JP7114945B2 - Differential signal transmission cable, multicore cable, and method for manufacturing differential signal transmission cable - Google Patents

Description

The present disclosure relates to a differential signal transmission cable, a multicore cable, and a method of manufacturing a differential signal transmission cable.

2. Description of the Related Art Conventionally, differential signal transmission cables are used for signal transmission between electronic devices or signal transmission between substrates in electronic devices. Examples of electronic devices include servers, routers, and storage products that handle high-speed signals of several Gbps or more. A cable for differential signal transmission has a pair of signal lines (see Patent Document 1).

Using the cable for differential signal transmission, it is possible to perform signal transmission using differential signals to the receiving side. In signal transmission using differential signals, signals having opposite phases are input to a pair of signal lines included in a cable for differential signal transmission. The receiving side obtains an output by synthesizing the difference between the signals having opposite phases.

JP-A-2002-289047

A conventional cable for differential signal transmission includes an insulator layer covering the periphery of each signal line and a metal foil tape wound around the outer peripheral surface of the insulator layer. A gap may be formed between the outer peripheral surface of the insulator layer and the metal foil tape due to looseness of the metal foil tape or the like. When this air gap occurs, a difference occurs in propagation time between the pair of signal lines. This phenomenon is called in-pair skew. When the intra-pair skew occurs, the differential components of the signals transmitted through the pair of signal lines are converted into in-phase components, so that the waveform of the output obtained on the receiving side becomes significantly degraded.

It is conceivable to form a plating layer on the outer peripheral surface of the insulator layer instead of winding the metal foil tape around the outer peripheral surface of the insulator layer. However, the adhesion between the conventional insulator layer and the plating layer is not sufficient. Therefore, when the cable for differential signal transmission is bent, the plating layer may separate from the insulating layer, creating a gap between the plating layer and the insulating layer. If a gap occurs between the plating layer and the insulator layer, the transmission characteristics of the cable for differential signal transmission are degraded.

An object of one aspect of the present disclosure is to provide a differential signal transmission cable, a multi-core cable, and a method for manufacturing a differential signal transmission cable, each having a plating layer with high adhesion.

One aspect of the present disclosure includes a pair of signal lines, an insulator layer covering the periphery of the signal lines, a plating catalyst and a resin, a buffer layer covering the insulator layers, and a buffer layer covering the buffer layer. and a plated layer.

A cable for differential signal transmission, which is one aspect of the present disclosure, includes a buffer layer and a plating layer. Since the buffer layer contains a plating catalyst, the adhesion between the buffer layer and the plating layer is high. Therefore, the gap between the buffer layer and the plating layer becomes smaller. As a result, the transmission characteristics of the cable for differential signal transmission, which is one aspect of the present disclosure, are less likely to deteriorate.

Another aspect of the present disclosure includes a pair of signal lines, an insulator layer covering the periphery of the signal lines, a buffer layer containing ABS resin and covering the insulator layer, and a plating covering the buffer layer. and a cable for differential signal transmission.

A cable for differential signal transmission, which is another aspect of the present disclosure, includes a buffer layer and a plating layer. The buffer layer contains ABS resin. Since the ABS resin has high adhesion to the plating layer, the adhesion between the buffer layer and the plating layer is high. Therefore, the gap between the buffer layer and the plating layer becomes smaller. As a result, the transmission characteristics of the cable for differential signal transmission, which is another aspect of the present disclosure, are less likely to deteriorate.

Another aspect of the present disclosure includes a plurality of differential signal transmission cables, a conductor layer collectively covering the plurality of differential signal transmission cables, and a jacket covering the conductor layer. A multicore cable, wherein each of the plurality of differential signal transmission cables includes a differential signal transmission cable according to one aspect or another aspect of the present disclosure and an outer insulating layer covering the plating layer. It is a multi-core cable composed of

A multicore cable, which is another aspect of the present disclosure, includes a plurality of cables for differential signal transmission. Each of the multiple differential signal transmission cables includes a buffer layer and a plating layer. Since the adhesion between the buffer layer and the plating layer is high, the gap between the buffer layer and the plating layer is reduced. As a result, the transmission characteristics of the multicore cable, which is another aspect of the present disclosure, are less likely to deteriorate.

Another aspect of the present disclosure is a method of manufacturing a cable for differential signal transmission, in which a pair of signal lines are covered with an insulating layer, and the outer peripheral surface of the insulating layer contains a plating catalyst and a resin. A method of manufacturing a cable for differential signal transmission in which the cable is covered with a buffer layer and the outer peripheral surface of the buffer layer is covered with a plating layer.

According to a method of manufacturing a cable for differential signal transmission, which is another aspect of the present disclosure, a cable for differential signal transmission including a buffer layer and a plating layer can be manufactured. Since the buffer layer contains a plating catalyst, the adhesion between the buffer layer and the plating layer is high. Therefore, the gap between the buffer layer and the plating layer becomes smaller. As a result, the transmission characteristics of the cable for differential signal transmission are less likely to deteriorate.

Another aspect of the present disclosure is a method of manufacturing a cable for differential signal transmission, comprising: covering a pair of signal lines with an insulating layer; and coating the outer peripheral surface of the buffer layer with a plating layer.

According to a method of manufacturing a cable for differential signal transmission, which is another aspect of the present disclosure, a cable for differential signal transmission including a buffer layer and a plating layer can be manufactured. The buffer layer contains ABS resin. Since the ABS resin has high adhesion to the plating layer, the adhesion between the buffer layer and the plating layer is high. Therefore, the gap between the buffer layer and the plating layer becomes smaller. As a result, the transmission characteristics of the cable for differential signal transmission are less likely to deteriorate.

1 is a perspective view showing a configuration of a differential signal transmission cable 1; FIG. FIG. 2A is an electron micrograph showing the results of the adhesion test in the comparative example, and FIG. 2B is an electron micrograph showing the results of the adhesion test in the example. FIG. 3A is an electron micrograph showing the surface state of the copper plating layer formed in the first comparative example, and FIG. 3B is an electron micrograph showing the surface state of the copper plating layer formed in the second comparative example. FIG. 3C is an electron micrograph showing the surface state of the copper plating layer formed after dry ice blasting and corona discharge exposure. It is a graph which shows the correlation between arithmetic mean roughness Ra of a polyethylene substrate after performing specific surface modification treatment, and a contact angle. It is a graph which shows the correlation between the arithmetic mean roughness Ra of a polyethylene substrate after performing specific surface-modification treatment, and adhesion-wetting surface free energy. 4 is an electron micrograph showing recesses formed on the outer peripheral surface of the insulator layer by dry ice blasting. It is an X-ray diffraction pattern in a sample of an insulator layer. It is an X-ray diffraction pattern in a sample of an insulator layer. FIG. 9A is a graph showing the correlation between the crystallinity _Xc and the contact angle of the polyethylene substrate after the specific surface modification treatment, and FIG. 9B is the crystal of the perfluoroethylene propene copolymer substrate after the specific surface modification treatment. 4 is a graph showing the correlation between the degree of quenching _Xc and the contact angle. It is an X-ray diffraction pattern in a sample of an insulator layer. It is an X-ray diffraction pattern in a sample of an insulator layer. 2 is a graph showing the correlation between the (100) crystal orientation degree O ₁₀₀ and the contact angle after specific surface modification treatment. FIG. 13A is a graph showing the correlation between the crystallite size D and the contact angle in the crystalline component of polyethylene after the specific surface modification treatment, and FIG. 13B is the crystal of the perfluoroethylene propene copolymer after the specific surface modification treatment. It is a graph showing the correlation between the crystallite size D and the contact angle in the component. 1 is an explanatory diagram showing the configuration of a manufacturing system 101; FIG. 2 is an explanatory diagram showing the configuration of a manufacturing system 201; FIG. 3 is an explanatory diagram showing the configuration of a surface modification unit 203; FIG. FIG. 4 is an explanatory diagram showing another configuration of the surface modification unit 203; FIG. 4 is an explanatory diagram showing another configuration of the surface modification unit 203; 3 is a cross-sectional view showing the configuration of a multicore cable 301. FIG. 3 is a cross-sectional view showing the configuration of a differential signal transmission cable 302 included in a multicore cable 301. FIG. 5 is a graph showing differential common-mode conversion amounts of the differential signal transmission cable 1 and a comparative example; 5 is a graph showing transmission loss of the differential signal transmission cable 1 and a comparative example; 4 is a graph showing the relationship between arithmetic mean roughness Ra and transmission loss Sdd21. 1 is a cross-sectional view showing the configuration of a differential signal transmission cable 1 having a buffer layer 6. FIG. FIG. 4 is a cross-sectional view showing a method of manufacturing the differential signal transmission cable 1 including the buffer layer 6;

Embodiments of the present disclosure will be described.
1. Differential signal transmission cable (1-1) Basic configuration of differential signal transmission cable The differential signal transmission cable of the present disclosure includes a pair of signal lines and an insulating layer covering the periphery of the signal lines. and a plating layer. The plating layer covers, for example, the insulator layer.

The cable for differential signal transmission of the present disclosure may further include, for example, a buffer layer. A buffer layer overlies the insulator layer. When the differential signal transmission cable of the present disclosure includes a buffer layer, the plating layer covers the buffer layer.

A differential signal transmission cable of the present disclosure has, for example, the configuration shown in FIG. As shown in FIG. 1 , the differential signal transmission cable 1 includes a pair of signal lines 3 , an insulator layer 5 and a plating layer 7 . The insulator layer 5 covers the periphery of the signal line 3 . In the example shown in FIG. 1, the insulator layer 5 collectively covers the pair of signal lines 3 . The signal line 3 is composed of, for example, a wire. The signal line 3 may be, for example, a twisted wire formed by twisting a plurality of strands. If it is a twisted wire, the flexibility of the signal wire 3 is improved.

A differential signal transmission cable of the present disclosure has, for example, the configuration shown in FIG. As shown in FIG. 24 , the differential signal transmission cable 1 includes a pair of signal lines 3 , an insulator layer 5 , a buffer layer 6 and a plating layer 7 . The insulator layer 5 covers the periphery of the signal line 3 . A buffer layer 6 covers the insulator layer. A plating layer 7 covers the buffer layer 6 .

In the example shown in FIG. 24, the insulator layer 5 collectively covers the pair of signal lines 3 . The signal line 3 is composed of, for example, a wire. The signal line 3 may be, for example, a twisted wire formed by twisting a plurality of strands. If it is a twisted wire, the flexibility of the signal wire 3 is improved.

The differential signal transmission cable of the present disclosure preferably has a maximum differential common-mode conversion amount of −26 dB or less in a frequency band of 50 GHz or less. The amount of differential common-mode conversion is measured before winding the cable for differential signal transmission around a drum or the like. In the cable for differential signal transmission of the present disclosure, voids are less likely to occur between the plating layer and the insulator layer or buffer layer. Therefore, the differential signal transmission cable of the present disclosure can suppress the amount of differential common-mode conversion.

The differential signal transmission cable of the present disclosure can be used, for example, for signal transmission between electronic devices or signal transmission between substrates in electronic devices. Examples of electronic devices include servers, routers, and storage products that handle high-speed signals of several Gbps or more. Also, the cable for differential signal transmission of the present disclosure can be used, for example, as an acoustic cable. A differential signal transmission cable of the present disclosure is, for example, a cable that transmits a high-speed signal of 25 GHz or higher.

(1-2) Insulator Layer It is preferable that the insulator layer collectively cover the pair of signal lines. Covering collectively means covering both a pair of signal lines with an integral insulating layer. When the insulator layer collectively covers a pair of signal lines, there is no gap between the insulator layers unlike the case where each signal line is individually covered. Therefore, variations in dielectric constant in the longitudinal direction of the cable for differential signal transmission can be suppressed. As a result, the differential/common-mode conversion amount can be further suppressed.

Further, when the insulator layer collectively covers the pair of signal lines, the plating layer can be formed more uniformly on the outer peripheral surface of the insulator layer. Also, the insulator layer covering one of the pair of signal lines and the insulator layer covering the other signal line may be separate bodies.

In a cross section orthogonal to the extending direction of the pair of signal lines, the shape of the outer edge of the insulator layer is preferably oval or elliptical. In this case, it becomes easy to form a uniform plating layer over the entire outer peripheral surface of the insulator layer. In addition, it becomes easy to uniformly roughen and modify the surface of the entire outer peripheral surface of the insulator layer. An ellipse is a shape composed of two parallel straight lines facing each other and arcs connecting the ends of the straight lines.

The insulator layer can be made, for example, by extrusion. The dielectric constant of the insulator layer is preferably in the range of 1.5 to 2.5. When the dielectric constant is 1.5 or more, the manufacturing cost of the cable for differential signal transmission can be suppressed. When the dielectric constant is 2.5 or less, the transmission loss of the cable for differential signal transmission can be suppressed.

The arithmetic average roughness Ra of the outer peripheral surface of the insulator layer is preferably 0.6 μm or more. In this case, the adhesion between the plated layer and the insulator layer is high, and the plated layer is difficult to peel off from the insulator layer. Moreover, when the arithmetic mean roughness Ra is 0.6 μm or more, the adhesion between the insulating layer and the plating layer is improved, and the gap is less likely to occur between the insulating layer and the plating layer. Therefore, the amount of differential common-mode conversion can be further suppressed.

As a method of making the arithmetic average roughness Ra of the outer peripheral surface of the insulator layer 0.6 μm or more, for example, a method of surface roughening treatment such as blasting, immersion in an acidic or alkaline solution, immersion in a chromic acid solution, immersion in a chelate solution, etc. There is

Examples of the powder to be sprayed onto the object to be treated in the blasting include powder composed of dry ice, metal particles, carbon particles, oxide particles, carbide particles, nitride particles, and the like. Powder made of dry ice is preferable because it is less likely to remain in the insulator layer after blasting.

In the blasting process, the higher the speed at which the powder is ejected, the larger the arithmetic mean roughness Ra of the outer peripheral surface of the insulator layer. The longer the blasting time, the larger the arithmetic average roughness Ra of the outer peripheral surface of the insulator layer. The smaller the distance between the tip of the nozzle that ejects the powder and the outer peripheral surface of the insulator layer, the larger the arithmetic mean roughness Ra of the outer peripheral surface of the insulator layer.

The arithmetic average roughness Ra of the outer peripheral surface of the insulator layer is preferably 10 μm or less, more preferably 5 μm or less. When the thickness is 10 μm or less, transmission loss can be suppressed.
A method for measuring the arithmetic mean roughness Ra is a method using a laser microscope VK8500 manufactured by Keyence. Specific measurement conditions are as follows. Among the outer peripheral surface of the insulator layer, two points (hereinafter referred to as first measurement position and second measurement position) that are located on opposite sides and are flat or have the smallest curvature are selected. At the first measurement position, a rectangular measurement area is set in which the length of the cable in the longitudinal direction is 150 μm and the length of the cable in the circumferential direction is 120 μm. In the measurement area, the arithmetic mean roughness Ra is measured using the above laser microscope. Also at the second measurement position, the arithmetic mean roughness Ra is similarly measured. Finally, the average value of the arithmetic average roughness Ra at the first measurement position and the arithmetic average roughness Ra at the second measurement position is calculated, and the average value is taken as the arithmetic average roughness Ra on the outer peripheral surface of the insulator layer. do. Arithmetic mean roughness Ra is a value before forming a plating layer.

It was confirmed by the following test (hereinafter referred to as a first test) that the plated layer is difficult to peel off from the insulating layer when the arithmetic mean roughness Ra of the outer peripheral surface of the insulating layer is 0.6 μm or more. A substrate made of polyethylene was prepared. This substrate corresponds to the insulator layer. The substrate was subjected to blasting using dry ice as powder (hereinafter referred to as dry ice blasting). Dry ice blasting corresponds to surface roughening. The arithmetic mean roughness Ra of the surface of the substrate after dry ice blasting was 0.6 μm or more. After that, the substrate was subjected to a corona discharge exposure treatment as a surface modification treatment. As the surface modification treatment, for example, electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, ozone-containing liquid immersion, or the like may be performed. The adhesion wetting surface free energy of the surface of the substrate after the corona discharge exposure treatment was 66 mJ/m ² or more, and the contact angle was 95° or more. A method for measuring the adhesion wetting surface free energy will be described later.

After the corona discharge exposure treatment, a copper plating layer was formed on the surface of the substrate by an electroless plating method. Next, the copper plating layer was cut in a grid pattern. The cut penetrated the copper plating layer and reached the substrate. Next, after sticking an adhesive tape to the copper plating layer, the adhesive tape was peeled off. The state of the copper plating layer at that time is shown in FIG. 2B. In FIG. 2B, 181 represents a notch. The copper plating layer did not peel off in any grid. That is, the adhesion between the copper plating layer and the substrate was high.

A comparative example was tested basically in the same manner. In the comparative example, the substrate was not subjected to surface roughening treatment and surface modification treatment. The arithmetic mean roughness Ra of the surface of the substrate was 0.13 μm. FIG. 2A shows the state of the copper plating layer when the adhesive tape was peeled off in the comparative example. In 17 out of 20 grids, the copper plating layer was peeled off, and portions 182 where the substrate was exposed were generated. That is, in the comparative example, the adhesion between the copper plating layer and the substrate was low.

The contact angle on the outer peripheral surface of the insulator layer is preferably 95° or less. In this case, it becomes easy to make the thickness of the plating layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

Examples of methods for making the contact angle on the outer peripheral surface of the insulator layer 95° or less include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, ozone-containing liquid immersion, and the like. and a method of performing surface modification treatment.

In any treatment, the contact angle can be reduced by increasing the intensity of the treatment. Also, the longer the treatment time, the smaller the contact angle. Examples of methods for enhancing the effect of surface modification by corona discharge exposure include a method of increasing voltage and a method of increasing oxygen concentration in the atmosphere for corona discharge exposure. The method of measuring the contact angle is a method of dropping a water droplet with a diameter of 1.5 mm onto the outer peripheral surface of the insulator layer and reading the contact angle. A contact angle is a value before forming a plating layer.

The absolute value of the adhesion wetting surface free energy on the outer peripheral surface of the insulator layer is preferably 66 mJ/m ² or more. In this case, it becomes easy to make the thickness of the plating layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

Examples of methods for increasing the absolute value of the adhesion wetting surface free energy on the outer peripheral surface of the insulator layer to 66 mJ/m ² or more include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ Examples include a method of surface modification treatment such as radiation irradiation and immersion in an ozone-containing liquid.

In any treatment, the higher the intensity of the treatment, the larger the absolute value of the adhesion wetting surface free energy. In addition, the longer the treatment time, the larger the absolute value of the adhesion wetting surface free energy.

The absolute value of the adhesion wetting surface free energy ΔG is calculated by the following equation (3).

式（３）におけるγ_ＬＧは定数であり、７２．７５ｍＪ／ｍ^２である。θは、絶縁体層の外周面における接触角である。付着ぬれ表面自由エネルギーΔＧは、めっき層を形成する前の時点における値である。

γ _LG in equation (3) is a constant and is 72.75 mJ/m ² . θ is the contact angle on the outer peripheral surface of the insulator layer. The adhesion wetting surface free energy ΔG is a value before forming the plating layer.

It was confirmed by the following test that a uniform plating layer can be formed when the contact angle on the outer peripheral surface of the insulator layer is 95° or less or the absolute value of the adhesion wetting surface free energy is 66 mJ/ ^m2 or more. .

A substrate made of polyethylene was prepared. This substrate corresponds to the insulator layer. The substrate was subjected to dry ice blasting treatment and then to corona discharge exposure treatment. Dry ice blasting corresponds to surface roughening. Corona discharge exposure treatment corresponds to surface modification treatment. The arithmetic mean roughness Ra of the surface of the substrate after the corona discharge exposure treatment was 0.6 μm or more. In addition, the absolute value of adhesion wetting surface free energy on the surface of the substrate after the corona discharge exposure treatment was 66 mJ/m ² or more, and the contact angle was 95° or less. Next, a copper plating layer was formed on the surface of the substrate by electrolytic plating. The thickness of the copper plating layer was three times the thickness of the copper plating layer formed in the first test. The formed copper plating layer is shown in FIG. 3C. The copper plating layer was uniformly formed. Moreover, the adhesion between the copper plating layer and the substrate was high, and the copper plating layer was not peeled off.

A first comparative example was produced basically in the same manner. However, in the first comparative example, the arithmetic mean roughness Ra of the surface of the substrate after the surface roughening treatment was less than 0.6 μm. In addition, the absolute value of adhesion wetting surface free energy on the surface of the substrate after the surface modification treatment was 66 mJ/m ² or more, and the contact angle was 95° or less. FIG. 3A shows the copper plating layer formed in the first comparative example. The copper plating layer was remarkably peeled off.

In addition, a second comparative example was produced basically in the same manner. However, in the second comparative example, the arithmetic mean roughness Ra of the surface of the substrate after the surface roughening treatment was 0.6 μm or more. In addition, the absolute value of the adhesion wetting surface free energy of the surface of the substrate after the surface modification treatment was less than 66 mJ/m ² and the contact angle was greater than 95°. The copper plating layer formed in the second comparative example is shown in FIG. 3B. A poor plating blister 191 called a blister was present on the surface of the copper plating layer, resulting in an inhomogeneous plating state.
Dry ice blasting is performed on the outer peripheral surface of the insulator layer, and then surface modification treatment (hereinafter referred to as specific surface modification treatment) that performs corona discharge exposure treatment is performed, so that arithmetic on the outer peripheral surface of the insulator layer The average roughness Ra and the contact angle or the absolute value of the adhesion wetting surface free energy can be controlled. This was confirmed by the following tests. Dry ice blasting corresponds to surface roughening. Corona discharge exposure treatment corresponds to surface modification treatment.

A substrate made of polyethylene was subjected to a specific surface modification treatment. The substrate corresponds to the insulator layer. There are multiple conditions for the specific modification treatment. FIG. 4 shows the correlation between the arithmetic mean roughness Ra and the contact angle after the specific surface modification treatment. By performing the specific surface modification treatment, the arithmetic mean roughness Ra can be made 0.6 μm or more and the contact angle can be made 95° or less.

FIG. 5 shows the correlation between the arithmetic mean roughness Ra and the adhesion wetting surface free energy after the specific surface modification treatment. By performing the specific surface modification treatment, the arithmetic mean roughness Ra can be made 0.6 μm or more, and the absolute value of the adhesion wetting surface free energy can be made 66 mJ/m ² or more.

The insulator layer preferably has recesses on its outer peripheral surface. In this case, the insulator layer and the plating layer are less likely to separate. It is preferable that the recess has a portion wider than the opening of the recess on the far side in the depth direction. In this case, the following effects are obtained. When forming the plating layer, the plating bath penetrates deep into the recess. Nucleation occurs on the inner side of the recess, and the plated layer grows on the inner side of the recess. Since the plating layer grown on the inner side of the recess is larger than the opening, it is difficult to remove from the opening. As a result, an anchor effect occurs, and the plating layer and the insulator layer are less likely to separate.

As a method of forming recesses in the insulator layer, there is a method of performing blasting. Examples of blasting include dry ice blasting. Dry ice blasting corresponds to surface roughening. FIG. 6 shows an example of recesses formed on the outer peripheral surface of the insulator layer by dry ice blasting. FIG. 6 is a cross-sectional view of the vicinity of the outer peripheral surface 72 of the insulator layer 71. As shown in FIG. A recess 73 is formed in the outer peripheral surface 72 . The recess 73 has a portion wider than the opening 74 in the recess 73 on the far side in the depth direction. The shape of this concave portion 73 is a takotsubo-like shape. In the example shown in FIG. 6, the material of the insulator layer 71 is polyethylene.

Materials for the insulator layer include, for example, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), perfluoroethylene propene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluorodiode Xol Copolymer (TFE/PDD), Polyvinylidene Fluoride (PVDF), Polychlorotrifluoroethylene (PCTFE), Ethylene-Chlorotrifluoroethylene Copolymer (ECTFE), Polyvinyl Fluoride (PVF), Silicone, Polyethylene (PE) etc.

The material of the insulator layer may be a foaming resin. When the material of the insulator layer is a foamed resin, the dielectric constant and dielectric loss tangent of the insulator layer are reduced. As a method of manufacturing an insulating layer made of a foamable resin, for example, there is a method in which a resin and a foaming agent are kneaded and foamed by controlling the temperature and pressure when molding the insulating layer. As another method of manufacturing an insulating layer made of foamable resin, for example, there is a method of injecting nitrogen gas or the like when the insulating layer is molded under high pressure, and then depressurizing and foaming.

Alternatively, an insulating layer made of a foamable resin may be manufactured as follows. An extrusion die of desired shape is installed in the extruder. The extruder is used to simultaneously extrude the pair of signal wires and the foamable resin. A foamable resin forms the insulator layer.

As the insulator layer, for example, one made of polyethylene and having a crystallinity _Xc represented by the following formula (1) of 0.744 or more is preferable. In this case, it becomes easy to make the thickness of the plating layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

前記式（１）におけるＩ_ｃは結晶成分のＸ線回折強度であり、Ｉ_ａは非晶質成分のＸ線回折強度である。

_Ic in the formula (1) is the X-ray diffraction intensity of the crystalline component, and _Ia is the X-ray diffraction intensity of the amorphous component.

Examples of methods for increasing the crystallinity _Xc of the insulating layer made of polyethylene to 0.744 or more include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, ozone A method of performing a surface modification treatment such as immersion in a containing liquid may be used. In any treatment, the crystallinity _Xc can be increased by increasing the intensity of the treatment. Further, the crystallinity _Xc can be increased as the treatment time is lengthened.

I _c and I _a in Equation (1) are calculated as follows. Using RINT2500, an X-ray diffractometer manufactured by Rigaku Corporation, the X-ray diffraction pattern of the insulator layer sample is obtained. Examples of X-ray diffraction patterns are shown in FIGS. 7 and 8. FIG. The horizontal axis of the X-ray diffraction patterns shown in FIGS. 7 and 8 is the diffraction angle 2θ. The range of diffraction angles 2θ in the X-ray diffraction pattern is 13 to 21°.

In the X-ray diffraction pattern, a broad halo with a diffraction peak near 16.4 to 16.5° (hereinafter referred to as an amorphous halo) corresponds to an amorphous component. In the X-ray diffraction pattern, a sharp spectrum with a peak at 17.7° (hereinafter referred to as a crystalline component spectrum) corresponds to the crystalline component.

A spectral fitting analysis using a Lorentzian function is performed on the amorphous halo to obtain _a smooth curve Fa that closely matches the amorphous halo. The acquired curve F _a is shown in FIGS. 7 and 8. FIG. _{Let Ia} be the intensity of the amorphous halo calculated by integrated intensity calculation based on this curve Fa.

Also, a spectral fitting analysis using a Lorentzian function is performed on the crystalline component spectrum to obtain a smooth curve _Fc that closely matches the crystalline component spectrum. The obtained curves Fc are _shown in FIGS. 7 and 8. FIG. Based on this curve _Fc , the intensity of the amorphous component spectrum calculated by integral intensity calculation is defined as _Ic . The crystallinity _Xc is the value before forming the plating layer.

As the insulator layer, for example, it is preferable that it is made of a perfluoroethylene propene copolymer and has a crystallinity _Xc of 0.47 or less, which is represented by the following formula (1). In this case, it becomes easy to make the thickness of the plating layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

前記式（１）におけるＩ_ｃは結晶成分のＸ線回折強度であり、Ｉ_ａは非晶質成分のＸ線回折強度である。Ｉ_ｃ、Ｉ_ａの算出方法は上述した方法である。結晶化度Ｘ_ｃは、めっき層を形成する前の時点における値である。

_Ic in the formula (1) is the X-ray diffraction intensity of the crystalline component, and _Ia is the X-ray diffraction intensity of the amorphous component. The calculation method of I _c and I _a is the method described above. The crystallinity _Xc is the value before forming the plating layer.

Examples of methods for reducing the crystallinity _Xc of the insulating layer made of perfluoroethylene propene copolymer to 0.47 or less include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ Examples include a method of surface modification treatment such as radiation irradiation and immersion in an ozone-containing liquid. In any treatment, the crystallinity _Xc can be increased by increasing the intensity of the treatment. Further, the crystallinity _Xc can be increased as the treatment time is lengthened.

The crystallinity _Xc has a correlation with the contact angle. This was confirmed by the following tests. A substrate made of polyethylene was subjected to a specific surface modification treatment. The substrate corresponds to the insulator layer. There are multiple conditions for the specific surface modification treatment. FIG. 9A shows the correlation between the crystallinity _Xc and the contact angle after the specific surface modification treatment. When the crystallinity _Xc was 0.744 or more, the contact angle was remarkably small.

Further, a specific surface modification treatment was performed on a substrate made of a perfluoroethylene propene copolymer. The substrate corresponds to the insulator layer. There are multiple conditions for the specific surface modification treatment. FIG. 9B shows the correlation between the crystallinity _Xc and the contact angle after the specific surface modification treatment. When the crystallinity _Xc was 0.47 or less, the contact angle was remarkably small.

As the insulator layer, for example, the following are preferable. The insulator layer consists of polyethylene. The polyethylene has a triclinic crystal structure, an orthorhombic crystal structure, or a state in which at least one of them coexists, and is preferentially oriented along two or less specific axes among the crystal axes. ing. In addition, the polyethylene has a (100) crystal orientation degree O ₁₀₀ represented by the following formula (2) of 0.26 or less. This insulator layer is hereinafter referred to as a specifically oriented polyethylene insulator layer.

前記式（２）においてＩ_２００は指数２００のＸ線回折強度であり、Ｉ_１１０は指数１１０のＸ線回折強度である。

In the above formula (2), I200 is the X-ray diffraction intensity with an index of ₂₀₀ , and I110 is the X-ray diffraction intensity with an index of ₁₁₀ .

When the insulator layer is a specifically oriented polyethylene insulator layer, it becomes easier to make the thickness of the plated layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

Examples of methods for making the insulating layer into a specifically oriented polyethylene insulating layer include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, and surface modification such as immersion in an ozone-containing liquid. and quality processing.

In any treatment, the degree of crystal orientation O ₁₀₀ can be reduced as the intensity of the treatment increases. In addition, the longer the treatment time, the smaller the degree of crystal orientation O ₁₀₀ can be.
I ₂₀₀ and I ₁₁₀ in the formula (2) are calculated as follows.

Using RINT2500, an X-ray diffractometer manufactured by Rigaku Corporation, the X-ray diffraction pattern of the insulator layer sample is obtained. Examples of X-ray diffraction patterns are shown in FIGS. 10 and 11. FIG. The horizontal axis of the X-ray diffraction patterns shown in FIGS. 10 and 11 is the diffraction angle 2θ. The range of diffraction angles 2θ in the X-ray diffraction pattern is 19 to 26°. 10 and 11 are X-ray diffraction patterns of samples of insulating layers made of polyethylene having an orthorhombic crystal structure. FIG. 10 is an X-ray diffraction pattern of polyethylene not subjected to surface modification treatment. FIG. 11 is an X-ray diffraction pattern of polyethylene subjected to corona discharge exposure treatment as a surface modification treatment.

A diffraction spectrum with a peak near about 21.5° (hereinafter referred to as a 110 diffraction spectrum) corresponds to a Miller index of 110 and represents the orientation of the (110) lattice plane. A diffraction spectrum with a peak near about 23.8° (hereinafter referred to as a 200 diffraction spectrum) corresponds to a Miller index of 200 and represents the (100) lattice plane.

A spectral fitting analysis using a Lorentzian function is performed on the 110 diffraction spectrum to obtain _a smooth curve F1 that closely matches the 110 diffraction spectrum. The obtained curve F1 is shown in FIGS. ₁₀ and 11. FIG. Based _on this curve F1, the intensity of the 110 diffraction spectrum calculated by integrated intensity calculation is assumed to be _I110 .

Also, spectral fitting analysis using a Lorentz function is performed on the ₂₀₀ diffraction spectrum to obtain a smooth curve F2 that well matches the 200 diffraction spectrum. The obtained curve F2 is shown in FIGS. 10 and 11. _FIG . Based on this curve F2, the intensity of the ₂₀₀ diffraction spectrum calculated by integral intensity calculation is defined as _I200 .

In addition, when individual crystal grains contained in a substance composed of polycrystals are in a state of preferential orientation in a certain direction, the X-ray diffraction intensity of a specific index plane is relatively high. Therefore, the orientation of a given lattice plane can be quantified by the ratio of X-ray diffraction intensities. The (100) crystal orientation O ₁₀₀ is an intensity ratio of X-ray diffraction intensities and represents the preferential orientation of the (100) plane.

The (100) crystal orientation O ₁₀₀ has a correlation with the contact angle. This was confirmed by the following tests. A substrate made of polyethylene was subjected to a specific surface modification treatment. The substrate corresponds to the insulator layer. There are multiple conditions for the specific surface modification treatment. FIG. 12 shows the correlation between the (100) crystal orientation degree O ₁₀₀ and the contact angle after the specific surface modification treatment. When the (100) crystal orientation degree O ₁₀₀ was 0.26 or less, the contact angle was remarkably small. The (100) crystal orientation degree O ₁₀₀ is the value before forming the plating layer.

As the insulator layer, for example, the following materials are preferable. The insulator layer consists of polyethylene. The crystallite size in the crystalline component of the polyethylene is 18 nm or more. When the insulator layer is as described above, it becomes easier to make the thickness of the plating layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

Examples of methods for making the insulating layer as described above include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, and surface modification treatment such as immersion in an ozone-containing liquid. method of doing so.

In any of the treatments, the higher the strength of the treatment, the larger the crystallite size in the crystalline component of polyethylene. In addition, the longer the treatment time, the larger the crystallite size in the crystalline component of polyethylene.

The crystallite size in the crystalline component of polyethylene is represented by the following formula (4).

式（４）においてＤはポリエチレンの結晶成分における結晶子サイズである。Ｋはシェラー定数である。Ｋの値は２／πとした。λはＸ線波長である。ＢはＸ線回折ピークの広がり幅である。θはＸ線回折角である。λ、Ｂ、θは、絶縁体層の試料のＸ線回折パターンから得られる値である。結晶子サイズは、めっき層を形成する前の時点における値である。

In formula (4), D is the crystallite size in the crystalline component of polyethylene. K is the Scherrer constant. The value of K was set to 2/π. λ is the X-ray wavelength. B is the broadening width of the X-ray diffraction peak. θ is the X-ray diffraction angle. λ, B, and θ are values obtained from the X-ray diffraction pattern of the insulator layer sample. The crystallite size is the value before forming the plating layer.

The crystallite size D in the crystalline component of polyethylene has a correlation with the contact angle. This was confirmed by the following tests. A substrate made of polyethylene was subjected to a specific surface modification treatment. The substrate corresponds to the insulator layer. There are multiple conditions for the specific surface modification treatment. FIG. 13A shows the correlation between the crystallite size D and the contact angle in the crystalline component of polyethylene after the specific surface modification treatment. When the crystallite size D in the crystalline component of polyethylene was 18 nm or more, the contact angle was significantly reduced.

As the insulator layer, for example, the following materials are preferable. The insulator layer consists of a perfluoroethylene propene copolymer. The crystallite size in the crystalline component of the perfluoroethylene propene copolymer is 13.6 nm or less. When the insulator layer is as described above, it becomes easier to make the thickness of the plating layer uniform. By making the thickness of the plating layer uniform, the transmission loss of the cable for differential signal transmission can be suppressed.

Examples of methods for making the insulating layer as described above include electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, and surface modification treatment such as immersion in an ozone-containing liquid. method of doing so.

In any treatment, the higher the intensity of the treatment, the larger the crystallite size in the crystalline component of the perfluoroethylene propene copolymer. In addition, the longer the treatment time, the larger the crystallite size in the crystalline component of the perfluoroethylene propene copolymer. The method for calculating the crystallite size in the crystalline component of the perfluoroethylene propene copolymer is the same as the method for calculating the crystallite size in the crystalline component of polyethylene. The crystallite size is the value before forming the plating layer.

The crystallite size D in the crystalline component of the perfluoroethylene propene copolymer has a correlation with the contact angle. This was confirmed by the following tests. A substrate made of perfluoroethylene propene copolymer was subjected to a specific surface modification treatment. The substrate corresponds to the insulator layer. There are multiple conditions for the specific surface modification treatment. FIG. 13B shows the correlation between the crystallite size D and the contact angle in the crystal component of the perfluoroethylene propene copolymer after the specific surface modification treatment. When the crystallite size D in the crystalline component of the perfluoroethylene propene copolymer was 13.6 nm or less, the contact angle was significantly reduced.

(1-3) Buffer Layer The buffer layer contains, for example, a plating catalyst and resin. Examples of plating catalysts include palladium, platinum, silver, and gold. Examples of resins include ABS resin, polypropylene, nylon, polycarbonate, polyacetal, polyester, and modified polyphenylene ether.

The buffer layer may contain, for example, a resin without containing a plating catalyst. In this case, the resin is preferably a resin to which the plated layer adheres more easily than the insulating layer. Examples of resins to which a plating layer is easily attached include ABS resin, polypropylene, nylon, polycarbonate, polyacetal, polyester, modified polyphenylene ether, and the like.

When the buffer layer contains a plating catalyst, the film thickness of the buffer layer is preferably 2.6 nm or more. When the film thickness of the buffer layer is 2.6 nm or more, it becomes easy to form a plated layer on the buffer layer.
The buffer layer can be made, for example, by extrusion. The buffer layer may appropriately contain components other than the plating catalyst and the resin.

When the differential signal transmission cable of the present disclosure includes a buffer layer, the adhesion between the buffer layer and the plating layer is high. Therefore, the gap between the buffer layer and the plating layer becomes smaller. As a result, the transmission characteristics of the cable for differential signal transmission are less likely to deteriorate.

When the buffer layer contains a plating catalyst, it is preferable to roughen the outer peripheral surface of the buffer layer before the step of forming the plating layer. If the outer peripheral surface of the buffer layer is roughened, the plating catalyst is likely to be exposed on the outer peripheral surface. When the plating catalyst is exposed, the adhesion between the buffer layer and the plating layer is further improved. Examples of methods for roughening the outer peripheral surface of the buffer layer include chromic acid etching and ice blast etching.

(1-4) Plated Layer The thickness of the plated layer is preferably 1 μm or more and 5 μm or less. When the thickness of the plating layer is 1 μm or more, the in-pair skew can be further reduced, and the amount of differential common-mode conversion can be further suppressed. In particular, when transmitting signals of 25 GHz or higher, the amount of differential common-mode conversion can be significantly suppressed.

When the thickness of the plating layer is 5 μm or less, the time required for forming the plating layer can be reduced. Moreover, when the thickness of the plating layer is 5 μm or less, the flexibility of the cable for differential signal transmission can be improved. Further, when the thickness of the plating layer is 5 μm or less, the outer diameter of the cable for differential signal transmission becomes small. The thickness of the plating layer can be controlled by a known method. For example, the longer the electroplating and/or electroless plating time, the thicker the plating layer. In addition, the plating layer becomes thicker as the amount of current in electrolytic plating increases.

The standard deviation of the thickness of the plating layer is preferably 0.8 μm or less. In this case, the transmission loss of the cable for differential signal transmission can be suppressed. In addition, noise can be further reduced because portions where the thickness of the plated layer is excessively small are less likely to occur.

The standard deviation of the thickness of the plating layer is calculated by the following method. A cross section perpendicular to the longitudinal direction of the cable for differential signal transmission is formed at four locations. The distance between each section is 3 m. Select any four points on each cross section. The thickness of each plating layer is measured at a total of 4×4 points. The standard deviation of the thickness of all the measured plating layers is adopted as the standard deviation of the thickness of the plating layer.

For example, the standard deviation of the thickness of the plating layer can be reduced by reducing the contact angle on the outer peripheral surface of the insulator layer or the buffer layer or by increasing the absolute value of the adhesion wetting surface energy.
By subjecting the insulator layer or buffer layer to surface modification treatment such as electron beam irradiation, ion irradiation, corona discharge exposure, plasma exposure, ultraviolet irradiation, X-ray irradiation, γ-ray irradiation, ozone-containing liquid immersion, etc. , the contact angle on the outer peripheral surface of the insulator layer or buffer layer can be reduced, and the absolute value of the adhesion wetting surface energy can be increased.

The plated layer may be formed by laminating a plurality of layers. The number of layers laminated in the plating layer can be, for example, 2, 3, or 4 or more. Of the plurality of layers, some layers can be magnetic layers made of ferrite or the like, and other layers can be non-magnetic layers made of copper or the like. In this case, the plated layer can have a shielding effect against strong magnetic fields and weak magnetic fields. In addition, the plating layer can exert a shielding effect against noise in a low frequency band of several tens to several hundred MHz and noise in a high frequency band of several tens of GHz.

For example, the plating layer can be formed by first performing electroless plating and then performing electrolytic plating. In this case, the plating layer can be easily formed on the insulator layer. Moreover, the time required for forming the plating layer can be shortened compared to the method of forming the entire plating layer by electroless plating.

2. Method for Manufacturing Cable for Differential Signal Transmission Of the cables for differential signal transmission according to the present disclosure, a cable for differential signal transmission that does not include a buffer layer can be manufactured, for example, by the following method. FIG. 14 shows a manufacturing system 101 used for manufacturing cables for differential signal transmission. The manufacturing system 101 includes a degreasing unit 103, a wet etching unit 105, a first activation unit 107, a second activation unit 109, an electroless plating unit 111, an electrolytic plating unit 113, a transport unit 115, Prepare.

The degreasing unit 103 comprises a degreasing tank 117 and a degreasing liquid 119 . A degreasing liquid 119 is contained in a degreasing tank 117 . The degreasing liquid 119 is, for example, sodium borate, sodium phosphate,
Contains one or more of surfactants and the like. The temperature of the degreasing liquid 119 is, for example, 40-60.degree.

A wet etching unit 105 for roughening the surface comprises an etching tank 121 and an etching solution 123 . The etchant 123 is contained in the etching bath 121 . The etchant 123 contains, for example, one or more of chromic acid, sulfuric acid, ozone, acid, alkali, chelate, and the like. The temperature of the etchant 123 is, for example, 65-70.degree.

The first activation unit 107 comprises a first activation bath 125 and a first activation liquid 127 . The first activation liquid 127 is contained in the first activation tank 125 . The first activation liquid 127 contains, for example, one or more of palladium chloride, stannous chloride, concentrated hydrochloric acid, and the like. The temperature of the first activation liquid 127 is, for example, 30-40.degree.

The second activation unit 109 comprises a second activation bath 129 and a second activation liquid 131 . The second activation liquid 131 is contained in the second activation tank 129 . The second activation liquid 131 contains, for example, sulfuric acid. The temperature of the second activation liquid 131 is, for example, 0 to 50.degree.

The electroless plating unit 111 consists of an electroless plating bath 133 and an electroless plating solution 135 . An electroless plating solution 135 is contained in an electroless plating bath 133 . The electroless plating solution 135 contains, for example, copper sulfate, Rossell salt, formaldehyde, sodium hydroxide, and the like. The temperature of the electroless plating solution 135 is, for example, 20-30.degree.

The electrolytic plating unit 113 includes an electrolytic plating bath 137 , an electrolytic plating solution 139 , a pair of anodes 141 and a power supply unit 143 . An electrolytic plating solution 139 is contained in an electrolytic plating bath 137 . The electrolytic plating solution 139 has a composition shown in Table 1 or Table 2, for example. The temperature of the electrolytic plating solution 139 is, for example, 20-25.degree.

アノード１４１は電解めっき液１３９の中に浸漬されている。アノード１４１は、例えば、銅湯から作製した溶融銅を圧延鋳造したものである。あるいは、アノード１４１は、以下のように製造されたものであってもよい。粗銅をアノードとし、ステンレス又はチタンをカソードとして種板電解を行う。カソード表面に析出した純銅板を剥ぎ取って、アノード１４１とする。電源ユニット１４３は、アノード１４１と、後述するボビン１６５、１６９との間に直流電圧を印加する。

Anode 141 is immersed in electrolytic plating solution 139 . The anode 141 is obtained, for example, by rolling and casting molten copper made from copper hot water. Alternatively, anode 141 may be manufactured as follows. Using blister copper as an anode and stainless steel or titanium as a cathode, electrolysis is performed on a seed plate. A pure copper plate deposited on the surface of the cathode is stripped off to form an anode 141 . The power supply unit 143 applies a DC voltage between the anode 141 and bobbins 165 and 169 which will be described later.

The transport unit 115 includes a plurality of bobbins 145 , 147 , 149 , 151 , 153 , 155 , 157 , 159 , 161 , 163 , 165 , 167 , 169 . In the following, these are sometimes collectively referred to as a bobbin group. Bobbins 165 and 169 are electrically conductive. The bobbin 167 has insulating properties.

The bobbin groups are basically arranged in series along the conveying direction D shown in FIG. A conveying direction D is a direction from the degreasing unit 103 to the electrolytic plating unit 113 through the wet etching unit 105, the first activation unit 107, the second activation unit 109, and the electroless plating unit 111 in sequence.

A portion of the bobbin 147 is immersed in the degreasing liquid 119 . A portion of the bobbin 151 is immersed in the etchant 123 . A portion of the bobbin 155 is immersed in the first activation liquid 127 . A portion of the bobbin 159 is immersed in the second activation liquid 131 . A portion of the bobbin 163 is immersed in the electroless plating solution 135 . The entire bobbin 167 is immersed in the electrolytic plating solution 139 .

The transport unit 115 continuously transports the differential signal transmission cable 171 along the transport direction D by the bobbin group. The differential signal transmission cable 171 to be conveyed has the signal line and the insulator layer in the initial state, but the plating layer is not yet formed. The insulator layer can be provided, for example, by known extrusion molding.

The transferred differential signal transmission cable 171 is first immersed in the degreasing liquid 119 in the degreasing unit 103 for 3 to 5 minutes. At this time, fats and oils adhering to the surface of the insulator layer are removed.
Next, the differential signal transmission cable 171 is immersed in the etchant 123 in the wet etching unit 105 for 8 to 15 minutes. At this time, an uneven shape is formed on the outer peripheral surface of the insulator layer. Moreover, functional groups such as carbonyl groups and hydroxyl groups are formed on the outer peripheral surface of the insulator layer. As a result, the outer peripheral surface of the insulator layer becomes hydrophilic and the surface wettability is improved.

Next, the differential signal transmission cable 171 is immersed in the first activation liquid 127 in the first activation unit 107 for 1 to 3 minutes. At this time, a catalyst layer is formed on the outer peripheral surface of the insulator layer.
Next, the differential signal transmission cable 171 is immersed in the second activation liquid 131 in the second activation unit 109 for 3 to 6 minutes. At this time, the surface of the catalyst layer is cleaned.

Next, the differential signal transmission cable 171 is immersed in the electroless plating solution 135 in the electroless plating unit 111 . The immersion time is, for example, 10 minutes or less. At this time, an electroless plated layer is formed on the outer peripheral surface of the insulator layer. The electroless plated layer corresponds to the plated layer. The longer the immersion time in the electroless plating solution 135, the thicker the electroless plating layer.

Next, the differential signal transmission cable 171 is immersed in the electrolytic plating solution 139 in the electrolytic plating unit 113 . The immersion time is, for example, 3 minutes or less. At this time, an electrolytic plated layer is formed on the outer peripheral surface of the electroless plated layer. The electroplated layer corresponds to the plated layer. The longer the immersion time in the electrolytic plating solution 139, the thicker the electrolytic plating layer. Specific conditions for electroplating in the electroplating unit 113 are as shown in Table 3. Through the above steps, the differential signal transmission cable 171 is completed.

なお、図１４では記載を省略しているが、各ユニットの間では、差動信号伝送用ケーブル１７１を純水で洗浄する。洗浄の方法として、超音波洗浄、揺動洗浄、流水洗浄等がある。純水で洗浄することにより、前のユニットで付着した残留薬剤が後のユニットに持ち込まれることを抑制できる。

Although not shown in FIG. 14, the differential signal transmission cable 171 is washed with pure water between each unit. Cleaning methods include ultrasonic cleaning, rocking cleaning, running water cleaning, and the like. By washing with pure water, it is possible to prevent the residual chemicals adhering to the previous unit from being brought into the subsequent unit.

The transport speed of the differential signal transmission cable 171 can be adjusted as appropriate. The transport speed may be changed in the middle of the transport, or the transport may be temporarily stopped.
A differential signal transmission cable may be manufactured using the manufacturing system 201 shown in FIG. The configuration of the manufacturing system 201 is basically the same as that of the manufacturing system 101, but is partially different. The differences will be mainly described below. The manufacturing system 201 does not include the degreasing unit 103 and the wet etching unit 105 , but includes a surface modification unit 203 . FIG. 16 shows a detailed configuration of the surface modification unit 203. As shown in FIG.

The surface modification unit 203 includes a housing 204 , a fine shape forming device 205 and a hydrophilic treatment device 207 . The housing 204 accommodates each component of the surface modification unit 203 . The housing 204 has an inlet 204A on the upstream side in direction D and an outlet 204B on the downstream side in direction D. As shown in FIG.

The transport unit 115 has four bobbins 209 , 211 , 213 , 215 inside the housing 204 . The differential signal transmission cable 171 is guided by the bobbin 145 and introduced into the housing 204 from the inlet 204A. The introduced differential signal transmission cable 171 is sent from the bobbin 209 to the bobbin 211 and conveyed along the figure-of-eight path returning to the bobbin 209 again. Next, differential signal transmission cable 171 is conveyed along a figure-of-eight path from bobbin 209 to bobbin 213 , from bobbin 213 to bobbin 215 , and back to bobbin 213 . Next, differential signal transmission cable 171 is led out from outlet 204 B, guided to bobbin 153 , and sent to first activation unit 107 .

The fine shape forming device 205 injects dry ice powder from the nozzle 205A to the differential signal transmission cable 171 between the bobbins 209 and 211 . The driving force for injection is air pressure. The arithmetic mean roughness Ra of the outer peripheral surface of the insulator layer increases by colliding with the dry ice powder. Therefore, the fine shape forming device 205 performs dry ice blasting. Dry ice blasting corresponds to surface roughening.

The outer surface of the insulating layer facing the nozzle 205A is opposite between when it is sent from the bobbin 209 to the bobbin 211 and when it returns from the bobbin 211 to the bobbin 209 . Therefore, the fine shape forming apparatus 205 can increase the arithmetic mean roughness Ra over the entire outer peripheral surface of the insulator layer.

The particle diameter of the dry ice powder, the distance from the tip of the nozzle 205A to the differential signal transmission cable 171, and the like can be appropriately set. The temperature of the differential signal transmission cable 171 is, for example, 20.degree.
The conditions for dry ice blasting can be changed as appropriate. Conditions for dry ice blasting include, for example, the particle size of dry ice powder, the flow rate of dry ice, the air pressure, the distance from the tip of the nozzle 205A to the differential signal transmission cable 171, and the transportation of the differential signal transmission cable 171. The speed, the temperature of the differential signal transmission cable 171, and the like can be mentioned. For example, dry ice blasting may be performed at a temperature below the glass transition temperature of the material of the insulator layer. A temperature lower than the glass transition temperature of the material of the insulator layer is, for example, -79°C or higher and 20°C or lower. The position of the nozzle 205A may be fixed, oscillating or scanning.

Hydrophilization treatment device 207 performs a hydrophilization treatment by exposure to corona discharge. Corona discharge exposure corresponds to a surface modification treatment. As shown in FIG. 16, the hydrophilization treatment device 207 has a total of four plate electrodes 208 . A pair of plate electrodes 208 face each other across a differential signal transmission cable 171 that is sent from bobbin 213 to bobbin 215 . Another pair of plate electrodes 208 face each other across a differential signal transmission cable 171 returning from the bobbin 215 to the bobbin 213 . A corona discharge is generated by applying a high frequency high voltage between the opposing plate electrodes 208 . By being exposed to corona discharge, the outer peripheral surface of the insulator layer becomes hydrophilic and wettability is improved. When the outer peripheral surface of the edge layer becomes hydrophilic and the wettability improves, the contact angle decreases and the absolute value of the adhesion wetting surface free energy increases.

The reason why the peripheral surface of the insulator layer becomes hydrophilic due to exposure to corona discharge and the wettability is improved is presumed to be as follows. High-energy electrons generated by exposure to corona discharge ionize and dissociate oxygen molecules present in the air, generating oxygen radicals, ozone, and the like. At the same time, the high-energy electrons that have reached the vicinity of the outer peripheral surface of the insulator layer cut and cleave main chains and side chains of, for example, polyethylene and perfluoroethylene propene copolymer contained in the insulator layer. The oxygen radicals, ozone, etc. generated by the corona discharge recombine with the cleaved main chain and side chains as described above, forming polar functional groups such as hydroxyl groups and carbonyl groups on the outer peripheral surface of the insulator layer. be. As a result, the outer peripheral surface of the insulator layer becomes hydrophilic and wettability is improved.
The applied voltage in corona discharge exposure is, for example, 2-14 kV and the frequency is 15 kV. The distance between the outer peripheral surface of the insulator layer and the plate electrode 208 is, for example, 0.1 to 3 mm. The atmosphere inside the housing 204 is, for example, the air.

Conditions for corona discharge exposure can be changed as appropriate. Conditions for corona discharge exposure include, for example, the magnitude of the applied voltage, the frequency of the applied voltage, the distance between the outer peripheral surface of the insulator layer and the plate electrode 208, the atmosphere inside the housing 204, and the like. The atmosphere within housing 204 may contain oxygen, nitrogen, carbon dioxide, rare gases, and the like. Also, a material such as silicone rubber may be sandwiched between the outer peripheral surface of the insulator layer and the flat plate electrode 208 . In this case, when performing corona discharge, the plate electrode 208 indirectly contacts the insulator layer and slides against the silicone rubber.
An exhaust mechanism for exhausting the air inside the housing 204 and a drying device for drying the inside of the housing 204 may be provided. In this case, rust on the differential signal transmission cable 171 can be suppressed. Also, a static eliminator may be provided in the housing 204 . In this case, static electricity inside the housing 204 can be suppressed.

As described above, in the method of manufacturing a differential signal transmission cable using the manufacturing system 201, dry ice blasting is performed on the outer peripheral surface of the insulator layer, and then corona discharge exposure is performed on the outer peripheral surface of the insulator layer. Thereafter, permanganic acid treatment is performed, and then a plating layer is formed on the outer peripheral surface of the insulator layer. Dry ice blasting corresponds to surface roughening. Corona discharge exposure treatment corresponds to surface modification treatment. By performing the permanganic acid treatment, the insulating layer is easily plated. Also, the permanganic acid treatment improves the transmission characteristics of the cable for differential signal transmission. A permanganic acid treatment may be performed after the surface roughening treatment, and then a corona discharge exposure treatment may be performed.

Surface modification unit 203 may be as shown in FIG. This surface modification unit 203 includes a cylindrical hydrophilization treatment device 207 . The hydrophilizing device 207 has a shaft hole 217 . A differential signal transmission cable 171 carried by bobbins 209 and 213 passes through shaft hole 217 . Hydrophilization treatment device 207 generates corona discharge in shaft hole 217 . By being exposed to the corona discharge, the outer peripheral surface of the insulator layer becomes hydrophilic and wettability is improved. When the outer peripheral surface of the edge layer becomes hydrophilic and the wettability improves, the contact angle decreases and the absolute value of the adhesion wetting surface free energy increases. Corona discharge exposure treatment corresponds to surface modification treatment.

Surface modification unit 203 may be as shown in FIG. Hydrophilization treatment device 207 includes arc-shaped electrodes 219 at portions facing bobbins 213 and 215 . The bobbins 213 and 215 are grounded. Hydrophilization treatment device 207 applies a voltage between electrode 219 and bobbins 213 and 215 to generate corona discharge. By being exposed to the corona discharge, the outer peripheral surface of the insulator layer becomes hydrophilic and wettability is improved. When the outer peripheral surface of the edge layer becomes hydrophilic and the wettability improves, the contact angle decreases and the absolute value of the adhesion wetting surface free energy increases. Corona discharge exposure treatment corresponds to surface modification treatment.

Of the differential signal transmission cables of the present disclosure, the differential signal transmission cable including the buffer layer 6 can be manufactured basically by the same method as described above. However, the differential signal transmission cable 171 to be carried further includes a buffer layer 6 . A buffer layer 6 covers the insulator layer 5 . Further, when the buffer layer 6 contains a plating catalyst, the step of forming the catalyst layer and the step of cleaning the surface of the catalyst layer can be omitted.

Further, among the differential signal transmission cables of the present disclosure, the differential signal transmission cable including the buffer layer 6 can be manufactured by the method shown in FIG. 25, for example. In step 1 of FIG. 25, a cable including a pair of signal lines 3, an insulator layer 5 and a buffer layer 6 is manufactured. The insulator layer 5 can be formed, for example, by first extrusion. The buffer layer 6 can be formed, for example, by a second extrusion. Then, as shown in step 1, the cable is cut. The cut surface of the cable is hereinafter referred to as the edge.

In step 2, part of the buffer layer 6 is removed at the end of the cable. For example, a portion of the buffer layer 6 can be removed by cutting the buffer layer 6 by a predetermined amount using a blade from the outer peripheral side of the buffer layer 6 . By removing part of the buffer layer 6, the outer peripheral surface of the insulator layer 5 is exposed at the end of the cable. In the following description, the portion of the insulator layer 5 where the outer peripheral surface is exposed is referred to as an exposed portion 5A.

Alternatively, in step 2, buffer layer 6 may not be removed. In this case, the outer peripheral surface of the buffer layer 6 on the end side may not be roughened, and the outer peripheral surface of the other portions may be roughened. In the portion of the buffer layer 6 where the outer peripheral surface is not roughened, the plated layer 7 is not formed in step 4 described later, and the plated layer 7 is formed on the portion where the outer peripheral surface is roughened.

In step 3, the pair of signal lines 3 are exposed by removing part of the exposed portion 5A on the end side.
In step 4 , a plating layer 7 is formed on the outer peripheral surface of the buffer layer 6 . The plating layer 7 is not formed on the exposed portion 5A. Through the above steps, the differential signal transmission cable 1 is completed.

A cable assembly can be manufactured by attaching a connector to the end of the differential signal transmission cable 1 . At the end of the differential signal transmission cable 1, the signal line 3 and the plating layer 7 are each connected to a board provided in the connector. Since the exposed portion 5A exists between the plated layer 7 and the signal line 3, the plated layer 7 and the signal line 3 are unlikely to be short-circuited.

In step 3, a connector may be attached to the end of the cable. Then, the outer peripheral surface of the buffer layer 6 may be covered with the plating layer 7 while the connector is connected to the end of the cable. In this case, the cable for differential signal transmission can be manufactured by batch processing.

3. Multicore Cable The multicore cable of the present disclosure includes a plurality of differential signal transmission cables, a conductor layer, and a jacket. The conductor layer collectively covers a plurality of cables for differential signal transmission. A jacket covers the conductor layer. Each of the plurality of differential signal transmission cables is basically the same as the differential signal transmission cable described in the section "1. Differential signal transmission cable", and is coated with a plating layer. It further comprises an outer insulating layer.

The multiple cables for differential signal transmission may or may not be twisted together. The number of differential signal transmission cables is not particularly limited, and may be, for example, 2, 8, 24, or the like. For example, a plurality of differential signal transmission cables may be divided into two or more groups, and an intervening group may be provided between the groups. Each group includes, for example, two or more cables for differential signal transmission.

The conductor layer can be composed of, for example, a shield tape conductor, a braided wire, or the like. The conductor layer may be, for example, a laminate of a shield tape conductor and a braided wire. Materials commonly used for cables can be used as materials for the shield tape conductor and the braided wire. As materials for the jacket, those commonly used for cables can be used.

Examples of the external insulating layer include an insulating tape, a laminate tape, a film formed by spray coating an insulator, and the like. As the laminate tape, for example, one commonly used for flat cables and the like can be used. It is preferable that the outer insulating layer can be formed at room temperature or low temperature. In this case, it is possible to suppress thermal deformation of the insulating layer when forming the outer insulating layer.

Examples of intervening materials include paper, thread, foam, and the like. Examples of foams include foamed polyolefins such as foamed polypropylene and foamed ethylene. The multicore cable of the present disclosure can suppress the amount of differential common mode conversion.

FIG. 19 shows an example of a multicore cable 301. As shown in FIG. The multicore cable 301 includes eight differential signal transmission cables 302 , a shield tape conductor 303 , a braided wire 305 and a jacket 307 . The shield tape conductor 303 and the braided wire 305 collectively cover the eight differential signal transmission cables 302 . The braided wire 305 is positioned on the outer peripheral side of the shield tape conductor 303 . A jacket 307 covers the braided wire 305 .

The eight differential signal transmission cables 1 are divided into two central groups and six surrounding groups. An interposer 309 is provided between the two groups.
Each of the eight differential signal transmission cables 302 has the configuration shown in FIG. The differential signal transmission cable 302 includes a pair of signal lines 3 , an insulator layer 5 , a plating layer 7 and an outer insulating layer 311 .

The insulator layer 5 collectively covers the pair of signal lines 3 . A plating layer 7 covers the insulator layer 5 . An outer insulating layer 311 covers the plating layer 7 . The differential signal transmission cable 302 has a maximum differential common-mode conversion amount of −26 dB or less in a frequency band of 50 GHz or less. The arithmetic average roughness Ra of the outer peripheral surface of the insulator layer 5 is 0.6 μm or more and 10 μm or less. The configurations of the signal line 3, the insulator layer 5, and the plating layer 7 are, for example, those described in the section "1. Differential signal transmission cable".

The differential signal transmission cable 302 may further include a buffer layer 6 . A buffer layer 6 covers the insulator layer 5 . A plating layer 7 covers the buffer layer 6 .
For each of the multiple cables for differential signal transmission included in the multi-core cable, the ends may be processed as shown in step 4 of FIG. 25 and a connector may be attached. In that case, for example, a plurality of differential signal transmission cables can be arranged flat along the width direction of the connector.

Moreover, after connecting a connector to the ends of a plurality of cables for differential signal transmission, the plating layer 7 may be formed on the plurality of cables for differential signal transmission.
4. Example (4-1) Example 1
A differential signal transmission cable 1 of the example having the structure shown in FIG. 1 was manufactured. The material of the insulator layer 5 is polyethylene. The insulator layer 5 collectively covers the pair of signal lines 3 . In a cross section orthogonal to the extending direction of the pair of signal lines 3, the shape of the outer edge of the insulator layer 5 is elliptical. The thickness of the plating layer 7 is 4.56 μm. The standard deviation of the thickness of the plating layer 7 is 0.68 μm. The variation coefficient of the thickness of the plating layer 7 is 0.15.

As shown in FIG. 20, the outer diameter of the insulator layer ₅ in the longitudinal direction is L1. Let L2 be the outer diameter of the insulator layer ₅ in the minor axis direction. Let L3 be the distance between the centers of the pair of signal lines ₃ . Let L4 be the distance between the center of the signal line ₃ and the outer peripheral surface of the insulator layer 5 in the longitudinal direction. Let L5 be the distance between the center of the signal line 3 and the outer peripheral surface of the insulator layer ₅ in the minor axis direction.

Note that even when the shape of the outer edge of the insulator layer 5 is oval, L ₁ to L ₅ can be similarly defined. However, when the shape of the outer edge of the insulator layer 5 is oval, the major axis direction is the direction parallel to the two straight lines forming the outer peripheral surface of the insulator layer 5 . Further, when the shape of the outer edge of the insulator layer 5 is oval, the minor axis direction is the direction perpendicular to the two straight lines.

In Example ₁ , L1 is 2.03 mm. L2 is 1.04 _mm . L3 is 0.55 _mm . _L4 is 0.74 mm. _L5 is 0.52 mm.
A surface roughening treatment was performed on the outer peripheral surface of the insulator layer 5 . The surface roughening treatment is chromic acid etching. Before the plating layer 7 is formed, the outer peripheral surface of the insulator layer 5 has an arithmetic average roughness Ra of 0.6 μm. Before the plating layer 7 is formed, the contact angle on the outer peripheral surface of the insulator layer 5 is 95°.

The amount of differential common-mode conversion of this differential signal transmission cable 1 was measured. The amount of differential common-mode conversion was measured before winding the cable for differential signal transmission around a drum or the like. The measurement result is shown as "131" in FIG. The horizontal axis in FIG. 21 is the frequency expressed on a logarithmic scale. The vertical axis represents the amount of differential common-mode conversion, and the unit is dB. The amount of differential common-mode conversion on the vertical axis corresponds to Scd21 of the mixed-mode S-parameter. The larger the value on the vertical axis (that is, the smaller the absolute value of the negative measurement value), the larger the amount of noise in the amount of differential common-mode conversion, indicating that the quality of the transmission signal is significantly degraded. .

The amount of differential common-mode conversion was also measured for the differential signal transmission cable R of the comparative example. The measurement result is shown as "132" in FIG. In the differential signal transmission cable R of the comparative example, the surface roughening treatment is not performed on the outer peripheral surface of the insulator layer. Therefore, the arithmetic average roughness Ra on the outer peripheral surface of the insulator layer is 0.13 μm, and the contact angle on the outer peripheral surface of the insulator layer is 82°. Further, the differential signal transmission cable R of the comparative example does not have a plating layer, but has a conductor layer around which a metal tape is wound.

In the differential signal transmission cable 1 of the example, the amount of differential common-mode conversion was smaller than that of the differential signal transmission cable R of the comparative example. In particular, the difference from the differential signal transmission cable R of the comparative example was remarkable in the high frequency region.

Further, transmission characteristics were measured for the differential signal transmission cable 1 of the example and the differential signal transmission cable R of the comparative example. The transmission characteristics were measured before winding the cable for differential signal transmission around a drum or the like. The measurement result of the differential signal transmission cable 1 of the example is indicated as "51" in FIG. 22, and the measurement result of the differential signal transmission cable R of the comparative example is indicated as "52". The horizontal axis in FIG. 22 is the frequency of the transmission signal. The vertical axis indicates transmission signal loss in units of dB. The transmission loss on the vertical axis corresponds to Sdd21 of the mixed-mode S-parameter. The smaller the value on the vertical axis (that is, the larger the absolute value of the negative measurement), the greater the attenuation of the transmitted signal, the greater the transmission degradation of the transmitted signal, and the greater the transmission loss. there is

In the differential signal transmission cable 1 of the example, the transmission loss was smaller than in the differential signal transmission cable R of the comparative example. Further, no suck-out occurred in the differential signal transmission cable 1 of the example. Although not shown in FIG. 22, no suck-out occurred in the range of 30 GHz or more and 50 GHz or less. Suck-out means abrupt attenuation of a transmission signal.

On the other hand, suck-out occurred in the differential signal transmission cable R of the comparative example. The reason why the suck-out does not occur in the differential signal transmission cable 1 of the embodiment is that the plating layer is continuously formed over the entire differential signal transmission cable 1, and the metal tape is wrapped around the conductor layer. It is presumed that this is because there are no overlaps or seams.
(4-2) Example 2
Differential signal transmission cables S1 to S7 were manufactured under the conditions shown in Table 4.

Ｓ１～Ｓ７はいずれも、ポリエチレンから成る絶縁体層を備える。Ｓ１～Ｓ７のいずれにおいても、一対の信号線３の延在方向に直交する断面において、絶縁体層の外縁の形状は楕円形である。実施例２において、Ｌ_１は１．２１ｍｍである。Ｌ_２は０．６２ｍｍである。Ｌ_３は０．３５ｍｍである。Ｌ_４は０．４３ｍｍである。Ｌ_５は０．３１ｍｍである。

All of S1-S7 are provided with an insulator layer made of polyethylene. In any of S1 to S7, the shape of the outer edge of the insulator layer is elliptical in the cross section perpendicular to the extending direction of the pair of signal lines 3. FIG. In Example ₂ , L1 is 1.21 mm. L2 is 0.62 _mm . _L3 is 0.35 mm. _L4 is 0.43 mm. _L5 is 0.31 mm.

S1-S6 comprise a conductive layer made of a plated layer. In S7, a conductive layer was formed by horizontally winding a Cu tape. In S1 to S5, the outer peripheral surface of the insulator layer was subjected to dry ice blasting treatment and then to corona discharge exposure treatment. Dry ice blasting corresponds to surface roughening treatment, and corona discharge exposure treatment corresponds to surface modification treatment. In S1 to S3, permanganic acid treatment was performed after the corona discharge exposure treatment. In S4 and S5, no permanganate treatment was performed after the corona discharge exposure treatment. In S6, the outer peripheral surface of the insulator layer was treated with chromic acid. In S7, the treatment before winding the Cu tape was not performed.

Arithmetic mean roughness Ra and transmission loss Sdd21 were measured for S1 to S7. The results are shown in Table 4 above. "1st Ra" in Table 1 represents the arithmetic average roughness Ra at the first measurement position, "2nd Ra" represents the arithmetic average roughness Ra at the second measurement position, and "average Ra" is their average value represents FIG. 23 shows the relationship between the arithmetic mean roughness Ra and the transmission loss Sdd21. The smaller the arithmetic mean roughness Ra, the smaller the transmission loss Sdd21. S1 to S3 with permanganate treatment had a smaller transmission loss than S4 to S5 without permanganate treatment.

5. Other Embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made.

(1) In Examples 1 and 2, the cable for differential signal transmission may further include a buffer layer 6 in addition to the signal line 3 , the insulator layer 5 and the plating layer 7 . A buffer layer 6 covers the insulator layer 5 . A plating layer 7 covers the buffer layer 6 . The buffer layer 6 contains, for example, a plating catalyst and resin. Moreover, the buffer layer 6 contains ABS resin, for example. Also, the buffer layer 6 contains, for example, ABS resin and a plating catalyst.

Even when the differential signal transmission cable 1 includes the buffer layer 6, the effects shown in the first and second embodiments are obtained. Furthermore, when the differential signal transmission cable 1 is provided with the buffer layer 6, the adhesion of the plating layer 7 is further enhanced. Therefore, the transmission characteristics of the cable for differential signal transmission are further improved.

(2) A function of one component in each of the above embodiments may be assigned to a plurality of components, or a function of a plurality of components may be performed by one component. Also, part of the configuration of each of the above embodiments may be omitted. Also, at least part of the configuration of each of the above embodiments may be added, replaced, etc. with respect to the configuration of the other above embodiments. It should be noted that all aspects included in the technical idea specified by the wording in the claims are embodiments of the present disclosure.

(3) In addition to the differential signal transmission cable or multicore cable described above, a system having at least one of them as a component, a multicore cable manufacturing method, a signal transmission/reception method using a differential signal transmission cable, etc. The present disclosure can also be implemented in various forms.

DESCRIPTION OF SYMBOLS 1... Cable for differential signal transmission, 3... Signal line, 5... Insulator layer, 6... Buffer layer, 7... Plating layer, 71... Insulator layer, 72... Outer peripheral surface, 73... Concave part, 101, 201... Production System 103 Degreasing unit 105 Wet etching unit 107 First activation unit 109 Second activation unit 111 Electroless plating unit 113 Electroplating unit 115 Transfer unit 117 Degreasing Tank 119 Degreasing liquid 121 Etching tank 123 Etching liquid 125 First activation tank 127 First activation liquid 129 Second activation tank 131 Second activation liquid 133 ... electroless plating bath, 135 ... electroless plating solution, 137 ... electrolytic plating bath, 139 ... electrolytic plating solution, 141 ... anode, 143 ... power supply unit, 145, 147, 149, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 209, 211, 213, 215... bobbin, 171... cable for differential signal transmission, 203... surface modification unit, 204... housing, 204A... inlet, 204B... outlet, 205 Fine shape forming device 205A Nozzle 207 Hydrophilic treatment device 208 Plate electrode 217 Shaft hole 219 Electrode 301 Multicore cable 302 Differential signal transmission cable 303 Shield tape Conductor 305 Braided wire 307 Jacket 309 Interposed 311 Outer insulating layer

Claims (6)

a pair of signal lines;
an insulator layer covering the periphery of the signal line;
It contains a plating catalyst and a resin, covers the insulating layer, and exposes the plating catalyst to a first portion that is a part of the outer peripheral surface, and a second portion of the outer peripheral surface excluding the first portion. A buffer layer in which the plating catalyst is not exposed more than the first part in the part ;
a plating layer that covers the first portion of the outer peripheral surface of the buffer layer and does not cover the second portion ;
cable for differential signal transmission. The cable for differential signal transmission according to claim 1,
The differential signal transmission cable, wherein the buffer layer includes ABS resin. a plurality of cables for differential signal transmission;
a conductor layer that collectively covers the plurality of differential signal transmission cables;
a jacket covering the conductor layer;
A multicore cable comprising
3. A multi-core cable, each of said plurality of differential signal transmission cables comprising the differential signal transmission cable according to claim 1 and an outer insulating layer covering said plating layer. A method for manufacturing a cable for differential signal transmission,
Covering a pair of signal lines with an insulating layer,
coating the outer peripheral surface of the insulator layer with a buffer layer containing a plating catalyst and a resin;
The plating catalyst is exposed to a first portion that is a part of the outer peripheral surface of the buffer layer, and the plating catalyst is more exposed than the first portion in a second portion excluding the first portion of the outer peripheral surface of the buffer layer. without exposing
A method of manufacturing a differential signal transmission cable, wherein the first portion of the outer peripheral surface of the buffer layer is covered with a plating layer and the second portion is not covered with a plating layer . A method for manufacturing a cable for differential signal transmission according to claim 4,
The method for manufacturing a cable for differential signal transmission, wherein the buffer layer includes ABS resin. 6. A method for manufacturing a cable for differential signal transmission according to claim 4 or 5,
A method for manufacturing a cable for differential signal transmission, wherein the outer peripheral surface of the buffer layer is coated with a plating layer while the end of the cable for differential signal transmission is connected to a connector.

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