Optical circuit board and mounting structure
Patent Information
- Application Number
- JP2025510882
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2025-09-25
- Publication Date
- 2025-12-15
Abstract
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, for example, optical circuit boards. As described in Patent Document 1, the optical circuit boards are provided with optical waveguides. Optical signals are transmitted and received via these optical waveguides.
[0003] Before mounting optical components on an optical circuit board, the core portion of the optical waveguide is irradiated with light to inspect the transmission and reception of optical signals. When inspecting a conventional optical circuit board such as that described in Patent Document 1, the array illumination optical system, which serves as the light source, may mistakenly recognize the side end of the upper cladding of the optical waveguide as the core portion. When such an erroneous recognition occurs, manual readjustment is required, which reduces inspection efficiency.
[0004] Japanese Patent Application Laid-Open No. 2001-281479
[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 second surface located opposite the surface in contact with 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 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 upper cladding has a pair of first and second side faces located along the extension direction, a third surface located opposite the surface in contact with the second surface, a first side portion that is a tangent portion between the first side face and the third surface, and a second side portion that is a tangent portion between the second side face and the third surface. The upper cladding further has at least one of a first recess contacting the first side portion and opening to the third surface and the first side surface, and a second recess contacting the second side portion and opening to the third surface and the second side surface.
[0006] A mounting structure according to the present disclosure includes the optical circuit board and an optical component mounted on the optical circuit board.
[0007] 5A 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 illustrating a cross section of region X shown in FIG. 1. A is a plan view of a main portion of an optical waveguide as seen from the direction of arrow A shown in FIG. 2, B is an enlarged explanatory diagram (perspective view) for illustrating region Y shown in FIG. 3A, and C is a front view of the optical waveguide as seen from the direction of arrow B shown in FIG. 3A. It is an explanatory diagram for illustrating an embodiment of a method for forming an optical waveguide on a wiring board. A is a plan view showing another embodiment of a main portion of an optical waveguide as seen from the direction of arrow A shown in FIG. 2, B is an enlarged explanatory diagram showing a cross section when cut along line X-X shown in FIG. 5A, and C is a side view of an optical circuit board (optical waveguide) as seen from the direction of arrow C shown in FIG. 5B. A is an explanatory diagram (perspective view) for illustrating yet another embodiment of recesses (first recesses and second recesses) formed in an optical waveguide, and B is a plan view as seen from the direction of arrow D shown in FIG. 6A. 10A is an explanatory view (perspective view) for explaining still another embodiment of recesses (first recesses and second recesses) formed in an optical waveguide. FIG.
[0008] When inspecting a conventional optical circuit board such as that described in Patent Document 1, the array illumination optical system, which is the light source, may erroneously recognize the side end of the upper cladding of the optical waveguide as the core portion. When such a misrecognition occurs, manual readjustment is required, which reduces inspection efficiency. Therefore, there is a need for an optical circuit board that allows for efficient optical waveguide inspection.
[0009] The optical circuit board according to the present disclosure has the configuration described in the section on means for solving the above problems, and thus can efficiently perform optical waveguide inspection.
[0010] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Figures 1 to 3. 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, similar to the core conductor layer. 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. The build-up layer has a structure in which at least one build-up insulating layer and at least one build-up conductor layer are laminated. Like the core insulating layer, 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] When two or more build-up insulation layers are present, the build-up insulation layers may be made of the same resin or different resins. The build-up insulation layers and the core insulation layer may be made of the same resin or different resins. The build-up layers usually have via-hole conductors for electrically connecting the layers.
[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 build-up conductor layer is not particularly limited as long as it is made of a conductive material, similar to the core conductor layer, and examples of the conductive material include metals such as copper.
[0020] 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.
[0021] 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. 3 , the lower cladding 31 has a second surface 312 located on the opposite side of the surface facing the first surface 21 of the wiring board 2. 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.
[0022] The upper clad 33 included in the optical waveguide 3 is positioned so as to cover the upper surface of the lower clad 31 and the core 32. Like the lower clad 31, the upper clad 33 is also formed of a resin such as an epoxy resin or a 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, 5 μm or more and 150 μm or less.
[0023] 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.
[0024] 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.
[0025] As described above, the upper cladding 33 is located on the upper surface of the lower cladding 31, i.e., the second surface 312 of the lower cladding 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. As shown in FIGS. 3A to 3C , the upper cladding 33 has a first side surface 331 and a second side surface 332 located along the extension direction of the core 32, a third surface 333 located opposite the surface that contacts the second surface 312 of the lower cladding 31, a first side portion 33a that is a tangent portion between the first side surface 331 and the third surface 333, and a second side portion 33b that is a tangent portion between the second side surface 332 and the third surface 333. FIG. 3A is a plan view of a main portion of the optical waveguide 3 as seen from the direction of arrow A shown in FIG. 2. FIG. 3B is an enlarged explanatory view (perspective view) for illustrating region Y shown in FIG. 3A. FIG. 3C is a front view of the optical waveguide 3 as seen from the direction of arrow B shown in FIG. 3A.
[0026] 3A, at least one recess 33c is located in the upper clad 33. Specifically, as shown in FIGS. 3A to 3C, at least one of a first recess 33c1 that contacts the first side portion 33a and opens to the third surface 333 and the first side surface 331 and a second recess 33c2 that contacts the second side portion 33b and opens to the third surface 333 and the second side surface 332 is located in the upper clad 33. The first recess 33c1 and the second recess 33c2 are described separately for convenience's sake, and the first recess 33c1 and the second recess 33c2 may be collectively referred to as recess 33c.
[0027] The optical circuit board 1 according to an embodiment has at least one such recess 33c on at least one of the first side 33a and the second side 33b of the upper clad 33, thereby enabling efficient optical waveguide inspection. Specifically, when light is irradiated onto the core 32 of the optical waveguide 3 to inspect transmission and reception of optical signals before mounting optical components 4 on the optical circuit board 1 according to an embodiment, the presence of the recess 33c causes light trapped by the refractive index difference between the upper clad 33 and air to be scattered by the recess 33c. This reduces light transmission through the first side 33a and the second side 33b of the upper clad 33 having the recess 33c, making it less likely that the first side 33a and the second side 33b will be mistaken for the core 32. As a result, manual readjustment is not required, and optical waveguide inspection can be performed efficiently.
[0028] At least one recess 33c needs to be located in the upper cladding 33, and multiple recesses 33c may be located. When multiple recesses 33c are located, at least one of the first recesses 33c1 and the second recesses 33c2 may be located multiple times, or multiple recesses of each may be located multiple times. When multiple recesses 33c are located, the irradiated light is more scattered, and light transmission to the edge portion of the upper cladding 33 is more efficiently reduced.
[0029] As shown in Fig. 3C, the recesses 33c (first recess 33c1 and second recess 33c2) have a rectangular shape when viewed from above. The size of the recesses 33c is not limited and is set appropriately depending on the size of the optical waveguide 3, etc., so as to scatter the irradiated light. The width W may be, for example, 5 µm or more and 20 µm or less. The length L may be, for example, 5 µm or more and 500 µm or less.
[0030] If the length L is 10 μm or more and 50 μm or less, the irradiated light is more scattered, and the transmission of light to the edge portion of the upper cladding 33 is more efficiently reduced. If the width W is 10 μm or more and 50 μm or less, the range in which light is confined due to the difference in refractive index between the upper cladding 33 and air can be covered.
[0031] 3B , the height H of the recess 33c (the second recess 33c2 is exemplified) corresponds to the thickness of the upper cladding 33. The height H of the recess 33c may be smaller than the thickness of the upper cladding 33. That is, in the recess 33c, the bottom farthest from the third surface 333 of the upper cladding 33 may be located on the second surface 312 of the upper cladding 33 or the lower cladding 31. In FIG. 3B , this bottom is located on the second surface 312 of the lower cladding 31. When the height H is within this range, light transmission through the first side portion 33a and the second side portion 33b can be reduced without impairing the strength of the optical waveguide 3.
[0032] When a plurality of recesses 33c are located, it is not necessary for all of the recesses 33c to have the same shape or size. Considering the efficiency of forming the recesses 33c, it is preferable to form all of the recesses 33c to have the same shape and size.
[0033] The arithmetic mean roughness of the inner wall surface of the recess 33c is not limited. The arithmetic mean roughness of the inner wall surface of at least a portion of the recess 33c may be, for example, 50 nm or less. When the arithmetic mean roughness is 50 nm or less, the inner wall surface is mirror-like, and the irradiated light can be efficiently reflected in a direction different from the irradiation direction. As a result, the light transmission through the first side portion 33a and the second side portion 33b is more efficiently reduced. The arithmetic mean roughness can be calculated by measuring any inner wall surface of the recess 33c using a laser displacement meter, an optical interference measuring instrument, or the like, after the recess 33c is formed, for example.
[0034] The method for forming the recess 33c in the edge portion of the upper cladding 33 is not limited, and may be formed, for example, by the following procedure. One embodiment of the method for forming the recess 33c will be described with reference to Fig. 4. Fig. 4 is an explanatory diagram for explaining one embodiment of the method for forming the optical waveguide 3 in the wiring substrate 2. For convenience, the wiring substrate 2 is omitted from Fig. 4B.
[0035] 4A, the lower clad 31 is formed on the first surface 21 of the wiring substrate 2. A metal layer 21a may be located between the lower clad 31 and the first surface 21.
[0036] Next, a core material 32a, which will be the material for the core 32, is deposited on the second surface 312 of the lower cladding 31. The material forming the core 32 is as described above, and a detailed description thereof will be omitted. Then, as shown in FIG. 4B , the surface of the core material 32a is covered with a mask 34. Specifically, the surface of the core material 32a is covered with a mask 34 having an opening in the portion where the core 32 will be formed, and the core material 32a located in the opening is hardened by exposure to light. After that, the mask 34 is removed, and the core material 32a in the portion covered by the mask 34 is removed by development, thereby forming the core 32 on the second surface 312 of the lower cladding 31, as shown in FIG. 4C .
[0037] Next, an upper clad material 33d, which will be the material for the upper clad 33, is deposited on the second surface 312 of the lower clad 31 so that the first end face 321 and the second end face 322 of the core 32 are exposed. The material forming the upper clad 33 is as described above, and a detailed description thereof will be omitted. Then, as shown in FIG. 4D , the surface of the upper clad material 33d is covered with a mask 35. The portions covered with the mask 35 are the portions to be removed by development after exposure. Specifically, when viewed from above in a plan view, both side portions of the upper clad material 33d and the portion forming the recess 33c may be covered with the mask 35 so as to conform to the core 32.
[0038] After being covered with the mask 35, the upper cladding material 33d is hardened by exposure to light. Then, as shown in FIG. 4E , the mask 35 is removed, and the portion of the upper cladding material 33d that was covered with the mask 35 is removed by development. Through this procedure, as shown in FIG. 4E , a first recess 33c1 that contacts the first side portion 33a and opens onto the third surface 333 and the first side surface 331, and a second recess 33c2 that contacts the second side portion 33b and opens onto the third surface 333 and the second side surface 332 are formed in the upper cladding 33. While FIG. 4E illustrates an example in which there is one first recess 33c1 and one second recess 33c2, the number of recesses 33c can be adjusted depending on the shape of the mask 35.
[0039] Next, other shapes of the recess 33c will be described with reference to Fig. 5. Fig. 5A is a plan view showing another embodiment of the main part of the optical waveguide 3 as seen from the direction of arrow A shown in Fig. 2. Fig. 5B is an enlarged explanatory view showing a cross section taken along line X-X shown in Fig. 5A. Fig. 5C is a side view of the optical circuit board 1 (optical waveguide 3) as seen from the direction of arrow C shown in Fig. 5B.
[0040] As described above, in the recess 33c (33c2) shown in FIG. 3B , the bottom portion farthest from the third surface 333 of the upper clad 33 is located on the second surface 312 of the lower clad 31. That is, the height H of the recess 33c (33c2) corresponds to the thickness of the upper clad 33. On the other hand, the height of the recess 33c shown in FIG. 5B is greater than the thickness of the upper clad 33. In this way, the bottom portion of the recess 33c farthest from the third surface 333 of the upper clad 33 may be located closer to the first surface 21 of the wiring substrate 2 than the second surface 312 of the lower clad 31. When multiple recesses 33c are located, it is sufficient that at least some of the recesses 33c have such a structure.
[0041] If the height of the recess 33c is greater than the thickness of the upper cladding 33, as shown in Figure 5C, the sealing resin 8 connecting the optical component 4 and the optical connector 5a will fill the recess 33c. As a result, the bonding strength between these components will be improved. Although the bottom is flat in Figure 5B, it may be uneven. In this case, the contact area between the sealing resin 8 and the bottom will be larger, which is advantageous in that the bonding strength will be improved.
[0042] In the recess 33c, the bottom portion farthest from the third surface 333 of the upper cladding 33 is not limited as long as it is located closer to the first surface 21 than the second surface 312 of the lower cladding 31. The bottom portion may be located at a depth from the second surface 312 to 100% or more of the thickness of the lower cladding 31. In other words, the recess 33c may penetrate the lower cladding 31.
[0043] The recess 33c, whose bottom is located closer to the first surface 21 than the second surface 312 of the lower clad 31, is formed by, for example, laser processing. Specifically, the mask 35 shown in FIG. 4D is not used to form the recess 33c, but is used to form only the first side surface 331 and the second side surface 332 of the upper clad 33. By exposure to light, the upper clad material 33d in the portion not covered by the mask 35 is hardened. After removing the mask 35, the upper clad material 33d in the portion covered by the mask 35 is removed by development. Then, the recess 33c is formed by laser processing.
[0044] Furthermore, as shown in Fig. 6, the recess 33c may have a protrusion 334 protruding in the opening direction (the direction from the first side surface 331 to the second side surface 332). Fig. 6A is an explanatory diagram (perspective view) for explaining yet another embodiment of the recess 33c (first recess 33c1 and second recess 33c2) formed in the optical waveguide 3. Fig. 6B is a plan view seen from the direction of arrow D shown in Fig. 6A.
[0045] When the convex portion 334 is located in the concave portion 33c, for example, a portion of light incident from the first end face 321 side and entering the concave portion 33c is reflected by the convex portion 334 to the outside of the optical waveguide 3, which makes it easy to reduce the light transmitted to the second end face 322 side. As shown in FIG. 6B , the angle θ between the incident direction F of light and the convex portion 334 is not limited and may be, for example, 15° to 75°. If the angle θ is within this range, light incident on the first side portion 33a and the second side portion 33b of the upper clad 33 is easily reflected to the outside of the optical waveguide 3. When multiple concave portions 33c are located, it is sufficient that at least some of the concave portions 33c have the convex portion 334.
[0046] 6B, when viewed from above, the convex portion 334 has a triangular shape. However, as long as the angle θ is less than 90°, the shape of the convex portion 334 is not limited to a triangular shape. When viewed from above, the convex portion 334 may have, for example, a semicircular shape or a trapezoidal shape.
[0047] 3 to 5 has a rectangular shape when viewed from above. That is, the third surface 333 and the side surface of the upper cladding 33 have a rectangular cutout so as to have an opening. However, the shape of the recess 33c is not limited to a rectangular shape.
[0048] 7, the shape of the recess 33c is not limited as long as it is in contact with the first side 33a (second side 33b) of the upper cladding 33 and opens to the third surface 333 and the first side surface 331 (second side surface 332) of the upper cladding 33. Fig. 7 is an explanatory diagram (perspective view) for explaining still another embodiment of the recess 33c (first recess 33c1 and second recess 33c2) formed in the optical waveguide 3.
[0049] Specifically, when viewed obliquely from above, as shown in FIG. 7, the third surface 333 and the side surface of the upper cladding 33 may have a triangular cutout shape, or a semicircular, trapezoidal, or other cutout shape so as to have an opening.
[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), a driver IC, and the like.
[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 ２ The silicon photonics device is a type of optical component having an optical transmission line 41 with a cladding of Si (silicon carbide) 321 (Si waveguide 41). 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 positioned at one end of the optical waveguide 3 (first end face 321 in FIG. 2 ) so as to face the core 32 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] Although the embodiments of the present disclosure have been described above, 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) and (8) below.
[0055] (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 opposite the surface in contact with 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 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 upper cladding has a pair of first and second side faces located along the extension direction, a third surface located opposite the surface in contact with the second surface, a first side portion that is a tangent portion between the first side face and the third surface, and a second side portion that is a tangent portion between the second side face and the third surface. The upper cladding further has at least one of a first recess contacting the first side portion and opening to the third surface and the first side surface, and a second recess contacting the second side portion and opening to the third surface and the second side surface.
[0056] The present disclosure further discloses the following embodiments (2) to (7).
[0057] (2) In the optical circuit board described in (1) above, at least some of the first and second recesses have convex portions protruding in the opening direction. (3) In the optical circuit board described in (1) or (2) above, the arithmetic mean roughness of the inner wall surfaces of at least some of the first and second recesses is 50 nm or less. (4) In the optical circuit board described in any of (1) to (3) above, the upper cladding has a plurality of at least one of the first and second recesses. (5) In the optical circuit board described in (4) above, the upper cladding has a plurality of each of the first and second recesses. (6) In the optical circuit board described in any of (1) to (5) above, the bottoms of at least some of the first and second recesses that are farthest from the third surface are located on the upper cladding or the second surface. (7) In the optical circuit board described in any one of (1) to (6) above, in at least a portion of the first recess and the second recess, the bottom furthest from the third surface is located closer to the first surface than the second surface in the lower cladding.
[0058] (8) A mounting structure according to the present disclosure includes the optical circuit board according to any one of (1) to (7) above, and an optical component mounted on the optical circuit board.
[0059] 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 331 First side surface 332 Second side surface 333 Third surface 33a First side portion 33b Second side portion 33c Recess 33d Upper clad material 33c1 First recess 33c2 Second recess 334 Convex portion 34 Mask 35 Mask 4 Optical component 41 Optical transmission path (silicon waveguide (Si waveguide)) 5 Optical fiber 5a Optical connector 6 Electronic component 7 Solder 8 Sealing resin 10 Mounting structure
Claims
1. a wiring substrate having a first surface; an optical waveguide located on the first surface; Including, 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 opposite to the surface in contact with the first surface; the core extends on the second surface and has a first end surface and a second end surface positioned opposite each other in an extending direction of the core; the upper cladding is located on the second surface, covers the core so that the first end surface and the second end surface are exposed, and has a pair of first and second side surfaces located along the extending direction, a third surface located opposite to the surface in contact with the second surface, a first side portion that is a tangent portion between the first side surface and the third surface, and a second side portion that is a tangent portion between the second side surface and the third surface, the upper clad further has at least one of a first recess in contact with the first side portion and opening to the third surface and the first side surface, and a second recess in contact with the second side portion and opening to the third surface and the second side surface. Optical circuit board.
2. 2. The optical circuit board according to claim 1, wherein at least a portion of the first recess and the second recess has a protrusion that protrudes in the direction of the opening.
3. 2. The optical circuit board according to claim 1, wherein the arithmetic mean roughness of the inner wall surfaces of at least a portion of the first recess and the second recess is 50 nm or less.
4. 2. The optical circuit board according to claim 1, wherein the upper clad has a plurality of at least one of the first recesses and the second recesses.
5. 5. The optical circuit board according to claim 4, wherein the upper clad has a plurality of the first recesses and a plurality of the second recesses.
6. The optical circuit board according to claim 1 , wherein the bottoms of at least some of the first recesses and the second recesses, which are farthest from the third surface, are located on the upper clad or the second surface.
7. 2. The optical circuit board according to claim 1, wherein in at least a portion of the first recess and the second recess, the bottom furthest from the third surface is located closer to the first surface than the second surface of the lower cladding.
8. An optical circuit board according to any one of claims 1 to 7; an optical component mounted on the optical circuit board; An implementation structure, including: