Optical waveguides and wiring boards

Abstract

To improve efficiency in optical coupling via a waveguide.SOLUTION: An optical waveguide 5 includes: a core unit 51 that has a first end 5a, and a second end 5b in a side opposite to the first end 5a, and transmits light between the first end 5a and the second end 5b; and a clad unit 52 surrounding the core unit 51. The clad unit 52 includes a first clad 521 having a surface 52a with a recess 50, and a second clad 522 laminated on the first clad 521, the core unit 51 includes a first part 511 that fills the recess 50, and a second part 512 that is formed on the first part 511 and the surface 52a and extends to the outside of the recess 50 on the surface 52a, and thicknesses T21, T23 of the second part 512 change between the first end 5a and the second end 5b.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses an optical waveguide connector including a mounting substrate, an optical waveguide mounted on the mounting substrate, and an optical interposer optically connected to the optical waveguide. The optical waveguide includes a core layer including a core portion through which light propagates and a side clad portion adjacent to the side surface of the core portion. The upper surface of the core layer faces the optical interposer, so that the core portion and the light guiding portion of the optical interposer are optically coupled.

[0003] Patent Document 2 discloses an optical waveguide connector including a mounting substrate, an optical waveguide mounted on the mounting substrate, and an optical element optically connected to the optical waveguide. The optical waveguide includes a core layer including a core portion through which light propagates and a side clad portion adjacent to the side surface of the core portion, and is joined via a mirror. The upper surface of the core layer is flattened, so that the core portion and the optical element are optically coupled.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the optical waveguide disclosed in Patent Document 1, the side cladding portion protrudes toward the optical interposer side from the core portion on the upper surface of the core layer. That is, on the upper surface of the core layer facing the optical interposer, the core portion is recessed in the opposite direction to the optical interposer side from the side cladding portion. Therefore, even if the optical interposer and the optical waveguide are placed close to each other, high optical coupling efficiency may not be obtained between the core portion and the optical guide portion of the optical interposer. Furthermore, in the optical waveguide disclosed in Patent Document 2, an optical element is joined to a tapered waveguide to which optical fibers are connected via a mirror, but the desired optical transmission effect may not be obtained in the core portion. [Means for solving the problem]

[0006] The optical waveguide of the present invention includes a core portion having a first end and a second end opposite the first end, which transmits light between the first end and the second end, and a cladding portion surrounding the core portion. The cladding portion includes a first cladding having a surface with recesses and a second cladding laminated on the first cladding, and the core portion has a first portion that fills the recesses and a second portion formed on the first portion and the surface and extending outward on the surface toward the recesses, wherein the thickness of the second portion changes between the first end and the second end.

[0007] The wiring board of the present invention includes a circuit board including an insulating layer and a conductor layer, and an optical waveguide placed on the circuit board. The optical waveguide includes a core portion having a first end and a second end opposite the first end and transmitting light between the first end and the second end, and a cladding portion surrounding the core portion, the cladding portion including a first cladding having a surface with recesses and a second cladding laminated on the first cladding, the core portion having a first portion filling the recesses and a second portion formed on the first portion and the surface and extending outward on the surface toward the outside of the recesses, the thickness of the second portion varying between the first end and the second end.

[0008] According to embodiments of the present invention, it is presumed that optical components connected optically via an optical waveguide or via an optical waveguide provided on a wiring board can be coupled with high optical coupling efficiency. [Brief explanation of the drawing]

[0009] [Figure 1] A plan view showing an example of an optical waveguide according to one embodiment of the present invention. [Figure 2] Front view of the optical waveguide in the example shown in Figure 1. [Figure 3] Cross-sectional view of the example optical waveguide in Figure 1 along line III-III. [Figure 4] A partially enlarged view of the cross-section of the optical waveguide at the IV-IV line in the example shown in Figure 1. [Figure 5A] A magnified view of the side of the first end of the optical waveguide in the example shown in Figure 1. [Figure 5B] A partially enlarged view of the side of the second end of the optical waveguide in the example shown in Figure 1. [Figure 6] Enlarged view of Figure 3. [Figure 7] A cross-sectional view showing a modified example of the core portion of an optical waveguide according to one embodiment. [Figure 8] A plan view showing a first modified example of an optical waveguide according to one embodiment. [Figure 9] A partially enlarged view of the side of the second end of a modified example of the core section in Figure 8. [Figure 10] A cross-sectional view showing a second modified example of an optical waveguide according to one embodiment. [Figure 11] A cross-sectional view showing an example of a wiring board according to one embodiment of the present invention. [Figure 12] Figure 11 is a plan view showing an example of a wiring board in a plan view. [Figure 13A] A cross-sectional view showing an example of the manufacturing process for an optical waveguide according to the embodiment. [Figure 13B] A cross-sectional view showing an example of the manufacturing process for an optical waveguide according to the embodiment. [Figure 13C] A cross-sectional view showing an example of the manufacturing process for an optical waveguide according to the embodiment. [Figure 13D] A plan view showing an example of the manufacturing process for an optical waveguide according to the embodiment. [Figure 13E]Cross-sectional view showing an example of the manufacturing process of the optical waveguide according to the embodiment. [Figure 13F] Cross-sectional view showing an example of the manufacturing process of the optical waveguide according to the embodiment. [Figure 14A] Cross-sectional view showing an example of the manufacturing process of the wiring board according to the embodiment. [Figure 14B] Cross-sectional view showing an example of the manufacturing process of the wiring board according to the embodiment. [Figure 14C] Cross-sectional view showing an example of the manufacturing process of the wiring board according to the embodiment. [Figure 14D] Cross-sectional view showing an example of the manufacturing process of the wiring board according to the embodiment. [Figure 14E] Cross-sectional view showing an example of the manufacturing process of the wiring board according to the embodiment.

Mode for Carrying Out the Invention

[0010] The optical waveguide and wiring board according to the embodiment of the present invention will be described while referring to the drawings. In each of the drawings referred to in the following description, specific parts may be enlarged so that the disclosed embodiments can be easily understood, and the components may not be drawn at the exact ratio between each other in terms of size and length.

[0011] <Structure of the Optical Waveguide of the Embodiment> FIG. 1 shows a plan view of an optical waveguide 5 which is an example of the optical waveguide according to an embodiment. An enlarged view of part I of FIG. 1 is shown within a circle B drawn by a one-dot chain line in FIG. 1. FIG. 2 shows a front view of the optical waveguide 5 of FIG. 1 (view from the lower side in FIG. 1), and FIG. 3 shows a cross-section of the optical waveguide 5 taken along line III-III of FIG. 1. Note that the optical waveguide 5 illustrated in FIG. 1 and the like is merely an example of the optical waveguide of the present embodiment. The structure of the optical waveguide of the embodiment is not limited to the structure shown in each drawing such as FIG. 1.

[0012] As shown in Figures 1 to 3, the optical waveguide 5 of this embodiment includes a light-transmitting core portion 51 and a cladding portion 52 surrounding the core portion 51. The core portion 51 has two ends in the direction of extension of the core portion 51 (a first end portion 5a and a second end portion 5b which is the end opposite to the first end portion 5a). The core portion 51 transmits light between the first end portion 5a and the second end portion 5b. That is, light propagating through the core portion 51 enters from the exposed surface of the core portion 51 at the first end portion 5a or the second end portion 5b and exits from the exposed surface of the core portion 51 at the first end portion 5a or the second end portion 5b.

[0013] The cladding portion 52 includes a first cladding 521 and a second cladding 522 laminated on the first cladding 521. The lamination direction of the first cladding 521 and the second cladding 522 is also referred to as the "Z direction" below. In the description of the optical waveguide of the embodiment, the side of the first cladding 521 is also referred to as the "lower side" or simply "down," and the side of the second cladding 522 is also referred to as the "upper side" or simply "up." The cladding portion 52 is provided around the core portion 51 and sandwiches the core portion 51 in any direction perpendicular to the extension direction of the core portion 51, that is, the direction of light propagation within the core portion 51 (collectively referred to as the "+X direction or -X direction"). In Figure 1, for ease of understanding, the outer edge of the core portion 51, including the portion covered by the second cladding 522, is shown with a solid line, while the outer edge 50a of the groove-shaped recess 50 (see Figure 4), which will be described later, is shown with a dashed line.

[0014] In the examples shown in Figures 1 to 3, the second cladding 522 of the cladding portion 52 is not formed up to the outer edge on the first end 5a side of the optical waveguide 5. Therefore, at the first end 5a, as shown in Figures 2 and 3, the surface 51a of the core portion 51 on the second cladding 522 side (the surface opposite to the first cladding 521) is exposed and not covered by the cladding portion 52. Similarly, at the first end 5a, as shown in Figures 1 and 2, the surface 52a of the first cladding 521 on the second cladding 522 side is also exposed and not covered by the second cladding 522.

[0015] The optical waveguide 5, i.e., the core portion 51 and the cladding portion 52, is formed from any translucent material. The optical waveguide 5 can be composed of, for example, an organic material (organic substance), an inorganic material (inorganic substance), or a hybrid material containing organic and inorganic components, such as an inorganic polymer. Examples of inorganic materials include quartz glass and silicon, while examples of organic materials include acrylic resins such as polymethyl methacrylate (PMMA), polyimide resins, polyamide resins, polyether resins, and epoxy resins. An optical waveguide 5 composed of organic material tends to be lightweight and have high toughness.

[0016] The core portion 51 and the cladding portion 52 may be made of different materials or of the same type of material. However, the core portion 51 is made of a material with a higher refractive index than the material used for the cladding portion 52, so that total internal reflection of light is possible at the interface between the core portion 51 and the cladding portion 52. The core portion 51 and the cladding portion 52 may be formed from materials with the same refractive index and then subjected to appropriate treatment to make their refractive indices different. The optical waveguide 5 may be formed on a support that supports the optical waveguide 5 during the manufacturing process, such as a support plate 6 (see Figure 13A) described later, and then used separately from the support, or used together with the support.

[0017] When the optical waveguide 5 is in use, the core portion 51 is optically coupled at the first end 5a and the second end 5b, respectively, to optical components such as photoelectric conversion components, including a semiconductor device containing a photoelectric conversion element, and / or connector members that connect to the outside of the waveguide, such as optical fibers and optical connectors. That is, the core portion 51 of the optical waveguide 5 is positioned relative to each optical component such that there is a positional relationship between the core portion 51 and these optical components that allows for the transmission and reception of light. In Figures 1 and 2, a component E1 equipped with a photoelectric conversion element (not shown) is shown by a dashed line as an example of an optical component optically coupled to the core portion 51 at the first end 5a of the core portion 51. On the other hand, a plurality of optical fibers F are shown by a dashed line as an example of an optical component optically coupled to the core portion 51 at the second end 5b. Note that "optically coupled" will also be referred to as "optically uncoupled" below.

[0018] Component E1 includes a light-receiving or light-emitting section E1b, as shown within circle B in Figure 1 and in Figure 2, which is the part into which light is incident or emitted from component E1. Component E1 is optically coupled with the core section 51 at the light-receiving or light-emitting section E1b. Light propagating through the optical fiber F enters the optical waveguide 5 from the second end 5b of the core section 51, propagates within the core section 51, and enters component E1 through its first end 5a via the light-receiving or light-emitting section E1b. On the other hand, light emitted from the light-receiving or light-emitting section E1b enters the optical waveguide 5 from the first end 5a, propagates within the core section 51, and exits to the optical fiber F from the second end 5b.

[0019] As an example, the optical waveguide 5 has eight parallel core sections 51 as shown in Figure 1. The optical waveguide 5 of this embodiment may have any number of core sections 51 in this manner. In that case, component E1 may include a number of light-receiving or light-emitting sections E1b corresponding to the number of core sections 51. In Figure 1, the arrangement pitch P1 at the first end 5a of the multiple core sections 51 is smaller than the arrangement pitch P2 at the second end 5b. For example, the multiple optical fibers F coupled with the core section 51 at the second end 5b may not be arranged at a pitch as small as the arrangement pitch of the multiple light-receiving or light-emitting sections E1b provided in component E1. In the example of Figure 1, the multiple core sections 51 are arranged at a larger pitch at the second end 5b than at the first end 5a. Therefore, it is considered that the core sections 51 and component E1 or optical fibers F are appropriately coupled at the first end 5a and the second end 5b, respectively, without requiring a separate pitch conversion means.

[0020] For example, the arrangement pitch P1 of the core portion 51 at the first end 5a is preferably 10 μm or more and 100 μm or less, and 20 μm or more and 80 μm or less. Similarly, the arrangement pitch P2 of the core portion 51 at the second end 5b is preferably, for example, 50 μm or more and 300 μm or less, and 100 μm or more and 250 μm or less. However, the arrangement pitch of the core portion 51 at each end is not limited to these numerical examples.

[0021] In the optical waveguide 5 of this embodiment, as shown in Figures 2 and 3, the core portion 51 is formed up to the second cladding 522 side of the interface IF between the first cladding 521 and the second cladding 522 of the core portion 51. That is, in Figure 2, the dashed line indicating the surface 51a of the core portion 51 on the second cladding 522 side, which is hidden by the cladding portion 52, is located on the second cladding 522 side of the interface IF between the first cladding 521 and the second cladding 522. The surface 51a of the core portion 51 exposed at the first end 5a is located on the second cladding 522 side in the Z direction, beyond the surface 52a of the first cladding 521. Also, in Figure 3, the dashed line indicating the interface IF is located on the first cladding 521 side of the surface 51a of the core portion 51.

[0022] The core portion 51 of the optical waveguide 5 of this embodiment, formed in this manner, will be further described with reference to Figures 4, 5A, 5B, and 6. Figure 4 is an enlarged view of a portion of the cross-section of the optical waveguide 5 along the IV-IV line in Figure 1, while Figures 5A and 5B show a portion of the side surface on the first end 5a side and a portion of the side surface on the second end 5b side of the optical waveguide 5, respectively. Figures 4, 5A, and 5B show only the side surfaces or cross-sections of two of the multiple core portions 51 included in the optical waveguide 5 and their surrounding areas, respectively. Figure 6 is an enlarged view of the cross-section shown in Figure 3.

[0023] In the optical waveguide of the embodiment, as shown in Figures 4 to 6, the surface 52a of the first cladding 521 has a recess 50. The core portion 51 has a first portion 511 and a second portion 512 that fill the recess 50. The second portion 512 is formed on the first portion 511 and on the surface 52a of the first cladding 521. That is, the second portion 512 protrudes toward the second cladding 522 side from the surface 52a of the first cladding 521 and penetrates into the second cladding 522. As a result, the core portion 51 protrudes toward the second cladding 522 side from the interface IF between the first cladding 521 and the second cladding 522. Therefore, the thickness of the portion of the core 51 that overlaps with the recess 50 in a plan view at any point from the first end 5a shown in Figure 5A to the second end 5b shown in Figure 5B (thicknesses T12, T11, T13, etc. in Figures 4, 5A, and 5B) is greater than the depth of the recess 50. Note that "plan view" means viewing the object with a line of sight along the Z direction.

[0024] The recess 50 may have a groove-like feature extending between the first end 5a and the second end 5b of the core portion 51, as shown in Figures 4, 5A, and 5B. The groove-like recess 50 has two opposing outer edges (walls) 50a, each aligned in the direction in which the recess 50 extends. The second portion 512 of the core portion 51, formed on the surface 52a, extends from above the recess 50 outwards along the surface 52a. That is, the second portion 512 extends beyond the outer edges 50a of the recess 50. The second portion 512 covers the surface 52a of the first cladding 521 around the recess 50. In examples such as Figure 4, the second portion 512 extends from both of the two opposing outer edges 50a of the recess 50 outwards along the surface 52a.

[0025] The first portion 511 of the core 51 in the example shown in Figure 4 has a substantially rectangular cross-sectional shape, or it may have a substantially square cross-sectional shape. The first portion 511 with a substantially rectangular cross-sectional shape has a width (the distance between opposing outer edges of the first portion 511 in a direction perpendicular to the direction of light propagation in a plan view) and a thickness. The width and thickness of the first portion 511 illustrated in Figure 4 are substantially constant from the first end 5a to the second end 5b, respectively. The width and thickness of the first portion 511 of the core 51 may be, for example, 1 μm or more and 15 μm or less, or 3 μm or more and 10 μm or less, respectively.

[0026] In this embodiment, the core portion 51 has a second portion 512 on top of the first portion 511 that fills the recess 50 of the first cladding 521. Therefore, the light-receiving or light-emitting portion of an optical component, such as the light-receiving or light-emitting portion E1b of component E1 (see Figure 5A), can be brought into close proximity to the core portion 51. As a result, the core portion 51 and the optical component can be coupled with higher efficiency compared to the aforementioned Patent Documents 1 and 2. Furthermore, optical components such as component E1 and optical fiber F (see Figure 1), which are optically connected via the optical waveguide 5, can be optically connected with high light transmission efficiency.

[0027] Furthermore, in this embodiment, as described above, the second portion 512 of the core portion 51 extends from above the recess 50 to the outside of the recess 50 on the surface 52a. That is, the width of the core portion 51 (the length between opposing outer walls of each core portion 51 in a direction perpendicular to the direction of light propagation in a plan view) is wider on the surface 52a of the first cladding 521 than within the first cladding 521. Therefore, even if the alignment of the optical component such as part E1 and the core portion 51 is slightly misaligned in the direction along the width of the core portion 51 (indicated by arrow Y in Figure 5A), it is considered that light emitted from one of the optical component and the core portion 51 is likely to easily enter the other. In other words, even if such a misalignment occurs, it is considered that the effective optical coupling efficiency between the optical component and the core portion 51 is likely to be easily maintained. In particular, in the examples of Figures 4, 5A, and 5B, the second portion 512 extends outward from both of the two outer edges 50a of the recess 50. Therefore, even if the alignment between the optical component and the core portion 51 is misaligned in any direction along the width of the core portion 51, the effective optical coupling efficiency is unlikely to decrease.

[0028] Furthermore, in this embodiment, since the core portion 51 has a second portion 512, it is easier to maintain a desired transmission mode in the optical waveguide 5. For example, in an optical guide member such as an optical waveguide 5, the size (thickness) of the cross-section of the optical path, such as the core portion 51 through which light actually propagates, is selected according to the refractive index difference between the constituent material of the optical path and the constituent material of the cladding portion 52 surrounding the optical path. That is, by realizing a core portion 51 with an appropriate cross-section, an optical waveguide 5 that propagates light in an optimal transmission mode, such as single mode, can be obtained. However, if the core portion 51 consists only of the first portion 511 filling the recess 50, it may be difficult to obtain the desired cross-sectional size of the core portion 51 due to the deformation of the first cladding 521 and / or the thermal contraction of the first portion 511 itself within the recess 50. As a result, the transmission mode may not be optimal, and the optical waveguide may not propagate light. In contrast, in this embodiment, since the core portion 51 has a second portion 512 in addition to the first portion 511, deviations from the desired size of the cross-section of the core portion 51 due to thermal shrinkage, etc., can be compensated for. As a result, in this embodiment, it is easier to realize the optimal transmission mode. Furthermore, even if the core portion 51 is formed of an organic material such as resin and some film thinning (a phenomenon in which the film thickness becomes less than a predetermined value) occurs during the manufacturing process, the desired cross-sectional size of the core portion 51 can be obtained, and the effective photocoupling efficiency can be maintained.

[0029] Furthermore, in the optical waveguide of the embodiment, as shown in Figures 4 to 6, the thickness of the second portion 512 of the core portion 51 changes between the first end 5a and the second end 5b. Therefore, in the example of Figures 4 to 6, the thickness T21 of the second portion 512 of the core portion 51 at the end face on the first end 5a side is different from the thickness T23 of the second portion 512 at the end face on the second end 5b side. Also, the thickness T21 of the second portion 512 at the end face on the first end 5a side is different from the thickness T23 of the second portion 512 at the end face on the second end 5b side, and the thickness T22 of the second portion 512 in the region between the first end 5a and the second end 5b shown in Figure 4 is different from each other. The thickness of the second portion 512 of the core portion 51 is the distance in the Z direction between the surface 52a of the first cladding 521 on the second cladding 522 side and the surface 51a of the core portion 51 on the second cladding 522 side (the surface facing the opposite side from the first cladding 521).

[0030] In the optical waveguide 5 of this embodiment, the thickness of the second portion 512 of the core portion 51 changes between the first end 5a and the second end 5b. Therefore, when the optical waveguide 5 is optically coupled with an optical component such as component E1 in the manner illustrated in Figure 2, positioning the end containing the thicker second portion 512 towards the optical component makes it easier to bring the optical component and the core portion 51 into close proximity. For example, since the thicker second portion 512 faces the light-receiving or light-emitting part of the optical component, such as the light-receiving or light-emitting part E1b of component E1, it is considered unlikely that the package portion (body portion) of the optical component and the second cladding 522 will come into contact, thus preventing the light-receiving part of the optical component from coming into close proximity with the core portion 51.

[0031] In the core portion 51 of the optical waveguide 5 in the examples shown in Figures 4 to 6, the thickness of the second portion 512 at the first end 5a is greater than the thickness of the second portion 512 at the second end 5b. As shown in Figure 6, the surface 51a of the core portion 51 on the second cladding 522 side is inclined at a constant angle with respect to the surface 51b of the core portion 51 on the first cladding 521 side, and with respect to the interface IF between the first cladding 521 and the second cladding 522. That is, the surface 51a of the core portion 51 is tapered so that the surface 51a of the core portion 51 approaches the surface 51b as it approaches the second end 5b side. Therefore, the thickness of the second portion 512 gradually increases from the end face on the second end 5b side toward the end face on the first end 5a side, and gradually decreases from the end face on the first end 5a side toward the end face on the second end 5b side. The thickness of the second portion 512 at the position between the end face on the first end 5a side and the end face on the second end 5b side is smaller than the thickness T21 of the second portion 512 at the end face on the first end 5a side and larger than the thickness T23 of the second portion 512 at the end face on the second end 5b side.

[0032] As shown in the examples in Figures 4 to 6, inside the core portion 51 where the thickness of the second portion 512 is greater on the first end 5a side than on the second end 5b side, the angle of incidence to the interface (surface 51a) between the core portion 51 and the second cladding 522 becomes larger for light coming from the second end 5b side. Therefore, light propagating from the second end 5b side is more likely to undergo total internal reflection, that is, it is less likely to pass through the second cladding 522, and thus it is considered that light is efficiently propagated from the second end 5b side to the first end 5a side. Accordingly, as shown in the example in Figure 6, the second end 5b may have the exposed surface of the core portion 51, which functions as a light receiving part for external light when the optical waveguide 5 is in use, as the light incidence surface 51i. On the other hand, the first end 5a may have the exposed surface of the core portion 51, which functions as a light emitting part when the optical waveguide 5 is in use, as the light emission surface 51e.

[0033] The second portion 512 of the core portion 51 may have any thickness extending from the first end 5a to the second end 5b. The thickness of the second portion 512 at any position between the first end 5a and the second end 5b is not particularly limited. The difference between the thickness of the second portion 512 at the first end 5a and the thickness of the second portion 512 at the second end 5b can also be any value. For example, the thickness of the second portion 512 at the first end 5a is preferably 0.1 μm or more and 3 μm or less, and 0.3 μm or more and 1.5 μm or less. It is thought that the effects of the second portion 512 as described above can be obtained, and the overall thickness including optical components such as component E1 can be easily avoided.

[0034] Furthermore, the surface 51a of the core portion 51 does not have to be inclined at a constant angle with respect to the surface 51b of the core portion 51 or the interface IF between the first cladding 521 and the second cladding 522, and may have an inclination angle that changes along the way. The surface 51a of the core portion 51 may have, for example, a portion parallel to the surface 51b. Also, the thickness of the second portion 512 of the core portion 51 does not have to always gradually decrease or increase from the first end 5a side to the second end 5b side, or from the second end 5b side to the first end 5a side, and for example, the core portion 51 may have a section in which the thickness of the second portion 512 is constant.

[0035] In the examples shown in Figures 1 to 6, the first portion 511 and the second portion 512 of the core 51 are integrally formed. Therefore, refraction and reflection of light at the interface between the first portion 511 and the second portion 512 are less likely to occur, and it is thought that light can propagate properly within the core 51. In addition, the surface 51a (upper surface) of the core 51 on the second cladding 522 side is substantially flat. Therefore, compared to the case where the surface 51a is curved, it is easier to realize a desired transmission mode, such as single mode. Note that "flat" of the surface 51a means that the surface 51a is not curved by a height difference exceeding 1 / 5 of the thickness of the second portion 512.

[0036] In the examples shown in Figures 1 to 6, as shown in Figure 5A, the second portions 512 of two adjacent core portions 51 are connected at the first end 5a. Thus, adjacent second portions 512 may be connected at the first end 5a. On the other hand, as shown in Figure 5B, the second portions 512 of two adjacent core portions 51 are separated and not connected at the second end 5b. In the range where adjacent second portions 512 are separated, the length L of the second portion 512 of the core portion 51 extending outward from each of the opposing outer edges 50a of the recess 50 can be approximately constant from the first end 5a side shown in Figure 5A to the second end 5b side shown in Figure 5B.

[0037] Figure 7 shows a cross-section of a modified example of the core portion 51 of the optical waveguide 5 in this embodiment, at the same cutting position as shown in Figure 4. In the example in Figure 7, the second portion 512 of the core portion 51 extends from only one of the two opposing outer edges 50a of the recess 50 to the outside of the recess 50 on the surface 52a. Thus, the second portion 512 of the core portion 51 in this embodiment may extend to the outside of only one of the two outer edges 50a of the recess 50. In the example of the core portion 51 in Figure 7, the effective optical coupling efficiency may be maintained depending on the orientation of the misalignment between the optical component and the core portion 51 as described above.

[0038] Figure 8 shows a plan view of optical waveguide 5α, which is a first modified example of the optical waveguide of this embodiment. Optical waveguide 5α differs from optical waveguide 5 in Figure 1 and other figures in that the width of the core portion 51 changes from the first end 5a side to the second end 5b side. Specifically, the width of the first portion 511 and the width of the second portion 512 of the core portion 51 each change from the first end 5a side to the second end 5b side. Except for the fact that the width of the core portion 51 changes from the first end 5a side to the second end 5b side, optical waveguide 5α includes the same components and has the same structure as optical waveguide 5 in Figure 1. For components that are the same as those in optical waveguide 5 in Figure 1, the same reference numerals as in Figure 1 are used in Figure 8, or they are omitted as appropriate, and repetitive explanations are omitted as appropriate.

[0039] In the optical waveguide 5α in Figure 8, the width of each core portion 51 at the first end 5a is smaller than the width of each core portion 51 at the second end 5b. The optical fiber F, which can be optically coupled with the core portion 51 at the second end 5b, may have a core diameter larger than the width of the light-receiving or light-emitting portion E1b (see Figure 1) of the component E1, which can be optically coupled with the core portion 51 at the first end 5a. In the example in Figure 8, since the width of each core portion 51 is larger at the second end 5b than at the first end 5a, it is considered that less light is lost between the optical waveguide 5α and the optical fiber F without entering the receiving side, and light is transmitted efficiently.

[0040] The width W11 of the first portion 511 of the core portion 51 at the first end 5a shown in Figure 8 is, for example, 1 μm or more and 15 μm or less, and may be 3 μm or more and 10 μm or less. On the other hand, the width W13 of the first portion 511 of the core portion 51 at the second end 5b is, for example, 3 μm or more and 20 μm or less, and may be 5 μm or more and 15 μm or less. When the core portion 51 has such widths for the first portion 511, highly efficient optical coupling between the core portion 51 and optical components such as component E1 and optical fiber F can be achieved.

[0041] Figure 9 shows a modified example of the core portion 51 in the optical waveguide 5α of Figure 8. Figure 9 shows a magnified and partial view of the side of the modified core portion 51 of the optical waveguide 5α on the second end 5b side (see Figure 8). In the modified example shown in Figure 9, the second portion 512 of each core portion 51 is connected to the second portion 512 of the adjacent core portion 51, similar to the second portion 512 at the first end 5a shown in Figure 5A. Thus, in the optical waveguide of this embodiment, the second portion 512 of the core portion 51 having a first portion 511 and a second portion 512 may also be connected to the second portion 512 of the adjacent core portion 51 at the second end 5b. The second portions 512 may be connected to each other across the entire length from the first end 5a to the second end 5b between adjacent core portions 51.

[0042] Figure 10 shows a cross-sectional view of optical waveguide 5β, which is a second modified example of the optical waveguide of this embodiment. Optical waveguide 5β differs from optical waveguide 5 illustrated in Figure 1, etc., in that the core portion 51 is not exposed from the cladding portion 52 on the first cladding 521 at the first end portion 5a. Except for the above point, optical waveguide 5β has substantially the same structure and is composed of substantially the same components as the example optical waveguide 5 in Figure 1, etc. In Figure 10, components similar to those included in Figure 1, etc., are either denoted by the same reference numerals as those in Figure 1, etc., or are omitted as appropriate, and redundant explanations are omitted.

[0043] In the example shown in Figure 10, the core portion 51 is covered by the second cladding 522 even at the first end 5a, and only its end face is exposed to the side surface of the optical waveguide 5β along with the end face of the cladding portion 52. The end face of the core portion 51 on the first end 5a side that is exposed to the side surface of the optical waveguide 5β is positioned, for example, to face the light-receiving or light-emitting surface E1c of a component E1 that is optically coupled to the core portion 51. In this case, the component E1 is positioned on the extension line from the first end 5a of the optical waveguide 5, and the end face of the core portion 51 exposed to the side surface of the optical waveguide 5β is optically coupled to the light-receiving or light-emitting surface E1c of the component E1 by butt coupling. The optical waveguide 5β, like the optical waveguide 5α in Figure 1, includes a core portion 51 having a first portion 511 and a second portion 512, and the thickness of the second portion 521 at the first end 5a is greater than the thickness of the second portion 521 at the second end 5b. Therefore, it is easier to position the component E1 in the Z direction such that the end face of the core portion 51 and the light-receiving or light-emitting surface E1c of the component E1 face each other.

[0044] <Structure of the wiring board in the embodiment> Next, a wiring board according to one embodiment will be described with reference to the drawings. Figure 11 shows a cross-sectional view of a wiring board 100, which is an example of a wiring board according to one embodiment, and Figure 12 shows an example of a plan view of the wiring board 100 of Figure 11. Note that the wiring board 100 shown in Figure 11 and the like is merely one example of a wiring board according to this embodiment. The laminated structure of the wiring board according to the embodiment, and the number of conductor layers and insulating layers, respectively, are not limited to the laminated structure of the wiring board 100 of Figure 11, and the number of conductor layers and insulating layers, respectively, included in the wiring board 100.

[0045] As shown in Figure 11, the wiring board 100 includes a circuit board 200 and an optical waveguide 5 placed on the circuit board 200. The optical waveguide 5 included in the wiring board 100 is the optical waveguide 5 shown in Figure 1 and other figures, which was described as an example of an optical waveguide in one embodiment. Therefore, the optical waveguide included in the wiring board of this embodiment may have the same structure as the optical waveguide of the embodiment described with reference to Figures 1 to 10, and may have the same characteristics as the optical waveguide of the embodiment. Note that in Figure 12, each core portion 51 of the optical waveguide 5 is simplified and shown by a single dashed line.

[0046] The optical waveguide 5 included in the wiring board 100 includes at least a core portion 51 having a first end 5a and a second end 5b and transmitting light between the first end 5a and the second end 5b, and a cladding portion 52 surrounding the core portion 51. The cladding portion 52 includes at least a first cladding 521 having a surface 52a with recesses and a second cladding 522 laminated on the first cladding 521. The core portion 51 has at least a first portion 511 that fills a recess 50 (see Figure 4) provided in the surface 52a, and a second portion 512 formed on the first portion 511 and the surface 52a and extending outward from the recess 50 on the surface 52a. The thickness of the second portion 512 of the core portion 51 changes between the first end 5a and the second end 5b.

[0047] The circuit board 200 includes an insulating layer and a conductive layer. Specifically, the circuit board 200 in the example of Figure 11 includes a core substrate 3 having a first surface 3a and a second surface 3b facing each other in the thickness direction, an insulating layer 21 and a conductive layer 11 sequentially laminated on the first surface 3a of the core substrate 3, and an insulating layer 22 and a conductive layer 12 sequentially laminated on the second surface 3b. Each of the insulating layer 21 and insulating layer 22 has via conductors 20 that connect the conductive layers sandwiching it. The core substrate 3 includes an insulating layer 32 and conductive layers 31 formed on both sides of the insulating layer 32. The insulating layer 32 is provided with through-hole conductors 33 that penetrate the insulating layer 32 and connect the conductive layers 31 on both sides. The inside of the cylindrical through-hole conductor 33 is filled with a filler 34 made of an insulating resin such as epoxy resin or a conductive resin containing metal particles.

[0048] In the description of the wiring board of the embodiment, the side of the wiring board 100 furthest from the insulating layer 32 in the thickness direction is also referred to as the "upper side," "upper," or simply "top." Furthermore, in each component of the wiring board 100, the surface facing away from the insulating layer 32 is also referred to as the "upper surface." The thickness direction of the wiring board 100 is also referred to as the "Z direction" because it aligns with the lamination direction of the first cladding 521 and the second cladding 522 as described above in the description of the optical waveguide 5.

[0049] The circuit board 200 further includes solder resist 23 formed on the first surface 3a and the second surface 3b of the core substrate 3, respectively. The solder resist 23 is formed of, for example, a photosensitive epoxy resin or polyimide resin.

[0050] The circuit board 200 further includes conductor posts 13 and 14 formed on the conductor layer 11. A connecting layer 15 is formed on the surfaces of the conductor posts 13 and 14 using, for example, tin-based solder or gold-based solder. The conductor posts 13 and 14 are conductors having a columnar shape, for example, extending from the conductor layer 11 in the direction opposite to the insulating layer 21. The conductor posts 13 and 14 penetrate the solder resist 23 and protrude from its surface.

[0051] The wiring board 100 in the example shown in Figure 11 further includes a support plate 6, and the optical waveguide 5 is placed on the support plate 6. The support plate 6 supports the optical waveguide 5 and also provides rigidity to the optical waveguide 5. The optical waveguide 5 and the support plate 6 may have substantially the same shape and substantially the same size in a plan view. In the example shown in Figure 11, the support plate 6 with the optical waveguide 5 is placed on the portion of the insulating layer 21 of the circuit board 200 that is exposed to the surface of the circuit board 200.

[0052] The support plate 6 is preferably made of a material having higher rigidity than the optical waveguide 5. The support plate 6 may further be made of a material having a lower coefficient of thermal expansion than the coefficient of thermal expansion of the optical waveguide 5. This can suppress the displacement of the optical waveguide 5 due to temperature changes. Examples of materials for the support plate 6 include glasses such as soda-lime glass, borosilicate glass, and quartz glass, various metals such as tungsten, titanium, and molybdenum, and various ceramics such as alumina, silicon nitride, and silicon oxide.

[0053] The insulating layers 21, 22, and 32 may be formed using thermosetting insulating resins such as epoxy resin, bismaleimide triazine resin (BT resin), or phenolic resin. The insulating layers 21, 22, and 32 may also be formed using thermoplastic insulating resins such as fluororesin, liquid crystal polymer (LCP), fluoroethylene fluorine (PTFE) resin, polyester (PE) resin, and modified polyimide (MPI) resin. Note that the resins listed as materials for these insulating layers are merely examples of materials that can form each insulating layer. Each insulating layer may be formed from any material that can provide insulation between the conductive layers in the circuit board 200. Although not shown, each insulating layer may contain a core material (reinforcement) formed from glass fibers or aramid fibers, and may also contain inorganic fillers consisting of fine particles such as silica (SiO2), alumina, or mullite.

[0054] The conductor layers 11, 12, and 31, the through-hole conductor 33, the via conductor 20, and the conductor posts 13, 14 can be formed using any metal with suitable conductivity, such as copper or nickel. Although each of these conductors is simplified and depicted as a single layer in Figure 11, it may have a multilayer structure including two or more films. For example, the conductor layers 11 and 12 may have a two-layer structure including an electroless plating film and an electrolytic plating film. The conductor posts 13 and 14 are formed, for example, by plating metal deposited by electroless plating and / or electrolytic plating.

[0055] The conductor layers 11, 12, and conductor layer 31 may each contain any conductor pattern. In the example in Figure 11, conductor layer 11 includes conductor pads 11a and 11b. Conductor posts 13 are formed on conductor pad 11a, and conductor posts 14 are formed on conductor pad 11b. When the wiring board 100 is used, an external component E1 is connected to the conductor post 13, and an external component E2 is connected to the conductor post 14. Therefore, the circuit board 200 has a component area A1 on which component E1 is mounted. Component area A1 is the area covered by component E1 when the wiring board 100 is used. The electrode E1a on component E1 is electrically connected to the conductor pad 11a via the conductor post 13. The electrode E2a on component E2 is electrically connected to the conductor pad 11b via the conductor post 14.

[0056] Component E1 shown in Figure 11 is an optical component equipped with a photoelectric conversion element and optically coupled to the optical waveguide 5, similar to component E1 described with reference to Figure 1, etc. Similar to component E1 shown in Figure 1, etc., component E1 illustrated in Figure 11 is equipped with a light-receiving or light-emitting section E1b, which is the part into which light is incident or from which light is emitted. Through the light-receiving or light-emitting section E1b, component E1 emits light that propagates through the core section 51 or receives light propagating through the core section 51 from the core section 51. The electrode E1a and the light-receiving or light-emitting section E1b of component E1 are provided on the side of component E1 facing the wiring board 100. That is, in the example in Figure 11, component E1 is mounted in a so-called face-down mounting (flip-chip mounting) manner.

[0057] Examples of component E1 include light-receiving elements such as photodiodes, and light-emitting elements such as light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), laser diodes (LDs), and vertical-cavity surface-emitting lasers (VCSELs). When component E1 is a light-emitting element, it generates light based on an electrical signal input to electrode E1a and emits light from a light-receiving or light-emitting part E1b that functions as a light-emitting part. When component E1 is a light-receiving element, an electrical signal is generated based on light entering the light-receiving or light-emitting part E1b that functions as a light-receiving part, and output from electrode E1a.

[0058] Component E2 may be an electronic component such as a semiconductor device that generates an electrical signal to cause component E1 to light up, and / or processes the electrical signal generated by component E1. Examples of component E2 include semiconductor devices such as general-purpose operational amplifiers, driver ICs, microcontrollers, and programmable logic devices (PLDs).

[0059] The end face of the core portion 51 on the second end 5b side is positioned to optically couple with the optical fiber F that is connected to the optical waveguide 5 when the wiring board 100 is in use, as shown in Figures 11 and 12. For example, as shown in Figure 11, the optical fiber F and the optical waveguide 5 are connected using a component such as a connector C. In the example of Figures 11 and 12, the end of the core portion 51 on the second end 5b side of the optical waveguide 5 protrudes to the outside of the circuit board 200. In particular, in the example of Figures 11 and 12, the end of the support plate 6 also protrudes to the outside of the circuit board 200 and supports the protruding portion of the optical waveguide 5. Therefore, it is considered that the connector C can be easily attached to the optical waveguide 5, and that the optical coupling between the end face of the core portion 51 on the second end 5b side and the optical fiber F is easy.

[0060] On the other hand, the first end 5a of the core portion 51 overlaps with the component area A1 in a plan view. The core portion 51 extends from the component area A1 toward the outer edge of the circuit board 200. In the optical waveguide 5 shown in Figure 11, similar to the optical waveguide 5 in Figure 1, the surface 52a of the first cladding 521 and the surface 51a of the core portion 51 on the second cladding 522 side are exposed at the first end 5a of the core portion 51 without being covered by the second cladding 522. When the wiring board 100 is in use, the core portion 51 is positioned such that its surface 51a and the light-receiving or light-emitting part E1b of the component E1 face each other at the first end 5a and are optically coupled (adiabatically coupled). That is, a portion of the light that has propagated through the core portion 51 toward the first end 5a leaks out from the surface 51a to the outside of the core portion 51 as evanescent light and enters the light-receiving or light-emitting part E1b of the component E1. Since surface 51a faces the light-receiving or light-emitting portion E1b of component E1 without passing through the cladding portion 52, it is believed that highly efficient coupling can be achieved.

[0061] Furthermore, as mentioned above in the description of the optical waveguide 5 shown in Figure 1, etc., in the optical waveguide 5 included in the wiring board 100 of the example in Figure 1, the thickness of the second portion 512 of the core portion 51 at the first end 5a is greater than the thickness of the second portion 512 at the second end 5b. Since the first end 5a, which includes the second portion 512 that is thicker than the second end 5b, is located on the component E1 side, it is easier to bring the component E1 and the core portion 51 into close proximity, as described above with reference to Figures 4 to 6 regarding the optical waveguide 5 of the embodiment.

[0062] In the example shown in Figure 11, where the optical waveguide 5 is arranged in this manner, light propagating through the optical fiber F enters the optical waveguide 5 from the second end 5b of the core 51, propagates within the core 51, and enters component E1 from its first end 5a via the light receiving or light emitting section E1b. The light that enters component E1 is converted into an electrical signal within component E1 and output from electrode E1a. The output electrical signal is input to component E2 via the conductor layer 11 and processed. On the other hand, the electrical signal output from component E2 toward component E1 is input into component E1 via electrode E1a and converted into light. This light is emitted from the light receiving or light emitting section E1b and enters the optical waveguide 5 from the first end 5a. The incoming light propagates within the core 51 and is emitted from the second end 5b to the optical fiber F.

[0063] Furthermore, the form of optical coupling between an optical element such as component E1 in the wiring board of the embodiment illustrated in Figure 11 and an optical waveguide may be the form of optical coupling (bad coupling) illustrated in Figure 10.

[0064] <Method for manufacturing an optical waveguide according to this embodiment> Next, a method for manufacturing an optical waveguide according to the embodiment will be described with reference to Figures 13A to 13F. In the following description, as an example, a method for manufacturing an optical waveguide 5 illustrated in Figures 1 to 6 on a support plate 6 in Figure 11 using the imprint method will be described. As shown in Figure 13A, for example, a glass plate is prepared as the support plate 6, and a first cladding 521 is formed on the surface of the support plate 6. For example, a material described above as a constituent material of the cladding portion 52 (see Figure 13E), such as PMMA, is formed into a film and heat-pressed onto the support plate 6.

[0065] A mold M is pressed against the first cladding 521. The mold M is provided with rib-shaped protrusions M1 on the surface that is pressed against the first cladding 521, corresponding to the recesses 50 that should be present on the surface 52a of the first cladding 521. By pressing the mold M against the first cladding 521, recesses 50 are formed on the surface 52a of the first cladding 521. In the formation of the optical waveguide 5 illustrated in Figure 1 and other examples, multiple recesses 50 are formed.

[0066] As shown in Figures 13B to 13D, a core portion 51 is formed. Figure 13D is a plan view of the first cladding 521 and the core portion 51 after the formation of the core portion 51. First, as shown in Figure 13B, the material described above as the constituent material of the core portion 51, such as an acrylic resin, is supplied to the recesses 50 on the surface 52a of the first cladding 521 and to the entire surface 52a by coating, printing, or lamination. In the manufacturing process of the optical waveguide of this embodiment, a core portion 51 is formed that fills the recesses 50 and protrudes above the surface 52a of the first cladding 521. Therefore, the constituent material of the core portion 51 is supplied such that its upper surface 51a is located above the dashed line showing the surface 52a of the first cladding 521 in Figure 13B. That is, a core portion 51 is formed having a first portion 511 that fills the recesses 50 and a second portion 512 that covers the first portion 511 and the surface 52a.

[0067] Subsequently, as shown in Figure 13C, the upper surface 51a of the core portion 51 is tapered such that the thickness of the second portion 512 varies between the first end 5a and the opposite second end 5b. For example, pressure is applied to the upper surface 51a from above such that stronger pressure is applied to the second end 5b side than to the first end 5a side. As another example, the portion of the core portion 51 near the upper surface 51a is machined away more on the second end 5b side than on the first end 5a side. For example, the upper surface 51a is tapered in this way.

[0068] As shown in Figure 13D, for example, exposure and development remove the excess material of the core portion 51 supplied onto the surface 52a of the first cladding 521. As a result, a second portion 512 with a predetermined planar shape is formed. In the formation of the optical waveguide 5 illustrated in Figure 1 and other examples, as shown in Figure 13D, a plurality of core portions 51 are formed to fill each of a plurality of parallel groove-shaped recesses 50. The core portions 51 may then be fully cured by heating or other means as needed. The constituent material of the core portion 51 may be supplied only to the interior of the recesses 50 and the area where the second portion 512 is to be formed by printing using an appropriate mask in the process shown in Figure 13B.

[0069] As shown in Figure 13E, the second cladding 522 is formed on the first cladding 521 and the core portion 51. For example, similar to the formation of the first cladding 521, the constituent material of the cladding portion 52, such as PMMA, is formed into a film and heat-pressed onto the first cladding 521 and the core portion 51. The second cladding 522 adheres closely to the first cladding 521, thereby forming the cladding portion 52 that surrounds the core portion 51.

[0070] As shown in Figure 13F, the portion of the second cladding 522 that covers the first end 5a of the core portion 51 is removed. As a result, a portion of the core portion 51 is exposed at the first end 5a. The removed portion of the second cladding 522 can be removed by, for example, exposure and development, or laser processing. The constituent material of the second cladding 522 may be heat-compressed so that a portion of the first end 5a side of the core portion 51 is not covered in the process shown in Figure 13E. For example, an optical waveguide 5 as illustrated in Figure 1 and the like is manufactured by going through the processes shown in Figures 13A to 13F.

[0071] <Method for manufacturing a wiring board according to an embodiment> Next, an example of a method for manufacturing the wiring board of the embodiment will be described using the wiring board 100 in Figure 11 as an example, with reference to Figures 14A to 14E.

[0072] As shown in Figure 14A, insulating layers 21, 22 and conductive layers 11, 12 are formed on both sides of the core substrate 3. For example, a conductive layer 31 having a desired conductive pattern and a through-hole conductor 33 are formed on a double-sided copper-clad laminate substrate including an insulating layer that will become the insulating layer 32 of the core substrate 3 by a subtractive method. The inside of the cylindrical through-hole conductor 33 is filled with a filler 34 by injecting a suitable resin, such as epoxy resin. Then, an insulating layer 21 is formed on the first surface 3a of the core substrate 3, and an insulating layer 22 is formed on the second surface 3b. The insulating layers 21 and 22 are formed, for example, by laminating a film-like epoxy resin onto the core substrate 3 and then thermocompressing it. Through holes for forming via conductors 20 are formed in each insulating layer, for example by irradiation with carbon dioxide laser light. Then, a conductive layer 11 is formed on the insulating layer 21, and a conductive layer 12 is formed on the insulating layer 22. The conductive layer 11 is formed to include a predetermined conductive pattern such as conductive pads 11a, 11b. Conductor layer 11 and conductor layer 12 are formed, for example, by a semi-additive method. Along with the formation of conductor layers 11 and 12, via conductors 20 are formed in through holes provided in insulating layers 21 and 22.

[0073] As shown in Figure 14B, the conductor post 13 is formed. Figure 14B shows an enlarged view of section XIVB in Figure 14A after the formation of the conductor post 13. Although not shown in Figure 14B, the conductor post 14 (see Figure 14C) is also formed together with the conductor post 13. In the formation of the conductor layer 11 and the like by the semi-additive method, as shown in Figure 14B, a metal film 111 is formed over the entire surface of the insulating layer 21, for example by electroless plating. The plated film 112 is formed by pattern plating, including electroplating, using the metal film 111 as a power supply layer.

[0074] After the plating resist (not shown) used for pattern plating is removed, the metal film 111 remains completely intact, and a plating resist R1 having an opening R1a at the location where the conductor post 13 is to be formed is formed on the conductor layer 11 and the insulating layer 21. Then, the conductor post 13 is formed within the opening R1a, for example, by electroplating using the metal film 111 as the power supply layer.

[0075] Furthermore, as shown in Figure 14B, a connecting layer 15 is formed on the end face of the conductor post 13 by electroplating, for example, using a metal film 111 as the power supply layer. The connecting layer 15 is formed by a metal film made of, for example, tin, a tin alloy, or a gold alloy. After the connecting layer 15 is formed, the plating resist R1 is removed using an appropriate stripping agent. Then, the portion of the metal film 111 that is not covered by the plating film 112 is removed, for example, by quick etching.

[0076] As shown in Figure 14C, a solder resist 23 is formed to cover the insulating layer 21, the conductor layer 11, the conductor posts 13 and 14, and the connecting layer 15. The solder resist 23 is formed by supplying, for example, a liquid or sheet-like epoxy resin or polyimide resin onto the insulating layer 21 and each component on its surface by methods such as printing, coating, spraying, or lamination. Solder resist 23 is also formed on the second surface 3b side of the core substrate 3 by coating or laminating epoxy resin or polyimide resin.

[0077] As shown in Figure 14D, a portion of the solder resist 23 in the thickness direction is removed. The reduction in the thickness of the solder resist 23 exposes the end of the conductor posts 13 and 14 opposite to the insulating layer 21. The portion of the solder resist 23 can be removed by dry etching, such as plasma etching using carbon tetrafluoride (CF4) gas, or by blasting.

[0078] As shown in Figure 14E, the portion of the solder resist 23 corresponding to the area where the optical waveguide 5 is located is removed, for example, by irradiation with a carbon dioxide laser. The area of ​​the insulating layer 21 surface where the optical waveguide 5 is located is exposed. This laser processing can form an opening 23a in the solder resist 23. The circuit board 200 is completed.

[0079] The optical waveguide 5 is prepared, for example, in the manner described with reference to Figures 13A to 13F. When the wiring board 100 of the example in Figure 11 is manufactured, a support plate 6 made of, for example, a glass plate is also prepared. The optical waveguide 5 may be formed on the support plate 6 as described with reference to Figures 13A to 13F, or it may be formed separately from the support plate 6 and then bonded to the separately prepared support plate 6 using any adhesive (not shown).

[0080] An adhesive Gu, such as a thermosetting, room-temperature curing, or photocuring adhesive, is applied to a predetermined portion of the surface of the insulating layer 21 exposed from the solder resist 23, and the support plate 6 and optical waveguide 5 are mounted on top of it. If necessary, the adhesive Gu is cured by heating or other means, and the optical waveguide 5 and support plate 6 are fixed to the circuit board 200. Furthermore, the connecting layer 15 is melted by a reflow process or the like and shaped into a hemispherical form. Through these steps, the wiring board 100 shown in the example in Figure 11 is completed.

[0081] The optical waveguides and wiring boards of the embodiments are not limited to the structures illustrated in each drawing, nor to the structures, shapes, and materials illustrated herein. As stated above, the wiring boards of the embodiments may have any laminated structure. For example, the wiring boards of the embodiments may be coreless boards that do not include a core board. The wiring boards of the embodiments may include any number of conductor layers and insulating layers. Furthermore, conductor pads 11b and conductor posts 14 may not be formed, and conductor posts 13 are not necessarily provided. Also, the thickness of the first portion of the core of the optical waveguide of the embodiments may differ between the first end and the second end of the core, and the cross-sectional shape of the first portion may be a shape other than rectangular. [Explanation of Symbols]

[0082] 100 Wiring boards 11, 12, 31 Conductor layers 21, 22, 32 Insulating layer 200 circuit boards 5, 5α, 5β optical waveguide 5a First end 5b Second end 50 recesses 50a Outer edge of recess 51 Core section 51a Surface of the second cladding side of the core 51e Output surface 51i entrance plane 511 Part 1 512 Part 2 52 Clad section 52a Surface of the first cladding 521 First Clad 522 Second clad A1 Component Area E1 part L The length of the second part of the core extending outward from the outer edge of the recess. T21~T23 Thickness of the second part of the core

Claims

1. A core portion having a first end and a second end opposite the first end, which transmits light between the first end and the second end, The cladding portion surrounding the core portion, An optical waveguide including, The cladding portion includes a first cladding having a surface with recesses and a second cladding laminated on the first cladding. The core portion has a first portion that fills the recess and a second portion that is formed on the first portion and the surface and extends outward from the recess on the surface. The thickness of the second portion changes between the first end and the second end.

2. The optical waveguide according to claim 1, wherein the thickness of the second portion at the first end is greater than the thickness of the second portion at the second end.

3. The optical waveguide according to claim 2, wherein the second end has an incident surface for light and the first end has an exit surface for light.

4. The optical waveguide according to claim 1, wherein the second portion extends outward from both of the two opposing outer edges of the recess along the surface.

5. The optical waveguide according to claim 1, wherein the first portion and the second portion are integrally formed.

6. The optical waveguide according to claim 1, wherein the length of the second portion of the core that extends outward from the recess is substantially constant from the first end to the second end.

7. An optical waveguide according to claim 1, wherein the optical waveguide is made of an organic material.

8. A circuit board including an insulating layer and a conductive layer, An optical waveguide placed on the aforementioned circuit board, A wiring board including, The optical waveguide includes a core portion having a first end and a second end opposite the first end, which transmits light between the first end and the second end, and a cladding portion surrounding the core portion. The cladding portion includes a first cladding having a surface with recesses and a second cladding laminated on the first cladding. The core portion has a first portion that fills the recess and a second portion that is formed on the first portion and the surface and extends outward from the recess on the surface. The thickness of the second portion changes between the first end and the second end.

9. A wiring board according to claim 8, The thickness of the second portion at the first end is greater than the thickness of the second portion at the second end. At the first end, the surface of the first cladding and the surface of the core portion on the second cladding side are exposed.

10. A wiring board according to claim 9, The circuit board has a component region covered by a component that emits or receives light propagating through the core portion. The first end of the core portion overlaps with the component area in a plan view.

Images