Ceramic plate and manufacturing method thereof, circuit board, and power module

Abstract

To provide a ceramic plate having through holes for screw fastening and sufficient strength, and a method for manufacturing the same.SOLUTION: Thee is provided a ceramic plate having through holes H penetrating in a direction perpendicular to the main surface, with the length of cracks per unit area on the inner wall surface of the through holes H being 0.01 (μm / μm2) or less. There is also provided a method for manufacturing a ceramic plate, which includes a step of forming the through holes H in a direction perpendicular to the main surface of a ceramic sintered body using fiber laser light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a ceramic plate and a manufacturing method thereof, a circuit board, and a power module. [Background technology]

[0002] Circuit boards mounted on electronic devices are produced by joining a metal plate to an insulating ceramic plate via a brazing material. Circuit boards are sometimes produced using ceramic plates with through holes. Patent Document 1 discloses a method for processing ceramic plates using a carbon dioxide laser to form through holes with high dimensional accuracy. Patent Document 2 discloses a method for processing ceramic plates using a mold and a laser in combination to form through holes with high dimensional accuracy and high processing speed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 59-045088 [Patent Document 2] Japanese Patent Application Publication No. 3-248792 Summary of the Invention [Problem to be solved by the invention]

[0004] Providing through holes in a circuit board including a ceramic plate allows for smooth screw fastening when mounting the board to an electronic component such as a power module. However, because a large force is applied to the ceramic plate when the screw fastening is performed, there is a concern that the ceramic plate may be damaged by the screw fastening if the ceramic plate does not have sufficient strength. Therefore, the present disclosure provides a ceramic plate having through holes for screw fastening and capable of suppressing damage when screwed, and a method for manufacturing the same. The present disclosure also provides a circuit board having through holes for screw fastening and capable of suppressing damage when screwed, and a power module including such a circuit board. [Means for solving the problem]

[0005] One aspect of the present disclosure provides the following ceramic plate.

[0006] [1] A through hole H is formed through the main surface in a direction perpendicular to the main surface, and the length of the crack per unit area on the inner wall surface of the through hole H is 0.01 (μm / μm 2 ) or less, ceramic plate.

[0007] The ceramic plate described in [1] above has sufficiently small cracks per unit area on the inner wall surface of the through hole. Even though the ceramic plate has a through hole, it has sufficient strength to withstand screw fastening. Therefore, breakage of the ceramic plate during screw fastening can be suppressed.

[0008] The ceramic substrate of the above [1] may be any one of the following [2] to [5].

[0009] [2] In a cross section passing through the center line of the through hole H and along a direction perpendicular to the main surface, The first opening edge C1 of the through hole H is larger than the second opening edge C2, a first imaginary straight line L1 that passes through the first opening edge C1 and is parallel to the center line; The ceramic plate according to [1], wherein an angle θ formed between a portion n of the inner wall surface closest to the center line and a second imaginary line L2 connecting the first opening edge C1 and the portion n is 10° or less. [3] The ceramic plate according to [2], wherein the shortest distance between the first virtual straight line L1 and the portion n is 30 μm or less.

[0010] In the ceramic plate of [2] or [3] above, the inner wall surface of the through hole is formed at an angle close to a right angle to the main surface, and the inner wall surface has high linearity. Therefore, when screwing, the screw can be smoothly inserted into the through hole, and damage to the ceramic plate can be further suppressed.

[0011] [4] The ceramic plate according to any one of [1] to [3], wherein the arithmetic mean roughness of the inner wall surface is 4.0 μm or less. [5] The ceramic plate according to any one of [1] to [4], wherein the maximum roughness of the inner wall surface is 18.0 μm or less.

[0012] The ceramic plate of [4] or [5] above has a smooth inner wall surface of the through hole, which allows the screw to be inserted smoothly into the through hole when fastening the screw, further reducing damage to the ceramic plate.

[0013] One aspect of the present disclosure provides the following method for manufacturing a ceramic plate.

[0014] [6] A method for manufacturing a ceramic plate, comprising the step of forming a through hole H in a direction perpendicular to a main surface of a ceramic sintered body using a fiber laser beam.

[0015] The method for manufacturing a ceramic plate according to [6] above includes a step of irradiating a main surface of a ceramic sintered body with fiber laser light to form a through hole H. Fiber laser light has a high power density and a small pulse width, so it reduces the thermal effect on the inner wall surface compared to carbon dioxide laser light, and can suppress the occurrence of cracks on the inner wall surface. Therefore, it is possible to obtain a ceramic plate having a through hole and capable of suppressing breakage when screwed.

[0016] The method for producing a ceramic substrate according to the above item [6] may be any one of the following items [7] to [9].

[0017] [7] The method for manufacturing a ceramic plate according to [6], wherein the frequency of the fiber laser light is 100 kHz or more.

[0018] In the method for manufacturing a ceramic plate described in [7] above, the high frequency of the fiber laser light allows the pulse width to be reduced, further reducing the thermal impact on the inner wall surface. This further reduces the occurrence of cracks on the inner wall surface. Therefore, a ceramic plate having a through hole and capable of further reducing breakage during screw fastening can be obtained.

[0019] [8] The method for manufacturing a ceramic plate according to [6] or [7], wherein the output of the fiber laser light is 100 W or less.

[0020] The ceramic plate manufacturing method [8] above uses a low output of fiber laser light, which further reduces the heat effect on the inner wall surface. This further reduces the occurrence of cracks on the inner wall surface. Therefore, it is possible to obtain a ceramic plate with through holes that can further reduce breakage during screw fastening.

[0021] [9] The method for manufacturing a ceramic plate according to any one of [6] to [8], wherein in the step of forming the through holes H, the scanning speed of the fiber laser light is 50 mm / sec or more.

[0022] The method for manufacturing a ceramic plate described in [9] above uses a fast scanning speed of the fiber laser beam, which further reduces the heat influence on the inner wall surface. This further reduces the occurrence of cracks on the inner wall surface. Therefore, a ceramic plate having a through hole and capable of further reducing breakage during screw fastening can be obtained.

[0023] One aspect of the present disclosure provides the following circuit board.

[0024]

[10] A ceramic plate according to any one of the above [1] to [5] or a ceramic plate obtained by the manufacturing method according to any one of the above [6] to [9]; a metal plate joined to the ceramic plate and having a through hole H1; The circuit board has a through hole E formed by connecting at least the through hole H and the through hole H1 in a direction perpendicular to the main surface of the ceramic plate.

[0025] The circuit board of

[10] above includes a ceramic board according to any one of [1] to [5] or a ceramic board obtained by the manufacturing method according to any one of [6] to [9] above. The circuit board also has a through hole E formed by connecting a through hole H1 formed in the metal plate with a through hole H formed in the ceramic plate. Despite the through hole, this circuit board has sufficient strength to withstand screw fastening. Therefore, damage to the circuit board during screw fastening can be suppressed.

[0026] One aspect of the present disclosure provides the following power module.

[0027]

[11] A power module comprising the circuit board described in

[10] above.

[0028] The power module of

[11] above can suppress damage to the circuit board and ceramic plate even when fastened with screws, thereby improving the reliability and performance of the power module. [Effects of the Invention]

[0029] The present disclosure can provide a ceramic plate having through holes for screwing and capable of suppressing breakage during screwing, a method for manufacturing the same, a circuit board having through holes for screwing and capable of suppressing breakage during screwing, and a power module including such a circuit board. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a perspective view showing an example of a ceramic plate. [Figure 2] FIG. 2 is a cross-sectional view showing a part of a cross section taken along line II-II in FIG. [Figure 3]Fig. 3(a) is a perspective view showing an example of a circuit board, and Fig. 3(b) is a cross-sectional view taken along line IIIb-IIIb in Fig. 3(a). [Figure 4] FIG. 4 is a perspective view showing an example of a bonded body. [Figure 5] FIG. 5 is a perspective view showing an example of a bonded body on which an etching resist is printed. [Figure 6] Fig. 6(a) is a perspective view showing an example of the bonded body after etching, and Fig. 6(b) is a cross-sectional view taken along line VIb-VIb in Fig. 6(a). [Figure 7] FIG. 7 is a perspective view showing an example of an aggregate circuit board. [Figure 8] Fig. 8(a) is a photograph of the inner wall surface of the ceramic plate in Example 1 observed with an SEM (magnification: 500x), and Fig. 8(b) is a photograph of the cross section of the ceramic plate in Example 1 observed with an SEM (magnification: 250x). [Figure 9] 9(a) is a photograph of the inner wall surface of the ceramic plate in Example 2 observed with an SEM (magnification: 500x), and FIG. 9(b) is a photograph of the cross section of the ceramic plate in Example 2 observed with an SEM (magnification: 250x). [Figure 10] Fig. 10(a) is a photograph of the inner wall surface of the ceramic plate in Example 3 observed with an SEM (magnification: 500x), and Fig. 10(b) is a photograph of the cross section of the ceramic plate in Example 3 observed with an SEM (magnification: 250x). [Figure 11] Fig. 11(a) is a photograph of the inner wall surface of the ceramic plate in Comparative Example 1 observed with an SEM (magnification: 500x), and Fig. 11(b) is a photograph of the cross section of the ceramic plate in Comparative Example 1 observed with an SEM (magnification: 250x). [Figure 12] FIG. 12 is a photograph of the inner wall surface of the ceramic plate in Comparative Example 2 observed with an SEM (magnification: 500 times). DETAILED DESCRIPTION OF THE INVENTION

[0031] Embodiments of the present disclosure are described below. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The upper or lower limit of a numerical range specified in this disclosure may be replaced with any value shown in the examples. Furthermore, individually stated upper and lower limit values ​​may be arbitrarily combined. The symbol "~" used in a numerical range indicates a numerical range that includes the upper and lower limit values. For example, "X~Y" indicates a numerical range "greater than or equal to X and less than or equal to Y." Unless otherwise specified, the materials or components exemplified in this disclosure can be used alone or in combination of two or more types. Furthermore, the dimensional ratios of each element in the drawings are not limited to those shown.

[0032] [Ceramic plate] FIG. 1 is a perspective view showing an example of a ceramic plate according to one embodiment. The ceramic plate 100 shown in FIG. 1 is, for example, a silicon nitride plate or an aluminum nitride plate. The ceramic plate 100 has a flat plate shape. The ceramic plate 100 has a first main surface 100A and a second main surface 100B on the opposite side. A through hole H for screwing is provided in the ceramic plate 100, penetrating in a direction perpendicular to the first main surface 100A and the second main surface 100B. The through hole H also has a first opening edge C1 on the first main surface 100A.

[0033] 1, the through hole H is formed in the center of the first main surface 100A of the ceramic plate 100, but the position of the through hole H is not limited to the center of the first main surface 100A. The ceramic plate 100 may have a plurality of through holes H. The shape of the first opening edge C1 may be circular.

[0034] The maximum length between two points on the first opening edge C1 may be 2 mm or more, 5 mm or more, or 10 mm or more from the viewpoint of smooth screw insertion. Also, the maximum length between two points on the first opening edge C1 may be 20 mm or less, 15 mm or less, or 10 mm or less from the viewpoint of improving processing efficiency. The maximum length between two points on the first opening edge C1 may be, for example, 2 to 20 mm.

[0035] The area of ​​the portion of the through hole H surrounded by the first opening edge C1 is set to 3 mm from the viewpoint of smooth screw insertion. 2 Over 20mm 2 or more, or 80 mm 2 In addition, the area of ​​the portion of the through hole H surrounded by the first opening edge C1 may be 320 mm 2 Below, 180mm 2 or less, or 80 mm 2 The area of ​​the through hole H formed by the first opening edge C1 may be, for example, 3 to 320 mm 2 may be.

[0036] The thickness of the ceramic plate 100 may be, for example, 0.2 to 2.0 mm, or 0.3 to 1.5 mm. When the thickness is in this range, the ceramic plate 100 can be suitably used as a component of a circuit board.

[0037] 2 is an enlarged cross-sectional view of a portion of the cross section taken along line II-II in FIG. 2. FIG. 2 is obtained by cutting the ceramic plate 100 along a direction perpendicular to the first and second main surfaces 100A and 100B, passing through the center line X of the through hole H. The center line X of the through hole H is perpendicular to the first and second main surfaces 100A and 100B of the ceramic plate 100. As shown in FIG. 2, the ceramic plate 100 has a second opening edge C2 at the portion where the through hole H intersects with the second main surface 100B, which is opposite the first main surface 100A. The area of ​​the portion surrounded by the first opening edge C1 is larger than the area of ​​the portion surrounded by the second opening edge C2. The second opening edge C2 may also be circular.

[0038] The crack length per unit area on the inner wall surface W of the through hole H is 0.01 (μm / μm 2 ) or less. This improves the strength of the ceramic plate 100, and prevents breakage of the ceramic plate 100 due to screw fastening. From the viewpoint of further preventing breakage of the ceramic plate 100, the length of the crack per unit area on the inner wall surface W of the through hole H is set to 0.008 (μm / μm 2 ) or less, 0.007(μm / μm 2 ) or less, 0.005(μm / μm 2) or less, or 0.003(μm / μm 2 ) or less. It is acceptable that no cracks are observed on the inner wall surface W of the through hole H, and the length of the cracks per unit area on the inner wall surface W is 0 (μm / μm 2 ) or more.

[0039] Cracks on the inner wall surface W of the through hole H can be confirmed in an SEM photograph of the inner wall surface W, which is observed at 500x magnification using an SEM. The SEM can be, for example, a "tabletop microscope" (product name: TM4000Plus, manufactured by Hitachi High-Tech Corporation). In the SEM photograph, cracks are detected if the maximum length of the straight lines connecting the endpoints of the black lines is 20 μm or more, and the total length of the cracks included in the field of view is calculated. If the black line branches, the length of the straight lines from the branching points to each endpoint is taken as the crack length. In this way, the crack length per unit area can be calculated. The maximum crack length can be measured visually using a scale bar or by image analysis.

[0040] In FIG. 2 , the angle θ between a first imaginary line L1 that passes through the first opening edge C1, which is larger than the second opening edge C2, and is parallel to the center line X, and a second imaginary line L2 that connects the first opening edge C1 and a portion n of the inner wall surface W that is closest to the center line X, may be 10° or less. When the angle θ is 10° or less, the inner wall surface W is formed at an angle close to a right angle with respect to the main surface, thereby improving the linearity of the inner wall surface W. Therefore, the screw can be smoothly inserted into the through hole H during screw fastening, and damage to the ceramic plate 100 during screw fastening can be further suppressed. From the viewpoint of further suppressing damage to the ceramic plate, the angle θ may be 7° or less, 6° or less, or 5° or less. Furthermore, from the viewpoint of reducing costs, the angle θ may be 1° or more, 2° or more, or 3° or more. For example, the angle θ may be in the range of 1 to 10°. The angle θ can be calculated by visual inspection or image analysis on a SEM photograph of the cross section.

[0041] From the viewpoint of further increasing the linearity of the inner wall surface W and further suppressing breakage of the ceramic plate 100 when screwed, the shortest distance between the first imaginary line L1 and the portion n may be 30 μm or less, or 25 μm or less. The shortest distance between the first imaginary line L1 and the portion n means the length of a perpendicular line drawn from the portion n to the first imaginary line L1. The shortest distance between the first imaginary line L1 and the portion n may be 10 μm or more. The shortest distance between the first imaginary line L1 and the portion n may be in the range of 10 to 30 μm. The shortest distance between the first imaginary line L1 and the portion n can be calculated by visual inspection or image analysis using an SEM image of the cross section.

[0042] The arithmetic mean roughness of the inner wall surface W of the through hole H may be 4.0 μm or less. With an arithmetic mean roughness of 4.0 μm or less, the surface of the inner wall surface W becomes smooth, allowing screws to be inserted smoothly into the through hole H. This further reduces damage to the ceramic plate 100 when screwed. From the viewpoint of further smoothing the surface of the inner wall surface W and further reducing damage to the ceramic plate 100 when screwed, the arithmetic mean roughness of the inner wall surface W of the through hole H may be 3.0 μm or less, 2.0 μm or less, 1.0 μm or less, or 0.6 μm or less. From the viewpoint of improving processing efficiency, the arithmetic mean roughness may be 0.1 μm or more. The arithmetic mean roughness of the inner wall surface W may be in the range of, for example, 0.1 to 4.0 μm.

[0043] The maximum roughness of the inner wall surface W of the through hole H may be 18.0 μm or less. A maximum roughness of 18.0 μm or less makes the surface of the inner wall surface W smooth, allowing screws to be inserted smoothly into the through hole H. This further reduces damage to the ceramic plate 100 when screwed. From the viewpoint of further smoothing the surface of the inner wall surface W and further reducing damage to the ceramic plate 100 when screwed, the maximum roughness of the inner wall surface W of the through hole H may be 15.0 μm or less, 12.0 μm or less, 10.0 μm or less, 8.0 μm or less, or 7.0 μm or less. From the viewpoint of improving processing efficiency, the maximum roughness may be 2.0 μm or more. The maximum roughness of the inner wall surface W may be in the range of, for example, 2.0 to 18.0 μm.

[0044] The arithmetic mean roughness and maximum roughness can be calculated by image analysis of an image of the inner wall surface of the through hole H observed with a microscope. The microscope may be, for example, a "digital microscope" (product name: VHX-8000, manufactured by Keyence Corporation). In this disclosure, the arithmetic mean roughness refers to the arithmetic mean roughness Ra defined in JIS B 0601:2013. Furthermore, in this disclosure, the maximum roughness refers to the maximum height roughness Rz defined in JIS B 0601:2013.

[0045] [Method of manufacturing ceramic plates] An example of a method for manufacturing the ceramic plate 100 is described below. First, a ceramic sintered body containing a ceramic material (e.g., silicon nitride powder or aluminum nitride powder) is prepared. The ceramic sintered body can be manufactured, for example, by the following procedure. First, a slurry containing silicon nitride powder or aluminum nitride powder, a binder resin, a sintering aid, a plasticizer, a dispersant, a solvent, etc. is molded to obtain a green sheet. Examples of sintering aids include rare earth metals, alkaline earth metals, metal oxides, fluorides, chlorides, nitrates, and sulfates. These may be used alone or in combination. The use of a sintering aid can promote sintering of the inorganic compound powder. Examples of binder resins include methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and (meth)acrylic resins.

[0046] Examples of plasticizers include purified glycerin, glycerin trioleate, diethylene glycol, phthalate-based plasticizers such as di-n-butyl phthalate, and dibasic acid-based plasticizers such as di-2-ethylhexyl sebacate. Examples of dispersants include poly(meth)acrylates and (meth)acrylic acid-maleate copolymers. Examples of solvents include organic solvents such as ethanol and toluene.

[0047] Examples of methods for forming the slurry include the doctor blade method and extrusion molding. A green sheet is produced by such a method. The green sheet is then degreased and sintered to obtain a substrate containing silicon nitride or aluminum nitride. Degreasing may be performed, for example, by heating the green sheet at 400 to 800°C for 0.5 to 20 hours. This can reduce the amount of residual organic matter (carbon) while suppressing oxidation and deterioration of the silicon nitride or aluminum nitride. Sintering may be performed by heating the green sheet at 1700 to 1900°C in a non-oxidizing gas atmosphere such as nitrogen, argon, ammonia, or hydrogen.

[0048] The above-mentioned degreasing and sintering may be performed with a plurality of green sheets stacked together. When the degreasing and sintering are performed with the green sheets stacked together, a release layer made of a release agent may be provided between the green sheets to facilitate separation of the sheets after firing. As the release agent, for example, boron nitride (BN) can be used. The release layer may be formed by applying a slurry of boron nitride powder by spraying, brushing, roll coating, screen printing, or other methods. The number of green sheets to be stacked may be, for example, 10 to 100 sheets, or 20 to 80 sheets, from the viewpoint of efficiently mass-producing ceramic sintered bodies while sufficiently progressing degreasing. A ceramic sintered body can be obtained by this procedure. The ceramic sintered body may be in the form of a plate.

[0049] The method for manufacturing the ceramic plate 100 includes a step of forming a through hole H in a direction perpendicular to the main surface of the ceramic sintered body using a fiber laser beam. The fiber laser beam may include near-infrared light having a wavelength of 800 to 2500 nm. Compared to a carbon dioxide laser beam, the fiber laser beam has a higher power density and a smaller pulse width, and therefore the thermal effect on the inner wall surface when forming the through hole H in the ceramic sintered body is small. Therefore, it is possible to suppress the occurrence of cracks on the inner wall surface of the through hole H. As an irradiation device for the fiber laser beam, for example, an "ultra-short pulse laser processing unit" (product name: TLFD-100P, manufactured by Takei Electric Co., Ltd.) can be used.

[0050] The frequency of the fiber laser light may be 100 kHz or more, 250 kHz or more, or 400 kHz or more. When the frequency of the fiber laser light is within the above range, the pulse width of the laser irradiated onto the ceramic sintered body can be further reduced, and the influence of heat imparted to the inner wall surface W of the through hole H can be further suppressed. This makes it possible to further suppress the occurrence of cracks on the inner wall surface W of the through hole H. Furthermore, when the frequency is within the above range, heat can be applied with high uniformity over the entire area of ​​the inner wall surface W of the through hole H, thereby improving the linearity of the inner wall surface W. Therefore, it is possible to obtain a ceramic plate 100 that can further suppress breakage during screw fastening.

[0051] From the viewpoint of reducing manufacturing costs, the frequency of the fiber laser light may be 5000 kHz or less, 4000 kHz or less, 3000 kHz or less, or 2000 kHz or less. The frequency of the fiber laser light may be in the range of 100 to 5000 kHz, for example.

[0052] The output of the fiber laser beam may be 100 W or less, 80 W or less, or 60 W or less. By setting the output of the fiber laser beam within the above range, the influence of heat on the inner wall surface W of the through hole H can be further suppressed. This makes it possible to further suppress the occurrence of cracks on the inner wall surface W of the through hole H. From the viewpoint of improving manufacturing efficiency, the output of the fiber laser beam may be 10 W or more, 20 W or more, or 30 W or more. The output of the fiber laser beam may be in the range of 10 to 100 W, for example.

[0053] The through hole H can be formed by moving the fiber laser beam relative to the ceramic sintered body. The scanning speed of the fiber laser beam may be 50 mm / sec or more, 100 mm / sec or more, 250 mm / sec or more, 500 mm / sec or more, or 750 mm / sec or more. When the scanning speed of the fiber laser beam is within the above range, the processing speed is improved, and the influence of heat imparted to the inner wall surface W of the through hole H can be further suppressed. This can further suppress the occurrence of cracks on the inner wall surface W of the through hole H. Furthermore, from the viewpoint of applying heat with high uniformity over the entire inner wall surface W and improving the linearity of the inner wall surface W, the scanning speed of the fiber laser beam may be 5,000 mm / sec or less, 4,000 mm / sec or less, 3,000 mm / sec or less, or 2,000 mm / sec or less. The scanning speed of the fiber laser beam may be in the range of, for example, 50 to 5,000 mm / sec.

[0054] The hole diameter of the portion irradiated with the fiber laser light may be 10 μm or less, 8 μm or less, or 5 μm or less. When the hole diameter of the irradiated portion is within the above range, the power density of the fiber laser light is increased, and the influence of heat imparted to the inner wall surface W of the through hole H can be further suppressed. This makes it possible to further suppress the occurrence of cracks on the inner wall surface W of the through hole H. From the viewpoint of reducing manufacturing costs, the hole diameter of the portion irradiated with the fiber laser light may be 1 μm or more, or 2 μm or more.

[0055] [Circuit board] FIG. 3(a) is a perspective view showing an example of a circuit board according to an embodiment. The circuit board 150 has a pair of conductors 170, 172 arranged facing each other on the ceramic plate 100. FIG. 3(b) is a cross-sectional view taken along line IIIb-IIIb in FIG. 3(a). The circuit board 150 has a through hole E that is perpendicular to the main surface and penetrates the conductors 170, 172 and the ceramic plate 100. As shown in FIG. 3(b), the through hole E is formed by connecting the through hole H in the ceramic plate 100, the through hole H1 in the conductor 170, and the through hole H2 in the conductor 172. The through hole E is preferably formed so that the center lines of the through hole H, the through holes H1, and the through holes H2 overlap. The area formed by the third opening edge M1 on the main surface of the conductor 170 may be larger than the area formed by the first opening edge C1 in the ceramic plate 100. If the area defined by the third opening edge M1 is larger than that of the first opening edge C1, the conductors 170 and 172 are more likely to be insulated by the ceramic plate, and electrical conduction between the conductors 170 and 172 can be suppressed.

[0056] The conductors 170, 172 are joined to the ceramic plate 100. Examples of the conductors 170, 172 include metal plates such as copper plates. A solder paste can be used for joining. The ceramic plate 100 and the conductors 170, 172 may have the same shape and size or may differ from each other. The thickness of the metal plate 120 may be, for example, 0.2 to 2.0 mm, or 0.3 to 1.5 mm.

[0057] The through holes E can be formed by etching the metal plate 120 according to the following procedure. First, a ceramic substrate 110 without through holes H and a metal plate 120 are bonded together to produce a bonded body 140 as shown in FIG. 4. Scribe lines SL1 and SL2 for dividing the ceramic substrate 110 into circuit boards are formed on the ceramic substrate 110. The scribe lines SL1 and SL2 may be formed on one main surface of the ceramic substrate 110, or on each of the pair of main surfaces. As shown in FIG. 5, an etching resist Er is applied to the bonded body 140 so as to surround the portion where the through holes H1 (H2) will be formed. Then, the portion where the etching resist Er is not applied is removed using an etching solution. As a result, as shown in FIG. 6(a), a conductor portion 170 (172) having a through hole H1 (H2) is formed at each position defined by the scribe lines SL1 and SL2. The metal plate 120, such as a copper plate, has a high reflectivity for fiber laser light. Therefore, by performing the etching described above, productivity can be further improved compared to directly processing the metal plate 120 with a fiber laser beam. Figure 6(b) shows a cross-sectional view of Figure 6(a) taken along line VIb-VIb. As shown in Figure 6(b), the through-hole H1 (H2) does not penetrate the ceramic substrate 110.

[0058] Next, the ceramic substrate 110 exposed inside the through hole H1 shown in FIG. 6(b) is irradiated with fiber laser light to form a ceramic plate 100 having a through hole H. As a result, the through hole H1 (H2) and the through hole H are formed so as to be continuous with each other, and an aggregate circuit substrate 200 having a through hole E as shown in FIG. 7 can be obtained. By dividing the aggregate circuit substrate 200 along the scribe lines SL1 and SL2, a circuit substrate 150 having a through hole E as shown in FIGS. 3(a) and 3(b) can be obtained. In this way, by etching the metal plate 120 to form the through hole H1 (H2), and then forming the ceramic plate 100 having the through hole H using fiber laser light, the through hole E can be formed with high dimensional accuracy and positioning accuracy. Because the circuit board 150 having the through hole E includes the ceramic plate 100, damage to the circuit board 150 due to screwing to the power module can be further suppressed.

[0059] From the viewpoint of improving production efficiency, a ceramic plate 100 having through holes H formed therein in advance may be joined to a metal plate 120, and the metal plate 120 may be etched to produce an aggregate circuit board 200 having through holes E, as shown in Figures 5 and 6(a). Such an aggregate circuit board 200 may be divided to produce circuit boards 150.

[0060] [Power module] A power module according to one embodiment includes the circuit board 150 described above. The circuit board 150 has through holes E, so that the circuit board 150 can be smoothly mounted on the power module by screwing. Furthermore, the circuit board 150 includes the ceramic plate 100, so that it has sufficient strength and is able to prevent breakage due to screwing. Such a power module has excellent reliability. The power module can be manufactured by mounting a semiconductor element electrically connected to the conductor portion of the circuit board 150 using solder, wire bonding, or the like, and then housing the circuit board 150 and the semiconductor element in a housing space of a housing and sealing them with resin.

[0061] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. [Example]

[0062] The present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0063] Example 1 [Ceramic substrate fabrication] Silicon nitride powder and sintering aids, magnesium oxide powder, yttrium oxide powder, and silicon dioxide powder, were prepared. These were mixed in a mass ratio of Si3N4:YO3:MgO:SiO2 = 91.3:6.0:1.6:1.1 to obtain a raw material powder. A binder, dispersant, and dispersion medium were added to this raw material powder to prepare a mixed raw material (raw material slurry). Next, the raw material slurry was applied to a release film using a doctor blade method, adjusting the coating thickness to 0.440 mm, and a green sheet was produced.

[0064] The green sheets were cut and 70 green sheets were stacked to obtain a laminate, which was then placed in an electric furnace equipped with a carbon heater and heated in air at 500°C for 20 hours to degrease the laminate, obtaining a degreased body.

[0065] Next, the pressure inside the firing furnace was reduced to 100 Pa or less, the temperature was raised to 900°C, and the degreased body was heat-treated under vacuum. Nitrogen gas was then introduced into the firing furnace, and the body was fired at 1800°C for 12 hours, yielding a flat-plate-shaped silicon nitride sintered body with a short side length of 135 mm, a long side length of 170 mm, and a thickness of 0.32 mm.

[0066] [Creating a circuit board] Scribe lines SL1 and SL2 were formed on one main surface of the fabricated silicon nitride sintered body, forming nine partitions. The nine partitions were arranged in a 3-row x 3-column configuration. Next, 0.3 mm thick copper plates were attached to each of the main surfaces of the silicon nitride sintered body using brazing material to obtain a laminate. The laminate was heated to 780°C in a vacuum while applying a pressure of 0.04 MPa to obtain a bonded body.

[0067] After the bonded body was cooled to room temperature, etching resist Er was applied to the copper plate. As shown in FIG. 5, the etching resist Er was applied so as to surround the circle in the center of the copper plate of each partition section. Then, an etching solution was sprayed onto the bonded body to perform etching. By etching, scribe lines SL1 and SL2 were exposed as shown in FIGS. 6(a) and 6(b), and conductors 170 and 172 having through holes H1 and H2 were formed on the copper plate.

[0068] Fiber laser light was irradiated onto the main surface of the silicon nitride sintered body exposed in the through hole H1 to form a through hole H. As a result, the through hole H1, through hole H, and through hole H2 were connected together to produce the aggregate circuit board 200 of FIG. 7 having the through hole E as shown in FIG. 3(b). The aggregate circuit board 200 was then divided along the scribe lines SL1 and SL2 to obtain the circuit board 150 shown in FIGS. 3(a) and 3(b).

[0069] The irradiation conditions of the fiber laser light were an output of 70 W, a frequency of 1000 kHz, and a scanning speed of 300 mm / sec. The length of cracks per unit area on the inner wall surface W of the ceramic plate 100 in the obtained circuit board 150 was calculated, the angle θ and the shortest distance in the cross section were measured, and the surface roughness of the inner wall surface W was measured according to the procedures shown below.

[0070] [Calculation of crack length per unit area on inner wall surface W] The obtained circuit board 150 was divided into four equal parts along a direction perpendicular to the main surface so as to pass through the center line X (Fig. 2) of the through hole H. In each piece of the divided circuit board, the inner wall surface W of the ceramic plate 100 was observed at a magnification of 500 times using an SEM, and an image was taken to obtain an SEM photograph. A "tabletop microscope" (product name: TM4000Plus, manufactured by Hitachi High-Technologies Corporation) was used as the SEM. The SEM photograph taken is shown in Fig. 8(a). In Fig. 8(a), cracks were detected when the maximum length of the straight line connecting the endpoints of the black lines was 20 µm or more, and the total length of the cracks detected in the photographed area was calculated using a scale bar. Thereafter, the crack length per unit area (µm / µm 2The results are shown in Table 1.

[0071] [Measurement of angle θ and shortest distance in cross section] The cross section of the ceramic plate 100 of each separated circuit board was observed at 250x magnification using an SEM, and an image was taken to obtain an SEM photograph. This SEM photograph is shown in FIG. 8(b). In FIG. 8(b), the angle θ between a first imaginary line L1 passing through the first opening edge C1 and parallel to the center line X and a second imaginary line L2 connecting the first opening edge C1 and a portion n of the inner wall surface W closest to the center line X was measured. The shortest distance between the portion n and the first imaginary line L1 was also measured. The results are shown in Table 1.

[0072] [Measurement of surface roughness of inner wall W] For each individual piece of the circuit board after separation, the arithmetic mean roughness and maximum roughness of the inner wall surface W of the ceramic plate 100 were calculated using a "digital microscope" (product name: VHX-8000, manufactured by Keyence Corporation). The measurement range was a 50 μm wide area connecting points moved 20 μm apart along the inner wall surface W from the first opening edge C1 and the second opening edge C2 of the ceramic plate 100. The results are shown in Table 1.

[0073] Example 2 A circuit board 150 was produced using the same procedures as in Example 1, except that the irradiation conditions for the fiber laser light were a scanning speed of 100 mm / sec. Calculation of the crack length per unit area on the inner wall surface W of the ceramic plate 100 in the circuit board 150, measurement of the angle θ and the shortest distance in the cross section, and measurement of the surface roughness of the inner wall surface W were carried out using the same procedures as in Example 1. An SEM photograph of the inner wall surface is shown in Fig. 9(a) and an SEM photograph of the cross section is shown in Fig. 9(b).

[0074] Example 3 A circuit board 150 was produced in the same manner as in Example 1, except that the irradiation conditions of the fiber laser light were an output of 30 W, a frequency of 500 kHz, and a scanning speed of 1000 mm / sec. Calculation of the crack length per unit area on the inner wall surface W of the ceramic plate 100 in the circuit board 150, measurement of the angle θ and the shortest distance in the cross section, and measurement of the surface roughness of the inner wall surface W were carried out in the same manner as in Example 1. An SEM photograph of the inner wall surface is shown in FIG. 10(a), and an SEM photograph of the cross section is shown in FIG. 10(b).

[0075] (Comparative Example 1) A circuit board was fabricated using the same procedures as in Example 1, except that the fiber laser light was replaced with a carbon dioxide laser, and the output was set to 150 W, the frequency to 5 kHz, and the scanning speed to 100 mm / sec. Calculation of the crack length per unit area on the inner wall surface of the ceramic plate in the circuit board, measurement of the angle θ and the shortest distance in the cross section, and measurement of the surface roughness of the inner wall surface were performed using the same procedures as in Example 1. An SEM photograph of the inner wall surface is shown in Figure 11(a), and an SEM photograph of the cross section is shown in Figure 11(b).

[0076] (Comparative Example 2) A circuit board was fabricated using the same procedure as in Example 1, except that the fiber laser beam was replaced with a carbon dioxide laser, and the carbon dioxide laser was irradiated using assist air. Note that in Comparative Example 2, the output, frequency, and scanning speed of the carbon dioxide laser were unknown. The length of cracks per unit area on the inner wall surface of the ceramic plate in the circuit board was calculated using the same procedure as in Example 1. An SEM photograph of the inner wall surface is shown in Figure 12.

[0077] [Table 1]

[0078] As shown in Table 1, in Examples 1, 2, and 3, in which the through holes H were formed using fiber laser light, the crack length per unit area on the inner wall surface W of the through holes H was smaller than in Comparative Examples 1 and 2, in which a carbon dioxide laser was used. Therefore, it is believed that the strength against screwing is improved, and breakage during screwing can be further suppressed.

[0079] Furthermore, in Examples 1, 2, and 3, the cross-sectional angle θ and the shortest distance from portion n in the cross-section to the first virtual straight line L1 were smaller than those in Comparative Example 1. Therefore, the linearity of the inner wall surface W was improved, allowing for smooth insertion of screws and further suppressing breakage during screw fastening. Furthermore, in Examples 1, 2, and 3, the arithmetic mean roughness and maximum roughness of the inner wall surface W were also smaller than those in Comparative Example 1. Therefore, because the inner wall surface W is smoothly formed, it is believed that smooth insertion of screws can be achieved and further suppressing breakage during screw fastening. [Industrial Applicability]

[0080] According to the present disclosure, it is possible to provide a ceramic plate having through holes for screw fastening and having sufficient strength, a manufacturing method thereof, a circuit board having through holes for screw fastening and capable of suppressing breakage during screw fastening, and a power module including such a circuit board. [Explanation of symbols]

[0081] 100...ceramic plate, 100A...first main surface, 100B...second main surface, H, H1, H2, E...through hole, C1...first opening edge, C2...second opening edge, W...inner wall surface, X...center line, L1...first imaginary line, L2...second imaginary line, θ...angle, n...portion, 150...circuit board, M1...third opening edge, 170, 172...conductor portion, 140...bonded body, 110...ceramic substrate, 120...metal plate, SL1, SL2...scribe line, Er...etching resist, 200...aggregate circuit board, K...crack.

Claims

1. The substrate has a through hole H penetrating in a direction perpendicular to the main surface, and the length of the crack per unit area on the inner wall surface of the through hole H is 0.01 (μm / μm ２ ) or less, ceramic plate.

2. In a cross section passing through the center line of the through hole H and along a direction perpendicular to the main surface, The first opening edge C1 of the through hole H is larger than the second opening edge C2, a first imaginary straight line L1 that passes through the first opening edge C1 and is parallel to the center line; 2. The ceramic plate according to claim 1, wherein an angle θ formed between a portion n of the inner wall surface closest to the center line and a second imaginary line L2 connecting the first opening edge C1 and the portion n is 10° or less.

3. The ceramic plate according to claim 2 , wherein the shortest distance between the first imaginary straight line L1 and the portion n is 30 μm or less.

4. The ceramic plate according to any one of claims 1 to 3, wherein the arithmetic mean roughness of the inner wall surface is 4.0 µm or less.

5. The ceramic plate according to any one of claims 1 to 3, wherein the maximum roughness of the inner wall surface is 18.0 µm or less.

6. A method for manufacturing a ceramic plate, comprising a step of forming a through hole H in a direction perpendicular to a main surface of a ceramic sintered body using a fiber laser beam.

7. The method for manufacturing a ceramic plate according to claim 6 , wherein the frequency of the fiber laser light is 100 kHz or more.

8. The method for manufacturing a ceramic plate according to claim 6 or 7, wherein the output of the fiber laser light is 100 W or less.

9. The method for manufacturing a ceramic plate according to claim 6 or 7, wherein in the step of forming the through holes H, the scanning speed of the fiber laser light is 50 mm / sec or more.

10. The ceramic plate according to any one of claims 1 to 3, a metal plate joined to the ceramic plate and having a through hole H1; The circuit board has a through hole E formed by connecting at least the through hole H and the through hole H1 in a direction perpendicular to the main surface of the ceramic plate.

11. A power module comprising the circuit board according to claim 10.

Images