Ceramic substrate, method for manufacturing same, and module

Abstract

A ceramic substrate (1) is formed by stacking and bonding a plurality of layers (10) including at least one wiring ceramic layer (10A) in a stacking direction (DS). The wiring ceramic layer (10A) includes a base portion (11) containing ceramic, and a plurality of electroconductive wiring portions (12). The base portion (11) includes a main surface (111) and a plurality of recessed portions (113). The main surface (111) faces one way in the stacking direction (DS). The main surface (111) extends in a direction that is substantially orthogonal to the stacking direction (DS). The plurality of recessed portions (113) are formed so as to be recessed from the main surface (111). The plurality of wiring portions (12) are respectively provided within the plurality of recessed portions (113). The shortest distance between the plurality of recessed portions (113) is 20 μm or less. The maximum inner width of each of the plurality of recessed portions (113) is 20 μm or less. Each of the plurality of recessed portions (113) has a tapered shape that is tapered on the side opposite from the main surface (111).

Description

Ceramic substrate, manufacturing method thereof, and module

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

[0002] Patent Document 1 (JP 2023-151269 A) discloses a multilayer chip inductor having a conductive layer. The multilayer chip inductor is manufactured by applying a paste for forming external electrodes to a laminate and then performing a firing process. The laminate comprises a ceramic substrate and multiple layers, each layer including a hardened glass film with precise grooves and a conductive hardened film formed in the grooves. The document also discloses an exposure process in which a photomask having a predetermined pattern is placed on the glass film, and portions of the glass film exposed through the openings are exposed to light, thereby forming the portions of the glass film into a hardened glass film, and a development process in which unhardened glass film is removed using a developer to form a hardened glass film with the predetermined grooves on the substrate.

[0003] Patent Document 2 (Japanese Patent No. 5533674) discloses a multilayer ceramic substrate having a laminate composed of multiple stacked ceramic layers. Various conductor patterns are provided in the laminate. The internal conductor patterns are provided on ceramic green sheets before lamination. When the green laminate is fired, the ceramic green layers are sintered and the conductive paste is also sintered, forming a circuit pattern made of sintered conductor films. The conductor patterns are formed by printing the conductive paste on the ceramic green sheets using a screen printing method.

[0004] Patent Document 3 (Japanese Patent No. 5024064) discloses a multilayer ceramic substrate having wiring conductors provided in association with the base ceramic layers and / or constraining layers. The wiring conductors include, for example, internal conductor films extending along the main surfaces of the base ceramic layers within the multilayer ceramic substrate. To obtain the multilayer ceramic substrate, a green laminate is prepared. The green laminate includes a plurality of stacked base green layers containing a low-temperature co-fired ceramic material. After firing, the base green layers become the aforementioned base ceramic layers. For the internal conductor films, a conductive paste is printed onto selected base green layers or selected constraining green layers, for example, by screen printing.

[0005] Patent Document 4 (JP 10-084056 A) discloses a ceramic substrate. The method for manufacturing the ceramic substrate includes laminating constraining layer green sheets containing sinter-resistant ceramic powder on both sides of a substrate green sheet containing ceramic powder, and firing the laminate while applying high pressure in the thickness direction. A conductive paste layer is formed on the surface of the substrate green sheet by screen printing.

[0006] JP-A-2023-151269 Patent No. 5533674 Patent No. 5024064 JP-A 10-084056

[0007] There is a demand for ceramic substrates with even finer wiring. When manufacturing ceramic substrates with finer wiring, it is conceivable to form grooves in the ceramic substrate by photolithography and place conductive portions in the grooves, rather than applying a conductive paste directly to the surface of a ceramic green sheet.

[0008] However, when a ceramic substrate with such fine wiring is manufactured using conventional techniques, the electric field of the conductive portion is concentrated near the corners of the grooves, which causes crosstalk between the fine wiring and degrades the signal transmission characteristics of the ceramic substrate.

[0009] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide a ceramic substrate in which degradation of signal transmission characteristics is suppressed.

[0010] A ceramic substrate according to the present disclosure is formed by stacking and bonding multiple layers, including at least one wiring ceramic layer, together in a stacking direction. The wiring ceramic layer includes a ceramic-containing base portion and multiple conductive wiring portions. The base portion includes a main surface and multiple groove portions. The main surface faces one side of the stacking direction. The main surface extends in a direction substantially perpendicular to the stacking direction. The multiple groove portions are formed so as to be recessed from the main surface. The multiple wiring portions are respectively provided within the multiple groove portions. The shortest distance between the multiple groove portions is 20 μm or less. The maximum inner width of each of the multiple groove portions is 20 μm or less. Each of the multiple groove portions has a tapered shape that narrows on the side opposite the main surface.

[0011] A method for manufacturing a ceramic substrate according to the present disclosure includes: irradiating a ceramic green sheet with a laser or ion beam to form a ceramic green sheet for wiring, the ceramic green sheet having a plurality of grooves on a main surface thereof, the grooves being spaced apart from one another by a shortest distance of 20 μm or less and having a maximum inner width of 20 μm or less; providing a conductive paste in the plurality of grooves; stacking the plurality of ceramic green sheets, including the ceramic green sheet for wiring, on top of each other to form a pre-fired laminate; and firing the pre-fired laminate while applying pressure.

[0012] According to the present disclosure, it is possible to provide a ceramic substrate in which degradation of signal transmission characteristics is suppressed.

[0013] 1 is a plan view showing a ceramic substrate according to Embodiment 1. FIG. 1 is a partial cross-sectional view of the ceramic substrate of FIG. 1 as seen in the direction of the arrows along line II-II. FIG. 1 is a partial cross-sectional view of the ceramic substrate of FIG. 1 as seen in the direction of the arrows along line III-III. FIG. 1 is a partial cross-sectional view of the ceramic substrate of FIG. 1 as seen in the direction of the arrows along line IV-IV. FIG. 2 is a partial cross-sectional view of a wiring ceramic layer in Embodiment 1. FIG. 3 is a schematic cross-sectional view showing an example of a module including the ceramic substrate of Embodiment 1. FIG. 4 is a schematic cross-sectional view showing another example of a module including the ceramic substrate according to the embodiment. FIG. 5 is a flowchart showing a method for producing a ceramic green sheet for wiring provided with a conductive paste in a method for producing a ceramic substrate according to Embodiment 1. FIG. 6 is a partial cross-sectional view showing a ceramic green sheet prepared in Embodiment 1. FIG. 7 is a partial cross-sectional view showing a state in which the ceramic green sheet has been formed into a ceramic green sheet for wiring in Embodiment 1. FIG. 8 is a cross-sectional view schematically showing a state in which a conductive paste is ejected by an impulse printing method. FIG. 9 is a cross-sectional view schematically showing a state in which a ceramic green sheet for wiring provided with a conductive paste has been prepared in Embodiment 1. FIG. 10 is a cross-sectional view schematically showing a state in which a ceramic green sheet for wiring provided with a conductive paste has been prepared. FIG. 1 is a flowchart showing a method after producing a ceramic green sheet for wiring provided with a conductive paste, among the methods for manufacturing a ceramic substrate according to embodiment 1. FIG. 2 is a cross-sectional view showing a pre-fired laminate formed by stacking a plurality of ceramic green sheets on one another in embodiment 1. FIG. 3 is a cross-sectional view showing a laminate immediately after being formed by firing the pre-fired laminate in embodiment 1. FIG. 4 is a cross-sectional view showing a ceramic green sheet for wiring provided with a conductive paste in comparative embodiment 1. FIG. 5 is a cross-sectional view showing a state immediately before stacking another ceramic green sheet on a plurality of ceramic green sheets for wiring in comparative embodiment 1. FIG. 6 is a cross-sectional view showing a state immediately after stacking another ceramic green sheet on a plurality of ceramic green sheets for wiring in comparative embodiment 1. FIG. 7 is a cross-sectional view showing a pre-fired laminate in comparative embodiment 2. FIG. 8 is a partial cross-sectional view showing a wiring portion and its vicinity of a ceramic substrate according to comparative embodiment 2.1 is a cross-sectional view schematically showing an example of a wiring ceramic layer in which warpage has occurred in Comparative Embodiment 2. FIG. 2 is a cross-sectional view schematically showing another example of a wiring ceramic layer in which warpage has occurred in Comparative Embodiment 2. FIG. 3 is a cross-sectional view showing a ceramic substrate according to Embodiment 2. FIG. 4 is a flowchart showing a method of producing a wiring ceramic green sheet provided with a conductive paste in a method of producing a ceramic substrate according to Embodiment 2. FIG. 5 is a cross-sectional view schematically showing a state in which a wiring ceramic green sheet provided with a conductive paste has been prepared in Embodiment 2. FIG. 6 is a flowchart showing a method after producing a wiring ceramic green sheet provided with a conductive paste in a method of producing a ceramic substrate according to Embodiment 2. FIG. 7 is a cross-sectional view showing a pre-fired laminate formed by stacking a plurality of ceramic green sheets on top of each other in Embodiment 2. FIG. 8 is a cross-sectional view showing a laminate immediately after being formed by firing the pre-fired laminate in Embodiment 2. FIG. 9 is a cross-sectional view showing a wiring ceramic green sheet provided with a conductive paste in Comparative Embodiment 3. FIG. 10 is a cross-sectional view showing a wiring ceramic green sheet provided with a conductive paste in Comparative Embodiment 4. FIG. 11 is a cross-sectional view showing a ceramic substrate according to Comparative Embodiment 4. FIG. 12 is a cross-sectional view showing a cross-sectional photograph of a laminate immediately after being formed by firing a pre-fired laminate in an experimental example. FIG. 13 is a cross-sectional photograph of a ceramic substrate according to an experimental example. FIG. 10 is a plan view of a ceramic substrate according to an experimental example.

[0014] Ceramic substrates according to embodiments of the present disclosure will be described below. In the following description of each embodiment, the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

[0015] (Embodiment 1) Fig. 1 is a plan view showing a ceramic substrate according to embodiment 1. Fig. 2 is a partial cross-sectional view of the ceramic substrate of Fig. 1 as seen in the direction of the arrows II-II. Fig. 3 is a partial cross-sectional view of the ceramic substrate of Fig. 1 as seen in the direction of the arrows III-III.

[0016] As shown in Figures 1 to 3, the ceramic substrate 1 according to the first embodiment of the present disclosure is formed by stacking and bonding a plurality of layers 10, including at least one wiring ceramic layer 10A, to one another in a stacking direction DS. At least one layer of the plurality of layers 10 may be the wiring ceramic layer 10A. Some layers of the plurality of layers 10 may be the wiring ceramic layer 10A. Figures 2 and 3 show a ceramic substrate 1 in which all of the plurality of layers 10 are wiring ceramic layers 10A.

[0017] The thickness of each of the multiple layers 10 is, for example, 5 μm or more and 150 μm or less. That is, the thickness of the wiring ceramic layer 10A is, for example, 5 μm or more and 150 μm or less. The multiple layers 10 are stacked and joined together in the stacking direction DS to form the laminate 2. The outer surface of the laminate 2 facing the stacking direction DS is substantially flat. This makes it easy to handle the ceramic substrate 1 by suction. In addition, the height of the ceramic substrate 1 is relatively uniform, allowing electronic components to be stably mounted on the ceramic substrate 1.

[0018] Fig. 4 is a partial cross-sectional view of the ceramic substrate of Fig. 1, as viewed in the direction of the arrows along line IV-IV. As shown in Figs. 1 to 4, the wiring ceramic layer 10A includes a base portion 11 containing ceramic and a plurality of conductive wiring portions 12.

[0019] The base portion 11 includes a low-temperature sintered ceramic material. The low-temperature sintered ceramic material is, for example, a ceramic that can be fired at a temperature of 1000° C. or less in a powder state. Examples of the low-temperature sintered ceramic material include alumina (Al ２ O ３ ) and borosilicate glass, and / or BaO—Al, which produces a glass component during firing. ２ O ３ -SiO ２ By including such a low-temperature sintering ceramic material in the base 11, the base 11 and the wiring 12 can be simultaneously formed by sintering, even if the wiring 12 includes a low-melting-point metal such as silver or copper. Examples of low-temperature sintering ceramic materials include silica (SiO２ ), boron oxide (B ２ O ３ ), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), magnesium oxide (MgO), and alumina (Al ２ O ３ The base portion 11 may include other ceramic materials.

[0020] 5 is a partial cross-sectional view of a wiring ceramic layer in embodiment 1. As shown in FIGS. 2 to 5, the base portion 11 includes a main surface 111, another main surface 112, and a plurality of grooves 113.

[0021] The main surface 111 faces in one of the stacking directions DS. The other main surface 112 faces in the other of the stacking directions DS. The main surface 111 and the other main surface 112 extend in a direction substantially perpendicular to the stacking direction DS.

[0022] The plurality of grooves 113 are formed to be recessed from the main surface 111. The shortest distance between the plurality of grooves 113 is 20 μm or less. The shortest distance between the plurality of grooves 113 is preferably 18 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less.

[0023] The maximum inner width of each of the plurality of grooves 113 is 20 μm or less. The maximum inner width of each of the plurality of grooves 113 is preferably 18 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or more. The depth of each of the plurality of grooves 113 is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less.

[0024] Each of the multiple recessed streak portions 113 has a tapered shape that tapers away from the main surface 111. Specifically, as shown in Fig. 5 , the multiple recessed streak portions 113 have a first inner surface 114 and a second inner surface 115. The first inner surface 114 extends in a direction away from the main surface 111. The second inner surface 115 extends in a direction away from the main surface 111. The second inner surface 115 faces the first inner surface 114.

[0025] At least one of the plurality of grooves 113 may further have a tip 116. The tip 116 is formed by connecting the edges of the first inner surface 114 and the second inner surface 115 on the side opposite to the main surface 111. The tip 116 is curved when viewed from the extension direction of the groove 113. The radius of curvature of the tip 116 when viewed from the extension direction may be 0.1 μm or more.

[0026] At least one of the plurality of grooves 113 may have a bottom surface 117. The bottom surface 117 connects the edges of the first inner surface 114 and the second inner surface 115 on the side opposite to the main surface 111. A deepest portion 117D of the bottom surface 117, which is the portion furthest from the main surface 111 in the stacking direction DS, is curved when viewed from the extension direction of the grooves 113. The radius of curvature of the deepest portion 117D when viewed from the extension direction may be 0.1 μm or more.

[0027] 2, the base portion 11 may further include one or more via holes 118. The via holes 118 penetrate the base portion 11 in the thickness direction (i.e., the stacking direction DS). The via holes 118 may be formed from the main surface 111 or from the groove portions 113. The maximum inner width of the via holes 118 may be 20 μm or less, or may exceed 20 μm, similar to the groove portions 113 (see FIG. 4).

[0028] 4, layers other than the wiring ceramic layers among the plurality of layers 10 may also have via holes 118. The via holes 118 in each of the plurality of layers 10 may be continuous in the stacking direction DS. The via holes 118 continuous in the stacking direction DS may be aligned diagonally relative to the stacking direction DS. This allows for more diverse design patterns for the wiring portion 12 located inside the laminate 2.

[0029] The base portion 11 may further include a plurality of other recessed streak portions 119. The plurality of other recessed streak portions 119 are formed so as to be recessed from the other main surface 112. Each of the plurality of other recessed streak portions 119 has a tapered shape that narrows on the side opposite to the other main surface 112. The configuration of the plurality of other recessed streak portions 119 relative to the other main surface 112 may be the same as the configuration of the plurality of recessed streak portions 113 relative to the main surface 111. Note that the above-mentioned via hole 118 may be formed from the other main surface 112 or from the plurality of other recessed streak portions 119.

[0030] The main surface 111 or the other main surface 112 of the wiring ceramic layer 10A may be located on the outer surface of the laminate 2 made up of a plurality of layers 10 stacked on top of one another. The main surface 111 or the other main surface 112 of the wiring ceramic layer 10A may be located inside the laminate 2 made up of a plurality of layers 10 stacked on top of one another.

[0031] The plurality of wiring portions 12 are conductive. The wiring portions 12 may contain a metal such as copper (Cu), silver (Ag), nickel (Ni), or palladium (Pd) as a conductive component. The wiring portions 12 preferably contain copper (Cu) as a main component. The wiring portions 12 may also contain an alloy containing the above metal as a conductive component. The wiring portions 12 may further contain an oxide of the above metal.

[0032] The multiple wiring portions 12 are respectively provided in the multiple groove portions 113. The position of the exposed surface 121 of the wiring portion 12 from the groove portion 113 in the stacking direction DS is preferably 1.0 μm or less relative to the main surface 111 of the base portion 11. This makes it easy to mount electronic components via a bonding material when the exposed surface 121 is located on the outer surface of the laminate 2. When the base portion 11 of another wiring ceramic layer 10A includes another groove portion 119, the wiring portion 12 may be provided in the groove portion 113.

[0033] The wiring ceramic layer 10A may further include one or more via electrodes 13. The via electrodes 13 are provided in the via holes 118. The via electrodes 13 are conductive. The via electrodes 13 may contain the conductive components that the wiring portion 12 may contain. The via electrodes 13 may be made of the same material as the wiring portion 12.

[0034] Of the plurality of layers 10, the layers other than the wiring ceramic layer 10A do not have a wiring portion 12. Of the plurality of layers 10, the layers other than the wiring ceramic layer 10A may have only a base portion 11 without a groove portion 113 formed therein, or may have only a base portion 11 without a groove portion 113 formed therein and a via electrode 13.

[0035] As described above, the ceramic substrate 1 according to the first embodiment of the present disclosure is formed by stacking and bonding multiple layers 10, including at least one wiring ceramic layer 10A, together in the stacking direction DS. The wiring ceramic layer 10A includes a ceramic-containing base portion 11 and multiple conductive wiring portions 12. The base portion 11 includes a main surface 111 and multiple groove portions 113. The main surface 111 faces one side of the stacking direction DS. The main surface 111 extends in a direction substantially perpendicular to the stacking direction DS. The multiple groove portions 113 are formed to be recessed from the main surface 111. The multiple wiring portions 12 are respectively provided within the multiple groove portions 113. The shortest distance between the multiple groove portions 113 is 20 μm or less. The maximum inner width of each of the multiple groove portions 113 is 20 μm or less. Each of the plurality of recessed streaks 113 has a tapered shape on the side opposite to the main surface 111 .

[0036] According to the above configuration, the shortest distance between the grooves 113 is 20 μm or less, and the maximum inner width between the grooves 113 is 20 μm or less. This allows for fine wiring (L / S of 20 / 20 μm or less) to be achieved by the multiple wiring portions 12 arranged within the multiple grooves 113. Furthermore, the tapered shape of the grooves 113 suppresses the concentration of the electric field at the corners of the wiring portions 12 arranged in the grooves 113. This in turn suppresses the occurrence of crosstalk between the multiple wiring portions 12. As a result, a ceramic substrate 1 can be provided that can suppress degradation of signal transmission characteristics.

[0037] In the present embodiment, preferably, at least one of the plurality of recessed streak portions 113 has a first inner surface 114, a second inner surface 115, and a tip portion 116. The first inner surface 114 extends in a direction away from the main surface 111. The second inner surface 115 extends in a direction away from the main surface 111. The second inner surface 115 faces the first inner surface 114. The tip portion 116 is formed by connecting the edges of the first inner surface 114 and the second inner surface 115 on the side opposite to the main surface 111.

[0038] According to the above configuration, the cross-sectional shape of the wiring portion 12 arranged inside the groove portion 113 is substantially triangular (inverted triangle in FIG. 5 and other figures) with an upward opening. Consequently, the density of the current flowing in the extending direction of the wiring portion 12 becomes relatively uniform in the wiring portion 12, and loss of signal transmission and distortion of the ceramic substrate 1 can be suppressed.

[0039] In this embodiment, the tip portion 116 is preferably curved when viewed from the extending direction of the groove portion 113 .

[0040] According to the above-described configuration, it is possible to suppress the occurrence of defects at the tip end 116 of the groove 113 that may occur when the base 11 is produced by firing.

[0041] In this embodiment, the radius of curvature of the tip portion 116 when viewed from the extending direction is preferably 0.1 μm or more.

[0042] According to the above-described configuration, it is possible to further suppress the occurrence of defects at the tip end 116 of the groove 113 that may occur when the base 11 is produced by firing.

[0043] In the present embodiment, preferably, at least one of the plurality of recessed streak portions 113 has a first inner surface 114, a second inner surface 115, and a bottom surface 117. The first inner surface 114 extends in a direction away from the main surface 111. The second inner surface 115 extends in a direction away from the main surface 111. The second inner surface 115 faces the first inner surface 114. The bottom surface 117 connects the edges of the first inner surface 114 and the second inner surface 115 on the opposite side from the main surface 111. A deepest portion 117D of the bottom surface 117, which is the portion furthest from the main surface 111 in the stacking direction DS, is curved when viewed from the extension direction of the recessed streak portion 113.

[0044] According to the above configuration, it is possible to suppress the occurrence of defects in the deepest part 117D of the bottom surface 117 that may occur when the base portion 11 is produced by firing.

[0045] In this embodiment, the radius of curvature of the deepest part 117D when viewed from the extending direction is preferably 0.1 μm or more.

[0046] According to the above configuration, it is possible to further suppress the occurrence of defects in the deepest part 117D of the bottom surface 117 that may occur when the base portion 11 is produced by firing.

[0047] In this embodiment, the main surface 111 of the wiring ceramic layer 10A is preferably located on the outer surface of the laminate 2 made up of a plurality of layers 10 stacked on top of each other.

[0048] This allows the ceramic substrate 1 having the above-described structure to be used as a substrate when connecting a substrate having fine wiring on its surface to an electronic component via a bonding material.

[0049] In this embodiment, the main surface 111 of the wiring ceramic layer 10A is preferably located inside the laminate 2 made up of a plurality of layers 10 stacked on top of each other.

[0050] This allows the ceramic substrate 1 having the above configuration to be used as an interposer disposed between an electronic component and another substrate when connecting them.

[0051] Next, applications of the ceramic substrate 1 according to the first embodiment of the present disclosure will be described. Fig. 6 is a schematic cross-sectional view showing an example of a module including the ceramic substrate according to the first embodiment. As shown in Fig. 6, a module 1000 includes the ceramic substrate 1 according to the first embodiment of the present disclosure and a plurality of electronic components 500. The plurality of electronic components 500 are mounted on the ceramic substrate 1 and electrically connected to at least one of the plurality of wiring portions 12.

[0052] This makes it possible to provide a module 1000 that includes a ceramic substrate 1 instead of a conventional substrate and a conventional interposer with fine wiring. Consequently, the module 1000 can be made even thinner and its manufacturing costs can be reduced. This is because the use of a single ceramic substrate 1 instead of a conventional substrate and a conventional interposer with fine wiring can eliminate the need for bonding materials and sealing resins that are disposed between the conventional substrate and the conventional interposer. Furthermore, in the module 1000, the overall length of the transmission lines can be shortened.

[0053] Specifically, a plurality of electronic components 500 are mounted on the ceramic substrate 1 via a first bonding material 510 such as solder bumps. The electronic components 500 can be electrically connected to one another via the first bonding material 510, via electrodes 13, and wiring portions 12. The module 1000 can further be mounted on the motherboard 2000 via a second bonding material 2100. The second bonding material 2100 can be electrically connected to the via electrodes 13 of the ceramic substrate 1.

[0054] 7 is a schematic cross-sectional view showing another example of a module including a ceramic substrate according to the embodiment. As shown in FIG. 7, the ceramic substrate 1 of the module 1000a may have the function of the motherboard 2000 shown in FIG. 6. This allows the module 1000 and the motherboard to be further reduced in height.

[0055] Next, a method for manufacturing the ceramic substrate according to the first embodiment of the present disclosure will be described. In the method for manufacturing the ceramic substrate 1 according to the first embodiment of the present disclosure, first, a ceramic green sheet for wiring provided with a conductive paste is prepared. Here, the term "paste" in this specification refers to a mixture in which a part or all of the solid content is dispersed in a solvent, and includes so-called "slurry," "ink," etc.

[0056] Fig. 8 is a flowchart showing a method for producing a ceramic green sheet for wiring provided with a conductive paste in the method for producing a ceramic substrate according to embodiment 1. As shown in Fig. 8, in this embodiment, the method for producing a ceramic green sheet for wiring provided with a conductive paste includes steps S11, S12, S131 or S132, S14, and S15.

[0057] FIG. 9 is a partial cross-sectional view showing a ceramic green sheet prepared in embodiment 1. The ceramic green sheet shown in FIG. 9 is produced as follows: First, a powdered low-temperature co-fired ceramic material to be contained in the base portion 11 is prepared. An organic binder, a dispersant, a plasticizer, an organic solvent, and the like are added to the powdered material, and these are mixed to produce a slurry. Next, the slurry is degassed and then formed into a sheet on a carrier film (not shown) by a doctor blade method. The sheet-shaped slurry is dried to obtain a ceramic green sheet. The thickness of the ceramic green sheet is adjusted in advance so that the thickness of the wiring ceramic layer after firing is 5 μm or more and 150 μm or less.

[0058] 10 is a partial cross-sectional view showing the state in which a ceramic green sheet has been formed into a ceramic green sheet for wiring in embodiment 1. As shown in FIGS. 9 and 10, in step S11, a laser or ion beam is irradiated onto the ceramic green sheet 11P to form a ceramic green sheet for wiring 11AP having a plurality of grooves 113P on the main surface 111P of the ceramic green sheet 11P, the grooves 113P being spaced apart from one another by a minimum distance of 20 μm or less and having a maximum inner width of 20 μm or less. The laser is, for example, a short-pulse laser.

[0059] In step S12, via holes 118P are formed in the wiring ceramic green sheet 11AP. The method for forming the via holes 118P may be the same as the method for forming the plurality of grooves 113P in the ceramic green sheet 11P. The via holes 118P may also be formed by other conventionally known methods.

[0060] 11 is a cross-sectional view showing a process of ejecting a conductive paste by impulse printing. As shown in FIG. 11, in step S131, a conductive paste 12P is first applied to a plate PL. The conductive paste is prepared by adding powder containing the conductive components of the wiring portion 12, ceramic material used to prepare ceramic green sheets, and other inorganic material powders to a binder resin.

[0061] 12 is a cross-sectional view schematically illustrating the preparation of a ceramic green sheet for wiring provided with a conductive paste in embodiment 1. As shown in FIGS. 11 and 12 , in step S14, conductive paste 12P is placed in the via holes 118P of the ceramic green sheet for wiring 11AP. The method for placing the conductive paste 12P in the via holes 118P is not particularly limited, but it is preferably the same as the method for placing the conductive paste 12P in the grooves 113P (details will be described later). This allows the conductive paste 12P to be placed in the via holes 118P and the conductive paste 12P to be placed in the grooves 113P.

[0062] In addition, when producing a ceramic green sheet in which the groove streak portion 113P is not formed, the ceramic green sheet in which the groove streak portion 113P is not formed may be produced in the same manner as in steps S11, S12, S131, and step S14 described above.

[0063] In step S15, the conductive paste 12P is provided in the plurality of grooves 113P. Specifically, the plate PL on which the conductive paste 12P is provided is instantly heated to eject the conductive paste 12P from the plate PL, thereby providing the conductive paste 12P in the plurality of grooves 113P.

[0064] A plurality of grooves PLa are formed in advance in the plate PL. The conductive paste 12P is provided in the plurality of grooves PLa. When the conductive paste 12P is to be ejected, the plate PL and the wiring ceramic green sheet 11AP are placed opposite each other so that the plurality of grooves PLa face the plurality of recessed stripes 113P, respectively.

[0065] Note that step S132 may be employed instead of step S131. FIG. 13 is a cross-sectional view schematically illustrating the transfer of conductive paste by the laser-induced forward transfer (LIFT) method. As shown in FIG. 13, in step S132, a layer of conductive paste 12P is provided on a transparent substrate TS. In this case, in step S15, a laser is irradiated onto the transparent substrate TS on which the conductive paste 12P is provided, thereby transferring the conductive paste 12P on the transparent substrate TS, thereby providing the conductive paste 12P in the plurality of grooves 113P. The laser may be, for example, a pulsed laser.

[0066] The conductive paste 12P on the transparent substrate TS is locally melted by the laser only in the portions facing the plurality of grooves 113P, thereby providing the conductive paste 12P in the plurality of grooves 113P.

[0067] Next, a method for manufacturing a ceramic substrate after preparing a plurality of ceramic green sheets including the wiring ceramic green sheet 11AP will be described. Fig. 14 is a flowchart showing a method for manufacturing a ceramic substrate according to embodiment 1 after preparing the wiring ceramic green sheets provided with a conductive paste. As shown in Fig. 14, the method for manufacturing a ceramic substrate according to the disclosed embodiment 1 further includes steps S20, S30, S40, and S50.

[0068] 15 is a cross-sectional view showing a pre-fired laminate formed by stacking a plurality of ceramic green sheets on one another in embodiment 1. As shown in Fig. 15, in step S20, a pre-fired laminate 2P is formed by stacking a plurality of ceramic green sheets 11P, including the wiring ceramic green sheet 11AP, on one another. Specifically, the pre-fired laminate 2P is formed by stacking a plurality of ceramic green sheets 11P, including the wiring ceramic green sheet 11AP, on the first constraining green layer 50P.

[0069] In step S30, a second constraining green layer 55P is further laminated on the side of the pre-fired laminate 2P opposite to the first constraining green layer 50P side.

[0070] The first constraining green layer 50P and the second constraining green layer 55P are prepared for the pre-fired laminate 2P as follows. First, an inorganic material powder is prepared. This inorganic material powder is not sintered at the sintering temperature of the low-temperature co-fired ceramic material as described above. The inorganic material powder is, for example, alumina (Al ２ O ３ ) and / or zirconia (ZrO ２ The inorganic material powder preferably contains titanium oxide (TiO ２ ), silica (SiO ２ ), niobium pentoxide (Nb ２ O ５ ), tantalum pentoxide (Ta ２ O ５ ) may also be included.

[0071] An organic binder, dispersant, plasticizer, organic solvent, etc. are added to this inorganic powder material and mixed to prepare a slurry. This slurry is then formed into a sheet on a carrier film by a doctor blade method. The sheet-like slurry is dried to obtain the first constraining green layer 50P and the second constraining green layer 55P. The first constraining green layer 50P and the second constraining green layer 55P may be provided by applying the slurry to a pre-fired laminate 2P or a ceramic green sheet and drying it.

[0072] The low-temperature co-fired ceramic material contained in the ceramic green sheets 11P is one in which some components, such as glass components, can penetrate into the first constraining green layers 50P and the second constraining green layers 55P during firing.

[0073] FIG. 16 is a cross-sectional view showing a laminate immediately after firing the pre-fired laminate in embodiment 1. As shown in FIG. 16 , in step S40, the pre-fired laminate 2P is fired under pressure. Specifically, the pre-fired laminate 2P is fired under pressure together with the first constraining green layer 50P and the second constraining green layer 55P. The pre-fired laminate 2P may be singulated before being fired under pressure. By firing the pre-fired laminate 2P under pressure, the glass component contained in the ceramic green sheet 11P is forced to flow, suppressing the occurrence of defects between the different materials. This ultimately improves the reliability of the ceramic substrate 1.

[0074] In step S50, the first constraining layer 50 formed by firing the first constraining green layer 50P and the second constraining layer 55 formed by firing the second constraining green layer 55P are removed from the laminate 2 formed by firing the pre-fired laminate 2P. This removal is performed by, for example, ultrasonic cleaning and wet blasting. In this manner, the ceramic substrate 1 (see FIG. 3 ) according to the first embodiment of the present disclosure is manufactured.

[0075] Here, a comparative example will be described to explain the effects of the method for manufacturing a ceramic substrate according to the first embodiment of the present disclosure.

[0076] First, comparative example 1 will be described. Fig. 17 is a cross-sectional view showing a ceramic green sheet for wiring provided with a conductive paste in comparative example 1. As shown in Fig. 17, in comparative example 1, no grooves were formed on the ceramic green sheet 611P, and the conductive paste 12P for wiring was formed directly on the main surface 111P of the ceramic green sheet 611P. Otherwise, the ceramic green sheet for wiring 611P was manufactured using the same method as the method for manufacturing the ceramic green sheet for wiring in embodiment 1.

[0077] Fig. 18 is a cross-sectional view showing a state immediately before stacking another ceramic green sheet on a plurality of ceramic green sheets for wiring in Comparative Example 1. Fig. 19 is a cross-sectional view showing a state immediately after stacking another ceramic green sheet on a plurality of ceramic green sheets for wiring in Comparative Example 1. As shown in Figs. 18 and 19 , when ceramic green sheets 611P provided with conductive paste 12P for wiring are stacked on top of each other and another ceramic green sheet 11P is further stacked on top of these, unevenness corresponding to the thickness of the conductive paste 12P is formed on the other ceramic green sheet 11P. Therefore, although the conductive paste 12P is finely arranged, it is not possible to produce a flat pre-fired laminate that can be used as a substrate after firing.

[0078] Next, comparative example 2 will be described. Fig. 20 is a cross-sectional view showing a pre-fired laminate in comparative example 2. Fig. 21 is a partial cross-sectional view showing a wiring portion and its vicinity of a ceramic substrate in comparative example 2.

[0079] In Comparative Example 2 shown in FIG. 20, a wiring ceramic green sheet 711AP provided with a conductive cured film 712P is produced as follows.

[0080] First, a cured film is formed by so-called photolithography on a ceramic green sheet prepared in the same manner as in Embodiment 1. The method for forming the cured film may include, for example, a first step, a first exposure step, a first development step, a second shaping step, and a second exposure step.

[0081] In the first step, a photosensitive glass composition is applied (printed) onto a green sheet and dried to form a glass film, which is a dried product of the photosensitive glass composition. In the first exposure step, a photomask having a predetermined pattern is placed over the glass film, and portions of the glass film exposed through the openings are exposed to light, converting the portions of the glass film into a cured glass film. In the first development step, a developer is used to remove the uncured glass film, forming a cured glass film with grooves on the green sheet. In the second molding step, a photosensitive conductive composition is applied (printed) into the grooves of the formed cured glass film and dried to form a conductive film, which is a dried product of the photosensitive conductive composition, in the grooves of the glass film. In the second exposure step, a photomask having a predetermined pattern is placed over the conductive film, and portions of the conductive film exposed through the openings are exposed to light, converting the portions of the conductive film into a cured conductive film. In the second development step, a developer is used to remove the uncured conductive film.

[0082] This forms an unfired cured glass film on the surface of the ceramic green sheet, and a conductive cured film in the grooves of the cured glass film. A wiring ceramic green sheet 711AP is formed in Comparative Example 2, with a conductive cured film 712P provided thereon. The grooves 7113P in the wiring ceramic green sheet 711AP correspond to the grooves of the cured glass film. A ceramic substrate 701 in Comparative Example 2, partially shown in FIG. 21 , was manufactured using the same manufacturing method as the ceramic substrate 1 in Embodiment 1. In Comparative Example 2, the wiring portion 712 is formed by firing the conductive cured film 712P.

[0083] As shown in Figure 21, in Comparative Example 2, the grooves 7113 do not have a tapered shape when viewed from the direction of extension. As a result, the electric field tends to concentrate at the corners of the wiring portions 712 arranged in the grooves 7113. This causes crosstalk between the multiple wiring portions 712, resulting in poor signal transmission characteristics. Furthermore, the grooves 7113P of the wiring ceramic green sheet 711AP have a substantially rectangular shape that opens upward when viewed from the direction of extension of the grooves 7113P. This makes it easier for defects to occur at the edges of the bottom surface of the grooves 7113 of the base portion 711 during firing.

[0084] Fig. 22 is a cross-sectional view schematically showing an example of a wiring ceramic layer in which warpage occurs in Comparative Example 2. Fig. 23 is a cross-sectional view schematically showing another example of a wiring ceramic layer in which warpage occurs in Comparative Example 2. Furthermore, as shown in Figs. 22 and 23, the groove portions 7113P of the wiring ceramic green sheet 711AP have a substantially rectangular outer shape that opens upward when viewed from the extending direction of the groove portions 7113P, and therefore warpage of the wiring ceramic layer 710A is likely to occur when the wiring ceramic green sheet 711AP is fired together with the first constraining green layer and the second constraining green layer.

[0085] Furthermore, in Comparative Example 2, since photolithography is used, the surface of the ceramic green sheet is roughened by printing the photosensitive glass composition or by the developer, which makes the wiring ceramic layer 710A more likely to peel off from other layers.

[0086] As described above, the method for manufacturing a ceramic substrate according to the first embodiment of the present disclosure includes: irradiating a ceramic green sheet 11P with a laser or an ion beam to form a wiring ceramic green sheet 11AP having a plurality of grooves 113P on a main surface 111P of the ceramic green sheet 11P, the grooves 113P being spaced apart from one another by a shortest distance of 20 μm or less and having a maximum inner width of 20 μm or less (S11); providing a conductive paste 12P in the plurality of grooves 113P (S15); stacking the plurality of ceramic green sheets 11P including the wiring ceramic green sheet 11AP on top of each other to form a pre-fired laminate 2P (S20); and firing the pre-fired laminate 2P while applying pressure (S40).

[0087] According to the above configuration, the shortest distance between the grooves 113P is 20 μm or less, and the maximum inner width between the grooves 113P is 20 μm or less. Therefore, fine wiring can be achieved by firing the conductive paste 12P disposed within the grooves 113P to form the wiring portion 12. Furthermore, by forming the grooves 113P using a laser or ion beam, the grooves 113P can have a tapered shape when viewed from the direction of extension of the grooves 113P. This suppresses the concentration of the electric field at the corners of the wiring portion 12 disposed in the grooves 113 after firing. This in turn suppresses the occurrence of crosstalk between the multiple wiring portions 12. As a result, a ceramic substrate 1 can be provided that can suppress degradation of signal transmission characteristics.

[0088] In this embodiment, preferably, the method for manufacturing the ceramic substrate 1 further includes providing the conductive paste 12P on the plate PL (S131). Then, the plate PL on which the conductive paste 12P is provided is heated to eject the conductive paste 12P from the plate PL, thereby providing the conductive paste 12P in the plurality of grooves 113P (S15).

[0089] When the conductive paste 12P is applied to the grooves 113P having a maximum inner width of 20 μm or less using conventional screen printing, the conductive paste 12P overflows from the grooves 113P of the wiring ceramic green sheet 11AP, potentially forming an excess conductive paste layer 15P on the main surface 111P. This makes it difficult to achieve fine wiring. However, by using the above configuration to eject the conductive paste 12P toward the grooves 113P of the ceramic green sheet 11P, the conductive paste 12P can be placed within the grooves 113P while suppressing the formation of an excess conductive paste layer 15P. This makes it easy to manufacture a ceramic substrate 1 having fine wiring.

[0090] In the present embodiment, the method for manufacturing the ceramic substrate 1 preferably further includes providing the conductive paste 12P on the transparent base material TS (S132). Then, the transparent base material TS on which the conductive paste 12P has been provided is irradiated with a laser to transfer the conductive paste 12P on the transparent base material TS, thereby providing the conductive paste 12P in the plurality of recessed streak portions 113P (S15).

[0091] When the conductive paste 12P is applied to the grooves 113P having a maximum inner width of 20 μm or less using conventional screen printing, the conductive paste 12P overflows from the grooves 113P of the wiring ceramic green sheet 11AP, potentially forming an excess conductive paste layer 15P. This makes it difficult to achieve fine wiring. However, by using the above configuration to transfer the conductive paste 12P to the grooves 113P of the ceramic green sheet 11P, the conductive paste 12P can be placed within the grooves 113P while suppressing the formation of an excess conductive paste layer 15P. This makes it easy to manufacture a ceramic substrate 1 having fine wiring.

[0092] In this embodiment, preferably, a pre-fired laminate 2P is formed by stacking multiple ceramic green sheets 11P, including the wiring ceramic green sheet 11AP, on the first constraining green layer 50P (S20). The method for manufacturing the ceramic substrate 1 further includes stacking a second constraining green layer 55P on the side of the pre-fired laminate 2P opposite the first constraining green layer 50P (S30). The pre-fired laminate 2P is then fired together with the first constraining green layer 50P and the second constraining green layer 55P under pressure (S40). The method for manufacturing the ceramic substrate 1 further includes removing the first constraining layer 50 formed by firing the first constraining green layer 50P and the second constraining layer 55 formed by firing the second constraining green layer 55P from the laminate 2 formed by firing the pre-fired laminate 2P (S50).

[0093] According to the above configuration, the first constraining layer 50 and the second constraining layer 55 can prevent the laminate 2 from shrinking in the direction along the main surface 111P during firing. This in turn makes it easier to manufacture a ceramic substrate 1 having fine wiring with improved dimensional accuracy and reduced surface distortion. Furthermore, because the grooves 113P have a tapered shape due to being formed with a laser or ion beam, warping of the laminate 2 during firing can be reduced compared to when the grooves 113P do not have a tapered shape.

[0094] Next, a ceramic substrate according to a second embodiment of the present disclosure will be described. The ceramic substrate according to the second embodiment of the present disclosure differs from ceramic substrate 1 according to the first embodiment of the present disclosure mainly in the method of forming the wiring ceramic layer. Therefore, the same configuration and effects as those of ceramic substrate 1 according to the first embodiment of the present disclosure will not be described repeatedly.

[0095] Fig. 24 is a cross-sectional view showing a ceramic substrate according to embodiment 2. As shown in Fig. 24 , in the ceramic substrate 1X according to embodiment 2, the main surface 111 of at least one wiring ceramic layer 10A is located on the outer surface of the laminate 2 made up of a plurality of layers 10. Specifically, embodiment 2 includes only one wiring ceramic layer 10A, and the main surface 111 of this wiring ceramic layer 10A is located on the outer surface of the laminate 2 made up of a plurality of layers 10.

[0096] A method for manufacturing a ceramic substrate according to embodiment 2 will now be described. Fig. 25 is a flowchart showing a method for producing a ceramic green sheet for wiring provided with a conductive paste in the method for manufacturing a ceramic substrate according to embodiment 2.

[0097] As shown in FIG. 25, the method for manufacturing a ceramic substrate according to the second embodiment of the present disclosure includes step S15a instead of steps S131, S132, and S15 (see FIG. 6) of the first embodiment.

[0098] 26 is a cross-sectional view schematically illustrating the preparation of a ceramic green sheet for wiring provided with a conductive paste in embodiment 2. As shown in Fig. 26, in step S15a, a conductive paste 12P is provided on the main surface 111P by screen printing to form an excess conductive paste layer 15P, and the conductive paste 12P is provided in the plurality of grooves 113P. Instead of screen printing, the conductive paste 12P may be provided by inkjet printing.

[0099] 27 is a flowchart showing a method after fabricating a ceramic green sheet for wiring provided with a conductive paste, among methods for manufacturing a ceramic substrate according to embodiment 2. The method for manufacturing a ceramic substrate according to embodiment 2 of the present disclosure includes steps S20a, S30a, and S40a, which are partially different from steps S20, S30, and S40 (see FIG. 14 ) of embodiment 1. The method for manufacturing a ceramic substrate according to embodiment 2 of the present disclosure further includes step S60a.

[0100] 28 is a cross-sectional view showing a pre-fired laminate formed by stacking multiple ceramic green sheets on one another in embodiment 2. As shown in FIG. 28 , in step S20a, the wiring ceramic green sheets 11AP provided with the conductive paste 12P are stacked so that the excess conductive paste layer 15P is located at the position farthest from the first constraining green layer 50P. In other words, the wiring ceramic green sheets 11AP are stacked so that the excess conductive paste layer 15P is located on the outer surface of the pre-fired laminate 2P. In addition, in step S30a, the second constraining green layer 55P is also stacked on the excess conductive paste layer 15P.

[0101] 29 is a cross-sectional view showing the laminate immediately after being formed by firing the pre-fired laminate in embodiment 2. As shown in Fig. 28 and Fig. 29, in step S40a, the pre-fired laminate 2P is fired together with the excess conductive paste layer 15P while being pressurized.

[0102] In step S60a, the excess conductive layer 15 formed by firing the excess conductive paste layer 15P is removed by polishing from the laminate 2 formed by firing the pre-fired laminate 2P. The method for removing the excess conductive layer 15 may be the same as the method for removing the first constraining green layer 50P and the second constraining green layer 55P. The removal of the excess conductive layer 15 may be performed subsequent to the removal of the second constraining green layer 55P. In this manner, the ceramic substrate 1X (see FIG. 24 ) according to the second embodiment of the present disclosure is manufactured.

[0103] Here, in order to explain the effect of the method for manufacturing a ceramic substrate according to the second embodiment of the present disclosure, another comparative example will be described.

[0104] FIG. 30 is a cross-sectional view showing a wiring ceramic green sheet provided with a conductive paste in Comparative Example 3. As shown in FIG. 30, the wiring ceramic green sheet 811AP is manufactured in the same manner as the wiring ceramic green sheet 11AP of Example 2 (see FIG. 26 ), but the wiring ceramic green sheet 811AP is intended to be laminated so that the main surface 111P is positioned inside the pre-fired laminate. With such a wiring ceramic green sheet 811AP, the excess conductive paste layer 15P cannot be removed after firing. In other words, step S60a in Example 2 cannot be performed on the excess conductive layer formed by the excess conductive paste layer 15P provided on this wiring ceramic green sheet 811AP. Therefore, in Comparative Example 3, multiple wiring portions are unintentionally connected to each other inside the laminate.

[0105] FIG. 31 is a cross-sectional view showing a ceramic green sheet for wiring provided with a conductive paste in Comparative Example 4. FIG. 32 is a cross-sectional view showing a ceramic substrate according to Comparative Example 4. As shown in FIGS. 31 and 32 , in Comparative Example 3, a ceramic green sheet for wiring 911AP is manufactured in the same manner as the ceramic green sheet for wiring 811AP in Comparative Example 3, except that the shortest distance between the multiple groove portions 113P is 30 μm or more. This causes the excess conductive paste layers 15P located on each groove portion 9113P to be spaced apart from each other. However, because the shortest distance between the groove portions 9113P exceeds 20 μm after firing, it becomes difficult to realize fine wiring using multiple wiring portions 912 within the laminate 92.

[0106] As described above, in the method for manufacturing the ceramic substrate 1X according to the second embodiment of the present disclosure, the conductive paste 12P is provided on the main surface 111P by screen printing to form an excess conductive paste layer 15P, while the conductive paste 12P is provided in the plurality of recesses 113P (S15a), and the pre-fired laminate 2P is fired together with the excess conductive paste layer 15P while being pressurized (S40a). The method for manufacturing the ceramic substrate 1X according to the second embodiment of the present disclosure further includes polishing to remove the excess conductive layer 15 formed by firing the excess conductive paste layer 15P from the laminate 2 formed by firing the pre-fired laminate 2P (S60a).

[0107] According to the above configuration, it is possible to prevent the wiring portions 12 arranged in the recessed stripes 113 from being connected to each other via the excess conductive layer 15. Consequently, it is possible to easily manufacture the ceramic substrate 1X having fine wiring.

[0108] (Experimental Example) Finally, an experimental example in which a ceramic substrate was manufactured and observed will be described. In this experimental example, a ceramic green sheet was prepared as follows. First, alumina powder and glass powder were mixed in a weight ratio of 40:60 to obtain a mixed powder. The glass powder contained SiO ２ :59% by weight, B ２ O ３ : 10% by weight, CaO: 25% by weight, Al ２ O ３ A borosilicate glass powder containing 6% by weight of SiO 2 was used. Appropriate amounts of binder, dispersant, plasticizer, and organic solvent were added to this mixed powder and mixed to obtain a ceramic slurry. After degassing the ceramic slurry, a 40 μm-thick ceramic green sheet was prepared on a carrier film using a doctor blade.

[0109] The grooves formed in the ceramic green sheets were formed using a short-pulse laser so that they had a depth of approximately 20 μm and a maximum inner width of approximately 10 μm. A pre-fired laminate was produced by stacking 14 ceramic green sheets, including one wiring ceramic green sheet. Sheets containing alumina as a main component were prepared as the first and second constraining layers. The firing temperature was 1000°C.

[0110] The ceramic substrate according to the experimental example was otherwise manufactured in the same manner as the ceramic substrate 1 according to embodiment 2. In the ceramic substrate according to the experimental example, the thickness of the wiring ceramic layer was about 20 μm.

[0111] 33 is a diagram showing a cross-sectional photograph of a laminate immediately after being formed by firing a pre-fired laminate in an experimental example. In this experimental example, the excess conductive layer shown in FIG. 33 was removed together with the second constraining layer. Note that the cross-sectional photograph in this experimental example and the planar photographs described below were photographs taken with a scanning electron microscope (SEM).

[0112] 34 is a cross-sectional photograph of a ceramic substrate according to an experimental example. As shown in Fig. 33 and Fig. 34, the depth of the grooves in the wiring ceramic layer was about 10 µm.

[0113] Figure 35 is a plan view of a ceramic substrate according to an experimental example. As shown in Figures 34 and 35, the shortest distance between the multiple grooves was approximately 10 μm. The maximum inner width of each of the multiple grooves was approximately 10 μm. Furthermore, each of the multiple grooves had a tapered shape on the side opposite the main surface. Thus, it can be seen from the experimental example that a ceramic substrate having fine wiring with an L / S ratio of approximately 10 / 10 μm and suppressing degradation of signal transmission characteristics could be fabricated.

[0114] (Additional Note) As described above, the embodiments of the present disclosure include the following disclosures.

[0115] <1> A ceramic substrate formed by stacking and bonding a plurality of layers, including at least one wiring ceramic layer, on top of each other in a stacking direction, the wiring ceramic layer including: a base portion including ceramic; and a plurality of wiring portions having electrical conductivity; the base portion including: a main surface facing either one of the stacking directions and extending in a direction substantially perpendicular to the stacking direction; and a plurality of grooves formed to be recessed from the main surface; the plurality of wiring portions are respectively provided within the plurality of grooves; the shortest distance between the plurality of grooves is 20 μm or less; the maximum inner width of each of the plurality of grooves is 20 μm or less; and each of the plurality of grooves has a tapered shape that narrows on the side opposite to the main surface.

[0116] <2> The ceramic substrate according to <1>, wherein at least one of the plurality of recessed streak portions has: a first inner side surface extending in a direction away from the main surface; a second inner side surface extending in a direction away from the main surface and facing the first inner side surface; and a tip portion formed by connecting edges of the first inner side surface and the second inner side surface on a side opposite to the main surface.

[0117] <3> The ceramic substrate according to <2>, wherein the tip portion is curved when viewed from the extending direction of the groove portion.

[0118] <4> The ceramic substrate according to <3>, wherein the tip end has a radius of curvature of 0.1 μm or more when viewed from the extending direction.

[0119] <5> The ceramic substrate according to any one of <1> to <4>, wherein at least one of the plurality of recessed streak portions has: a first inner side surface extending in a direction away from the main surface; a second inner side surface extending in a direction away from the main surface and facing the first inner side surface; and a bottom surface connecting edges of the first inner side surface and the second inner side surface on the side opposite to the main surface, and a deepest portion of the bottom surface that is the portion farthest from the main surface in the stacking direction is curved when viewed from the extension direction of the recessed streak portion.

[0120] <6> The ceramic substrate according to <5>, wherein the radius of curvature of the deepest part when viewed from the extending direction is 0.1 μm or more.

[0121] <7> The ceramic substrate according to any one of <1> to <6>, wherein the main surface of the wiring ceramic layer is located on an outer surface of a laminate made up of the plurality of layers stacked on top of each other.

[0122] <8> The ceramic substrate according to any one of <1> to <6>, wherein the main surface of the wiring ceramic layer is located inside a laminate made up of the plurality of layers stacked on top of each other.

[0123] <9> A module comprising: the ceramic substrate according to any one of <1> to <8>; and a plurality of electronic components mounted on the ceramic substrate and electrically connected to at least one of the plurality of wiring portions.

[0124] <10> A method for manufacturing a ceramic substrate, comprising: irradiating a ceramic green sheet with a laser or an ion beam to form a ceramic green sheet for wiring, the ceramic green sheet having a plurality of recessed streaks on a main surface of the ceramic green sheet, the recessed streaks being spaced apart from one another by a shortest distance of 20 μm or less and having a maximum inner width of 20 μm or less; providing a conductive paste in the plurality of recessed streaks; stacking the plurality of ceramic green sheets including the ceramic green sheet for wiring on one another to form a pre-fired laminate; and firing the pre-fired laminate while applying pressure.

[0125] <11> The method for manufacturing a ceramic substrate according to <10>, further comprising providing the conductive paste on a plate, wherein the plate on which the conductive paste is provided is heated to eject the conductive paste from the plate, thereby providing the conductive paste in the plurality of grooves.

[0126] <12> The method for manufacturing a ceramic substrate according to <10>, further comprising providing the conductive paste on a transparent base material, wherein the conductive paste is provided in the plurality of grooves by irradiating the transparent base material with a laser to transfer the conductive paste on the transparent base material.

[0127] <13> The method for manufacturing a ceramic substrate according to <10>, further comprising: providing the conductive paste on the main surface by screen printing to form an excess conductive paste layer while providing the conductive paste in the plurality of recessed streaks; firing the pre-fired laminate together with the excess conductive paste layer while applying pressure; and removing, by polishing, the excess conductive layer formed by firing the excess conductive paste layer from the laminate formed by firing the pre-fired laminate.

[0128] <14> The method for manufacturing a ceramic substrate according to any one of <10> to <13>, further comprising: forming the pre-fired laminate by stacking the plurality of ceramic green sheets, including the wiring ceramic green sheet, on a first constraining green layer; further stacking a second constraining green layer on the side of the pre-fired laminate opposite to the first constraining green layer side; firing the pre-fired laminate together with the first constraining green layer and the second constraining green layer while applying pressure; and removing, from the laminate formed by firing the pre-fired laminate, a first constraining layer formed by firing the first constraining green layer and a second constraining layer formed by firing the second constraining green layer.

[0129] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0130] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0131] 1, 1X Ceramic substrate, 2 Laminate, 2P Pre-fired laminate, 10 Layer, 10A Wiring ceramic layer, 11 Base portion, 11AP Wiring ceramic green sheet, 11P Ceramic green sheet, 111, 111P Main surface, 112 Other main surface, 113, 113P Concave portion, 114 First inner surface, 115 Second inner surface, 116 Tip portion, 117 Bottom surface, 117D Deepest portion, 118, 118P Via hole, 119 Other concave portion, 12 Wiring portion, 12P Conductive paste, 121 Exposed surface, 13 Via electrode, 15 Excess conductive layer, 15P Excess conductive paste layer, 50 First constraining layer, 50P First constraining green layer, 55 Second constraining layer, 55P Second constraining green layer, 500 Electronic component, 510 First bonding material, 1000, 1000a module, 2000 motherboard, 2100 second bonding material, DS stacking direction, PL plate, PLa groove portion, TS transparent substrate.

Claims

1. A ceramic substrate formed by stacking and bonding a plurality of layers, including at least one wiring ceramic layer, together in a stacking direction, wherein the wiring ceramic layer includes a base portion containing ceramic and a plurality of conductive wiring portions, the base portion including a main surface facing either one of the stacking directions and extending in a direction substantially perpendicular to the stacking direction, and a plurality of grooves formed to be recessed from the main surface, the plurality of wiring portions being respectively provided within the plurality of grooves, the shortest distance between the plurality of grooves being 20 μm or less, the maximum inner width of each of the plurality of grooves being 20 μm or less, and each of the plurality of grooves having a tapered shape on the side opposite to the main surface.

2. The ceramic substrate according to claim 1, wherein at least one of the plurality of recessed streaks has a first inner side surface extending in a direction away from the main surface, a second inner side surface extending in a direction away from the main surface and facing the first inner side surface, and a tip portion formed by connecting edges of the first inner side surface and the second inner side surface on the side opposite to the main surface.

3. The ceramic substrate according to claim 2, wherein the tip portion is curved when viewed from the extending direction of the groove portion.

4. The ceramic substrate according to claim 3, wherein the radius of curvature of the tip portion when viewed from the extending direction is 0.1 μm or more.

5. A ceramic substrate according to any one of claims 1 to 4, wherein at least one of the plurality of grooves has a first inner side surface extending in a direction away from the main surface, a second inner side surface extending in a direction away from the main surface and facing the first inner side surface, and a bottom surface connecting edges of the first inner side surface and the second inner side surface on the side opposite to the main surface, and the deepest part of the bottom surface, which is the part farthest from the main surface in the stacking direction, is curved when viewed from the extension direction of the groove.

6. The ceramic substrate according to claim 5, wherein the radius of curvature of the deepest portion when viewed from the extending direction is 0.1 μm or more.

7. A ceramic substrate according to any one of claims 1 to 6, wherein the main surface of the wiring ceramic layer is located on the outer surface of a laminate consisting of the plurality of layers stacked on top of each other.

8. A ceramic substrate according to any one of claims 1 to 6, wherein the main surface of the wiring ceramic layer is located inside a laminate made up of the plurality of layers stacked on top of each other.

9. A module comprising: the ceramic substrate according to any one of claims 1 to 8; and a plurality of electronic components mounted on the ceramic substrate and electrically connected to at least one of the plurality of wiring portions.

10. A method for manufacturing a ceramic substrate, comprising: irradiating a ceramic green sheet with a laser or ion beam to form a ceramic green sheet for wiring, the ceramic green sheet having a plurality of grooves on a main surface thereof, the grooves being spaced apart from one another by a minimum distance of 20 μm or less and having a maximum inner width of 20 μm or less; providing a conductive paste in the plurality of grooves; stacking a plurality of ceramic green sheets, including the ceramic green sheet for wiring, on top of each other to form a pre-fired laminate; and firing the pre-fired laminate while applying pressure.

11. The method for manufacturing a ceramic substrate according to claim 10, further comprising providing the conductive paste on a plate, and heating the plate on which the conductive paste has been provided to cause the conductive paste to be ejected from the plate, thereby providing the conductive paste in the plurality of grooves.

12. A method for manufacturing a ceramic substrate as described in claim 10, further comprising providing the conductive paste on a transparent base material, and irradiating the transparent base material on which the conductive paste has been provided with a laser to transfer the conductive paste on the transparent base material, thereby providing the conductive paste in the multiple groove portions.

13. A method for manufacturing a ceramic substrate as described in claim 10, further comprising: providing the conductive paste on the main surface by screen printing to form an excess conductive paste layer while providing the conductive paste in the plurality of grooves; firing the pre-fired laminate together with the excess conductive paste layer while applying pressure; and removing the excess conductive layer formed by firing the excess conductive paste layer from the laminate formed by firing the pre-fired laminate by polishing.

14. A method for manufacturing a ceramic substrate as described in any one of claims 10 to 13, further comprising: forming the pre-fired laminate by stacking the plurality of ceramic green sheets, including the wiring ceramic green sheet, on a first constraining green layer; further stacking a second constraining green layer on the side of the pre-fired laminate opposite the first constraining green layer; firing the pre-fired laminate together with the first constraining green layer and the second constraining green layer while applying pressure; and removing the first constraining layer formed by firing the first constraining green layer and the second constraining layer formed by firing the second constraining green layer from the laminate formed by firing the pre-fired laminate.

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