JP2023003107A - wiring board - Google Patents

Abstract

To provide a wiring board capable of improving the shielding effect of a ground layer while achieving impedance matching.SOLUTION: A wiring board 1 includes a signal line 21, an upper ground layer 50, and a lower ground layer 60. The upper ground layer 50 has a first mesh shape 51 with a plurality of periodically arranged openings 55, and the lower ground layer 60 has a mesh shape 61 with a plurality of periodically arranged openings 65, which satisfy the following formulas (1) and (2). D1<D2 (1). R1>R2 (2). In addition, formula (1), D1 is a distance between the upper ground layer 50 and the signal line 21 in cross section, D2 is a distance between the lower ground layer 60 and the signal line 21 in cross section, and in the formula (2), R1 is the aperture ratio of the upper ground layer 50, and R2 is the aperture ratio of the lower ground layer 60.SELECTED DRAWING: Figure 1

Description

The present invention relates to wiring boards.

A flexible printed wiring board (FPC) having a strip structure includes a signal wiring layer having signal lines, and a pair of ground layers laminated on both sides of the signal wiring layer via an insulator layer (for example, See Patent Document 1).

JP 2019-192786 A

In the above flexible printed wiring board, the shape of the mesh part of the upper ground layer and the shape of the mesh part of the lower ground layer are the same, and the aperture ratio of the upper ground layer and the aperture ratio of the lower ground layer are the same. are equal. In such a flexible printed wiring board, when the distances from the signal line to the upper and lower ground layers are different, if the aperture ratios of the upper and lower ground layers are made equal for impedance matching, the shielding effect of the ground layers is sacrificed. Sometimes.

The problem to be solved by the present invention is to provide a wiring board that can improve the shielding effect of the ground layer while maintaining impedance matching even when the distances from the signal line to the upper and lower ground layers are different. It is to be.

[1] A wiring board according to the present invention is a wiring board having a strip structure, comprising: a signal line; a first ground layer facing the signal line through a first insulating layer; a second ground layer located opposite to the first ground layer and facing the signal line via a second insulating layer, wherein the first ground layer has a periodicity The second ground layer has a first mesh shape with a plurality of regularly arranged first openings, and the second ground layer has a second mesh shape with a plurality of periodically arranged second openings. and satisfies the following formulas (1) and (2).
D ₁ < D ₂ (1)
R ₁ >R ₂ (2)
However, in the above equation ( ₁ ), D1 is the distance between the first ground layer and the signal line in cross section, and D2 is the distance between the _second ground layer and the signal line in cross section. In the above equation (2), _R1 is the aperture ratio of the first ground layer and _R2 is the aperture ratio of the second ground layer.

[2] In the above invention, the first ground layer includes a plurality of first ground lines and a plurality of second ground lines arranged to intersect the first ground lines, The second ground layer includes a plurality of third ground lines and a plurality of fourth ground lines arranged to intersect the third ground lines, and the first openings are: The first ground line and the second ground line are formed by crossing, the second opening is formed by crossing the third ground line and the fourth ground line, and the The pitch between the first ground lines is substantially the same as the pitch between the second ground lines, and the pitch between the third ground lines is substantially the same as the pitch between the fourth ground lines. and may satisfy the following formula (3).
P ₁ >P ₃ (3)
However, in the above equation ( ₃ ), P1 is the pitch between the _first ground lines, and P3 is the pitch between the third ground lines.

[3] In the above invention, the following formula (4) may be satisfied.
P ₁ ×0.85≧P ₃ (4)

[4] In the above invention, the first ground layer includes a plurality of first ground lines and a plurality of second ground lines arranged to intersect the first ground lines, The second ground layer includes a plurality of third ground lines and a plurality of fourth ground lines arranged to intersect the third ground lines, and The line width is substantially the same as the line width of the second ground line, and the line width of the third ground line is substantially the same as the line width of the fourth ground line. (5) Formula may be satisfied.
W1 < W3 _{( 5} )
However, in the above equation (5), W1 is the line width of the _first ground line, and W3 is the line width of the _third ground line.

[5] In the above invention, the following formula (6) may be satisfied.
P _A1 <P _A2 (6)
However, in the above equation (6), P _A1 is the pitch between the first openings, and P _A2 is the pitch between the second openings.

[6] In the above invention, the following formula (7) may be satisfied.
S ₁ >S ₂ (7)
However, in the above equation (7), S1 is the area of the _first opening and S2 is the area of the _second opening.

According to the present invention, the above formulas (1) and (2) are satisfied in the wiring board having the strip structure. That is, the aperture ratio of the second ground layer, which is farther from the signal line, is smaller than the aperture ratio of the first ground layer, which is close to the signal line. For impedance matching, since the aperture ratio of the ground layer close to the signal line is dominant, according to the wiring board of the present invention, the impedance is adjusted by adjusting the aperture ratio of the first ground layer. By reducing the aperture ratio of the second ground layer while achieving matching, the shielding effect of the second ground layer can be improved.

FIG. 1 is a plan view showing part of a wiring board in an embodiment of the invention. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a plan view showing a lower ground layer in an embodiment of the invention. FIG. 4 is a diagram corresponding to the IV part of FIG. 1, and is a diagram for explaining the aperture ratio in the embodiment of the present invention. FIG. 5 is a plan view showing a first modification of the wiring board according to the embodiment of the invention. FIG. 6 is a plan view showing the lower ground layer of the first modification of the wiring board according to the embodiment of the invention. FIG. 7 is a plan view showing a second modification of the wiring board according to the embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing a part of the wiring board in this embodiment, and FIG. 2 is a cross-sectional view taken along line II-II in FIG.

The wiring board 1 in this embodiment is a flexible printed circuit board (FPC) having a strip structure. As shown in FIGS. 1 and 2, the wiring board 1 includes a lower base film 10, a signal layer 20, an adhesive layer 30, an upper base film 40, an upper ground layer 50, and a lower ground layer 60. and have.

The lower base film 10 is a flexible film. The lower base film 10 is made of an electrically insulating material such as a resin material. Materials constituting the lower base film 10 include, but are not limited to, polyimide (PI), liquid crystal polymer (LCP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyetherimide (PEI). , polyetheretherketone (PEEK), polystyrene (PS), cycloolefin polymer (COP), fluororesin, and aramid.

A signal layer 20 is formed on the upper surface 11 of the lower base film 10 . The signal layer 20 has a signal line 21 and a pair of ground lines 22 and 23 . The signal line 21 in this embodiment corresponds to an example of the "signal line" in the present invention. The number of signal lines 21 included in the signal layer 20 is not particularly limited, and the signal layer 20 may include a plurality of signal lines. Also, the pair of ground lines 22 and 23 may be omitted depending on the transmission characteristics required for the signal line 21 .

As shown in FIG. 1, the signal line 21 extends linearly along the X direction in the drawing. The signal line 21 in this embodiment is a signal line for single-ended signal transmission (single-ended line), but is not particularly limited to this. The signal lines of the signal layer 20 may be signal lines for differential signal transmission (differential pair lines).

A pair of ground lines 22 , 23 are arranged on both sides of the signal line 21 . The pair of ground lines 22 and 23 extend in substantially the same direction (the X direction in the drawing) as the signal line 21, and the signal line and the ground lines 22 and 23 are substantially parallel to each other. extended. The interval between one ground line 22 and the signal line 21 and the interval between the other ground line 23 and the signal line 21 are substantially the same. These ground lines 22 and 23 are connected to ground layers 50 and 60 via through holes T, and have a function of shielding noise generated from the signal line 21 and noise entering from the outside. Note that the width of the ground lines 22 and 23 is not particularly limited to the above, and may be narrower than the width of the signal line 21 .

The signal layer 20 including the signal line 21 and ground lines 22 and 23 is made of a conductive material such as metal or carbon. Examples of metals forming the signal layer 20 include copper, silver, and gold. In this embodiment, copper is used as the material for forming the signal layer 20 . Although not particularly limited, the signal layer 20 is formed using a method such as a subtractive method or a semi-additive method, and is formed by etching a copper foil laminated on the lower base film 10 into a predetermined shape. It is In addition, the signal layer 20 may further include a plated layer, although not particularly limited.

As shown in FIG. 2, an upper base film 40 is laminated on the lower base film 10 so as to cover the signal layer 20 . The upper base film 40 is a flexible and electrically insulating film, like the lower base film 10 described above. As a material constituting the upper base film 40, the same material as the material constituting the lower base film 10 described above can be exemplified. The upper base film 40 may be made of the same material as the lower base film 10 or may be made of a material different from the lower base film 10 .

This upper base film 40 is fixed to the lower base film 10 via the adhesive layer 30 . The adhesive constituting the adhesive layer 30 is not particularly limited, but a thermoplastic adhesive made of modified polyphenylene ether resin (m-PPE) can be used. Note that an epoxy-based adhesive, an acrylic-based adhesive, or the like may be used as the adhesive that forms the adhesive layer 30 .

An upper ground layer 50 is formed on the upper surface 41 of the upper base film 40 . A coverlay may be laminated on the upper surface 41 of the upper base film 40 so as to cover the upper ground layer 50 .

Although not particularly limited, the thickness of the upper base film 40 is 5 to 100 μm, and the thickness of the lower base film 10 is 10 to 300 μm. In this embodiment, the thickness of the lower base film 10 is larger than the thickness of the upper base film 40 .

In this embodiment, the thickness of the lower base film 10 is larger than the thickness of the upper base film 40, so that the distance D ₁ between the signal line 21 and the upper ground layer 50 and the distance between the signal line 21 and the upper ground layer 50 are reduced. A distance D2 between the _lower ground layers 60 satisfies the following equation (8).
D ₁ < D ₂ (8)

In this embodiment, each of the lower base film 10, the upper base film 40, and the adhesive layer 30 is a single layer, but each may be composed of a plurality of layers.

As shown in FIG. 1, the upper ground layer 50 has a strip-like shape as a whole that extends linearly along the X direction in the drawing, and the center line of the upper ground layer 50 extends along the X direction in plan view. It is arranged so as to substantially match the center line of the signal line 21 . Also, the upper ground layer 50 has a mesh shape 51 with a plurality of openings 55 arranged periodically. This upper ground layer 50 has a function of shielding noise generated from the signal line 21 and noise entering from the outside. Further, by adjusting the aperture ratio (described later) of the mesh shape 51 of the upper ground layer 50, the impedance of the wiring board 1 can be adjusted.

This upper ground layer 50 includes two types of fine wires 52 and 53 forming a mesh shape 51 . The mesh shape 51 in the present embodiment corresponds to an example of the "first mesh shape" in the present invention, and the thin wire 52 in the present embodiment corresponds to an example of the "first ground line" in the present invention. corresponds to an example of the "second ground line" in the present invention.

_One thin wire 52 has a width W1 and extends linearly along the first direction U. As shown in FIG. On the other hand, the other thin wire 53 has a width W2 and extends linearly along a _second direction V substantially orthogonal to the first direction U. As shown in FIG. In this embodiment, the width W1 of _one fine line 52 and the width W2 of the _other fine line 53 _are substantially the same (W1 ₌ W2). Widths W ₁ and W ₂ of thin lines 52 and 53 are preferably 10 to 1000 μm, respectively, although not particularly limited. In this embodiment, "substantially the same" means that the error is within a range of ±5%.

The first direction U is 52° with respect to the extension direction of the signal line 21 (the X direction in the drawing), while the second direction V -38° to the direction. That is, in the present embodiment, the crossing angle θ ₁ of one thin wire 52 with respect to the signal line 21 is 52° (θ ₁ =52°), whereas the crossing angle θ 1 of the other thin wire 53 with respect to the signal line 21 is 52° ₂ is −38° (θ ₂ =−38°). In this embodiment, the clockwise rotation direction with respect to the reference line (+X direction in this example) is indicated by a positive angle, and the counterclockwise rotation direction with respect to the reference line is indicated by a negative angle.

In addition, the plurality of thin wires 52 are arranged at substantially equal intervals along the second direction V, and the pitch (center-to-center distance) between the mutually adjacent thin wires 52 along the second direction V is _P1 . Similarly, the plurality of thin wires 53 are also arranged at substantially equal intervals along the first direction U, and the pitch along the _first direction U between the mutually adjacent thin wires 53 is P2. ing. _In this embodiment, the pitch P1 of the fine wires 52 and the pitch P2 of the fine wires 53 _are substantially the same ( _{P1 =} P2).

Therefore, the thin wires 52 and 53 intersect each other at the intersections 54 to form the mesh shape 51 having a plurality of openings 55 . Each intersection 54 has a square shape and each opening 55 also has a square shape. Also, the mesh shape 51 of the upper ground layer 50 has an arrangement in which a plurality of openings 55 are arranged along the first and second directions U and V. As shown in FIG. That is, the arrangement directions of the openings 55 in the mesh shape of the upper ground layer 50 are the first and second directions U and V. As shown in FIG. The opening 55 in this embodiment corresponds to an example of the "first opening" in the invention.

Further, the upper ground layer 50 has a pair of outer edge lines 56 defining both edges (upper and lower edges in the drawing) of the strip shape. The outer edge line 56 extends linearly along the X direction in the figure, and connects the ends of the fine lines 52 and 53 forming the mesh shape 51 along the X direction in the figure. Note that the upper ground layer 50 may not have the outer edge line 56 .

Note that the width _W1 of the thin wire 52 and the width _W2 of the thin wire 53 may be different. Also, the first and second directions U and V are not particularly limited to the above. Although not particularly limited, for example, even if the first direction U is 45° with respect to the extending direction of the signal line 21 and the second direction V is −45° with respect to the signal line 21 good.

Furthermore, the crossing angle between the first direction U and the second direction V is not limited to 90°. Also, the pitch P1 of the fine wires 52 and the pitch _P2 of the fine _wires 53 may be different. When the crossing angle between the _first direction U and the second direction V is not a right angle, or when the pitch P1 of the thin wires 52 and the pitch P2 of the thin wires 53 _are different, the shape of the openings 55 is a rectangle other than a square. becomes.

As the material forming the upper ground layer 50, the same material as the material forming the signal layer 20 described above can be exemplified. The upper ground layer 50 may be made of the same material as the signal layer 20 or may be made of a material different from the signal layer 20 . As a method for manufacturing the upper ground layer 50, the same manufacturing method as the method for manufacturing the signal layer 20 described above can be exemplified. The upper ground layer 50 may be formed by the same manufacturing method as the signal layer 20 or by a different manufacturing method from the signal layer 20 .

On the other hand, the lower ground layer 60 is formed on the lower surface 12 of the lower base film 10, as shown in FIG. A coverlay may be laminated on the lower surface 12 of the lower base film 10 so as to cover the lower ground layer 60 .

As shown in FIG. 1, the lower ground layer 60 has a strip shape as a whole extending linearly along the X direction in the figure, and has substantially the same width as the upper ground layer 50. has a width of Also, the lower ground layer 60 is arranged such that the center line of the lower ground layer 60 substantially coincides with the center line of the signal line 21 in plan view. Furthermore, as shown in FIG. 3, this lower ground layer 60 has a mesh shape 61 with a plurality of openings 65 arranged periodically. This lower ground layer 60 has a function of shielding noise generated from the signal line 21 and noise entering from the outside. FIG. 3 is a plan view showing the lower ground layer in this embodiment.

As the material forming the lower ground layer 60, the same material as the material forming the signal layer 20 described above can be exemplified. The lower ground layer 60 may be made of the same material as the signal layer 20 or may be made of a material different from the signal layer 20 . As a method for manufacturing the lower ground layer 60, the same manufacturing method as the method for manufacturing the signal layer 20 described above can be exemplified. The lower ground layer 60 may be formed by the same manufacturing method as the signal layer 20 or by a different manufacturing method from the signal layer 20 .

The lower ground layer 60 includes two types of thin wires 62 and 63 forming a mesh shape 61. As shown in FIG. The mesh shape 61 in this embodiment corresponds to an example of the "second mesh shape" in the present invention, and the thin wire 62 in this embodiment corresponds to an example of the "third ground line" in the present invention. corresponds to an example of the "fourth ground line" in the present invention.

One thin wire 62 has a width W3 and extends linearly along the _first direction U. As shown in FIG. _On the other hand, the other thin wire 63 has a width W4 and extends linearly along the second direction V. As shown in FIG. _In this embodiment, the width W3 of one fine line 62 and the width W4 of the other fine line 63 are substantially the same _{( W3} = _W4 ). Note that the width W3 of the thin wire 62 and the width _W4 of the thin wire ₆₃ may be different.

In addition, the plurality of thin wires 62 are arranged at substantially equal intervals along the second direction V _, and the pitch along the second direction V between the mutually adjacent thin wires 62 is P3. there is Similarly, the plurality of thin wires 63 are also arranged at substantially equal intervals along the first direction U, and the pitch along the first direction U between the mutually adjacent thin wires 63 is _P4 . ing. In this embodiment, the pitch P3 of the fine wires 62 and the pitch _P4 of the fine wires 63 are substantially the same _{( P3} = _P4 ).

Therefore, the thin wires 62 and 63 intersect each other at the intersections 64 to form a mesh shape 61 having a plurality of openings 65 . Each intersection 64 has a square shape and each opening 65 also has a square shape. Also, the mesh shape 61 of the lower ground layer 60 has an arrangement in which a plurality of openings 65 are arranged along the first and second directions U and V. As shown in FIG. That is, the arrangement directions of the openings 65 in the mesh shape of the lower ground layer 60 are the first and second directions U and V. As shown in FIG. The opening 65 in this embodiment corresponds to an example of the "second opening" in the present invention.

Further, the lower ground layer 60 has a pair of outer edge lines 66 defining both edges (upper and lower edges in the figure) of the strip shape. The outer edge line 66 extends linearly along the X direction in the figure, and connects the ends of the fine lines 62 and 63 forming the mesh shape 61 along the X direction in the figure. Note that the lower ground layer 60 may not have the outer edge line 66 .

In this embodiment, the width W3 of one fine wire 62 of the lower ground layer ₆₀ and the width W1 of _one fine wire 52 of the upper ground layer 50 are substantially the same ₍ W3=W ₁ ), the width _W4 of the other fine wire 63 of the lower ground layer 60 and the width W2 of the other fine wire 53 of the upper ground layer 50 _are substantially the same ₍ W4 ₌ W2). . Therefore, all the widths W ₁ to W ₄ of the thin wires 52, 53 of the upper ground layer 50 and the thin wires 62, 63 of the lower ground layer 60 are substantially the same (W ₁ =W ₂ =W ₃ = _W4 ).

Moreover, in this embodiment, the following formulas (9) and (10) are satisfied.
P1 > _P3 ( ₉ )
P2 > P4 _{( 10} )

Furthermore, although not particularly limited, it is desirable that the following formulas (11) and (12) are satisfied, and more preferably that the following formulas (13) and (14) are satisfied.
P ₁ ×0.85≧P ₃ (11)
P ₂ ×0.85≧P ₄ (12)
P ₁ ×0.6≧P ₃ (13)
P ₂ ×0.6≧P ₄ (14)

Furthermore, in this embodiment, the area S1 of the opening 55 of the upper ground layer ₅₀ and the area S2 of the opening 65 of the _lower ground layer 60 satisfy the following equation (15). That is, the area S ₁ of the opening 55 in the upper ground layer 50 is larger than the area S ₂ of the opening 65 in the lower ground layer 60 .
S ₁ >S ₂ (15)

In addition to the above, the crossing angle θ3 of the one thin wire 62 with respect to the signal line 21 is substantially the same as the crossing angle θ1 of the _one thin wire 52 of the upper ground layer _{50 ( θ3} =θ1). , the crossing angle θ ₄ of the other thin wire 63 with respect to the signal line 21 is also substantially the same as the crossing angle θ ₄ of the other thin wire 53 of the upper ground layer 50 (θ ₄ =θ ₂ ).

In addition, in this embodiment, the following formula (16) is satisfied, and the aperture ratio _R1 of the upper ground layer is larger than the aperture ratio _R2 of the lower ground layer.
R ₁ >R ₂ (16)

Here, the opening ratio _R1 of the upper ground layer can be calculated from the opening ratio of the openings 55 in the mesh shape 51. FIG. As shown in FIG. 4, the opening ratio of the openings 55 is such that the thin lines 52 and 53 are formed in the area surrounded by the center lines CL _1a and CL _1b of the thin lines 52 and the center lines CL _2a and CL _2b of the thin lines 53. It is the ratio of the area that is not covered, and can be expressed by the following formula (17). FIG. 4 is a diagram corresponding to the IV part of FIG. 1, and is a diagram for explaining the aperture ratio in this embodiment.

Similarly, the aperture ratio R ₂ of the lower ground layer can be calculated from the aperture ratio of the openings 65 in the mesh shape 61 . Although not shown, the opening ratio _R2 of the opening 65 is the ratio of the area surrounded by the center lines of the thin lines 62 and 63 where the thin lines 62 and 63 are not formed.

In this embodiment, all the widths W ₁ to W ₄ of the thin wires 52 and 53 of the upper ground layer 50 and the thin wires 62 and 63 of the lower ground layer 60 are substantially the same (W ₁ =W ₂ = W ₃ =W ₄ ) and by satisfying the above expressions (9) and (10), the above expression (16) is satisfied.

As described above, in the present embodiment, the strip-structured wiring board 1 satisfies the expression (8) and the expression (16). That is, in this embodiment, the distance D1 between the signal line 21 and the upper ground layer 50 is smaller _than the distance D2 between the signal line 21 and the _lower ground layer 60, and the aperture ratio of the upper ground layer is R ₁ is larger than the aperture ratio R ₂ of the lower ground layer 60 . With respect to impedance matching, the aperture ratio of the ground layer closer to the signal line is dominant. The shielding effect of the lower ground layer 60 is improved by reducing the aperture ratio _R2 of the lower ground layer 60 far from the signal line 21 while achieving impedance matching by adjusting the aperture ratio _R1 of the layer 50. be able to.

In this embodiment, the configuration of the mesh shape 51 of the upper ground layer 50 is not particularly limited as long as the formula (8) and the formula (16) are satisfied. Further, the configuration of the mesh shape 61 of the lower ground layer 60 is not particularly limited as long as it satisfies the formula (8) and the formula (16).

For example, in the above-described embodiment, the widths W ₁ to W ₄ of all the thin wires 52, 53 of the upper ground layer 50 and the thin wires 62, 63 of the lower ground layer 60 are substantially the same. , but not particularly limited to this. For example, W ₁ and W ₃ may satisfy the following formula (18), and W ₂ and W ₄ may satisfy the following formula (19). That is, as shown in FIGS. 5 and ₆ , the width W1 of one fine wire 52 of the upper ground layer 50 is smaller than the width W3 of _one fine wire 62 of the lower ground layer 60. The width W ₂ of the other thin wire 53 of the ground layer 50 may be smaller than the width W ₄ of the other thin wire 63 of the lower ground layer 60 . FIG. 5 is a cross-sectional view showing a first modification of the wiring board according to this embodiment, and FIG. 6 is a plan view showing a lower ground layer of the first modification of this embodiment.
W ₁ < W ₃ (18)
W2< _{W4 (} 19)

5 and 6 satisfy the above formula (15), and the area S1 of the opening 55 in the upper ground layer 50 is larger _than the area S2 of the opening 65 in the lower _ground layer 60. ing.

5 and 6, the pitch P3 between the openings 65 adjacent to each other along the _second direction V in the lower ground layer 60 is is substantially the same as the pitch P1 between the openings 55 adjacent to _each other in the lower ground layer 60, and the pitch P4 between the openings 65 adjacent to _each other along the first direction U in the lower ground layer 60 is It is substantially the same as the pitch P2 between the openings 55 adjacent to _each other along the first direction U in the upper ground layer 50 . Therefore, all the pitches P ₁ to P ₄ of the thin wires 52, 53 of the upper ground layer 50 and the thin wires 62, 63 of the lower ground layer 60 are substantially the same (P ₁ =P ₂ =P ₃ = _P4 ).

5 and 6, unlike the embodiment of FIG. 1, all the pitches P ₁ to P ₄ are substantially the same, while the above expressions (15), (18), And, by satisfying the expression (19), the above expression (16) is satisfied.

Alternatively, although not shown, the width W1 of one fine wire 52 of the upper ground layer 50 is smaller than the width W3 of _one fine wire 62 of the lower ground layer ₆₀ as long as the formula (16) is satisfied. At the same time, the width W2 of the other thin wire 53 of the upper ground layer 50 is smaller _than the width _W4 of the other thin wire 63 of the lower ground layer 60, satisfying the above equations (18) and (19). In addition, the area S ₁ of the opening 55 and the area S ₂ of the opening 65 may be equal (S ₁ =S ₂ ). Also, the pitches P ₁ to P ₄ of the fine wires 52 and 53 of the upper ground layer 50 and the fine wires 62 and 63 of the lower ground layer 60 may be different.

Alternatively, although not shown, the width W1 of the fine wire 52 of the upper ground layer 50 is different from the width W3 of the fine wire 62 of the lower _ground layer ₆₀ as long as the expression (16) is satisfied, and the width W3 of the fine wire 62 of the upper ground layer 50 is _The width W2 of the thin wire 53 and the width _W4 of the thin wire 63 of the _{lower ground} line 60 may be different, and the area S1 of the opening 55 and the area S2 of the opening 65 may be different.

Further, the relationship between the widths W ₁ to W ₄ of the fine lines 52, 53, ₆₂ , 63 is not particularly limited to the above as long as the expression (16) is satisfied. ₄ may be included within a range of ±20% of the average value W _ave of the widths W ₁ to W ₄ . That is, the widths W ₁ to W ₄ of the thin wires 52, 53, 62, 63 may satisfy the following expressions (20) to (24).
_Wave ×0.8≦W1≦ _Wave × _1.2 (20)
_{Wave×0.8≤W2≤Wave × 1.2} (21)
_{Wave×0.8≤W3≤Wave ×} 1.2 ₍ 22)
_{Wave×0.8≤W4≤Wave ×} 1.2 ₍ 23)
_Wave = ₍ W1+W2 ₊ W3+ _W4 )/ ₄ (24)

As described above, in the present embodiment, the relationship between the widths W ₁ to W ₄ of the thin lines 52, 53, 62, 63, the relationship between the areas S ₁ , S ₂ of the openings 55, 65, and the thin lines 52, 53, 62 , 63 are not particularly limited, and can be set arbitrarily as long as the expression _{( 16} ) is satisfied.

In addition, in the embodiment of FIG. 1, both the mesh-shaped openings 55 of the upper ground layer 50 and the mesh-shaped openings 65 of the lower ground layer 61 are square, but are not limited to squares, triangles, or squares. It may be hexagonal, elliptical, or the like. For example, as shown in FIG. 7, the shape of the opening 55 may be circular and the shape of the opening 65 may be circular. FIG. 7 is a plan view showing a second modification of the wiring board in this embodiment.

In the embodiment of FIG. 7, the upper ground layer 50 is composed of a ground plane 57 and openings 55 periodically arranged in the ground plane 57 . The ground plane 57 is made of the same material as the fine wires 52 and 53 . In FIG. 7, the aperture ratio _R1 of the upper ground layer 50 is the ratio of the area where the ground plane 57 is not formed to the area of the upper ground layer 50 .

Similarly, the lower ground layer 60 is composed of a ground plane 67 and openings 65 periodically arranged in the ground plane 67 . The ground plane 67 is made of the same material as the fine wires 62 and 63 . In FIG. 7, the opening ratio _R2 of the lower ground layer 60 is the ratio of the area of the portion where the ground surface 67 is not formed to the area of the lower ground layer 60. In FIG.

In the form of FIG. ₇ , the area S1 of the opening 55 and the area S2 of the opening 65 _{are equal} (S1 ₌ S2), and the following expression (25) is satisfied. That is, the pitch P _A1 between the openings 55 of the ground layer 50 is smaller than the pitch P _A2 between the openings 65 of the ground layer 60, thereby satisfying the above equation (21).
P _A1 <P _A2 (25)

Further, when the openings 55 and 65 are circular in shape as shown in FIG. 7, the structures of the upper ground layer 50 and the lower ground layer 60 are not particularly limited as long as they satisfy the formula (16). For example, the pitch P _A1 between the openings 55 in the upper ground layer 50 is _equal to the pitch P _A2 between the openings 65 in the lower _ground layer 60, and the area S1 of the openings 55 is made larger than the area S1 of the openings 65. (S ₁ >S ₂ ).

Alternatively, when the shape of the openings 55 and 65 is circular, as long as the formula ( ₁₆ ) is satisfied, the pitch P _A1 and the pitch P _A2 are made different, and the area S1 of the opening 55 and the area S1 of the opening 65 are _S1 may be different.

Although the wiring board 1 in this embodiment has a three-layer strip structure including the upper ground layer 50, the signal layer 20, and the lower ground layer 60, it may be composed of four or more layers. good. For example, although not shown, another conductor layer may be formed inside the lower base film 10 . However, in a cross-sectional view, only the insulating material forming the lower base film 10 is interposed in the region between the signal line 21 and the mesh shape 61 of the lower ground layer 60 . Even in such a case, by satisfying the equations (8) and (16), it is possible to enhance the shielding effect of the lower ground layer 60 while achieving impedance matching.

It should be noted that the embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is meant to include all design changes and equivalents that fall within the technical scope of the present invention.

REFERENCE SIGNS LIST 1 wiring board 10 lower base film 11 upper surface 12 lower surface 20 signal layer 21 signal line 22 ground wire 23 ground wire 30 contact layer 40 upper base film 41 upper surface 50 upper ground layer 51 ... Mesh shape 52, 53 ... Fine line CL _1a , CL _1b ... Center line 54 ... Intersection 55 ... Opening 56 ... Outer edge line 57 ... Ground surface 60 ... Lower ground layer 61 ... Mesh shape 62, 63 ... Fine line CL _2a , CL _2b ...Center line 64...Intersection 65...Opening 66...Outer edge line 67...Ground plane T...Through hole

Claims (6)

A wiring board having a strip structure,
a signal line;
a first ground layer facing the signal line via a first insulating layer;
a second ground layer positioned opposite to the first ground layer with respect to the signal line and facing the signal line via a second insulating layer;
the first ground layer has a first mesh shape with a plurality of periodically arranged first openings;
the second ground layer has a second mesh shape with a plurality of periodically arranged second openings,
A wiring board that satisfies the following formulas (1) and (2).
D ₁ < D ₂ (1)
R ₁ >R ₂ (2)
However, in the above equation ( ₁ ), D1 is the distance between the first ground layer and the signal line in cross section, and D2 is the distance between the _second ground layer and the signal line in cross section. is the distance between the signal lines,
In the above formula (2), _R1 is the aperture ratio of the first ground layer, and _R2 is the aperture ratio of the second ground layer. The wiring board according to claim 1,
The first ground layer is
a plurality of first ground lines;
a plurality of second ground lines arranged to cross the first ground line,
The second ground layer is
a plurality of third ground lines;
a plurality of fourth ground lines arranged to cross the third ground line;
The first opening is formed by crossing the first ground line and the second ground line,
the second opening is formed by crossing the third ground line and the fourth ground line;
the pitch between the first ground lines is substantially the same as the pitch between the second ground lines;
the pitch between the third ground lines is substantially the same as the pitch between the fourth ground lines;
A wiring board that satisfies the following formula (3).
P ₁ >P ₃ (3)
However, in the above equation ( ₃ ), P1 is the pitch between the _first ground lines, and P3 is the pitch between the third ground lines. The wiring board according to claim 2,
A wiring board that satisfies the following formula (4).
P ₁ ×0.85≧P ₃ (4) The wiring board according to any one of claims 1 to 3,
The first ground layer is
a plurality of first ground lines;
a plurality of second ground lines arranged to cross the first ground line,
The second ground layer is
a plurality of third ground lines;
a plurality of fourth ground lines arranged to cross the third ground line;
the line width of the first ground line is substantially the same as the line width of the second ground line;
the line width of the third ground line is substantially the same as the line width of the fourth ground line;
A wiring board that satisfies the following formula (5).
W1 < W3 _{( 5} )
However, in the above equation (5), W1 is the line width of the _first ground line, and W3 is the line width of the _third ground line. The wiring board according to any one of claims 1 to 4,
A wiring board that satisfies the following formula (6).
P _A1 <P _A2 (6)
However, in the above equation (6), P _A1 is the pitch between the first openings, and P _A2 is the pitch between the second openings. The wiring board according to any one of claims 1 to 5,
A wiring board that satisfies the following formula (7).
S ₁ >S ₂ (7)
However, in the above equation (7), S1 is the area of the _first opening and S2 is the area of the _second opening.

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