JP5874595B2 - Differential signal transmission cable - Google Patents

Description

  The present invention relates to a differential signal transmission cable.

  As a differential signal transmission cable, a twinax cable in which two insulated wires are arranged in parallel without being twisted and covered with a shield conductor is known. The twinax cable is used for high-speed signal transmission of several Gbps or more.

  The twinax cable includes a cable using a tape with a conductor as a shield conductor and a cable using a braided wire. When a tape with metal foil (tape material is an insulator such as PET) is used as a shield conductor and is wound around an insulated wire so as to have a spiral shape and an overlap portion, the attenuation-frequency characteristic of the cable is 10 GHz. A sudden drop (this is usually referred to as a sac-out) occurs in the above high frequency region. This is considered to be caused by a structure in which the insulator is sandwiched between the metal foil and the metal foil at the overlap portion. Therefore, since it is greatly affected by sackout in high-speed signal transmission applications of 10 Gbps or more, it is difficult to use the cable for the same application.

  In recent years, as the speed of signal transmission has been accelerated, a twinax cable capable of suppressing suck-out has been demanded.

  On the other hand, as a single-core coaxial cable, an insulating layer is provided around the signal line, and a metal vapor-deposited tape in which metal is vapor-deposited on at least one surface of the insulating tape is spirally wound around the insulating layer. A coaxial cable in which a shield ground layer is formed, and the metal vapor-deposited tape with the metal surface facing inward is overlapped with a plurality of spiral loops made of the metal vapor-deposited tape with the metal surface facing outward. Patent Document 1 discloses a coaxial cable characterized by joining the spiral loops in the winding axis direction. Patent Document 1 describes that the invention can be developed into a two-core parallel coaxial cable.

  Further, in Patent Document 1, as a problem in the horizontal winding in which the shield tape is wound in a spiral shape, a gap that cannot be conducted caused by winding the metal vapor-deposited tape a little overlapped, the signal return current is applied to the shield ground layer. It describes that transmission loss deteriorates as a coaxial cable because it functions as a slot antenna when it flows (paragraph [0011]).

JP 2010-33928 A (Claim 1, paragraph [0032])

  According to the invention described in Patent Document 1, it is considered that the above problem can be solved in a single-core coaxial cable (paragraph [0014]), but when applied to a twinax cable, the cross-section of the twinax cable is single. Since it is not circular like a core coaxial cable, it is difficult to wind two layers of metal foil tape with a uniform pitch and a half pitch, and a portion where the upper and lower two layers of tape are almost overlapped is formed. Since this overlapping portion causes sack out, the manufacturing yield is deteriorated. Moreover, since the tape with metal foil is wound twice, the manufacturing process becomes complicated. Furthermore, there is a problem that attenuation due to slight resonance occurs.

  Therefore, an object of the present invention is to provide a differential signal transmission cable with a small attenuation in a high frequency region of 10 GHz or more.

  In order to achieve the above object, the present invention provides the following differential signal transmission cables [1] to [6].

[1] An insulated wire formed by covering two core wires arranged in parallel with an insulator, and a shield tape wound around the insulated wire in a spiral shape so as to have an overlap portion Prepared,
The cable for differential signal transmission, wherein the shield tape is made of a metal foil having a tensile strength of 150 to 450 N / mm ² at room temperature and has a roughened surface subjected to a roughening process .
[ 2 ] The differential signal transmission cable according to [ 1 ], wherein the shield tape is spirally wound around the insulated wire so that the roughened surface faces outward. .
[ 3 ] The differential signal transmission cable according to [ 1 ] or [ 2 ], wherein the roughened surface has a surface roughness (Rz) of 1 to 2 μm.
[ 4 ] The differential signal transmission cable according to any one of [1] to [ 3 ], wherein the metal foil is a copper foil.
[ 5 ] The differential signal transmission cable according to [ 4 ], wherein the copper foil is a rolled copper foil.

  ADVANTAGE OF THE INVENTION According to this invention, the cable for differential signal transmission with a small attenuation amount of the high frequency area | region of 10 GHz or more can be provided.

It is a perspective view of the cable for differential signal transmission (in the middle of manufacture) concerning an embodiment of the invention. It is sectional drawing which shows the principal part of the cable longitudinal direction of the cable for differential signal transmission which concerns on embodiment of this invention. It is a figure which shows the attenuation amount-frequency characteristic of the cable for differential signal transmission which concerns on an Example and a comparative example.

(Configuration of differential signal transmission cable)
FIG. 1 is a perspective view of a differential signal transmission cable (during manufacturing) according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the main part in the cable longitudinal direction of the differential signal transmission cable according to the embodiment of the present invention.

A differential signal transmission cable 10 according to an embodiment of the present invention is an insulated wire formed by covering two core wires (signal line conductors) 1 forming a differential pair arranged in parallel with an insulator 2. 3 and a shield tape 4 wound around the insulated wire 3 in a spiral shape so as to have an overlap portion 40. The shield tape 4 has a tensile strength of 150 to 450 N / mm ² at room temperature. Made of metal foil. In addition, normal temperature is 5-35 degreeC, and should just be 150-450 N / mm < ² > in any temperature within the range of 5-35 degreeC.

  As shown in FIG. 1, the cable 10 for differential signal transmission is wound around the shield tape 4 so that the presser winding tape 5 is spirally reversed from the shield tape 4 and has an overlap portion 50. It is preferable in that the winding of the shield tape 4 after the manufacturing process and after manufacturing can be prevented. The overlap portion 50 refers to a portion where the press winding tape 5 wound around the nth winding and the presser winding tape 5 wound around the (n + 1) th winding overlap each other around the shield tape 4 in a spiral manner. (N is a positive integer not including 0).

  The core wire 1 is, for example, a single wire of a good electric conductor such as copper, or a single wire obtained by plating the electric conductor.

  The insulator 2 is formed using a material having a small dielectric constant and dielectric loss tangent, for example. This material is, for example, a foamed insulating resin such as polytetrafluoroethylene (PTFE), polyethylene, perfluoroalkoxyalkane (PFA), foamed polyethylene or foamed Teflon.

  As shown in FIG. 1, the insulated wire 3 may have a form in which two core wires 1 are each covered with a separate insulator 2, or a form in which the two core wires 1 are collectively covered with the insulator 2. (Not shown). In the case of batch coating, the cross-sectional shape of the insulator 2 may be a flat elliptical shape having a flat portion parallel to the alignment direction of the two core wires 1 or an elliptical shape long in the alignment direction of the two core wires 1. Also good. The insulated wire 3 can be manufactured, for example, by two-core batch extrusion.

  The shield tape 4 is wound around the insulated wire 3 so as to have a spiral shape and an overlap portion 40. The overlap part 40 refers to a portion where the shield tape 4 wound around the nth winding and the shield tape 4 wound around the (n + 1) th winding overlap each other around the insulated wire 3 in a spiral manner (n Is a positive integer not including 0). The width of the overlap portion 40 is preferably 1/4 to 4/5 of the tape width of the shield tape, more preferably 1/3 to 3/4, and more preferably 1/3 to 1/2. More preferably.

The shield tape 4 is made of a metal foil having a tensile strength of 150 to 450 N / mm ² at room temperature. Tensile strength is preferably 200~450N / mm ² at room temperature, more preferably 350~450N / mm ² at room temperature. The metal foil is preferably a copper foil. The copper foil is preferably a rolled copper foil, but an electrolytic copper foil can also be used.

  The shield tape 4 preferably has a roughened surface 41 that has been roughened and a non-roughened surface 42 that has not been roughened.

  The shield tape 4 is preferably spirally wound around the insulated wire 3 so that the roughened surface 41 faces outward (the non-roughened surface 42 faces inward).

  The surface roughness (Rz) of the roughened surface 41 is preferably 1 to 2 μm.

  The shield tape 4 may have various thicknesses and widths as appropriate, but is preferably 8 to 12 μm thick and 4 to 10 mm wide, more preferably 9 to 10 μm thick and 5 to 6 mm wide. preferable.

  As a material of the presser winding tape 5, for example, PET (polyethylene terephthalate) can be used.

(Application of differential signal transmission cable)
The differential signal transmission cable 10 according to the present embodiment is suitable for high-speed transmission with a large capacity of several Gbps or more, and can be suitably used for high-speed transmission of 10 Gbps or more class. It can be used for each cable of multi-core harnesses that perform high-speed signal transmission, and can be applied to cable assemblies used in routers, switches, and servers installed in data centers and the like. Further, the present invention can be applied to a cable assembly used for a personal computer (PC), a hard disk (HDD) or the like. Furthermore, the present invention can be applied to a cable device (active cable) used for the above purpose. You may use for the active cable combined with the transmission / reception IC.

(Effect of the embodiment of the present invention)
According to the present embodiment, the following effects can be obtained.
(1) A differential signal transmission cable having a small attenuation in a high frequency region of 10 GHz or more can be provided.

(2) Since a suck-out in a high frequency region of 10 GHz or more can be suppressed, a differential signal transmission cable capable of transmission of 10 Gbps or more can be realized.

(3) Since one side of the shield tape is a roughened conductor surface, the roughened surface comes into contact with the smooth surface (non-roughened surface) where the tape overlaps. A differential signal transmission cable that hardly generates slight attenuation can be realized.

(4) Since the shield tape is spirally wound around the insulated wire so that the roughened surface faces outward, an increase in attenuation in the high frequency region is seen compared to the case without the roughened surface. Absent. This is because the high-frequency signal flows only on the conductor surface due to the skin effect of the conductor and flows so as to oppose the current of the core wire, and therefore flows only inside the shield tape, that is, on the non-roughened surface. For this reason, there is no increase in attenuation due to high-frequency signals flowing through the roughened surface. In addition, since “in-phase signal components” that are noise and extra signal components flow on the roughened surface of the shield tape, there is an effect of reducing “in-phase signal components”. This is effective in improving noise resistance and removing in-phase signal components.

(5) Since there is no need to wind the shield tape twice, the manufacturing process can be simplified and can be produced stably and at low cost.

  FIG. 3 is a diagram illustrating attenuation-frequency characteristics of the differential signal transmission cables according to the example and the comparative example.

  The attenuation-frequency characteristics of the differential signal transmission cables (Examples 1 and 2) according to the embodiment of the present invention and the conventional differential signal transmission cable (Comparative Example 1) were measured. The differential signal transmission cables used are as shown in Table 1 below, and the shield tape was wound spirally so that the overlap portion was 1/3 of the tape width of the shield tape.

  As shown in FIG. 3, while Comparative Example 1 using a PET tape with Cu foil as the shield tape is drastically attenuated near 15 GHz, Cu foil (outer surface is roughened) is used as the shield tape. Example 1 used was not attenuated, and Example 2 using Cu foil (no roughened surface, non-roughened surface on both sides) as a shield tape had almost no attenuation (attenuation amount was a comparative example). It was confirmed that it was very small compared to 1.

10: Cable for differential signal transmission 1: Core wire (signal line conductor) 2: Insulator 3: Insulated wire 4: Shield tape 40: Overlapping part, 41: Roughened surface, 42: Non-roughened surface 5: Presser winding tape 50: Overlap part

Claims (5)

An insulated electric wire formed by covering two core wires arranged in parallel with an insulator, and a shield tape wound around the insulated wire in a spiral shape so as to have an overlap portion;
The cable for differential signal transmission, wherein the shield tape is made of a metal foil having a tensile strength of 150 to 450 N / mm ² at room temperature and has a roughened surface subjected to a roughening process . The differential signal transmission cable according to claim 1 , wherein the shield tape is spirally wound around the insulated wire so that the roughened surface faces outward. Differential signal transmission cable according to claim 1 or claim 2 surface roughness of the roughened surface (Rz) is characterized in that it is a 1 to 2 [mu] m. The differential signal transmission cable according to any one of claims 1 to 3 , wherein the metal foil is a copper foil. The cable for differential signal transmission according to claim 4 , wherein the copper foil is a rolled copper foil.

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