio of the first region in the main surface of the above-mentioned ceramic substrate can be 30 to 90%, and the area ratio of the second region in the main surface can be 10 to 70%. If it is such a ceramic substrate, the reliability can be improved in various uses.

[0018] The above-mentioned ceramic substrate can contain silicon nitride, and a metal oxide having Y and Mg as constituent elements, and the proportion of the metal oxide in the first region and the second region with respect to the silicon nitride is different from each other. Such a ceramic substrate can sufficiently make the surface roughness of the first region and the second region different.

[0019] One aspect of the present disclosure relates to a circuit substrate provided with any of the above-mentioned ceramic substrates, and a conductor portion joined to at least a part of the above-mentioned first region, the first region having a surface roughness Ra1 that is smaller than that of the second region. Since the first region has a surface roughness Ra1 that is smaller than the surface roughness Ra2 of the second region, the conductor portion can be sufficiently firmly joined by using, for example, a solder or the like. Therefore, the circuit substrate has excellent reliability as a member.

[0020] At least a portion of the second region in the aforementioned circuit board is bonded to resin, and the second region may have a larger surface roughness Ra2 than the first region. Since the second region has a larger surface roughness Ra2 than the first region, the adhesion to the resin can be improved by utilizing the anchoring effect.

[0021] One aspect of this disclosure relates to a power module comprising any of the circuit boards described above, and a resin sealing the circuit board, wherein at least a portion of the second region is bonded to the resin. With such a power module, the adhesion between the resin and the ceramic substrate is excellent, thus resulting in excellent reliability.

[0022] The aforementioned power module includes a conductive portion of a circuit board and a semiconductor element electrically connected to the conductive portion. Furthermore, the semiconductor element and the circuit board can be sealed together with resin. In such a power module, even if the semiconductor element generates heat, for example, the adhesion between the resin and the ceramic substrate can be maintained. Therefore, high reliability can be maintained.

[0023] One aspect of this disclosure relates to a method for manufacturing a circuit board, comprising: a step of bonding a metal substrate to the main surface of a ceramic substrate having a surface roughness Ra1 to obtain a composite substrate; and a step of removing a portion of the metal substrate from the composite substrate by etching to form a conductor portion, wherein a region having a surface roughness Ra2 greater than the surface roughness Ra1 is formed on the main surface of the ceramic substrate. According to this manufacturing method, a region having a surface roughness Ra2 can be formed on the main surface of the ceramic substrate simultaneously with etching of the metal substrate. Therefore, a circuit board having excellent reliability as a component can be manufactured without increasing the number of processes.

[0024] The effects of the invention

[0025] According to this disclosure, a ceramic substrate with excellent reliability as a component can be provided. Furthermore, a circuit board with excellent reliability as a component and a method for manufacturing the same can be provided. Additionally, a power module with excellent reliability by incorporating such a circuit board can be provided. Attached Figure Description

[0026] [ Figure 1 ] Figure 1 This is a perspective view of a ceramic substrate according to one embodiment.

[0027] [ Figure 2 ] Figure 2 This is a cross-sectional view of a circuit board according to one embodiment.

[0028] [ Figure 3 ] Figure 3 This is a cross-sectional view of a power module according to one implementation method.

[0029] [ Figure 4 ] Figure 4 This is an optical microscope photograph of the main surface of the ceramic substrate of Example 1.

[0030] [ Figure 5 ] Figure 5 This is a scanning electron microscope image of a cross-section of the ceramic substrate of Example 1.

[0031] [ Figure 6 ] Figure 6 This is an optical microscope photograph of the main surface of the ceramic substrate in Example 2.

[0032] [ Figure 7 ] Figure 7 This is a scanning electron microscope image of a cross-section of the ceramic substrate of Example 2. Detailed Implementation

[0033] Hereinafter, one embodiment of this disclosure will be described with reference to the accompanying drawings, as appropriate. However, the following embodiments are merely examples for illustrating this disclosure and are not intended to limit the invention to the following content. In the description, the same elements or elements having the same function are referred to by the same reference numerals, and repeated descriptions are omitted as appropriate. The dimensional ratios of the elements are not limited to those shown in the drawings.

[0034] Figure 1 This is a perspective view of a ceramic substrate according to one embodiment. Figure 1 The ceramic substrate 100 is flat. A main surface 100A of the ceramic substrate 100 is divided into a first region 10 and a second region 20 having different surface roughnesses. The first region 10 is surrounded by the second region 20. The dividing line VL between the first region 10 and the second region 20 is a boundary line representing the boundary between them, and can be a virtual line. Each of the first region 10 and the second region 20 has a diameter of 100 mm. 2 The above area.

[0035] The surface roughness Ra2 of the second region 20 can be greater than the surface roughness Ra1 of the first region 10. The ratio of the surface roughness Ra2 of the second region 20 to the surface roughness Ra1 of the first region 10 can be 1.5 or more, 1.8 or more, or 2.0 or more. By increasing this ratio, the tightness or bonding with the component can be adequately adjusted according to the type of component that contacts the main surface 100A. Such a ceramic substrate 100 has superior reliability as a component. From the same point of view, the difference between the surface roughness Ra2 of the second region 20 and the surface roughness Ra1 of the first region 10 can be 0.1 μm or more, or 0.2 μm or more.

[0036] The ratio of the surface roughness Ra2 of the second region 20 to the surface roughness Ra1 of the first region 10 can be 5.0 or less, 4.0 or less, or 3.0 or less. By reducing this ratio, the surface roughness Ra2 can be prevented from becoming too large, and the strength of the ceramic substrate 100 can be maintained at a sufficiently high level. From the same point of view, the difference between the surface roughness Ra2 of the second region 20 and the surface roughness Ra1 of the first region 10 can be 1.5 μm or less, or 0.5 μm or less.

[0037] At least a portion of the first region 10 is bonded to a conductor portion, for example, via solder. The first region 10 has a surface roughness Ra1 smaller than surface roughness Ra2, thus enabling a sufficiently firm bond with the conductor portion using solder. At least a portion of the second region 20 is bonded to, for example, resin. The second region 20 has a surface roughness Ra2 larger than surface roughness Ra1, thus enabling improved adhesion to the resin using an anchoring effect.

[0038] From the viewpoint of easy manufacturing and good bonding with the conductor, the surface roughness Ra1 of the first region 10 can be, for example, 0.05–1.0 μm, 0.1–0.8 μm, or 0.15–0.4 μm. From the viewpoint of maintaining the strength of the ceramic substrate 100 and improving the adhesion to the resin, the surface roughness Ra2 of the second region 20 can be, for example, 0.2–3.0 μm, 0.3–2.0 μm, or 0.45–1.0 μm. The surface roughness Ra1 and surface roughness Ra2 in this disclosure are centerline average roughness, measured according to JIS B 0601-2001.

[0039] The surface roughness at various locations within region 10 may be somewhat uneven, but this unevenness is less than 0.1 μm. That is, a region 10 can be considered as having a difference between its maximum and minimum values ​​of less than 0.1 μm. Similarly, the surface roughness at various locations within region 20 may also be somewhat uneven, but this unevenness is less than 0.1 μm. That is, a region 20 can be considered as having a difference between its maximum and minimum values ​​of less than 0.1 μm.

[0040] In the case of having multiple first regions 10 as in this embodiment, the surface roughness Ra1 of each first region 10 is within the range of the average surface roughness Ra1 of the three first regions 10 ± 0.05 μm. In the case of having multiple second regions 20, the surface roughness Ra2 of each second region 20 is also within the range of the average surface roughness Ra2 of the multiple second regions 20 ± 0.05 μm.

[0041] The main surface 100A of the ceramic substrate 100 is composed of a first region 10 and a second region 20. The area ratio of the first region 10 can be 30-90%, or 40-80%. The area ratio of the second region 20 in the main surface 100A can be 10-70%, or 20-60%. In this embodiment, the first region 10 and the second region 20 are adjacent to each other in the main surface 100A. In a variation, the main surface 100A may have one first region 10 and one second region 20. In another variation, the first region 10 and the second region 20 may be arranged alternately side by side. In addition, the main surface 100A of the ceramic substrate 100 may also have other regions with a surface roughness different from that of the first region 10 and the second region 20.

[0042] There are no particular limitations on the types of ceramic components that form the main component of the ceramic substrate 100. Examples include carbides, oxides, and nitrides. Specifically, examples include silicon carbide, alumina, silicon nitride, aluminum nitride, and boron nitride. In addition to ceramics, the ceramic substrate 100 may also contain metal oxides that differ from the ceramic components.

[0043] Examples of metal oxides include those having Y and Mg as constituent elements. The mass ratio of Y to Mg in the metal oxide, when converted to Y₂O₃ and MgO respectively, can be 0.3 to 3, or 0.5 to 2. With such a ceramic substrate, the surface roughness of the main surface 100A can be adjusted with a high degree of freedom using etching. Therefore, for example, in a composite substrate of a ceramic substrate 100 and a metal substrate, when the metal substrate is removed by etching to form a conductor portion, the surface roughness of the main surface 100A can be adjusted simultaneously. Thus, the first region 10 and the second region 20 can be smoothly formed on the main surface 100A. It should be noted that when comparing under the same etching conditions, there is a tendency that the surface roughness increases as the mass ratio of Y to Mg approaches 1. On the other hand, there is a tendency that the surface roughness decreases as the mass ratio of Y to Mg deviates from 1. This is believed to be because the metal oxide or components derived from the metal oxide are removed from the main surface 100A of the ceramic substrate 100 by etching.

[0044] The proportions of metal oxide relative to silicon nitride in region 10 and region 20 can be different. For example, the proportion in region 10 can be higher than that in region 20. For such a ceramic substrate 100, the surface roughness Ra2 of region 20 can be set to be sufficiently larger than the surface roughness Ra1 of region 10.

[0045] Figure 2This is a cross-sectional view of a circuit board 200 according to one embodiment. The circuit board 200 includes: a ceramic substrate 100; a conductor portion 11 disposed on a main surface 100A; and a conductor portion 12 disposed on a main surface 100B. The conductor portion 11 is bonded to a first region 10 of the main surface 100A. The conductor portion 11 can be bonded to the main surface 100A by means of solder (not shown). On the other hand, a second region 20 of the main surface 100A is exposed without being covered by the conductor portion 11. Therefore, when the circuit board 200 is sealed with resin, the resin can bond to the second region 20. It should be noted that a portion of the first region 10 may be exposed without being covered by the conductor portion 11.

[0046] For example, in the first region 10 as a whole, the area ratio of the region covered by the conductor portion 11 can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. A portion of the second region 20 can be covered by the conductor portion 11. For example, in the second region 20 as a whole, the area ratio of the region exposed and not covered by the conductor portion 11 can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0047] A conductor portion 12, with a different shape than the conductor portion 11, is bonded to the main surface 100B of the ceramic substrate 100. Similar to the conductor portion 11, the conductor portion 12 is bonded to the first region 10 in the main surface 100B. The conductor portion 12 may also be bonded to the main surface 100B via solder (not shown). On the other hand, the second region 20 in the main surface 100B is exposed and not covered by the conductor portion 12.

[0048] In a modified example, the circuit board 200 may have a resin bonded to the second region 20. Furthermore, the conductor portions in main surfaces 100A and 100B may have the same shape, and one of main surfaces 100A and 100B may not have a conductor portion.

[0049] The first region 10 of the ceramic substrate 100 of the circuit board 200 has a surface roughness Ra1 smaller than that of Ra2, thus enabling it to be firmly bonded to the conductor portions 11 and 12 using solder. Furthermore, the second region 20 exhibits good adhesion to the resin due to the anchoring effect. Therefore, the circuit board 200 provides excellent reliability as a component.

[0050] Figure 3 This is a schematic cross-sectional view of a power module 300 according to one embodiment. The power module 300 includes a substrate 70 and a circuit board 200 bonded to one side of the substrate 70 by solder 32. The conductor portion 12 of the circuit board 200 is bonded to the solder 32.

[0051] On the conductor portion 11 of the circuit board 200, a semiconductor element 60 is mounted via solder 31. The semiconductor element 60 is connected to a predetermined portion of the conductor portion 11 via metal leads 34, such as aluminum leads (aluminum wires). In order to make the outside of the housing 36 electrically connected to the conductor portion 11, a predetermined portion of the conductor portion 11 is connected to an electrode 33 provided through the housing 36 via solder 35.

[0052] A housing 36 is disposed on one side of the substrate 70 to accommodate the circuit board 200. The accommodating space formed by the one side of the substrate 70 and the housing 36 is filled with a resin 30, such as silicone. The resin 30 is bonded to a second region 20 in the main surfaces 100A and 100B of the ceramic substrate 100. Because the second region 20 has a large surface roughness Ra1, the adhesion to the resin 30 is excellent. Therefore, the power module 300 exhibits excellent reliability.

[0053] On the other side of the base plate 70, a cooling fin 72, serving as a heat dissipation component, is bonded by grease 74. Screws 73 are installed at the end of the base plate 70 to secure the cooling fin 72 to it. The base plate 70 and the cooling fin 72 may be made of aluminum. Due to their high thermal conductivity, the base plate 70 and the cooling fin 72 function well as heat dissipation components.

[0054] Conductor portion 11 and conductor portion 12 are electrically insulated from each other via the ceramic substrate 100. Conductor portion 11 may or may not form a circuit. Conductor portion 11 and conductor portion 12 may be made of the same or different materials. Conductor portion 11 and conductor portion 12 may be made of copper. However, their material is not limited to copper.

[0055] The power module 300 includes: conductor portions 11 and 12 of a circuit board 200; and a semiconductor element 60 electrically connected to the conductor portion 11. The semiconductor element 60 and the circuit board 200 are sealed together by a resin 30. In this power module 300, even if the semiconductor element 60 heats up, the adhesion between the resin 30 and the ceramic substrate 100 can be maintained.

[0056] The resin bonded to the second region 20 of the ceramic substrate 100 is not limited to a sealing resin. For example, if the ceramic substrate is used as a ceramic heat sink material for a press-fit structure, the resin bonded to the second region 20 can be a thermosetting resin or a light-curing resin.

[0057] Next, an example of a method for manufacturing a ceramic substrate will be described. First, ceramic powder composed of ceramic components and an oxide-based sintering aid functioning as a sintering promoter are prepared. Examples of oxide-based sintering promoters include substances containing Y₂O₃, MgO, SiO₂, and Al₂O₃. From the viewpoint of obtaining a ceramic substrate (sintered body) capable of simultaneously achieving high thermal conductivity and excellent insulation at a high level, the content of the oxide-based sintering promoter in the raw material powder can, for example, be 4.0–8.0% by mass, or 4.0–5.0% by mass.

[0058] The raw material powder is pressurized at a molding pressure of, for example, 3.0 to 10.0 MPa to obtain a molded body. The molded body can be manufactured by uniaxial pressing or by CIP (Computer-In-Place) fabrication. Alternatively, it can be molded and fired simultaneously using a hot press. Firing of the molded body can be carried out in an inert gas atmosphere such as nitrogen or argon. The firing pressure can be 0.7 to 0.9 MPa. When the ceramic composition is silicon nitride, the firing temperature can be, for example, 1600 to 2100°C or 1800 to 2000°C. The firing time at this firing temperature can be 6 to 20 hours or 8 to 16 hours.

[0059] A ceramic substrate is obtained by processing the sintered body obtained in this manner as needed. At this point, both main surfaces have a surface roughness Ra1. After masking a portion of the main surfaces of the ceramic substrate obtained in this manner with tape or the like, a physical polishing process based on sandblasting or a chemical treatment based on etching is performed. As a result, a portion of the main surfaces of the ceramic substrate becomes a second region with a surface roughness Ra2, and the remaining portion becomes a first region with a surface roughness Ra1. Conductive tape or the like can be adhered to the first region on the main surfaces of the ceramic substrate obtained in this manner to form a conductor portion. Since the surface roughness Ra1 of the first region is less than the surface roughness Ra2, the conductive tape bonds to the first region of the conductor portion with high adhesive strength.

[0060] The method for forming the second region is not limited to the methods described above. It can be performed using, for example, honing, or by roughening the main surface using a laser. Alternatively, it can be formed using etching. Etching can be repeated more than twice.

[0061] An example of a method for manufacturing a circuit board is described. A ceramic substrate with a surface roughness Ra1 is prepared. A metal substrate is laminated onto the main surface of the ceramic substrate using solder, and the substrate is heated in a furnace to obtain a composite substrate. The solder is applied to the main surface of the ceramic substrate using methods such as roll coating, screen printing, or transfer printing. The solder may contain metals and metal compounds such as Ag, Cu, Sn, and Ti, organic solvents, and binders. The viscosity of the solder may be, for example, 5–20 Pa·s. The content of organic solvent in the solder may be, for example, 5–25% by mass, and the content of binder may be, for example, 2–15% by mass.

[0062] The heating temperature in the furnace can be, for example, 700–900°C. The atmosphere inside the furnace can be an inert gas such as nitrogen, or it can be carried out under reduced pressure (below atmospheric pressure) or under vacuum. The furnace can be a continuous furnace for continuously manufacturing multiple joints, or a continuous furnace for intermittently manufacturing one or more joints. Heating can be performed while pressing the joint between the ceramic substrate and the metal substrate along the lamination direction.

[0063] Next, a portion of the metal substrate in the composite substrate is removed by etching to form a conductor portion. After the portion of the metal substrate is removed, a portion of the main surface of the ceramic substrate exposed by the removal of this portion is also etched. As a result, this portion of the main surface is also roughened, forming a first region with a surface roughness Ra1 and a second region with a surface roughness Ra2 that is larger than the surface roughness Ra1.

[0064] Thus, according to the manufacturing method of this example, a circuit board is obtained from a composite substrate, and a ceramic substrate having multiple regions with different surface roughness can be obtained. Therefore, it is possible to manufacture ceramic substrates and circuit boards with excellent reliability as components without increasing the number of processes.

[0065] Using the circuit board obtained in this manner, a power module can be manufactured. The power module can be manufactured by mounting semiconductor components on the circuit board using solder and wire bonding, housing the circuit board and semiconductor components within the housing space of a casing, and then sealing them with resin.

[0066] Several embodiments have been described above, but this disclosure is not limited to any of the embodiments described above. For example, the circuit board may include semiconductor elements electrically connected to the conductor portion. Furthermore, it is not necessary to have a first region and a second region on both main surfaces; having a first region and a second region on either main surface is sufficient.

[0067] Example

[0068] The contents of this disclosure will be described in more detail with reference to the embodiments and reference examples, but this disclosure is not limited to the specific examples below.

[0069] (Example 1)

[0070] <Preparation of silicon nitride sintered bodies>

[0071] Silicon nitride powder, magnesium oxide powder, and yttrium oxide powder were prepared as sintering aids. These were mixed in a mass ratio of Si3N4:Y2O3:MgO = 94.0:3.0:3.0 to obtain a raw material powder. The raw material powder was then subjected to uniaxial pressure molding to produce a sintered body. This sintered body was placed in an electric furnace equipped with a carbon heater and sintered at 1800°C for 12 hours under a nitrogen atmosphere to obtain a flat silicon nitride sintered body.

[0072] <Etching>

[0073] After partially masking the silicon nitride sintered body with adhesive tape, it was immersed in a commercially available etching solution (aqueous copper chloride solution) for 60 minutes. After removing the silicon nitride sintered body from the etching solution, it was immersed again in the same etching solution for 60 minutes. This etching process was repeated twice to obtain a ceramic substrate. The adhesive tape was removed, and the appearance of the obtained ceramic substrate was observed using an optical microscope.

[0074] <Appearance Evaluation>

[0075] Figure 4 This is an optical microscope image of a ceramic substrate. (Example:) Figure 4 As shown, a first region 10 and a second region 20 with different shades are formed on the main surface of the ceramic substrate. The surface roughness of each region was measured using a small surface roughness measuring machine (manufactured by Mitutoyo Co., Ltd., trade name: SURFTEST SJ-310). The results showed that the surface roughness Ra1 of the first region 10 was 0.25 μm, and the surface roughness Ra2 of the second region 20 was 0.50 μm.

[0076] <Cross-section evaluation>

[0077] The ceramic substrate was cut along its thickness direction, and the cross-section near the main surface was observed using a scanning electron microscope (SEM). Figure 5 This is an SEM image showing a cross-section near the main surface in the second region of the ceramic substrate of Example 1. Figure 5 As shown, it was confirmed that the surface was roughened in the second region.

[0078] (Example 2)

[0079] <Preparation of silicon nitride sintered bodies>

[0080] Prepare silicon nitride powder, and magnesium oxide powder, yttrium oxide powder, and silicon dioxide powder as sintering aids. Mix them in a ratio of Si3N4:Y2O3:MgO:SiO2 = 91.35:6.0:1.58:

[0081] The raw material powder was prepared by mixing in a ratio of 1.07 (mass ratio). A planar silicon nitride sintered body was obtained using the same steps as in Example 1, except that the raw material powder was used. Then, etching was performed using the same steps as in Example 1 to obtain a ceramic substrate. The adhesive tape was removed, and the appearance of the obtained ceramic substrate was observed using an optical microscope.

[0082] <Appearance Evaluation>

[0083] Figure 6 This is an optical microscope image of a ceramic substrate. (Example:) Figure 6 As shown, a first region 10 and a second region 20 with different shades are formed on the main surface of the ceramic substrate. However, the difference in shades is smaller compared to Example 1. Figure 6 In the diagram, a virtual line VL1 is drawn at the boundary between region 10 and region 20. The surface roughness Ra1 of region 10 is 0.30 μm, and the surface roughness Ra2 of region 20 is 0.31 μm.

[0084] <Cross-section evaluation>

[0085] Similar to Example 1, a scanning electron microscope (SEM) was used to observe the cross section near the main surface. Figure 7 This is an SEM image showing a cross-section near the main surface in the second region of the ceramic substrate of Example 2. Figure 7 As shown, it was confirmed that the surface was roughened in region 2. However, it was not roughened to the point of being... Figure 5 The degree indicated.

[0086] The flexural strength of the ceramic substrates of Examples 1 and 2 was measured. The flexural strength was measured as a three-point bending strength test, according to JIS R 1601:2008, using a commercially available flexural strength tester (Shimadzu Corporation, device name: AG-2000). The results showed that the flexural strength of the ceramic substrate of Example 1 was 802 MPa. Furthermore, the flexural strength of the ceramic substrate of Example 2 was 769 MPa.

[0087] (Refer to Example 1)

[0088] As a sintering aid, metal oxide powders with a Y to Mg mass ratio of 0.1 (converted to Y₂O₃ and MgO, respectively) were prepared. These powders were then combined with silicon nitride powder to obtain a raw material powder. A planar silicon nitride sintered body was obtained using the same steps as in Example 1, except that the raw material powder was used. Although etching was performed in the same manner as in Example 1, the roughening of the main surface was insufficient, and the surface roughness of the main surface could not be adjusted. However, if a method other than etching (e.g., sandblasting) was used, a portion of the main surface could be roughened, forming the same first and second regions as in Examples 1 and 2.

[0089] (See Example 2 for reference)

[0090] As a sintering aid, a metal oxide powder with a Y to Mg mass ratio of 5.0 (converted to Y₂O₃ and MgO, respectively) was prepared. This powder was then combined with silicon nitride powder to obtain a raw material powder. A planar silicon nitride sintered body was obtained using the same steps as in Example 1, except that the raw material powder was used. Although etching was performed as in Example 1, the roughening of the main surface was insufficient, and the surface roughness of the main surface could not be adjusted. However, if a method other than etching (e.g., sandblasting) was used as in Example 1, a portion of the main surface could be roughened, forming the same first and second regions as in Examples 1 and 2.

[0091] Industrial availability

[0092] According to this disclosure, a ceramic substrate with excellent reliability as a component can be provided. Furthermore, a circuit board with excellent reliability as a component and a method for manufacturing the same can be provided. Additionally, by having such a circuit board, a power module with excellent reliability can be provided.

[0093] Explanation of reference numerals in the attached figures

[0094] 10… Region 1, 11, 12… Conductor section, 20… Region 2, 30… Resin, 31, 32, 35… Solder, 33… Electrode, 34… Metal lead, 36… Housing, 60… Semiconductor element, 70… Substrate, 72… Cooling plate, 73… Screw, 74… Grease, 100… Ceramic substrate, 100A, 100B… Main surface, 200… Circuit board, 300… Power module.

Claims

1. A ceramic substrate containing a ceramic component, and a metal oxide different from the ceramic component and having Y and Mg as constituent elements, at least one main surface has a first region and a second region having surface roughness different from each other, the proportions of the metal oxide in the first region and the second region with respect to the ceramic component are different from each other.

2. The ceramic substrate of claim 1, wherein, The ratio of the surface roughness Ra2 of the second region to the surface roughness Ra1 of the first region is 1.5 or more.

3. The ceramic substrate of claim 1 or 2, wherein, The second region has a surface roughness Ra2 larger than that of the first region, At least a part of the second region is bonded with a resin.

4. The ceramic substrate of claim 1 or 2, wherein, The first region has a surface roughness Ra1 smaller than that of the second region, A conductor portion is joined to at least a part of the first region.

5. The ceramic substrate according to claim 1 or 2, containing silicon nitride, and a metal oxide having Y and Mg as constituent elements, The mass ratio of Y to Mg in the metal oxide is 0.3 to 3 when converted to Y2O3 and MgO, respectively.

6. The ceramic substrate of claim 1 or 2, wherein, The area ratio of the first region in the main surface is 30 to 90%, and the area ratio of the second region in the main surface is 10 to 70%.

7. A circuit substrate provided with: the ceramic substrate according to any one of claims 1 to 6; and a conductor portion joined to at least a part of the first region, The first region has a surface roughness Ra1 smaller than that of the second region.

8. The circuit substrate according to claim 7, wherein At least a part of the second region is bonded with a resin, The second region has a surface roughness Ra2 larger than that of the first region.

9. A power module provided with: the circuit substrate according to claim 7 or 8; and a resin sealing the circuit substrate, wherein At least a part of the second region is bonded with the resin.

10. The power module according to claim 9, provided with the conductor portion of the circuit substrate, and a semiconductor element electrically connected to the conductor portion, The semiconductor element is sealed with the resin together with the circuit substrate.

11. A method of manufacturing a circuit substrate, comprising the following steps: a step of joining a metal substrate to a main surface of a ceramic substrate to obtain a composite substrate, the ceramic substrate containing a ceramic component, and a metal oxide different from the ceramic component and having Y and Mg as constituent elements, the ceramic substrate having a surface roughness Ra1; and a step of forming a conductor portion by removing a part of the metal substrate in the composite substrate using etching, by the etching, a first region having the surface roughness Ra1 and a second region having a surface roughness Ra2 larger than the surface roughness Ra1 are formed on the main surface of the ceramic substrate, the proportions of the metal oxide in the first region and the second region with respect to the ceramic component are different from each other.

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