JP4352935B2 - Shielded cable and terminal forming method thereof - Google Patents

Description

  The present invention relates to a shielded cable in which an inner insulator, an outer conductor, and a jacket are sequentially formed on the outer circumference of an inner conductor in a coaxial manner, and a method for forming a terminal thereof.

  In recent years, with the spread of notebook computers, mobile phones, small video cameras, and the like, in addition to the reduction in size and weight of these information communication devices, high speed and high image quality are required. In order to cope with this, an extremely thin electric wire (sometimes referred to as a cable) in which an inner insulator, an outer conductor, and a jacket are sequentially formed on the outer periphery of the inner conductor in a coaxial manner is used. In addition, in order to prevent unnecessary noise from being mixed in other control devices such as a medical ultrasonic probe, a similar electric wire is used as a shielded electric wire. Hereinafter, the coaxial cable or the shielded cable including the shielded cable is referred to as a shielded cable.

  Usually, a plurality of shielded cables are used by bundling them, and the ends of the shielded cables are made flat and an electrical connector is connected. When connecting to the electrical connector, it is necessary to form a terminal for electrically connecting the inner conductor and the outer conductor to the shielded cable. However, when the outer diameter of the cable is as fine as 1 mm or less and the thickness of the internal insulator is about several tens of μm, it is not easy to form a connection terminal without impairing the cable arrangement pitch and electrical performance. .

  For this reason, various proposals have heretofore been made for the terminal formation of this type of shielded cable. For example, Patent Document 1 discloses a shielded cable that prevents electrical continuity from being generated in an internal insulator when an external conductor is cut using a laser. FIG. 3 is a diagram showing an outline of the configuration disclosed in Patent Document 1, in which 1 is a shielded cable, 2 is an internal conductor, 3 is an internal insulator, 4 is an external conductor, 5 is a jacket, and 6 is a cover. The coating layer is shown.

  This shielded cable 1 has a covering layer 6 made of a material having a higher thermal deformation temperature than that of the foamed fluororesin between the inner insulator 3 made of foamed fluororesin and coaxially disposed on the outer periphery of the inner conductor 2. Is arranged. The inner conductor 2 is formed by twisting seven tin-plated copper alloy wires having an outer diameter of 0.03 mm, and the inner insulator 3 is formed by winding a foamed fluororesin tape having a thickness of 0.03 mm in two layers. The covering layer 6 is formed by winding a polymer film having a thickness superior to that of the foamed fluororesin and having a thickness of about 0.005 mm. The outer conductor 4 is formed by winding a large number of copper wires having an outer diameter of 0.03 mm, and the outer sheath 5 is formed by winding a polyester resin film or by a molding machine.

The shielded cable 1 configured as described above is cut from the outer conductor 4 by cutting the outer jacket 5 using machining or a CO ₂ laser. Next, the outer circumference of the outer conductor 4 is irradiated with a CO ₂ laser adjusted so that the outer conductor can be cut, and the outer conductor 4 is removed by melting and cutting. Thereafter, the exposed coating layer 6 and the internal insulator 3 are cut by machining or using a CO ₂ laser, and the internal conductor 2 is exposed. When the outer conductor 4 is cut with a laser, the irradiation time is controlled so that the laser beam does not reach the inner coating layer 6, and the thermal energy of the laser is applied to the inner insulator 3 by the coating layer 6 having excellent heat resistance. It is supposed to suppress the spread and avoid an electrical short circuit.

  Patent Document 2 discloses a method of simultaneously removing the outer conductors of a multi-core cable in which a plurality of shielded cables are arranged in a flat shape. FIG. 4 is a diagram showing an outline of the method disclosed in Patent Document 2, in which W is a multi-core cable, 7, 7a is an adhesive tape, 8 is a solder material, 9 is a processing groove, and other symbols Are omitted by using the same reference numerals as those used in FIG.

  The multi-core cable W shown in FIG. 4 is formed by arranging a plurality of shielded cables 1 at a predetermined pitch at least at the end portion and bonding and integrating them using an adhesive tape 7. The shielded cable 1 itself has substantially the same shape as that shown in FIG. 3, and a layer of an inner insulator 3 and an outer conductor 4 is coaxially arranged on the outer periphery of an inner conductor (not shown), and the outer side thereof. Is covered with a jacket 5. That is, in FIG. 4, it has shown by the structure which is not provided with the heat resistant coating layer 6 in FIG.

Multi-fiber cable W, which is configured as described above, as shown in FIG. 4 (A), a slit in C0 ₂ laser from the end portion at a position of a predetermined distance, and the cover fabric cut adhesive tape 7a 5 are collectively shifted in the direction a to expose the outer conductor 4. Next, as shown in FIG. 4B, the exposed portion of the external conductor 4 is immersed in a solder bath and covered with the solder material 8 in a lump. Next, a processing groove 9 is formed by a YAG laser in the central portion of the portion bundled with the solder material 8. The processed groove 9 is formed in a shape in which the outer conductor 4 is exposed at a portion where the outer conductor 4 is present and a through hole is formed between the core wires without the outer conductor 4.

Next, with the machining groove 9 as a fulcrum, the outer conductor 4 is cut by bending the portion collectively with the solder material 8 in the vertical direction. Thereafter, as shown in FIG. 4C, the soldered outer conductor 4 and the offset adhesive tape 7a are removed by pulling them together to expose the inner insulator 3. Then, the inner insulator 3 which is exposed to maintain the Paste by SEQ hold the insulating film on both sides, in FIG. 4 (A) and similar methods, are exposed to the inner conductor by a slit in C0 ₂ laser .
Japanese Patent Application Laid-Open No. 11-144533 JP 2000-244502 A

  As in Patent Document 1, the configuration in which the internal insulator is covered with a heat-resistant coating layer is costly because the insulator has a multilayer structure. Examples of the heat resistant coating layer include tetrafluoroethylene resin, ethylene / tetrafluoroethylene copolymer resin, tetrafluoroethylene / hexafluoropropylene copolymer resin, perfluoroalkoxy resin, and polyimide resin. ing. However, these resin materials alone are not sufficient for suppressing the thermal energy of the laser and ensuring the electrical insulation characteristics, and means for providing a separate laser light reflecting layer is necessary.

In addition, as in Patent Document 2, batch fixing with a solder material requires a soldering operation and is costly, and is not efficient for a single-core shielded cable.
The present invention has been made in view of the above-described circumstances, and the outer conductor is directly melted by laser without adding a heat-resistant coating layer inside the outer conductor or fixing the outer conductor with a solder material. It is an object of the present invention to provide a shielded cable that can maintain electrical insulation characteristics even when it is cut and a method of forming a terminal thereof.

  The shielded cable according to the present invention is a shielded cable in which an inner insulator, an outer conductor, and a jacket are sequentially formed on the outer periphery of the inner conductor in a coaxial manner, and the inner insulator is made of a fluororesin, and has a carbon black of 0.025 wt% to It is configured using a material colored by adding 0.14 wt%. As the fluororesin, a tetrafluoroperfluoroalkyl vinyl ether copolymer is preferably used, and the coating thickness of the internal insulator is 55 μm or less. The shield cable terminal forming method according to the present invention is also characterized by stripping the outer cover of the end portion of the shielded cable for a predetermined length to expose the outer conductor, cutting the outer conductor with a YAG laser, and stripping off the inner conductor. Expose the insulator.

  According to the present invention, it is possible to cut and peel off the outer conductor using a processing laser without providing an additional coating layer on the outer periphery of the inner insulator or fixing the outer conductor using a solder material. Moreover, it can be carried out at a low cost without degrading the electrical insulation characteristics of the internal insulator.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an example of the structure of a shielded cable according to the present invention, and FIG. 2 is a diagram for explaining a verification result of an internal insulator according to the present invention. Description of the reference numerals in the figure is omitted by using the same reference numerals as used in FIG. The shielded cable according to the present invention is structurally the same as the conventional one, and is formed by sequentially forming an inner insulator 3, an outer conductor 4, and a jacket 5 on the outer circumference of the inner conductor 2 in a coaxial manner.

  For example, the inner conductor 2 is formed by twisting seven tin-plated copper alloy wires having an outer diameter of about 0.025 mm, and the outer surface is made of an insulating material made of fluororesin and has a thickness of about 0.04 mm to 0.055 mm. The inner insulator 3 is covered. The outer conductor 4 disposed on the outer peripheral surface of the inner insulator 3 is formed, for example, by winding a plurality of copper alloy wires having an outer diameter of about 0.03 mm in a horizontal winding and having a thickness of about 0.004 mm on the outer surface. Two polyester tapes are wound on top of each other and fused together to form a jacket 5, so that a shielded cable 1 having an outer diameter of about 0.3 mm or less is obtained. Note that a copper vapor-deposited tape (not shown) may be wound around the outer surface of the outer conductor 4 with the copper vapor-deposited surface inside, and the outer conductor 4 is wound in two layers with the winding direction of the copper alloy wire being opposite. An attached structure may be used, and in addition, a braided structure may be used.

  When the inventor of the present invention cuts the outer conductor 4 by laser irradiation, the inner insulator 3 is colored by adding a coloring pigment (blue or purple) or carbon black (black) to the inner insulator 3. It has been clarified that the deterioration of the insulation characteristics of can be suppressed. This is considered to be related to the transmittance or absorption rate of the laser beam due to the coloration of the internal insulator 3, but when the color density is changed or carbon black is used for black coloring, Since the behavior is different, it has not been fully elucidated.

  FIG. 2 is a diagram showing a result of verifying the insulation resistance of the internal insulator 3 and the appearance of the cut portion when the external conductor 4 is cut with a YAG laser while changing the thickness of the internal insulator 3 and the type of coloring material. It is. The thickness of the internal insulator 3 was 40 μm for samples 1 to 4, 50 μm for samples 5 to 10 and 60 μm for sample 11. Samples 1 and 5 were added with a pigment so that the inner insulator was “light blue”, and samples 2 and 6 were added with carbon black so that the inner insulator was “light black”. No. 7 is obtained by adding a pigment such that the internal insulator becomes “light purple”. Sample 8 is obtained by adding a large amount of carbon black so that it becomes dark “black”, and adding a pigment that makes dark “purple” to samples 9 and 11. In Samples 4 and 10, the internal insulator is a conventional non-colored natural color.

  Further, as the fluororesin used for the internal insulator 3 of the samples 1 to 11, a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (abbreviation: PFA) having excellent electrical characteristics and heat resistance was used. Then, the insulation resistance of the internal insulator 3 after the outer conductor 4 was cut with a YAG laser was measured, and a value of 2000 MΩ or more was regarded as an acceptable product, and a value less than that was regarded as a defective product. Further, when the outer conductor 4 was cut, the internal conductor was damaged, or the internal insulator 3 was melted or damaged, and the appearance was particularly poor, and when the external conductor 4 was not damaged, the appearance was good.

  From the verification results of FIG. 2, samples 4 and 10 in which the inner insulator is an uncolored natural color were tested by producing 10 samples each, but none of them could clear the insulation resistance of 2000 MΩ, resulting in damage to the inner conductor. Besides, the appearance was not good. This is presumably because the YAG laser originally has the property of being easily absorbed by the metal that is the inner conductor. On the other hand, in other samples in which the internal insulator was colored, the insulation characteristics and appearance after laser processing were improved, indicating that it is effective to color the internal insulator.

  Further, since the number of acceptable insulation resistances is increased by increasing the thickness of the internal insulator from 40 μm → 50 μm → 60 μm, it is considered possible to improve the insulation characteristics. However, if the thickness of the internal insulator is increased, the wire diameter of the shield cable is increased. Therefore, it is not preferable to improve the insulation resistance by increasing the insulation thickness, and the insulator thickness is desirably suppressed to 55 μm or less.

  In addition, it was confirmed that the darker the color of the internal insulator had less influence on the internal conductor, but the insulation resistance was not improved in comparison with the samples 7 and 9, and the darker the color was not necessarily. Not good. This is considered to be due to the fact that the coloring pigment contains a metal, and there is a concern about destabilization when the insulating thickness is limited. On the other hand, when colored with carbon black, the behavior was found to be slightly different compared to when other colored pigments were used. That is, the inner insulators of samples 2 and 6 are “light black” and the inner insulator of sample 8 is dark “black”, but “light black” sample 6 has good insulation resistance and appearance. It is. Sample 2 also has some instability in insulation resistance, but it is better than other samples. However, when the sample 8 is dark “black”, both the insulation resistance and the appearance are poor.

  This seems to be due to the fact that carbon black different from the pigment is used for coloring “light black” and “black”. That is, “light black” of sample 6 showed a good result because the laser beam was not absorbed by adding moderate carbon black and the internal conductor was not damaged, and the insulation resistance was maintained at a predetermined value or more. It seems that he was able to. Then, in order to obtain a dark “black” as in Sample 8, the amount of carbon black, which is an electrically good conductor, is increased in electrical terms. Therefore, it is conceivable that the insulating properties deteriorate due to laser irradiation.

  Thus, the appropriate amount of carbon black added was verified. Samples were prepared by adding 0.025 wt%, 0.06 wt%, 0.14 wt%, 0.33 wt% of carbon black to the base resin (PFA) of the inner insulator, and the outer conductor was cut with a YAG laser. . Thereafter, when the insulation resistance of the internal insulator and the appearance of the cut portion were verified, the carbon black added by 0.33 wt% was defective, but the other samples obtained good results. That is, when the added amount of carbon black is in the range of about 0.025 wt% to 0.14 wt%, even if the outer conductor is cut by a YAG laser, the inner conductor is not damaged, and the electrical insulation resistance is predetermined. It became clear that the appearance of the cut portion can be maintained satisfactorily while being able to keep above the value.

Sample 11 also showed good results in both insulation resistance and appearance, but the insulation thickness needs to be 60 μm or more, and the shielded cable has a large diameter. In addition to PFA used in the sample, tetrafluoroethylene (abbreviation: PTFE) or tetrafluoroethylene hexafluoropropylene copolymer (abbreviation: FEP) can be used as the fluororesin. However, PFA having a high heat-resistant temperature, particularly excellent high-frequency characteristics and good coating moldability is most suitable. Further, a CO ₂ laser is used for forming the outer cover and the inner insulator. However, for cutting the outer conductor, a YAG laser that has a good light-condensing property to a small area and can stably obtain a high output. Is most suitable.

  As described above, the shielded cable according to the present invention adds 0.025 wt% to 0.14 wt% of carbon black to the fluororesin of the base resin of the inner insulator and colors it to “light black”, thereby forming an inner conductor. The outer conductor can be directly cut by laser processing without causing damage and without deteriorating the insulating properties of the inner insulator. For this reason, it is not necessary to arrange a heat-resistant layer between the inner insulator and the outer conductor as shown in FIG. 3, or to use a step of applying a solder material as shown in FIG. In the above description, the example of the terminal formation of the single-core shielded cable has been described. However, the terminal formation can be performed in the same manner also in a multi-core cable in which a plurality of shielded cables are arranged in a flat shape. .

It is a figure explaining the structural example of the shielded cable by this invention. It is a figure for demonstrating the verification result about the internal insulator of this invention. It is a figure explaining an example of the conventional shielded cable. It is a figure explaining the other example of the conventional shielded cable.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Shielded cable, 2 ... Internal conductor, 3 ... Internal insulator, 4 ... External conductor, 5 ... Outer coating, 6 ... Coating layer, 7, 7a ... Adhesive tape, 8 ... Solder material, 9 ... Processing groove | channel.

Claims (5)

  A shielded cable in which an inner insulator, an outer conductor, and a jacket are sequentially formed on the outer circumference of the inner conductor in a coaxial manner. The inner insulator is made of a fluororesin, and carbon black of 0.025 wt% to 0.14 wt% is added. Shielded cable characterized by being colored.   The shielded cable according to claim 1, wherein the fluororesin is a tetrafluoroperfluoroalkyl vinyl ether copolymer.   The shield cable according to claim 1 or 2, wherein the coating thickness of the internal insulator is 55 µm or less.   The outer cover of the end portion of the shielded cable according to any one of claims 1 to 3 is peeled off by a predetermined length to expose the outer conductor, and the outer conductor is cut and cut with a YAG laser to expose the inner insulator. A method for forming a terminal of a shielded cable.   5. The shield cable terminal forming method according to claim 4, wherein a plurality of the shield cables are arranged in a flat shape at a predetermined pitch.

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