Optical circuit board and mounting structure

Abstract

An optical circuit board according to the present disclosure comprises a wiring board having a first surface, and an optical waveguide positioned on the first surface. The optical waveguide comprises a lower cladding, a core, and an upper cladding. The lower cladding is positioned on the first surface and has a second surface positioned on the first surface side and a third surface positioned on the opposite side of the second surface. The core extends to the third surface and has a first end surface and a second end surface positioned in the extension direction of the core. The upper cladding is positioned on the third surface and covers the core so that the first end surface and the second end surface are exposed. The optical waveguide has a first side surface including a first end surface and a second side surface including a second end surface. The core includes a first core, a second core, and a third core. In a plan view, the second core and the third core are each inclined with respect to the first core and are positioned across the first core. In the first side surface, a first distance between the first core and the second core and a second distance between the first core and the third core are the same. In the second side surface, a third distance between the first core and the second core and a fourth distance between the first core and the third core are the same.

Description

Optical circuit board and mounting structure

[0001] The present disclosure 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] Japanese Patent Application Laid-Open No. 2003-161853

[0004] 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 second surface located on the first surface side and a third surface located opposite the second surface. The core extends to the third surface and has a first end face and a second end face located in the extension direction of the core. The upper cladding is located on the third 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. The core includes a first core, a second core, and a third core. In a plan view, the second core and the third core are each inclined relative to the first core and are located on either side of the first core. On the first side, a first distance between the first core and the second core and a second distance between the first core and the third core are the same. On the second side surface, the third distance between the first core and the second core and the fourth distance between the first core and the third core are the same.

[0005] 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.

[0006] 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. It is an enlarged explanatory diagram for explaining a cross section of region X shown in FIG. 1. It is an enlarged plan view showing one embodiment of the optical waveguide portion in FIG. 2 (excluding the upper clad). FIG. 4A is an enlarged explanatory diagram showing one embodiment as seen from the direction of arrow A shown in FIG. 3, and FIG. 4B is an enlarged explanatory diagram showing one embodiment as seen from the direction of arrow B shown in FIG. 3. It is an enlarged plan view showing another embodiment of the optical waveguide portion in FIG. 2 (excluding the upper clad). FIGS. 6A to 6D are explanatory diagrams for explaining one embodiment of a method for forming an optical waveguide.

[0007] An optical signal emitted from an optical component is incident on an end face of a core included in an optical waveguide and transmitted to an optical fiber. For example, during the manufacturing process of an optical waveguide, misalignment during dicing or exposure may occur, resulting in a core position that differs from the actual design. If the core position is misaligned, for example, the optical signal emitted from the optical component may not be efficiently incident on the end face of the core, or the optical signal may not be efficiently transmitted from the core to the optical fiber. As such, if the core position is misaligned, the transmission efficiency between the optical waveguide and the optical component, and between the optical waveguide and the optical fiber, deteriorates. Therefore, there is a need for an optical circuit board that allows for easy confirmation of core position misalignment and that has excellent transmission efficiency between the optical waveguide and the optical component, and between the optical waveguide and the optical fiber.

[0008] The optical circuit board according to the present disclosure has a configuration as described in the section on means for solving the above problems, thereby making it possible to easily check the positional misalignment of the cores, and has excellent transmission efficiency between the optical waveguide and optical components, and between the optical waveguide and optical fiber.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The conductor layer for build-up is not particularly limited as long as it is made of a conductive material, for example, a metal such as copper.

[0020] 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 made of a metal such as copper. The via-hole conductors are connected to build-up conductor layers that are 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.

[0021] 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.

[0022] 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 second surface 312 located on the first surface 21 side of the wiring board 2 and a third surface 313 located on the opposite side of the second surface 312. 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.

[0023] The core 32 included in the optical waveguide 3 includes a first core 32 a, a second core 32 b, and a third core 32 c, as shown in Fig. 3. Fig. 3 is an enlarged plan view showing one embodiment of the optical waveguide 3 portion in Fig. 2 (however, the upper cladding 33 is excluded).

[0024] The first core 32a is a portion through which light that has entered the optical waveguide 3 propagates. The first core 32a extends to the third surface 313 of the lower cladding 31, and has a first end face 321 and a second end face 322 located in the extending direction of the core 32. In other words, the first end face 321 and the second end face 322 can be said to be two end faces located 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 the optical component 4 mounted in the mounting region of the wiring board 2 is positioned to face a first end face 321 of the core 32 of the optical waveguide 3 (first end face 321 of the first core 32a). With this configuration, optical signals are transmitted and received between the first core 32a and the optical transmission path 41. The material forming the first core 32a 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 first core 32a has a thickness of, for example, 3 μm or more and 50 μm or less.

[0026] The second core 32b and the third core 32c are located outside the first core 32a, sandwiching the first core 32a between them. The second core 32b and the third core 32c are not cores for transmitting optical signals, but are positioned as so-called dummy cores.

[0027] As shown in Fig. 3, the second core 32b and the third core 32c are positioned at an angle relative to the first core 32a. The angle of inclination, specifically the angle θ1 between the second core 32b and an imaginary line L parallel to the first core 32a, and the angle θ2 between the third core 32c and an imaginary line L parallel to the first core 32a, are not limited. The angles θ1 and θ2 may be, for example, 0.1° or greater and 5° or less. If the angles θ1 and θ2 are 0.1° or greater and 5° or less, the length of the optical waveguide 3 in the direction perpendicular to the extension direction of the cores 32 can be reduced.

[0028] The material forming the second core 32b and the third core 32c is not limited. Examples of such materials include resins such as epoxy resin and silicone resin. The second core 32b and the third core 32c have a thickness of, for example, 3 μm or more and 50 μm or less. The first core 32a, the second core 32b, and the third core 32c may be made of the same material or different materials. Furthermore, the first core 32a, the second core 32b, and the third core 32c may have the same thickness or different thicknesses. If the first core 32a, the second core 32b, and the third core 32c have the same thickness, for example, the difference in brightness between the cores 32 when light passes through each core 32 is reduced. As a result, the first distance D1, the second distance D2, the third distance D3, and the fourth distance D4 can be easily measured.

[0029] The upper cladding 33 included in the optical waveguide 3 is located on the second surface 312 of the lower cladding 31 and covers the cores 32 (first core 32a, second core 32b, and third core 32c) so that the first end face 321 and second end face 322 of the lower cladding 31 are exposed. The upper cladding 33 is also formed of a resin such as epoxy resin or silicone resin. The lower cladding 31 and the upper cladding 33 may be made of the same material or different materials. Furthermore, the lower cladding 31 and the upper cladding 33 may have the same thickness or different thicknesses. The lower cladding 31 and the upper cladding 33 each have a thickness of, for example, 3 μm or more and 150 μm or less.

[0030] 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.

[0031] In the optical circuit board 1 according to one embodiment, as shown in Fig. 4A, on the first side surface 3a, the distance between the first core 32a located in the outermost portion on the second core 32b side and the second core 32b is defined as a first distance D1. The distance between the first core 32a located in the outermost portion on the third core 32c side and the third core 32c is defined as a second distance D2. In the optical circuit board 1 according to one embodiment, the first distance D1 and the second distance D2 are the same. Fig. 4A is an enlarged explanatory view showing one embodiment as viewed from the direction of arrow A shown in Fig. 3.

[0032] 4B , on the second side surface 3b, the distance between the first core 32a located at the outermost portion on the second core 32b side and the second core 32b is a third distance D3. The distance between the first core 32a located at the outermost portion on the third core 32c side and the third core 32c is a fourth distance D4. In the optical circuit board 1 according to the embodiment, the third distance D3 and the fourth distance D4 are the same. FIG. 4B is an enlarged explanatory view showing the embodiment as viewed from the direction of arrow B shown in FIG. 3.

[0033] If the first distance D1 and the second distance D2 are the same on the first side surface 3a and the third distance D3 and the fourth distance D4 are the same on the second side surface 3b, then, for example, there is no misalignment during dicing when processing the end faces of the optical waveguide 3 or during exposure when forming the core 32 in the lower cladding 31. As a result, it can be determined that the first core 32a is positioned with almost no misalignment from the actual designed location. In this specification, if the difference between the first distance D1 and the second distance D2 is not 0 but is 1.0 μm or less, it is defined that "the first distance D1 and the second distance D2 are the same." If the difference between the third distance D3 and the fourth distance D4 is not 0 but is 1.0 μm or less, it is defined that "the third distance D3 and the fourth distance D4 are the same."

[0034] Specifically, if the angle θ1 and the angle θ2 are the same, the first distance D1 and the second distance D2 will be the same, and the third distance D3 and the fourth distance D4 will be the same. If misalignment occurs during dicing or exposure, causing the position of the first core 32a to shift, at least one of the difference between the first distance D1 and the second distance D2 and the difference between the third distance D3 and the fourth distance D4 will become large.

[0035] Therefore, in the optical circuit board 1 according to the embodiment, misalignment of the first core 32a can be easily confirmed by checking the first distance D1 and the second distance D2, and the third distance D3 and the fourth distance D4. Furthermore, in the optical circuit board 1 according to the embodiment, the first distance D1 and the second distance D2 are the same, and the third distance D3 and the fourth distance D4 are the same. Therefore, as in the actual design, the position of the first core 32a is hardly misaligned. As a result, the optical circuit board 1 according to the embodiment has excellent transmission efficiency between the optical waveguide 3 and the optical component 4, and between the optical waveguide 3 and the optical fiber 5.

[0036] In a plan view, the width of the first core 32a, the width of the second core 32b, and the width of the third core 32c in the direction perpendicular to the extension direction may be the same. If the first core 32a, the second core 32b, and the third core 32c have the same width, for example, when light passes through each core 32, the difference in luminance among the cores 32 is reduced. As a result, it becomes easier to measure the first distance D1, the second distance D2, the third distance D3, and the fourth distance D4.

[0037] 3 illustrates an embodiment in which a plurality of first cores 32a are located on the third surface 313 of the lower cladding 31. However, as shown in Fig. 5, only one first core 32a may be located. Fig. 5 is an enlarged plan view showing another embodiment of the optical waveguide 3 portion in Fig. 2 (excluding the upper cladding 33).

[0038] When there is only one first core 32a, on the first side surface 3a, the first distance D1 is the distance between the first core 32a and the second core 32b, and the second distance D2 is the distance between the first core 32a and the third core 32c. On the second side surface 3b, the third distance D3 is the distance between the first core 32a and the second core 32b, and the fourth distance D4 is the distance between the first core 32a and the third core 32c.

[0039] When the third distance D3 and the fourth distance D4 are greater than the first distance D1 and the second distance D2, the optical connector 5a connected to the optical waveguide 3 may be connected to the side having the third distance D3 and the fourth distance D4. In this case, it becomes easy to connect the optical connector 5a without contacting the end faces of the second core 32b and the third core 32c. As a result, the optical connector 5a is less susceptible to optical noise.

[0040] 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 6A to 6D. Figures 6A to 6D are explanatory diagrams for explaining one embodiment of a method for forming the optical waveguide 3.

[0041] First, as shown in Fig. 6A, a lower clad 31 is formed on the first surface 21 of the wiring substrate 2. Next, as shown in Fig. 6B, a core material 32d that will be the material for the core 32 is disposed on the third surface 313 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. When a metal layer 21a is located on the first surface 21 of the wiring substrate 2, the lower clad 31 is formed on the surface of the metal layer 21a.

[0042] After the core material 32d is placed, the surface of the core material 32d is covered with a mask so that the designed first core 32a, second core 32b, and third core 32c are formed. Then, the core 32 (first core 32a, second core 32b, and third core 32c) is formed by exposure and development.

[0043] After the core 32 is formed, as shown in FIG. 6C , an upper clad material 33a is formed to cover the third surface 313 of the lower clad 31 and the cores 32 (first core 32a, second core 32b, and third core 32c). In FIG. 6C , the upper clad material 33a appears to cover only the core 32 because only a portion of the covered area is shown. In the portion of the third surface 313 of the lower clad 31 where the core 32 is not located, the upper clad material 33a is located. After the upper clad material 33a is formed, it is subjected to exposure and development to form the upper clad 33. In this manner, a stack including the lower clad 31, the core 32, and the upper clad 33 is obtained.

[0044] Next, as shown in Fig. 6D, the obtained laminate is subjected to dicing, and the diced laminate is washed with water to remove dicing debris. Although only one end of the laminate is subjected to dicing in Fig. 6D, both ends of the laminate may be subjected to dicing.

[0045] The first side surface 3a and the second side surface 3b of the optical waveguide 3 formed in this manner are observed. As shown in Figures 4A and 4B, if the first distance D1 and the second distance D2 are the same and the third distance D3 and the fourth distance D4 are the same, it can be determined that the first core 32a is positioned with almost no deviation from the actually designed location. In this way, it is easy to check whether the position of the first core 32a is deviated. If the first core 32a is positioned in the actually designed location, the transmission efficiency between the optical waveguide 3 and the optical component 4 and the transmission efficiency between the optical waveguide 3 and the optical fiber 5 are excellent.

[0046] 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.

[0047] 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.

[0048] 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 ２ The 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.

[0049] 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.

[0050] 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 (5) below.

[0051] (1) An 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 second surface located on the first surface side and a third surface located opposite the second surface. The core extends to the third surface and has a first end face and a second end face located in the extension direction of the core. The upper cladding is located on the third 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. The core includes a first core, a second core, and a third core. In a plan view, the second core and the third core are each located at an angle with respect to the first core, sandwiching the first core. On the first side face, a first distance between the first core and the second core and a second distance between the first core and the third core are the same. On the second side surface, the third distance between the first core and the second core and the fourth distance between the first core and the third core are the same. (2) In the optical circuit board described in (1) above, a plurality of first cores are located between the second core and the third core. On the first side surface, the first distance between the first core located at the outermost portion on the second core side and the second core and the second distance between the first core located at the outermost portion on the third core side are the same. On the second side surface, the third distance between the first core located at the outermost portion on the second core side and the second core and the fourth distance between the first core located at the outermost portion on the third core side are the same. (3) In the optical circuit board described in (1) or (2) above, the angle formed by the second core and the third core with an imaginary line parallel to the first core is 0.1° or more and 5° or less. (4) In the optical circuit board according to any one of (1) to (3) above, the width of the first core, the width of the second core, and the width of the third core in a direction perpendicular to the extending direction are the same in a plan view. (5) A mounting structure according to the present disclosure includes the optical circuit board according to any one of (1) to (4) above and an optical component mounted on the optical circuit board.

[0052] 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 313 Third surface 32 Core 321 First end surface 322 Second end surface 32a First core 32b Second core 32c Third core 32d Core material 33 Upper clad 3a First side surface 3b Second side surface 33a Upper clad material 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. A wiring board having a first surface; and an optical waveguide located on the first surface, wherein the optical waveguide includes a lower clad, a core, and an upper clad, wherein the lower clad is located on the first surface and has a second surface located on the first surface side and a third surface located on the opposite side of the second surface, wherein the core extends to the third surface and has a first end face and a second end face located in the extending direction of the core, wherein the upper clad is located on the third surface and covers the core so that the first end face and the second end face are exposed, wherein the optical waveguide has a first side face including the first end face and a second side face including the second end face, wherein the core includes a first core, a second core, and a third core, wherein in a plan view, the second core and the third core are each located at an angle with respect to the first core and sandwich the first core, and wherein a first distance between the first core and the second core and a second distance between the first core and the third core are the same on the first side, an optical circuit board, wherein a third distance between the first core and the second core and a fourth distance between the first core and the third core are the same on the second side surface.

2. The optical circuit board according to claim 1, wherein a plurality of the first cores are located between the second core and the third core, and on the first side surface, the first distance between the first core and the second core located in the outermost portion on the second core side and the second distance between the first core and the third core located in the outermost portion on the third core side are the same, and on the second side surface, the third distance between the first core and the second core located in the outermost portion on the second core side and the fourth distance between the first core and the third core located in the outermost portion on the third core side are the same.

3. An optical circuit board according to claim 1 or 2, wherein the angle formed by the second core and the third core with an imaginary line parallel to the first core is 0.1° or more and 5° or less.

4. An optical circuit board according to any one of claims 1 to 3, wherein, in a plan view, the width of the first core, the width of the second core, and the width of the third core in a direction perpendicular to the extension direction are the same.

5. A mounting structure comprising the optical circuit board according to any one of claims 1 to 4 and an optical component mounted on the optical circuit board.

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