Manufacturing method for optical circuit boards

Abstract

An optical circuit board (1) according to the present disclosure comprises: a wiring board (2); and an optical waveguide (3) located on the wiring board (2). The optical waveguide (3) includes a lower clad (31), a core (32), and an upper clad (33) in order from the upper surface side of the wiring board (2). The core (32) extends on the upper surface of the lower clad (31). The upper clad (33) covers the upper surface of the lower clad (31) and the core (32). The lower clad (31) has at least one recess (34) located along the core (32). A part of the upper clad (33) is located in the recess (34).

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an optical circuit substrate. board

Background Art

[0002] In recent years, optical fibers capable of communicating a large amount of data at high speed have been used for information communication. Transmission and reception of optical signals are performed between this optical fiber and optical components. Such optical components are mounted on, for example, an optical circuit board. The optical circuit board is provided with an optical waveguide. The optical signal is transmitted and received through this optical waveguide.

[0003] As described in Patent Document 1, for example, an optical waveguide is formed by applying a radiation-curable resin composition as a core material, pressing a mold mask having a predetermined pattern, and performing exposure and curing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0005] The optical circuit board according to the present disclosure includes a wiring board and an optical waveguide located on the wiring board. The optical waveguide includes a lower cladding, a core, and an upper cladding from the upper surface side of the wiring board. The core extends on the upper surface of the lower cladding. The upper cladding covers the upper surface of the lower cladding and the core. The lower cladding has at least one recess located along the core. A part of the upper cladding is located in the recess.

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

[0007] The method for manufacturing an optical circuit board according to this disclosure includes the steps of: preparing a wiring board; forming a lower cladding having a recess on the upper surface of the wiring board; applying a core resin to the upper surface of the lower cladding; preparing a light-transmitting mold having a first surface and a second surface on the opposite side of the first surface, with a groove for a core pattern on the first surface and a light-shielding portion in the part other than the groove for the core pattern; placing the mold such that, in a planar perspective view, the groove for the core pattern follows the recess without overlapping, and the first surface is in contact with the core resin; and a core pattern The process includes: pressing a mold placed on the core resin so that the core resin is positioned in the grooves and recesses for the core pattern; exposing the mold from the second side to partially cure the core resin located in the grooves and recesses for the core pattern; removing the mold, developing and removing the uncured core resin located on the upper surface and recesses of the lower cladding, and then curing the core resin to form the core; and covering the upper surface and core of the lower cladding to form the upper cladding located in the recesses. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view showing an optical component mounting structure in which optical components and electronic components are mounted on an optical circuit board according to one embodiment of the present disclosure. [Figure 2] This is an enlarged explanatory diagram illustrating the cross-section of region X shown in Figure 1. [Figure 3] This is a plan view from the direction of arrow A shown in Figure 2 (however, the upper cladding is omitted). [Figure 4] This is an explanatory diagram illustrating the cross-section of region Y as viewed from the direction of arrow B shown in Figure 3. [Figure 5] This is an explanatory diagram illustrating variations of the recess and other arrangement examples. [Figure 6] This is an explanatory diagram illustrating variations in the depth of the recess. [Figure 7] This is an explanatory diagram illustrating another cross-section of region Y as viewed from the direction of arrow B shown in Figure 3. [Figure 8]This is an explanatory diagram illustrating the process for manufacturing an optical circuit board according to one embodiment of the present disclosure. [Figure 9] This is an explanatory diagram illustrating the process for manufacturing an optical circuit board according to one embodiment of the present disclosure. [Figure 10] This is an explanatory diagram illustrating the process for manufacturing an optical circuit board according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] As described above, an optical waveguide is formed by applying a radiation-curable resin composition, which is the core material, pressing a mold mask with a predetermined pattern onto it, and then exposing and curing it. However, due to the high melt viscosity of the core material, the core material becomes thicker in areas without a pattern. As a result, variations in core thickness occur, leading to increased optical signal transmission loss. Therefore, there is a need for an optical circuit board that exhibits low optical signal transmission loss and excellent adhesion between the upper and lower cladding layers.

[0010] The optical circuit board according to this disclosure has a configuration as described in the section on means for solving the above problems, thereby reducing the transmission loss of optical signals and improving the adhesion between the upper cladding and the lower cladding. Furthermore, the manufacturing method of the optical circuit board according to this disclosure can reduce variations in core thickness, providing an optical circuit board with low optical signal transmission loss and excellent adhesion between the upper cladding and the lower cladding.

[0011] An optical circuit board according to one embodiment of the present disclosure will be described with reference to Figures 1 to 4. Figure 1 is a plan view showing an optical component mounting structure 10 on an optical circuit board 1 according to one embodiment of the present disclosure, on which optical components 4 and electronic components 6 are mounted.

[0012] An optical circuit board 1 according to one embodiment of this 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 is a wiring board that is generally used in optical circuit boards.

[0013] Such a wiring board 2, although not specifically shown in the diagram, includes, for example, a core substrate and build-up layers laminated on both sides of the core substrate. The core substrate 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 individually or in combination of two or more. The core substrate usually has through-hole conductors to electrically connect the upper and lower surfaces of the core substrate.

[0014] The core substrate may contain reinforcing materials. Examples of reinforcing materials include insulating fabrics such as glass fibers, glass nonwoven fabrics, aramid nonwoven fabrics, aramid fibers, and polyester fibers. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, inorganic fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide may be dispersed in the core substrate. Only one type of inorganic filler may be used, or two or more types may be used in combination.

[0015] The build-up layer has a structure in which insulating layers and conductive layers are alternately stacked. A portion of the conductive layer located on the outermost surface (the conductive layer located on the upper surface of the wiring board 2) includes a metal layer 21a on which the optical waveguide 3 is located. The conductive layer is made of a metal such as copper. The insulating layer included in the build-up layer is not particularly limited as long as it is made of an insulating material, similar to the core substrate. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used individually or in combination of two or more.

[0016] When there are two or more insulating layers in the build-up layer, each insulating layer may be made of the same resin or different resins. The insulating layer and the core substrate included in the build-up layer may be made of the same resin or different resins. The build-up layer usually has via-hole conductors for electrically connecting the layers.

[0017] The insulating layer included in the build-up layer may contain a reinforcing material. Examples of the reinforcing material include insulating fabric materials such as glass fiber, glass non-woven fabric, aramid non-woven 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, inorganic fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide may be dispersed in the insulating layer included in the build-up layer. Only one type of inorganic filler may be used, or two or more types may be used in combination.

[0018] 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 existing on the surface of the wiring board 2. FIG. 2 is an enlarged explanatory diagram for explaining the cross-section of the region X shown in FIG. 1. The optical waveguide 3 has a structure in which a lower cladding 31, a core 32, and an upper cladding 33 are laminated in this order from the metal layer 21a side.

[0019] The lower cladding 31 included in the optical waveguide 3 is located on the surface of the metal layer 21a existing on the surface of the wiring board 2, specifically, 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 include resins such as epoxy resin and silicone resin. Only one type of these resins may be used, or two or more types may be used in combination.

[0020] The upper cladding 33 included in the optical waveguide 3 is located so as to cover the upper surface of the lower cladding 31 and the core 32. Similarly to the lower cladding 31, the upper cladding 33 is formed of a resin such as epoxy resin and silicone resin. Only one type of these resins may be used, or two or more types may be used in combination.

[0021] 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. For example, the lower cladding 31 and the upper cladding 33 may each have a thickness of 5 μm or more and 200 μm or less.

[0022] The core 32 contained within the optical waveguide 3 is the portion through which light that enters the optical waveguide 3 propagates. Specifically, the side surface of the optical transmission path 41 contained within the optical component 4 mounted on the mounting area of ​​the wiring board 2 and the side surface of the core 32 of the optical waveguide 3 are positioned opposite each other. With this configuration, optical signals are transmitted and received between the core 32 and the optical transmission path 41.

[0023] The material forming the core 32 is not limited and is appropriately set considering, for example, light transmittance and the wavelength characteristics of propagating light. Examples of materials include resins such as epoxy resin and silicone resin. These resins may be used individually or in combination of two or more. The core 32 has a thickness of, for example, 1 μm to 60 μm.

[0024] The lower cladding 31 has at least one recess 34, as shown in Figure 3. Figure 3 is a plan view taken from the direction of arrow A shown in Figure 2 (the upper cladding 33 is omitted). The recess 34 is located along the core 32. A portion of the upper cladding 33 is located in the recess 34, as shown in Figure 4. Figure 4 is an explanatory diagram illustrating a cross-section of region Y as seen from the direction of arrow B shown in Figure 3.

[0025] In one embodiment of the optical circuit substrate 1, a portion of the upper cladding 33 is located in the recess 34, which increases the bonding area between the upper cladding 33 and the lower cladding 31. As a result, the adhesion force between the upper cladding 33 and the lower cladding 31 is improved.

[0026] The recess 34 is not limited to having at least one recess in the lower cladding 31. For example, as shown in Figure 3, the recess 34 may have a first recess 341 and a second recess 342 in a planar perspective, with the core 32 in between. When the first recess 341 and the second recess 342 are positioned with the core 32 in between, the lifting that occurs in the upper cladding 33 is reduced. "Lifting" means that the upper cladding 33 partially separates from the lower cladding 31, causing the upper cladding to lift up. There may be only one core 32, or there may be multiple cores 32 adjacent to each other and forming a group, as shown in Figure 3.

[0027] Furthermore, as shown in Figure 3, in a planar perspective view, multiple cores 32 may be located adjacent to each other, and multiple recesses 34 may be located between each of the multiple cores 32. Having such a configuration increases the bonding area between the upper cladding 33 and the lower cladding 31. As a result, the adhesion force between the upper cladding 33 and the lower cladding 31 is further improved.

[0028] In a cross-sectional view perpendicular to the direction in which the core 32 extends, the shape of the cross-section of the recess 34 is not limited. The recess 34 may have approximately the same width from the opening to the bottom, or it may have different widths from the opening to the bottom. As shown in Figure 4, for example, the width W2 of the opening of the recess 34 may be greater than the width W1 of the bottom of the recess 34. In this case, the width of the recess 34 may widen in a tapered manner from the bottom to the opening, or it may widen in a stepped manner. When the width of the recess 34 widens in a tapered manner from the bottom to the opening, the upper cladding 33 is easily formed inside the recess 34.

[0029] When the width W2 of the opening of the recess 34 is greater than the width W1 of the bottom of the recess 34, the upper cladding 33 can easily fit into the recess 34. This facilitates close contact between the upper cladding 33 and the lower cladding 31, further improving the adhesion between them. Furthermore, as shown in Figure 4, the recess 34 penetrates from the top surface to the bottom surface of the lower cladding 31. In such cases, reducing the width W1 of the bottom of the recess 34 increases the contact area between the lower cladding 31 and the wiring board 2 (metal layer 21a). As a result, the lower cladding 31 becomes less likely to peel off.

[0030] The width W2 of the opening of the recess 34 is not limited and may be, for example, 50 μm or more and 200 μm or less. The width W1 of the bottom of the recess 34 is not limited and may be, for example, 40 μm or more and 190 μm or less.

[0031] If multiple recesses 34 exist, the shapes of the recesses 34 (for example, the width W2 of the opening, the width W1 of the bottom, etc.) may be the same or different. For example, when viewed from above, not all recesses 34 need to have the same width.

[0032] The arithmetic mean roughness of the inner wall surface of the recess 34 is not limited and may be greater than, for example, the arithmetic mean roughness of the upper surface of the lower cladding 31. When the arithmetic mean roughness of the inner wall surface of the recess 34 is large, a greater anchoring effect is exerted between the inner wall surface of the recess 34 and the upper cladding 33. As a result, the adhesion force between the upper cladding 33 and the lower cladding 31 is further improved. The arithmetic mean roughness can be calculated, for example, by measuring any inner wall surface of the recess 34 and any upper surface of the lower cladding 31 with a laser displacement meter or optical interferometer after the lower cladding 31 has been formed.

[0033] The length of the recess 34 is not limited, as long as it is positioned along the core 32. The length of the recess 34 may be approximately the same as the length of the core 32, as shown in Figure 3, for example, or it may be shorter than the length of the core 32. Alternatively, the recess 34 may be positioned intermittently along the core 32, as shown in Figure 5. Figure 5 is an explanatory diagram illustrating other shapes and arrangements of the recess.

[0034] In Figure 5, the recess 34 has a circular shape when viewed from above, but this shape is not limited. When viewed from above, the recess 34 may be elliptical or polygonal (triangle, quadrilateral, pentagon, hexagon, etc.). If the recess 34 is located intermittently, each recess 34 may have the same shape, size, and depth, or they may have different shapes, sizes, and depths. Furthermore, as shown in Figure 5, continuous recesses 34 and intermittent recesses 34 may be mixed together.

[0035] The depth of the recess 34 is not limited; it may penetrate from the top to the bottom surface of the lower cladding 31 as shown in Figure 4, or it may not penetrate as shown in Figure 6. Figure 6 is an explanatory diagram illustrating a modified example regarding the depth of the recess. In order to efficiently exert adhesion between the upper cladding 33 and the lower cladding 31, it is preferable that the recess 34 has a depth of at least 20% of the thickness of the lower cladding 31.

[0036] As shown in Figure 4, when the optical waveguide 3 is located on the surface of the metal layer 21a, that is, when the lower cladding 31 is located on the surface of the metal layer 21a, it is preferable that the recess 34 penetrates from the top surface to the bottom surface of the lower cladding 31. With such a configuration, the metal layer 21a is exposed at the bottom of the recess 34. As a result, the upper cladding 33 located in the recess 34 and the metal layer 21a come into contact, and the adhesion between the upper cladding 33 and the metal layer 21a is improved by the anchoring effect. As a result, the upper cladding 33 becomes less likely to peel off. The surface of the metal layer 21a is usually roughened, for example, having an arithmetic mean roughness of 100 nm to 800 nm.

[0037] The upper cladding 33 may have a recess 331 in the region that overlaps with the recess 34 when viewed from above, for example, as shown in Figure 7. That is, the recess 331 of the upper cladding 33 is located in the region that overlaps with the recess 34 of the lower cladding 31. The recess 331 is located on the surface of the upper cladding 33, for example, indicated by arrow C in Figure 7. The presence of such a recess 331 allows the approximate position of the core 32 to be visually determined. This facilitates alignment during inspections, etc. The size and depth of the recess 331 are not limited, as long as they are of a size and depth that can be visually determined.

[0038] Next, the method for manufacturing an optical circuit board according to this disclosure will be described with reference to Figures 8 to 10. Figures 8 to 10 are explanatory diagrams for illustrating the process for manufacturing an optical circuit board 1 according to one embodiment of this disclosure. The method for manufacturing an optical circuit board 1 according to one embodiment includes the following steps (a) to (i). (a) The process of preparing the wiring board. (b) A step of forming a lower cladding having a recess on the upper surface of the wiring board. (c) A step of applying core resin to the upper surface of the lower cladding. (d) A step of preparing a light-transmitting mold having a first surface and a second surface on the opposite side of the first surface, with a groove for a core pattern on the first surface and a light-shielding portion in the portion other than the groove for the core pattern. (e) A step of placing the mold so that, in planar perspective, the grooves for the core pattern follow the contours of the recesses without overlapping, and the first surface is in contact with the core resin. (f) A step of pressing a mold placed on the core resin so that the core resin is positioned in the grooves and recesses for the core pattern. (g) A step of exposing the mold from the second side to light and partially curing the core pattern groove and the core resin located below the core pattern groove. (h) A step of forming a core by removing the mold, developing and removing the uncured core resin located on the upper surface and recesses of the lower cladding, and then curing the core resin. (i) A step of covering the upper surface and core of the lower cladding and forming the upper cladding located in the recess.

[0039] Step (a) is the step of preparing the wiring board 2. The wiring board 2 is as described above, so a detailed explanation will be omitted.

[0040] Step (b) is a step of forming a lower cladding 31 having recesses 34 on the upper surface of the wiring board 2. As shown in Figure 8A, a resin film 31a, which will be the material for the lower cladding 31, is placed on the upper surface of the wiring board 2 (the upper surface of the metal layer 21a). As described above for the lower cladding 31, the resin film 31a can be a film made of resin such as epoxy resin and silicone resin. The resin film 31a has a thickness of, for example, 5 μm to 200 μm, taking into consideration the thickness of the lower cladding 31 that will be obtained. Although the metal layer 21a is formed in Figure 8A, the metal layer 21a is not required.

[0041] Next, as shown in Figure 8B, the resin film 31a is covered with a mold 35. The mold 35 has a light-shielding portion 35a formed therein that acts as a mask during exposure. The light-shielding portion 35a is made of a metal such as chromium or a resin, for example. After covering the resin film 31a with the mold 35, it is exposed and developed, and a recess 34 is formed in the lower cladding 31, as shown in Figure 8C. Specifically, the portion shielded by the light-shielding portion 35a does not harden and is removed during development, thereby forming the recess 34.

[0042] Step (c) is the step of applying the core resin 32a to the upper surface of the lower cladding 31. As shown in Figure 9A, the core resin 32a is applied so as to cover the lower cladding 31. As for the core resin 32a, as explained above for the core 32, for example, a film formed of a resin such as epoxy resin and silicone resin is used. The core resin 32a has a thickness of, for example, 1 μm to 65 μm, taking into consideration the thickness of the resulting core 32.

[0043] Step (d) is the step of preparing a light-transmitting mold 36 having a first surface 361 and a second surface 362 opposite to the first surface 361, with a core pattern groove 363 on the first surface 361 and a light-shielding portion 364 in the portion other than the core pattern groove 363. As shown in Figure 9B, the core pattern groove 363 is formed on the first surface 361 of the mold 36, taking into consideration the width, height and shape of the desired core 32. The light-shielding portion 364 is located in the portion other than the core pattern groove 363 and is made of a metal such as chromium.

[0044] Step (e) is the step of placing the mold 36 on the core resin 32a so that the first surface 361 is in contact with the core resin 32a, with the core pattern groove 363 following the recess 34 without overlapping in a planar perspective view. After placing the mold 36, the mold 36 is pressed by step (f).

[0045] Step (f) is the step of pressing the mold 36 placed on the core resin 32a so that the core resin 32a is positioned in the core pattern grooves 363 and recesses 34. As shown in Figure 9C, by pressing the mold 36, a portion of the core resin 32a flows into the recesses 34. That is, by the excess core resin 32a flowing into the recesses 34, variations in the thickness of the resulting core 32 can be reduced. As a result, the transmission loss of optical signals can be reduced. The core resin 32a that has flowed into the recesses 34 has a depression. That's good too.

[0046] Furthermore, if the recesses 34 are positioned so as to sandwich the core 32 between them, when the mold 36 is pressed, excess core resin 32a will disperse and flow into each recess 34. As a result, variations in the thickness of the resulting core 32 can be reduced more efficiently.

[0047] As described above, the proportion occupied by the recesses 34 in the lower cladding 31 is not limited. For example, the total volume of the recesses 34 may be larger than the total volume of the core 32. If the total volume of the recesses 34 is large, excess core resin 32a will flow more easily into the recesses 34. As a result, variations in the thickness of the resulting core 32 can be reduced more efficiently.

[0048] Step (g) is a step in which the mold 36 is exposed from the second surface 362 side to partially cure the core pattern groove 363 and the core resin 32a located below the core pattern groove 363. As shown in Figure 9C, exposure is performed, for example, by irradiating with ultraviolet (UV) light. The amount (intensity) of UV light and the exposure time for partially curing the core resin 32a are set appropriately depending on the type of core resin 32a used. The core resin 32a covered by the light-shielding portion 364 is not partially cured and remains uncured.

[0049] As shown in Figure 10A, the width of the recess 34 may widen from the bottom towards the opening. When the width of the recess 34 widens from the bottom towards the opening, excess core resin 32a can flow more easily into the recess 34. As a result, variations in the thickness of the resulting core 32 can be reduced more efficiently.

[0050] Step (h) is a step in which the mold 36 is removed, the uncured core resin 32a located on the upper surface of the lower cladding 31 and in the recess 34 is developed and removed, and then the core resin 32a is cured to form the core 32. As shown in Figure 10A, after removing the mold 36, as shown in Figure 10B, the uncured core resin 32a in the area covered by the light-shielding portion 364 is developed and removed.

[0051] After removing the core resin 32a from the portion covered by the light-shielding portion 364, the remaining semi-cured core resin 32a (the core resin 32a in the portion not covered by the light-shielding portion 364) is cured. Curing is performed, for example, by irradiation with ultraviolet light. In this way, as shown in Figure 10B, the core 32 is formed on the upper surface of the lower cladding 31 with reduced variations in each core's thickness.

[0052] Step (i) is a step of covering the upper surface of the lower cladding 31 and the core 32 to form the upper cladding 33 located in the recess 34. As an example of a method for forming the upper cladding 33, first, a resin film to be used as the material for the upper cladding 33 is prepared. As for the resin film, as described above for the upper cladding 33, for example, a film made of a resin such as epoxy resin and silicone resin can be used. The resin film has a thickness of, for example, 5 μm to 250 μm, taking into consideration the thickness of the upper cladding 33 to be obtained.

[0053] Next, the resin film that will be the material for the upper cladding 33 is placed on the upper surface of the lower cladding 31 and the upper surface of the core 32, as shown in Figure 10B. Then, the resin film is heated and pressurized to cover the upper surface of the lower cladding 31 and the core 32, and laminated so that a portion of the resin film is located in the recess 34, thereby forming the upper cladding 33 as shown in Figure 10C.

[0054] Through these processes (a) to (i), variations in core thickness can be reduced, resulting in an optical circuit board 1 according to one embodiment that exhibits low optical signal transmission loss and excellent adhesion between the upper and lower cladding.

[0055] Next, the optical component mounting structure of this disclosure will be described. As shown in Figure 1, the optical component mounting structure 10 according to one embodiment of this disclosure has a structure in which optical components 4 and electronic components 6 are mounted on an optical circuit board 1 according to one embodiment. The optical component 4 mounted on the optical component mounting structure 10 according to one embodiment includes an optical transmission path 41. Examples of such optical components 4 including an optical transmission path 41 include silicon photonic devices. Examples of electronic components 6 include ASICs (Application Specific Integrated Circuits). Driver ICs are one example.

[0056] As shown in Figure 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 (optical component mounting area) of the wiring board 2 via solder 7. The pad 21b is part of the conductive layer located on the upper surface of the wiring board 2.

[0057] As an example of optical component 4, a silicon photonic device will be described. A silicon photonic device is a type of optical component having an optical transmission path 41, for example, with a silicon (Si) core and silicon dioxide (SiO2) cladding. The silicon photonic device includes a Si waveguide as the optical transmission path 41 and, although not shown, further includes a passivation film, a light source, and a photodetector. As described above, the optical transmission path 41 (Si waveguide 41) is positioned at one end of the optical waveguide 3 so as to face the core 32 included in the optical waveguide 3.

[0058] For example, an electrical signal from the wiring board 2 is propagated via the solder 7 to a light source included in the optical component 4 (silicon photonic device). The light source, upon receiving the propagated electrical signal, emits light. The emitted light signal is propagated via the optical transmission path 41 (Si waveguide 41) and the core 32 to the optical fiber 5 connected via the optical connector 5a.

[0059] Furthermore, the inventions relating to this disclosure are not limited to the embodiments described above, and various modifications and improvements are possible within the scope of this disclosure as shown in (1), (11), and (12) below.

[0060] (1) The optical circuit board relating to this disclosure includes a wiring board and an optical waveguide located on the wiring board. The optical waveguide includes a lower cladding, a core, and an upper cladding from the upper surface side of the wiring board. The core extends from the upper surface of the lower cladding. The upper cladding covers the upper surface of the lower cladding and the core. The lower cladding has at least one recess located along the core. A portion of the upper cladding is located in the recess.

[0061] With regard to embodiments of the present disclosure, embodiments shown in (2) to (10) below are further disclosed.

[0062] (2) In the optical circuit board described in (1) above, the recess has a first recess and a second recess positioned with a core in between. (3) In the optical circuit board described in (2) above, multiple cores are located adjacent to each other. (4) In the optical circuit board described in (1) above, multiple cores are located adjacent to each other, and multiple recesses are located between each of the multiple cores. (5) In the optical circuit board described in any of (1) to (4) above, the recess has a bottom and an opening. In a cross-sectional view in a direction perpendicular to the direction in which the core extends, the width of the opening of the recess is greater than the width of the bottom of the recess. (6) In the optical circuit board described in (5) above, the width of the recess increases from the bottom toward the opening. (7) In the optical circuit board described in any of (1) to (6) above, the arithmetic mean roughness of the inner wall surface of the recess is greater than the arithmetic mean roughness of the upper surface of the lower cladding. (8) In the optical circuit board described in any of (1) to (7) above, the wiring board further includes a metal layer, and the optical waveguide is located on the upper surface of the metal layer. (9) In the optical circuit board described in any of (8) above, the recess is located from the upper surface of the lower cladding to the metal layer, and the upper cladding is in contact with the metal layer. (10) In the optical circuit board described in any of (1) to (9) above, the upper cladding has a recess in the region that overlaps with the recess when viewed from a planar perspective.

[0063] (11) The optical component mounting structure relating to this disclosure includes an optical circuit board described in any of (1) to (10) above and an optical component mounted on the optical circuit board.

[0064] (12) A method for manufacturing an optical circuit board according to the present disclosure includes the steps of: preparing a wiring board; forming a lower cladding having a recess on the upper surface of the wiring board; applying a core resin to the upper surface of the lower cladding; preparing a light-transmitting mold having a first surface and a second surface on the opposite side of the first surface, with a groove for a core pattern on the first surface and a light-shielding portion in the portion other than the groove for the core pattern; and placing the mold such that, in planar perspective, the groove for the core pattern follows the recess without overlapping, and the first surface is in contact with the core resin. The process includes: pressing a mold placed on the core resin so that the core resin is positioned in the turn grooves and recesses; exposing the mold from the second side to partially cure the core pattern grooves and the core resin located below the core pattern grooves; removing the mold, developing and removing the uncured core resin located on the upper surface and recesses of the lower cladding, and then curing the core resin to form the core; and covering the upper surface and core of the lower cladding to form the upper cladding located in the recesses.

[0065] (13) In the manufacturing method described in (12) above, the wiring board further includes a metal layer, and the lower cladding is formed on the metal layer. [Explanation of symbols]

[0066] 1 Optical circuit board 2 Wiring board 21a Metal layer 21b pad 3 Optical waveguide 31 Lower cladding 32 cores 33 Upper cladding 331 Indentation 34 recess 35 molds 35a Light shielding part 36 molds 361 Page 1 362 2nd page 363 Grooves for core pattern 364 Light-shielding part 4 Optical components 41. Optical transmission lines (silicon waveguides (Si waveguides)) 5 Optical Fiber 5a Optical Connector 6 Electronic Components 7 solder 10 Optical component mounting structure

Claims

1. The process of preparing the wiring board, The process of forming a lower cladding having a recess on the upper surface of the wiring board, The process involves applying a core resin to the upper surface of the lower cladding, A step of preparing a light-transmitting mold having a first surface and a second surface on the opposite side of the first surface, the first surface having a groove for a core pattern and a light-shielding portion in the part other than the groove for the core pattern, A step of placing the mold such that, in a planar perspective view, the groove for the core pattern follows the recess without overlapping, and the first surface is in contact with the core resin, A step of pressing the mold placed on the core resin so that the core resin is positioned in the grooves and recesses for the core pattern, A step of exposing the mold from the second surface to partially cure the core pattern groove and the core resin located below the core pattern groove, The process of forming a core involves removing the mold, developing and removing the uncured core resin located on the upper surface of the lower cladding and in the recess, and then curing the core resin. A step of covering the upper surface of the lower cladding and the core, and forming the upper cladding located in the recess, A method for manufacturing an optical circuit board, including [the specified part of the method].

2. The method for manufacturing an optical circuit board according to claim 1, wherein the wiring board further includes a metal layer, and the lower cladding is formed on the metal layer.

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