WO2024204111A1

WO2024204111A1 - Optical circuit board and mounting structure

Info

Publication number: WO2024204111A1
Application number: PCT/JP2024/011777
Authority: WO
Inventors: 俊樹山本
Original assignee: 京セラ株式会社
Priority date: 2023-03-30
Filing date: 2024-03-25
Publication date: 2024-10-03

Abstract

An optical circuit board according to the present disclosure comprises a wiring board having a first surface, and an optical waveguide located on the first surface. The optical waveguide comprises a lower cladding, a core, and an upper cladding. The lower cladding is located on the first surface, and comprises a second surface located on the opposite side of a surface of the lower cladding bordering the first surface. The core extends to the second surface, and comprises a first end surface and second end surface that are located facing opposite one another in a direction of extension of the core. The upper cladding is located on the second surface and covers the core such that the first end surface and the second end surface are exposed, the upper cladding comprising: a pair of a first side surface and a second side surface located along the direction of extension, a third surface located on the opposite side of the surface bordering on the second surface, a first edge that is a tangent of the first side surface and the third surface, and a second edge that is a tangent of the second side surface and the third surface. The upper cladding also includes: a first recess bordering on the first edge and opening on the third surface and the first side surface; and/or a second recess bordering on the second edge and opening on the third surface and the second side surface.

Description

Optical circuit board and mounting structure

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

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. The optical circuit boards are provided with optical waveguides as described in Patent Document 1. Optical signals are transmitted and received via these optical waveguides.

Before mounting optical components on an optical circuit board, light is irradiated onto the core portion of the optical waveguide 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 is the light source, may mistakenly 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.

JP 2001-281479 A

The 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 second surface located opposite 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 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 surface and the second end surface are exposed, and has a pair of first and second side surfaces located along the extension direction, a third surface located opposite the surface in contact with the second surface, a first edge portion that is a tangent portion between the first side surface and the third surface, and a second edge portion that is a tangent portion between the second side surface and the third surface. The upper cladding further has at least one of a first recess that contacts the first edge portion and opens to the third surface and the first side surface, and a second recess that contacts the second edge portion and opens to the third surface and the second side surface.

The mounting structure according to the present disclosure includes the optical circuit board and an optical component mounted on the optical circuit board.

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. 2 is an enlarged explanatory view for illustrating a cross section of a region X shown in FIG. 1 . FIG. 3A is a plan view of a main part of the optical waveguide as viewed from the direction of the arrow A shown in FIG. 2, B is an enlarged explanatory view (perspective view) for explaining the region Y shown in FIG. 3A, and C is a front view of the optical waveguide as viewed from the direction of the arrow B shown in FIG. 3A. 1A to 1C are explanatory diagrams for explaining an embodiment of a method for forming an optical waveguide in a wiring board. 5A is a plan view showing another embodiment of the main part of the optical waveguide as viewed from the direction of the arrow A shown in FIG. 2, FIG. 5B is an enlarged explanatory view showing a cross section taken along the line X-X shown in FIG. 5A, and FIG. 5C is a side view of the optical circuit board (optical waveguide) as viewed from the direction of the arrow C shown in FIG. 5B. 6A is an explanatory diagram (oblique view) for explaining yet another embodiment of the recesses (first recess and second recess) formed in the optical waveguide, and FIG. 6B is a plan view seen from the direction of arrow D shown in FIG. 6A. FIG. 13A is an explanatory view (perspective view) for explaining still another embodiment of the recesses (first recess and second recess) formed in the optical waveguide.

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 mistakenly 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 the efficiency of the inspection. Therefore, there is a demand for an optical circuit board that allows for efficient inspection of optical waveguides.

The optical circuit board disclosed herein has the configuration described in the section on means for solving the above problems, making it possible to efficiently perform optical waveguide inspection.

An optical circuit board according to one 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 one embodiment of the present disclosure.

The optical circuit board 1 according to one embodiment of the present disclosure includes a wiring board 2 and an optical waveguide 3. The wiring board 2 included in the optical circuit board 1 according to one embodiment includes a wiring board that is generally used for optical circuit boards.

Such a wiring board 2 includes, for example, a core layer and build-up layers laminated on both sides of the core layer, although not specifically illustrated. 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. Only one type of these resins may be used, or two or more types may be used in combination.

The core insulating layer may contain a reinforcing material. Examples of reinforcing materials include insulating cloth 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 inorganic insulating fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide dispersed therein. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

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 material that is conductive. Examples of conductive materials include metals such as copper.

In the core insulating layer, a through-hole conductor is located 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. Like the core conductor 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 be filled in the through-hole. The through-hole conductor is connected to the core conductor layer on the surface of the core insulating layer.

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 resins, bismaleimide-triazine resins, polyimide resins, and polyphenylene ether resins. These resins may be used alone or in combination of two or more types.

When there are two or more build-up insulation layers, 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. The build-up layers usually have via-hole conductors to electrically connect the layers.

The build-up insulating layer may contain a reinforcing material. Examples of reinforcing materials include insulating cloth 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 inorganic insulating fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide dispersed therein. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

　The conductor layer for the build-up is not particularly limited as long as it is made of a material that is conductive, similar to the conductor layer for the core. An example of a material that is conductive is a metal such as copper.

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 the metal layer 21a present on the surface of the wiring board 2. FIG. 2 is an enlarged explanatory diagram for explaining the 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 layered in this order from the metal layer 21a side.

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 forming region of the wiring board 2. The material forming the lower cladding 31 is not limited, and examples 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 to the surface facing the first surface 21 of the wiring board 2. The metal layer 21a is an optional member and may or may not be used. In other words, the wiring board 2 does not need to include the metal layer 21a.

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 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, 5 μm or more and 150 μm or less.

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 surface 321 and a second end surface 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 the sake of convenience, the first end surface 321 of the core 32 is the end surface on the optical component 4 side, and the second end surface 322 of the core 32 is the end surface on the optical connector 5a side.

Specifically, the end face of the optical transmission path (Si waveguide) 41 included in the optical component 4 mounted in the mounting area of the wiring board 2 is positioned to face the 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 set taking into consideration, for example, the light transmittance and the wavelength characteristics of the propagating light. Examples of materials 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.

As described above, the upper clad 33 is located on the upper surface of the lower clad 31, i.e., 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. As shown in Figures 3A to 3C, the upper clad 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 on the opposite side of the surface that contacts the second surface 312 of the lower clad 31, a first side portion 33a which is a tangent portion between the first side surface 331 and the third surface 333, and a second side portion 33b which is a tangent portion between the second side surface 332 and the third surface 333. Figure 3A is a plan view of the main part of the optical waveguide 3 as seen from the direction of the arrow A shown in Figure 2. Figure 3B is an enlarged explanatory view (perspective view) for explaining the region Y shown in Figure 3A. FIG. 3C is a front view of the optical waveguide 3 as seen from the direction of arrow B shown in FIG. 3A.

As shown in Figure 3A, at least one recess 33c is located in the upper cladding 33. Specifically, as shown in Figures 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 cladding 33. The first recess 33c1 and the second recess 33c2 are described separately only for convenience, and the first recess 33c1 and the second recess 33c2 may be collectively referred to as recess 33c.

The optical circuit board 1 according to one 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, which allows efficient optical waveguide inspection. Specifically, when inspecting the transmission and reception of optical signals by irradiating light to the core 32 of the optical waveguide 3 before mounting the optical components 4 on the optical circuit board 1 according to one embodiment, the presence of the recess 33c causes the light trapped by the refractive index difference between the upper clad 33 and the air to be scattered by the recess 33c. Therefore, the transmission of light through the first side 33a and the second side 33b of the upper clad 33 having the recess 33c is reduced, making it difficult to mistakenly recognize the first side 33a and the second side 33b as the core 32. As a result, manual readjustment is no longer necessary, and optical waveguide inspection can be performed efficiently.

It is sufficient that at least one recess 33c is 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 of each may be located. When multiple recesses 33c are located, the irradiated light is scattered more, and the transmission of light to the edge portion of the upper cladding 33 is more efficiently reduced.

As shown in FIG. 3C, the recesses 33c (first recess 33c1 and second recess 33c2) have a rectangular shape when viewed from above in a plan view. 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.

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 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 trapped due to the difference in refractive index between the upper cladding 33 and air can be covered.

In FIG. 3B, the height H of the recess 33c (second recess 33c2 is exemplified) corresponds to the thickness of the upper clad 33. The height H of the recess 33c may be less than the thickness of the upper clad 33. That is, in the recess 33c, the bottom farthest from the third surface 333 of the upper clad 33 may be located on the second surface 312 of the upper clad 33 or the lower clad 31. In FIG. 3B, this bottom is located on the second surface 312 of the lower clad 31. When the height H is in this range, the transmission of light through the first side 33a and the second side 33b can be reduced without compromising the strength of the optical waveguide 3.

When multiple 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.

The arithmetic mean roughness of the inner wall surface of the recess 33c is not limited. In at least a portion of the recess 33c, the arithmetic mean roughness of the inner wall surface may be, for example, 50 nm or less. When the arithmetic mean roughness is 50 nm or less, the 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, optical interference measuring device, or the like, for example, after the recess 33c is formed.

The method for forming the recess 33c in the edge portion of the upper cladding 33 is not limited, and for example, the recess 33c is formed 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 board 2. For convenience, the wiring board 2 is omitted from FIG. 4B.

First, as shown in FIG. 4A, a lower clad 31 is formed on the first surface 21 of the wiring board 2. A metal layer 21a may be located between the lower clad 31 and the first surface 21.

Next, core material 32a, which will be the material for core 32, is attached to the second surface 312 of lower cladding 31. The material forming core 32 is as described above, and detailed description will be omitted. Then, as shown in FIG. 4B, the surface of core material 32a is covered with mask 34. Specifically, the surface of core material 32a is covered with mask 34 having an opening in the portion where core 32 is to be formed, and the core material 32a located in the opening is hardened by exposure to light. After that, mask 34 is removed, and the core material 32a in the portion covered by mask 34 is removed by development, thereby forming core 32 on second surface 312 of lower cladding 31, as shown in FIG. 4C.

Next, upper clad material 33d, which will be the material of upper clad 33, is attached to second surface 312 of lower clad 31 so that first end surface 321 and second end surface 322 of core 32 are exposed. The material forming upper clad 33 is as described above, and detailed description will be omitted. Then, as shown in FIG. 4D, the surface of upper clad material 33d is covered with mask 35. The portion covered with mask 35 is the portion that will be removed by development after exposure. Specifically, when viewed in a plan view from above, both sides of upper clad material 33d and the portion that will form recess 33c should be covered with mask 35 so as to follow core 32.

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 upper cladding material 33d in the portion covered by 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 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 are formed in the upper cladding 33. Although FIG. 4E illustrates an example in which there is one each of the first recess 33c1 and the second recess 33c2, the number of recesses 33c can be adjusted according to the shape of the mask 35.

Next, other shapes of the recess 33c will be described with reference to Figure 5. Figure 5A is a plan view showing another embodiment of the main part of the optical waveguide 3 as viewed from the direction of the arrow A shown in Figure 2. Figure 5B is an enlarged explanatory view showing a cross section taken along line X-X shown in Figure 5A. Figure 5C is a side view of the optical circuit board 1 (optical waveguide 3) as viewed from the direction of the arrow C shown in Figure 5B.

As described above, in the recess 33c (33c2) shown in FIG. 3B, the bottom 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, in the recess 33c, the bottom farthest from the third surface 333 of the upper clad 33 may be located closer to the first surface 21 of the wiring board 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.

When the height of the recess 33c is greater than the thickness of the upper cladding 33, as shown in FIG. 5C, the sealing resin 8 that connects the optical component 4 and the optical connector 5a enters the recess 33c. As a result, the bonding strength between these components is improved. Although the bottom is flat in FIG. 5B, it may be uneven. In this case, the contact area between the sealing resin 8 and the bottom is increased, which is advantageous in that the bonding strength is improved.

The bottom of the recess 33c, which is furthest 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 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.

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, for example, by laser processing. Specifically, the mask 35 shown in FIG. 4D is not used to form the recess 33c, but is used so that only the first side surface 331 and the second side surface 332 of the upper clad 33 are formed. By exposing 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. The recess 33c is then formed by subjecting it to laser processing.

Furthermore, the recess 33c may have a protrusion 334 protruding in the opening direction (direction from the first side surface 331 toward the second side surface 332) as shown in Fig. 6. 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 the arrow D shown in Fig. 6A.

When the convex portion 334 is located in the concave portion 33c, for example, a portion of the light incident from the first end face 321 side and entering the concave portion 33c is reflected at the convex portion 334 to the outside of the optical waveguide 3, making it easier 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 the light and the convex portion 334 is not limited, and may be, for example, 15° or more and 75° or less. If the angle θ is in this range, it becomes easier to reflect the light incident on the first side portion 33a and the second side portion 33b of the upper cladding 33 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 convex portions 334.

In FIG. 6B, when viewed from above in a plane, the convex portion 334 has a triangular shape. However, if the angle θ is less than 90°, the shape of the convex portion 334 is not limited to a triangular shape. When viewed in a plane, the convex portion 334 may have, for example, a semicircular shape or a trapezoidal shape.

As described above, the recess 33c shown in Figures 3 to 5 has a rectangular shape when viewed from above in a plan view. In other words, the third surface 333 and the side surface of the upper cladding 33 have a rectangular cutout shape so as to have an opening. However, the shape of the recess 33c is not limited to a rectangular shape.

For example, as shown in Figure 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. Figure 7 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.

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 so as to have an opening, or may have a semicircular, trapezoidal, or other cutout shape.

Next, the mounting structure of 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 optical components 4 including such optical transmission paths 41 include silicon photonics devices. Examples of electronic components 6 include ASICs (Application Specific Integrated Circuits) and driver ICs.

As shown in FIG. 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 the mounting area (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.

A silicon photonics device will be described as an example of the optical component 4. The silicon photonics device is, for example, a type of optical component having an optical transmission path 41 with a core of silicon (Si) and a clad of silicon dioxide (SiO ₂ ). The silicon photonics device includes a Si waveguide as the optical transmission path 41, and further includes a passivation film, a light source unit, a light detection unit, and the like, although not shown. As described above, the optical transmission path 41 (Si waveguide 41) is located at one end of the optical waveguide 3 (first end surface 321 in FIG. 2) so as to face the core 32 included in the optical waveguide 3.

For example, an electrical signal from the wiring board 2 is transmitted via the solder 7 to the light source section included in the optical component 4 (silicon photonics device). The light source section 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.

The above describes the embodiments of the present disclosure. However, the invention of 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.

(1) The 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 second surface located opposite 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 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 surface and the second end surface are exposed, and has a pair of first and second side surfaces located along the extension direction, a third surface located opposite the surface in contact with the second surface, a first edge portion that is a tangent portion between the first side surface and the third surface, and a second edge portion that is a tangent portion between the second side surface and the third surface. The upper cladding further has at least one of a first recess that contacts the first edge portion and opens to the third surface and the first side surface, and a second recess that contacts the second edge portion and opens to the third surface and the second side surface.

With regard to the embodiments of the present disclosure, the following embodiments (2) to (7) are further disclosed.

(2) In the optical circuit board described in (1) above, at least a portion of the first recess and the second recess has a protrusion protruding in the direction of the opening.
(3) In the optical circuit board according to (1) or (2) above, the arithmetic mean roughness of the inner wall surface of at least a part of the first recess and the second recess is 50 nm or less.
(4) In the optical circuit board according to any one of (1) to (3) above, the upper clad has at least one of the first recesses and the second recesses in a plurality of portions.
(5) In the optical circuit board described in (4) above, the upper clad has a plurality of first recesses and a plurality of second recesses.
(6) In the optical circuit board according to any one of (1) to (5) above, in at least a portion of the first recess and the second recess, the bottom portion farthest from the third surface is 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.

(8) The mounting structure according to the present disclosure includes an optical circuit board described in any one of (1) to (7) above, and an optical component mounted on the optical circuit board.

REFERENCE SIGNS LIST 1 Optical circuit board 2 Wiring board 21 First surface 21a Metal layer 21b Pad 3 Optical waveguide 31 Lower cladding 312 Second surface 32 Core 321 First end surface 322 Second end surface 32a Core material 33 Upper cladding 331 First side surface 332 Second side surface 333 Third surface 33a First side portion 33b Second side portion 33c Convex portion 33d Upper cladding material 33c1 First concave portion 33c2 Second concave portion 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

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 a 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 extension 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 on the opposite side to a surface in contact with the second surface, a first side portion which is a tangent portion between the first side surface and the third surface, and a second side portion which is a tangent portion between the second side surface and the third surface,
the upper cladding 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.
The optical circuit board according to claim 1, wherein at least a portion of the first recess and the second recess has a protrusion protruding in the direction of the opening.
The optical circuit board according to claim 1 or 2, wherein the arithmetic mean roughness of the inner wall surface of at least a portion of the first recess and the second recess is 50 nm or less.
The optical circuit board according to any one of claims 1 to 3, wherein the upper cladding has a plurality of at least one of the first recesses and the second recesses.
The optical circuit board according to claim 4, wherein the upper cladding has a plurality of the first recesses and a plurality of the second recesses.
An optical circuit board according to any one of claims 1 to 5, wherein the bottoms of at least a portion of the first recess and the second recess that are furthest from the third surface are located on the upper cladding or the second surface.
An optical circuit board according to any one of claims 1 to 6, 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.
An optical circuit board according to any one of claims 1 to 7,
an optical component mounted on the optical circuit board;
An implementation struct, including: