TRANSMISSION LINE AND ELECTRONIC DEVICE

A transmission line includes an element body, a signal conductor layer, and a ground conductor layer. The element body includes an insulator layer. The signal conductor layer is below the insulator layer, and the ground conductor layer is above the insulator layer in an element body up-down direction. A hole is located at a surface of the insulator layer and penetrates the insulator layer in the element body up-down direction. At least a portion of the hole overlaps the signal conductor layer when viewed in the element body up-down direction. The hole extends between a left hole-defining surface and a right hole-defining surface. In a cross section orthogonal to the element body front-back direction, the left hole-defining surface includes a left upper end and a left lower end in the element body left-right direction, and the right hole-defining surface includes a right upper end and a right lower end in the element body left-right direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission line through which a high-frequency signal is transmitted, and an electronic device.

2. Description of the Related Art

As an invention related to a transmission line in the past, for example, a signal transmission line described in Japanese Patent No. 6489265 has been known. The signal transmission line includes a laminated body, a signal conductor, and a ground conductor. The laminated body has a structure in which a plurality of resin layers is laminated. The signal conductor and the ground conductor overlap each other when viewed in a lamination direction of the laminated body. In addition, a hollow portion is provided between the signal conductor and the ground conductor.

In such a signal transmission line, air having a low dielectric constant is present in the hollow portion. The hollow portion is provided near the signal conductor. Therefore, the dielectric constant around the signal conductor is lowered. As a result, in the signal transmission line, the occurrence of a dielectric loss in the high-frequency signal transmitted through the signal conductor is reduced or prevented, so that a transmission loss of the signal transmission line is reduced.

SUMMARY OF THE INVENTION

Incidentally, in the field of the signal transmission line described in Japanese Patent No. 6489265, there is a demand for further reducing the transmission loss of the signal transmission line.

Preferred embodiments of the present invention provide transmission lines and electronic devices each capable of reducing a transmission loss of the transmission line.

A transmission line according to an aspect of a preferred embodiment of the present invention includes an element body including a first insulator layer and a main surface with a normal line extending in an element body up-down direction, a signal conductor layer below the first insulator layer in the element body in the element body up-down direction, and a first ground conductor layer above the first insulator layer in the element body in the element body up-down direction; wherein the first insulator layer includes a first hole penetrating the first insulator layer in the element body up-down direction, a direction in which the signal conductor layer extends is an element body front-back direction, a line width direction of the signal conductor layer is an element body left-right direction, at least a portion of the first hole overlaps the signal conductor layer when viewed in the element body up-down direction, the first hole extends between a first left hole-defining surface and a first right hole-defining surface, and in a cross section orthogonal to the element body front-back direction, the first left hole-defining surface includes a first left upper end and a first left lower end in the element body left-right direction, and the first right hole-defining surface includes a first right upper end and a first right lower end in the element body left-right direction.

The transmission lines and the electronic devices according to preferred embodiments of the present invention achieve reduced transmission loss.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred Embodiments

Structure of Transmission Line

Hereinafter, a structure of a transmission line10according to a preferred embodiment of the present invention will be described with reference to the drawings.FIG.1is an exploded perspective view of the transmission line10. Note that inFIG.1, only representative interlayer connection conductorsv1andv2among the plurality of interlayer connection conductorsv1andv2are denoted by reference numerals.FIG.2is a cross-sectional view of the transmission line10taken along a line A-A ofFIG.1.

In this specification, directions are defined as follows. A direction in which a normal line of a main surface of an element body12of the transmission line10extends is defined as an element body up-down direction. In addition, a direction in which a signal conductor layer22of the transmission line10extends is defined as an element body front-back direction. Further, a line width direction of the signal conductor layer22is defined as an element body left-right direction. The element body up-down direction, the element body front-back direction, and the element body left-right direction are orthogonal to each other.

Hereinafter, X is a component or member of the transmission line10. In this specification, unless otherwise specified, each portion of X is defined as follows. The front portion of X means the front half of X. The rear portion of X means the rear half of X. The left portion of X means the left half of X. The right portion of X means the right half of X. The upper portion of X means the upper half of X. The lower portion of X means the lower half of X. The front end of X means an end in the front direction of X. The rear end of X means an end in the rear direction of X. The left end of X means an end in the left direction of X. The right end of X means an end in the right direction of X. The upper end of X means an end in the upward direction of X. The lower end of X means an end in the downward direction of X. The front end portion of X means the front end of X and its vicinity. The rear end portion of X means the rear end of X and its vicinity. The left end portion of X means the left end of X and its vicinity. The right end portion of X means the right end of X and its vicinity. The upper end portion of X means the upper end of X and its vicinity. The lower end portion of X means the lower end of X and its vicinity.

First, the structure of the transmission line10will be described with reference toFIG.1. The transmission line10transmits a high-frequency signal. The transmission line10is used to electrically connect two circuits in an electronic device such as a smartphone. As illustrated inFIG.1, the transmission line10includes the element body12, protective layers20aand20b, the signal conductor layer22, a first ground conductor layer24, a second ground conductor layer26, a third ground conductor layer27, signal terminals28aand28b, the plurality of interlayer connection conductorsv1andv2, and a plurality of interlayer connection conductorsv3andv4.

The element body12has a plate shape. Thus, the element body12includes an upper main surface and a lower main surface (main surface). The upper main surface and the lower main surface (main surface) of the element body12have a normal line extending in the element body up-down direction. The upper main surface and the lower main surface of the element body12each have a rectangular or substantially rectangular shape having long sides extending in the element body front-back direction. Therefore, the length of the element body12in the element body front-back direction is longer than the length of the element body12in the element body left-right direction.

As illustrated inFIG.1, the element body12includes insulator layers16ato16c,18a, and18b. The element body12has a structure in which the insulator layers16a,18a,16b,18b, and16care laminated in this order from top to bottom in the element body up-down direction. The insulator layers16ato16c,18a, and18bhave the same rectangular or substantially rectangular shape as the element body12when viewed in the element body up-down direction. The insulator layers16ato16care dielectric sheets having flexibility. The material of the insulator layers16ato16cis, for example, thermoplastic resin. The thermoplastic resin is, for example, a liquid crystal polymer, polytetrafluoroethylene (PTFE), or the like. In addition, the material of the insulator layers16ato16cmay be polyimide. The insulator layer18ais an adhesive layer that adheres the insulator layer16ato the insulator layer16b. The insulator layer18ais a single insulator layer. The insulator layer18abeing a single layer means that the insulator layer18adoes not have a structure in which a plurality of insulator layers is bonded to each other. The insulator layer18bis an adhesive layer that adheres the insulator layer16bto the insulator layer16c. The insulator layer18bis a single insulator layer. The insulator layer18b(second insulator layer) is provided below the insulator layer18a(first insulator layer) in the element body up-down direction. In this specification, “the insulator layer18bis provided below the insulator layer18ain the element body up-down direction” refers to the following state. The insulator layer18bis arranged below a plane (upper main surface) that passes through an upper end of the insulator layer18aand is orthogonal to the element body up-down direction in the element body up-down direction. In this case, the insulator layer18aand the insulator layer18bmay be arranged, and are not necessary to be arranged in the element body up-down direction. Each of the insulator layers18aand18bis an adhesive sheet, a liquid adhesive applied by printing or the like, a viscous bonding sheet adhered in a sheet state, or the like. The material of the insulator layers18aand18bis, for example, epoxy resin, fluorine-based resin, acrylic resin, or the like. As described above, the material of the insulator layer18a(first insulator layer) is different from the material of the insulator layer16b(third insulator layer) provided below the insulator layer18a(first insulator layer) in the element body up-down direction.

As illustrated inFIG.1, the signal conductor layer22is provided below the insulator layer18a(first insulator layer) in the element body12in the element body up-down direction. In addition, the signal conductor layer22is provided above the insulator layer18b(second insulator layer) in the element body12in the element body up-down direction. In the present preferred embodiment, the signal conductor layer22is provided on the upper main surface of the insulator layer16b. Thus, the signal conductor layer22is provided in the element body12. The signal conductor layer22has a linear shape. The signal conductor layer22extends in the element body front-back direction. The signal conductor layer22is located at the center of the upper main surface of the insulator layer16bin the element body left-right direction.

The first ground conductor layer24is provided above the insulator layer18a(first insulator layer) in the element body12in the element body up-down direction. In the present preferred embodiment, the first ground conductor layer24is provided on the upper main surface of the insulator layer16a. Thus, the first ground conductor layer24is located above the signal conductor layer22in the element body up-down direction. In this specification, “the first ground conductor layer24being located above the signal conductor layer22in the element body up-down direction” refers to the following state. At least a portion of the first ground conductor layer24is arranged in a region through which the signal conductor layer22passes when moving in parallel in an element body upward direction. Therefore, the first ground conductor layer24may be located within the region through which the signal conductor layer22passes when moving in parallel in the element body upward direction, or may protrude from the region through which the signal conductor layer22passes when moving in parallel in the element body upward direction. In the present preferred embodiment, the first ground conductor layer24covers the entire or substantially the entire upper main surface of the insulator layer16a. Therefore, the first ground conductor layer24protrudes from the region through which the signal conductor layer22passes when moving in parallel in the element body upward direction. In addition, the first ground conductor layer24overlaps the signal conductor layer22when viewed in the element body up-down direction.

The second ground conductor layer26is provided below the insulator layer18b(second insulator layer) in the element body12in the element body up-down direction. In the present preferred embodiment, the second ground conductor layer26is provided on the lower main surface of the insulator layer16c. Thus, the second ground conductor layer26is located below the signal conductor layer22in the element body up-down direction. In the present preferred embodiment, the second ground conductor layer26covers the entire or substantially the entire lower main surface of the insulator layer16c. Thus, the second ground conductor layer26overlaps the signal conductor layer22when viewed in the element body up-down direction. As a result, the signal conductor layer22, the first ground conductor layer24, and the second ground conductor layer26have a strip line structure.

The third ground conductor layer27is provided below the insulator layer18a(first insulator layer) in the element body12in the element body up-down direction. In the present preferred embodiment, the third ground conductor layer27is provided on the upper main surface of the insulator layer16b. The third ground conductor layer27surrounds the signal conductor layer22when viewed in an up-down direction. Therefore, the third ground conductor layer27is provided on the left and right of the signal conductor layer22in the element body left-right direction.

The plurality of interlayer connection conductorsv1andv2electrically connects the first ground conductor layer24, the second ground conductor layer26, and the third ground conductor layer27. More specifically, the plurality of interlayer connection conductorsv1andv2passes through the insulator layers16ato16c,18a, and18bin the element body up-down direction. Upper ends of the plurality of interlayer connection conductorsv1andv2are connected to the first ground conductor layer24. Lower ends of the plurality of interlayer connection conductorsv1andv2are connected to the second ground conductor layer26. Intermediate portions of the plurality of interlayer connection conductorsv1andv2are connected to the third ground conductor layer27. The plurality of interlayer connection conductorsv1is provided on the left of the signal conductor layer22in the element body left-right direction. The plurality of interlayer connection conductorsv1is arranged in a row at equal or substantially equal intervals in the element body front-back direction. The plurality of interlayer connection conductorsv2is provided on the right of the signal conductor layer22in the element body left-right direction. The plurality of interlayer connection conductorsv2is arranged in a row at equal or substantially equal intervals in the element body front-back direction.

The signal terminal28ais provided on the upper main surface of the element body12. More specifically, the signal terminal28ais provided at the front end portion of the upper main surface of the insulator layer16a. The signal terminal28aoverlaps the left end portion of the signal conductor layer22when viewed in the element body up-down direction. However, the signal terminal28adoes not overlap a first hole H1and a second hole H2described later when viewed in the element body up-down direction. The signal terminal28aeach have a rectangular or substantially rectangular shape when viewed in the element body up-down direction. The first ground conductor layer24is not provided around the signal terminal28aso that the signal terminal28ais insulated from the first ground conductor layer24.

The interlayer connection conductorv3electrically connects the signal terminal28ato the signal conductor layer22. To be specific, the interlayer connection conductorv3passes through the insulator layers16aand18ain the element body up-down direction. The upper end of the interlayer connection conductorv3is connected to the signal terminal28a. The lower end of the interlayer connection conductorv3is connected to the front end portion of the signal conductor layer22. Thus, the signal terminal28ais electrically connected to the signal conductor layer22. A high-frequency signal is input to and output from the signal conductor layer22through the signal terminal28a.

Note that the signal terminal28band the interlayer connection conductorv4have structures that are bilaterally symmetrical to the signal terminal28aand the interlayer connection conductorv3. Therefore, description of the signal terminal28band the interlayer connection conductorv4will be omitted.

The signal conductor layer22, the first ground conductor layer24, the second ground conductor layer26, the third ground conductor layer27, and the signal terminals28aand28bdescribed above are formed by, for example, applying etching to metal foil provided on the upper main surfaces or the lower main surfaces of the insulator layers16ato16c. The metal foil is, for example, copper foil. In addition, the interlayer connection conductorsv1tov4are, for example, through-hole conductors. The through-hole conductors are produced by forming through-holes in the insulator layers16ato16c,18a, and18band plating the through-holes.

The protective layers20aand20bare flexible insulator layers. However, the protective layers20aand20bare not part of the element body12. The protective layers20aand20bhave the same rectangular or substantially rectangular shape as the element body12when viewed in the element body up-down direction.

The protective layer20acovers the entire or substantially the entire upper main surface of the insulator layer16a. Thus, the protective layer20aprotects the first ground conductor layer24. However, openingsh1toh6are provided in the protective layer20a. The openingh1overlaps the signal terminal28awhen viewed in the element body up-down direction. Thus, the signal terminal28ais exposed to the outside from the transmission line10through the openingh1. The openingh2is provided on the left of the openingh1in the element body left-right direction. The openingh3is provided on the right of the openingh1in the element body left-right direction. Thus, the first ground conductor layer24is exposed to the outside from the transmission line10through the openingsh2andh3. Note that the structures of the openingsh4toh6are bilaterally symmetrical to the structures of the openingsh1toh3. Therefore, description of the openingsh4toh6will be omitted.

Next, the first hole H1and the second hole H2will be described with reference toFIG.1andFIG.2. The insulator layer18ais provided with the first hole H1penetrating through the insulator layer18ain the element body up-down direction. More specifically, as illustrated inFIG.1, when viewed in the element body up-down direction, the first hole H1has a rectangular or substantially rectangular shape having long sides extending in the element body front-back direction. The first hole H1is provided at the center of the insulator layer18ain the element body left-right direction. Thus, at least a portion of the first hole H1overlaps the signal conductor layer22when viewed in the element body up-down direction. As illustrated inFIG.2, the signal conductor layer22is located in the first hole H1. However, the front end and the rear end of the signal conductor layer22do not overlap the first hole H1when viewed in the element body up-down direction. That is, the front end and the rear end of the signal conductor layer22are not located in the first hole H1.

In addition, as illustrated inFIG.2, the right end portion of the left portion of the third ground conductor layer27is located in the first hole H1. The left end portion of the right portion of the third ground conductor layer27is located in the first hole H1.

Here, as illustrated inFIG.2, a surface on which the insulator layer18aincludes the first hole H1is defined as a first hole forming surface S1. In addition, the first hole forming surface S1includes a left portion S1L and a right portion S1R. Further, the left portion S1L of the first hole forming surface S1has an upper end P1LU and a lower end P1LD. The right portion S1R of the first hole forming surface S1includes an upper end P1RU and a lower end P1RD.

The left portion S1L of the first hole forming surface S1has an arc shape protruding in an element body left direction when viewed in the element body front-back direction. That is, the left portion S1L of the first hole forming surface S1is curved so as to protrude in the element body left direction from the upper end P1LU of the left portion S1L of the first hole forming surface S1and the lower end P1LD of the left portion S1L of the first hole forming surface S1in a cross section orthogonal to the element body front-back direction. Thus, the center of the left portion S1L of the first hole forming surface S1in the element body up-down direction is at the leftmost position in the left portion S1L. As described above, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the left portion S1L of the first hole forming surface S1includes a portion located on the left of the upper end P1LU of the left portion S1L of the first hole forming surface S1and the lower end P1LD of the left portion S1L of the first hole forming surface S1in the element body left-right direction.

The right portion S1R of the first hole forming surface S1has an arc shape protruding in an element body right direction when viewed in the element body front-back direction. That is, the right portion S1R of the first hole forming surface S1is curved so as to protrude in the element body right direction from the upper end P1RU of the right portion S1R of the first hole forming surface S1and the lower end P1RD of the right portion S1R of the first hole forming surface S1in the cross section orthogonal to the element body front-back direction. Thus, the center of the right portion S1R of the first hole forming surface S1in the element body up-down direction is on the rightmost position in the right portion S1R. As described above, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the right portion S1R of the first hole forming surface S1includes a portion located on the right of the upper end P1RU of the right portion S1R of the first hole forming surface S1and the lower end P1RD of the right portion S1R of the first hole forming surface S1in the element body left-right direction.

The insulator layer18bis provided with the second hole H2penetrating through the insulator layer18bin the element body up-down direction. More specifically, as illustrated inFIG.1, when viewed in the element body up-down direction, the second hole H2has a rectangular or substantially rectangular shape having long sides extending in the element body front-back direction. The second hole H2is provided at the center of the insulator layer18bin the element body left-right direction. Thus, at least a portion of the second hole H2overlaps the signal conductor layer22when viewed in the element body up-down direction. However, the front end and the rear end of the signal conductor layer22do not overlap the second hole H2when viewed in the element body up-down direction.

Here, a surface on which the insulator layer18bincludes the second hole H2is defined as a second hole forming surface S2. In addition, the second hole forming surface S2includes a left portion S2L and a right portion S2R. Further, the left portion S2L of the second hole forming surface S2includes an upper end P2LU and a lower end P2LD. The right portion S2R of the second hole forming surface S2includes an upper end P2RU and a lower end P2RD.

The left portion S2L of the second hole forming surface S2has an arc shape protruding in the element body left direction when viewed in the element body front-back direction. That is, the left portion S2L of the second hole forming surface S2is curved so as to protrude in the element body left direction from the upper end P2LU of the left portion S2L of the second hole forming surface S2and the lower end P2LD of the left portion S2L of the second hole forming surface S2in the cross section orthogonal to the element body front-back direction. Thus, the center of the left portion S2L of the second hole forming surface S2in the element body up-down direction is on the leftmost position in the left portion S2L. As described above, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the left portion S2L of the second hole forming surface S2includes a portion located on the left of the upper end P2LU of the left portion S2L of the second hole forming surface S2and the lower end P2LD of the left portion S2L of the second hole forming surface S2in the element body left-right direction.

The right portion S2R of the second hole forming surface S2has an arc shape protruding in the element body right direction when viewed in the element body front-back direction. That is, the right portion S2R of the second hole forming surface S2is curved so as to protrude in the element body right direction from the upper end P2RU of the right portion S2R of the second hole forming surface S2and the lower end P2RD of the right portion S2R of the second hole forming surface S2in the cross section orthogonal to the element body front-back direction. Thus, the center in the element body up-down direction of the right portion S2R of the second hole forming surface S2is on the rightmost position in the right portion S2R. As described above, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the right portion S1R of the second hole forming surface S2includes a portion located on the right of the upper end P2RU of the right portion S2R of the second hole forming surface S2and the lower end P2RD of the right portion S2R of the second hole forming surface S2in the element body left-right direction.

A non-limiting example of a method of forming the first hole H1and the second hole H2as described above will be described. As a method of forming the first hole H1and the second hole H2, there are a thermal expansion method, a volatilization method, and a pressure method.

In the thermal expansion method, a difference between a coefficient of linear expansion of the insulator layers16ato16cand a coefficient of linear expansion of the insulator layers18aand18bis used. When the insulator layers16ato16c,18a, and18bare subjected to thermal pressure-bonding, the first hole H1is reduced in size due to the pressure of thermal pressure-bonding. Here, the coefficient of linear expansion of the insulator layers18aand18bare larger than the coefficient of linear expansion of the insulator layers16ato16c. For this reason, when the thermal pressure-bonding of the insulator layers16ato16c,18a, and18bis completed and the insulator layers16ato16c,18a, and18bare cooled, the insulator layers18aand18bare contracted more than the insulator layers16ato16c. However, the upper main surface of the insulator layer18ais bonded to the lower main surface of the insulator layer16a. The lower main surface of the insulator layer18ais bonded to the upper main surface of the insulator layer16b. Therefore, the upper main surface and the lower main surface of the insulator layer18aare respectively constrained by the lower main surface of the insulator layer16aand the upper main surface of the insulator layer16b. Therefore, the left portion S1L of the first hole forming surface S1is deformed so as to protrude in the element body left direction. Similarly, the right portion S1R of the first hole forming surface S1is deformed so as to protrude in the element body right direction. Similarly, the left portion S2L of the second hole forming surface S2is deformed so as to protrude in the element body left direction. Similarly, the right portion S2R of the second hole forming surface S2is deformed so as to protrude in the element body right direction. Thus, the first hole H1and the second hole H2are formed.

In the volatilization method, volatilization of components contained in the insulator layers18aand18bby thermal pressure-bonding of the insulator layers16ato16c,18a, and18bis used. More specifically, when the insulator layers16ato16c,18a, and18bare subjected to thermal pressure-bonding, the first hole H1and the second hole H2are reduced in size due to the pressure of thermal pressure-bonding. Here, components contained in the insulator layers18aand18bare volatilized by the thermal pressure-bonding of the insulator layers16ato16c,18a, and18b. Therefore, the rate of decrease in the volumes of the insulator layers18aand18bbefore and after thermal pressure-bonding is greater than the rate of decrease in the volumes of the insulator layers16ato16cbefore and after thermal pressure-bonding. However, the upper main surface of the insulator layer18ais bonded to the lower main surface of the insulator layer16a. The lower main surface of the insulator layer18ais bonded to the upper main surface of the insulator layer16b. Therefore, the upper main surface and the lower main surface of the insulator layer18aare respectively constrained by the lower main surface of the insulator layer16aand the upper main surface of the insulator layer16b. Therefore, the left portion S1L of the first hole forming surface S1is deformed so as to protrude in the element body left direction. Similarly, the right portion S1R of the first hole forming surface S1is deformed so as to protrude in the element body right direction. Similarly, the left portion S2L of the second hole forming surface S2is deformed so as to protrude in the element body left direction. Similarly, the right portion S2R of the second hole forming surface S2is deformed so as to protrude in the element body right direction. Thus, the first hole H1and the second hole H2are formed.

In the pressure method, expansion of the first hole H1and the second hole H2after thermal pressure-bonding of the insulator layers16ato16c,18a, and18bis used. More specifically, when the insulator layers16ato16c,18a, and18bare subjected to thermal pressure-bonding, the first hole H1and the second hole H2are reduced in size due to the pressure of thermal pressure-bonding. When the thermal pressure-bonding of the insulator layers16ato16c,18a, and18bis completed, the pressures applied to the first hole H1and the second hole H2become small, and thus the first hole H1and the second hole H2become large. However, the upper main surface of the insulator layer18ais bonded to the lower main surface of the insulator layer16a. The lower main surface of the insulator layer18ais bonded to the upper main surface of the insulator layer16b. Therefore, the upper main surface and the lower main surface of the insulator layer18aare respectively constrained by the lower main surface of the insulator layer16aand the upper main surface of the insulator layer16b. Therefore, the left portion S1L of the first hole forming surface S1is deformed so as to protrude in the element body left direction. Similarly, the right portion S1R of the first hole forming surface S1is deformed so as to protrude in the element body right direction. Similarly, the left portion S2L of the second hole forming surface S2is deformed so as to protrude in the element body left direction. Similarly, the right portion S2R of the second hole forming surface S2is deformed so as to protrude in the element body right direction. Thus, the first hole H1and the second hole H2are formed.

Structure of Electronic Device

Next, a structure of an electronic device1including the transmission line10will be described with reference to the drawings.FIG.3is a left side view of the electronic device1including the transmission line10. The electronic device1is, for example, a portable wireless communication terminal. The electronic device1is, for example, a smartphone.

The transmission line10is bent as illustrated inFIG.3. “The transmission line10is bent” means that the transmission line10is deformed and bent by an external force being applied to the transmission line10. Hereinafter, a section in which the transmission line10is bent is referred to as a bending section A2. Sections in which the transmission line10is not bent are referred to as non-bending sections A1and A3. An x-axis, a y-axis, and a z-axis in the electronic device1are defined as follows. The x-axis is the element body front-back direction in the non-bending section A1. The y-axis is the element body left-right direction in the non-bending section A1. The z-axis is the element body up-down direction in the non-bending section A1. The non-bending section A1, the bending section A2, and the non-bending section A3are arranged in this order in the positive direction of the x-axis.

As illustrated inFIG.3, the bending section A2is bent in a z-axis direction. Therefore, as illustrated inFIG.3, the element body up-down direction and the element body front-back direction differ depending on the position of the transmission line10. In the non-bending section A1and the non-bending section A3(for example, a position (1)) in which the element body12is not bent, the element body up-down direction and the element body front-back direction coincide with the z-axis direction and an x-axis direction, respectively. On the other hand, in the bending section A2(for example, a position (2)) in which the element body12is bent, 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.

As illustrated inFIG.3, the electronic device1includes the transmission line10, connectors30a,30b,102a, and102b, and circuit substrates100and110.

The circuit substrates100and110have a plate shape. The circuit substrate100includes main surfaces S5and S6. The main surface S5is located on the negative direction side of the z-axis relative to the main surface S6. The circuit substrate110includes main surfaces S11and S12. Main surface S11is located on the negative direction side of the z-axis relative to the main surface S12. The circuit substrates100and110includes a wiring conductor layer, a ground conductor layer, an electrode, and the like (not illustrated).

The connectors30aand30bare mounted on main surfaces (upper main surfaces) of the non-bending section A1and the non-bending section A3on the positive direction side of the z-axis, respectively. More specifically, the connector30ais mounted on the signal terminal28aand the first ground conductor layer24exposed from the openingsh1toh3. The connector30bis mounted on the signal terminal28band the first ground conductor layer24exposed from the openingsh4toh6.

The connectors102aand102bare mounted on the main surface S5of the circuit substrate100and the main surface S11of the circuit substrate110, respectively. The connectors102aand102bare connected to the connectors30aand30b, respectively. Thus, the transmission line10electrically connects the circuit substrate100and the circuit substrate110.

Effects

According to the transmission line10, it is possible to reduce the transmission loss of the transmission line10. More specifically, the insulator layer18ais provided with the first hole H1penetrating through the insulator layer18ain the element body up-down direction. Air having a low dielectric constant is present in the first hole H1. At least a portion of the first hole H1overlaps the signal conductor layer22when viewed in the element body up-down direction. Therefore, the dielectric constant around the signal conductor layer22is reduced. As a result, in the transmission line10, the occurrence of dielectric loss in the high-frequency signal transmitted through the signal conductor layer22is reduced or prevented, and thus the transmission loss of the transmission line10is reduced. The second hole H2also contributes to a reduction in the transmission loss of the transmission line10for the same reason as the first hole H1.

Further, according to the transmission line10, it is possible to reduce the transmission loss of the transmission line10while reducing or preventing separation between the insulator layer16aand the insulator layer18aand separation between the insulator layer16band the insulator layer18a. More specifically, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the left portion S1L of the first hole forming surface S1includes a portion located on the left of the upper end P1LU of the left portion S1L of the first hole forming surface S1and the lower end P1LD of the left portion S1L of the first hole forming surface S1in the element body left-right direction. Accordingly, the upper end P1LU of the left portion S1L of the first hole forming surface S1is away from the left surface of the element body12. That is, a region where the insulator layer16aand the insulator layer18aare bonded to each other is widened. Similarly, the lower end P1LD of the left portion S1L of the first hole forming surface S1is away from the left surface of the element body12. That is, a region where the insulator layer16band the insulator layer18aare bonded to each other is widened. As a result, the separation between the insulator layer16aand the insulator layer18aand the separation between the insulator layer16band the insulator layer18aare reduced or prevented.

Further, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the left portion S1L of the first hole forming surface S1includes a portion located on the left of the upper end P1LU of the left portion S1L of the first hole forming surface S1and the lower end P1LD of the left portion S1L of the first hole forming surface S1in the element body left-right direction. As a result, the left portion S1L of the first hole forming surface S1has a shape protruding in the element body left direction in the cross section orthogonal to the element body front-back direction. Therefore, the volume of the first hole H1is large. As a result, in the transmission line10, the occurrence of dielectric loss in the high-frequency signal transmitted through the signal conductor layer22is reduced or prevented, and thus the transmission loss of the transmission line10is reduced. For the same reason as the first hole H1, the second hole H2also contributes to reduction or prevention of separation between the insulator layer16band the insulator layer18b, reduction or prevention of separation between the insulator layer16cand the insulator layer18b, and reduction or prevention of the transmission loss of the transmission line10.

Note that the right portion S1R of the first hole forming surface S1has a shape that is bilaterally symmetrical to the left portion S1L of the first hole forming surface S1. Thus, according to the transmission line10, it is possible to reduce the transmission loss of the transmission line10while reducing or preventing the separation between the insulator layer16aand the insulator layer18aand the separation between the insulator layer16band the insulator layer18a.

In addition, the left portion S1L of the first hole forming surface S1has a shape protruding in the element body left direction in the cross section orthogonal to the element body front-back direction. The left portion S1L of the first hole forming surface S1is curved. As a result, when force is applied to the transmission line10, concentration of stress on a portion of the left portion S1L is reduced or prevented. That is, the transmission line10is less likely to be damaged.

In addition, according to the transmission line10, since the first hole H1is provided, the element body12is easily deformed. As a result, it becomes easy to bend the transmission line10to be used. Further, the amount of an adhesive used in the transmission line10is reduced. Therefore, the manufacturing cost of the transmission line10can be reduced and the reduction in weight of the transmission line10can be achieved. Note that like the first hole H1, the second hole H2also contributes to easily deforming the element body12and reducing the amount of the adhesive.

Further, according to the transmission line10, the transmission loss of the transmission line10can be reduced for the following reason. More specifically, an electric field is radiated from the signal conductor layer22. The electric field is more likely to pass through the insulator layer16ahaving a higher dielectric constant than the first hole H1having a lower dielectric constant. Therefore, when the insulator layer16ais present near the signal conductor layer22, the electric field radiated by the signal conductor layer22extends in the element body left direction and passes through the insulator layer16a. In this case, on the left surface of the signal conductor layer22, the electric field is concentrated at the corner of the signal conductor layer22. Such concentration of the electric field causes concentration of current at the corner of the signal conductor layer22. As a result, the transmission loss of the transmission line10may increase.

Therefore, as illustrated inFIG.2, in the cross section orthogonal to the element body front-back direction, the left portion S1L of the first hole forming surface S1includes a portion located on the left of the upper end P1LU of the left portion S1L of the first hole forming surface S1and the lower end P1LD of the left portion S1L of the first hole forming surface S1in the element body left-right direction. Therefore, the left portion S1L of the first hole forming surface S1protrudes in a direction away from the signal conductor layer22. Thus, the insulator layer18alocated near the signal conductor layer22is reduced. Therefore, the electric field radiated by the signal conductor layer22spreads in an upper left direction of the element body. In this case, on the left surface of the signal conductor layer22, concentration of the electric field at the corner of the signal conductor layer22is reduced or prevented. As a result, according to the transmission line10, the transmission loss of the transmission line10can be reduced or prevented.

In the transmission line10, since the first hole H1is located near the interlayer connection conductorsv1andv2, capacitance is less likely to be generated between the signal conductor layer22and the interlayer connection conductorsv1andv2. This makes it possible to bring the signal conductor layer22close to the interlayer connection conductorsv1andv2. Note that “the first hole H1is located near the interlayer connection conductor v1” means, for example, that the distance between the left end of the first hole H1and the interlayer connection conductorv1located on the left of the first hole H1in the element body left-right direction is shorter than the distance between the interlayer connection conductorv1and the signal conductor layer22.

In the transmission line10, since the first hole H1is located near the interlayer connection conductorsv1andv2, the wavelengths of the high-frequency signals transmitted through the plurality of interlayer connection conductorsv1andv2become longer. As a result, an interval between the plurality of interlayer connection conductorsv1and an interval between the plurality of interlayer connection conductorsv2are increased.

Water vapor or the like in the air may oxidize a conductor layer such as the signal line conductor layer20and degrade signal characteristics. In the transmission line10, since a contact area between the air in the first hole H1and resin18ais increased, performance of suction of the unnecessary gas contained in the air in the resin18ais increased, and the water vapor or the like contained in the air is reduced. As described above, according to the transmission line10, it is possible to reduce or prevent deterioration of characteristics by reducing water vapor or the like in the air.

In the transmission line10, the separation between the insulator layer16band the insulator layer18ais reduced or prevented. More specifically, when the right end portion of the left portion of the third ground conductor layer27is not located in the first hole H1, the right end portion of the left portion of the third ground conductor layer27is located on the left of the left portion S1L of the first hole forming surface S1. In this case, a gap is formed between the insulator layer16band the insulator layer18ain the vicinity of the lower end P1LD of the left portion S1L of the first hole forming surface S1. Such a gap may cause the separation between the insulator layer16band the insulator layer18a. Thus, the right end portion of the left portion of the third ground conductor layer27is located in the first hole H1. That is, a portion of the third ground conductor layer27is located in the first hole H1. As a result, no gap is formed between the insulator layer16band the insulator layer18ain the vicinity of the lower end P1LD of the left portion S1L of the first hole forming surface S1. As a result, in the transmission line10, the insulator layer16band the insulator layer18aare reduced or prevented from being separated from each other.

In addition, in the transmission line10, as illustrated inFIG.2, the signal conductor layer22is located in the first hole H1. As a result, the signal conductor layer22comes into contact with air, so that the dielectric constant around the signal conductor layer22is lowered. As a result, the occurrence of dielectric loss in a high-frequency signal transmitted through the signal conductor layer22is reduced or prevented.

In addition, in the transmission line10, the signal terminal28adoes not overlap the first hole H1and the second hole H2described later when viewed in the element body up-down direction. As a result, the transmission line10is reduced or prevented from being damaged due to stress during thermal pressure-bonding when the transmission line10is manufactured.

First Modification

Hereinafter, a transmission line10aaccording to a first modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.4is a cross-sectional view of the transmission line10a.

The transmission line10ais different from the transmission line10in the positions where the first ground conductor layer24and the second ground conductor layer26are provided. More specifically, the first ground conductor layer24is provided on the lower main surface of the insulator layer16a. Thus, the first ground conductor layer24faces the first hole H1. The second ground conductor layer26is provided on the upper main surface of the insulator layer16c. Thus, the second ground conductor layer26faces the second hole H2. Since the other structure of the transmission line10ais the same as that of the transmission line10, the description thereof will be omitted. In addition, the transmission line10acan achieve the same effect as the transmission line10.

Second Modification

Hereinafter, a transmission line10baccording to a second modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.5is a cross-sectional view of the transmission line10b.FIG.6is a cross-sectional view of a transmission line500according to a comparative example.

The transmission line10bis different from the transmission line10in that the transmission line10bdoes not include the insulator layers16aand16c, the protective layers20aand20b, and the interlayer connection conductorsv1andv2. As described above, the insulator layers16aand16c, the protective layers20aand20b, and the interlayer connection conductorsv1andv2are not essential configurations. Note that in the transmission line10b, the first ground conductor layer24is attached to the upper main surface of the insulator layer18aby, for example, a transfer method. The second ground conductor layer26is attached to the lower main surface of the insulator layer18bby, for example, a transfer method. Since the other structure of the transmission line10bis the same as that of the transmission line10, the description thereof will be omitted. In addition, the transmission line10bcan achieve the same effect as the transmission line10.

The inventor of the present application performed a computer simulation described below in order to further clarify the effects of the transmission line10b. To be specific, a first model having the structure of the transmission line10band a second model having the structure of the transmission line500were created. A different point between the first model and the second model is each of the shapes of the first hole H1and the second hole H2. Note that a distance L1between the upper end P1LU and the upper end P1RU in the first model is equal to a distance L2between the upper end P1LU and the upper end P1RU in the second model. The inventor of the present application used a computer to calculate the distribution of the electric field around the signal conductor layer22using the first model and the second model. In addition, the inventor of the present application used a computer to calculate the relationship between the frequencies of the first model and the second model and the transmission losses of the first model and the second model. At this time, the inventor of the present application performed the calculation under a condition in which a high-frequency signal is applied between the first ground conductor layer24and the second ground conductor layer26while being electrically connected to each other, and the signal conductor layer22.

FIG.7is a diagram illustrating an electric field distribution of the first model.FIG.8is a diagram illustrating an electric field distribution of the second model. InFIG.7andFIG.8, a dark portion is a portion where the intensity of the electric field is high, and a light portion is a portion where the intensity of the electric field is low. WhenFIG.7andFIG.8are compared with each other, it can be seen that the region where the intensity of the electric field is low in the first model is wider than the region where the intensity of the electric field is low in the second model. In addition, it can be seen that the intensity of the electric field of the insulator layer having a larger dielectric loss than air is smaller in the first model than in the second model. It is considered that this is because the volumes of the first hole H1and the second hole H2of the first model are larger than the volumes of the first hole H1and the second hole H2of the second model. As described above, when the region where the intensity of the electric field is low in the first model becomes wider than the region where the intensity of the electric field is low in the second model and the intensity of the electric field of the insulator layer becomes low, the transmission loss of the high-frequency signal generated in the first model becomes smaller than the transmission loss of the high-frequency signal generated in the second model.

FIG.9is a diagram illustrating an electric field distribution at the left end portion of the signal conductor layer22of the first model.FIG.10is a diagram illustrating an electric field distribution at the left end portion of the signal conductor layer22of the second model. WhenFIG.9andFIG.10are compared with each other, it can be seen that the concentration of the electric field at the corner of the signal conductor layer22is more reduced or prevented in the first model than in the second model. As a result, in the first model, concentration of current at the corner of the signal conductor layer22is reduced or prevented. As a result, in the first model, the transmission loss of the high-frequency signal is reduced more than in the second model.

FIG.11is a graph illustrating a relationship between frequencies of the first model and the second model and transmission losses of the first model and the second model. The horizontal axis represents the frequency of the high-frequency signal transmitted through the signal conductor layer22. The vertical axis represents the transmission loss of the transmission line per meter of the first model and the second model. According toFIG.11, it is understood that the transmission loss of the first model (transmission line10a) is smaller than the transmission loss of the second model (transmission line500).

Third Modification

Hereinafter, a transmission line10caccording to a third modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.12is a cross-sectional view of the transmission line10c.

The transmission line10cis different from the transmission line10ain that the transmission line10cfurther includes an insulator layer16dand third ground conductor layers27aand27b. More specifically, the insulator layer16dis provided between the insulator layer18aand the insulator layer16b. Thus, the signal conductor layer22is located between the insulator layer16dand the insulator layer16b. That is, the signal conductor layer22is not located in the first hole H1. As described above, since the signal conductor layer22is surrounded by the insulator layers16band16d, a short circuit between the signal conductor layer22and another conductor layer is reduced or prevented. Furthermore, deterioration of the signal conductor layer22due to oxidation or the like is reduced or prevented.

In addition, the third ground conductor layer27ais provided on the upper main surface of the insulator layer16b. The third ground conductor layer27bis provided on the lower main surface of the insulator layer16d. Since the other structure of the transmission line10cis the same as that of the transmission line10a, description thereof will be omitted. The transmission line10ccan achieve the same effect as the transmission line10.

In addition, the third ground conductor layer27ais located above the signal conductor layer22in the element body up-down direction, and the third ground conductor layer27bis located below the signal conductor layer22in the element body up-down direction. This improves a shielding property with respect to the signal conductor layer22.

Fourth Modification

Hereinafter, a transmission line10daccording to a fourth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.13is a cross-sectional view of the transmission line10d.

The transmission line10dis different from the transmission line10cin the position where the first ground conductor layer24and the second ground conductor layer26are provided. More specifically, the first ground conductor layer24is provided on the upper main surface of the insulator layer16a. The second ground conductor layer26is provided on the lower main surface of the insulator layer16c. Since the other structure of the transmission line10dis the same as that of the transmission line10c, description thereof will be omitted. In addition, the transmission line10dcan achieve the same effect as the transmission line10c.

Fifth Modification

Hereinafter, a transmission line10eaccording to a fifth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.14is a cross-sectional view of the transmission line10e.

The transmission line10eis different from the transmission line10in the thicknesses of the insulator layers16a,16c,18a, and18band the presence or absence of the holes H3and H4. More specifically, in the transmission line10e, the thicknesses of the insulator layers18aand18bare smaller than the thicknesses of the insulator layers16aand16c. In addition, the holes H3and H4are provided in the insulator layers16aand16c, respectively. The holes H3and H4penetrate the insulator layers16aand16cin the element body up-down direction, respectively. Further, the hole H3is connected to the first hole H1. The hole H4is connected to the second hole H2. Since the other structure of the transmission line10eis the same as that of the transmission line10, the description thereof will be omitted.

The insulator layers18aand18bare adhesive layers. Therefore, the thicknesses of the insulator layers18aand18bare likely to change when the element body12is pressure-bonded. Thus, the thicknesses of the insulator layers18aand18bare smaller than the thicknesses of the insulator layers16aand16b. The amount of change in the thicknesses of the insulator layers18aand18bduring pressure-bonding of the element body12is reduced. This reduces or prevents the occurrence of variations in the sizes of the first hole H1and the second hole H2in the element body up-down direction.

Sixth Modification

Hereinafter, a transmission line10faccording to a sixth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.15is a cross-sectional view of the transmission line10f.

The transmission line10fis different from the transmission line10ein that a first hole H11, a second hole H12, and holes H13and H14are provided in the element body12. More specifically, the first hole H1, the second hole H2, and the holes H3and H4are arranged on the left of the center of the element body12in the element body left-right direction. In addition, the first hole H11, the second hole H12, and the holes H13and H14are arranged on the right side of the center of the element body12in the element body left-right direction. Each of the first hole H11, the second hole H12, and the holes H13and H14has a bilaterally symmetrical structure with respect to the first hole H1, the second hole H2, and the holes H3and H4. Since the other structure of the transmission line10fis the same as that of the transmission line10e, description thereof will be omitted. In addition, the transmission line10fcan achieve the same effect as the transmission line10e.

According to the transmission line10f, a portion of each of the insulator layers16ato16c,18a, and18bis present between the first hole H1, the second hole H2, and the holes H3and H4and the first hole H11, the second hole H12, and the holes H13and H14. Thus, a portion of each of the insulator layers16ato16c,18a, and18bfunctions as a support. As a result, when the transmission line10fis bent, deformation of each of the first holes H1and H11, the second holes H2and H12, and the holes H3, H4, H13, and H14is reduced or prevented.

Seventh Modification

Hereinafter, a transmission line10gaccording to a seventh modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.16is a cross-sectional view of the transmission line10g.

The transmission line10gis different from the transmission line10fin that a first hole H21, a second hole H22, and holes H23and H24are provided in the element body12. More specifically, the first hole H21, the second hole H22, and the holes H23and H24are arranged on the right of the first hole H1, the second hole H2, and the holes H3and H4in the element body left-right direction. The first hole H21, the second hole H22, and the holes H23and H24are arranged on the left of the first hole H11, the second hole H12, and the holes H13and H14in the element body left-right direction. The first hole H21, the second hole H22, and the holes H23and H24have the same structure as the first hole H1, the second hole H2, and the holes H3and H4, respectively. Since the other structure of the transmission line10gis the same as that of the transmission line10f, description thereof will be omitted. In addition, the transmission line10gcan achieve the same effect as the transmission line10f.

According to the transmission line10g, a portion of each of the insulator layers16ato16c,18a, and18bis present between the first hole H1, the second hole H2, and the holes H3and H4and the first hole H21, the second hole H22, and the holes H23and H24. A portion of each of the insulator layers16ato16c,18a, and18bis present between the first hole H11, the second hole H12, and the holes H13and H14and the first hole H21, the second hole H22, and the holes H23and H24. Thus, a portion of each of the insulator layers16ato16c,18a, and18bfunctions as a support. As a result, when the transmission line10gis bent, the deformation of each of the first holes H1, H11, and H21, the second holes H2, H12, and H22, and the holes H3, H4, H13, H14, H23, and H24is reduced or prevented.

Eighth Modification

Hereinafter, a transmission line10haccording to an eighth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.17is a cross-sectional view of the transmission line10h.

The transmission line10his different from the transmission line10ein that the transmission line10hfurther includes insulator layers18cand18dand a first hole H31and a second hole H41are provided in the element body12. The insulator layer18cis provided above the insulator layer16ain the element body up-down direction. Therefore, the first ground conductor layer24is provided on the upper main surface of the insulator layer18c. The insulator layer18dis provided below the insulator layer16cin the element body up-down direction. Therefore, the second ground conductor layer26is provided on the lower main surface of the insulator layer18d.

The first hole H31penetrates the insulator layer18cin the element body up-down direction. The shape of the first hole H31is the same as that of the first hole H1. The first hole H31is connected to the hole H3. The second hole H41penetrates the insulator layer18din the element body up-down direction. The shape of the second hole H41is the same as that of the first hole H1. The second hole H41is connected to the hole H4. Since the other structure of the transmission line10his the same as that of the transmission line10e, description thereof will be omitted. In addition, the transmission line10hcan achieve the same effect as the transmission line10e.

The insulator layers18ato18dare adhesive layers. Therefore, the thicknesses of the insulator layers18ato18dare likely to change when the element body12is pressure-bonded. Thus, the thicknesses of the insulator layers18ato18dare smaller than the thicknesses of the insulator layers16aand16c. The amount of change in the thicknesses of the insulator layers18ato18dduring pressure-bonding of the element body12is reduced. This reduces or prevents the occurrence of variations in the sizes of the first holes H1and H31, the second holes H2and H41, and the holes H3and H4in the element body up-down direction.

In addition, when a material having a dielectric constant lower than that of the material of the insulator layer16bor a material having a dielectric loss tangent lower than that of the material of the insulator layer16bis used as the material of the insulator layers16aand16c, the reduction in the transmission loss of the transmission line10hcan be achieved.

Ninth Modification

Hereinafter, a transmission line10iaccording to a ninth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.18is a cross-sectional view of the transmission line10i.

The transmission line10iis different from the transmission line10cin that the transmission line10iincludes a plurality of conductor objects200instead of the interlayer connection conductorsv1andv2. More specifically, the plurality of conductor objects200is, for example, metallic balls whose surfaces are covered with solder or a conductive adhesive. The diameters of the metallic balls of the plurality of conductor objects200are uniform. The plurality of conductor objects200is provided in the insulator layer18a(first insulator layer). The plurality of conductor objects200electrically connects the first ground conductor layer24and the third ground conductor layer27a.

The plurality of conductor objects200is provided in the insulator layer18b. The plurality of conductor objects200electrically connects the second ground conductor layer26and the third ground conductor layer27b. The plurality of conductor objects200is bonded to the second ground conductor layer26and the third ground conductor layer27b. Since the other structure of the transmission line10iis the same as that of the transmission line10c, description thereof will be omitted. In addition, the transmission line10ican achieve the same effect as the transmission line10c.

According to the transmission line10i, the interlayer connection conductorsv1andv2become unnecessary. Therefore, a plating step for forming the interlayer connection conductorsv1andv2is not required. Therefore, the plating solution does not enter the transmission line10i.

According to the transmission line10i, a distance between the insulator layer16aand the insulator layer16dis substantially determined by the diameters of the metallic balls of the plurality of conductor objects200. Similarly, a distance between the insulator layer16band the insulator layer16cis substantially determined by the diameters of the metallic balls of the plurality of conductor objects200. This reduces or prevents variations in the distance between the insulator layer16aand the insulator layer16dand the distance between the insulator layer16band the insulator layer16c. That is, variations in the size of the first hole H1in the element body up-down direction and the size of the second hole H2in the element body up-down direction are reduced or prevented.

Tenth Modification

Hereinafter, a transmission line10jaccording to a tenth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.19is a cross-sectional view of the transmission line10j.

The transmission line10jis different from the transmission line10cin that the transmission line10jfurther includes insulator layers16eand16fand conductor layers150,152,160, and162. More specifically, the insulator layer16eis provided above the insulator layer16ain the element body up-down direction. The insulator layer16fis provided below the insulator layer16cin the element body up-down direction. The conductor layer150is provided on the lower main surface of the insulator layer16e. The conductor layer152is provided on the upper main surface of the insulator layer16e. The conductor layer160is provided on the upper main surface of the insulator layer16f. The conductor layer162is provided on the lower main surface of the insulator layer16f. The conductor layers150,152,160, and162are signal wirings or ground conductors. By providing the conductor layers150,152,160, and162in this manner, an electric circuit is added to the transmission line10j. Since the other structure of the transmission line10jis the same as that of the transmission line10c, description thereof will be omitted. In addition, the transmission line10jcan achieve the same effect as the transmission line10c.

Eleventh Modification

Hereinafter, a transmission line10kaccording to an eleventh modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.20is a cross-sectional view of the transmission line10k.

The transmission line10kis different from the transmission line10jin that the transmission line10kincludes the plurality of conductor objects200instead of the interlayer connection conductorsv1andv2. More specifically, the diameters of the plurality of conductor objects200are uniform. The plurality of conductor objects200is provided in the insulator layer18a(first insulator layer). The plurality of conductor objects200electrically connects the first ground conductor layer24and the third ground conductor layer27a.

The plurality of conductor objects200is provided in the insulator layer18b. The plurality of conductor objects200electrically connects the second ground conductor layer26and the third ground conductor layer27b. Since the other structure of the transmission line10kis the same as that of the transmission line10j, description thereof will be omitted. In addition, the transmission line10kcan achieve the same effect as the transmission line10j.

Twelfth Modification

Hereinafter, a transmission line101according to a twelfth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.21is a cross-sectional view of the transmission line101.

The transmission line101is different from the transmission line10in that the transmission line101does not include the insulator layers16aand16c, the material of the insulator layer16bis the same as the material of the insulator layers18aand18b, and the interlayer connection conductorsv1andv2are via-hole conductors. More specifically, the insulator layer16b(third insulator layer) is provided below the insulator layer18a(first insulator layer) in the element body up-down direction. The material of the insulator layer16b(third insulator layer) is the same as the material of the insulator layers18aand18b(first insulator layer). The material of the insulator layers16b,18a, and18bis thermoplastic resin such as polyimide, liquid crystal polymer, and PTFE (polytetrafluoroethylene).

The first ground conductor layer24is provided on the upper main surface of the insulator layer18a. The second ground conductor layer26is provided on the lower main surface of the insulator layer18b. The interlayer connection conductorsv1andv2electrically connect the first ground conductor layer24and the second ground conductor layer26. The interlayer connection conductorsv1andv2are via-hole conductors. The via-hole conductors are produced by forming through-holes in the insulator layers16b,18a, and18b, filling the through-holes with a conductive paste, and then sintering the conductive paste. Since the other structure of the transmission line101is the same as that of the transmission line10, the description thereof will be omitted. In addition, the transmission line101can achieve the same effect as the transmission line10.

In the transmission line101, it is possible to reduce the transmission loss of the transmission line101. More specifically, in the transmission line, an adhesive layer may be used to bond a plurality of insulator layers. However, since the adhesive layer is required to have high adhesiveness, it may be difficult to use a material having a low dielectric constant or a low dielectric loss tangent for the adhesive layer. Therefore, in the transmission line101, the material of the insulator layers18aand18bis thermoplastic resin, which is the same as the material of the insulator layer16b. Therefore, the insulator layers18a,16b, and18bcan be bonded by thermal pressure-bonding. This eliminates the need for the adhesive layer for bonding the insulator layers. As a result, in the transmission line101, it is possible to reduce the transmission loss of the transmission line101.

In the transmission line101, the material of the insulator layer16bis the same as the material of the insulator layers18aand18b. Therefore, the coefficient of linear expansion of the insulator layer16bis equal to the coefficient of linear expansion of the insulator layers18aand18b. When the temperature of the transmission line101changes, this reduces or prevents stress generated in the element body12due to the difference between the coefficient of linear expansion of the insulator layer16band the coefficient of linear expansion of the insulator layers18aand18b.

In the transmission line101, the interlayer connection conductorsv1andv2, which are via-hole conductors, can be formed when the element body12is thermal pressure-bonded.

Thirteenth Modification

Hereinafter, a transmission line10maccording to a thirteenth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.22is a cross-sectional view of the transmission line10m.

The transmission line10mis different from the transmission line101in that the interlayer connection conductorsv1andv2are through-hole conductors. Since the other structure of the transmission line10mis the same as that of the transmission line101, description thereof will be omitted. In addition, the transmission line10mcan achieve the same effect as the transmission line101.

Fourteenth Modification

Hereinafter, a transmission line10naccording to a fourteenth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.23is a cross-sectional view of the transmission line10n.

The transmission line10nis different from the transmission line10in that the second hole H2is not provided. Since the other structure of the transmission line10nis the same as that of the transmission line10, the description thereof will be omitted. In addition, the transmission line10ncan achieve the same effect as the transmission line10. Note that also in the transmission lines10ato10m, the second hole H2is not necessary to be provided.

Fifteenth Modification

Hereinafter, a transmission line10oaccording to a fifteenth modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG.24is a cross-sectional view of the transmission line10o.

The transmission line10ois different from the transmission line10in that the transmission line10ofurther includes signal conductor layers22aand22b. The signal conductor layer22ais provided on the left of the signal conductor layer22in the element body left-right direction. The signal conductor layer22bis provided on the right of the signal conductor layer22in the element body left-right direction. Since the other structure of the transmission line10ois the same as that of the transmission line10, the description thereof will be omitted. In addition, the transmission line10ocan achieve the same effect as the transmission line10. Note that the transmission line10omay include two signal conductor layers or may include four or more signal conductor layers. In addition, two adjacent signal conductor layers among the plurality of signal conductor layers may constitute a differential transmission line. Note that the transmission lines10ato10mmay further include the signal conductor layers22aand22b.

Other Preferred Embodiments

Transmission lines according to preferred embodiments of the present invention are not limited to the transmission lines10and10ato10o, and can be changed within the scope of the gist of the present invention. Note that the configurations of the transmission lines10and10ato10omay be arbitrarily combined.

Note that in all cross sections of the transmission lines10and10ato10o, the left portion S1L of the first hole forming surface S1does not need to include a portion located on the left of the upper end P1LU and the lower end P1LD in the element body left-right direction. Therefore, in a portion of the cross sections of the transmission lines10and10ato10o, the left portion S1L of the first hole forming surface S1may include a portion located on the left of the upper end P1LU and the lower end P1LD in the element body left-right direction.

Note that in all the cross sections of the transmission lines10and10ato10o, the right portion S1R of the first hole forming surface S1does not need to include a portion located on the right of the upper end P1RU and the lower end P1RD in the element body left-right direction. Therefore, in a portion of the cross sections of the transmission line10and10ato10o, the right portion S1R of the first hole forming surface S1may include a portion located on the right of the upper end P1RU and the lower end P1RD in the element body left-right direction.

Note that in the transmission lines10and10ato10o, the second ground conductor layer26is not an essential configuration. In addition, when the transmission line10does not include the second ground conductor layer26, the insulator layers18band16c, and the protective layer20b, the signal conductor layer22and the first ground conductor layer24may have a microstrip line structure.

Note that in the transmission lines10and10ato10o, the right portion S1R of the first hole forming surface S1is not necessary to have a portion located on the right of the upper end P1RU and the lower end P1RD in the element body left-right direction in the cross section orthogonal to the element body front-back direction. However, in the case where both of the left portion S1L and the right portion S1R are curved, it is possible to effectively reduce the transmission loss of the transmission line10while effectively reducing or preventing the separation between the insulator layer16aand the insulator layer18aand the separation between the insulator layer16band the insulator layer18a, as compared with the case where either one of the left portion S1L and the right portion S1R is curved. Note that in each of the transmission lines10iand10k, the insulator layer18amay be an anisotropic conductive film. In this case, the plurality of conductor objects200is minute metal particles of the anisotropic conductive film.

Note that in the transmission lines10and10ato10o, the signal terminals28aand28bmay be provided on the lower main surface of the element body12.

Note that the transmission lines10and10ato10omay further include other circuits in addition to the strip line.

Note that electronic components other than the connectors30aand30bmay be mounted on the transmission lines10and10ato10o.

Note that the transmission lines10and10ato10ohave a linear shape when viewed in the element body up-down direction. However, the transmission lines10and10ato10omay be bent. Here, “the transmission lines10and10ato10oare bent” means that the transmission lines10and10ato10ohave a bent shape in a state where no external force is applied to the transmission lines10and10ato10o.

Note that in the transmission lines10and10ato10o, the first hole H1and the second hole H2may be provided in the non-bending sections A1and A3and are not necessary to be provided in the bending section A2.

Note that in the transmission line10, the right portion S1R of the first hole forming surface S1may have a shape that is not bilaterally symmetrical to the left portion S1L of the first hole forming surface S1. For example, when the distance between the signal conductor layer22and the lower end P1LD is different from a distance between the signal conductor layer22and the lower end of the side P1RD, the right portion S1R of the first hole forming surface S1has a shape that is not bilaterally symmetrical to the left portion S1L of the first hole forming surface S1. In such a case, one of the left portion S1L and the right portion S1R that is closer to the signal conductor layer22may be curved. In addition, one of the left portion S1L and the right portion S1R that is closer to the signal conductor layer22may be curved more than the other of the right portion S1R and the left portion S1L that is farther from the signal conductor layer22. However, when the curves of the left portion S1L and the right portion S1R are too large, the transmission line10is easily damaged by impact. Thus, the widths of the left portion S1L in the left-right direction and the right portion S1R in the left-right direction may be smaller than the thicknesses of the transmission line10in the up-down direction.