Transmission line and electronic device

Abstract

This transmission line (101) is provided with a laminate comprising: a plurality of laminated insulator layers (11, 12, 13); and a conductor layer joined to a surface along the insulator layers (11, 13). The conductor layer includes a reference ground conductor layer (21) and a signal line conductor layer (23) overlapping the reference ground conductor layer (21) when the laminate is viewed in the lamination direction. The laminate has a recess (RC) that is recessed in the lamination direction, and when the laminate is viewed in the lamination direction, the signal line conductor layer (23) is disposed at a position overlapping the recess (RC).

Description

Transmission lines and electronic devices

[0001] The present invention relates to a transmission line and an electronic device including the same.

[0002] A transmission line for high-frequency signals made of laminated substrates generally has a structure including a reference ground conductor layer and a signal line conductor layer arranged opposite the reference ground conductor layer. As shown in Patent Document 1, a transmission line further including side ground conductor layers on the left and right of the signal line conductor layer in the direction of extension is also used. A coplanar waveguide is also used, in which side ground conductor layers are provided on the left and right of the signal line conductor layer in the direction of extension of the signal line conductor layer.

[0003] Japanese Patent Application Laid-Open No. 2018-121076

[0004] The transmission line disclosed in Patent Document 1 has a hollow space formed between the signal line conductor layer and the reference ground conductor layer. This structure makes it possible to effectively reduce transmission loss by taking advantage of the low dielectric constant and dielectric loss tangent of the hollow space.

[0005] However, in conventional general transmission lines in which a signal line conductor layer and a ground conductor layer are arranged in a predetermined positional relationship, including the transmission line of Patent Document 1, the insulator layer on which the signal line conductor layer is provided or the insulator layer in contact with the signal line conductor layer is flat.

[0006] When such a transmission line is incorporated into an electronic device and a conductive member is placed close to the signal line conductor layer side of the transmission line, the change in capacitance between the signal line conductor layer and the conductive member becomes large, causing a significant change in the electrical characteristics of the transmission line.

[0007] Therefore, an object of the present invention is to provide a transmission line that suppresses changes in characteristics due to the influence of nearby conductive members while maintaining a reduction in transmission loss due to the presence of a hollow portion near the signal line conductor layer, and an electronic device equipped with this transmission line.

[0008] (1) A transmission line as an example of the present disclosure is characterized in that a laminate is formed with a plurality of stacked insulator layers and conductor layers formed by bonding to surfaces of all or some of the insulator layers among the plurality of insulator layers, the conductor layers including a reference ground conductor layer and a signal line conductor layer overlapping the reference ground conductor layer when the laminate is viewed in the stacking direction, the laminate has a recessed portion recessed in the stacking direction, and when the laminate is viewed in the stacking direction, the signal line conductor layer is positioned so as to overlap the recessed portion.

[0009] (2) An electronic device as an example of the present disclosure includes the transmission line and an electronic circuit connected to the transmission line.

[0010] (3) Also, an example of an electronic device disclosed herein includes the transmission line and an object made of a conductor, a dielectric, or a composite thereof, and the recessed portion faces the object.

[0011] According to the present invention, it is possible to obtain a transmission line in which the reduction in transmission loss due to the presence of a hollow portion near the signal line conductor layer is maintained and characteristic changes due to the influence of nearby conductive members are suppressed, and an electronic device equipped with this transmission line.

[0012] FIG. 1A is a plan view of each layer showing the configuration of a transmission line according to the first embodiment. FIG. 1B is a cross-sectional view of each layer before lamination, showing the configuration of the transmission line according to the first embodiment. FIG. 1C is a cross-sectional view of the transmission line according to the first embodiment. FIG. 2A is a cross-sectional view taken along Y1-Y1 in FIG. 1A, FIG. 2B is a cross-sectional view taken along Y2-Y2 in FIG. 1A, FIG. 2C is a cross-sectional view taken along Y3-Y3 in FIG. 1A, and FIG. 2D is a cross-sectional view taken along Y4-Y4 in FIG. 1A. FIG. 3 is a diagram showing the relationship between the transmission line according to the first embodiment and an object close to it. FIG. 4A is a plan view of each layer showing the configuration of a transmission line according to the second embodiment. FIG. 4B is a cross-sectional view of each layer before lamination, showing the configuration of the transmission line according to the second embodiment. FIG. 4C is a cross-sectional view of the transmission line according to the second embodiment. FIG. 5(A) is a cross-sectional view taken along line Y1-Y1 in FIG. 4(A), FIG. 5(B) is a cross-sectional view taken along line Y2-Y2 in FIG. 4(A), and FIG. 5(C) is a cross-sectional view taken along line Y3-Y3 in FIG. 4(A). FIG. 6(A) is a partial plan view of the transmission line shown in FIG. 4(C) with components mounted on both ends. FIG. 6(B) is a cross-sectional view taken along line Y1-Y1 in FIG. 6(A), and FIG. 6(C) is a cross-sectional view taken along line Y2-Y2 in FIG. 6(A). FIG. 7 is a diagram showing a transmission line according to a second embodiment and its placement in an electronic device. FIGS. 8(A), 8(B), 8(C), 8(D), 8(E), and 8(F) are plan views of each layer showing the configuration of a transmission line according to a third embodiment. FIG. 9(A) is a cross-sectional view taken along line Y1-Y1 in FIGS. 8(A), 8(B), 8(C), 8(D), 8(E), and 8(F). FIG. 9(B) is a cross-sectional view taken along line Y2-Y2 in FIGS. 8(A), 8(B), 8(C), 8(D), 8(E), and 8(F). FIG. 9(C) is a cross-sectional view taken along line Y3-Y3 in FIGS. 8(A), 8(B), 8(C), 8(D), 8(E), and 8(F). FIG. 10 is a cross-sectional view of a transmission line according to a fourth embodiment. FIG. 11 is a cross-sectional view of a transmission line according to a fifth embodiment. FIG. 12 is a cross-sectional view of a transmission line according to a sixth embodiment. FIG. 13 is a cross-sectional view of a transmission line according to a seventh embodiment. FIG. 14 is a cross-sectional view of a transmission line according to an eighth embodiment.FIG. 15(A) is a cross-sectional view of a transmission line according to the ninth embodiment, and FIG. 15(B) is a cross-sectional view of another transmission line according to the ninth embodiment. FIG. 16 is a cross-sectional view of a transmission line according to the tenth embodiment. FIG. 17 is a cross-sectional view of a transmission line according to the eleventh embodiment. FIG. 18 is a cross-sectional view of a transmission line according to the eleventh embodiment. FIG. 19 is a cross-sectional view of a transmission line according to the twelfth embodiment. FIG. 20 is a cross-sectional view of a transmission line according to the thirteenth embodiment. FIG. 21 is a cross-sectional view of a transmission line according to the fourteenth embodiment. FIG. 22 is a cross-sectional view of a transmission line according to the fifteenth embodiment. FIG. 23 is a cross-sectional view of a transmission line according to the fifteenth embodiment. FIG. 24 is a cross-sectional view of a transmission line according to the sixteenth embodiment. FIG. 25 is a cross-sectional view of a transmission line according to the seventeenth embodiment. FIG. 26 is a cross-sectional view of a transmission line according to the eighteenth embodiment. FIGS. 27(A), 27(B), 27(C), 27(D), 27(E), 27(F), 27(G), and 27(H) are plan views of a transmission line according to a 19th embodiment. FIG. 28(A) is a cross-sectional view of each layer before lamination, showing the configuration of a transmission line according to a 20th embodiment. FIG. 28(B) is a cross-sectional view of the transmission line according to the 20th embodiment. FIGS. 29(A), 29(B), 29(C), and 29(D) are cross-sectional views of the transmission line in the Y direction. FIGS. 30(A), 30(B), 30(C), and 30(D) are cross-sectional views of a transmission line 116 according to a 21st embodiment and during its manufacturing. FIGS. 31(A), 31(B), and 31(C) are plan views of three transmission lines according to a 22nd embodiment. FIG. 32 is a cross-sectional view of an electronic device according to a 23rd embodiment.

[0013] Hereinafter, several specific examples will be given with reference to the drawings to illustrate several embodiments for carrying out the present invention. The same reference numerals are used for the same parts in each drawing. To facilitate explanation and understanding of the main points, the embodiments for carrying out the present invention are shown divided into several embodiments for the sake of convenience. However, partial omission, substitution, or combination of the configurations shown in different embodiments is possible. From the second embodiment onwards, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0014] First Embodiment In the first embodiment, a transmission line that functions as a grounded coplanar waveguide will be exemplified.

[0015] FIG. 1A is a plan view of each layer showing the configuration of the transmission line according to the first embodiment. FIG. 1B is a cross-sectional view of each layer before lamination, showing the configuration of the transmission line according to the first embodiment. FIG. 1C is a cross-sectional view of the transmission line 101 according to the first embodiment. Both FIG. 1B and FIG. 1C are cross-sectional views taken along the line X-X in FIG. 1A. Note that in FIG. 1A, the conductor layers are shown separated from the insulator layers.

[0016] Fig. 2(A) is a cross-sectional view taken along line Y1-Y1 in Fig. 1(A), Fig. 2(B) is a cross-sectional view taken along line Y2-Y2 in Fig. 1(A), Fig. 2(C) is a cross-sectional view taken along line Y3-Y3 in Fig. 1(A), and Fig. 2(D) is a cross-sectional view taken along line Y4-Y4 in Fig. 1(A). Of course, all of these are cross-sectional views after the layers have been stacked to form a laminate (in a state where transmission line 101 has been configured).

[0017] In each cross-sectional view, lines that appear in the cross section (appearing due to cutting) are drawn, and lines that exist behind the cross section are not shown. This also applies to each embodiment described later. Furthermore, the directional symbols X, Y, and Z in each view merely indicate the direction from which each view is taken, and are not symbols that indicate the origin of the three orthogonal axes.

[0018] Although each figure shows a single transmission line, in the intermediate stage of manufacturing such a single transmission line, the continuous line is made up of multiple transmission lines, and the continuous line is cut into single lines at the final stage of the manufacturing process or just before the final stage. This relationship between the continuous line and single lines is similar in other figures.

[0019] In the first embodiment, the transmission line 101 comprises three insulator layers 11, 12, 13 in stacked relationship.

[0020] The "laminate" comprises a plurality of stacked insulator layers and a conductor layer formed by bonding to the surfaces of all or some of the insulator layers among the plurality of insulator layers.

[0021] As shown in Figures 1A and 1B, a signal line conductor layer 23 and a side ground conductor layer 22 are provided on the lower surface of the insulator layer 13. The upper surfaces of the signal line conductor layer 23 and the side ground conductor layer 22 are roughened compared to their lower surfaces. As a result, the signal line conductor layer 23 and the side ground conductor layer 22 are mainly supported by the insulator layer 13. As shown in Figure 1A, the signal line conductor layer 23 is a conductor pattern that extends in the X direction with a constant width. Both ends of the signal line conductor layer 23 function as signal electrodes. These signal electrodes will be described in detail later.

[0022] The reference ground conductor layer 21 is a conductor layer formed by being bonded to a surface along the insulator layer 11, and the signal line conductor layer 23 and the side ground conductor layer 22 are conductor layers formed by being bonded to a surface along the insulator layer 13.

[0023] 1A and 1B, a main ground conductor layer 21 is provided on the top surface of the insulator layer 11. The main ground conductor layer 21 is a conductor layer formed along substantially the entire top surface of the insulator layer 11. The side ground conductor layers 22 are provided in parallel with the sides of the signal line conductor layers 23 when viewed in the stacking direction (Z direction) of the laminate.

[0024] A plurality of openings 12H are formed in the insulating layer 12 along the extending direction of the signal line conductor layer 23. In this example, the openings 12H are rectangular in plan view.

[0025] As shown in Figures 1(A), 1(B), and 1(C), the opening 12H formed in the insulator layer 12 forms a hollow portion HS in the stacked state of the insulator layers 11, 12, and 13 on which various conductor layers are formed.

[0026] 2A and 2B , the laminate including the insulator layers 11, 12, and 13, the reference ground conductor layer 21, the signal line conductor layer 23, and the side ground conductor layer 22 has a recessed portion RC that is recessed toward the hollow portion HS. In the first embodiment, the recessed portion RC of the laminate is a portion of the insulator layer 13 that is recessed toward the hollow portion HS.

[0027] When the laminate is viewed in the stacking direction (Z direction), the signal line conductor layer 23 is disposed at a position overlapping the recessed portion RC.

[0028] As shown in FIG. 2B and other figures, a portion of the main ground conductor layer 21 faces the signal line conductor layer 23 via the hollow portion HS.

[0029] As shown in FIG. 1B, the side ground conductor layer 22 is formed on the insulator layer 13 on which the signal line conductor layer 23 is formed.

[0030] 2A and 2B , the side ground conductor layer 22 is disposed in a position opposite to the recess direction relative to the signal line conductor layer 23 formed in the recess RC. That is, the side ground conductor layer 22 is farther away in the Z direction from the main ground conductor layer 21 than the signal line conductor layer 23. In FIGS. 2A and 2B , the dimension PA in the stacking direction (Z direction) indicates the relative positional arrangement in the Z direction between the side ground conductor layer 22 and the signal line conductor layer 23.

[0031] 1A, 2C, and 2D, eight openings 13H are formed in the insulator layer 13. These openings 13H expose both ends of the signal line conductor layer 23 and parts of the side ground conductor layer 22. This exposure forms signal electrodes 23E and ground electrodes 22E for mounting components. These components will be described in detail later.

[0032] The single opening 12H and the multiple openings 13H are resin removal portions. For example, the openings 12H and 13H are formed by removing the resin by irradiating the resin with laser light, or by forming a resist mask pattern in a portion where the resin is not to be removed and then immersing the resist mask pattern in an alkaline solution, for example, to remove the resin.

[0033] The signal line conductor layer 23 faces the main ground conductor layer 21 at a predetermined distance in the thickness direction of the insulator layer 12 .

[0034] The side ground conductor layers 22 are arranged on the sides of the signal line conductor layers 23 in the direction in which the signal line conductor layers 23 extend.

[0035] The side ground conductor layers 22 are arranged along the extension direction (X direction) of the signal line conductor layer 23 and at predetermined intervals in the left-right direction (Y direction) of the signal line conductor layer 23 .

[0036] The recessed portion RC of the insulator layer 13 is formed, for example, as shown in Figures 1(C), 2(A), 2(B), 2(C), and 2(D), by pressing the insulator layers 11, 12, and 13 together using a mold having a protrusion facing the portion where the recess is to be formed, during or after the formation of the laminate by stacking the insulator layers 11, 12, and 13. Alternatively, the recessed portion RC may be formed by pressing the entire laminate through a cushioned sheet during or after the formation of the laminate by stacking the insulator layers 11, 12, and 13. Alternatively, the recessed portion RC may be formed by pressing the insulator layer 13 before stacking. Alternatively, the recessed portion RC may be formed by heating and pressurizing the insulator layers 11, 12, and 13 to form a laminate, and then cooling to room temperature to shrink the hollow portion HS, thereby forming the recessed portion RC.

[0037] The side ground conductor layer 22 acts as a shielding ground conductor. The transmission line according to the first embodiment acts as a microstrip line. That is, the microstrip line is mainly composed of the reference ground conductor layer 21, the signal line conductor layer 23, the insulator layer 12, and the insulator layer 13. The insulator layer 11 mainly acts as a protective layer.

[0038] An electric field is also generated between the signal line conductor layer 23 and the side ground conductor layer 22. However, compared to the distance between the signal line conductor layer 23 and the reference ground conductor layer 21, the distance between the signal line conductor layer 23 and the side ground conductor layer 22 is wider and the opposing area in terms of the electric field is smaller. Therefore, although the side ground conductor layer 22 is part of the transmission line, it acts as a shielding ground conductor.

[0039] When the electric field generated between the side ground conductor layer 22 and the signal line conductor layer 23 is relatively large due to the narrow gap between the side ground conductor layer 22 and the signal line conductor layer 23, the transmission line 101 acts as a grounded coplanar waveguide. Note that the examples shown in Figures 1 and 2 do not clearly indicate the difference between the transmission line 101 being a simple "microstrip line" and a "grounded coplanar waveguide."

[0040] In the transmission line 101, the interlayer connection conductor 4 is formed only on the insulator layer 12. That is, the interlayer connection conductor 4 is formed only on one insulator layer. The interlayer connection conductor 4 may be processed using a conductive paste or may be processed by, for example, copper plating.

[0041] For example, flexible polyimide or rigid glass epoxy may be used as the material for the insulator layers 11, 12, and 13. When rigid glass epoxy is used, recesses may be formed by applying heat and pressure using a mold with protrusions.

[0042] The insulating layers 11, 12, and 13 are each made of a thermoplastic resin such as LCP. It is preferable that adjacent insulating layers 11, 12, and 13 are bonded to each other without an adhesive layer therebetween, i.e., are self-adhesive.

[0043] The insulator layers 11, 12, and 13 have no path for gas to pass between the hollow portion HS and the outside of the laminate, and the hollow portion HS is made airtight by the insulator layers 11, 12, and 13. In other words, the insulator layers 11, 12, and 13 have no path for gas to pass between the hollow portion HS and the outside of the laminate. The insulator layers 11, 12, and 13 are preferably made of a material with low water absorption, such as LCP, or low gas permeability. This prevents gas and water vapor from entering the hollow portion HS, preventing corrosion of exposed conductor layers such as copper foil.

[0044] 3 is a cross-sectional view showing the relationship between the transmission line 101 according to the first embodiment and an object 210 located nearby. When the transmission line 101 is incorporated into, for example, an electronic device, the transmission line 101 is located nearby an object 210 located inside the electronic device. The object 210 includes a conductor layer 211 and a dielectric layer 212 covering the surface of the conductor layer 211.

[0045] In the example shown in FIG. 3, the transmission line 101 and the object 210 are arranged such that the signal line conductor layer 23 of the transmission line 101 is closer to the object 210 than the reference ground conductor layer 21 .

[0046] According to the first embodiment, the following effects are achieved.

[0047] (a) In the stacking direction of the laminate, the side ground conductor layers 22 are located closer to the outside of the transmission line 101 (at the top in the direction (Z direction) away from the reference ground conductor layer 21) than the signal line conductor layers 23, which enhances the electromagnetic field shielding effect of the side ground conductor layers 22. That is, the radiated electromagnetic field of the signal line conductor layer 23 spreads in the direction (Z direction) away from the reference ground conductor layer 21 and in the planar direction along the surface of the reference ground conductor layer 21. However, because the side ground conductor layers 22 are located farther from the reference ground conductor layer 21 than the signal line conductor layers 23, i.e., because the side ground conductor layers 22 are closer to the surface than the signal line conductor layers 23, the electromagnetic field shielding effect of the side ground conductor layers 22 is enhanced.

[0048] (b) Because the portion of the transmission line 101 where the signal line conductor layer 23 is formed is recessed, even if the recessed surface of the transmission line 101 is close to the conductor layer 211 and dielectric layer 212 of the object 210, air with a low dielectric constant and dielectric loss tangent is disposed between the signal line conductor layer 23 and the object 210. As a result, the change in capacitance between the signal line conductor layer 23 and ground due to the transmission line 101 being close to the object 210 is small, and the change in the electrical characteristics of the transmission line 101, such as the characteristic impedance, is also small. As a result, low reflection loss and low insertion loss characteristics are maintained.

[0049] (c) The hollow space HS is sealed by the insulating layers 11, 12, and 13, and gas and water vapor do not enter the hollow space HS, so that the exposed conductive layer such as copper foil does not corrode.

[0050] (d) Since the interlayer connection conductor 4 is formed on only one insulating layer (insulating layer 12), the number of processing steps is small and the manufacturing cost is low.

[0051] (e) Since the adjacent insulator layers 11, 12, and 13 are self-adhered to each other, no adhesive is required to bond the insulator layers together.

[0052] Second Embodiment In a second embodiment, a transmission line in which a plurality of hollow portions are arranged discretely along the extending direction of the signal line conductor layers will be exemplified.

[0053] Fig. 4(A) is a plan view of each layer showing the configuration of the transmission line according to the second embodiment. Fig. 4(B) is a cross-sectional view of each layer before lamination, showing the configuration of the transmission line according to the second embodiment. Fig. 4(C) is a cross-sectional view of the transmission line 102 according to the second embodiment. Both Fig. 4(B) and Fig. 4(C) are cross-sectional views taken along X-X in Fig. 4(A).

[0054] The lower surfaces of the signal line conductor layers 23 and the side ground conductor layers 22 are roughened compared to their upper surfaces, so that the signal line conductor layers 23 and the side ground conductor layers 22 are supported mainly by the insulator layer 12.

[0055] Fig. 5(A) is a cross-sectional view taken along line Y1-Y1 in Fig. 4(A), Fig. 5(B) is a cross-sectional view taken along line Y2-Y2 in Fig. 4(A), and Fig. 5(C) is a cross-sectional view taken along line Y3-Y3 in Fig. 4(A). All of these are cross-sectional views after the layers have been stacked to form a laminate (in a state where transmission line 102 has been configured).

[0056] In the transmission line 101 shown in the first embodiment, the hollow portion HS is continuous along the extension direction of the signal line conductor layer 23, but in the transmission line 102 according to the second embodiment, a plurality of hollow portions HS are discretely arranged along the extension direction of the signal line conductor layer 23. A plurality of cylindrical openings 12H are discretely arranged in the insulator layer 12 before lamination. When the insulator layers 11, 12, and 13 are laminated, the openings 12H form the hollow portion HS.

[0057] 4C and 5B, the laminate of the insulator layers 11, 12, and 13 has a recess RC on its outer surface that is recessed toward the hollow HS. As shown in Fig. 5A, there is no recess where there is no hollow HS below the signal line conductor layer 23. Even if there is a recess due to the influence of the adjacent recess RC, the amount of recess is smaller than in a location where there is a hollow HS below.

[0058] Fig. 6(A) is a partial plan view showing a state in which components 9 are mounted on both ends of the transmission line 102 shown in Fig. 4(C). Fig. 6(B) is a cross-sectional view taken along line Y1-Y1 in Fig. 6(A), and Fig. 6(C) is a cross-sectional view taken along line Y2-Y2 in Fig. 6(A).

[0059] The mounted component 9 is, for example, one side of a connector. Three ground terminals 9G and one signal terminal 9S protrude from the mounted component 9. This connector is, for example, a coaxial connector, but the electrodes of the connector are not shown in Figure 6(A).

[0060] 6B, a ground electrode 22E is an exposed portion of the side ground conductor layer 22. A ground terminal 9G of the mounted component is joined to the ground electrode 22E with solder S.

[0061] 5C and 6C, the exposed portion of the signal line conductor layer 23 is a signal electrode 23E. A signal terminal 9S of the mounted component is joined to this signal electrode 23E with solder S.

[0062] 7 is a diagram showing a transmission line 102 according to the second embodiment and a state in which the transmission line 102 is arranged in an electronic device. The electronic device includes substrates 201A and 201B and a battery 202. The battery 202 is a composite of a conductor and a dielectric.

[0063] The transmission line 102 is connected to the substrates 201A and 201B via the mounting components 9 serving as connectors. The transmission line 102 is arranged such that the signal line conductor layer 23 of the transmission line 102 is closer to the battery 202 than the reference ground conductor layer 21.

[0064] The arrangement pitch of the hollow portions HS is preferably 1 / 2λ or less. Here, the "arrangement pitch" refers to the distance between the centers of adjacent hollow portions HS. Furthermore, the distance between adjacent interlayer connection conductors 4 is preferably 1 / 4λ or less. Here, λ is one wavelength in the frequency band of the transmission signal. This reduces the change in characteristic impedance of the microstrip line depending on the position in the signal propagation direction. In other words, the transmission loss caused by the discrete arrangement of hollow portions HS is suppressed.

[0065] According to the second embodiment, the support portion of the signal line conductor layer 23 is larger than that of the example shown in the first embodiment, which improves the stability of the position of the signal line conductor layer 23. This also stabilizes the electrical characteristics of the transmission line.

[0066] Third Embodiment In a third embodiment, a transmission line in which electrodes that are electrically connected to signal line conductor layers are formed on the top and bottom surfaces of a laminate will be exemplified.

[0067] 8A, 8B, 8C, 8D, 8E, and 8F are plan views of each layer showing the configuration of the transmission line according to the third embodiment.

[0068] Fig. 9(A) is a cross-sectional view taken along line Y1-Y1 in Fig. 8(A), Fig. 8(B), Fig. 8(C), Fig. 8(D), Fig. 8(E), and Fig. 8(F). Fig. 9(B) is a cross-sectional view taken along line Y2-Y2 in Fig. 8(A), Fig. 8(B), Fig. 8(C), Fig. 8(D), Fig. 8(E), and Fig. 8(F). Fig. 9(C) is a cross-sectional view taken along line Y3-Y3 in Fig. 8(A), Fig. 8(B), Fig. 8(C), Fig. 8(D), Fig. 8(E), and Fig. 8(F). All of these are cross-sectional views (in a state where transmission line 103 has been configured) after the layers have been stacked to form a laminate.

[0069] 9A, 9B, and 9C, the transmission line 103 has a reference ground conductor layer 21 formed on the bottom surface of the insulator layer 11, and a signal line conductor layer 23 and a side ground conductor layer 22A formed on the top surface of the insulator layer 12. Furthermore, a side ground conductor layer 22C is formed on the bottom surface of the insulator layer 15, and a side ground conductor layer 22B is formed on the top surface of the insulator layer 16.

[0070] As shown in Figures 8(C) and 8(D), openings 12H are formed in the insulating layers 15 and 16, and as shown in Figure 9(B), a hollow portion HS is formed by lamination. A recess portion RC is formed in the upper portion of this hollow portion HS.

[0071] Unlike the example described in the first embodiment, the transmission line 103 has electrodes on the top and bottom surfaces for mounting components. That is, by forming four openings 13H in the insulator layer 13, a portion of the left end of the signal line conductor layer 23 is exposed as a signal electrode 23E1, and three portions of the side ground conductor layer 22A are exposed from the insulator layer 13, serving as electrodes for mounting components on the top surface. The right end of the signal line conductor layer 23 is extended to an electrode formed on the insulator layer 11 via an interlayer connection conductor. Furthermore, by forming four openings 14H in the insulator layer 14, the signal electrode 23E2 extended to the insulator layer 11 is exposed, and three portions of the reference ground conductor layer 21 are exposed from the insulator layer 14, serving as electrodes for mounting components on the bottom surface.

[0072] The transmission line 103 differs from the example shown in the first embodiment in that the conductor layers formed on the respective insulating layers are connected by conductive paste.

[0073] The outermost insulator layers 13 and 14 are resist films for protecting the conductor layers, and are, for example, coverlays made of polyimide or the like. The outermost insulator layers 13 and 14 may be made of the same insulator as the insulator layers 11, 12, 15, and 16. In this case, since all layers are made of the same material, mechanical stress is uniformed, and reliability against mechanical stress is improved.

[0074] The third embodiment provides the following effects.

[0075] (a) Since the conductor layer is not exposed to the hollow portion HS, corrosion of the conductor layer can be prevented.

[0076] (b) Since the conductor layer (electrode) is formed on the surface layer of the laminate of insulating layers, the conductor layer (electrode) can be patterned after lamination processing.

[0077] (c) Because there are many insulator layers between the signal line conductor layer 23 and the reference ground conductor layer 21, the thickness of the insulator layers between the signal line conductor layer 23 and the reference ground conductor layer 21 can be increased to a predetermined thickness even when using only thin insulator layers. Furthermore, since it is possible to form a conductor pattern on each insulator layer and then bond this conductor pattern to the insulator layer, a predetermined circuit can be configured by forming a conductor pattern on the insulator layer. Furthermore, by electrically connecting multiple side ground conductor layers using interlayer connection conductors that pass through the insulating layers, the ground conductors are expanded in the thickness direction (the stacking direction of the insulator layers), thereby improving shielding properties.

[0078] Furthermore, by increasing the thickness of the insulator layer between the signal line conductor layer 23 and the reference ground conductor layer 21 to a predetermined thickness, the electric field density between the signal line conductor layer 23 and the reference ground conductor layer 21 is reduced, reducing the dielectric loss therebetween and effectively reducing transmission loss. Furthermore, the line width of the signal line conductor layer 23 is increased to optimize the capacitance between the signal line conductor layer 23 and the reference ground conductor layer 21, thereby reducing the conductor loss of the signal line conductor layer 23 and effectively reducing transmission loss.

[0079] Fourth Embodiment In a fourth embodiment, an example in which the interlayer connection conductor 4 is formed as a through-hole is shown.

[0080] 10 is a cross-sectional view of a transmission line 104 according to the fourth embodiment. The cross-sectional view is taken along a line corresponding to the cross-sectional line Y1-Y1 of the transmission line shown in FIG. 1A in the first embodiment. The transmission line 104 includes insulator layers 11, 12, and 13, a reference ground conductor layer 21, a signal line conductor layer 23, a side ground conductor layer 22, and an interlayer connection conductor 4.

[0081] An opening is disposed in the insulator layer 12 before lamination, and the opening forms a hollow portion HS when the insulator layers 11, 12, and 13 are laminated. The laminate of the insulator layers 11, 12, and 13 has a recessed portion RC on its outer surface that is recessed toward the hollow portion HS.

[0082] The outermost insulating layers 14 and 15 are resist films for protecting the conductor layers, and are coverlays such as polyimide.

[0083] According to the fourth embodiment, the interlayer connection conductors 4 are formed as through holes, thereby reducing the number of steps required for drilling holes for interlayer connection to each layer and filling them with conductive paste.

[0084] Fifth Embodiment In a fifth embodiment, a transmission line having a microstrip line structure will be exemplified.

[0085] 11 is a cross-sectional view of a transmission line 105 according to the fifth embodiment. A reference ground conductor layer 21 is formed on the upper surface of an insulator layer 11, and a signal line conductor layer 23 is formed on the lower surface of an insulator layer 13.

[0086] An opening is formed in the insulating layer 12, and a hollow portion HS is formed by laminating the insulating layers 11, 12, and 13. A recess portion RC is formed in the upper portion of this hollow portion HS.

[0087] The transmission line 105 differs from the transmission lines described so far in that no side ground conductor layers are arranged along the extension direction (X direction) of the signal line conductor layer 23 and at a predetermined distance to the left and right (Y direction) of the signal line conductor layer 23.

[0088] The transmission line 105 is a microstrip line that includes a reference ground conductor layer 21, a signal line conductor layer 23, insulating layers 12 and 13, and a hollow portion HS.

[0089] In this way, the present invention can also be applied to a microstrip line that does not have a side ground conductor layer that acts as a shielding ground conductor.

[0090] According to the fifth embodiment, there is no need to form a side ground conductor layer or to perform processing for interlayer connection between the main ground conductor layer 21 and the side ground conductor layer.

[0091] Sixth Embodiment In a sixth embodiment, a transmission line in which insulator layers adjacent in the stacking direction are joined together via an adhesive layer will be exemplified.

[0092] FIG. 12 is a cross-sectional view of a transmission line 106 according to the sixth embodiment.

[0093] In the transmission line 106, a reference ground conductor layer 21 is formed on the upper surface of the insulator layer 11, a side ground conductor layer 22 is formed on the upper surface of the insulator layer 12, and a signal line conductor layer 23 is formed on the lower surface of the insulator layer 13.

[0094] The insulator layer 11 on which the main ground conductor layer 21 is formed is bonded to the insulator layer 12 via an adhesive layer 51. The insulator layer 12 on which the side ground conductor layer 22 is formed is bonded to the insulator layer 13 on which the signal line conductor layer 23 is formed via an adhesive layer 52.

[0095] An opening is formed in the insulating layer 12, and a hollow portion HS is formed by laminating the insulating layers 11, 12, and 13. A recess portion RC is formed in the upper portion of this hollow portion HS.

[0096] The transmission line 106 may be manufactured, for example, as follows.

[0097] First, the reference ground conductor layer 21 is formed on the insulator layer 11 , the side ground conductor layer 22 is formed on the insulator layer 12 , and the signal line conductor layer 23 is formed on the insulator layer 13 .

[0098] Next, the insulator layer 11 on which the main ground conductor layer 21 is formed and the insulator layer 12 on which the side ground conductor layer 22 is formed are bonded together via an adhesive layer 51 .

[0099] Next, an opening for forming the hollow portion HS is formed in the insulator layer 12. Also, a via hole is opened and the inside of the via hole is plated to form the interlayer connection conductor 4.

[0100] Thereafter, the insulator layer 12 on which the side ground conductor layer 22 is formed and the insulator layer 13 on which the signal line conductor layer 23 is formed are bonded together via the adhesive layer 52 .

[0101] At an initial stage when the adhesive layers 51 and 52 are in a film state, openings for forming part of the hollow portion HS may be formed in the adhesive layers 51 and 52 .

[0102] The insulator layers 11, 12, and 13 are made of a resin with a low dielectric constant and dielectric loss tangent, such as LCP, MPI, PI, or PTFE. The adhesive layers 51 and 52 are made of a thermosetting resin, such as an epoxy resin or an acrylic resin. The adhesive layers 51 and 52 may be applied to the surfaces of the insulator layers, but it is preferable to heat the layers after laminating them in film form. This makes it easier to uniformize the spacing between the main ground conductor layer 21 and the signal line conductor layer 23, and the spacing between the main ground conductor layer 21 and the side ground conductor layer 22.

[0103] As described above, in the sixth embodiment, the insulating layers 11, 12, and 13 are laminated via the adhesive layers 51 and 52 made of a material different from that of the insulating layers 11, 12, and 13.

[0104] According to the sixth embodiment, the pressure required for bonding the conductor layer and the insulator layer or the insulator layers together is small, so deformation of the hollow space HS is small, which makes it easier to stabilize the electrical characteristics of the waveguide.

[0105] Seventh Embodiment In the seventh embodiment, a transmission line in which an insulator layer on which a reference ground conductor layer is formed also has a recessed portion facing the hollow portion will be described as an example.

[0106] 13 is a cross-sectional view of a transmission line 107 according to the seventh embodiment. The cross-sectional position corresponds to the position Y1-Y1 of the transmission line shown in FIG.

[0107] In the transmission line 107, similarly to the transmission line 101 described in the first embodiment, a reference ground conductor layer 21 is formed on the upper surface of the insulator layer 11, and a signal line conductor layer 23 and a side ground conductor layer 22 are formed on the lower surface of the insulator layer 13.

[0108] An opening is formed in the insulating layer 12, and a hollow portion HS is formed by laminating the insulating layers 11, 12, and 13. Recesses RC are formed above and below the hollow portion HS.

[0109] According to the seventh embodiment, the signal line conductor layer 23 can be easily brought close to the reference ground conductor layer 21. This allows the electric field to be concentrated in the lower part of the laminate (toward the center of the hollow portion HS) and the electric field in the upper part of the laminate to be weakened, thereby further reducing the influence of nearby objects.

[0110] Eighth Embodiment In the eighth embodiment, a transmission line in which the hollow portion does not reach the reference ground conductor layer will be exemplified.

[0111] 14 is a cross-sectional view of a transmission line 108 according to the eighth embodiment. The cross-sectional position corresponds to the position Y1-Y1 of the transmission line shown in FIG. 1A in the first embodiment.

[0112] 14 , the transmission line 108 has a reference ground conductor layer 21 formed on the upper surface of the insulator layer 11, and a signal line conductor layer 23 and a side ground conductor layer 22 formed on the lower surface of the insulator layer 13. A non-penetrating opening is formed in the insulator layer 12, and a hollow space HS is formed by laminating the insulator layer 12 and the insulator layer 13. In other words, the hollow space HS does not extend from the signal line conductor layer 23 to the reference ground conductor layer 21.

[0113] In this way, even in a transmission line in which the hollow portion HS does not reach the reference ground conductor layer 21, the hollow portion HS exists in the portion with high electric field density, and therefore the loss reduction effect of the hollow portion HS can be utilized.

[0114] According to the eighth embodiment, the laminate has high strength because the openings are not through-holes in the insulator layer 12. Furthermore, the main ground conductor layer 21 is highly corrosion-resistant because it is surrounded by an insulator layer.

[0115] Ninth Embodiment In a ninth embodiment, a transmission line having a recessed portion with a shape different from the examples shown so far will be illustrated.

[0116] 15A is a cross-sectional view of a transmission line 109A according to the ninth embodiment, and FIG. 15B is a cross-sectional view of a transmission line 109B according to the ninth embodiment. Both cross-sectional positions correspond to Y1-Y1 of the transmission line shown in FIG. 1A according to the first embodiment.

[0117] 15A and 109B, a reference ground conductor layer 21 is formed on the upper surface of the insulator layer 11, and a signal line conductor layer 23 and a side ground conductor layer 22 are formed on the lower surface of the insulator layer 13. An opening is formed in the insulator layer 12, and a hollow space HS is formed by laminating the insulator layer 12 and the insulator layer 13.

[0118] The main difference between the transmission line 109A and the transmission line 109B is the shape of the outer surface of the recessed portion RC. In the transmission line 109A, both the surface on which the signal line conductor layer 23 is formed and the outer surface of the recessed portion RC are flat, whereas in the transmission line 109B, the surface on which the signal line conductor layer 23 is formed is flat, and the outer surface of the recessed portion RC is curved (cylindrical).

[0119] According to the structure of transmission line 109A, it is easy to avoid the influence of an object because the volume of air between the surface of transmission line 109A on the side of signal line conductor layer 23 can be easily increased. Furthermore, according to the structure of transmission line 109B, insulator layer 12 and insulator layer 13 are joined at a portion of the side surface of hollow portion HS, so that the strength of the transmission line is high and the stability of the shape of hollow portion HS and the stability of its electrical characteristics can be maintained.

[0120] Tenth Embodiment In a tenth embodiment, a transmission line in which a plurality of side ground conductor layers are present along the extending direction of the signal line conductor layers will be exemplified.

[0121] 16 is a cross-sectional view of a transmission line 110 according to the tenth embodiment. The cross-sectional position corresponds to the position Y1-Y1 of the transmission line shown in FIG.

[0122] 16 , a transmission line 110 has a reference ground conductor layer 21 formed on the top surface of an insulator layer 11, and a signal line conductor layer 23 and a side ground conductor layer 22A formed on the bottom surface of an insulator layer 13. An insulator layer 14 is additionally inserted between the insulator layer 11 and the insulator layer 12. A side ground conductor layer 22B is formed on the top surface of the insulator layer 14. The reference ground conductor layer 21 and the side ground conductor layers 22A and 22B are electrically connected via an interlayer connection conductor 4.

[0123] 16 , the side ground conductor layers 22A and 22B are indirectly stacked, providing high strength in the stacking direction. Therefore, the base of the recess RC is located near the side ground conductor layer 22A. This structure allows the width RCW of the recess RC to be easily made larger than the hollow portion HS, thereby increasing the depth of the recess.

[0124] According to the tenth embodiment, not only is the topmost side ground conductor layer 22A located above the signal line conductor layer 23, but there are also multiple side ground conductor layers (22A, 22B), so that the side ground conductor layers 22A and 22B provide a high shielding effect.

[0125] Eleventh Embodiment In the eleventh embodiment, similar to the tenth embodiment, a transmission line in which a plurality of side ground conductor layers are present along the extending direction of the signal line conductor layer will be illustrated.

[0126] The lower part of Fig. 17 is a cross-sectional view of the transmission line 111 according to the eleventh embodiment. The upper part of Fig. 17 is a cross-sectional view of the transmission line 111 in a state before laminating an insulating layer, which is a part of the transmission line 111. These cross-sections are taken at positions where there are no interlayer connection conductors.

[0127] 17 , a transmission line 111 has a reference ground conductor layer 21 formed on the top surface of the insulator layer 11, a side ground conductor layer 22B formed on the top surface of the insulator layer 14, and a side ground conductor layer 22A formed on the top surface of the insulator layer 12. In addition, a signal line conductor layer 23 is formed on the bottom surface of the insulator layer 13. The reference ground conductor layer 21 and the side ground conductor layers 22A and 22B are electrically connected via interlayer connection conductors not shown.

[0128] The transmission line 111 according to this embodiment and the transmission line 110 shown in FIG. 16 are different in the shapes of the side ground conductor layers 22A present on the outer layer in the stacking direction (Z direction) and the side ground conductor layers 22B present on the inner layer.

[0129] In the transmission line 111, an end (inner end) EB of the side ground conductor layer 22B located on an inner layer in the stacking direction (Z direction) on the side of the recess RC is farther from the center of the recess RC than an end (inner end) EA of the side ground conductor layer 22A located on an outer layer on the side of the recess RC. This structure results in a region where the side ground conductor layer 22A and the side ground conductor layer 22B overlap and a region where the side ground conductor layer 22B does not overlap (where the side ground conductor layer 22B is absent) when viewed in the stacking direction (Z direction).

[0130] The region where the side ground conductor layer 22B does not overlap is more likely to be recessed than the region where the side ground conductor layer 22A and the side ground conductor layer 22B overlap, so that when forming the recess RC, the region where the side ground conductor layer 22B does not overlap is recessed more than the region where the side ground conductor layer 22A and the side ground conductor layer 22B overlap.

[0131] In the example shown in the lower part of FIG. 17, the inner end of the outer ground conductor layer 22A is deformed to conform to the recessed shape of the recess RC.

[0132] 18 is a cross-sectional view showing the relationship between the transmission line 111 and a nearby object 210. The object 210 is made of a conductor or a dielectric. The distance SO between the signal line conductor layer 23 and the object 210 increases in accordance with the recess distance of the recess RC.

[0133] According to this embodiment, the separation distance SG between the inner end of the outer side ground conductor layer 22A and the signal line conductor layer 23 can be relatively narrowed, while the gap SO between the signal line conductor layer 23 and the object 210 can be increased. This ensures isolation between the transmission line 111 and the object 210. Furthermore, the proportion of the air space between the signal line conductor layer 23 and the object 210 can be increased, effectively suppressing dielectric loss.

[0134] Twelfth Embodiment In a twelfth embodiment, a transmission line having outer side ground conductor layers with a different shape from that of the example shown in the eleventh embodiment will be illustrated.

[0135] FIG. 19 is a cross-sectional view of a transmission line 112 according to the twelfth embodiment.

[0136] 19 , a main ground conductor layer 21 is formed on the top surface of the insulator layer 11, and a side ground conductor layer 22B is formed on the top surface of the insulator layer 14. Furthermore, a side ground conductor layer 22A and a signal line conductor layer 23 are formed on the bottom surface of the insulator layer 13. The main ground conductor layer 21 and the side ground conductor layers 22A and 22B are electrically connected via interlayer connection conductors not shown.

[0137] 17 , the transmission line 112 has a side ground conductor layer 22A that is present on the outer layer in the stacking direction partially exposed in the hollow space HS. In other words, the inner end of the outer layer side ground conductor layer 22A protrudes into the hollow space HS.

[0138] According to this embodiment, the area of ​​the side ground conductor layer 22A at the start of the recess RC is relatively increased, stabilizing the shape of the recess RC. This allows the space of the hollow portion HS to be increased while maintaining a predetermined distance SG between the inner end of the outer side ground conductor layer 22A and the signal line conductor layer 23. This allows for the construction of a transmission line with low dielectric loss.

[0139] Thirteenth Embodiment In a thirteenth embodiment, a transmission line in which the thickness of a side ground conductor layer present in an inner layer is different from that of the examples shown so far will be illustrated.

[0140] 20A is a cross-sectional view of a transmission line 113A according to the thirteenth embodiment, and FIG. 20B is a cross-sectional view of a transmission line 113B according to the thirteenth embodiment. In the transmission line 113A, the thickness of the inner side ground conductor layer 22B is greater than the thickness of the outer side ground conductor layer 22A. In the transmission line 113B, the thickness of the inner side ground conductor layer 22B is less than the thickness of the outer side ground conductor layer 22A.

[0141] By determining the thickness of the inner ground conductor layer 22B relative to the thickness of the outer ground conductor layer 22A, the width RCW of the recess RC and the recess amount of the recess RC can be set.

[0142] When the thickness of the inner ground conductor layer 22B is greater than the thickness of the outer ground conductor layer 22A, as in the transmission line 113A, the slope from the inner end EB of the inner ground conductor layer 22B on the recess RC side to the inner end EA of the outer ground conductor layer 22A becomes steeper. This allows the recess amount of the recess RC to be increased and the width RCW of the recess RC to be narrowed.

[0143] On the other hand, when the thickness of the inner ground conductor layer 22B is thinner than the thickness of the outer ground conductor layer 22A, as in the transmission line 113B, the slope from the inner end EB of the inner ground conductor layer 22B on the recess RC side to the inner end EA of the outer ground conductor layer 22A becomes gentler, which allows the width RCW of the recess RC to be increased.

[0144] In this way, by determining the thickness of the inner ground conductor layer 22B relative to the thickness of the outer ground conductor layer 22A, the width R of the recessed portion RC, the recess amount of the recessed portion RC, and the width R of the recessed portion RC can be set. This makes it easier to optimize the high-frequency characteristics of the transmission line while ensuring isolation from nearby objects.

[0145] Fourteenth Embodiment In a fourteenth embodiment, a transmission line having a plurality of inner side ground conductor layers will be exemplified.

[0146] 21A is a cross-sectional view of a transmission line 114A according to the fourteenth embodiment, and Fig. 21B is a cross-sectional view of a transmission line 114B according to the fourteenth embodiment. Both the transmission line 114A and the transmission line 114B include an outer ground conductor layer 22A and inner ground conductor layers 22B and 22C.

[0147] In the transmission line 114A, the inner ends EB of the inner ground conductor layers 22B and 22C are aligned, whereas in the transmission line 114B, the inner end EB of the inner ground conductor layer 22B is different from the inner end EC of the inner ground conductor layer 22C.

[0148] When the inner ends EB of the inner-layer side ground conductor layers 22B, 22C are aligned as in the transmission line 114A, the slope from the inner ends EB on the recessed portion RC side of the inner-layer side ground conductor layers 22B, 22C to the inner end EA of the outer-layer side ground conductor layer 22A can be made steeper, as in the example shown in FIG. 20A .

[0149] On the other hand, when the inner end EB of the inner ground conductor layer 22B and the inner end EC of the inner ground conductor layer 22C do not coincide with each other as in the transmission line 114B, the slope of the recess RC at the beginning of the recess becomes gentler.

[0150] In this way, by determining the positions of the inner ends of the multiple inner ground conductor layers 22B and 22C, it becomes easier to optimize the high-frequency characteristics of the transmission line while ensuring isolation from nearby objects.

[0151] Fifteenth Embodiment In a fifteenth embodiment, unlike the transmission lines described so far, a transmission line including a support portion that supports a signal line conductor layer between the signal line conductor layer and the reference ground conductor layer will be illustrated.

[0152] 22 is a cross-sectional view of a transmission line 115A according to the fifteenth embodiment. The cross-sectional position corresponds to the position Y1-Y1 of the transmission line shown in FIG. 1A in the first embodiment.

[0153] 22 , a reference ground conductor layer 21 is formed on the upper surface of the insulator layer 11, and a signal line conductor layer 23 and a side ground conductor layer 22 are formed on the lower surface of the insulator layer 13. The reference ground conductor layer 21 and the side ground conductor layer 22 are electrically connected to each other via the interlayer connection conductor 4.

[0154] A signal line conductor layer support portion 12S is formed between the signal line conductor layer 23 and the reference ground conductor layer 21. The signal line conductor layer support portion 12S is an insulating layer that is aligned along the extension direction of the signal line conductor layer 23 and supports the recessed portion RC of the signal line conductor layer 23 within the hollow portion HS.

[0155] During press working when the insulator layer 13 is laminated on the laminate of the insulator layers 11 and 12, the insulator layer 13 is recessed up to the position of the opening in the insulator layer 12. The amount of this recess is stabilized by the support of the signal line conductor layer support portion 12S.

[0156] The recess amount of the recessed portion RC may be determined by previously processing the signal line conductor layer support portion 12S to be thinner than other portions of the insulator layer 12. Furthermore, the signal line conductor layer support portion 12S may also be deformed during the press working to determine the recess amount of the recessed portion RC.

[0157] 23 is a cross-sectional view of another transmission line 115B according to the fifteenth preferred embodiment. In the transmission line 115B, a reference ground conductor layer 21 is formed on the top surface of the insulator layer 11, a side ground conductor layer 22B is formed on the top surface of the insulator layer 14, a side ground conductor layer 22A is formed on the top surface of the insulator layer 12, and a signal line conductor layer 23 is formed on the bottom surface of the insulator layer 13.

[0158] A signal line conductor layer support portion 14S is formed between the signal line conductor layer 23 and the reference ground conductor layer 21. This signal line conductor layer support portion 14S is a part of the insulator layer 14. The signal line conductor layer support portion 14S is aligned along the extension direction of the signal line conductor layer 23 and supports the signal line conductor layer 23 at the recess portion RC within the hollow portion HS.

[0159] As in this transmission line 115B, the number of the insulating layers 14, 12 on which the side ground conductor layers 22A, 22B are formed may be different from the number of the signal line conductor layer supporting portions 14S.

[0160] According to the fifteenth embodiment, the signal line conductor layer 23 is supported by the signal line conductor layer supports 12S, 14S, which makes it easy to stabilize the distance between the signal line conductor layer 23 and the reference ground conductor layer 21 during processing. Furthermore, changes in capacitance between the signal line conductor layer 23 and the reference ground conductor layer 21 due to deformation of the entire transmission line can be suppressed.

[0161] In the example shown in FIG. 22 , the signal line conductor layer 23 protrudes in the width direction beyond the signal line conductor layer support portion 12S, so that the electric field concentration portion at the end of the signal line conductor layer 23 is exposed to the hollow portion HS, which has a low dielectric constant and a low dielectric dissipation factor, and this effectively suppresses dielectric loss.

[0162] Sixteenth Embodiment In a sixteenth embodiment, a transmission line in which a signal line conductor layer is formed on an insulating layer in a structure different from the examples shown so far will be illustrated.

[0163] The lower part of Fig. 24 is a cross-sectional view of the transmission line 116 according to the sixteenth embodiment. The upper part of Fig. 24 is a cross-sectional view of the transmission line 116 in a state before laminating an insulating layer, which is a part of the transmission line 116. These cross-sections are taken at positions where there are no interlayer connection conductors.

[0164] 24 , a transmission line 116 has a reference ground conductor layer 21 formed on the top surface of the insulator layer 11, a side ground conductor layer 22B formed on the top surface of the insulator layer 14, and a side ground conductor layer 22A and a signal line conductor layer 23 formed on the top surface of the insulator layer 13. An insulator layer 12 is laminated between the insulator layer 13 and the insulator layer 14.

[0165] The signal line conductor layer 23 is located outside the hollow portion HS and is covered with an insulating layer 17. The side ground conductor layer 22A is also covered with an insulating layer 17.

[0166] In this embodiment, the insulator layer 17 is a covering layer that covers the signal line conductor layer 23. The insulator layer 17 is, for example, a solder resist film.

[0167] The insulator layer 13 on which no conductor layer is formed may be an insulator layer made of a different material from the insulator layers 11, 14, and 12. For example, the insulator layers 11, 14, and 12 are made of LCP, and the insulator layer 13 is made of LCP with a lower dielectric constant.

[0168] According to this embodiment, the signal line conductor layer 23 is not exposed in the hollow space HS, thereby protecting the signal line. In addition, the distance between the signal line conductor layer 23 and the main ground conductor layer 21 is increased, thereby reducing parasitic capacitance.

[0169] Seventeenth Embodiment In the seventeenth embodiment, a transmission line in which a plurality of signal line conductor layers are arranged in parallel will be illustrated.

[0170] 25 is a cross-sectional view of a transmission line 117 according to the seventeenth embodiment. The cross-sectional position corresponds to the position Y1-Y1 of the transmission line shown in FIG.

[0171] 25 , a main ground conductor layer 21 is formed on the upper surface of the insulator layer 11, and signal line conductor layers 23A and 23B and a side ground conductor layer 22 are formed on the lower surface of the insulator layer 13. The main ground conductor layer 21 and the side ground conductor layer 22 are electrically connected to each other via the interlayer connection conductor 4.

[0172] The signal line conductor layers 23A and 23B are used as, for example, differential lines, in which case the main ground conductor layer 21 and the side ground conductor layer 22 function as shielding ground conductors.

[0173] The signal line conductor layer may also be configured as a plurality of separate signal line conductor layers, in which case each signal line conductor layer acts as a signal line of the microstrip line.

[0174] According to the seventeenth embodiment, even though one hollow portion HS is used, the recessed portion RC can improve the characteristics of a plurality of signal lines.

[0175] Eighteenth Embodiment In the eighteenth embodiment, an example in which the present invention is applied to a transmission line having a coplanar waveguide structure will be described.

[0176] 26 is a cross-sectional view of a transmission line 118 according to the eighteenth embodiment, taken along a plane perpendicular to the direction in which the signal line conductor layer 23 extends.

[0177] An insulator layer 12 having an opening is laminated on top of an insulator layer 11, and an insulator layer 13 is laminated on top of this insulator layer 12. The opening forms a hollow portion HS. A recess portion RC is formed in the insulator layer 13 at the hollow portion HS.

[0178] A signal line conductor layer 23 and a side ground conductor layer 22 are formed on the lower surface of the insulator layer 13. The signal line conductor layer 23 is disposed in the recessed portion RC. In this example, the signal line conductor layer 23 is exposed in the hollow portion HS. Therefore, the signal line conductor layer 23 is located lower than the side ground conductor layer 22 in the Z direction.

[0179] In this way, in the case of a coplanar waveguide that does not have the reference ground conductor layer 21, the electric field is more concentrated below the laminate when the insulator layer 11, which is a dielectric, is brought closer to the signal line conductor layer 23, thereby reducing the effect of a conductive or dielectric object being close to the top surface of the laminate.

[0180] Furthermore, when the reference ground conductor layer is not provided, a recess that is recessed toward the hollow portion HS may be provided in the insulator layer 11 as shown in Fig. 13. This improves the symmetry of the top and bottom of the transmission line, thereby reducing warping of the transmission line during processing. Furthermore, since the mechanical stress on each part of the transmission line is uniform, damage to the transmission line due to mechanical stress is suppressed.

[0181] In this way, the present invention can also be applied to a coplanar waveguide.

[0182] According to the thirteenth embodiment, each conductor layer is patterned in only one layer, and no interlayer connection conductor is required, so processing is easy.

[0183] Nineteenth Embodiment In the nineteenth embodiment, a transmission line having a hollow portion with a different shape from the examples shown so far will be illustrated.

[0184] 27(A), 27(B), 27(C), 27(D), 27(E), 27(F), 27(G), and 27(H) are plan views of the transmission line according to the nineteenth embodiment. These plan views are views looking downward from the signal line conductor layer 23 and the side ground conductor layer 22. In other words, these plan views are views in a state where only the uppermost insulating layer 13 has been removed.

[0185] In the example shown in FIG. 4A etc., the hollow portion is cylindrical, but the present invention is not limited to this.

[0186] For example, in the example shown in Figure 27(A), the opening 12H, which becomes a hollow portion by laminating an insulating layer on the surface, has a rectangular cylindrical shape. In the example shown in Figure 27(B), the opening 12H has a hexagonal cylindrical shape. As such, the shape of the opening 12H can be selected from a variety of shapes depending on the processing method. Because the line segment is in contact with the signal line conductor layer 23, the signal line conductor layer 23 can be used to process the opening 13H, which improves the processability of the opening 13H.

[0187] 27C also has an opening 12H in the shape of a hexagonal cylinder, but the opening 12H reaches the side ground conductor layer 22. With this structure, the side ground conductor layer 22 can also be used to process the opening 12H, and the width of the hollow portion is determined by the position of the side ground conductor layer 22, thereby improving the dimensional accuracy of the hollow portion.

[0188] In the example shown in Fig. 27(D), the opening 12H has a rounded rectangular cylindrical shape, and in the example shown in Fig. 27(E), the opening 12H has an elliptical cylindrical shape or an elongated cylindrical shape.

[0189] In the example shown in Fig. 27(F), the opening 12H has a shape in which a plurality of cylinders are stacked and connected. In the example shown in Fig. 27(G), the opening 12H has a shape in which a plurality of elliptical cylinders are stacked. With such a structure, the opening 12H is a combination of cylinders, which makes it easy to process with a laser.

[0190] 27(H), the opening 12H is triangular tubular, and its left-right positions relative to the extension direction of the signal line conductor layer 23 are alternately arranged along the extension direction of the signal line conductor layer 23. That is, the hollow portions are arranged at a plurality of mutually separated positions at a predetermined pitch, and the positions of the hollow portions are shifted in the extension direction by half or approximately half of the pitch on the left and right sides in the extension direction of the signal line conductor layer 23. With this structure, the volume ratio of the hollow portions in the signal propagation direction of the transmission line is stable. This stabilizes the characteristic impedance of the transmission line in the signal propagation direction of the transmission line, thereby suppressing reflection loss.

[0191] Twentieth Embodiment In a twentieth embodiment, a transmission line having a signal line conductor layer with a different thickness from that of the transmission line shown in the first embodiment will be illustrated.

[0192] Fig. 28(A) is a cross-sectional view of each layer before lamination, showing the configuration of a transmission line according to the twentieth embodiment. Fig. 28(B) is a cross-sectional view of a transmission line 120 according to the twentieth embodiment. Both Fig. 28(A) and Fig. 28(B) are cross-sectional views taken along a line corresponding to X-X in Fig. 1(A) in the first embodiment.

[0193] 29(A), 29(B), 29(C), and 29(D) are cross-sectional views in the Y direction of the transmission line 120. These cross-sectional views are taken at positions corresponding to those in FIGS. 2(A), 2(B), 2(C), and 2(D) in the first embodiment.

[0194] The basic structure of the transmission line 120 of the twentieth embodiment is similar to that of the transmission line 101 described in the first embodiment. One difference is that, before lamination, the signal line conductor layer 23 is attached to the upper surface of the insulator layer 12, rather than to the lower surface of the insulator layer 13. Another major difference between the transmission line 120 and the transmission line 101 is the relative relationship between the thickness of the signal line conductor layer 23 and the thicknesses of the side ground conductor layer 22 and the reference ground conductor layer 21.

[0195] The signal line conductor layer 23 of the transmission line 120 is thicker than the side ground conductor layer 22. The signal line conductor layer 23 of the transmission line 120 is also thicker than the reference ground conductor layer 21.

[0196] According to this embodiment, while the product thickness is the same, the thicker signal line conductor layer 23 reduces conductor loss and can be used as a waveguide with low transmission loss. Furthermore, the thicker signal line conductor layer effectively suppresses deformation of the signal line conductor layer portion, making it easier to obtain a waveguide with stable electrical characteristics.

[0197] Twenty-First Embodiment In the twenty-first embodiment, a transmission line having a signal line conductor layer with a different thickness from that of the transmission line shown in the first embodiment will be illustrated.

[0198] 30A, 30B, and 30C are cross-sectional views of a transmission line 121 according to the 21st embodiment and during its manufacture. Fig. 30D is a cross-sectional view of the transmission line 121. All of these are cross-sectional views taken along the line Y2-Y2 in Fig. 1A.

[0199] The transmission line 121 includes three insulator layers 11, 12, and 13. Various conductor layers are bonded to one surface of the insulator layers 11, 12, and 13. In the transmission line 116, not only is the signal line conductor layer 23 thicker than the side ground conductor layer 22, but the reference ground conductor layer 21 is also thicker than the side ground conductor layer 22. In other words, the side ground conductor layer 22 is thinner than the signal line conductor layer 23 and the reference ground conductor layer 21.

[0200] 30A , a conductor layer is first formed on the insulator layer 11 to form the reference ground conductor layer 21. A conductor layer is then formed on the insulator layer 12 to form the side ground conductor layer 22. A conductor layer is then formed on the insulator layer 13 to form the signal line conductor layer 23.

[0201] Next, as shown in FIG. 30B , the insulator layer 12 having the side ground conductor layer 22 formed thereon is stacked on the insulator layer 11 having the main ground conductor layer 21 formed thereon, and the bonding surfaces are joined by applying pressure and heat.

[0202] Thereafter, as shown in FIG. 30C, an opening 12H is formed in the insulating layer 12.

[0203] Thereafter, as shown in FIG. 30D, the insulator layer 13 on which the signal line conductor layer 23 is formed is laminated on the insulator layer 12, and the bonding surfaces are bonded by applying pressure and heat.

[0204] The opening 12H formed in the insulator layer 12 forms a hollow portion HS in the laminated state of the insulator layers 11, 12, and 13 on which various conductor layers are formed. The laminate including the insulator layers 11, 12, and 13, the reference ground conductor layer 21, the signal line conductor layer 23, and the side ground conductor layer 22 has a recessed portion RC that is recessed toward the hollow portion HS.

[0205] The recessed portion RC of the insulator layer 13 is formed, for example, by pressing the insulator layers 11, 12, and 13 with a mold having a protrusion facing the portion where the recess is to be formed, during or after laminating the insulator layers 11, 12, and 13 to form a laminate. Alternatively, the recessed portion RC may be formed by pressing the entire laminate through a cushioned sheet during or after laminating the insulator layers 11, 12, and 13 to form a laminate. The recessed portion RC may also be formed by pressing the insulator layer 13 before lamination. Alternatively, the recessed portion RC may be formed by pressurizing and heating the insulator layers 11, 12, and 13 to form a laminate, and then cooling to room temperature causes the hollow portion HS to shrink, thereby forming the recessed portion RC.

[0206] In this way, the transmission line 121 is configured in which the distance in the thickness direction between the main ground conductor layer and the signal line conductor layer is narrower than the distance in the thickness direction between the main ground conductor layer and the side ground conductor layer.

[0207] According to this embodiment, a transmission line with a thin overall thickness can be obtained due to the thin thickness of the side ground conductor layer 22. Furthermore, by ensuring the thickness of the reference ground conductor layer 21, which has a high current density, electrical characteristics such as conductor loss can be maintained.

[0208] The first main surface of each of the main ground conductor layers 21, the side ground conductor layers 22, and the signal line conductor layers 23 has a different surface roughness from that of the second main surface, which is the surface opposite to the first main surface. In Fig. 30, a surface with a relatively rough surface roughness (rough surface) is represented as a surface with a simple array of protrusions.

[0209] The rough surface of the reference ground conductor layer 21 is bonded to the insulator layer 11. The rough surface of the side ground conductor layer 22 is bonded to the insulator layer 12. The rough surface of the signal line conductor layer 23 is bonded to the insulator layer 13. With this structure, each conductor layer has a roughened surface and a non-roughened surface. The effects of the roughened / non-roughened surface structure of each conductor layer are as follows:

[0210] The bonding strength of the main ground conductor layer 21 to the insulator layer 11, the bonding strength of the side ground conductor layer 22 to the insulator layer 12, and the bonding strength of the signal line conductor layer 23 to the insulator layer 13 are all high. Furthermore, the surface of the signal line conductor layer 23 opposite to the bonding surface to the insulator layer 13 (the surface facing the main ground conductor layer 21) is non-rough, so high-frequency signal transmission loss due to skin resistance on the surface of this signal line conductor layer 23 is small. Furthermore, the surface of the side ground conductor layer 22 not facing the main ground conductor layer 21 is non-rough, so high-frequency signal transmission loss due to skin resistance on the surface of this side ground conductor layer 22 is small. Furthermore, the surface of the main ground conductor layer 21 facing the signal line conductor layer 23 is non-rough, so high-frequency signal transmission loss due to skin resistance on the surface of the main ground conductor layer 21 is small.

[0211] Twenty-Second Embodiment In the twenty-second embodiment, a transmission line including a plurality of parallel signal line conductor layers and characterized by the periodic arrangement of the hollow portions in relation to these signal line conductor layers will be exemplified.

[0212] 31A is a partial plan view of the transmission line 122A, FIG. 31B is a partial plan view of the transmission line 122B, and FIG. 31C is a partial plan view of the transmission line 122C.

[0213] Similar to the transmission lines described in the first embodiment and the like, the transmission lines 122A, 122B, and 122C include a main ground conductor layer, a signal line conductor layer 23 that faces the main ground conductor layer in the thickness direction of the insulator layers, and side ground conductor layers 22 that face the main ground conductor layer in the thickness direction of the insulator layers and are disposed on the left and right sides along the extension direction of the signal line conductor layer 23. That is, when viewed in the stacking direction of the multiple insulator layers (Z direction), the signal line conductor layer 23 overlaps the main ground conductor layer. The transmission lines 122A, 122B, and 122C also include side ground conductor layers 22 that are located on the sides of the signal line conductor layer 23 and along the extension direction of the signal line conductor layer 23 when viewed in the stacking direction of the multiple insulator layers (Z direction).

[0214] The transmission lines 122A, 122B, and 122C have a hollow portion HS in an insulator layer that is present between the signal line conductor layer 23 and the reference ground conductor layer, among a plurality of insulator layers.

[0215] The transmission lines 122A, 122B, and 122C have three signal line conductor layers 23 arranged in parallel. The hollow spaces HS are periodically arranged along the three signal line conductor layers 23.

[0216] The hollow portions HS are rectangular with their long sides in the extending direction (X direction) of the signal line conductor layer 23, and have rounded corners. The hollow portions HS are arranged at equal intervals in the X direction.

[0217] In the example of the transmission line 122A, the hollow portions HS are arranged at the same position in the parallel direction (Y direction) of the signal line conductor layers 23.

[0218] On the other hand, in the example of the transmission line 122B, the hollow portions HS adjacent to each other in the parallel direction (Y direction) of the signal line conductor layer 23 are arranged at different positions (two positions) in the extension direction (X direction) of the signal line conductor layer 23.

[0219] Also in the example of the transmission line 122C, the hollow portions HS adjacent to each other in the parallel direction (Y direction) of the signal line conductor layers 23 are arranged at different positions, but the position of the hollow portion HS is different for each signal line conductor layer 23. In other words, there are three possible positions for the hollow portion HS.

[0220] In a structure like the transmission line 122A in which a plurality of signal line conductor layers 23 are arranged in parallel to one another and hollow portions HS are present periodically along the extension direction (X direction) of the plurality of signal line conductor layers 23 and at the same position in the parallel direction (Y direction) of the plurality of signal line conductor layers 23, the portions of the insulator layer that are not hollow portions HS are aligned at the same positions, so that the strength against stress in the parallel direction (Y direction) of the plurality of signal line conductor layers 23 is high.

[0221] On the other hand, in a structure such as transmission lines 122B and 122C in which a plurality of signal line conductor layers 23 are arranged in parallel with each other and hollow portions HS are present periodically along the extension direction (X direction) of the plurality of signal line conductor layers 23 and at different positions in the parallel direction (Y direction) of the plurality of signal line conductor layers 23, the locations where the hollow portions HS are formed and the locations where the hollow portions HS are not formed are offset in the extension direction (X direction) for each signal line conductor layer 23, so that unnecessary coupling of the electromagnetic field between adjacent signal line conductor layers is small and isolation between the transmission paths is high.

[0222] Furthermore, when the position of the hollow portion HS differs for each signal line conductor layer 23, as in the transmission line 122C, the hollow-formed portions and non-hollow-formed portions are misaligned in the three transmission lines, so that isolation is high not only between adjacent signal line conductor layers but also between signal line conductor layers beyond the adjacent signal line conductor layers.

[0223] Twenty-Third Embodiment In the twenty-third embodiment, an electronic device according to the present invention will be illustrated.

[0224] 32 is a cross-sectional view of an electronic device 401 according to the twenty-third embodiment. The electronic device 401 includes substrates 201A and 201B, a battery 202, a transmission line 101, a housing 203, and the like.

[0225] A mounting component 9 serving as a connector is mounted on the transmission line 101. This connector is connected to each of the substrates 201A and 201B. A battery 202 is disposed between the substrates 201A and 201B, and the transmission line 101 is disposed between the outer surface of the battery 202 and the inner surface of the housing 203. An electronic circuit connected to the transmission line 101 is configured on the substrates 201A and 201B. The battery 202 and the housing 203 are made of a conductor, a dielectric, or a composite thereof.

[0226] The positional relationship between the transmission line 101 and nearby objects such as the battery 202 and the housing 203 is important. That is, it is preferable to determine the orientation of the transmission line 101 so that the amount of change in the electrical characteristics of the transmission line 101 is small relative to the amount of change in the proximity distance of the object. For example, when comparing the side of the housing 203 made of metal with the side of the battery 202 containing a large amount of conductive material, if the electrical characteristics of the transmission line 101 are more strongly affected by the portion of the housing 203 close to the transmission line 101, it is preferable to position the transmission line 101 so that the reference ground conductor layer 21 (see FIG. 1 ) faces the inner surface of the housing 203. Furthermore, in this orientation, it is even more preferable to provide a gap between the signal line conductor layer 23 (see FIG. 1 ) of the transmission line 101 and the battery 202 to reduce the influence of the battery 202.

[0227] Conversely, if the electrical characteristics of the transmission line are more strongly affected by the battery 202, it is better to arrange the transmission line 101 so that the reference ground conductor layer 21 faces the battery 202. In this arrangement, it is even better to provide a gap between the signal line conductor layer 23 of the transmission line 101 and the housing 203 to reduce the influence of the housing 203.

[0228] In the case of a transmission line that does not have the reference ground conductor layer 21, it is preferable to arrange the transmission line so that the surface on which the recessed portion RC is present faces the object side that is strongly affected.

[0229] In the example shown in FIG. 32, the substrates 201A and 201B are connected to both ends of the transmission line via connectors, but it is also possible to use a structure in which one end of the transmission line is connected to the antenna.

[0230] The transmission line 101 transmits a high-frequency signal between the circuit configured on the substrate 201A and the circuit configured on the substrate 201B. This high-frequency signal is, for example, a signal in the 1 GHz to 1 THz band.

[0231] Various embodiments of the present invention have been presented so far, but these are all examples and are not intended to limit the scope of the present invention. Various omissions, substitutions, and modifications can be made to the embodiments of the present invention without departing from the spirit of the invention. Embodiments with such omissions, substitutions, and modifications are included within the scope and spirit of the present invention, and are also included in the scope of the invention and its equivalents as set forth in the claims of this application.

[0232] For example, the insulating layers 11, 12, 13, 14, 15, 16 are preferably made of a resin material with a low dielectric constant and dielectric loss tangent, such as LCP or PTFE, in order to reduce dielectric loss.

[0233] 6A, 6B, and 6C show examples in which the mounted component 9 is provided as a connector on the transmission line, but the mounted component is not limited to a connector. For example, it may be a semiconductor element or a circuit element.

[0234] Furthermore, although each embodiment has exemplified a transmission line having a single recessed portion RC, a transmission line may be configured by providing multiple recessed portions RC in a parallel relationship (running side by side) and having a signal line conductor layer in each recessed portion.

[0235] Furthermore, lines other than the transmission line of the present invention may be arranged in the same substrate formed by laminating the insulating layers 11, 12, 13, etc.

[0236] In addition, although each embodiment has exemplified a transmission line having a recessed portion RC on one side of a laminate of multiple insulator layers, a transmission line may also be configured by providing recessed portions RC on both sides of the laminate and having a signal line conductor layer in each recessed portion.

[0237] The signal line conductor layer may have a shape that is curved in the plane direction of the plurality of insulating layers 11, 12, 13, etc.

[0238] The entire transmission line may also have a curved shape in the lamination direction (thickness direction) of the plurality of insulating layers 11, 12, 13, etc.

[0239] Furthermore, the signal propagating through the transmission line may be an analog signal or a digital signal.

[0240] In addition, in each embodiment, an example has been shown in which an opening 12H or the like is formed in the insulator layer to form the hollow portion HS. The opening 12H or the like may be formed by processing the insulator layer, or the insulator layer having the opening may be formed during the insulator layer formation stage. For example, a porous insulator layer may be formed, and some of the pores may be used as the opening. That is, the hollow portion HS may be formed in the portion of the insulator layer overlapping the opening, and this hollow portion HS may provide a recess portion RC in the laminate.

[0241] EA...Inner end of outer layer side ground conductor layer EB...Inner end of inner layer side ground conductor layer HS...Hollow portion SG...Separation distance RC...Recessed portion RCW...Recessed portion width 4...Interlayer connection conductor 9...Mounted component 9G...Ground terminal 9S...Signal terminal 11, 12, 13, 14, 15, 16, 17...Insulator layer 12H, 13H, 14H...Opening 12S, 14S...Signal line conductor layer support portion 21...Reference ground conductor layer 22, 22A, 22B, 22C...Side ground conductor layer 22E...Ground electrode 23, 23A, 23B...Signal line conductor layer 23E, 23E1, 23E2...Signal electrodes 51, 52...Adhesive layer 101, 102, 103, 104, 105, 106, 107, 108, 109A, 109B, 110, 111, 112, 113A, 113B, 114A, 114B, 115A, 115B, 116, 117, 118, 120, 121, 122A, 122B, 122C... transmission line 201A, 201B... substrate 202... battery 203... housing 210... object 211... conductor layer 212... dielectric layer 401... electronic device

Claims

1. A transmission line comprising a laminate comprising a plurality of stacked insulator layers and conductor layers formed by bonding to surfaces of all or some of the insulator layers among the plurality of insulator layers, wherein the conductor layers include a reference ground conductor layer and a signal line conductor layer overlapping the reference ground conductor layer when the laminate is viewed in the stacking direction, wherein the laminate has a recessed portion recessed in the stacking direction, and wherein the signal line conductor layer is positioned so as to overlap the recessed portion when the laminate is viewed in the stacking direction.

2. The transmission line according to claim 1, further comprising: a side ground conductor layer that is located on a side of the signal line conductor layer and along the extending direction of the signal line conductor layer when the laminate is viewed in the stacking direction.

3. The transmission line according to claim 2, wherein at least a portion of the side ground conductor layer is formed on one of the plurality of insulator layers on which the signal line conductor layer is formed.

4. The transmission line according to claim 2 or 3, wherein at least a portion of the side ground conductor layer is disposed at a position farther from the recess in the stacking direction than the signal line conductor layer.

5. The transmission line according to any one of claims 2 to 4, wherein a portion of the signal line conductor layer or at least a portion of the side ground conductor layer is embedded between the plurality of laminated insulator layers.

6. The transmission line according to any one of claims 2 to 5, wherein there are a plurality of the side ground conductor layers, and among the plurality of side ground conductor layers, an end of a side ground conductor layer that is an inner layer and that is located on the side of the recess is farther away from the center of the recess than an end of a side ground conductor layer that is an outer layer in the stacking direction and that is located on the side of the recess.

7. The transmission line according to claim 6, wherein there are a plurality of side ground conductor layers present in the inner layer, and ends of the plurality of side ground conductor layers present in the inner layer on the side of the recessed portion are not aligned when viewed in the stacking direction.

8. The transmission line according to claim 6, wherein the thickness of the side ground conductor layer existing in the outer layer in the stacking direction is different from the thickness of the side ground conductor layer existing in the inner layer.

9. A transmission line according to any one of claims 2 to 8, wherein a hollow portion is formed inside the laminate, and a portion of the side ground conductor layer that is present in an outer layer in the stacking direction is exposed to the hollow portion.

10. A transmission line according to any one of claims 1 to 8, wherein a hollow portion is formed inside the laminate, and the recessed portion has a shape in which some of the plurality of insulating layers are recessed toward the hollow portion.

11. The transmission line according to claim 10, wherein some of the plurality of insulating layers are insulating layers that support the recessed portion inside the hollow portion.

12. The transmission line according to claim 10 or 11, wherein a plurality of the hollow portions are arranged discretely along the extending direction of the signal line conductor layer.

13. The transmission line according to claim 12, wherein, where λ represents the wavelength of the frequency of the transmission signal, the arrangement pitch of the hollow portions is 1 / 2λ or less, and the interval between adjacent hollow portions is 1 / 4λ or less.

14. The transmission line according to any one of claims 10 to 13, wherein at least a portion of the signal line conductor layer or a portion of the reference ground conductor layer is exposed in the hollow portion.

15. A transmission line according to any one of claims 10 to 14, wherein the plurality of insulating layers have no path through which gas passes between the hollow portion and the outside of the laminate.

16. A transmission line according to any one of claims 10 to 15, wherein the signal line conductor layer is composed of a plurality of signal line conductor layers arranged in parallel to one another, and the hollow portions are present periodically along the extension direction of the plurality of signal line conductor layers and are present at the same position in the parallel direction of the plurality of signal line conductor layers.

17. A transmission line according to any one of claims 10 to 15, wherein the signal line conductor layer is composed of a plurality of signal line conductor layers arranged in parallel to one another, and the hollow portions are present periodically along the extension direction of the plurality of signal line conductor layers and are present at different positions in the parallel direction of the plurality of signal line conductor layers.

18. A transmission line according to any one of claims 1 to 17, wherein a portion of the signal line conductor layer or at least a portion of the reference ground conductor layer is embedded between the plurality of laminated insulator layers.

19. A transmission line according to any one of claims 1 to 18, wherein the signal line conductor layer is located outside the recessed portion, and further comprising a covering layer that covers the signal line conductor layer.

20. A transmission line according to any one of claims 1 to 19, wherein the signal line conductor layer is thicker than the reference ground conductor layer.

21. A transmission line according to any one of claims 1 to 20, wherein the plurality of insulating layers include insulating layers of different materials.

22. A transmission line according to any one of claims 1 to 21, wherein the material of the plurality of insulating layers is a thermoplastic resin.

23. A transmission line according to any one of claims 1 to 22, wherein the plurality of insulating layers are laminated with a material different from that of the plurality of insulating layers therebetween.

24. An electronic device comprising the transmission line according to any one of claims 1 to 23 and an electronic circuit connected to the transmission line.

25. An electronic device comprising the transmission line according to any one of claims 1 to 23 and an object made of a conductor, a dielectric, or a composite thereof, wherein the recessed portion faces the object.

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