Optical waveguides and wiring boards

Abstract

To provide an optical waveguide in which, during storage of the optical waveguide with the core exposed, or during operations such as component mounting, other components or tools are prevented from coming into contact with the core, thereby suppressing damage to the core. [Solution] The optical waveguide 1 of this embodiment includes a lower cladding 21, a core 3, and an upper cladding 22. The optical waveguide 1 consists of a core exposed portion 1a and a core non-exposed portion 1b. In the core exposed portion 1a, the upper surface of the core 3 is exposed, and in the core non-exposed portion 1b, the upper cladding 22 is formed on the core 3 and the lower cladding 21. Within the core exposed portion 1a, an element placement region 1c and an element non-placement region 1d are provided. The element placement region 1c is the region where an optical element E1 optically connected to the core 3 is placed, and a protrusion R1 is formed in the element non-placement region 1d.

Description

Technical Field

[0001] The present invention relates to an optical waveguide and a wiring board.

Background Art

[0002] Patent Document 1 discloses a structure in which a silicon waveguide and a polymer waveguide are optically coupled. By exposing a part of the upper surface of the core formed on the lower cladding, an adiabatic coupling that optically couples the core of the polymer waveguide and the core of the silicon waveguide is realized.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the optical waveguide disclosed in Patent Document 1, the core of the polymer waveguide is in an exposed state. Therefore, when storing the optical waveguide or performing operations such as element mounting, parts and instruments may come into contact, and the core may be damaged. If the core is damaged, it is considered that optical coupling cannot be achieved well.

Means for Solving the Problems

[0005] The optical waveguide of the present invention includes a lower cladding, a core, and an upper cladding. The optical waveguide consists of a core exposed portion and a core non-exposed portion. In the core exposed portion, the upper surface of the core is exposed. In the core non-exposed portion, an upper cladding is formed on the core and the lower cladding. An element arrangement region and an element non-arrangement region are provided in the core exposed portion of the optical waveguide. The element arrangement region is a region where an optical element optically connected to the core is arranged, and a convex portion is formed in the element non-arrangement region.

[0006] The wiring board of the present invention includes a substrate having an insulating layer and a conductive layer formed on the insulating layer, and an optical waveguide disposed on the substrate.

[0007] According to embodiments of the present invention, it is believed that contact between components and equipment with the core is suppressed during storage of the optical waveguide or during operations such as element mounting, thereby preventing damage to the core. As a result, since damage to the core is prevented, optical coupling becomes possible. [Brief explanation of the drawing]

[0008] [Figure 1A] A plan view showing an example of an optical waveguide in an embodiment of the present invention. [Figure 1B] A cross-sectional view of the optical waveguide shown in Figure 1A. [Figure 2A] A plan view illustrating the mounting configuration of optical elements in an optical waveguide according to an embodiment of the present invention. [Figure 2B] A cross-sectional view of the optical waveguide shown in Figure 2A, along line II-II. [Figure 3] A cross-sectional view illustrating the mounting configuration of an optical element in an optical waveguide according to an embodiment of the present invention. [Figure 4A] A plan view showing an example of a modified optical waveguide in an embodiment of the present invention. [Figure 4B] A cross-sectional view of the optical waveguide shown in Figure 4A, along line III-III. [Figure 5A] A plan view showing an example of a modified optical waveguide in an embodiment of the present invention. [Figure 5B] Figure 5A shows a cross-sectional view of the IV-IV line of the optical waveguide. [Figure 5C] A plan view showing an example of a modified optical waveguide in an embodiment of the present invention. [Figure 6A] A plan view showing an example of a modified optical waveguide in an embodiment of the present invention. [Figure 6B] A cross-sectional view of the VV line of the optical waveguide shown in Figure 6A. [Figure 6C] A plan view showing an example of a modified optical waveguide in an embodiment of the present invention. [Figure 7] A cross-sectional view showing an example of a wiring board according to an embodiment of the present invention. [Modes for carrying out the invention]

[0009] An optical waveguide of the embodiment will be described with reference to the drawings. Figure 1A shows a plan view of optical waveguide 1, which is an example of an optical waveguide of the embodiment. Figure 1B shows a cross-sectional view along line II of Figure 1A. Note that optical waveguide 1 is merely one example of an optical waveguide of the embodiment. Optical waveguide 1 is formed or arranged on a substrate 10, as will be described in detail later with reference to Figure 7, and is optically coupled to optical elements such as light-emitting elements and light-receiving elements mounted on the substrate 10. The referenced drawings are drawn to facilitate understanding of the features of the present invention, and the size and proportions of each component may not be accurate.

[0010] As shown in Figures 1A and 1B, the optical waveguide 1 of the embodiment includes a core 3 that transmits optical signals, and a lower cladding 21 and an upper cladding 22 surrounding the core 3. The core 3 and the upper cladding 22 are formed on one side of the lower cladding 21.

[0011] In the following description, among the surfaces constituting the lower cladding, the side on which the core and upper cladding are formed will be referred to as "upper," "upper side," "upward," or "upward direction," and the surface facing upward will be referred to as the "upper surface." The side facing the opposite direction from the "upper surface" will be referred to as "lower," "lower side," "downward," or "downward direction," and the surface facing downward will be referred to as the "lower surface."

[0012] Furthermore, the thickness direction of the optical waveguide 1 is also referred to as the "Z direction," with the upward direction being called the +Z direction and the downward direction being called the -Z direction. In addition, the core 3 in the optical waveguide 1 is formed along the "X direction," and the optical signal propagating through the core 3 propagates in the +X direction or the -X direction. The direction perpendicular to the X and Z directions is referred to as the "Y direction."

[0013] As shown in Fig. 1A, the optical waveguide 1 is formed of a core exposed portion 1a and a core non-exposed portion 1b. Specifically, one or more cores 3 are formed on the upper surface of the lower cladding 21. The upper cladding 22 is formed to cover the core 3 and the lower cladding 21 in the core non-exposed portion 1b, but is not formed in the core exposed portion 1a. For the sake of convenience of explanation, the core 3 consists of a core 31a and a core 31b. In the core exposed portion, it is the core 31a, and in the core non-exposed portion, it is the core 31b. Also, the lower cladding 21 consists of a lower cladding 21a and a lower cladding 21b. In the core exposed portion, it is the lower cladding 21a, and in the core non-exposed portion, it is the lower cladding 21b. Therefore, in the core non-exposed portion 1b, the core 31b and the lower cladding 21b are not exposed in a plan view.In the core exposed portion 1a, the core 31a which is a part of the core 3 and the lower cladding 21a which is a part of the lower cladding 21 are exposed. Note that for the optical waveguide 1, the range where the lower cladding 21 is formed is the formation region of the optical waveguide 1, and the range where the core 3 is formed is the formation region of the core 3. Hereinafter, the lower cladding 21 and the upper cladding 2 are also collectively referred to as the cladding 2.

[0014] The optical waveguide 1 has one end 1g and the other end 1f which are two opposite ends in the X direction. In the optical waveguide 1, an optical signal is incident on one end 1g or the other end 1f, and the optical signal is emitted from the other end 1f or one end 1g. In Fig. 1A, only one end 1g of the optical waveguide 1 is provided with the core exposed portion 1a, but the core exposed portion 1a may be provided at both the one end 1g and the other end 1f.

[0015] The optical waveguide 1 of the embodiment has three cores 3, but the number of cores 3 is not limited to three and may be any number of 1 or more. For example, the number of cores 3 is a number in the range of 2 or more and 64 or less. When a plurality of cores 3 are formed in parallel, the arrangement pitch of the cores 3 is not particularly limited, but for example, it is 10 to 300 μm, and preferably 20 to 250 μm. Also, as shown in FIG. 1A, the plurality of cores 3 do not necessarily have to be arranged in parallel, nor do they have to be linear. These shapes may be changed according to the shape and structure of an optical component or the like connected to the other end 1f side of the optical waveguide 1, for example, as shown in FIG. 1A, where the cores 3 are formed radially.

[0016] The core 3 and the cladding 2 forming the optical waveguide 1 are formed of an arbitrary light-transmissive material. The optical waveguide 1 can be constituted by, for example, a resin material or a hybrid material containing a resin material such as an inorganic polymer and an inorganic material. As the resin material, a thermosetting resin or a photocurable resin is preferable. Specifically, examples include single resins or plural resins such as acrylic resins such as polymethyl methacrylate (PMMA), polyimide resins, polyamide resins, polyether resins, phenol resins, fluorine resins, silicone resins, and epoxy resins. By constituting the optical waveguide 1 with a resin material, it can have light weight and high toughness and can be provided with flexibility. Note that an inorganic material such as glass or silicon may be used.

[0017] The core 3 and the cladding 2 may be constituted of different materials from each other, or may be constituted of materials of the same system. In either case, a material having a refractive index higher than that of the material used for the cladding 2 is used for the core 3. Alternatively, the core 3 and the cladding 2 may be formed of materials having the same refractive index and then the refractive indices of each other may be made different using a method called the photo-bleaching method.

[0018] The optical waveguide 1 can be fabricated, for example, by thermocompression bonding of the core 3 and cladding 2 components, which are formed into a film, onto a substrate, or by forming a film by spin-coating a resin composition. Alternatively, the optical waveguide 1 may be formed on a separately prepared support, and then the support may be removed to form a standalone optical waveguide 1, which can then be placed on the substrate.

[0019] When the optical waveguide 1 is in use, core 3 is optically coupled at one end 1g and the other end 1f to optical components such as photoelectric conversion elements like light-emitting diodes (LEDs) and photodiodes (PDs), and / or connector members that connect to optical fibers. In other words, the positional relationship between each optical element and core 3 is adjusted so that optical signals can be transmitted and received between core 3 and these optical elements.

[0020] In Figures 1A and 1B, the exposed core portion 1a consists of an element placement region 1c and an element non-placement region 1d. The element placement region 1c is the area indicated by the dashed line in the figure, and is the area in which the optical element E1, which is optically coupled with the core 3 at one end 1g of the optical waveguide 1, is placed. The dashed line indicating the boundary between the element placement region 1c and the element non-placement region 1d coincides with both ends of the optical element when the optical element is placed. The optical element E1 has, for example, a photoelectric conversion function and includes an optical terminal E1a, which is the part into which the optical signal is incident or the part into which the optical signal is emitted. Examples of optical elements E1 include light-emitting elements such as LEDs, organic light-emitting diodes (OLEDs), laser diodes (LDs), and vertical-cavity surface-emitting lasers (VCSELs), as well as photodetectors such as photodiodes (PDs).

[0021] In the element placement region 1c within the exposed core portion 1a, the optical terminal E1a of the optical element E1 is superimposed with the core 3 of the optical waveguide to transmit optical signals. In the examples of Figures 1A and 1B, the optical terminal E1a of the optical element E1 and the upper surface of the core 31a are positioned opposite each other to perform adibatic coupling. As a result, for example, an optical signal propagating through the core 3 toward one end 1g is incident as evanescent light from the upper surface of the core 31a toward the optical terminal E1a of the optical element E1. Optical coupling is achieved because the optical terminal E1a and the upper surface of the core 31a are opposite each other without the upper cladding 22. It is preferable that the space between the optical element E1 and the optical waveguide 1 in the element placement region 1c and its periphery be filled with an arbitrary transparent resin TR that is optically transparent and has an appropriate refractive index. This stabilizes the optical coupling efficiency.

[0022] The mounting configuration of the optical waveguide 1 and optical element E1 on the substrate 10 will be described using Figures 2A and 2B. Figure 2A shows a plan view of the optical waveguide 1 arranged on the substrate 10. Figure 2B shows a cross-sectional view along line II-II in Figure 2A. Figures 2A and 2B show only a portion of the outermost layer of the substrate 10. The structure of the substrate 10 is not particularly limited, but as an example, it is explained using Figure 7. Specifically, the substrate 10 has a conductor layer 41 formed on the outermost insulating layer 51 and in vias penetrating the insulating layer 51, a conductor layer 42 formed below the insulating layer 51, and a solder resist layer 61 formed on the insulating layer 51 and the conductor layer 41. By providing an opening 6c in the solder resist layer 61, a conductor pad 4P is formed which is part of the conductor layer 41 but is exposed. The optical waveguide 1 and optical element E1 are arranged on the substrate 10. The optical element E1 includes an optical terminal E1a and a ball-shaped electrode E1b. The optical element E1 is mounted on the substrate 10 by connecting the electrode E1b to the conductor pad 4P at one end 1g of the optical waveguide 1, for example, using solder. In Figures 2A and 2B, the optical element E1 is arranged face-down (flip-chip mounting). The optical terminal E1a is positioned so that the upper surface of the core 31a of the core exposed portion 1a provided on the end 1g side of the optical waveguide 1 faces the terminal.

[0023] Furthermore, the optical coupling method between the core 3 and the optical component at the other end 1f of the optical waveguide 1 is not limited to adibatic coupling. For example, without providing a core exposure portion in the optical waveguide 1, end-face coupling may be used, in which the end face 3f of the core 3 and the optical terminal of the optical component are aligned and optically coupled. Alternatively, as shown in Figure 3, an optical element may also be placed at the other end 1f, and end-face coupling may be used, or a core exposure portion 1a may be provided on the other end 1f side, and adibatic coupling may be used at both ends of the optical waveguide 1. Moreover, an external connection such as an optical fiber or optical waveguide may be used instead of an optical element. That is, in the X direction, the regions may be arranged in the order of core exposure portion 1a, core non-exposure portion 1b, core exposure portion 1a, and adibatic coupling may be used at both ends of one end 1g and the other end 1f of the optical waveguide.

[0024] In Figures 1A to 2A, a protrusion R1 is formed in the element-less region 1d within the core-exposed portion 1a. Although two protrusions R1 are formed in the element-less region 1d, one or more may be formed. Here, a protrusion refers to a portion formed upward with respect to the upper surface of the lower cladding 21. The cross-sectional shape of the protrusion R1 in Figures 1B and 2B is rectangular, but the cross-sectional shape of the protrusion R1 is not limited. The planar shape of the protrusion R1 in Figures 1A and 2A is rectangular, but the planar shape of the protrusion R1 is not limited. In the figures, the protrusion R1 is formed in the element-less regions 1d on both sides of the element-placed region 1c in a direction (Y direction) perpendicular to the formation direction (X direction) of the core 3. The thickness T1 of the protrusion R1 is not particularly limited, but it is preferably greater than or equal to the height of the core 31a in the element-placed region 1c. Furthermore, it is more preferable that the thickness T1 (in the Z direction) of the protrusion R1 satisfies Equation 1 with respect to the thickness T2 (in the Z direction) of the upper cladding 22. 0.5≦T1 / T2≦1.0...Equation 1

[0025] As shown in Figures 1A and 1B, the protrusion R1 may be formed integrally with the upper cladding 22 formed in the core non-exposed portion 1b. In this case, the thickness T1 of the protrusion R1 is 0.5 ≤ T1 / T2 ≤ 1.0 relative to the thickness T2 of the upper cladding 22, satisfying Equation 1. Because the thickness T1 of the protrusion R1 satisfies Equation 1, the protrusion R1 is formed higher in the Z direction than the core 3. By forming the protrusion R1 in the element non-placement region 1d, the opportunity for other parts or tools to inadvertently come into contact with the core 3 during storage of the optical waveguide 1 or during work such as element mounting can be reduced, thereby suppressing damage to the core 3. Furthermore, when the transparent resin TR is filled between the optical element E1 and the optical waveguide 1 in the element placement region 1c, the protrusion R1 acts as a dam, suppressing the outflow of the transparent resin TR and stabilizing the optical coupling efficiency. Here, the thickness of core 3 is not particularly limited, but is preferably 1 to 20 μm, and more preferably 3 to 10 μm. The thickness T2 of the upper cladding 22 is not particularly limited, but is preferably 10 to 100 μm, and more preferably 15 to 50 μm. The thickness of the lower cladding 21 is not particularly limited, but is preferably 10 to 100 μm, and more preferably 15 to 50 μm. The thickness T1 of the protrusion is preferably greater than the thickness of core 31a. Furthermore, the thickness T1 of the protrusion is more preferably 125% or more of the thickness of core 31a. In addition, it is preferable that the protrusion is positioned so as not to contact the core. Therefore, since the protrusion is spaced apart from the core, the effects of thermal shrinkage of the protrusion do not affect the core. It is also preferable that the upper surface of the protrusion does not come into contact with the optical element.

[0026] The protrusion R1 may be formed with a size and shape that is more visually identifiable than the core 3. Specifically, the protrusion R1 may be formed with a width and / or length greater than the core 31a exposed on the core exposure portion 1a in a plan view. This allows it to be used as an alignment mark to adjust the positional relationship between the optical element E1 and the core 3 when mounting the optical element E1 to the optical waveguide 1. Furthermore, the upper surface of the protrusion R1 may have a different color from the core 3 and / or cladding 2. By changing the color, the identifiability of the alignment mark using the protrusion R1 can be improved, and the optical element E1 can be mounted on the substrate.

[0027] The material of the protrusion R1 is not particularly limited, but it is preferably made of a resin material. That is, the protrusion R1 can be made of, for example, a resin material, or a hybrid material containing a resin material and an inorganic material, such as an inorganic polymer. As shown in Figures 1A and 1B, the protrusion R1 formed integrally with the upper cladding 22 is made of the same material as the upper cladding 22. By being formed integrally, in the fabrication of the optical waveguide 1, the protrusion R1 can be formed simultaneously with the upper cladding 22 during the formation process of the upper cladding 22. In this case, the thickness T1 of the protrusion R1 is 0.5 ≤ T1 / T2 ≤ 1.0 with respect to the thickness T2 of the upper cladding 22.

[0028] Figure 4A shows a plan view illustrating a modified configuration of the optical waveguide 1 in the embodiment. Figure 4B shows a cross-sectional view taken along line III-III in Figure 4A. As shown in Figures 4A and 4B, in the optical waveguide 1, the protrusions R2 are located in the element-free regions 1d on both sides of the element-placement region 1c in the core-exposed region 1a, and are formed independently of the upper cladding 22. The cross-sectional shape of the protrusions R2 is rectangular, but the cross-sectional shape of the protrusions R2 is not limited. The planar shape of the protrusions R2 is rectangular, but the planar shape of the protrusions R2 is not limited. The planar shape of the protrusions R2 can be rectangular, square, circular, elliptical, etc., in addition to rectangular. The thickness T1 of the protrusions R2 is not particularly limited, but it is preferable that it is greater than or equal to the height of the core in the element-placement region 1c. Furthermore, it is more preferable that the thickness T1 (Z direction) of the protrusions R2 satisfies Equation 1 with respect to the thickness T2 (Z direction) of the upper cladding 22. 0.5≦T1 / T2≦1.0...Equation 1

[0029] Furthermore, the protrusion R2 may be formed integrally with the upper cladding 22 formed in the core non-exposed portion 1b, similar to Figures 1A and 1B. In this case, the thickness T1 of the protrusion R2 is 0.5 ≤ T1 / T2 ≤ 1.0 relative to the thickness T2 of the upper cladding 22, satisfying Equation 1. As the thickness T1 of the protrusion R2 satisfies Equation 1, the protrusion R2 is formed higher in the Z direction than the core 3. By forming the protrusion R2 in the element non-placement region 1d, the opportunity for other parts or tools to inadvertently come into contact with the core 3 during storage of the optical waveguide 1 or during work such as element mounting can be reduced, thereby suppressing damage to the core 3. In addition, when the transparent resin TR is filled between the optical element E1 and the optical waveguide 1 in the element placement region 1c, the protrusion R2 acts as a dam, suppressing the outflow of the transparent resin TR and stabilizing the optical coupling efficiency.

[0030] The material of the protrusion R2 is not particularly limited, but it is preferably made of a resin material. It may be made of the same resin material as the upper cladding 22, or it may be made of a different material. When the protrusion R2 is made of the same material as the upper cladding 22, the protrusion R2 can be formed at the same time as the upper cladding 22. As an example, when the resin film of the upper cladding 22 is formed, the area in which the protrusion R2 is formed may also be formed as a resin film, and then the protrusion R2 may be formed independently of the upper cladding 22 by a method such as photoetching.

[0031] If the protrusion R2 is formed from a different material than the upper cladding 22, the protrusion R2 is formed in a separate process from the formation of the upper cladding 22. For example, the protrusion R2 may be formed using a resin material different from the resin material of the upper cladding 22, or a resin material containing color. In this case, after the upper cladding 22 is formed, a resin layer for the protrusion R2 may be formed on the core exposed portion 1a using the resin material for the protrusion R2, and the protrusion R2 may be formed independently of the upper cladding 22 by a method such as photoetching. Furthermore, a film of resin or metal may be laminated onto the protrusion R2. In this case, the laminated film can be processed to create alignment marks, allowing the optical element to be mounted on the substrate. Alternatively, a component formed in advance from resin or a material other than resin may be placed as the protrusion R2 using adhesive.

[0032] Figure 5A shows a plan view illustrating a second modification of the configuration of the optical waveguide 1 in the embodiment. Figure 5B shows a cross-sectional view along line IV-IV in Figure 5A. As shown in Figures 5A and 5B, in the optical waveguide 1, the protrusion R3 is located only on one side of the element-less region 1d in the core-exposed portion 1a and is formed integrally with the upper cladding 22. The thickness T1 of the protrusion R3 is not particularly limited, but is preferably greater than or equal to the height of the core 31a in the element-placed region 1c. Furthermore, it is more preferable that the thickness T1 (Z direction) of the protrusion R3 satisfies Equation 1 with respect to the thickness T2 (Z direction) of the upper cladding 22. 0.5≦T1 / T2≦1.0...Equation 1

[0033] Furthermore, similar to Figures 1A and 1B, the protrusion R3 is formed integrally with the upper cladding 22 formed on the core non-exposed portion 1b. As a result, the thickness T1 of the protrusion R3 is 0.5 ≤ T1 / T2 ≤ 1.0 relative to the thickness T2 of the upper cladding 22, satisfying Equation 1. Because the thickness T1 of the protrusion R3 satisfies Equation 1, the protrusion R3 is formed higher in the Z direction than the core 3.

[0034] Furthermore, as shown in Figure 5C, the optical waveguide 1 may have two sets of cores 3 formed in parallel on the upper surface of the lower cladding 21. In Figure 5C, the optical waveguide 1 is formed from a core-exposed portion 1a and a core-non-exposed portion 1b, similar to Figure 5A, and the upper cladding 22 is formed to cover the two sets of cores 3 and the lower cladding 21 in the core-non-exposed portion 1b. In the core-exposed portion 1a, a core 31a, which is part of the two sets of cores 3, and a lower cladding 21a, which is part of the lower cladding 21, are exposed. The core-exposed portion 1a has two element placement regions 1c so that two optical elements E1 can be placed corresponding to the two sets of cores 3, and has element-non-placement regions 1d on both sides thereof. In Figure 5C, a protrusion R3 is placed on only one side of each element placement region 1c and is formed integrally with the upper cladding 22. This reduces the chances of other components or tools inadvertently coming into contact with the core 3 during storage of the optical waveguide 1 or during operations such as element mounting, thereby suppressing damage to the core 3. Furthermore, when the transparent resin TR is filled between the optical element E1 and the optical waveguide 1 in the element placement region 1c, the protrusion R3 acts as a dam, suppressing the outflow of the transparent resin TR and stabilizing the optical coupling efficiency. The optical waveguide 1 may have three or more sets of cores 3 formed in parallel on the upper surface of the lower cladding 21, and the protrusions R3 may be placed at both ends thereof.

[0035] The protrusion R3 may be formed with a size and shape that is more visually identifiable than the core 3. Specifically, the protrusion R3 may be formed with a width and / or length greater than the core 31a exposed on the core exposure portion 1a in a plan view. This allows it to be used as an alignment mark to adjust the positional relationship between the optical element E1 and the core 3 when mounting the optical element E1 to the optical waveguide 1. Furthermore, the upper surface of the protrusion R3 may have a different color from the core 3 and / or cladding 2. By changing the color, the identifiability of the alignment mark using the protrusion R3 can be improved, and the optical element E1 can be mounted on the substrate.

[0036] The material of the protrusion R3 is not particularly limited, but it is preferably made of a resin material. That is, the protrusion R3 can be made of, for example, a resin material, or a hybrid material containing a resin material and an inorganic material, such as an inorganic polymer. As shown in Figures 5A, 5B, and 5C, the protrusion R3 formed integrally with the upper cladding 22 is made of the same material as the upper cladding 22. By being formed integrally, in the fabrication of the optical waveguide 1, the protrusion R3 can be formed simultaneously with the upper cladding 22 during the formation process of the upper cladding 22. In this case, the thickness T1 of the protrusion R3 is 0.5 ≤ T1 / T2 ≤ 1.0 with respect to the thickness T2 of the upper cladding 22.

[0037] Figure 6A shows a plan view illustrating a third modification of the configuration of the optical waveguide 1 in the embodiment. Figure 6B shows a cross-sectional view of Figure 6A along the VV line. As shown in Figures 6A and 6B, in the optical waveguide 1, the protrusion R4 is located only on one side of the element-less region 1d in the core-exposed portion 1a and is formed independently of the upper cladding 22. The thickness T1 of the protrusion R4 is not particularly limited, but is preferably greater than or equal to the height of the core in the element-placed region 1c. Furthermore, it is more preferable that the thickness T1 (Z direction) of the protrusion R4 satisfies Equation 1 with respect to the thickness T2 (Z direction) of the upper cladding 22. 0.5≦T1 / T2≦1.0...Equation 1

[0038] Furthermore, the protrusion R4 may be formed integrally with the upper cladding 22 formed on the core non-exposed portion 1b, similar to Figures 1A and 1B. In this case, the thickness T1 of the protrusion R4 is 0.5 ≤ T1 / T2 ≤ 1.0 with respect to the thickness T2 of the upper cladding 22, satisfying Equation 1. As the thickness T1 of the protrusion R4 satisfies Equation 1, the protrusion R4 is formed to be higher in the Z direction than the core 3.

[0039] Furthermore, as shown in Figure 6C, the optical waveguide 1 may have two sets of cores 3 formed in parallel on the upper surface of the lower cladding 21. In Figure 6C, the optical waveguide 1 is formed from a core-exposed portion 1a and a core-non-exposed portion 1b, similar to Figure 6A, and the upper cladding 22 is formed in the core-non-exposed portion 1b so as to cover the two sets of cores 3 and the lower cladding 21. In the core-exposed portion 1a, a core 31a, which is part of the two sets of cores 3, and a lower cladding 21a, which is part of the lower cladding 21, are exposed. The core-exposed portion 1a has two element placement regions 1c so that two optical elements E1 can be placed corresponding to the two sets of cores 3, and has element-non-placement regions 1d on both sides thereof. In Figure 6C, a protrusion R4 is placed on only one side of each element placement region 1c and is formed independently of the upper cladding 22. This reduces the chances of other components or tools inadvertently coming into contact with the core 3 during storage of the optical waveguide 1 or during operations such as element mounting, thereby suppressing damage to the core 3. Furthermore, when the transparent resin TR is filled between the optical element E1 and the optical waveguide 1 in the element placement region 1c, the protrusions R4 act as dams, suppressing the outflow of the transparent resin TR and stabilizing the optical coupling efficiency. The optical waveguide 1 may have three or more sets of cores 3 formed in parallel on the upper surface of the lower cladding 21, and the protrusions R4 may be placed at both ends thereof.

[0040] The material of the protrusion R4 is not particularly limited, but it is preferably made of a resin material. It may be made of the same resin material as the upper cladding 22, or it may be made of a different material. When the protrusion R4 is made of the same material as the upper cladding 22, the protrusion R4 can be formed at the same time as the upper cladding 22. As an example, when the resin film of the upper cladding 22 is formed, the area in which the protrusion R4 is formed may also be formed as a resin film, and then the protrusion R4 may be formed independently of the upper cladding 22 by a method such as photoetching. In this case, the thickness T1 of the protrusion R4 is 0.5 ≤ T1 / T2 ≤ 1.0 with respect to the thickness T2 of the upper cladding 22.

[0041] If the protrusion R4 is formed from a different material than the upper cladding 22, the protrusion R4 is formed in a separate process from the formation of the upper cladding 22. For example, the protrusion R4 may be formed using a resin material different from the resin material of the upper cladding 22, or a resin material containing color. In this case, after the upper cladding 22 is formed, a resin layer for the protrusion R4 may be formed on the core exposed portion 1a using the resin material for the protrusion R4, and the protrusion R4 may be formed independently of the upper cladding 22 by a method such as photoetching. Furthermore, a film of resin or metal may be laminated onto the protrusion R4. At this time, the laminated film can be processed to create alignment marks, allowing the optical element to be mounted on the substrate. Alternatively, a component with the protrusion R4 pre-formed from resin or a material other than resin may be placed using an adhesive.

[0042] Next, the wiring board of the embodiment will be described in detail with reference to the drawings. Figure 7 shows a cross-sectional view of a wiring board 100 including an optical waveguide 1 arranged on a substrate 10. Note that the optical waveguide 1 and wiring board 100 shown in Figure 7 are merely examples of the optical waveguide and wiring board of the embodiment. The lamination structure and number of layers of the substrate on which the optical waveguide is arranged are not limited to the lamination structure and number of layers of the substrate 10 shown in Figure 7.

[0043] As shown in Figure 7, the wiring board 100 includes a substrate 10 and an optical waveguide 1 disposed on the substrate 10. The substrate 10 includes alternatingly stacked insulating layers and conductive layers. The substrate 10 includes conductive layers 41-43 as conductive layers and insulating layers 51, 52 as insulating layers. The substrate 10 has a mounting surface U for the optical element E1. The substrate 10 has conductive pads 4P included in the conductive layer 41 on the mounting surface U. The optical waveguide 1 is formed on the mounting surface U of the substrate 10.

[0044] The conductor layers 41-43 and insulating layers 51 and 52 are stacked in the order of conductor layer 43, insulating layer 52, conductor layer 42, insulating layer 51, and conductor layer 41, from the bottom to the mounting surface U side of the substrate 10. Conductor layer 41 and conductor layer 42 are connected by via conductors 71 that penetrate the insulating layer 51. Conductor layer 42 and conductor layer 43 are connected by via conductors 72 that penetrate the insulating layer 52. The substrate 10 includes a solder resist layer 61 covering the conductor layer 41 and insulating layer 51, and a solder resist layer 62 covering the conductor layer 43 and insulating layer 52. The substrate 10 includes bumps 8 that are connected to each conductor pad of the conductor layer 43 and protrude from the solder resist layer 62. The bumps 8 are made of a conductor such as solder and are used for electrical and mechanical connections between the substrate 10 and external components (for example, the motherboard of any electrical device). Note that the substrate 10 may be used as a motherboard without bumps 8. Furthermore, wiring is formed by the conductor layer.

[0045] The insulating layers 51 and 52 are formed using insulating resins such as epoxy resin, polyimide resin, BT resin (bismaleimide-triazine resin), polyphenylene ether resin, and phenolic resin. The insulating layers 51 and 52 may also contain any of the following: fluororesin, liquid crystal polymer (LCP), fluoroethylene resin (PTFE), polyester resin (PE), and modified polyimide resin (MPI). The insulating layers 51 and 52 may also contain inorganic fillers such as fine particles made of silica (SiO2), alumina, or mullite. The insulating layers 51 and 52 may also contain a core material (reinforcement material) made of glass fiber or aramid fiber. Note that these resins are merely examples of materials that can form insulating layers. Each insulating layer can be formed from any material capable of providing insulation between the conductive layers in the substrate 10.

[0046] The conductor layers 41-43 and via conductors 71 and 72 are formed using any material having appropriate conductivity. The conductor layers 41-43 and via conductors 71 and 72 may have a single-layer structure or a multilayer structure including two or more films. For example, the conductor layers 41-43 and via conductors 71 and 72 have a two-layer structure consisting of a metal film layer and a plating layer formed on the metal film layer. The metal film layer is preferably a sputtered film layer. The plating layer is preferably an electroplated layer with the metal film layer as the power supply layer. The metal film layer is preferably formed using a conductive material including titanium, titanium alloy, nickel, nickel alloy, copper, or copper alloy. The plating layer is preferably formed using a conductive material including copper or copper alloy.

[0047] The solder resist layers 61 and 62 are formed using, for example, a photosensitive polyimide resin or epoxy resin, and form an insulating layer on the surface of the substrate 10.

[0048] As shown in Figure 7, the optical waveguide 1 is formed on the solder resist layer 61 that constitutes the surface layer of the substrate 10. The optical waveguide 1 is an optical waveguide of an embodiment such as the optical waveguide 1 shown in Figures 1A to 6B. That is, the optical waveguide 1 in Figure 7 includes a stacked lower cladding 21, a core 3, and an upper cladding 22, and has a core exposed portion 1a and a core non-exposed portion 1b, an element placement region 1c and an element non-placement region 1d (not shown), and has a protrusion R1 in the element non-placement region 1d.

[0049] An optical element E1 is placed on the substrate 10. The optical element E1 is an optical component having a photoelectric conversion function, as described in Figure 1A and other figures. The optical element E1 is equipped with an optical terminal E1a and a ball-shaped electrode E1b. Examples of optical elements E1 include light-emitting elements such as LEDs, OLEDs, LDs, and VCSELs, and light-receiving elements such as PDs.

[0050] An opening 6c is formed in the solder resist layer 61, and the upper surface of the conductor pad 4P, which is part of the conductor layer 41, is exposed at the bottom of the opening 6c. An optical element E1 is placed on the solder resist layer 61, and the optical element E1 is mounted on the substrate 10 by being electrically connected to the conductor pad 4P via an electrode E1b. In Figure 7, the optical element E1 is flip-chip mounted. The optical terminal E1a and the upper surface of the core 3 in the core exposed portion 1a of the optical waveguide 1 are positioned opposite each other to achieve adibatic coupling. When the optical element E1 is a light-emitting element, the optical element E1 generates an optical signal based on an electrical signal input to the electrode E1b, and emits this optical signal from the optical terminal E1a, which functions as a light-emitting part, toward the core 3. When the optical element E1 is a light-receiving element, the optical element E1 receives an optical signal from the optical terminal E1a, which functions as a light-receiving part, generates an electrical signal based on that optical signal, and outputs it from the electrode E1b.

[0051] In the optical waveguide 1, the protrusion R1 is formed integrally with the upper cladding 22 in the element-less regions 1d on both sides of the element-placement region 1c within the core-exposed region 1a. Furthermore, the thickness T1 (Z direction) of the protrusion R1 preferably satisfies Equation 1 with respect to the thickness T2 (Z direction) of the upper cladding 22. This makes it possible to suppress damage to the core 3 during storage of the optical waveguide or during operations such as element mounting with a simpler configuration. In addition, it is possible to suppress the outflow of the transparent resin TR filled between the optical element E1 and the optical waveguide 1 with a simpler configuration, thereby stabilizing the optical coupling efficiency.

[0052] The protrusion R1 may be formed in a size and shape that is more visually identifiable than the core 3, and preferably, the upper surface of the protrusion R1 may be formed in a different color from the core 3 and / or cladding 2. This allows it to be used as an alignment mark to adjust the positional relationship between the optical element E1 and the core 3 when mounting the optical element E1 to the optical waveguide 1, enabling the optical element E1 to be placed in the optical waveguide 1 with high positional accuracy.

[0053] The protrusion R1 can be formed from any material, but preferably from a resin material. The protrusion R1, which is formed integrally with the upper cladding 22, may more preferably be formed from the same material as the upper cladding 22. This allows the protrusion R1 to be formed simultaneously with the upper cladding 22 during the fabrication of the optical waveguide 1.

[0054] As described above, in the optical waveguide 1 of this embodiment, protrusions are formed on both sides or one side of the element placement region 1c of the core exposed portion 1a related to adiabatic coupling, and preferably, their thickness is appropriately set in relation to the thickness of the upper cladding 22. This is thought to prevent components and tools from coming into contact with the core 3 during storage of the optical waveguide 1 or during work such as element mounting, thereby suppressing damage to the core 3. [Explanation of Symbols]

[0055] 1 Optical waveguide 1a Core exposed portion 1b Non-exposed core portion 1c Element placement area 1d element non-placement region 2 clad 21, 21a, 21b Lower cladding 22 Upper cladding 3, 31a, 31b cores 10 circuit boards 41, 42, 43 Conductor layers 51, 52 Insulating layer 61, 62 Solder Resist Layer 71, 72 via conductors 100 Wiring boards R1, R2, R3, R4 protrusions E1, E2 optical elements TR transparent resin T1 Thickness of the protrusion T2 Upper cladding thickness

Claims

1. An optical waveguide comprising a lower cladding, a core, and an upper cladding, The optical waveguide consists of a core exposed portion and a core non-exposed portion. In the core exposed portion, the upper surface of the core is exposed. In the core non-exposed portion, the upper cladding is formed on the core and the lower cladding. Within the exposed core portion, an element placement region and an element non-placement region are provided. The element arrangement region is an area in which optical elements optically connected to the core are arranged. A protrusion is formed in the region where the element is not placed.

2. The optical waveguide according to claim 1, The aforementioned protrusion is formed integrally with the upper cladding.

3. The optical waveguide according to claim 1, The aforementioned protrusion is formed independently of the upper cladding.

4. The optical waveguide according to claim 1, The thickness T1 of the protrusion and the thickness T2 of the upper cladding satisfy the relationship in Equation 1. 0.5≦T1 / T2≦1.0 ...Formula 1

5. The optical waveguide according to claim 1, The aforementioned protrusion is formed of a resin material.

6. The optical waveguide according to claim 1, The aforementioned protrusion is formed from the same material as the upper cladding.

7. The optical waveguide according to claim 1, The aforementioned protrusions are located on one or both sides of the element arrangement region.

8. The optical waveguide according to claim 1, The aforementioned protrusions are used as alignment marks.

9. A substrate including an insulating layer and a conductive layer formed on the insulating layer, The optical waveguide according to claim 1, disposed on the substrate, A wiring board that includes this component.

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