JP2016225164A - Hollow film cable and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin hollow film cable having a little insertion loss of an electric signal in high-frequency transmission and giving a constant characteristic impedance over the whole length of a signal line.SOLUTION: The thin hollow film cable is constituted by a film cable comprising a signal line 11 and a shield conductor 13a interposing an insulation resin layer 12a, or a film cable having insulation resin layers 12a, 12b on either surface of a signal line 11, and shield conductors 13a, 13b outside the insulation resin layers 12a, 12b, respectively. A hollow part 15 is formed between the signal line and the shield conductor along an extending direction of the signal line, by chemically or mechanically removing a part of the insulation resin layer; and the hollow part 15 is formed continuously along the extending direction of the signal line 11. Further, a void ratio of the insulation resin layer in a region corresponding to a line width of the signal line between the signal line 11 and the shield conductor is set to 50% or more.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a hollow film cable suitable for relaying a high-frequency signal from an antenna element mounted on, for example, a mobile device to a main board of the device main body and a method for manufacturing the same.

For example, in an electronic device such as a network device, a server, a semiconductor test apparatus, or a communication device, various coaxial cables are used for transmitting a high-frequency signal. The frequency of the signal is used in the range of several GHz to several tens GHz, and a thin coaxial cable is required for parallel multi-core transmission in order to reduce the size of the device.
Also, in recent mobile devices such as smartphones and tablet PCs, a thin cable capable of high-speed signal transmission is required in order to reduce the weight and size of the device, and at the same time to transmit and receive large amounts of data. Has been.

In the above-mentioned fields, coaxial cables have been frequently used in the past, and the wire diameter is about 1 to 10 mm for servers and semiconductor test equipment, and about 0.3 to 1.0 mm for mobile devices such as smartphones. ing.
This coaxial cable has a constant and stable characteristic impedance, is not affected by external noise, and does not radiate electromagnetic waves from the cable body to the outside. Therefore, it is preferably used in the field of high-frequency signal transmission. ing.

In recent smartphones in particular, a coaxial cable having a small diameter of about φ0.6 to 0.8 mm is used for signal transmission from the antenna, and the diameter tends to be further reduced. However, there are problems such as a problem that signal transmission characteristics are inferior with a decrease in diameter and that it is difficult to assemble with a connector.
Therefore, it has been studied to replace the insulating resin in the cable with a foamed resin or to improve the structure to have many hollows.

As is well known, the electromagnetic field is most easily transmitted in vacuum, followed by air, followed by low dielectric constant and low dielectric loss tangent resin, and then ceramic. Transmission characteristics are improved by using resin.
However, in reality, the round cable using the above-described foamed resin or hollow resin has not been put into practical use due to the problems of mechanical properties, bending durability, processing difficulty, and manufacturing cost of the cable.

  On the other hand, instead of the coaxial cable described above, a film cable using an FPC (flexible printed wiring board) having a microstrip structure or a strip structure in which an insulating resin layer is interposed between a signal line and a shield conductor (ground layer) made of copper foil Is provided.

  FIG. 1A shows an FPC having a microstrip structure, which is provided with a shield conductor (ground layer) made of a copper foil 3 with an insulating resin layer 2 sandwiched with respect to a signal line 1. FIG. 1B shows an FPC having a strip structure, in which insulating resin layers 2a and 2b exist on both surfaces of the signal line 1, and shield conductors made of copper foils 3a and 3b are provided on both outer sides of the insulating resin layer. Yes. Conventionally, polyimide is used as an interlayer insulating layer in this type of FPC. However, polyimide has a relative dielectric constant of about 3.5 at 1 GHz and a dielectric loss tangent as large as about 0.01, and thus has a problem such as a large signal loss for high-frequency transmission at 1 GHz or higher.

For this reason, recently, a strip structure of an LCP cable having an LCP (liquid crystal polymer) disclosed in, for example, Patent Document 1 as an interlayer insulating material and copper foils on both sides thereof has also been put into practical use. .
This LCP has a relative dielectric constant of about 2.5 at 1 GHz and a dielectric loss tangent as small as about 0.003. Therefore, it is attracting attention for use in antenna modules, high-speed signal transmission cables, and recently, high-speed signal system multilayer boards. ing.

Japanese Patent No. 3522513

  Although the above-mentioned LCP has excellent characteristics in terms of dielectric constant and dielectric loss tangent at high frequencies, the cost of this resin is expensive, and the manufacturing process is more complicated in cable production than conventional polyimide base films. However, there are problems in practical use, such as an increase in final price, a thickness of about 0.3 mm, and poor flexibility.

  Accordingly, the present invention eliminates the technical problems described above and reduces the insertion loss of an electric signal in high-frequency transmission, and makes it possible to obtain a constant characteristic impedance over the entire length of the signal line. It is an object of the present invention to provide a film cable and a manufacturing method thereof.

  The hollow film cable according to the present invention made to solve the above-mentioned problems is a film cable having a shield conductor with an insulating resin layer sandwiched between signal lines, or an insulating resin layer on both sides of the signal line, A film cable provided with shield conductors on both outer sides of each insulating resin layer, and a part of the insulating resin layer between the signal line and the shield conductor along the extending direction of the signal line A hollow portion is formed by chemically or mechanically removing the.

In this case, in one preferable embodiment, the hollow portion is formed continuously along the extending direction of the signal line.
Moreover, it is desirable that the porosity of the insulating resin layer in the region of the line width of the signal line between the signal line and the shield conductor is set to 50% or more.

  On the other hand, a first method for producing a hollow film cable according to the present invention, which has been made to solve the above-described problems, is a film cable having a shield conductor with an insulating resin layer sandwiched between signal wires, or both sides of a signal wire. A film cable having an insulating resin layer and shield conductors on both outer sides of each insulating resin layer, and intermittently etched by etching along the extending direction of the signal line with respect to the shield conductor Forming an opening in the substrate, and using the shield conductor having the opening as a mask, partially removing the insulating resin layer by etching to reach the signal line from the shield conductor to the insulating resin layer Forming a hollow portion, and obtaining a film cable in which the hollow portion is continuously formed along the extending direction of the signal line.

  In addition, the second method for producing a hollow film cable according to the present invention, which has been made to solve the above-described problem, is to form a part of an insulating resin layer having a shield conductor on one side into a groove shape by laser light or etching. A step of forming a hollow portion by deleting, a step of forming a rib member by an exposure phenomenon of a photosensitive resin in the hollow portion formed in the insulating resin layer, and a rib member formed in the groove-shaped hollow portion Having a pair of insulating resin layers facing each other and interposing a sheet provided with a signal line between them, and laminating the signal lines facing each other along the opposing rib member, A film cable in which a signal line is supported by line contact with an end face of the rib member is obtained.

  Furthermore, a third method for producing a hollow film cable according to the present invention, which has been made to solve the above-described problems, is to form a part of an insulating resin layer having a shield conductor on one side into a groove shape by laser light or etching. A step of forming a hollow portion by deleting, a step of forming a rib member by an exposure phenomenon of a photosensitive resin in the hollow portion formed in the insulating resin layer, and an insulating resin layer in which the rib member is formed. A step of arranging a sheet having a signal line facing each other and a step of laminating the signal line along the rib member in a state of facing the signal line, the signal line being connected by an end surface of the rib member. A film cable supported by contact is obtained.

According to the hollow film cable having the above-described structure, in the film cable having a strip structure or a microstrip structure, the insulating resin layer (electrically insulating dielectric resin) existing between the signal line and the shield conductor is chemically or By mechanically deleting, a structure having a hollow portion is formed.
According to this, since the electromagnetic field between the signal line and the shield conductor (ground layer) has a transmission structure in which most of the electromagnetic field propagates through the air (hollow part), the insertion of the electrical signal in high-frequency transmission It is possible to provide a thin transmission / reception cable with little loss and capable of obtaining a constant characteristic impedance over the entire length of the signal line.

It is sectional drawing (a) orthogonal to the longitudinal direction of the film cable made into the conventional microstrip structure, and a perspective view (b). It is sectional drawing (a) orthogonal to the longitudinal direction of the film cable made into the conventional strip structure, and a perspective view (b). It is the perspective view which showed 1st Embodiment of the hollow film cable which concerns on this invention. It is the perspective view which similarly showed 2nd Embodiment. It is the schematic diagram which showed the manufacturing process of the hollow film cable of 1st Embodiment concerning this invention. It is the schematic diagram which showed the manufacturing process following FIG. 4A. It is the schematic diagram which showed the manufacturing process of the hollow film cable of 3rd Embodiment concerning this invention. It is the schematic diagram which showed the manufacturing process following FIG. 5A. It is the schematic diagram which showed the manufacturing process following FIG. 5B. It is the graph which compared the electrical transmission characteristic of the hollow film cable which concerns on this invention, and another existing coaxial cable.

  A hollow film cable according to the present invention will be described based on an embodiment shown in the drawings. In each figure shown below, the same parts are indicated by the same reference numerals, but in some drawings, representative parts are given reference numerals for convenience of the paper, and detailed configurations are given in other drawings. In some cases, reference numerals are used for explanation.

FIG. 2 shows a basic configuration of the first embodiment, and the example shown in FIG. 2 shows a hollow film cable having a strip structure.
That is, with the signal line 11 in the center, insulating resin layers 12a and 12b are provided on both surfaces of the signal line 11, and shield conductors (ground layers) 13a and 13b are further provided on both outer sides of the insulating resin layers 12a and 12b. It has been.
In this example, polyimide is used as the insulating resin layers 12a and 12b, copper foil is used for the signal line 11 and the shield conductors 13a and 13b, and the shield conductors 13a and 13b are the insulating resin layers 12a and 12b. A solid electrode is formed along the surface 12b.

In the embodiment shown in FIG. 2, along the extending direction of the signal line 11, a broken-line opening 14 is formed by etching the shield conductors 13a and 13b on both sides.
The broken-line-shaped opening 14 formed by etching is for removing a part of the insulating resin layer made of polyimide by etching along the extending direction of the signal line 11 as described in the description of the manufacturing method later. Used.
That is, by using the shield conductors 13a and 13b on both sides as a mask, the etching liquid enters the insulating resin layers 12a and 12b from the opening 14, and a part of the insulating resin layer is removed by etching, whereby the signal line The hollow portion 15 reaching 11 is formed.

For this purpose, the opening 14 formed in the shield conductors 13 a and 13 b is formed in two lines along the extending direction of the signal line 11. As a result, as shown in FIG. 2, hollow portions 15 that reach both ends in the line width direction are formed by etching with respect to the insulating resin layers 12a and 12b made of polyimide, leaving the central portion of the signal line 11 in the line width direction. Is done.
Due to the arrangement pattern of the openings 14, the porosity of the insulating resin layer in the line width region of the signal line between the signal line 11 and the shield conductors 13a and 13b is set to 50% or more. In the embodiment, the hollow portion 15 is formed continuously (in communication) along the extending direction of the signal line 11.
The hollow portion 15 is formed so as to be symmetrical on both surfaces of the signal line 11 as shown in FIG.

FIG. 3 shows a basic configuration of the second embodiment, and the example shown in FIG. 3 also shows a hollow film cable having a strip structure. In FIG. 3, portions that perform the same functions as those shown in FIG. 2 are denoted by the same reference numerals. Therefore, the overlapping description is omitted.
In the example shown in FIG. 3, the arrangement form of the openings 14 formed in the shield conductors 13a and 13b is different from the example shown in FIG. The form of the hollow part 15 to be molded is also different. The example shown in FIG. 3 is the same as that of the first embodiment shown in FIG. 2 except for the points described above.

In the second embodiment shown in FIG. 3, circular openings 14 are intermittently formed by etching along the extending direction of the signal line 11 with respect to the shield conductors 13a and 13b on both sides. ing.
The circular openings 14 are formed in a pair of left and right (two) along the extending direction of the signal line 11, and one next to the center is formed at the center, and the two and one are formed. The pattern is repeated.

As shown in FIG. 3, the shield conductor 13b on the lower surface side corresponding to the position where the pair of openings 14 is formed in the shield conductor 13a on the upper surface side has one opening portion 14 formed in the center portion. The repeated patterns of the openings 14 are shifted from each other on the upper surface side and the lower surface side.
Due to the arrangement pattern of the circular openings 14 described above, the porosity of the insulating resin layer in the region of the signal line width between the signal line 11 and the shield conductors 13a and 13b is set to 50% or more. Yes.

4A and 4B sequentially show the manufacturing process of the hollow film cable according to the first embodiment shown in FIG.
In the pre-manufacturing process, as shown in FIG. 4A (a), a laminate (double-sided copper-clad laminate) having 10 μm copper foils on both sides of an insulating resin layer 12b made of polyimide as the first substrate A is provided. Prepared.
The copper foil on one surface of the first base material A is formed with a signal line 11 having a width of 150 μm and a pad connection region 11a following the signal line 11 by etching. The copper foil on the other side is used as a solid copper foil and is used as the shield conductor 13b.
Further, as the second base material B, a laminated board (single-sided copper-clad laminated board) having a 10 μm copper foil on one side of the insulating resin layer 12a made of polyimide is used, and the copper foil is used as a solid copper foil. 13a is made.

  Next, as shown in FIG. 4A (b), the insulating resin layer 12a in the second base material B is disposed opposite to the surface of the first base material A on which the signal line 11 is formed, and between them, An adhesive sheet 17 having a thickness of 12 μm is interposed, and the first base material A and the second base material B are laminated by thermocompression bonding. FIG. 4A (c) shows a state in which the first base material A and the second base material B are laminated with the adhesive sheet 17 in between.

  FIG. 4B (a) shows a manufacturing process following FIG. 4A (c). In this process, the through hole 18 is appropriately formed by, for example, a drill, avoiding the arrangement position of the signal line 11 in the laminated sheet. It is formed at the position. A through hole 19 is also formed at a substantially central position of the pad connection region 11a. These through holes 18 and 19 are plated with copper vias, whereby the outer shield conductors 13a and 13b are electrically connected to form a hollow film cable having a strip structure. .

Subsequently, as shown in FIG. 4B (b), the broken line-shaped opening 14 is formed by broken line etching along the signal line 11 with respect to the copper solid film (shield conductors 13a and 13b) on both surfaces of the laminated sheet. Is formed in two muscles.
Then, the inner layer polyimide (insulating resin layers 12a and 12b) is etched using the shield conductors 13a and 13b in which the broken-line opening 14 is formed as a mask. In this case, only polyimide on the signal line 11 is overetched with respect to the copper film (shield conductors 13a and 13b), so that 70% or more of the polyimide on the signal line 11 is etched while leaving the polyimide wall. delete.

Finally, as shown in FIG. 4B (c), the signal line pad 21 is formed at the end of the laminated sheet. The signal line pad 21 is formed by etching away the copper foil in the rectangular region outside the circular pad 21 with the through hole 19 passing through the pad connection region 11a as the center. Formed with. The etching area at this time is indicated by reference numeral 22.
Then, the signal line 11 and the signal line pad 21 arranged between the insulating resin layers 12a and 12b are connected through the via plating formed in the through hole 19.
The signal line pad 21 is formed in the same form on the opposite surface of the laminated sheet as necessary.

Through the steps described above, the hollow film cable according to the first embodiment shown in FIG. 2 can be obtained.
Note that the hollow film cable according to the second embodiment shown in FIG. 3 is different only in the shape of the opening 14 formed in the shield conductor as described above. Can be adopted.

  Next, FIG. 5A-FIG. 5C show this by the schematic diagram according to the manufacturing process about 3rd Embodiment of the hollow film cable which concerns on this invention. Note that this third embodiment also constitutes a hollow film cable having a strip structure.

  As shown in FIG. 5A, a laminate (single-sided copper-clad laminate) having a copper foil (shield conductor) 32 on one side of an insulating resin layer 31 made of polyimide is prepared. The insulating resin layer 31 has a thickness of 100 μm, and a groove 33 is formed in the insulating resin layer 31 by laser light or etching. The groove 33 functions as a hollow portion along the signal line after the completion of the hollow film cable.

A rib member 34 is formed in the groove 33 formed in the insulating resin layer 31 by the photosensitive resin exposure phenomenon as shown in FIG. 5B.
The rib member 34 can be formed by, for example, using a dry film resist (DFR) and developing it after partially exposing it.
That is, a dry film resist (DFR) is embedded in the groove 33 formed in the insulating resin layer 31, and a mask film (not shown) is placed on the dry film resist.

In this state, the dry film resist is partially exposed by projecting UV light onto the dry film resist through the mask film. Thereafter, the unexposed portion of the dry film resist is removed with a solvent (development), whereby the rib member 34 having a honeycomb-shaped hexagonal column wall surface can be formed as shown in FIG. 5B.
The rib member 34 constitutes a hexagonal column wall surface in the example shown in the figure, but the rib member 34 can have an arbitrary three-dimensional wall surface structure according to the mask film formation pattern described above.

In order to form a strip-structured hollow film cable, two laminated sheets with rib members 34 are prepared and arranged so that the surfaces on which the rib members 34 are formed face each other as shown in FIG. 5C (a). Is done. The lower laminated sheet shown in FIG. 5C (a) is referred to as a first substrate A, and the upper laminated sheet is referred to as a second substrate B.
A thin polyimide sheet 37 having a signal line 36 formed at the center is disposed between the first substrate A and the second substrate B, and adhesive sheets 38 and 39 are interposed above and below the sheet 37. Thus, the first base material A and the second base material B are laminated by thermocompression bonding.

FIG. 5C (b) shows a state in which the first base material A and the second base material B are laminated by the adhesive sheets 38 and 39 with the sheet 37 on which the signal line 36 is formed interposed therebetween.
As shown in FIG. 5C (b), in the state where the first base material A and the second base material B are laminated, the narrow end portion 37a of the sheet 37 on which the signal line 36 is formed is It is exposed from the laminated sheet. A signal line pad 36a electrically connected to the signal line 36 is formed at the end 37a.

  Next, in the step shown in FIG. 5C (c), the through hole 41 is formed at an appropriate position by, for example, a drill, avoiding the arrangement position of the signal line 36 in the laminated sheet. These through holes 41 are filled with, for example, silver paste, so that the shield conductors 32 on both outer sides are electrically connected to form a hollow film cable having a strip structure.

According to the hollow film cable according to the above-described manufacturing process, the signal line 36 formed on the sheet 37 is in a state of being supported in line contact by the end surface of the opposing rib member 34.
And according to this embodiment provided with the rib member 34, the porosity of the insulating resin layer reaches 90% in the area of the line width of the signal line between the signal line 36 and the shield conductors 32 on both outer sides. It becomes.

FIG. 6 is a graph showing electrical transmission characteristics compared with the hollow film cable according to the present invention described above and other existing coaxial cables and the like.
That is, the horizontal axis in FIG. 6 indicates the frequency of the transmission signal, and the vertical axis indicates the signal attenuation (dB).

And the characteristic a shown in FIG. 6 is a measured value of the hollow film cable (thickness 0.2 mm, width 0.8 mm) according to the manufacturing method shown to FIG. 4A and 4B. The characteristic impedance Zo of this hollow film cable was 47Ω, and its frequency characteristic was the same as that of the existing φ0.6 mm coaxial cable shown as characteristic c.
Moreover, the characteristic b shown in FIG. 6 is an actual measurement value of the hollow film cable (thickness 0.2 mm, width 0.8 mm) according to the manufacturing method shown in FIGS. 5A to 5C. The characteristic impedance Zo of this hollow film cable was 47Ω, and the frequency characteristic was equivalent to that of the existing φ0.75 mm coaxial cable shown as characteristic d.

  The characteristic e shown in FIG. 6 is illustrated for comparison, and this is a film cable (thickness 0.3 mm, width 1.5 mm) using the existing LCP described in the background section at the beginning. It is a measured value.

  In each of the embodiments described above, a strip-structured film cable is taken as an example, but the present invention can also be applied to the microstrip-structured film cable illustrated in FIG. Can be obtained.

DESCRIPTION OF SYMBOLS 11 Signal line 11a Pad connection area | region 12a, 12b Insulation resin layer 13a, 13b Shield conductor 14 Opening part 15 Hollow part 17 Adhesive sheet 18 Through-hole 19 Through-hole 21 Signal line pad 22 Etching area 31 Insulating resin layer 32 Shield conductor 33 Groove ( Hollow part)
34 Rib member 36 Signal line 36a Signal line pad 37 Sheet 37a Sheet end 38, 39 Adhesive sheet 41 Through hole A First base material B Second base material

Claims (6)

A film cable having a shield conductor sandwiching an insulating resin layer with respect to a signal line, or a film cable having an insulating resin layer on both sides of the signal line and having a shield conductor on both outer sides of each of the insulating resin layers, ,
A hollow part is formed between the signal line and the shield conductor by chemically or mechanically removing a part of the insulating resin layer along the extending direction of the signal line. A featured hollow film cable.   The hollow film cable according to claim 1, wherein the hollow portion is continuously formed along an extending direction of the signal line.   The void ratio of the insulating resin layer in a region of the line width of the signal line between the signal line and the shield conductor is set to 50% or more. Hollow film cable. Prepare a film cable with a shield conductor with an insulating resin layer sandwiched between the signal lines, or a film cable with an insulating resin layer on both sides of the signal line and with shield conductors on both outer sides of each of the insulating resin layers. ,
A step of intermittently forming openings by etching along the extending direction of the signal line with respect to the shield conductor;
Using the shield conductor in which the opening is formed as a mask, partially removing the insulating resin layer by etching, and forming a hollow portion reaching the signal line from the shield conductor in the insulating resin layer;
A method of manufacturing a hollow film cable, comprising: obtaining a film cable having the hollow portion formed along the extending direction of the signal line. Forming a hollow part by removing a part of the insulating resin layer having a shield conductor on one side into a groove shape by laser light or etching; and
Forming a rib member in the hollow portion formed in the insulating resin layer by an exposure phenomenon of a photosensitive resin;
A step of facing a pair of insulating resin layers in which rib members are formed in a groove-shaped hollow portion, and interposing a sheet provided with a signal line therebetween,
Laminating the signal lines facing each other along the opposing rib members;
A method of manufacturing a hollow film cable, comprising: obtaining a film cable having the signal line supported by an end surface of the rib member. Forming a hollow part by removing a part of the insulating resin layer having a shield conductor on one side into a groove shape by laser light or etching; and
Forming a rib member in the hollow portion formed in the insulating resin layer by an exposure phenomenon of a photosensitive resin;
A step of disposing a sheet provided with a signal line facing the insulating resin layer on which the rib member is formed;
Laminating in a state where the signal lines are opposed to each other along the rib member;
A method of manufacturing a hollow film cable, comprising: obtaining a film cable having the signal line supported by an end surface of the rib member.

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