Method for manufacturing signal transmission cable

Abstract

To provide a manufacturing method of a signal transmission cable capable of manufacturing a signal transmission cable having high adhesion between a metal oxide layer and an insulator layer.SOLUTION: A method of manufacturing a signal transmission cable includes a conductor and an insulator layer covering the conductor. A first metal layer covering the insulator layer is formed. Next, a metal oxide layer is formed by oxidizing the first metal layer. Next, a second metal layer is formed on the outer peripheral side of the metal oxide layer. For example, the surface roughness of the metal oxide layer on the side of the insulator layer is greater than the surface roughness of the metal oxide layer on the side of the second metal layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a signal transmission cable. [Background technology]

[0002] Patent Document 1 discloses a signal transmission cable. The signal transmission cable includes a conductor and an insulating layer. The insulating layer covers the conductor. The signal transmission cable includes a shield and a metal oxide layer. The shield is located around the outer periphery of the insulating layer. The metal oxide layer is located between the shield and the insulating layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2022 / 176121 A1 Summary of the Invention [Problem to be solved by the invention]

[0004] Signal transmission cables are sometimes bent. When a signal transmission cable is bent, if the adhesion between the metal oxide layer and the insulator layer is low, the metal oxide layer peels off from the insulator layer. In one aspect of the present disclosure, it is preferable to provide a method for manufacturing a signal transmission cable that can manufacture a signal transmission cable having high adhesion between the metal oxide layer and the insulator layer. [Means for solving the problem]

[0005] One aspect of the present disclosure is a method for manufacturing a signal transmission cable including a conductor and an insulating layer covering the conductor, the method including depositing a first metal layer covering the insulating layer, oxidizing the first metal layer to form a metal oxide layer, and depositing a second metal layer on the outer periphery of the metal oxide layer.

[0006] According to a method for producing a signal transmission cable that is one aspect of the present disclosure, a signal transmission cable having high adhesion between the metal oxide layer and the insulator layer can be produced. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a signal transmission cable according to a first embodiment. [Figure 2] 3A to 3C are explanatory views showing a method for forming a metal oxide layer and a second metal layer. [Figure 3] FIG. 4 is a cross-sectional view illustrating the configuration of a signal transmission cable according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Exemplary embodiments of the present disclosure will now be described with reference to the drawings. First Embodiment 1. Structure of signal transmission cable 1 The configuration of the signal transmission cable 1 will be described with reference to Fig. 1. The signal transmission cable 1 includes a conductor 3, an insulating layer 5, a metal oxide layer 7, and a second metal layer 9.

[0009] The conductor 3 is, for example, made of a single wire. The conductor 3 may be, for example, a twisted wire formed by twisting a plurality of single wires. When the conductor 3 is a twisted wire, the flexibility of the conductor 3 is improved. The single wire is, for example, a copper wire whose surface is plated. Examples of plating include tin plating and silver plating. Examples of materials for the conductor 3 include copper and copper alloy. The diameter of the conductor 3 is, for example, 0.032 mm or more and 0.41 mm or less. In this embodiment, the number of conductors 3 is one. The conductor 3 is, for example, located at the center of the signal transmission cable 1 in the cross section.

[0010] The insulator layer 5 covers the conductor 3. The conductor 3 is embedded inside the insulator layer 5. The material of the insulator layer 5 is preferably one with a low dielectric constant. Examples of the material of the insulator layer 5 include polyethylene, polypropylene, and fluorine-based resin. The insulator layer 5 may be made of two layers.

[0011] The metal oxide layer 7 covers the insulator layer 5. For example, the inner circumferential surface of the metal oxide layer 7 is in contact with the outer circumferential surface of the insulator layer 5. The metal oxide layer 7 is made of a metal oxide. The metal oxide is, for example, an oxide of copper, aluminum, iron, zinc, nickel, or the like. The metal oxide layer 7 may be made of only a metal oxide, or may further contain a component other than a metal oxide.

[0012] The thickness of the metal oxide layer 7 is preferably 2 μm or more and 5 μm or less. For example, the surface roughness of the metal oxide layer 7 on the insulator layer 5 side is greater than the surface roughness of the metal oxide layer 7 on the second metal layer 9 side.

[0013] The second metal layer 9 is provided on the outer peripheral side of the metal oxide layer 7. The second metal layer 9, for example, covers the metal oxide layer 7. For example, the inner peripheral surface of the second metal layer 9 is in contact with the outer peripheral surface of the metal oxide layer 7.

[0014] The second metal layer 9 is made of a metal. Examples of metals include copper, silver, aluminum, iron, zinc, and nickel. The second metal layer 9 may consist solely of metal, or may further contain components other than metal. The thickness of the second metal layer 9 is preferably 1 μm or more and 10 μm or less. The second metal layer 9 functions as a shield. The signal transmission cable 1 is used, for example, for internal and external wiring of high-speed transmission servers, communication base stations, etc.

[0015] 2. Manufacturing method of signal transmission cable 1 A method for manufacturing a signal transmission cable 1 according to the present disclosure will be described with reference to Fig. 2. First, the conductor 3 is covered with an insulating layer 5. As a method for covering the conductor 3 with the insulating layer 5, a known method can be appropriately selected, and examples thereof include an extrusion method.

[0016] The arithmetic mean roughness Sa of the surface of the insulator layer 5 is preferably 0.8 μm or more and 3 μm or less, and more preferably 1.2 μm or more and 1.6 μm or less. When the arithmetic mean roughness Sa is 1.2 μm or more, the anchor effect described below is significant. When the arithmetic mean roughness Sa is 1.6 μm or less, it is easy to fill recesses on the surface of the insulator layer 5 with plating.

[0017] For example, roughening treatment can be performed on the surface of the insulator layer 5 to form irregularities on the surface of the insulator layer 5. Examples of roughening treatment include a method of immersing the surface in a chromic acid solution, and a method of blasting the surface followed by exposure to corona discharge.

[0018] Next, as shown in S1 of FIG. 2, the insulator layer 5 is coated with a first metal layer 11. The first metal layer 11 is made of a metal. Examples of metals include copper, aluminum, iron, zinc, and nickel. The first metal layer 11 may be made of metal only, or may further contain a component other than a metal. The thickness of the first metal layer 11 is preferably 2 μm or more and 5 μm or less. Methods for forming the first metal layer 11 include, for example, electroless plating, sputtering, and vapor deposition.

[0019] When the first metal layer 11 is formed by electroless plating, the first metal layer 11 is an electroless plated layer. The electroless plating solution used in the electroless plating is, for example, a solution containing copper sulfate, Rochelle's salt, formaldehyde, sodium hydroxide, etc. The temperature of the electroless plating solution is, for example, 20°C or higher and 30°C or lower. The time for which the insulator layer 5 is immersed in the electroless plating solution is, for example, 3 minutes or higher and 10 minutes or lower. The longer the immersion time in the electroless plating solution, the thicker the electroless plated layer becomes.

[0020] If the surface roughness of the insulator layer 5 is high, it is preferable to prolong the immersion time in the electroless plating solution so that the insulator layer 5 is not exposed after electroless plating. The arithmetic mean roughness Sa of the surface of the electroless plated layer is preferably 2 μm or less, and more preferably 1.2 μm or less. When the arithmetic mean roughness Sa of the surface of the electroless plated layer is 1.2 μm or less, high-frequency signal transmission is less likely to be impeded. For example, the surface roughness of the electroless plated layer on the insulator layer 5 side is greater than the surface roughness of the electroless plated layer on the outer periphery side.

[0021] For example, the surface of the insulator layer 5 is uneven. The first metal layer 11 has a plurality of protrusions 13 that penetrate into recesses on the surface of the insulator layer 5. The greater the surface roughness of the insulator layer 5, the greater the surface roughness of the first metal layer 11 on the insulator layer 5 side. The greater the surface roughness of the first metal layer 11 on the insulator layer 5 side, the greater the surface roughness of the metal oxide layer 7 on the insulator layer 5 side. Therefore, by increasing the surface roughness of the insulator layer 5, the surface roughness of the metal oxide layer 7 on the insulator layer 5 side can be increased.

[0022] Next, as shown in S1 and S2 of FIG. 2, the first metal layer 11 is oxidized to form the metal oxide layer 7. One method of oxidizing the first metal layer 11 to form the metal oxide layer 7 is to place the first metal layer 11 in a high-temperature, high-humidity environment. The temperature in the high-temperature, high-humidity environment is, for example, 80°C or higher and 120°C or lower. The humidity in the high-temperature, high-humidity environment is, for example, 60% or higher and 95% or lower.

[0023] The time for which first metal layer 11 is placed in the high-temperature, high-humidity environment is, for example, 1 minute or more and 60 minutes or less. The time for which first metal layer 11 is placed in the high-temperature, high-humidity environment is preferably longer as the thickness of first metal layer 11 increases. For example, the electroless plated layer may be oxidized in-line immediately after electroless plating using high-temperature steam or a tubular furnace.

[0024] For example, the first metal layer 11 can be oxidized by placing the first metal layer 11 in a thermo-humidistat bath, a thermostatic bath, or both. For example, the temperature inside the thermo-humidistat bath is 85°C, and the humidity inside the thermostatic bath is 85%. For example, the temperature inside the thermostatic bath is 80°C or higher and 120°C or lower.

[0025] When the first metal layer 11 is oxidized to become the metal oxide layer 7, the protrusions 13 expand in volume as shown in S2 in FIG. 2. The arrow in S2 in FIG. 2 indicates the direction in which the protrusions 13 expand in volume. Methods for oxidizing the first metal layer 11 include, for example, (a) a method in which the first metal layer 11 is oxidized after the formation of the first metal layer 11 is completed, or (b) a method in which the first metal layer 11 is oxidized in parallel with the formation of the first metal layer 11. Method (a) is advantageous in that there is a wide range of options for oxidation means and conditions. Method (b) is advantageous in that it has a high productivity rate.

[0026] 2, a second metal layer 9 is formed on the outer periphery of the metal oxide layer 7. The thickness of the second metal layer 9 is, for example, 1 μm or more and 10 μm or less. Examples of methods for forming the second metal layer 9 include sputtering, vapor deposition, electroless plating, and electrolytic plating.

[0027] Methods for forming the second metal layer 9 include, for example, (c) a method of forming the second metal layer 9 on the surface of the metal oxide layer 7 by electroless plating, or (d) a method of reducing the surface of the metal oxide layer 7 to make it conductive and then forming the second metal layer 9 by electrolytic plating. Method (c) is advantageous in that it does not require an electrode member for current application, thereby simplifying the equipment. Method (d) can achieve a high film formation speed, thereby offering excellent productivity, especially when forming a thick plating film. In method (d), a method for reducing the surface of the metal oxide layer 7 to make it conductive includes, for example, immersing the metal oxide layer 7 in a liquid reducing agent.

[0028] An example of a liquid reducing agent is a solution containing sodium borohydride. The temperature of the solution containing sodium borohydride is, for example, 20°C or higher and 30°C or lower. The time for immersing the metal oxide layer 7 in the solution containing sodium borohydride is, for example, 1 minute or higher and 5 minutes or lower. Another example of a liquid reducing agent is a solution containing dimethylamine borane.

[0029] When the second metal layer 9 is formed by electroplating, the electroplating solution is, for example, a solution containing copper sulfate and sulfuric acid. In the electroplating, the current density is, for example, 1.5 A / dm 2 More than 5A / dm 2 The treatment time for electrolytic plating is, for example, 1 minute or more and 15 minutes or less.

[0030] 3. Effects of the manufacturing method for signal transmission cable 1 (1A) In the signal transmission cable 1 manufactured by the manufacturing method of the present disclosure, the metal oxide layer 7 and the insulating layer 5 have high adhesion. Therefore, even when the signal transmission cable 1 is bent, the metal oxide layer 7 is unlikely to peel off from the insulating layer 5.

[0031] The reason for the high adhesion between the metal oxide layer 7 and the insulator layer 5 is presumed to be as follows: When the first metal layer 11 is oxidized to become the metal oxide layer 7, the protrusions 13 that penetrate into the recesses on the surface of the insulator layer 5 expand in volume, as shown in S2 in FIG. 2 . Therefore, the protrusions 13 function as anchors for the insulator layer 5. As a result, the adhesion between the metal oxide layer 7 and the insulator layer 5 is high.

[0032] (1B) In the technology described in Patent Document 1, a metal oxide layer and a metal layer are successively formed by electroless plating. By changing the oxygen concentration in the electroless plating solution during the electroless plating process, the layer being formed is switched from a metal oxide layer to a metal layer. Because of this manufacturing method, a gradation layer, in which metal oxide and metal are mixed, is formed at the interface between the metal oxide layer and the metal layer. This gradation layer significantly reduces transmission characteristics at high frequencies.

[0033] In contrast, with the manufacturing method of the present disclosure, a gradation layer in which metal oxide and metal are mixed is unlikely to occur at the interface between metal oxide layer 7 and second metal layer 9. As a result, signal transmission cable 1 has excellent transmission characteristics at high frequencies.

[0034] (1C) In the technology described in Patent Document 1, the oxygen concentration in the electroless plating solution is changed during electroless plating. The oxygen concentration in the electroless plating solution has a sensitive effect on the stability and deposition rate of the electroless plating solution. Therefore, in the technology described in Patent Document 1, the electroless plating solution is prone to decomposition. In contrast, in the manufacturing method disclosed herein, the oxygen concentration in the electroless plating solution does not need to be changed when electroless plating is performed. Therefore, the electroless plating solution is less likely to decompose.

[0035] (1D) For example, the surface roughness of the metal oxide layer 7 on the side of the insulator layer 5 is greater than the surface roughness of the metal oxide layer 7 on the side of the second metal layer 9. In this case, the adhesion between the metal oxide layer 7 and the insulator layer 5 is further improved. In addition, since the surface roughness of the metal oxide layer 7 on the side of the second metal layer 9 is small, the transmission characteristics at high frequencies are further improved.

[0036] (1E) In the signal transmission cable 1 manufactured by the manufacturing method of the present disclosure, high-frequency signals flow mainly through the second metal layer 9, not through the highly resistive metal oxide layer 7. The second metal layer 9 is less susceptible to the effects of irregularities on the surface of the insulator layer 5. Therefore, even if the surface of the insulator layer 5 is irregular, high-frequency loss can be suppressed.

[0037] Second Embodiment 1. Differences from the first embodiment The second embodiment has the same basic configuration as the first embodiment, so differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and reference will be made to the preceding description.

[0038] In the first embodiment described above, the number of conductors 3 is 1. In contrast, in the second embodiment, as shown in Fig. 3, the signal transmission cable 1 is a differential signal transmission cable in which the number of conductors 3 is two, which is different from the first embodiment.

[0039] 2. Manufacturing method of signal transmission cable 1 The signal transmission cable 1 can be manufactured in the same manner as in the first embodiment. 3. Effects of the manufacturing method for signal transmission cable 1 According to the second embodiment described above in detail, the effects of the first embodiment described above are achieved.

[0040] <Example> 1. Formation of insulator layer 5 An Ag-plated annealed copper wire was prepared as the conductor 3. The diameter of the conductor 3 was 0.255 mm. The conductor 3 was covered with an insulating layer 5 by extrusion. The material of the insulating layer 5 was polyethylene. The conductor 3 and the insulating layer 5 constituted a coaxial cable.

[0041] 2. Roughening treatment The coaxial cable was subjected to a roughening treatment. The roughening treatment was a treatment for forming irregularities on the surface of the insulator layer 5. Specifically, the coaxial cable was immersed in a chromic acid solution at 75°C for 30 minutes. After the roughening treatment, the arithmetic mean roughness Sa of the surface of the insulator layer 5 was measured and found to be 1.2 µm.

[0042] 3. Deposition of the first metal layer 11 After the roughening treatment, the coaxial cable was immersed in a first activation solution at 40°C for 5 minutes. The first activation solution contained Pd and Sn. By immersing the cable in the first activation solution, a catalyst layer for electroless plating was formed.

[0043] Next, the coaxial cable was immersed in a second activation solution for 15 seconds. The second activation solution contained sulfuric acid. The temperature of the second activation solution was 25°C. By immersing the cable in the second activation solution, the surface of the catalyst layer was cleaned.

[0044] Next, electroless plating was performed on the surface of the insulator layer 5 to form an electroless plated layer made of copper. The electroless plated layer corresponded to the first metal layer 11. The thickness of the electroless plated layer was 2 μm. The electroless plating solution used for the electroless plating contained copper sulfate, Rochelle's salt, formaldehyde, and sodium hydroxide. The temperature of the electroless plating solution was 27°C. The immersion time in the electroless plating solution was 6 minutes. The arithmetic mean roughness Sa of the surface of the electroless plated layer was 0.9 μm.

[0045] 4. Formation of Metal Oxide Layer 7 After the first metal layer 11 was formed, the coaxial cable was placed in a thermo-hygrostat. The temperature inside the thermo-hygrostat was 85°C and the humidity was 85%. The time spent in the thermo-hygrostat was 60 minutes. The first metal layer 11 was oxidized, and a metal oxide layer 7 was formed.

[0046] 5. Deposition of second metal layer 9 After the metal oxide layer 7 was formed, the coaxial cable was immersed in a solution containing sodium borohydride. The temperature of the solution containing sodium borohydride was 50°C. The immersion time was 2 minutes. During this time, the surface of the metal oxide layer 7 was reduced to copper. As a result, the surface of the metal oxide layer 7 became conductive.

[0047] Next, a second metal layer 9 made of copper was formed on the surface of the copper produced by reduction by electroplating. The electroplating solution used in the electroplating was a solution containing copper sulfate and sulfuric acid. When performing the electroplating, the coaxial cable serving as the cathode and the copper plate serving as the anode were immersed in the electroplating solution, and a DC voltage was applied. In the electroplating, the current density was 3 A / dm 2 The electrolytic plating process took 4 minutes. The second metal layer 9 had a thickness of 3 μm. Through the above steps, a signal transmission cable 1 was obtained.

[0048] <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 can be implemented in various modified forms.

[0049] (1) The function of one component in each of the above embodiments may be shared among multiple components, or the functions of multiple components may be performed by one component. Also, part of the configuration of each of the above embodiments may be omitted. Furthermore, at least part of the configuration of each of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0050] (2) In addition to the method for manufacturing the signal transmission cable 1 described above, the present disclosure can also be realized in various forms, such as a method for forming the signal transmission cable 1 and the shield.

[0051] [Technical idea disclosed in this specification] [Item 1] A method for manufacturing a signal transmission cable including a conductor and an insulating layer covering the conductor, depositing a first metal layer covering the insulator layer; oxidizing the first metal layer to form a metal oxide layer; forming a second metal layer on the outer periphery of the metal oxide layer; A method for manufacturing a signal transmission cable. [Item 2] A method for manufacturing the signal transmission cable according to item 1, a surface roughness of the metal oxide layer on the side of the insulator layer is greater than a surface roughness of the metal oxide layer on the side of the second metal layer; A method for manufacturing a signal transmission cable. [Item 3] A method for producing a signal transmission cable according to item 1 or 2, The method of oxidizing the first metal layer is (a) a method of oxidizing the first metal layer after the formation of the first metal layer is completed, or (b) a method of oxidizing the first metal layer in parallel with the formation of the first metal layer. A method for manufacturing a signal transmission cable. [Item 4] A method for producing a signal transmission cable according to any one of items 1 to 3, The method for forming the second metal layer is (c) a method for forming the second metal layer on the surface of the metal oxide layer by electroless plating, or (d) a method for reducing the surface of the metal oxide layer to make it conductive, and then forming the second metal layer by electrolytic plating. A method for manufacturing a signal transmission cable. [Explanation of symbols]

[0052] REFERENCE SIGNS LIST 1... signal transmission cable, 3... conductor, 5... insulator layer, 7... metal oxide layer, 9... second metal layer, 11... first metal layer, 13... protrusion

Claims

1. A method for manufacturing a signal transmission cable including a conductor and an insulating layer covering the conductor, depositing a first metal layer covering the insulator layer; oxidizing the first metal layer to form a metal oxide layer; forming a second metal layer on the outer periphery of the metal oxide layer; A method for manufacturing a signal transmission cable.

2. 2. A method for manufacturing a signal transmission cable according to claim 1, comprising: a surface roughness of the metal oxide layer on the side of the insulator layer is greater than a surface roughness of the metal oxide layer on the side of the second metal layer; A method for manufacturing a signal transmission cable.

3. 3. A method for manufacturing a signal transmission cable according to claim 1 or 2, comprising: The method of oxidizing the first metal layer is (a) a method of oxidizing the first metal layer after the formation of the first metal layer is completed, or (b) a method of oxidizing the first metal layer in parallel with the formation of the first metal layer. A method for manufacturing a signal transmission cable.

4. 3. A method for manufacturing a signal transmission cable according to claim 1 or 2, comprising: The method for forming the second metal layer is (c) a method for forming the second metal layer on the surface of the metal oxide layer by electroless plating, or (d) a method for reducing the surface of the metal oxide layer to make it conductive, and then forming the second metal layer by electrolytic plating. A method for manufacturing a signal transmission cable.

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