JP2020035839A - Multilayer printed wiring board - Google Patents

Abstract

To reduce the number of holes for via formation for interlayer connection of differential signal lines to improve transmission characteristics.SOLUTION: In a multilayer printed wiring board 1A, a plurality of wiring layers are formed with an insulating layer therebetween. Differential signal lines S1, S2 are formed on one wiring layer L1 and the other wiring layer L2; two or more interlayer connection conductors isolated with gaps therebetween are provided on an inner peripheral surface of one hole 11 penetrating a layer between one wiring layer and the other wiring layer; the signal lines S1 are interlayer-connected by an interlayer connection conductor 21, and the signal lines S2 are interlayer-connected by an interlayer connection conductor 23.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a multilayer printed wiring board in which a differential wiring is formed via an interlayer connection via.

Generally, when a differential wiring is formed via an interlayer connection via, two vias are required for differential signals. Further, at least one via is required for the ground. For example, as shown in FIG. 18, a differential signal from one wiring layer L1 to another wiring layer L4 via a power supply layer L2 on which a power supply solid pattern E is formed and a ground layer L3 on which a ground solid pattern G is formed. A case of forming a wiring will be described. First, two signal vias V1 and V2 are required for the differential signal lines S1 and S2. As described in Patent Document 1, ground vias V3 and V4 are often arranged adjacent to both sides of signal vias V1 and V2. In this case, four vias are required.
Note that, specifically, in one wiring layer L1, the differential signal lines S1 and S2 are connected to the signal vias V1 and V2. In the power supply layer L2, the signal vias V1 and V2 and the ground vias V3 and V4 pass through the power supply solid pattern E without clearance while maintaining a clearance. In the ground layer L3, the signal vias V1 and V2 pass through the ground solid pattern G without disconnection while maintaining a clearance, and the ground vias V3 and V4 are connected to the ground solid pattern G. In the other wiring layer L4, the signal vias V1, V2 are connected to the differential signal lines S1, S2.

  In addition, there may be a case where one ground via is used in the configuration shown in FIG. 18 and interlayer connection is performed by three vias including two signal vias and one ground via.

JP 2007-258358 A

Since the differential signal is transmitted by combining two signals, that is, a positive signal and a negative signal, it becomes a pair wiring pair. Therefore, two signal vias are required only for the differential signal as described above. Further, at least one ground via is required for securing a return path in the via portion and for impedance matching. Therefore, a large area was required for the via.
In addition, since the via pitch is wider than the wiring pitch in the wiring layer, the pitch must be increased when connecting vias, and the gap between the differential signal wiring and the ground conductor cannot be maintained appropriately. There was a possibility that the transmission characteristics would be reduced.

  A multilayer printed wiring board according to one embodiment of the present disclosure is a multilayer printed wiring board in which a plurality of wiring layers are formed with an insulating layer interposed therebetween, wherein a differential signal line is formed in one wiring layer and another wiring layer. Two or more interlayer connection conductors are provided on an inner peripheral surface of one hole penetrating a layer between the one wiring layer and the another wiring layer, the two or more interlayer connection conductors being separated by a gap in a circumferential direction; One of the above-mentioned interlayer connection conductors is connected to one signal line constituting the differential signal line by one interlayer connection conductor, and the other signal line is constituted by another interlayer connection conductor to constitute the differential signal line. Are connected between layers.

  According to the multilayer printed wiring board of the present disclosure, the number of interlayer connection vias for interlayer connection of differential signal lines can be reduced to one in which a plurality of interlayer connection conductors are provided in one hole. A ground conductor can also be wired in the interlayer connection via by the hole, and the number of via forming holes can be reduced (the area occupied by the via can be reduced). Further, the gap between the differential signal wirings or between the signal line and the ground conductor can be kept appropriately small even in the interlayer connection section, and the transmission characteristics can be improved.

It is a top view which shows an example of the formation process of an interlayer connection via | veer. FIG. 2 is a plan view illustrating a layer configuration of the multilayer printed wiring board according to Embodiment 1. (a) is a plan view showing a configuration of an interlayer connection via of Embodiment 2, (b) is a plan view showing a configuration of an interlayer connection via of Embodiment 3, and (c) is an interlayer connection of Embodiment 4. FIG. 3 is a plan view showing a configuration of a via. FIG. 9 is a perspective view illustrating a structure of a comparative example. It is a top view showing the via shape of the comparative example. It is a top view of the signal wiring layer L1 of a comparative example. It is a top view of the power supply layer L2 of a comparative example. It is a top view of the ground layer L3 of a comparative example. It is a top view of the signal wiring layer L4 of a comparative example. It is the perspective view which showed the structure of the Example. It is a top view showing the via | veer shape of an Example. It is a top view of the signal wiring layer L1 of an Example. It is a top view of the power supply layer L2 of an Example. It is the top view (a) of the ground layer L3 of an Example, and its partial enlarged view (b). It is a top view of the signal wiring layer L4 of an Example. It is a sectional view common to a comparative example and an example. 7 is a graph comparing the variation of the differential impedance between the comparative example and the example. It is a top view showing the layer composition of the multilayer printed wiring board of the conventional example.

  A multilayer printed wiring board according to an embodiment of the present disclosure will be described with reference to the drawings.

[Formation of interlayer connection via]
First, a process of forming an example of an interlayer connection via will be disclosed.
As shown in FIG. 1A, a hole 11 is formed in the multilayer printed wiring board 1, and a conductor 12 is formed around the hole 11. The conductor 12 includes an interlayer connection conductor formed on the entire inner peripheral surface of the hole 11 and connection lands extending from the interlayer connection conductor to the wiring layer.
As shown in FIG. 1 (b), the conductor 12 is divided in half to form two conductors 13 and 14, and each of the two conductors 13 and 14 is divided in half as shown in FIG. Are used as the interlayer connection conductors 21, 22, 23, 24 to form a composite type interlayer connection via V11. The division of the conductor can be performed by selective etching or the like using a resist mask pattern, but the production method is not limited. Further, the process of dividing the conductor formed on the inner peripheral surface of the hole 11 in the circumferential direction is not essential, and the conductors may be provided in regions separated from each other in the circumferential direction.
In the above, an example in which four interlayer connection conductors are provided for one hole has been described. However, a composite-type interlayer connection via having a desired number of conductors is formed and applied to the following embodiments.

[Embodiment 1]
The multilayer printed wiring board 1A according to the first embodiment will be described. As shown in FIG. 2, the multilayer printed wiring board 1A has a wiring layer L1 on which differential signal lines S1 and S2 are formed, a power layer L2 on which a power solid pattern E is formed, and a ground solid pattern via an insulating layer. A ground layer L3 on which G is formed and a wiring layer L4 on which differential signal lines S1 and S2 are formed are stacked in the above order.

  One hole 11 is formed in the multilayer printed wiring board 1A so as to penetrate a layer between the wiring layer L1 and the wiring layer L4. Four interlayer connection conductors 21, 22, 23, and 24 are provided on the inner peripheral surface of the hole 11 with a gap therebetween in the circumferential direction, and a composite type interlayer including the four interlayer connection conductors 21, 22, 23, and 24 is provided. A connection via V11 is formed. Each of the interlayer connection conductors 21, 22, 23, and 24 extends from the wiring layer L1 to the wiring layer L4 on the inner peripheral surface of the hole 11.

Of the four interlayer connection conductors 21, 22, 23, 24, two interlayer connection conductors 21, 23 are used for interlayer connection of the differential signal line, and the other two interlayer connection conductors 22, 24 are connected to ground conductor interlayer connection. It is used.
Specifically, in one wiring layer L1, the differential signal lines S1 and S2 are connected to the interlayer connection conductors 21 and 23. In the power supply layer L <b> 2, the interlayer connection conductors 21 and 23 and the interlayer connection conductors 22 and 24 pass through the power supply solid pattern E in a disconnected manner while maintaining a clearance. In the ground layer L3, the interlayer connection conductor 21.23 passes through the ground solid pattern G in a non-connected state while maintaining a clearance, and the interlayer connection conductors 22 and 24 are connected to the ground solid pattern G. In the other wiring layer L4, the interlayer connection conductor 21.23 and the differential signal lines S1 and S2 are connected.

As described above, the number of the interlayer connection conductors 21, 22, 23, and 24 of the interlayer connection via V11 is four and is equally divided into four. The quadrant structure has a gap on the radius line of the hole 11 at every 90 degrees. One of the four interlayer connection conductors is connected between one signal line S1 forming a differential signal line by one interlayer connection conductor 21 and the other signal forming a differential signal line by another one interlayer connection conductor 23. The line S2 is connected between layers, and the ground conductor is connected between the other two interlayer connection conductors 22 and 24.
The four interlayer connection conductors 21, 22, 23, and 24 are connected to one signal line (21), the ground conductor (22), the other signal line (23), and the ground conductor (24) in the circumferential direction of the hole 11. Are assigned in order.
In the interlayer connection via V11, each signal line S1, S2 (21, 23) is adjacent to the two ground connection conductors 22, 24 in the circumferential direction of the hole 11, and the signal lines S1, S2 (21, 23). Each has a structure facing each other via the hole 11.

  According to the multilayer printed wiring board 1A having the above structure, a total of four wirings of two signal lines and two ground wirings constituting a differential signal line are formed by the composite interlayer connection via V11 formed in one hole 11. Can be connected between layers. Therefore, reduction of the number of holes for via formation (reduction of the area occupied by vias) can be achieved. Further, the gap between the differential signal wirings or between the signal line and the ground conductor can be kept appropriately small even in the interlayer connection section, and the transmission characteristics can be improved.

[Embodiment 2]
A multilayer printed wiring board 1B according to Embodiment 2 will be described. In the first embodiment, the number of interlayer connection conductors provided in one hole is four. On the other hand, in the multilayer printed wiring board 1B according to the second embodiment, the number of interlayer connection conductors provided in one hole is reduced. In this example, an interlayer connection via V12 having a value of 2 is applied.
As shown in FIG. 3A, the number of the interlayer connection conductors 31 and 32 of the interlayer connection via V12 is two and is equally divided into two. In the bisecting structure, a gap is provided on the radius line of the hole 11 every 180 degrees. One of the two interlayer connection conductors 31, 32 is connected to one signal line S1 constituting a differential signal line by one interlayer connection conductor 31, and the other is a differential signal line by one interlayer connection conductor 32. The other signal line S2 is connected between layers.
A ground conductor is connected between layers by an interlayer connection conductor 33 of another interlayer connection via V13 provided in another hole. This is a structure in which the interlayer connection conductor 33 for ground is arranged at the same distance from the two interlayer connection conductors 31 and 32 for differential signals.
Further, in the interlayer connection via V12, the signal lines S1, S2 (31, 32) are adjacent to each other on both sides in the circumferential direction of the hole 11 and face each other via the hole 11.
It should be noted that there is provided a structure including a total of three interlayer connection vias in which two 1-hole, 1-conductor type interlayer connection vias for ground are provided, one of which is arranged close to the interlayer connection conductor 31 and the other is arranged close to the interlayer connection conductor 32. May be implemented.

Also with the multilayer printed wiring board 1B having the above structure, two signal lines constituting the differential signal line can be connected between layers by the composite type interlayer connection via V12 formed in one hole 11. Therefore, reduction of the number of holes for via formation (reduction of the area occupied by vias) can be achieved. Further, the gap between the differential signal wirings can be kept appropriately small even in the interlayer connection section, and the transmission characteristics can be improved.
Compared with the first embodiment, although the number of holes for forming vias used for differential signals and ground is increased, no interlayer connection conductor for ground is interposed between the two interlayer connection conductors 31 and 32. Since the signal lines S1 and S2 are adjacent to each other in the circumferential direction of the hole 11, it is easy to connect to the via while maintaining the wiring pitch in the wiring layer.

[Embodiment 3]
A multilayer printed wiring board 1C according to Embodiment 3 will be described. In the first embodiment, the number of interlayer connection conductors provided in one hole is set to four. On the other hand, in the multilayer printed wiring board 1C according to the third embodiment, the number of interlayer connection conductors provided in one hole is reduced. In this example, an interlayer connection via V14 having a value of 3 is applied.
As shown in FIG. 3 (b), the number of the interlayer connection conductors 41, 42, 43 of the interlayer connection via V14 is 3, which is equally divided into three. In the structure of three equal parts, a gap is provided on the radius line of the hole 11 every 120 degrees.
One of the three interlayer connection conductors 41, 42, and 43 connects one signal line S <b> 1 constituting a differential signal line between the interlayer connection conductors 41 and another one interlayer connection conductor 43 connects the differential signal line. In this structure, the other signal line S2 is connected between layers, and the ground conductor is connected between layers by the remaining one interlayer connection conductor.
In the interlayer connection via V14, one side of the signal lines S1 and S2 (41, 43) is adjacent to each other in the circumferential direction of the hole 11, and the other side is adjacent to the interlayer connection conductor 42 for ground. .

Also with the multilayer printed wiring board 1C having the above structure, a total of three wirings of two signal lines constituting a differential signal line and one ground wiring are formed by the composite type interlayer connection via V14 formed in one hole 11. It can be connected between layers. Therefore, reduction of the number of holes for via formation (reduction of the area occupied by vias) can be achieved. Further, the gap between the differential signal wirings or between the signal line and the ground conductor can be kept appropriately small even in the interlayer connection section, and the transmission characteristics can be improved.
Compared to the first embodiment, although the number of interlayer connection conductors used for ground connection is changed from 2 to 1, one side of the interlayer connection conductor 41 and one side of the interlayer connection conductor 43 are connected to the ground interlayer connection conductor. Since they are adjacent to each other without the intermediary of 42, it is easy to connect to vias while maintaining the wiring pitch in the wiring layer as in the second embodiment.
Compared to the second embodiment, it is possible to reduce the number of holes for forming vias (reduce the area occupied by vias).

[Embodiment 4]
A multilayer printed wiring board 1D according to Embodiment 4 will be described. In the third embodiment, the interlayer connection conductor provided in one hole is divided into three equal parts by radius lines every 120 degrees. On the other hand, the multilayer printed wiring board 1D according to the fourth embodiment has a T-shaped An interlayer connection via V15, which is divided by a line and has a larger interlayer connection conductor 52 for ground than the others, is applied.
As shown in FIG. 3C, the number of interlayer connection conductors 51, 52, 53 of the interlayer connection via V15 is three. When viewed in the axial direction of the hole 11, a gap separating the interlayer connection conductors forming the three interlayer connection conductors 51, 52, and 53 is formed on the straight line 54 passing through the hole 11 and in the hole 11 on the straight line 54. It is provided on a half line 56 extending from the point 55 to one side perpendicular to the straight line 54. Since the point 55 and the center of the hole 11 coincide with each other, the interlayer connection conductor 52 for ground is made larger than the other interlayer connection conductors 51 and 53, and the interlayer connection conductors 51 and 53 for signal have the same size. Have been.
One of the three interlayer connection conductors 51, 52, 53 is connected between one signal line S <b> 1 constituting a differential signal line by one interlayer connection conductor 51, and is connected to another differential signal line by another one interlayer connection conductor 53. In this structure, the other signal line S2 is connected between layers, and a ground conductor is connected between layers by the remaining one interlayer connection conductor 52.
In the interlayer connection via V15, one side of the signal lines S1 and S2 (51, 53) is adjacent to each other in the circumferential direction of the hole 11, and the other side is adjacent to the interlayer connection conductor 42 for ground. .

Also with the multilayer printed wiring board 1D having the above structure, a total of three wirings of two signal lines constituting a differential signal line and one ground wiring are formed by the composite type interlayer connection via V15 formed in one hole 11. It can be connected between layers. Therefore, reduction of the number of holes for via formation (reduction of the area occupied by vias) can be achieved. Further, the gap between the differential signal wirings or between the signal line and the ground conductor can be kept appropriately small even in the interlayer connection section, and the transmission characteristics can be improved.
Compared to the first embodiment, although the number of interlayer connection conductors used for ground connection is changed from 2 to 1, one side of the interlayer connection conductor 41 and one side of the interlayer connection conductor 43 are connected to the ground interlayer connection conductor. Since they are adjacent to each other without the intermediary of 42, it is easy to connect to vias while maintaining the wiring pitch in the wiring layer as in the second embodiment.
Compared to the second embodiment, it is possible to reduce the number of holes for forming vias (reduce the area occupied by vias).
Compared to the third embodiment, the gap separating the conductor can be formed only by the vertical and horizontal lines, so that it is easy to manufacture with high accuracy. The interlayer connection conductor 52 for ground can be enlarged, and a relatively large cross-sectional area of the ground conductor can be secured in the interlayer connection section.

〔simulation〕
Here, a comparison of the differential impedance between the comparative example and the embodiment will be disclosed.
The comparative example is based on the conventional example shown in FIG. 18, and the example is based on the first embodiment. Corresponding elements have the same reference characters.

FIG. 4 is a perspective view showing the structure of the comparative example. FIG. 5 shows the via shape of the comparative example including the outer diameter of the connection land, the hole diameter, and the thickness of the conductor plating on the inner peripheral surface of the hole (all units are mm). FIGS. 6 to 9 show plan views of the wiring layers L1 to L4 in the comparative example.
FIG. 10 is a perspective view showing the structure of the embodiment. FIG. 11 shows the via shape of the embodiment, including the outer diameter of the connection land, the hole diameter, the thickness of the conductor plating on the inner peripheral surface of the hole, the gap size, and the like (all units are mm). FIGS. 12 to 15 show plan views of the wiring layers L1 to L4 according to the embodiment.

FIG. 16 shows a cross-sectional structure common to the comparative example and the example. The physical properties of each constituent material are as follows.
Cu: conductivity = 5.8e + 07 [S / m] (common to L1, L2, L3, and L4 layers)
FR-4: relative permittivity = 4.6, dielectric loss tangent = 0.016
SR: relative dielectric constant = 4.3, dielectric loss tangent = 0.021
Note that FR-4 is a glass cloth base epoxy resin, and SR is a solder resist.
Further, as common conditions of the comparative example and the example, the differential impedance of the differential signal lines S1 and S2 on the wiring layers L1 and L4 is 100 [Ω], the wiring width is 0.175 [mm], and the wiring gap is 0. 2 [mm].

FIG. 17 shows a comparison result of the differential impedance.
The broken line graph in FIG. 17 relates to the comparative example, and the solid line graph relates to the example.
In the comparative example, the vibration oscillates so as to return six peaks. On the other hand, in the example, the peak falls about three times. In the embodiment, the amplitude is suppressed to be smaller than that of the comparative example.
That is, the embodiment has an impedance variation width (up and down variation width) that is superior to the comparative example.
Furthermore, in the example, the number of times of impedance fluctuation (number of times of undulation) is smaller than that of the comparative example, and signal reflection is less than that of the comparative example (because signal reflection occurs at the timing of undulation).
From the above, it was confirmed that the example had better transmission characteristics than the comparative example.

[Summary, other]
As described above, according to the multilayer printed wiring board of the present embodiment, the interlayer connection via for interlayer connection between the differential signal lines S1 and S2 is changed to one in which a plurality of interlayer connection conductors are provided in one hole 11. It is possible to reduce the size, and furthermore, a ground conductor can also be wired to the interlayer connection via formed by the common hole 11, so that the number of holes for forming vias (reduction of the area occupied by the vias) can be reduced. Further, the gap between the differential signal wirings or between the signal line and the ground conductor can be kept appropriately small even in the interlayer connection section, and the transmission characteristics can be improved.
In the above embodiment, only the four layers L1 to L4 are shown, but an insulating layer, a wiring layer, or the like adjacent to, above, or below the four layers L1 to L4, or both may be provided. . In that case, the hole 11 may be closed by an adjacent layer. Further, it is possible to fill the hole 11 with an insulating material or the like.

REFERENCE SIGNS LIST 1 multilayer printed wiring board 1A multilayer printed wiring board 1B multilayer printed wiring board 1C multilayer printed wiring board 1D multilayer printed wiring board 11 holes 21, 22, 23, 24 interlayer connection conductors 31, 32 interlayer connection conductor 33 interlayer connection conductors 41, 42 , 43 Interlayer connection conductors 51, 52, 53 Interlayer connection conductor E Power solid pattern G Ground solid pattern L1 Signal wiring layer L2 Power layer L3 Ground layer L4 Signal wiring layer S1, S2 Differential signal line

Claims (6)

A multilayer printed wiring board formed with a plurality of wiring layers via an insulating layer,
Differential signal lines are formed in one wiring layer and another wiring layer,
Two or more interlayer connection conductors are provided on an inner peripheral surface of one hole penetrating a layer between the one wiring layer and the another wiring layer, the two or more interlayer connection conductors being separated by a gap in a circumferential direction.
One of the two or more interlayer connection conductors is connected to one signal line constituting the differential signal line by one interlayer connection conductor, and the other signal line is constituted by the other one of the interlayer connection conductors to constitute the differential signal line. A multilayer printed wiring board in which signal lines are connected between layers. The number of the two or more interlayer connection conductors is three,
One of the three interlayer connection conductors connects one signal line constituting the differential signal line by one interlayer connection conductor, and the other signal line constitutes the differential signal line by another one interlayer connection conductor. 2. The multilayer printed wiring board according to claim 1, wherein the layers are connected between layers, and the ground conductor is connected between layers by the remaining one interlayer connection conductor. When viewed in the axial direction of the hole, a gap separating the interlayer connection conductors constituting the three interlayer connection conductors is formed on a straight line passing through the hole and on one side from a point in the hole on the straight line. 3. The multilayer printed wiring board according to claim 2, wherein the multilayer printed wiring board is provided on a semi-linear line extending perpendicularly to the printed circuit board. The number of the two or more interlayer connection conductors is four,
One of the four interlayer connection conductors is connected to one of the signal lines constituting the differential signal line by one interlayer connection conductor, and the other signal line is constituted by the other one of the interlayer connection conductors to constitute the differential signal line. The multilayer printed wiring board according to claim 1, wherein the layers are connected between layers, and the ground conductors are connected between layers by the remaining two interlayer connection conductors. The multilayer printed wiring board according to claim 4, wherein the four interlayer connection conductors are assigned in the circumferential direction of the hole in the order of one signal line, a ground conductor, the other signal line, and a ground conductor. The multilayer printed wiring board according to claim 4, wherein the four interlayer connection conductors are equally divided into four parts in the circumferential direction of the hole.

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