Optical waveguide

Abstract

This optical waveguide is provided with: a core (51) having a first surface (511) and a second surface (512) on the opposite side from the first surface (511); a first coating layer (521) formed in contact with the first surface (511); and a second coating layer (522) formed in contact with the second surface (512). One end of the optical waveguide (5) has a first end surface (F1), which is a surface in which the core (51) and the first cladding layer (521) are substantially coplanar and the core is exposed, and a second end surface (F2), which is a surface of the second cladding layer (522) extending from the first end surface (F1).

Description

Technical Field

[0001] The present invention relates to optical waveguides. Background Art

[0002] Patent document 1 discloses an optical waveguide having a core layer, a first cladding layer stacked on the first main surface side of the core layer, and a second cladding layer stacked on the second main surface side of the core layer. The end face of the second cladding layer is set back from the end faces of the core layer and the first cladding layer, and a portion of the second main surface of the core layer is exposed. When the optical interposer is connected to the optical waveguide, the light guide portion exposed on the lower surface of the optical interposer is arranged to face the exposed second main surface of the core layer, thereby achieving optical connection.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-141910 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the optical waveguide disclosed in Patent Document 1, it is considered that the alignment of the light guide portion of the optical intermediary layer with respect to the core layer is sometimes difficult when the optical intermediary layer is connected to the optical waveguide. In addition, since the optical intermediary layer is disposed on the exposed core layer, it is considered that the core layer may be damaged by contact.

[0008] Means for solving problems

[0009] The optical waveguide of the present invention comprises: a core having a first surface and a second surface on the side opposite to the first surface; a first cladding layer formed in contact with the first surface; and a second cladding layer formed in contact with the second surface. One end of the optical waveguide comprises a first end surface and a second end surface, the first end surface being a surface where the core and the first cladding layer are substantially coplanar and where the core is exposed, and the second end surface being a surface of the second cladding layer extending from the first end surface.

[0010] According to an embodiment of the present invention, an optical waveguide can be provided in which a light receiving portion or a light emitting portion, i.e., a light guiding portion, of an electronic component (e.g., an optical element, an optical interposer) connected to the optical waveguide is easily aligned with a core portion of the optical waveguide in the thickness direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a cross-sectional view showing an example of a wiring substrate including an optical waveguide according to an embodiment of the present invention.

[0012] Figure 2 It is shown Figure 1 A top view of an example of a wiring substrate in a top view.

[0013] Figure 3 yes Figure 1 An enlarged view of Part III.

[0014] Figure 4 It is a cross-sectional view showing a modified example of a wiring substrate including an optical waveguide according to an embodiment of the present invention.

[0015] Figure 5A It is a cross-sectional view showing an example of a manufacturing process of the optical waveguide according to the embodiment.

[0016] Figure 5B It is a cross-sectional view showing an example of a manufacturing process of the optical waveguide according to the embodiment.

[0017] Figure 5C It is a cross-sectional view showing an example of a manufacturing process of the optical waveguide according to the embodiment.

[0018] Figure 5D It is a cross-sectional view showing an example of a manufacturing process of the optical waveguide according to the embodiment.

[0019] Figure 5E It is a cross-sectional view showing an example of a manufacturing process of the optical waveguide according to the embodiment.

[0020] Fig. 5F It is a cross-sectional view showing an example of a manufacturing process of the optical waveguide according to the embodiment.

[0021] Figure 6 It is a cross-sectional view showing an example of a manufacturing process of a wiring substrate having an optical waveguide according to an embodiment. DETAILED DESCRIPTION

[0022] A wiring board according to an embodiment of the present invention will be described with reference to the drawings. Figure 1 An optical waveguide 5 is shown as an example of an optical waveguide according to one embodiment. Figure 1 2 shows a state where the optical waveguide 5 is mounted on the electric wiring portion 200 via the support plate 6 to form the wiring substrate 100. Figure 2 In the figure, Figure 1 FIG. 1 is a top view of wiring substrate 100 when viewed from above. Figure 1 is along Figure 2 A cross-sectional view taken along line II of FIG. 1. In addition, “viewed from above” means viewing the wiring substrate 100 from a line along the thickness direction of the wiring substrate 100. Figure 2 The circle B drawn with a single dotted line shows Figure 2 An enlarged view of part II. Figure 3 Shown in Figure 1 An enlarged view of Part III.

[0023] Figure 1The wiring substrate 100 of the example shown includes an electric wiring portion 200 and an optical wiring portion 300 placed on a surface 203 of the electric wiring portion 200. The optical wiring portion 300 includes the optical waveguide 5 and the support plate 6 of the embodiment. The electric wiring portion 200 includes an insulating layer and a conductor layer. Figure 4 The wiring substrate 100a of the modified example shown does not include a support plate, and the optical wiring portion is provided with an optical waveguide 5 on the wiring substrate 100a. Figure 4 The optical waveguide 5 in the embodiment is formed on the insulating layer 21 , but the optical waveguide 5 may also be formed on the solder resist 23 .

[0024] Figure 1 The electrical wiring portion 200 includes: a core substrate 3 having one surface 3a and another surface 3b opposite to each other in the thickness direction thereof; an insulating layer 21 and a conductor layer 11, which are sequentially stacked on one surface 3a of the core substrate 3; and an insulating layer 22 and a conductor layer 12, which are sequentially stacked on the other surface 3b. The insulating layer 21 is an interlayer insulating layer between the conductor layer 11 and the conductor layer 31, and the insulating layer 22 is an interlayer insulating layer between the conductor layer 12 and the conductor layer 31. Via conductors 20 are formed on the insulating layer 21 and the insulating layer 22, respectively, to connect the conductor layers sandwiched therebetween. The core substrate 3 includes an insulating layer 32 and conductor layers 31 formed on both surfaces of the insulating layer 32. A through-hole conductor 33 is provided on the insulating layer 32 to penetrate the insulating layer 32 and connect the conductor layers 31 on both sides to each other.

[0025] In the electric wiring portion 200, solder resist 23 is formed on one surface 3a side and the other surface 3b side of the core substrate 3. The solder resist 23 on the one surface 3a side covers the necessary parts of the insulating layer 21 and the conductor layer 11. In addition, the solder resist 23 on the other surface 3b side covers the necessary parts of the insulating layer 22 and the conductor layer 12.

[0026] In the electric wiring section 200, conductor posts 13 and 14 are formed on the conductor layer 11. A connection layer 15 is formed on the surface of the conductor posts 13 and 14 using, for example, tin-based solder, gold-based solder, or silver-based solder. The conductor posts 13 and 14 have a columnar shape, for example, extending from the conductor layer 11 in a direction opposite to the insulating layer 21. The conductor posts 13 and 14 protrude from the surface of the solder resist 23. An external component E1 is connected to the conductor post 13, and an external component E2 is connected to the conductor post 14. Therefore, the electric wiring section 200 has a component mounting area A1, which is an area where the component E1 is mounted when the wiring substrate 100 is used. The component mounting area A1 is covered by the component E1 when the wiring substrate 100 is used.

[0027] The insulating layers 21, 22 and the insulating layer 32 are formed of insulating resins such as epoxy resin, bismaleimide triazine resin (BT resin) or phenolic resin. Although not shown, each insulating layer may further include a core material (reinforcement material) formed of glass fiber, aramid fiber, etc., and may also include an inorganic filler formed of microparticles such as silicon dioxide (SiO2), aluminum oxide or mullite. On the other hand, the solder resist 23 is formed of, for example, a photosensitive epoxy resin, a polyimide resin, etc.

[0028] The conductor layers 11, 12, 31, through-hole conductors 33, via-hole conductors 20, and conductor posts 13, 14 can be formed using any metal such as copper or nickel. Figure 1 Although it is simplified and depicted as one layer in the figure, it is preferably a multilayer structure of two or more metal layers. For example, the conductor layers 11 and 12 may have a two-layer structure including a chemically plated film and an electroplated film. The conductor posts 13 and 14 are formed of, for example, plated metal deposited by chemical plating and / or electroplating. In addition, the conductor posts 13 and 14 may be formed not only by forming a plating layer, but also by sputtering, coating of a conductive paste, and the like.

[0029] The conductor layers 11, 12 and the conductor layer 31 may each include an arbitrary conductor pattern. Figure 1 In the example of , the conductor layer 11 includes conductor pads 11a and 11b. A conductor post 13 is formed on the conductor pad 11a, and the electrode E1a of the component E1 is electrically connected to the conductor pad 11a via the conductor post 13. Similarly, a conductor post 14 is formed on the conductor pad 11b, and the electrode E2a of the component E2 is electrically connected to the conductor pad 11b via the conductor post 14.

[0030] When the wiring substrate 100 is used, electric components including a light receiving element and / or a light emitting element having a photoelectric conversion function are mounted as components E1 in the component mounting region A1. Figure 1 to Figure 3 The component E1 of the example has a light guide portion E1b as a light receiving portion or a light emitting portion in addition to the electrode E1a. Figure 3 The light guide E1b as a light receiving part or light emitting part has a light receiving surface or a light emitting surface E1c. The electrode E1a and the light guide E1b as a light receiving part or light emitting part are provided on the surface of the component E1 facing the wiring substrate 100 side. Figure 1 to Figure 3 In the example of FIG. 1 , the component E1 is mounted so-called face-down (flip-chip mounting).

[0031] As the component E1, a light receiving element such as a photodiode and a light emitting element such as a light emitting diode (LED), an organic light emitting diode (OLED), a laser diode (LD), and a vertical resonance surface emitting laser (VCSEL) are exemplified. When the component E1 is a light emitting element, the component E1 generates a light signal based on the electric signal input to the electrode E1a, and emits the light signal from the light receiving part or the light emitting part, that is, the light guiding part E1b, which functions as a light emitting part. In addition, when the component E1 is a light receiving element, an electric signal based on the light signal incident to the light receiving part or the light emitting part, that is, the light guiding part E1b, which functions as a light receiving part, is generated and output from the electrode E1a.

[0032] Component E2 may be, for example, an electronic component such as a semiconductor device that generates an electrical signal for causing component E1 to emit light and / or processes the electrical signal generated by component E1. Component E2 includes, for example, a semiconductor device such as a general-purpose operational amplifier, a driver IC, a microcomputer, a programmable logic device (PLD), and the like.

[0033] The optical waveguide 5 of the embodiment is included in the optical wiring section 300. The optical waveguide 5 includes a core 51 for transmitting an optical signal and a cladding 52 surrounding the core 51. Figure 1 In the embodiment, the optical wiring section 300 has a support plate 6. The support plate 6 is arranged on the electrical wiring section 200. The optical waveguide 5 is arranged on the support plate 6. As the material of the support plate 6, glasses such as soda lime glass, borosilicate glass and quartz glass, various metals such as tungsten, titanium and molybdenum, and various ceramics such as aluminum oxide, silicon nitride and silicon oxide can be exemplified. The various metals constituting the support plate 6 can be in the form of a metal plate or in the form of a metal foil. In addition, the optical waveguide 5 can also be arranged on the surface 203 of the electrical wiring section 200.

[0034] The cladding 52 includes a first cladding layer 521 and a second cladding layer 522. The cladding 52 is disposed around the core 51, and sandwiches the core 51 in a direction extending from the surface exposed from the core 51, that is, in any direction perpendicular to the propagation direction (+X direction or -X direction, hereinafter also referred to as "X direction") of the optical signal in the core 51. Specifically, the core 51 has a first surface 511 (the upper part of the core 51) and a second surface 512 (the lower part of the core 51), the first cladding layer 521 of the cladding 52 is in contact with the first surface 511 of the core 51, and the second cladding layer 522 is in contact with the second surface 512 of the core 51.

[0035] The core 51 has a first end 5a and a second end 5b as ends in the extending direction. The second end 5b is an end on the opposite side of the first end 5a. At the end of the core 51, the optical signal is incident from the outside of the optical waveguide 5 through the surface of the core 51 not covered by the cladding 52. In addition, at the end of the core 51, the optical signal is emitted from the core 51 to the outside of the optical waveguide 5 through the surface of the core 51 not covered by the cladding 52. The first end 5a and the second end 5b each have a light transmission surface, which is a surface of the core 51 exposed to the outside of the optical waveguide 5 and not covered by the cladding 52, so that the optical signal propagating in the core 51 is transmitted.

[0036] The core 51 and the cladding 52 constituting the optical waveguide 5 are formed using materials having an appropriate refractive index. The core 51 and the cladding 52 can be made of, for example, any of an organic material (organic matter), an inorganic material (inorganic matter), or an organic-inorganic mixed material containing an organic component and an inorganic component such as an inorganic polymer. As inorganic materials, quartz glass, silicon, etc. can be exemplified, and as organic materials, thermosetting resins, ultraviolet curing resins, thermoplastic resins, etc. are provided, and thermosetting resins or ultraviolet curing resins are preferably used. Specifically, acrylic resins such as polymethyl methacrylate (PMMA), polyimide resins, polyamide resins, polyether resins, and epoxy resins can be exemplified. The optical waveguide 5 composed of organic materials is easy to be lightweight and has high toughness. In addition, the processability of the waveguide of the organic material is excellent, and it is easy to form the first end face and the second end face as the end of the waveguide. In addition, the surface roughness of the first end face and the surface roughness of the second end face as the end of the waveguide obtained from the organic material can be adjusted to a desired numerical range. In a waveguide made of an organic material, a depression (recess) can also be formed relatively easily.

[0037] The core 51 and the cladding 52 may be made of different materials or the same system of materials. However, the core 51 uses a material having a higher refractive index than the material used for the cladding 52 so that the optical signal can be totally reflected at the interface between the core 51 and the cladding 52. The core 51 and the cladding 52 may be formed of materials having the same refractive index and then subjected to appropriate treatment to make their refractive indices different from each other.

[0038] In the optical waveguide 5 of the embodiment, as shown in the figure, one end of the core 51 on the first end 5 a side is formed by a first end face and a second end face.

[0039] (First end face)

[0040] The exposed surface of the first end portion 5a has a light-transmitting surface, which is a surface that is consistent with the exposed surface of the core portion extending perpendicular to the X direction of the first cladding layer 521. The surface where the exposed surface of the core portion in the first end portion 5a of the core portion 51 is consistent with the side surface of the first cladding layer 521 is called the first end surface F1. In the first end surface F1, the exposed surface of the core portion 51 in the first end portion 5a of the core portion 51 is formed to be roughly coplanar with the end surface of the first cladding layer 521 in the first end portion 5a. In other words, in the first end surface F1, the core portion 51 and the first cladding layer 521 are roughly coplanar.

[0041] (Second end face)

[0042] On the first end 5a side of the core 51 of the optical waveguide 5, there is a second cladding layer 522 provided on the side of the core 51 opposite to the first cladding layer 521, and the second cladding layer 522 extends from the first end face F1 along the propagation direction (X direction) of the optical waveguide 5. That is, at the end of the optical waveguide 5 on the first end face F1 side in the X direction, a portion of the surface of the second cladding layer 522 on the side in contact with the core 51 extends and is exposed. The exposed surface of the second cladding layer 522 on the side in contact with the core 51 is referred to as the second end face F2. Figure 1 In the example of FIG. 1 , the second end surface F2 overlaps with the component mounting area A1 of the wiring substrate 100 . Alternatively, the second end surface F2 may not overlap with the component mounting area A1 of the wiring substrate 100 .

[0043] like Figure 2 In circle B and Figure 3 As shown, in the use of the wiring substrate 100, the first end face F1 of the first end portion 5a of the core portion 51 has a light transmission surface, which is arranged in a manner opposite to the light receiving portion or light emitting portion of the component E1, that is, the light guiding portion E1b. That is, when the component E1 is mounted on the component mounting area A1, the light receiving surface or light emitting surface E1c of the component E1 is exposed and aligned with the light transmission surface of the first end face F1 in the first end portion 5a. Specifically, as Figure 3 As shown, the component E1 is arranged on the second end surface F2 inside the cladding layer of the second cladding layer 522 in such a manner that the light receiving surface or light emitting surface E1c of the component E1 faces the light transmission surface of the first end surface F1 in the first end portion 5a of the core 51 and optically couples with it. Figure 1 as well as Figure 2 As shown, the end surface of the core 51 on the second end 5b side is positioned so as to be optically coupled to the optical fiber F when the wiring substrate 100 is used. Figure 1 As shown, the optical fiber F is connected to the optical waveguide 5 using a connector C. In addition, the optical waveguide 5 may be connected to another optical waveguide instead of the optical fiber F.

[0044] Since the optical waveguide 5 is configured in this way, the optical signal propagating in the optical fiber F enters the optical waveguide 5 from the second end 5b of the core 51, propagates in the core 51, and enters the component E1 from the first end 5a of the waveguide via the light receiving portion or the light emitting portion, that is, the light guiding portion E1b. That is, the component E1 is optically coupled with the optical signal transmitted through the optical waveguide 5. Specifically, the optical signal propagating toward the first end 5a in the core 51 enters the light receiving portion or the light emitting portion, that is, the light guiding portion E1b of the component E1 via the light transmission surface in the propagation direction of the optical signal. That is, when the wiring substrate 100 is used, the light transmission surface of the core 51 is butt-coupled with the light receiving portion or the light emitting portion, that is, the light guiding portion E1b of the component E1.

[0045] The optical signal incident on the component E1 is converted into an electrical signal in the component E1 and output from the electrode E1a. The output electrical signal is input to the component E2 via the conductor layer 11 and processed. On the other hand, the electrical signal output from the component E2 toward the component E1 is input into the component E1 via the electrode E1a and converted into an optical signal. The optical signal is emitted from the light receiving portion or the light emitting portion, that is, the light guiding portion E1b, and is incident on the optical waveguide 5 from the first end 5a. The incident optical signal propagates in the core 51 and is emitted from the second end 5b to the optical fiber F.

[0046] like Figure 2 As shown in FIG. 1 , the optical waveguide 5 has eight cores 51 arranged in parallel. In this way, the optical waveguide 5 of the embodiment has any number of cores 51. For example, the plurality of optical fibers F optically coupled to the cores 51 at the second end 5b may not be arranged at a pitch as small as the arrangement pitch of the plurality of light receiving or light emitting portions, i.e., the light guiding portion E1b, of the component E1. Therefore, as Figure 2 As shown in the example of , a plurality of optical fibers F are sometimes arranged at a pitch greater than the arrangement pitch of the light receiving portion or light emitting portion, that is, the light guiding portion E1b. Figure 2 In the example, the plurality of cores 51 are arranged at a larger pitch at the second end 5b than at the first end 5a. Therefore, it is considered that the component E1 and the core 51 or the optical fiber F and the core 51 are optically coupled appropriately at the first end 5a and the second end 5b without requiring an additional pitch conversion unit. In addition, the number of cores 51 included in the optical waveguide 5 is not particularly limited, but is preferably 4 to 32.

[0047] In the optical waveguide 5 of the embodiment, the core 51 is exposed at the first end face F1 of the first end 5a of the core 51, and when the electrical wiring portion 200 is mounted with the optical wiring portion 300, the position of the light transmission surface of the core 51 at the first end face F1 can be easily identified. In addition, when the component E1 is mounted on the component mounting area A1, the light receiving surface or light emitting surface E1c of the component E1 is aligned with the light transmission surface of the first end face F1 in the first end 5a in an exposed state. Specifically, the component E1 is placed on the second end face F2. Therefore, it is relatively easy to align the light receiving surface or light emitting surface E1c of the component E1 with the light transmission surface exposed at the first end 5a of the core 51. Specifically, the distance (inter-surface distance) between the light transmission surface of the first end 5a of the core 51 and the light receiving surface or light emitting surface E1c of the component E1 can be relatively easily adjusted so as to achieve good optical coupling between the light receiving portion or light emitting portion of the component E1, that is, the light guiding portion E1b and the core 51.

[0048] In addition, in the optical waveguide 5, the first end face F1 is preferably a polished surface. The surface roughness (R1) of the first end face F1 is preferably, for example, 0.10 μm or less in terms of arithmetic mean roughness, and more preferably 0.01 μm to 0.09 μm in terms of arithmetic mean roughness. Therefore, a more precise adjustment can be made in the inter-surface distance in the alignment between the light transmission surface of the first end 5a of the core 51 and the light receiving surface or light emitting surface E1c of the component E1. In addition, a light-transmitting filling resin (not shown) can be formed in the gap between the light transmission surface of the first end 5a of the core 51 and the light receiving surface or light emitting surface E1c of the component E1 after the component E1 is arranged on the optical waveguide 5. In addition, by making the surface roughness (R1) of the first end face F1 0.10 μm or less in terms of arithmetic mean roughness, the light signal can be efficiently incident on the core 51 and emitted from the core 51 at the first end face F1. Furthermore, by making the surface roughness (R1) of the first end face F1 less than 0.10 μm in terms of arithmetic mean roughness, the formation of the filling resin is not easily hindered. In addition, by making the surface roughness (R1) of the first end face F1 between 0.01 μm and 0.09 μm in terms of arithmetic mean roughness, the incidence of the optical signal on the core 51 and the emission of the optical signal from the core 51 at the first end face F1 can be performed more efficiently, and in addition, it is not easy to form a gap in the formation of the filling resin, and it is easy to fill it well.

[0049] The second end face F2 of the mounting component E1 in the optical waveguide 5 extends from the first end face F1 in the X direction. The length of the second end face F2 extending from the first end face F1 in the X direction is not particularly limited, but is preferably greater than the length of the first end face F1. In this case, the length of the first end face F1 refers to the total value of the thickness of the first cladding layer 521 and the thickness of the core 51. In addition, the surface roughness (R2) of the second end face F2 is not particularly limited, but is preferably less than 0.10 μm in terms of arithmetic mean roughness, and more preferably 0.001 μm to 0.08 μm in terms of arithmetic mean roughness. It is believed that by making the surface roughness (R2) of the second end face F2 less than 0.10 μm in terms of arithmetic mean roughness, it is difficult to hinder the formation of a light-transmitting filling resin when configuring the component E1. It is believed that by making the surface roughness (R2) of the second end face F2 0.001μm to 0.08μm in terms of arithmetic mean roughness, a translucent filling resin can be formed without gaps when configuring component E1. Component E1 is relatively stably placed on the second cladding layer 522. In addition, it is believed that the accuracy of the alignment of component E1 relative to the optical waveguide 5 in the thickness direction is improved. Specifically, when aligning the light-receiving surface or the light-emitting surface E1c of component E1 relative to the light-transmitting surface exposed at the first end 5a of the core 51, the accuracy of the alignment in the thickness direction is improved. As an example of an embodiment, the surface roughness (R1) of the first end face F1 is 0.04μm in terms of arithmetic mean roughness, and the surface roughness (R2) of the second end face F2 is 0.006μm in terms of arithmetic mean roughness.

[0050] It should be noted that the "surface roughness" in the description of this specification refers to the arithmetic mean roughness Sa defined by ISO 25178. In the measurement of the surface roughness, a measurement target area in the range of 30 μm×30 μm is specified, and the measurement is performed using a laser surface roughness measuring device (VK-X210 manufactured by Keyence Corporation), and the average value of the measurement results of 5 points in the measurement target area is taken as the surface roughness.

[0051] like Figure 3 As shown, the second cladding layer 522 of the optical waveguide 5 has a recess (concave portion) GR at the corner between the second end face F2 and the first end face F1 (the periphery of the first end face F1). Figure 2 As can be seen from the top view shown, the recess GR extends along the width direction of the optical waveguide 5 which is perpendicular to the X direction. Figure 3 As shown, the inner wall surface of the recess GR on the first end face F1 side is substantially coplanar with the first end face F1. In addition, the corner between the second end face F2 and the first end face F1 is also the periphery of the first end face F1. Sometimes, the recess GR is formed at the periphery of the first end face F1, that is, at the corner between the second end face F2 and the first end face F1.

[0052] The recess GR is formed in the area between the component mounting area A1 and the first end face F1. That is, the recess GR is formed in the second cladding layer 522 in the range between the first end face F1 and the surface of the component E1 opposite to the first end face F1 in the state where the component E1 is mounted on the wiring substrate 100 (in the state where the component E1 is mounted on the optical waveguide 5). The depth of the recess GR in the thickness direction (Y direction) of the second cladding layer 522 (the shortest distance from the upper surface of the second end face F2 to the bottom of the recess GR) is preferably 5 μm or more. The width of the recess GR in the direction (X direction) in which the optical waveguide 5 extends (the shortest distance from one inner wall surface to the other inner wall surface) is preferably, for example, 1 μm or more. In addition, the state where the component E1 is mounted on the wiring substrate 100 also means the state where the component E1 is mounted on the optical waveguide 5. In addition, the width of the recess GR refers to the shortest distance from one inner wall surface of the recess to the other inner wall surface in the cross section.

[0053] When the component E1 is placed on the optical waveguide 5, a light-transmitting filling resin may be formed in the gap between the light-transmitting surface of the first end 5a of the core 51 and the light-receiving surface or light-emitting surface E1c of the component E1. In this case, the resin filled in the gap may be filled in the recess GR. By forming the filling resin in the recess GR, an anchoring effect of the resin filling the recess GR can be obtained, and the contact area between the filling resin and the surface of the component E1 and the surface of the optical waveguide 5 is also increased, so that the component E1 and the optical waveguide 5 can be fixed more firmly via the resin. Therefore, it is considered that the possibility of a decrease in light propagation efficiency caused by a positional deviation of the light-receiving surface or light-emitting surface E1c of the component E1 relative to the light-transmitting surface exposed at the first end 5a of the core 51 can be suppressed. In addition, the filling resin may not be formed in the gap between the light-transmitting surface of the first end 5a of the core 51 and the light-receiving surface or light-emitting surface E1c of the component E1.

[0054] Next, refer to Figure 5A to Figure 5F illustrate Figure 1 The method for forming the optical waveguide 5 described below is an example, and the method for forming the optical waveguide 5 can also be implemented by referring to Figure 5A to Figure 5F Methods other than those described.

[0055] First, if Figure 5A As shown, for example, a glass plate is prepared as the support plate 6, and a second coating layer 522 is formed on the surface of the support plate 6. For example, PMMA is used as the coating portion 52 (see Figure 1 ) is formed into a film and thermally pressed onto the support plate 6. In addition to thermal pressing, the support plate 6 may be formed by applying the resin material to the support plate 6 by spin coating or the like.

[0056] Then, if Figure 5BAs shown, an acrylic resin or the like as a resin material constituting the core 51 is formed into a film and laminated on the surface of the second cladding layer 522 opposite to the support plate 6. Alternatively, the resin material constituting the core 51 may be formed by coating by spin coating or the like.

[0057] Then, if Figure 5C As shown, the core 51 having a desired pattern is formed by photolithography using a mask having an opening corresponding to the pattern that the core 51 on the second cladding layer 522 should have. In the pattern formation of the core 51, the core 51 corresponding to the second end face F2 is completely removed. For example, in the pattern formation of the core 51, the core 51 corresponding to the range where the external components of the second cladding layer 522 should be placed is completely removed.

[0058] Then, if Figure 5D As shown, the first cladding layer 521 is formed on the core 51 and the second cladding layer 522 exposed from the pattern of the core 51. For example, similarly to the formation of the second cladding layer 522, a resin material such as PMMA is formed into a film, and the film-like resin material is thermally pressed to the second cladding layer 522 and the core 51. The first cladding layer 521 and the second cladding layer 522 are integrated or at least closely bonded to form the cladding portion 52 surrounding the core 51. In addition, the resin material constituting the first cladding layer 521 can also be formed by coating based on spin coating or the like.

[0059] Then, if Figure 5E As shown, unnecessary portions of the first cladding layer 521 are removed by photolithography. Specifically, the first cladding layer 521 corresponding to the region where the core 51 is not formed when viewed from above is removed. In the second cladding layer 522, the second end face F2 corresponding to the range of the external components to be placed on the second cladding layer 522 is exposed. Figure 5D In the illustrated process, the resin material of the first cladding layer 521 may be formed on the core portion 51 by thermocompression bonding or coating so as not to cover the second end surface F2 of the second cladding layer 522 .

[0060] Then, if Fig. 5F As shown in FIG. 1 , the first end face F1 is formed by laser processing using, for example, a carbon dioxide laser or a UV laser. In forming the first end face F1, the first end face F1 can be formed by laser processing. Figure 5E The core 51 and a part of the first cladding layer 521 in the state shown are cut and mirror-finished. In addition, the mirror-finishing can also be performed by cutting processing or chemical treatment other than laser processing. The first end face F1 is formed as a surface having a roughness of 0.1 μm or less in arithmetic mean roughness.

[0061] In addition, at the same time as the first end face F1 is formed by cutting the core 51 and the first cladding layer 521, a recess GR is formed in the second cladding layer 522. The recess is formed so that the depth in the thickness direction of the second cladding layer 522 is 5 μm or more. The width of the recess GR in the extending direction of the optical waveguide 5 (the shortest distance from one inner wall surface to the other inner wall surface) is, for example, 1 μm or more. Fig. 5F The first end face F1 and the recess GR described above may be formed by cutting, for example, in addition to laser processing. Fig. 5F In the state shown, the surface roughness (R2) of the second end face F2 has a roughness of, for example, 0.1 μm or less in the arithmetic mean roughness. In addition, the surface roughness (R1) of the first end face F1 has a roughness of, for example, 0.1 μm or less in the arithmetic mean roughness. The relationship between the surface roughness (R2) of the second end face F2 and the surface roughness (R1) of the first end face F1 is preferably expressed by Formula 1: R1>R2. By making the surface roughness (R2) of the second end face F2 and the surface roughness (R1) of the first end face F1 satisfy the relationship of Formula 1, it is difficult to hinder the formation of a light-transmitting filling resin in the gap between the component E1 and the first end face F1 of the optical waveguide 5. When the resin is filled in the gap between the first end face F1 and the component E1, it is considered that the filling resin is formed without a gap between the second end face F2.

[0062] go through Figure 5A to Figure 5F The steps shown in the figure complete the formation of the optical waveguide 5 arranged on the support plate 6. Figure 1 The optical wiring section 300 is shown in the example. In addition, the optical waveguide 5 may be formed independently of the support plate 6, for example, by fixing the optical waveguide 5 to the support plate 6 using any adhesive (not shown). In forming the optical wiring section 300, the optical waveguide 5 may be fixed to the support plate 6 by any means. Figure 4 In the case of the wiring substrate 100 a shown in the figure which does not have a support plate, the optical waveguide 5 may be formed on the electric wiring portion 200 , or the optical waveguide 5 may be fixed in contact with the electric wiring portion 200 .

[0063] In manufacturing Figure 1 In the case of the wiring substrate 100 of the example shown, an optical waveguide 5 fixed to a support plate 6 is prepared as the optical wiring portion 300. The support body 6 formed with the optical waveguide 5 is attached to the electrical wiring portion 200. The optical wiring portion 300 can be fixed to the surface of the insulating layer 21 by any means. The support plate 6 can be fixed to the surface of the insulating layer 21 using, for example, any adhesive G.

[0064] An adhesive G of any type, such as a thermosetting adhesive, a room temperature curing adhesive, or a light curing adhesive, is applied to a predetermined portion of the surface of the insulating layer 21 exposed from the solder resist 23, and the optical wiring portion 300 having the optical waveguide 5 is mounted thereon. If necessary, the adhesive G is cured by heating or the like to fix the optical wiring portion 300. After the above steps, the optical wiring portion 300 is completed. Figure 1 A wiring substrate 100 is an example.

[0065] The optical waveguide of the embodiment is not limited to the structure, shape and material illustrated in the drawings and in the present specification. The optical waveguide of the embodiment only needs to have a first end face where the core and the first cladding are exposed in a substantially coplanar manner and a second end face that is a surface of the second cladding on the core side extending from the first end face. For example, the optical waveguide of the embodiment can have any number of cores. In addition, the thickness of the core may also change from the first end 51a to the second end 51b.

[0066] Description of symbols

[0067] 100: wiring substrate; 200: electrical wiring portion; 300: optical wiring portion; 11, 12: conductor layer; 21, 22: insulating layer; 23: solder resist; 5: optical waveguide; 51: core; 5a: first end portion; 5b: second end portion; 52: cladding portion; 521: first cladding layer; 522: second cladding layer; 6: supporting plate; A1: component mounting area; E1, E2: component; E1a: electrode; E1b: light guiding portion; E1c: light receiving surface or light emitting surface; F1: first end face; F2: second end face; GR: recess.

Claims

1. An optical waveguide, comprising: a core having a first surface and a second surface opposite to the first surface; A first cladding layer formed in contact with the first surface; and a second cladding layer formed in contact with the second surface, in, One end of the optical waveguide has a first end surface and a second end surface, The first end surface is a surface where the core and the first cladding layer are substantially coplanar and the core is exposed. The second end surface is a surface of the second cladding layer extending from the first end surface.

2. The optical waveguide according to claim 1, wherein The second coating layer has a recess at a periphery of the first end surface.

3. The optical waveguide according to claim 2, wherein: The inner wall surface of the recess is substantially coplanar with the first end surface.

4. The optical waveguide according to claim 1, wherein The core, the first cladding layer, and the second cladding layer are made of organic matter.

5. The optical waveguide according to claim 1, wherein The surface roughness (R1) of the first end surface is 0.10 μm or less in terms of arithmetic mean roughness.

6. The optical waveguide according to claim 1, wherein The surface roughness (R2) of the second end surface is 0.10 μm or less in terms of arithmetic mean roughness.

7. The optical waveguide according to claim 1, wherein The surface roughness (R1) of the first end surface and the surface roughness (R2) of the second end surface satisfy the relationship of Formula 1, Formula 1: R1>R2.

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