Circuit board

Abstract

To provide a circuit board that reduces loss while reducing a manufacturing cost.SOLUTION: A circuit board comprises: a first electric conductor; a second electric conductor; a transmission line that is arranged between the first electric conductor and the second electric conductor; a first dielectric layer that is a layer arranged between the first electric conductor and the transmission line and includes at least one first dielectric substance; and a second dielectric layer that is a layer arranged between the second electric conductor and the transmission line and includes at least one second dielectric substance. The second dielectric layer is configured to be thicker than the first dielectric layer. The dielectric constant and / or dielectric loss tangent of the first dielectric substance is(are) configured to be smaller than the dielectric constant and / or dielectric loss tangent of the second dielectric substance.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a circuit board.

Background Art

[0002] Devices that transmit and receive radio waves, such as smartphones or millimeter-wave radars, incorporate various components such as antennas and circuit boards for radio wave transmission and reception. In such devices, it is desirable to reduce losses (dielectric losses) in, for example, antenna feed lines. Several proposals have been made to reduce losses in antenna feed lines and the like.

[0003] For example, the circuit board described in Patent Document 1 discloses reducing the effective relative permittivity by physically providing voids in the insulating layer between the metal conductor and the power supply layer. Further, the circuit board described in Patent Document 2 discloses reducing the effective relative permittivity by providing a cavity between the center conductor and the electrode. Further, Patent Document 3 discloses disposing a dielectric material having a lower dielectric constant than the dielectric layer sandwiching the layer including these differential wirings between pairs of differential wirings in the inner layer of the printed circuit board. Further, the circuit board described in Patent Document 4 discloses using a low-loss dielectric on the side of the insulating layer with a thin layer thickness in the signal layer sandwiched between insulating layers, thereby concentrating the electric field generated by the signal on the low-loss dielectric side to achieve low loss.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is desirable to reduce the loss in the antenna power supply line of the circuit board. Also, it is advantageous if the manufacturing cost of such a circuit board can be suppressed.

[0006] An object of the present disclosure is to provide a circuit board with reduced loss while suppressing the manufacturing cost.

Means for Solving the Problems

[0007] A circuit board according to one embodiment includes a first conductor, a second conductor, a transmission line disposed between the first conductor and the second conductor, a first dielectric layer disposed between the first conductor and the transmission line and including at least one first dielectric, a second dielectric layer disposed between the second conductor and the transmission line and including at least one second dielectric, and is provided with. The second dielectric layer is configured to be thicker than the first dielectric layer. The dielectric constant and / or dielectric tangent of the first dielectric is configured to be smaller than the dielectric constant and / or dielectric tangent of the second dielectric. The second dielectric layer includes a third conductor different from the first conductor and the second conductor at a position not overlapping with the transmission line in the thickness direction of the circuit board. No conductor exists between the transmission line and the second conductor in the thickness direction of the circuit board.

Advantages of the Invention

[0008] According to one embodiment, it is possible to provide a circuit board with reduced loss while suppressing the manufacturing cost.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0010] Hereinafter, an embodiment will be described in detail with reference to the drawings.

[0011] FIG. 1 is a diagram schematically showing the overall configuration of a circuit board according to an embodiment. The application of the circuit board according to an embodiment is not particularly limited, but for example, it may be used in devices that transmit and receive radio waves, such as smartphones or millimeter-wave radars.

[0012] As shown in FIG. 1, the circuit board 1 according to an embodiment may be, for example, a hybrid-type multilayer substrate. FIG. 1 is a diagram showing a cross-section of the circuit board 1 according to an embodiment. The circuit board 1 shown in FIG. 1 has a multilayer structure in the Z-axis direction shown in the figure. That is, the circuit board 1 shown in FIG. 1 may have the Z-axis direction shown in the figure as the thickness direction. As will be described later, the circuit board 1 according to an embodiment may constitute a signal line (strip line). In the circuit board 1 shown in FIG. 1, signals may be transmitted in the Y-axis direction shown in the figure.

[0013] As shown in FIG. 1, the circuit board 1 according to an embodiment includes conductors 11 - 18. Each of the conductors 11 - 18 may be configured to contain, for example, copper. FIG. 1 shows a case of an 8-layer structure of the conductors 11 - 18 as an example of the circuit board 1 according to an embodiment. However, the circuit board 1 according to an embodiment is not limited to an 8-layer structure and may have a multilayer structure with an arbitrary number of layers.

[0014] Also, as shown in FIG. 1, the circuit board 1 according to one embodiment includes dielectric layers 21-27. The dielectric layers 21-27 may each be disposed between conductors 11-18. Each of the dielectric layers 21-27 may be configured to include any dielectric. In one embodiment, for example, a resin material of the FR-4 standard may be used for each of the dielectric layers 21-27.

[0015] Among the dielectric layers 21-27 shown in FIG. 1, for example, for the dielectric layer 21 and the dielectric layer 27, a base material having a relatively low dielectric constant and / or dielectric tangent may be used. That is, the dielectric constant and / or dielectric tangent of the dielectric layer 21 and the dielectric layer 27 may be lower than a predetermined value. The dielectric layers 21 and 27 may be used, for example, for applications such as in the millimeter wave band. In the present disclosure, the dielectric loss of the transmission line can be expressed as α (transmission loss) in the following formula (1). In formula (1), K represents a proportionality constant, f represents a frequency, εr represents a relative dielectric constant, and tanδ represents a dielectric tangent. α = K × f × √εr × tanδ (1)

[0016] The dielectric loss of the transmission line indicated by α in the above formula (1) is proportional to both the dielectric constant and the dielectric tangent. Therefore, in the circuit board 1 according to one embodiment, at least one of the dielectric constant and the dielectric tangent of the dielectric layer 21 and the dielectric layer 27 may be lowered. Also, as an example of values of a low dielectric constant and a low dielectric tangent, for example, in the case of materials used in conventional millimeter wave radars, the following values can be cited. That is, in a resin material of the FR-4 standard, for example, the dielectric constant Dk is 4.4, and the dielectric tangent Df is 0.02 at 10 GHz, whereas the dielectric constant Dk is 3.0 and the dielectric tangent Df is 0.001 at a frequency of 10 GHz. However, the above values may vary depending on the material manufacturer, model number, frequency used, and / or ambient temperature, etc.

[0017] In the present disclosure, the permittivity may be the relative permittivity. Also, the dielectric tangent (tanδ) is a numerical value representing the degree of electrical energy loss (energy loss rate) in the dielectric body. The dielectric tangent (tanδ) can be expressed as in the following formula (2) with the signal current Ic and the loss current Ir. tanδ = Ir / Ic (2)

[0018] As shown in FIG. 1, in the circuit board 1 according to one embodiment, the dielectric layer 24 may be used as a core material, and the copper plates of the conductors 14 and 15 may be pressed. Also, the dielectric layers 22, 23, 25, and 26 may be, for example, prepregs.

[0019] FIG. 2 is a diagram showing a comparative example for explaining the circuit board 1 according to one embodiment. That is, FIG. 2 is a diagram showing a part of the circuit board 100 as a comparative example for comparison with the circuit board 1 according to one embodiment. Also, FIG. 3 is a diagram showing a part of the circuit board 1 according to one embodiment. In FIGS. 2 and 3, the signal may be transmitted in the Y-axis direction shown in the figure.

[0020] Both the circuit board 100 shown in FIG. 2 and the circuit board 1 shown in FIG. 3 have signal lines formed in the inner layer of the substrate. The circuit board 100 shown in FIG. 2 includes a transmission line 12 between the conductors 11 and 13. Also, the circuit board 100 shown in FIG. 2 includes dielectric layers 21 and 22 between the conductors 11 and 13. The circuit board 1 shown in FIG. 3 includes a transmission line 12 between the conductors 11 and 14. Also, the circuit board 1 shown in FIG. 3 includes dielectric layers 21, 22, and 23 between the conductors 11 and 14. Thus, both the circuit board 100 shown in FIG. 2 and the circuit board 1 shown in FIG. 3 form a stripline in which the transmission line 12 used as a signal line is sandwiched between conductors and dielectric layers in the vertical direction (Z-axis direction).

[0021] In the circuit board 100 shown in FIG. 2, the distance between the conductor 11 and the transmission line 12 is larger than the distance between the transmission line 12 and the conductor 13. That is, in the circuit board 100 shown in FIG. 2, the dielectric layer 21 having a relatively low dielectric constant and / or dielectric tangent is thicker (the size in the Z-axis direction shown in the figure) than the dielectric layer 22 of the prepreg. Here, the dielectric constant and / or dielectric tangent of the dielectric layer 22 may be larger than the dielectric constant and / or dielectric tangent of the dielectric layer 21. In such a configuration, the electric field distribution of the signal line (transmission line 12) enters more into the conductor 13 on the side closer to the ground plane as shown in FIG. 2. That is, in the electric field distribution of the signal line, the dielectric layer 22 having a large dielectric constant and / or dielectric tangent becomes dominant.

[0022] On the other hand, in the circuit board 1 shown in FIG. 3, compared with the structure of FIG. 1, it has a structure in which the conductor 13 is omitted. For this reason, in the circuit board 1 shown in FIG. 3, the distance between the conductor 11 and the transmission line 12 is smaller than the distance between the transmission line 12 and the conductor 14. In such a configuration, the electric field distribution of the signal line (transmission line 12) enters more into the conductor 11 on the side closer to the ground plane as shown in FIG. 3. That is, in the electric field distribution of the signal line, the dielectric layer 21 having a small dielectric constant and / or dielectric tangent becomes dominant. Therefore, in the circuit board 1 shown in FIG. 3, the transmission loss of the transmission line 12 can be reduced.

[0023] As described above, the circuit board 1 according to one embodiment includes a first conductor 11, a second conductor 14, a transmission line 12, a first dielectric layer 21, and a second dielectric layer (22, 23). The transmission line 12 may be disposed between the first conductor 11 and the second conductor 14. The first dielectric layer 21 is a layer disposed between the first conductor 11 and the transmission line 12 and may include at least one first dielectric. The second dielectric layer (22, 23) is a layer disposed between the second conductor 14 and the transmission line 12 and may include at least one second dielectric.

[0024] Also, in the circuit board 1 according to one embodiment, the second dielectric layers (22, 23) are configured to be thicker than the first dielectric layer 21. Further, in the circuit board 1 according to one embodiment, the dielectric constant and / or the dielectric tangent of the first dielectric in the first dielectric layer 21 are configured to be smaller than the dielectric constant and / or the dielectric tangent of the second dielectric in the second dielectric layers (22, 23).

[0025] According to the circuit board 1 according to one embodiment, the transmission loss of the transmission line 12 can be reduced. Also, the usage amount of a dielectric having a relatively high cost and a small dielectric constant and / or dielectric tangent can be suppressed. Therefore, according to the circuit board 1 according to one embodiment, a circuit board with reduced loss while suppressing the manufacturing cost can be provided.

[0026] Also, in the circuit board 1 according to one embodiment, in order to better direct electrolysis to a dielectric having a small dielectric constant and / or dielectric tangent, the materials of the dielectric layers in the vertical (Z-axis shown in the figure) direction may be of the same type. That is, in the circuit board 1 according to one embodiment, the first dielectric in the first dielectric layer 21 and the second dielectric in the second dielectric layers (22, 23) may be composed of the same type of material.

[0027] In the circuit board 1 shown in FIG. 3, a structure in which the conductor 13 is omitted is described as compared with the structure of FIG. 1. In FIG. 3, an example in a state where the conductor 13 is completely omitted is described. On the other hand, in the circuit board 1 according to one embodiment, a structure in which a part of the conductor 13 is omitted may be used as compared with the structure of FIG. 1. For example, as in the circuit board 1 shown in FIG. 4, only the conductor 13 existing directly below the signal line (transmission line 12) (in the negative direction of the Z-axis shown in the figure) may be removed. In this way, other regions of the conductor 13 existing in parts other than directly below the signal line (transmission line 12) (in the negative direction of the Z-axis shown in the figure) may be used as, for example, a ground plane. Further, in one embodiment, as shown in FIG. 4, the conductor 13 existing in a region with a little margin rather than directly below the transmission line 12 (in the negative direction of the Z-axis shown in the figure) may be removed.

[0028] The effects of the circuit board 1 according to an embodiment will be further described below.

[0029] For example, as in Patent Document 1 described above, it is also conceivable to reduce the effective dielectric constant by physically providing voids in the insulating layer between the conductor and the power supply layer. Since the dielectric constant of air (or vacuum) is 1, air can be said to be ideal as an insulating layer. However, a special manufacturing process is required to create voids as in Patent Document 1. Therefore, such a structure is assumed to lead to an increase in cost. Also, since the insulating layer has a very thin structure, it is also assumed that it is difficult to accurately provide voids.

[0030] Also, as in Patent Document 2 described above, when forming a depression to reduce the dielectric constant, a special manufacturing process is required, and it is assumed that this will lead to an increase in cost.

[0031] For example, in a structure where the signal layer is sandwiched between dielectric layers (so-called stripline), if the upper and lower layers are replaced with materials having a low dielectric constant, particularly a low dielectric tangent, the material cost becomes high. Therefore, such a circuit board tends to have an increase in manufacturing cost. Thus, for example, it is also conceivable to replace only one side with a material having a low dielectric constant, particularly a low dielectric tangent. Patent Document 4 described above focuses the electric field generated by the signal on the low-loss dielectric side by using a low-loss dielectric for the insulating layer side with a thin layer thickness in the signal layer sandwiched between insulating layers (i.e., forming a stripline). The printed wiring board disclosed in Patent Document 4 described above can be expected to have low loss and can suppress the cost increase to some extent by using an expensive low-loss dielectric only on one side. However, such a configuration using a low-loss dielectric is limited to the case where the thickness of the low-dielectric-constant material layer is made thin.

[0032] According to the circuit board 1 according to an embodiment, the problems as described in each of the above-mentioned patent documents can be overcome.

[0033] That is, according to the circuit board 1 according to one embodiment, the radiated electric field from the signal line enters a large amount into the conductor located near the signal line. Therefore, the circuit board 1 according to one embodiment can equivalently reduce the dielectric constant and / or the dielectric tangent by making the dielectric constant and / or the dielectric tangent of the dielectric between the conductor located near the signal line relatively small. For this reason, according to the circuit board 1 according to one embodiment, the loss (dielectric loss) can be kept low.

[0034] Generally, a material with a low dielectric constant and / or a low dielectric tangent may cause an increase in cost. However, according to the circuit board 1 according to one embodiment, a material with a low dielectric constant and / or a low dielectric tangent is mounted only on one side. For this reason, according to the circuit board 1 according to one embodiment, an increase in material cost can be suppressed. Further, according to the circuit board 1 according to one embodiment, even if the layer with a low dielectric constant and / or a low dielectric tangent is thick, the loss (dielectric loss) can be kept low only by changing the pattern without changing the thickness of the layer. That is, according to the circuit board 1 according to one embodiment, since it can be manufactured by a conventional process without going through a special manufacturing process, an increase in manufacturing cost can be suppressed.

[0035] Each of the above-described embodiments has been described as an invention of the circuit board 1, but not only such an embodiment but also an invention of various methods performed by adopting such a circuit board may be implemented.

Description of reference numerals

[0036] 1 Circuit board 11-18 Conductor 11 First conductor 13 Third conductor 14 Second conductor 12 Transmission line 21-27 Dielectric layer 21 First dielectric layer 22,23 Second dielectric layer

Claims

1. a first conductor, a second conductor, a transmission line disposed between the first conductor and the second conductor, a first dielectric layer disposed between the first conductor and the transmission line and including at least one first dielectric, a second dielectric layer disposed between the second conductor and the transmission line and including at least one second dielectric, a circuit board comprising: the second dielectric layer is configured to be thicker than the first dielectric layer, the dielectric constant and / or the loss tangent of the first dielectric is configured to be smaller than the dielectric constant and / or the loss tangent of the second dielectric, the second dielectric layer includes a third conductor different from the first conductor and the second conductor at a position where the second dielectric layer does not overlap with the transmission line in the thickness direction of the circuit board, a circuit board in which no conductor exists between the transmission line and the second conductor in the thickness direction of the circuit board.

2. The circuit board according to claim 1, wherein the second dielectric layer between the transmission line and the second conductor in the thickness direction of the circuit board is formed of the same dielectric material.

3. The circuit board according to claim 1, wherein the third conductor is surrounded by the second dielectric layer of the same dielectric material.

4. The circuit board according to claim 1, wherein the second dielectric layer includes at least two layers of dielectric materials.

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