JP2019192844A - Printed-circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To match impedance while suppressing resonance between a signal wire and a ground without impairing transmission characteristics of the signal wire. A printed wiring board (1) has a signal wiring (10), a first ground conductor (20), and a second ground conductor (30) formed in different layers. The first ground conductor 20 has an opening 21 between the signal line and the second ground conductor when viewed in the stacking direction Z. The opening width W of the opening changes depending on the position of the signal wiring in the extending direction X. [Selection diagram] Figure 1

Description

  The present invention relates to a printed wiring board.

  Generally, when the impedance value of the signal wiring is lower than the target, the following measures may be taken.

One is a technique of matching the impedance by narrowing the width of the signal wiring.
As another example, when the interlayer (insulating material 115) between the signal wiring 101 and the ground plane 102 is thin as shown in FIG. 10A, the ground pattern 102B immediately below is formed as shown in FIG. In this method, impedance is matched with the ground plane 103 in the lower layer after providing the gap 102A.
As shown in FIG. 10A, when the interlayer thickness between the signal wiring 101 and the ground plane 102 is reduced, the characteristic impedance is lowered. Even if the wiring width of the signal wiring 101 is reduced, a target characteristic impedance value is obtained. It may not be possible.
Therefore, as shown in FIG. 10B, in order to obtain a target characteristic impedance value, a portion just below the signal wiring 101 is cut out, and another ground plane 103 is provided below the cut out ground plane 102B. A target characteristic impedance value may be obtained.
The problem with this method is that, firstly, a new ground plane is required, and the printed wiring board becomes thicker. Second, the characteristic impedance value is governed by the interlayer thickness between the signal wiring 101 and the ground plane 103. In some cases, it may be necessary to cut out more layers in addition to cutting out the layer 102B immediately below the signal wiring 101.

Furthermore, as another one, the ground layer immediately below the signal wiring 201 is changed from a ground plane 202 having a solid pattern as shown in FIG. 11A to a ground mesh 203 having a mesh pattern as shown in FIG. It is a technique to make.
In this case, by changing the size of the mesh opening of the ground mesh 203, the electromagnetic coupling between the signal wiring 201 and the ground mesh 203 is changed, and the characteristic impedance can be matched.
In the case of the ground plane 202 having a full-surface pattern, the characteristic impedance value had to be adjusted only by the width of the signal wiring 201, but by using the ground mesh 203, the characteristics depend on the width and mesh size of the signal wiring 201. Impedance can be adjusted, and the range of selection is expanded.
However, in the case of this method, the characteristic impedance value changes depending on the intersection position 204 between the signal wiring 201 and the ground mesh 203. This means that if there are multiple signal wires for which the characteristic impedance is to be adjusted, the position where the signal wires intersect the ground mesh
It must be in the same position for all signal wiring. That is, there is a problem that the degree of freedom of wiring is lowered.

  In addition, as shown in FIG. 12, there is also a method of arranging ground wirings 302 and 302 in parallel on the same layer surface as the signal wiring 301. The conventional example A shown in FIG. 12A and the conventional example B shown in FIG. 12B are different in the intersection position of the signal wiring 301 and the ground mesh 203. The graph of FIG. 13 shows the TDR waveform by these simulations. As shown in FIG. 13, a difference of about 7Ω occurs between the conventional example A and the conventional example B. This difference occurs due to the difference in the intersection position between the signal wiring and the ground mesh.

In order to reduce the difference in characteristic impedance depending on the mesh position of the ground pattern, there is a method of creating a ground mesh 303 having a pattern in the X direction along the signal wiring 301 as shown in FIG.
Considering the return current of the signal flowing to the ground in this method, the pattern 303X in the X direction along the signal wiring 301 is also required in the ground mesh 303. In the configuration shown in FIG. 14, the characteristic impedance varies depending on the distance (X direction) between the signal wiring 301 and the pattern 303Y in the Y direction.

As shown in FIG. 15, there is also a method of creating a ground mesh 403 that combines a pattern in the X direction along the signal wiring 401 (402) and a pattern in the Y direction having a length connecting adjacent X direction patterns. By making the pitch in the X direction of the pattern in the Y direction constant, even if there are a plurality of signal wirings, the mesh structure has the same characteristic impedance.
However, the area overlapping the mesh cannot be made the same in all signal wiring arrangements. In the case of FIG. 15, the signal wiring 401 and the signal wiring 402 have different areas overlapping with the ground mesh 403.

JP 2014-116574 A JP-A-7-235741

The conventional technology has the following problems.
First, if a gap is provided in the ground plane immediately below the signal wiring, a resonance phenomenon is likely to occur. That is, when a gap is formed in the conductor layer immediately below and impedance is matched with the ground plane in the lower layer, the signal wiring is connected to the ground plane in the lower layer and the ground plane in the lower layer. There is a problem of being affected by both, resulting in resonance.
On the other hand, when the width of the signal wiring is narrowed, the resistance of the signal wiring is increased and the transmission characteristics are deteriorated. The width of the signal wiring may become less than the manufacturing limit. To adjust the impedance, the following must be considered. That is, when the distance between the signal wiring and the ground plane becomes short, the electromagnetic field coupling becomes strong, so that the impedance decreases. When the distance increases, the electromagnetic field coupling becomes weak and the impedance increases. Further, when the width of the signal wiring is increased, the impedance is decreased, and when the width is decreased, the impedance is increased. If it is thicker, the area of the opposing conductors of the signal wiring and the ground plane increases, so that electromagnetic field coupling becomes stronger and impedance decreases. If the signal wiring is made thinner, the area of the opposing conductor is reduced, so that electromagnetic field coupling is weakened and impedance is increased.
In the case of a thin printed wiring board, the interlayer thickness is 50 μm or less, and the adjustment of the wiring width only makes the signal wiring width less than the manufacturing limit, and may not be adjusted.

  The present invention has been made in view of the above problems in the prior art, and in a printed wiring board, impedance matching is achieved without impairing transmission characteristics of signal wiring and suppressing resonance between signal wiring and ground. The task is to do.

The invention according to claim 1 for solving the above problems is a printed wiring board in which the signal wiring, the first ground conductor, and the second ground conductor are formed in different layers,
The first ground conductor has an opening between the signal wiring and the second ground conductor when viewed in the stacking direction,
The opening width of the opening is a printed wiring board that changes according to the position in the extending direction of the signal wiring.

  The invention according to claim 2 is the printed wiring board according to claim 1, wherein the change in the opening width is periodic.

  According to a third aspect of the present invention, the pitch of the periodic change of the opening width is not more than one fifth of the resonance wavelength of a signal generated when the opening width is made constant. It is a wiring board.

  According to a fourth aspect of the present invention, the pitch of the periodic change of the opening width is equivalent to the first and second average values from the lowest resonance frequency of the signal generated when the opening width is constant. The printed wiring board according to claim 2, wherein the printed wiring board is one fifth or less.

  The invention according to claim 5 is the printed wiring board according to any one of claims 1 to 4, wherein a minimum value of the opening width is equal to or less than a width of the signal wiring.

  According to a sixth aspect of the present invention, the distance (B) between the last retracted position of the outline defining the opening with respect to the signal wiring and the edge of the signal wiring adjacent to the outermost line is defined as follows. The printed wiring board according to any one of claims 1 to 5, wherein the printed wiring board is equal to or shorter than an interlayer distance (A) between the two ground conductors.

According to the present invention, by providing the opening in the first ground conductor, the density of the conductor is reduced and electromagnetic field coupling is weaker than when the entire area directly below the signal wiring is solid. As a result, the impedance increases, the width of the signal wiring is increased, the wiring resistance can be reduced, and the transmission characteristics are improved.
In addition, by spatially changing the opening width of the opening to create a portion where the first ground conductor approaches the signal wiring, the coupling between the portion and the signal wiring is strengthened, and resonance can be suppressed.
As described above, the impedance can be matched without impairing the transmission characteristics of the signal wiring and suppressing the resonance between the signal wiring and the ground.

It is sectional drawing (a) which shows the printed wiring board of one Embodiment of this invention, and the top view (b) of a 1st ground conductor. FIG. 4 is a plan view (a) of a signal wiring layer, a plan view (b) of a first ground conductor, and a plan view (c) of a second ground conductor according to a printed wiring board of an embodiment of the present invention. It is sectional drawing (a) which shows the printed wiring board of the comparative example 1, and the top view (b) of wiring. It is sectional drawing (a) which shows the printed wiring board of the comparative example 2, and the top view (b) of wiring. It is sectional drawing (a) which shows the printed wiring board of the example of this invention, and the top view (b) of wiring. It is a graph which shows the TDR waveform of the comparative examples 1 and 2 and the example of this invention by simulation. It is a graph which shows the permeation | transmission characteristic (S21) of the comparative examples 1 and 2 and the example of this invention by simulation. 4 is a graph showing a TDR waveform corresponding to a change pitch of an opening width of a first ground conductor 20. It is a graph which shows the permeation | transmission characteristic (S21) according to the change pitch of the opening width of the 1st ground conductor. It is sectional drawing of the printed wiring board of a prior art example. It is a top view of the wiring which concerns on the printed wiring board of a prior art example. FIG. 6 is a plan view (a) of wiring of a printed wiring board according to Conventional Example A and a plan view (b) of wiring of a printed wiring board according to Conventional Example B. It is a graph which shows the TDR waveform of the prior art example A and the prior art example B by simulation. It is a top view of the wiring which concerns on the printed wiring board of a prior art example. It is the perspective view (a) and top view (b) of the wiring which concern on the printed wiring board of a prior art example.

  An embodiment of the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention.

First, an embodiment of the present invention will be described with reference to FIGS. The printed wiring board 1 of this embodiment includes a signal wiring 10, a first ground conductor 20, and a second ground conductor 30. The signal wiring 10, the first ground conductor 20, and the second ground conductor 30 are multilayer wiring boards formed in different layers. The XYZ coordinates are shown in the figure, where X is the extending direction of the signal wiring 10, Y is the width direction of the signal wiring 10, and Z is the stacking direction.
The presence layer of the signal wiring 10 is L1 layer, the existence layer of the first ground conductor 20 is L2, and the existence layer of the second ground conductor 30 is L3 layer. The first insulating material layer 15 is between the L1 layer and the L2 layer. The second insulating material layer 25 is between the L2 layer and the L3 layer. The signal wiring 10 is covered with a solder resist 5. The solder resist 5 is an SR layer.

The first ground conductor 20 has an opening 21. The opening 21 is disposed between the signal wiring 10 and the second ground conductor 30 when viewed in the stacking direction Z. The opening 21 is filled with an insulating material. The opening 21 is arranged in the stacking direction Z with respect to the signal wiring 10. In the present embodiment, the opening 21 is always present in the stacking direction Z of the signal wiring 10 in the L2 layer. The opening 21 is a continuous opening that extends in the same way as the signal wiring 10 along the extending direction X of the signal wiring 10, and an intersection of the signal wiring 10 and the first ground conductor 20 when viewed in the stacking direction Z. There is no.
The second ground conductor 30 is configured as a solid pattern as a whole. The first ground conductor 20 and the second ground conductor 30 are connected by a ground via 26 (FIGS. 2B and 2C).

As shown in the plan view of FIG. 1B, the first ground conductor 20 includes a convex conductor portion 22 on both sides in the Y direction of the opening 21 and a solid conductor portion 23 on the outer side of the convex conductor portion 22.
The opening 21 includes a thinnest straight line portion 21 a corresponding to the stacking direction Z of the signal wirings 10 and a widened portion 21 b on both sides in the Y direction. The outlines TL and TR defining the opening 21 are formed in such a manner that the opening width W of the opening 21 along the Y direction is changed according to the position in the X direction. The change in the opening width W is periodic, and the outer contour line TL on one side and the outer contour line TR on the other side are symmetric about the center line TC. A center line TC indicates a position obtained by projecting the center line of the signal wiring 10 in the Z direction. The minimum value of the opening width W is equal to or smaller than the width of the signal wiring 10. In the present embodiment, the minimum value of the opening width W is made equal to the width of the signal wiring 10.

The last retracted position P <b> 1 of the outlines TL and TR with respect to the signal wiring 10 is the edge position of the solid conductor portion 23. The distance B is the distance between the edge P2 of the signal wiring 10 adjacent to the last retracted position P1 and the last retracted position P1. The distance between the signal wiring 10 and the second ground conductor 30 is the distance A. The distance B is not more than the distance A. This is to prevent the electric field and magnetic field generated from the signal wiring 10 of the L1 layer from reaching the L3 layer as much as possible.
The distance B is determined below the distance A, and the distance C is automatically determined based on the thickness of the first insulating material layer 15 and the distance B. The distance C corresponds to the width in the Y direction of the widened portion 21b. The distance C corresponds to a half of the difference between the maximum value and the minimum value of the opening width W. Further, a position where the edge P2 of the signal wiring 10 is projected in the Z direction up to the L2 layer is defined as P3. The distance C corresponds to the distance between P1 and P3.

  Furthermore, in order to reduce the influence on the L3 layer, a convex conductor portion 22 extending inward from the solid conductor portion 23 was provided. The tip end portion (P3 position) of the convex conductor portion 22 was provided so that the Y coordinate was coincident with the outside (P2) of the signal wiring 10. Thereby, the opening of the first ground conductor 20 was secured in the region facing the signal wiring 10.

The role of the convex conductor portion 22 is as follows.
First, a convex conductor 22 that narrows the opening 21 of the first ground conductor 20 immediately below the signal wiring 10 is formed in the first ground conductor 20, so that the first ground conductor is formed on the outer edge P <b> 2 of the signal wiring 10 as much as possible. 20 (convex conductor portion 22) is brought closer so that the influence of the electric field and magnetic field of the signal wiring 10 does not affect the second ground conductor 30 of the L3 layer as much as possible.
Further, by providing the convex conductor portion 22 that forms the narrow width portion of the opening 21 and forming the outlines TL and TR that change the opening width W periodically, the pitch of the convex conductor portion 22, that is, the opening Occurs when the signal conductor and the solid conductor with a solid conductor are arranged in different layers according to the pitch of the periodic change of the width W, and further, a ground conductor with an opening corresponding to the Z direction of the signal wiring is placed between them. The resonance of the transmission characteristics (S21) is suppressed.
In addition, the dimension of an example was shown in FIG. The convex conductor portion 22 has a trapezoidal shape with a long side at the position P1 and a short side at the position P3.

(simulation)
Next, a simulation of a TDR waveform and transmission characteristics (S21) and an embodiment based on the simulation result will be disclosed.
The simulation target models are Comparative Examples 1 and 2 and the present invention example. FIG. 3A shows a cross-sectional structure, a layer thickness, and a characteristic value of Comparative Example 1, and FIG. 3B shows a plan view of the wiring. FIG. 4A shows the cross-sectional structure, layer thickness, and characteristic values of Comparative Example 2, and FIG. 4B shows a plan view of the wiring. FIG. 5A shows a cross-sectional structure, a layer thickness, and a characteristic value of the example of the present invention, and FIG. 5B shows a plan view of the wiring.
In Comparative Example 1, the ground conductor 120 of the L2 layer has a solid pattern on the entire surface and has no opening. In Comparative Example 2, a linear opening 221 along the signal wiring 210 is provided in the first ground conductor 220 in the L2 layer adjacent to the signal wiring 210, and the second ground conductor 230 having a solid pattern is formed in the L3 layer. Provided. The example of the present invention is in accordance with the above embodiment, and further has the structure and characteristic values shown in FIG.
As a common matter, a glass cloth base epoxy resin is applied to the insulating material and copper is applied to the conductive material, and the characteristics between A1 and A2 having a wiring distance of 15 mm are simulated.
The simulation result of the TDR waveform is shown in FIG. 6, and the simulation result of the transmission characteristic (S21) is shown in FIG.

The characteristic impedances of Comparative Examples 1 and 2 and the inventive example were adjusted to 50Ω from the TDR waveform as a target.
As shown in FIG. 6, the following characteristics appear due to the difference in the shape of the L2 layer even when the characteristic impedances are almost the same.
In Comparative Example 1, there is no resonance phenomenon as shown in FIG. 7, but since no opening is provided in the ground conductor 120 of the L2 layer, the width of the signal wiring 110 is narrow and loss is large (transmission is small).
On the other hand, in Comparative Example 2, the opening 221 is provided in the first ground conductor 220 immediately below the signal wiring 210 to increase the width of the signal wiring 210. However, due to the effect of providing the opening 221 in the L2 layer, FIG. As shown in FIG.
On the other hand, in the example of the present invention, the opening 21 is provided in the first ground conductor 20 immediately below the signal wiring 10, and the convex conductor 22 facing the opening 21 is provided as described above.
Since the comparative example 2 and the example of the present invention have the same signal wiring width, the transmission characteristics show the same inclination, but the resonance in the comparative example 2 is suppressed in the example of the present invention.
From the above, by providing the convex conductor portion 22 facing the opening portion 21 as in the present invention example, the signal wiring width is made wider than in the comparative example 1, and the quality in which resonance is suppressed more than in the comparative example 2 Good transmission characteristics can be obtained. According to the example of the present invention, it is superior to transmission of a high frequency signal.

In the transmission characteristic (S21) of Comparative Example 2, since there is resonance in the vicinity of 25 GHz and 27 GHz, the reference frequency for suppressing the resonance was set to 26 GHz. That is, 26 GHz was adopted as the first and second average values from the lowest resonance frequency of the signal generated when the aperture width is constant.
In general, since a resonance phenomenon does not occur in a wiring having a wavelength of 1/10 or less, 1/10 wavelength (540 μm) of 26 GHz is set as a reference dimension for determining the pitch of the convex conductor portion 22.
Considering the TDR waveform and transmission characteristics (S21), the convex conductor part 22 is arranged with a pitch dimension that is gradually increased from 1/10 wavelength, and the impedance is close to 50Ω, and the resonance is up to 50 GHz. The pitch dimension of the convex conductor portion 22 that provides a small transmission characteristic (S21) was obtained by simulation (HFSS). Wavelength calculation is shown in Table I, TDR waveforms of 1/3 wavelength to 1/7 wavelength are shown in FIG. 8, and transmission characteristics (S21) are shown in FIG.
As a result, the result was satisfied at a 1/5 wavelength (1080 μm) of 26 GHz, and the pitch dimension of the convex conductor portion 22 was 1080 μm.

As described above, by providing the opening 21 in the first ground conductor 20, the conductor density is reduced and electromagnetic field coupling is weaker than in the case where the entire area directly below the signal wiring 10 is solid (Comparative Example 1).
As a result, the impedance increases, the width of the signal wiring 10 can be increased, the wiring resistance can be reduced, and the transmission characteristics are improved.
Further, by changing the opening width W of the opening 21 in accordance with the position in the extending direction of the signal wiring 10, a portion (convex conductor portion 22) where the first ground conductor 20 approaches the signal wiring 10 is formed. And the signal wiring 10 become stronger and resonance can be suppressed.
As described above, the impedance can be matched without impairing the transmission characteristics of the signal wiring and suppressing the resonance between the signal wiring and the ground.

DESCRIPTION OF SYMBOLS 1 Printed wiring board 5 Solder resist 10 Signal wiring 15 1st insulating material layer 20 1st ground conductor 21 Opening part 21a Thinnest straight line part 21b Widening part 22 Convex conductor part 23 Solid conductor part 25 2nd insulating material layer 26 Ground via 30 Second ground conductor TC Center line TL, TR Opening outline W Opening width X Extending direction Z Laminating direction

Claims (6)

A printed wiring board in which signal wiring, a first ground conductor, and a second ground conductor are formed in different layers,
The first ground conductor has an opening between the signal wiring and the second ground conductor when viewed in the stacking direction,
The printed wiring board in which the opening width of the opening changes in accordance with the position in the extending direction of the signal wiring. The printed wiring board according to claim 1, wherein the change in the opening width is periodic. The printed wiring board according to claim 2, wherein a pitch of the periodic change in the opening width is equal to or less than one fifth of a resonance wavelength of a signal generated when the opening width is made constant. The pitch of the periodic change of the aperture width is equal to or less than one fifth of the equivalent wavelength of the first and second average values from the lowest resonance frequency of the signal generated when the aperture width is constant. The printed wiring board according to claim 2. The printed wiring board according to claim 1, wherein a minimum value of the opening width is equal to or less than a width of the signal wiring. The distance (B) between the last retracted position of the outline defining the opening with respect to the signal wiring and the edge of the signal wiring adjacent thereto is the interlayer distance between the signal wiring and the second ground conductor ( A) The printed wiring board according to any one of claims 1 to 5, which is:

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