JP6098917B2 - Opto-electric composite flexible wiring board - Google Patents

Description

  The present invention relates to an optical waveguide and an opto-electric composite flexible wiring board.

  High-speed transmission is required in the field of medium- and long-distance communication, specifically in the field of FTTH (Fiber To The Home) and in-vehicle, and in order to realize this, an optical fiber cable is used as a transmission medium. Has been.

  High-speed transmission has been demanded even in short-distance communication, for example, communication within 1 m. Also, in the field of such short distance communication, performance that is difficult to achieve with optical fiber cables is also required. Specifically, the required performance includes high-density wiring such as narrow pitch, branching, crossing, and multilayering, surface mountability, integration with an electric circuit board, and a small radius of curvature. For example, it can be bent. As a basis for satisfying these requirements, it is conceivable to use an optical wiring board having an optical waveguide.

  In addition, in such an optical wiring board, a light emitting element such as a vertical cavity surface emitting laser (VCSEL), a light receiving element such as a photodiode (PD), A semiconductor element such as an integrated circuit (IC) is preferably mounted. In order to drive these elements, an electric circuit needs to be provided on the optical wiring board or the like. From this, it is preferable that the photoelectric composite wiring board is provided with not only an optical waveguide but also an electric circuit. Examples of such a photoelectric composite wiring board include a bendable photoelectric composite flexible wiring board. This opto-electric composite flexible wiring board can be used in place of a flexible wiring board disposed across a hinge of a small terminal device, for example, and has attracted attention.

  As a conventional manufacturing method of such an optical waveguide, for example, the following method can be cited.

  First, a core portion of an optical waveguide is formed on the surface of the first cladding layer, and the core portion is processed into a predetermined shape. Thereafter, a second cladding layer is formed on the upper surface of the first cladding. By doing so, it is possible to manufacture an optical waveguide that wraps the core portion with the clad layer composed of the first clad layer and the second clad layer. In the optical waveguide obtained by this method, the interface between the first cladding layer and the second cladding layer is exposed on the side surface of the optical waveguide.

  Moreover, as another manufacturing method of an optical waveguide, the manufacturing method of patent document 1, etc. are mentioned, for example.

  In Patent Document 1, a plurality of optical waveguide bodies having a clad layer and a core portion are formed on a top surface of a first coating layer formed on the surface of a substrate with a predetermined interval, and then a first The liquid resin composition is applied to the surface of the coating layer and the plurality of optical waveguide bodies, and the second coating layer is formed by drying and / or heating. At this time, in the gaps between the optical waveguide bodies A method of forming a laminated portion of the first coating layer and the second coating layer is described.

JP 2008-203694 A

  An optical waveguide manufactured by a conventional manufacturing method of an optical waveguide and having an interface between the first cladding layer and the second cladding layer exposed on the side surface may be cracked on the side surface of the optical waveguide due to repeated bending. It was. This crack is considered to be a crack starting from the interface between the first cladding layer and the second cladding layer.

  Patent Document 1 discloses that an optical waveguide having a coating layer formed on all outer surfaces can be manufactured. With such a manufacturing method, it is considered that the occurrence of cracks at the interface of the cladding layer as described above can be suppressed.

  However, even the optical waveguide manufactured by the method described in Patent Document 1 may not sufficiently suppress the occurrence of cracks due to repeated bending.

  First, when manufacturing the optical waveguide, before forming the second coating layer, the interface between the lower cladding layer and the upper cladding layer as a cladding layer is exposed on the side surface of the optical waveguide body. For this reason, it is considered that the generation of cracks at this interface cannot be sufficiently suppressed during production. In addition, even if the optical waveguide body is covered with a layer other than the layer constituting the optical waveguide, such as a coating layer, it is made of a material different from the layer constituting the optical waveguide. In some cases, the occurrence of cracks could not be sufficiently suppressed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to suitably suppress the occurrence of cracks due to bending or the like and provide a highly reliable optical waveguide. It is another object of the present invention to provide an opto-electric composite flexible wiring board having such an optical waveguide.

  An optical waveguide according to the present invention includes a first clad layer, a core portion formed on the first clad layer, and a second clad formed on the first clad layer so as to embed the core portion. With layers. And it has the structure which the said 2nd clad layer has covered from the upper surface to the side surface of the said 1st clad layer. In the optical waveguide according to the present invention, since the interface between the first cladding layer and the second cladding layer formed thereon is not exposed on the side surface of the optical waveguide, the optical waveguide of the present invention is free from cracks due to bending or the like. Occurrence is prevented.

  The present invention also provides an optoelectric composite flexible wiring board having the configuration of the optical waveguide. That is, an optoelectric composite flexible wiring board according to the present invention includes a substrate on which an electric circuit is formed, a first cladding layer formed on the substrate, a core portion formed on the first cladding layer, And a second cladding layer formed on the first cladding layer so as to embed the core portion. And it has the structure which the said 2nd clad layer has covered from the upper surface to the side surface of the said 1st clad layer.

  In the optoelectric composite flexible wiring board of the present invention, it is preferable that the second cladding layer is formed so as to cover at least a part of the electric circuit.

  In the opto-electric composite flexible wiring board of the present invention, it is preferable that a distance between the electric circuit and the core portion is 0.5 mm or more.

  According to the present invention, it is possible to suitably suppress the occurrence of cracks due to bending or the like and provide a highly reliable optical waveguide. Moreover, an opto-electric composite flexible wiring board provided with such an optical waveguide can be provided.

It is a schematic sectional drawing which shows the optical waveguide which concerns on one Embodiment of this invention. It is a schematic sectional drawing which shows an example of the conventional optical waveguide as a reference example. It is a schematic sectional drawing which shows the photoelectric composite flexible wiring board which concerns on one Embodiment of this invention. 6 is a schematic diagram for explaining a method of manufacturing the optical waveguide according to Example 1. FIG. 6 is a schematic diagram for explaining a method of manufacturing an opto-electric composite flexible wiring board according to Example 2. FIG. It is the graph which plotted the result of Examples 2-5.

  Embodiments according to the present invention will be described below.

  FIG. 1 is a schematic sectional view showing an optical waveguide according to an embodiment of the present invention. In the optical waveguide according to this embodiment, the vertical and horizontal directions are not particularly defined in actual use. However, for convenience of explanation of the configuration, the configuration of each configuration is shown with the vertical and horizontal directions of FIG. The positional relationship is specified.

  The optical waveguide 10 includes a first cladding layer 12 at a lower position thereof. The material of the first cladding layer 12 is not particularly limited as long as it is made of a transparent material, but can be formed of, for example, a transparent resin.

  A core portion 11 is formed on the first cladding layer 12. The core portion 11 has a shape extending in the depth direction of FIG. 1 with the direction in which the optical signal is to be transmitted as the longitudinal direction. The number of the core portions 11 is not particularly limited in the optical waveguide 10, and the number can be set according to the purpose of use. In this embodiment, as shown in FIG. 1, an optical waveguide 10 having four core portions 11 is illustrated. The core 11 is not particularly limited as long as it is made of a transparent material having a lower refractive index than that of the first cladding layer, and can be formed of, for example, a transparent resin.

  In the optical waveguide 10, a second cladding layer 13 is formed on the core portion 11 and the first cladding layer 12 so as to embed the core portion 11. The second cladding layer 13 is formed of the same material as the first cladding layer 12. The second cladding layer 13 is formed so as to cover not only the upper surface 12 a of the core portion 11 and the first cladding layer 12 but also the left and right side surfaces 12 b of the first cladding layer 12. As a result, the left and right side surfaces of the optical waveguide 10 are covered with the second cladding layer 13, so that the interface between the first cladding layer 12 and the second cladding layer 13 does not exist.

  As described above, the optical waveguide 10 does not expose the side surface, which is likely to be the starting point of cracking due to stress when bent, and therefore, cracking is suitably suppressed and the optical waveguide 10 is highly reliable.

  Next, for comparison with the embodiment according to the present invention, an example of a conventional optical waveguide will be described as a reference example.

  An example of this reference is an optical waveguide 20 as shown in FIG. In the optical waveguide 20 in this reference example, a core portion 21 is formed on a first clad layer 22 and the second clad layer embeds the core portion 21 on the same as the optical waveguide 10 shown in FIG. However, the second cladding layer does not cover the side surface of the first cladding layer. That is, the second cladding layer 23 is formed so as to cover only the core portion 21 and the upper surface 22 a of the core portion 21 and the first cladding layer 22. Therefore, an interface between the first cladding layer 22 and the second cladding layer 23 exists on the side surface of the optical waveguide 20 of this reference example.

  Therefore, in the optical waveguide 20 shown in this reference example, there is a tendency that cracks due to repeated bending tend to occur starting from the sea surface exposed on the side surfaces, and the occurrence of cracks cannot be sufficiently suppressed. In detail, the following is considered.

  First, when the optical waveguide 20 is bent, on the outer side of the bend, that is, on the surface far from the center of curvature, a force is applied to pull the optical waveguide 20 from the bent portion toward the side surface of the optical waveguide 20. The force increases as the distance from the center of curvature increases, and decreases as the distance from the center of curvature decreases. Further, when the optical waveguide 20 is bent, a force to compress the optical waveguide 20 in a direction approaching the bent portion is applied to the inner side of the bending, that is, the surface near the center of curvature. The force becomes larger as it is closer to the center of curvature, and becomes smaller as it is farther from the center of curvature. Therefore, the magnitude of the stress varies depending on the position of the optical waveguide 20 in the thickness direction. The action of this stress is the same in the optical waveguide 10 of the embodiment shown in FIG. Therefore, when the optical waveguide 20 is bent, a difference is generated between the force applied to the first cladding layer side and the force applied to the second cladding layer side, and the difference in the force is determined between the first cladding layer 22 and the second cladding layer. It is considered that a shearing stress that tries to shift the layer between the layer 23 works. Even if the first clad layer 22 and the second clad layer 23 are layers made of the same material, they are different layers that are hardened separately. It is considered that cracks are likely to occur at the interface with the second cladding layer 23. For this reason, it is considered that the optical waveguide 20 of the reference example cannot sufficiently suppress the occurrence of cracks due to repeated bending and cannot sufficiently increase the reliability.

  On the other hand, since the optical waveguide 10 according to the present embodiment has no interface between the first cladding layer 12 and the second cladding layer 13 on its side surface, the above-described shearing is achieved even if the optical waveguide is bent. It is considered that stress does not work and cracking is suppressed.

  Next, an optoelectric composite flexible wiring board according to another embodiment of the present invention will be described. FIG. 3 is a schematic cross-sectional view showing an opto-electric composite flexible wiring board 30 according to another embodiment. Similar to the description of the optical waveguide 10 according to the above-described embodiment, the opto-electric composite flexible wiring board 30 will be described by defining the top, bottom, left and right in FIG.

  As shown in FIG. 3, the opto-electric composite flexible wiring board 30 has a flexible base 16 disposed at the bottom. The substrate 16 is not particularly limited as long as it is a flexible material that can meet the purpose of use, but it is preferable to use a material having durability against mechanical stress such as bending. A resin sheet such as can be used.

  An electric circuit 15 made of a conductive material such as a metal is formed on the upper surface of the base material 16, thereby constituting a circuit board 17. On the circuit board 17, an optical waveguide having the above-described configuration is formed. Specifically, in the circuit board 17, the electric circuit 15 is formed in the left and right regions on the upper surface of the base material 16, and the first cladding layer 12 is formed on the upper surface of the base material 16 in the region where the electric circuit 15 is not present. . A core portion 11 is formed on the first cladding layer 12. A second cladding layer 13 is formed on the first cladding layer 12 so as to embed the core portion 11.

  The position of the electric circuit 15 is not limited to the left and right positions of the base material 16 and can be a pattern shape according to the purpose of use, but the position is designed so as not to overlap with the first cladding layer 12. The

At this time, the electric circuit 15 is preferably not in contact with the first cladding layer 12. Further, the distances d ₁ and d ₃ between the electric circuit 15 and the core portion 11 are suitable for reducing waveguide loss (loss of light guided through the core portion 11) and reducing the size of the opto-electric composite flexible wiring board 30. It is desirable to set it in a preferable range in consideration of a proper balance. Here, the interval between the electric circuit 15 and the core portion 11 is a distance at a location where the electric circuit 15 and the core portion 11 are closest to each other. If the distance between the electric circuit 15 and the core part 11 is too small, the core part 11 is likely to be thermally affected by the electric circuit 15 during storage in a high-temperature environment, for example, and the loss of light guided through the core part 11 There is a possibility that an increase in (waveguide loss) cannot be sufficiently suppressed. That is, the reliability during heat tends to be lowered. In consideration of reducing this loss, the distances d ₁ and d ₃ are preferably set to be 0.5 mm or more. On the other hand, if the distance between the electric circuit 15 and the core portion 11 is too large, the photoelectric composite flexible wiring board 30 tends to be reduced in size. If the upper limit of the distances d ₁ and d ₃ is determined in consideration of the level at which the heat loss can be sufficiently reduced, it is practically preferable to set the distances around 2-3 mm.

  In the photoelectric composite flexible wiring board 30, the second cladding layer 13 is formed so as to cover not only the upper surface 12 a of the core portion 11 and the first cladding layer 12 but also the side surface 12 b of the first cladding layer 12. Yes. Further, the second cladding layer 13 further covers at least a part of the electric circuit 15 as well as the first cladding layer 12. At this time, the second cladding layer 13 may cover the entire electric circuit 15 or may partially cover the electric circuit 15 while exposing a part thereof. When the second clad layer 13 covers the entire electric circuit 15, it is preferable that a via hole is formed in the second clad layer 13 or the base material 16 so that the electric circuit 15 can be electrically connected from the outside. When the second cladding layer 13 partially covers the electric circuit 15 and exposes a part thereof, the exposed portion can be used as an electrical connection portion from the outside.

  Thus, the formation process of forming the second cladding layer 13 on the core portion 11 and the first cladding layer 12 by forming the second cladding layer 13 including the electric circuit 15 over the left and right sides of the substrate 16. As compared with the case where the circuit is formed avoiding the electric circuit 15, the alignment accuracy is not required, and it becomes easy. In addition, since the second cladding layer 13 covers the electric circuit 15, an effect of protecting the electric circuit 15 can be expected. Further, as shown in FIG. 3, the second clad layer 13 is formed up to the left and right edges of the base material 16, so that the cross-sectional shape becomes a thin rectangular shape. In addition, it is possible to expect an effect that the stress generated when deformed is prevented from being locally concentrated due to partial bias or the like.

  As described above, since the second clad layer 13 covers the side surface 12b of the first clad layer 12 in the optoelectronic composite flexible wiring board 30 of the embodiment, the interface between them is the side surface of the optoelectronic composite flexible wiring board 30. Not exposed to. Therefore, the occurrence of cracks when the photoelectric composite flexible wiring board 30 is deformed by bending or the like is suitably suppressed, and the reliability becomes high.

  Examples for explaining the present invention more specifically are shown below.

  First, a method for producing the resin film used in this example will be described.

(Manufacture of resin film for first cladding layer)
7 parts by mass of polypropylene glycol glycidyl ether (“PG207” manufactured by Nippon Steel Chemical Co., Ltd.), 25 parts by mass of liquid hydrogenated bisphenol A type epoxy resin (“YX8000” manufactured by Mitsubishi Chemical Corporation), solid hydrogenated bisphenol Type A epoxy resin (“YL7170” manufactured by Mitsubishi Chemical Corporation), 20 parts by mass, 1,2-epoxy-4- (2-oxiranyl) cyclohexane adduct of 2,2-bis (hydroxymethyl) -1-butanol ( 8 parts by mass of “EHPE3150” manufactured by Daicel Corporation, 2 parts by mass of solid bisphenol A type epoxy resin (“Epicoat 1006FS” manufactured by Mitsubishi Chemical Corporation), and phenoxy resin (“YP50” manufactured by Nippon Steel Chemical Co., Ltd.) 20 parts by mass, photocationic curing initiator (“SP170” manufactured by ADEKA Corporation) 1 mass , 0.1 parts by mass of each surface preparation agent (“F470” manufactured by DIC Corporation) was dissolved in 30 parts by mass of toluene and 70 parts by mass of methyl ethyl ketone (MEK), and filtered through a membrane filter having a pore size of 1 μm. Then, an epoxy resin varnish was prepared by degassing under reduced pressure. This epoxy resin varnish is applied on a PET film (“A4100” manufactured by Toyobo Co., Ltd.) as a release film using a multi-coater of a comma coater head manufactured by Hirano Technoseed Co., Ltd. Was dried. By doing so, a resin film for a first cladding (lower cladding layer) having a predetermined thickness was obtained. The first clad resin film thus obtained had a thickness of 10 μm.

(Manufacture of resin film for core part)
3,4-epoxycyclohexenylmethyl-3 ′, 4′-epoxycyclohexene carboxylate (“Celoxide 2021P (also referred to as CEL2021P)” manufactured by Daicel Corporation) 8 parts by weight, epoxy resin (“EHPE3150” manufactured by Daicel Corporation) 1,2-epoxy-4- (2-oxiranyl) cyclosoxane adduct of 2,2-bis (hydroxymethyl) -1-butanol), 12 parts by mass of solid bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation) "Epicoat 1006FS") 37 parts by mass, trifunctional epoxy resin ("VG-3101" manufactured by Mitsui Chemicals, Inc.) 15 parts by mass, solid novolac epoxy resin ("EPPN201" manufactured by Nippon Kayaku Co., Ltd.) 18 parts by mass , Liquid bisphenol A type epoxy resin ("DIC Corporation""Piclone850s") 10 parts by mass, photocationic curing initiator ("SP-170" manufactured by ADEKA Corporation) 0.5 part by mass, thermal cationic curing initiator ("SI-150L" manufactured by Sanshin Chemical Industry Co., Ltd.) ) 0.5 parts by mass and a surface conditioner (“F470” manufactured by DIC Corporation) of 0.1 parts by mass were dissolved in a mixed solvent of 30 parts by mass of toluene and 70 parts by mass of MEK. Then, the solution was filtered through a membrane filter having a pore size of 1 μm, and then degassed under reduced pressure to prepare an epoxy resin varnish. This epoxy resin varnish was applied onto a PET film (“A4100” manufactured by Toyobo Co., Ltd.) using a multi coater of a comma coater head manufactured by Hirano Technoseed Co., Ltd., and the coated film was dried. Thereby, the resin film for core parts of predetermined thickness was obtained. The core portion resin film thus obtained had a thickness of 30 μm.

(Manufacture of resin film for second cladding layer)
A second clad layer resin film was produced in the same manner as the second clad layer (upper clad layer) resin film except that the thickness was changed to 50 μm.

Example 1
Example 1 will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining a method of manufacturing the optical waveguide according to the first embodiment.

  First, a polycarbonate substrate was prepared as the temporary substrate 41. As shown in FIG. 4A, a first clad layer resin film 42 is placed on the temporary substrate 41, and a pressure-type vacuum laminator (V-130 manufactured by Nichigo Morton Co., Ltd., The first clad layer resin film 42 was laminated on the temporary substrate 41 by applying pressure under the conditions of 80 ° C. and 0.2 MPa using “vacuum laminator V-130”.

Then, as shown in FIG. 4B, the first clad layer resin film 42 is subjected to ultraviolet light under an ultrahigh pressure mercury lamp under the condition of ² J / cm ² so as to obtain a first clad layer having a predetermined shape. It was exposed by irradiating light. Specifically, a mask 43 having a linear pattern of slits having a width of 1 mm and a length of 120 mm is positioned above the first cladding layer resin film 42, and the first cladding layer resin film is interposed through the mask 43. 42 was exposed. By doing so, the portion corresponding to the first cladding layer was cured.

  Next, the release film was peeled off from the cured first clad layer resin film 42 and then heat treated at 140 ° C. for 2 minutes. And it developed using the aqueous | water-based flux washing | cleaning liquid (Arakawa Chemical Co., Ltd. make Pine alpha ST-100SX) adjusted to 55 degreeC as a developing solution. By doing so, the unexposed part of the resin film 42 for 1st cladding layers was melt | dissolved and removed. Furthermore, after finishing washing with water, air blowing was performed. Then, it was dried at 100 ° C. for 10 minutes. As a result, a first cladding layer 44 was formed on the temporary substrate 41 as shown in FIG.

  Next, as shown in FIG. 4D, the core portion resin film 45 is placed on the surface of the temporary substrate 41 on the side where the first cladding layer 44 is formed, and the vacuum laminator V-130 is mounted. The core part layer resin film 45 was laminated on the first clad layer 44 by applying pressure at 80 ° C. under a pressure of 0.2 MPa.

Then, as shown in FIG. 4D, the core portion resin film 45 is irradiated with ultraviolet light under a condition of ³ J / cm ² with an ultrahigh pressure mercury lamp so that a core portion having a predetermined shape is obtained. It was exposed by. Specifically, a mask 46 in which four linear pattern slits having a width of 30 μm and a length of 120 mm are arranged, and the mask 46 is positioned so that the slit is positioned at an appropriate position above the first cladding layer 44. Then, exposure was performed through the mask 46. By doing so, the part corresponding to a core part was hardened.

  Next, after peeling off the release film from the cured core portion resin film 45, heat treatment was performed at 140 ° C. for 2 minutes. And it developed using the aqueous | water-based flux washing | cleaning liquid (Arakawa Chemical Co., Ltd. make Pine alpha ST-100SX) adjusted to 55 degreeC as a developing solution. By doing so, the unexposed part of the core part resin film 45 was dissolved and removed. Furthermore, after finishing washing with water, air blowing was performed. Then, it was dried at 100 ° C. for 10 minutes. As a result, a core portion 47 was formed on the first cladding layer 44 as shown in FIG.

Next, a second clad layer resin film is placed on the surface of the temporary substrate 41 on the side where the first clad layer 44 and the core portion 47 are formed, and is 100 ° C. using a vacuum laminator V-130. The second clad layer resin film was laminated on the entire surface of the temporary substrate 41 by applying pressure under a pressure of 0.3 MPa. Thereafter, the surface of the second cladding layer resin film was irradiated with ultraviolet light with an ultrahigh pressure mercury lamp under the condition of ² J / cm ² . Then, after peeling off the release film from the cured resin film for the second cladding layer, heat treatment was performed at 150 ° C. for 30 minutes. By doing so, the resin film for 2nd clad layers was hardened, and the 2nd clad layer 48 was formed as shown in FIG.4 (f).

Then, as shown in FIG. 4G, the temporary substrate 41 was peeled from the clad layer composed of the first clad layer 44 and the second clad layer 48. Thereafter, as shown in FIG. 4 (h), using a CO ₂ laser, and cut into a predetermined size. Specifically, the first cladding layer was disposed in the center and cut so that the width was 2 mm. As a result, an optical waveguide as shown in FIG. 4H was obtained. This optical waveguide corresponds to the optical waveguide 10 shown in FIG.

(Example 2)
Example 2 will be described with reference to FIG. FIG. 5 is a schematic diagram for explaining a method of manufacturing the photoelectric composite flexible wiring board according to the second embodiment.

  First, as shown in FIG. 5A, a glass substrate was prepared as the temporary substrate 51. Further, a circuit board 54 having an electric circuit 53 formed on a base material 52 as shown in FIG. 5B was prepared. Specifically, it prepared as follows. Using a flexible double-sided copper-clad laminate (FELIOS (R-F775) manufactured by Panasonic Electric Works Co., Ltd.) in which a copper foil having a thickness of 12 μm is laminated on both sides of a polyimide film having a thickness of 20 μm, a circuit as shown in FIG. Specifically, two electric circuits having a width of 0.3 mm and a length of 100 mm were formed by removing the copper foil so that the distance between them was 1.4 mm. The side on which the circuit is formed is also referred to as the inner layer side. The back side of the inner layer side is also referred to as a mounting side. Although not shown, the copper foil was removed from the surface on the mounting side so that a predetermined electric circuit was formed. Then, the inner layer side electric circuit and the mounting side electric circuit were electrically connected through a through hole.

  Then, as shown in FIG. 5B, the substrate was bonded to the temporary substrate 51 via the adhesive layer 55 on the surface of the circuit board 54 on the mounting side. The adhesive layer 55 is a layer configured to be detachable from the temporary substrate 51 and the circuit substrate 54.

  Next, as shown in FIG.5 (c), the 1st clad layer resin film 56 is mounted on the surface of the inner side of the circuit board 54, and 80 degreeC, 0 degree using vacuum laminator V-130. The first clad layer resin film 56 was laminated on the circuit board 54 by applying pressure under a pressure of 2 MPa.

Then, as shown in FIG. 5 (d), the first clad layer resin film 56 is subjected to ultraviolet rays under a condition of ² J / cm ² with an ultra-high pressure mercury lamp so that a first clad layer having a predetermined shape is obtained. It was exposed by irradiating light. Specifically, a mask 57 having a linear pattern of slits having a width of 1 mm and a length of 120 mm is positioned above the first cladding layer resin film 56, and the first cladding layer resin film is interposed through the mask 57. 56 was exposed. The mask 57 is arranged so that the exposed position is the center of the two electric circuits 53. As a result, the portion corresponding to the first cladding layer was cured.

  Next, the release film was peeled off from the cured first clad layer resin film 56 and then heat treated at 140 ° C. for 2 minutes. And it developed using the aqueous | water-based flux washing | cleaning liquid (Arakawa Chemical Co., Ltd. make Pine alpha ST-100SX) adjusted to 55 degreeC as a developing solution. By doing so, the unexposed portion of the first cladding layer resin film 56 was dissolved and removed. Furthermore, after finishing washing with water, air blowing was performed. Then, it was dried at 100 ° C. for 10 minutes. By doing so, the first cladding layer 58 was formed on the circuit board 54 as shown in FIG.

  Next, as shown in FIG. 5 (f), the core portion resin film 59 is placed on the surface of the circuit board 54 on the side where the first cladding layer 58 is formed, and the vacuum laminator V-130 is mounted. The core part layer resin film 59 was laminated on the first cladding layer 58 by applying pressure under pressure conditions of 80 ° C. and 0.2 MPa.

Then, as shown in FIG. 5 (f), the core part resin film 59 is irradiated with ultraviolet light under a condition of ³ J / cm ² with an ultrahigh pressure mercury lamp so that a core part of a predetermined shape is obtained. It was exposed by. Specifically, using a mask 60 in which four slits of a linear pattern with a width of 30 μm and a length of 120 mm are arranged, the mask 60 is positioned so that the slit is at an appropriate position above the first cladding layer 59. Then, exposure was performed through the mask 60. Thereby, the part corresponding to a core part was hardened.

  Next, after releasing the release film from the cured core portion resin film 59, heat treatment was performed at 140 ° C. for 2 minutes. And it developed using the aqueous | water-based flux washing | cleaning liquid (Arakawa Chemical Co., Ltd. make Pine alpha ST-100SX) adjusted to 55 degreeC as a developing solution. By doing so, the unexposed part of the core part resin film 59 was dissolved and removed. Furthermore, after finishing washing with water, air blowing was performed. Then, it was dried at 100 ° C. for 10 minutes. Thereby, as shown in FIG. 5G, the core portion 61 was formed on the first cladding layer 58.

Next, the second clad layer resin film is placed on the inner layer side surface of the circuit board 54, and is pressurized using a vacuum laminator V-130 at a pressure of 100 ° C. and 0.3 MPa. The second clad layer resin film was laminated on the entire surface of the circuit board 54. Thereafter, the surface of the second cladding layer resin film was irradiated with ultraviolet light with an ultrahigh pressure mercury lamp under the condition of ² J / cm ² . Then, after peeling off the release film from the cured resin film for the second cladding layer, heat treatment was performed at 150 ° C. for 30 minutes. As a result, the resin film for the second cladding layer was cured, and the second cladding layer 62 was formed as shown in FIG.

Then, as shown in FIG. 5I, the temporary substrate 51 was peeled off from the circuit substrate 54 together with the adhesive layer 55. Thereafter, as shown in FIG. 5 (j), it was cut into a predetermined size using a CO ₂ laser. Specifically, the first cladding layer was disposed in the center and was cut so that the width was 2.2 mm. As a result, an opto-electric composite flexible wiring board as shown in FIG. 5J was obtained. This optical waveguide corresponds to the opto-electric composite flexible wiring board shown in FIG. The distance d between the electric circuits was 1.4 mm, and the distances d ₁ and d ₃ between the electric circuit and the core part were 0.3 mm.

(Comparative example)
An optical waveguide was manufactured in the same manner as in Example 1 except that no mask was used when forming the first cladding layer. The obtained optical waveguide corresponds to the optical waveguide 20 shown in FIG.

[Evaluation]
The evaluation shown below was performed about the formed optical waveguide and the photoelectric composite flexible wiring board.

(Bending test)
A circumferential test (IPC standard TM-650) standardized by the IPC was performed as a bending test of a slide-type mobile phone on the optical waveguide and the photoelectric composite flexible wiring board. Specifically, the bending in this bending test is bending using IPC-02 manufactured by Toyo Seiki Seisakusho Co., Ltd., having a bending radius (curvature radius) of 1 mm and a bending frequency of 120 times / minute. When this bending was repeated 200,000 times, the number of times until the optical waveguide and the photoelectric composite flexible wiring board were broken was measured.

  As a result, Example 1 was 80,000 times. Further, Example 2 was not broken after 200,000 times. On the other hand, the comparative example was 30,000 times.

  From this, the optical waveguide and the optoelectric composite flexible wiring board (Example 1 and Example 2) according to the present embodiment are compared with the comparative example in which the interface between the first cladding layer and the second cladding layer is present on the side surface. In the bending test, it was found that the number of times until breakage occurred was small. This is considered to be because the optical waveguide and the optoelectric composite flexible wiring board according to the present embodiment can suitably suppress the occurrence of cracks due to bending or the like.

  Next, the distance between the electric circuit and the core portion was examined.

(Example 3)
Although the thing to the shape corresponded to FIG.5 (j) was created by the method similar to Example 2, in the dimension condition surface, the width | variety of the obtained optical waveguide shall be 3 mm, and the distance d between electric circuits is the following. The distances d ₁ and d ₃ between the electric circuit and the core portion were changed to be 0.7 mm.

Example 4
The width of the obtained optical waveguide was 4 mm, the distance d between the electric circuits was 3.2 mm, and the distances d ₁ and d ₃ between the electric circuit and the core part were changed to 1.2 mm. Except for this, this is the same as Example 3.

(Example 5)
The width of the obtained optical waveguide was 5 mm, the distance d between the electric circuits was 4.2 mm, and the distances d ₁ and d ₃ between the electric circuit and the core part were changed to 1.7 mm. Except for this, this is the same as Example 3.

[Evaluation]
The following evaluation was performed about the formed photoelectric composite flexible wiring board.

<Heat reliability>
First, the waveguide loss of the obtained photoelectric composite flexible wiring board was measured. Thereafter, a pressure cooker test was performed. And the waveguide loss of the photoelectric composite flexible wiring board after a pressure cooker test was measured. And the change of the waveguide loss before and behind a pressure cooker test was computed. The pressure cooker test and the method for measuring the waveguide loss are as follows.

(Pressure cooker test)
By using “PLAMOUNST HAST CHMBER PM220” manufactured by Enomoto Kasei Co., Ltd., the temperature is set to 120 ° C., and the humidity is set to an unsaturated state of about 100 RH%. A pressure cooker test (PCT) was performed on the wiring board.

(Waveguide loss measurement)
First, by polishing both ends of the photoelectric composite flexible wiring board, a 110 mm long optical waveguide was exposed at the end.

  At one end (incident side end) of the optical waveguide of this opto-electric composite flexible wiring board, NAO. The ends of the 21 optical fibers were connected via matching oil (silicone oil). At the other end (output side end), NAO. The ends of the four optical fibers were connected via matching oil. Light from an LED light source with a wavelength of 850 nm was made incident on the optical waveguide through an optical fiber connected to the input side end. Then, the emitted light from the optical waveguide was made incident on the power meter through the optical fiber connected to the output side end, and the light quantity P1 of the emitted light was measured.

  On the other hand, when the optical fiber connected to the input side end and the optical fiber connected to the output side end are directly connected without going through the optical waveguide, the output from the optical fiber connected to the output side end The amount of incident light P0 was measured in the same manner as described above.

  And the insertion loss (waveguide loss) L1 of the optical waveguide with a micromirror was calculated | required by following formula (1).

L1 = -10 log (P1 / P0) (1)
(Heat reliability)
As described above, the waveguide loss of the photoelectric composite flexible wiring board before and after the PCT was measured. And the difference of the waveguide loss before PCT and the waveguide loss after PCT was computed, and the value was made into the loss by PCT. The reliability during heating was evaluated based on the loss due to the PCT.

As a result, the loss due to PCT was as follows. Example 2 (d ₁ = 0.3 mm) is 1.68 dB, Example 3 (d ₁ = 0.7 mm) is 0.57 dB, and Example 4 (d ₁ = 1.2 mm) is 0. 29 dB, and Example 5 (d ₁ = 1.7 mm) was 0.20 dB. FIG. 6 is a graph plotting the results.

As can be seen from FIG. 6, the loss is less than 1.0 mm when the distance d ₁ (d ₃ ) between the electric circuit and the core is 0.5 mm or less. From this, the following can be understood. In addition, when d ₁ exceeds 2.0 mm and at least around 3 mm, the loss is expected to be reduced to a sufficiently small level below 0.2 dB.

DESCRIPTION OF SYMBOLS 10,20 Optical waveguide 11,21 Core part 12,22 1st clad layer 13,23 2nd clad layer 14,24 clad layer 15 Electric circuit 16 Base material 17 Circuit board 30 Opto-electric composite flexible wiring board

Claims (1)

A substrate on which an electric circuit is formed;
An optical waveguide formed on the substrate,
The optical waveguide is formed on the first clad layer so as to embed the first clad layer formed on the substrate, a core part formed on the first clad layer, and the core part. A second cladding layer,
The substrate is made of polyimide,
The electrical circuit is spaced apart from the first cladding layer;
The second cladding layer covers from the upper surface to the side surface of the first cladding layer , and further covers the edge of the substrate on the surface side where the electric circuit is formed ;
A side surface of the optical waveguide is covered with the second cladding layer ,
The photoelectric composite flexible wiring board , wherein an interval between the electric circuit and the core portion is 0.5 mm or more .

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