JP7327265B2 - Differential signal transmission cable - Google Patents

Description

The present invention relates to a differential signal transmission cable.

A differential signal transmission cable for transmitting differential signals, comprising a pair of conductors, an insulator covering the pair of conductors, and a shield layer provided to cover the periphery of the insulator It has been known. 2. Description of the Related Art As a differential signal transmission cable for high-speed signal transmission, a differential signal transmission cable is generally used in which a metal tape is longitudinally wound around an insulator to form a shield layer.

In addition, there exists patent document 1 as prior art document information relevant to the invention of this application.

JP 2017-162565 A

In recent years, there has been a demand to use differential signal transmission cables not only for signal transmission between devices but also for signal transmission within devices. When used as wiring in equipment, it is required to be capable of being mounted at high density. In order to mount the cables for differential signal transmission at high density, it is necessary to solder the cables for differential signal transmission with a narrow pitch, and high heat resistance is required. For example, if a resin such as PE (polyethylene) with a relatively low melting point is used as an insulator for a cable for differential signal transmission, the heat generated during soldering deforms the insulator, degrading transmission characteristics. A problem arises.

In order to solve this problem, it is conceivable to use a fluororesin having a relatively high melting point as the insulator. However, when an insulator made of fluororesin is extruded, if the extrusion speed is increased, surface roughness called melt fracture occurs on the surface of the insulator. When a shield layer is formed by vertically wrapping a metal tape around an insulator with melt fracture, a gap is created between the surface of the insulator and the shield layer, resulting in a mode conversion amount (Scd21, differential mode to the common mode) becomes large, degrading the transmission characteristics. In order to suppress the occurrence of melt fracture, it is conceivable to suppress the extrusion speed of the insulator, but in this case, the productivity is lowered and the cost is increased.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a differential signal transmission cable that has a small amount of mode conversion, heat resistance that enables high-density mounting, and high productivity.

In order to solve the above problems, the present invention includes a pair of conductors, an insulator covering the pair of conductors, and a shield layer provided to cover the periphery of the insulator. The insulator is made of a fluororesin and has a surface roughness Ra of 1.9 μm or more, and the shield layer is a metal tape having a metal layer provided on one surface of a resin tape. To provide a cable for differential signal transmission, which is spirally wound around the body.

ADVANTAGE OF THE INVENTION According to this invention, the amount of mode conversions is small, it has the heat resistance which enables high-density mounting, and the cable for differential signal transmission with high productivity can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the cable for differential signal transmission based on one Embodiment of this invention, (a) is sectional drawing which shows a cross section perpendicular|vertical to a longitudinal direction, and its enlarged view, (b) is a perspective view. FIG. 4 is a graph showing the relationship between the line speed during extrusion molding of an insulator and the surface roughness of the insulator. It is a sectional view of a metal tape. FIG. 2 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a multi-pair cable using the cable for differential signal transmission of FIG. 1;

[Embodiment]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings.

1A and 1B show a differential signal transmission cable according to the present embodiment, FIG. As shown in FIGS. 1A and 1B, the differential signal transmission cable 1 includes a pair of conductors 2, an insulator 3 covering the pair of conductors 2, and a It has a shield layer 4 provided as above and a pressure winding tape 5 wound around the shield layer 4. - 特許庁

A pair of conductors 2 are conductor wires made of copper or the like, and transmit differential signals. The pair of conductors 2 are each formed to have a circular cross-sectional shape perpendicular to the longitudinal direction, and are arranged in parallel so that the distance between the conductors 2 is constant. In this embodiment, the conductor 2 made of a silver-plated annealed copper wire with an outer diameter of 165 μm is used. Also, the arrangement pitch of the pair of conductors 2 (the distance between the centers of the conductors 2) was set to 355 μm.

In this embodiment, the insulator 3 is configured to collectively cover the pair of conductors 2 . That is, the differential signal transmission cable 1 according to the present embodiment has a two-core collective covering structure.

The insulator 3 has an elliptical or elliptical shape in cross section (a shape consisting of two parallel straight lines of equal length and a semicircular arc connecting the ends of the two straight lines, or a rectangular shape with rounded corners). ) so that its long axis direction coincides with the arrangement direction of the conductors 2 and the center of the long axis direction and short axis direction coincides with the center point of the line connecting the centers of the conductors 2 is formed in Here, the insulator 3 was formed in an elliptical shape with a major axis of 1194 μm and a minor axis of 614 μm.

In this embodiment, the insulator 3 is made of fluororesin having a high melting point and high heat resistance. This makes it possible to suppress the deformation of the insulator 3 due to heat during mounting such as soldering. can be given.

Here, the insulator 3 is made of FEP (perfluoroethylene propene copolymer), which has a small dielectric loss tangent and a small transmission loss in the GHz band. However, the fluororesin used for the insulator 3 is not limited to this, and polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluorodiode Xol copolymer (TFE/PDD), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), and the like can be used.

The insulator 3 is formed by extrusion so as to collectively cover the pair of conductors 2 . In order to increase productivity and reduce costs, it is required that the line speed (extrusion speed) during extrusion molding of the insulator 3 be as high as possible. In particular, when FEP is used as the insulator 3, since FEP is a corrosive material, if the line speed during extrusion is slowed, for example, to less than 2 m/min, the manufacturing cost will increase, and the differential signal transmission It becomes difficult to manufacture the cable 1 at low cost. However, when the insulator 3 made of fluororesin is extruded at high speed, surface roughness (microscopic irregularities, see the enlarged view in FIG. 1(a)) called melt fracture occurs on the surface of the insulator 3. put away. Due to the effect of this fine unevenness, a gap 3a is generated between the surface of the insulator 3 and the inner surface of the shield layer 6, and the effect of the gap 3a makes it easier for mode conversion from differential to common mode to occur. .

The present inventors confirmed the relationship between the linear velocity during extrusion molding and the surface roughness Ra (arithmetic mean roughness) of the insulator 3 through experiments. In the experiment, the linear speed during extrusion molding was set to 1.5 m / min, 2.0 m / min, 3.6 m / min, 7.5 m / min, and 15 m / min, and the surface roughness of the samples produced at each linear speed Ra was measured at three points, and an average value of surface roughness Ra was obtained. As the conductor 2, a 34 AWG silver-plated annealed copper wire was used, and as the insulator 3, one made of FEP was used. The extruded dimensions of the insulator 3 were 1.243 mm in major diameter and 0.637 mm in minor diameter. The surface roughness Ra was measured using a laser microscope (Keyence VK-8500) at the center of the insulator 3 in the longitudinal direction, and three different positions in the longitudinal direction. The measurement length at one point was 260 μm, and the interval between the measurement points was 1 mm. The results are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 2, the surface roughness Ra of the insulator 3 increases as the linear velocity during extrusion molding increases. In this embodiment, the extrusion molding is performed at a high speed of 2.0 m/min or more in order to increase productivity and reduce costs. Therefore, the surface roughness Ra of the insulator 3 becomes 1.9 μm or more. Therefore, it is unavoidable that a gap 3a is formed between the surface of the insulator 3 and the inner surface of the shield layer 6. Due to the influence of the gap 3a, mode conversion from differential to common mode is likely to occur. there is

Although the details will be described later, in order to suppress the influence of this mode conversion, in the present embodiment, the shield layer 4 is of a horizontally wound type to intentionally increase the common mode loss, thereby suppressing the mode conversion amount (Scd21). are doing. If the line speed during extrusion is too fast and the surface roughness Ra becomes too large, it becomes difficult to wind the shield layer 4 around the insulator 3. Therefore, the surface roughness Ra of the insulator 3 is set to 30. 0 μm or less. In addition, when the shield layer 4 (metal tape 41) is wound around the insulator 3, the insulator 3 covering the conductor 2 is formed into a cylindrical shaft alignment member having a hollow portion along the outer shape of the insulator 3. A shield layer 4 (metal tape 41) is wound around the insulator 3 after aligning the central axis by passing through. Here, since the size of the hollow portion of the shaft alignment member needs to be large considering the surface roughness Ra of the insulator 3, the surface roughness Ra of the insulator 3 becomes too large (30.0 μm larger), the axis of the insulator 3 covering the conductor 2 tends to wobble, making it difficult to wind the shield layer 4 (metal tape 41) around the insulator 3.

The shield layer 4 is configured by spirally winding a metal tape 41 around the insulator 3 . As shown in FIG. 3, the metal tape 41 is configured by providing a metal layer 41b on one surface of a resin tape 41a. In the present embodiment, a copper PET tape is used as the metal tape 41, in which a metal layer 41b made of copper with a thickness of 8 μm is provided on one surface of a resin tape 41a made of PET (polyethylene terephthalate) with a thickness of 4 μm. The width of the metal tape 41 was set to 3.5 mm. The shield layer 4 is spirally wound around the insulator 3 so that the metal layer 41b faces inside (on the insulator 3 side). Moreover, the shield layer 4 is lap-wound so that a part of the width direction of the shield layer 4 overlaps.

As described above, in the present embodiment, the shield layer 4 employs a so-called horizontal winding type shield system in which the metal tape 41 is helically wound around the insulator 3 . By adopting a horizontally wound type shielding method for the shield layer 4, it is possible to increase the common-mode loss and greatly attenuate the signal of the common-mode component, as described in Patent Document 1, for example. As a result, it is possible to reduce the amount of mode conversion (Scd21) by reducing the signal of the in-phase component that reaches the terminal. In addition, by adopting the shielding method of the horizontal winding type for the shield layer 4, compared with the case of using the shielding method of the vertical winding type in which the metal tape 41 is vertically wound, the metal tape 1 and the insulator It is also possible to reduce the gap 3a by increasing the adhesion with the 3. In other words, by adopting a horizontal winding type shielding method for the shield layer 4, the gap 3a itself between the insulator 3 and the shield layer 4 can be made smaller, and even if the gap 3a exists, the in-phase component is attenuated. It is possible to reduce the amount of mode conversion.

Note that when the shield layer of the tandem winding type shielding method is used, since the common mode loss is small, the signal of the common mode component is not attenuated, and the mode conversion amount (Scd21) becomes large. Further, the differential loss is substantially the same between the horizontal winding type shield layer 4 and the vertical side winding type shield layer 4 .

By the way, when the shield layer 4 is of a horizontal winding type, a phenomenon called suck-out occurs in which a differential signal is greatly attenuated in a specific frequency range. Therefore, it is necessary to adjust the suck-out frequency, which is the frequency at which the differential signal is greatly attenuated, so that the differential signal to be transmitted is not affected by the suck-out.

It has been found through experiments that the suck-out frequency Fs (GHz) is inversely proportional to the winding pitch P (mm) of the metal tape 41 forming the shield layer 4.
is expressed by the empirical formula of Therefore, when the band of the differential signal to be transmitted is F (GHz), the suckout frequency Fs is transmitted by setting the winding pitch P (mm) of the metal tape 41 in the shield layer 4 to be less than 72/F. It is possible to suppress the influence of suck-out by making it larger than the band F of the differential signal. If the band F of the differential signal and the suck-out frequency Fs are close to each other, the transmission loss may increase. Therefore, it is preferable to adjust the suck-out frequency Fs as large as possible to separate it from the band F of the differential signal. In this embodiment, assuming transmission at 25 Gbit, the winding pitch P of the metal tape 41 is set to 2.4 mm.

A pressure winding tape 5 is spirally wound around the shield layer 4. - 特許庁The pressing tape 5 is made of a flexible belt-like member, and has a structure in which a flexible insulating resin layer such as PET and an adhesive layer containing an adhesive are laminated. The adhesive layer may also serve as a colored layer.

The pressure winding tape 5 is spirally wound around the shield layer 4 so that the adhesive layer is inside and the resin layer is outside. By providing the pressure winding tape 5 , it is possible to suppress the separation of the metal tape 41 from the insulator 3 in the shield layer 4 . Here, a 6-mm-wide pressing tape 5 was used, which was formed by providing a 1.5-μm-thick colored layer and a 1.5-μm-thick adhesive layer on one side of a 4-μm-thick PET resin layer.

Next, a multi-pair cable 10 using the differential signal transmission cable 1 will be described. FIG. 4 is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of a multi-pair cable 10 using the cable 1 for differential signal transmission. The multi-pair cable 10 includes a plurality of bundled differential signal transmission cables 1, a shield tape 12 wrapped around the plurality of differential signal transmission cables 1, and a shield tape 12 covering the circumference of the shield tape 12. and a jacket 14 covering the braided wire 13 . A plurality of differential signal transmission cables 1 are collectively shielded by a shield tape 12 and a braided wire 13 .

The number of differential signal transmission cables 1 is eight in the example shown in FIG. In the example shown in FIG. 4, two differential signal transmission cables 1 are arranged in the cross-sectional center of a multi-pair cable 10, and six differential signal transmission cables 1 are arranged around them via interpositions 11. placed at intervals.

As materials for the shield tape 12, the braided wire 13, and the jacket 14, materials used in general cables can be used. Interposer 11 consists of paper, thread or foam, for example. The foam is, for example, expanded polyolefin such as expanded polypropylene or expanded ethylene.

(Actions and effects of the embodiment)
As described above, in the differential signal transmission cable 1 according to the present embodiment, the insulator 3 is made of fluororesin, the surface roughness Ra of the insulator 3 is 1.9 μm or more, and the shield layer 4 is A metal tape 41 having a metal layer 41b provided on one surface of a resin tape 41a is spirally wound around the insulator 3. As shown in FIG.

By using a fluororesin such as FEP, which has a relatively high melting point, as the insulator, deformation of the insulator 3 during soldering can be suppressed and, for example, high-density mounting within equipment becomes possible. Further, in the differential signal transmission cable 1, the surface roughness Ra of the insulator 3 may be 1.9 μm or more due to melt fracture. , can be manufactured at low cost with high productivity. Furthermore, by adopting a horizontally wound type shielding method for the shield layer 4, even if a gap 3a occurs between the insulator 3 and the shield layer 4 due to the influence of melt fracture, the common-mode signal is attenuated and the mode It is possible to reduce the conversion amount (Scd21) and realize good transmission characteristics.

As described above, according to the present embodiment, it is possible to realize the differential signal transmission cable 1 that has a small amount of mode conversion, heat resistance that enables high-density mounting, and high productivity.

Note that the surface roughness Ra may be set to 3.0 μm or more in order to further improve productivity. In this case, extrusion molding can be performed at a high speed of 4.0 m/min or more, for example, and it is possible to further improve productivity and manufacture the differential signal transmission cable 1 at low cost.

(Summary of embodiment)
Next, technical ideas understood from the embodiments described above will be described with reference to the reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description do not limit the constituent elements in the claims to the members and the like specifically shown in the embodiment.

[1] A pair of conductors (2), an insulator (3) covering the pair of conductors (2), and a shield layer (4) provided to cover the periphery of the insulator (3) and, the insulator (3) is made of fluororesin, the surface roughness Ra of the insulator (3) is 1.9 μm or more, and the shield layer (4) is a resin tape (41a) A differential signal transmission cable (1) comprising a metal tape (41) having a metal layer (41b) provided on one surface of the insulator (3) spirally wound around the insulator (3).

[2] The differential signal transmission cable (1) according to [1], wherein the insulator (3) is configured to collectively cover the pair of conductors (2).

[3] The differential signal transmission cable (1) according to [1] or [2], wherein the insulator (3) is made of a perfluoroethylene propene copolymer.

[4] The winding pitch of the metal tape (41) on the shield layer (4) is less than 72/F (mm), where F (GHz) is the band of the differential signal to be transmitted. A differential signal transmission cable (1) according to any one of [3].

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the scope of claims. Also, it should be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

The present invention can be appropriately modified and implemented without departing from the gist thereof. For example, in the above embodiment, the insulator 3 is formed so as to cover the pair of conductors 2 together. structure.

DESCRIPTION OF SYMBOLS 1...Cable for differential signal transmission 2...Conductor 3...Insulator 4...Shield layer 41...Metal tape 41a...Resin tape 41b...Metal layer 5...Pressure winding tape

Claims (4)

a pair of conductors;
an insulator covering the pair of conductors;
a shield layer provided to cover the periphery of the insulator,
the insulator is made of fluororesin,
The insulator has a surface roughness Ra of 1.9 μm or more,
The shield layer is configured by spirally winding a metal tape having a metal layer on one side of a resin tape around the insulator.
Cable for differential signal transmission. The insulator is configured to collectively cover the pair of conductors,
The cable for differential signal transmission according to claim 1. wherein the insulator consists of a perfluoroethylene propene copolymer;
The cable for differential signal transmission according to claim 1 or 2. When the band of the differential signal to be transmitted is F (GHz),
The winding pitch of the metal tape in the shield layer is less than 72/F (mm).
The cable for differential signal transmission according to any one of claims 1 to 3.

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