Transmission line

A transmission line includes a substrate including insulator layers, a mounting electrode on a front layer of the substrate, a signal conductor, a first ground conductor, a first connecting electrode that electrically connects the mounting electrode and the signal conductor and is between the signal conductor and the first ground conductor in a laminating direction, a first inter-layer connecting conductor that is electrically connected between the mounting electrode and the first connecting electrode and is bonded to the first connecting electrode, and a second inter-layer connecting conductor that is electrically connected between the signal conductor and the first connecting electrode, is bonded to the first connecting electrode, and does not overlap with the first inter-layer connecting conductor when viewed in the laminating direction. The first ground conductor does not overlap with at least a portion of the first connecting electrode when viewed in the laminating direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission line included in a substrate.

2. Description of the Related Art

Examples of a conventional transmission line include the signal transmission line described in International Publication No. 2016/163436. This signal transmission line includes a laminated insulator, a signal conductor pattern, and two ground conductor patterns. The laminated insulator is composed of a plurality of insulator layers that are laminated. The signal conductor pattern and the ground conductor patterns are formed in the laminated insulator. The signal conductor pattern is arranged between the ground conductor patterns.

In the signal transmission line described in International Publication No. 2016/163436, inter-layer connecting conductors are arranged in series below a mounting electrode on which an electronic component is mounted and accordingly, flatness of the mounting electrode may be degraded. Mounting electrodes preferably have higher flatness so as to realize favorable connection on the mounting electrodes. However, if a conductor pattern is used for maintaining flatness of mounting electrodes, deviation of characteristic impedance may occur on the other hand.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide transmission lines that each maintain flatness of a mounting electrode, and reduce or prevent deviation of characteristic impedance.

A transmission line according to a preferred embodiment of the present invention includes a substrate including a plurality of insulator layers, a mounting electrode on a front layer of the substrate, a signal conductor in the substrate, a first ground conductor on the substrate and overlapping with the signal conductor when viewed in a laminating direction of the plurality of insulator layers, a first connecting electrode that electrically connects the mounting electrode and the signal conductor with each other and is between the signal conductor and the first ground conductor in the laminating direction, a first inter-layer connecting conductor that is electrically connected between the mounting electrode and the first connecting electrode and is bonded to the first connecting electrode, and a second inter-layer connecting conductor that is electrically connected between the signal conductor and the first connecting electrode, is bonded to the first connecting electrode, and does not overlap with the first inter-layer connecting conductor when viewed in the laminating direction. The first ground conductor does not overlap with at least a portion of the first connecting electrode when viewed in the laminating direction.

According to preferred embodiments of the present invention, flatness of a mounting electrode is maintained and deviation of characteristic impedance in a transmission line is reduced or prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A plurality of preferred embodiments of the present invention will be shown below. Each of the preferred embodiments is exemplary and partial substitution or combination of configurations described in different preferred embodiments can be performed. Each preferred embodiment will provide description on points that differ from points described before that preferred embodiment. In particular, the same advantageous effects obtained from the same configuration will not be sequentially mentioned in each preferred embodiment.

First Preferred Embodiment

FIG.1is a plan view of a transmission line10according to a first preferred embodiment of the present invention.FIG.2is an A-A sectional view of the transmission line10.FIG.3is a plan view of a main portion of the transmission line10.FIG.3omits the illustration of a resist film191.

The transmission line10has a planar shape and extends in one direction. The transmission line10includes a substrate11, a mounting electrode12, a signal conductor13, ground conductors141and142, inter-layer connecting conductors16, and connecting electrodes17. The connecting electrodes17include a first connecting electrode171and second connecting electrodes172and173. The inter-layer connecting conductors16include a first inter-layer connecting conductor161, a second inter-layer connecting conductor162, and inter-layer connecting conductors163,164, and165. The ground conductor141is an example of a “first ground conductor”. The ground conductor142is an example of a “second ground conductor”. An electronic component20is mounted on a first main surface S1of the substrate11. The electronic component20includes a connection terminal (signal terminal)21and a connection terminal (ground terminal)22that are aligned.

The transmission line10includes a connecting portion151that connects the mounting electrode12and the signal conductor13with each other, and a connecting portion152that connects the ground conductor141and the ground conductor142with each other. The connecting portion151includes the first inter-layer connecting conductor161, the second inter-layer connecting conductor162, and the first connecting electrode171. The connecting portion152includes the inter-layer connecting conductors163,164, and165and the second connecting electrodes172and173. The transmission line10includes a first region Z1in which the connecting portion151is provided and a second region Z2in which the signal conductor13is provided.

The substrate11includes a plurality of insulator layers111,112,113, and114that are laminated. The mounting electrode12is provided on a front layer of the substrate11. The signal conductor13is provided in the substrate11. The ground conductor141is provided on the substrate11and overlaps with the signal conductor13when viewed in a laminating direction of the plurality of insulator layers111to114(hereinafter, merely referred to as the laminating direction) (in plan view). The ground conductor142is provided on the substrate11and overlaps with the mounting electrode12, the signal conductor13, and the first connecting electrode171in plan view. The signal conductor13, the first connecting electrode171, and the second connecting electrodes172and173are arranged between the ground conductor141and the ground conductor142in the laminating direction.

The signal conductor13is defined with respect to each signal line. The signal conductor13is a continuous (non-isolated) conductor pattern in one layer and has the largest area among conductor patterns that are included in the signal line and transmit signals.

The first connecting electrode171electrically connects the mounting electrode12and the signal conductor13with each other and is located between the signal conductor13and the ground conductor141in the laminating direction. The distance between the first connecting electrode171and the ground conductor142in the laminating direction is greater than or equal to the distance between the first connecting electrode171and the ground conductor141in the laminating direction. The first inter-layer connecting conductor161is electrically connected between the mounting electrode12and the first connecting electrode171and is bonded to the first connecting electrode171. The second inter-layer connecting conductor162is electrically connected between the signal conductor13and the first connecting electrode171and is bonded to the first connecting electrode171. Further, the second inter-layer connecting conductor162does not overlap with the first inter-layer connecting conductor161in plan view. In other words, the first inter-layer connecting conductor161and the second inter-layer connecting conductor162are not linearly aligned in the laminating direction. The ground conductor141does not overlap with the first connecting electrode171in plan view.

The second connecting electrodes172and173electrically connect the ground conductor141and the ground conductor142with each other. The first connecting electrode171does not overlap with the second connecting electrodes172and173in plan view.

When viewed in a direction that is orthogonal to an extending direction of the first connecting electrode171and is orthogonal to the laminating direction, the inter-layer connecting conductors163to165of the connecting portion152do not overlap with the first inter-layer connecting conductor161and the second inter-layer connecting conductor162of the connecting portion151.

The insulator layers111to114are arranged in this order from the upper side to the lower side. The insulator layers111to114are made of thermoplastic resin such as liquid crystal polymer (LCP), but may be made of other insulating materials. The insulator layers111to114are integrated by, for example, heat pressing, but may be bonded to each other with an adhesive.

In the specification of the present application, the terms “upper side” and “lower side” are used for convenience to distinguish one side from the other side, but are not limiting. Similarly, the terms “upper surface” and “lower surface” are used for convenience to distinguish a main surface on one side from a main surface on the other side, but are not limiting.

The mounting electrode12and the ground conductor141are provided on the first main surface S1of the substrate11, that is, on an upper surface of the insulator layer111. The first connecting electrode171and the second connecting electrode172are provided on an upper surface of the insulator layer112. The signal conductor13and the second connecting electrode173are provided on an upper surface of the insulator layer113. The ground conductor142is provided on a second main surface S2, which is on the opposite side to the first main surface S1, of the substrate11, that is, on a lower surface of the insulator layer114. The mounting electrode12, the signal conductor13, the ground conductors141and142, and the connecting electrode17are conductor patterns and are formed by patterning a Cu foil, for example.

The first inter-layer connecting conductor161and the inter-layer connecting conductor163are provided in the insulator layer111. The second inter-layer connecting conductor162and the inter-layer connecting conductor164are provided in the insulator layer112. The inter-layer connecting conductor165is provided in the insulator layers113and114. The inter-layer connecting conductors16are formed, for example, by solidifying an electrical paste filled in through holes of the insulator layers111to114.

The signal conductor13extends in the same direction as the extending direction of the transmission line10and is located between the ground conductors141and142that are opposed to each other. A stripline structure is thus provided.

The ground conductor141includes a slit SL1. The slit SL1has a rectangular shape, but may have another shape. The mounting electrode12and the first connecting electrode171are located in the slit SL1in plan view. The slit SL1preferably extends along the extending direction of the first connecting electrode171so as to improve signal characteristics.

Here, a plurality of slits SL1are separately provided in the ground conductor141, but some or all of the slits SL1may be connected with each other.

FIG.4is a plan view of the first connecting electrode171according to the first preferred embodiment.FIG.4more specifically illustrates the shape of the first connecting electrode171thanFIG.3.FIG.4shows the positions of the first inter-layer connecting conductor161and the second inter-layer connecting conductor162, and also shows a direction α of a straight line connecting the position of the first inter-layer connecting conductor161with the position of the second inter-layer connecting conductor162and a direction β that is orthogonal to the direction α. The first connecting electrode171includes a portion bonded to the first inter-layer connecting conductor161, a portion bonded to the second inter-layer connecting conductor162, and a portion extending between the above two portions.

Here, the width of the first connecting electrode, the width of the signal conductor, and the width of the mounting electrode will be described. The width of the first connecting electrode is the length of the first connecting electrode in a direction orthogonal to the direction of the straight line connecting the position of the first inter-layer connecting conductor with the position of the second inter-layer connecting conductor, in plan view. The width of the signal conductor is the length of the signal conductor in a direction orthogonal to the extending direction of the signal conductor, in plan view. The width of the mounting electrode is the length of the mounting electrode in a direction orthogonal to the direction of the straight line connecting the position of the inter-layer connecting conductor bonded to the mounting electrode and the position of the connection terminal bonded to the mounting electrode, in plan view.

FIGS.5A to5Eare plan views of the first connecting electrode171according to a modification of the first preferred embodiment.FIGS.5A to5Eshow the positions of the first inter-layer connecting conductor161and the second inter-layer connecting conductor162, and also show the direction α of the straight line connecting the position of the first inter-layer connecting conductor161with the position of the second inter-layer connecting conductor162and the direction β that is orthogonal to the direction α. The first connecting electrode171may have the larger width at its central portion in the direction α, as illustrated inFIG.5A. The first inter-layer connecting conductor161or the second inter-layer connecting conductor162may protrude from the first connecting electrode171in plan view, as illustrated inFIG.5B. The first connecting electrode171may be constricted at its central portion in the direction α, as illustrated inFIG.5C. The first connecting electrode171may have a protrusion portion that is not bonded to either the first inter-layer connecting conductor161or the second inter-layer connecting conductor162, as illustrated inFIG.5D. The first connecting electrode171may be bent in the middle of its extending direction, as illustrated inFIG.5E.

Description will now be provided on a modification of the connecting portion151in a configuration in which the substrate11includes three or more insulator layers between the mounting electrode12and the signal conductor13.

The connecting portion151may include one first connecting electrode and two or more inter-layer connecting conductors. The connecting portion151may also include a plurality of first connecting electrodes and three or more inter-layer connecting conductors. In this configuration, some of the inter-layer connecting conductors of the connecting portion151may overlap with each other in plan view. Also, the connecting portion151may include an inter-layer connecting conductor extending across a plurality of insulator layers or may include a plurality of inter-layer connecting conductors that are linearly aligned in the laminating direction.

For example, when the substrate11includes three layers between the mounting electrode12and the signal conductor13, the connecting portion151may include one first connecting electrode, one inter-layer connecting conductor extending across one layer, and one inter-layer connecting conductor extending across two layers. Alternatively, the connecting portion151may include one first connecting electrode, two inter-layer connecting conductors that are linearly aligned with each other, and one inter-layer connecting conductor that is not linearly aligned with the above two inter-layer connecting conductors. Alternatively, the connecting portion151may include two first connecting electrodes and three inter-layer connecting conductors.

Even when the substrate11includes three or more insulator layers between the mounting electrode12and the signal conductor13, the connecting portion151may have at least one first connecting electrode. That is, it is enough that the first inter-layer connecting conductor and the second inter-layer connecting conductor do not overlap with each other in the laminating direction. Accordingly, flatness of the mounting electrode12is improved as described later.

However, an inter-layer connecting conductor that is physically connected with the mounting electrode12and is provided directly under the mounting electrode12largely affects the flatness of the mounting electrode12. In a similar manner, an inter-layer connecting conductor that is connected with the inter-layer connecting conductor, which is provided directly under the mounting electrode12, via one first connecting electrode sometimes largely affects the flatness of the mounting electrode12. Therefore, these inter-layer connecting conductors preferably do not overlap with any other inter-layer connecting conductors in the substrate11. Further, it is preferable that these inter-layer connecting conductors do not extend across a plurality of insulator layers or are not linearly aligned with other inter-layer connecting conductors.

When the connecting portion151includes a plurality of connecting electrodes and three or more inter-layer connecting conductors, the connecting portion151may have a stepped shape, a zigzag shape, or another shape.

The inter-layer connecting conductors163and164do not overlap with each other in plan view. On the other hand, the inter-layer connecting conductors163and165overlap with each other in plan view. The connecting portion152thus has a zigzag shape, but may have a stepped shape or another shape.

The connecting portions151and152are arranged with an interval in the width direction of the transmission line10so as to correspond to the arrangement of the connection terminals21and22of the electronic component20. The connecting portion152is positioned to be closer to the electronic component20than the connecting portion151or is positioned to overlap with the electronic component20, in plan view.

The resist film191is provided on the first main surface S1of the substrate11. A resist film192is provided on the second main surface S2of the substrate11. The resist films191and192cover conductor patterns on the surfaces of the substrate11. However, an opening for exposing a portion of the mounting electrode12and an opening for exposing a portion of the ground conductor141are provided on the resist film191.

The electronic component20is structured so that the connection terminals21and22thereof are aligned in the width direction of the transmission line10. The connection terminal21is connected to the mounting electrode12, which is exposed from the opening of the resist film191, with solder231interposed therebetween. The connection terminal22is connected to the ground conductor141, which is exposed from the opening of the resist film191, with solder interposed therebetween. The electronic component20is an electronic component including a signal terminal such as a connector and an IC.

Design parameters of the transmission line are determined as appropriate so as to be able to obtain desired characteristics. Specific non-limiting examples of the design parameters of the transmission line will be shown below.Layer thickness T1of insulator layer: 50 μmThickness T2of conductor pattern: 12 μmMinimum width W1of first connecting electrode and minimum width W3of signal conductor: from 60 μm to 100 μm inclusiveInterval D1between mounting electrode and ground conductor: 40 μm or greater

When the width of the connecting electrode is set to be smaller than that of the signal conductor, the minimum width W1of the connecting electrode is set as W3-20 μm or greater and W3-10 μm or smaller, for example. Further, the conductor pattern is actually buried in the insulator layer for about 1 μm to about 2 μm, for example.

According to the first preferred embodiment, the first connecting electrode171is closer to the ground conductor141than the signal conductor13in the laminating direction, but does not overlap with the ground conductor141in plan view. This configuration prevents an excessive capacitance value between the first connecting electrode171and the ground conductor141compared to the capacitance value between the signal conductor13and the ground conductor141. This reduces or prevents deviation of the characteristic impedance in the first region Z1of the transmission line10from the characteristic impedance in the second region Z2of the transmission line10.

If the inter-layer connecting conductors16that are harder than a resin sheet are linearly aligned in forming the substrate11by thermo-compression bonding of resin sheets, the surface of the substrate11may be protruded on forming positions of the inter-layer connecting conductors16. According to the first preferred embodiment, the first inter-layer connecting conductor161and the second inter-layer connecting conductor162are not linearly aligned, thus reducing or preventing degradation in flatness of the mounting electrode12. As a result, a favorable connection between the mounting electrode12and the electronic component20can be obtained.

When viewed in the direction that is orthogonal to the extending direction of the first connecting electrode171and is orthogonal to the laminating direction (the width direction of the transmission line10), the inter-layer connecting conductors163to165of the connecting portion152do not overlap with the first inter-layer connecting conductor161and the second inter-layer connecting conductor162of the connecting portion151. Therefore, even if the interval between the connection terminals21and22of the electronic component20is small, the interval between the first and second inter-layer connecting conductors161and162of the connecting portion151and the inter-layer connecting conductors163to165of the connecting portion152is secured. This reduces or prevents capacitance coupling between the first and second inter-layer connecting conductors161and162of the connecting portion151and the inter-layer connecting conductors163to165of the connecting portion152.

Further, the first connecting electrode171does not overlap with the second connecting electrodes172and173in plan view. This reduces or prevents capacitance coupling between the first connecting electrode171and the second connecting electrodes172and173.

Furthermore, the first inter-layer connecting conductor161, the second inter-layer connecting conductor162, and the inter-layer connecting conductors163to165are not linearly aligned, and are connected with each other via the first connecting electrode171and the second connecting electrodes172and173. Therefore, the first connecting electrode171and second connecting electrodes172and173that are easily deformable are bent in response to bending of the transmission line10, thus maintaining bendability of the transmission line10.

FIG.6is a plan view of a main portion of a transmission line30according to another modification of the first preferred embodiment. The transmission line30differs from the transmission line10on the following point. Namely, the transmission line30includes a ground conductor341including a slit SL2, instead of the ground conductor141including the slit SL1. The slit SL2is arc-shaped or rounded at an end portion closer to the first connecting electrode171.

The end portion of the slit is thus changed from a rectangular shape into an arc shape, being able to increase the interval between the first connecting electrode171and the ground conductor in the extending direction of the first connecting electrode171without increasing the area of the slit. Accordingly, the capacitance coupling between the first connecting electrode171and the ground conductor can be further reduced or prevented without increasing radiation noise from the slit.

The slit may be circular so as to increase the interval between the first connecting electrode171and the ground conductor. However, when the slit is circular, the width of the slit is increased. Therefore, when the interval between the connection terminals21and22of the electronic component20is small, a slit including an arc-shaped end portion is more preferable than a circular slit.

FIG.7is a plan view of a main portion of a transmission line40according to still another modification of the first preferred embodiment. The transmission line40differs from the transmission line10on the following point. Namely, the transmission line40includes a mounting electrode42, a signal conductor43, and a first connecting electrode471, instead of the mounting electrode12, the signal conductor13, and the first connecting electrode171.

FIG.8is a plan view of the mounting electrode42, the signal conductor43, and the first connecting electrode471.FIG.8illustrates the mounting electrode42, the signal conductor43, and the first connecting electrode471in such a manner that positions of these three are shifted from each other. The minimum width W1of the first connecting electrode471is larger than the minimum width W3of the signal conductor43. The maximum width W2of the first connecting electrode471is smaller than the minimum width W4of the mounting electrode42.

Conductor loss at the first connecting electrode is reduced or prevented by setting the minimum width W1of the first connecting electrode larger than the minimum width W3of the signal conductor.

Second Preferred Embodiment

In a second preferred embodiment, a first connecting electrode includes a first portion that overlaps with a ground conductor on the upper surface side of a substrate, and a second portion that does not overlap with the ground conductor on the upper surface side of the substrate, in plan view.

FIG.9is a sectional view of a transmission line70according to the second preferred embodiment of the present invention.FIG.10is a plan view of a main portion of the transmission line70.FIG.10omits the illustration of the resist film191.

The transmission line70differs from the transmission line10according to the first preferred embodiment on the following point. Namely, the transmission line70includes a ground conductor741including a slit SL3, instead of the ground conductor141including the slit SL1. Further, the transmission line70includes a connecting portion751including a first connecting electrode771, instead of the connecting portion151having the first connecting electrode171. The length of the slit SL3is shorter than the length of the slit SL1and the first connecting electrode771partially overlaps with the ground conductor741in plan view. The minimum width W1of the first connecting electrode771is smaller than the minimum width W3of the signal conductor13.

FIG.11is a plan view of the first connecting electrode771.FIG.11more specifically illustrates the shape of the first connecting electrode771thanFIG.10. The first connecting electrode771includes a first portion7711that overlaps with the ground conductor741and a second portion7712that does not overlap with the ground conductor741in plan view. The minimum width W5of the first portion7711is smaller than the maximum width W6of the second portion7712. An area of the first portion7711is smaller than an area of the second portion7712.

FIGS.12A and12Bare plan views of first connecting electrodes871and971according to a modification of the second preferred embodiment. The transmission line70may include the first connecting electrode871illustrated inFIG.12Aor the first connecting electrode971illustrated inFIG.12B, instead of the first connecting electrode771.

The first connecting electrode871includes a first portion8711that overlaps with the ground conductor741and a second portion8712that does not overlap with the ground conductor741in plan view. The width of the first connecting electrode871changes in the middle of its extending direction. The minimum width W5of the first portion8711is smaller than the maximum width W6of the second portion8712. An area of the first portion8711is smaller than an area of the second portion8712.

The first connecting electrode971includes a first portion9711that overlaps with the ground conductor741and a second portion9712that does not overlap with the ground conductor741in plan view. The minimum width W5of the first portion9711is smaller than the maximum width W6of the second portion9712. The minimum width W5of the first portion9711is smaller than the minimum width W7of the second portion9712. An area of the first portion9711is smaller than an area of the second portion9712.

In the second preferred embodiment, the ground conductor741extends up to immediately before the mounting electrode12in the extending direction of the transmission line70. Therefore, superimposition of external noise on a high-frequency signal is prevented until immediately before the high-frequency signal is outputted from the transmission line70. The intensity of electric field is stronger especially at a position on which the second inter-layer connecting conductor162, raising a signal line of the transmission line70in the laminating direction, is positioned, than other positions. In the second preferred embodiment, this position is covered by the ground conductor741and accordingly, superimposition of external noise on a high-frequency signal is effectively prevented.

Also, noise radiation from the slit SL3is further reduced or prevented.

Furthermore, the first connecting electrodes771,871, and971are positioned so that each of the first connecting electrodes771,871, and971overlaps with the ground conductor741in plan view but each has a smaller area facing the ground conductor741. This reduces or prevents an increase in a capacitance value between the first connecting electrode771,871, or971and the ground conductor741and consequently reduces or prevents a deviation of the characteristic impedance of the transmission line70.

Other Preferred Embodiments

FIGS.13,14,15,16, and17are sectional views of transmission lines according to other preferred embodiments. In order to avoid unwanted conduction, coupling, or interference with an electronic component or wiring mounted in the substrate11, for example, the connecting portion151may detour to the second main surface S2side, as illustrated inFIGS.13to17. In this configuration, the first connecting electrode171is between the signal conductor13and the ground conductor142. The ground conductor142is partially removed and does not overlap with at least a portion of the first connecting electrode171. This configuration reduces or prevents capacitance coupling between the first connecting electrode171and the ground conductor142.

Here,FIGS.13to17omit illustration of electronic components and wiring mounted in the substrate11described above.

The inter-layer connecting conductor16may be a via hole that penetrates through a plurality of layers, as illustrated inFIG.13. Further, one inter-layer connecting conductor16may penetrate through a plurality of insulator layers511and512that respectively include mutually-different kinds of resin sheets, as illustrated inFIG.18. The connecting portion151may include three or more inter-layer connecting conductors16and a plurality of connecting electrodes17, as illustrated inFIGS.14to17. The connecting portion151may include the inter-layer connecting conductors16that overlap with each other in plan view, as illustrated inFIG.17. Further, the ground conductor142may be provided on an inner layer, as illustrated inFIG.17.

The connecting electrodes17of the connecting portion151do not overlap with a connecting portion551that connects the ground conductor141and a ground conductor143with each other, in plan view, as illustrated inFIG.16. Thus, it is preferable that the connecting electrode17of the connecting portion151does not overlap with a wiring portion connected to the ground, in plan view. This reduces or prevents capacitance coupling between the connecting electrode17of the connecting portion151and the wiring portion.