Optical circuit board and mounting structure

Abstract

An optical circuit board (1) according to the present disclosure includes a wiring board (2) having a first surface (21), and an optical waveguide (3) positioned on the first surface (21). The optical waveguide (3) includes a lower cladding (31), a core (32), and an upper cladding (33). The lower cladding (31) is positioned on the first surface (21) and has a surface positioned on the first surface (21) side and a second surface (312) positioned on the opposite side from the surface. The core (32) extends to the second surface (312), and has a first end surface (321) and second end surface (322) that are positioned facing opposite one another in the extension direction of the core. The upper cladding (33) is positioned on the second surface (312) and covers the core (32) so that the first end surface (321) and the second end surface (322) are exposed. The optical waveguide (3) has a first side surface (3a) including the first end surface (321) and a second side surface (3b) including the second end surface (322). A first protruding part (34) in which a region including a boundary between the core (32) and the upper cladding (33) and a boundary between the core (32) and the lower cladding (31) is raised is positioned in at least one of the first side surface (3a) and the second side surface (3b).

Description

Optical circuit board and mounting structure

[0001] The present invention relates to an optical circuit board and a mounting structure using the optical circuit board.

[0002] In recent years, optical fibers capable of transmitting large volumes of data at high speeds have come to be used in information communications. Optical signals are transmitted and received between the optical fibers and optical components. Such optical components are mounted on optical circuit boards equipped with optical waveguides, as described in, for example, Patent Document 1. Optical signals are transmitted and received via these optical waveguides.

[0003] For example, an optical signal emitted from an optical element is incident on the end face of a core included in an optical waveguide and is sent to an optical fiber. A portion of the optical signal emitted from the optical element may not be incident on the end face of the core but may be irradiated on the end face of the cladding. The optical signal irradiated on the end face of the cladding may be reflected and returned to the optical element.

[0004] Japanese Patent Application Laid-Open No. 2003-161853

[0005] The optical circuit board according to the present disclosure includes a wiring substrate having a first surface and an optical waveguide located on the first surface. The optical waveguide includes a lower cladding, a core, and an upper cladding. The lower cladding is located on the first surface and has a surface located on the first surface side and a second surface located opposite the first surface. The core extends to the second surface and has a first end face and a second end face located opposite each other in the extension direction of the core. The upper cladding is located on the second surface and covers the core so that the first end face and the second end face are exposed. The optical waveguide has a first side face including the first end face and a second side face including the second end face. A first protrusion is located on at least one of the first side face and the second side face, where the region including the boundary between the core and the upper cladding and the region including the boundary between the core and the lower cladding is raised.

[0006] A mounting structure according to the present disclosure includes the above-described optical circuit board and an optical component mounted on the optical circuit board.

[0007] 1 is a plan view showing a mounting structure in which optical components and electronic components are mounted on an optical circuit board according to an embodiment of the present disclosure. FIG. 1 is an enlarged explanatory diagram for explaining a cross section of region X shown in FIG. 1. FIG. 2 is an enlarged explanatory diagram for explaining an embodiment of region Y shown in FIG. 2. FIG. 3 is an enlarged explanatory diagram showing an embodiment as viewed from the direction of arrow A shown in FIG. 3. FIG. 3 is image data showing an embodiment of a first protrusion and a second protrusion as viewed from the direction of arrow B shown in FIG. 3. FIG. 4 is an enlarged explanatory diagram for explaining another embodiment of region Y shown in FIG. 2. FIG. 7A to FIG. 7F are explanatory diagrams for explaining an embodiment of a method for forming an optical waveguide.

[0008] In conventional optical circuit boards such as those described in Patent Document 1, the optical signal emitted from the optical element may interfere with the reflected optical signal, resulting in attenuation of the optical signal emitted from the optical element. Furthermore, the reflected optical signal may cause a malfunction of the light source of the optical element. Therefore, there is a demand for an optical circuit board that has excellent transmission efficiency of optical signals between optical components and optical waveguides.

[0009] The optical circuit board according to the present disclosure has a configuration as described in the section on means for solving the above problems, and thus has excellent transmission efficiency of optical signals between optical components and optical waveguides.

[0010] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Figures 1 to 5. Figure 1 is a plan view showing a mounting structure 10 in which an optical component 4 and an electronic component 6 are mounted on an optical circuit board 1 according to an embodiment of the present disclosure.

[0011] An optical circuit board 1 according to an embodiment of the present disclosure includes a wiring board 2 and an optical waveguide 3. Examples of the wiring board 2 included in the optical circuit board 1 according to an embodiment include wiring boards that are generally used for optical circuit boards.

[0012] Although not specifically illustrated, such a wiring board 2 includes, for example, a core layer and build-up layers laminated on both sides of the core layer. The core layer includes a core insulating layer and a core conductor layer. The core insulating layer is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used alone or in combination of two or more.

[0013] The core insulating layer may contain a reinforcing material. Examples of reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the core insulating layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0014] The core conductor layer is located on the surface of the core insulating layer. The core conductor layer is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper.

[0015] A through-hole conductor is located in the core insulating layer to electrically connect the upper and lower surfaces of the core insulating layer. The through-hole conductor is located in a through-hole that penetrates the upper and lower surfaces of the core insulating layer. The through-hole conductor is formed of a metal such as copper. The through-hole conductor may be formed only on the inner wall surface, or may fill the through-hole. The through-hole conductor is connected to the core conductor layer on the surface of the core insulating layer.

[0016] The build-up layer is located on one or both sides of the core layer, and has a structure in which at least one build-up insulating layer and at least one build-up conductor layer are laminated.

[0017] The build-up insulating layer is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used alone or in combination of two or more.

[0018] The build-up insulation layers may be made of the same resin or different resins. The build-up insulation layers and the core insulation layers may be made of the same resin or different resins. Furthermore, the build-up insulation layers may have the same thickness or different thicknesses.

[0019] The build-up insulating layer may contain a reinforcing material. Examples of reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the build-up insulating layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0020] The conductor layer for build-up is not limited as long as it is a conductor such as a metal, etc. Specifically, the conductor layer for build-up is formed of a metal foil such as a copper foil, or a metal plating such as copper plating.

[0021] Via-hole conductors are located in the build-up insulating layer to electrically connect the upper and lower surfaces of the build-up insulating layer. The via-hole conductors are located in via holes that penetrate the upper and lower surfaces of the build-up insulating layer. The via-hole conductors are formed, for example, by metal plating such as copper plating. The via-hole conductors are connected to build-up conductor layers located on both sides of the build-up insulating layer. The via-hole conductors may fill the via holes, or may be located only on the inner surfaces of the via holes.

[0022] As shown in Fig. 2, the optical waveguide 3 included in the optical circuit board 1 according to one embodiment is located on the surface of a metal layer 21a present on the surface of the wiring board 2. Fig. 2 is an enlarged explanatory view for illustrating a cross section of region X shown in Fig. 1. The optical waveguide 3 has a structure in which a lower clad 31, a core 32, and an upper clad 33 are laminated in this order from the metal layer 21a side.

[0023] The lower cladding 31 included in the optical waveguide 3 is located on the first surface 21 of the wiring board 2, specifically, on the surface of the metal layer 21a present on the surface of the optical waveguide formation region of the wiring board 2. The material forming the lower cladding 31 is not limited, and examples thereof include resins such as epoxy resin and silicone resin. As shown in FIG. 2 , the lower cladding 31 has a surface located on the first surface 21 side of the wiring board 2 and a second surface 312 located on the opposite side of this surface. The metal layer 21a is an optional component and may or may not be used. In other words, the wiring board 2 does not need to include the metal layer 21a.

[0024] The core 32 included in the optical waveguide 3 is a portion through which light that has entered the optical waveguide 3 propagates. The core 32 extends to the second surface 312 of the lower cladding 31, and has a first end face 321 and a second end face 322 that are positioned opposite each other in the extending direction of the core 32. In the optical circuit board 1 according to one embodiment, for convenience, the first end face 321 of the core 32 is the end face on the optical component 4 side, and the second end face 322 of the core 32 is the end face on the optical connector 5a side.

[0025] Specifically, an end face of an optical transmission path (Si waveguide) 41 included in an optical component 4 mounted in the mounting area of ​​the wiring board 2 is positioned opposite a first end face 321 of the core 32 of the optical waveguide 3. With this configuration, optical signals are transmitted and received between the core 32 and the optical transmission path 41. The material forming the core 32 is not limited and is appropriately selected taking into consideration, for example, the light transmittance and the wavelength characteristics of the propagating light. Examples of the material include resins such as epoxy resin and silicone resin. The core 32 has a thickness of, for example, 3 μm or more and 50 μm or less.

[0026] The upper clad 33 included in the optical waveguide 3 is located on the second surface 312 of the lower clad 31 and covers the core 32 so that the first end surface 321 and the second end surface 322 of the core 32 are exposed. The upper clad 33 is also formed of a resin such as epoxy resin or silicone resin. The lower clad 31 and the upper clad 33 may be made of the same material or different materials. Furthermore, the lower clad 31 and the upper clad 33 may have the same thickness or different thicknesses. The lower clad 31 and the upper clad 33 each have a thickness of, for example, 3 μm or more and 150 μm or less.

[0027] The optical waveguide 3 has a first side surface 3a including a first end surface 321 of the core 32 and a second side surface 3b including a second end surface 322 of the core 32. In other words, the first side surface 3a refers to a surface including an end surface of the upper cladding 33 and an end surface of the lower cladding 31 that are adjacent to the first end surface 321 of the core 32. The second side surface 3b refers to a surface including an end surface of the upper cladding 33 and an end surface of the lower cladding 31 that are adjacent to the second end surface 322 of the core 32.

[0028] 3, the optical waveguide 3 has a first protrusion 34 located on the first side surface 3a, which is a protrusion of an area including the boundary between the core 32 and the upper clad 33 and the boundary between the core 32 and the lower clad 31. Fig. 3 is an enlarged explanatory view for explaining one embodiment of the area Y shown in Fig. 2.

[0029] As described above, when the optical signal output from the optical component 4 is incident on the first end face 321 of the core 32, a portion of the optical signal output from the optical component 4 may not be incident on the end face of the core 32, but may be irradiated onto the end face of the lower clad 31 or the upper clad 33. The optical signal irradiated onto the end face of the lower clad 31 or the upper clad 33 may be reflected and returned to the optical component 4. As a result, the optical signal output from the optical component 4 and the reflected and returned optical signal interfere with each other, and the optical signal output from the optical component 4 is attenuated. Furthermore, the reflected and returned optical signal may cause a malfunction of the light source of the optical component 4.

[0030] The optical circuit board 1 according to one embodiment has the first protrusion 34, which can scatter an optical signal irradiated onto the end face of the lower cladding 31 or the upper cladding 33. As a result, there is less interference between the optical signal emitted from the optical component 4 and the optical signal that is reflected back, and the optical signal emitted from the optical component 4 is less likely to attenuate. Therefore, the optical circuit board 1 according to one embodiment has excellent transmission efficiency of the optical signal between the optical component 4 and the optical waveguide 3. Furthermore, the risk of failure of the light source of the optical component 4 is reduced.

[0031] As shown in Fig. 4 and Fig. 5 , the optical circuit board 1 according to an embodiment may further include a second protrusion 35 formed by raising a region including the boundary between the upper cladding 33 and the lower cladding 31 on the first side surface 3a. Fig. 4 is an enlarged explanatory view showing one embodiment as viewed from the direction of arrow A shown in Fig. 3. Fig. 5 is image data showing one embodiment of the first protrusion 34 and the second protrusion 35 as viewed from the direction of arrow B shown in Fig. 3.

[0032] The optical circuit board 1 according to the embodiment has the second protrusion 35, which makes it possible to more efficiently scatter an optical signal irradiated onto the end face of the lower cladding 31 or the upper cladding 33. Furthermore, the boundary between the upper cladding 33 and the lower cladding 31 becomes visible from the side face (first side face 3 a), allowing the thicknesses of the upper cladding 33 and the lower cladding 31 to be easily measured.

[0033] In Fig. 3, the first protrusion 34 is located on the first side surface 3a. However, it is sufficient that the first protrusion 34 is located on at least one of the first side surface 3a and the second side surface 3b. Furthermore, in Figs. 4 and 5, the second protrusion 35 is located on the first side surface 3a. However, it is sufficient that the second protrusion 35 is located on at least one of the first side surface 3a and the second side surface 3b.

[0034] 3 , the first end surface 321 of the core 32 may be curved in a concave shape (hereinafter, may be referred to as a “first curved surface”). When the first end surface 321 of the core 32 is curved in a concave shape, an optical signal irradiated to the first end surface 321 is more likely to be scattered in directions other than the optical component 4 when it is reflected. As a result, the optical signal reflected toward the optical component 4 is further reduced, and the transmission efficiency of the optical signal between the optical component 4 and the optical waveguide 3 is further improved.

[0035] 3 , the end faces of the upper cladding 33 and the lower cladding 31 may be concavely curved at the first side surface 3 a (hereinafter, these may be referred to as “second curved surfaces”). When the end faces of the upper cladding 33 and the lower cladding 31 are concavely curved, an optical signal irradiated onto the end face of the lower cladding 31 or the upper cladding 33 is more likely to be scattered in directions other than the optical component 4 when it is reflected. As a result, the optical signal reflected toward the optical component 4 is further reduced, and the transmission efficiency of the optical signal between the optical component 4 and the optical waveguide 3 is further improved.

[0036] 3 , the concavely curved portions are the first end face 321 of the core 32, the end face of the upper cladding 33 on the first side face 3a, and the end face of the lower cladding 31. However, the second end face 322 of the core 32, the end face of the upper cladding 33 on the second side face 3b, and the end face of the lower cladding 31 may also be concavely curved. That is, at least one of the first end face 321 and the second end face 322 of the core 32 may be concavely curved, or at least one of the end faces of the upper cladding 33 and the lower cladding 31 on at least one of the first side face 3a and the second side face 3b may be concavely curved.

[0037] The first curved surface and the second curved surface are not limited as long as they are curved. For example, the curvature of the first curved surface may be greater than that of the second curved surface. If the curvature of the first curved surface is greater than that of the second curved surface, i.e., if the first curved surface is more curved than the second curved surface, it becomes easier to input an optical signal to the center of the core 32, even if the optical signal has a long wavelength and tends to spread. Furthermore, if the second side surface 3b, in particular the second curved surface, is a gently curved surface, it can be easily connected to the optical connector 5a.

[0038] There are no limitations on the cross-sectional shape of the core 32, i.e., the shapes of the first end face 321 and the second end face 322 of the core 32. The first end face 321 and the second end face 322 of the core 32 may have, for example, a polygonal shape such as a triangular shape or a quadrangular shape, a circular shape, an elliptical shape, or the like.

[0039] 4 , when the first end face 321 and the second end face 322 of the core 32 have a rectangular shape, the first protrusion 34 includes a 1a protrusion 341, a 1b protrusion 342, a 1c protrusion 343, and a 1d protrusion 344. The 1a protrusion 341 is located in a region including the boundary between the core 32 and the lower cladding 31. The 1b protrusion 342 is located in a region facing the 1a protrusion 341, in a region including the boundary between the core 32 and the upper cladding 33. The 1c protrusion 343 and the 1d protrusion 344 are located in a region between the 1a protrusion 341 and the 1b protrusion 342.

[0040] The 1a protrusion 341, the 1b protrusion 342, the 1c protrusion 343, and the 1d protrusion 344 may have different heights, or at least two of them may have the same height. Here, the "height" can be defined as the length from a virtual perpendicular line S to the wiring substrate 2 to the peak of each protrusion, when the virtual perpendicular line S is provided to the optical waveguide 3, as shown in FIG. 3 . For example, the 1c protrusion 343 and the 1d protrusion 344 may be higher than the 1a protrusion 341 and the 1b protrusion 342, i.e., protrude in a direction away from the optical waveguide 3.

[0041] If the 1c protrusion 343 and the 1d protrusion 344 protrude further away from the optical waveguide 3 than the 1a protrusion 341 and the 1b protrusion 342, for example, when multiple cores 32 are positioned in parallel, it is possible to reduce interference of optical signals between adjacent cores 32. Specifically, when using optical signals that have long wavelengths and tend to spread, for example, the optical signals may leak to adjacent cores 32. If the first protrusion 34 has such a structure, it is possible to reduce leakage of optical signals, thereby reducing crosstalk between adjacent cores 32. The 1c protrusion 343 and the 1d protrusion 344 are higher than the 1a protrusion 341 and the 1b protrusion 342, for example, by approximately 10 nm to 200 nm.

[0042] Fig. 6 is an enlarged explanatory view for explaining another embodiment of the region Y shown in Fig. 2. As shown in Fig. 6, when the optical waveguide 3 is viewed in cross section in the longitudinal direction, the end face of the upper clad 33 may be located closer to the center of the optical waveguide 3 in the longitudinal direction than the end face of the lower clad 31.

[0043] In other words, the end face of the lower cladding 31 has a portion that protrudes further away from the optical waveguide 3 than the upper cladding 33. This makes it less likely for the optical component 4 to come into contact with the upper cladding 33. Even if the optical component 4 comes into contact with the lower cladding 31, resin fragments generated from the lower cladding 31 are less likely to adhere to the core 32. As a result, the transmission efficiency of optical signals between the optical component 4 and the optical waveguide 3 is further improved.

[0044] There are no limitations on the method for forming the optical waveguide 3 on the first surface 21 of the wiring substrate 2. One embodiment of a method for forming the optical waveguide 3 will be described with reference to Figures 7A to 7F. Figures 7A to 7F are explanatory diagrams for explaining one embodiment of a method for forming the optical waveguide 3.

[0045] First, as shown in Fig. 7A, a lower clad 31 is formed on the first surface 21 of the wiring substrate 2. Next, as shown in Fig. 7B, a core material 32a that will become the material for the core 32 is disposed on the second surface 312 of the lower clad 31. The materials that form the lower clad 31 and the core 32 are as described above, and detailed description thereof will be omitted. After the core material 32a is disposed, it is subjected to exposure and development, thereby forming the core 32.

[0046] 7C, an upper clad material 33a is disposed so as to cover the second surface 312 of the lower clad 31 and the pre-cured core material 32a. The material forming the upper clad 33 is as described above, and a detailed description thereof will be omitted. After disposing the upper clad material 33a, the upper clad 33 is formed by exposure and development. In this manner, a laminate is obtained.

[0047] Next, as shown in Fig. 7D, the resulting laminate is subjected to a dicing process, and the diced laminate is washed with water to remove dicing debris. After washing with water, the laminate is placed in an oven or the like and heated. Heating may be performed at a temperature of 100°C to 150°C for approximately 5 minutes to 30 minutes.

[0048] The cure shrinkage rate of the core 32 is different from the cure shrinkage rates of the upper cladding 33 and the lower cladding 31. Therefore, heating causes a shrinkage difference at the boundary between the core 32 and the upper cladding 33 and the boundary between the core 32 and the lower cladding 31. As a result, a first protrusion 34 is formed in the region including the boundary between the core 32 and the upper cladding 33 and the boundary between the core 32 and the lower cladding 31. By adjusting the heating temperature, the first end face 321 of the core 32, the end face of the upper cladding 33, and the end face of the lower cladding 31 can be curved into a concave shape while controlling the degree of curvature. The second protrusion 35 including the boundary between the lower cladding 31 and the upper cladding 33 is formed, for example, by varying the amount of heat applied to the lower cladding 31 and the upper cladding 33 or the amount of heat dissipation. The second protrusion 35 can be formed by using materials with different cure shrinkage rates for the lower cladding 31 and the upper cladding 33.

[0049] Furthermore, when forming a structure in which the end face of the upper cladding 33 is located closer to the center of the optical waveguide 3 in the longitudinal direction than the end face of the lower cladding 31 when viewed in cross section in the longitudinal direction of the optical waveguide 3 as shown in Fig. 6, a metal layer 21a may be located between the lower cladding 31 and the first surface 21 as shown in Fig. 7F. The lower cladding 31 hardens and shrinks when returned to room temperature after heating, but the metal layer 21a, even if thermally expanded during heating, returns to its exact pre-heating dimensions when returned to room temperature. Therefore, the lower cladding 31 in contact with the metal layer 21a is pulled by the metal layer 21a, which does not shrink even when returned to room temperature. Therefore, the lower cladding 31 in contact with the metal layer 21a is likely to protrude from the upper cladding 33 and the core 32.

[0050] Next, a mounting structure according to the present disclosure will be described. As shown in FIG. 1 , a mounting structure 10 according to an embodiment of the present disclosure has a structure in which an optical component 4 and an electronic component 6 are mounted on an optical circuit board 1 according to an embodiment. The optical component 4 mounted on the mounting structure 10 according to an embodiment includes an optical transmission path 41. Examples of the optical component 4 including such an optical transmission path 41 include a silicon photonics device. Examples of the electronic component 6 include an ASIC (Application Specific Integrated Circuit) and a driver IC.

[0051] 2 , the optical component 4 is electrically connected to the wiring board 2. Specifically, the optical component 4 is electrically connected to a pad 21b located in a mounting area (an area for mounting the optical component 4) of the wiring board 2 via solder 7. The pad 21b is part of a conductor layer located on the upper surface of the wiring board 2.

[0052] A silicon photonics device will be described as an example of the optical component 4. The silicon photonics device has, for example, a silicon (Si) core and silicon dioxide (SiO ２The silicon photonics device is a type of optical component having an optical transmission line 41 with a cladding of silicon carbide (Si) waveguide. The silicon photonics device includes a Si waveguide as the optical transmission line 41, and further includes a passivation film, a light source unit, a photodetector unit, and the like, which are not shown. As described above, the optical transmission line 41 (Si waveguide 41) is located on the first side surface 3 a of the optical waveguide 3 so as to face the core 32 (first end surface 321) included in the optical waveguide 3.

[0053] For example, an electrical signal from the wiring board 2 is transmitted to a light source unit included in the optical component 4 (silicon photonics device) via the solder 7. The light source unit receives the transmitted electrical signal and emits light. The emitted optical signal is transmitted via the optical transmission path 41 (Si waveguide 41) and the core 32 to the optical fiber 5 connected via the optical connector 5a.

[0054] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (9) below.

[0055] (1) An optical circuit board according to the present disclosure includes a wiring board having a first surface and an optical waveguide located on the first surface. The optical waveguide includes a lower cladding, a core, and an upper cladding. The lower cladding is located on the first surface and has a surface located on the first surface side and a second surface located opposite the first surface. The core extends to the second surface and has a first end face and a second end face located opposite each other in the extension direction of the core. The upper cladding is located on the second surface and covers the core so that the first end face and the second end face are exposed. The optical waveguide has a first side face including the first end face and a second side face including the second end face. A first protrusion is located on at least one of the first side face and the second side face, where the region including the boundary between the core and the upper cladding and the region including the boundary between the core and the lower cladding is raised. (2) In the optical circuit board described in (1) above, a second protrusion is further located on at least one of the first and second side surfaces, the second protrusion being a protrusion of a region including the boundary between the upper cladding and the lower cladding. (3) In the optical circuit board described in (1) or (2) above, the wiring board further includes a metal layer on the first surface, and the optical waveguide is located on the upper surface of the metal layer. (4) In the optical circuit board described in any of (1) to (3) above, at least one of the first end face and the second end face is concavely curved. (5) In the optical circuit board described in any of (1) to (4) above, at least one end face of the upper cladding and the lower cladding is concavely curved on at least one of the first and second side surfaces. (6) In the optical circuit board described in any of (1) to (5) above, at least one of the first end face and the second end face has a first curved surface that is concavely curved. At least one end face of the upper cladding and the lower cladding has a concavely curved second curved surface on the first side face and the second side face. The curvature of the first curved surface is greater than the curvature of the second curved surface. (7) In the optical circuit board described in any one of (1) to (6) above, the first end face and the second end face of the core are rectangular. In the first protrusion, protrusion 1a is located in a region including the boundary between the core and the lower cladding. Protrusion 1b is located in a region facing protrusion 1a within the region including the boundary between the core and the upper cladding. Protrusions 1c and 1d are located in a region between protrusions 1a and 1b.The 1c protrusion and the 1d protrusion protrude further away from the optical waveguide than the 1a protrusion and the 1b protrusion. (8) In the optical circuit board according to any one of (1) to (7) above, when the optical waveguide is viewed in cross section in the longitudinal direction, the end face of the upper cladding is located closer to the center of the optical waveguide in the longitudinal direction than the end face of the lower cladding. (9) A mounting structure according to the present disclosure includes the optical circuit board according to any one of (1) to (8) above and an optical component mounted on the optical circuit board.

[0056] REFERENCE SIGNS LIST 1 Optical circuit board 2 Wiring board 21 First surface 21a Metal layer 21b Pad 3 Optical waveguide 31 Lower clad 312 Second surface 32 Core 321 First end surface 322 Second end surface 32a Core material 33 Upper clad 3a First side surface 3b Second side surface 33a Upper clad material 34 First protrusion 341 1a protrusion 342 1b protrusion 343 1c protrusion 344 1d protrusion 35 Second protrusion 4 Optical component 41 Optical transmission path (silicon waveguide (Si waveguide)) 5 Optical fiber 5a Optical connector 6 Electronic component 7 Solder 10 Mounting structure

Claims

1. An optical circuit board comprising: a wiring board having a first surface; and an optical waveguide located on the first surface, wherein the optical waveguide includes a lower cladding, a core, and an upper cladding, the lower cladding is located on the first surface and has a surface located on the first surface side and a second surface located on the opposite side of the first surface, the core extends to the second surface and has a first end face and a second end face located opposite to each other in the extending direction of the core, the upper cladding is located on the second surface and covers the core so that the first end face and the second end face are exposed, the optical waveguide has a first side face including the first end face and a second side face including the second end face, and a first protrusion is located on at least one of the first side face and the second side face, the first protrusion being a raised region including the boundary between the core and the upper cladding and the boundary between the core and the lower cladding.

2. An optical circuit board according to claim 1, further comprising a second protrusion on at least one of the first side surface and the second side surface, the second protrusion being a raised area including the boundary between the upper clad and the lower clad.

3. The optical circuit board according to claim 1 or 2, wherein the wiring board further includes a metal layer on the first surface, and the optical waveguide is located on the upper surface of the metal layer.

4. The optical circuit board according to any one of claims 1 to 3, wherein at least one of the first end face and the second end face is curved concavely.

5. An optical circuit board according to any one of claims 1 to 4, wherein at least one end face of the upper clad and the lower clad on at least one of the first side face and the second side face is concavely curved.

6. An optical circuit board according to any one of claims 1 to 5, wherein at least one of the first end face and the second end face has a first curved surface that is concavely curved, and at least one end face of the upper clad and the lower clad on the first side face and the second side face has a second curved surface that is concavely curved, and the curvature of the first curved surface is greater than the curvature of the second curved surface.

7. An optical circuit board according to any one of claims 1 to 6, wherein the first end face and the second end face of the core are rectangular, and in the first protrusion, protrusion 1a is located in a region including the boundary between the core and the lower cladding, protrusion 1b is located in a region facing protrusion 1a within the region including the boundary between the core and the upper cladding, protrusion 1c and protrusion 1d are located in a region between protrusion 1a and protrusion 1b, and protrusion 1c and protrusion 1d protrude in a direction away from the optical waveguide further than protrusion 1a and protrusion 1b.

8. An optical circuit board according to any one of claims 1 to 7, wherein, when the optical waveguide is viewed in cross section in the longitudinal direction, the end face of the upper clad is located closer to the center of the optical waveguide in the longitudinal direction than the end face of the lower clad.

9. A mounting structure comprising the optical circuit board according to any one of claims 1 to 8 and an optical component mounted on the optical circuit board.

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