transmission line

Abstract

To provide a transmission line which can materialize reduction of a transmission loss thereof.SOLUTION: The transmission line comprises: an element body; a signal conductor layer; and a first ground conductor layer. The element body includes a first insulator layer and a second insulator layer of a single layer. The signal conductor layer is arranged below the first insulator layer side in a vertical direction of the element body. The first ground conductor layer is arranged above the first ground conductor layer in the vertical direction of the element body from the ground conductor layer. In the first ground conductor layer, a first vacancy hole is arranged for penetrating the first ground conductor layer to the vertical direction of the element body. In the second insulation layer, a second vacancy hole for penetrating the second insulation layer to the vertical direction of the element body is arranged. At least a part of the first vacancy hole is overlapped with the signal conductor layer in view of the vertical direction of the element. A left portion of a surface where the first vacancy hole is formed includes a portion positioned in the left in a longitudinal direction from a surface where the second vacancy hole is formed in a cross section orthogonal to a cross direction of the element body.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a transmission line through which a high-frequency signal is transmitted. [Background technology]

[0002] A known example of a conventional invention relating to a transmission line is the signal transmission line described in Patent Document 1. This signal transmission line includes a laminate, a signal conductor, and a ground conductor. The laminate has a structure in which multiple resin layers are stacked. The signal conductor and the ground conductor overlap when viewed in the stacking direction of the laminate. A hollow portion is provided between the signal conductor and the ground conductor.

[0003] In such a signal transmission line, air with a low dielectric constant exists in the hollow portion. The hollow portion is located near the signal conductor. This reduces the dielectric constant around the signal conductor. As a result, the signal transmission line suppresses the occurrence of dielectric loss in the high-frequency signal transmitted through the signal conductor, thereby reducing the transmission loss of the signal transmission line. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6489265 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, in the field of the signal transmission line described in Patent Document 1, there is a demand for further reduction in transmission loss in the signal transmission line.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a transmission line that can reduce transmission loss in the transmission line. [Means for solving the problem]

[0007] A transmission line according to one aspect of the present invention comprises: an element body having a main surface with a normal extending in the vertical direction of the element body, the element body including a single first insulator layer and a single second insulator layer; a signal conductor layer provided below the first insulator layer in the element body in the vertical direction of the element body; a first ground conductor layer provided above the first insulator layer in the element body in the vertical direction of the element body; It is equipped with the first insulator layer is provided with a first hole penetrating the first insulator layer in the vertical direction of the element body, the second insulator layer is provided with a second hole penetrating the second insulator layer in the vertical direction of the element body, The direction in which the signal conductor layers extend is defined as the front-rear direction of the element body, The line width direction of the signal conductor layer is defined as the left-right direction of the element body, At least a portion of the first hole overlaps with the signal conductor layer when viewed in the vertical direction of the element body, a surface of the first insulating layer on which the first voids are formed is defined as a first void-formed surface; a surface of the second insulating layer on which the second voids are formed is defined as a second void-formed surface; The left portion of the first void formation surface has a portion located to the left of the second void formation surface in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body. [Effects of the Invention]

[0008] According to the transmission line of the present invention, it is possible to reduce transmission loss. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an exploded perspective view of a transmission line 10. [Figure 2] FIG. 2 is a cross-sectional view of the transmission line 10 taken along line AA in FIG. [Figure 3] FIG. 3 is a left side view of the electronic device 1 including the transmission line 10. As shown in FIG. [Figure 4]FIG. 4 is a cross-sectional view of the transmission line 10a. [Figure 5] FIG. 5 is a cross-sectional view of the transmission line 10b. [Figure 6] FIG. 6 is a cross-sectional view of a transmission line 500 according to a comparative example. [Figure 7] FIG. 7 is a diagram showing the electric field distribution of the first model. [Figure 8] FIG. 8 is a diagram showing the electric field distribution of the second model. [Figure 9] FIG. 9 is a diagram showing the electric field distribution at the left end of the signal conductor layer 22 of the first model. [Figure 10] FIG. 10 is a diagram showing the electric field distribution at the left end of the signal conductor layer 22 of the second model. [Figure 11] FIG. 11 is a graph showing the relationship between frequency and transmission loss for the first model and the second model. [Figure 12] FIG. 12 is a cross-sectional view of the transmission line 10c. [Figure 13] FIG. 13 is a cross-sectional view of the transmission line 10d. [Figure 14] FIG. 14 is a cross-sectional view of the transmission line 10e. [Figure 15] FIG. 15 is a cross-sectional view of the transmission line 10f. [Figure 16] FIG. 16 is a cross-sectional view of the transmission line 10g. [Figure 17] FIG. 17 is a cross-sectional view of the transmission line 10h. [Figure 18] FIG. 18 is a cross-sectional view of the transmission line 10i. [Figure 19] FIG. 19 is a cross-sectional view of the transmission line 10j. [Figure 20] FIG. 20 is a cross-sectional view of the transmission line 10k. [Figure 21] FIG. 21 is a cross-sectional view of the transmission line 10l. [Figure 22] FIG. 22 is a cross-sectional view of a 10 m transmission line. [Figure 23] FIG. 23 is a cross-sectional view of the transmission line 10n. [Figure 24]FIG. 24 is a cross-sectional view of the transmission line 10o. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment) [Transmission line structure] The structure of a transmission line 10 according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is an exploded perspective view of the transmission line 10. Note that in Fig. 1, only representative interlayer connection conductors v1 and v2 among a plurality of interlayer connection conductors v1 and v2 are designated by reference numerals. Fig. 2 is a cross-sectional view of the transmission line 10 taken along line AA in Fig. 1.

[0011] In this specification, directions are defined as follows: The direction in which the normal to the main surface of the element body 12 of the transmission line 10 extends is defined as the element body up-down direction. The direction in which the signal conductor layer 22 of the transmission line 10 extends is defined as the element body front-back direction. The line width direction of the signal conductor layer 22 is defined as the element body left-right direction. The element body up-down direction, element body front-back direction, and element body left-right direction are perpendicular to each other.

[0012] Hereinafter, X is a component or member of the transmission line 10. In this specification, unless otherwise specified, each part of X is defined as follows: The front part of X means the front half of X. The rear part of X means the rear half of X. The left part of X means the left half of X. The right part of X means the right half of X. The upper part of X means the upper half of X. The lower part of X means the lower half of X. The front end of X means the front end of X. The rear end of X means the rear end of X. The left end of X means the left end of X. The right end of X means the right end of X. The upper end of X means the upper end of X. The lower end of X means the lower end of X. The front end of X means the front end of X and its vicinity. The rear end of X means the rear end of X and its vicinity. The left end of X means the left end of X and its vicinity. The right end of X means the right end of X and its vicinity. The upper end of X means the upper end of X and its vicinity. The lower end of X means the lower end of X and its vicinity.

[0013] First, the structure of a transmission line 10 will be described with reference to FIG. 1. The transmission line 10 transmits high-frequency signals. The transmission line 10 is used to electrically connect two circuits in electronic devices such as smartphones. As shown in FIG. 1, the transmission line 10 includes an element body 12, protective layers 20a and 20b, a signal conductor layer 22, a first ground conductor layer 24, a second ground conductor layer 26, a third ground conductor layer 27, signal terminals 28a and 28b, and a plurality of interlayer connection conductors v1, v2, and interlayer connection conductors v3 and v4.

[0014] The element body 12 has a plate shape. Therefore, the element body 12 has an upper main surface and a lower main surface (main surfaces). The upper and lower main surfaces (main surfaces) of the element body 12 have normals that extend in the vertical direction of the element body. The upper and lower main surfaces of the element body 12 have a rectangular shape with long sides that extend in the front-to-rear direction of the element body. Therefore, the length of the element body 12 in the front-to-rear direction of the element body is longer than the length of the element body 12 in the left-to-right direction of the element body.

[0015] As shown in FIG. 1, the element body 12 includes insulator layers 16a to 16c, 18a, and 18b. The element body 12 has a structure in which the insulator layers 16a, 18a, 16b, 18b, and 16c are stacked in this order from top to bottom in the vertical direction of the element body. The insulator layers 16a to 16c, 18a, and 18b have the same rectangular shape as the element body 12 when viewed in the vertical direction of the element body. The insulator layers 16a to 16c are flexible dielectric sheets. The insulator layers 16a to 16c are made of, for example, a thermoplastic resin. Examples of thermoplastic resin include liquid crystal polymer and PTFE (polytetrafluoroethylene). The insulator layers 16a to 16c may also be made of polyimide. The insulator layer 18a is an adhesive layer that bonds the insulator layer 16a and the insulator layer 16b together. The insulator layer 18a is a single insulator layer. The insulator layer 18a being a single layer means that the insulator layer 18a does not have a structure in which multiple insulator layers are bonded together. The insulator layer 18b is an adhesive layer that bonds the insulator layer 16b and the insulator layer 16c. The insulator layer 18b is a single insulator layer. The insulator layer 18b (second insulator layer) is provided below the insulator layer 18a (first insulator layer) in the vertical direction of the element body. In this specification, the phrase "the insulator layer 18b is provided below the insulator layer 18a in the vertical direction of the element body" refers to the following state: The insulator layer 18b is disposed below a plane (upper main surface) that passes through the upper end of the insulator layer 18a and is perpendicular to the vertical direction of the element body. In this case, the insulator layers 18a and 18b may or may not be aligned in the vertical direction of the element body. The insulator layers 18a, 18b are made of an adhesive sheet, a liquid adhesive applied by printing or the like, or a viscous bonding sheet that is attached in sheet form. The material of the insulator layers 18a, 18b is, for example, epoxy resin, fluorine-based resin, acrylic resin, etc. In this way, the material of the insulator layer 18a (first insulator layer) is different from the material of the insulator layer 16b (third insulator layer) provided below the insulator layer 18a (first insulator layer) in the vertical direction of the element body.

[0016] As shown in FIG. 1 , the signal conductor layer 22 is provided below the insulator layer 18a (first insulator layer) in the element body 12 in the vertical direction of the element body. The signal conductor layer 22 is also provided above the insulator layer 18b (second insulator layer) in the vertical direction of the element body. In this embodiment, the signal conductor layer 22 is provided on the upper main surface of the insulator layer 16b. As a result, the signal conductor layer 22 is provided within the element body 12. The signal conductor layer 22 has a linear shape. The signal conductor layer 22 extends in the front-to-rear direction of the element body. The signal conductor layer 22 is located at the center of the upper main surface of the insulator layer 16b in the left-to-right direction of the element body.

[0017] The first ground conductor layer 24 is provided on the element body 12 above the insulator layer 18a (first insulator layer) in the vertical direction of the element body. In this embodiment, the first ground conductor layer 24 is provided on the upper main surface of the insulator layer 16a. As a result, the first ground conductor layer 24 is located above the signal conductor layer 22 in the vertical direction of the element body. In this specification, the phrase "the first ground conductor layer 24 is located above the signal conductor layer 22 in the vertical direction of the element body" refers to the following state: At least a portion of the first ground conductor layer 24 is located within a region through which the signal conductor layer 22 passes when moving in a parallel direction in the element body upward. Therefore, the first ground conductor layer 24 may be located within a region through which the signal conductor layer 22 passes when moving in a parallel direction in the element body upward, or may protrude from a region through which the signal conductor layer 22 passes when moving in a parallel direction in the element body upward. In this embodiment, the first ground conductor layer 24 covers substantially the entire upper main surface of the insulator layer 16a. Therefore, the first ground conductor layer 24 protrudes from the area through which the signal conductor layer 22 passes when moving parallel to the upper direction of the element body. Furthermore, the first ground conductor layer 24 overlaps with the signal conductor layer 22 when viewed in the vertical direction of the element body.

[0018] The second ground conductor layer 26 is provided below the insulator layer 18b (second insulator layer) in the element body 12 in the vertical direction of the element body. In this embodiment, the second ground conductor layer 26 is provided on the lower main surface of the insulator layer 16c. As a result, the second ground conductor layer 26 is located below the signal conductor layer 22 in the vertical direction of the element body. In this embodiment, the second ground conductor layer 26 covers almost the entire lower main surface of the insulator layer 16c. As a result, the second ground conductor layer 26 overlaps with the signal conductor layer 22 when viewed in the vertical direction of the element body. As a result, the signal conductor layer 22, the first ground conductor layer 24, and the second ground conductor layer 26 have a stripline structure.

[0019] The third ground conductor layer 27 is provided below the insulator layer 18a (first insulator layer) in the element body 12 in the vertical direction of the element body. In this embodiment, the third ground conductor layer 27 is provided on the upper main surface of the insulator layer 16b. The third ground conductor layer 27 surrounds the periphery of the signal conductor layer 22 when viewed in the vertical direction. Therefore, the third ground conductor layer 27 is provided on the left and right of the signal conductor layer 22 in the horizontal direction of the element body.

[0020] The interlayer connection conductors v1, v2 electrically connect the first ground conductor layer 24, the second ground conductor layer 26, and the third ground conductor layer 27. More specifically, the interlayer connection conductors v1, v2 penetrate the insulator layers 16a-16c, 18a, and 18b in the up-down direction of the element body. The upper ends of the interlayer connection conductors v1, v2 are connected to the first ground conductor layer 24. The lower ends of the interlayer connection conductors v1, v2 are connected to the second ground conductor layer 26. The middle portions of the interlayer connection conductors v1, v2 are connected to the third ground conductor layer 27. The interlayer connection conductors v1 are provided on the left of the signal conductor layer 22 in the left-right direction of the element body. The interlayer connection conductors v1 are arranged in a row at equal intervals in the front-rear direction of the element body. The interlayer connection conductors v2 are provided on the right of the signal conductor layer 22 in the left-right direction of the element body. The interlayer connection conductors v2 are arranged in a row at equal intervals in the front-rear direction of the element body.

[0021] The signal terminal 28a is provided on the upper main surface of the element body 12. More specifically, the signal terminal 28a is provided at the front end of the upper main surface of the insulator layer 16a. When viewed in the vertical direction of the element body, the signal terminal 28a overlaps with the front end of the signal conductor layer 22. However, when viewed in the vertical direction of the element body, the signal terminal 28a does not overlap with a first air hole H1 and a second air hole H2, which will be described later. When viewed in the vertical direction of the element body, the signal terminal 28a has a rectangular shape. To insulate the signal terminal 28a from the first ground conductor layer 24, the first ground conductor layer 24 is not provided around the signal terminal 28a.

[0022] The interlayer connection conductor v3 electrically connects the signal terminal 28a and the signal conductor layer 22. Specifically, the interlayer connection conductor v3 penetrates the insulator layers 16a and 18a in the vertical direction of the element body. The upper end of the interlayer connection conductor v3 is connected to the signal terminal 28a. The lower end of the interlayer connection conductor v3 is connected to the front end of the signal conductor layer 22. This electrically connects the signal terminal 28a to the signal conductor layer 22. High-frequency signals are input / output to / from the signal conductor layer 22 via the signal terminal 28a.

[0023] The signal terminal 28b and the interlayer connection conductor v4 have a structure symmetrical to the signal terminal 28a and the interlayer connection conductor v3, and therefore, a description of the signal terminal 28b and the interlayer connection conductor v4 will be omitted.

[0024] The signal conductor layer 22, the first ground conductor layer 24, the second ground conductor layer 26, the third ground conductor layer 27, and the signal terminals 28a and 28b are formed by, for example, etching metal foil provided on the upper or lower principal surfaces of the insulator layers 16a to 16c. The metal foil is, for example, copper foil. The interlayer connection conductors v1 to v4 are, for example, through-hole conductors. The through-hole conductors are fabricated by forming through-holes in the insulator layers 16a to 16c, 18a, and 18b and plating the through-holes.

[0025] The protective layers 20a and 20b are flexible insulating layers, but are not part of the element body 12. The protective layers 20a and 20b have the same rectangular shape as the element body 12 when viewed in the vertical direction of the element body.

[0026] The protective layer 20a covers substantially the entire upper main surface of the insulator layer 16a. Thus, the protective layer 20a protects the first ground conductor layer 24. The protective layer 20a has openings h1 to h6. The opening h1 overlaps with the signal terminal 28a when viewed in the vertical direction of the element body. Thus, the signal terminal 28a is exposed from the transmission line 10 to the outside through the opening h1. The opening h2 is located to the left of the opening h1 in the horizontal direction of the element body. The opening h3 is located to the right of the opening h1 in the horizontal direction of the element body. Thus, the first ground conductor layer 24 is exposed from the transmission line 10 to the outside through the openings h2 and h3. The structures of the openings h4 to h6 are symmetrical to those of the openings h1 to h3. Therefore, a description of the openings h4 to h6 will be omitted.

[0027] Next, the first air holes H1 and the second air holes H2 will be described with reference to FIGS. 1 and 2. The insulator layer 18a has a first air hole H1 penetrating the insulator layer 18a in the vertical direction of the element body. More specifically, as shown in FIG. 1, the first air hole H1 has a rectangular shape with long sides extending in the front-rear direction of the element body when viewed in the vertical direction of the element body. The first air hole H1 is provided in the center of the insulator layer 18a in the left-right direction of the element body. As a result, at least a portion of the first air hole H1 overlaps with the signal conductor layer 22 when viewed in the vertical direction of the element body. The signal conductor layer 22 is located within the first air hole H1 as shown in FIG. 2. However, the front and rear ends of the signal conductor layer 22 do not overlap with the first air hole H1 when viewed in the vertical direction of the element body. In other words, the front and rear ends of the signal conductor layer 22 are not located within the first air hole H1.

[0028] 2, the right end of the left portion of the third ground conductor layer 27 is located inside the first air hole H1. The left end of the right portion of the third ground conductor layer 27 is located inside the first air hole H1.

[0029] 2, the surface of the insulator layer 18a where the first holes H1 are formed is defined as the first hole-forming surface S1. The first hole-forming surface S1 has a left portion S1L and a right portion S1R. The left portion S1L of the first hole-forming surface S1 has an upper end P1LU and a lower end P1LD. The right portion S1R of the first hole-forming surface S1 has an upper end P1RU and a lower end P1RD.

[0030] The left portion S1L of the first hole forming surface S1 has an arc shape that protrudes to the left of the element body when viewed in the front-rear direction of the element body. That is, the left portion S1L of the first hole forming surface S1 has a curved shape that protrudes to the left of the element body from an upper end P1LU of the left portion S1L of the first hole forming surface S1 and a lower end P1LD of the left portion S1L of the first hole forming surface S1 in a cross section perpendicular to the front-rear direction of the element body. As a result, the center of the left portion S1L of the first hole forming surface S1 in the vertical direction of the element body is located at the leftmost position on the left portion S1L. As described above, as shown in FIG. 2, the left portion S1L of the first hole forming surface S1 has a portion that is located to the left of the upper end P1LU of the left portion S1L of the first hole forming surface S1 and the lower end P1LD of the left portion S1L of the first hole forming surface S1 in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body.

[0031] The right portion S1R of the first hole forming surface S1 has an arc shape that protrudes to the right of the element body when viewed in the front-rear direction of the element body. That is, in a cross section perpendicular to the front-rear direction of the element body, the right portion S1R of the first hole forming surface S1 has a curved shape that protrudes to the right of the element body from an upper end P1RU of the right portion S1R of the first hole forming surface S1 and a lower end P1RD of the right portion S1R of the first hole forming surface S1. As a result, the center of the right portion S1R of the first hole forming surface S1 in the vertical direction of the element body is located at the rightmost position of the right portion S1R. As described above, as shown in FIG. 2, the right portion S1R of the first hole forming surface S1 has a portion that is located to the right of the upper end P1RU of the right portion S1R of the first hole forming surface S1 and the lower end P1RD of the right portion S1R of the first hole forming surface S1 in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body.

[0032] The insulator layer 18b has a second air hole H2 that penetrates the insulator layer 18b in the vertical direction of the element body. More specifically, as shown in FIG. 1, the second air hole H2 has a rectangular shape with long sides extending in the front-rear direction of the element body when viewed in the vertical direction of the element body. The second air hole H2 is provided in the center of the insulator layer 18b in the left-right direction of the element body. As a result, at least a portion of the second air hole H2 overlaps with the signal conductor layer 22 when viewed in the vertical direction of the element body. However, the front end and rear end of the signal conductor layer 22 do not overlap with the second air hole H2 when viewed in the vertical direction of the element body.

[0033] Here, the surface of the insulator layer 18b where the second holes H2 are formed is defined as the second hole-forming surface S2. The second hole-forming surface S2 has a left portion S2L and a right portion S2R. The left portion S2L of the second hole-forming surface S2 has an upper end P2LU and a lower end P2LD. The right portion S2R of the second hole-forming surface S2 has an upper end P2RU and a lower end P2RD.

[0034] The left portion S2L of the second hole forming surface S2 has an arc shape that protrudes to the left of the element body when viewed in the front-rear direction of the element body. That is, the left portion S2L of the second hole forming surface S2 has a curved shape that protrudes to the left of the element body from an upper end P2LU of the left portion S2L of the second hole forming surface S2 and a lower end P2LD of the left portion S2L of the second hole forming surface S2 in a cross section perpendicular to the front-rear direction of the element body. As a result, the center of the left portion S2L of the second hole forming surface S2 in the vertical direction of the element body is located at the leftmost position on the left portion S2L. As described above, as shown in FIG. 2, the left portion S2L of the second hole forming surface S2 has a portion that is located to the left of the upper end P2LU of the left portion S2L of the second hole forming surface S2 and the lower end P2LD of the left portion S2L of the second hole forming surface S2 in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body.

[0035] The right portion S2R of the second hole forming surface S2 has an arc shape that protrudes to the right of the element body when viewed in the front-rear direction of the element body. That is, in a cross section perpendicular to the front-rear direction of the element body, the right portion S2R of the second hole forming surface S2 has a curved shape that protrudes to the right of the element body from an upper end P2RU of the right portion S2R of the second hole forming surface S2 and a lower end P2RD of the right portion S2R of the second hole forming surface S2. As a result, the center of the right portion S2R of the second hole forming surface S2 in the vertical direction of the element body is located at the rightmost position of the right portion S2R. As described above, as shown in FIG. 2, the right portion S1R of the second hole forming surface S2 has a portion that is located to the right of the upper end P2RU of the right portion S2R of the second hole forming surface S2 and the lower end P2RD of the right portion S2R of the second hole forming surface S2 in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body.

[0036] The following describes a method for forming the first voids H1 and the second voids H2. The methods for forming the first voids H1 and the second voids H2 include a thermal expansion method, a volatilization method, and a pressure method.

[0037] The thermal expansion method utilizes the difference between the linear expansion coefficients of the insulator layers 16a-16c and the insulator layers 18a and 18b. When the insulator layers 16a-16c, 18a, and 18b are thermocompression-bonded, the first voids H1 become smaller due to the pressure of the thermocompression bonding. The linear expansion coefficients of the insulator layers 18a and 18b are greater than that of the insulator layers 16a-16c. Therefore, when the thermocompression bonding of the insulator layers 16a-16c, 18a, and 18b is completed and the insulator layers 16a-16c, 18a, and 18b are cooled, the insulator layers 18a and 18b shrink more than the insulator layers 16a-16c. However, the upper main surface of the insulator layer 18a is bonded to the lower main surface of the insulator layer 16a. The lower main surface of the insulator layer 18a is bonded to the upper main surface of the insulator layer 16b. Therefore, the upper and lower major surfaces of the insulator layer 18a are constrained by the lower major surface of the insulator layer 16a and the upper major surface of the insulator layer 16b, respectively. As a result, the left portion S1L of the first void-forming surface S1 deforms so as to protrude to the left of the element body. Similarly, the right portion S1R of the first void-forming surface S1 deforms so as to protrude to the right of the element body. Similarly, the left portion S2L of the second void-forming surface S2 deforms so as to protrude to the left of the element body. Similarly, the right portion S2R of the second void-forming surface S2 deforms so as to protrude to the right of the element body. This forms the first voids H1 and the second voids H2.

[0038] The volatilization method utilizes the phenomenon that components contained in the insulator layers 18a and 18b volatilize when the insulator layers 16a to 16c, 18a, and 18b are bonded together by thermocompression. More specifically, when the insulator layers 16a to 16c, 18a, and 18b are bonded together by thermocompression, the first voids H1 and the second voids H2 become smaller due to the pressure of the thermocompression bonding. Here, components contained in the insulator layers 18a and 18b volatilize when the insulator layers 16a to 16c, 18a, and 18b are bonded together by thermocompression. Therefore, the volumetric reduction rate of the insulator layers 18a and 18b before and after thermocompression bonding is greater than the volumetric reduction rate of the insulator layers 16a to 16c before and after thermocompression bonding. However, the upper main surface of the insulator layer 18a is bonded to the lower main surface of the insulator layer 16a. The lower main surface of the insulator layer 18a is bonded to the upper main surface of the insulator layer 16b. Therefore, the upper and lower major surfaces of the insulator layer 18a are constrained by the lower major surface of the insulator layer 16a and the upper major surface of the insulator layer 16b, respectively. As a result, the left portion S1L of the first void-forming surface S1 deforms so as to protrude to the left of the element body. Similarly, the right portion S1R of the first void-forming surface S1 deforms so as to protrude to the right of the element body. Similarly, the left portion S2L of the second void-forming surface S2 deforms so as to protrude to the left of the element body. Similarly, the right portion S2R of the second void-forming surface S2 deforms so as to protrude to the right of the element body. This forms the first voids H1 and the second voids H2.

[0039] The pressure method utilizes the expansion of the first voids H1 and the second voids H2 after thermocompression bonding of the insulator layers 16a-16c, 18a, and 18b. More specifically, when the insulator layers 16a-16c, 18a, and 18b are thermocompression bonded, the first voids H1 and the second voids H2 become smaller due to the pressure of the thermocompression bonding. Once the thermocompression bonding of the insulator layers 16a-16c, 18a, and 18b is completed, the pressure applied to the first voids H1 and the second voids H2 decreases, causing the first voids H1 and the second voids H2 to become larger. However, the upper main surface of the insulator layer 18a is bonded to the lower main surface of the insulator layer 16a. The lower main surface of the insulator layer 18a is bonded to the upper main surface of the insulator layer 16b. Therefore, the upper and lower main surfaces of the insulator layer 18a are constrained by the lower main surface of the insulator layer 16a and the upper main surface of the insulator layer 16b, respectively. As a result, the left portion S1L of the first void forming surface S1 deforms so as to protrude to the left of the element body. Similarly, the right portion S1R of the first void forming surface S1 deforms so as to protrude to the right of the element body. Similarly, the left portion S2L of the second void forming surface S2 deforms so as to protrude to the left of the element body. Similarly, the right portion S2R of the second void forming surface S2 deforms so as to protrude to the right of the element body. This forms first voids H1 and second voids H2.

[0040] [Electronic device structure] Next, the structure of the electronic device 1 including the transmission line 10 will be described with reference to the drawings. Fig. 3 is a left side view of the electronic device 1 including the transmission line 10. The electronic device 1 is, for example, a mobile wireless communication terminal. The electronic device 1 is, for example, a smartphone.

[0041] The transmission line 10 is bent as shown in FIG. 3. "The transmission line 10 is bent" means that an external force is applied to the transmission line 10, causing the transmission line 10 to deform and bend. Hereinafter, the section where the transmission line 10 is bent will be referred to as the bent section A2. The sections where the transmission line 10 is not bent will be referred to as the non-bent sections A1 and A3. The x-axis, y-axis, and z-axis of the electronic device 1 are defined as follows: The x-axis is the front-to-back direction of the element body in the non-bent section A1. The y-axis is the left-to-right direction of the element body in the non-bent section A1. The z-axis is the up-to-down direction of the element body in the non-bent section A1. The non-bent section A1, bent section A2, and non-bent section A3 are arranged in this order in the positive direction of the x-axis.

[0042] As shown in Figure 3, the bending section A2 is bent in the z-axis direction. Therefore, the element body up-down direction and the element body front-back direction differ depending on the position of the transmission line 10, as shown in Figure 3. In the non-bending sections A1 and A3 where the element body 12 is not bent (for example, position (1)), the element body up-down direction and the element body front-back direction coincide with the z-axis direction and the x-axis direction, respectively. On the other hand, in the bending section A2 where the element body 12 is bent (for example, position (2)), the element body up-down direction and the element body front-back direction do not coincide with the z-axis direction and the x-axis direction, respectively.

[0043] As shown in FIG. 3, the electronic device 1 includes a transmission line 10, connectors 30a, 30b, 102a, and 102b, and circuit boards 100 and 110.

[0044] The circuit boards 100 and 110 have a plate shape. The circuit board 100 has main surfaces S5 and S6. The main surface S5 is located on the negative side of the z-axis relative to the main surface S6. The circuit board 110 has main surfaces S11 and S12. The main surface S11 is located on the negative side of the z-axis relative to the main surface S12. The circuit boards 100 and 110 include wiring conductor layers, ground conductor layers, electrodes, etc., which are not shown.

[0045] The connectors 30a and 30b are mounted on the main surfaces (upper main surfaces) on the positive side of the z-axis of the non-bending sections A1 and A3, respectively. More specifically, the connector 30a is mounted on the signal terminals 28a exposed through the openings h1 to h3 and the first ground conductor layer 24. The connector 30b is mounted on the signal terminals 28b exposed through the openings h4 to h6 and the first ground conductor layer 24.

[0046] The connectors 102a and 102b are mounted on the main surface S5 of the circuit board 100 and the main surface S11 of the circuit board 110, respectively. The connectors 102a and 102b are connected to the connectors 30a and 30b, respectively. In this way, the transmission line 10 electrically connects the circuit board 100 and the circuit board 110.

[0047] [effect] The transmission line 10 can reduce transmission loss of the transmission line 10. More specifically, the insulator layer 18a has first voids H1 that penetrate the insulator layer 18a in the vertical direction of the element body. Air with a low dielectric constant exists in the first voids H1. At least a portion of the first voids H1 overlaps with the signal conductor layer 22 when viewed in the vertical direction of the element body. This reduces the dielectric constant around the signal conductor layer 22. As a result, in the transmission line 10, dielectric loss in a high-frequency signal transmitted through the signal conductor layer 22 is suppressed, thereby reducing transmission loss of the transmission line 10. The second voids H2 also contribute to reducing transmission loss of the transmission line 10 for the same reason as the first voids H1.

[0048] Furthermore, according to the transmission line 10, peeling between the insulator layer 16a and the insulator layer 18a and peeling between the insulator layer 16b and the insulator layer 18a can be suppressed, while reducing transmission loss of the transmission line 10. More specifically, as shown in FIG. 2 , the left portion S1L of the first air hole-forming surface S1 has a portion located to the left of the upper end P1LU and the lower end P1LD of the left portion S1L of the first air hole-forming surface S1 in the cross section perpendicular to the front-rear direction of the element body. As a result, the upper end P1LU of the left portion S1L of the first air hole-forming surface S1 is spaced apart from the left surface of the element body 12. That is, the area where the insulator layer 16a and the insulator layer 18a are bonded together is widened. Similarly, the lower end P1LD of the left portion S1L of the first air hole-forming surface S1 is spaced apart from the left surface of the element body 12. That is, the area where the insulator layer 16b and the insulator layer 18a are bonded to each other is increased, which in turn suppresses peeling between the insulator layer 16a and the insulator layer 18a, and between the insulator layer 16b and the insulator layer 18a.

[0049] Furthermore, as shown in FIG. 2 , the left portion S1L of the first air hole-forming surface S1 has a portion located to the left of the upper end P1LU and the lower end P1LD of the left portion S1L of the first air hole-forming surface S1 in the cross section perpendicular to the front-rear direction of the element body. As a result, the left portion S1L of the first air hole-forming surface S1 has a shape that protrudes toward the left of the element body in the cross section perpendicular to the front-rear direction of the element body. Therefore, the volume of the first air holes H1 is large. As a result, in the transmission line 10, dielectric loss in the high-frequency signal transmitted through the signal conductor layer 22 is suppressed, thereby reducing the transmission loss of the transmission line 10. For the same reasons as the first air holes H1, the second air holes H2 also contribute to suppressing peeling between the insulator layer 16b and the insulator layer 18b and between the insulator layer 16c and the insulator layer 18b, and reducing the transmission loss of the transmission line 10.

[0050] The right portion S1R of the first hole-formed surface S1 has a shape symmetrical to the left portion S1L of the first hole-formed surface S1. As a result, the transmission line 10 can reduce transmission loss of the transmission line 10 while suppressing peeling between the insulator layer 16a and the insulator layer 18a and between the insulator layer 16b and the insulator layer 18a.

[0051] Furthermore, a left portion S1L of the first air hole-forming surface S1 has a shape that protrudes to the left of the element body in a cross section perpendicular to the front-rear direction of the element body. The left portion S1L of the first air hole-forming surface S1 is curved. As a result, when a force is applied to the transmission line 10, stress is prevented from concentrating on a part of the left portion S1L. In other words, the transmission line 10 is less likely to be damaged.

[0052] Furthermore, according to the transmission line 10, the first air holes H1 make it easier for the element body 12 to deform. As a result, the transmission line 10 can be easily bent for use. Furthermore, the amount of adhesive used in the transmission line 10 is reduced. This reduces the manufacturing cost of the transmission line 10 and makes the transmission line 10 lighter. Note that, like the first air holes H1, the second air holes H2 also contribute to easier deformation of the element body 12 and a reduction in the amount of adhesive used.

[0053] Furthermore, the transmission line 10 can reduce the transmission loss of the transmission line 10 for the following reasons. More specifically, an electric field is radiated from the signal conductor layer 22. The electric field easily passes through the insulator layer 16a, which has a higher dielectric constant than the first air holes H1, which have a low dielectric constant. Therefore, if the insulator layer 16a is present near the signal conductor layer 22, the electric field radiated from the signal conductor layer 22 extends leftward and passes through the insulator layer 16a. In this case, the electric field concentrates at the corners of the signal conductor layer 22 on the left surface of the signal conductor layer 22. This electric field concentration causes current concentration at the corners of the signal conductor layer 22. As a result, the transmission loss of the transmission line 10 may increase.

[0054] Therefore, as shown in FIG. 2, the left portion S1L of the first air hole forming surface S1 has a portion located to the left of the upper end P1LU and the lower end P1LD of the left portion S1L of the first air hole forming surface S1 in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body. Therefore, the left portion S1L of the first air hole forming surface S1 protrudes in a direction away from the signal conductor layer 22. This reduces the amount of insulator layer 18a located near the signal conductor layer 22. Therefore, the electric field radiated from the signal conductor layer 22 spreads toward the upper left of the element body. In this case, electric field concentration at the corners of the signal conductor layer 22 is suppressed on the left surface of the signal conductor layer 22. As a result, the transmission line 10 can reduce transmission loss of the transmission line 10.

[0055] In the transmission line 10, the first air hole H1 is located near the interlayer connection conductors v1 and v2, which makes it difficult for capacitance to form between the signal conductor layer 22 and the interlayer connection conductors v1 and v2. This allows the signal conductor layer 22 and the interlayer connection conductors v1 and v2 to be closer to each other. Note that "the first air hole H1 is located near the interlayer connection conductor v1" means, for example, that the distance between the left end of the first air hole H1 and the interlayer connection conductor v1 located to the left of the first air hole H1 in the left-right direction of the element body is shorter than the distance between the interlayer connection conductor v1 and the signal conductor layer 22.

[0056] In the transmission line 10, the first air holes H1 are located near the interlayer connection conductors v1 and v2, so the wavelength of the high-frequency signal transmitted through the interlayer connection conductors v1 and v2 becomes longer, resulting in longer intervals between the interlayer connection conductors v1 and between the interlayer connection conductors v2.

[0057] Water vapor and the like in the air may oxidize conductor layers such as the signal line conductor layer 20, degrading signal characteristics. In the transmission line 10, the contact area between the air in the first holes H1 and the resin 18a increases, which improves the ability of the resin 18a to adsorb unnecessary gases contained in the air and reduces the amount of water vapor and the like contained in the air. In this way, the transmission line 10 can suppress deterioration of characteristics by reducing the amount of water vapor and the like in the air.

[0058] In the transmission line 10, separation between the insulator layer 16b and the insulator layer 18a is suppressed. More specifically, if the right end of the left portion of the third ground conductor layer 27 is not located within the first air hole H1, the right end of the left portion of the third ground conductor layer 27 is located to the left of the left portion S1L of the first air hole-forming surface S1. In this case, a gap is formed between the insulator layer 16b and the insulator layer 18a near the bottom end P1LD of the left portion S1L of the first air hole-forming surface S1. Such a gap can cause separation between the insulator layer 16b and the insulator layer 18a. Therefore, the right end of the left portion of the third ground conductor layer 27 is located within the first air hole H1. That is, a portion of the third ground conductor layer 27 is located within the first air hole H1. As a result, no gap is formed between the insulator layer 16b and the insulator layer 18a near the bottom end P1LD of the left portion S1L of the first air hole-forming surface S1. As a result, in the transmission line 10, the insulator layer 16b and the insulator layer 18a are prevented from peeling off from each other.

[0059] 2, the signal conductor layer 22 of the transmission line 10 is located within the first air hole H1. This brings the signal conductor layer 22 into contact with air, thereby reducing the dielectric constant around the signal conductor layer 22. As a result, dielectric loss in a high-frequency signal transmitted through the signal conductor layer 22 is suppressed.

[0060] Furthermore, in the transmission line 10, the signal terminal 28a does not overlap with a first air hole H1 and a second air hole H2 (described later) when viewed in the vertical direction of the element body, thereby preventing the transmission line 10 from being damaged by stress during thermocompression bonding during production of the transmission line 10.

[0061] (First Modification) A transmission line 10a according to a first modification will be described below with reference to the drawings. Fig. 4 is a cross-sectional view of the transmission line 10a.

[0062] The transmission line 10a differs from the transmission line 10 in the positions where the first ground conductor layer 24 and the second ground conductor layer 26 are provided. More specifically, the first ground conductor layer 24 is provided on the lower main surface of the insulator layer 16a. As a result, the first ground conductor layer 24 faces the first air holes H1. The second ground conductor layer 26 is provided on the upper main surface of the insulator layer 16c. As a result, the second ground conductor layer 26 faces the second air holes H2. The other structure of the transmission line 10a is the same as that of the transmission line 10, so a description thereof will be omitted. Furthermore, the transmission line 10a can achieve the same effects as the transmission line 10.

[0063] (Second Modification) A transmission line 10b according to a second modification will be described below with reference to the drawings. Fig. 5 is a cross-sectional view of the transmission line 10b. Fig. 6 is a cross-sectional view of a transmission line 500 according to a comparative example.

[0064] The transmission line 10b differs from the transmission line 10 in that it does not include the insulator layers 16a and 16c, the protective layers 20a and 20b, and the interlayer connection conductors v1 and v2. Thus, the insulator layers 16a and 16c, the protective layers 20a and 20b, and the interlayer connection conductors v1 and v2 are not essential components. In the transmission line 10b, the first ground conductor layer 24 is attached to the upper main surface of the insulator layer 18a by, for example, a transfer method. The second ground conductor layer 26 is attached to the lower main surface of the insulator layer 18b by, for example, a transfer method. The other structural features of the transmission line 10b are the same as those of the transmission line 10, and therefore will not be described here. Furthermore, the transmission line 10b can achieve the same effects as those of the transmission line 10.

[0065] The present inventors conducted the following computer simulation to clarify the effects of the transmission line 10b. Specifically, they created a first model having the structure of the transmission line 10b and a second model having the structure of the transmission line 500. The first and second models differ in the shapes of the first and second air holes H1 and H2. The distance L1 between the upper end P1LU and the upper end P1RU in the first model is equal to the distance L2 between the upper end P1LU and the upper end P1RU in the second model. The present inventors used the first and second models to calculate the electric field distribution around the signal conductor layer 22 using a computer. The present inventors also calculated the relationship between the frequency of the first and second models and the transmission loss of the first and second models using a computer. The present inventors performed the simulation under the condition that the first ground conductor layer 24 and the second ground conductor layer 26 were electrically connected and a high-frequency signal was applied between them.

[0066] FIG. 7 shows the electric field distribution of the first model. FIG. 8 shows the electric field distribution of the second model. In FIGS. 7 and 8, darker areas indicate areas with higher electric field strength, and lighter areas indicate areas with lower electric field strength. Comparing FIGS. 7 and 8, it can be seen that the area with lower electric field strength in the first model is wider than the area with lower electric field strength in the second model. It can also be seen that the electric field strength of the insulator layer, which has a higher dielectric loss than air, is lower in the first model than in the second model. This is thought to be because the volumes of the first voids H1 and second voids H2 in the first model are larger than the volumes of the first voids H1 and second voids H2 in the second model. As such, when the area with lower electric field strength in the first model is wider than the area with lower electric field strength in the second model and the electric field strength of the insulator layer is lower, the transmission loss of high-frequency signals generated in the first model is smaller than the transmission loss of high-frequency signals generated in the second model.

[0067] FIG. 9 is a diagram showing the electric field distribution at the left end of the signal conductor layer 22 of the first model. FIG. 10 is a diagram showing the electric field distribution at the left end of the signal conductor layer 22 of the second model. Comparing FIG. 9 and FIG. 10, it can be seen that the first model is more effective at preventing the electric field from concentrating at the corners of the signal conductor layer 22 than the second model. This prevents current from concentrating at the corners of the signal conductor layer 22 in the first model. As a result, the first model has lower transmission loss of high-frequency signals than the second model.

[0068] 11 is a graph showing the relationship between the frequency of the first and second models and the transmission loss of the first and second models. The horizontal axis represents the frequency of the high-frequency signal transmitted through the signal conductor layer 22. The vertical axis represents the transmission loss of the transmission line per meter of the first and second models. FIG. 11 shows that the transmission loss of the first model (transmission line 10a) is smaller than the transmission loss of the second model (transmission line 500).

[0069] (Third Modification) A transmission line 10c according to a third modification will be described below with reference to the drawings. Fig. 12 is a cross-sectional view of the transmission line 10c.

[0070] The transmission line 10c differs from the transmission line 10a in that it further includes an insulator layer 16d and third ground conductor layers 27a and 27b. More specifically, the insulator layer 16d is provided between the insulator layer 18a and the insulator layer 16b. As a result, the signal conductor layer 22 is located between the insulator layer 16d and the insulator layer 16b. In other words, the signal conductor layer 22 is not located within the first air hole H1. As described above, the signal conductor layer 22 is surrounded by the insulator layers 16b and 16d, which prevents the signal conductor layer 22 from shorting out with other conductor layers. Furthermore, deterioration of the signal conductor layer 22 due to oxidation or the like is prevented.

[0071] The third ground conductor layer 27a is provided on the upper main surface of the insulator layer 16b. The third ground conductor layer 27b is provided on the lower main surface of the insulator layer 16d. The other structures of the transmission line 10c are the same as those of the transmission line 10a, so a description thereof will be omitted. The transmission line 10c can achieve the same effects as the transmission line 10.

[0072] Furthermore, the third ground conductor layer 27a is located above the signal conductor layer 22 in the vertical direction of the element body, and the third ground conductor layer 27b is located below the signal conductor layer 22 in the vertical direction of the element body. This improves the shielding effect for the signal conductor layer 22.

[0073] (Fourth Modification) A transmission line 10d according to a fourth modification will be described below with reference to the drawings. Fig. 13 is a cross-sectional view of the transmission line 10d.

[0074] The transmission line 10d differs from the transmission line 10c in the positions where the first ground conductor layer 24 and the second ground conductor layer 26 are provided. More specifically, the first ground conductor layer 24 is provided on the upper main surface of the insulator layer 16a. The second ground conductor layer 26 is provided on the lower main surface of the insulator layer 16c. The other structures of the transmission line 10d are the same as those of the transmission line 10c, and therefore, a description thereof will be omitted. Furthermore, the transmission line 10d can achieve the same effects as the transmission line 10c.

[0075] (Fifth Modification) A transmission line 10e according to a fifth modification will be described below with reference to the drawings. Fig. 14 is a cross-sectional view of the transmission line 10e.

[0076] The transmission line 10e differs from the transmission line 10 in the thicknesses of the insulator layers 16a, 16c, 18a, and 18b and in the presence or absence of air holes H3 and H4. More specifically, in the transmission line 10e, the thicknesses of the insulator layers 18a and 18b are smaller than the thicknesses of the insulator layers 16a and 16c. Air holes H3 and H4 are provided in the insulator layers 16a and 16c, respectively. The air holes H3 and H4 penetrate the insulator layers 16a and 16c in the vertical direction of the element body. The air hole H3 is connected to the first air hole H1. The air hole H4 is connected to the second air hole H2. The other structure of the transmission line 10e is the same as that of the transmission line 10, and therefore a description thereof will be omitted.

[0077] The insulator layers 18a, 18b are adhesive layers. Therefore, the thickness of the insulator layers 18a, 18b is likely to change when the element body 12 is crimped. Therefore, the thickness of the insulator layers 18a, 18b is smaller than the thickness of the insulator layers 16a, 16b. This reduces the amount of change in the thickness of the insulator layers 18a, 18b when the element body 12 is crimped. This suppresses variations in the size of the first voids H1 and the second voids H2 in the vertical direction of the element body.

[0078] (Sixth Modification) A transmission line 10f according to a sixth modified example will be described below with reference to the drawings. Fig. 15 is a cross-sectional view of the transmission line 10f.

[0079] The transmission line 10f differs from the transmission line 10e in that a first air hole H11, a second air hole H12, and air holes H13 and H14 are provided in the element body 12. More specifically, the first air hole H1, the second air hole H2, and air holes H3 and H4 are arranged to the left of the center of the element body 12 in the left-right direction of the element body. The first air hole H11, the second air hole H12, and air holes H13 and H14 are arranged to the right of the center of the element body 12 in the left-right direction of the element body. The first air hole H11, the second air hole H12, and air holes H13 and H14 have structures symmetrical to the first air hole H1, the second air hole H2, and air holes H3 and H4, respectively. The other structures of the transmission line 10f are the same as those of the transmission line 10e, and therefore will not be described again. Moreover, the transmission line 10f can achieve the same effects as the transmission line 10e.

[0080] In the transmission line 10f, parts of the insulator layers 16a-16c, 18a, and 18b are present between the first air holes H1, the second air holes H2, and the air holes H3 and H4 and the first air holes H11, the second air holes H12, and the air holes H13 and H14. This allows parts of the insulator layers 16a-16c, 18a, and 18b to function as pillars. As a result, deformation of the first air holes H1 and H11, the second air holes H2 and H12, and the air holes H3, H4, H13, and H14 is suppressed when the transmission line 10f is bent.

[0081] (Seventh Modification) A transmission line 10g according to the seventh modification will be described below with reference to the drawings. Fig. 16 is a cross-sectional view of the transmission line 10g.

[0082] The transmission line 10g differs from the transmission line 10f in that the first air hole H21, the second air hole H22, and the air holes H23 and H24 are provided in the element body 12. More specifically, the first air hole H21, the second air hole H22, and the air holes H23 and H24 are arranged to the right of the first air hole H1, the second air hole H2, and the air holes H3 and H4 in the left-right direction of the element body. The first air hole H21, the second air hole H22, and the air holes H23 and H24 are arranged to the left of the first air hole H11, the second air hole H12, and the air holes H13 and H14 in the left-right direction of the element body. The first air hole H21, the second air hole H22, and the air holes H23 and H24 have the same structure as the first air hole H1, the second air hole H2, and the air holes H3 and H4, respectively. The rest of the structure of the transmission line 10g is the same as that of the transmission line 10f, and therefore a description thereof will be omitted. Furthermore, the transmission line 10g can achieve the same effects as the transmission line 10f.

[0083] In the transmission line 10g, parts of the insulator layers 16a-16c, 18a, and 18b are present between the first air hole H1, the second air hole H2, and the air holes H3 and H4 and the first air hole H21, the second air hole H22, and the air holes H23 and H24. Parts of the insulator layers 16a-16c, 18a, and 18b are present between the first air hole H11, the second air hole H12, and the air holes H13 and H14 and the first air hole H21, the second air hole H22, and the air holes H23 and H24. This allows parts of the insulator layers 16a-16c, 18a, and 18b to function as pillars. As a result, when the transmission line 10g is bent, deformation of the first air holes H1, H11, H21, the second air holes H2, H12, H22, and the air holes H3, H4, H13, H14, H23, H24 is suppressed.

[0084] (Eighth Modification) A transmission line 10h according to an eighth modification will be described below with reference to the drawings. Fig. 17 is a cross-sectional view of the transmission line 10h.

[0085] The transmission line 10h differs from the transmission line 10e in that it further includes insulator layers 18c and 18d and that first air holes H31 and second air holes H41 are provided in the element body 12. The insulator layer 18c is provided above the insulator layer 16a in the vertical direction of the element body. Therefore, the first ground conductor layer 24 is provided on the upper main surface of the insulator layer 18c. The insulator layer 18d is provided below the insulator layer 16c in the vertical direction of the element body. Therefore, the second ground conductor layer 26 is provided on the lower main surface of the insulator layer 18d.

[0086] The first air holes H31 penetrate the insulator layer 18c in the vertical direction of the element body. The shape of the first air holes H31 is the same as that of the first air holes H1. The first air holes H31 are connected to the air holes H3. The second air holes H41 penetrate the insulator layer 18d in the vertical direction of the element body. The shape of the second air holes H41 is the same as that of the first air holes H1. The second air holes H41 are connected to the air holes H4. The other structure of the transmission line 10h is the same as that of the transmission line 10e, so a description thereof will be omitted. Furthermore, the transmission line 10h can achieve the same effects as those of the transmission line 10e.

[0087] The insulator layers 18a to 18d are adhesive layers. Therefore, the thickness of the insulator layers 18a to 18d is likely to change when the element body 12 is compressed. Therefore, the thickness of the insulator layers 18a to 18d is smaller than the thickness of the insulator layers 16a and 16c. This reduces the amount of change in the thickness of the insulator layers 18a to 18d when the element body 12 is compressed. This suppresses variations in the sizes of the first holes H1 and H31, the second holes H2 and H41, and the holes H3 and H4 in the vertical direction of the element body.

[0088] Furthermore, if the insulating layers 16a and 16c are made of a material having a lower dielectric constant or a lower dielectric loss tangent than the material of the insulating layer 16b, the transmission loss of the transmission line 10h can be reduced.

[0089] (Ninth Modification) A transmission line 10i according to a ninth modification will be described below with reference to the drawings. Fig. 18 is a cross-sectional view of the transmission line 10i.

[0090] The transmission line 10i differs from the transmission line 10c in that it includes a plurality of conductor objects 200 instead of the interlayer connection conductors v1 and v2. More specifically, the plurality of conductor objects 200 are, for example, metal spheres whose surfaces are covered with solder or a conductive adhesive. The diameters of the metal spheres of the plurality of conductor objects 200 are uniform. The plurality of conductor objects 200 are provided on the insulator layer 18a (first insulator layer). The plurality of conductor objects 200 electrically connect the first ground conductor layer 24 and the third ground conductor layer 27a.

[0091] The plurality of conductor objects 200 are provided on the insulator layer 18b. The plurality of conductor objects 200 electrically connect the second ground conductor layer 26 and the third ground conductor layer 27b. The plurality of conductor objects 200 are joined to the second ground conductor layer 26 and the third ground conductor layer 27b. The other structures of the transmission line 10i are the same as those of the transmission line 10c, and therefore, a description thereof will be omitted. Furthermore, the transmission line 10i can achieve the same effects as those of the transmission line 10c.

[0092] The transmission line 10i does not require the interlayer connection conductors v1 and v2. Therefore, the plating process for forming the interlayer connection conductors v1 and v2 is not required. Therefore, the plating liquid does not penetrate into the transmission line 10i.

[0093] In the transmission line 10i, the distance between the insulator layer 16a and the insulator layer 16d is substantially determined by the diameter of the metal spheres of the plurality of conductor objects 200. Similarly, the distance between the insulator layer 16b and the insulator layer 16c is substantially determined by the diameter of the metal spheres of the plurality of conductor objects 200. This suppresses variation in the distance between the insulator layer 16a and the insulator layer 16d and the distance between the insulator layer 16b and the insulator layer 16c. In other words, variation in the size of the first air hole H1 in the vertical direction of the element body and the size of the second air hole H2 in the vertical direction of the element body is suppressed.

[0094] (Tenth Modification) A transmission line 10j according to a tenth modification will be described below with reference to the drawings. Fig. 19 is a cross-sectional view of the transmission line 10j.

[0095] The transmission line 10j differs from the transmission line 10c in that it further includes insulator layers 16e and 16f and conductor layers 150, 152, 160, and 162. More specifically, the insulator layer 16e is provided above the insulator layer 16a in the vertical direction of the element body. The insulator layer 16f is provided below the insulator layer 16c in the vertical direction of the element body. The conductor layer 150 is provided on the lower main surface of the insulator layer 16e. The conductor layer 152 is provided on the upper main surface of the insulator layer 16e. The conductor layer 160 is provided on the upper main surface of the insulator layer 16f. The conductor layer 162 is provided on the lower main surface of the insulator layer 16f. The conductor layers 150, 152, 160, and 162 are signal wiring and ground conductors. In this way, by providing the conductor layers 150, 152, 160, and 162, an electric circuit is added to the transmission line 10j. The other structure of the transmission line 10j is the same as that of the transmission line 10c, so a description thereof will be omitted. Furthermore, the transmission line 10j can achieve the same effects as the transmission line 10c.

[0096] (Eleventh Modification) A transmission line 10k according to an eleventh modification will be described below with reference to the drawings. Fig. 20 is a cross-sectional view of the transmission line 10k.

[0097] The transmission line 10k differs from the transmission line 10j in that it includes multiple conductor objects 200 instead of the interlayer connection conductors v1 and v2. More specifically, the multiple conductor objects 200 have a uniform diameter. The multiple conductor objects 200 are provided on the insulator layer 18a (first insulator layer). The multiple conductor objects 200 electrically connect the first ground conductor layer 24 and the third ground conductor layer 27a.

[0098] The plurality of conductor objects 200 are provided on the insulator layer 18b. The plurality of conductor objects 200 electrically connect the second ground conductor layer 26 and the third ground conductor layer 27b. The other structures of the transmission line 10k are the same as those of the transmission line 10j, and therefore, a description thereof will be omitted. Furthermore, the transmission line 10k can achieve the same effects as those of the transmission line 10j.

[0099] (Twelfth Modification) A transmission line 10l according to a twelfth modification will be described below with reference to the drawings. Fig. 21 is a cross-sectional view of the transmission line 10l.

[0100] The transmission line 10l differs from the transmission line 10 in that it does not include the insulator layers 16a and 16c, that the material of the insulator layer 16b is the same as the material of the insulator layers 18a and 18b, and that the interlayer connection conductors v1 and v2 are via-hole conductors. More specifically, the insulator layer 16b (third insulator layer) is provided below the insulator layer 18a (first insulator layer) in the vertical direction of the element body. The material of the insulator layer 16b (third insulator layer) is the same as the material of the insulator layers 18a and 18b (first insulator layer). The material of the insulator layers 16b, 18a, and 18b is a thermoplastic resin such as polyimide, liquid crystal polymer, or PTFE (polytetrafluoroethylene).

[0101] The first ground conductor layer 24 is provided on the upper main surface of the insulator layer 18a. The second ground conductor layer 26 is provided on the lower main surface of the insulator layer 18b. The interlayer connection conductors v1 and v2 electrically connect the first ground conductor layer 24 and the second ground conductor layer 26. The interlayer connection conductors v1 and v2 are via-hole conductors. The via-hole conductors are fabricated by forming through-holes in the insulator layers 16b, 18a, and 18b, filling the through-holes with conductive paste, and then sintering the conductive paste. The other structure of the transmission line 10l is the same as that of the transmission line 10, so a description thereof will be omitted. The transmission line 10l can also achieve the same effects as the transmission line 10.

[0102] The transmission line 10l can reduce the transmission loss of the transmission line 10l. More specifically, in a transmission line, an adhesive layer may be used to bond multiple insulator layers. However, because the adhesive layer is required to have high adhesiveness, it may be difficult to use a material with a low dielectric constant or low dielectric tangent for the adhesive layer. Therefore, in the transmission line 10l, the material of the insulator layers 18a and 18b is the same thermoplastic resin as the material of the insulator layer 16b. Therefore, the insulator layers 18a, 16b, and 18b can be bonded by thermocompression bonding. This eliminates the need for an adhesive layer to bond the insulator layers. As a result, the transmission line 10l can reduce the transmission loss of the transmission line 10l.

[0103] In the transmission line 10l, the material of the insulator layer 16b is the same as the material of the insulator layers 18a and 18b. Therefore, the linear expansion coefficient of the insulator layer 16b is equal to the linear expansion coefficient of the insulator layers 18a and 18b. This prevents stress from occurring inside the element body 12 due to the difference between the linear expansion coefficient of the insulator layer 16b and the linear expansion coefficient of the insulator layers 18a and 18b when the temperature of the transmission line 10l changes.

[0104] In transmission line 10l, when element body 12 is thermocompression bonded, interlayer connection conductors v1 and v2, which are via-hole conductors, can be formed.

[0105] (13th Modification) A transmission line 10m according to a thirteenth modification will be described below with reference to the drawings. Fig. 22 is a cross-sectional view of the transmission line 10m.

[0106] The transmission line 10m differs from the transmission line 10l in that the interlayer connection conductors v1 and v2 are through-hole conductors. The rest of the structure of the transmission line 10m is the same as that of the transmission line 10l, so a description thereof will be omitted. Furthermore, the transmission line 10m can achieve the same effects as the transmission line 10l.

[0107] (14th Modification) A transmission line 10n according to a fourteenth modification will be described below with reference to the drawings. Fig. 23 is a cross-sectional view of the transmission line 10n.

[0108] The transmission line 10n differs from the transmission line 10 in that the second air holes H2 are not provided. Other structures of the transmission line 10n are the same as those of the transmission line 10, and therefore description thereof will be omitted. Furthermore, the transmission line 10n can achieve the same effects as the transmission line 10. Note that the second air holes H2 do not necessarily have to be provided in the transmission lines 10a to 10m either.

[0109] (15th Modification) A transmission line 10o according to a fifteenth modification will be described below with reference to the drawings. Fig. 24 is a cross-sectional view of the transmission line 10o.

[0110] The transmission line 10o differs from the transmission line 10 in that it further includes signal conductor layers 22a and 22b. The signal conductor layer 22a is provided on the left of the signal conductor layer 22 in the left-right direction of the element body. The signal conductor layer 22b is provided on the right of the signal conductor layer 22 in the left-right direction of the element body. The other structures of the transmission line 10o are the same as those of the transmission line 10, so explanations will be omitted. The transmission line 10o can achieve the same effects as the transmission line 10. The transmission line 10o may include two signal conductor layers, or may include four or more signal conductor layers. Furthermore, two adjacent signal conductor layers among the multiple signal conductor layers may form a differential transmission line. The transmission lines 10a to 10m may further include signal conductor layers 22a and 22b.

[0111] (Other embodiments) The transmission lines according to the present invention are not limited to the transmission lines 10, 10a to 10o, and can be modified within the scope of the present invention. Note that the configurations of the transmission lines 10, 10a to 10o may be combined arbitrarily.

[0112] In all cross sections of the transmission lines 10, 10a to 10o, the left portion S1L of the first air hole forming surface S1 does not need to have a portion located to the left of the upper end P1LU and the lower end P1LD in the left-right direction of the element body. Therefore, in some cross sections of the transmission lines 10, 10a to 10o, the left portion S1L of the first air hole forming surface S1 may have a portion located to the left of the upper end P1LU and the lower end P1LD in the left-right direction of the element body.

[0113] In all cross sections of the transmission lines 10, 10a to 10o, the right portion S1R of the first air hole forming surface S1 does not need to have a portion located to the right of the upper end P1RU and the lower end P1RD in the left-right direction of the element body. Therefore, in some cross sections of the transmission lines 10, 10a to 10o, the right portion S1R of the first air hole forming surface S1 only needs to have a portion located to the right of the upper end P1RU and the lower end P1RD in the left-right direction of the element body.

[0114] The second ground conductor layer 26 is not an essential component of the transmission lines 10, 10a to 10o. Furthermore, since the transmission line 10 does not include the second ground conductor layer 26, the insulator layers 18b and 16c, and the protective layer 20b, the signal conductor layer 22 and the first ground conductor layer 24 may have a microstrip line structure.

[0115] In the transmission lines 10, 10a to 10o, the right portion S1R of the first hole-forming surface S1 may not have a portion located to the right of the upper end P1RU and the lower end P1RD in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body. However, when both the left portion S1L and the right portion S1R are curved, peeling between the insulator layer 16a and the insulator layer 18a and between the insulator layer 16b and the insulator layer 18a can be more effectively suppressed and the transmission loss of the transmission line 10 can be more effectively reduced than when only one of the left portion S1L or the right portion S1R is curved. In the transmission lines 10i and 10k, the insulator layer 18a may be an anisotropic conductive film. In this case, the multiple conductors 200 are minute metal particles of the anisotropic conductive film.

[0116] In the transmission lines 10, 10a to 10o, the signal terminals 28a, 28b may be provided on the lower main surface of the element body 12.

[0117] The transmission lines 10, 10a to 10o may further include other circuits in addition to the strip lines.

[0118] It should be noted that electronic components other than the connectors 30a and 30b may be mounted on the transmission lines 10, 10a to 10o.

[0119] The transmission lines 10, 10a to 10o have a straight shape when viewed in the vertical direction of the element body. However, the transmission lines 10, 10a to 10o may be curved. Here, "the transmission lines 10, 10a to 10o are curved" means that the transmission lines 10, 10a to 10o have a curved shape when no external force is applied to them.

[0120] In the transmission lines 10, 10a to 10o, the first air holes H1 and the second air holes H2 may be provided in the non-bending sections A1 and A3, and may not be provided in the bending section A2.

[0121] In the transmission line 10, the right portion S1R of the first air hole-forming surface S1 may have a shape that is asymmetrical with respect to the left portion S1L of the first air hole-forming surface S1. For example, if the distance between the signal conductor layer 22 and the lower end P1LD is different from the distance between the signal conductor layer 22 and the lower end P1RD, the right portion S1R of the first air hole-forming surface S1 may have a shape that is asymmetrical with respect to the left portion S1L of the first air hole-forming surface S1. In such a case, it is sufficient that the left portion S1L or the right portion S1R, whichever is closer to the signal conductor layer 22, is curved more. Also, it is sufficient that the left portion S1L or the right portion S1R, whichever is closer to the signal conductor layer 22, is curved more than the right portion S1R or the left portion S1L, whichever is farther from the signal conductor layer 22. However, if the curvature between the left portion S1L and the right portion S1R is too great, the transmission line 10 may be easily damaged by impact. Therefore, the width of the left portion S1L in the left-right direction or the width of the right portion S1R in the left-right direction may be smaller than the thickness of the transmission line 10 in the up-down direction. [Explanation of symbols]

[0122] 1:Electronic equipment 10, 10a to 10o: Transmission lines 12: Base body 16a to 16f, 18a to 18d: Insulator layers 20a, 20b: Protective layer 22, 22a, 22b: signal conductor layers 24: First ground conductor layer 26: Second ground conductor layer 27, 27a, 27b: third ground conductor layer 28a, 28b: Signal terminal 30a, 30b, 102a, 102b: Connectors 100, 110: Circuit board 150, 152, 160, 162: Conductor layers 200: Conductive materials 500: Transmission line A1, A3: Non-bending section A2: Bending section H1, H11, H21, H31: First empty hole H2, H12, H22, H41: Second cavity H3, H4, H13, H14, H23, H24: Holes P1LU, P1RU, P2LU, P2RU: Upper end P1LD, P1RD, P2LD, P2RD: Lower end S1: First void formation surface S1L, S2L: Left side S1R, S2R: Right side S2: Second void formation surface h1~h6: Openings v1~v4: Interlayer continuous conductor

Claims

1. an element body having a main surface with a normal extending in the vertical direction of the element body, the element body including a single layer of a first void-forming insulator layer and a second void-forming insulator layer; a signal conductor layer provided below the first hole-forming insulator layer in the element body in the vertical direction of the element body; a first ground conductor layer provided above the first void-forming insulator layer in the element body in the vertical direction of the element body; It is equipped with the first void-forming insulator layer is provided with a first void penetrating the first void-forming insulator layer in the vertical direction of the element body, the second void-forming insulator layer is provided with a second void penetrating the second void-forming insulator layer in the vertical direction of the element body, the second holes are connected to the first holes, The direction in which the signal conductor layers extend is defined as the front-rear direction of the element body, The line width direction of the signal conductor layer is defined as the left-right direction of the element body, At least a portion of the first hole overlaps with the signal conductor layer when viewed in the vertical direction of the element body, a surface of the first void-forming insulator layer on which the first voids are formed is defined as a first void-forming surface; a surface of the second void-forming insulator layer on which the second voids are formed is defined as a second void-forming surface; a left portion of the first void formation surface has a portion located to the left of the second void formation surface in the left-right direction of the element body in a cross section perpendicular to the front-rear direction of the element body, At least a portion of the second hole overlaps with the first ground conductor layer when viewed in the vertical direction of the element body, the signal conductor layer is located within the first hole; When viewed in the vertical direction of the element body, the first holes are larger than the second holes. Transmission line.

2. the first void-forming insulator layer is thinner than the second void-forming insulator layer; The transmission line according to claim 1 .

3. the first void-forming insulator layer is an adhesive layer; The transmission line according to claim 1 or 2.

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