Core substrate and interposer

Abstract

A first conductor part (201) penetrates a ceramic substrate (100) in the thickness direction. A first magnetic body portion (301) is intended for increasing the inductance of the first conductor part (201), and is embedded in the ceramic substrate (100). A second portion (301b) of the first magnetic body (301) has a higher magnetic permeability than the magnetic permeability of a first portion (301a) at one frequency, which is lower than the frequency at which the first portion (301a) of the first magnetic body (301) has a magnetic permeability peak. In at least one cross-sectional view perpendicular to the thickness direction, the first conductor part (201), the first portion (301a) of the first magnetic body part (301), and the second portion (301b) of the first magnetic body part (301) are positioned in the stated order so as to pass through one virtual straight line (LV) extending from the first conductor part (201).

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 into the core substrate 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 an inductor built into 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 first conductor portion made of a sintered body and penetrating the ceramic substrate in the thickness direction; and a first magnetic material portion made of ceramic and embedded in the ceramic substrate for increasing the inductance of the first conductor portion, wherein the first magnetic material portion includes a plurality of magnetic material portions, each of which includes a first portion and a second portion having a higher magnetic permeability than the first portion at a frequency lower than the frequency at which the first portion has a peak in magnetic permeability; and in at least one cross-sectional view perpendicular to the thickness direction, the first conductor portion, the first portion of the first magnetic material portion, and the second portion of the first magnetic material portion are arranged in this order so as to be penetrated by a single imaginary straight line extending from the first conductor portion.

[0011] Aspect 2 is a core substrate described in aspect 1, wherein, in at least one cross-sectional view, the first portion of the first magnetic material portion is in contact with the first conductor portion, and the second portion of the first magnetic material portion is spaced from the first conductor portion.

[0012] Aspect 3 is the core substrate according to aspect 1, wherein, in the at least one cross-sectional view, the first portion of the first magnetic material portion surrounds the first conductor portion.

[0013] A fourth aspect is the core substrate according to the third aspect, wherein, in the at least one cross-sectional view, the second portion of the first magnetic material portion surrounds the first portion of the first magnetic material portion.

[0014] Aspect 5 is a core substrate according to any one of aspects 1 to 4, comprising a second conductor portion made of a sintered body and penetrating the ceramic substrate in the thickness direction, and a second magnetic portion embedded in the ceramic substrate for increasing the inductance of the second conductor portion.

[0015] A sixth aspect of the present invention is the core substrate according to the fifth aspect, wherein the first magnetic body portion and the second magnetic body portion are spaced apart from each other.

[0016] A seventh aspect is the core substrate according to the fifth aspect, wherein the first magnetic material portion and the second magnetic material portion are connected to each other.

[0017] Aspect 8 is a core substrate described in any one of aspects 5 to 7, wherein, in at least one cross-sectional view, the first conductor portion is offset from the center of the first magnetic material portion, the second conductor portion is offset from the center of the second magnetic material portion, and 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.

[0018] A ninth aspect is the core substrate according to any one of the fifth to eighth aspects, wherein the first conductor portion and the second conductor portion form a series circuit.

[0019] Aspect 10 is a core substrate according to aspect 9, wherein the ceramic substrate has a surface to which an end of the first conductor portion and an end of the second conductor portion reach, and further includes a connection portion that electrically connects the end of the first conductor portion and the end of the second conductor portion to each other.

[0020] Aspect 11 is a core substrate according to any one of aspects 1 to 10, wherein the at least one cross-sectional view includes any cross-sectional view perpendicular to the thickness direction in which the first magnetic material portion appears.

[0021] A twelfth aspect of the present invention is the core substrate according to any one of the first to eleventh aspects, wherein the first conductor portion is a solid body.

[0022] A thirteenth aspect of the present invention is the core substrate according to any one of the first to twelfth aspects, wherein the ceramic substrate is made of low-temperature co-fired ceramics or a composite material of glass and alumina.

[0023] A fourteenth aspect of the present invention is the core substrate according to any one of the first to thirteenth aspects, wherein a sintered interface is formed between the first conductor portion and a portion of the core substrate other than the first conductor portion.

[0024] Aspect 15 is an interposer comprising a core substrate according to any one of aspects 1 to 14, 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.

[0025] According to the first aspect, the multiple magnetic material portions for increasing the inductance of the first conductor portion include a first portion and a second portion having a higher magnetic permeability than the first portion at a certain frequency. The first conductor portion, the first portion, and the second portion are arranged in this order so as to be pierced by a virtual line extending from the first conductor portion. This allows the first portion having a lower magnetic permeability to be arranged closer to the first conductor portion along the virtual line, and the second portion having a higher magnetic permeability to be arranged farther away from the first conductor portion. First, since the magnetic material is more likely to be magnetically saturated by the magnetic field generated by the current in the first conductor portion in a region closer to the first conductor portion, arranging the first portion having a lower magnetic permeability closer to the first conductor portion can suppress the occurrence of magnetic saturation. Second, by arranging the second portion having a higher magnetic permeability than the first portion in a more distant region, the inductance of the first conductor portion can be increased compared to when the first portion having a lower magnetic permeability is arranged in the region. From the above, the inductor built into the core substrate can have a sufficiently large inductance per unit area and also have sufficiently good DC bias characteristics.

[0026] According to the second aspect, the first portion of the first magnetic material portion is in contact with the first conductor portion, and the second portion of the first magnetic material portion is spaced apart from the first conductor portion, thereby more fully achieving the effect of the first aspect.

[0027] According to the third aspect, the first portion of the first magnetic material portion surrounds the first conductor portion, thereby improving the inductance by disposing some magnetic material portion around the entire periphery of the first conductor portion, and also improving the DC bias characteristics by using the first magnetic material portion having low magnetic permeability.

[0028] According to the above-mentioned aspect 4, not only does the first portion surround the first magnetic material portion as defined in the above-mentioned aspect 3, but the second portion surrounds the first portion. As a result, the action described in the above-mentioned aspect 1 can be obtained in any direction around the first conductor portion. Therefore, the effect described in the above-mentioned aspect 1 can be more fully obtained.

[0029] According to the fifth aspect, in addition to the inductor formed by the first conductor portion and the first magnetic material portion, an inductor can be formed by the second conductor portion and the second magnetic material portion.

[0030] According to the sixth aspect, the first magnetic material portion and the second magnetic material portion are separated from each other, which allows the inductor formed by the first conductor portion and the first magnetic material portion and the inductor formed by the second conductor portion and the second magnetic material portion to be designed separately.

[0031] According to the seventh aspect, the first magnetic body portion and the second magnetic body portion are connected to each other. As a result, when the first magnetic body portion and the second magnetic body portion each have a predetermined area in a plan view, the first magnetic body portion and the second magnetic body portion are arranged within a smaller area than when the first magnetic body portion and the second magnetic body portion are separated by a ceramic substrate. This allows the area of ​​the core substrate to be reduced.

[0032] According to the eighth 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 makes it possible to suppress magnetic saturation caused by the mutually enhancing magnetic fields when the magnetic fields caused by the currents flowing through the first conductor portion and the second conductor portion enhance each other.

[0033] According to the above-mentioned Aspect 9, the first conductor portion and the second conductor portion form a series circuit. As a result, first, by connecting the first conductor portion and the second conductor portion in series, approximately double the inductance can be obtained. Second, in this series circuit, the magnetic field caused by the current flowing through the first conductor portion and the magnetic field caused by the current flowing through the second conductor portion may reinforce each other between the first conductor portion and the second conductor portion. In such a case, as described in relation to the above-mentioned Aspect 1, etc., magnetic saturation due to the mutually reinforced magnetic fields can be suppressed.

[0034] According to the above-mentioned aspect 10, the core substrate is provided with a connection portion that electrically connects the end of the first conductor portion and the end of the second conductor portion. As a result, in a series circuit of the first conductor portion and the second conductor portion, the current flowing through the first conductor portion and the current flowing through the second conductor portion are approximately opposite in direction. Therefore, the magnetic field caused by the current flowing through the first conductor portion and the magnetic field caused by the current flowing through the second conductor portion reinforce each other between the first conductor portion and the second conductor portion. Magnetic saturation due to this mutually reinforced magnetic field can be suppressed, as described in relation to the above-mentioned aspect 1, etc.

[0035] According to the above-mentioned Aspect 11, in each of the above-mentioned aspects, at least one cross-sectional view includes any cross-sectional view perpendicular to the thickness direction in which the first magnetic material portion appears. This makes it possible to more fully obtain the effects of each aspect.

[0036] According to the twelfth aspect, the first conductor is solid. This prevents an increase in electrical resistance due to a hollow portion, thereby reducing the electrical resistance of the first conductor.

[0037] According to the thirteenth aspect, the ceramic substrate is made of low-temperature co-fired ceramics or a composite material of glass and alumina, which makes it easier to form the ceramic substrate and the first conductors by co-firing in manufacturing the core substrate.

[0038] According to the above-mentioned Aspect 14, the core substrate has a sintered interface between the first conductor and the portion of the core substrate other than the first conductor. 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 first conductor is bonded to the portion of the core substrate other than the first conductor via an organic adhesive. Therefore, the heat resistance of the core substrate can be improved.

[0039] According to the above-described aspect 15, the multiple magnetic material portions for increasing the inductance of the first conductor portion include a first portion and a second portion having a magnetic permeability higher than that of the first portion at a certain frequency. The first conductor portion, the first portion, and the second portion are arranged in this order so as to be pierced by a virtual line extending from the first conductor portion. As a result, along the virtual line from the first conductor portion, the first portion having a lower magnetic permeability is arranged closer to the first conductor portion, and the second portion having a higher magnetic permeability is arranged farther away. First, since the magnetic material is more likely to be magnetically saturated by the magnetic field generated by the current in the first conductor portion in a region closer to the first conductor portion, by arranging the first portion having a lower magnetic permeability closer to the first conductor portion, the occurrence of magnetic saturation can be suppressed. Second, by arranging the second portion having a magnetic permeability higher than that of the first portion in a more distant region, the inductance of the first conductor portion can be increased compared to when the first portion having a low magnetic permeability is arranged in the region. From the above, the inductor of the interposer can have a sufficiently large inductance per unit area and also have sufficiently good DC superposition characteristics.

[0040] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

[0041] 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 facing 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 connection of the first inductor and the second inductor shown in FIG. 5. FIG. 7 is a partial cross-sectional view schematically showing the configuration of a core substrate of a comparative example. FIG. 8 is a diagram schematically showing the configuration of a core substrate in embodiment 1, and is a partial cross-sectional view taken along line VIII-VIII in FIG. 9. FIG. 9 is a partial cross-sectional view taken along line IX-IX in FIG. 8. FIG. 10 is a top view schematically showing the configuration of the core substrate of FIG. 8. FIG. 11 is a bottom view schematically showing the configuration of the core substrate of FIG. 8. FIG. 12 is a graph illustrating the frequency dependence of the relative permeability of each of the first to third magnetic materials. FIG. 13 is a partial cross-sectional view schematically showing the configuration of a core substrate in accordance with the second embodiment. FIG. 14 is a partial cross-sectional view schematically showing the configuration of a core substrate in accordance with the third embodiment. FIG. 15 is a partial cross-sectional view schematically showing the configuration of a core substrate in accordance with the fourth embodiment. FIG. 16 is a partial cross-sectional view schematically showing the configuration of a core substrate in accordance with the fifth embodiment. FIG. 17 is a partial cross-sectional view schematically showing the configuration of a core substrate in accordance with the sixth embodiment, taken along line XVII-XVII in FIG. 18. FIG. 18 is a partial cross-sectional view taken along line XVIII-XVIII in FIG. 17. FIG. 19 is a partial cross-sectional view showing a first modified example of the configuration of FIG. 18. FIG. 20 is a partial cross-sectional view showing a second modified example of the configuration of FIG. 18. FIG. 21 is a partial cross-sectional view schematically showing the configuration of a core substrate in accordance with the seventh embodiment, taken along line XXI-XXI in FIG. Fig. 22 is a partial cross-sectional view taken along line XXII-XXII in Fig. 21. Fig. 23 is a partial cross-sectional view showing a first modified example of the configuration of Fig. 22. Fig. 24 is a partial cross-sectional view showing a second modified example of the configuration of Fig. 22.

[0042] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0043] First Embodiment FIG. 1 is a cross-sectional view schematically illustrating the configuration of electronic device 901 according to the first embodiment. Electronic device 901 includes interposer 700, semiconductor element 811, motherboard 812, and package substrate 813. Interposer 700 includes core substrate 601, 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 601, respectively. In other words, wiring layer 791 is provided on the surface of core substrate 601 facing semiconductor element 811, and wiring layer 792 is provided on the surface of core substrate 601 opposite to the surface facing semiconductor element 811. Wiring layer 791 and wiring layer 792 may be laminated on core substrate 601 by a build-up method, a sputtering method, or the like, or may be bonded as separate wiring boards.

[0044] 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 601. 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.

[0045] 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 that can mount a semiconductor element 811 having a small terminal pitch even if the wiring dimensions (L / S) of the core substrate 601 are not particularly high. Specifically, the wiring layer 791 may be a laminate of a normal wiring layer facing the core substrate 601 and a fine wiring layer facing the semiconductor element 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.

[0046] 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.

[0047] 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 601. 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 5 is a schematic diagram showing the configuration of inductors L1 to L6 built into core substrate 601. Core substrate 601 has multiple inductors L1 and L2 built into it, and may also have additional inductors L3 to L6 built into it, with any number of inductors. Note that, although the configurations of inductors L1 and L2 will be described in detail below, other inductors may have similar configurations.

[0053] FIG. 6 is a circuit diagram showing an example of the electrical connection of inductor L1 and inductor L2 shown in FIG. 5. In this embodiment, the series connection of inductor L1 and inductor L2 forms an inductor having a combined inductance greater than the inductance of each of the inductors, and both ends of the inductor are disposed on the second surface SF2 that faces the semiconductor element 811 ( FIG. 1 ). This allows an inductor having a sufficiently large inductance to be easily connected to the semiconductor element 811. Note that the electrical connections between the multiple inductors built into the core substrate are not limited to those shown in FIG. 6 and may be designed appropriately depending on the application of the core substrate. This may form a series structure of any number of inductors, a parallel structure of any number of inductors, or a combination thereof.

[0054] FIG. 7 is a partial cross-sectional view showing the configuration of a core substrate 690 of a comparative example. 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. The first conductor portion 291 has 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. The second conductor portion 292 has a hollow structure filled with a resin material 282. The first conductor portion 291 and the second conductor portion 292 form 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.

[0055] 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 of 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. 5 ), and the relative permeability is, for example, approximately 6.

[0056] 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.

[0057] FIG. 8 is a diagram schematically illustrating the configuration of the core substrate 601 in the first embodiment, and is a partial cross-sectional view taken along line VIII-VIII in FIG. 9 . FIG. 9 is a partial cross-sectional view taken along line IX-IX in FIG. 8 . Specifically, FIG. 9 shows a cross-sectional view perpendicular to the thickness direction in which the first magnetic body portion 301 appears. FIG. 9 also shows a cross-sectional view perpendicular to the thickness direction in which the first magnetic body portion 301 and the second magnetic body portion 302 appear. FIGS. 10 and 11 are a top view and a bottom view, respectively, schematically illustrating the configuration of the core substrate 601 in FIG. 8 . Note that the core substrate 601 may be manufactured using multilayer ceramic technology, and in FIG. 8 , the boundaries between layers in the multilayer structure are indicated by dashed lines.

[0058] As described above, the core substrate 601 is used to form the interposer 700 (FIG. 1) on which the semiconductor element 811 is mounted, and has multiple inductors built in. In FIGS. 8 and 9, the multiple inductors are shown as inductor L1 and inductor L2.

[0059] 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 opposite to each other in the thickness direction (the vertical direction in FIG. 8 ) of the ceramic substrate 100. The ceramic substrate 100 has a plurality of through holes between the first surface SF1 and the second surface SF2, in which the inductors L1 and L2 are embedded.

[0060] The core substrate 601 has a first conductor portion 201 that constitutes the inductor L1 and a first magnetic material portion 301 that increases the inductance of the first conductor portion 201. The first conductor portion 201 penetrates the ceramic substrate 100 in the thickness direction. Unlike the hollow first conductor portion 291 ( FIG. 7 (comparative example)), the first conductor portion 201 may be a solid body. In other words, the first conductor portion 201 does not need to have a hollow space inside. The first magnetic material portion 301 is embedded in the ceramic substrate 100 and penetrates the ceramic substrate 100 in the example shown in FIG. 8.

[0061] The first magnetic body 301 is embedded in the ceramic substrate 100 to increase the inductance of the first conductor body 201. The first magnetic body 301 is made of ceramic. Therefore, the first magnetic body 301 is made of a sintered body and does not contain any organic components. To reduce the volume of the inductor, the magnetic material constituting the first magnetic body 301 preferably has high magnetic permeability, and the first magnetic body 301 preferably has a density of 70% or more. To reduce the electrical loss of the inductor, the magnetic material constituting the first magnetic body 301 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 preferably used. To reduce magnetic loss at high frequencies, the magnetic material constituting the first magnetic body 301 preferably has a high volume resistivity, and specifically, is preferably an electrical insulator. The first magnetic body 301 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 (vertical direction in Figure 8).

[0062] The first magnetic material portion 301 includes a plurality of magnetic material portions, including a first portion 301a and a second portion 301b. In the cross-sectional view of FIG. 9 , the first conductor portion 201, the first portion 301a, and the second portion 301b are arranged in this order so as to be penetrated by a single imaginary straight line LV extending from the first conductor portion 201. Note that in the core substrate 601, not only the single imaginary straight line LV shown in the cross-sectional view of FIG. 9 , but also imaginary straight lines extending in any direction from the first conductor portion 201 penetrate the first conductor portion 201, the first portion 301a, and the second portion 301b in this order. In addition, in the cross-sectional view of FIG. 9 , the first portion 301a is in contact with the first conductor portion 201, and the second portion 301b of the first magnetic material portion 301 is separated from the first conductor portion 201. 9, the first portion 301a surrounds the first conductor 201. Furthermore, the second portion 301b surrounds the first portion 301a.

[0063] The second portion 301b has a higher magnetic permeability than the first portion 301a at a frequency lower than the frequency at which the first portion 301a has a peak magnetic permeability. Considering that the inductor L1 is for the interposer 700 (FIG. 1), frequency characteristics below 1 MHz may be ignored, and the one frequency is, for example, 50 MHz.

[0064] FIG. 12 is a graph illustrating the frequency dependence of the relative permeability of each of the first magnetic material RA to the third magnetic material RC. Each of the first magnetic material RA to the third magnetic material RC has a peak relative permeability at a first to third frequency, which decreases in this order. Generally, if a low peak frequency is permitted in the design of a magnetic material, it is easy to ensure a high relative permeability in the frequency range below the peak frequency. On the other hand, if the non-permeability is high, magnetic saturation is more likely to occur. Specifically, the first magnetic material RA is relatively inferior in terms of relative permeability value, but is relatively superior in terms of suppressing magnetic saturation. Conversely, the third magnetic material RC is relatively inferior in terms of suppressing magnetic saturation, but is relatively superior in terms of relative permeability value. The second magnetic material RB has intermediate characteristics between the characteristics of the first magnetic material RA and the third magnetic material RC.

[0065] If the entire first magnetic body 301 were made of the third magnetic material RC, its high relative permeability would make it easier to increase inductance under low current conditions, but its DC bias characteristics would be easily degraded due to magnetic saturation. On the other hand, if the entire first magnetic body 301 were made of the first magnetic material RA, its low relative permeability would make it difficult to ensure sufficient inductance, but its high relative permeability would make it difficult to ensure sufficient inductance. If the entire first magnetic body 301 were made of the second magnetic material RB, it would simply achieve intermediate characteristics in the above trade-off relationship. Thus, simply selecting the magnetic material for the first magnetic body 301 makes it difficult to simultaneously achieve sufficiently large inductance and sufficiently good DC bias characteristics.

[0066] In contrast, the first magnetic body 301 of the first embodiment includes a first portion 301a and a second portion 301b made of different magnetic materials. The first conductor portion 201, the first portion 301a, and the second portion 301b are arranged in this order so as to be pierced by a virtual straight line LV extending from the first conductor portion 201. The second portion 301b has a higher magnetic permeability than the first portion 301a at a frequency lower than the frequency at which the first portion 301a has a peak magnetic permeability. For example, the first portion 301a is made of a first magnetic material RA, and the second portion 301b is made of a second magnetic material RB or a third magnetic material RC. Alternatively, the first portion 301a is made of the second magnetic material RB, and the second portion 301b is made of a third magnetic material RC. The frequency at which the second portion 301b has a peak in magnetic permeability may be lower than the frequency at which the first portion 301a has a peak in magnetic permeability.

[0067] 9 (one of the cross-sectional views perpendicular to the thickness direction in which the first magnetic material portion 301 appears) may be present in any cross-sectional view perpendicular to the thickness direction in which the first magnetic material portion 301 appears. This makes it possible to more fully obtain the effects associated with each feature (described in detail below).

[0068] The core substrate 601 also has a second conductor portion 202 that constitutes the inductor L2 and a second magnetic material portion 302 that increases the inductance of the second conductor portion 202. In the first embodiment, the first magnetic material portion 301 and the second magnetic material portion 302 are spaced apart from each other. The second magnetic material portion 302 includes a first portion 302a and a second portion 302b, similar to how the first magnetic material portion includes a first portion 301a and a second portion 301b. The configurations of the second conductor portion 202 and the second magnetic material portion 302 are substantially similar to the configurations of the first conductor portion 201 and the first magnetic material portion, respectively, and therefore detailed description thereof will not be repeated.

[0069] The ceramic substrate 100 is a substrate made of a sintered body. 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 a composite material of glass and ceramics, specifically a composite material of glass and alumina. The ceramic substrate 100 is preferably made of LTCC. LTCC is a ceramic that can be sintered at approximately 900°C or less, which is well below the melting point of Ag or Cu. This allows for the co-sintering of a low-electrical resistance conductor primarily composed of Ag or Cu. 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.

[0070] The first conductor 201 is made of a sintered body and is made of, for example, Ag and / or Cu.

[0071] The manufacturing method of the core substrate 601 may be performed using the multilayer ceramic technology as described above. The manufacturing method includes a firing process. In this firing process, the first conductor portion 201, the second conductor portion 202, the first magnetic material portion 301, and the second magnetic material portion 302 may be fired simultaneously with the ceramic substrate 100. As a result, the core substrate 601 has a sintered interface between the first conductor portion 201 and a portion of the core substrate 601 other than the first conductor portion 201. In other words, the first conductor portion 201 and the other portion are sintered to each other. Specifically, in FIG. 9 , the core substrate 601 has a sintered interface between the first conductor portion 201 and the first magnetic material portion 301. In other words, the first conductor portion 201 and the first magnetic material portion 301 are sintered to each other. Specifically, in FIG. 9 , a sintered interface is formed between the first conductor portion 201 and the first portion 301 a of the first magnetic material portion 301. In other words, the first conductor portion 201 and the first portion 301a of the first magnetic material portion 301 are sintered to each other. The core substrate 601 also has a sintered interface between the first magnetic material portion 301 and the ceramic substrate 100. In other words, the first magnetic material portion 301 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 bonding.

[0072] 8, the ends of the first conductor portion 201 and the second conductor portion 202 reach the first surface SF1 of the ceramic substrate 100, and the core substrate 601 has a connection portion 450 that electrically connects these portions to each other. As a result, the first conductor portion 201 of the inductor L1 and the second conductor portion 202 of the inductor L2 form a series circuit as shown in FIG.

[0073] According to the first embodiment, the multiple magnetic material portions for increasing the inductance of the first conductor portion 201 include a first portion 301a and a second portion 301b having a higher magnetic permeability than the first portion 301a at a certain frequency. The first conductor portion 201, the first portion 301a, and the second portion 301b are arranged in this order so as to be pierced by a virtual straight line LV extending from the first conductor portion 201. As a result, the first portion 301a having a lower magnetic permeability is arranged closer to the first conductor portion 201 along the virtual straight line LV, and the second portion 301b having a higher magnetic permeability is arranged farther away from the first conductor portion 201. First, since the magnetic material is more likely to become magnetically saturated due to the magnetic field generated by the current in the first conductor portion 201 in a region closer to the first conductor portion 201, the occurrence of magnetic saturation can be suppressed by arranging the first portion 301a having a lower magnetic permeability closer to the region. Second, by arranging the second portion 301b, which has a higher magnetic permeability than the first portion 301a, in a more distant region, the inductance of the first conductor 201 can be increased compared to when the first portion 301a, which has a low magnetic permeability, is arranged in that region. Due to the above effects, the inductor built into the core substrate 601 can have a sufficiently large inductance per unit area and also have sufficiently good DC superposition characteristics.

[0074] The core substrate 601 may constitute an interposer 700. For the reasons described above, the inductor included in the interposer 700 can have a sufficiently large inductance per unit area and also have sufficiently good DC superposition characteristics.

[0075] The first portion 301a of the first magnetic material portion 301 is in contact with the first conductor portion 201, and the second portion 301b of the first magnetic material portion 301 is spaced apart from the first conductor portion 201. This makes it possible to more fully obtain the above-mentioned effect.

[0076] The first portion 301a of the first magnetic material portion 301 surrounds the first conductor portion 201. This improves inductance by arranging some magnetic material portion around the entire circumference of the first conductor portion 201, while the magnetic material portion is the first magnetic material portion 301, which has low magnetic permeability, thereby improving DC bias characteristics. Furthermore, the second portion 301b surrounds the first portion 301a. This allows the above-mentioned effect to be obtained in any direction around the first conductor portion 201.

[0077] The first conductor portion 201 and the second conductor portion 202 may form a series circuit. As a result, first, by connecting the first conductor portion 201 and the second conductor portion 202 in series, approximately twice the inductance can be obtained. Second, in this series circuit, the magnetic field caused by the current flowing through the first conductor portion 201 and the magnetic field caused by the current flowing through the second conductor portion 202 may reinforce each other between the first conductor portion 201 and the second conductor portion 202. In such cases, for the reasons described above, magnetic saturation due to the mutually reinforced magnetic fields can be suppressed.

[0078] When the connection portion 450 (FIGS. 8 and 11) is provided, in the series circuit of the first conductor portion 201 and the second conductor portion 202, the current flowing through the first conductor portion 201 and the current flowing through the second conductor portion 202 are in roughly opposite directions. Therefore, the magnetic field caused by the current flowing through the first conductor portion 201 and the magnetic field caused by the current flowing through the second conductor portion 202 reinforce each other between the first conductor portion 201 and the second conductor portion 202. Magnetic saturation caused by this mutually reinforced magnetic field can be suppressed as described above.

[0079] The first conductor 201 may be solid, which prevents an increase in electrical resistance due to a hollow portion, thereby reducing the electrical resistance of the first conductor 201.

[0080] The ceramic substrate 100 may be made of low-temperature co-fired ceramics or a composite material of glass and alumina, which makes it easier to form the ceramic substrate 100 and the first conductors 201 by co-firing in the manufacture of the core substrate 601.

[0081] The core substrate 601 may have a sintered interface between the first conductor 201 and the portion of the core substrate 601 other than the first conductor 201. 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 first conductor 201 is joined to the portion of the core substrate 601 other than the first conductor 201 via an organic adhesive. Therefore, the heat resistance of the core substrate 601 can be improved.

[0082] <Embodiment 2> Fig. 13 is a partial cross-sectional view schematically illustrating the configuration of a core substrate 602 according to embodiment 2. Specifically, Fig. 13 illustrates one cross-sectional view perpendicular to the thickness direction in which the first magnetic material portion 301 appears. Fig. 13 also illustrates one cross-sectional view perpendicular to the thickness direction in which the first magnetic material portion 301 and the second magnetic material portion 302 appear.

[0083] In the core substrate 602, in the cross-sectional view of FIG. 13 , the first conductor portion 201 is offset from the center CM1 of the first magnetic material portion 301, and the second conductor portion 202 is offset from the center CM2 of the second magnetic material portion 302. The distance between the center CC1 of the first conductor portion 201 and the center CC2 of the second conductor portion 202 is 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 particular, in the example shown in FIG. 13 , the centers CC1, CM1, CM2, and CC2 are arranged in this order on a common imaginary line, thereby satisfying the distance requirement described above. However, these do not necessarily need to be located on a common imaginary line. The center CC1 of the first conductor portion 201 may be offset 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 center CC2 of the second conductor portion 202 may be located away 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.

[0084] Other than this, the configuration is almost the same as that of the first embodiment described above, so the same or corresponding elements are given the same reference numerals and their description will not be repeated.

[0085] According to the second embodiment, the distance between the center CC1 of the first conductor portion 201 and the center CC2 of the second conductor portion 202 is 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. As a result, when the magnetic field caused by the current flowing through the first conductor portion 201 and the magnetic field caused by the current flowing through the second conductor portion 202 reinforce each other between the first conductor portion 201 and the second conductor portion 202, magnetic saturation due to the mutually reinforced magnetic fields can be suppressed.

[0086] In the example shown in FIG. 13 , the first conductor portion 201 and the second conductor portion 202 have a circular shape, and the centers CC1 and CC2 are the centers of the circles. As a modified example, an ellipse may be used instead of the circle. The shapes of the first conductor portion 201 and the second conductor portion 202 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. In the example shown in FIG. 13 , 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 modified example, an ellipse may be used instead of the circle. The shapes of the outer edges of the first magnetic material portion 301 and the second magnetic material portion 302 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.

[0087] Third Embodiment FIG. 14 is a partial cross-sectional view schematically illustrating the configuration of a core substrate 603 according to a third embodiment. In the cross-sectional view of FIG. 14 , the first conductor portion 201 of the core substrate 603 contacts the ceramic substrate 100 without crossing the tangent line LT at the boundary between the first magnetic material portion 301 and the ceramic substrate 100. The remaining configuration is substantially the same as that of the second embodiment, and therefore the same or corresponding elements are denoted by the same reference numerals and will not be described again. According to the third embodiment, the effect of suppressing magnetic saturation described in the second embodiment can be further enhanced. Furthermore, compared to the fourth embodiment described below, a sufficient inductance can be more easily ensured.

[0088] <Fourth Embodiment> Fig. 15 is a partial cross-sectional view schematically illustrating the configuration of a core substrate 604 according to a fourth embodiment. In the cross-sectional view of Fig. 15, the first conductor portion 201 of the core substrate 604 protrudes toward the ceramic substrate 100, crossing the tangent line LT of the boundary between the first magnetic material portion 301 and the ceramic substrate 100. The remaining configuration is substantially the same as that of the second embodiment, and therefore the same or corresponding elements are denoted by the same reference numerals, and their description will not be repeated. According to the fourth embodiment, the effect of suppressing magnetic saturation, as described in the second embodiment, can be further enhanced compared to the third embodiment.

[0089] Fifth Embodiment Figure 16 is a partial cross-sectional view schematically illustrating the configuration of a core substrate 605 according to a fifth embodiment. In the core substrate 605, the first magnetic material portion 301 includes not only the first portion 301a and the second portion 301b but also the third portion 301c as a plurality of magnetic material portions. In the cross-sectional view of Figure 16, the first conductor portion 201, the first portion 301a, the second portion 301b, and the third portion 301c are arranged in this order so as to be penetrated by a single imaginary straight line LV extending from the first conductor portion 201. Note that in the cross-sectional view of the core substrate 605 in Figure 16, not only the single imaginary straight line LV illustrated, but also any imaginary line extending in any direction from the first conductor portion 201 penetrates the first conductor portion 201, the first portion 301a, the second portion 301b, and the third portion 301c in this order. 16, not only the second portion 301b but also the third portion 301c are separated from the first conductor 201. In addition, in the cross-sectional view of FIG. 16, the third portion 301c surrounds the second portion 301b.

[0090] The third portion 301c has a higher magnetic permeability than the second portion 301b at a frequency lower than the frequency at which the second portion 301b has a peak magnetic permeability. Considering that the inductor L1 is for the interposer 700 ( FIG. 1 ), frequency characteristics below 1 MHz may be ignored, as described in the first embodiment, and the one frequency is, for example, 50 MHz. When the magnetic materials illustrated in FIG. 12 are used, the first portion 301a is a first magnetic material RA, the second portion 301b is a second magnetic material RB, and the third portion 301c is a third magnetic material RC.

[0091] The second magnetic material part 302 includes a first portion 302a to a third portion 302c, in the same way that the first magnetic material part includes a first portion 301a to a third portion 301c.

[0092] Note that the configuration other than that described above is substantially the same as that of the first embodiment, and therefore the same or corresponding elements are given the same reference numerals and their description will not be repeated.

[0093] Sixth Embodiment FIG. 17 is a diagram schematically illustrating the configuration of a core substrate 611 according to a sixth embodiment, and is a partial cross-sectional view taken along line XVII-XVII in FIG. 18 . FIG. 18 is a partial cross-sectional view taken along line XVIII-XVIII in FIG. 17 . In the core substrate 611, the first magnetic material portion 301 and the second magnetic material portion 302 are connected to each other. Specifically, the second portion 301b of the first magnetic material portion 301 and the second portion 302b of the second magnetic material portion 302 are connected to each other, thereby constituting one magnetic member 300b. Of the magnetic member 300b, a portion closer to the center of the first conductor portion 201 than the center of the second conductor portion 202 belongs to the first magnetic material portion 301, and a portion closer to the center of the second conductor portion 202 than the center of the first conductor portion 201 belongs to the second magnetic material portion 302. On the other hand, the first portion 301a of the first magnetic material part 301 and the first portion 302a of the second magnetic material part 302 are separated from each other via the magnetic member 300b.

[0094] Note that the configuration other than that described above is substantially the same as that of the first embodiment, and therefore the same or corresponding elements are given the same reference numerals and their description will not be repeated.

[0095] According to the sixth embodiment, the first magnetic material portion 301 and the second magnetic material portion 302 are connected to each other. As a result, when the first magnetic material portion 301 and the second magnetic material portion 302 each have a predetermined area in a plan view, the first magnetic material portion 301 and the second magnetic material portion 302 are arranged in a smaller area than when the ceramic substrate 100 separates the first magnetic material portion 301 and the second magnetic material portion 302. This allows the area of ​​the core substrate 611 to be reduced.

[0096] Although the above description has been given of the case where the first and second conductor portions are used, more generally, first to nth conductor portions (n≧2) may be used. In this case, k is an integer between 1 and n, and the portion of the magnetic member 300b that is closest to the center of the kth conductor portion among the centers of the first to nth conductor portions belongs to the kth magnetic material portion. This definition also applies to the magnetic member 300a in the seventh embodiment described below.

[0097] 18, the outer edge shape of the magnetic member 300b is configured by mutually opposing straight lines and mutually opposing arcs, but the outer edge shape is not limited to this. The shape is an ellipse in the core substrate 612 of the first modified example (FIG. 19), and a rectangle in the core substrate 613 of the second modified example (FIG. 20).

[0098] Seventh Embodiment Fig. 21 is a diagram schematically illustrating the configuration of a core substrate 621 in a seventh embodiment, and is a partial cross-sectional view taken along line XXI-XXI in Fig. 22. Fig. 22 is a partial cross-sectional view taken along line XXII-XXII in Fig. 20. In the core substrate 621, the first portion 301a of the first magnetic material portion 301 and the first portion 302a of the second magnetic material portion 302 are connected to each other, thereby constituting one magnetic member 300a. Of the magnetic member 300a, a portion closer to the center of the first conductor portion 201 than the center of the second conductor portion 202 belongs to the first magnetic material portion 301, and a portion closer to the center of the second conductor portion 202 than the center of the first conductor portion 201 belongs to the second magnetic material portion 302.

[0099] Note that, other than the above, the configuration is almost the same as that of the sixth embodiment described above, and therefore the same or corresponding elements are given the same reference numerals and their description will not be repeated.

[0100] In the seventh embodiment, similarly to the sixth embodiment, the first magnetic material portion 301 and the second magnetic material portion 302 are connected to each other. As a result, when the first magnetic material portion 301 and the second magnetic material portion 302 each have a predetermined area in a plan view, the first magnetic material portion 301 and the second magnetic material portion 302 are arranged in a smaller area than when the ceramic substrate 100 separates the first magnetic material portion 301 and the second magnetic material portion 302. This allows the area of ​​the core substrate 611 to be reduced. Comparing the sixth embodiment with the seventh embodiment, the former is advantageous for ensuring inductance, while the latter is advantageous for improving DC superposition characteristics.

[0101] 22, the outer edge shape of the magnetic member 300b is configured by mutually opposing straight lines and mutually opposing arcs, but the outer edge shape is not limited to this. The shape is an ellipse in the core substrate 622 of the first modified example (FIG. 23), and a rectangle in the core substrate 623 of the second modified example (FIG. 24).

[0102] <Simulation> Generally, as a DC superposition characteristic of inductance, the inductance in a state where a DC current is superposed decreases from the initial inductance (i.e., the inductance in a state where the DC current is zero) as the DC current increases.

[0103] In consideration of the DC bias characteristics required of inductors for semiconductor elements mounted on an interposer, the inventors have classified the DC bias characteristics of inductors into the following types.

[0104]

[0105] Furthermore, in consideration of the initial inductance required for an inductor for a semiconductor element mounted on an interposer, the inventors have classified the initial inductance of an inductor as follows.

[0106]

[0107] Simulation conditions for the DC bias characteristics and initial inductance are described below with reference to FIG. 9 . The first conductor portion 201 and the second conductor portion 202 are circular with a diameter of 100 μm. The outer edges of the first portions 301a and 302a are circular with a diameter of 225 μm. The second portions 301b and 302b are circular with a diameter of 350 μm. The in-plane shape of the ceramic substrate 100 is a square with sides of 50 mm. The thickness of the ceramic substrate 100 is 1 mm. The gap between the first magnetic material portion 301 and the second magnetic material portion 302 is 150 μm. The frequency of the applied current is 50 MHz.

[0108] Under the above common conditions, the magnetic materials for the first portions 301a and 302a and the magnetic materials for the second portions 301b and 302b are selected from the first magnetic material RA to the third magnetic material RC (FIG. 12), and a simulation is performed. The results are shown below.

[0109]

[0110] In the above, in Examples 1 to 3, the magnetic material of the first portions 301a and 302a and the magnetic material of the second portions 301b and 302b are selected as described in Embodiment 1. On the other hand, in Comparative Examples 1 and 2, the magnetic material of the first portions 301a and 302a and the magnetic material of the second portions 301b and 302b are the same, and have a different configuration from that of Embodiment 1.

[0111] As can be seen from the above simulations, in Comparative Examples 1 and 2, it is possible to improve one of the evaluation results of the DC bias characteristics and the evaluation results of the initial inductance, but the other is significantly deteriorated accordingly. In other words, there is a significant trade-off between the two. In contrast, the above simulations show that according to Examples 1 to 3, this trade-off can be improved.

[0112] 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.

[0113] 100: Ceramic substrate 201: First conductor portion 202: Second conductor portion 301: First magnetic portion 302: Second magnetic portion 301a, 302a: First portion 301b, 302b: Second portion 301c, 302c: Third portion 450: Connection portion 601 to 605, 611 to 613, 621 to 623: Core substrate 700: Interposer 791: Wiring layer 811: Semiconductor element

Claims

1. A core substrate with an embedded inductor for forming an interposer on which a semiconductor element is mounted, comprising: a ceramic substrate having a thickness direction; a first conductor portion made of a sintered body and penetrating the ceramic substrate in the thickness direction; and a first magnetic material portion made of ceramic and embedded in the ceramic substrate for increasing the inductance of the first conductor portion, wherein the first magnetic material portion includes a plurality of magnetic material portions, each of which includes a first portion and a second portion having a higher magnetic permeability than the first portion at a frequency lower than the frequency at which the first portion has a peak in magnetic permeability; and wherein, in at least one cross-sectional view perpendicular to the thickness direction, the first conductor portion, the first portion of the first magnetic material portion, and the second portion of the first magnetic material portion are arranged in this order so as to be pierced by a virtual straight line extending from the first conductor portion.

2. A core substrate as described in claim 1, wherein, in at least one cross-sectional view, the first portion of the first magnetic material portion is in contact with the first conductor portion, and the second portion of the first magnetic material portion is spaced apart from the first conductor portion.

3. A core substrate according to claim 1, wherein, in at least one cross-sectional view, the first portion of the first magnetic material portion surrounds the first conductor portion.

4. A core substrate according to claim 3, wherein, in at least one cross-sectional view, the second portion of the first magnetic material portion surrounds the first portion of the first magnetic material portion.

5. A core substrate according to any one of claims 1 to 4, comprising: a second conductor portion made of a sintered body and penetrating the ceramic substrate in the thickness direction; and a second magnetic portion embedded in the ceramic substrate for increasing the inductance of the second conductor portion.

6. A core substrate according to claim 5, wherein the first magnetic body portion and the second magnetic body portion are spaced apart from each other.

7. A core substrate according to claim 5, wherein the first magnetic material portion and the second magnetic material portion are connected to each other.

8. A core substrate as described in claim 5, wherein, in at least one cross-sectional view, the first conductor portion is offset from the center of the first magnetic material portion, the second conductor portion is offset from the center of the second magnetic material portion, and 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.

9. A core substrate according to claim 5, wherein the first conductor portion and the second conductor portion form a series circuit.

10. A core substrate according to claim 9, wherein the ceramic substrate has a surface to which an end of the first conductor portion and an end of the second conductor portion reach, and further comprises a connection portion that electrically connects the end of the first conductor portion and the end of the second conductor portion to each other.

11. A core substrate according to any one of claims 1 to 4, wherein the at least one cross-sectional view includes any cross-sectional view perpendicular to the thickness direction in which the first magnetic material portion appears.

12. A core substrate according to any one of claims 1 to 4, wherein the first conductor portion is a solid body.

13. A core substrate according to any one of claims 1 to 4, wherein the ceramic substrate is made of low-temperature co-fired ceramics or a composite material of glass and alumina.

14. A core substrate according to any one of claims 1 to 4, wherein a sintered interface is formed between the first conductor portion and a portion of the core substrate other than the first conductor portion.

15. An interposer comprising: a core substrate according to any one of claims 1 to 4; 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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