JP2005332883A - Circuit substrate built-in optical fiber, its manufacturing method and portable type radio communication apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit substrate with built-in optical fiber which can reduce a product cost by suppressing a transmission loss at a bending time, and to provide a method of manufacturing the same and a portable radio communication apparatus using the same. <P>SOLUTION: The circuit substrate built in the optical fiber includes an electrical insulation substrate (2a-2c), a conductor wiring circuit (3) formed between the front surface of the electrical insulation substrate (2a, 2c) and the respective electrical insulation substrates (2a-2c), and optical fibers (5, 6) built in the electrical insulation substrate (2b). The optical fibers (5, 6) include a first optical fiber (5), and a second optical fiber (6) having a core (6a) finer than the core (5a) of the first optical fiber (5). The first optical fiber (5) and the second optical fiber (6) are coupled to the optical fiber built-in circuit substrate (1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a circuit board incorporating an optical fiber, a method of manufacturing the circuit board, and a portable wireless communication device using the circuit board.

  In recent years, portable wireless communication devices such as mobile phones have become widespread, and the data capacity transmitted and received by the portable wireless communication devices has increased. Therefore, large-scale integrated circuits (LSIs) that operate at high frequencies are used in portable wireless communication devices so that large amounts of data can be transmitted and received at high speed. A circuit board provided with a plurality of LSIs is required to have characteristics such as enabling accurate switching of high-frequency signals in order to transmit signals between LSIs. In such a background, a conductor wiring such as a copper wiring in a conventional circuit board has a limit in data capacity for signal transmission, and improvement in system performance is being hindered. Therefore, a method for transmitting a signal between LSIs via an optical transmission line such as an optical fiber has been studied. In addition to the conventional conductor wiring, characteristics such as a broadband property, a low electromagnetic wave disturbance property (low EMI property), and a high density property have been studied. A circuit board having an optical transmission line having the above is considered to be an indispensable technology. As an example of such a circuit board, a circuit board (an optical fiber built-in circuit board) in which an optical fiber is built in an electrically insulating base material has been proposed in, for example, Patent Document 1.

  On the other hand, portable wireless communication devices such as mobile phones have recently been provided with a main body having key buttons and the like, a lid having a display, etc., and a hinge that foldably connects the main body and the lid. Communication devices (hereinafter referred to as “foldable portable communication devices”) are widely used. In this foldable portable communication device, the hinge portion is bent at an angle of approximately 180 degrees in the folded state.

  However, an optical fiber has a problem in that a signal transmission loss (hereinafter simply referred to as “transmission loss”) increases when it is bent, that is, it is inferior in flexibility. FIG. 5 is a schematic diagram showing a light (signal) transmission system using a typical single-core optical fiber. As shown in FIG. 5, the optical fiber 100 includes a core layer 102 that transmits light 101 and a cladding layer 103 formed on the outer periphery of the core layer 102. The core layer 102 and the clad layer 103 are formed with a difference in refractive index so that the transmitted light 101 is totally reflected between the core layer 102 and the clad layer 103. However, if the optical fiber 100 is bent, the entrance angle θ of the light 101 is increased at the bent portion, and the light 101 is not totally reflected but partially leaked, resulting in an increase in transmission loss.

  FIG. 6 shows a typical single-core optical fiber when bent in a plastic optical fiber using polymethyl methacrylate resin (core diameter: 980 μm) and fluororesin (cladding diameter: 1 mm) for the core layer and the cladding layer, respectively. The transmission characteristics are shown. In FIG. 6, the horizontal axis indicates the bending radius of the plastic optical fiber, and the vertical axis indicates the magnitude of the transmission loss compared to the case where the plastic optical fiber is not bent. As shown in FIG. 6, in the conventional plastic optical fiber, it is understood that the transmission loss becomes very large when the bending radius is 15 mm or less. In the above-described foldable mobile communication device, the circuit board provided inside the hinge portion may be required to bend to allow a bending radius of 10 mm or less. When it is provided inside the hinge portion of the portable communication device, transmission loss may increase when used in a folded state.

One method for suppressing transmission loss during bending is to use an optical fiber having a thin core diameter. For example, when polymethylmethacrylate resin having a core diameter of 480 μm is used as the core layer and fluororesin having a cladding diameter of 500 μm is used as the cladding layer, the transmission loss is suppressed to about 0.9 dB even when the bending radius is 10 mm. be able to.
JP 2000-340907 A

  However, since the optical fiber having a small core diameter is expensive, the product cost is increased. Accordingly, in order to solve the above problems, the present invention provides an optical fiber built-in circuit board capable of reducing the product cost while suppressing transmission loss during bending, a manufacturing method thereof, and a portable radio using the same. Provide communication equipment.

  The circuit board with a built-in optical fiber of the present invention includes one or more layers of an electrically insulating substrate, a conductor wiring circuit formed between the surface of the electrically insulating substrate and each of the electrically insulating substrates, and the electrically insulating substrate. An optical fiber built-in circuit board comprising a built-in optical fiber, wherein the optical fiber includes a first optical fiber and a second optical fiber having a core thinner than a core of the first optical fiber, The first optical fiber and the second optical fiber are connected to each other.

  The method for manufacturing a circuit board with a built-in optical fiber according to the present invention includes forming an optical fiber housing portion including a through groove or a bottomed groove on an electrically insulating base material containing an uncured thermosetting resin, and housing the optical fiber. The first optical fiber and the second optical fiber having a core thinner than the core of the first optical fiber are fitted so that both end faces are in contact with each other, and metal foil is laminated on the upper and lower surfaces of the electrically insulating base material, The first optical fiber and the second optical fiber are connected by heating and pressurizing with a hot press, and the thermosetting resin is connected to the inner wall of the optical fiber housing portion and the first and second optical fibers. The metal foil is patterned to form a conductor wiring circuit.

  A portable wireless communication device according to the present invention includes a main body portion including a first circuit board, a lid portion including a second circuit board, and a hinge portion that foldably connects the main body portion and the lid portion. An optical fiber built-in circuit board of the present invention is provided in the hinge part as a connector part for transmitting a signal between the first circuit board and the second circuit board. Furthermore, it is characterized by providing.

  The circuit board with a built-in optical fiber of the present invention is connected to a first optical fiber and a second optical fiber having a core thinner than the core of the first optical fiber and is built in an electrically insulating base material. The second optical fiber having a thinner core is disposed at a bent portion of the device to be bent, and the first optical fiber having a thicker core is disposed at a portion not bent, thereby suppressing transmission loss at the time of bending. Thus, the product cost can be reduced.

  According to the method for manufacturing a circuit board with a built-in optical fiber of the present invention, when the first and second optical fibers are built in the electrically insulating substrate, the first optical fiber and the second optical fiber can be connected simultaneously. Therefore, the circuit board with a built-in optical fiber of the present invention can be easily manufactured.

  According to the portable wireless communication device of the present invention, the optical fiber of the present invention is provided in the hinge portion as a connector portion for transmitting a signal between the first circuit board of the main body portion and the second circuit board of the lid portion. Since the built-in circuit board is provided, it is possible to provide a portable wireless communication device with low transmission loss even in a folded state.

  The circuit board with a built-in optical fiber of the present invention is built in one or more layers of an electrically insulating substrate, a conductor wiring circuit formed between the surface of the electrically insulating substrate and each of the electrically insulating substrates, and the electrically insulating substrate. And an optical fiber. The electrically insulating substrate is not particularly limited, but preferably contains at least 20% by weight to 70% by weight of aramid nonwoven fabric or glass woven fabric and 30% by weight to 80% by weight of thermosetting resin. Can be used. In this case, the thermosetting resin preferably contains at least one selected from an epoxy resin, an aramid epoxy resin, a phenol resin, and a cyanate resin. The thickness of the electrically insulating substrate is preferably 300 to 1000 μm. The conductor wiring circuit can be formed by a known method, and for example, can be formed by patterning a metal foil adhered on an electrically insulating substrate by hot pressing or the like by a known photolithography method.

  The optical fiber incorporated in the electrically insulating substrate includes a first optical fiber and a second optical fiber having a core thinner than the core of the first optical fiber. The material of the first and second optical fibers is not particularly limited, and known glass fibers and plastic fibers can be used. Further, not only a single-core optical fiber (see FIG. 5) described in the background art but also a multi-core optical fiber, a graded index optical fiber, or the like can be used. When an optical fiber having a single-core structure is used, a first optical fiber having a core diameter of 480 μm to 980 μm and a cladding diameter of 50 μm to 1000 μm is used, and a second optical fiber having a core diameter of 240 μm to It is preferable to use one having a thickness of 480 μm and a cladding diameter of 250 μm to 500 μm.

  In the circuit board with built-in optical fiber of the present invention, the first optical fiber and the second optical fiber are connected. Thereby, for example, by arranging the second optical fiber having a thinner core at the bent portion of the device to be used, and by arranging the first optical fiber having a thicker core at the portion not to be bent, The product cost can be reduced while suppressing the transmission loss.

  In the circuit board with built-in optical fiber of the present invention, it is preferable that the first optical fiber has a single-core core and the second optical fiber has a multi-core core. Thereby, even if it uses the 2nd optical fiber with a small core diameter, the fall of the data capacity which can be transmitted / received can be suppressed.

  The manufacturing method of the circuit board with a built-in optical fiber of the present invention, first, an electrical insulating base material containing an uncured thermosetting resin, using means such as machining such as a drill or thermal processing such as laser, An optical fiber housing portion comprising a through groove or a bottomed groove is formed. Next, the first optical fiber and the second optical fiber having a core thinner than the core of the first optical fiber are fitted into the optical fiber housing portion so that both end faces are in contact with each other. Subsequently, metal foils are laminated on the upper and lower surfaces of the electrically insulating base material, heated and pressurized by hot press to connect the first optical fiber and the second optical fiber, and the thermosetting resin is applied to the optical fiber. It is made to flow between the inner wall of a storage part and the 1st and 2nd optical fibers, and is hardened. Then, the metal foil is patterned to form a conductor wiring circuit. As described above, in the method for manufacturing a circuit board with a built-in optical fiber according to the present invention, when the first and second optical fibers are built in the electrically insulating base, the first optical fiber and the second optical fiber are simultaneously connected. Therefore, the circuit board with a built-in optical fiber of the present invention can be easily manufactured.

  In the manufacturing method, it is preferable that the first optical fiber has a single-core core and the second optical fiber has a multi-core core. As a general method of coupling (fusion) between optical fibers, two optical fibers are fixed in grooves formed into V-shapes, and the optical axes are aligned by camera recognition to fuse the optical fibers together. Is adopted. At this time, it is very difficult to align the optical axes between the optical fibers. However, in the above configuration, since the first optical fiber having a single-core core and the second optical fiber having a multi-core core are connected, some optical axis misalignment is allowed. As a result, the first optical fiber and the second optical fiber can be more easily connected, and further, since it is not necessary to process a V-shaped groove, the cost can be reduced.

  A portable wireless communication device of the present invention includes a main body portion incorporating a first circuit board, a lid portion incorporating a second circuit board, and a hinge portion that foldably connects the main body portion and the lid portion, Furthermore, the optical fiber built-in circuit board of the present invention is provided in the hinge part as a connector part for transmitting a signal between the first circuit board and the second circuit board. Thereby, even in the folded state, it is possible to provide a portable wireless communication device with a small transmission loss. Hereinafter, embodiments of the present invention will be described in detail.

[First Embodiment]
First, a first embodiment of the present invention will be described with reference to the drawings as appropriate. FIG. 1 to be referred to is an explanatory diagram of the circuit board with a built-in optical fiber according to the first embodiment. Among these, A is a top view showing the positional relationship between the wiring pattern on the surface (upper surface) of the circuit board with built-in optical fiber and the built-in optical fiber, and B is a cross-sectional view taken along line II of A. C is a sectional view taken along line II-II of A. FIG.

  As shown in FIGS. 1B and 1C, the circuit board 1 with a built-in optical fiber according to the first embodiment includes electrically insulating base materials 2a, 2b, and 2c, the surfaces of the electrically insulating base materials 2a and 2c, and the electrically insulating base material 2a, Conductive wiring circuit 3 formed between the base materials 2b and 2c, conductive via hole 4 for electrically connecting the upper and lower conductive wiring circuits 3, and the first optical fiber 5 built in the electrically insulating base material 2b And a second optical fiber 6 built in the electrically insulating base material 2b.

The first optical fiber 5 has a single-core structure composed of a core 5a and a clad 5b. Further, the second optical fiber 6 has a single-core structure composed of a core 6 a and a clad 6 b that are thinner than the core 5 a of the first optical fiber 5. And as shown to FIG. 1A, the 1st optical fiber 5 and the 2nd optical fiber 6 are connected by each end surface 5c, 6c. Thereby, for example, the second optical fiber 6 having a thinner core 6a is arranged at a bent portion of a device in which the circuit board with a built-in optical fiber 1 is used, and the first light having a thicker core 5a is not bent. By arranging the fiber 5, it is possible to reduce the product cost while suppressing the transmission loss at the time of bending. The first and second optical fibers 5 and 6 preferably have the same fiber diameters D ₁ and D ₂ . Moreover, it is preferable that the diameter of the core 6a of the second optical fiber 6 is configured to increase as it approaches the end face 6c. Thereby, the leak of the light in a connection part is suppressed.

  Next, a method for manufacturing the optical fiber built-in circuit board 1 according to the first embodiment will be described with reference to the drawings as appropriate. FIG. 2 to be referred to is a cross-sectional view showing a part of the manufacturing method of the circuit board 1 with a built-in optical fiber. The same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  First, an electrically insulating substrate 2b containing an uncured thermosetting resin (such as an epoxy resin) is prepared (FIG. 2A). Then, the optical fiber accommodating part 11 which consists of a bottomed groove | channel is formed in the electrical insulation base material 2b by mechanical processing, such as a drill, thermal processing, such as a laser (FIG. 2B). Here, the length, width, and height of the optical fiber housing portion 11 may be formed to a size that can accommodate the optical fiber to be used. Next, the first optical fiber 5 and the second optical fiber 6 (see FIG. 1C) are fitted into the optical fiber housing 11 (FIG. 2C). At this time, the optical fiber housing 11 is fitted so that the end surface 5c of the first optical fiber 5 and the end surface 6c of the second optical fiber 6 are in contact with each other (see FIG. 1A). Then, a metal foil 13 such as a copper foil is laminated on the upper and lower portions of the electrical insulating substrate 2b (FIG. 2D). Subsequently, the first optical fiber 5 and the second optical fiber 6 are connected (fused) by heating and pressurizing with a hot press, and the thermosetting resin is connected to the inner wall 11a of the optical fiber housing 11. Between the first and second optical fibers 5 and 6 (gap 11b) and hardened (FIG. 2E). It is preferable that the hot pressing is performed so that the gap 11b is filled. For example, when an electrically insulating substrate containing an epoxy resin is used as the thermosetting resin, the temperature may be 150 to 250 ° C., the pressure may be 0.1 to 10 MPa, and the time may be 10 minutes to 2 hours. In addition, if the conditions for filling the gap 11b cannot be set due to the characteristics of the electrically insulating substrate used, the gap 11b may be filled with an adhesive of the resin composition in advance.

  Subsequently, the metal foil 13 is patterned into a desired shape by means such as photolithography to form the conductor wiring circuit 3 (FIG. 2F). Further, in the case of multi-layering, circuit boards may be laminated on the upper and lower sides of the electrical insulating base material 2b in which the first and second optical fibers 5 and 6 are built by means such as hot pressing. The conductive via hole 4 (see FIGS. 1B and 1C) can be formed by a known method, for example, by filling the via hole formed by a laser or the like with a conductive paste and then compressing it. Moreover, although this embodiment demonstrated the optical fiber built-in circuit board provided with the electrical insulation base materials 2a-2c of 3 layers, this invention is not limited to this, The electrical insulation base material of 4 layers or more was provided. An optical fiber built-in circuit board may be used, or an optical fiber built-in circuit board having only one layer of an electrically insulating base material may be used.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to the drawings as appropriate. FIG. 3 to be referred to is a cross-sectional view of the circuit board with a built-in optical fiber according to the second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 3, the circuit board 20 with a built-in optical fiber according to the second embodiment includes a second optical fiber 21 having a multicore structure including a plurality of cores 21a and a clad 21b as the second optical fiber. in use. Other configurations are similar to those of the circuit board 1 with a built-in optical fiber. Since the optical fiber built-in circuit board 20 also includes the second optical fiber 21 having a thinner core 21a, the same effect as the above-described optical fiber built-in circuit board 1 according to the first embodiment is exhibited. Furthermore, since the second optical fiber 21 has a multi-core structure, it is possible to suppress a decrease in data capacity that can be transmitted and received. The manufacturing method of the circuit board with a built-in optical fiber 20 according to the second embodiment is the same as that of the circuit board with a built-in optical fiber according to the first embodiment described above, but the first optical fiber 5 having a single-core structure, Since the second optical fiber 21 having a multi-core structure is connected, some optical axis deviation is allowed. Thereby, the 1st optical fiber 5 and the 2nd optical fiber 21 can be connected more easily.

  The optical fiber built-in circuit board and the manufacturing method thereof according to one embodiment of the present invention have been described above, but the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the optical fiber housing portion including the bottomed groove is formed, but the optical fiber housing portion including the through groove may be formed. In the embodiment, only the first and second optical fibers are connected, but three or more optical fibers may be connected.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to the drawings as appropriate. FIG. 4 to be referred to is a schematic perspective view of a portable wireless communication device according to the third embodiment of the present invention.

  As shown in FIG. 4, the portable wireless communication device 50 according to the third embodiment includes a main body 52 having a key button 51 and the like, a lid 54 having a display 53 and the like, and the main body 52 and the lid 54. And a hinge portion 55 for connecting the two in a foldable manner. A first circuit board 56 and a second circuit board 57 are provided inside the main body 52 and the lid part 54, respectively. Furthermore, as a connector part for transmitting a signal between the first circuit board 56 and the second circuit board 57 in the hinge part 55, the light according to any one of the first and second embodiments described above. A circuit board 58 with a built-in fiber is provided. As a result, the portable wireless communication device 50 includes the optical fiber built-in circuit board 58 of the present invention having a small transmission loss at the time of bending as a connector portion, so that the transmission loss can be suppressed even in a folded state. .

  The circuit board with a built-in optical fiber of the present invention is useful as a circuit board for use in a bent state. It is particularly suitable for portable wireless communication devices such as folding portable communication devices.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the circuit board with a built-in optical fiber which concerns on 1st Embodiment of this invention, A is a top view which shows the positional relationship of the wiring pattern of the surface (upper surface) of a circuit board with a built-in optical fiber, and the built-in optical fiber. B is a cross-sectional view taken along line II of A, and C is a cross-sectional view taken along line II-II of A. It is sectional drawing which shows a part of manufacturing method of the circuit board with a built-in optical fiber which concerns on 1st Embodiment of this invention. It is sectional drawing of the circuit board with a built-in optical fiber which concerns on 2nd Embodiment of this invention. It is a schematic perspective view of the portable radio | wireless communication apparatus which concerns on 3rd Embodiment of this invention. It is a schematic diagram which shows the transmission system of the light (signal) using the conventional optical fiber. It is a graph which shows the transmission characteristic of the signal at the time of the bending in the conventional optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20,58 Optical fiber built-in circuit board 2a, 2b, 2c Electrical insulation base material 3 Conductor wiring circuit 5 1st optical fiber 5a, 6a, 21a Core 5c, 6c End face 6,21 2nd optical fiber 11 Optical fiber accommodating part 11a Inner wall 13 Metal foil 50 Portable wireless communication device 52 Main body part 54 Lid part 55 Hinge part 56 First circuit board 57 Second circuit board

Claims (5)

Light comprising one or more layers of an electrically insulating substrate, a surface of the electrically insulating substrate and a conductor wiring circuit formed between each of the electrically insulating substrates, and an optical fiber incorporated in the electrically insulating substrate A circuit board with built-in fiber,
The optical fiber includes a first optical fiber and a second optical fiber having a core thinner than the core of the first optical fiber,
The circuit board with a built-in optical fiber, wherein the first optical fiber and the second optical fiber are connected. The first optical fiber has a single-core core.
The circuit board with a built-in optical fiber according to claim 1, wherein the second optical fiber has a multi-core core. In an electrically insulating base material containing a thermosetting resin in an uncured state, an optical fiber housing portion consisting of a through groove or a bottomed groove is formed,
Into the optical fiber housing portion, a first optical fiber and a second optical fiber having a core thinner than the core of the first optical fiber are fitted so that both end faces are in contact with each other,
Metal foils are laminated on the upper and lower surfaces of the electrically insulating base material, heated and pressurized by hot press to connect the first optical fiber and the second optical fiber, and the thermosetting resin is Flowing between the inner wall of the optical fiber housing part and the first and second optical fibers to cure,
A method for manufacturing a circuit board with a built-in optical fiber, wherein a conductive wiring circuit is formed by patterning the metal foil. The first optical fiber has a single-core core.
The method of manufacturing a circuit board with a built-in optical fiber according to claim 3, wherein the second optical fiber has a multi-core core. A portable wireless communication device comprising: a main body portion that incorporates a first circuit board; a lid portion that incorporates a second circuit board; and a hinge portion that foldably connects the main body portion and the lid portion. ,
The optical fiber built-in circuit board according to claim 1 or 2, further comprising a connector part for transmitting a signal between the first circuit board and the second circuit board in the hinge part. A portable wireless communication device characterized by the above.

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