JP6060759B2 - Differential signal transmission cable connection structure and cable connector assembly - Google Patents

Description

  The present invention relates to a connection structure between a differential signal transmission cable and a substrate.

  In electronic devices such as servers, routers, and storages that handle high-speed digital signals of several Gbit / s or more, a differential interface standard (for example, LVDS (Low Voltage Differential Signal)) is adopted, and each circuit between or within each device. Differential transmission using a differential signal transmission cable is performed between the substrates.

  A general differential signal transmission cable includes a pair of core wires. A positive side (positive) signal and a negative side (negative) signal with the phase inverted by 180 degrees are transmitted to each core wire. The potential difference between these two signals (plus signal and minus signal) becomes the signal level. For example, if the potential difference is plus, it is “High”, and if it is minus, it is “Low”. It can be recognized.

  FIG. 6 is a perspective view showing an example of a conventional connection structure between a differential signal transmission cable and a substrate. The illustrated differential signal transmission cable 101 includes a pair of core wires 102 a and 102 b arranged in parallel at a predetermined interval, and these core wires 102 a and 102 b are covered with an insulator 103. The insulator 103 is covered with a shield conductor 104, and the shield conductor 104 is covered with an outer skin 105.

  In the connection structure shown in FIG. 6, the two core wires 102 a and 102 b of the differential signal transmission cable 101 are respectively connected to a pair of differential grant coplanar wires 122 and 123 formed on the surface of the substrate 110. Yes. Further, the shield conductor 104 of the differential signal transmission cable 101 is connected to the outer ground layer 120 which is also formed on the surface of the substrate 110. The outer ground layer 120 is connected to an inner ground layer (not shown) formed inside the substrate 110 via a via (not shown).

JP 2012-64338 A

  There are two differential signal transmission modes, “differential mode” and “common mode”. In the differential mode, two signals whose phases are inverted by 180 degrees are transmitted, and in the in-phase mode, two signals having the same phase are transmitted. In the differential transmission, it is desirable to always maintain the differential mode. However, the transmission mode changes from the differential mode to the common mode or from the common mode to the differential mode due to various factors.

  Here, when a differential signal is transmitted using surface layer wiring such as the differential grant coplanar wiring 122 and 123 shown in FIG. 6, the transmission speed in the differential mode is the effective dielectric constant between the surface layer wirings. Determined by. That is, the transmission speed in the differential mode depends on the dielectric constant of air and the substrate. On the other hand, the transmission speed in the common mode depends on the dielectric constant of the substrate interposed between the surface layer wiring and the ground layer below it. Therefore, the signal propagation speed differs between the differential mode and the common mode. For this reason, the signal deteriorates due to the dispersion between the differential mode and the common mode. Further, since the signal propagates through the surface wiring, noise is likely to be radiated and susceptible to noise. For this reason, when a plurality of cables for differential signal transmission are arranged at high density, signal degradation due to crosstalk tends to occur.

  An object of the present invention is to further improve the transmission quality of differential signals.

  In the connection structure between the differential signal transmission cable and the substrate of the present invention, the outer ground layer provided on the surface of the substrate, the inner ground layer provided on the inner side of the substrate, the inner side of the substrate, A wiring layer provided between the inner ground layer and the outer ground layer, and an interlayer connection conductor that connects the outer ground layer and the inner ground layer through the substrate are provided. The core of the differential signal transmission cable is connected to a part of the wiring layer exposed on the surface of the substrate, and the shield conductor of the differential signal transmission cable is exposed on the surface of the substrate. Connected to a portion of the inner ground layer.

  In one aspect of the present invention, the shield conductor of the differential signal transmission cable is connected to the outer ground layer via a connection conductor.

  In another aspect of the present invention, the core wire of the differential signal transmission cable and a part of the wiring layer to which the core wire is connected are covered with the connection conductor.

  In another aspect of the invention, the substrate includes a first dielectric layer, a second dielectric layer stacked on the first dielectric layer with the inner ground layer interposed therebetween, and the wiring layer. A third dielectric layer stacked on the second dielectric layer and having the outer ground layer formed on a surface thereof; A part of the wiring layer to which the core wire of the differential signal transmission cable is connected protrudes outward from the end surface of the third dielectric layer. A part of the inner ground layer extending to the surface and connected to the shield conductor of the differential signal transmission cable protrudes outward from an end face of the second dielectric layer. Extending on the surface of the dielectric layer.

  The cable connector assembly of the present invention includes a connector board having the same configuration as the board in any of the above aspects, and a differential signal transmission cable connected to the connector board.

  According to the present invention, further improvement in transmission quality of differential signals is realized.

It is a perspective view which shows an example of the cable for differential signal transmission, and the board | substrate connected by the connection structure of this invention. (A) is a schematic sectional view of the cable for differential signal transmission and the substrate shown in FIG. 1, and (b) is a plan view of the same. It is a perspective view which shows another example of the cable for differential signal transmission, and the board | substrate connected by the connection structure of this invention. It is a perspective view which shows another example of the cable for differential signal transmission and the board | substrate connected by the connection structure of this invention. It is a typical top view which shows one of the modifications of a connection conductor. It is a perspective view of the cable for differential signal transmission and the board | substrate connected by the conventional connection structure.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. First, each of the differential signal transmission cable and the board to be connected will be described, and then the connection structure between them will be described.

  As shown in FIG. 1, the differential signal transmission cable 1 includes a pair of core wires 2a and 2b. A positive signal is transmitted as a differential signal to one of the cores 2a and 2b, and a negative signal is transmitted as a differential signal to the other of the cores 2a and 2b. The Each of the core wires 2a and 2b is formed of, for example, an annealed copper wire (Tinned Annealed Copper Wire) whose surface is tin-plated. The pair of core wires 2 a and 2 b are collectively covered with a common insulator 3.

  The insulator 3 is formed of, for example, polyethylene resin, fluorine resin, polyvinyl chloride resin, etc. in order to give the differential signal transmission cable 1 flexibility, and the differential signal transmission cable 1. The shape in a cross section (transverse cross section) orthogonal to the longitudinal direction is substantially elliptical.

  The insulator 3 holds the core wires 2a and 2b so that the pair of core wires 2a and 2b are arranged in parallel at a predetermined interval. The insulator 3 is formed so that the thicknesses around the cores 2a and 2b are substantially equal. The material of the insulator 3 in this embodiment is foamed polyethylene, and its melting temperature is set to 110 [° C.] to 120 [° C.].

  The insulator 3 is covered with a shield conductor 4 in order to suppress the influence of external noise. The shield conductor 4 is covered with an outer skin (sheath) 5. The outer skin 5 is made of polyethylene resin, fluorine resin, polyvinyl chloride resin, or the like. Although illustration is omitted, the shield conductor 4 has a double structure including a sheet-like base material and a metal conductor layer formed on one surface of the base material. The metal conductor layer is formed of, for example, copper foil.

  As shown in FIGS. 1 and 2, the substrate 10 forms a lower substrate 11 that forms a first dielectric layer, an intermediate substrate 12 that forms a second dielectric layer, and a third dielectric layer. The upper substrate 13 is laminated in this order, and is an integrated laminate. The lower substrate 11, the intermediate substrate 12, and the upper substrate 13 are all made of a dielectric material. That is, the substrate 10 is a dielectric substrate.

  As shown in FIG. 1, an outer ground layer 20 is formed on the surface of the substrate 10. An inner ground layer 21 is formed inside the substrate 10. Further, a pair of strip-like wiring layers 22 and 23 are formed inside the substrate 10 and above the inner ground layer 21. Here, the outer ground layer 20 and the inner ground layer 21 are formed so as to overlap with the wiring layers 22 and 23 in plan view. That is, a strip line is formed on the substrate 10.

  The laminated structure of the substrate 10 will be described in more detail. As shown mainly in FIGS. 2A and 2B, an inner ground layer 21 is provided between the lower substrate 11 and the intermediate substrate 12. A pair of wiring layers 22 and 23 are provided between the intermediate substrate 12 and the upper substrate 13. Further, an outer ground layer 20 is provided on the surface of the upper substrate 13. In other words, the inner ground layer 21 is provided between the first dielectric layer and the second dielectric layer. The wiring layers 22 and 23 are provided between the second dielectric layer and the third dielectric layer. Further, the outer ground layer 20 is provided on the surface of the third dielectric layer. The outer ground layer 20 and the inner ground layer 21 are connected through vias 24 as interlayer connection conductors that penetrate the substrate 10. That is, the outer ground layer 20 and the inner ground layer 21 are kept at the same potential (ground potential).

  As shown in FIG. 1, the lower substrate 11, the intermediate substrate 12, and the upper substrate 13 have the same width (W). On the other hand, the overall lengths of the lower substrate 11, the intermediate substrate 12, and the upper substrate 13 are different from each other. Specifically, the total length (L1) of the lower substrate 11 is the longest, and the total length (L3) of the upper substrate 13 is the shortest. The total length (L2) of the intermediate substrate 12 is shorter than the total length (L1) of the lower substrate 11 and longer than the total length (L3) of the upper substrate 13.

  As described above, the lower substrate 11, the intermediate substrate 12, and the upper substrate 13 having different overall lengths are stacked so that one end surface in the longitudinal direction thereof is flush with each other. As a result, the other ends in the longitudinal direction of these three substrates 11, 12, 13 are shifted stepwise. Specifically, as shown in FIGS. 2A and 2B, the end of the lower substrate 11 on the right side of the paper surface protrudes outward from the end surface of the intermediate substrate 12 on the right side of the paper surface. Further, the end of the intermediate substrate 12 on the right side of the paper surface protrudes outward from the end surface of the upper substrate 13 on the right side of the paper surface. The inner ground layer 21 provided between the lower substrate 11 and the intermediate substrate 12 extends to the surface of the protruding end portion 11 a of the lower substrate 11 protruding from the end surface of the intermediate substrate 12. In addition, the wiring layers 22 and 23 provided between the intermediate substrate 12 and the upper substrate 13 extend to the surface of the protruding end portion 12 a of the intermediate substrate 12 protruding from the end surface of the upper substrate 13. . That is, most of the inner ground layer 21 and the wiring layers 22 and 23 are embedded inside the substrate 10, but a part is exposed on the surface of the substrate 10. Therefore, in the following description, a part of the inner ground layer 21 exposed on the surface of the substrate 10 is referred to as an “exposed portion 21a”. Also, a part of each of the wiring layers 22 and 23 exposed on the surface of the substrate 10 is referred to as “exposed portion 22a” and “exposed portion 23a”.

  Next, a connection structure between the differential signal transmission cable 1 and the substrate 10 will be described. As shown in FIG. 1, the differential signal transmission cable 1 is subjected to terminal processing, and the core wires 2 a and 2 b protrude from the end face of the insulator 3. Further, a part of the outer skin 5 is removed and a part of the shield conductor 4 is exposed.

  Please refer to FIG. In the differential signal transmission cable 1, the exposed shield conductor 4 is placed on the protruding end portion 11 a of the lower substrate 11 and overlaps the exposed portion 21 a of the inner ground layer 21, and the core wires 2 a and 2 b are protruded from the intermediate substrate 12. It is placed on the end portion 12 a and overlapped with the exposed portions 22 a and 23 a of the wiring layers 22 and 23. The lower portion in the radial direction of the shield conductor 4 superimposed on the exposed portion 21a of the inner ground layer 21 is joined to the exposed portion 21a by solder. Similarly, the core wires 2a and 2b superimposed on the exposed portions 22a and 23a of the wiring layers 22 and 23 are joined to the exposed portions 22a and 23a by solder.

  As shown in FIG. 1, the radial direction upper part of the shield conductor 4 of the differential signal transmission cable 1 and the outer ground layer 20 provided on the surface of the upper substrate 13 are connected via a plate-like connection conductor 30. Has been. The connection conductor 30 includes a covering portion 31 that covers an upper portion in the radial direction of the shield conductor 4 and a pair of arm portions 32a and 32b that extend from both sides in the width direction of the covering portion 31 toward the outer ground layer 20 in plan view. Presents a substantially U-shaped shape. That is, an opening 33 exists between the pair of arms 32 a and 32 b, and the core wires 2 a and 2 b of the differential signal transmission cable 1 are exposed from the opening 33. The covering portion 31 of the connection conductor 30 is joined to the shield conductor 4 by solder, and the respective arm portions 32a and 32b are joined to the outer ground layer 20 by solder. Here, as described above, the outer ground layer 20 and the inner ground layer 21 are maintained at the ground potential. That is, the inner ground layer 21, the outer ground layer 20, the connection conductor 30, and the shield conductor 4 are kept at the same potential (ground potential).

  In the present embodiment, wiring layers 22 and 23 to which the core wires 2 a and 2 b of the differential signal transmission cable 1 are connected are provided inside the substrate 10. That is, the signal input from the differential signal transmission cable 1 to the substrate 10 is transmitted via the inner layer wiring. Therefore, the effective dielectric constants in the differential mode and the in-phase mode are uniform, and the propagation speeds between the two modes match. Furthermore, since the ground layers (the inner ground layer 21 and the outer ground layer 20) are provided above and below the wiring layers 22 and 23, noise emission from the substrate 10 is reduced, and signal degradation due to crosstalk is suppressed. In addition, since the inner ground layer 21, the outer ground layer 20, the connection conductor 30, and the shield conductor 4 are kept at the same potential, impedance matching is facilitated. According to the simulation conducted by the present inventors, improvement of the characteristic impedance was confirmed in both the differential mode and the common mode. Specifically, the maximum fluctuation range of the characteristic impedance in the differential mode was reduced from around 7% to around 4%. In addition, the maximum fluctuation width of the characteristic impedance in the common mode was reduced from around 18% to around 7%.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to FIG. However, the same components as those already described are denoted by the same reference numerals in FIG.

  In the substrate 10 shown in FIG. 3, the entire length of the intermediate substrate 12 is expanded, and the end opposite to the protruding end 12 a of the intermediate substrate 12 also protrudes outward from the end surfaces of the lower substrate 11 and the upper substrate 13. The wiring layers 22, 23 provided between the intermediate substrate 12 and the upper substrate 13 are the surfaces of the protruding end portions 12 b of the intermediate substrate 12 protruding outward from the end surfaces of the lower substrate 11 and the upper substrate 13. It extends to. That is, in the first embodiment, only one end side in the longitudinal direction of each wiring layer 22, 23 is exposed on the surface of the substrate 10, whereas in this embodiment, the longitudinal direction of the wiring layers 22, 23, etc. The end side is also exposed on the surface of the substrate 10.

  The substrate 10 having the above structure functions as a connector substrate. For example, the exposed portions 22a and 23a of the wiring layers 22 and 23 exposed on the surface of the protruding end 12b are inserted into the mating connector (female connector) (not shown) by inserting the protruding end 12b of the intermediate substrate 12 into the mating connector. It can be connected to a wiring layer or a contact terminal provided in the connector. That is, the differential signal transmission cable 1 can be connected to another substrate in the same device, a substrate in another device, or the like. In other words, the board 10 shown in FIG. 3 and the differential signal transmission cable 1 connected to the board 10 constitute a cable connector assembly as a whole.

  As shown in FIG. 4, the substrate 10 shown in FIG. 3 can be widened, and a plurality of differential signal transmission cables 1 can be connected to the common substrate 10. In this case, a plurality of differential signal transmission cables 1 can be collectively connected to another substrate in the same device, a substrate in another device, or the like via the substrate 10 functioning as a connector substrate.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. One modification of the above embodiment is shown in FIG. The illustrated modification is different from the above embodiment with respect to the connection conductor 30. Specifically, in the connection conductor 30 shown in FIG. 1, FIG. 3, and the like, an opening 33 exists between the pair of arms 32 a and 32 b, and the differential signal transmission cable 1 extends from the opening 33. The core wires 2a and 2b were exposed. On the other hand, the connection conductor 30 shown in FIG. 5 has no opening. That is, the connecting conductor 30 shown in FIG. 5 is rectangular in plan view, and the exposed portions 22a and 23a of the wiring layers 22 and 23 and the core wires 2a and 2b joined to the exposed portions 22a and 23a are connected to the connecting conductor 30. Covered by. Since the connection portions between the wiring layers 22 and 23 and the core wires 2a and 2b are covered by the connection conductor 30, impedance matching is further facilitated, and noise emission from the connection portions is reduced, which is caused by crosstalk. Signal degradation is further suppressed. That is, the connection conductor 30 also has a function as a shield cover.

  In the above embodiment, the lower substrate 11, the intermediate substrate 12, and the upper substrate 13 have different overall lengths, so that the inner ground layer 21 and the wiring layers 22 and 23 are partially exposed (FIG. 1). However, it is also possible to expose the inner ground layer by notching a part of the second substrate that is overlaid on the first substrate on which the inner ground layer is formed. Further, a part of the third substrate which is overlaid on the second substrate on which the wiring layer is formed can be cut out to expose a part of the wiring layer.

  Rather than superimposing a plurality of substrates on which conductor layers are formed in advance, the formation of the dielectric film and the conductor film and the etching are repeated, so that the first dielectric layer is sandwiched between the first dielectric layer and the inner ground layer. It is also possible to form a second dielectric layer laminated on the layer and a third dielectric layer laminated on the second dielectric layer with the wiring layer interposed therebetween and having an outer ground layer formed on the surface. .

  The shape of the connection conductor is not limited to a specific shape. For example, the connection conductor may be T-shaped or U-shaped in plan view. In short, the shape of the connection conductor may be any shape that can connect the outer ground layer of the substrate and the shield conductor of the differential signal transmission cable, and can cover the connection portion between the wiring layer and the core wire. If better.

DESCRIPTION OF SYMBOLS 1 Differential signal transmission cable 2a, 2b Core wire 4 Shield conductor 10 Board | substrate 11 Lower board 12 Intermediate board 13 Upper board | substrate 11a, 12a, 12b Projection end part 20 Outer ground layer 21 Inner ground layer 22, 23 Wiring layer 21a, 22a , 23a Exposed portion 24 Via 30 Connection conductor

Claims (6)

A connection structure between a differential signal transmission cable and a board,
An outer ground layer provided on the surface of the substrate;
An inner ground layer provided inside the substrate;
A wiring layer provided inside the substrate and between the inner ground layer and the outer ground layer;
An interlayer connection conductor passing through the substrate and connecting the outer ground layer and the inner ground layer;
The substrate includes a first dielectric layer, a second dielectric layer stacked on the first dielectric layer with the inner ground layer interposed therebetween, and a second dielectric layer with the wiring layer interposed therebetween. A third dielectric layer laminated and having the outer ground layer formed on a surface thereof;
The core wire of the differential signal transmission cables, a portion of the third dielectric layer and the wiring layer that extend to the surface of the projecting outwardly second dielectric layer from the end face of Connected,
Shield conductor of the differential signal transmission cables, a portion of the inner ground layer that extend to the surface of the second dielectric layer and the first dielectric layer that protrudes out of the end faces of the A connection structure between the differential signal transmission cable and the substrate, which is connected to the outer ground layer via a connection conductor that is overlaid and connected to the shield conductor, and is connected to the upper portion in the radial direction of the shield conductor . In the connection structure between the differential signal transmission cable and the substrate according to claim 1,
The connection conductor includes a covering portion that covers an upper portion in the radial direction of the shield conductor, and a pair of arms that extend from both sides in the width direction of the covering portion toward the outer ground layer, and a substrate for differential signal transmission Connection structure with. In the connection structure between the differential signal transmission cable and the substrate according to claim 1 ,
A connection structure between a differential signal transmission cable and a substrate, wherein the core of the differential signal transmission cable and a part of the wiring layer to which the core is connected are covered with the connection conductor. A cable connector assembly comprising a connector board and a differential signal transmission cable connected to the connector board,
An outer ground layer provided on the surface of the connector board;
An inner ground layer provided inside the connector board;
A wiring layer provided inside the connector board and between the inner ground layer and the outer ground layer;
An interlayer connection conductor connecting the outer ground layer and the inner ground layer through the connector board,
The substrate includes a first dielectric layer, a second dielectric layer stacked on the first dielectric layer with the inner ground layer interposed therebetween, and a second dielectric layer with the wiring layer interposed therebetween. A third dielectric layer laminated and having the outer ground layer formed on a surface thereof;
The core wire of the differential signal transmission cables, a portion of the third dielectric layer and the wiring layer that extend to the surface of the projecting outwardly second dielectric layer from the end face of Connected,
Shield conductor of the differential signal transmission cables, a portion of the inner ground layer that extend to the surface of the second dielectric layer and the first dielectric layer that protrudes out of the end faces of the A cable connector assembly that is connected to the outer ground layer via a connection conductor that is overlaid on and connected to a radial upper portion of the shield conductor . The cable connector assembly according to claim 4 , wherein
The connection conductor includes a covering portion that covers a radially upper portion of the shield conductor, and a pair of arm portions that extend from both sides in the width direction of the covering portion toward the outer ground layer . The cable connector assembly according to claim 4 , wherein
A cable connector assembly in which the core wire of the differential signal transmission cable and a part of the wiring layer to which the core wire is connected are covered with the connection conductor.

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