JP2023050453A - Ceramic substrate, ceramic circuit board, and method of manufacturing ceramic substrate - Google Patents

Abstract

To provide a ceramic substrate capable of improving the removal rate of an unnecessary brazing material while ensuring the bonding strength with a metal circuit or a metal heat sink.SOLUTION: A ceramic substrate 1 has a main surface 1a and a main surface 1b, and the surface roughness Ra1 of the main surface 1a is 0.50 μm or less, the surface roughness Ra2 of the main surface 1b is 0.50 μm or more, and the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a ceramic substrate, a ceramic circuit substrate, and a method of manufacturing a ceramic substrate, and more particularly, to a ceramic substrate having different surface roughness Ra between one principal surface and the other principal surface, a ceramic circuit substrate using the ceramic substrate, and The present invention relates to a method of manufacturing a ceramic substrate in which one principal surface and the other principal surface have different surface roughnesses Ra.

2. Description of the Related Art Conventionally, ceramic circuit substrates, in which ceramic substrates, metal circuits, and metal heat sinks are bonded together, have been used in semiconductor modules, power modules, and the like.

The ceramic circuit substrates used in power modules and other devices are formed by bonding metal circuits and metal heat sinks to ceramic substrates with high insulation, high mechanical strength, and high thermal conductivity. A semiconductor chip or the like is joined. Since the semiconductor chip generates heat during its operation, the ceramic substrate, the metal circuit and the metal heat sink are required to have good thermal conductivity so that the heat can be dissipated. At the same time, the ceramic substrate is also required to have high insulation (electrical resistivity).

In recent years, ceramic substrates having silicon nitride (Si ₃ N ₄ ) as a main component have attracted attention as ceramic substrates having such characteristics, and various studies have been conducted (see, for example, Patent Document 1).

JP 2007-197226 A

In order to form a ceramic circuit board using such a ceramic substrate, for example, a brazing material is applied to the surface of the ceramic substrate, and a metal circuit or a metal heat sink is joined to the ceramic substrate via the brazing material.

When bonding via brazing filler metal, it is generally possible to increase the bonding strength between the ceramic substrate and the metal circuit or metal heat sink by sufficiently roughening the surface of the ceramic substrate to which the brazing filler metal is applied. It is done.

By the way, in forming a metal circuit bonded to a ceramic substrate, first, a metal plate is bonded to the surface of the ceramic substrate via a brazing material, and the metal plate is etched to form a circuit pattern. Therefore, the brazing material in the portion removed by etching or the like is exposed on the surface and is unnecessary for the ceramic circuit board, so a removal process is performed.

At this time, the surfaces of the ceramic substrates are roughened in order to secure the bonding strength, and the brazing filler metal cannot be sufficiently removed in some cases. That is, the roughened substrate surface has relatively large unevenness, and the brazing filler metal enters into the unevenness, making it difficult to remove the brazing filler metal that has entered the unevenness.

Accordingly, an object of the present invention is to provide a ceramic substrate and a ceramic circuit substrate using the ceramic substrate that can facilitate the removal of unnecessary brazing material while ensuring the bonding strength of the metal circuit and the metal heat sink. It was made as

A ceramic substrate in one embodiment is a ceramic substrate having a first principal surface and a second principal surface, wherein the first principal surface has a surface roughness Ra1 of 0.50 μm or less, and the second principal surface has a surface roughness Ra1 of 0.50 μm or less. has a surface roughness Ra2 of 0.50 μm or more, and the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more.

A ceramic circuit board in one embodiment comprises a ceramic substrate having a first principal surface and a second principal surface, a metal circuit bonded to the first principal surface of the ceramic substrate, and the and a metal heat sink bonded to a second main surface, wherein the surface roughness Ra1 of the first main surface is 0.50 μm or less, and the surface of the second main surface The roughness Ra2 is 0.50 μm or more, and the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more.

A method for manufacturing a ceramic substrate according to one embodiment includes the steps of (a) preparing a slurry containing silicon powder, (b) obtaining a sheet-like compact from the slurry, and (c) firing the sheet-like compact. wherein the step (c) includes a nitriding step, the ceramic substrate has a first principal surface and a second principal surface, and the second principal surface; The first principal surface has a surface roughness Ra1 of 0.50 μm or less, and the second principal surface has a surface roughness Ra2 of 0.50 μm or more, and the surface roughness Ra2 is greater than the surface roughness Ra1. 0.10 μm or more.

According to the ceramic substrate of one embodiment, it is possible to facilitate the removal of unnecessary brazing material while securing the bonding strength with the metal circuit and the metal heat sink. A ceramic circuit board using this ceramic substrate can facilitate the removal of unnecessary brazing material while ensuring the bonding strength of the metal circuit and the metal heat sink, thereby forming a highly reliable semiconductor device. can.

BRIEF DESCRIPTION OF THE DRAWINGS It is the figure which showed schematic structure of the ceramic substrate in embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is the figure which showed schematic structure of the ceramics circuit board in embodiment. It is a figure for demonstrating the manufacturing process of the ceramics circuit board in embodiment. FIG. 4 is a diagram for explaining the manufacturing process of the ceramic circuit board following FIG. 3 ; FIG. 5 is a diagram for explaining the manufacturing process of the ceramic circuit board following FIG. 4; FIG. 6 is a diagram for explaining the manufacturing process of the ceramic circuit board following FIG. 5; 3 is a diagram of a semiconductor chip and a heat sink connected to the ceramic circuit board shown in FIG. 2; FIG. FIG. 2 is a diagram showing a schematic configuration of a laminate of ceramic substrates during sintering used in Examples.

In principle, the same members are denoted by the same reference numerals throughout the drawings for describing the embodiments, and repeated description thereof will be omitted. In order to make the drawing easier to understand, even a plan view or a side view may be hatched.

<Ceramic substrate>
The ceramic substrate in the present embodiment is a ceramic substrate having two main surfaces. For example, as shown in FIG. A ceramic substrate 1 having 1b can be mentioned. The terms front surface and back surface are used for convenience in order to distinguish each surface.

In the present embodiment, the main surface 1a and the main surface 1b indicate surfaces on which a metal circuit and a metal heat sink are formed, respectively, and the ceramic substrate 1 is a substrate used for forming a ceramic circuit substrate. is. This case will be described below as an example.

In this embodiment, the surface roughness Ra1 of the principal surface 1a is 0.5 μm or less, and the surface roughness Ra2 of the principal surface 1b is 0.5 μm or more. The surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more. That is, the difference between the surface roughness Ra1 and the surface roughness Ra2 is 0.10 μm or more.

By setting the surface roughness Ra1 to 0.5 μm or less, unnecessary brazing material can be easily removed from the surface of the ceramic substrate exposed by the etching process for forming the metal circuit. Moreover, the surface roughness Ra1 is preferably 0.2 μm or more, more preferably 0.35 μm or more. By setting it as such a range, the joint strength of a ceramic substrate and a metal circuit can be ensured. That is, the surface roughness Ra1 is set to 0.2 μm or more and 0.5 μm or less so that the bonding strength between the ceramic substrate and the metal circuit is not impaired, and the brazing material is less likely to remain in the irregularities. is adjusted to be relatively small.

Further, by setting the surface roughness Ra2 to 0.5 μm or more, the bonding strength between the ceramic substrate and the metal heat sink can be improved. In addition, by improving the bonding strength between the ceramic substrate and the metal heat sink, it becomes possible to increase the thickness of the metal heat sink. By increasing the thickness of the metal heat sink, for example, the heat generated by the operation of the semiconductor chip mounted on the metal circuit can be efficiently released to the outside through the metal heat sink. Moreover, the surface roughness Ra2 is preferably 1.0 μm or less, more preferably 0.7 μm or less. With such a range, it is possible to make it difficult for the brazing material to remain in the ceramics portion exposed by etching. That is, by setting the surface roughness Ra2 to 0.5 μm or more and 1.0 μm or less, the bonding strength between the ceramic substrate and the metal heat dissipation plate is improved, the heat dissipation efficiency of the metal heat dissipation plate is improved, and excess solder is removed. It is adjusted as a range that makes it easier to remove the material.

Furthermore, the surface roughness Ra2 is set to be greater than the surface roughness Ra1 by 0.10 μm or more. As a result, it is possible to secure both the functions and effects of the main surfaces described above in a favorable state. The difference between the surface roughness Ra1 and the surface roughness Ra2 is preferably 0.80 μm or less, more preferably 0.65 μm or less, still more preferably 0.50 μm or less, and particularly preferably 0.35 μm or less.

In addition, in this specification, the surface roughness Ra is the arithmetic mean roughness calculated according to JIS B 0601:2001.

<Method for producing ceramic substrate>
The ceramic substrate of this embodiment can be used, for example, as an insulating substrate used in power modules. A power module is, for example, an electric vehicle, a hybrid electric vehicle, a railway vehicle, or an electronic device that constitutes an inverter circuit that controls a motor provided in industrial equipment.

As the ceramic substrate, as described above, a ceramic substrate for providing a metal circuit and a metal heat sink on each main surface is preferable. and a silicon nitride substrate is preferred.

Next, a method for manufacturing a ceramic substrate according to this embodiment will be described. The ceramic substrate can be manufactured according to a known manufacturing method, and can be obtained by processing the surface roughness Ra of each main surface so as to have a desired relationship. An example of manufacturing a silicon nitride substrate will be described below.

(1-1) Preparation of slurry (slurry preparation step)
First, a raw material powder is prepared by adding a rare earth element oxide and a magnesium compound as sintering aids to silicon powder, which is a raw material for the substrate, and pulverized by a method such as media dispersion to prepare a slurry. The raw materials to be used are described in detail below.

(a) Silicon As the silicon used here, industrially available grade silicon powder can be used. The silicon before pulverization has a median diameter D50 of 6 μm or more, a BET specific surface area of 3 m ² /g or less, an oxygen content of 1.0% by mass or less, and an impurity C content in silicon of 0.15% by mass or less. More preferably, the powder has a median diameter D50 of 7 μm or more, a BET specific surface area of 2.5 m ² /g or less, an oxygen content of 0.5% by mass or less, and an impurity C content in silicon of 0.10% by mass or less. . The purity of the silicon powder is preferably 99% or higher, more preferably 99.5% or higher.

Impurity oxygen contained in silicon is one of the factors that hinder the heat conduction of the silicon nitride substrate obtained by reaction sintering, and is preferably as small as possible. Furthermore, in the present embodiment, as will be described later, it is preferable to adjust the total amount of impurity oxygen contained in the silicon powder and oxygen from the magnesium compound by limiting the amount of oxygen from the magnesium compound. At this time, in the raw material powder, the total amount of oxygen is preferably in the range of 0.1 to 1.1% by mass with respect to silicon converted to silicon nitride.

In addition, impurity carbon contained in silicon may inhibit the growth of silicon nitride grains in the silicon nitride substrate obtained by reaction sintering. As a result, the densification is insufficient, which is one of the factors that reduce heat conduction and insulation.

In the specification of the present application, the BET specific surface area (m ² /g) is measured by the BET one-point method (JIS R 1626: 1996 "Method for measuring the specific surface area of fine ceramic powder by the gas adsorption BET method") using a BET specific surface area meter. The median diameter D50 (μm) is the particle diameter when the cumulative frequency is 50% in the particle size distribution determined by the laser diffraction/scattering method.

Although not essential in the manufacturing method of the present embodiment, the raw material powder may contain silicon nitride powder. However, since silicon nitride is more expensive than silicon, the amount of silicon nitride used should be as small as possible. In addition, when silicon nitride is used as the raw material powder, the contribution of the nitriding step, which will be described later, is small, and thus the difference in surface roughness between the main surfaces obtained in the present embodiment may be difficult to obtain. Therefore, the amount of silicon nitride used is preferably 20 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less of silicon (in terms of silicon nitride).

(b) Rare Earth Element Oxides As the rare earth element oxides used here, oxides of Y, Yb, Gd, Er, Lu, etc., which are readily available and stable as oxides, are preferable. Specific examples of rare earth element oxides include Y ₂ O ₃ , Yb ₂ O ₃ , Gd ₂ O ₃ , Er ₂ O ₃ and Lu ₂ O ₃ . The content of the rare earth element oxide is 0.5 mol % or more and less than 3 mol % with respect to the total of silicon (converted to silicon nitride), rare earth element oxide (converted to trivalent oxide) and magnesium compound (converted to MgO). is.

If the content of the rare earth element oxide is less than 0.5 mol %, the effect as a sintering aid will be insufficient and the density will not be sufficiently increased, which is not preferable. On the other hand, when the content of the rare earth element oxide is 3 mol% or more, the grain boundary phase with low thermal conductivity increases, thereby lowering the thermal conductivity of the sintered body and increasing the amount of the expensive rare earth element oxide used. Therefore, it is not desirable. The content of the rare earth element oxide is preferably 0.6 mol % or more and less than 3 mol %, more preferably 1 mol % or more and 2 mol % or less.

In this specification, the number of moles of silicon nitride (Si ₃ N ₄ ) obtained when all silicon is nitrided and the rare earth element oxide to the trivalent oxide RE ₂ O ₃ (RE is a rare earth element) The sum of the number of moles when converted and the number of moles when the magnesium compound is converted to MgO is simply "silicon (converted to silicon nitride), rare earth element oxide (converted to trivalent oxide) and magnesium compound ( MgO conversion) is sometimes called "total".

(c) Magnesium compound As the magnesium compound, one or more magnesium compounds containing silicon (Si), nitrogen (N) or oxygen (O) can be used. In particular, it is preferable to use magnesium oxide (MgO), magnesium silicon nitride (MgSiN ₂ ), magnesium silicide (Mg ₂ Si), magnesium nitride (Mg ₃ N ₂ ), and the like.

Here, it is preferable to select more than 87% by weight of MgSiN ₂ relative to the sum of the magnesium compounds. By using 87% by mass or more of MgSiN ₂ , the oxygen concentration in the resulting silicon nitride substrate can be reduced. If the content of MgSiN ₂ in the magnesium compound is less than 87% by mass, the amount of oxygen in the silicon nitride particles after sintering increases, which may result in a low thermal conductivity of the sintered body. _MgSiN2 in the magnesium compound is preferably 90% by weight or more.

The magnesium compound content (in terms of MgO) in the silicon nitride substrate is 8 mol with respect to the total of silicon (in terms of silicon nitride), rare earth element oxides (in terms of trivalent oxides) and magnesium compounds (in terms of MgO). % or more and less than 15 mol %. If the content of the magnesium compound is less than 8 mol %, the effect as a sintering aid will be insufficient and the density will not be sufficiently increased, which is not preferable. If the content of the magnesium compound is 15 mol % or more, the grain boundary phase with low thermal conductivity increases, which lowers the thermal conductivity of the sintered body, which is not preferable. The content of the magnesium compound is preferably 8 mol % or more and less than 14 mol %, more preferably 9 mol % or more and less than 13 mol %.

(d) Grinding To the silicon powder, a rare earth element oxide and a magnesium compound are added as sintering aids in a predetermined ratio, a dispersion medium (organic solvent) and, if necessary, a dispersant are added, and ball milling is performed. to prepare slurry (dispersion of raw material powder). It is preferable that the media have a diameter of 5 mm or more, the concentration of the raw material powder in the slurry (also referred to as slurry concentration) is 40% by mass or more, and the pulverization is preferably carried out for 6 hours or more. The media should preferably be made of a material that does not contain Al or Fe as main components, which are factors that lower the thermal conductivity of silicon nitride, and particularly preferably made of silicon nitride. The types of dispersion medium and dispersant are not particularly limited, and can be arbitrarily selected according to the sheet forming method and the like.

As the dispersion medium, ethanol, n-butanol, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), etc. can be used. As the dispersant, for example, sorbitan ester type dispersant, polyoxyalkylene type dispersant agents, etc. can be used. The amount of the dispersion medium used is preferably, for example, 40 to 70% by mass with respect to the total amount of the powder, and the amount of the dispersant is preferably, for example, 0.3 to 2% by mass with respect to the total amount of the powder. After dispersion, if necessary, the dispersion medium may be removed or replaced with another dispersion medium.

The time for pulverization is not particularly limited because it varies depending on the milling apparatus to be used, the amount and characteristics of the starting materials, etc., but it is preferable to select the time so that the raw material powder can be sufficiently pulverized and mixed. The pulverization time is, for example, preferably 6 hours or more and 48 hours or less, more preferably 12 hours or more and 24 hours or less. If the pulverization time is too short, sufficient pulverization may not be achieved and a silicon nitride substrate having the characteristics required in the present embodiment may not be obtained. If the pulverization time is too long, the amount of impurity oxygen gradually increases, and the thermal conductivity of the silicon nitride substrate may decrease.

The silicon particles after pulverization preferably have an oxygen content of 1.0% by mass or less, more preferably 0.7% by mass or less. The thermal conductivity of silicon nitride can be improved by using silicon particles with as little oxygen as possible. Since it is difficult to measure the oxygen content of only the silicon particles after mixing with the sintering aid, a slurry of only silicon particles without the sintering aid was prepared under the same grinding conditions as a sample. can be used to measure the oxygen content of silicon particles. For example, silicon particles are extracted from the slurry, and the oxygen content of the silicon particles can be measured using an inert gas fusion-nondispersive infrared absorption method oxygen analyzer.

The BET specific surface area (m ² /g), median diameter D50 (μm), and oxygen content of the silicon particles in the slurry obtained by pulverization were measured in the same manner as pulverized silicon except that the rare earth element oxide and magnesium compound were not added. It is obtained as a value measured using particles. Since the rare earth element oxide powder and the magnesium compound powder are added in very small amounts to the silicon powder, they hardly affect the pulverization efficiency. are considered to be substantially the same.

(1-2) Preparation of sheet-like molded body (sheet molding step)
A dispersion medium, an organic binder, a dispersant, etc. are added to the obtained slurry as necessary, vacuum defoaming is performed as necessary, the viscosity is adjusted within a predetermined range, and the slurry for coating is prepared. make. The slurry viscosity is preferably adjusted within the range of 1 Pa·s or more and less than 15 Pa·s. The viscosity of the slurry is a value measured using a rotational viscometer at a temperature of 25° C. and a rotation speed of 10 rpm. In some cases, removal or replacement of the dispersion medium may be performed as described above.

The prepared coating slurry is formed into a sheet by using a sheet forming machine, cut into a predetermined size, and dried to obtain a sheet-shaped formed body. The organic binder used to prepare the slurry for coating is not particularly limited, but examples thereof include PVB resin (polyvinyl butyral resin), ethyl cellulose resin, and acrylic resin. It is preferable to appropriately adjust the amount of the dispersion medium, organic binder, dispersant, etc. added according to the coating conditions.

The method for forming the coating slurry into a sheet is not particularly limited, but for example, a sheet forming method such as a doctor blade method can be used. In the method for manufacturing a silicon nitride substrate according to the present embodiment, in order to make the surface roughness Ra between the main surfaces of the substrate different, it is preferable to make the surface roughness Ra different in the step of forming the substrate into a sheet shape. .

When forming a sheet-like molded body by the doctor blade method, after forming the sheet, one main surface is in contact with the transport film, and the other main surface is dried in a free state. It is easy to adjust the surface roughness Ra of one main surface in contact (main surface 1a) to be small and the surface roughness Ra of the other main surface in the released state (main surface 1b) to be large. At this stage, the surface roughness Ra does not have to satisfy the required relationship of the surface roughness Ra of the ceramic substrate.

The conveying film used at this time preferably has a surface roughness Ra of 0.03 to 0.20 μm, more preferably 0.04 to 0.10 μm, on the contact surface with the sheet-like formed body. By using a conveying film having such a surface roughness Ra, a sheet-like formed article having a main surface with a surface roughness Ra smaller than that of the open state surface can be obtained.

The material of the transport film is not particularly limited as long as it is used for known transport films, and examples thereof include polyester such as polyethylene terephthalate (PET).

In this doctor blade method, the forming speed of the coating slurry is preferably 600 mm/min or less. Since the coating slurry used in the present embodiment has thixotropic properties, when the coating slurry passes through a doctor blade in the doctor blade method, shear stress is applied to the coating slurry. A decrease in viscosity occurs. Therefore, if the molding speed exceeds 600 mm/min, the coating slurry will flow easily, and bubbles that cause voids will easily be involved, which may hinder densification.

The sheet-like slurry formed on the transport film is then transported to a drying chamber set at a predetermined temperature and humidity to evaporate the solvent to form a dried sheet-like compact. At this time, the drying rate of the coating slurry is preferably 0.8% by mass/min or less. If the drying rate of the coating slurry exceeds 0.8% by mass/min, the dispersion medium will evaporate rapidly, and air bubbles may easily form in the sheet. After the coating, the sheet is passed through a drying zone so that it is gradually heated and dried. Therefore, it is preferable that the maximum drying rate does not exceed 0.8 mass %/min.

The thickness of the sheet-shaped molding formed in the molding process can be adjusted so that the finally obtained ceramic substrate has a desired thickness, for example, 0.15 mm or more and 0.8 mm or less. The sheet-shaped molding can be cut into a predetermined size with a punch or the like, if necessary.

(1-3) Sintering compact (sintering step)
By heating the obtained sheet-like compact, silicon contained in the compact is nitrided and then densified. This sintering step includes a degreasing step for removing the organic binder in the compact, a nitriding step for nitriding by reacting silicon (Si) and nitrogen (N) contained in the compact, and a densifying step for densifying after nitriding. Includes sintering process. These steps may be performed sequentially in separate furnaces or continuously in the same furnace.

In the present embodiment, in performing this sintering step, powdery boron nitride (BN) is applied to the main surface 1a of the sheet-shaped compact to form a boron nitride (BN powder) layer. When stacking a plurality of sheet-shaped compacts, this boron nitride (BN) also functions as a separating material that facilitates separation after sintering. , boron nitride (BN) is present between the sheet-like molded bodies, and each sintered body can be easily separated from the sintered body laminate obtained after sintering.

The sheet-like molded body coated with boron nitride powder (BN powder) in this way is placed in an electric furnace, degreased (removed organic binder, etc.), decarbonized at 900 to 1300 ° C. in a nitriding device, nitrogen In an atmosphere, the temperature is raised to a predetermined temperature for nitriding, and then sintered in a sintering device. At this time, it is preferable to heat the compact while applying a load of 10 to 1000 Pa. Degreasing is preferably performed at a temperature of 800° C. or less.

A BN powder layer having a thickness of about 3 to 20 μm is preferably used as the separation material. A BN powder layer can be formed by, for example, spraying, brush coating or screen printing a BN powder slurry on one surface of each sheet-like compact. The BN powder preferably has a purity of 95% or higher and an average particle size (D50) of 1-20 μm.

In the nitriding step, the nitrogen partial pressure during nitriding is preferably 0.05 to 0.7 MPa, more preferably 0.07 to 0.2 MPa. The nitriding temperature is preferably 1,350 to 1,500.degree. C., more preferably 1,400 to 1,450.degree. The holding time after heating to the nitriding temperature is preferably 3 to 12 hours, more preferably 5 to 10 hours.

If the nitriding temperature is less than 1350° C. or if the holding time is less than 3 hours, unreacted silicon powder remains in the sheet-like molded body, and a dense body can be obtained by the densifying sintering process performed after the nitriding process. Sometimes you can't. If the nitriding temperature is higher than 1500° C., the silicon powder may melt before nitriding and may remain without nitriding, or the sintering aid component may volatilize and sinter during the sintering process. In some cases, it becomes difficult to obtain a dense sintered body due to a shortage of the cohesive agent component. If the holding time is longer than 12 hours, the sintering aid component may volatilize and the sintering aid component may become insufficient in the sintering step, making it difficult to obtain a dense sintered body.

The nitrogen partial pressure during compaction sintering is preferably 0.1 to 0.9 MPa, more preferably 0.5 to 0.9 MPa. The sintering temperature is preferably 1800-1950°C, more preferably 1850-1900°C. The holding time (sintering time) after heating to the sintering temperature is preferably 3 to 12 hours, more preferably 5 to 12 hours. If the sintering temperature is less than 1800° C. or if the holding time is less than 3 hours, the growth and rearrangement of the silicon nitride particles may be insufficient and a dense body may not be obtained. If the sintering temperature exceeds 1950° C. or if the holding time exceeds 12 hours, the sintering aid component may volatilize and become insufficient, making it difficult to obtain a dense sintered body.

A ceramic substrate (silicon nitride substrate) according to the present embodiment is obtained by the method described above. Incidentally, at the stage of obtaining the above-described sheet-shaped molded body, the difference in surface roughness between both main surfaces of the sheet-shaped molded body is generally not 0.10 μm or more, but in the present embodiment. Then, by the subsequent sintering process (including the nitriding process), the difference in surface roughness Ra between both main surfaces can be made 0.10 μm or more.

The reason for this is that, although the principle is not clear, boron nitride (BN) present on the surface of the sheet-like compact suppresses the growth of sintered particles formed by sintering, thereby It is considered that the difference in surface roughness Ra of the main surface is increased by the sintering operation. It is presumed that this is because the content of silicon nitride is higher than in the case of using ), grain growth becomes easier, and the difference becomes more pronounced. That is, it is presumed that the main surface 1b, which is the surface on which the BN powder layer is not formed, of the sheet-shaped compact tends to have a larger surface roughness Ra than the main surface 1a, which is the surface on which the BN powder layer is formed. .

Moreover, after the sintering process, a blasting treatment may be appropriately performed. The blasting treatment generally increases the surface roughness Ra of the substrate surface, and any known method can be used without particular limitation. Examples of blasting include dry blasting in which an abrasive is sprayed with compressed air and wet blasting in which a mixture of abrasive and solution is sprayed with compressed air.

This blasting treatment may be performed, for example, to finely adjust the surface roughness Ra of the ceramic substrate obtained above, or may be performed to adjust the surface roughness Ra between the main surfaces of the ceramic substrate obtained after the sintering step. If the difference does not satisfy the relationship defined above, this blasting may be performed to satisfy the relationship.

The silicon nitride substrate thus obtained has, for example, a shape having two main surfaces and four side surfaces (FIG. 1), and one main surface 1a has a surface roughness Ra1 of 0.50 μm or less. , the surface roughness Ra2 of the other main surface 1b is 0.50 μm or more, and the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more.

It is preferable that the silicon nitride substrate has a rectangular shape and each side is 100 mm or more. Silicon nitride substrates have good thermal conductivity and are suitable for the above-described applications, such as power modules. Its thermal conductivity is preferably 100 W/m·K or more, more preferably 110 W/m·K or more, and even more preferably 130 W/m·K or more. In the method of manufacturing a silicon nitride substrate including the nitriding step described in detail above, since the purity of silicon nitride can be improved, a substrate having a thermal conductivity of 110 W/m·K or more can be easily manufactured, which is preferable.

The silicon nitride substrate after sintering is mainly composed of β-phase silicon nitride and contains rare earth elements and magnesium. The rare earth element may be in a single state, or may form a compound with another substance. Magnesium contained in the silicon nitride substrate may be in a single state or in a compound with other substances.

The silicon nitride substrate formed as described above is a silicon nitride sintered body having silicon nitride particles and grain boundary phases forming grain boundaries of the silicon nitride particles. The content of rare earth elements (in terms of trivalent oxide RE ₂ O ₃ (RE is a rare earth element)) in the grain boundary phase is 0.5 to 3.0 mol %, and the content of magnesium (in terms of MgO) is 0.5. ~10 mol% is preferred. In the silicon nitride substrate of the present embodiment, the content of the rare earth element and the content of magnesium are determined by the number of moles of silicon nitride (Si ₃ N ₄ ) and the trivalent oxide RE ₂ O ₃ containing the rare earth element. (RE is a rare earth element) and the sum of the number of moles when the magnesium is converted to MgO is 100 mol%. Hereinafter, the above total may be simply referred to as "the total of silicon nitride, rare earth elements (calculated as trivalent oxides) and magnesium (calculated as MgO)".

Here, the sum of the content of the rare earth element (in terms of trivalent oxide RE ₂ O ₃ (RE is a rare earth element)) and the content of magnesium (in terms of MgO) in the grain boundary phase (total amount of grain boundary phase) is preferably 1.0 to 12.3 mol %.

The contents of silicon nitride, rare earth element and magnesium in the silicon nitride substrate depend on the amount of silicon powder added during production and the amount of rare earth element oxide and magnesium compound added as sintering aids.

In the above method, the content of magnesium in the silicon nitride substrate after sintering decreases with respect to the amount added during manufacture, since the magnesium compound is mainly reduced by volatilization during firing. On the other hand, since rare earth element oxides hardly volatilize, the content of silicon nitride, rare earth elements (converted to trivalent oxides) and magnesium (converted to MgO) may slightly increase due to the decrease in magnesium compounds. There is The volatilization amount of the magnesium compound varies depending on the shape of the compact, firing conditions, and the like.

The oxygen content in the silicon nitride particles is preferably 0.05% by mass or less. If the oxygen content exceeds 0.05% by mass, high thermal conductivity may not be obtained. Two silicon nitride substrates under the same conditions are prepared as samples, one silicon nitride substrate can be used as a substrate, and the other silicon nitride substrate can be used for measuring the amount of oxygen. For example, the other silicon nitride substrate is pulverized and pickled to extract silicon nitride particles (the grain boundary phase is removed by pickling). Measure the amount of oxygen using the oxygen analyzer.

(1-4) Others The silicon nitride substrate manufactured as described above preferably has a dense structure with a relative density of 98% or more. If the relative density of the silicon nitride substrate is less than 98%, high thermal conductivity cannot be obtained. In such a dense silicon nitride substrate, voids are less likely to hinder heat conduction, and it is particularly preferable that the silicon nitride substrate of the present embodiment has a heat conductivity of 110 W/m·K or more in the thickness direction.

Moreover, it is preferable that the bending strength of the silicon nitride substrate is, for example, 600 MPa or more. As will be described later, in the case of a silicon nitride circuit board for a power module in which a circuit such as a metal plate is bonded to the silicon nitride board through a brazing material, high stress is applied during mounting and driving, so it depends on the method. However, the bending strength is preferably 600 MPa or more. Moreover, since the bending strength is as high as 600 MPa or more, the thickness of the silicon nitride substrate can be reduced.

The thickness of the silicon nitride substrate is not particularly limited and can be any thickness. For example, when used as an insulating and heat-dissipating substrate for semiconductor devices or electronic devices, the thickness is preferably 0.05 to 2.5 mm, more preferably 0.1 to 1 mm, and in particular, silicon nitride circuit substrates for power modules. 0.2 to 0.7 mm is more preferable. The thickness of the silicon nitride substrate after sintering can be adjusted to a desired thickness by adjusting the thickness of the sheet compact in the sheet forming process, taking into consideration the effect on the thickness during sintering. can be done.

<Ceramic circuit board>
The ceramic circuit board of the present embodiment includes the ceramic substrate described above, a metal circuit bonded to one main surface of the ceramic substrate, a metal heat sink bonded to the other main surface of the ceramic substrate, One main surface has a surface roughness Ra1 of 0.50 μm or less, the other main surface has a surface roughness Ra2 of 0.50 μm or more, and the surface roughness Ra2 is 0 less than the surface roughness Ra1 .10 μm or more.

For example, as shown in FIG. 2, this ceramics circuit board comprises a ceramics substrate 1, a metal circuit 11 bonded to one main surface 1a of the ceramics substrate 1, and the other main surface 1b of the ceramics substrate 1. and a metal heat sink 12 bonded to the ceramic circuit board 10 . Further, the ceramic circuit board 10 has a brazing material layer 13 that joins the ceramic board 1 and the metal circuit 11 and a brazing material layer 14 that joins the ceramic board 1 and the metal heat sink 12 .

As the ceramic substrate 1, the ceramic substrate of the present embodiment described above can be used.

The metal circuit 11 can have the same structure as a known metal circuit formed on this type of ceramic circuit board, and is not particularly limited.

The metal circuit 11 can be made of, for example, copper, aluminum, alloys thereof, or the like. The thickness of the metal circuit 11 is not particularly limited, but is preferably 0.2 mm or more and 2.0 mm or less, more preferably 0.5 mm or more and 1.2 mm or less. For example, 0.8 mm.

The metal heat sink 12 can have the same structure as a known metal heat sink formed on this type of ceramic circuit board, and is not particularly limited.

The metal heat sink 12 can be made of, for example, copper, aluminum, alloys thereof, or the like. The thickness of the metal heat sink 12 is not particularly limited, but is preferably 0.2 mm or more and 2.0 mm or less, more preferably 0.5 mm or more and 1.2 mm. For example, 0.8 mm.

The metal heat sink 12 may be thicker than the metal circuit 11 . By doing so, the amount of heat transferred from the metal heat sink 12 to the heat sink or the like can be increased, and heat can be efficiently dissipated. For example, the metal heat sink 12 is preferably thicker than the metal circuit 11 by 0.1 mm or more.

The brazing material layer 13 is a bonding material for bonding the ceramic substrate 1 and the metal circuit 11 , and the brazing material layer 14 is a bonding material for bonding the ceramic substrate 1 and the metal heat sink 12 .

These brazing layer 13 and brazing layer 14 may be formed using known brazing layers used in this type of ceramic circuit board, and are generally made of a paste containing brazing powder and an organic binder. be. The brazing powder used here includes, for example, a brazing powder containing silver, copper, etc. in a predetermined composition, and various organic resins can be used as the organic binder. For example, an Ag—Cu active brazing filler metal mainly composed of eutectic composition Ag and Cu to which active metals such as Ti, Zr, and Hf are added is preferable in terms of obtaining high strength, high sealing property, and the like. Further, from the viewpoint of bonding strength between the ceramic substrate and the metal plate, a ternary Ag--Cu--In system active brazing material obtained by adding In to the Ag--Cu system active brazing material is more preferable.

Although the thickness of the brazing material layer 13 is not particularly limited, it is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less. The thickness of the brazing material layer 14 is also not particularly limited, but is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less.

At this time, the brazing material layer 14 may be thicker than the brazing material layer 13 . By doing so, the brazing material layer can easily absorb the thermal stress and the like generated during the operation of the semiconductor device, and the effects of deformation of the substrate and the like due to heat can be suppressed.

<Method for producing ceramic circuit board>
Next, a method for manufacturing a ceramic circuit board according to this embodiment will be described. The ceramic circuit board can be manufactured according to a known manufacturing method, and is not particularly limited. A detailed description will be given below with reference to FIGS. 3 to 6. FIG.

(2-1) Formation of Brazing Material Layer (Brazing Material Layer Forming Step)
First, the ceramic substrate 1 described in the above embodiment is prepared. As described above, the ceramic substrate 1 has main surfaces with different surface roughnesses Ra, and it should be noted that the members to be joined differ depending on the surface roughnesses Ra.

At this stage, brazing material layers are formed on both main surfaces in order to join a metal circuit or a metal heat sink to either of the main surfaces. The brazing material layer 13 is formed on the first main surface 1a side, and the brazing material layer 14 is formed on the second main surface 1b side by applying the brazing material by a method such as screen printing ( Figure 3).

The brazing material used for forming the brazing material layers 13 and 14 is the brazing material described above for the ceramic circuit board.

(2-2) Bonding of metal plates (bonding process)
A metal plate 21 for forming a circuit and a metal plate 22 for forming a heat radiating plate are laminated on the ceramic substrate 1 with a brazing material layer 13 interposed therebetween, respectively, and fixed.

By heating the obtained laminated material, the ceramic substrate 1 and the circuit forming metal plate 21, and the ceramic substrate 1 and the heat sink forming metal plate 22 are joined via brazing material layers, respectively, to form laminated plates. (Fig. 4).

Heating during this bonding is preferably carried out in a vacuum or in a reducing atmosphere. Further, in order to remove the organic component in the brazing filler metal paste in the process of raising the temperature, it is preferable to temporarily hold the paste near the volatilization temperature of the organic binder and then heat it up to the brazing temperature. This heating is preferably continued for 10 minutes or longer. Brazing temperature means a temperature at which a brazing material layer can be properly formed, that is, a temperature above the melting point of the brazing material. The brazing temperature is usually the highest temperature in the heating process.

After the heating, the temperature may be lowered to normal temperature by a known method, and the method is not particularly limited. For example, it is preferable to lower the temperature to 350° C. over 50 minutes or more, and then lower the temperature from 350° C. to room temperature.

In the holding step during the bonding step, if the holding temperature for removing the organic binder is low, the organic binder component cannot volatilize, and there is a possibility that the residue of the organic binder remains. Therefore, the holding temperature for removing the organic binder is preferably 300° C. or higher. For example, in the case of an organic binder containing acrylic resin, the holding temperature is preferably 360° C. or higher. In order to prevent the active metal in the brazing material from being oxidized by the oxygen contained in the resin, etc. in the organic binder, the holding temperature for removing the organic binder should be higher than the brazing temperature in the heating process (brazing process). also lower.

Using the brazing material described in the above bonding step, the bonding between the ceramic substrate and the metal plate can be performed using the brazing material paste containing the brazing material powder and the organic binder, as described above. For the brazing material, for example, when a brazing material having a predetermined melting point is used, it is preferable to set the brazing temperature to a temperature in the vicinity of the melting point. When the brazing filler metal is heated to the melting point or higher, the brazing filler metal is sufficiently melted and the formation of voids can be suppressed. In addition, it is preferable not to set the temperature to a high temperature far from the melting point so that the brazing material does not spread excessively.

The time for holding at the brazing temperature depends on the amount used, but considering normal productivity, it is preferably within 5 hours, more preferably within 2 hours. The time for holding at the brazing temperature is appropriately adjusted and set according to the number of samples to be charged, and, for example, in the case of a vacuum atmosphere, according to the volume of the heating furnace for bonding and the displacement of the vacuum pump. In order to bond the metal plate and the ceramics without voids, it is preferable to apply a load and fix them in the mounting process and then heat them in the bonding process.

(2-3) Formation of circuit pattern (pattern formation step)
A circuit pattern is formed on the laminate obtained in the bonding step. To form the circuit pattern, first, resist films are formed in desired patterns on the surfaces of the circuit forming metal plate 21 and the heat sink forming metal plate 22, respectively.

A resist film can be formed by a known method. Once a resist film is formed on the entire surface of the metal plate, a desired pattern of the resist film can be formed by photolithography or the like. Using the formed resist film, a metal pattern is formed by etching, and then the resist film is removed to form the metal circuit 11 and the metal radiator plate 12 (FIG. 5).

The resist film formed in the pattern forming step preferably has a thickness of 10 to 80 μm, more preferably 30 to 70 μm. As the resist film, an ultraviolet curable resist material is preferable.

In FIG. 5, a pair of metal circuits 11 and a metal heat sink 12 are formed for the sake of explanation. Multiple sets are formed. A plurality of sets of metal circuits 11 and metal heat sinks 12 thus formed are subjected to the steps described later, and finally cut by dicing or the like to form a plurality of ceramic circuit boards.

(2-4) Brazing material layer removal process After the pattern forming process (3), an unnecessary brazing material layer exists on the ceramic substrate 1 in the etched portion, so it is removed (Fig. 6) ).

The brazing filler metal can be removed by a known method, and examples of the solvent used for removal include a chemical solution containing hydrogen peroxide and acid ammonium fluoride. A preferable chemical solution is an aqueous solution containing ∼40% by mass (2.9 to 8.8 mol/L) of hydrogen peroxide and 1 to 8% by mass (0.7 to 2.1 mol/L) of ammonium acid fluoride. I can give an example.

If the amount of hydrogen peroxide is less than 10% by mass, the ability to remove the brazing filler metal may be insufficient. It may get worse. If the ammonium acid fluoride content is less than 1% by mass, the ability to remove the reaction layer containing the active metal generated at the bonding interface between the brazing material layer and the ceramic substrate may decrease. may dissolve the crystal grains forming the ceramic substrate and reduce the electrical insulation and strength required of the ceramic substrate.

(2-5) Washing Step After removing the brazing material layer, the patterned laminate is immersed in a chemical and washed. For example, if oxygen is not sufficiently reduced from the treatment atmosphere and the surface of the metal plate is oxidized in the heating step, the electrical conductivity and solderability may be lowered, which is undesirable. Therefore, the oxide on the surface of the metal plate can be removed by immersing and washing the patterned laminate in a chemical containing at least one selected from hydrogen peroxide, sulfuric acid, hydrochloric acid and ammonium chloride. Sulfuric acid is preferably used as the chemical.

After the pattern forming step to the cleaning step, the deposits that reduce the insulation resistance between the metal plates on the substrate are removed or reduced, which is preferable.

Furthermore, after the cleaning process, a plated layer of nickel, gold, silver, or the like may be formed on the surface of the metal plate. When forming such a plating layer, for example, when performing nickel plating, an electroless plating solution (85 ° C.) containing nickel (Ni) as the main component and phosphorus (P) concentration adjusted to 8% by mass A Ni plating layer having a thickness of about 5 μm can be formed on the surface of the metal plate by immersing it in the solution for 20 to 30 minutes.

The ceramic circuit board 10 of the present embodiment is obtained by forming a plated layer as necessary in the brazing material layer forming step to the cleaning step.

As shown in FIG. 7, the circuit board 10 obtained in this manner is formed by connecting a semiconductor chip 51 to the metal circuit 11 to form a semiconductor device, and by connecting a heat sink 52 and the like to the metal heat sink 12 to achieve the heat dissipation characteristics of the circuit board 10. can be improved.

The present embodiment will be described in more detail with examples, but the present invention is not limited to these.

(1) Preparation of Silicon Nitride Substrate (Slurry Preparation Step)
Silicon powder having a BET specific surface area of 2.1 m ² /g, a median diameter D50 of 8.2 μm, and an oxygen content of 0.3% by mass, silicon (in terms of silicon nitride), a rare earth element oxide (in terms of trivalent oxide ) and magnesium compound (converted to MgO), 1.2 mol% Y ₂ O ₃ powder and 9.8 mol% MgSiN ₂ powder were added as sintering aids to obtain raw material powder. To this raw material powder, 0.5% by mass of a dispersant (sorbitan acid trioleate) is added to the total of the dispersion medium (toluene) and the raw material powder to obtain a slurry having a concentration of 42% by mass, and a ball mill is used. , using silicon nitride 5φ balls as media, pulverization was carried out for 24 hours.

The addition amount of the magnesium compound is shown in mol % when all magnesium compounds are converted to MgO. The BET specific surface area, median diameter D50, and oxygen content of the silicon powder before pulverization were measured by a BET single-point BET specific surface area meter, a laser diffraction/scattering particle size distribution meter, and an inert gas fusion-nondispersive infrared absorption method, respectively. was measured using an oxygen analyzer.

(Sheet forming process)
The resulting slurry was adjusted in concentration by adding a dispersion medium and an organic binder (acrylic resin), and subjected to defoaming treatment to obtain a slurry-like coating liquid. This coating slurry is applied to a carrier film by a doctor blade method, molded into a sheet having a thickness of 0.38 mm at a molding speed of 600 mm/min or less, and cut into sheets of 240 mm × 200 mm. A shaped compact was obtained. The surface roughness Ra of the coated surface of the transport film is 0.1 μm. Here, the surface that was in contact with the transport film of the sheet-shaped molded body was one main surface (main surface 1a), and the surface that was not in contact with the transport film and was in an open state was the other main surface (main surface). 1b).

(Sintering process)
A boron nitride (BN powder) layer is formed on the main surface 1a of the obtained sheet-like compact. As shown in FIG. 8, a layered body 100A is prepared by laminating a plurality of sheet-shaped molded bodies with a boron nitride powder (BN powder) layer (4.5 μm thick) (not shown) sandwiched therebetween, and placed on a BN A separation material was placed on the plate 200 . A weight plate 300 made of BN was placed on the laminate 100A.

Such laminated bodies 100A were placed in multiple stages, and a plurality of such laminated bodies 100A were prepared.

Next, the plurality of laminates 100A are degreased at 750° C. for 5 hours under a nitrogen atmosphere (nitrogen partial pressure 0.1 MPa) (degreasing step), and placed in a nitriding apparatus under a nitrogen atmosphere (nitrogen partial pressure 0.5 MPa) at 1400°C. °C for 10 hours (nitriding step).

Next, the laminate 100A taken out of the nitriding apparatus is placed in a BN crucible, carried into a sintering apparatus, and sintered at 1900° C. for 12 hours in a nitrogen atmosphere (nitrogen partial pressure 0.9 MPa). (a densification sintering step), the BN powder layer was removed, and a silicon nitride substrate made of a silicon nitride sintered body was obtained.

Finally, the surface of the silicon nitride substrate was subjected to liquid honing for the purpose of cleaning and making it moderately rough. The honing treatment was carried out by adding an appropriate amount of alumina abrasive grains to water and spraying it onto the front and back surfaces of the sintered body at a pressure of 0.5 MPa. The obtained silicon nitride substrate had a size of 200 mm×170 mm and a thickness of 0.32 mm.

After cleaning and liquid honing treatment, 10 silicon nitride substrates were randomly selected from a large number of obtained silicon nitride substrates, and the surface roughness Ra was measured at 6 points on each main surface 1a and 1b of the silicon nitride substrates. The surface roughness Ra of the surface was taken as the average value, and the results are summarized in Table 1.

As another lot, the surface roughness Ra of the main surfaces 1a and 1b was similarly measured when a silicon nitride substrate was produced by the same operation, and the results are shown in Table 2.

(Comparative example)
Silicon nitride powder having a BET specific surface area of 2.1 m ² /g, a median diameter D50 of 8.2 μm, and an oxygen content of 0.3% by mass, silicon nitride, a rare earth element oxide (calculated as trivalent oxide) and magnesium 1.2 mol % of Y ₂ O ₃ powder and 9.8 mol % of MgSiN ₂ powder were added as sintering aids to the total compound (in terms of MgO) to obtain raw material powder.

In the above examples, the silicon nitride substrates were formed in the same manner as in the examples except that the nitriding step in the sintering step was not performed, and the surface roughness Ra (μm) of the two main surfaces of the silicon nitride substrates was measured. The results, including the difference (μm) in surface roughness Ra between the main surfaces, are shown below.

Comparative substrate 1: main surface 1a 0.581, main surface 1b 0.585, difference 0.004
Comparative substrate 2: main surface 1a 0.583, main surface 1b 0.572, difference 0.011
Comparative substrate 1 and comparative substrate 2 have a difference in surface roughness Ra between the principal surfaces of less than 0.10 μm, and both surface roughnesses Ra1 and Ra2 exceed 0.50 μm. Moreover, in the comparative substrate 2, Ra2 is smaller than Ra1.

From the above results, the ceramic substrate of the present embodiment, which is produced by a manufacturing method including a nitriding step in which a BN powder layer is formed on the main surface 1a of the sheet-shaped molded body and the sheet-shaped molded body is nitrided, has a metal circuit and It has been found that the surfaces on which the metal heat sinks are formed can each have a suitable surface roughness Ra, and the surfaces can have a desired relationship. As a result, when the ceramic substrate is joined to the metal circuit and the metal heat sink, the surface roughness is relatively small so that the brazing material can be easily removed from the main surface 1a to which the metal circuit is joined. The main surface 1b to which the metal heat sink is bonded can have a relatively large surface roughness so as to improve the bonding strength with the metal heat sink.

Although the invention made by the present inventor has been specifically described based on the embodiment, the invention is not limited to the embodiment, and can be variously modified without departing from the gist of the invention. Needless to say.

Reference Signs List 1 ceramic substrate 1a, 1b main surface 10 ceramic circuit substrate 11 metal circuit 12 metal radiator plate 13, 14 brazing material layer 51 semiconductor chip 52 heat sink

Claims (11)

A ceramic substrate having a first main surface and a second main surface,
The surface roughness Ra1 of the first main surface is 0.50 μm or less,
The surface roughness Ra2 of the second main surface is 0.50 μm or more,
The ceramic substrate, wherein the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more. In the ceramic substrate according to claim 1,
The planar shape of the ceramic substrate is a rectangular shape,
A ceramic substrate, wherein each side of the ceramic substrate is 100 mm or more. In the ceramic substrate according to claim 1 or 2,
The ceramic substrate is a silicon nitride substrate. In the ceramic substrate according to claim 3,
A ceramic substrate, wherein the ceramic substrate has a thermal conductivity of 110 W/(m·K) or more. In the ceramic substrate according to any one of claims 1 to 4,
The first main surface is a metal circuit forming surface,
The ceramic substrate, wherein the second main surface is a surface on which a metal heat sink is formed. a ceramic substrate having a first principal surface and a second principal surface;
a metal circuit bonded to the first main surface of the ceramic substrate;
A ceramic circuit board comprising: a metal heat sink bonded to the second main surface of the ceramic substrate,
The surface roughness Ra1 of the first main surface is 0.50 μm or less,
The surface roughness Ra2 of the second main surface is 0.50 μm or more,
The ceramic circuit board, wherein the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more. In the ceramic circuit board according to claim 6,
A ceramic circuit board, wherein the ceramic substrate is a silicon nitride substrate. In the ceramic circuit board according to claim 7,
A ceramic circuit board, wherein the ceramic substrate has a thermal conductivity of 110 W/(m·K) or more. In the ceramic circuit board according to any one of claims 6 to 8,
A ceramic circuit board, wherein the thickness of the metal radiator plate is thicker than the thickness of the metal circuit. In the ceramic circuit board according to any one of claims 6 to 9,
The ceramic substrate and the metal circuit are bonded via a first brazing material layer, and the ceramic substrate and the metal heat sink are bonded via a second brazing material layer,
A ceramic circuit board, wherein the thickness of the second brazing material layer is greater than the thickness of the first brazing material layer. (a) preparing a slurry containing silicon powder;
(b) obtaining a sheet-like compact from the slurry;
(c) a step of sintering the sheet-shaped compact;
A method for manufacturing a ceramic substrate, comprising
The step (c) includes a nitriding step,
The ceramic substrate has a first main surface and a second main surface,
The surface roughness Ra1 of the first main surface is 0.50 μm or less,
The surface roughness Ra2 of the second main surface is 0.50 μm or more,
The method for manufacturing a ceramic substrate, wherein the surface roughness Ra2 is greater than the surface roughness Ra1 by 0.10 μm or more.

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