Multilayer wiring board

Abstract

A multilayer wiring board according to the present invention comprises a first transmission path that transmits a differential signal, a second transmission path that has a shorter wiring length than the first transmission path and transmits a differential signal, a first insulation layer, and a second insulation layer. Differential wiring is formed from the first transmission path and the second transmission path as provided between the first insulation layer and the second insulation layer in a direction that intersects the layering direction. A high-dielectric-constant material that has a higher relative dielectric constant than the first insulation layer and the second insulation layer is provided to the second transmission path such that lines of electric force that go from the second transmission path toward first ground wiring and second ground wiring pass through the high-dielectric-constant material. The high-dielectric-constant material is provided to surfaces of the second transmission path that are opposite the first ground wiring and the second ground wiring in the layering direction.

Description

multilayer wiring board

[0001] The present invention relates to a multilayer wiring board.

[0002] Conventionally, various products (hereinafter referred to as "AD / ADAS products") such as in-vehicle ECUs (Electronic Control Units) for Advanced Driver Assistance Systems (ADAS) or Autonomous Driving (AD) have been provided. In AD / ADAS products, signal transmission paths used for high-speed communication are wired on a circuit board. Furthermore, as AD / ADAS products have become more sophisticated in recent years, the wiring density of circuit boards has increased, and the number of layers in the circuit boards has tended to increase. Conventionally, to adjust signal delays in high-speed communication wiring (referred to as "skew adjustment"), a method of wiring the transmission paths in a meandering shape (see the lower left diagram in Figure 10, described later) has been adopted.

[0003] Patent Document 1 describes a printed wiring board in which "among a plurality of signal lines, at least two adjacent signal lines are each partially covered in the wiring direction with a covering member made of a dielectric having a higher dielectric constant than the dielectric of the dielectric layer, and of the two adjacent signal lines, the length of one signal line is longer than the length of the other signal line, the length of the covering member formed on one signal line in the direction along one of the wirings is equal to or less than the length of the covering member formed on the other signal line in the direction along the other wiring, and the covering member formed on one signal line and the covering member formed on the other signal line have non-adjacent sections that are not adjacent to each other."

[0004] JP 2015-130391 A

[0005] In the past, matching the wiring lengths of two transmission lines transmitting differential signals was considered an effective way to reduce the effects of skew that occurs between the two transmission lines. Therefore, meander-shaped wiring was used for the shorter transmission line, and the wiring length was made the same as that of the longer transmission line. However, meander-shaped wiring reduces the space available for wiring the transmission lines on a board. Therefore, wiring transmission lines in a meander shape increases the number of board layers required to provide a specified number of transmission lines. Furthermore, since transmission lines are routed on inner layers of multiple stacked boards, the manufacturing costs of the board increase. Therefore, there was a need for a space-saving method for wiring transmission lines without increasing the number of board layers formed on the board.

[0006] The technology disclosed in Patent Document 1 aims to improve signal quality by adjusting the propagation time of a signal propagating through a signal line, reducing the coupling capacitance between two adjacent signal lines, and reducing crosstalk jitter. However, in the technology disclosed in Patent Document 1, only the upper side of the wiring pattern is covered with a covering material, and the lower side of the wiring pattern is not covered. With this shape, as shown in Figure 2 (described later), the amount of change in relative dielectric constant is small, so a meander shape is required to compensate for the difference in wiring length that occurs depending on the wiring method. For this reason, the above-mentioned space-saving wiring could not be achieved.

[0007] The present invention has been made in view of the above circumstances, and has as its object to reduce the space required for wiring of transmission paths that transmit differential signals and to enable skew adjustment.

[0008] A multilayer wiring board according to the present invention includes a plurality of layers stacked one on top of the other, and differential wiring included in some of the layers transmits differential signals. The multilayer wiring board includes a first transmission line that transmits differential signals, a second transmission line that is shorter in length than the first transmission line and transmits differential signals, a first insulating layer stacked between the first and second transmission lines and a first ground wiring, and a second insulating layer stacked between the first and second transmission lines and the second ground wiring. The differential wiring is composed of the first and second transmission lines that are arranged between the first and second insulating layers in a direction that intersects with the stacking direction in which the first and second insulating layers are stacked in that order. A high-permittivity material having a higher dielectric constant than the first and second insulating layers is arranged for the second transmission line, and through which electric field lines pass from the second transmission line toward the first and second ground wiring. The high-permittivity material is arranged on a surface facing the first and second ground wiring in the stacking direction relative to the second transmission line.

[0009] The present invention forms a high-dielectric-constant material having a higher dielectric constant than the first and second insulating layers on the second transmission lines of differential wiring having different wiring lengths. This high-dielectric-constant material is disposed on a surface facing the first and second ground wiring in the stacking direction of the second transmission lines. This enables skew adjustment without using a meandering shape for the second transmission lines, and also saves space for the wiring of the second transmission lines. Issues, configurations, and effects other than those described above will become clear from the description of the following embodiments.

[0010] FIG. 1 is a simplified cross-sectional view of a simplified multilayer wiring board according to one embodiment of the present invention. FIG. 2 is a diagram showing an example of the configuration of a first transmission line and a second transmission line provided in a conventional multilayer wiring board. FIG. 3 is a diagram showing an example of the configuration of a first transmission line and a second transmission line provided in a multilayer wiring board according to one embodiment of the present invention. FIG. 4 is a diagram showing an example of the configuration of a multilayer wiring board according to one embodiment of the present invention. FIG. 5 is a diagram showing a method for manufacturing a multilayer wiring board according to one embodiment of the present invention. FIG. 6 is a diagram showing a modified example of a high dielectric constant material according to one embodiment of the present invention. FIG. 7 is a diagram showing an example in which the thickness of a high dielectric constant material in the stacking direction is doubled according to one embodiment of the present invention. FIG. 8 is a top view of a multilayer wiring board in which first and second transmission lines are wired on a surface layer and an inner layer according to one embodiment of the present invention. FIG. 9 is a side view of a multilayer wiring board B in which the first and second transmission lines are wired in a BGA arrangement according to one embodiment of the present invention. FIG. 10 is a diagram showing differences in the configuration of the first and second transmission lines according to one embodiment of the present invention. FIG. 11 is a partial enlarged view of a multilayer wiring board having a second configuration according to one embodiment of the present invention. FIG. 12 is a diagram showing an example of measurement results of skew adjustment according to one embodiment of the present invention. FIG. 13 is a top view of a multilayer wiring board according to one embodiment of the present invention. FIG. 14 is a cross-sectional view showing an example of wiring when the IC is a footprint according to one embodiment of the present invention. FIG. 15 is a cross-sectional view showing an example of wiring when the IC is a BGA according to one embodiment of the present invention. 1 is a diagram showing an example of an inner layer wiring for explaining a characteristic impedance value of a transmission line according to an embodiment of the present invention;

[0011] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functions or configurations are designated by the same reference numerals, and redundant description will be omitted. The present invention is applicable, for example, to a multilayer wiring board mounted on a vehicle control computing device with which an on-board ECU, which is an AD / ADAS product, can communicate.

[0012] [One Embodiment] Figure 1 is a cross-sectional view of a multilayer wiring board 10 according to one embodiment of the present invention. In the multilayer wiring board 10 according to this embodiment, multiple layers are stacked in the stacking direction indicated by the downward arrow in the figure, and differential wiring included in some of the layers transmits differential signals, with the insulating layers and differential wiring being configured in multiple layers. Here, an example of a multilayer wiring board 10 is shown in which multiple layers are stacked in the stacking direction from top to bottom in the order of layer 1, layer 2, and layer 3. Layers numbered 1, 2, and so on have ground wiring or regular wiring formed, for example, using copper foil. An insulating layer is provided between each layer.

[0013] A first ground wiring 1 made of copper foil is formed on the first layer, and a second ground wiring 4 made of copper foil is formed on the third layer. Note that a transmission path capable of transmitting a signal may also be formed on the first and third layers.

[0014] The first and second insulating layers 2, 3 are formed of a resin such as glass cloth or prepreg, or an intermediate material such as resin-impregnated fiber other than glass cloth.

[0015] In both layers, copper foil is formed and then etched to form differential wiring arranged in a direction intersecting the stacking direction (horizontal direction in the figure). The differential wiring is composed of a first transmission path (first transmission path 11) and a second transmission path (second transmission path 12) arranged between the first insulating layer (first insulating layer 2) and the second insulating layer (second insulating layer 3) in a direction intersecting the stacking direction in which the first insulating layer (first insulating layer 2) and the second insulating layer (second insulating layer 3) are stacked in this order.

[0016] The second layer is provided with a first transmission line (first transmission line 11) that transmits a differential signal and a second transmission line (second transmission line 12) that transmits a differential signal and has a shorter wiring length than the first transmission line (first transmission line 11). The first transmission line 11 and the second transmission line 12 have different wiring lengths, like a first transmission line 41 and a second transmission line 42 shown in FIG. 8, which will be described later.

[0017] The first insulating layer (first insulating layer 2) is laminated between the first transmission path (first transmission path 11) and the second transmission path (second transmission path 12) and the first ground wiring (first ground wiring 1). The second insulating layer (second insulating layer 3) is laminated between the first transmission path (first transmission path 11) and the second transmission path (second transmission path 12) and the second ground wiring (second ground wiring 4).

[0018] A high-permittivity material 21 is disposed on the second transmission path (second transmission path 12). The high-permittivity material 21 is formed of a high-permittivity material having a higher relative permittivity than the first insulating layer (first insulating layer 2) and the second insulating layer (second insulating layer 3), and is a member through which electric field lines pass from the second transmission path (second transmission path 12) toward the first ground wiring (first ground wiring 1) and the second ground wiring (second ground wiring 4). The high-permittivity material 21 is disposed on a surface of the second transmission path (second transmission path 12) that faces the first ground wiring (first ground wiring 1) and the second ground wiring (second ground wiring 4) in the stacking direction. The high-permittivity material 21 covers, for example, the top and bottom surfaces and the right surface of the second transmission path 12. Note that the high-permittivity material 21 is not disposed on the surface of the second transmission path 12 that faces the first transmission path 11.

[0019] In this embodiment, the signal transmission speed due to the difference in wiring length between the first transmission line 11 and the second transmission line 12 is adjusted not by the physical wiring length such as a meandering shape, but by the relative dielectric constant εr as shown in the following equation (1).

[0020]

[0021] In equation (1), v represents the transmission speed of the differential signal, c represents the speed of light, and εr represents the relative dielectric constant. Equation (1) shows that as the relative dielectric constant increases, the signal transmission speed v decreases, and as the relative dielectric constant εr decreases, the signal transmission speed v increases.

[0022] The skew adjustment of the differential wiring due to the difference in wiring length between the first transmission line 11 and the second transmission line 12 is achieved by delaying the signal speed not by the physical length but by changing the relative dielectric constant of the second transmission line 12. For this reason, the high dielectric constant material 21 is configured so as to increase the amount of change in the relative dielectric constant of the second transmission line 12. As a result, it is not necessary to configure the second transmission line 12 in a meandering shape, and the wiring space for the second transmission line 12 is reduced.

[0023] Next, examples of wiring layout of the first and second transmission lines will be described with reference to Figures 2 and 3. Here, the first and second transmission lines formed on the substrate will be described as simplified schematic diagrams.

[0024] 2 is a diagram showing an example of the configuration of a first transmission line 101 and a second transmission line 102 provided in a conventional multilayer wiring board 100. The conventional multilayer wiring board 100 does not have a ground wiring on the first layer. For comparison with the multilayer wiring board 10 according to the present embodiment shown in FIG. 3 (to be described later), the first, second, and third layers are indicated.

[0025] In the conventional multilayer wiring board 100, a first transmission line 101 and a second transmission line 102 are also arranged side by side in the horizontal direction in two layers. However, the upper surfaces of the first transmission line 101 and the second transmission line 102 are only covered with a first insulating layer 2, and do not have a first ground wiring 1. For this reason, the wiring between the first transmission line 101 and the second transmission line 102 is called the "surface layer wiring." The surface layer corresponds to layer 2 in the configuration of FIG. 2. The first transmission line 101 and the second transmission line 102 are separated by a distance d11.

[0026] A high-permittivity material 103 is disposed on the upper and left-right surfaces of the second transmission line 102. Electric field lines 104 are generated from the second transmission line 102 to the ground wiring on the third layer. The electric field lines 104 cause current to leak from the second transmission line 102 to the ground wiring on the third layer.

[0027] For example, if the dielectric constant of the high dielectric constant material 103 is 6.0, the dielectric constant of the first transmission line 101 is 3.8 in the conventional configuration, whereas the dielectric constant of the second transmission line 102 in which the high dielectric constant material 103 is disposed changes to 3.9. In other words, the amount of change in the dielectric constant of the second transmission line 102 with respect to the dielectric constant of the first transmission line 101 is 0.1.

[0028] FIG. 3 is a diagram showing an example of the configuration of the first transmission line 11 and the second transmission line 12 provided in the multilayer wiring board 10 according to this embodiment.

[0029] In the multilayer wiring board 10 according to this embodiment, the first transmission line 11 and the second transmission line 12 are also arranged side by side in the horizontal direction on two layers. The first transmission line 11 and the second transmission line 12 are separated by a distance d11. Since the first transmission line 11 and the second transmission line 12 are both formed on layers sandwiched between the ground wiring on the first and third layers, the wiring between the first transmission line 11 and the second transmission line 12 is referred to as "inner layer wiring." The inner layer corresponds to layer 2 in the configuration of FIG. 3 .

[0030] High-dielectric-constant materials 21 are disposed on the top and bottom surfaces and the right surface of the second transmission line 12. Electric field lines 14 are generated in the directions toward the first ground wiring 1 and the second ground wiring 4 of the first transmission line 11 and the second transmission line 12, respectively, and current leaks to the first ground wiring 1 and the second ground wiring 4 on the first and third layers.

[0031] The high-dielectric-constant material 21 is formed of a high-dielectric-constant material having a higher dielectric constant than the first insulating layer 2 and the second insulating layer 3. The high-dielectric-constant material 21 is formed in a location where the electric field lines 14 generated from the second transmission line 12 can easily pass through. For example, the dielectric constant of the high-dielectric-constant material 21 is 6.0. In the configuration according to this embodiment, the dielectric constant of the first transmission line 11 is, for example, 4.0, while the dielectric constant of the second transmission line 12 in which the high-dielectric-constant material 21 is disposed changes to, for example, 4.5. That is, the change in the dielectric constant of the second transmission line 12 relative to the dielectric constant of the first transmission line 11 is 0.5, which is greater than the change in the dielectric constant in the conventional configuration shown in FIG. 2 . This indicates that the amount of electric field lines 14 passing through the high-dielectric-constant material 21 is greater when the high-dielectric-constant material 21 is formed inside the multilayer wiring substrate 10 than when a member made of a high-dielectric-constant material is formed on the surface of the multilayer wiring substrate 10.

[0032] Generally, the phenomenon in which part of the current flowing between differential lines flows into the ground wiring, converting the signal flowing through the differential lines, is called mode conversion loss. When mode conversion loss occurs, the current flowing between the signals generates noise from the ground wiring, or external noise intrudes into the transmission path. For this reason, it is desirable for multilayer wiring boards to have little effect from mode conversion loss.

[0033] While a conventional multilayer wiring board 100 has a structure related to surface wiring, the multilayer wiring board 10 according to this embodiment has a structure related to inner layer wiring. Inner layer wiring has more electric field lines passing through high-dielectric-constant materials, resulting in a larger range of change in the relative dielectric constant of the second transmission line 12, which is surrounded by the high-dielectric-constant material. Therefore, as explained with reference to the above formula (1), the transmission speed of signals transmitted through the second transmission line 12, which has a shorter total wiring length than the first transmission line 11, is reduced compared to the transmission speed before the relative dielectric constant was adjusted. As a result, the arrival timing of signals transmitted through the first transmission line 11 and the second transmission line 12 can be synchronized, thereby reducing skew.

[0034] In the future, the trend in wiring design for high-speed signal-carrying boards, such as those for AD / ADAS products, will be toward inner layer layouts that offer strong noise resistance (external noise resistance and radiation noise suppression), and this is expected to become more frequently used in designs. Therefore, by disposing a high-permittivity material 21 made of a high-permittivity material on the surface of the second transmission line 12 that faces the upper and lower ground layers through which the electric field lines 14 pass, the relative permittivity of the second transmission line 12 can be increased. Furthermore, the multilayer wiring board 10 according to this embodiment has superior mode conversion loss characteristics compared to the conventional multilayer wiring board 100. Furthermore, the noise resistance of the first transmission line 11 and the second transmission line 12, which are provided in the inner layers, is enhanced.

[0035] Next, a method for manufacturing the multilayer wiring board 10 according to this embodiment will be described with reference to FIGS.

[0036] 4 is a diagram showing an example of the configuration of the multilayer wiring board 10. In FIG. 4, the first and third layers are omitted.

[0037] First, a second insulating layer (second insulating layer 3) is formed as a base for high-dielectric-constant material 21. A recess into which high-dielectric-constant material 21 can be embedded is formed in second insulating layer (second insulating layer 3). When multilayer wiring substrate 10 is constructed, high-dielectric-constant material 21 is formed by combining high-dielectric-constant materials 21A and 21B. Therefore, high-dielectric-constant material 21B is embedded in the recess formed in second insulating layer (second insulating layer 3).

[0038] Next, the first transmission line 11 and the second transmission line 12 are wired on the upper surface of the second insulating layer (second insulating layer 3). After that, a high dielectric constant material 21A is formed so as to cover the second transmission line 12 using a dispenser or the like.

[0039] 5 is a diagram showing a manufacturing method of the multilayer wiring board 10. First, a second ground wiring 4 made of copper foil is formed in three layers. Next, a second insulating layer (second insulating layer 3) is formed on the second ground wiring 4. The second insulating layer (second insulating layer 3) may be made of, for example, prepreg FR4 (an insulating material including glass cloth). The recesses in the second insulating layer (second insulating layer 3) may be formed by masking the relevant portions when forming the second insulating layer (second insulating layer 3), or may be formed by cutting using etching, pressing using a stamper, or the like after the second insulating layer (second insulating layer 3) is formed.

[0040] Next, a high-dielectric-constant material 21B is formed in the recess of the second insulating layer (second insulating layer 3). A high-dielectric-constant material such as a dielectric paste or a processable prepreg is used as the high-dielectric-constant material 21B. Next, a copper layer 13 is formed on the second insulating layer (second insulating layer 3) and the high-dielectric-constant material 21B. The portions of the copper layer 13 indicated by the two-dot chain line are removed by etching or the like, and the first transmission path 11 and the second transmission path 12 are formed.

[0041] Next, a high-dielectric-constant material 21A is formed on the second transmission line 12. The high-dielectric-constant material 21A is a high-dielectric-constant material such as a dielectric paste or a processable prepreg. Next, a first insulating layer 2 is formed. The first insulating layer 2 is made of, for example, prepreg FR4. Finally, a first ground wiring 1 (see FIG. 1) is formed. In this manner, the multilayer wiring board 10 is manufactured.

[0042] The relative permittivity of the second transmission line 12 varies depending on the location through which the electric field lines 14 formed by the second transmission line 12 and the first and second ground wirings 1 and 4 on the upper and lower layers pass. For this reason, various modified shapes of the high permittivity material 21 are expected. Modified examples of the high permittivity material 21 will be described with reference to FIG. 6 .

[0043] 6 is a diagram showing a modified example of the high-dielectric-constant material 21. In the multilayer wiring substrate 10 according to the modified example (1) of FIG. 6, all four surfaces of the second transmission line 12 are covered with the high-dielectric-constant material 22. This high-dielectric-constant material 22 is disposed in contact with the entire peripheral surface of the second transmission line (second transmission line 12). The second transmission line 12 using the high-dielectric-constant material 22 in this manner has the largest change in relative dielectric constant.

[0044] In the multilayer wiring board 10 according to the modified example (2) of FIG. 6 , a high-permittivity material 23 is disposed in contact with the peripheral surfaces of the second transmission line (second transmission line 12) other than the surface facing the first transmission line (first transmission line 11). That is, the high-permittivity material 23 does not cover the surface of the second transmission line 12 facing the first transmission line 11, but covers three sides of the second transmission line 12 other than the surface facing the first transmission line 11. Furthermore, the horizontal length of the high-permittivity material 23 is greater than the horizontal length of the second transmission line 12. The second transmission line 12 using the high-permittivity material 23 in this manner has a smaller change in relative permittivity than the high-permittivity material 22 according to the modified example (1), but still has a sufficient change in relative permittivity compared to the conventional multilayer wiring board 100.

[0045] 6 , a high-dielectric-constant material 24 is also disposed in contact with the peripheral surface of the second transmission path (second transmission path 12) other than the surface facing the first transmission path (first transmission path 11). The multilayer wiring substrate 10 according to the modification (3) has the same configuration as the multilayer wiring substrate 10 according to the modification (2), but the horizontal length of the high-dielectric-constant material 24 is shorter than the horizontal length of the second transmission path 12. The amount of change in the relative dielectric constant of the second transmission path 12 using the high-dielectric-constant material 24 configured in this manner is smaller than that of the high-dielectric-constant material 23 according to the modification (2), but a sufficient amount of change in the relative dielectric constant can be obtained compared to the conventional multilayer wiring substrate 100.

[0046] 6 has a configuration in which the upper and lower surfaces of the second transmission line 12 are covered with high-dielectric-constant materials 25A and 25B. The high-dielectric-constant materials 25A and 25B are arranged in contact with the surfaces of the second transmission line (second transmission line 12) in the stacking direction. The second transmission line 12 using the high-dielectric-constant materials 25A and 25B in this configuration can obtain a sufficient change in relative dielectric constant compared to the conventional multilayer wiring board 100.

[0047] The multilayer wiring board 10 according to the modified example (5) of FIG. 6 has a configuration in which high-dielectric-constant materials 26A and 26B are disposed at positions away from the top-bottom surfaces of the second transmission line 12. The high-dielectric-constant materials 26A and 26B are disposed at positions away from the stacking direction surfaces of the second transmission line (second transmission line 12). Therefore, a first insulating layer 2 is disposed between the top surface of the second transmission line 12 and the opposing surface of the high-dielectric-constant material 26A. Similarly, a second insulating layer 3 is disposed between the bottom surface of the second transmission line 12 and the opposing surface of the high-dielectric-constant material 26B. The second transmission line 12 using the high-dielectric-constant materials 26A and 26B configured in this manner can achieve a sufficient change in relative dielectric constant compared to the conventional multilayer wiring board 100.

[0048] The thickness of the high dielectric constant material 21 in the stacking direction may be greater than the thickness of the second transmission line 12 in the stacking direction. Therefore, it is possible to further increase the thickness of the high dielectric constant material 21 shown in Fig. 1 and the high dielectric constant materials 22, 23, 24, 25A, 25B, 26A, and 26B shown in Fig. 6 in the stacking direction. Fig. 7 is a diagram showing an example of a high dielectric constant material 27 in which the thickness of the high dielectric constant material 21 in the stacking direction is doubled.

[0049] The high-dielectric-constant material 27 shown in FIG. 7 is formed to a thickness approximately twice the thickness in the stacking direction of the high-dielectric-constant material 21 shown in FIG. 1. By increasing the thickness of the high-dielectric-constant material 27 in this manner, a sufficient amount of change in relative dielectric constant can be obtained compared to the conventional multilayer wiring board 100. Furthermore, the high-dielectric-constant materials of the multilayer wiring boards 10 according to the modifications (1) to (5) shown in FIG. 6 may also be formed to have a large thickness, similar to the high-dielectric-constant material 27. Alternatively, the relative dielectric constant of the second transmission line 12 in each multilayer wiring board 10 may be adjusted depending on the characteristics of the high-dielectric-constant material.

[0050] Next, examples of wiring of the first transmission line 41 and the second transmission line 42, which have a difference in wiring length, in the multilayer wiring board 10 according to this embodiment will be described with reference to FIGS. 8 to 12. FIG.

[0051] 8 is a top view of a multilayer wiring board 10A in which a first transmission line 41 and a second transmission line 42 are wired on a surface layer and an inner layer. The first transmission line 41 and the second transmission line 42 are denoted by different reference numerals from the first transmission line 11 and the second transmission line 12 shown in FIG. 3 in order to explain how they are wired in the multilayer wiring board 10A. A high-dielectric-constant material 22 is disposed in at least a portion of the second transmission line 42. The first transmission line 41 and the second transmission line 42 can be wired at any angle.

[0052] Two integrated circuits (ICs) 31 and 32 are attached to the multilayer wiring board 10A. The ICs 31 and 32 are wired via a first transmission path 41 and a second transmission path 42. Of the first transmission path 41, the portion indicated by the solid line is wired on the surface layer of the multilayer wiring board 10A, and the portion indicated by the dashed line is wired on an inner layer of the multilayer wiring board 10A. Similarly, of the second transmission path 42, the portion indicated by the solid line is wired on the surface layer of the multilayer wiring board 10A, and the portion indicated by the two-dot chain line is wired on an inner layer of the multilayer wiring board 10A. The line length of the first transmission path 41 is 123 mm, and the line length of the second transmission path 42 is 100 mm. In FIG. 12 described later, in order to explain the signals transmitted to the first transmission path 41 and the second transmission path 42, "A 123 mm" is written near the wiring of the first transmission path 41, and "B 100 mm" is written near the wiring of the second transmission path 42.

[0053] FIG. 9 is a side view of a multilayer wiring board 10B in which a first transmission line 41 and a second transmission line 42 are wired in a BGA (Ball Grid Array) arrangement.

[0054] Two ICs 31 and 32 are also attached to the multilayer wiring board 10B. The first transmission line 41 and the second transmission line 42 are both formed in a BGA arrangement on an inner layer (between the L1 layer and the L2 layer) of the multilayer wiring board 10B. In the multilayer wiring board 10B as well, the line length of the first transmission line 41 is set to 123 mm, and the line length of the second transmission line 42 is set to 100 mm.

[0055] 10 is a diagram showing the difference in the configuration between the first transmission line 41 and the second transmission line 42. In the following description, it is assumed that the high-dielectric-constant material 21 is disposed around the second transmission line 42, but a configuration in which each of the high-dielectric-constant materials according to the modifications (1) to (5) shown in FIG. 6 or the high-dielectric-constant material 27 shown in FIG. 7 is disposed may also be used.

[0056] The upper side of Fig. 10 shows a top view of the multilayer wiring board 10A shown in Fig. 8. As described above, in conventional multilayer wiring boards, when there is a difference in wiring length between two transmission lines, a meandering shape is used to make the wiring lengths of the two transmission lines approximately the same in order to prevent signal transmission delays.

[0057] 10 shows a partially enlarged view of a multilayer wiring board 10A having a conventional configuration. In the conventional configuration, the second transmission line 42 is configured in a meander shape to match the wiring length of the first transmission line 41, and the wiring length of the second transmission line 42 is long in the partially enlarged region. As a result, the second transmission line 42 takes up extra space at a portion 110 where the meander shape is configured.

[0058] 10 shows a partially enlarged view of a multilayer wiring board 10A having a first configuration according to this embodiment. In the first configuration according to this embodiment, a high-dielectric-constant material 21 is disposed around the second transmission line 42, changing the relative dielectric constant of the second transmission line 42. This eliminates the need for the second transmission line 42 to have a meandering shape, eliminating the need for the extra space required for the meandering-shaped second transmission line 42 in the conventional configuration.

[0059] 11 is a partially enlarged view of a multilayer wiring board 10A having a second configuration according to this embodiment. In the second configuration, a high-dielectric-constant material 21 is also disposed in the second transmission line 42, changing the relative dielectric constant of the second transmission line 42. However, the high-dielectric-constant material 22 does not necessarily have to be disposed over the entire wiring length of the second transmission line 42. In this case, a portion of the second transmission line 42 is configured in a meandering shape as in the conventional case.

[0060] However, the meander-shaped portion 111 of the second transmission line 42 occupies a smaller space than the meander-shaped portion 110 of the second transmission line 42 shown as the conventional configuration in Fig. 10. Therefore, the area of ​​the meander shape of the second transmission line 42 can be made smaller than that of the conventional configuration. Therefore, the extra space of the second transmission line 42 of the multilayer wiring board 10A having the second configuration can be reduced compared to the second transmission line 42 having the conventional configuration.

[0061] 12 is a diagram showing an example of the measurement results of skew adjustment. In each graph of FIG. 12, the horizontal axis represents time [nanoseconds], and the vertical axis represents voltage [V].

[0062] Graph (1) at the top of Figure 12 shows an example of differential signal changes in a multilayer wiring board 10 with a non-meandered wiring and a difference in wiring length. The multilayer wiring board 10 with a difference in wiring length has an unadjusted dielectric constant εr. Graph (A), shown by a dashed line above graph (1), represents the change in differential signal of the first transmission line 41 with a wiring length of 123 mm. Graph (B), shown by a dashed line below graph (1), represents the change in differential signal of the second transmission line 42 with a wiring length of 100 mm. The first transmission line 41 and the second transmission line 42 both have the same dielectric constant εr of "4." Therefore, the arrival timing of the differential signal of the first transmission line 41, which has a longer wiring length, is delayed by a skew sk1 from the arrival timing of the differential signal of the second transmission line 42, which has a shorter wiring length. Skew represents the difference in signal arrival time, i.e., delay, between differential signals transmitted through two transmission lines.

[0063] Graph (2) at the bottom of Figure 12 shows an example of differential signal changes in a multilayer wiring board 10 configured according to this embodiment. With the configuration according to this embodiment, the relative permittivity εr of the second transmission line 42, which has a shorter wiring length than the first transmission line 41, is adjusted to "6." As a result, the differential signal flowing through the second transmission line 42 is delayed, reducing the skew sk1, which is the difference in signal arrival time between the differential signals. By reducing the difference in signal arrival time between the differential signals, the timing at which the differential signal changes in the first transmission line 41 and the second transmission line 42 begin to approximately coincide. Adjusting the relative permittivity εr of the second transmission line 42 in this manner makes it possible to adjust the timing of differential signal transmission and the skew sk1. Furthermore, among the transmission lines provided in the multilayer wiring board 10, the second transmission line 42, which has a shorter wiring length, does not need to be configured in a meandering shape, thereby saving space for wiring on the board.

[0064] Next, examples of wiring having a configuration according to this embodiment will be described with reference to Figures 13 to 15. Figure 13 is a top view showing an example of the configuration of a multilayer wiring board 10C according to this embodiment.

[0065] In the multilayer wiring board 10C, the ICs 31 and 32 are wired by a first transmission line 41 and a second transmission line 42 via footprints provided on the top surface of the board. As described above, the wiring length of the second transmission line 42 is shorter than the wiring length of the first transmission line 41. The solid line portions of the first transmission line 41 and the second transmission line 42 represent the portions that are wired on the surface layer of the multilayer wiring board 10C. The dashed line portions represent the portions that are wired on the inner layer of the multilayer wiring board 10C. The circled portions in the figure represent layer switching vias.

[0066] In the multilayer wiring board 10C, the first transmission line 41 and the second transmission line 42 are wired side by side in the horizontal direction on the same layer. An example of the wiring of the first transmission line 41 is shown in the lower left of Fig. 13, and an example of the wiring of the second transmission line 42 is shown in the lower right of Fig. 13. This figure also shows that the wiring length of the second transmission line 42 is shorter than the wiring length of the first transmission line 41.

[0067] Fig. 14 is a cross-sectional view showing an example of wiring when ICs 31 and 32 are footprints. Fig. 14 is a cross-sectional view of the multilayer wiring board 10C shown in Fig. 13. The layer numbers shown in Fig. 14 correspond to the layer numbers shown in Fig. 4, and layer numbers are not assigned to layers not used in the description.

[0068] 14 , the first transmission line 41 and the second transmission line 42 are both routed via footprints on inner layers of the multilayer wiring board 10C, and have different wiring lengths. A first insulating layer 2 is provided between the first and second layers, and a second insulating layer 3 is provided between the third and fourth layers. As a result, even if the first transmission line 41 and the second transmission line 42 partially overlap in the stacking direction, skew in the differential wiring can be suppressed.

[0069] Fig. 15 is a cross-sectional view showing an example of wiring when ICs 31 and 32 are BGA. Fig. 15 is a cross-sectional view of multilayer wiring board 10C shown in Fig. 13 when ICs 31 and 32 of multilayer wiring board 10C are installed as BGA. The layer numbers shown in Fig. 15 correspond to the layer numbers shown in Fig. 4, and layer numbers are not assigned to layers not used in the description.

[0070] Even when the ICs 31 and 32 are BGAs, the first transmission path 41 and the second transmission path 42 are wired on inner layers of the multilayer wiring substrate 10C and have different wiring lengths. A first insulating layer 2 is provided between the first and second layers, and a second insulating layer 3 is provided between the third and fourth layers. Even when the first transmission path 41 and the second transmission path 42 are formed on the same layer, skew in the differential wiring can be suppressed.

[0071] Next, the characteristic impedance of the transmission line formed by the wiring configured according to this embodiment will be described with reference to Fig. 16. Fig. 16 is a diagram showing an example of inner layer wiring for explaining the characteristic impedance value Zo of the transmission line.

[0072] When a designer designs the wiring between the first transmission line 11 and the second transmission line 12, for example, the designer needs to design a characteristic impedance value Zo of 50 Ω for single-ended wiring. In order to ensure signal stability and prevent noise in differential wiring, the characteristic impedance values ​​Zo of the first transmission line 11 and the second transmission line 12 need to be the same. The following formula (2) is a simple formula for calculating the general characteristic impedance for inner layer wiring.

[0073]

[0074] In equation (2), εr represents the relative dielectric constant, b represents the height of the insulating layer in the stacking direction, t represents the height of the inner layer wiring in the stacking direction, and w represents the horizontal line width of the inner layer wiring. As shown in equation (2), when the relative dielectric constant εr changes, the characteristic impedance value Zo also changes. For example, when the relative dielectric constant εr increases, the characteristic impedance value Zo decreases. Conversely, when the relative dielectric constant εr decreases, the characteristic impedance value Zo increases.

[0075] When the relative dielectric constant εr changes, the line width w of the inner layer wiring (second transmission line 12) must be adjusted. Therefore, the width of the second transmission line in the direction intersecting the stacking direction is adjusted so that the characteristic impedance of the first transmission line (first transmission line 11) and the characteristic impedance of the second transmission line (second transmission line 12) are the same. Even if this adjustment increases the line width w of the inner layer wiring from its original line width, the increase in the horizontal space of the inner layer wiring (second transmission line 12) is much smaller than with conventional meandering shape adjustments. Conversely, when the relative dielectric constant εr increases, the characteristic impedance value Zo decreases, so adjustment can be made by narrowing the line width w of the inner layer wiring (second transmission line 12).

[0076] In the multilayer wiring boards 10 to 10D according to the embodiment described above, when the first transmission line 11 and the second transmission line 12 used in the differential wiring have different wiring lengths, a high-dielectric-constant material 21 formed of a high-dielectric-constant material is disposed around the second transmission line 12, which has a shorter wiring length than the first transmission line 11. The amount of change in the relative dielectric constant of the second transmission line 12 in which the high-dielectric-constant material 21 is disposed is greater than the amount of change in a conventional wiring structure. This allows the arrival timing of the differential signal transmitted through the second transmission line 12 to be aligned with the arrival timing of the differential signal transmitted through the first transmission line 11, thereby reducing skew sk1. In other words, in the multilayer wiring boards 10 to 10D, the transmission speed of the differential signal can be adjusted by adjusting the relative dielectric constant of the high-dielectric-constant material 21 according to the embodiment, rather than increasing or decreasing the wiring length using a conventional meandering shape.

[0077] Furthermore, by disposing a high dielectric constant material 21 around the second transmission line 12 and changing the relative dielectric constant of the second transmission line 12, it is possible to adjust the skew without reducing the wiring efficiency of the multilayer wiring boards 10 to 10D. Furthermore, even if the first transmission line 11 and the second transmission line 12, which perform high-speed communication, are wired close to each other, it is possible to realize wiring with enhanced noise resistance suitable for high-speed transmission in AD / ADAS products.

[0078] Furthermore, by arranging the first transmission path 11 and the second transmission path 12 horizontally and further arranging a high dielectric constant material 21 around the second transmission path 12, it is possible to reduce mode conversion loss in the multilayer wiring boards 10 to 10D and improve noise resistance.

[0079] Furthermore, the number of layers in the multilayer wiring boards 10 to 10D according to the present embodiment can be made smaller than that of conventional multilayer wiring boards, which also reduces the manufacturing costs of the boards.

[0080] Furthermore, although the above-described multilayer wiring boards 10 to 10D have a three-layer structure, the total number of layers may be increased to four or more by combining two insulating layers into a multilayer structure.

[0081] The present invention is not limited to the above-described embodiments, and various other applications and modifications are possible without departing from the spirit of the present invention as defined in the claims. For example, the above-described embodiments have described the configuration of a multilayer wiring board in detail and specifically in order to clearly explain the present invention, and are not necessarily limited to those having all of the described configurations. Furthermore, it is possible to add, delete, or replace some of the configurations of the present embodiments with other configurations. Furthermore, the control lines and information lines shown are those considered necessary for explanation, and do not necessarily represent all control lines and information lines in the product. In reality, it can be assumed that almost all of the configurations are interconnected.

[0082] REFERENCE SIGNS LIST 1...first ground wiring, 2...first insulating layer, 3...second insulating layer, 4...second ground wiring, 10, 10A to 10C...multilayer wiring board, 11...first transmission path, 12...second transmission path, 14...electric field lines, 21 to 27...high dielectric constant material, 31, 32...IC, 41...first transmission path, 42...second transmission path

Claims

1. A multilayer wiring board in which a plurality of layers are stacked, and differential wiring included in some of the layers transmits differential signals, comprising: a first transmission path that transmits the differential signals; a second transmission path that is shorter in length than the first transmission path and transmits the differential signals; a first insulating layer stacked between the first and second transmission paths and a first ground wiring; and a second insulating layer stacked between the first and second transmission paths and the second ground wiring, wherein the differential wiring is composed of the first transmission path and the second transmission path that are arranged between the first and second insulating layers in a direction that intersects with the stacking direction in which the first and second insulating layers are stacked in that order, and wherein a high-permittivity material having a higher relative dielectric constant than the first and second insulating layers is arranged for the second transmission path, and through which electric force lines pass from the second transmission path toward the first and second ground wiring, and the high-permittivity material is arranged on a surface of the second transmission path that faces the first ground wiring and the second ground wiring in the stacking direction.

2. The multilayer wiring board according to claim 1, wherein the high dielectric constant material is disposed in contact with the surface surrounding the second transmission line other than the surface facing the first transmission line.

3. The multilayer wiring board according to claim 1, wherein the high dielectric constant material is disposed in contact with the entire periphery of the second transmission line.

4. The multilayer wiring board according to claim 1, wherein the high dielectric constant material is disposed in contact with a surface of the second transmission line in the lamination direction.

5. The multilayer wiring board according to claim 1, wherein the high dielectric constant material is disposed at a location away from the surface of the second transmission line in the lamination direction.

6. The multilayer wiring board according to claim 2, wherein the thickness of the high dielectric constant material in the lamination direction is greater than the thickness of the second transmission line in the lamination direction.

7. The multilayer wiring board according to claim 3, wherein the width of the second transmission path in a direction intersecting the stacking direction is adjusted so that the characteristic impedance of the first transmission path and the characteristic impedance of the second transmission path are the same.

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