JP7603751B2 - Firing setter - Google Patents

Description

This specification discloses technology related to a firing setter. In particular, it discloses technology related to a firing setter having a coating layer on the substrate surface.

Patent Document 1 discloses a firing setter in which a coating layer is provided on the surface of a substrate. The coating layer is provided to prevent the substrate from reacting with the object to be fired. In Patent Document 1, two or more coating layers made of different materials are provided on the substrate surface to reliably prevent the substrate from reacting with the object to be fired. In Patent Document 1, a coating layer is formed by providing two or more spray coating layers, or a thermal spray layer on the surface of a spray coating layer. Patent Document 1 also provides a coating layer of 50 to 1000 μm on the substrate surface.

JP 2002-154884 A

As in Patent Document 1, by providing a coating layer of 50 to 1000 μm on the surface of the substrate, the reaction between the sintered object and the substrate can be sufficiently suppressed. However, if a coating layer of 50 μm or more is provided on the surface of the substrate, the heat capacity of the sintering setter increases, and the temperature tracking ability of the sintering setter decreases. In addition, since a coating layer of 50 μm or more is formed by spraying or thermal spraying, the raw material yield of the coating layer is poor (high cost). The above problem can be solved by making the coating layer thinner, but in that case, unevenness in the coating may occur, and the reaction between the sintered object and the substrate may not be reliably suppressed. In other words, in the past, in order to fulfill the function of the coating layer, it was acceptable to make the coating layer thick despite the increase in heat capacity. This specification provides a technology that realizes a sintering setter with a thin coating layer and good temperature tracking ability.

The firing setter disclosed in this specification may include a ceramic substrate and a coating layer covering the substrate surface, the coating layer having a thickness of 1 μm or more and 20 μm or less and a surface roughness Ra of 1 μm or less.

This specification also discloses a method for manufacturing a firing setter having a ceramic substrate and a coating layer that covers the substrate surface and has a coating thickness of 1 μm to 20 μm. The manufacturing method may include a step of printing a coating layer forming paste on the substrate surface and producing a molded body having a coating layer forming film on the substrate surface.

FIG. 2 is a perspective view of a baking setter according to the first embodiment. FIG. 2 is an enlarged view of the surface of the baking setter of the first embodiment. FIG. 2 shows an enlarged cross-sectional view of the baking setter of the first embodiment. FIG. 4 shows an enlarged view of the surface of a baking setter according to a second embodiment. FIG. 4 shows an enlarged cross-sectional view of a baking setter according to a second embodiment. FIG. 13 is an enlarged view of the surface of a baking setter according to a third embodiment. A summary of the experimental examples is given below.

The firing setter disclosed in this specification includes a substrate and a coating layer covering the substrate surface. The firing setter disclosed in this specification is preferably used in the manufacturing process (firing process) of ceramic electronic components (ceramic capacitors, etc.), although not particularly limited thereto. Examples of the shape of the firing setter include polygons such as triangles, squares, pentagons, and hexagons. The substrate is plate-shaped and made of ceramics. Examples of the substrate material include SiC, alumina, and mullite. In particular, SiC has good thermal conductivity, and the in-plane temperature of the coating layer surface (the surface on which the fired object is placed) tends to be uniform. An example of SiC is Si-SiC. "Si-SiC" means a material mainly composed of SiC particles, with metal Si being contained between the SiC particles. The thickness of the substrate may be, for example, 0.1 to 5 mm. The substrate of a firing setter refers to the part that is covered by the coating layer, and refers to the thickest part of the parts (substrate, coating layer) that make up the firing setter when the cross section of the firing setter is observed.

As described above, the coating layer is provided on the surface of the substrate and covers the substrate surface. The coating layer may have a coating thickness (thickness of the substrate surface) of 1 μm or more and 20 μm or less. The coating layer may be a single layer or a multilayer structure in which multiple layers are laminated. When the coating layer has a multilayer structure, the material of each layer can be changed to suppress deterioration of the coating layer due to, for example, a difference in thermal expansion coefficient. When the coating layer has a multilayer structure, the total thickness of the multiple layers may be 1 μm or more and 20 μm or less as described above. If the total thickness of the coating layer is 1 μm or more, it is possible to suppress contact between the substrate and the object to be baked, and it is possible to prevent the substrate and the object to be baked from reacting. If the total thickness of the coating layer is 20 μm or less, the heat capacity of the coating layer is reduced, and it is possible to suppress the deviation of the surface temperature of the coating layer (the temperature of the part in contact with the object to be baked) from the substrate temperature. In other words, if the total thickness of the coating layer is 20 μm or less, a firing setter with good temperature tracking properties can be realized. Also, if the coating thickness is 1 μm or more and 20 μm or less, when a SiC-based substrate with high thermal conductivity is used, it is possible to effectively suppress the effect of reduced thermal conductivity due to the oxide coating layer, which has a lower thermal conductivity than SiC.

The thickness (total thickness) of the coating layer can be obtained by taking an SEM image of the cross section (cross section near the surface) of the firing setter using a scanning electron microscope (SEM), measuring the film thickness of the coating layer at five points in the cross-sectional SEM image, and calculating the average of the measured values. The total thickness of the coating layer may be 2 μm or more, 4 μm or more, 6 μm or more, 8 μm or more, 10 μm or more, or 12 μm or more. The total thickness of the coating layer may be 18 μm or less, 16 μm or less, 14 μm or less, 12 μm or less, or 10 μm or less.

The coating layer may have a surface roughness Ra of 1 μm or less. If the surface roughness Ra is 1 μm or less, even if the coating layer is thin, the coating unevenness on the substrate surface can be suppressed. Such a thin coating layer with small surface roughness can be produced using a printing technique such as screen printing. Specifically, the coating layer can be produced by mixing raw material particles for forming the coating layer with an organic solvent to produce a coating layer forming paste, printing the coating layer forming paste on the substrate surface to produce a molded body (intermediate molded body), and then firing the molded body. When the coating layer is produced using a printing technique, the degree of freedom in the raw material size (particle size) is high. Therefore, in the printing method, fine raw materials that are difficult to use in spraying, thermal spraying, etc. can be used. By forming the coating layer using fine raw materials, a thin coating layer with small surface roughness can be formed. The surface roughness Ra of the coating layer may be 0.5 μm or less, or may be 0.2 μm or less. The lower limit of the surface roughness Ra is not particularly limited, but may be 0.05 μm or more. The surface roughness Ra of the coating layer can be measured by a stylus contact method.

The coating layer may have a thickness variation (in the case of a multi-layer structure, the variation in the total thickness) of 40% or less of the coating thickness and ±3 μm of the coating thickness. For example, when the coating layer has a thickness of 1 μm, the condition of "40% or less of the coating thickness" is substantially applied, and the coating layer may have a thickness of 1 ±0.4 μm. When the coating layer has a thickness of 20 μm, the condition of "±3 μm of the coating thickness" is substantially applied, and the coating layer may have a thickness of 20 ±3 μm. The thickness variation of the coating layer can be obtained by randomly selecting 10 locations on the coating layer, obtaining SEM images of the cross sections (cross sections near the surface), measuring the maximum and minimum coating thicknesses for each image, and calculating the ratio of the maximum and minimum coating thicknesses to the coating thickness for each image.

The coating layer may cover the entire substrate surface without gaps, or may cover the substrate surface with a portion of the substrate surface exposed. Specifically, the coating layer may include a plurality of coating pieces covering the substrate surface, and a gap may be provided between each coating piece. The gap between each coating piece may be 5 μm or more and 50 μm or less. If the gap between the coating pieces is 5 μm or more, the force caused by the difference in thermal expansion coefficient between the coating layer (coating piece) and the substrate can be suppressed from being applied to the coating layer. As a result, damage to the coating layer is suppressed, and the durability of the coating layer is improved. If the gap between the coating pieces is 50 μm or less, the sintered object and the substrate are prevented from coming into contact with each other, and the sintered object and the substrate are suppressed from reacting with each other. The gap between each coating piece may be 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, or 40 μm or more. The gap between each coating piece may be 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less. The gap between the coating pieces can be obtained by selecting multiple locations from a 250 μm x 200 μm area of a SEM observation sample (a sample for observing a cross section near the surface), obtaining an SEM image of the cross section (cross section near the surface), selecting and measuring 10 gaps from the obtained image, and calculating the average of the measured values.

By using the printing method described above, a coating layer having gaps between the coating pieces can be formed on the surface of the substrate. Furthermore, by using the printing method, coating pieces of any shape can be formed on the surface of the substrate, and coating pieces of a geometric pattern can be formed. The shape of the coating pieces is not particularly limited, but may be a circle or a polygon (triangle, square, pentagon, hexagon, etc.). Furthermore, by using the printing method, coating pieces can be formed at any position on the surface of the substrate. However, from the viewpoint of uniformly heating the object to be fired, it is preferable that the coating pieces appear regularly on the surface of the substrate. For example, each coating piece may be formed at equal intervals on the surface of the substrate, and the gaps between each coating piece may be uniform.

As described above, the coating layer may have a multilayer structure in which multiple layers are stacked. In this case, a coating piece (second coating piece) may be provided on the surface of the coating piece (first coating piece) provided on the substrate surface. A coating layer having gaps between the coating pieces can be obtained while having a multilayer structure. In this case, the spacing (size of the gap) between the first coating pieces and the spacing between the second coating pieces may be different. For example, the spacing between the second coating pieces may be larger than the spacing between the first coating pieces. The contact area between the coating layer (second coating layer) and the baked object can be reduced while suppressing the migration of substrate components to the coating layer (coating piece). A coating layer in which the spacing between the first coating pieces and the spacing between the second coating pieces are different can also be easily produced by using a printing method. In addition, third, fourth, ... nth coating pieces may be provided on the surface of the second coating piece.

The material of the coating layer can be appropriately selected according to the type of substrate material and the sintered _object . For example, the material of the coating layer (coating piece) may be _ZrO2 / _Y2O3 ( _Y2O3 stabilized _ZrO2 ), _ZrO2 / _CaO ( _CaO stabilized _ZrO2 ), _Y2O3 , _Al2O3 , MgO, mullite, etc., or _a mixture of these materials. In addition, when the coating layer has a multi-layer structure, the material of each layer may be different, for example, the first coating layer (coating piece) is mullite, and the second coating layer (coating piece) is _ZrO2 / _{Y2O3 .}

The porosity of the coating layer may be 5% or more and 50% or less. If the porosity is 5% or more, the gas generated from the fired object during firing passes through the coating layer, and the gas can be prevented from stagnation between the fired object and the coating layer. If the porosity is 50% or less, the strength of the coating layer is maintained and the durability of the firing setter is improved. The porosity of the coating layer may be 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, or 35% or more. The porosity of the coating layer may be 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, or 15% or less. The porosity of the coating layer can be measured in accordance with JIS R2205-1992.

(First embodiment)
The firing setter 10 will be described with reference to Figures 1 to 3. As shown in Figure 1, the firing setter 10 is flat and includes a SiC base material 2 and a coating layer 4 provided on the surface of the base material 2. The coating layer 4 has a two-layer structure and includes an intermediate layer 6 provided on the surface of the base material 2 and a surface layer 8 provided on the surface of the intermediate layer 6. The intermediate layer 6 and the surface layer 8 will be described in detail later.

2 and 3, the intermediate layer 6 covers the entire surface of the substrate 2. The material of the intermediate layer 6 is mullite. The intermediate layer 6 is formed on the surface of the substrate 2 by a printing method, and has a thickness T6 of approximately 1 μm. A surface layer 8 is provided on the surface of the intermediate layer 6. The material of the surface layer 8 is yttria. The surface layer 8 is composed of a plurality of coating pieces 8a. The coating pieces 8a are rectangular, and the gap G8 between each coating piece 8a is approximately 10 μm. The surface layer 8 (coating pieces 8a) is formed on the surface of the intermediate layer 6 by a printing method, and has a thickness T8 of approximately 1 μm. In addition, the surface roughness Ra of the surface of the coating layer 4 (surface of the surface layer 8) is suppressed to 1 μm or less.

The firing setter 10 has the coating layer 4 (middle layer 6, surface layer 8) formed by a printing method, so that a coating layer 4 that is thin and has a small surface roughness Ra can be easily realized. By making the coating layer 4 thin, the heat capacity of the coating layer 4 is reduced, and temperature variations within the surface of the firing setter 10 during firing are suppressed, improving the temperature tracking ability of the firing setter 10. In addition, since the surface layer 8 has multiple coating pieces 8a and gaps are provided between each coating piece 8a, the force caused by the difference in thermal expansion coefficient between the substrate 2 and the coating layer 4 is suppressed from being applied to the coating layer 4, and damage to the coating layer 4 is suppressed.

Below, we will explain modified examples (second and third examples) of the baking setter 10. In the baking setters 10a and 10b described below, the features common to the baking setter 10 will be given the same reference numbers as the baking setter 10, and explanations of these features may be omitted.

Second Example
The firing setter 10a will be described with reference to Figs. 4 and 5. In the firing setter 10a, the coating layer 4 has a three-layer structure, and includes an intermediate layer 6 provided on the surface of the substrate 2, a surface layer 8 provided on the surface of the intermediate layer, and an outermost layer 9 provided on the surface of the surface layer 8. The intermediate layer 6 is made of mullite, and the surface layer 8 and the outermost layer 9 are made of yttria. The outermost layer 9 is composed of a plurality of coating pieces 9a. The coating pieces 9a are rectangular, and one coating piece 9a is provided on the surface of one coating piece 8a. The size of the coating pieces 9a is smaller than the size of the coating pieces 8a. Therefore, the gap G9 between each coating piece 9a is larger than the gap G8 between each coating piece 8a. Specifically, the gap G9 is approximately 20 μm. The thickness of the outermost layer 9 (coating pieces 9a) is approximately 1 μm.

As shown in FIG. 5, when the object to be sintered 20 is placed on the sintering setter 10a, the object to be sintered 20 comes into contact with the outermost layer 9. As described above, the size of the coating piece 9a is smaller than the size of the coating piece 8a. Therefore, the sintering setter 10a can reduce the contact area between the object to be sintered 20 and the coating layer 4 compared to the sintering setter 10. By reducing the contact area between the object to be sintered 20 and the coating layer 4, gas generated from the object to be sintered during sintering is prevented from accumulating around the object to be sintered 20, and uneven sintering of the object to be sintered can be prevented.

(Third Example)
The firing setter 10b will be described with reference to FIG. 6. In the firing setter 10b, the coating layer 4 has a two-layer structure. The coating layer 4 includes an intermediate layer 6 that covers the entire surface of the substrate (see FIG. 1) and a surface layer 8 that is provided on the surface of the intermediate layer 6. The surface layer 8 is composed of a plurality of circular coating pieces 8a. The gap (shortest distance) G8 between each coating piece 8a is approximately 10 μm. That is, the firing setter 10b differs from the firing setter 10 in the shape of the coating pieces 8a that constitute the surface layer 8.

Other Embodiments
In the above examples, the firing setter in which the surface layer 8 and the outermost layer 9 are rectangular (first and second examples) and circular (third example) has been exemplified, but the surface layer 8 (outermost layer 9) may be polygonal, such as triangular, pentagonal, or hexagonal. Alternatively, the surface layer 8 (outermost layer 9) may cover the entire surface of the intermediate layer 6. That is, the surface layer 8 (outermost layer 9) may not be formed by a coating piece. In addition, in the firing setter 10b of the third example, the outermost layer 9 may be further provided on the surface of the surface layer 8, as in the firing setter 10a of the second example. When the outermost layer 9 is provided on the surface of the surface layer 8, the shape of the coating piece 8a of the surface layer 8 and the shape of the coating piece 9a of the outermost layer 9 may be different. In addition, three or more surface layers may be provided on the surface of the intermediate layer 6.

In the above embodiment, the intermediate layer 6 is provided on the surface of the substrate 2, but the intermediate layer 6 may be omitted. When the intermediate layer 6 is omitted, the surface layer 8 (outermost layer 9) may cover the entire surface of the substrate 2, or may be formed by multiple coating pieces.

(Experimental Example)
Setters 10 for firing (samples 1 to 4) with different configurations of the coating layer 4 were produced, and the in-plane temperature variation during heating and cooling of the setters 10 for firing was evaluated. The characteristics of each sample are shown in Figure 7. First, the manufacturing methods of samples 1 to 4 will be described.

For sample 1, first, mullite particles with a particle size (D50) of 0.5 μm were mixed with an organic solvent to prepare a mullite paste (paste for forming a coating layer). Next, the mullite paste was printed on the entire surface of a 150 mm x 150 mm x 1 mm SiC substrate with a thickness of 1 μm, and fired at 1300 ° C for 2 hours to prepare a mullite layer (intermediate layer) on the surface of the SiC substrate. Then, yttria particles with a particle size (D50) of 0.5 μm were mixed with an organic solvent to prepare an yttria paste. Then, the yttria paste was printed on the surface of the mullite layer with a thickness of 1 μm, and fired at 1350 ° C for 2 hours to prepare an yttria layer (surface layer) on the surface of the mullite layer. As a result, sample 1 having a coating layer of 2 μm (mullite layer 1 μm, yttria layer 1 μm) on the surface of the SiC substrate was obtained. The yttria layer was not printed on the entire surface of the mullite layer, but instead multiple rectangular pieces were printed with a gap of 10 μm between adjacent pieces. The surface roughness of the obtained sample was 0.5 μm.

Sample 2 was made using the same materials and manufacturing method as sample 1, except that the mullite layer was 5 μm thick and the yttria layer was 5 μm thick. The surface roughness of sample 2 was 0.2 μm.

For sample 3, mullite particles with a particle size (D50) of 70 μm were sprayed onto the entire surface of the SiC substrate to create a mullite layer of 50 μm on the surface of the SiC substrate. Then, yttria particles with a particle size (D50) of 20 μm were sprayed onto the entire surface of the mullite layer to create a 50 μm yttria layer (surface layer) on the surface of the mullite layer. The surface roughness of the resulting sample was 5 μm.

Sample 4 was made by spraying the mullite particles used in making Sample 1 (Sample 2) onto the entire surface of the SiC substrate in the same manner as Sample 3, and then spraying the yttria particles used in making Sample 1 (Sample 2) onto the entire surface of the mullite layer. However, in Sample 4, the particles (mullite particles, yttria particles) did not adhere sufficiently to the surface of the SiC substrate, and a stable coating layer could not be obtained. As mentioned above, the particles used in Samples 1 and 2 had a small particle size (D50) of 0.5 μm, and were too light to be repelled from the coating surface (surface of the SiC substrate), so it is presumed that the particles did not adhere sufficiently to the surface of the SiC substrate.

As mentioned above, a stable coating layer was not obtained for sample 4. Therefore, heating and cooling tests were performed on samples 1 to 3 to evaluate the in-plane temperature variation during heating and cooling of the firing setter 10. In the heating and cooling tests, each sample was placed in a heating furnace, the temperature inside the furnace was raised from room temperature to 1200°C at a rate of 600°C/min, and the temperature difference between both ends of the firing setter 10 when the temperature inside the furnace was 1200°C was measured. In addition, the temperature inside the furnace was lowered from 1200°C to room temperature at a rate of 600°C/min, and the temperature difference between both ends of the firing setter 10 when the temperature inside the furnace reached room temperature was measured. The results are shown in Figure 7.

As shown in FIG. 7, it was confirmed that the temperature variation within the surface of the firing setter 10 was small for samples 1 and 2, which have a thin coating layer (20 μm or less), both during heating and cooling (temperature difference less than 15°C during heating, temperature difference less than 10°C during cooling). In contrast, it was confirmed that the temperature variation within the surface of the firing setter 10 was large for sample 3, which has a thick coating layer (more than 20 μm), both during heating and cooling (temperature difference 15°C or more during heating, temperature difference 10°C or more during cooling). This result shows that the coating layer of samples 1 and 2 is thinner than that of sample 3, so the heat capacity of the coating layer is smaller and the temperature of the coating layer follows the temperature inside the furnace well. The surface roughness Ra of samples 1 and 2 is smaller than that of sample 3. This result reflects the difference in the particle size of the raw material particles used. That is, in samples 1 and 2, the particle size of the raw material particles is small, so the surface roughness Ra of the coating layer is small (1 μm or less). In other words, the thickness of the coating layer can be made thin by forming the coating layer using raw material with a particle size that results in a surface roughness Ra of 1 μm or less.

Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exert technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful.

2: Substrate 4: Coating layer 10: Setter for firing

Claims (15)

A ceramic substrate;
A coating layer that coats the substrate surface, has a coating thickness of 1 μm or more and 20 μm or less, and has a surface roughness Ra of 1 μm or less,
A firing setter in which the thickness variation of the coating layer is 40% or less of the coating thickness and is within ±3 μm of the coating thickness. the coating layer includes a plurality of coating strips covering a substrate surface;
2. The firing setter according to claim 1, wherein a gap of 5 μm to 50 μm is provided between each of the coating pieces. The firing setter according to claim 2, in which the coating pieces are of a predetermined circular or polygonal shape and appear regularly on the surface of the substrate. 4. The firing setter according to any one of claims 1 to 3 , wherein the material of the coating layer comprises _{ZrO2 / Y2O3 , ZrO2} / _CaO , _Y2O3 , _Al2O3 , MgO, mullite, or a mixture of these materials. 5. The firing setter according to claim 1 , wherein the material of the substrate is SiC. 6. The setter for firing according to claim 1 , wherein the coating layer has a multi-layer structure having two or more layers. 7. The setter for firing according to claim 1 , wherein the coating layer has a porosity of 5% or more and 50% or less. A method for producing a firing setter having a ceramic substrate and a coating layer that coats the substrate surface and has a coating thickness of 1 μm or more and 20 μm or less, comprising the steps of:
a step of printing a paste for forming a coating layer on the surface of the substrate so that the thickness variation of the coating layer is 40% or less of the coating thickness and is within ±3 μm of the coating thickness, thereby producing a molded body having a coating film for forming a coating layer provided on the surface of the substrate. A ceramic substrate;
A coating layer that coats the substrate surface, has a coating thickness of 1 μm or more and 20 μm or less, and has a surface roughness Ra of 1 μm or less,
the coating layer includes a plurality of coating strips covering a substrate surface;
A firing setter in which gaps of 5 μm or more and 50 μm or less are provided between each of the coating pieces. 10. The firing setter according to claim 9 , wherein the coating pieces have a predetermined circular or polygonal shape and appear regularly on the surface of the substrate. A second piece of coating is provided on a surface of each piece of coating;
11. The bake setter of claim 10 , wherein the spacing between the coated pieces is different from the spacing between the second coated pieces. 12. The firing setter according to any one of claims 9 to 11 , wherein the material of the coating layer comprises _{ZrO2 / Y2O3 , ZrO2} / _CaO , _Y2O3 , _Al2O3 , MgO, mullite, or a mixture of these materials. 13. The setter for firing according to claim 9 , wherein the material of the substrate is SiC. 14. The setter for firing according to claim 9 , wherein the coating layer has a multi-layer structure having two or more layers. 15. The setter for firing according to claim 9 , wherein the coating layer has a porosity of 5% or more and 50% or less.

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