Multilayer substrate and electronic device

Abstract

The present invention addresses the problem of reducing transmission loss. In a multilayer substrate (100), a hollow section (6) overlaps a signal line (2) in a plan view from the thickness direction (D1) of a laminated substrate (1). The laminated substrate (1) comprises a first base material layer (11), a second base material layer (12), and a third base material layer (13). The first base material layer (11) has a through hole (110) that forms a part of the hollow section (6). The second base material layer (12) has a recess (120) that overlaps the through hole (110) in the thickness direction (D1) of the laminated substrate (1). The third base material layer (13) connects the first base material layer (11) and the second base material layer (12). A ground electrode (3) is in contact with the second base material layer (12). In a plan view from the thickness direction (D1) of the laminated substrate (1), an opening edge (124) of the recess (120) is positioned further to the outer side than an opening edge (114) of the through hole (110). The third base material layer (13) does not overlap the through hole (110) in a plan view from the thickness direction (D1) of the laminated substrate (1).

Description

Multilayer boards and electronic devices

[0001] The present invention generally relates to a multilayer board and an electronic device, and more particularly to a multilayer board having a signal line and an electronic device having a multilayer board.

[0002] Patent Document 1 discloses a transmission line (multilayer substrate). The transmission line disclosed in Patent Document 1 includes a laminate, a signal conductor layer, and a ground conductor layer. The signal conductor layer is provided on the laminate. The ground conductor layer is provided on the laminate and overlaps the signal conductor layer when viewed from the stacking direction of the laminate. The laminate has a hollow portion. The hollow portion overlaps the signal conductor layer when viewed from the stacking direction of the laminate.

[0003] The transmission line disclosed in Patent Document 1 includes a first insulator layer provided with a signal conductor layer, a second insulator layer provided with a ground conductor layer, and a third insulator layer connecting the first and second insulator layers. The third insulator layer has a resin layer, a first adhesive layer, and a second adhesive layer. The first adhesive layer bonds the resin layer to the first insulator layer. The second adhesive layer bonds the resin layer to the second insulator layer.

[0004] International Publication No. 2022 / 114092

[0005] In the transmission line disclosed in Patent Document 1, the second adhesive layer may protrude into the hollow portion, resulting in increased transmission loss.

[0006] An object of the present invention is to provide a multilayer substrate and an electronic device that can reduce transmission loss.

[0007] A multilayer substrate according to one aspect of the present invention includes a laminated substrate, a signal line, and a ground electrode. The laminated substrate has a hollow portion. The signal line is disposed within the laminated substrate. The ground electrode overlaps the signal line in a plan view in the thickness direction of the laminated substrate. The hollow portion overlaps the signal line in a plan view in the thickness direction of the laminated substrate. The laminated substrate includes a first substrate layer, a second substrate layer, and a third substrate layer. The first substrate layer has a through hole or a recess that forms part of the hollow portion. The second substrate layer has a recess or a through hole that overlaps the through hole or the recess in the first substrate layer in the thickness direction of the laminated substrate. The third substrate layer connects the first substrate layer and the second substrate layer. The second substrate layer is disposed such that the internal space of the recess or the through hole in the second substrate layer is in communication with the through hole or the recess in the first substrate layer. In a plan view from the thickness direction of the laminated substrate, an opening edge of the recess in the second base material layer or an opening edge of the through hole in the second base material layer is located outside an opening edge of the through hole in the first base material layer or an opening edge of the recess in the first base material layer. The third base material layer does not overlap with the through hole in the first base material layer or the recess in the first base material layer in a plan view from the thickness direction of the laminated substrate. In the thickness direction of the laminated substrate, the hollow portion is located between the signal line and the ground electrode.

[0008] An electronic device according to one aspect of the present invention includes the multilayer substrate according to the above aspect and a housing, the housing housing housing the multilayer substrate.

[0009] The multilayer substrate and electronic device according to the above aspects of the present invention can reduce transmission loss.

[0010] FIG. 1 is a cross-sectional view of a multilayer board according to the first embodiment. FIG. 2 is another cross-sectional view of the same multilayer board. FIG. 3 is a plan view of the same multilayer board. FIG. 4 is a plan view of a fourth base material layer, two second interlayer connection conductors, and a plurality of third interlayer connection conductors in the same multilayer board. FIG. 5 is a plan view of a first base material layer, a signal line, a third ground electrode, and two second interlayer connection conductors in the same multilayer board. FIG. 6 is a plan view of a second base material layer and a plurality of first interlayer connection conductors in the same multilayer board. FIG. 7 is a schematic configuration diagram of an electronic device including the same multilayer board. FIG. 8 is a cross-sectional view of a multilayer board according to a first modification of the first embodiment. FIG. 9 is a cross-sectional view of a multilayer board according to a second modification of the first embodiment. FIG. 10 is a cross-sectional view of a multilayer board according to a second embodiment. FIG. 11 is another cross-sectional view of the same multilayer board. FIG. 12 is a cross-sectional view of a multilayer board according to a third embodiment. FIG. 13 is a cross-sectional view of a multilayer board according to a fourth embodiment. FIG. 14 is a cross-sectional view of a multilayer board according to a fifth embodiment. Fig. 15 is a cross-sectional view of a multilayer substrate according to a sixth embodiment. Fig. 16 is a cross-sectional view of a multilayer substrate according to a seventh embodiment. Fig. 17 is a schematic configuration diagram of an electronic device including the multilayer substrate. Fig. 18 is a cross-sectional view of a multilayer substrate according to an eighth embodiment. Fig. 19 is a cross-sectional view of a multilayer substrate according to a ninth embodiment.

[0011] Hereinafter, embodiments 1 to 9 will be described with reference to the drawings. The drawings referred to in the following embodiments 1 to 9 are schematic diagrams, and the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensions, and the size and thickness ratios between the components do not necessarily reflect the actual dimensional ratios. Furthermore, each drawing is depicted using a defined Cartesian coordinate system having three mutually orthogonal axes: the X-axis, the Y-axis, and the Z-axis. The X-axis, the Y-axis, and the Z-axis are all imaginary axes, and the arrows indicating "X," "Y," and "Z" in the drawings are depicted merely for the purpose of explanation and do not have any physical substance.

[0012] Embodiment 1 A multilayer substrate 100 and an electronic device 500 according to embodiment 1 will be described with reference to Figures 1 to 7. Figure 1 is a cross-sectional view taken along line X1-X1 in Figure 3. Figure 2 is a cross-sectional view taken along line Y1-Y1 in Figure 3. Furthermore, Figure 3 omits the illustration of the second resist layer 52 shown in Figures 1 and 2.

[0013] (1) Multilayer Substrate As shown in FIGS. 1 and 2 , a multilayer substrate 100 according to a first embodiment includes a laminated substrate 1, a signal line 2, and a ground electrode 3. The laminated substrate 1 has a plurality of hollow portions 6 (hereinafter, also referred to as first hollow portions 6) (three in the example of FIG. 2 ). The signal line 2 is disposed within the laminated substrate 1. The ground electrode 3 (hereinafter, also referred to as first ground electrode 3) overlaps the signal line 2 in a planar view from the thickness direction D1 of the laminated substrate 1. The plurality of first hollow portions 6 overlap the signal line 2 in a planar view from the thickness direction D1 of the laminated substrate 1. The laminated substrate 1 includes a first base layer 11, a second base layer 12, and a third base layer 13. The first base layer 11 has a plurality of through holes 110 (hereinafter, also referred to as first through holes 110) (three in the example of FIG. 2 ) that form a portion of each of the plurality of first hollow portions 6. The second base layer 12 has a plurality of recesses 120 (also referred to as first recesses 120) (three in the example of FIG. 2 ). The plurality of first recesses 120 correspond one-to-one to the plurality of first through holes 110. In the thickness direction D1 of the laminated substrate 1, each of the plurality of first recesses 120 overlaps a corresponding one of the plurality of first through holes 110. The second base layer 12 is arranged such that the internal space of each of the plurality of first recesses 120 communicates with the corresponding one of the plurality of first through holes 110. The third base layer 13 connects the first base layer 11 and the second base layer 12. The first ground electrode 3 is in contact with the second base layer 12. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 124 of each of the multiple first recesses 120 in the second base layer 12 is located outside an opening edge 114 of a first through hole 110 corresponding to the first recess 120 among the multiple first through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the multiple first through holes 110 in the first base layer 11 in a plan view from the thickness direction D1 of the laminated substrate 1. The thickness direction D1 of the laminated substrate 1 is the stacking direction of the first base layer 11, the third base layer 13, and the second base layer 12. The thickness direction D1 of the multilayer substrate 100 is a direction along the Z axis, but if the multilayer substrate 100 is bent, the thickness direction D1 may differ from the direction along the Z axis depending on the position on the multilayer substrate 100.

[0014] The laminated substrate 1 further has a plurality of second hollow portions 7 (three in the example of FIG. 2 ). The second hollow portions 7 correspond one-to-one to the first hollow portions 6. The second hollow portions 7 overlap the signal line 2 in a plan view in the thickness direction D1 of the laminated substrate 1. Furthermore, in the thickness direction D1 of the laminated substrate 1, each of the second hollow portions 7 overlaps a corresponding one of the first hollow portions 6. The laminated substrate 1 includes a fourth base layer 14, a fifth base layer 15, and a sixth base layer 16. The fourth base layer 14 has a plurality of second through holes 140 (three in the example of FIG. 2 ) that form a portion of each of the second hollow portions 7. The fifth base layer 15 has a plurality of second recesses 150 (three in the example of FIG. 2 ). The second recesses 150 correspond one-to-one to the second through holes 140. In the thickness direction D1 of the laminated substrate 1, each of the multiple second recesses 150 overlaps a corresponding one of the multiple second through holes 140. The fifth base layer 15 is arranged such that the internal space of each of the multiple second recesses 150 in the fifth base layer 15 communicates with a corresponding one of the multiple second through holes 140 in the fourth base layer 14. The sixth base layer 16 connects the fourth base layer 14 and the fifth base layer 15. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 154 of each of the multiple second recesses 150 in the fifth base layer 15 is located outside an opening edge 144 of a second through hole 140 corresponding to the second recess 150 in the fourth base layer 14. The sixth base layer 16 does not overlap the multiple second through holes 140 in the fourth base layer 14 in a plan view from the thickness direction D1 of the laminated substrate 1.

[0015] The multilayer substrate 100 further includes two first pad electrodes P1 (see FIG. 2), two second pad electrodes P2 (see FIG. 2), a second ground electrode 4, a third ground electrode 8, a plurality (ten in the example of FIG. 5) of first interlayer connection conductors 91, two second interlayer connection conductors 92 (see FIG. 2), and a plurality (ten in the example of FIG. 4) of third interlayer connection conductors 93. The multilayer substrate 100 also includes a first resist layer 51 and a second resist layer 52.

[0016] The multilayer substrate 100 is housed in a housing 501 of an electronic device 500, for example, as shown in Fig. 7. The electronic device 500 is, for example, a communication device. The communication device is, for example, a mobile phone (e.g., a smartphone), but is not limited to a mobile phone and may be, for example, a notebook personal computer, a wearable device (e.g., a smart watch), etc.

[0017] Hereinafter, each component of the multilayer substrate 100 according to this embodiment will be described with reference to the drawings.

[0018] (1.1) Laminated Substrate When viewed from above in the thickness direction D1 of the laminated substrate 1 (see FIGS. 1 and 2), the laminated substrate 1 has an elongated shape in which the length along the Y axis is longer than the length along the X axis, as shown in FIG. 3. When viewed from above in the thickness direction D1 of the laminated substrate 1, the shape of the laminated substrate 1 may be a shape other than an elongated shape.

[0019] 1 and 2 , the laminated substrate 1 has a first substrate layer 11, a second substrate layer 12, a third substrate layer 13, a fourth substrate layer 14, a fifth substrate layer 15, a sixth substrate layer 16, and a seventh substrate layer 17. In the laminated substrate 1, the second substrate layer 12, the third substrate layer 13, the first substrate layer 11, the seventh substrate layer 17, the fourth substrate layer 14, the sixth substrate layer 16, and the fifth substrate layer 15 are stacked in this order: the second substrate layer 12, the third substrate layer 13, the first substrate layer 11, the seventh substrate layer 17, the fourth substrate layer 14, the sixth substrate layer 16, and the fifth substrate layer 15. A thickness direction D1 of the laminated substrate 1 is the stacking direction of the first substrate layer 11, the third substrate layer 13, and the second substrate layer 12.

[0020] The thickness of each of the second substrate layer 12, the third substrate layer 13, the first substrate layer 11, the seventh substrate layer 17, the fourth substrate layer 14, the sixth substrate layer 16 and the fifth substrate layer 15 is, for example, 10 μm or more and 120 μm or less.

[0021] The second substrate layer 12, the third substrate layer 13, the first substrate layer 11, the seventh substrate layer 17, the fourth substrate layer 14, the sixth substrate layer 16, and the fifth substrate layer 15 each have electrical insulation properties. The material of the first substrate layer 11 and the fourth substrate layer 14 includes, for example, polyimide (PI) or liquid crystal polymer. The first substrate layer 11 and the fourth substrate layer 14 may each include a filler in addition to polyimide or liquid crystal polymer. The material of the third substrate layer 13 and the sixth substrate layer 16 includes, for example, perfluoroalkoxy resin (PFA), an acrylic resin, or an epoxy resin. The third substrate layer 13 and the sixth substrate layer 16 may each include a filler in addition to perfluoroalkoxy resin, an acrylic resin, or an epoxy resin. The material of the second substrate layer 12 and the fourth substrate layer 14 includes, for example, glass epoxy resin. Each of the second base material layer 12 and the fourth base material layer 14 may contain a filler in addition to the glass epoxy resin.

[0022] In the multilayer substrate 100, from the viewpoint of suppressing deformation of the first ground electrode 3 in contact with the second substrate layer 12, it is preferable that the Young's modulus of the second substrate layer 12 be larger than that of the first substrate layer 11. In addition, in the multilayer substrate 100, from the viewpoint of mitigating stress applied to the signal line 2, it is preferable that the Young's modulus of the third substrate layer 13 be smaller than that of each of the first substrate layer 11 and the second substrate layer 12.

[0023] In addition, from the viewpoint of reducing the thermal stress generated in the laminated substrate 1, it is preferable that the material of the fourth substrate layer 14 is the same as the material of the first substrate layer 11, the material of the fifth substrate layer 15 is the same as the material of the second substrate layer 12, and the material of the sixth substrate layer 16 is the same as the material of the third substrate layer 13.

[0024] The first substrate layer 11 has a first main surface 111 and a second main surface 112. As shown in FIG. 2 , the first main surface 111 of the first substrate layer 11 is a main surface that contacts the signal line 2, the two first pad electrodes P1, and the third ground electrode 8. The second main surface 112 of the first substrate layer 11 is a main surface that faces the first ground electrode 3. The first substrate layer 11 has a plurality of first through holes 110 (three in the example of FIG. 2 ). The first through holes 110 of the first substrate layer 11 are spaced apart from one another in the signal transmission direction of the signal line 2 (a direction parallel to the Y-axis in FIG. 2 ). In a plan view from the thickness direction D1 of the laminated substrate 1, the opening edge 114 of each of the plurality of first through holes 110 of the first substrate layer 11 is circular, as shown in FIG. 5 . The opening edge 114 of each of the plurality of first through holes 110 is not limited to a circular shape and may be, for example, a rectangular shape.

[0025] 1 and 2 , the second base layer 12 has a first main surface 121 and a second main surface 122. The first main surface 121 of the second base layer 12 is a main surface facing the first base layer 11 in the thickness direction D1 of the laminated substrate 1. The second main surface 122 of the second base layer 12 is a main surface in contact with the first ground electrode 3. The second base layer 12 has a plurality of first recesses 120 (three in the example of FIG. 2 ). The plurality of first recesses 120 of the second base layer 12 are formed on the first main surface 121 of the second base layer 12. The plurality of first recesses 120 of the second base layer 12 are spaced apart from one another in the direction along the signal transmission direction of the signal line 2. The plurality of first recesses 120 of the second base layer 12 correspond one-to-one to the plurality of first through holes 110 of the first base layer 11. Each of the multiple first recesses 120 overlaps with a corresponding one of the multiple first through holes 110 in the thickness direction D1 of the laminated substrate 1. In a plan view from the thickness direction D1 of the laminated substrate 1, the opening edge 124 of each of the multiple first recesses 120 in the second base layer 12 is circular, as shown in FIG. 6 . The diameter R124 of the opening edge 124 of each of the multiple first recesses 120 is larger than the diameter R114 (see FIG. 5 ) of the opening edge 114 of the corresponding one of the multiple first through holes 110. In the second base layer 12, the depth H2 of each of the multiple first recesses 120 is equal to or greater than the thickness T131 of the first portion 131 of the third base layer 13, for example, as shown in FIG. 1 . The first portion 131 of the third base material layer 13 is a portion of the third base material layer 13 that is interposed between the second main surface 112 of the first base material layer 11 and the first main surface 121 of the second base material layer 12 .

[0026] 1 and 2 , the third base layer 13 has a plurality of third through holes 130 (three in the example of FIG. 2 ). The third through holes 130 of the third base layer 13 correspond one-to-one to the first through holes 110 of the first base layer 11. Each of the third through holes 130 overlaps with a corresponding one of the first through holes 110 in the thickness direction D1 of the laminated substrate 1. Each of the third through holes 130 communicates with a corresponding one of the first through holes 110. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 134 of each of the third through holes 130 of the third base layer 13 is circular. The diameter of an opening edge 134 of each of the plurality of third through holes 130 is larger than the diameter R114 (see FIG. 5 ) of the opening edge 114 of a corresponding one of the plurality of first through holes 110, and is smaller than the diameter R124 (see FIG. 6 ) of the opening edge 124 of a corresponding one of the plurality of first recesses 120. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the plurality of first recesses 120 contains a corresponding one of the plurality of third through holes 130. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the plurality of third through holes 130 contains a corresponding one of the plurality of first through holes 110.

[0027] The third base layer 13 has the above-described first portion 131 and a plurality of second portions 132. The first portion 131 is a portion interposed between the second main surface 112 of the first base layer 11 and the first main surface 121 of the second base layer 12. The plurality of second portions 132 are portions interposed between the second main surface 112 of the first base layer 11 and the inner bottom surfaces of the respective first recesses 120 of the second base layer 12. In the third base layer 13, the thickness T132 of each of the plurality of second portions 132 is greater than the thickness T131 of the first portion 131.

[0028] The fourth substrate layer 14 has a first main surface 141 and a second main surface 142. The first main surface 141 of the fourth substrate layer 14 is a main surface that faces the second ground electrode 4 in the thickness direction D1 of the laminated substrate 1. The second main surface 142 of the fourth substrate layer 14 is a main surface that faces the first substrate layer 11 in the thickness direction D1 of the laminated substrate 1. The fourth substrate layer 14 has a plurality of second through holes 140 (three in the example of FIG. 2 ). The second through holes 140 in the fourth substrate layer 14 are spaced apart from one another in the signal transmission direction of the signal line 2. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 144 of each of the second through holes 140 in the fourth substrate layer 14 is circular, as shown in FIG. 4 . The diameter R144 of the opening edge 144 of each of the plurality of second through holes 140 is the same as the diameter R114 (see FIG. 5 ) of the opening edge 114 of the corresponding one of the plurality of first through holes 110, but may be different from the diameter R114. The opening edge 144 of each of the plurality of second through holes 140 is not limited to a circular shape and may be, for example, a rectangular shape.

[0029] As shown in FIGS. 1 and 2 , the fifth base layer 15 has a first main surface 151 and a second main surface 152. The first main surface 151 is a main surface that contacts the second ground electrode 4. The second main surface 152 is a main surface that faces the fourth base layer 14. The fifth base layer 15 has a plurality of second recesses 150. The plurality of second recesses 150 of the fifth base layer 15 are formed on the second main surface 152 of the fifth base layer 15. The plurality of second recesses 150 of the fifth base layer 15 are spaced apart from one another in the signal transmission direction of the signal line 2. The plurality of second recesses 150 of the fifth base layer 15 correspond one-to-one to the plurality of second through holes 140 of the fourth base layer 14. Each of the plurality of second recesses 150 overlaps a corresponding one of the plurality of second through holes 140 in the thickness direction D1 of the laminated substrate 1. In a plan view from the thickness direction D1 of the laminated substrate 1, the opening edge 154 of each of the plurality of second recesses 150 in the fifth base layer 15 is circular. The diameter of the opening edge 154 of each of the plurality of second recesses 150 is larger than the diameter R124 (see FIG. 6 ) of the opening edge 124 of a corresponding one of the plurality of second through holes 140. In the fifth base layer 15, the depth H5 of each of the plurality of second recesses 150 is equal to or greater than the thickness T161 of the first portion 161 of the sixth base layer 16, as shown in FIG. 1 . The first portion 161 of the sixth base layer 16 is a portion of the sixth base layer 16 that is interposed between the first main surface 141 of the fourth base layer 14 and the second main surface 152 of the fifth base layer 15.

[0030] 1 and 2 , the sixth base layer 16 has a plurality of fourth through holes 160 (three in the example of FIG. 2 ). The plurality of fourth through holes 160 of the sixth base layer 16 correspond one-to-one to the plurality of second through holes 140 of the fourth base layer 14. Each of the plurality of fourth through holes 160 overlaps with a corresponding one of the plurality of second through holes 140 in the thickness direction D1 of the laminated substrate 1. Each of the plurality of fourth through holes 160 communicates with a corresponding one of the plurality of second through holes 140. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 164 of each of the plurality of fourth through holes 160 of the sixth base layer 16 is circular. The diameter of the opening edge 164 of each of the plurality of fourth through holes 160 is larger than the diameter R144 (see FIG. 4 ) of the opening edge 144 of the corresponding one of the plurality of second through holes 140, and is smaller than the diameter of the opening edge of the corresponding one of the plurality of second recesses 150. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the plurality of second recesses 150 contains a corresponding one of the plurality of fourth through holes 160. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the plurality of fourth through holes 160 contains a corresponding one of the plurality of second through holes 140. The sixth base layer 16 has the above-mentioned first portion 161 and a plurality of second portions 162. The first portion 161 is a portion interposed between the first main surface 141 of the fourth base layer 14 and the second main surface 152 of the fifth base layer 15. The plurality of second portions 162 are portions interposed between the first main surface 141 of the fourth base layer 14 and the inner bottom surfaces of the plurality of second recesses 150 of the fifth base layer 15. In the sixth base layer 16, the thickness T162 of each of the plurality of second portions 162 is greater than the thickness T161 of the first portion 161.

[0031] Furthermore, in the laminated substrate 1, the seventh base material layer 17 has a plurality of fifth through holes 170 (three in the example of FIG. 2 ). The plurality of fifth through holes 170 of the seventh base material layer 17 correspond one-to-one to the plurality of first through holes 110 of the first base material layer 11. The plurality of fifth through holes 170 of the seventh base material layer 17 also correspond one-to-one to the plurality of second through holes 140 of the fourth base material layer 14. Each of the plurality of fifth through holes 170 overlaps with a corresponding one of the plurality of first through holes 110 in the thickness direction D1 of the laminated substrate 1 and is in communication with the corresponding one of the first through holes 110. Each of the plurality of fifth through holes 170 overlaps with a corresponding one of the plurality of second through holes 140 in the thickness direction D1 of the laminated substrate 1 and is in communication with the corresponding one of the second through holes 140. In this embodiment, the multiple first hollow portions 6 correspond one-to-one to the multiple second hollow portions 7. Each of the multiple first hollow portions 6 overlaps with a corresponding one of the multiple second hollow portions 7 in the thickness direction D1 of the laminated substrate 1 and is in communication with the corresponding second hollow portion 7.

[0032] The multiple fifth through holes 170 in the seventh base layer 17 are spaced apart from one another in the signal transmission direction of the signal line 2. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 174 of each of the multiple fifth through holes 170 in the seventh base layer 17 is circular. The seventh base layer 17 does not overlap with any of the multiple first through holes 110 or the multiple second through holes 140 in the thickness direction D1 of the laminated substrate 1. The diameter of the opening edge 174 of each of the multiple fifth through holes 170 is the same as the diameter R114 (see FIG. 5 ) of the opening edge 114 of the corresponding first through hole 110 among the multiple first through holes 110, but may be larger than the diameter R114.

[0033] The plurality of first through holes 110 in the first substrate layer 11, the plurality of fifth through holes 170 in the seventh substrate layer 17, and the plurality of second through holes 140 in the fourth substrate layer 14 are formed by, for example, drilling in the laminate structure that is the original laminate of the first substrate layer 11, the seventh substrate layer 17, and the fourth substrate layer 14. However, they may be formed by other methods than drilling, such as laser processing or etching. The plurality of first recesses 120 in the second substrate layer 12 are formed by, for example, laser processing or etching in the resin sheet that is the original of the second substrate layer 12 before the second substrate layer 12 and the first substrate layer 11 are connected by the third substrate layer 13. The plurality of second recesses 150 in the fifth substrate layer 15 are formed by, for example, laser processing or etching in the resin sheet that is the original of the fifth substrate layer 15 before the fifth substrate layer 15 and the fourth substrate layer 14 are connected by the sixth substrate layer 16.

[0034] (1.2) Signal Line As shown in FIGS. 1 and 2, the signal line 2 is disposed within the laminate substrate 1. The signal line 2 is electrically conductive. The material of the signal line 2 is, for example, copper. The signal line 2 is formed in a predetermined pattern. The signal line 2 is formed by patterning a copper foil (hereinafter also referred to as a first copper foil) attached to a resin sheet (hereinafter also referred to as a first resin sheet) that serves as the first base layer 11.

[0035] The signal line 2 is a line through which a high-frequency signal is transmitted. The frequency of the high-frequency signal is, for example, 1 GHz or higher, but is not limited to 1 GHz or higher and may be less than 1 GHz. The multilayer substrate 100 of this embodiment is designed so that the impedance of the signal line 2 is 50Ω.

[0036] In a plan view from the thickness direction D1 of the laminated substrate 1, the signal line 2 is linear. The length of the signal line 2 along the Y axis is longer than the length along the X axis. In this embodiment, the signal line 2 has a line width in the X axis direction. In the X axis direction, the line width of the signal line 2 is narrower than the width of the laminated substrate 1. In the Y axis direction, the length of the signal line 2 is shorter than the length of the laminated substrate 1. The signal line 2 has a first main surface 21 and a second main surface 22. The first main surface 21 of the signal line 2 faces the second ground electrode 4 in the thickness direction D1 of the laminated substrate 1. The second main surface 22 of the signal line 2 faces the first ground electrode 3 in the thickness direction D1 of the laminated substrate 1. Multiple portions (three in the example of FIG. 2 ) of the first main surface 21 of the signal line 2 are exposed within the laminated substrate 1 by multiple second hollow portions 7. A plurality of (three in the example of FIG. 2 ) portions of the first main surface 21 of the signal line 2 are in contact with the gas in the plurality of second hollow portions 7. A plurality of (three in the example of FIG. 2 ) portions of the second main surface 22 of the signal line 2 are exposed within the laminated substrate 1 by the plurality of first hollow portions 6. A plurality of (three in the example of FIG. 2 ) portions of the second main surface 22 of the signal line 2 are in contact with the gas in the plurality of first hollow portions 6. When viewed in a plan view from the thickness direction D1 of the laminated substrate 1, the signal line 2 may have a shape other than a straight line, for example, a curved shape or a bent shape.

[0037] (1.3) First Pad Electrode As shown in FIG. 2, two first pad electrodes P1 are arranged in the laminate substrate 1. Each of the two first pad electrodes P1 is conductive. The material of the two first pad electrodes P1 is, for example, copper. Each of the two first pad electrodes P1 is formed in a predetermined pattern (circular in the example of FIG. 5). The two first pad electrodes P1 are formed by patterning a first copper foil attached to a first resin sheet that is the basis of the first base layer 11.

[0038] 5 , in a plan view of the multilayer substrate 100 in the thickness direction D1 of the multilayer substrate 1, the signal line 2 is located between two first pad electrodes P1. One of the two first pad electrodes P1 is seamlessly connected to a first end 201 of the signal line 2, and the remaining first pad electrode P1 is seamlessly connected to a second end 202 of the signal line 2.

[0039] 5, when viewed from above in the thickness direction D1 of the laminated substrate 1, each of the two first pad electrodes P1 has a circular shape, but the shape is not limited to a circular shape and may be, for example, a rectangular shape. The width of each first pad electrode P1 in the width direction of the signal line 2 (in this embodiment, the direction parallel to the X-axis) is equal to or greater than the line width of the signal line 2 (in the example of FIG. 5, it is larger than the line width of the signal line 2). Note that the width of each first pad electrode P1 is the maximum width in the width direction of the signal line 2, and when each first pad electrode P1 is circular, the width of each first pad electrode P1 means the diameter of the first pad electrode P1.

[0040] (1.4) Second Pad Electrodes As shown in FIG. 2, two second pad electrodes P2 are disposed on the first main surface 151 of the fifth base layer 15 in the laminated substrate 1.

[0041] The two second pad electrodes P2 correspond one-to-one to the two first pad electrodes P1. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the two second pad electrodes P2 overlaps a corresponding one of the two first pad electrodes P1. The first pad electrode P1 and the second pad electrode P2 that overlap in the thickness direction D1 of the laminated substrate 1 are spaced apart in the thickness direction D1 of the laminated substrate 1. The material of the two second pad electrodes P2 is, for example, copper. The two second pad electrodes P2 are formed by patterning copper foil attached to a resin sheet that is the basis of the fifth base layer 15.

[0042] 3, when viewed from above in the thickness direction D1 of the laminated substrate 1, each of the two second pad electrodes P2 has a circular shape, but the shape is not limited to a circular shape and may be, for example, a rectangular shape. The width of each second pad electrode P2 in the width direction of the signal line 2 (in this embodiment, the direction parallel to the X-axis) is equal to or greater than the line width of the signal line 2 (in the example of FIG. 3, it is larger than the line width of the signal line 2). Note that the width of each second pad electrode P2 is the maximum width in the width direction of the signal line 2, and when each second pad electrode P2 is circular, the width of each second pad electrode P2 means the diameter of the second pad electrode P2.

[0043] (1.5) Multiple First Interlayer Connection Conductors A multiple number (ten in the examples of FIGS. 5 and 6 ) of first interlayer connection conductors 91 are connection conductor portions that penetrate the first base material layer 11, the third base material layer 13, and the second base material layer 12, as shown in FIG. 1 , and connect the first ground electrode 3 and the third ground electrode 8. Each of the ten first interlayer connection conductors 91 is formed by through-hole plating. The material of the through-hole plating is, for example, copper.

[0044] 5 and 6 , the ten first interlayer connection conductors 91 are arranged in two rows, with five first interlayer connection conductors 91 in each row spaced apart in a direction parallel to the signal transmission direction of the signal line 2 (the direction of the Y axis).

[0045] (1.6) Two Second Interlayer Connection Conductors The two second interlayer connection conductors 92 shown in FIG. 2 correspond one-to-one to the two first pad electrodes P1. The two second interlayer connection conductors 92 also correspond one-to-one to the two second pad electrodes P2. Each second interlayer connection conductor 92 is disposed within the laminated substrate 1. Each of the two second interlayer connection conductors 92 is a connection conductor portion connecting a corresponding one of the two first pad electrodes P1 to a corresponding one of the two second pad electrodes P2. In other words, each second interlayer connection conductor 92 connects the first pad electrode P1 and the second pad electrode P2 that overlap in the thickness direction D1 of the laminated substrate 1.

[0046] Each of the two second interlayer connection conductors 92 is cylindrical. As shown in FIG. 5 , in a plan view from the thickness direction D1 of the laminated substrate 1, each of the two second interlayer connection conductors 92 is smaller than the corresponding one of the two first pad electrodes P1. Also, as shown in FIG. 3 , in a plan view from the thickness direction D1 of the laminated substrate 1, each of the two second interlayer connection conductors 92 is smaller than the corresponding one of the two second pad electrodes P2. Each of the two second interlayer connection conductors 92 is formed by through-hole plating. The through-hole plating is made of, for example, copper.

[0047] (1.7) Multiple Third Interlayer Connection Conductors A plurality (ten in the example of FIG. 3 ) of third interlayer connection conductors 93 are connection conductor portions that penetrate the seventh substrate layer 17, the fourth substrate layer 14, the sixth substrate layer 16, and the fifth substrate layer 15, as shown in FIG. 1 , and connect the third ground electrode 8 and the second ground electrode 4. Each of the ten third interlayer connection conductors 93 is formed by through-hole plating. The material of the through-hole plating is, for example, copper.

[0048] 5 and 6 , the ten first interlayer connection conductors 91 are arranged in two rows, and five third interlayer connection conductors 93 in each row are spaced apart in a direction parallel to the signal transmission direction of the signal line 2 (the direction of the Y axis).

[0049] 1 and 2 , the first ground electrode 3 is disposed on the second main surface 122 of the second base layer 12. The first ground electrode 3 is in contact with the second main surface 122 of the second base layer 12. The first ground electrode 3 faces the signal line 2, the two first pad electrodes P1, and the third ground electrode 8 in the thickness direction D1 of the laminated substrate 1.

[0050] The first ground electrode 3 is conductive. The material of the first ground electrode 3 is, for example, copper. The first ground electrode 3 is formed in a predetermined pattern. In a plan view of the laminated substrate 1 in the thickness direction D1, the first ground electrode 3 has, for example, an elongated shape in which the length along the Y-axis is longer than the length along the X-axis. The first ground electrode 3 is disposed on the second main surface 122 of the second base layer 12 so as to cover most of the second main surface 122 of the second base layer 12. The first ground electrode 3 is formed, for example, by patterning copper foil (hereinafter also referred to as second copper foil) attached to a resin sheet (hereinafter also referred to as second resin sheet) that is the basis for the second base layer 12.

[0051] 1 and 2 , the second ground electrode 4 is disposed on the first main surface 151 of the fifth base layer 15. The second ground electrode 4 is in contact with the first main surface 151 of the fifth base layer 15. The second ground electrode 4 faces the signal line 2 and the third ground electrode 8 in the thickness direction D1 of the laminated substrate 1.

[0052] The second ground electrode 4 is conductive. The material of the second ground electrode 4 is, for example, copper. The second ground electrode 4 is formed in a predetermined pattern. In a plan view of the laminated substrate 1 in the thickness direction D1, the second ground electrode 4 has, for example, an elongated shape in which the length along the Y axis is longer than the length along the X axis. The second ground electrode 4 is disposed on the first main surface 151 of the fifth base layer 15 so as to cover most of the first main surface 151 of the fifth base layer 15. The second ground electrode 4 is formed, for example, by patterning copper foil attached to a resin sheet that is the basis for the fifth base layer 15.

[0053] 1 and 2, the third ground electrode 8 is disposed within the laminate substrate 1. More specifically, the third ground electrode 8 is disposed on the first main surface 111 of the first base layer 11. In a plan view in the thickness direction D1 of the laminate substrate 1, the third ground electrode 8 has a frame shape surrounding the two first pad electrodes P1 and the signal line 2, as shown in Fig. 5. Like the signal line 2 and the two first pad electrodes P1, the third ground electrode 8 is formed by patterning a first copper foil attached to a first resin sheet.

[0054] (1.11) First Resist Layer As shown in FIGS. 1 and 2, the first resist layer 51 covers the second main surface 122 of the second base layer 12 and the first ground electrode 3.

[0055] The first resist layer 51 includes, for example, a polyimide film and an adhesive layer. The material of the adhesive layer includes, for example, an acrylic resin, a silicone resin, an epoxy resin, or a urethane resin. The first resist layer 51 is not limited to a configuration including a polyimide film and an adhesive layer, and may be, for example, a resist layer formed using spin coating technology and photolithography technology.

[0056] 1 and 2, the second resist layer 52 covers the first main surface 151 of the fifth base layer 15 and the second ground electrode 4. The second resist layer 52 has two openings 520 that expose the two second pad electrodes P2.

[0057] The second resist layer 52 includes, for example, a polyimide film and an adhesive layer. The material of the adhesive layer includes, for example, an acrylic resin, a silicone resin, an epoxy resin, or a urethane resin. The second resist layer 52 is not limited to a configuration including a polyimide film and an adhesive layer, and may be, for example, a resist layer formed using spin coating technology and photolithography technology.

[0058] (2) First Hollow Section and Second Hollow Section As shown in FIGS. 1 and 2 , each of the first hollow sections 6 includes a corresponding first through hole 110 among the first through holes 110 in the first base layer 11, a corresponding third through hole 130 among the third through holes 130 in the third base layer 13, and an internal space of a corresponding first recess 120 among the first recesses 120 in the second base layer 12. Each of the first hollow sections 6 exposes a portion of the second main surface 22 of the signal line 2. In a plan view from the thickness direction D1 of the laminated substrate 1, the third base layer 13 does not overlap with the first through holes 110 of the first hollow sections 6. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the third through holes 130 includes a corresponding first through hole 110 among the first through holes 110.

[0059] Each of the second hollow portions 7 includes a corresponding fifth through hole 170 of the seventh base layer 17, a corresponding second through hole 140 of the fourth base layer 14, a corresponding fourth through hole 160 of the sixth base layer 16, and an internal space of a corresponding second recess 150 of the fifth base layer 15. Each of the second hollow portions 7 exposes a portion of the first main surface 21 of the signal line 2 and portions of each of the two side surfaces 23, 24 of the signal line 2. In a plan view from the thickness direction D1 of the laminated substrate 1, each of the fourth through holes 160 encapsulates a corresponding second through hole 140 of the second through holes 140. The sixth base layer 16 does not overlap with the second through holes 140 of the plurality of second hollow portions 7 in a plan view in the thickness direction D1 of the laminated substrate 1 .

[0060] (3) Method for Manufacturing Multilayer Substrate In the method for manufacturing the multilayer substrate 100 of this embodiment, for example, a first step, a second step, a third step, and a fourth step are performed.

[0061] In the first step, a laminated structure is formed including the first substrate layer 11, the seventh substrate layer 17, and the fourth substrate layer 14. More specifically, in the first step, the signal line 2, the two first pad electrodes P1, and the third ground electrode 8 are arranged on a first resin film that will form the first substrate layer 11, and a resin film that will form the fourth substrate layer 14 are stacked on top of each other with an adhesive layer that will form the seventh substrate layer 17 interposed therebetween, and are then pressed from above while being heated, thereby forming a laminated structure that will form the first substrate layer 11, the seventh substrate layer 17, and the fourth substrate layer 14.

[0062] In the second step, the laminated structure is subjected to, for example, drilling to form a first base material layer 11 having a plurality of first through holes 110, a seventh base material layer 17 having a plurality of fifth through holes 170, and a fourth base material layer 14 having a plurality of second through holes 140. In the second step, the processing of the laminated structure is not limited to drilling, and may also be performed, for example, by laser processing or etching.

[0063] In the third step, after the second step, the third substrate layer 13, the second substrate layer 12, the sixth substrate layer 16, and the fifth substrate layer 15 are laminated on the laminated structure. More specifically, in the third step, the second substrate layer 12 is disposed on the second main surface 112 of the first substrate layer 11 of the laminated structure via the adhesive that will become the third substrate layer 13. The first ground electrode 3 is disposed in advance on the second main surface 122 of the second substrate layer 12. Furthermore, the fifth substrate layer 15 is disposed on the first main surface 141 of the fourth substrate layer 14 of the laminated structure via the adhesive that will become the sixth substrate layer 16. Two second pad electrodes P2 and a second ground electrode 4 are disposed in advance on the first main surface 151 of the fifth substrate layer 15. The third substrate layer 13, the second substrate layer 12, the sixth substrate layer 16, and the fifth substrate layer 15 are stacked on the laminated structure and placed on a metal plate (not shown), and pressed from above while being heated, to form the laminated substrate 1.

[0064] In the fourth step, a first resist layer 51 is formed to cover the second main surface 122 of the second substrate layer 12 and the first ground electrode 3, and a second resist layer 52 is formed to cover the first main surface 151 of the fifth substrate layer 15 and the second ground electrode 4.

[0065] (4) Electronic Device As shown in FIG. 7, the electronic device 500 according to the first embodiment includes the multilayer substrate 100 and a housing 501 that houses the multilayer substrate 100 .

[0066] Electronic device 500 further includes a first printed wiring board 504, a second printed wiring board 505, a connector 514 mounted on first printed wiring board 504, and a connector 515 mounted on second printed wiring board 505. A battery 503 serving as a power source for electronic device 500 is housed within housing 501 of electronic device 500.

[0067] In electronic device 500, one of two connectors 410 connected to two second pad electrodes P2 of multilayer substrate 100 in a one-to-one relationship is connected to connector 514, and the other connector 410 is connected to connector 515. As a result, in electronic device 500, first printed wiring board 504 and second printed wiring board 505 are connected via multilayer substrate 100.

[0068] At least one of the first printed wiring board 504 and the second printed wiring board 505 is provided with, for example, a signal processing circuit for processing high frequency signals.

[0069] (5) Effects The multilayer substrate 100 according to the first embodiment includes a laminated substrate 1, a signal line 2, and a ground electrode 3. The laminated substrate 1 has a plurality of first hollow portions 6. The signal line 2 is disposed within the laminated substrate 1. The first ground electrode 3 overlaps the signal line 2 in a planar view in the thickness direction D1 of the laminated substrate 1. The plurality of first hollow portions 6 overlap the signal line 2 in a planar view in the thickness direction D1 of the laminated substrate 1. The laminated substrate 1 includes a first base layer 11, a second base layer 12, and a third base layer 13. The first base layer 11 has a plurality of first through holes 110 that form a portion of each of the plurality of first hollow portions 6. The second base layer 12 has a plurality of first recesses 120 that overlap the plurality of first through holes 110 in a one-to-one correspondence in the thickness direction D1 of the laminated substrate 1. The second substrate layer 12 is arranged such that the internal space of each of the plurality of first recesses 120 communicates with a corresponding one of the plurality of first through holes 110. The third substrate layer 13 connects the first substrate layer 11 and the second substrate layer 12. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 124 of each of the plurality of first recesses 120 in the second substrate layer 12 is located outside an opening edge 114 of a corresponding one of the plurality of first through holes 110 in the first substrate layer 11. The third substrate layer 13 does not overlap with the plurality of first through holes 110 in the first substrate layer 11 in a plan view from the thickness direction D1 of the laminated substrate 1. In the thickness direction D1 of the laminated substrate 1, the plurality of first hollow portions 6 are located between the signal line 2 and the first ground electrode 3.

[0070] This configuration reduces transmission loss. More specifically, in the multilayer substrate 100 according to the first embodiment, the third substrate layer 13 connecting the first substrate layer 11 and the second substrate layer 12 does not overlap with the first through holes 110 of the first substrate layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1. This allows each of the first hollow portions 6, which have a lower dielectric constant and a smaller dielectric loss tangent than the third substrate layer 13, to be wider than when the third substrate layer 13 overlaps with the first through holes 110, thereby reducing transmission loss of the signal line 2. The effect of reducing transmission loss using hollow portions is the same as that described in Patent Document 1. Furthermore, this configuration reduces variation in transmission loss between multilayer substrates 100. More specifically, in the multilayer substrate 100 according to the first embodiment, even if adhesive that forms the third base material layer 13 flows into the third through hole 130 when pressing is performed in the third step described above during the manufacture of the multilayer substrate 100, the adhesive can be absorbed by the first recess 120 of the second base material layer 12, so that the adhesive does not flow into the first through hole 110, and a hollow portion overlapping the first through hole 110 is secured. Also, in the multilayer substrate 100 according to the first embodiment, the third through hole 130 is slightly larger than the first through hole 110 in a plan view from the thickness direction D1 of the laminated substrate 1, so that a hollow portion overlapping the first through hole 110 is secured even if the first base material layer 11 and the second base material layer 12 are misaligned in the third step described above during the manufacture of the multilayer substrate 100.

[0071] Furthermore, in the multilayer substrate 100 according to the first embodiment, the signal line 2 is exposed within the multilayer substrate 1 through the plurality of first hollow portions 6 .

[0072] With the above configuration, it is possible to further reduce transmission loss compared to when the signal line 2 is not exposed within the laminate substrate 1 by the multiple first hollow portions 6. Furthermore, with the above configuration, since multiple first hollow portions 6 are provided, it is possible to reduce transmission loss while suppressing changes in the shape of the first ground electrode 3 compared to when there is only one first hollow portion 6 and the first hollow portion 6 is elongated in the signal transmission direction of the signal line 2.

[0073] In the multilayer substrate 100 according to the first embodiment, the laminate substrate 1 further includes a plurality of second hollow portions 7. The second hollow portions 7 correspond one-to-one to the first hollow portions 6. The second hollow portions 7 overlap the signal line 2 in a plan view in the thickness direction D1 of the laminate substrate 1. In addition, in the thickness direction D1 of the laminate substrate 1, each of the second hollow portions 7 overlaps a corresponding one of the first hollow portions 6. The laminate substrate 1 includes a fourth base layer 14, a fifth base layer 15, and a sixth base layer 16. The fourth base layer 14 includes a plurality of second through holes 140 that form a portion of each of the second hollow portions 7. The fifth base layer 15 includes a plurality of second recesses 150 that overlap one-to-one with the second through holes 140 in the thickness direction D1 of the laminate substrate 1. The fifth base layer 15 is arranged such that the internal spaces of the plurality of second recesses 150 in the fifth base layer 15 are in communication with the corresponding second through holes 140 of the plurality of second through holes 140 in the fourth base layer 14. The sixth base layer 16 connects the fourth base layer 14 and the fifth base layer 15. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 154 of each of the plurality of second recesses 150 in the fifth base layer 15 is positioned outward from an opening edge 144 of a second through hole 140 corresponding to the second recess 150, among the plurality of second through holes 140 in the fourth base layer 14. The sixth base layer 16 does not overlap with the plurality of second through holes 140 of the fourth base layer 14 in a plan view from the thickness direction D1 of the laminated substrate 1.

[0074] This configuration further reduces transmission loss even in a structure in which ground conductors (the first ground electrode 3 and the second ground electrode 4 in this embodiment) are arranged on both sides of the signal line 2 in the thickness direction D1 of the laminated substrate 1 to enhance shielding. More specifically, in the multilayer substrate 100 according to the first embodiment, the sixth substrate layer 16 connecting the fourth substrate layer 14 and the fifth substrate layer 15 does not overlap with the second through holes 140 in the fourth substrate layer 14 in a plan view in the thickness direction D1 of the laminated substrate 1. This allows each of the second hollow portions 7, which have a lower dielectric constant and a smaller dielectric loss tangent than the sixth substrate layer 16, to be wider than when the sixth substrate layer 16 overlaps with the second through holes 140, thereby reducing transmission loss of the signal line 2. This also reduces variation in transmission loss between products of the multilayer substrate 100.

[0075] Furthermore, in the multilayer substrate 100 according to the first embodiment, the signal line 2 is exposed within the multilayer substrate 1 through the plurality of second hollow portions 7 .

[0076] With this configuration, it is possible to further reduce transmission loss compared to when the signal line 2 is not exposed within the laminate substrate 1 by the multiple second hollow portions 7. Furthermore, with this configuration, since there are multiple second hollow portions 7, it is possible to reduce transmission loss while suppressing changes in the shape of the second ground electrode 4 compared to when there is only one second hollow portion 7 and the second hollow portion 7 is elongated in the signal transmission direction of the signal line 2.

[0077] The electronic device 500 according to the first embodiment includes the multilayer substrate 100 and a housing 501 that houses the multilayer substrate 100 .

[0078] According to the above configuration, it is possible to realize electronic device 500 with reduced transmission loss.

[0079] (6) Modifications (6.1) Modification 1 In a multilayer substrate 100 (see FIG. 8 ) according to Modification 1 of Embodiment 1, the second base layer 12 having a plurality of first recesses 120 (only one is shown in FIG. 8 ) is formed by stacking a substrate 12a having a plurality of through holes 120a (only one is shown in FIG. 8 ) and a substrate 12b having no through holes. Furthermore, the fifth base layer 15 having a plurality of second recesses 150 (only one is shown in FIG. 8 ) is formed by stacking a substrate 15a having a plurality of through holes 150a (only one is shown in FIG. 8 ) and a substrate 15b having no through holes. Each of the substrates 12a, 12b, 15a, and 15b is, for example, a resin film containing a thermoplastic resin. The multilayer substrate 100 according to Modification 1 of Embodiment 1 achieves the same effects as the multilayer substrate 100 according to Embodiment 1. In the first modification, one of the second base material layer 12 and the fifth base material layer 15 may have the same configuration as that of the first embodiment.

[0080] (6.2) Modification 2 A multilayer substrate 100 (see FIG. 9 ) according to Modification 2 of Embodiment 1 includes a first substrate layer 11 having a plurality of recesses 116 (only one is shown in FIG. 9 ), instead of the first substrate layer 11 having a plurality of first through holes 110 in the multilayer substrate 100 (see FIGS. 1 and 2 ) of Embodiment 1. In a plan view from the thickness direction D1 of the laminated substrate 1, an opening edge 124 of each of the plurality of first recesses 120 in the second substrate layer 12 is located outside an opening edge 117 of a recess 116 corresponding to the first recess 120 among the plurality of recesses 116 in the first substrate layer 11. In a plan view from the thickness direction D1 of the laminated substrate 1, the third substrate layer 13 does not overlap with the plurality of recesses 116 in the first substrate layer 11. In a plan view from the thickness direction D1 of the laminated substrate 1, a plurality of first hollow portions 6 (only one is shown in FIG. 9 ) are located between the signal line 2 and the first ground electrode 3. The multilayer substrate 100 according to the second modification of the first embodiment has the same effects as the multilayer substrate 100 according to the first embodiment. Note that the second modification may employ at least one of the second base material layer 12 and the fifth base material layer 15 of the first modification.

[0081] Second Embodiment A multilayer substrate 100A according to a second embodiment will be described with reference to Figures 10 and 11. Regarding the multilayer substrate 100A according to the second embodiment, components that are the same as those in the multilayer substrate 100 according to the first embodiment (see Figures 1 to 7) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0082] (1) The multilayer substrate 100A according to the second embodiment includes a laminate substrate 1A instead of the laminate substrate 1 (see FIGS. 1 and 2) of the multilayer substrate 100 according to the first embodiment. The laminate substrate 1A differs from the laminate substrate 1 in that the material of the second base material layer 12 in the laminate substrate 1A is the same as the material of the first base material layer 11. The laminate substrate 1A also differs from the laminate substrate 1 in that the material of the fifth base material layer 15 in the laminate substrate 1A is the same as the material of the fourth base material layer 14.

[0083] The material of the first substrate layer 11 and the second substrate layer 12 includes, for example, polyimide or liquid crystal polymer. The first substrate layer 11 and the second substrate layer 12 may include a filler in addition to polyimide or liquid crystal polymer.

[0084] The material of the fourth base layer 14 and the fifth base layer 15 includes, for example, polyimide or liquid crystal polymer. The fourth base layer 14 and the fifth base layer 15 may include a filler in addition to polyimide or liquid crystal polymer.

[0085] (2) Effects The multilayer substrate 100A according to the second embodiment has the same configuration as the multilayer substrate 100 according to the first embodiment, and therefore can reduce transmission loss.

[0086] In addition, in the multilayer substrate 100A according to the second embodiment, the material of the second base material layer 12 is the same as the material of the first base material layer 11, and the material of the fifth base material layer 15 is the same as the material of the fourth base material layer 14.

[0087] According to the above configuration, it is possible to reduce thermal stress when the temperature changes, and to improve reliability.

[0088] Third Embodiment A multilayer substrate 100B according to a third embodiment will be described with reference to Fig. 12. With respect to the multilayer substrate 100B according to the third embodiment, components that are the same as those in the multilayer substrate 100 according to the first embodiment (see Figs. 1 to 7) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0089] (1) A multilayer substrate 100B according to configuration embodiment 3 includes a laminated substrate 1B instead of the laminated substrate 1 (see FIGS. 1 and 2 ) of the multilayer substrate 100 according to embodiment 1. The laminated substrate 1B differs from the laminated substrate 1 in that the second base layer 12 further includes a plurality of grooves 125 (only one of which is shown in FIG. 12 ) that correspond one-to-one to the plurality of first recesses 120 (only one of which is shown in FIG. 12 ). The laminated substrate 1B also differs from the laminated substrate 1 in that the fifth base layer 15 further includes a plurality of grooves 155 (only one of which is shown in FIG. 12 ) that correspond one-to-one to the plurality of second recesses 150 (only one of which is shown in FIG. 12 ).

[0090] In a plan view from the thickness direction D1 of the laminated substrate 1B, each of the multiple first grooves 125 surrounds a corresponding one of the multiple first recesses 120. In a plan view from the thickness direction D1 of the laminated substrate 1B, each of the multiple first grooves 125 has an annular shape, but may have a shape other than an annular shape. The depth H25 of each of the multiple first grooves 125 is equal to or greater than the thickness T13 of the third base layer 13 and equal to or less than the thickness T12 of the second base layer 12. The thickness T13 of the third base layer 13 is the thickness of a portion of the third base layer 13 located between the second main surface 112 of the first base layer 11 and the first main surface 121 of the second base layer 12. The thickness T12 of the second base layer 12 is the thickness of a portion of the second base layer 12 between the first main surface 121 and the second main surface 122 of the second base layer 12. The depth H25 of each of the plurality of first grooves 125 is the same as the depth of the corresponding first recess 120 among the plurality of first recesses 120, but may be different from the depth of the first recess 120.

[0091] In a plan view from the thickness direction D1 of the laminated substrate 1B, a distance L25 between the first recess 120 and the first groove 125 in the width direction of the first groove 125 is greater than or equal to the thickness T13 of the third base layer 13 and less than or equal to the thickness T12 of the second base layer 12. In a plan view from the thickness direction D1 of the laminated substrate 1B, the width direction of the first groove 125 is a direction perpendicular to the direction along the opening edge 124 of the first recess 120. The thickness T13 of the third base layer 13 is the thickness of a first portion 131 interposed between the second main surface 122 of the first base layer 11 and the first main surface 121 of the second base layer 12 in the thickness direction D1 of the laminated substrate 1. The third base layer 13 has a second portion 133 disposed within the first groove 125. The second portion 133 is a convex portion protruding from the first portion 131.

[0092] In a plan view from the thickness direction D1 of the laminated substrate 1B, each of the multiple second grooves 155 surrounds a corresponding one of the multiple second recesses 150. In a plan view from the thickness direction D1 of the laminated substrate 1B, each of the multiple second grooves 155 has an annular shape, but may have a shape other than an annular shape. The depth H55 of each of the multiple second grooves 155 is greater than or equal to the thickness T16 of the sixth base layer 16 and less than or equal to the thickness T15 of the fifth base layer 15. The thickness T16 of the sixth base layer 16 is the thickness of a portion of the sixth base layer 16 that is located between the first main surface 141 of the fourth base layer 14 and the second main surface 152 of the fifth base layer 15. The thickness T15 of the fifth base layer 15 is the thickness of a portion of the fifth base layer 15 that is located between the first main surface 151 and the second main surface 152 of the fifth base layer 15. The depth of each of the plurality of second grooves 155 is the same as the depth of the corresponding second recess 150 among the plurality of second recesses 150 , but may be different from the depth of the second recess 150 .

[0093] A distance L55 between the second recess 150 and the second groove 155 in the width direction of the second groove 155 in a plan view from the thickness direction D1 of the laminated substrate 1B is greater than or equal to the thickness T16 of the sixth base layer 16 and less than or equal to the thickness T15 of the fifth base layer 15. In a plan view from the thickness direction D1 of the laminated substrate 1B, the width direction of the second groove 155 is a direction perpendicular to the direction along the opening edge 154 of the second recess 150. The thickness T16 of the sixth base layer 16 is the thickness of a first portion 161 interposed between the first main surface 141 of the fourth base layer 14 and the second main surface 152 of the fifth base layer 15 in the thickness direction D1 of the laminated substrate 1B. The sixth base layer 16 has a plurality of second portions 163 arranged in the plurality of second grooves 155. The plurality of second portions 163 correspond one-to-one to the plurality of second grooves 155. Each of the plurality of second portions 163 is disposed in a corresponding one of the plurality of second grooves 155. The plurality of second portions 163 are convex portions protruding from the first portion 161.

[0094] In the present embodiment, in a plan view from the thickness direction D1 of the laminated substrate 1B, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 overlaps with the opening edge 134 of the third through hole 130 corresponding to the first recess 120 among the plurality of third through holes 130 in the third base layer 13, but may be outside the opening edge 134 of the third through hole 130 or inside the opening edge 134 of the third through hole 130 as long as it is positioned outside the opening edge 114 of the first through hole 110. The third base layer 13 does not overlap with the plurality of first through holes 110 in the first base layer 11 in a plan view from the thickness direction D1 of the laminated substrate 1B.

[0095] (2) Effect In the multilayer substrate 100B according to the third embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1B, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 is located outside the opening edge 114 of the first through hole 110 corresponding to the first recess 120 among the plurality of first through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the plurality of first through holes 110 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1B. The plurality of first hollow portions 6 are located between the signal line 2 and the first ground electrode 3 in the thickness direction D1 of the laminated substrate 1B.

[0096] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100 according to the first embodiment.

[0097] Furthermore, in the multilayer substrate 100B according to the third embodiment, the second base layer 12 further includes a plurality of first grooves 125 surrounding the plurality of first recesses 120. More specifically, the plurality of first grooves 125 correspond one-to-one to the plurality of first recesses 120. Each of the plurality of first grooves 125 surrounds a corresponding first recess 120.

[0098] According to the above configuration, it becomes easier to prevent the adhesive that forms the third base layer 13 from flowing into the internal space of each first recess 120 during manufacturing, making it easier to reduce the transmission loss of the multilayer substrate 100B.

[0099] Furthermore, in the multilayer substrate 100B according to the third embodiment, the fifth base layer 15 further has a plurality of second grooves 155 surrounding the plurality of second recesses 150. More specifically, the plurality of second grooves 155 correspond one-to-one to the plurality of second recesses 150. Each of the plurality of second grooves 155 surrounds the corresponding second recess 150.

[0100] According to the above configuration, it becomes easier to prevent the adhesive that forms the sixth base layer 16 from flowing into the internal space of each second recess 150 during manufacturing, making it easier to reduce the transmission loss of the multilayer substrate 100B.

[0101] Fourth Embodiment A multilayer substrate 100C according to a fourth embodiment will be described with reference to Fig. 13. With respect to the multilayer substrate 100C according to the fourth embodiment, components that are the same as those in the multilayer substrate 100 according to the first embodiment (see Figs. 1 to 7) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0102] (1) The laminated substrate 1C of the multilayer substrate 100C according to the fourth embodiment differs from the laminated substrate 1 of the multilayer substrate 100 according to the first embodiment (see FIGS. 1 and 2 ) in that the laminated substrate 1C includes a laminate of a seventh substrate layer 17C and an eighth substrate layer 18C instead of the seventh substrate layer 17. The seventh substrate layer 17C covers the second main surface 22 of the signal line 2. The eighth substrate layer 18C covers the first main surface 21 and each of the side surfaces 23 and 24 of the signal line 2.

[0103] In this embodiment, the material of each of the first substrate layer 11, the seventh substrate layer 17C, the eighth substrate layer 18C, and the fourth substrate layer 14 includes, for example, a thermoplastic resin. The thermoplastic resin is, for example, a liquid crystal polymer. The thermoplastic resin is not limited to a liquid crystal polymer, and may be, for example, PTFE (polytetrafluoroethylene). In this embodiment, the first substrate layer 11 and the seventh substrate layer 17C are self-adhered, and the first substrate layer 11 and the seventh substrate layer 17C are in direct contact with each other. Furthermore, in this embodiment, the seventh substrate layer 17C and the eighth substrate layer 18C are self-adhered, and the seventh substrate layer 17C and the eighth substrate layer 18C are in direct contact with each other. Furthermore, in this embodiment, the eighth substrate layer 18C and the fourth substrate layer 14 are self-adhered, and the eighth substrate layer 18C and the fourth substrate layer 14 are in direct contact with each other.

[0104] The thickness of each of the first base material layer 11, the seventh base material layer 17C, the eighth base material layer 18C, and the fourth base material layer 14 is, for example, not less than 10 μm and not more than 120 μm.

[0105] (2) Effect In the multilayer substrate 100C according to the fourth embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1C, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 is located outside the opening edge 114 of the first through hole 110 corresponding to the first recess 120 among the plurality of first through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the plurality of first through holes 110 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1C. In the thickness direction D1 of the laminated substrate 1C, the plurality of first hollow portions 6 are located between the signal line 2 and the first ground electrode 3.

[0106] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100 according to the first embodiment.

[0107] Furthermore, in the multilayer substrate 100C according to the fourth embodiment, the signal line 2 is covered by the seventh base layer 17C and the eighth base layer 18C within the multilayer substrate 100C. This allows the signal line 2 to be protected by the seventh base layer 17C and the eighth base layer 18C, thereby improving reliability.

[0108] Fifth Embodiment A multilayer substrate 100D according to a fifth embodiment will be described with reference to Fig. 14. With respect to the multilayer substrate 100D according to the fifth embodiment, components that are the same as those in the multilayer substrate 100 according to the first embodiment (see Figs. 1 to 7) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0109] (1) The multilayer substrate 100D according to the fifth configuration embodiment differs from the multilayer substrate 100 according to the first configuration embodiment in that it does not include the second ground electrode 4 (see Figures 1 and 2) of the multilayer substrate 100 according to the first configuration embodiment.

[0110] In the multilayer substrate 100D of the present embodiment, the second ground electrode 4 of the multilayer substrate 100 of the first embodiment is not provided, and therefore the signal line 2 forms a microstrip line. In the present embodiment, the signal line 2 forms a microstrip line, and therefore the line width of the signal line 2 is wider than in the first embodiment, in which the signal line 2 forms a strip line.

[0111] (2) Effects In the multilayer substrate 100D according to the fifth embodiment, similarly to the multilayer substrate 100 according to the first embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 is located outside the opening edge 114 of the first through hole 110 corresponding to the first recess 120 among the plurality of first through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the plurality of first through holes 110 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1. In the thickness direction D1 of the laminated substrate 1, the plurality of first hollow portions 6 are located between the signal line 2 and the ground electrode 3.

[0112] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100 according to the first embodiment.

[0113] Furthermore, the multilayer substrate 100D of the fifth embodiment employs a microstrip line configuration, which allows the line width of the signal line 2 to be wider than that of the multilayer substrate 100 of the first embodiment, thereby enabling transmission loss to be reduced.

[0114] Sixth Embodiment A multilayer substrate 100E according to a sixth embodiment will be described with reference to Fig. 15. With respect to the multilayer substrate 100E according to the sixth embodiment, components that are the same as those in the multilayer substrate 100 according to the first embodiment (see Figs. 1 to 7) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0115] (1) Configuration The multilayer substrate 100E of this embodiment differs from the multilayer substrate 100 of embodiment 1 in that it includes a laminated substrate 1E instead of the laminated substrate 1 (see Figures 1 and 2) of the multilayer substrate 100 of embodiment 1.

[0116] The laminated substrate 1E has only the hollow portion 6 of the hollow portion 6 (first hollow portion 6) and the second hollow portion 7 of the laminated substrate 1. The laminated substrate 1E has a fourth base material layer 14E instead of the seventh base material layer 17, the fourth base material layer 14, the sixth base material layer 16, and the fifth base material layer 15 of the laminated substrate 1. In this embodiment, the material of each of the first base material layer 11 and the fourth base material layer 14E includes, for example, a thermoplastic resin. The thermoplastic resin is, for example, a liquid crystal polymer. The thermoplastic resin is not limited to a liquid crystal polymer, and may be, for example, PTFE. In this embodiment, the first base material layer 11 and the fourth base material layer 14E are self-adhesive, and the first base material layer 11 and the fourth base material layer 14E are in direct contact with each other.

[0117] The thickness of each of the first base material layer 11 and the fourth base material layer 14E is, for example, not less than 10 μm and not more than 120 μm.

[0118] In this embodiment, the second ground electrode 4 is arranged on the first main surface 141 of the fourth base layer 14E, and the signal line 2 and the third ground electrode 8 are arranged on the second main surface 142 of the fourth base layer 14E.

[0119] (2) Effect In the multilayer substrate 100E according to the sixth embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1E, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 is located outside the opening edge 114 of the first through hole 110 corresponding to the first recess 120 among the plurality of first through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the plurality of first through holes 110 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1E. The first hollow portion 6 is located between the signal line 2 and the first ground electrode 3 in the thickness direction D1 of the laminated substrate 1E.

[0120] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100 according to the first embodiment.

[0121] Furthermore, the multilayer substrate 100E according to the sixth embodiment does not have the second hollow portion 7 of the multilayer substrate 100 according to the first embodiment. With this configuration, compared to the multilayer substrate 100, the absence of the second hollow portion 7 on one side of the signal line 2 in the thickness direction D1 of the multilayer substrate 100E secures the signal line 2 and provides excellent stability against stress.

[0122] Seventh Embodiment A multilayer substrate 100F and an electronic device 500F according to a seventh embodiment will be described with reference to Figures 16 and 17. With regard to the multilayer substrate 100F and the electronic device 500F according to the seventh embodiment, the same components as those of the multilayer substrate 100 (see Figures 1 to 7) and the electronic device 500 (see Figure 7) according to the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0123] (1) Multilayer substrate The multilayer substrate 100F of this embodiment differs from the multilayer substrate 100 of embodiment 1 in that it includes a laminated substrate 1F instead of the laminated substrate 1 (see Figures 1 and 2) of the multilayer substrate 100 of embodiment 1.

[0124] In the multilayer substrate 100F, the portion of the laminated substrate 1F where the third substrate layer 13 and the second substrate layer 12 are laminated on the first substrate layer 11 is the rigid portion 101, and the portion where the third substrate layer 13 and the second substrate layer 12 are not laminated on the first substrate layer 11 is the flexible portion 102, and the thickness of the flexible portion 102 is thinner than the thickness of the rigid portion 101.

[0125] The multilayer substrate 1F has one rigid portion 101 and two flexible portions 102. In the multilayer substrate 100F, the signal line 2 is arranged across the one rigid portion 101 and the two flexible portions 102.

[0126] In the multilayer substrate 100F, two first pad electrodes P1 are arranged one in each of the two flexible portions 102. In addition, in the multilayer substrate 100F, two second pad electrodes P2 are arranged one in each of the two flexible portions 102. Each of the two second pad electrodes P2 is arranged on the first main surface 141 of the fourth base layer 14 in the corresponding one of the two flexible portions 102.

[0127] In the multilayer substrate 100F, a fourth ground electrode 37 is disposed on the second main surface 112 of the first base material layer 11 in each of the two flexible portions 102. In the multilayer substrate 100F, a fifth ground electrode 47 is disposed on the first main surface 141 of the fourth base material layer 14 in each of the two flexible portions 102.

[0128] The multilayer substrate 100F further includes two fourth interlayer connection conductors 94 that connect the two fourth ground electrodes 37 to the first ground electrode 3, respectively, in the rigid portion 101. The multilayer substrate 100F further includes two fifth interlayer connection conductors 95 that connect the two fifth ground electrodes 47 to the second ground electrode 4, respectively, in the rigid portion 101.

[0129] (2) Electronic Device An electronic device 500F according to a seventh embodiment includes a multilayer substrate 100F and a housing 501 that houses the multilayer substrate 100F, as shown in FIG.

[0130] In electronic device 500F, multilayer substrate 100F is accommodated in a bent state within housing 501. In the example of Fig. 17, multilayer substrate 100F is bent at each of two flexible portions 102. If multilayer substrate 100F is bent by plastically deforming thermoplastic resin (polyimide or liquid crystal polymer), multilayer substrate 100F can maintain its shape by itself.

[0131] (3) Effect In the multilayer substrate 100F according to the seventh embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1F, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 is located outside the opening edge 114 of the first through hole 110 corresponding to the first recess 120 among the plurality of first through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the plurality of first through holes 110 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1C. The first hollow portion 6 is located between the signal line 2 and the first ground electrode 3 in the thickness direction D1 of the laminated substrate 1C.

[0132] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100 according to the first embodiment.

[0133] When the storage space for the multilayer substrate 100F in the housing 501 of the electronic device 500F is a curved space, the multilayer substrate 100F can be easily arranged inside the housing 501. Note that the multilayer substrate 100F is not limited to a configuration having one rigid part 101 and two flexible parts 102, and may be a configuration having one rigid part 101 and one flexible part.

[0134] Eighth Embodiment A multilayer substrate 100G according to an eighth embodiment will be described with reference to Fig. 18. In the multilayer substrate 100G according to the eighth embodiment, the same components as those in the multilayer substrate 100C according to the fourth embodiment (see Fig. 13) are denoted by the same reference numerals, and description thereof will be omitted.

[0135] (1) Configuration The multilayer substrate 100G of this embodiment differs from the multilayer substrate 100C of Embodiment 4 in that it includes a laminate substrate 1G instead of the laminate substrate 1C of the multilayer substrate 100C of Embodiment 4. In this embodiment, the first substrate layer 11 having a recess 113 is provided instead of the first substrate layer 11 and the seventh substrate layer 17C of the multilayer substrate 100C of Embodiment 4, and the fourth substrate layer 14G having a recess 143 is provided instead of the fourth substrate layer 14 and the eighth substrate layer 18C of the multilayer substrate 100C. In this embodiment, the first substrate layer 11 covers the second main surface 22 of the signal line 2. In addition, in this embodiment, the fourth substrate layer 14 covers the first main surface 21 and each side surface 23, 24 of the signal line 2.

[0136] In this embodiment, the first substrate layer 11 and the fourth substrate layer 14 are self-adhered, and the first substrate layer 11 and the fourth substrate layer 14 are in direct contact with each other.

[0137] The third base layer 13 does not overlap with the multiple recesses 113 of the first base layer 11 in a plan view from the thickness direction D1 of the laminated substrate 1G. Furthermore, the sixth base layer 16 does not overlap with the multiple recesses 143 of the fourth base layer 14 in a plan view from the thickness direction D1 of the laminated substrate 1G. In a plan view from the thickness direction D1 of the laminated substrate 1G, the opening edge 124 of each of the multiple first recesses 120 of the second base layer 12 is located outside the opening edge 115 of the recess 113 corresponding to the first recess 120 among the multiple recesses 113 of the first base layer 11. In a plan view from the thickness direction D1 of the laminated substrate 1G, the opening edge 154 of each of the multiple second recesses 150 of the fifth base layer 15 is located outside the opening edge 145 of the recess 143 corresponding to the second recess 150 among the multiple recesses 143 of the fourth base layer 14.

[0138] (2) Effect In the multilayer substrate 100G according to the eighth embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1G, the opening edge 124 of each of the plurality of first recesses 120 in the second base layer 12 is located outside the opening edge 115 of the recess 113 corresponding to the first recess 120 among the plurality of recesses 113 in the first base layer 11. The third base layer 13 does not overlap with the plurality of recesses 113 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1G. The first hollow portion 6 is located between the signal line 2 and the first ground electrode 3 in the thickness direction D1 of the laminated substrate 1G.

[0139] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100C according to the fourth embodiment.

[0140] Ninth Embodiment A multilayer substrate 100H according to a ninth embodiment will be described with reference to Fig. 19. With respect to the multilayer substrate 100H according to the ninth embodiment, components that are the same as those in the multilayer substrate 100 according to the first embodiment (see Figs. 1 to 7) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0141] (1) Configuration The multilayer substrate 100H of this embodiment differs from the multilayer substrate 100 of embodiment 1 in that it includes a laminate substrate 1H instead of the laminate substrate 1 (see FIGS. 1 and 2) of the multilayer substrate 100 of embodiment 1. In this embodiment, a second base material layer 12 having a plurality of through holes 123 is provided instead of the second base material layer 12 (see FIGS. 1 and 2) of the multilayer substrate 100 of embodiment 1, and a fifth base material layer 15 having a plurality of through holes 153 is provided instead of the fifth base material layer 15 (see FIGS. 1 and 2) of the multilayer substrate 100.

[0142] In a plan view from the thickness direction D1 of the laminated substrate 1H, an opening edge 126 of each of the plurality of through holes 123 in the second base layer 12 is located outside an opening edge 114 of a corresponding one of the plurality of through holes 110 in the first base layer 11. In a plan view from the thickness direction D1 of the laminated substrate 1H, an opening edge 156 of each of the plurality of through holes 153 in the fifth base layer 15 is located outside an opening edge 144 of a corresponding one of the plurality of through holes 140 in the fourth base layer 14.

[0143] (2) Effect In the multilayer substrate 100H according to the ninth embodiment, in a plan view in the thickness direction D1 of the laminated substrate 1H, the opening edge 126 of each of the plurality of through holes 123 in the second base layer 12 is located outside the opening edge 114 of the through hole 110 corresponding to the through hole 123 among the plurality of through holes 110 in the first base layer 11. The third base layer 13 does not overlap with the plurality of through holes 110 in the first base layer 11 in a plan view in the thickness direction D1 of the laminated substrate 1H. In the thickness direction D1 of the laminated substrate 1H, the plurality of first hollow portions 6 are located between the signal line 2 and the first ground electrode 3.

[0144] According to the above configuration, it is possible to reduce transmission loss, similarly to the multilayer substrate 100 according to the first embodiment.

[0145] (Modifications) The above-described first to ninth embodiments are merely examples of various embodiments of the present invention. The above-described first to ninth embodiments can be modified in various ways depending on the design and the like, and may be combined as appropriate, as long as the object of the present invention can be achieved.

[0146] For example, in the multilayer substrates 100, 100A, 100F, and 100H, the first substrate layer 11 and the fourth substrate layer 14 may be directly stacked without the seventh substrate layer 17 being interposed between them.

[0147] Furthermore, the multilayer substrate 100 and 100A to 100D may further include a conductor pattern portion disposed on the first main surface 141 of the fourth base layer .

[0148] Furthermore, in the multilayer substrates 100, 100A to 100C, 100D, and 100E to 100H, the laminate substrates 1 to 1C, 1E to 1H may further include a base material layer that covers the second main surface 122 of the second base material layer 12 and the first ground electrode 3. Furthermore, in the multilayer substrates 100, 100A to 100C, 100E, 100F, 100G, and 100H, the laminate substrates 1 to 1C, 1E, 1F, 1G, and 1H may further include a base material layer that covers the first main surface 151 of the fifth base material layer 15 and the second ground electrode 4.

[0149] In the multilayer substrates 100, 100A to 100H, each of the multiple interlayer connection conductors (multiple first interlayer connection conductors 91, two second interlayer connection conductors 92, and multiple third interlayer connection conductors 93) is formed by through-hole plating, but is not limited to through-hole plating and may be formed of, for example, a composition containing copper, a copper-tin alloy, and resin. In this case, each of the multiple interlayer connection conductors is formed, for example, by filling a via hole with a conductive paste containing copper, a low-melting-point metal (for example, tin), and resin, and heating it.

[0150] In the multilayer substrate 100, the multiple first interlayer connection conductors 91 and the multiple third interlayer connection conductors 93 correspond one-to-one, and corresponding first interlayer connection conductors 91 and third interlayer connection conductors 93 overlap in the thickness direction D1 of the multilayer substrate 1, but the first interlayer connection conductors 91 and the third interlayer connection conductors 93 may be arranged with a shift in the signal transmission direction of the signal line 2. Furthermore, the number of first interlayer connection conductors 91 and the number of third interlayer connection conductors 93 may be different.

[0151] In the multilayer substrate 100, the first hollow portion 6 and the second hollow portion 7 may overlap the entire area of ​​the signal line 2 in a plan view in the thickness direction D1 of the multilayer substrate 1. In the multilayer substrates 100 to 100C, 100D, and 100E to 100H, the number of first hollow portions 6 is not limited to multiple and may be one. Furthermore, the number of second hollow portions 7 is not limited to multiple and may be one.

[0152] Furthermore, electronic device 500 may include multilayer substrates 100A to 100E, 100G, and 100H instead of multilayer substrate 100. Multilayer substrates 100, 100A to 100E, 100G, and 100H may be curved.

[0153] Furthermore, the multilayer substrates 100 and 100A to 100H may be configured without at least one of the first resist layer 51 and the second resist layer 52.

[0154] The multilayer substrate 100, 100A to 100H may include a plurality of signal lines 2. In this case, the multilayer substrate 100, 100A to 100H may have a plurality of signal lines 2 grouped together and arranged in parallel.

[0155] Furthermore, the signal line 2 may be branched into two or more parts midway along its length in the signal transmission direction.

[0156] The signal line 2 may also be a differential line.

[0157] When viewed from above in the thickness direction D1 of the laminated substrates 1, 1A to 1C, and 1E to 1H, the hollow portion 6 is not limited to a circular shape but may also be a rectangular or polygonal shape. Furthermore, when viewed from above in the thickness direction D1 of the laminated substrates 1, 1A to 1C, and 1E to 1G, the hollow portion 7 is not limited to a circular shape but may also be a rectangular or polygonal shape.

[0158] Each of the plurality of first through holes 110 in the first base material layer 11 may have a shape such that the opening area decreases from the second main surface 112 to the first main surface 111 of the first base material layer 11. Furthermore, each of the plurality of third through holes 130 in the fourth base material layer 14 may have a shape such that the opening area decreases from the first main surface 141 to the second main surface 142 of the fourth base material layer 14.

[0159] (Aspects) The present specification discloses the following aspects.

[0160] A multilayer substrate (100; 100A; 100B; 100C; 100D; 100E; 100F; 100G; 100H) according to a first aspect includes a laminate substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H), a signal line (2), and a ground electrode (3). The laminate substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H) has a hollow portion (6). The signal line (2) is disposed within the laminate substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H). The ground electrode (3) overlaps the signal line (2) in a plan view from the thickness direction (D1) of the laminate substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H). The hollow portion (6) overlaps the signal line (2) in a plan view in the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H). The laminated substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H) includes a first substrate layer (11), a second substrate layer (12), and a third substrate layer (13). The first substrate layer (11) has a through hole (110) or a recess (113) that forms part of the hollow portion (6). The second substrate layer (12) has a recess (120) or a through hole (123) that overlaps the through hole (110) of the first substrate layer (11) or the recess (113) of the first substrate layer (11) in the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H). The third substrate layer (13) connects the first substrate layer (11) and the second substrate layer (12). The second substrate layer (12) is arranged so that the internal space of the recess (120) of the second substrate layer (12) or the through-hole (123) of the second substrate layer (12) communicates with the through-hole (110) of the first substrate layer (11) or the recess (113) of the first substrate layer (11). In a plan view from the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H), the opening edge (124) of the recess (120) of the second base material layer (12) or the opening edge (126) of the through hole (123) of the second base material layer (12) is located outside the opening edge (114) of the through hole (110) of the first base material layer (11) or the opening edge (115) of the recess (113) of the first base material layer (11). In a plan view from the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1E; 1F; 1G; 1H), the third base material layer (13) does not overlap with the through hole (110) or the recess (113) of the first base material layer (11).The hollow portion (6) is located between the signal line (2) and the ground electrode (3) in the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1E; 1F; 1G).

[0161] According to this aspect, it is possible to reduce transmission loss.

[0162] The multilayer substrate (100; 100A; 100B; 100D; 100E; 100F; 100H) according to the second aspect is the first aspect in which the laminated substrate (1; 1A; 1B; 1E; 1F; 1H) has a hollow portion (6) that exposes the signal line (2) within the laminated substrate (1; 1A; 1B; 1E; 1F; 1H).

[0163] According to this aspect, it is possible to further reduce transmission loss compared to when the signal line (2) is not exposed within the laminated substrate (1; 1A; 1B; 1E; 1F; 1H) by the hollow portion (6).

[0164] In the multilayer substrate (100; 100A; 100B; 100C; 100D; 100F) according to the third aspect, in the first or second aspect, the laminated substrate (1; 1A; 1B; 1C; 1F) further has a second hollow portion (7) that overlaps the signal line (2) and the first hollow portion (6) in a plan view in the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1F). The laminated substrate (1; 1A; 1B; 1C; 1F) includes a fourth base layer (14), a fifth base layer (15), and a sixth base layer (16). The fourth base layer (14) has a second through hole (140) that forms part of the second hollow portion (7), different from the first through hole (110) that is the through hole (110) of the first base layer (11). The fifth substrate layer (15) has a second recess (150) that overlaps the second through hole (140) in the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1F), unlike the first recess (120) that is the recess (120) of the second substrate layer (12). The fifth substrate layer (15) is arranged so that the internal space of the second recess (150) is connected to the second through hole (140). The sixth substrate layer (16) connects the fourth substrate layer (14) and the fifth substrate layer (15). In a plan view from the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1F), the opening edge (154) of the second recess (150) is located outside the opening edge (144) of the second through hole (140). The sixth base material layer (16) does not overlap the second through hole (140) when viewed in a plan view from the thickness direction (D1) of the laminated substrate (1; 1A; 1B; 1C; 1F).

[0165] According to this aspect, it is possible to further reduce the transmission loss.

[0166] In the multilayer substrate (100; 100A; 100B; 100D; 100F) according to the fourth aspect, in the third aspect, the laminated substrate (1; 1A; 1B; 1C; 1F) has a second hollow portion (7) that exposes the signal line (2) within the laminated substrate (1; 1A; 1B; 1C; 1F).

[0167] According to this aspect, it is possible to further reduce transmission loss compared to when the signal line (2) is not exposed within the laminated substrate (1; 1A; 1B; 1C; 1F) by the second hollow portion (7).

[0168] In the multilayer substrate (100; 100A; 100B; 100C; 100D; 100F) according to the fifth aspect, in the third aspect, the material of the fourth substrate layer (14) is the same as the material of the first substrate layer (11), the material of the fifth substrate layer (15) is the same as the material of the second substrate layer (12), and the material of the sixth substrate layer (16) is the same as the material of the third substrate layer (13).

[0169] According to this aspect, it is possible to reduce thermal stress and improve reliability.

[0170] In the multilayer substrate (100B) according to the sixth aspect, in any one of the first to fifth aspects, the second base layer (12) further has a groove (125) surrounding the recess (120) of the second base layer (12).

[0171] According to this aspect, it is possible to reduce the variation in transmission loss.

[0172] In the multilayer substrate (100B) according to the seventh aspect, in the sixth aspect, the depth (H25) of the groove (125) is equal to or greater than the thickness (T13) of the third base material layer (13) and equal to or less than the thickness (T12) of the second base material layer (12). In a plan view from the thickness direction (D1) of the laminated substrate (1), the distance (L25) between the recess (120) of the second base material layer (12) and the groove (125) in the width direction of the groove (125) is equal to or greater than the thickness (T13) of the third base material layer (13) and equal to or less than the thickness (T12) of the second base material layer (12).

[0173] In the multilayer substrate (100; 100B; 100C; 100D; 100E; 100F; 100G) according to the eighth aspect, in any one of the first to seventh aspects, the Young's modulus of the second base material layer (12) is greater than the Young's modulus of the first base material layer (11).

[0174] According to this aspect, it is possible to suppress deformation of the ground electrode (3) in contact with the second base layer (12).

[0175] The multilayer substrate (100; 100B; 100C; 100D; 100E; 100F; 100G) according to the ninth aspect is any one of the first to eighth aspects, in which the Young's modulus of the third base material layer (13) is smaller than the Young's modulus of each of the first base material layer (11) and the second base material layer (12).

[0176] According to this aspect, it is possible to reduce the stress applied to the signal line (2).

[0177] A multilayer substrate (100; 100A; 100C; 100D; 100F; 100G) according to a tenth aspect further includes a second ground electrode (4) different from the first ground electrode (3) that is the ground electrode (3) of the third aspect. The second ground electrode (4) is in contact with the fifth base layer (15).

[0178] According to this aspect, it is possible to reduce transmission loss compared to a case where the second ground electrode (4) is not provided.

[0179] The multilayer substrate (100F) according to the eleventh aspect is any one of the first to tenth aspects, in which the laminated substrate (1F) has a rigid portion (101) at a portion where the third substrate layer (13) and the second substrate layer (12) are laminated on the first substrate layer (11), and a flexible portion (102) at a portion where the third substrate layer (13) and the second substrate layer (12) are not laminated on the first substrate layer (11), and the thickness of the flexible portion (102) is thinner than the thickness of the rigid portion (101).

[0180] According to this aspect, the multilayer substrate (100F) can be easily bent at the flexible portion (102).

[0181] In the multilayer substrate (100F) according to the twelfth aspect, in the eleventh aspect, the multilayer substrate (100F) is bent at the flexible portion (102).

[0182] According to this aspect, when the storage space for the multilayer substrate (100F) in the housing (501) of the electronic device (500F) is a curved space, it becomes easier to arrange the multilayer substrate (100F) in the housing (501) of the electronic device (500F).

[0183] An electronic device (500:500F) according to a thirteenth aspect includes a multilayer substrate (100; 100A; 100B; 100C; 100D; 100E; 100F; 100G; 100H) according to any one of the first to twelfth aspects, and a housing (501). The housing (501) houses the multilayer substrate (100; 100A; 100B; 100C; 100D; 100E; 100F; 100G; 100H).

[0184] According to this aspect, it is possible to realize an electronic device (500:500F) with reduced transmission loss.

[0185] 1, 1A, 1B, 1C, 1E, 1F, 1G, 1H Laminated substrate 2 Signal line 201 First end 202 Second end 3 Ground electrode (first ground electrode) 4 Second ground electrode 11 First base material layer 110 Through hole (first through hole) 111 First main surface 112 Second main surface 113 Recess 114 Opening edge 115 Opening edge 12 Second base material layer 120 Recess (first recess) 121 First main surface 122 Second main surface 123 Through hole 124 Opening edge 125 Groove (first groove) 126 Opening edge 13 Third base material layer 130 Third through hole 131 First portion 132 Second portion 134 Opening edge 14 Fourth base material layer 140 Through hole (second through hole) 141 First main surface 142 Second main surface 144 Opening edge 15 Fifth base material layer 150 Recess (second recess) 153 Through hole 154 Opening edge 155 Groove (second groove) 156 Opening edge 16 Sixth base material layer 160 Fourth through hole 164 Opening edge 17 Seventh base material layer 51 First resist layer 52 Second resist layer 6 Hollow portion (first hollow portion) 7 Second hollow portion 8 Third ground electrode 91 First interlayer connection conductor 92 Second interlayer connection conductor 93 Third interlayer connection conductor 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G, 100H Multilayer substrate 101 Rigid portion 102 Flexible portion 500, 500F Electronic device 501 Housing D1 Thickness direction H2 Depth H5 Depth H25 Depth H55 Depth L25 Distance L55 Distance P1 First pad electrode P2 Second pad electrode T131 Thickness T132 Thickness R114 Diameter R124 Diameter R144 Diameter

Claims

1. A laminated substrate having a hollow portion, a signal line arranged in the laminated substrate, and a ground electrode overlapping the signal line in a planar view in the thickness direction of the laminated substrate, wherein the hollow portion overlaps the signal line in a planar view in the thickness direction of the laminated substrate, the laminated substrate including: a first base layer having a through hole or a recess forming a part of the hollow portion; a second base layer having a recess or a through hole that overlaps the through hole or the recess of the first base layer in the thickness direction of the laminated substrate; and a third base layer connecting the first base layer and the second base layer, wherein the second base layer is arranged such that the internal space of the recess or the through hole of the second base layer is in communication with the through hole of the first base layer or the recess of the first base layer, a multilayer substrate, wherein, in a plan view from the thickness direction of the laminated substrate, an opening edge of the recess of the second base material layer or an opening edge of the through hole of the second base material layer is located outside an opening edge of the through hole of the first base material layer or an opening edge of the recess of the first base material layer; the third base material layer does not overlap with the through hole of the first base material layer or the recess of the first base material layer in a plan view from the thickness direction of the laminated substrate; and the hollow portion is located between the signal line and the ground electrode in the thickness direction of the laminated substrate.

2. The multilayer board according to claim 1, wherein the signal line is exposed within the laminate board by the hollow portion.

3. The multilayer substrate according to claim 1 or 2, further comprising a second hollow portion overlapping the signal line and the first hollow portion as the hollow portion in a planar view from the thickness direction of the laminate substrate, the laminate substrate including: a fourth base material layer having a second through hole different from the first through hole as the through hole of the first base material layer and forming part of the second hollow portion; a fifth base material layer having a second recess different from the first recess as the recess of the second base material layer and overlapping the second through hole in the thickness direction of the laminate substrate, the fifth base material layer being arranged so that the internal space of the second recess communicates with the second through hole; and a sixth base material layer connecting the fourth base material layer and the fifth base material layer, wherein an opening edge of the second recess is located outside an opening edge of the second through hole as viewed from the thickness direction of the laminate substrate, and the sixth base material layer does not overlap with the second through hole as viewed from the thickness direction of the laminate substrate.

4. The multilayer substrate according to claim 3, wherein the signal line is exposed within the laminate substrate by the second hollow portion.

5. A multilayer board as described in claim 3, wherein the material of the fourth base material layer is the same as the material of the first base material layer, the material of the fifth base material layer is the same as the material of the second base material layer, and the material of the sixth base material layer is the same as the material of the third base material layer.

6. The multilayer board according to any one of claims 1 to 5, wherein the second base material layer further has a groove surrounding the recess of the second base material layer.

7. A multilayer substrate as described in claim 6, wherein the depth of the groove is equal to or greater than the thickness of the third base material layer and equal to or less than the thickness of the second base material layer, and the distance between the recess of the second base material layer and the groove in the width direction of the groove when viewed in a plan view from the thickness direction of the laminated substrate is equal to or greater than the thickness of the third base material layer and equal to or less than the thickness of the second base material layer.

8. A multilayer substrate according to any one of claims 1 to 7, wherein the Young's modulus of the second base material layer is greater than the Young's modulus of the first base material layer.

9. A multilayer substrate according to any one of claims 1 to 8, wherein the Young's modulus of the third base material layer is smaller than the Young's modulus of each of the first base material layer and the second base material layer.

10. The multilayer board according to claim 3, further comprising a second ground electrode different from the first ground electrode, the second ground electrode being in contact with the fifth base material layer.

11. A multilayer substrate as described in any one of claims 1 to 10, wherein the laminated substrate has a rigid section where the third substrate layer and the second substrate layer are laminated on the first substrate layer, and a flexible section where the third substrate layer and the second substrate layer are not laminated on the first substrate layer, and the thickness of the flexible section is thinner than the thickness of the rigid section.

12. The multilayer substrate according to claim 11, wherein the multilayer substrate is bent at the flexible portion.

13. An electronic device comprising: a multilayer substrate according to any one of claims 1 to 12; and a housing that houses the multilayer substrate.

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