Method for manufacturing ceramic substrate

Abstract

The present invention provides a method for manufacturing a ceramic substrate capable of appropriately setting the amount of a release agent adhered to a ceramic green sheet. According to an embodiment of the present invention, a method for manufacturing a ceramic substrate is provided with: an adhesion step for adhering a mold release agent to both surfaces of a ceramic green sheet having a first surface and a second surface; and a sintering step in which the plurality of ceramic green sheets to which the release agent has been adhered are stacked and sintered. In the ceramic green sheet after the adhesion step, the adhesion rate of the release agent to the first surface and the adhesion rate of the release agent to the second surface are respectively 5% or more and 30% or less. The difference between the adhesion rate of the release agent to the first surface and the adhesion rate of the release agent to the second surface is 20% or less.

Description

TECHNICAL FIELD

[0001] Embodiments relate to a manufacturing method of a ceramic substrate. BACKGROUND

[0002] In recent years, with the development of power electronics, next-generation power semiconductors, and other semiconductor elements requiring large current, the demand for ceramic substrates that have both heat dissipation and electrical insulation properties has been increasing year by year. In particular, with miniaturization and high performance, the heat generation of elements increases, and in order to efficiently dissipate heat, there is a tendency for the thickness of ceramic substrates to be thinned.

[0003] On the other hand, in order to reduce the manufacturing cost of ceramic substrates, a technique for manufacturing a ceramic substrate in a larger shape is disclosed (Patent Literature 1). A silicon nitride substrate has high strength and high toughness among ceramic substrates, and has high heat dissipation. According to Patent Literature 1, a silicon nitride substrate of 220 mm x 220 mm x 0.32 mm is obtained.

[0004] As a manufacturing method of a ceramic substrate, a technique of laminating multiple green sheets with a separation material in between is disclosed (Patent Literature 2). The laminated green sheets are separated from each other after sintering. Thus, multiple ceramic substrates are manufactured. According to Patent Literature 2, a separation material in which boron nitride powder is dispersed is applied to one or both surfaces of the cut green sheet. Then, the laminated multiple green sheets are sintered and separated, and thus multiple silicon nitride sintered bodies are obtained.

[0005] In addition, a method of applying a release agent to a ceramic green sheet using a roll coater is disclosed (Patent Literature 3). According to Patent Literature 3, multiple ceramic green sheets are laminated, and a sintering plate made of boron nitride (BN) is pressed against the upper and lower surfaces of the laminate to sinter, and thus multiple ceramic sintered bodies are obtained.

[0006] PRIOR ART DOCUMENTS PATENT LITERATURE Patent Literature 1: Japanese Patent No. 6399252 Patent Literature 2: Japanese Patent No. 5339214 Patent Literature 3: Japanese Patent No. 3369819 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION A green sheet of a ceramic substrate is manufactured by mixing an organic binder in a ceramic powder and drying it. The green sheet does not have the strength of a resin film or a metal foil and is easily broken by tension. On the other hand, with the miniaturization of products, there is a tendency for ceramic substrates to be thinned. In addition, in order to manufacture efficiently and reduce costs, there is a tendency for the size of the ceramic green sheet to be increased.

[0008] The amount of the release agent attached to the ceramic green sheet affects the quality and productivity of the ceramic substrate, and thus it is desirable to be properly managed. For example, when the amount of the release agent is small, the separation of the ceramic substrates from each other after sintering becomes difficult. Thus, it takes time to separate the ceramic substrates from each other. In a case where the separation is not possible, the ceramic substrates become defective products. If the release agent is attached in a large amount, although the separation becomes easy, the cost of the release agent increases. In addition, in a case where the amount of the attached release agent is uneven, the unevenness of the ceramic substrate becomes large, which becomes a cause of defects. Thus, in the production of the ceramic substrate, it is desirable to properly manage the amount of the release agent attached to the ceramic green sheet.

[0009] Means for solving the problem The production method of the ceramic substrate of the embodiment includes an attaching step and a sintering step. In the attaching step, a release agent is attached to both surfaces of a ceramic green sheet having a first surface and a second surface. In the sintering step, a plurality of the ceramic green sheets to which the release agent is attached are overlapped and sintered. In the ceramic green sheet after the attaching step, the attachment rate of the release agent to the first surface and the attachment rate of the release agent to the second surface are each 5% or more and 30% or less. The difference between the attachment rate of the release agent to the first surface and the attachment rate of the release agent to the second surface is 20% or less. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a perspective view showing an example of the ceramic green sheet of the embodiment.

[0011] Figure 2 is a cross-sectional view showing an example of the ceramic green sheet of the embodiment.

[0012] Figure 3 is a flowchart showing the production method of the ceramic substrate of the embodiment.

[0013] Figure 4 is a cross-sectional view showing an example of the production step of the ceramic substrate of the embodiment.

[0014] Figure 5 is a cross-sectional view showing an example of the production step of the ceramic substrate of the embodiment. DETAILED DESCRIPTION

[0015] The manufacturing method of the ceramic substrate of the embodiment includes an attaching step and a sintering step. In the attaching step, a release agent is attached to both surfaces of a ceramic green sheet having a first surface and a second surface. In the sintering step, a plurality of the ceramic green sheets to which the release agent is attached are overlapped and sintered. In the ceramic green sheet after the attaching step, the attachment rate of the release agent to the first surface and the attachment rate of the release agent to the second surface are each 5% or more and 30% or less. The difference between the attachment rate of the release agent to the first surface and the attachment rate of the release agent to the second surface is 20% or less.

[0016] A ceramic sintered body such as a ceramic substrate is manufactured by sintering a shaped body in which a raw material is fixed to a prescribed shape. A ceramic green sheet is a shaped body before sintering, and is produced in order to manufacture a thin ceramic sintered body such as a ceramic substrate. The ceramic green sheet is formed of a ceramic raw material powder, a sintering aid powder, and an organic substance. The ceramic raw material powder is a main constituent element of the ceramic substrate. The sintering aid powder is added in order to sinter the ceramic raw material. The organic substance is a resin or the like, and is used to shape the powder into a sheet shape. The ceramic green sheet is manufactured by mixing these powders and the organic substance in a solvent, shaping the mixture into a sheet shape, and drying the shaped body. The ceramic green sheet is soft, and thus can be easily cut with a cutting tool or the like. However, the ceramic green sheet has no strength, and thus is easily broken if a force such as a tensile force is applied.

[0017] The manufactured ceramic substrate is preferably any one of an alumina substrate, an aluminum nitride substrate, or a silicon nitride substrate. An Alusil high-silicon heat-resistant aluminum alloy substrate is cited as one of the alumina substrates. The Alusil high-silicon heat-resistant aluminum alloy is a sintered body in which the remaining portion other than 20 to 80 wt% of alumina is zirconia. The three-point bending strength of the aluminum nitride substrate or the alumina substrate is about 300 to 450 MPa. The strength of the Alusil high-silicon heat-resistant aluminum alloy substrate is about 550 MPa. The three-point bending strength of the silicon nitride substrate is 600 MPa or more, and can be further increased to 700 MPa or more. The thermal conductivity of the silicon nitride substrate is 50 W / (m·K) or more, and can be further increased to 80 W / (m·K) or more. In particular, in recent years, there are also silicon nitride substrates that have both high strength and high thermal conductivity. The silicon nitride substrate is high in strength, and thus can be thinned, and can further improve heat dissipation.

[0018] The thickness of the ceramic green sheet of the embodiment is preferably 1.0 mm or less. If the ceramic green sheet is thick, the strength is increased. However, in a case where a release agent is attached to a thick ceramic green sheet and is dried, cracks are easily generated on the surface due to the force of bending. In a case where a release agent is applied to both surfaces of the ceramic green sheet before cutting, the ceramic green sheet is often bent and handled. Therefore, a thick ceramic green sheet is easily cracked. The thickness of the ceramic green sheet is more preferably 0.8 mm or less, and is further preferably 0.6 mm or less.

[0019] In order to obtain a plurality of ceramic substrates by superimposed sintering of ceramic green sheets, the release agent attached to the ceramic green sheet is preferably a substance that is stable at a high temperature at the time of sintering and does not easily react with the ceramic substrate. As a representative release agent attached to the ceramic green sheet, boron nitride (BN) can be given. Boron nitride enables the powder of boron nitride to be dispersed in water or an organic solvent and attached.

[0020] Figure 1 is a perspective view showing an example of a ceramic green sheet of the embodiment. As shown in Figure 1 , a release agent 3 is attached to the surface of the ceramic green sheet 2. Figure 2 is a cross-sectional view showing an example of a ceramic green sheet of the embodiment. The ceramic green sheet 2 has a first surface 2a and a second surface 2b. The second surface 2b is the surface on the opposite side of the first surface 2a. As shown in Figure 2 , a release agent 3 is attached to the first surface 2a and the second surface 2b, respectively.

[0021] In the present embodiment, the attachment rate of the release agent 3 to the first surface 2a and the attachment rate of the release agent 3 to the second surface 2b are each 5% or more and 30% or less. The "attachment rate" indicates the proportion of the area to which the release agent is attached per unit area. In addition, in the present embodiment, the release agent 3 is depicted as a layer for the sake of explanation of the concept, but in reality, the portion to which the release agent is not attached is more than the portion to which the release agent is attached. Figure 2

[0022] The attachment rate is measured by the following method. First, a threshold value for measuring the attachment rate is set. The release agent in a state before being dispersed in a liquid is photographed to obtain a photo of the release agent. Next, the ceramic green sheet in a state before the release agent is attached is photographed to obtain a photo of the ceramic green sheet. The conditions at the time of photographing the release agent and the conditions at the time of photographing the ceramic green sheet are set to be the same. For example, in the photographing of the release agent and the photographing of the ceramic green sheet, all of the photographing conditions such as the illuminance of light, the direction of light, the direction of the camera, the distance between the light source and the subject (the release agent or the ceramic green sheet), the distance between the camera and the subject, the setting of the camera, and the like are set to be the same. Next, in the photo of the release agent, the pixel value of the region in which the release agent is photographed is referred to. In the photo of the ceramic green sheet, the pixel value of the region in which the ceramic green sheet is photographed is referred to. In the vicinity of the outer edge of the subject, the pixel value can be different from usual due to a shadow or noise, and therefore it is preferable to refer to the pixel value of the region far from the outer edge. In addition, it is preferable to average the pixel values of a plurality of pixels in the region far from the outer edge. After the pixel value of the subject is obtained, the intermediate value of the pixel value of the release agent and the pixel value of the ceramic green sheet is calculated. The intermediate value is used as the threshold value at the time of calculating the attachment rate.

[0023] ​After the threshold value is set, the adhesion rate of the ceramic green sheet to which the release agent is adhered is measured. First, the ceramic green sheet to which the release agent is adhered is imaged. The imaging conditions of the ceramic green sheet at this time are set to be the same as the imaging conditions of the release agent and the imaging conditions of the ceramic green sheet at the time of setting the threshold value. Next, the image of the ceramic green sheet is binarized. As the threshold value at the time of binarization, the intermediate value calculated in advance is used. By binarization, the pixels having a pixel value lower than the threshold value are represented in black, and the pixels having a pixel value higher than the threshold value are represented in white. In the binarization, a general-purpose image processing software (for example, Image-J) can be used. In the region imaged to the ceramic green sheet, the proportion of the region represented in white is taken as the adhesion rate.

[0024] For example, in the case where boron nitride is used as the release agent, a granular material in which boron nitride powder is fixed is prepared in advance. The boron nitride powder is white and has a luster. The ceramic green sheet formed of silicon nitride is light gray and looks darker than the boron nitride powder. By imaging the granular material, the pixel value of the release agent is obtained. The color of the boron nitride of the granular material is substantially the same as the color of the boron nitride of the powder. Therefore, it is also possible to image the boron nitride in a powder state obtained by pulverizing the granular material. If a liquid in which boron nitride is dispersed is adhered to the ceramic green sheet, the region to which the boron nitride is adhered is brighter and looks to have a luster. Therefore, the pixel value of the region to which the boron nitride is adhered is higher than the pixel value of the region to which the boron nitride is not adhered.

[0025] The adhesion rate can be measured before the ceramic green sheet is cut, or can be measured after the ceramic green sheet is cut. In the case where the adhesion rate is measured before the ceramic green sheet is cut, the entire region of the cut-out ceramic green sheet is imaged, and the adhesion rate is calculated. In the case where the adhesion rate is measured after the ceramic green sheet is cut, the entire region of the ceramic green sheet used in the manufacture of one ceramic substrate is imaged, and the adhesion rate is calculated.

[0026] In the method for manufacturing the ceramic substrate of the embodiment, when the release agent is adhered to both surfaces of the ceramic green sheet 2, the adhesion rate of the first surface 2a and the adhesion rate of the second surface 2b are each 5% or more and 30% or less. If the adhesion rate of the release agent is less than 5%, the region to which the release agent is adhered is too small, and it takes effort to peel the sintered ceramic substrates from each other. In addition, the ceramic substrates are adhered to each other and cannot be peeled, and a defective product can be produced. Therefore, the adhesion rate of the release agent is preferably 10% or more, and further preferably 15% or more. If the adhesion rate of the release agent is more than 30%, the peeling of the ceramic substrates from each other becomes easy, but unevenness in the amount of adhesion is likely to occur. Between the portion to which the release agent is adhered thickly and the portion to which the release agent is adhered thinly, the ceramic substrate is likely to have a relief, which becomes a cause of defects. Therefore, the adhesion rate of the release agent is preferably 25% or less, and further preferably 20% or less.

[0027] The amount of the release agent 3 attached to the ceramic green sheet 2 also affects the quality of the ceramic substrate. Therefore, in the production of the ceramic substrate, it is preferable to manage the attached amount of the release agent 3. Conventionally, after the ceramic green sheet 2 is cut, the weight of the ceramic green sheet 2 before the release agent 3 is attached and the weight of the ceramic green sheet 2 after the release agent 3 is attached are measured, and the attached amount of the release agent 3 is calculated from the change in the weight. However, since the ceramic green sheet 2 is thin and large-sized, it is difficult to manage by the weight. In addition, in order to suppress the generation of defects and improve the productivity, it is preferable to attach the release agent 3 to the ceramic green sheet 2 in a small and uniform amount. For example, if the release agent is attached only to a limited area of one side while managing the attached amount, the layered ceramic substrates sometimes adhere to each other at the time of sintering. According to the embodiment of the present application, the attachment rates of both sides of the ceramic green sheet 2 are managed in the range of 5% or more and 30% or less, respectively. Thereby, it becomes easy to peel the ceramic substrates from each other, and it is possible to suppress the generation of undulations of the ceramic substrates. It is possible to suppress the generation of defects and improve the productivity of the ceramic substrates.

[0028] Note that the attachment rate of 5% or more and 30% or less does not mean that the release agent is attached to only an area of 5% or more and 30% or less of the surface. Even in the area where the release agent is attached, the area is converted to black by binarization if the amount thereof is small enough. That is, the attachment rate of 5% or more and 30% or less means that the release agent is attached to the entire surface, and the proportion of the area where the release agent is attached thickly is 5% or more and 30% or less.

[0029] In addition, in the production method of the ceramic substrate of the embodiment, when the release agent is attached to both sides of the ceramic green sheet 2, the difference between the attachment rate of the first side 2a and the attachment rate of the second side 2b is 20% or less. The release agent is attached to the ceramic green sheet in a state of being dispersed in a solvent. The solvent attached to the ceramic green sheet penetrates into the ceramic green sheet. If the difference between the attachment rate of the first side 2a and the attachment rate of the second side 2b is large, a difference between the state of the first side and the state of the second side is generated due to the difference in the amount of the release agent, the difference in the penetrated solvent, or the like. As a result, a difference between the state of the first side and the state of the second side is generated after drying. As a result, warping or undulation is generated in the ceramic substrate after sintering. In particular, the thinner the ceramic green sheet, the more likely the ceramic substrate is to generate warping or undulation caused by the difference between the state of the first side and the state of the second side. Therefore, the difference between the attachment rate of the first side 2a and the attachment rate of the second side 2b is preferably 15% or less, and further preferably 10% or less.

[0030] To make it easy to separate the sintered ceramic substrates from each other, it is preferable that the release agent be uniformly attached to the ceramic green sheet 2. For example, after the release agent is attached, the first surface 2a is divided into four regions, and the attachment rate of the release agent to each region is measured. The method of measuring the attachment rate of each region is the same as the method of measuring the attachment rate of the first surface 2a and the second surface 2b. Four measurement values of the attachment rate are obtained from the four regions of the first surface 2a. The difference between the maximum attachment rate and the minimum attachment rate of the first surface 2a is preferably 20% or less. Similarly, the second surface 2b is divided into four regions, and the attachment rate of the release agent to each region is measured. Four measurement values of the attachment rate are obtained from the four regions of the second surface 2b. The difference between the maximum attachment rate and the minimum attachment rate of the second surface 2b is preferably 20% or less.

[0031] The smaller the deviation of the attachment rate is in the first surface 2a or the second surface 2b, the easier it is to separate the sintered ceramic substrates from each other. In addition, the smaller the deviation of the attachment rate is, the more it is possible to reduce the unevenness of the ceramic substrate. Therefore, in each of the first surface 2a and the second surface 2b, the difference between the maximum attachment rate and the minimum attachment rate is more preferably 15% or less, and most preferably 10% or less.

[0032] Figure 3 is a flowchart showing a manufacturing method of a ceramic substrate according to the embodiment. Figure 4 (a) Figure 4 (d), Figure 5 (a) and Figure 5 (b) is a cross-sectional view showing an example of a manufacturing process of a ceramic substrate according to the embodiment. With reference to these drawings, a preferred example of a manufacturing method of a ceramic substrate according to the embodiment is described. The manufacturing method according to the embodiment only needs to have the above-described features related to the attachment rate, and the specific process and the like included in the manufacturing method are not particularly limited. Here, an example of a method for obtaining a ceramic substrate with a good yield is described. In addition, an example in which silicon nitride is used as the ceramic and boron nitride powder is used as the release agent is described.

[0033] First, a raw material powder of a ceramic and a sintering aid are prepared. In the case of producing a silicon nitride substrate, the raw material powder is a silicon nitride powder. The sintering aid uses oxides of rare earth elements, magnesium, titanium, hafnium, and the like. By adding the sintering aid in the form of a metal oxide, it is easy to form a liquid phase component in the sintering process. The silicon nitride powder and the sintering aid powder are mixed at a predetermined ratio, and further an organic binder is added, thereby preparing a mixture. The mixture is subjected to a defoaming treatment, and a raw material slurry is produced (step S1). The defoaming treatment is a treatment for removing bubbles in a raw material solution by stirring the raw material solution in a vacuum. By reducing the bubbles in the raw material solution, it is also possible to reduce the bubbles in the sintered body. By performing the defoaming treatment, it is possible to perform slurryization with improved viscosity.

[0034] AsFigure 4 (a) shown, a raw material slurry is formed, and a ceramic green sheet 2 formed of silicon nitride is produced (step S2). The sheet formation is preferably performed using a doctor blade method. If the doctor blade method is used, a thin and large green sheet can be produced, and thus mass productivity is improved.

[0035] Separately from the production of the green sheet, a boron nitride powder is prepared as a release agent raw material. The boron nitride powder and a binder are dispersed in water, and a slurry of boron nitride is produced. As shown in Figure 4 (b) shown, the release agent 3 is attached to the first face 2a and the second face 2b of the ceramic green sheet 2, respectively (step S3). More specifically, as shown in Figure 4 (b) shown, the release agent 3 is attached to the first face 2a and the second face 2b of the ceramic green sheet 2, respectively (step S3). More specifically, as shown in Figure 4 (c) shown, the release agent 3 is attached to the first face 2a and the second face 2b of the ceramic green sheet 2, respectively (step S3). More specifically, as shown in

[0036] As shown in Figure 4 (d) shown, the ceramic green sheet 2 to which the release agent 3 is attached is cut into a predetermined size using a cutter or the like (step S4).

[0037] As shown in Figure 5 (a) shown, the cut ceramic green sheet 2 is stacked in a sintering container 21 (step S5). The sintering container 21 is formed of boron nitride or the like, and is composed of a setter 22 and a setter 23, for example. The setter 22 is arranged in a horizontal direction, and the setter 23 is arranged in a vertical direction. The ceramic green sheet 2 is arranged in a space surrounded by a plurality of setters 22 and a plurality of setters 23.

[0038] The stacked ceramic green sheet is heated at a temperature of 1000°C or lower, and a debinding body is produced (step S6). The atmosphere of the debinding process is preferably a non-active atmosphere such as nitrogen or argon. An oxygen-containing atmosphere in which oxygen is contained in the non-active atmosphere can also be provided.

[0039] The debinding body is sintered at a temperature of 1600°C or higher and 2000°C or lower (step S7). The inside of the sintering container is preferably a pressurized atmosphere. The debinding and the sintering can be continuously performed in the same sintering container. The stacked sintered body is separated from each other, and the release agent is removed by honing or the like (step S8). Thus, as shown in Figure 5 (b) shown, a ceramic substrate 4 is produced. Then, as needed, surface processing such as polishing processing can be performed on the surface of the ceramic substrate 4. In the case where the ceramic substrate 4 is used as a circuit substrate, a process of joining a metal plate or the like to the ceramic substrate 4 can also be further performed.

[0040] Regarding the aforementioned manufacturing method, it is preferable to apply the release agent to the second side 2b within 30 minutes after applying it to the first side 2a of the ceramic green sheet 2. The release agent is mostly dispersed in a solvent. If the release agent is applied only to one side of the ceramic green sheet 2 and then dried, the ceramic green sheet 2 is prone to warping due to tension when placed in the sintering container. If the warping of the ceramic green sheet 2 is significant, positional shifts can easily occur when the ceramic green sheets 2 are stacked in the sintering container. Due to this positional shift, the ceramic substrate 4 deforms during sintering. To suppress warping of the ceramic green sheet 2, it is preferable to apply the release agent to the second side 2b quickly after applying it to the first side 2a. By applying the release agent to the second side 2b within 30 minutes after applying it to the first side 2a, warping of the ceramic green sheet 2 can be suppressed. As a result, deformation of the manufactured ceramic substrate can be suppressed. The time from when the release agent adheres to the first surface 2a to when the release agent adheres to the second surface 2b is more preferably within 20 minutes, and even more preferably within 10 minutes.

[0041] As long as the adhesion rate of the first surface 2a and the second surface 2b is 5% or more and 30% or less, and the difference in adhesion rate between the first surface 2a and the second surface 2b is 20% or less, the relationship between the adhesion rate of the release agent 3 to the first surface 2a and the adhesion rate of the release agent 3 to the second surface 2b can be arbitrarily set. Preferably, the adhesion rate of the release agent 3 to the first surface 2a is higher than the adhesion rate of the release agent 3 to the second surface 2b. As described above, after the release agent is adhered to the first surface 2a, the release agent on the first surface 2a is dried. Then, the release agent is adhered to the second surface 2b, and the release agent on the second surface 2b is dried. That is, two drying processes are performed on the release agent adhered to the first surface 2a. Therefore, even if the adhesion rate of the release agent 3 to the first surface 2a is higher than that to the second surface 2b, the release agent 3 on the first surface 2a can be sufficiently dried. In addition, by making the release agent 3 adhered to the second surface 2b thinner, the drying time required for the release agent 3 can be shortened. As a result, the processing time required for ceramic green sheets 2 can be shortened, and the production efficiency of ceramic green sheets 2 can be improved.

[0042] For example, after cutting the ceramic green sheet 2, multiple ceramic green sheets 2 are stacked and sintered. At this time, the multiple ceramic green sheets 2 are stacked in such a way that the first surface 2a, to which the release agent is relatively thickly attached, is in contact with the second surface 2b, to which the release agent is relatively thinly attached. As a result, after sintering, the ceramic green sheets 2 can be separated from each other more easily.

[0043] In addition, such as Figure 4As shown in (d), it is preferable to cut the ceramic green sheet 2 after applying the release agent 3 to the first surface 2a and the second surface 2b. If the ceramic green sheet 2 is cut using a cutter or the like, chips will be generated during the cutting process. When the release agent 3 is applied after cutting the ceramic green sheet 2, the surface of the ceramic green sheet 2 with chips is covered by the release agent 3. If the ceramic green sheet 2 is sintered in this state, the chips will adhere to the surface of the ceramic substrate 4 and will be difficult to remove. As a result, foreign matter defects on the ceramic substrate 4 are easily generated. When the ceramic green sheet 2 is cut after applying the release agent 3, the chips are placed on the release agent 3. That is, the chips do not directly contact the surface of the ceramic green sheet 2. After sintering, when removing the release agent from the surface of the ceramic substrate 4, the chips are also easily removed. Therefore, the generation of foreign matter defects on the ceramic substrate 4 can be suppressed.

[0044] In applying the release agent, rollers or brushes can be used instead of the spray gun. However, from the viewpoints of ease of controlling the amount of release agent and uniformity of the amount of release agent, spraying with a spray gun is preferred. For example, the spray gun moves horizontally back and forth in a direction perpendicular to the conveying direction of the ceramic green sheet 2. By spraying the release agent while moving back and forth, the release agent can be more evenly attached to the ceramic green sheet 2.

[0045] The amount of adhesive applied to the first surface 2a, the uniformity of the amount applied to the first surface 2a, the amount of adhesive applied to the second surface 2b, and the uniformity of the amount applied to the second surface 2b can be adjusted by controlling the reciprocating speed of the spray gun. As an example, a ceramic green sheet 2 with a width of 1000 mm is conveyed at a conveying speed of 1 cm / s. In this case, the release agent is sprayed while the spray gun reciprocates at a speed of 10 cm / s or more but less than 20 cm / s. The pressure of the spray gun is set to 0.1 MPa or more but less than 0.5 MPa.

[0046] Example (Examples 1-13, Comparative Examples 1-11) Two types of raw material powders are prepared as ceramics: silicon nitride powder and aluminum nitride powder. Magnesium oxide, hafnium oxide, and titanium oxide are added to the silicon nitride powder as sintering aids. Then, the raw material powder containing silicon nitride powder is mixed with acrylic resin and toluene to prepare a slurry. Yttrium oxide is added to the aluminum nitride powder as a sintering aid. Then, the raw material powder containing aluminum nitride powder is mixed with polyvinyl alcohol resin and toluene to prepare a slurry.

[0047] The prepared slurry was dried at 100°C and then formed into green sheets with the thicknesses shown in Table 1. In Table 1, green sheets using silicon nitride are listed as Si3N4. Green sheets using aluminum nitride are listed as AlN. In Examples 1-11, silicon nitride green sheets were prepared. In Examples 12 and 13, aluminum nitride green sheets were prepared.

[0048] As the releasing agent, a boron nitride slurry was prepared. The boron nitride slurry was produced by dispersing boron nitride powder and cellulose in water.

[0049] Next, an adhering step was performed. In Examples 1 to 13, the releasing agent was sprayed toward the first face 2a of the ceramic green sheet 2 so as to adhere the releasing agent to the first face 2a. The releasing agent was sprayed from above the ceramic green sheet 2 in a state in which the first face 2a faced upward. The spraying used a spray gun. The pressure of the spray gun was set to 0.15 MPa. While the releasing agent was being sprayed, the spray gun was moved horizontally back and forth in a direction at right angles to the transport direction of the ceramic green sheet 2. The ceramic green sheet 2 to which the releasing agent had been adhered was dried in the atmosphere at a temperature of 100°C.

[0050] The ceramic green sheet 2 was turned upside down, and the releasing agent was sprayed toward the second face 2b in a state in which the second face 2b faced upward. The conditions for spraying the second face 2b were set to be the same as the conditions for spraying the first face 2a. The ceramic green sheet 2 to which the releasing agent had been adhered was dried in the atmosphere at a temperature of 100°C.

[0051] The adhering of the releasing agent used two spray guns. One spray gun sprayed the releasing agent toward the first face 2a. The other spray gun sprayed the releasing agent toward the second face 2b. The ceramic green sheet of long dimensions was continuously fed into the apparatus for adhering the releasing agent, and the releasing agent was continuously adhered to the ceramic green sheet 2 using the two spray guns. At this time, the time from when the releasing agent was adhered to the first face 2a to when the releasing agent was adhered to the second face 2b was controlled by adjusting the positions of the two spray guns, the transport speed of the ceramic green sheet, and the like. In Table 1, this time is recorded as "interval". In Example 8, the interval was set to 5 minutes. In Example 7, the interval was set to 10 minutes. In Examples 1 to 5, 9, 10, and 12, the interval was set to 20 minutes. In Examples 6 and 11, the interval was set to 30 minutes.

[0052] After the releasing agent was adhered to the first face 2a and the second face 2b, a cutting step was performed. The ceramic green sheet was divided into five in the width direction. Also, the ceramic green sheet 20 of 4000 mm in length was divided. Here, the dimension of the ceramic green sheet in the transport direction is referred to as "length". The dimension of the ceramic green sheet 2 in a direction perpendicular to the transport direction is referred to as "width". The size of one ceramic green sheet after cutting was width 200 mm x length 200 mm. In each example, 100 pieces of the cut ceramic green sheet were obtained.

[0053] In Comparative Examples 1 to 11, boron nitride slurry was also attached to the ceramic green sheet as in the Examples. However, as shown in Table 1, in Comparative Examples 1 to 5, a release agent was attached before the ceramic green sheet was cut, in contrast to which, in Comparative Examples 6 to 11, a release agent was attached after the ceramic green sheet was cut. The size of the cut ceramic green sheet was the same as in the Examples, 200 mm in width x 200 mm in length. In addition, in Comparative Examples 1 to 6 and 9 to 11, the release agent was attached to both the first face 2a and the second face 2b of the ceramic green sheet (both faces), in contrast to which, in Comparative Examples 7 and 8, the release agent was attached to only the first face 2a of the ceramic green sheet (one face). In Comparative Examples 1 to 4 and 6, the interval was set to 20 minutes. In Comparative Examples 5 and 9 to 11, the interval was set to 35 minutes.

[0054] After the ceramic green sheet was cut, the first face 2a (front face) and the second face 2b (back face) of the ceramic green sheet to which boron nitride was attached were photographed. The images were subjected to binary processing using Image-J, and the attachment rate of boron nitride to the ceramic green sheet was calculated. In addition, the difference between the attachment rate of the first face 2a and the attachment rate of the second face 2b was calculated. In each of the Examples and Comparative Examples, 100 pieces of the ceramic green sheet were measured, and the average thereof was calculated. The results are shown in Table 2.

[0055] In Examples 1 to 11, the attachment rate of the first face 2a (front face), the attachment rate of the second face 2b (back face), and the difference between the attachment rate of the first face 2a and the attachment rate of the second face 2b were within the preferable ranges, respectively. On the other hand, in Comparative Examples 1 to 11, these values were outside the preferable ranges.

[0056] Next, the ceramic green sheet was arranged inside a sintering container made of boron nitride. The ceramic green sheet was placed in a state in which the first face 2a faced upward. The ceramic green sheet was heated at a temperature of 600°C or higher and 800°C or lower in a nitrogen atmosphere, whereby a debinding process was performed.

[0057] After the debinding process, a sintering process was performed. In the sintering process, the silicon nitride green sheet was sintered by heating at 1850°C for 10 hours in a nitrogen atmosphere. The aluminum nitride green sheet was sintered by heating at 1800°C for 5 hours in a nitrogen atmosphere.

[0058] Ten pieces of the ceramic green sheet were arranged in a stack inside the sintering container. In each of the Examples and Comparative Examples, the debinding process and the sintering process were repeated 10 times in order to process 100 pieces of the ceramic green sheet. Thus, in each of the Examples and Comparative Examples, 100 pieces of the ceramic substrate were obtained.

[0059] The sintered ceramic substrate was taken out of the sintering vessel, and the releasability was confirmed. In the case where the substrates were easily released from each other with a slight force, the ceramic substrate was regarded as a good product. In the case where the substrates were not easily released from each other and there were bonded portions, the ceramic substrate was regarded as a release failure. The failure rate was calculated in each of the examples and comparative examples.

[0060] The ceramic substrate after release was subjected to a sandblasting treatment to remove boron nitride. Then, the ceramic substrate was passed between two flat plates parallel to each other. The distance between the flat plates was set to 120% of the thickness of the ceramic substrate. The ceramic substrate that could pass between the flat plates was regarded as a good product. The ceramic substrate that could not pass between the flat plates was regarded as a warpage failure. The failure rate was calculated in each of the examples and comparative examples.

[0061] In addition, the surface of the ceramic substrate after release was confirmed using a magnifying glass, and the presence or absence of foreign matter such as cutting chips was investigated. The ceramic substrate in which foreign matter was not confirmed to be attached was regarded as a good product. The ceramic substrate in which foreign matter was confirmed to be attached was regarded as a foreign matter failure. The failure rate was calculated in each of the examples and comparative examples. The release failure rate, the warpage failure rate, and the foreign matter failure rate are shown in Table 2.

[0062] In Examples 1 to 11, the release failure rate, the warpage failure rate, and the foreign matter failure rate were low, and these failure rates were within the preferable ranges. This is because, by controlling the attachment rate of the release agent on the first face 2a, the attachment rate of the release agent on the second face 2b, and the interval of the attachment within the preferable ranges, respectively, the ceramic substrates were easily released from each other, and the generation of warpage of the ceramic substrates could be suppressed. In addition, in Examples 1 to 11, the ceramic green sheet was cut after the release agent was attached to both faces of the ceramic green sheet. Thus, it is considered that the generation of foreign matter failure could be suppressed by suppressing the direct attachment of cutting chips and the like to the surface of the green sheet.

[0063] On the other hand, in some of Comparative Examples 1 to 11, a large number of ceramic substrates were not released from each other, and release failure occurred. This is considered to be due to the fact that the attachment rate on the surface of the ceramic green sheet was not sufficient, and thus the releasability of the ceramic substrate was reduced.

[0064] In most of the ceramic substrates after sintering in Comparative Examples 1 to 11, warpage was large, and warpage failure was many. This is considered to be because the difference between the attachment rate of the release agent on the first face 2a and the attachment rate of the release agent on the second face 2b was large, or the interval of the attachment of the release agent was too long. It is considered that a difference between the state of the first face 2a and the state of the second face 2b was generated, and this became a cause of warpage of the ceramic substrate.

[0065] In some of Comparative Examples 1 to 11, a large number of foreign matter failures were confirmed on the surface of the ceramic substrate. This is considered to be because the ceramic green sheet was cut before the release agent was attached, and thus cutting chips and the like were attached to the surface of the green sheet.

[0066] The above describes the case where the ceramic green sheet is a silicon nitride green sheet or an aluminum nitride green sheet and the release agent is boron nitride using water as a solvent. However, the embodiments of the present application are not limited to this example. For example, the present application can also be applied to a case where an alumina release agent is attached to another ceramic green sheet such as alumina. In this case, the release agent is alumina that does not contain an additive and has been heat-treated at a high temperature. The composition of the alumina that does not contain an additive and has been heat-treated at a high temperature is different from the composition of the ceramic green sheet of alumina and can function as a release agent.

[0067] (Feature 1) A method of manufacturing a ceramic substrate, comprising: an attaching step of attaching a release agent to both surfaces of a ceramic green sheet having a first surface and a second surface; and a sintering step of stacking and sintering a plurality of the ceramic green sheets to which the release agent is attached, wherein in the ceramic green sheet after the attaching step, the attachment rate of the release agent to the first surface and the attachment rate of the release agent to the second surface are each 5% or more and 30% or less, the difference between the attachment rate of the release agent to the first surface and the attachment rate of the release agent to the second surface is 20% or less.

[0068] (Feature 2) The method of manufacturing a ceramic substrate according to Feature 1, wherein in the attaching step, the release agent is attached to the second surface within 30 minutes after the release agent is attached to the first surface.

[0069] (Feature 3) The method of manufacturing a ceramic substrate according to Feature 2, wherein the attachment rate of the release agent to the first surface is higher than the attachment rate of the release agent to the second surface.

[0070] (Feature 4) The method of manufacturing a ceramic substrate according to any one of Features 1 to 3, wherein after the attaching step, when the attachment rate of the release agent to each of four regions into which the first surface and the second surface are each divided is measured, the difference between the largest attachment rate and the smallest attachment rate of the first surface is 20% or less, and the difference between the largest attachment rate and the smallest attachment rate of the second surface is 20% or less.

[0071] (Feature 5) The method of manufacturing a ceramic substrate according to any one of Features 1 to 4, wherein after the attaching step, the method further comprises a cutting step of cutting the ceramic green sheet, In the sintering process, the cut ceramic green sheet is overlapped.

[0072] (Feature 6) The manufacturing method of the ceramic substrate according to any one of features 1 to 5, wherein the ceramic green sheet contains any one of silicon nitride, aluminum nitride, or aluminum oxide.

[0073] (Feature 7) The manufacturing method of the ceramic substrate according to any one of features 1 to 6, wherein the thickness of the ceramic green sheet is 1.0 mm or less.

[0074] Several embodiments of the present application are exemplified, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various ways, and various omissions, substitutions, changes, etc. can be made within the scope of the gist of the invention. Modified examples of these embodiments are included in the scope and gist of the invention, and are included in the invention recited in the claims and the equivalent thereof. In addition, each of the above-described embodiments can be implemented in combination with each other.

[0075] Explanation of Reference Signs 2... Ceramic green sheet 2a... First surface of ceramic green sheet 2b... Second surface of ceramic green sheet 3... Release agent 4... Ceramic substrate

Claims

1. A method for manufacturing a ceramic substrate, comprising the following steps: The adhesion process involves attaching a release agent to both sides of a ceramic green sheet having a first side and a second side; and In the sintering process, multiple ceramic green sheets coated with the release agent are overlapped and sintered. in, In the ceramic green sheet after the adhesion process, the adhesion rate of the release agent to the first surface and the adhesion rate of the release agent to the second surface are both 5% or more and 30% or less. The difference between the adhesion rate of the release agent to the first surface and the adhesion rate of the release agent to the second surface is less than 20%.

2. The method for manufacturing a ceramic substrate according to claim 1, wherein, In the attachment process, after the release agent is attached to the first surface, the release agent is attached to the second surface within 30 minutes.

3. The method for manufacturing a ceramic substrate according to claim 2, wherein, The adhesion rate of the release agent to the first surface is higher than the adhesion rate of the release agent to the second surface.

4. The method for manufacturing a ceramic substrate according to claim 1 or 2, wherein, After the adhesion process, when the first surface and the second surface are divided into four equal regions to measure the adhesion rate of the release agent to each region, the difference between the maximum and minimum adhesion rates of the first surface is less than 20%, and the difference between the maximum and minimum adhesion rates of the second surface is less than 20%.

5. The method for manufacturing a ceramic substrate according to claim 1 or 2, wherein, Following the attachment process, a cutting process is also performed to cut the ceramic green sheet. In the sintering process, the cut ceramic green sheets are overlapped.

6. The method for manufacturing a ceramic substrate according to claim 1 or 2, wherein, The ceramic green sheet comprises any one of silicon nitride, aluminum nitride, or aluminum oxide.

7. The method for manufacturing a ceramic substrate according to claim 1 or 2, wherein, The thickness of the ceramic green sheet is less than 1.0 mm.

Images