Multilayer substrate structure and impedance matching method

Abstract

To provide "a multilayer substrate structure and an impedance matching method", capable of suppressing erosion of a wiring design region and adjusting characteristic impedance with relatively high degree of freedom.SOLUTION: Among a plurality of GND layers 11, 12, and 13 provided hierarchically with respect to a differential transmission path formed by a pair of signal lines 1, the GND layers of one or more layers from a layer close to the uppermost layer includes openings 17 and 18 penetrating in a layer direction. Here, in addition to formation of a first opening 17 in a first region facing a region 7 including capacitive loads 4 and 6 connected to the signal line 1 in the uppermost layer, and formation of the second opening 18 in the second region facing a region 8 not including the capacitive loads 4 and 6 but including the signal line 1 in the uppermost layer makes it possible to adjust a separation distance in the layer direction in which the uppermost layer and the GND layer face each other via one or more openings, and to adjust the area of the second opening 18.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer substrate structure and an impedance matching method, and is particularly suitable for use in a multilayer substrate structure in which a plurality of GND layers are hierarchically provided for a differential transmission line formed by a pair of signal lines and an impedance matching method for the differential transmission line.

Background Art

[0002] Conventionally, differential transmission is known as a signal transmission method that is resistant to external noise. Differential transmission is a method of transmitting a signal using the potential difference between two signal lines by flowing currents of opposite phases through the two signal lines laid in parallel. That is, the potential difference between the two signal lines becomes the signal level, and for example, if the potential difference is positive, it is recognized as "H", and if it is negative, it is recognized as "L". Since signals of opposite phases flow simultaneously through a pair of signal lines, even when noise occurs, it is canceled, making it less likely to malfunction.

[0003] When configuring a differential transmission line, it is necessary to match the characteristic impedance on the transmission line so that it falls within a predetermined threshold range. In a distributed constant circuit applied in a high-frequency circuit, when the inductance per unit length is L and the capacitance per unit length is C, the characteristic impedance Z0 of a uniform transmission line without loss is Z0 = (L / C) 1 / 2 represented by. Here, by appropriately designing the distance between the two signal lines, the conductor width, the thickness of the insulator layer provided between the signal line and the GND line, etc., it is possible to match the characteristic impedance within a predetermined threshold range.

[0004] On the other hand, when a passive component is mounted by connecting a land for component mounting or the like in the middle of the signal line, the characteristic impedance of the differential transmission line changes (decreases) under the influence of the capacitance of the passive component. Therefore, it is necessary to adjust the characteristic impedance according to the passive component to be mounted and the land for component mounting.

[0005] Conventionally, in a multilayer substrate structure in which a plurality of GND layers are hierarchically provided with respect to signal lines, a method of matching characteristic impedance by adjusting the distance between passive components and the GND layer is known. Note that Patent Document 1 discloses a method of adjusting characteristic impedance by changing the distance between a wiring pattern and a GND layer in a pattern wiring structure of a multilayer substrate configured in a hierarchical manner, although it is a single-ended transmission configuration.

[0006] FIG. 3 is a diagram for explaining a conventional method of adjusting characteristic impedance that decreases when a passive component is mounted in the middle of a signal line. FIG. 3(a) is a plan view of the multilayer substrate structure as viewed from above, and FIG. 3(b) is a cross-sectional view of the multilayer substrate structure as viewed from the side. In FIG. 3, a pair of signal lines 101 parallel to each other in the horizontal direction are provided between a connector pin 102a erected on a connector 102 and a device pin 103a provided on a device 103, whereby a differential transmission line is formed by the pair of signal lines 101. Further, a land 104 is connected in the middle of the signal line 101, and another land 105 is formed with a gap interposed therebetween from the land 104, and a passive component 106 is mounted on the lands 104 and 105.

[0007] As shown in FIG. 3(b), with the signal line 101 as the first layer, a plurality of GND layers 111, 112, and 113 are provided vertically downward. That is, a first GND layer 111 is formed in the second layer with a prepeg layer 114 interposed between the signal line 101 of the first layer, a second GND layer 112 is formed in the third layer with a core material 115 interposed between the first GND layer 111, and a third GND layer 113 is formed in the fourth layer with a prepeg layer 116 interposed between the second GND layer 112.

[0008] In the plurality of GND layers 111, 112, 113 hierarchically configured below the signal line 101, by extracting one or more regions facing the region including the land 104 connected to the signal line 101 in order from the upper layer, the distance between the land 104 and the GND layer is increased to vary the capacitance C, thereby adjusting the characteristic impedance Z0. How many of the GND layers 111, 112, 113 are extracted from the upper layer is determined by the magnitude of the decrease in the characteristic impedance Z0 caused by the mounting of the passive component 106. That is, the number of layers to be extracted is adjusted so that the characteristic impedance determined as a result of the extraction is closest to the desired value.

[0009] In FIG. 3(b), for the two GND layers 111, 112 formed in the second layer and the third layer, a state is shown in which an opening 107 is formed by cutting out the region facing the region 107 including the land 104. In this way, for the portion where the opening 107 is formed, the capacitance is determined by the relationship between the distance between the land 104 and the third GND layer 113. Therefore, the capacitance decreases when cutting is performed compared to the capacitance determined by the relationship between the distance between the land 104 and the first GND layer 111 when cutting is not performed. Thereby, it is possible to correct the decrease in the characteristic impedance Z0 caused by mounting the passive component 106 on the land 104.

[0010] However, in the structure shown in FIG. 3, the number of layers of the GND layers 111, 112, 113, the interlayer thickness composed of the prepreg layers 114, 116 and the core material 115, etc. are fixed in the product specifications and cannot be changed. Therefore, there is a problem that there is a limit to the range in which the characteristic impedance can be adjusted by cutting out the GND layer, and there may be a case where it cannot be appropriately matched to fall within a predetermined threshold value. Also, when extracting the second GND layer 112 in addition to the first GND layer 111, there is also a problem that the wiring design area of the core material 115 is eroded, which inhibits wiring.

[0011] As a method for correcting a decrease in characteristic impedance when a capacitive load is connected in the middle of the wiring of a signal conductor, a multilayer wiring board is known in which the gap between a pair of signal conductors is widened in the impedance decrease region centered on the capacitive load to increase the differential impedance (see, for example, Patent Document 2). However, in the configuration described in this Patent Document 2, since a pair of signal lines are not parallel and the interval between the signal lines also becomes wide, there arises a problem that the effect of noise cancellation by differential transmission decreases.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] The present invention has been made to solve the above problems, and in a multilayer substrate structure in which a plurality of GND layers are hierarchically provided with respect to a differential transmission path formed by a pair of signal lines, erosion of the wiring design region is suppressed and the characteristic impedance can be adjusted with relatively high freedom.

Means for Solving the Problems

[0014] In order to solve the above-described problems, in the present invention, among a plurality of GND layers hierarchically provided with respect to a differential transmission path formed by a pair of signal lines, one or more GND layers from the layer closest to the top layer on which the signal lines are formed are provided with openings penetrating in the layer direction. In the present invention, in addition to a first region facing the region including the capacitive load connected to the signal line in the top layer, an opening is formed in a second region facing the region including the signal line but not including the capacitive load in the top layer.

Effects of the Invention

[0015] According to the present invention configured as described above, in addition to adjusting the separation distance in the layer direction between the topmost layer and the GND layer in the first region and the second region through one or more openings, the area of the second opening can be adjusted in the second region. In a multilayer substrate structure in which the number of layers and the interlayer thickness of a plurality of GND layers are fixed, compared with the case of adjusting the separation distance in the layer direction by the first opening formed in the first region, the area of the second opening formed in the second region can be adjusted on a finer scale. Therefore, by adjusting the size of the second opening formed in the second region, the characteristic impedance can be adjusted with relatively high degrees of freedom. Further, according to the present invention, since the characteristic impedance can be adjusted by the second opening formed in the second region instead of increasing the number of layers in which the first opening is formed in the first region, erosion of the wiring design area can be reduced.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration example of a multilayer substrate structure according to the present embodiment including a differential transmission line. FIG. 1(a) is a plan view of the multilayer substrate structure seen from above, and FIG. 1(b) is a cross-sectional view of the multilayer substrate structure seen from the side.

[0018] As shown in Fig. 1, the first layer (the top layer) of the multilayer substrate structure is a rectangular annular substrate having a rectangular void in the center. A device 3 is mounted on one short side, and at the other short side opposite thereto, there is an end of a connector pin 2a erected on a connector 2. A pair of parallel signal lines 1 are connected between the connector pin 2a and a device pin 3a protruding from the device 3, and a differential transmission line is formed by the pair of signal lines 1. Hereinafter, for convenience of explanation, the long side direction of the rectangular annular substrate is defined as the X direction, the short side direction as the Y direction, and the layer direction of the multilayer substrate structure as the Z direction.

[0019] Also, in the middle of the pair of signal lines 1, lands 4 extending from each of the pair of signal lines 1 toward the long side (Y direction) of the rectangular annular substrate are connected. At a position facing across the Y-direction void from the lands 4, lands 5 extending from the long side of the rectangular annular substrate toward the lands 4 are formed, and passive components 6 are mounted on the lands 4 and 5. Here, an example where the passive components 6 are mounted on both sides of the pair of signal lines 1 is shown, but a configuration where the passive components 6 are mounted on only one side may also be used.

[0020] As shown in Fig. 1(b), in the multilayer substrate structure of this embodiment, a plurality of GND layers 11, 12, 13 are hierarchically provided vertically (Z direction) downward from the first layer with respect to the differential transmission line formed by the pair of signal lines 1. That is, a first GND layer 11 is formed in the second layer with a prepreg layer 14 interposed between the signal lines 1 of the first layer, a second GND layer 12 is formed in the third layer with a core material 15 interposed between the first GND layer 11, and a third GND layer 13 is formed in the fourth layer with a prepreg layer 16 interposed between the second GND layer 12.

[0021] In such a multilayer substrate structure configured as described above, in order to effectively operate the differential transmission line, it is necessary to match the characteristic impedance on the differential transmission line so that it falls within a predetermined threshold range. Basically, when no passive component 6 is mounted in the middle of the signal line 1, by appropriately designing the distance between the pair of signal lines 1, the conductor width, the thickness of the insulator layer provided between the signal line 1 and the GND layers 11, 12, 13, etc., it is possible to match the characteristic impedance within the range of the predetermined threshold value.

[0022] On the other hand, when a land 4 is connected in the middle of the signal line 1 and a passive component 6 is mounted as shown in FIG. 1, since the land 4 and the passive component 6 connected to the signal line 1 act as a capacitive load on the differential transmission line, the characteristic impedance of the differential transmission line changes (decreases) under the influence. In this case, among the plurality of GND layers 11, 12, 13, in one or more GND layers in the layer closest to the top layer where the signal line 1 is formed, by providing openings 17, 18 that penetrate in the layer direction by extracting a part, the characteristic impedance is adjusted to correct the decrease in the characteristic impedance. In the example of FIG. 1(b), an example is shown in which openings 17, 18 are provided in the first GND layer 11 in the second layer closest to the first layer.

[0023] In the present embodiment, as shown in FIG. 1, the first opening 17 is formed in the first region after the second layer facing the region 7 including the capacitive load (land 4 and the passive component 6 mounted thereon) connected to the signal line 1 in the first layer. The region 7 in the first layer includes the region where the land 4 exists, and is a region further including a certain margin region in the X direction and the Y direction from the boundary of the land 4. The width of the margin region is, for example, about the same as or slightly larger than the thickness of the prepreg layer 14 directly below the first layer.

[0024] In the present embodiment, in addition to the first opening 17, the second opening 18 is also formed as needed. "As needed" means a case where it is not possible to successfully match the characteristic impedance within the range of the predetermined threshold value only by adjusting the number of the first openings 17 provided in the first region facing the region 7 in the first layer in one or more of the GND layers 11, 12, 13.

[0025] As shown in FIG. 1, the second opening 18 is formed in a second region after the second layer that faces a region 8 including the signal line 1 and not including a capacitive load in the first layer where a differential transmission line is formed. This second region is a region continuous from the first region where the first opening 17 is formed. That is, the first opening 17 and the second opening 18 are continuous openings. The region 8 in the first layer includes a region where a pair of signal lines 1 exist, and is a region further including a certain margin region in the Y direction from the signal line 1. The width of this margin region is preferably equal to or greater than the thickness of the pre-bonding layer 14 directly below the first layer. For example, it can be set to a width about 2 to 3 times the width of the signal line 1.

[0026] Since the region 7 is a region including the signal line 1 and the land 4, while the region 8 is a region including only the signal line 1, the region 8 is narrower than the region 7 in the Y direction, and the second opening 18 is smaller than the first opening 17 in the Y direction. Since the second opening 18 has a role of finely adjusting the characteristic impedance, the size in the X direction is arbitrary, and may be smaller than, equal to, or larger than the width in the X direction of the first opening 17.

[0027] In the example of FIG. 1, as the width in the X direction of the second opening 18 in the second layer increases, the region where the signal line 1 in the first layer and the GND layer 12 in the third layer face each other (that is, the region where they face each other at a distance longer than the distance where the signal line 1 in the first layer and the GND layer 11 in the second layer face each other) increases, so the value of the characteristic impedance increases. Also, when the decrease in the characteristic impedance due to the capacitive load cannot be compensated by the openings 17 and 18 provided in the GND layer 11 of the second layer, the first opening 17 is provided in the first region facing the region 7 also in the GND layer 12 of the third layer, and then the characteristic impedance is finely adjusted by the second opening 18 formed in the GND layer 11 of the second layer. Note that a second opening 18 may be further formed in the GND layer 12 of the third layer as well.

[0028] Thus, in this embodiment, among the plurality of GND layers 11, 12, and 13, openings 17 and 18 that penetrate in the layer direction (Z direction) are provided in one or more GND layers starting from the layer closest to the top layer where the signal line 1 is formed, thereby correcting a decrease in the characteristic impedance of the differential transmission line caused by the connection of a capacitive load to the signal line 1. In this embodiment, in addition to the first opening 17 in the first region facing the region 7 including the capacitive load connected to the signal line 1 in the top layer, a second opening 18 is also formed in the second region facing the region 8 including the signal line 1 but not including the capacitive load in the top layer, so that the characteristic impedance of the differential transmission line can be finely adjusted.

[0029] FIG. 2 is a diagram showing the result of analyzing the characteristic impedance of the multilayer substrate structure shown in FIG. 1 by an electromagnetic field simulator. Here, for the purpose of showing the effects of the embodiment, the analysis result of the characteristic impedance when only the first opening 17 is formed is also shown. FIG. 2(a) shows the characteristic impedance of the multilayer substrate structure with only the first opening 17 formed, and FIG. 2(b) shows the characteristic impedance of the multilayer substrate structure with the first opening 17 and the second opening 18 formed as in FIG. 1.

[0030] Here, the characteristic impedance that appears on the differential transmission line when a current is flowing from the connector pin 2a to the device pin 3a direction is simulated. The horizontal axis represents time (i.e., corresponding to the distance from the connector pin 2a to the device pin 3a direction), and the vertical axis represents the characteristic impedance. Note that the characteristic impedance fluctuates greatly in the portion of 0.1 to 0.3 [ns], which is the influence of the connector pin 2a.

[0031] As shown in Fig. 2(a), near 0.4 [ns] of the time corresponding to region 7, the characteristic impedance of the differential transmission line decreases under the influence of the capacitive load. When only the first opening 17 is provided, the characteristic impedance decreases until it is below 90 Ω and cannot be matched to fall within the threshold range of 90 Ω to 110 Ω. On the other hand, when the second opening 18 is provided in addition to the first opening 17 as shown in Fig. 1, as shown in Fig. 2(b), the characteristic impedance can be matched to fall within the range of 90 Ω to 110 Ω.

[0032] As described in detail above, in the present embodiment, among the plurality of GND layers 11, 12, 13 provided hierarchically with respect to the differential transmission line formed by the pair of signal lines 1, in one or more layers of GND layers starting from the layer closest to the top layer on which the signal lines 1 are formed, openings 17, 18 penetrating in the layer direction are provided. In the present embodiment, in addition to the first opening 17 in the first region facing the region 7 including the capacitive load (land 4 and the passive component 6 mounted thereon) connected to the signal line 1 in the top layer, the second opening 18 is also formed in the second region facing the region 8 including the signal line 1 without the capacitive load in the top layer.

[0033] According to the present embodiment configured as described above, in addition to adjusting the layer-direction distance at which the top layer and the GND layer face each other through one or more openings 17, 18 in the first region and the second region, the area of the second opening 18 can be adjusted in the second region. In a multilayer substrate structure in which the number of layers and the interlayer thickness of the plurality of GND layers are fixed, compared to the case where the layer-direction separation distance is adjusted by the first opening 17 formed in the first region, the area of the second opening 18 formed in the second region can be adjusted on a finer scale. Therefore, the characteristic impedance can be adjusted with relatively high freedom by adjusting the size of the second opening 18 formed in the second region. Further, according to the present embodiment, since the characteristic impedance can be adjusted by the second opening 18 formed in the second region instead of increasing the number of layers in which the first opening 17 is formed in the first region, erosion of the wiring design area can be reduced.

[0034] In the above embodiment, an example in which the second opening 18 is formed to face the region 8 on the side of the device 3 from the land 4 has been described. However, the second opening 18 may be formed to face the region on the side of the connector 2 from the land 4. Alternatively, the second opening 18 may be formed to face both the region on the side of the device 3 and the region on the side of the connector 2 from the land 4.

[0035] Also, in the above embodiment, an example in which the first opening 17 and the second opening 18 are configured as continuous openings has been described. However, they may be non - continuous openings. However, if they are non - continuous openings, the variation in characteristic impedance between the first opening 17 and the second opening 18 may be large. Therefore, it is preferable that they are continuous openings.

[0036] In addition, each of the above embodiments merely shows an example of implementation when carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner thereby. That is, the present invention can be implemented in various forms without departing from the gist or its main features.

Explanation of Reference Numerals

[0037] 1 Signal line (differential transmission line) 2 Connector 2a Connector pin 3 Device 3a Device pin 4, 5 Land (capacitive load) 6 Passive component (capacitive load) 11, 12, 13 GND layer 17 First opening 18 Second opening

Claims

1. In a multilayer substrate structure in which a plurality of GND layers are provided hierarchically for a differential transmission path formed by a pair of signal lines, Among the plurality of GND layers, an opening penetrating in a layer direction is provided in one or more GND layers from the layer closest to the uppermost layer on which the signal line is formed, The opening is formed in a first region facing a region including a capacitive load connected to the signal line on the top layer, and in a second region facing a region including the signal line but not including the capacitive load on the top layer. A multilayer substrate structure characterized by:

2. 2. The multilayer substrate structure according to claim 1, wherein the second region is a region continuous with the first region.

3. An impedance matching method for a multilayer substrate structure in which a plurality of GND layers are hierarchically provided for a differential transmission path formed by a pair of signal lines, in which when a capacitive load is connected to the signal lines, the characteristic impedance of the differential transmission path is matched so as to fall within a predetermined threshold range, comprising: an opening penetrating in the layer direction in one or more GND layers among the plurality of GND layers, starting from the layer closest to the top layer on which the signal line is formed, and forming the opening in a first region facing a region on the top layer that includes a capacitive load connected to the signal line, and in a second region on the top layer that faces a region that does not include the capacitive load but includes the signal line, thereby correcting a decrease in the characteristic impedance of the differential transmission path caused by connecting the capacitive load to the signal line.

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