Circuit board

Abstract

To provide a circuit board that can suppress the formation of differential signal lines in places where the dielectric constant changes and the occurrence of skew due to manufacturing errors when forming differential signal line pairs on a multilayer circuit board.SOLUTION: A differential signal line pair is a first signal line 10 and a second signal line 20 in a stripline configuration formed on the same insulating layer, and the first signal line 10 and the second signal line 20 are switched at one or more intersections 61, 62 using line-switching electrode patterns 14, 24 along the way, and the total length of the first signal line 10 via the intersections 61, 62 and the length of the second signal line 20 via the intersection 62 is the same, and the total length of the odd-numbered signal line spacings separated by the intersections 60 is the same as the total length of the even-numbered signal line spacings.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a circuit board that can suppress the occurrence of skew due to manufacturing errors and the formation of differential signal lines in a location where the dielectric constant changes when forming a differential signal line pair on a multilayer circuit board. [Background technology]

[0002] In recent years, signal transmission speeds have increased, and GHz-band signals are now being used for such signal transmission. When designing circuit boards equipped with transmission lines for transmitting such high-speed signals, differential wiring signal transmission, which has high common-mode noise resistance, is useful and widely used. For example, differential wiring signal transmission is used in circuit boards such as switch devices in optical communication devices equipped with optical transceivers, as described in Patent Document 1.

[0003] A differential signal is ideally characterized by the fact that data with a 180-degree phase difference or reversed polarity are transmitted over two transmission paths, canceling out common-mode noise. In differential transmission, signals with a 180-degree phase difference or reversed polarity are transmitted over two signal paths. However, if there is a difference in the signal path length, even if the signals are synchronized at the transmitting end, there will be a difference in the arrival timing of the positive and negative data at the receiving end, resulting in an increase in common-mode components and a deterioration in signal quality. Therefore, adjusting the skew (phase difference) between the positive and negative signals is important in differential wiring. Differential signal structures include strip, microstrip, and broadside coupling. Patent Document 2 uses a strip structure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-027147 [Patent Document 2] Japanese Patent Publication No. 2022-007340 Summary of the Invention [Problem to be solved by the invention]

[0005] Multilayer insulators are often used as circuit boards for differential signal line pairs. For example, circuit boards may have a multilayer structure with insulating layers containing fibers and insulating material filled between the fibers. In this case, the effective dielectric constant of the insulator may change depending on the difference between the fiber direction and the signal line direction, or whether the signal line is between or on the fibers, which can cause skew between the signal line pairs. In differential transmission using striplines, the signal line pairs extend in the plane direction of the circuit board, which can cause skew.

[0006] On the other hand, when a differential signal line pair has a broadside coupling structure, skew does not occur even if the signal lines are bent. However, even in this case, manufacturing errors can occur, such as differences in dielectric constant between layers or differences in line width between layers, which can result in skew between the signal line pair.

[0007] The present invention has been made in view of the above, and aims to provide a circuit board that can suppress the formation of differential signal lines in places where the dielectric constant changes and the occurrence of skew due to manufacturing errors when forming a differential signal line pair on a multi-layer circuit board. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the circuit board of the present invention is a circuit board on which a transmission line consisting of a differential signal line pair is formed, the differential signal line pair being a first signal line and a second signal line of a stripline configuration formed on the same insulating layer, the first signal line and the second signal line are line-switched at one or more intersections along the way using a line-switching electrode pattern, the total length of the first signal line through the intersections and the total length of the second signal line through the intersections are the same, and the total length of the odd-numbered signal line spacings separated by the intersections is the same as the total length of the even-numbered signal line spacings.

[0009] Furthermore, a circuit board according to the present invention is a circuit board on which a transmission line consisting of a differential signal line pair is formed, the differential signal line pair being a first signal line and a second signal line arranged on at least two or more inner layers and configured in a broadside coupling configuration, the first signal line and the second signal line are switched between layers at one or more intersections using a line switching electrode pattern along the way, the total length of the first signal line via the intersections and the total length of the second signal line via the intersections are the same, and the total length of the odd-numbered signal line spacings separated by the intersections is the same as the total length of the even-numbered signal line spacings.

[0010] In addition, in the circuit board according to the present invention, the number of intersections is an odd number, and signal line interval lengths between the intersections, including the line ends, are equal.

[0011] Furthermore, the circuit board according to the present invention is characterized in that, in the above invention, the circuit board has a multi-layer structure with an insulating layer having fibers and an insulating material filled between the fibers, and the first signal line and the second signal line are formed on the insulating layer. [Effects of the Invention]

[0012] According to the present invention, when a differential signal line pair is formed on a multilayer circuit board, it is possible to prevent the differential signal lines from being formed in a location where the dielectric constant changes and to prevent skew from occurring due to manufacturing errors. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a plan view of an optical communication device equipped with a switch device using a circuit board according to an embodiment of the present invention. [Figure 2] FIG. 2 is a three-view diagram showing the wiring structure of a conventional circuit board corresponding to FIG. [Figure 3] FIG. 3 is a three-view diagram showing the wiring structure of a circuit board according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a three-view diagram showing the wiring structure of a conventional circuit board corresponding to FIG. [Figure 5] FIG. 5 is a diagram showing the effect of suppressing skew when there is a dielectric constant difference between layers and when there is no dielectric constant difference between layers in the wiring structure of FIG. [Figure 6] FIG. 6 is a diagram schematically illustrating an example in which an odd number of intersections are provided in the wiring structure of the first embodiment. [Figure 7] FIG. 7 is a diagram schematically illustrating an example of a wiring structure in which an even number of intersections are provided in the wiring structure of the first embodiment. [Figure 8] FIG. 8 is a schematic diagram showing an example of a wiring structure in which the line lengths at the intersections in FIG. 7 are different. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0015] <First Embodiment> Fig. 1 is a three-sided view showing the wiring structure of a circuit board 1 according to a first embodiment of the present invention. Fig. 1(c) is a front view of the circuit board 1, Fig. 1(a) is a cross-sectional view of the circuit board 1 taken along line AA, and Fig. 1(b) is a right side view of the circuit board 1.

[0016] In Fig. 1, the circuit board 1 is made of glass cloth in which glass cloth fibers 51 extending in the X direction and glass cloth fibers 52 extending in the Y direction are woven so as to intersect at right angles, and these glass cloth fibers 51, 52 are filled with an insulator. The circuit board 1 is a multilayer board, and in Fig. 1 has a first layer L1 and a second layer. A differential signal pair, a first signal line 10 (11, 12) and a second signal line 20 (21, 22), are formed on the top surface of the second layer L2 as strip lines in the XY plane.

[0017] The first signal line 10 and the second signal line 20 each extend substantially parallel to the glass cloth fibers 51, with one or more intersections 60 (61, 62) formed along the way, where the first signal line 10 and the second signal line 20 are interchanged. The intersection 61 has an electrode pattern 14 for signal line interchange formed on the upper surface of the first layer L1, i.e., the front surface of the circuit board 1, and vias 13 and 15 for interlayer connection between the electrode pattern 14 and the first signal lines 11 and 12. Similarly, the intersection 62 has an electrode pattern 24 for signal line interchange formed on the back surface of the second layer L2, i.e., the back surface of the circuit board 1, and vias 23 and 25 for interlayer connection between the second signal lines 21 and 22 and the electrode pattern 24.

[0018] 2 is a three-view diagram showing the wiring structure of a conventional circuit board 1 corresponding to FIG. 1. FIG. 2(a) is a cross-sectional view taken along line BB in FIG. 2(c). In FIG. 2, the first signal line 11 is formed to extend continuously and substantially parallel to the glass cloth fibers 51, and the second signal line 21 is formed to extend continuously and substantially parallel to the glass cloth fibers 51. In other words, the first signal line 11 and the second signal line 21 are not interchanged due to the intersections 61 and 62.

[0019] As shown in FIG. 2(b), when the positional relationship between the first signal line 11 and the glass cloth fiber 51 differs from the positional relationship between the second signal line 21 and the glass cloth fiber 52, the effective dielectric constant for the first signal line 11 differs from the effective dielectric constant for the second signal line 21, resulting in skew in the differential signal line pair between the first signal line 11 and the second signal line 21.

[0020] In contrast, in the circuit board 1 of the first embodiment shown in Fig. 1, the first signal line 11 shown in Fig. 1 is switched onto the second signal line 21 shown in Fig. 2 via the intersection 60, becoming the first signal line 12. Similarly, the second signal line 21 shown in Fig. 1 is switched onto the first signal line 11 shown in Fig. 2, becoming the second signal line 22.

[0021] As a result, the skew caused by the difference in effective dielectric constant between the first signal line 11 and the second signal line 21 and the skew caused by the difference in effective dielectric constant between the first signal line 12 and the second signal line 22 are offset, thereby suppressing the occurrence of skew between the first signal lines 11, 12 and the second signal lines 21, 22.

[0022] In the first embodiment, the direction of the glass cloth fibers 51, 52 and the direction of arrangement of the first signal lines 11, 12 and the second signal lines 21, 22 are arbitrary, and the occurrence of skew is suppressed regardless of the directional arrangement relationship.

[0023] Furthermore, in the first embodiment, the first signal lines 11 and 12 have the same length, and the intersection 61 is located at the midpoint of the first signal line consisting of the first signal lines 11 and 12. Similarly, the intersection 62 is located at the midpoint of the second signal line consisting of the second signal lines 21 and 22. By making the lengths of the first signal lines 11 and 12 equal and the lengths of the second signal lines 21 and 22 equal, it is possible to reliably suppress the occurrence of skew.

[0024] Here, the line lengths of the intersections 61 and 62 are also made equal. As a result, the total length of the first signal lines 11 and 12 via the intersection 61 is the same as the total length of the second signal lines 21 and 22 via the intersection 62. As will be described later, a plurality of intersections 60 may be provided, and the total length of the odd-numbered signal line intervals separated by the intersections 60 is made equal to the total length of the even-numbered signal line intervals. Note that in FIG. 1 , the odd-numbered signal line intervals are the lengths of the first signal line 11 or the second signal line 21 in the X direction, and the even-numbered signal line intervals are the lengths of the first signal line 12 or the second signal line 22 in the X direction.

[0025] <Embodiment 2> Fig. 3 is a three-sided view showing the wiring structure of a circuit board 1 according to a second embodiment of the present invention. Fig. 3(c) is a front view of the circuit board 1, Fig. 3(a) is a cross-sectional view of the circuit board 1 taken along line CC, and Fig. 3(b) is a right side view of the circuit board 1.

[0026] In the second embodiment, the differential signal line pair is arranged on at least two inner layers to form a broadside coupling configuration. The circuit board 1 has a three-layer structure, with the first signal line 31 and the second signal line 42 formed on the top surface of the second layer, and the second signal line 41 and the second signal line 42 formed on the top surface of the third layer.

[0027] The first signal lines 31, 32 and the second signal lines 41, 42 are switched between layers at one or more intersections 71 using the line-switching electrode patterns 33, 35 and intersections 72 using the electrode patterns 43, 45. The electrode patterns 33, 35 are connected between layers by vias 34. The electrode patterns 43, 45 are also connected between layers by vias 44.

[0028] The total length of the first signal lines 31 and 32 via the intersection 71 and the total length of the second signal lines 41 and 42 via the intersection 72 are the same, and the total length of the odd-numbered signal line spacings separated by the intersection 70 is the same as the total length of the even-numbered signal line spacings.

[0029] On the other hand, Fig. 4 is a three-sided view showing the wiring structure of the conventional circuit board 1 corresponding to Fig. 3. Fig. 4(a) is a cross-sectional view taken along line DD in Fig. 4(c). As shown in Fig. 4, when no intersection 70 is provided, the first signal line 31 is formed extending directly onto the top surface of the second layer, and the second signal line 41 is formed extending directly onto the top surface of the third layer.

[0030] In this case, if the effective dielectric constants between layers differ due to manufacturing errors, or if the line widths of the signal lines are manufactured differently between layers, skew will occur between the first signal line 31 and the second signal line 41.

[0031] In contrast, in the circuit board 1 of the second embodiment shown in Fig. 3, the first signal line 31 shown in Fig. 3 is line-swapped (inter-layer swapped) onto the second signal line 41 shown in Fig. 4 via the intersection 70, thereby becoming the first signal line 32. Similarly, the second signal line 41 shown in Fig. 1 is line-swapped (inter-layer swapped) onto the first signal line 31 shown in Fig. 3, thereby becoming the second signal line 42. As a result, the skew occurring between the first signal line 31 and the second signal line 41 and the skew occurring between the first signal line 32 and the second signal line 42 can be canceled out.

[0032] As a result, in the second embodiment, even when the differential signal line pair has a broadside coupling configuration, the occurrence of skew can be reliably suppressed even when there is a difference in the effective dielectric constant between layers due to manufacturing errors or a difference in the line width between layers.

[0033] FIG. 5 is a diagram showing the skew suppression effect when there is and is not a dielectric constant difference between layers in the wiring structure of FIG. 3. FIG. 5(a) is a diagram confirming the skew suppression by the wiring structure of the second embodiment shown in FIG. 3 and the conventional wiring structure shown in FIG. 4 when there is no dielectric constant difference between layers. FIG. 5(a) shows the frequency characteristics of propagation loss, with characteristic 5a1 of the wiring structure of the second embodiment shown by a solid line and characteristic 5a2 of the conventional wiring structure shown by a dashed line. As is clear from FIG. 5(a), there is no significant difference between characteristic 5a1 of the wiring structure of the second embodiment and characteristic 5a2 of the conventional wiring structure.

[0034] In contrast, FIG. 5(b) is a diagram confirming the suppression of skew by the wiring structure of the second embodiment shown in FIG. 3 and the conventional wiring structure shown in FIG. 4 when there is a dielectric constant difference between layers. FIG. 5(b) shows the frequency characteristics of propagation loss, with characteristic 5b1 of the wiring structure of the second embodiment shown by a solid line and characteristic 5b2 of the conventional wiring structure shown by a dashed line. In FIG. 5(b), characteristic 5b1 of the wiring structure of the second embodiment is improved compared to characteristic 5b2 of the conventional wiring structure, and propagation loss is suppressed. In other words, it was confirmed that skew is suppressed by adopting the wiring structure of the second embodiment.

[0035] <Multiple intersections> Here, the provision of a plurality of intersections will be described. The provision of a plurality of intersections is common to both the first and second embodiments, but for convenience of explanation, the wiring structure of the first embodiment will be described.

[0036] 6A and 6B are diagrams illustrating an example in which an odd number of intersections are provided in the wiring structure of embodiment 1. Fig. 6A illustrates the wiring structure of Fig. 1, in which skew caused by a difference in effective dielectric constant between regions E1 and E2 is suppressed.

[0037] 6(b), three intersections 60a to 60c are provided between end points P1 and P2 in the wiring structure of FIG. 1. Here, intersections 60a to 60c corresponding to intersection 60 shown in FIG. 6(a) are provided at equal intervals between points P1 and P2. Therefore, the signal line spacing lengths between point P1 and intersection 60a, between intersections 60a and 60b, between intersections 60b and 60c, and between intersection 60c and point P2 are all the same length L20.

[0038] When the signal lines are spaced at equal intervals, the number of intersections is odd, and the line lengths within each of the intersections 60a to 60c must be equal.

[0039] Fig. 7 is a diagram schematically illustrating an example of a wiring structure in which an even number of intersections are provided in the wiring structure of embodiment 1. In Fig. 7, two intersections 60a and 60b are provided between end points P1 and P2 in the wiring structure of Fig. 1. Here, intersections 60a and 60b corresponding to intersection 60 shown in Fig. 6(a) are provided between points P1 and P2, but are not equally spaced.

[0040] When an even number of intersections are provided, the total length L2×2 of the odd-numbered signal line spacing lengths L20 divided by the intersections 60a and 60b must be the same as the total length L40 of the even-numbered signal line spacing lengths L40. Note that the line lengths within each intersection 60a, 60b must be equal.

[0041] 8 is a schematic diagram showing an example of a wiring structure in which the line lengths at the intersections 60a and 60b in FIG. 7 are different (asymmetric). In this case, the total length L2×2 of the odd-numbered signal line spacing lengths L20 divided by the intersections 60a and 60b must be the same as the total length L40 of the even-numbered signal line spacing lengths L40. Furthermore, the total length (L61a+L62b) of the lines connecting the first signal lines 10 within the intersections 60a and 60b must be equal to the total length (L62a+L61b) of the lines connecting the second signal lines 20 within the intersections 60a and 60b. This also applies when an even number of intersections are arranged. This results in the total lengths of the first signal lines 10 and the second signal lines 20 being equal.

[0042] In the above description, the terms "equal" and "same" mean "equal" and "same" within an allowable range. An example of the allowable range here is the skew that is allowable in a specific frequency band.

[0043] Although the present invention has been described above with reference to the embodiments and modifications thereof, the present invention is not limited to the descriptions and drawings that form part of the disclosure of the present invention. In other words, all other embodiments, examples, and operational techniques that are made by those skilled in the art based on the present embodiments are included in the scope of the present invention. [Explanation of symbols]

[0044] 1 circuit board 5a1,5a2,5b1,5b2 characteristics 10,11,12,31,32 First signal line 13,15,23,25,34,44 via 14,24,33,35,43,45 Electrode patterns 20, 21, 22, 41, 42 Second signal line 51,52 Glass cloth fiber 60, 60a, 60b, 60c, 61, 62, 70, 71, 72 Intersection E1, E2 fields L1 Layer 1 L2 Layer 2 Points P1 and P2

Claims

1. A circuit board on which a transmission line consisting of a differential signal line pair is formed, The differential signal line pair is a first signal line and a second signal line having a stripline configuration formed on the same insulating layer; the first signal line and the second signal line are switched at one or more intersections using a line switching electrode pattern; a total length of the first signal line through the intersection and a total length of the second signal line through the intersection are the same, and a total length of the odd-numbered signal line spacings separated by the intersection are the same as a total length of the even-numbered signal line spacings.

2. A circuit board on which a transmission line consisting of a differential signal line pair is formed, The differential signal line pair is a first signal line and a second signal line arranged in at least two inner layers and configured in a broadside coupling configuration; the first signal line and the second signal line are switched between layers at one or more intersections using a line switching electrode pattern; a total length of the first signal line through the intersection and a total length of the second signal line through the intersection are the same, and a total length of the odd-numbered signal line spacings separated by the intersection are the same as a total length of the even-numbered signal line spacings.

3. the number of intersections is odd, 3. The circuit board according to claim 1, wherein the signal lines have equal intervals between the intersections, including the line ends.

4. 3. The circuit board according to claim 1, wherein the circuit board has a multi-layer structure with an insulating layer having fibers and an insulating material filled between the fibers, and the first signal line and the second signal line are formed on the insulating layer.

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