JP4084595B2 - Manufacturing method of high frequency flexible multi-core coaxial cable and its applied electronic equipment - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for manufacturing a high-frequency flexible multi-core coaxial cable used in electronic equipment, medical equipment, etc., and in particular, has a high-frequency characteristic of 1 GHz or more and can be realized at a cost approximately half that of a conventional flexible multi-wire. The present invention relates to a method for manufacturing a core-type coaxial cable.
[0002]
[Prior art]
Recently, there has been an increasing demand for video and high-speed, large-capacity broadband services, and the speedup of electronic devices and medical devices such as personal computers (hereinafter abbreviated as personal computers), digital cameras, 8 mm cameras, and portable information and communication terminals. It is mandatory. Already, in these devices, some of the cables that connect the liquid crystal display that provides the display screen and the control circuit have a signal transmission speed exceeding 1 GHz, and this high-speed trend is expected to continue in the future. ing. In the notebook computer market, the annual shipment volume in FY2000 is 24 million units, of which 60 to 70% are fine-coaxial cables and the rest are flexible multi-core cables.
[0003]
Conventionally, in these devices, a flexible multi-core cable, a flexible multi-core thin wire coaxial cable, or the like has been used as a cable for connecting a liquid crystal display providing a display screen and a control circuit. FIG. 6 shows a conventional structure example of a flexible multicore cable. In this cable, as shown in FIG. 6, a plurality of central conductors 2 for transmitting signals are arranged in parallel on an insulating film 1 such as polyimide or epoxy resin, and then the central conductor 2 is covered with the insulating film 3. Has a microstrip structure. FIG. 7 shows an example of a conventional structure of a flexible multi-core thin wire coaxial cable. In this cable, a plurality of fine coaxial cables, in which a central conductor 5 for transmitting a signal is surrounded by a first insulating film 6 and the outside thereof is covered with an outer conductor 7 serving as a ground plane and a second insulating film 8. The structure 9 is connected in parallel. The former is a simple structure in which the central conductor 2 is formed on the insulating film 1 and is therefore inexpensive and is often used in electronic devices that require a signal transmission / reception speed of 100 MHz or less. The latter is mainly used in a cable connection system of an electronic device such as a medical device that requires a signal transmission / reception speed of 300 to 400 MHz, and can perform high-speed signal transmission / reception.
[0004]
[Problems to be solved by the invention]
The electronic devices and medical devices described above are required to be faster, smaller, thinner, and lower cost, and the cables used are also required to be thinner, thinner, and cost-reduced. Yes. However, narrowing and thinning of cables leads to transmission loss and band degradation of transmission lines, transmission quality deterioration due to crosstalk between transmission lines and external noise, etc., so to realize high quality and high speed transmission, Overcoming these challenges is essential. Since the flexible multi-core cable shown in FIG. 6 has a microstrip structure, the center conductor 2 formed on the side opposite to the ground plane is open, so that the crosstalk between the center conductors, that is, between the signal transmission paths. In addition to being easily affected by external noise and the impedance of the cable when the cable is bent, it is difficult to prevent deterioration in signal transmission quality. In addition, the flexibility of the cable at the hinge part of the notebook PC is inferior (breaking at 2,000 times in a bending test with a radius of 2.5 mm: about one tenth of the target), and the transmission band can only be up to about 100 MHz. Not. The thin coaxial cable shown in FIG. 7 was developed to realize high-speed transmission, high noise resistance, and suppression of impedance fluctuations that occur when the cable is bent, which was a problem in the flexible cable structure of FIG. Widely used in personal computers and medical equipment. However, the price of the thin coaxial cable is about four times the price of the flexible cable, which is very expensive.
[0005]
An object of the present invention is to solve the problems of the above prior art and the prior art, enable high-speed transmission, be inexpensive, have excellent noise resistance, and have low impedance fluctuation when bending the cable. It is in providing the manufacturing method of.
[0006]
In the method for manufacturing a high-frequency flexible multi-core coaxial cable according to the present invention, only a plurality of upper and lower outer conductors covering the first insulating film are etched, and a plurality of parallel conductors having a constant width and a gap are etched. By forming the wired central conductor at once, the basic part of the rectangular high-frequency flexible multi-core coaxial cable is created,
Next, the created rectangular high-frequency flexible multi-core coaxial cable basic portion is laminated in multiple stages with the second insulating film sandwiched between them, and the outer conductors are stacked on the top to adhere each layer.
Next, press the top and bottom using a press to crimp each layer,
Next, the crimped product is cut so that the central conductors are aligned in the vertical direction, and a plurality of rectangular high-frequency flexible multicore coaxial cables are cut out.
That is, it has a rectangular coaxial structure in which a plurality of central conductors formed in parallel on a first insulating film are embedded with a second insulating film, and the insulating film is further covered with an outer conductor serving as a ground plane. A method for manufacturing a flexible multicore cable is provided. The manufacturing method is as follows. First, only the upper surface conductor of the insulating film whose upper and lower surfaces are entirely covered with an external conductor is etched to form a plurality of central conductors having a constant width and a gap through which signals are transmitted. At this time, the width and gap of the center conductor are determined so as to be a predetermined impedance of the cable used, for example, 50Ω. Next, the second insulating film on which the outer conductor is not formed is bonded to the surface on which the central conductor is formed to form a flexible cable corresponding to one layer. Therefore, a desired rectangular high-frequency flexible multi-core coaxial cable can be obtained by laminating a large number of the single layer flexible cables, pressurizing them with a press machine, pressing the layers, and slicing them in the vertical direction. At this time, since the insulating film is still exposed on the side surface, a rectangular flexible multi-core cable can be realized by forming an external conductor on the side surface using means such as plating. The flexible multi-core coaxial cable according to the means provided by the present invention has basically the same structure as a conventional round thin coaxial cable, and the central conductor through which a signal is transmitted is an outer conductor that forms a ground plane. Is surrounded. For this reason, an arbitrary line impedance can be set, high-speed transmission is possible, and impedance fluctuation at the time of cable bending can be suppressed to be small. In addition, since the electromagnetic field radiated from the central conductor is confined in the insulating film by the external conductor, the crosstalk between the transmission paths can be prevented, and the influence on various noises jumping from the outside can be blocked. It is possible to improve noise resistance. Furthermore, since the present invention has the same properties as the conventional flexible cable, it is flexible and can be realized at about half the price of the conventional thin coaxial cable. Can be provided.
Further, in the method for manufacturing a high-frequency flexible multi-core coaxial cable described above, when a plurality of the rectangular high-frequency flexible multi-core coaxial cable basic portions are stacked and bonded together, An alignment hole for aligning the conductor may be provided, and an alignment pin may be inserted through the alignment hole.
The electronic device of the present invention is a high-frequency flexible manufactured using the method for manufacturing a high-frequency flexible multi-core coaxial cable according to claim 1 or 2 between a liquid crystal display providing a display screen and a cable connecting a control circuit. It is connected by a multi-core coaxial cable.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a structure of a high-frequency flexible multicore coaxial cable according to the manufacturing method of the present invention as an embodiment, and FIG. 2 shows a basic flow of the manufacturing method. As shown in FIG. 1A, the high-frequency flexible multicore coaxial cable 15 of this embodiment has a rectangular coaxial structure in which a central conductor 10 is embedded with an insulating film 11 and the insulating film 11 is covered with an outer conductor 12. , They are formed by bundling them in parallel. In this structure, the signal current is transmitted through the center conductor 10 and the outer conductor 12 functioning as a ground plane. The cable according to the present invention has basically the same single strip line structure as a conventional coaxial cable, can set an arbitrary line impedance, and can perform high-speed transmission. For example, the characteristic impedance Zo of the transmission line can be calculated by the following equation using the sectional view of the basic single strip line structure of the rectangular coaxial cable shown in FIG.
Zo = 60 / √εr * ln {2 * (2H + T) / (0.8W + T)} (1)
Here, εr is the relative dielectric constant of the insulating film 11, H is the thickness of the insulating film 11, and T and W are the thickness and width of the central conductor 10. From the equation (1), it can be seen that an arbitrary impedance can be realized if the width and thickness of the central conductor 10 and the insulating film 11 and the relative dielectric constant are appropriately selected. Incidentally, the thickness H of the insulating film 11 is 47.5 μm when Zo is 50Ω, εr is 3.4, T is 25 μm, and W is 30 μm. Therefore, even if the thickness of the outer conductor 12 is 30 μm, the width of one cable can be configured as 150 μm. According to the simulation result in this structure, it has been confirmed that a standing wave ratio of 1.1 or less can be realized up to 3 GHz at a line impedance of 50Ω. Note that the outer covering insulating film 13 shown in FIG. 1A is for protecting the coaxial cable and does not affect the high-frequency transmission characteristics, so it may be essentially omitted.
[0008]
Next, a method for manufacturing a rectangular high-frequency flexible multi-core coaxial cable according to the present invention will be described using the embodiment of FIG. First, of the upper and lower outer conductors 21 and 22 covering the first insulating film 23 prepared as a material shown in FIG. 2A, only the upper outer conductor 21 is etched to obtain a predetermined impedance of the cable. A plurality of centrally-wired central conductors 24 having a constant width and a gap determined by the above are collectively formed. The processed cross section at this time is shown in FIG. 2B, and it can be seen that the basic portion 25 of the rectangular high-frequency flexible multicore coaxial cable is formed. As an etching method, either dry etching or wet etching may be used. Further, copper or copper-nickel-gold or the like can be used as the electrode material of the center conductor 24, and epoxy or polyimide film or the like can be used as the insulating film. An adhesive layer may be sandwiched between the central conductor 24 and the insulating film 23 in order to strengthen the adhesive force. Next, as shown in FIG. 2 (c), second rectangular insulating films 26-1 to 26-5 for forming the outer conductor on the upper surface of the prepared rectangular high-frequency flexible multi-core coaxial cable basic portion 25 are provided. The layers are stacked in multiple layers, and the outer conductors 27 are stacked on the top to bond the layers. In this state, as shown in FIG.2 (d), it pressurizes up and down using a press, and each layer is crimped | bonded. At this time, if the press is uneven depending on the location, air bubbles are mixed in, and a complete coaxial cable cannot be realized. Therefore, the introduction of a vacuum hot press technique or the like is effective for avoiding the mixing of bubbles. In addition, optimization of time and temperature required for pressing is also an important factor. Next, in the state of FIG.
As shown in FIG. 2 (e), a large number of rectangular high-frequency flexible multi-core coaxial cables 28 can be cut out by cutting in the vertical direction using a slicer or the like. The side is bare. Therefore, if the outer conductors 29-1 and 29-2 are formed on the side surface of the rectangular high-frequency flexible multi-core coaxial cable 28 by plating or the like, the rectangular high-frequency flexible multi-core coaxial cable 15 shown in FIG. . FIG. 2G shows a case where the rectangular high-frequency flexible multi-core coaxial cable 28 manufactured as described above is covered with an insulating film 30. The influence of the covering of the insulating film 30 on the high-frequency characteristics is shown in FIG. There is no. In the embodiment of the present invention described with reference to FIG. 2, the number of layers of the coaxial structure is five, but it is obvious that the number of layers is not limited.
[0009]
FIG. 3 shows an embodiment of the rectangular high-frequency flexible multi-core coaxial cable 31. This figure has the same structure as the rectangular high-frequency flexible multi-core coaxial cable 28 produced in FIG. When the thickness H of the insulating films 32 and 33 defined by the expression (1) is about 1/3 in the width direction, the side external conductors may be omitted. This is because the electromagnetic field radiated from the center conductor 34 is almost absorbed by the outer conductor 35, so that the influence on the adjacent center conductor, that is, the amount of crosstalk can be greatly reduced. Also, most of the external noise radio waves coming from the outside are absorbed by the external conductor 35, so the influence on the signal transmission quality is small. As for the dimensions of the cable in the embodiment of FIG. 3, if the width ratio between the center conductor 34 and the outer conductor 35 is set to 3 times, the thickness becomes 345 μm, which is about 70% of the thickness of the conventional thin coaxial cable. Can be realized. In this embodiment, the step of attaching the outer conductor on the side surface can be omitted, which is effective for shortening the manufacturing period and reducing costs by simplifying the steps.
[0010]
By the way, if the position between the center conductors in each layer is shifted in FIG. 2C, the center conductor is shifted from the center of the insulating films 23 and 26 when the cable is cut out in the process of FIG. A value different from the predetermined value is taken. For this reason, there is a slight difference in transmission characteristics depending on each layer. In order to avoid this, FIG. 4 shows an embodiment of a method for aligning the center conductors of the rectangular high-frequency flexible multicore coaxial cable 15 manufactured according to the present invention. In the present invention, in order to perform alignment between the center conductors 24 of each layer, about 2 to 4 alignment holes are formed for each layer, and positioning pins 41 are set up in each of the holes to perform alignment between the center conductors 24. While pressing. If this method is used, alignment on the order of several μm is possible.
[0011]
FIG. 5 shows an embodiment of a personal computer 51 equipped with a rectangular high-frequency flexible multi-core coaxial cable manufactured according to the present invention. The personal computer includes a signal processing unit 53 that reads, writes, calculates, and controls data according to information input by tapping the keyboard 52, and a liquid crystal display 54 that displays the processing results. The cable 55 according to the present invention is used for batch data transfer. Note that although the example of a personal computer is described as an application example in FIG. 5, it is obvious that the present invention can be applied to any electronic device including a liquid crystal display, a signal processing unit, and a control circuit.
[0012]
【The invention's effect】
The cable portion according to the present invention has basically the same structure as a conventional coaxial cable, and a central conductor through which a signal is transmitted is surrounded by an outer conductor that forms a ground plane with an insulating film interposed therebetween. Therefore, an arbitrary line impedance can be set, high-speed transmission is possible, and impedance fluctuation at the time of cable bending can be suppressed. In addition, since the electromagnetic wave radiated from the central conductor can be confined in the insulating film by the external conductor, it is possible to prevent the crosstalk between the transmission lines, and to block the influence on various noises entering from the outside. Noise resistance can be improved. Furthermore, another advantage of the present invention is that it has the same properties as a conventional flexible cable, so that it is flexible and can be realized at low cost. Therefore, it is widely applied to electronic devices and medical devices such as personal computers, digital cameras, handy cams, broadband communication compatible information communication portable terminals, etc., where the demand for high speed is increasing, and to increase the speed, size and cost of the system. Can contribute. In addition, according to the present invention, the thin coaxial cable mainly used as a high-speed transmission line at present is considered to be replaced with the rectangular high-frequency flexible multi-core coaxial cable according to the present invention in terms of cost competitiveness. .
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a basic structure of a high-frequency flexible multicore coaxial cable manufactured according to the present invention.
FIG. 2 is a basic production flow diagram showing a method for producing a high-frequency flexible multicore coaxial cable according to the present invention.
FIG. 3 is a diagram showing an embodiment of the present invention.
FIG. 4 is a diagram showing an embodiment of a method for aligning positions between central conductors in a method for manufacturing a high-frequency flexible multicore coaxial cable according to the present invention.
FIG. 5 is a diagram showing an example of an electronic apparatus to which the present invention is applied.
FIG. 6 is a view showing a conventional example of a flexible multicore cable.
FIG. 7 is a view showing another conventional example of a flexible multi-core cable.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 3, 6, 8: Insulating film 2, 5: Center conductor 7: Outer conductor 9: High frequency flexible multi-core coaxial cable 10: Center conductor 11, 13: Insulating film 12: Outer conductor 15: Square type high frequency flexible multi-core Coaxial cables 21, 22: outer conductor 23: insulating film 24: center conductor 25: square high-frequency flexible multi-core coaxial cable 26-1 to 26-5: insulating film 27: outer conductor 28: square high-frequency flexible multi-core coaxial cable 29-1, 29-2: External conductor 30: Insulating film 31: Square high-frequency flexible multi-core coaxial cable 32, 33: Insulating film 34: Center conductor 35: External conductor 41: Alignment pin 51: Personal computer 52: Keyboard 53: Signal processor 54: Liquid crystal display 55: Square high-frequency flexible multi-core coaxial cable

Claims (3)

By etching only the upper outer conductors of the upper and lower outer conductors covering the first insulating film to form a plurality of parallel conductors having a constant width and gap, the square conductors are formed in a square shape. Create a high-frequency flexible multicore coaxial cable basic part,
Next, the created rectangular high-frequency flexible multi-core coaxial cable basic portion is laminated in multiple stages with the second insulating film sandwiched between them, and the outer conductors are stacked on the top to adhere each layer.
Next, press the top and bottom using a press to crimp each layer,
Next, the crimped product is cut so that the central conductors are arranged in parallel in the vertical direction, and a plurality of rectangular high-frequency flexible multi-core coaxial cables are cut out. . 2. The method of manufacturing a high-frequency flexible multi-core coaxial cable according to claim 1 , wherein a plurality of the square high-frequency flexible multi-core coaxial cable basic portions are stacked and crimped to each of the square high-frequency flexible multi-core coaxial cable basic portions. A method of manufacturing a high-frequency flexible multi-core cable, wherein an alignment hole for aligning conductors is provided, and an alignment pin is inserted through the alignment hole. A liquid crystal display providing a display screen and a cable connecting the control circuit are connected by a high frequency flexible multi-core cable manufactured using the method for manufacturing a high-frequency flexible multi-core cable according to claim 1 or 2 . An electronic device characterized by that.

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