Transmission line and electronic device

Abstract

A transmission line (101A) comprises: a flexible substrate part (FSP) that includes flexible substrates (11), hollow sections (HS), and a signal line (12); and a rigid substrate part (RSP) that includes a rigid substrate (21) having a higher Young's modulus than the flexible substrate (11), a conductor layer (23) not in contact with the flexible substrate (11), and an interlayer connection conductor. The transmission line (101A) is configured to have: a thick section (TS) in which the rigid substrate part (RSP) is laminated on the flexible substrate part (FSP); and a thin section (TP) in which the rigid substrate part (RSP) is not laminated on the flexible substrate part (FSP). When viewed in the lamination direction, the signal line (12) continuously runs from the thick section (TS) to the thin section (TP), in the flexible substrate part (FSP). In the thick section (TS), the hollow sections (HS) are formed at positions overlapping the signal line (12) when viewed in the lamination direction.

Description

Transmission lines and electronic devices

[0001] The present invention relates to a transmission line for transmitting high-frequency signals and an electronic device including such a transmission line.

[0002] Patent Document 1 discloses a transmission line that reduces transmission loss and facilitates deformation. This patent document discloses a transmission line that includes a flexible laminate formed by stacking multiple resin layers, each of which has flexibility, and a hollow portion and a reinforcing conductor inside the laminate, the hollow portion being formed by arranging a signal conductor at a midpoint in the stacking direction of the multiple resin layers in the laminate and providing openings in some of the multiple resin layers.

[0003] Japanese Patent Application Laid-Open No. 2020-141406

[0004] In the high-frequency signal transmission line described in Patent Document 1, a flexible material is used as the substrate to make the thin portion of the laminate flexible. Therefore, the rigidity of the hollow portion formed in the thick portion of the laminate is low. This makes it prone to deformation due to external stress, resulting in unstable electrical characteristics. Furthermore, it is difficult to form the walls of the hollow portion and bond the layers together in the thin portion of the laminate.

[0005] Therefore, an object of the present invention is to provide a transmission line that maintains stable electrical characteristics even when deformed, and that facilitates the formation of walls in the hollow portion and interlayer bonding, and an electronic device equipped with such a transmission line.

[0006] a rigid substrate portion having a rigid substrate having a Young's modulus higher than that of the flexible substrate, and a conductive layer and an interlayer connection conductor that are not in contact with the flexible substrate; and a thick portion in which the rigid substrate portion is laminated on the flexible substrate portion, and a thin portion in which the rigid substrate portion is not laminated on the flexible substrate portion; the signal line passes continuously through the flexible substrate portion from the thick portion to the thin portion when viewed in the lamination direction; the hollow portion is formed in the thick portion at a position overlapping the signal line when viewed in the lamination direction; at least a portion of the rigid substrate is located between the conductive layer of the rigid substrate portion and the signal line; and at least a portion of the flexible substrate is located between the conductive layer of the flexible substrate portion and the signal line.

[0007] Furthermore, an electronic device as an example of the present disclosure is characterized by including the transmission line.

[0008] According to the present invention, a transmission line that maintains stable electrical characteristics even when deformed and that facilitates the formation of walls in the hollow portion and interlayer bonding, and an electronic device that includes the transmission line can be obtained.

[0009] FIG. 1A is a cross-sectional view of a transmission line 101A according to a first embodiment, and FIG. 1B is a cross-sectional view of a transmission line 101B according to the first embodiment. FIGS. 2A and 2B are cross-sectional views of a transmission line 102 according to a second embodiment. FIG. 3 is a cross-sectional view of each layer of the flexible substrate section and each layer obtained by separating the rigid substrate section. FIG. 4 is a plan view of each layer of the flexible substrate section and each layer obtained by separating the rigid substrate section. FIG. 5 is a cross-sectional view of a transmission line 103 according to a third embodiment. FIG. 6A is a cross-sectional view of a transmission line 104 according to a fourth embodiment, and FIG. 6B is a cross-sectional view of each layer of the flexible substrate section and each layer obtained by separating the rigid substrate section. FIG. 7 is a plan view of each layer of the flexible substrate section and each layer obtained by separating the rigid substrate section. FIG. 8 is a cross-sectional view of a transmission line 105 according to a fifth embodiment. FIG. 9 is a plan view of each layer of the flexible substrate section and each layer obtained by separating the rigid substrate section (before lamination). FIG. 10 is a cross-sectional view of a transmission line 106 according to a sixth embodiment. FIG. 11 is a plan view of each layer of the flexible substrate portion and each layer of the rigid substrate portion of the transmission line 106 separated (before lamination). FIGS. 12A and 12B are cross-sectional views of a transmission line 107 according to a seventh embodiment. FIG. 13 is a plan view of each layer of the flexible substrate portion and each layer of the transmission line 107 according to the seventh embodiment separated from the rigid substrate portion. FIG. 14 is a cross-sectional view of a transmission line 108 according to an eighth embodiment. FIG. 15 is a cross-sectional view of a transmission line 109 according to a ninth embodiment. FIG. 16 is a cross-sectional view of a transmission line 110 according to a tenth embodiment. FIG. 17 is a cross-sectional view of an electronic device 211 according to an eleventh embodiment.

[0010] Hereinafter, several specific examples will be given with reference to the drawings to illustrate several embodiments for carrying out the present invention. The same reference numerals are used for the same parts in each drawing. To facilitate explanation and understanding of the main points, the embodiments for carrying out the present invention are shown divided into several embodiments for the sake of convenience. However, partial omission, substitution, or combination of the configurations shown in different embodiments is possible. From the second embodiment onwards, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0011] First Embodiment In the first embodiment, basic components of a transmission line will be illustrated.

[0012] 1A is a cross-sectional view of a transmission line 101A according to the first embodiment, and FIG. 1B is a cross-sectional view of a transmission line 101B according to the first embodiment. Note that in the cross-sectional view, lines that appear in the cross section (appearing due to cutting) are depicted, and lines that exist behind the cross section are not shown in some places. This also applies to each embodiment described later.

[0013] 1A includes a flexible substrate portion FSP and a rigid substrate portion RSP. The flexible substrate portion FSP includes a flexible substrate 11, a hollow portion HS, a signal line 12, and a conductive layer 13. The rigid substrate portion RSP includes a rigid substrate 21 and a conductive layer 23.

[0014] The transmission line 101A is configured with a thick portion TS and a thin portion TP. The thick portion TS is a portion where the rigid substrate portion RSP is laminated on one surface (XY plane) of the flexible substrate portion FSP. The thin portion TP is a portion where the rigid substrate portion RSP is not laminated on the flexible substrate portion FSP.

[0015] The signal line 12 runs continuously through the flexible substrate portion FSP from the thick portion TS to the thin portion TP when viewed in the stacking direction (Z direction).

[0016] The hollow portion HS is formed in the thick portion TS at a position that overlaps the signal line 12 when viewed in the stacking direction (Z direction).

[0017] At least a portion of the rigid base material 21 is located between the signal line 12 and the conductor layer (rigid board portion side conductor layer) 23 of the rigid board portion RSP.

[0018] At least a part of flexible substrate 11 is located between signal line 12 and a conductive layer (conductive layer on the flexible substrate portion side) 13 of flexible substrate portion FSP.

[0019] With this configuration, in the thin portion TP, a stripline is formed by the signal line 12, the flexible board portion side conductor layer 13, and the flexible substrate 11 between the signal line 12 and the flexible board portion side conductor layer 13. In the thick portion TS, a stripline is formed by the signal line 12, the flexible board portion side conductor layer 13, the rigid board portion side conductor layer 23, the rigid substrate 21 between the signal line 12 and the rigid board portion side conductor layer 23, the flexible substrate 11 and hollow portion HS, and the flexible substrate 11 between the signal line 12 and the flexible board portion side conductor layer 13.

[0020] Although not shown in Fig. 1A, the flexible substrate portion FSP includes interlayer connection conductors, and the rigid substrate portion RSP also includes interlayer connection conductors.

[0021] When the conductive layer 13 on the flexible substrate side and the conductive layer 23 on the rigid substrate side are ground conductor layers of the same potential, the conductive layer 13 on the flexible substrate side and the conductive layer 23 on the rigid substrate side are electrically connected via an interlayer connecting conductor provided in the rigid substrate side.

[0022] 1B includes a flexible substrate portion FSP and a rigid substrate portion RSP. The rigid substrate portions RSP are stacked above and below both ends of the flexible substrate portion FSP. The flexible substrate portion FSP includes a flexible substrate 11, a hollow portion HS, a signal line 12, and a conductive layer 13. The rigid substrate portion RSP includes a rigid substrate 21 and a conductive layer 23.

[0023] With this configuration, in the thin portion TP, a stripline is formed by the signal line 12, the flexible board portion-side conductor layer 13, and the flexible substrate 11 between the signal line 12 and the flexible board portion-side conductor layer 13. In addition, in the thick portion TS, a stripline is formed by the signal line 12, the rigid board portion-side conductor layer 23, the rigid substrate 21 between the signal line 12 and the rigid board portion-side conductor layer 23, the flexible substrate 11, and the hollow portion HS. In this way, when viewed in the stacking direction (Z direction), the signal line 12 passes continuously through the flexible board portion FSP in the order of thick portion TS-thin portion TP-thick portion TS. In other words, the thick portions TS are present on both sides of the thin portion TP in the extension direction of the signal line 12.

[0024] In the example shown in FIG. 1B, the hollow portion HS is located both above and below the signal line 12 in the stacking direction.

[0025] The conductive foil attached to the flexible substrate 11 is, for example, copper foil, and the material of the flexible substrate 11 is, for example, liquid crystal polymer, polyimide, PTFE, etc. The Young's modulus of this flexible substrate 11 is approximately 5 GPa.

[0026] The conductive foil attached to the rigid substrate 21 is copper foil, and the material of the rigid substrate 21 is, for example, a glass-epoxy substrate (epoxy + glass cloth FR4), bismaleimide triazine + glass cloth, ceramic (LTCC, etc.), etc. In this way, by using an inorganic material or a mixed material in which an inorganic material is mixed with an organic material as the material of the rigid substrate 21, the Young's modulus can be increased. The Young's modulus of the rigid substrate 21 is approximately 20 GPa. It is preferable that the Young's modulus of the rigid substrate 21 is at least twice that of the flexible substrate 11. This is because the difference between rigidity and flexibility becomes clear, making the effects of the present invention more effective.

[0027] The dielectric constant of flexible substrate 11 is lower than that of rigid substrate 21. For example, the relative dielectric constant of rigid substrate 21 is 3.5 to 5.0, and the relative dielectric constant of flexible substrate 11 is 2.2 to 3.5.

[0028] Furthermore, the dielectric loss tangent of flexible substrate 11 is lower than that of rigid substrate 21. For example, the dielectric loss tangent of flexible substrate 11 is 0.0005 to 0.003, and the dielectric loss tangent of rigid substrate 21 is 0.002 to 0.01.

[0029] In the thick portion TS, a flexible substrate 11 with a lower dielectric constant than the rigid substrate 21 is disposed in the portion adjacent to the signal line 12, and a hollow portion HS is further formed. This allows the dielectric constant of the portion adjacent to the signal line 12 (region of high electric field strength) to be lower than that of other portions (regions of low electric field strength). As a result, the signal line 12 can be made thick while the characteristic impedance of the stripline is matched to the characteristic impedance in the thin portion TP, thereby effectively suppressing conductor loss.

[0030] Furthermore, the dielectric loss tangent of the flexible substrate 11 is lower than that of the rigid substrate 21. Therefore, the transmission loss of the stripline in the thin portion TP is lower than when a material with a higher dielectric loss tangent is used. In the thick portion TS, although the dielectric loss tangent of the rigid substrate 21 is relatively higher than that of the flexible substrate 11, a hollow portion HS is formed in the flexible substrate 11. Because the hollow portion HS is essentially filled with air, the dielectric loss tangent of the hollow portion HS is lower than that of the flexible substrate 11. Therefore, the overall (average) dielectric loss tangent of the dielectric between the signal line 12 and the rigid board portion-side conductor layer 23 in the thick portion TS is lower than when the hollow portion HS is absent. As a result, the transmission loss of the stripline in the thick portion TS is also lower than when the hollow portion HS is absent. In particular, because the dielectric loss tangent of the flexible substrate 11 close to the signal line (in the region of high electric field strength) is lower than that of other portions (in the region of low electric field strength), high-frequency loss can be effectively suppressed.

[0031] If the distance between adjacent hollow portions HS is less than a quarter wavelength of the transmission signal, the periodic change in the characteristic impedance caused by the change in the dielectric constant around the signal line 12 does not pose a problem.

[0032] The first embodiment provides the following effects.

[0033] (a) The thick portion TS is formed in the portion where the rigid substrate portion RSP is laminated on the flexible substrate portion FSP, and the thin portion TP is formed in the portion where the rigid substrate portion RSP is not laminated, and the hollow portion HS is formed in the thick portion TS where the rigid substrate portion is laminated, so that deformation of the flexible substrate portion FSP in the thin portion TP is easy, and since there is no hollow portion HS in the thin portion TP, changes in electrical characteristics due to deformation of the flexible substrate portion FSP in the thin portion TP are suppressed.

[0034] (b) The flexible substrate section FSP has a structurally continuous flexible substrate 11 as its main component, and the hollow section HS is formed in the structurally continuous substrate, making it easy to process. In other words, the hollow section HS can be processed without being affected by the step at the boundary between the thick section TS and the thin section TP. Furthermore, it is only necessary to adhere a flat rigid substrate onto the hollow section HS, making it easy to adhere each layer.

[0035] 1B, the hollow portion HS is formed in the flexible substrate 11, which is continuous from the thick portion TS to the thin portion TP and back to the thick portion TS, and therefore the relative positional accuracy of the hollow portions HS formed in the left and right thick portions TS is high. For this reason, it is also possible to configure a high-frequency filter by forming the hollow portions HS in the left and right thick portions TS in consideration of the phase of the signal flowing through the signal line 12.

[0036] (d) A transmission line with low dielectric loss can be obtained even when using a rigid substrate portion RSP with a relatively high dielectric loss tangent.

[0037] (e) Since the entire surface of the signal line 12 is covered with the conductive layers 13 and 23 serving as grounded conductive layers, there is no leakage of electromagnetic waves and no interference occurs with surrounding electronic circuits.

[0038] Second Embodiment In the second embodiment, an example is given of a transmission line illustrating a connection between a conductive layer on the flexible substrate portion side and a conductive layer on the rigid substrate portion side, a connection between a signal line and a signal line terminal, an interlayer connection conductor on the flexible substrate portion side, an interlayer connection conductor on the rigid substrate portion side, etc.

[0039] 2A and 2B are cross-sectional views of a transmission line 102 according to the second embodiment, with Fig. 2B being a cross-sectional view taken along line YY in Fig. 2A.

[0040] Figure 3 is a cross-sectional view of each layer of the flexible substrate portion and each layer of the rigid substrate portion separated (before lamination). Figure 4 is a plan view of each layer of the flexible substrate portion and each layer of the rigid substrate portion separated (before lamination). However, in Figures 3 and 4, the protective film PF shown in Figures 2(A) and 2(B) is omitted. Also, in Figure 4, the adhesive layer 3 shown in Figures 2(A), 2(B), and 3 is omitted. Also, the adhesive layer 3 between the conductor layer 13 and the rigid base material 21 in Figure 3 is omitted.

[0041] As shown in Fig. 3, the flexible substrate section FSP is a laminate of flexible substrates 11, each with a conductive foil attached to one side. This conductive foil is patterned before lamination. The rigid substrate section RSP is a substrate in which the conductive foil is patterned based on a rigid substrate in which a conductive foil is attached to one side of each of the rigid substrates 21.

[0042] The flexible substrate section FSP is formed by heating and pressing flexible substrates 11 each having a patterned conductive foil on one side thereof, and the rigid substrate section RSP is formed by heating and pressing rigid substrates 21 each having a patterned conductive foil on one side thereof.

[0043] The transmission line 102 according to the second embodiment is configured by adhering (stacking) a rigid substrate portion RSP to a flexible substrate portion FSP via an adhesive layer 3. In this example, a protective film PF is applied to the outer surface of the laminate of the flexible substrate portion FSP and the rigid substrate portion RSP. However, the signal line terminals ST, which will be described later, are exposed. The protective film PF is, for example, a solder resist film.

[0044] The flexible substrate portion FSP has a flexible substrate 11, a hollow portion HS, a signal line 12, a conductive layer 13, and an interlayer connection conductive pattern 15S. The rigid substrate portion RSP has a rigid substrate 21, a conductive layer 23, a signal line terminal ST, and interlayer connection conductors 24G, 24S.

[0045] The interlayer connection conductors 24S of the rigid substrate part RSP are filled vias formed by plating, for example, and are made of copper, while the interlayer connection conductors 14S of the flexible substrate part FSP are sintered bodies of conductive paste, for example, and are made of tin, silver, copper, or alloys thereof.

[0046] As shown in FIGS. 2A, 2B, and 4, the flexible substrate section FSP has a conductive layer 13, an interlayer connection conductive pattern 15S, and interlayer connection conductors 14G and 14S.

[0047] The transmission line 102 is composed of a thick portion TS and a thin portion TP. The thick portion TS is a portion where the rigid substrate portion RSP is laminated on one surface (XY plane) of the flexible substrate portion FSP. The thin portion TP is a portion where the rigid substrate portion RSP is not laminated on the flexible substrate portion FSP.

[0048] When viewed in the stacking direction (Z direction), the signal line 12 passes continuously through the flexible substrate portion FSP in the order of thick portion TS-thin portion TP-thick portion TS. As shown in Figure 4, when viewed in the stacking direction, the line width of the signal line 12 at the portion overlapping with the flexible substrate portion side conductive layer 13 is narrower than the line width at other portions.

[0049] The characteristic impedance at the location where the flexible substrate portion side conductor layer 13 is used as the ground conductor layer of the stripline is determined by the line width of the signal line 12, the dielectric constant of the flexible substrate 11, and the thickness of the flexible substrate 11. The characteristic impedance at the location where the rigid substrate portion side conductor layer 23 is used as the ground conductor layer of the stripline is determined by the line width of the signal line 12, the dielectric constant and thickness of the rigid substrate 21, the thickness of the flexible substrate 11, and the structure of the hollow portion HS.

[0050] The flexible substrate side interlayer connection conductor 14S electrically connects the end of the signal line 12 to the interlayer connection conductor pattern 15S of the flexible substrate.

[0051] The rigid board portion side interlayer connection conductor 24G electrically connects the rigid board portion side conductive layer 23 and the flexible board portion side conductive layer 13 to each other.

[0052] The rigid board portion side interlayer connection conductor 24S electrically connects the signal line terminal ST and the interlayer connection conductor pattern 15S of the flexible board portion.

[0053] As in the example shown in the first embodiment, the conductive foil attached to the flexible substrate 11 is, for example, copper foil, and the material of the flexible substrate 11 is, for example, liquid crystal polymer, polyimide, PTFE, etc. The conductive foil attached to the rigid substrate 21 is copper foil, and the material of the rigid substrate 21 is, for example, a glass-epoxy substrate (epoxy + glass cloth FR4), bismaleimide triazine + glass cloth, ceramic (LTCC, etc.), etc.

[0054] 3 and 4, a plurality of openings OH are formed in the flexible substrate 11 at positions overlapping the signal lines 12 when viewed in the stacking direction. In this way, by stacking the flexible substrates 11 to which the conductive foils are attached, the hollow portions HS shown in FIGS. 2A and 2B are formed in the thick portions TS at positions overlapping the signal lines 12 when viewed in the stacking direction.

[0055] As shown in FIGS. 2A and 2B, the flexible substrate portion FSP is thicker than the rigid substrate portion RSP.

[0056] 2A and 2B, the spacing between the rigid board portion side conductor layers 23 that are positioned to sandwich the signal line 12 in the stacking direction (Z direction) is greater than the spacing between the flexible board portion side conductor layers 13 that are positioned to sandwich the signal line 12 in the stacking direction. In other words, the spacing between the rigid board portion side conductor layers 23 that serve as ground conductor layers in the thick portion TS is greater than the spacing between the flexible board portion side conductor layers 13 that serve as ground conductor layers in the thin portion TP.

[0057] As shown by the dashed double-dashed line in Figure 4, when viewed in the stacking direction, in the area where the end of the rigid substrate part RSP overlaps with the flexible substrate part FSP, the conductor density, including the conductor layer 23 of the rigid substrate part RSP and at least the interlayer connection conductor 24G of the rigid substrate part RSP, is higher than the conductor density in other areas.

[0058] According to the second embodiment, the following effects are achieved.

[0059] (a) When viewed from the stacking direction (Z direction), almost the entire surface of the signal line 12 is covered with the ground conductor layer, so there is no leakage of electromagnetic waves from the stripline and the shielding properties of the transmission line are improved, effectively suppressing interference with surrounding electronic circuits.

[0060] (b) Because the rigid substrate of the surface layer has high rigidity, the shape of the hollow portion HS can be maintained even if the overall thickness is reduced. In addition, the thickness of the hollow portion HS can be increased, and the total planar area or average area can be increased, which reduces the dielectric constant and dielectric loss tangent, thereby reducing dielectric loss.

[0061] (c) When viewed in the stacking direction, the conductor density, including the conductor layer 23 of the rigid substrate portion RSP and at least the interlayer connection conductor 24G of the rigid substrate portion RSP, in the region where the end of the rigid substrate portion RSP overlaps with the flexible substrate portion FSP is higher than the conductor density in other regions, so the rigidity of the boundary between the thick portion TS and the thin portion TP is higher than in other portions. Therefore, even if the thin portion TP is deformed, deformation of the thick portion TS is suppressed, deformation of the hollow portion HS is small, and damage to the boundary can be suppressed. This makes it possible to configure a transmission line with stable electrical characteristics.

[0062] (d) Since the rigid substrate portion RSP is laminated on the flexible substrate portion FSP via the adhesive layer 3, a laminated structure of the flexible substrate portion FSP and the rigid substrate portion RSP can be easily formed.

[0063] (e) By providing the protective film PF on the outer surface, the stress applied to the transmission line 102 from the outside is alleviated by the protective film PF, and a decrease in the strength of the transmission line due to the presence of the hollow portion HS is suppressed.

[0064] (f) By adjusting the line width of the signal line 12 so that the characteristic impedance of the stripline in the thick portion TS and the characteristic impedance of the stripline in the thin portion TP are constant, signal reflection at the boundary between the thick portion TS and the thin portion TP can be suppressed.

[0065] Third Embodiment In a third embodiment, a transmission line on which a mounting component is mounted will be illustrated.

[0066] 5 is a cross-sectional view of a transmission line 103 according to the third embodiment. The configuration in which a rigid substrate portion RSP is stacked on a flexible substrate portion FSP is the same as the examples shown in the first and second embodiments. In the transmission line 103 according to the third embodiment, mounted components EP1, EP2, EP3, and EP4 are mounted on the upper rigid substrate portion RSP. Terminal electrodes for mounting the mounted components are patterned on the upper surface of the upper rigid substrate portion RSP. The mounted components EP1 and EP4 are connectors connected to a signal line 12. These mounted components EP1 and EP4 as connectors function as signal input / output terminals to be connected to other substrates or components.

[0067] The structural features and effects of the transmission line according to the third embodiment are as follows.

[0068] (1) Components such as electronic parts are mounted on the outer surface of the rigid board portion RSP. The rigid board portion RSP has high rigidity and flatness, making it easy to mount components.

[0069] (2) A plurality of hollow portions HS are formed in the flexible substrate portion FSP, and the hollow portions HS are formed at positions of the flexible substrate portion FSP where the mounted components overlap when viewed from the stacking direction. In the example shown in Fig. 5, hollow portions HS are formed below all of the mounted components EP1, EP2, EP3, and EP4.

[0070] In this way, even if the mounting position of the mounted components overlaps the hollow portion HS when viewed in the stacking direction, the rigidity and flatness of the mounting portion of the mounted components can be ensured. Furthermore, deformation of the hollow portion HS due to stress when mounting the mounted components EP1, EP2, EP3, and EP4 is small. This makes it possible to suppress changes in the electrical characteristics of the transmission line. Therefore, there is a high degree of freedom in arranging the hollow portion HS of the flexible printed circuit board portion FSP.

[0071] (3) Hollow portions HS (hollow portions HS at both the left and right ends in FIG. 5 ) are formed at positions that overlap, when viewed in the stacking direction, with the interlayer connection conductor 14S on the flexible substrate side formed near the end of the signal line 12, the interlayer connection conductor pattern 15S on the flexible substrate side, the interlayer connection conductor 24S on the rigid substrate side, and the pads to which the terminals of the mounted components are connected (pads (via receiving pads) to which the interlayer connection conductor 24S is conductive).

[0072] In this way, the hollow portion HS can be arranged in a position overlapping the via receiving pad at the extraction portion from the signal line 12. Furthermore, by forming the hollow portion HS overlapping the via receiving pad, it is possible to adjust the impedance of the line from near the end of the signal line 12 to the pad to which the terminal of the mounted component is connected.

[0073] Fourth Embodiment In a fourth embodiment, a transmission line in which a strip line is configured in the thick portion TS and a microstrip line is configured in the thin portion TP will be exemplified.

[0074] Fig. 6A is a cross-sectional view of a transmission line 104 according to the fourth embodiment, Fig. 6B is a cross-sectional view of each layer of the flexible substrate section and each layer of the rigid substrate section (before lamination), and Fig. 7 is a plan view of each layer of the flexible substrate section and each layer of the rigid substrate section (before lamination).

[0075] The configuration in which the rigid substrate portion RSP is stacked on the flexible substrate portion FSP is similar to the transmission line in each of the embodiments shown so far. In the transmission line 104 according to the fourth embodiment, a conductive layer 13 is formed on the upper surface of the uppermost flexible substrate 11 of the three flexible substrate layers 11, but no conductive layer 13 is formed on the thin portion TP. The conductive layer 13 is formed on the lower surface of the lowermost flexible substrate 11, similar to the transmission lines in each of the embodiments shown so far.

[0076] The structural features of the transmission line 104 according to the fourth embodiment are as follows.

[0077] In the thick portion TS, the stripline is formed by the signal line 12, the flexible substrate portion side conductive layer 13, the rigid substrate portion side conductive layer 23, the rigid substrate 21 between the signal line 12 and the rigid substrate portion side conductive layer 23, the flexible substrate 11 and the hollow portion HS, and the flexible substrate 11 between the signal line 12 and the flexible substrate portion side conductive layer 13.

[0078] In the thin portion TP, a microstrip line is formed by the signal line 12, the flexible substrate side conductive layer 13, and the flexible substrate 11 between the signal line 12 and the flexible substrate side conductive layer 13.

[0079] The signal line width of the signal line 12 may be determined by the thick portion TS and the thin portion TP so that the characteristic impedance of the strip line is constant.

[0080] According to the fourth embodiment, the number of conductive layers in the thin portion TP is small, so the thin portion TP is soft and therefore easy to bend.

[0081] Fifth Embodiment In a fifth embodiment, a transmission line that constitutes a coplanar line will be exemplified.

[0082] Fig. 8 is a cross-sectional view of a transmission line 105 according to the fifth embodiment. Fig. 9 is a plan view of each layer of the flexible substrate portion of the transmission line 105 and each layer of the rigid substrate portion separated (before lamination).

[0083] The configuration in which the rigid substrate portion RSP is stacked on the flexible substrate portion FSP is the same as that of the transmission line in each of the embodiments shown so far. In the transmission line 105 according to the fifth embodiment, a conductive layer 13 is formed on the upper surface of the uppermost flexible substrate 11 of the three-layer flexible substrates 11, but the conductive layer 13 is not formed on the thin portion TP. A conductive layer 13 is formed on the lower surface of the lowermost flexible substrate 11, but the conductive layer 13 is not formed on the thin portion TP.

[0084] A coplanar line is formed by the signal line 12, the flexible board portion side conductor layer 13, the flexible substrate 11, and the hollow portion HS. The characteristic impedance of this coplanar line is determined by the distance between the signal line 12 and the flexible board portion side conductor layer 13, the opposing area between the signal line 12 and the flexible board portion side conductor layer 13, the dielectric constant of the flexible substrate 11, etc.

[0085] According to the fifth embodiment, the number of conductive layers 13 in the thin portion TP is small, so the thin portion is soft and easy to bend.

[0086] Sixth Embodiment In a sixth embodiment, a transmission line in which a rigid substrate portion is provided only on one surface of a flexible substrate portion will be exemplified.

[0087] Fig. 10 is a cross-sectional view of a transmission line 106 according to the sixth embodiment. Fig. 11 is a plan view of each layer of the flexible substrate portion of the transmission line 106 and each layer of the rigid substrate portion separated (before lamination).

[0088] The configuration in which the rigid substrate portion RSP is stacked on the flexible substrate portion FSP is similar to the transmission line in each of the embodiments shown so far. However, in the transmission line 106 according to the sixth embodiment, the rigid substrate portion RSP is stacked only on the upper surface of the flexible substrate portion FSP. In addition, in this sixth embodiment, as shown in FIG. 11 , an opening OH is formed only in the upper flexible substrate 11 of the two-layer flexible substrate 11, and this opening OH forms the hollow portion HS shown in FIG.

[0089] According to the sixth embodiment, a transmission line with a small overall thickness can be configured.

[0090] Seventh Embodiment In the seventh embodiment, a transmission line will be illustrated in which the number of layers of the flexible substrate, the number of layers of the flexible substrate portion side conductive layer, the interlayer connection structure, and the structure of the adhesive layer are different from the examples shown so far.

[0091] 12A and 12B are cross-sectional views of a transmission line 107 according to the seventh embodiment, and Fig. 12B is a cross-sectional view taken along line YY in Fig. 12A.

[0092] Fig. 13 is a plan view of each layer of the flexible substrate portion and each layer of the rigid substrate portion separated from each other. However, Fig. 13 does not show the protective film PF shown in Figs. 12(A) and 12(B). Also, Fig. 13 does not show the adhesive layer 3 shown in Figs. 12(A) and 12(B).

[0093] 12(A) and 12(B), the flexible substrate section FSP has two layers of flexible substrate 11. A conductive foil is attached to the top surface of the lower layer flexible substrate 11, but no conductive foil is attached to the upper layer flexible substrate 11. The rigid substrate section RSP is a rigid substrate in which a conductive foil is attached to one surface of each of the rigid substrates 21. Therefore, there are only two layers of flexible substrate 11, and three layers of conductive foil, consisting of the flexible substrate section FSP and the rigid substrate section RSP.

[0094] In the examples shown in FIGS. 12A and 12B, the adhesive layer 3 is not formed in the hollow portion HS.

[0095] For example, this transmission line 107 is formed by laminating all layers of the flexible substrate portion FSP and the rigid substrate portion RSP to form a laminate, forming through holes in the laminate, and plating the inner wall surfaces or interiors of the through holes with, for example, copper. This may form through-hole vias (signal vias VS and ground vias VG) that combine the interlayer connection conductors of the flexible substrate portion FSP and the rigid substrate portion RSP. The laminate of the flexible substrate portion FSP and the rigid substrate portion RSP may also be made by a build-up method.

[0096] According to the seventh embodiment, the total number of layers and interlayer connection conductors can be reduced, resulting in lower costs. Furthermore, by eliminating the adhesive layer in the hollow portion HS, the dielectric loss due to the dielectric constant and dielectric loss tangent of the adhesive layer 3 can be reduced.

[0097] Eighth Embodiment In the eighth embodiment, a transmission line in which the signal line is not exposed to the hollow portion will be exemplified.

[0098] 14 is a cross-sectional view of a transmission line 108 according to the eighth embodiment. This transmission line 108 includes four flexible substrates 11, each with a conductive foil attached to one side. Of these four flexible substrates 11, the topmost and bottommost flexible substrates 11 have hollow portions HS formed by openings. The other flexible substrates 11 do not have hollow portions HS.

[0099] Although the number of interlayer connection conductors 14S and interlayer connection conductor patterns 15S differs from the example shown in the first embodiment, the other configurations are the same as those shown in the first embodiment.

[0100] According to the eighth embodiment, the signal line 12 is not exposed in the hollow portion HS, which reduces corrosion of the signal line 12. Furthermore, since the entire signal line 12 is sandwiched between the flexible substrates 11, the mechanical strength of the signal line 12 is high.

[0101] Ninth Embodiment In the ninth embodiment, a transmission line in which multiple layers of rigid base materials are laminated will be exemplified.

[0102] 15 is a cross-sectional view of a transmission line 109 according to the ninth embodiment. The configuration in which a rigid substrate portion RSP is stacked on a flexible substrate portion FSP is the same as the examples shown in the previous embodiments. In the transmission line 109 according to the ninth embodiment, the upper rigid substrate portion RSP is composed of a laminate of two rigid base materials 21. Mounted components EP1, EP2, EP3, and EP4 are mounted on the upper rigid substrate portion RSP. Terminal electrodes for mounting the mounted components are patterned on the upper surface of the upper rigid substrate portion RSP.

[0103] The upper rigid board portion RSP has a rigid base material 21 , a conductive layer 23 , interlayer connection conductors 24 G and 24 S, and a rigid board portion conductive pattern 25 .

[0104] According to the ninth embodiment, the rigid substrate portion RSP has high rigidity, which increases the rigidity of the transmission line and stabilizes the shape of the hollow portion HS. In addition, since there are many layers on which conductor patterns can be wired, the degree of freedom in wiring is high.

[0105] 15, the upper rigid board portion RSP is multi-layered, but both the upper and lower rigid board portions RSP may be multi-layered.Mounted components may also be mounted on both the upper and lower rigid board portions RSP.

[0106] Tenth Embodiment In a tenth embodiment, a transmission line having a bent portion in a thin portion will be exemplified.

[0107] FIG. 16 is a cross-sectional view of a transmission line 110 according to the tenth embodiment.

[0108] The basic configuration of this transmission line 110 is similar to that of the transmission line 102 shown in the second embodiment. In particular, the flexible substrate 11 of the transmission line 110 is made of a thermoplastic resin, and the thin portion TP can be plastically deformed.

[0109] In the example shown in FIG. 16, a bent portion BS that is plastically deformed into a crank shape is provided in a part of the thin portion TP.

[0110] According to the tenth embodiment, a transmission line that has been deformed into a predetermined shape in advance can be easily incorporated into an electronic device.

[0111] The shape of the bent portion is not limited to a crank shape, but may be a shape curved at a predetermined angle such as 45 degrees, 90 degrees, or 180 degrees.

[0112] Eleventh Embodiment In the eleventh embodiment, an electronic device will be exemplified.

[0113] Fig. 17 is a cross-sectional view of an electronic device 211 according to an eleventh embodiment. This electronic device 211 includes a circuit board BP and a transmission line 110. Mounting pads PE are formed on the upper surface of the circuit board BP. The signal line terminals ST of the transmission line 110 are soldered to these pads PE, thereby mounting the transmission line 110 on the circuit board BP. Note that the internal structure of the circuit board BP is not shown in Fig. 17.

[0114] According to the eleventh embodiment, the transmission line can be mounted along a circuit board having a step, which makes it easy to mount the transmission line.

[0115] Various embodiments of the present invention have been presented so far, but these are all examples and are not intended to limit the scope of the present invention. Various omissions, substitutions, and modifications can be made to the embodiments of the present invention without departing from the spirit of the invention. Embodiments with such omissions, substitutions, and modifications are included within the scope and spirit of the present invention, and are also included in the scope of the invention and its equivalents as set forth in the claims of this application.

[0116] For example, in each of the above-described embodiments, the cylindrical hollow portion HS is formed by a circular opening OH when viewed from the stacking direction, but the shape of the hollow portion HS when viewed from the stacking direction is not limited to this and may be a polygonal shape such as an ellipse, an oval, a square, a rectangle, etc. Furthermore, the hollow portion HS may be laminated after forming an opening OH in each of the flexible base materials 11, or the hollow portion HS may be processed after forming the flexible substrate portion FSP.

[0117] Although each embodiment has shown a transmission line having a single signal line 12, a transmission line may also have a plurality of signal lines. The plurality of signal lines may also be arranged in the layer direction of the flexible substrate 11. The plurality of signal lines may also be arranged in one hollow space HS, or a separate hollow space HS may be formed for each signal line.

[0118] In addition, in each embodiment, an unbalanced transmission line such as a strip line, a microstrip line, or a coplanar line is shown, but a differential balanced transmission line may also be configured.

[0119] In addition, in each embodiment, the high-frequency signal transmission line has been shown to have a rectangular shape when viewed from the stacking direction of the resin layers, but this shape is arbitrary. For example, the signal line may be curved when viewed from the stacking direction. That is, the signal line may be curved or partially curved when viewed from the stacking direction.

[0120] Furthermore, a separate wiring pattern without a hollow portion HS may be provided on the flexible substrate portion that constitutes a part of the transmission line. This wiring pattern may be used as a transmission line for another high-frequency signal, a transmission line for a digital signal, a conductor for a power supply, or the like.

[0121] Furthermore, in each embodiment, an example has been shown in which no interlayer connection conductor is provided in the thin portion, but an interlayer connection conductor may be disposed in the flexible substrate portion of the thin portion.

[0122] The transmission line and electronic device of the present invention may be provided in the following aspects.

[0123] <1> A transmission line comprising: a flexible substrate section having a flexible substrate, a hollow portion, and a signal line; and a rigid substrate section having a rigid substrate having a higher Young's modulus than the flexible substrate, a conductive layer not in contact with the flexible substrate, and an interlayer connection conductor; wherein the transmission line is configured with a thick portion in which the rigid substrate section is laminated on the flexible substrate section, and a thin portion in which the rigid substrate section is not laminated on the flexible substrate section; the signal line passes continuously through the flexible substrate section from the thick portion to the thin portion as viewed in the lamination direction; the hollow portion is formed in the thick portion at a position overlapping the signal line as viewed in the lamination direction; and at least a part of the rigid substrate is located between the conductive layer of the rigid substrate section and the signal line.

[0124] <2> The transmission line according to <1>, wherein the Young's modulus of the rigid substrate is at least twice as large as the Young's modulus of the flexible substrate.

[0125] <3> The transmission line according to <1> or <2>, wherein the conductor layer of the rigid board portion is a ground conductor layer.

[0126] <4> The transmission line according to any one of <1> to <3>, wherein the thick portion is present on both sides of the thin portion in the extending direction of the signal line.

[0127] <5> The transmission line according to any one of <1> to <4>, wherein the permittivity of the flexible substrate is lower than the permittivity of the rigid substrate, and the dielectric loss tangent of the flexible substrate is lower than the dielectric loss tangent of the rigid substrate.

[0128] <6> The transmission line according to any one of <1> to <5>, wherein the hollow portions are located both above and below the signal line in the stacking direction.

[0129] <7> The transmission line according to any one of <1> to <6>, wherein a portion of the signal line is exposed to the hollow portion.

[0130] <8> The transmission line according to any one of <1> to <7>, wherein the rigid substrate portion is laminated above and below the flexible substrate portion.

[0131] <9> The transmission line according to any one of <1> to <8>, wherein the conductor layer of the rigid substrate portion is a ground conductor layer located on both the upper and lower surfaces of the signal line in the stacking direction or on one surface of the signal line, and a stripline is formed by the ground conductor layer, the signal line, and a dielectric material including the rigid substrate and the hollow portion between the signal line and the ground conductor layer.

[0132] <10> The transmission line according to any one of <1> to <9>, wherein the flexible substrate section includes a conductive layer formed on the flexible substrate, the conductive layer of the flexible substrate section is a ground conductor layer located so as not to overlap the signal line in the stacking direction, and a coplanar line is formed by the ground conductor layer, the signal line, and at least the flexible substrate and the hollow portion between the signal line and the ground conductor layer.

[0133] <11> The transmission line according to any one of <1> to <10>, wherein the rigid substrate portion is laminated to the flexible substrate portion via an adhesive layer that bonds the rigid substrate and the flexible substrate.

[0134] <12> The transmission line according to any one of <1> to <11>, wherein the flexible substrate portion is thicker than the rigid substrate portion.

[0135] <13> The transmission line according to any one of <1> to <12>, wherein, in a region where an end of the rigid substrate section and the flexible substrate section overlap, a conductor density including the conductor layer of the rigid substrate section and the interlayer connection conductor of the rigid substrate section is higher than a conductor density in other regions, as viewed in the stacking direction.

[0136] <14> The transmission line according to any one of <1> to <13>, wherein a mounting component is mounted on the rigid substrate portion, and the mounting component is arranged at a position overlapping the hollow portion when viewed in the stacking direction.

[0137] <15> The transmission line according to any one of <1> to <14>, wherein the rigid substrate is made of a mixture of an organic material and an inorganic material or an inorganic material.

[0138] <16> The transmission line according to any one of <1> to <15>, wherein the flexible substrate portion includes an interlayer connection conductor formed on the flexible substrate, and the interlayer connection conductor of the rigid substrate portion and the interlayer connection conductor of the flexible substrate portion are made of different materials.

[0139] <17> The transmission line according to any one of <1> to <15>, wherein the flexible substrate portion includes an interlayer connection conductor formed on the flexible substrate, and the interlayer connection conductor of the rigid substrate portion and the interlayer connection conductor of the flexible substrate portion are configured as continuous through-hole vias.

[0140] <18> The transmission line according to any one of <1> to <17>, wherein the flexible substrate is made of a thermoplastic resin, and the thin portion has a bent portion that is plastically deformed.

[0141] <19> An electronic device comprising the transmission line according to any one of <1> to <18>.

[0142] BP...circuit board EP1, EP2, EP3, EP4...mounted components FSP...flexible board section HS...hollow section OH...opening PE...pad PF...protective film RSP...rigid board section ST...signal line terminal TP...thin section TS...thick section VS...signal via VG...ground via 3...adhesive layer 11...flexible substrate 12...signal line 13...flexible board section side conductive layer 14G, 14S...flexible board section side interlayer connection conductor 15S...interlayer connection conductive pattern 21...rigid substrate 23...rigid board section side conductive layer 24G, 24S...rigid board section side interlayer connection conductor 25...rigid board section conductive pattern 101A, 101B, 102, 103, 104, 105, 106, 107, 108, 109, 110...transmission line 211...electronic device

Claims

1. A transmission line comprising: a flexible substrate section having a flexible substrate, a hollow section, and a signal line; and a rigid substrate section having a rigid substrate with a higher Young's modulus than the flexible substrate, a conductive layer not in contact with the flexible substrate, and an interlayer connecting conductor; wherein the transmission line is configured with a thick section in which the rigid substrate section is laminated on the flexible substrate section, and a thin section in which the rigid substrate section is not laminated on the flexible substrate section; the signal line passes continuously through the flexible substrate section from the thick section to the thin section when viewed in the direction of lamination; the hollow section is formed in the thick section at a position overlapping the signal line when viewed in the direction of lamination; and at least a portion of the rigid substrate is located between the conductive layer of the rigid substrate section and the signal line.

2. The transmission line according to claim 1, wherein the Young's modulus of the rigid substrate is at least twice as large as the Young's modulus of the flexible substrate.

3. The transmission line according to claim 1 or 2, wherein the conductive layer of the rigid board portion is a ground conductive layer.

4. The transmission line according to any one of claims 1 to 3, wherein the thick portion is present on both sides of the thin portion in the direction in which the signal line extends.

5. A transmission line according to any one of claims 1 to 4, wherein the permittivity of the flexible substrate is lower than the permittivity of the rigid substrate, and the dielectric loss tangent of the flexible substrate is lower than the dielectric loss tangent of the rigid substrate.

6. A transmission line according to any one of claims 1 to 5, wherein the hollow portions are located both above and below the signal line in the direction of lamination.

7. The transmission line according to any one of claims 1 to 6, wherein a portion of the signal line is exposed in the hollow portion.

8. The transmission line according to any one of claims 1 to 7, wherein the rigid substrate portion is laminated above and below the flexible substrate portion.

9. A transmission line as claimed in any one of claims 1 to 8, wherein the conductor layer of the rigid substrate portion is a ground conductor layer located on either or both of the upper and lower surfaces of the signal line in the lamination direction, and a stripline is formed by the ground conductor layer, the signal line, and the dielectric material between the signal line and the ground conductor layer, including the rigid substrate and the hollow portion.

10. A transmission line as claimed in any one of claims 1 to 9, wherein the flexible substrate section comprises a conductive layer formed on the flexible substrate, the conductive layer of the flexible substrate section being a ground conductor layer positioned so as not to overlap the signal line in the stacking direction, and a coplanar line is formed by the ground conductor layer, the signal line, and at least the flexible substrate and the hollow portion between the signal line and the ground conductor layer.

11. A transmission line according to any one of claims 1 to 10, wherein the rigid substrate section is laminated onto the flexible substrate section via an adhesive layer that bonds the rigid substrate and the flexible substrate together.

12. The transmission line according to any one of claims 1 to 11, wherein the flexible substrate portion is thicker than the rigid substrate portion.

13. A transmission line as described in any one of claims 1 to 12, wherein, when viewed in the stacking direction, the conductor density, including the conductor layer of the rigid board section and the interlayer connecting conductor of the rigid board section, in the area where the end of the rigid board section and the flexible board section overlap is higher than the conductor density in other areas.

14. A transmission line according to any one of claims 1 to 13, wherein a component is mounted on the rigid board portion, and the component is arranged at a position overlapping the hollow portion when viewed in the stacking direction.

15. A transmission line according to any one of claims 1 to 14, wherein the rigid substrate is made of a mixture of organic and inorganic materials or an inorganic material.

16. A transmission line according to any one of claims 1 to 15, wherein the flexible substrate section has an interlayer connection conductor formed on the flexible substrate, and the interlayer connection conductor of the rigid substrate section and the interlayer connection conductor of the flexible substrate section are made of different materials.

17. A transmission line as claimed in any one of claims 1 to 15, wherein the flexible substrate section has an interlayer connection conductor formed on the flexible substrate, and the interlayer connection conductor of the rigid substrate section and the interlayer connection conductor of the flexible substrate section are constituted by continuous through-hole vias.

18. A transmission line according to any one of claims 1 to 17, wherein the flexible substrate is made of a thermoplastic resin, and the thin portion has a plastically deformed bent portion.

19. An electronic device comprising the transmission line according to any one of claims 1 to 18.

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