Substrate with built-in electronic component

Abstract

A substrate 1 with a built-in electronic component includes: a substrate 10 having a first main surface 11 and a second main surface 12 facing each other in a thickness direction; a cavity 70 opening on the first main surface 11 of the substrate 10; and an electronic component 50 housed in the cavity 70. In a cross-sectional view taken along the thickness direction, there is an inflection point 76 where the width of the cavity changes on a side surface 75 of the cavity, and the side surface 75 of the cavity 70 has a shape spreading in an oblique direction toward a bottom surface 78 on the bottom surface 78 side of the cavity 70 from the inflection point 76.

Description

Electronic component embedded board

[0001] The present invention relates to a substrate with built-in electronic components.

[0002] Patent Document 1 discloses a ceramic multilayer substrate with a cavity, in which electronic components are mounted.

[0003] Patent Document 1 describes that the joint between the mounting portion and the ceramic substrate is susceptible to stress, which can cause cracks, etc. As a solution to this problem, a recess is formed on the main surface opposite the main surface having the cavity, and a resin layer is provided that covers the recess and has a flat surface, which increases the thickness of the resin layer in the recess, thereby improving the strength of the ceramic layer that forms the bottom portion of the cavity and improving impact resistance.

[0004] Patent Document 2 describes a method of forming a cavity by removing the sheet inside the cutout. Figures 9(a) to 9(d) describe a method of forming a widened portion on the bottom surface of the cavity by using a first fitting sheet that is larger than the size of the cutout for forming the cavity.

[0005] JP 2006-310498 A JP 2007-59863 A

[0006] The structure described in Patent Document 1 can improve the strength of the bottom portion of the cavity. However, when mounting a component in the cavity, it is necessary to form the cavity slightly larger than the location where the mounting land is to be formed so that the mounting land can be reliably formed on the bottom surface of the cavity. Furthermore, the cavity shape is often such that the opening at the top of the cavity is larger than the bottom surface. Therefore, if the bottom surface of the cavity is enlarged, the opening at the top of the cavity becomes even larger. However, in a situation where there is a demand for reducing the dimensions of electronic component-embedded substrates and increasing packaging density, it is not desirable to increase the dimensions of the cavity.

[0007] In the configuration of Patent Document 2, the region where the first mating sheet is removed becomes a widened region at the bottom of the cavity, so the shape can only be controlled in units of the thickness of the first mating sheet (number of sheet layers). Therefore, it is not possible to adjust the thickness of the widened region at the bottom of the cavity, for example, to the thickness of 1.5 sheets. Furthermore, because the shape of the widened region at the bottom of the cavity follows the step of the sheet, the cross-sectional shape of the cavity becomes stepped. If the step angle is close to 90 degrees, stress will concentrate, making defects such as cracks more likely to occur.

[0008] The present invention has been made to solve the above problems, and aims to provide a substrate with built-in electronic components in which mounting lands can be easily formed on the bottom surface of the cavity and cracks are less likely to occur in the cavity.

[0009] The electronic component-embedded substrate of the present invention is an electronic component-embedded substrate comprising a substrate having a first main surface and a second main surface opposing each other in the thickness direction, a cavity opening to the first main surface of the substrate, and an electronic component accommodated in the cavity, wherein, in a cross-sectional view cut in the thickness direction, there is an inflection point on the side of the cavity where the width of the cavity changes, and the side of the cavity has a shape that widens diagonally toward the bottom surface of the cavity closer to the inflection point.

[0010] According to the present invention, it is possible to provide an electronic component built-in substrate in which mounting lands can be easily formed on the bottom surface of the cavity and cracks are less likely to occur in the cavity.

[0011] Fig. 1 is a cross-sectional view schematically showing one example of the configuration of an electronic component built-in substrate of the present invention. Fig. 2 is a cross-sectional view schematically showing one example of the cross-sectional shape of a cavity. Fig. 3 is a cross-sectional view schematically showing another example of the configuration of an electronic component built-in substrate of the present invention. Fig. 4 is a cross-sectional view schematically showing another example of the cross-sectional shape of a cavity. Fig. 5 is a cross-sectional view schematically showing another example of the cross-sectional shape of a cavity.

[0012] The electronic component-embedded substrate of the present invention will be described below. However, the present invention is not limited to the following configuration, and can be appropriately modified and applied within the scope of the present invention. Note that a combination of two or more of the individual preferred configurations described below also falls within the scope of the present invention.

[0013] [Electronic component built-in substrate] Fig. 1 is a cross-sectional view schematically showing an example of the configuration of an electronic component built-in substrate of the present invention. The electronic component built-in substrate 1 shown in Fig. 1 has a substrate 10 formed by laminating an insulating layer 30 and a constraining layer 40. The substrate 10 has a first main surface 11 and a second main surface 12 that face each other in the thickness direction (Z direction in Fig. 1).

[0014] Wiring 21 and interlayer connection conductors 22 are provided inside the substrate 10. The wiring conductors and interlayer connection conductors are preferably made of a material that can be co-fired with the low-temperature co-fired ceramic material, such as Cu, Ag, Au, and alloys thereof. Cu, Ag, and Au have low resistance and are therefore particularly suitable for use in high-frequency applications of the ceramic substrate. The patterns of the wiring and interlayer connection conductors are not particularly limited.

[0015] The insulating layer preferably contains a low-temperature co-fired ceramic material (LTCC material). The low-temperature co-fired ceramic material is a ceramic material that can be fired at a temperature of 1000°C or less and can be co-fired with Au, Ag, Cu, or the like, which have low resistivity. Specific examples of the low-temperature co-fired ceramic material include glass composite low-temperature co-fired ceramic materials obtained by mixing ceramic powder such as alumina, zirconia, magnesia, or forsterite with borosilicate glass; ZnO-MgO-Al ２ O ３ -SiO ２ Glass-ceramic low-temperature fired ceramic material using BaO-Al ２ O ３ -SiO ２ ceramic powder and Al ２ O ３ -CaO-SiO ２ -MgO-B ２ O ３Examples of suitable ceramic materials include non-glass-based low-temperature fired ceramic materials using ceramic powders.

[0016] The constraining layer is a layer containing a metal oxide that does not substantially sinter at the sintering temperature of the low-temperature co-fired ceramic material and does not shrink or shrinks only slightly during firing. Examples of metal oxides that do not substantially sinter at the sintering temperature of the low-temperature co-fired ceramic material include alumina, silica, zirconia, titania, silica, niobium pentoxide, tantalum pentoxide, and magnesia, with alumina and silica being preferred. These metal oxides can be used alone or in combination, taking into account the high-frequency characteristics of the ceramic substrate.

[0017] The metal oxide contained in each of the plurality of constraining layers of the substrate is preferably the same type, more preferably at least one of alumina and silica, and even more preferably alumina.

[0018] The constraining layer preferably contains glass in addition to the metal oxide. When the constraining layer contains glass, examples of the glass contained in the constraining layer include B—Si-M (M is an alkali metal or alkaline earth metal) based glasses.

[0019] The insulating layers and constraining layers that make up the substrate are preferably stacked alternately, but in some cases, two or more insulating layers may be stacked continuously, or two or more constraining layers may be stacked continuously. In the substrate 10 shown in Figure 1, the insulating layers 30 and the constraining layers 40 are stacked alternately. Also, the substrate 10 does not need to be provided with the constraining layers 40, and only the insulating layers 30 may be stacked continuously.

[0020] An electronic component 51 is mounted on the first main surface 11 of the substrate 10, and an electronic component 52 is mounted on the second main surface 12. In addition, a mounting electrode 61 is provided on the second main surface 12, and the mounting electrode 61 is used to mount the electronic component built-in substrate 1 on another substrate. A plating layer 62 is provided on the surface of the mounting electrode 61.

[0021] The substrate 10 is provided with a cavity 70 that opens to the first main surface 11 of the substrate 10, and an electronic component 50 is housed in the cavity 70. In the electronic component-embedded substrate 1 shown in FIG. 1 , the electronic component 50 is mounted on a bottom surface 78 of the cavity 70, and the top surface of the electronic component 50 (the surface on the first main surface 11 side of the substrate 10) protrudes above an opening 79 of the cavity 70 (coplanar with the first main surface 11). In such a case, the electronic component is also considered to be housed in the cavity. Furthermore, the electronic component is also considered to be housed in the cavity when the top surface of the electronic component is located below the opening of the cavity (coplanar with the first main surface). Details of the shape of the cavity will be described later.

[0022] Examples of the electronic components (electronic components 50, 51, 52) included in the electronic component built-in substrate 1 include semiconductor chips (dies), passive components such as capacitors and coils, and filters.

[0023] The interior of the cavity 70, the periphery of the electronic component 51, and the periphery of the electronic component 52 are sealed with a sealing material 80. The sealing material 80 is made of a sealing resin, and either a thermosetting resin or a thermoplastic resin may be used as the sealing resin. Examples of thermosetting resins include phenolic resin, epoxy resin, polyester resin, silicone resin, and polyimide resin. Examples of thermoplastic resins include thermoplastic liquid crystal polymer (LCP), thermoplastic polyimide resin, polyether ether ketone resin (PEEK), and polyphenylene sulfide resin (PPS).

[0024] The sealing resin may contain additives such as fillers, for example, glass, silica, aluminum oxide, aluminum nitride, boron nitride, and the like.

[0025] An external shielding film 90 is provided around the electronic component built-in substrate 1. The external shielding film 90 is provided on the surface of the substrate 10 other than the surface on the second main surface 12 side (the surface where the mounting electrodes 61 are exposed from the sealing material 80).

[0026] In the electronic component built-in substrate of the present invention, electronic components do not have to be mounted on the first and second main surfaces of the substrate, and an external shielding film does not have to be provided around the electronic component built-in substrate.

[0027] In the electronic component-embedded substrate of the present invention, when viewed in cross section in the thickness direction, there is an inflection point on the side of the cavity where the width of the cavity changes, and on the bottom side of the cavity closer to the inflection point, the side of the cavity has a shape that widens diagonally toward the bottom.

[0028] 2 is a cross-sectional view schematically illustrating an example of the cross-sectional shape of a cavity. Fig. 2 shows the cross-sectional shape of a cavity 70. A mounting land 74 is provided on a bottom surface 78 of the cavity 70. A side surface 75 of the cavity 70 has an inflection point 76 where the width of the cavity 70 changes. The side surface 75 of the cavity 70 is divided into a first side surface 75a located closer to an opening 79 of the cavity 70 than the inflection point 76, and a second side surface 75b located closer to the bottom surface 78 than the inflection point 76.

[0029] In the cavity 70 shown in FIG. 2 , the width of the cavity 70 is constant along the thickness direction on the first side surface 75a. On the other hand, the second side surface 75b has a shape that expands obliquely along the thickness direction from an inflection point 76 toward a bottom surface 78 of the cavity. On the second side surface 75b, the width of the cavity 70 is smallest at the inflection point 76 and largest at the bottom surface 78. In FIG. 2 , the width of the cavity 70 at the inflection point 76 is indicated by a double-headed arrow W1, and the width of the cavity 70 at the bottom surface 78 is indicated by a double-headed arrow W2. On the second side surface 75b, the width of the cavity 70 monotonically increases from width W1 at the inflection point 76 to width W2 at the bottom surface 78.

[0030] 2, the bottom surface of the cavity can be enlarged, making it easier to form a mounting land on the bottom surface of the cavity. In addition, the opening at the top of the cavity can be made smaller than the bottom surface of the cavity, preventing the overall size of the cavity from becoming too large.

[0031] Furthermore, since the shape of the side of the cavity is sloped and not stepped, stress is prevented from concentrating at a specific point on the side of the cavity, resulting in an electronic component-embedded substrate that is less likely to develop cracks in the cavity.

[0032] In the electronic component-embedded substrate of the present invention, the substrate may have a configuration in which insulating layers and constraining layers are alternately stacked, and in a cross-sectional view cut in the thickness direction, the inflection point may be located on a side surface of the insulating layer.

[0033] The fact that the inflection point is located on the side of the insulating layer indicates that the width of the cavity is not controlled by adjusting the size of the space that will become the cavity in each layer that makes up the substrate before stacking them. By locating the inflection point on the side of the insulating layer, the inflection point can be located anywhere without being limited to the boundary position of each layer that makes up the substrate, thereby increasing the degree of freedom in design.

[0034] The electronic component-embedded substrate of the present invention may further include a second cavity opening to the second main surface of the substrate and a second electronic component housed in the second cavity. Figure 3 is a cross-sectional view schematically showing another example of the configuration of the electronic component-embedded substrate of the present invention. The electronic component-embedded substrate 2 shown in Figure 3 is provided with a second cavity 170 opening to the second main surface 12 of the substrate 10, and a second electronic component 150 is housed in the second cavity 170. When a second cavity is provided, the cavity opening to the first main surface of the substrate may be referred to as the first cavity to distinguish the name. Furthermore, when the second cavity houses the second electronic component, the electronic component housed in the first cavity may be referred to as the first electronic component to distinguish the name.

[0035] The second cavity 170 may have the same form as or a different form from the cavity 70 (first cavity) that opens to the first main surface 11. That is, in a cross section of the second cavity cut in the thickness direction, the side surface of the cavity may have an inflection point where the width of the cavity changes, and the side surface of the cavity may have a shape that widens obliquely toward the bottom surface closer to the bottom surface of the cavity than the inflection point, or the side surface of the cavity may have no inflection point and the width of the cavity may be constant in the thickness direction.

[0036] The electronic components described above can be used as the second electronic component 150. The electronic component 52 mounted on the second main surface 12 of the electronic component-embedded substrate 1 shown in FIG. 1 may be accommodated in the second cavity 170.

[0037] By providing cavities on both the first and second main surfaces of the substrate and accommodating electronic components in the respective cavities, it is possible to improve the volumetric efficiency of component mounting.

[0038] In the electronic component-embedded substrate of the present invention, when viewed in a cross section cut in the thickness direction, the side surface of the cavity may have a shape that widens obliquely toward the inflection point on the cavity opening side relative to the inflection point, and the side surface of the cavity may have a shape that widens further obliquely toward the bottom surface on the cavity bottom side relative to the inflection point.

[0039] 4 is a cross-sectional view schematically illustrating another example of the cross-sectional shape of a cavity. Fig. 4 shows the cross-sectional shape of a cavity 71. A side surface 75 of the cavity 71 has an inflection point 76 where the width of the cavity 71 changes. The side surface 75 of the cavity 71 is divided into a first side surface 75a located closer to an opening 79 of the cavity 71 than the inflection point 76, and a second side surface 75b located closer to a bottom surface 78 than the inflection point 76.

[0040] The first side surface 75a has a shape that widens obliquely along the thickness direction from the opening 79 toward the inflection point 76. On the first side surface 75a, the width of the cavity 71 is smallest at the opening 79 and largest at the inflection point 76. In Figure 4, the width of the cavity 71 at the inflection point 76 is indicated by a double-headed arrow W1, and the width of the cavity 71 at the opening 79 is indicated by a double-headed arrow W3. On the first side surface 75a, the width of the cavity 71 monotonically increases from the width W3 at the opening 79 to the width W1 at the inflection point 76.

[0041] The second side surface 75b has a shape that further widens obliquely from the inflection point 76 toward the bottom surface 78 of the cavity along the thickness direction. On the second side surface 75b, the width of the cavity 71 is smallest at the inflection point 76 and largest at the bottom surface 78. In FIG. 4, the width of the cavity 71 at the inflection point 76 is indicated by a double-headed arrow W1, and the width of the cavity 71 at the bottom surface 78 is indicated by a double-headed arrow W2. On the second side surface 75b, the width of the cavity 71 monotonically increases from the width W1 at the inflection point 76 to the width W2 at the bottom surface 78, but the rate of increase is greater than the rate of monotonically increasing from the width W3 at the opening 79 to the width W1 at the inflection point 76.

[0042] When the cavity has such a shape, the bottom surface of the cavity can be made larger while the opening can be made smaller, thereby reducing the volume of the cavity and improving the degree of freedom in design.

[0043] Although the width of the cavity in a cross-sectional view is not particularly limited, it is preferable that the difference (W2-W1) between the width W2 of the cavity at the bottom surface and the width W1 of the cavity at the inflection point be 0.010 mm or more and 0.100 mm or less. Furthermore, when the first side surface has a shape that expands obliquely along the thickness direction from the opening toward the inflection point, it is preferable that the difference (W1-W3) between the width W1 of the cavity at the inflection point and the width W3 of the cavity at the opening be 0.030 mm or more and 0.200 mm or less.

[0044] In the electronic component-embedded substrate of the present invention, in a cross section cut in the thickness direction, the side surface of the cavity has a shape having a recess and a protrusion, and the recess may be curved. Furthermore, the substrate may have a configuration in which insulating layers and constraining layers are alternately laminated, and the insulating layers may form the recesses and the constraining layers form the protrusions.

[0045] Fig. 5 is a cross-sectional view schematically showing another example of the cross-sectional shape of a cavity, showing the cross-sectional shape of a cavity 72. Fig. 5 shows the cavity 72 provided in the substrate 10 on which the insulating layer 30 and the constraining layer 40 are stacked.

[0046] A recess 75c1 and a protrusion 75c2 are provided on the side surface 75 of the cavity 72. The recess 75c1 is a curved recessed portion of the side surface of the insulating layer 30. The protrusion 75c2 is a portion where the side surface (end) of the constraining layer 40 protrudes beyond the side surface of the insulating layer 30.

[0047] When the insulating layer is made of a material containing a low-temperature co-fired ceramic (LTCC) material, the LTCC material shrinks upon firing. However, the presence of constraining layers on the upper and lower surfaces in contact with the LTCC material suppresses shrinkage. Because shrinkage occurs in the insulating layer at the center in the thickness direction, far from the constraining layers, the side surface 75 of the insulating layer 30 is recessed in a curved shape, forming a recess 75c1.

[0048] Since the material that forms the constraining layer does not shrink during firing, the constraining layer 40 forms a convex portion 75c2 that protrudes beyond the concave portion 75c1.

[0049] In the manufacturing process of a substrate with built-in electronic components, if firing is performed after drilling holes that will become cavities, recesses and protrusions may be formed on the side surfaces of the cavities due to the difference in the amount of shrinkage for the reasons described above.On the other hand, if a method is used in which holes that will become cavities are machined after firing, recesses and protrusions are not formed on the side surfaces of the cavities, and the side surfaces remain flat.

[0050] If the recessed and protruding portions are provided on the side surface of the cavity, the adhesion with the sealing resin filled in the cavity is improved.

[0051] The method for producing the electronic component built-in substrate of the present invention is not particularly limited, but can be, for example, as follows: The electronic component built-in substrate is preferably produced by a method in which an electronic component built-in substrate aggregate sheet having multiple electronic component built-in substrate units attached thereto is produced, and then the sheet is cut to obtain a plurality of electronic component built-in substrates.

[0052] First, an insulating layer sheet that will serve as an insulating layer and a constraining layer sheet that will serve as a constraining layer are laminated to obtain a laminate. A predetermined conductor pattern may be formed on the insulating layer sheet and the constraining layer sheet. The conductor pattern becomes the wiring and interlayer connection conductor provided inside the substrate body. A hole that will become a cavity is machined in part of the laminate using a laser or router. A laminate with a hole that will become a cavity is called a cavity laminate. A hole that will become a cavity is drilled from the surface of the cavity laminate that will become the first main surface of the substrate. In this hole, the side of the cavity is approximately parallel to the thickness direction, and the cavity width is constant. Alternatively, a cavity laminate may be obtained by machining a hole that will become a cavity in each of the insulating layer sheet and the constraining layer sheet, and then laminating the sheets with the hole position aligned.

[0053] Next, a shallow hole is drilled obliquely using a laser from the surface of the cavity-forming laminate opposite the surface intended to become the first main surface of the substrate. This process creates a cavity with a shape in which the side of the cavity widens obliquely toward the bottom, closer to the bottom of the cavity than the inflection point.

[0054] Furthermore, instead of performing the step of drilling shallow diagonal holes using a laser from the surface opposite to the surface intended to become the first main surface of the substrate, it is possible to form a cavity with a shape that widens near the bottom surface by adjusting the pressing conditions (using a higher pressing pressure) in the step of stacking and pressing the base laminate and the cavity laminate, as described below. Note that when laser drilling is performed only once, it is preferable to drill the holes from the surface opposite to the surface intended to become the first main surface of the substrate.

[0055] Separately, an insulating layer sheet that will become the insulating layer and a constraining layer sheet that will become the constraining layer are laminated to obtain a laminate. No holes that will become cavities are machined in this laminate. The laminate with holes that will become cavities is called the base laminate.

[0056] The base laminate and the cavity laminate are stacked and pressed together, and then fired to obtain a substrate. The surface of the base laminate exposed through the hole in the cavity laminate becomes the bottom of the cavity.

[0057] An electronic component is housed in the cavity of the substrate, and if necessary, electronic components are also mounted on the first and second main surfaces of the substrate. Furthermore, the cavity and the first and second main surfaces of the substrate are sealed with a sealing material.

[0058] The electronic component built-in substrate assembly sheet is then cut to obtain electronic component built-in substrates. An external shielding film may be provided on the periphery of the electronic component built-in substrate.

[0059] Furthermore, by stacking cavity laminates on both sides of the base laminate, it is possible to manufacture a substrate with built-in electronic components that has a second cavity.

[0060] When creating a cavity as shown in Figure 4, a method can be used in which the angle of the laser is oblique when drilling a hole to form the cavity from the surface of the cavity-forming laminate that is intended to be the first main surface of the substrate.

[0061] The present specification discloses the following:

[0062] The present disclosure (1) is an electronic component-embedded substrate including a substrate having a first main surface and a second main surface opposing each other in a thickness direction, a cavity opening to the first main surface of the substrate, and an electronic component accommodated in the cavity, wherein, in a cross-sectional view cut in the thickness direction, a side surface of the cavity has an inflection point where the width of the cavity changes, and the side surface of the cavity has a shape that widens obliquely toward the bottom surface of the cavity closer to the inflection point.

[0063] The present disclosure (2) is the electronic component-embedded substrate described in the present disclosure (1), further comprising a second cavity that opens to the second main surface of the substrate, and a second electronic component accommodated in the second cavity.

[0064] The present disclosure (3) is the electronic component-embedded substrate according to the present disclosure (1) or (2), in which, in a cross-sectional view cut in the thickness direction, the side surface of the cavity has a shape that widens obliquely toward the inflection point on the opening side of the cavity relative to the inflection point, and the side surface of the cavity has a shape that widens further obliquely toward the bottom side of the cavity relative to the inflection point.

[0065] The present disclosure (4) is the electronic component-embedded substrate according to any one of the present disclosures (1) to (3), in which, in a cross-sectional view cut in the thickness direction, the side surface of the cavity has a shape having a recess and a protrusion, and the recess is recessed in a curved shape.

[0066] The present disclosure (5) is the electronic component-embedded substrate according to the present disclosure (4), wherein the substrate has a configuration in which insulating layers and constraining layers are alternately stacked, the insulating layers being the recesses and the constraining layers being the protrusions.

[0067] The present disclosure (6) is the electronic component-embedded substrate according to any one of the present disclosures (1) to (5), wherein the substrate has a configuration in which insulating layers and constraining layers are alternately stacked, and in a cross-sectional view cut in the thickness direction, the inflection point is located on a side surface of the insulating layer.

[0068] DESCRIPTION OF SYMBOLS 1, 2 Electronic component built-in substrate 10 Substrate 11 First main surface of substrate 12 Second main surface of substrate 21 Wiring 22 Interlayer connection conductor 30 Insulating layer 40 Constraint layer 50 Electronic component (electronic component accommodated in cavity: first electronic component) 51 Electronic component (electronic component mounted on first main surface) 52 Electronic component (electronic component mounted on second main surface) 61 Mounting electrode 62 Plating layer 70, 71, 72 Cavity (first cavity) 74 Mounting land 75 Side surface of cavity 75a First side surface 75b Second side surface 75c1 Convex portion 75c2 Convex portion 76 Inflection point 78 Bottom surface of cavity 79 Opening of cavity 80 Sealant 90 External shielding film 150 Second electronic component 170 Second cavity

Claims

1. An electronic component-embedded substrate comprising: a substrate having a first main surface and a second main surface opposing each other in a thickness direction; a cavity opening to the first main surface of the substrate; and an electronic component housed in the cavity, wherein, in a cross-sectional view cut in the thickness direction, there is an inflection point on the side of the cavity where the width of the cavity changes, and the side of the cavity has a shape that widens obliquely toward the bottom surface of the cavity closer to the bottom surface of the cavity than the inflection point.

2. The electronic component-embedded substrate according to claim 1, further comprising: a second cavity that opens to the second main surface of the substrate; and a second electronic component housed in the second cavity.

3. An electronic component-embedded substrate according to claim 1 or 2, wherein, in a cross-sectional view cut in the thickness direction, the side surface of the cavity has a shape that widens obliquely toward the inflection point on the opening side of the cavity relative to the inflection point, and the side surface of the cavity has a shape that widens further obliquely toward the bottom side of the cavity relative to the inflection point.

4. An electronic component-embedded substrate according to any one of claims 1 to 3, wherein, in a cross-sectional view cut in the thickness direction, the side surface of the cavity has a shape having a recess and a protrusion, and the recess is recessed in a curved shape.

5. The electronic component-embedded substrate according to claim 4, wherein the substrate has a structure in which insulating layers and constraining layers are alternately laminated, the insulating layers forming the recesses and the constraining layers forming the protrusions.

6. The electronic component-embedded substrate according to any one of claims 1 to 5, wherein the substrate has a configuration in which insulating layers and constraining layers are alternately laminated, and in a cross section cut in the thickness direction, the inflection point is located on a side surface of the insulating layer.

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