Core substrate and interposer

Abstract

According to the present invention, a plurality of conductor parts (200) are made of a sintered body material, pass through a ceramic substrate (100) in the thickness direction, are electrically connected to each other so as to constitute a series circuit, and include a first conductor part (201), a second conductor part (202), and a third conductor part (203). At least one magnetic body part (300) is for increasing the inductance of the plurality of conductor parts (200), is embedded in the ceramic substrate (100), and is made of a ceramic.

Description

Core substrate and interposer

[0001] The present invention relates to a core substrate and an interposer, and more particularly to a core substrate with a built-in inductor for constituting an interposer on which a semiconductor element is mounted.

[0002] According to Japanese Patent Laid-Open Publication No. 2019-179792 (Patent Document 1), in a semiconductor device, an interposer is disposed between a semiconductor element and a motherboard. The semiconductor element and the motherboard are each connected to the interposer using solder balls. The interposer is shown to be a multilayer printed wiring board, which includes a core substrate, three conductor circuit layers stacked on the core substrate so as to face the semiconductor element, and three conductor circuit layers stacked on the core substrate so as to face the motherboard. On the semiconductor element mounting side of the interposer, the wiring dimensions are gradually reduced by passing through the three conductor circuit layers.

[0003] Efficient power management is sometimes required for semiconductor devices such as integrated circuits (ICs). Typically, a voltage regulator controls the supply voltage to each of multiple computing cores in a processor chip (semiconductor device) depending on the processor's processing power, etc. A voltage regulator typically requires switches, capacitors, and inductors. Controlling the supply voltage for each computing core requires a separate switch, capacitor, and inductor for each computing core. In particular, inductors are difficult to incorporate into semiconductor devices and are typically prepared separately from the semiconductor device. High-performance processors, particularly those for data servers, have many computing cores to enhance their processing power, and correspondingly, the inductance required per unit area of ​​the processor chip is increasing. The inductance of an inductor can be increased by increasing the magnetic permeability near the inductor's current path. It is widely known to use magnetic materials for this purpose.

[0004] U.S. Patent Application Publication No. 2019 / 0279806 (Patent Document 2) discloses a package substrate (interposer) with an embedded inductor that is disposed between a die (semiconductor element) and a board (motherboard). The specification exemplifies forming a substrate core primarily made of organic material with conductive through-holes (conductor portions) and a magnetic coating (magnetic material portion) containing magnetic particles and disposed around the conductor portions. In this case, the magnetic material portion must be formed at a temperature equal to or lower than the heat resistance temperature of the organic material of the substrate core. A typical method for achieving this is to solidify a resin in which magnetic particles are dispersed. However, when the magnetic material portion is formed from magnetic particles dispersed in a resin, it is difficult to ensure a sufficiently high magnetic permeability due to limitations on the magnetic particle filling rate (the proportion of magnetic particles per volume).

[0005] International Publication No. 2022 / 163588 (Patent Document 3) discloses a core substrate with an inductor built in for forming an interposer on which a semiconductor element is mounted. The core substrate includes a ceramic substrate, a conductor portion, and a magnetic material portion. The ceramic substrate has a first surface and a second surface opposite the first surface in the thickness direction, and a through hole between the first surface and the second surface. The conductor portion passes through the through hole. The conductor portion is made of sintered metal. The magnetic material portion surrounds the conductor portion at the through hole. The magnetic material portion is made of ceramics rather than resin with dispersed magnetic particles. By densely sintering the ceramics, the magnetic permeability of the magnetic material portion can be sufficiently increased. Therefore, the core substrate can incorporate an inductor with a large inductance per unit area.

[0006] JP 2019-179792 A U.S. Patent Application Publication No. 2019 / 0279806 WO 2022 / 163588

[0007] Generally, as the DC bias current applied to an inductor increases from zero, the magnetic material of the magnetic body approaches magnetic saturation, and therefore its permeability decreases. As a result, the inductance of the inductor decreases. This characteristic is called the DC bias characteristic. The smaller the rate of decrease, the better the DC bias characteristic. If a magnetic material with high permeability is used with the intention of increasing the inductance, the DC bias characteristic tends to deteriorate.

[0008] According to the technology disclosed in WO 2022 / 163588, an inductor having a large inductance per unit area can be built into a core substrate. However, the inventors have found that, according to this technology, the DC superposition characteristics of the inductor built into the core substrate tend to be insufficient when a large current flows, such as when power is supplied to a semiconductor element.

[0009] The present invention has been made to solve the above problems, and one object of the present invention is to provide a core substrate in which an inductor built therein has a sufficiently large inductance per unit area while also having sufficiently good DC bias characteristics. Another object of the present invention is to provide an interposer in which a semiconductor element is to be mounted, in which an inductor built in a core substrate of the interposer has a sufficiently large inductance per unit area while also having sufficiently good DC bias characteristics.

[0010] Aspect 1 is a core substrate with an inductor built in for forming an interposer on which a semiconductor element is mounted, comprising: a ceramic substrate having a thickness direction; a plurality of conductor portions made of a sintered material, penetrating the ceramic substrate in the thickness direction, electrically connected to each other to form a series circuit, and including a first conductor portion, a second conductor portion, and a third conductor portion; and at least one magnetic portion made of ceramic, embedded in the ceramic substrate, for increasing the inductance of the plurality of conductor portions.

[0011] Aspect 2 is a core substrate according to Aspect 1, wherein the ceramic substrate has a first surface to which a first end of the first conductor portion, a first end of the second conductor portion, and a first end of the third conductor portion reach, and a second surface to which a second end of the first conductor portion, a second end of the second conductor portion, and a second end of the third conductor portion reach, and further includes a first connection portion that electrically connects the first end of the first conductor portion and the first end of the second conductor portion to each other, and a second connection portion that electrically connects the second end of the second conductor portion and the second end of the third conductor portion to each other.

[0012] Aspect 3 is a core substrate described in aspect 1 or 2, wherein in at least one cross-sectional view perpendicular to the thickness direction across the at least one magnetic material portion, the shortest distance between the first conductor portion and the third conductor portion is smaller than the shortest distance between the first conductor portion and the second conductor portion.

[0013] Aspect 4 is a core substrate described in any one of aspects 1 to 3, wherein the at least one magnetic material portion includes a first magnetic material portion in contact with the first conductor portion and the third conductor portion, and a second magnetic material portion in contact with the second conductor portion and spaced apart from the first magnetic material portion.

[0014] Aspect 5 is a core substrate described in Aspect 4, wherein in at least one cross-sectional view perpendicular to the thickness direction that crosses the first magnetic material portion and the second magnetic material portion, the distance between the center of the first conductor portion and the center of the second conductor portion is greater than the distance between the center of the first magnetic material portion and the center of the second magnetic material portion.

[0015] A sixth aspect is the core substrate according to any one of the first to third aspects, wherein the at least one magnetic material portion is a common magnetic material portion for increasing the inductance of the plurality of conductor portions.

[0016] Aspect 7 is a core substrate according to any one of aspects 1 to 6, wherein the plurality of conductor portions includes at least one conductor portion in contact with one magnetic material portion included in the at least one magnetic material portion.

[0017] Aspect 8 is the core substrate according to aspect 7, wherein the at least one conductor portion is in contact with the ceramic substrate.

[0018] Aspect 9 is a core substrate described in aspect 8, wherein in at least one cross-sectional view perpendicular to the thickness direction across the one magnetic material portion, the at least one conductor portion protrudes toward the ceramic substrate across a tangent to the boundary between the one magnetic material portion and the ceramic substrate.

[0019] Aspect 10 is a core substrate described in Aspect 7, wherein in at least one cross-sectional view perpendicular to the thickness direction crossing the one magnetic material portion, the at least one conductor portion is in contact with the ceramic substrate without crossing the tangent to the boundary between the one magnetic material portion and the ceramic substrate.

[0020] Aspect 11 is the core substrate according to aspect 7, wherein the at least one conductor portion is spaced apart from the ceramic substrate.

[0021] A twelfth aspect of the present invention is the core substrate according to any one of the first to sixth aspects, wherein the plurality of conductor portions include at least one conductor portion that is spaced apart from the at least one magnetic material portion and that is in contact with the ceramic substrate.

[0022] A thirteenth aspect of the present invention is the core substrate according to any one of the first to twelfth aspects, wherein each of the plurality of conductor portions is a solid body.

[0023] Aspect 14 is the core substrate according to any one of aspects 1 to 13, wherein the ceramic substrate is made of a low-temperature co-fired ceramic material or glass alumina.

[0024] A fifteenth aspect of the present invention is the core substrate according to any one of the first to fourteenth aspects, wherein a sintered interface is formed between the plurality of conductor portions and a portion of the core substrate other than the plurality of conductor portions.

[0025] Aspect 16 is an interposer comprising a core substrate according to any one of aspects 1 to 15, and a wiring layer stacked on the core substrate, the wiring layer having a mounting surface on which the semiconductor element is to be mounted.

[0026] According to the first aspect, first, at least one magnetic body embedded in the ceramic substrate of the core substrate is made of ceramic. By densely sintering the ceramic of the at least one magnetic body, the magnetic permeability of the at least one magnetic body can be increased. Therefore, the inductor built into the core substrate can have a sufficiently large inductance per unit area. Second, the first conductor, the second conductor, and the third conductor penetrate the ceramic substrate in the thickness direction and are electrically connected to each other to form a series circuit. This allows a series circuit to be formed in the thickness direction of the ceramic substrate, such that a current passes through the first conductor, then passes through the second conductor, turns around, and passes through the third conductor. In this case, the directional vector of the current in the first conductor and the directional vector of the current in the third conductor can be roughly the same. In this case, in the regions near both the first conductor and the third conductor, the magnetic field caused by the current in the first conductor and the magnetic field caused by the current in the third conductor cancel each other out according to Ampere's law. Therefore, in this region, it is possible to prevent at least one magnetic material portion from approaching a magnetic saturation state. As a result, the inductor built into the core substrate can have a sufficiently large inductance per unit area and also have sufficiently good DC bias characteristics.

[0027] According to the second aspect, the core substrate has the first connection portion, the second connection portion, and the third connection portion, which allows the first conductor portion, the second conductor portion, and the third conductor portion to be electrically connected to one another so as to form the series circuit.

[0028] According to the third aspect, the shortest distance between the first conductor and the third conductor is shorter than the shortest distance between the first conductor and the second conductor. In this case, the mutual cancellation effect between the magnetic field caused by the current in the first conductor and the magnetic field caused by the current in the third conductor is enhanced in the regions near both the first conductor and the third conductor, and the mutual reinforcement effect between the magnetic field caused by the current in the first conductor and the magnetic field caused by the current in the second conductor is mitigated in the regions near both the first conductor and the second conductor. This makes it more difficult for at least one magnetic material portion to approach a magnetic saturation state. This improves the DC bias characteristics of the built-in inductor.

[0029] According to the fourth aspect, the at least one magnetic material portion includes a first magnetic material portion in contact with the first conductor portion and the third conductor portion, and a second magnetic material portion in contact with the second conductor portion and spaced apart from the first magnetic material portion. This configuration makes it difficult for the first magnetic material portion to approach magnetic saturation due to the mutual cancellation of magnetic fields caused by the current in the first conductor portion and the current in the third conductor portion. Second, a region is provided to separate the first magnetic material portion in contact with the first conductor portion and the second magnetic material portion in contact with the second conductor portion. Since this region is not included in the at least one magnetic material portion, it is not affected by the mutual reinforcement of magnetic fields caused by the current in the first conductor portion and the current in the second conductor portion. This prevents deterioration of DC bias characteristics due to magnetic saturation in this region. These two effects improve the DC bias characteristics of the built-in inductor.

[0030] According to the fifth aspect, the distance between the center of the first conductor portion and the center of the second conductor portion is greater than the distance between the center of the first magnetic material portion and the center of the second magnetic material portion. This reduces the mutual reinforcement effect of the magnetic field caused by the current in the first conductor portion and the magnetic field caused by the current in the second conductor portion compared to when the distance between the center of the first conductor portion and the center of the second conductor portion is smaller than the distance between the center of the first magnetic material portion and the center of the second magnetic material portion. This makes it difficult for at least one magnetic material portion in the regions near both the first conductor portion and the second conductor portion to approach magnetic saturation. This improves the DC bias characteristics of the built-in inductor.

[0031] According to the sixth aspect, at least one magnetic body part is a common magnetic body part, which ensures a larger inductance than when a plurality of magnetic body parts that are separate from each other are used.

[0032] According to the seventh aspect, the plurality of conductor portions includes at least one conductor portion that is in contact with one magnetic material portion, thereby making it possible to further increase the inductance of the inductor formed by the at least one conductor portion.

[0033] According to the above-mentioned Aspect 8, in order to increase the inductance, at least one conductor portion is in contact with not only one magnetic portion as defined in the above-mentioned Aspect 7, but also the ceramic substrate, thereby making it easier to balance between obtaining a sufficiently large inductance and obtaining sufficiently good DC bias characteristics.

[0034] According to the above-mentioned Aspect 9, not only does the at least one conductor portion contact each of the one magnetic material portion and the ceramic substrate as defined in the above-mentioned Aspect 8, but in at least one cross-sectional view perpendicular to the thickness direction across the at least one magnetic material portion, the at least one conductor portion protrudes toward the ceramic substrate across a tangent to the boundary between the one magnetic material portion and the ceramic substrate. This allows the DC bias characteristics to be given some importance in the above-mentioned Aspect 8, which strikes a balance between obtaining a sufficiently large inductance and obtaining sufficiently good DC bias characteristics.

[0035] According to the above-mentioned aspect 10, at least one conductor portion not only contacts one magnetic portion as defined in the above-mentioned aspect 7 in order to increase the inductance, but also contacts the ceramic substrate without crossing the tangent line of the boundary between the one magnetic portion and the ceramic substrate. This makes it possible to balance between obtaining a sufficiently large inductance and obtaining sufficiently good DC bias characteristics, while placing a slightly greater emphasis on the magnitude of the inductance than in the above-mentioned aspect 9.

[0036] According to the above-mentioned aspect 11, at least one conductor portion is not only in contact with one magnetic material portion as defined in the above-mentioned aspect 7, but is also spaced apart from the ceramic substrate. This allows greater emphasis to be placed on the magnitude of inductance compared to the above-mentioned aspect 8.

[0037] According to the twelfth aspect, the at least one conductor portion is in contact with the ceramic substrate and is spaced apart from the at least one magnetic portion, which allows for greater emphasis on good DC bias characteristics.

[0038] According to the thirteenth aspect, each of the plurality of conductors is solid. This prevents an increase in electrical resistance due to hollow portions. This reduces the electrical resistance of each of the plurality of conductors.

[0039] According to the fourteenth aspect, the ceramic substrate is made of a low-temperature co-fired ceramic material or glass alumina, which makes it easier to form the ceramic substrate and the plurality of conductor portions by co-firing in the production of the core substrate.

[0040] According to the above-mentioned aspect 15, the core substrate has a sintered interface between the plurality of conductors and the portion of the core substrate other than the plurality of conductors. This prevents the heat resistance of the core substrate from being reduced due to the low heat resistance of the organic adhesive, unlike when the plurality of conductors are bonded to the portion of the core substrate other than the plurality of conductors via an organic adhesive. Therefore, the heat resistance of the core substrate can be improved.

[0041] According to the sixteenth aspect, first, at least one magnetic body embedded in the ceramic substrate of the core substrate is made of ceramic. By densely sintering the ceramic of the at least one magnetic body, the magnetic permeability of the at least one magnetic body can be increased. Therefore, the inductor built into the core substrate can have a sufficiently large inductance per unit area. Second, the first conductor, the second conductor, and the third conductor penetrate the ceramic substrate in the thickness direction and are electrically connected to each other to form a series circuit. This allows a series circuit to be formed in the thickness direction of the ceramic substrate, such that a current passes through the first conductor, then passes through the second conductor, turns around, and passes through the third conductor. In this case, the directional vector of the current in the first conductor and the directional vector of the current in the third conductor can be roughly the same. In this case, in the regions near both the first conductor and the third conductor, the magnetic field caused by the current in the first conductor and the magnetic field caused by the current in the third conductor cancel each other out according to Ampere's law. Therefore, in this region, it is possible to prevent at least one magnetic material portion from approaching a magnetic saturation state. As a result, the inductor built into the core substrate of the interposer on which the semiconductor element is to be mounted can have a sufficiently large inductance per unit area and also have sufficiently good DC bias characteristics.

[0042] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

[0043] FIG. 1 is a cross-sectional view schematically showing the configuration of an electronic device having an interposer. FIG. 2 is a schematic view showing an example of the configuration of a wiring layer provided on a surface of a core substrate of an interposer that faces a semiconductor element. FIG. 3 is a schematic view showing an example of the configuration of a wiring layer provided on a surface of a core substrate of an interposer opposite to the surface that faces the semiconductor element. FIG. 4 is a cross-sectional view showing an electronic device of a modified example of FIG. 1. FIG. 5 is a schematic view showing the configuration of an inductor built into a core substrate. FIG. 6 is a circuit diagram showing an example of electrical connections of inductors built into a core substrate of a comparative example. FIG. 7 is a partial cross-sectional view schematically showing the configuration of a core substrate of a comparative example. FIG. 8 is a circuit diagram showing an example of electrical connections of first to fourth inductors built into a core substrate of the first embodiment. FIG. 9 is a diagram schematically showing the configuration of a core substrate of the first embodiment, and is a partial cross-sectional view taken along line IX-IX in each of FIGS. 10 and 11 . FIG. 10 is a top view schematically showing the configuration of a core substrate of the first embodiment. FIG. 11 is a bottom view schematically showing the configuration of a core substrate in Embodiment 1. FIG. 12 is a partial cross-sectional view taken along line XII-XII in FIG. 9 . FIG. 13 is a partial cross-sectional view schematically showing the configuration of a core substrate in Embodiment 2. FIG. 14 is a partial cross-sectional view schematically showing a core substrate of a first modified example of Embodiment 2. FIG. 15 is a partial cross-sectional view schematically showing a core substrate of a second modified example of Embodiment 2. FIG. 16 is a partial cross-sectional view schematically showing a core substrate of a third modified example of Embodiment 2. FIG. 17 is a cross-sectional view showing the configuration of a core substrate in Example 1 under simulation conditions. FIG. 18 is a schematic diagram showing the configurations of first to sixth inductors built into the core substrate in Example 1 under simulation conditions. FIG. 19 is a cross-sectional view showing the configuration of a core substrate of a comparative example under simulation conditions.

[0044] Hereinafter, embodiments will be described with reference to the drawings. In some of the drawings, an XYZ Cartesian coordinate system is shown to facilitate understanding of the directional relationships between the drawings.

[0045] <Electronic Device Having an Interposer> Prior to describing the embodiments, a general configuration of an electronic device having an interposer will be described below as a preliminary explanation.

[0046] FIG. 1 is a cross-sectional view schematically illustrating the configuration of electronic device 901. Electronic device 901 includes interposer 700, semiconductor element 811, motherboard 812, and package substrate 813. Interposer 700 includes core substrate 600, wiring layer 791, and wiring layer 792. Wiring layer 791 and wiring layer 792 are laminated on first surface SF1 and second surface SF2 of core substrate 600, respectively. In other words, wiring layer 791 is provided on the surface of core substrate 600 facing semiconductor element 811, and wiring layer 792 is provided on the surface of core substrate 600 opposite the surface facing semiconductor element 811. Wiring layer 791 and wiring layer 792 may be laminated on core substrate 600 by a build-up method, a sputtering method, or the like, or may be bonded as separate wiring boards.

[0047] 2 is a schematic diagram showing an example of the configuration of the wiring layer 791. The wiring layer 791 has a stacking surface SG2 and a mounting surface SC that are opposite to each other. The stacking surface SG2 is stacked on the second surface SF2 of the core substrate 600. A semiconductor element 811 is mounted on the mounting surface SC. The wiring layer 791 also has an insulating portion 791i and a wiring portion 791j. The wiring portion 791j electrically connects the stacking surface SG2 and the mounting surface SC. The wiring portion 791j has a wiring group W1a that reaches the stacking surface SG2, a wiring group W1b that reaches the mounting surface SC, and wiring (not shown) that connects the wiring group W1a and the wiring group W1b.

[0048] The wiring layer 791 is preferably a multi-layer wiring layer configured so that the wiring dimensions (e.g., line and space (L / S) dimensions) are reduced from the stacking surface SG2 to the mounting surface SC. This makes it possible to configure an interposer 700 capable of mounting semiconductor elements 811 having a small terminal pitch even if the wiring dimensions (L / S) of the core substrate 600 are not particularly high. Specifically, the wiring layer 791 may be a laminate of a normal wiring layer facing the core substrate 600 and a fine wiring layer facing the semiconductor elements 811. In this case, the wiring group W1a belongs to the normal wiring layer, and the wiring group W1b belongs to the fine wiring layer.

[0049] A typical wiring layer may be formed by providing a wiring structure on a plate-shaped organic material (e.g., an epoxy-based member) or inorganic material (e.g., a low temperature co-fired ceramics (LTCC) material or a non-magnetic ferrite material). To form the wiring structure on this organic material, for example, Cu plating is used. To form the wiring structure on an inorganic material, when the inorganic material is formed by a firing process, the wiring structure is simultaneously formed by firing Ag (silver) or Cu (copper). From the viewpoint of ease of forming fine wiring, it is preferable that a fine wiring layer be formed by providing a wiring structure on a plate-shaped organic material (e.g., an epoxy-based or polyimide-based member). To form the wiring structure on this organic material, for example, Cu plating is used.

[0050] FIG. 3 is a schematic diagram showing an example of the configuration of the wiring layer 792. The wiring layer 792 has a stacking surface SG1 and a bottom surface SB that are opposite to each other. The stacking surface SG1 is stacked on the first surface SF1 of the core substrate 600. In the electronic device 901 of FIG. 3, the bottom surface SB faces the package substrate 813. The wiring layer 792 also has an insulating portion 792i and a wiring portion 792j. The wiring portion 792j electrically connects the stacking surface SG1 and the bottom surface SB. The wiring portion 792j has a wiring group W2a that reaches the bottom surface SB, a wiring group W2b that reaches the stacking surface SG1, and wiring (not shown) that connects the wiring group W2a and the wiring group W2b.

[0051] The semiconductor element 811 is connected to the wiring layer 791 of the interposer 700 by, for example, solder balls 821. The semiconductor element 811 may be an IC (Integrated Circuit) chip. In particular, when the IC chip is a processor chip having multiple processing cores, the voltage regulator described above can be configured using an inductor, which will be described later.

[0052] The interposer 700 is mounted on the package substrate 813 by bonding the wiring layer 792 to the package substrate 813. This bonding is performed, for example, by solder balls 823. The package substrate 813 is mounted on the motherboard 812, and this bonding is performed, for example, by using solder balls 822.

[0053] In the wiring layer 791 (FIG. 2), the pitch of the terminal group connected to the wiring group W1b on the mounting surface SC may be smaller than the pitch of the terminal group connected to the wiring group W1a on the stacking surface SG2, and in this case, the interposer 700 (FIG. 1) has the function of converting the terminal pitch. As a modified example, depending on the application of the interposer, either or both of the wiring layer 791 and the wiring layer 792 may be omitted.

[0054] 4 is a cross-sectional view showing an electronic device 902, which is a modified example of the electronic device 901 (FIG. 1). In the electronic device 902, the interposer 700 is bonded to the motherboard 812 without the package substrate 813 (FIG. 1), and this bonding is performed by, for example, solder balls 822.

[0055] 5 is a schematic diagram illustrating the configuration of inductors L1 to L6 built into the core substrate 600. The core substrate 600 has multiple inductors L1 and L2 built into it, and may also have additional inductors L3 to L6 built into it, with the number of inductors being arbitrary.

[0056] To configure an interposer such as interposer 700, a core substrate according to the present embodiment or its modified example, which will be described later, may be applied in place of the above-described core substrate 600. Therefore, detailed description of the interposer will not be repeated below.

[0057] <Core substrate using resin (comparative example)> Fig. 6 is a circuit diagram showing an example of the electrical connection of an inductor built into a core substrate 690 of a comparative example. Fig. 7 is a partial cross-sectional view showing the configuration of core substrate 690 of the comparative example. The built-in inductor of core substrate 690 has a series circuit of inductor L1 and inductor L2, which results in a combined inductance greater than the individual inductances of inductor L1 and inductor L2.

[0058] In the core substrate 690, a first magnetic material portion 391 and a first conductor portion 291 are formed in this order on the side wall of one through hole of a resin substrate 190 made of glass epoxy resin, with the first conductor portion 291 having a hollow structure filled with a resin material 281. Similarly, a second magnetic material portion 392 and a second conductor portion 292 are formed in this order on the side wall of another through hole of the resin substrate 190, with the second conductor portion 292 having a hollow structure filled with a resin material 282. The first conductor portion 291 and the second conductor portion 292 constitute inductors L1 and L2, respectively. The first conductor portion 291 and the second conductor portion are connected to each other by a connecting portion 450, thereby forming a series circuit of inductors L1 and L2. The first conductor portion 291 and the second conductor portion 292 are also collectively referred to as conductor portions 290.

[0059] As described above, the first magnetic material portion 391 and the second magnetic material portion 392 (collectively referred to as the magnetic material portion 390) are formed within the resin substrate 190. Therefore, the process for forming the magnetic material portion 390 must be performed at a temperature below the heat resistance temperature of the resin substrate 190. Due to this constraint, the magnetic material portion 390 is not made of a sintered ceramic body but of a resin in which magnetic particles are dispersed. In this case, the gaps between the magnetic particles in the magnetic material portion 390 are filled with resin, and it is generally difficult to increase this filling rate to 70% or more. As a result, it is difficult to increase the relative permeability of the first magnetic material portion 391 and the second magnetic material portion 392 compared to the first magnetic material portion 301 and the second magnetic material portion 302 ( FIG. 9 : Embodiment 1), which will be described later, and the relative permeability is, for example, approximately 6.

[0060] A design example of the core substrate 690 is described below. The resin substrate 190 has a square shape with sides of 50 mm in the in-plane direction and a dimension of 1000 μm in the thickness direction. The multiple through holes described above are arranged at a pitch of 500 μm. Each of the magnetic material portions 390 has an outer diameter of 400 μm and an inner diameter of 200 μm. Each of the conductor portions 290 has an outer diameter of 200 μm. The conductor portions 290 are formed by Cu plating. The magnetic material portions 390 are made of resin with dispersed magnetic particles, and their relative permeability is estimated to be 6. In this case, the inductance of one inductor (e.g., inductor L1) is estimated by the inventor to be approximately 1 nH at 140 MHz.

[0061] <First Embodiment> Figure 8 is a circuit diagram showing an example of the electrical connection of inductors L1 to L4 built into a core substrate 601 in the first embodiment. A built-in inductor LB is composed of four inductors L1 to L4. The series circuit has an input terminal TMin and an output terminal TMout, which are not short-circuited to each other. In this embodiment, the input terminal TMin and the output terminal TMout are arranged on the second surface SF2 of the core substrate 601. Because the second surface SF2 faces the semiconductor element 811 (Figure 1), the input terminal TMin and the output terminal TMout can be easily electrically connected to the semiconductor element 811.

[0062] Fig. 9 is a diagram schematically showing the configuration of core substrate 601, and is a partial cross-sectional view taken along line IX-IX in each of Fig. 10 and Fig. 11. Fig. 10 and Fig. 11 are a top view and a bottom view, respectively, schematically showing the configuration of core substrate 601. Fig. 12 is a partial cross-sectional view taken along line XII-XII in Fig. 9. Note that core substrate 601 may be manufactured using multilayer ceramic technology, and in Fig. 9, the boundaries between layers of the multilayer structure are indicated by dashed lines.

[0063] The core substrate 601 has a ceramic substrate 100. The ceramic substrate 100 forms a first surface SF1 and a second surface SF2 of the core substrate 601. The first surface SF1 and the second surface SF2 are surfaces of the ceramic substrate 100 that are opposite to each other in the thickness direction (Z direction in FIG. 9 ).

[0064] The core substrate 601 has a plurality of conductor portions made of a sintered material, and in this embodiment, the conductor portions include a first conductor portion 201, a second conductor portion 202, a third conductor portion 203, and a fourth conductor portion 204. Hereinafter, these conductor portions may be collectively referred to as conductor portions 200. Each of the conductor portions 200 penetrates the ceramic substrate 100 in the thickness direction. Specifically, a first end (lower end in FIG. 8 ) of the first conductor portion 201, a first end (lower end in FIGS. 8 and 9 ) of the second conductor portion 202, a first end (lower end in FIGS. 8 and 9 ) of the third conductor portion 203, and a first end (lower end in FIG. 8 ) of the fourth conductor portion 204 reach a first surface SF1 (lower surface in FIG. 9 ) of the ceramic substrate 100. The second end (upper end in Figure 8) of the first conductor portion 201, the second end (upper end in Figures 8 and 9) of the second conductor portion 202, the second end (upper end in Figures 8 and 9) of the third conductor portion 203, and the second end (upper end in Figure 8) of the fourth conductor portion 204 reach the second surface SF2 (upper surface in Figure 9) of the ceramic substrate 100.

[0065] The first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 respectively constitute inductors L1 to L4. The first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 are electrically connected to one another to form the series circuit shown in FIG. 8 . For this electrical connection, the core substrate 601 has a first connecting portion 451, a second connecting portion 452, and a third connecting portion 453. The first connecting portion 451 electrically connects the first end (the lower end in FIG. 8 ) of the first conductor portion 201 to the first end (the lower end in FIG. 8 and FIG. 9 ) of the second conductor portion 202 to one another. The second connecting portion 452 electrically connects the second end (the upper end in FIG. 8 and FIG. 9 ) of the second conductor portion 202 to the second end (the upper end in FIG. 8 and FIG. 9 ) of the third conductor portion 203 to one another. The third connection portion 453 electrically connects the first end (the lower end in FIGS. 8 and 9) of the third conductor portion 203 and the first end (the lower end in FIG. 8) of the fourth conductor portion 204 to each other.

[0066] The shortest distance between members in the cross-sectional view of FIG. 12 (at least one cross-sectional view perpendicular to the thickness direction across the magnetic material portion 300) will be described below. Here, the "shortest distance" refers to the smallest dimension between the edge of one member and the edge of the other member in the cross-sectional view, and a distance of zero means that the two members are in contact with each other. The shortest distance D13 between the first conductor portion 201 and the third conductor portion 203 may be smaller than the shortest distance D12 between the first conductor portion 201 and the second conductor portion 202. The shortest distance D13 between the first conductor portion 201 and the third conductor portion 203 may also be smaller than the shortest distance between the first conductor portion 201 and the third conductor portion 203. The shortest distance between the second conductor portion 202 and the fourth conductor portion 204 may also be smaller than the shortest distance between the third conductor portion 203 and the fourth conductor portion 204. Furthermore, the shortest distance between the second conductor section 202 and the fourth conductor section 204 may be shorter than the shortest distance between the fourth conductor section 204 and the second conductor section 202 .

[0067] The core substrate 601 has at least one magnetic material portion 300 for increasing the inductance of the plurality of conductor portions 200, and in this embodiment has a first magnetic material portion 301 and a second magnetic material portion 302 as the plurality of magnetic material portions 300. The second magnetic material portion 302 is spaced apart from the first magnetic material portion 301. The magnetic material portions 300 are embedded in the ceramic substrate 100. In the example shown in FIG. 9 , each of the magnetic material portions 300 penetrates the ceramic substrate 100.

[0068] 12 , the shortest distance between the first conductor portion 201 and the first magnetic material portion 301 is smaller than the shortest distance between the first conductor portion 201 and the second magnetic material portion 302, and is zero on the core substrate 601. The shortest distance between the third conductor portion 203 and the first magnetic material portion 301 is smaller than the shortest distance between the third conductor portion 203 and the second magnetic material portion 302, and is zero on the core substrate 601. The shortest distance between the second conductor portion 202 and the second magnetic material portion 302 is smaller than the shortest distance between the second conductor portion 202 and the first magnetic material portion 301, and is zero on the core substrate 601. The shortest distance between the fourth conductor portion 204 and the second magnetic material portion 302 is smaller than the shortest distance between the fourth conductor portion 204 and the first magnetic material portion 301, and is zero on the core substrate 601. Therefore, in the core substrate 601, the first magnetic material portion 301 is in contact with the first conductor portion 201 and the third conductor portion 203. Furthermore, the second magnetic material portion 302 is in contact with the second conductor portion 202 and the fourth conductor portion 204. In this way, in the core substrate 601, at least one of the multiple conductor portions 200 (the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204) is in contact with the first magnetic material portion 301 or the second magnetic material portion 302 (one magnetic material portion) included in at least one magnetic material portion 300.

[0069] 12 , the first magnetic material portion 301 may surround the first conductor portion 201 and / or the third conductor portion 203. The second magnetic material portion 302 may surround the second conductor portion 202 and / or the fourth conductor portion 204.

[0070] At least one of the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 may be spaced apart from the ceramic substrate 100. In the core substrate 601, each of the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 is spaced apart from the ceramic substrate 100.

[0071] The ceramic substrate 100 is a substrate made of a sintered material. The ceramic sintered body is substantially free of organic components and may contain glass components. In other words, the ceramic substrate 100 may be made of glass ceramics, specifically glass alumina. The ceramic substrate 100 is preferably made of an LTCC material. LTCC is a ceramic that can be sintered at approximately 900°C or less, well below the melting point of Ag or Cu. This allows for the simultaneous sintering of embedded conductors with low electrical resistance, primarily composed of Ag or Cu. The ceramic substrate 100 has multiple through-holes between the first surface SF1 and the second surface SF2, in which inductors L1 to L4 are embedded. The ceramic substrate 100 preferably has a thermal expansion coefficient of 4 ppm / °C or more and 16 ppm / °C or less. The ceramic substrate 100 preferably has a relative dielectric constant of 8 or less and a dielectric loss tangent of 0.01 or less at 1 GHz.

[0072] Each of the conductor parts 200 may be a solid body, unlike the hollow first conductor part 291 ( FIG. 7 (comparative example)). In other words, each of the conductor parts 200 does not need to have a hollow space inside. The conductor parts 200 are made of a sintered material. In terms of composition, the conductor parts 200 are made of, for example, Ag and / or Cu.

[0073] The magnetic body portion 300 is made of ceramics. Therefore, the magnetic body portion 300 is made of a sintered material and does not contain organic components. To reduce the volume of the inductor, the magnetic material constituting the magnetic body portion 300 preferably has high magnetic permeability, and the magnetic body portion 300 preferably has a density of 70% or more. To reduce the electrical loss of the inductor, the magnetic material constituting the magnetic body portion 300 is preferably a soft magnetic material with low magnetic loss at high frequencies. For example, a soft magnetic material with a magnetic loss tangent of 0.1 or less at a frequency of 100 MHz is desirable. To reduce magnetic loss at high frequencies, the magnetic material constituting the magnetic body portion 300 preferably has a high volume electrical resistivity, specifically, is preferably an electrical insulator. The magnetic body 300 is preferably made of a ferrite-based material, and the crystal structure of the material is preferably a spinel structure from the viewpoint of ease of manufacturing, for example, Ni-Zn ferrite or Ni-Zn-Cu ferrite, and from the viewpoint of high magnetic permeability, it is preferably a hexagonal structure with c-axis orientation along the thickness direction (Z direction in Figure 9).

[0074] In the cross-sectional view of FIG. 12 (at least one cross-sectional view perpendicular to the thickness direction crossing the first magnetic material portion 301 and the second magnetic material portion 302), the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 each have a center CC1 to CC4. In the example shown in FIG. 12, the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 each have a circular shape, and the centers CC1 and CC2 are the centers of the circles. Alternatively, an ellipse may be used instead of a circle. The shapes of the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 may be any shape other than a circle or an ellipse, in which case the center of the shape may be defined by the center of gravity. The first magnetic material portion 301 and the second magnetic material portion 302 each have a center CM1 and a center CM2. 12, the outer edges of the first magnetic material portion 301 and the second magnetic material portion 302 have a circular shape, and the centers CM1 and CM2 are the centers of the circles. As a variant, an ellipse may be used instead of a circle. The outer edges of the first magnetic material portion 301 and the second magnetic material portion 302 may have any shape other than a circle or an ellipse, and in that case, the center of the shape may be defined by the center of gravity.

[0075] 12 , the distance between the center CC1 of the first conductor portion 201 and the center CC2 of the second conductor portion 202 may be greater than the distance between the center CM1 of the first magnetic material portion 301 and the center CM2 of the second magnetic material portion 302. In addition, the distance between the center CC3 of the third conductor portion 203 and the center CC4 of the fourth conductor portion 204 may be greater than the distance between the center CM1 of the first magnetic material portion 301 and the center CM2 of the second magnetic material portion 302.

[0076] 12 , the first conductor portion 201 may be offset from the center CM1 of the first magnetic material portion 301. Preferably, the center CC1 of the first conductor portion 201 is separated from the center CM1 of the first magnetic material portion 301 by 10% or more of the diameter of a circle having the area of ​​the first magnetic material portion 301. Similarly, the second conductor portion 202 is offset from the center CM2 of the second magnetic material portion 302. Preferably, the center CC2 of the second conductor portion 202 is separated from the center CM2 of the second magnetic material portion 302 by 10% or more of the diameter of a circle having the area of ​​the second magnetic material portion 302.

[0077] 12 (one of the cross-sectional views perpendicular to the thickness direction transverse to the magnetic body part 300) may have the respective features mentioned above in any cross-sectional view perpendicular to the thickness direction transverse to the magnetic body part 300. This makes it possible to more fully obtain the effects associated with each feature.

[0078] The manufacturing method of the core substrate 601 may include a firing step as described above. The firing step may fire the conductor portion 200 and the magnetic material portion 300 simultaneously with the ceramic substrate 100. In this case, the core substrate 601 has a sintered interface between the conductor portion 200 and the portion of the core substrate 601 other than the conductor portion 200. In other words, the conductor portion 200 and the other portion are sintered to each other. Specifically, in FIG. 9 , the core substrate 601 has a sintered interface between the conductor portion 200 (the second conductor portion 202 and the third conductor portion 203 in FIG. 9 ) and the magnetic material portion 300. In other words, the conductor portion 200 and the magnetic material portion 300 are sintered to each other. The core substrate 601 also has a sintered interface between the magnetic material portion 300 and the ceramic substrate 100. In other words, the magnetic material portion 300 and the ceramic substrate 100 are sintered to each other. These interfaces do not contain organic materials, but are formed by bonding between inorganic materials. In other words, these interfaces are formed by inorganic bonds.

[0079] A design example of the core substrate 601 is described below. The ceramic substrate 100 has a square shape with sides of 50 mm in the XY plane and a dimension of 550 μm in the Z direction (thickness direction). The through holes provided in the ceramic substrate 100 are arranged at a pitch of 450 μm. The ceramic substrate 100 is formed, for example, from an LTCC material primarily composed of Ba-Si-Al-O elements or glass alumina. The first magnetic body 301 and the second magnetic body 302 (FIGS. 10 to 12) each have an outer diameter of 350 μm and an inner diameter of 100 μm. The first conductor body 201, the second conductor body 202, the third conductor body 203, and the fourth conductor body 204 each have an outer diameter of 100 μm. The first conductor body 201, the second conductor body 202, the third conductor body 203, and the fourth conductor body 204 are formed by sintering Ag powder. The first magnetic material part 301 and the second magnetic material part 302 are made of sintered ferrite, and the relative permeability thereof can be estimated to be about 16. In this case, the inductance of each of the inductors L1 to L4 is estimated by the inventors to be about 2 nH at 140 MHz.

[0080] In this embodiment, the core substrate 601 has four inductors L1 to L4. However, even if the inductor L4 is omitted, the above-described effects of the inductors L1 to L3 can be obtained.

[0081] According to the core substrate 601 of this embodiment, first, at least one magnetic material portion 300 embedded in the ceramic substrate 100 of the core substrate 601 is made of ceramic. This allows the ceramic of the at least one magnetic material portion 300 to be densely sintered, thereby increasing the magnetic permeability of the at least one magnetic material portion 300. Therefore, the inductor LB ( FIG. 8 ) built into the core substrate 601 can have a sufficiently large inductance per unit area. Second, the first conductor portion 201, the second conductor portion 202, and the third conductor portion 203 penetrate the ceramic substrate 100 in the thickness direction and are electrically connected to each other to form a series circuit. This allows a series circuit to be formed in the thickness direction of the ceramic substrate 100, in which a current passes through the first conductor portion 201, then passes through the second conductor portion 202, turns around, and passes through the third conductor portion 203. In this case, the directional vector of the current in the first conductor portion 201 and the directional vector of the current in the third conductor portion 203 can be roughly the same. In this case, in the regions near both the first conductor portion 201 and the third conductor portion 203, the magnetic field caused by the current in the first conductor portion 201 and the magnetic field caused by the current in the third conductor portion 203 cancel each other out according to Ampere's law. Therefore, in this region, it is possible to prevent at least one magnetic material portion 300 from approaching a magnetic saturation state. From the above, the inductor LB built into the core substrate 601 can have a sufficiently large inductance per unit area and sufficiently good DC superposition characteristics.

[0082] The core substrate 601 may have a first connection portion 451, a second connection portion 452, and a third connection portion 453. This allows the first conductor portion 201, the second conductor portion 202, and the third conductor portion 203 to be electrically connected to one another so as to configure the above-mentioned series circuit.

[0083] The shortest distance D13 between the first conductor portion 201 and the third conductor portion 203 may be smaller than the shortest distance D12 between the first conductor portion 201 and the second conductor portion 202. In this case, the mutual cancellation effect between the magnetic field caused by the current in the first conductor portion 201 and the magnetic field caused by the current in the third conductor portion 203 is enhanced in the regions near both the first conductor portion 201 and the third conductor portion 203, and the mutual reinforcement effect between the magnetic field caused by the current in the first conductor portion 201 and the magnetic field caused by the current in the second conductor portion 202 is mitigated in the regions near both the first conductor portion 201 and the second conductor portion 202. This makes it more difficult for at least one magnetic material portion 300 to approach a magnetic saturation state. This improves the DC superposition characteristics of the built-in inductor LB.

[0084] In the present embodiment, the at least one magnetic material part 300 includes a first magnetic material part 301 in contact with the first conductor part 201 and the third conductor part 203, and a second magnetic material part 302 in contact with the second conductor part 202 and spaced apart from the first magnetic material part 301. As a result, first, the magnetic field caused by the current in the first conductor part 201 and the magnetic field caused by the current in the third conductor part 203 cancel each other out, making it difficult for the first magnetic material part 301 to approach a magnetic saturation state. Second, although a region is provided to separate the first magnetic material part 301 in contact with the first conductor part 201 and the second magnetic material part 302 in contact with the second conductor part 202, this region is not included in the at least one magnetic material part 300 and is therefore not affected by the mutual reinforcement of the magnetic field caused by the current in the first conductor part 201 and the magnetic field caused by the current in the second conductor part 202. This makes it possible to avoid deterioration of the DC bias characteristics due to magnetic saturation in the region. These two effects make it possible to improve the DC bias characteristics of the built-in inductor LB.

[0085] The distance between the center CC1 of the first conductor portion 201 and the center CC2 of the second conductor portion 202 may be greater than the distance between the center CM1 of the first magnetic material portion 301 and the center CM2 of the second magnetic material portion 302. This reduces the mutual reinforcement effect of the magnetic fields caused by the currents in the first conductor portion 201 and the second conductor portion 202 compared to when the distance between the center CC1 of the first conductor portion 201 and the center CC2 of the second conductor portion 202 is smaller than the distance between the center CM1 of the first magnetic material portion 301 and the center CM2 of the second magnetic material portion 302. This makes it difficult for at least one magnetic material portion 300 to approach a magnetic saturation state in regions near both the first conductor portion 201 and the second conductor portion 202. This improves the DC superposition characteristics of the built-in inductor LB.

[0086] At least one of the first conductor portion 201, the second conductor portion 202, the third conductor portion 203, and the fourth conductor portion 204 (all of them in this embodiment) is in contact with the first magnetic material portion 301 or the second magnetic material portion 302 (one magnetic material portion). This makes it possible to increase the inductance of the inductor formed by this at least one conductor portion. In this embodiment, this at least one conductor portion is separated from the ceramic substrate 100. This makes it possible to place more importance on the magnitude of the inductance than when this at least one conductor portion is in contact with the ceramic substrate 100.

[0087] Each of the plurality of conductor portions 200 may be solid, which prevents an increase in electrical resistance due to a hollow portion, thereby reducing the electrical resistance of each of the plurality of conductor portions 200.

[0088] The ceramic substrate 100 is made of an LTCC material or glass alumina, which makes it easier to form the ceramic substrate 100 and the plurality of conductor portions 200 by simultaneous firing in the manufacture of the core substrate 601.

[0089] The core substrate 601 has a sintered interface between the conductor portion 200 and the portion of the core substrate 601 other than the conductor portion 200. This prevents the heat resistance of the core substrate 601 from being reduced due to the low heat resistance of the organic adhesive, unlike when the conductor portion 200 is joined to the portion of the core substrate 601 other than the conductor portion 200 via an organic adhesive. Therefore, the heat resistance of the core substrate 601 can be improved.

[0090] According to the interposer 700 ( FIG. 1 ) of this embodiment, first, at least one magnetic material portion 300 ( FIGS. 9 to 12 ) embedded in the ceramic substrate 100 of the core substrate 601 is made of ceramic. By densely sintering the ceramic of the at least one magnetic material portion 300, the magnetic permeability of the at least one magnetic material portion 300 can be increased. This allows the inductor LB ( FIG. 8 ) embedded in the core substrate 601 to have a sufficiently large inductance per unit area. Second, the first conductor portion 201, the second conductor portion 202, and the third conductor portion 203 penetrate the ceramic substrate 100 in the thickness direction and are electrically connected to each other to form a series circuit. This allows a series circuit to be formed in the thickness direction of the ceramic substrate 100, in which a current passes through the first conductor portion 201, then turns around through the second conductor portion 202, and then passes through the third conductor portion 203. In this case, the directional vector of the current in the first conductor portion 201 and the directional vector of the current in the third conductor portion 203 can be made roughly the same. In this case, in the regions near both the first conductor portion 201 and the third conductor portion 203, the magnetic field caused by the current in the first conductor portion 201 and the magnetic field caused by the current in the third conductor portion 203 cancel each other out according to Ampere's law. Therefore, in this region, it is possible to prevent at least one magnetic material portion 300 from approaching a magnetic saturation state. From the above, the inductor LB built into the core substrate 601 of the interposer 700 on which the semiconductor element 811 will be mounted can have a sufficiently large inductance per unit area and sufficiently good DC superposition characteristics.

[0091] Note that Figure 9 illustrates a case where the range in the XY plane of each conductor portion 200 (see, for example, the third conductor portion 203) is constant in the thickness direction (Z direction). However, this range does not necessarily have to be constant in the thickness direction. For example, when the core substrate 601 is manufactured using multilayer ceramic technology, slight stacking errors may occur at the boundaries between layers in the laminated structure (dashed lines in Figure 9). As a result, the above range is not completely constant in the thickness direction. On the other hand, in a configuration in which this range is significantly dependent on the thickness direction (Z direction), the difference between the direction of the current flowing through each of the inductors L1 to L4 and the thickness direction may become significant. In this case, the aforementioned magnetic field cancellation effect may be weaker than in an ideal case. To suppress this weakening of the cancellation effect, it is preferable that, for each conductor portion 200, there exists an imaginary straight line that penetrates the conductor portion 200 along the Z direction (thickness direction) and does not deviate from the conductor portion 200 in the XY plane.

[0092] Second Embodiment FIG. 13 is a partial cross-sectional view schematically illustrating the configuration of a core substrate 611 according to a second embodiment. While the core substrate 601 ( FIG. 12 ) of the first embodiment uses a first magnetic material portion 301 and a second magnetic material portion 302 as at least one magnetic material portion 300 for increasing the inductance of the conductor portion 200, a common magnetic material portion 300 is used in the second embodiment. The remaining configuration is substantially the same as that of the first embodiment, and therefore the same or corresponding elements are denoted by the same reference numerals and will not be described again. According to the second embodiment, a larger inductance can be ensured compared to when multiple separate magnetic material portions, such as the first magnetic material portion 301 and the second magnetic material portion 302, are used.

[0093] FIG. 14 is a partial cross-sectional view schematically illustrating a core substrate 612 according to a first modification of the second embodiment, showing a cross section perpendicular to the thickness direction across the magnetic body portion 300 (one magnetic body portion). In this cross-sectional view, the first conductor portion 201 contacts the ceramic substrate 100 without crossing the tangent line LT at the boundary between the magnetic body portion 300 and the ceramic substrate 100. In the example shown in FIG. 14 , the conductor portions 200 other than the first conductor portion 201 have similar characteristics. According to this modification, the conductor portion 200 not only contacts the magnetic body portion 300 to increase inductance, but also contacts the ceramic substrate 100 without crossing the tangent line LT at the boundary between the magnetic body portion 300 and the ceramic substrate 100. This allows for a balance between obtaining a sufficiently large inductance and obtaining sufficiently good DC bias characteristics, while placing a slightly greater emphasis on the magnitude of inductance than in the second modification ( FIG. 15 ) described below.

[0094] FIG. 15 is a partial cross-sectional view schematically illustrating a core substrate 613 according to a second modification of the second embodiment, showing a cross section perpendicular to the thickness direction across the magnetic body portion 300 (one magnetic body portion). In this cross-sectional view, the first conductor portion 201 contacts the ceramic substrate 100. Furthermore, the first conductor portion 201 protrudes toward the ceramic substrate 100 across the tangent line LT at the boundary between the magnetic body portion 300 and the ceramic substrate 100. In the example shown in FIG. 15, the conductor portions 200 other than the first conductor portion 201 have similar characteristics. According to this modification, the conductor portion 200 not only contacts the magnetic body portion 300 to increase inductance, but also contacts the ceramic substrate 100. This makes it easier to balance between achieving a sufficiently large inductance and achieving sufficiently good DC bias characteristics. Furthermore, in the cross-sectional view of FIG. 15, the first conductor portion 201 protrudes toward the ceramic substrate 100 across the tangent line LT. This makes it possible to strike a balance between obtaining a sufficiently large inductance and obtaining sufficiently good DC bias characteristics, while placing a slightly greater emphasis on the DC bias characteristics than in the first modified example (FIG. 14) described above.

[0095] Fig. 16 is a partial cross-sectional view schematically illustrating a core substrate 614 according to a third modified example of the second embodiment. In the core substrate 614, the conductor portion 200 is spaced from the magnetic material portion 300 and in contact with the ceramic substrate 100. In the example shown in Fig. 16, the conductor portions 200 other than the first conductor portion 201 also have similar characteristics. According to the core substrate 614 according to this modified example (Fig. 16), better DC bias characteristics can be emphasized compared to the core substrates 611 to 613 (Figs. 13 to 15).

[0096] <Simulation> Generally, the DC bias characteristic of inductance is such that the inductance when a DC current is superimposed decreases from the initial inductance (i.e., the inductance when the DC current is zero) as the DC current increases. For an inductor for a semiconductor element mounted on an interposer, it is desirable to suppress the rate of decrease from the initial inductance. Therefore, the inventors performed a simulation of the DC bias characteristic under three conditions corresponding to Example 1, Example 2, and a comparative example.

[0097] FIG. 17 is a cross-sectional view showing the configuration of core substrate 621 of Example 1 under simulation conditions. FIG. 18 is a schematic diagram showing the configuration of inductors L1 to L6 built into core substrate 621 of Example 1 under simulation conditions. Example 1 is similar to core substrate 612 ( FIG. 14 ), in that conductor portion 200 contacts ceramic substrate 100 without crossing the tangent line (not shown in FIG. 17 ) at the boundary between magnetic material portion 300 and ceramic substrate 100. Core substrate 612 has first conductor portion 201, second conductor portion 202, third conductor portion 203, and fourth conductor portion 204 corresponding to inductors L1 to L4, respectively, while core substrate 621 further has fifth conductor portion 205 and sixth conductor portion 206 corresponding to inductors L5 and L6, respectively. Correspondingly, the core substrate 621 also has a fourth connection portion 454 that connects the fourth conductor portion 204 and the fifth conductor portion 205 to each other on the second surface SF2, and a fifth connection portion 455 that connects the fifth conductor portion 205 and the sixth conductor portion 206 to each other on the first surface SF1.

[0098] The configuration of the core substrate of Example 2 under the simulation conditions is the same as that of the core substrate 612 (FIG. 14).

[0099] 19 is a cross-sectional view showing the configuration of a core substrate 691 of a comparative example under simulation conditions. This configuration corresponds to the configuration of the core substrate 612 ( FIG. 14 ) corresponding to Example 2, with the third conductor portion 203, the fourth conductor portion 204, and the third connection portion 453 connecting these to each other being omitted.

[0100] The simulation results are shown below. Note that the "number of unit inductors" in Table 1 indicates how many of the inductors L1 to L6 the core substrate has.

[0101]

[0102] These results show that Examples 1 and 2 have a smaller inductance reduction rate than the comparative example, and therefore have better DC bias characteristics. Furthermore, it can be seen that Example 1, which has a built-in inductor LB composed of six inductors L1 to L6 (FIG. 18), has better DC bias characteristics than Example 2, which has a built-in inductor LB composed of four inductors L1 to L4 (FIG. 8).

[0103] The above-described embodiments and modifications may be freely combined with each other. Although the present invention has been described in detail, the above description is illustrative in all respects and does not limit the present invention. It is understood that countless modifications not illustrated can be envisioned without departing from the scope of the present invention.

[0104] 100: Ceramic substrate 200: Conductor portion 201-206: First to sixth conductor portions 300: Magnetic material portion 301, 302: First and second magnetic material portions 451-455: First to fifth connection portions 601, 611-614: Core substrate 700: Interposer 791: Wiring layer 811: Semiconductor element SC: Mounting surface SF1: First surface SF2: Second surface

Claims

1. A core substrate with an inductor built in, for forming an interposer on which a semiconductor element is mounted, comprising: a ceramic substrate having a thickness direction; a plurality of conductor parts made of a sintered material, penetrating the ceramic substrate in the thickness direction, and electrically connected to each other to form a series circuit, the conductor parts including a first conductor part, a second conductor part, and a third conductor part; and at least one magnetic part made of ceramic, embedded in the ceramic substrate, for increasing the inductance of the plurality of conductor parts.

2. A core substrate as claimed in claim 1, wherein the ceramic substrate has a first surface to which the first end of the first conductor portion, the first end of the second conductor portion and the first end of the third conductor portion reach, and a second surface to which the second end of the first conductor portion, the second end of the second conductor portion and the second end of the third conductor portion reach, and further comprises a first connection portion that electrically connects the first end of the first conductor portion and the first end of the second conductor portion to each other, and a second connection portion that electrically connects the second end of the second conductor portion and the second end of the third conductor portion to each other.

3. A core substrate as described in claim 1 or 2, wherein in at least one cross-sectional view perpendicular to the thickness direction across the at least one magnetic material portion, the shortest distance between the first conductor portion and the third conductor portion is smaller than the shortest distance between the first conductor portion and the second conductor portion.

4. A core substrate as described in claim 1 or 2, wherein the at least one magnetic material portion includes a first magnetic material portion in contact with the first conductor portion and the third conductor portion, and a second magnetic material portion in contact with the second conductor portion and spaced apart from the first magnetic material portion.

5. A core substrate as described in claim 4, wherein in at least one cross-sectional view perpendicular to the thickness direction that crosses the first magnetic material portion and the second magnetic material portion, the distance between the center of the first conductor portion and the center of the second conductor portion is greater than the distance between the center of the first magnetic material portion and the center of the second magnetic material portion.

6. A core substrate according to claim 1 or 2, wherein the at least one magnetic part is a common magnetic part for increasing the inductance of the plurality of conductor parts.

7. A core substrate according to claim 1 or 2, wherein the plurality of conductor portions include at least one conductor portion in contact with one magnetic material portion included in the at least one magnetic material portion.

8. A core substrate according to claim 7, wherein said at least one conductor portion is in contact with said ceramic substrate.

9. A core substrate as claimed in claim 8, wherein in at least one cross-sectional view perpendicular to the thickness direction and crossing the one magnetic material part, the at least one conductor part protrudes towards the ceramic substrate, crossing a tangent to the boundary between the one magnetic material part and the ceramic substrate.

10. A core substrate as described in claim 7, wherein, in at least one cross-sectional view perpendicular to the thickness direction crossing the one magnetic material portion, the at least one conductor portion is in contact with the ceramic substrate without crossing the tangent to the boundary between the one magnetic material portion and the ceramic substrate.

11. A core substrate according to claim 7, wherein said at least one conductor portion is spaced apart from said ceramic substrate.

12. A core substrate according to claim 1 or 2, wherein the plurality of conductor portions include at least one conductor portion that is spaced apart from the at least one magnetic portion and that is in contact with the ceramic substrate.

13. A core substrate according to claim 1 or 2, wherein each of the plurality of conductor portions is a solid body.

14. A core substrate according to claim 1 or 2, wherein the ceramic substrate is made of a low-temperature co-fired ceramic material or glass alumina.

15. A core substrate according to claim 1 or 2, wherein a sintered interface is formed between the plurality of conductor portions and portions of the core substrate other than the plurality of conductor portions.

16. An interposer comprising: a core substrate according to claim 1 or 2; and a wiring layer laminated on the core substrate, the wiring layer having a mounting surface on which the semiconductor element is to be mounted.

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