Optical waveguide mounting substrate and optical communication device

Abstract

To provide an optical waveguide mounted board on which an optical waveguide having a protrusion of a hardly breakable shape for metal film formation, is mounted.SOLUTION: The present optical waveguide mounted board comprises a wiring board, and an optical waveguide that is formed on the wiring board. The optical waveguide includes a first clad layer, a first protrusion for metal film formation that has a top face and an inclined face that connects to the top face and is tilted with respect to the top face, and that is formed on the top face of the first clad layer, a first metal film that is formed on at least the inclined face of the first protrusion for metal film formation, a core layer that is formed on the top face of the first clad layer so as to partly cover the first metal film, and a second clad layer that is formed on the top face of the first clad layer so as to cover at least the top face and side faces of the core layer. A first region that includes the top face and the inclined face of the first protrusion for metal film formation in a plan view does not have a bent part where two line segments intersect, except a side of the inclined face that is in contact with the top face of the first clad layer.SELECTED DRAWING: Figure 2

Description

Technical Field

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[0001] The present invention relates to a substrate on which an optical waveguide is mounted and an optical communication device.

Background Art

[0002] In an optical waveguide mounting substrate on which an optical waveguide is mounted with a core layer sandwiched between a first cladding layer and a second cladding layer, a technique is known in which an inclined surface is formed on a protrusion for forming a metal film, the inclined surface being inclined at approximately 45 degrees with respect to the optical propagation direction of the core layer, and a metal film is provided on the inclined surface. The metal film is formed, for example, by disposing a mask made of metal or the like above the protrusion for forming the metal film and depositing the metal film on the protrusion for forming the metal film through the mask.

Prior Art Documents

[0007] According to the disclosed technology, it is possible to provide an optical waveguide mounting substrate equipped with an optical waveguide having a metal film formation projection with a shape that is resistant to damage. [Brief explanation of the drawing]

[0008] [Figure 1] This figure illustrates the structure of a substrate for mounting an optical waveguide according to the first embodiment. [Figure 2] This is a partially enlarged plan view of the first and second metal film forming protrusions according to the first embodiment. [Figure 3] This is a diagram (part 1) illustrating the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 4] This is a diagram (part 2) illustrating the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 5] This is a diagram (part 3) illustrating the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 6] This is a diagram (part 4) illustrating the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 7] This is Figure (5) illustrating the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 8]This is a diagram (6) illustrating the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 9] Figure (7) illustrates the manufacturing process of a substrate with an optical waveguide according to the first embodiment. [Figure 10] This is a partially enlarged plan view (part 1) of the first and second metal film forming protrusions according to a modified example of the first embodiment. [Figure 11] This is a partially enlarged plan view (part 2) of the first and second metal film forming protrusions according to a modified example of the first embodiment. [Figure 12] This is a cross-sectional view illustrating an optical transceiver according to the second embodiment. [Figure 13] This is a cross-sectional view illustrating an optical transceiver according to a modified example of the second embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> [Structure of the optical waveguide mounting substrate] First, the structure of the optical waveguide mounting substrate will be described. Figure 1 is an example of the structure of the optical waveguide mounting substrate according to the first embodiment, where Figure 1(a) is a plan view and Figure 1(b) is a cross-sectional view along line AA in Figure 1(a). Note that in Figure 1(a), the second cladding layer 33 shown in Figure 1(b) is omitted from the illustration. Also, in Figure 1, mutually orthogonal X, Y, and Z directions are defined for reference. Similar directions may be defined in subsequent figures as needed.

[0011] As shown in FIG. 1, the optical waveguide-mounted substrate 1 according to the first embodiment has a wiring substrate 10 and an optical waveguide 30 formed on the wiring substrate 10. Here, as an example, it is assumed that the planar shape of the wiring substrate 10 is rectangular, the long side of the rectangle is parallel to the X direction, and the short side of the rectangle is parallel to the Y direction. The Z direction is the stacking direction of each layer constituting the wiring substrate 10.

[0012] [Wiring Substrate] In the wiring substrate 10, wiring layers and insulating layers are stacked on both surfaces of the core substrate 10C. Specifically, in the wiring substrate 10, a wiring layer 12, an insulating layer 13, a wiring layer 14, and a solder resist layer 15 are sequentially stacked on one surface (upper surface) of the core substrate 10C. Also, a wiring layer 22, an insulating layer 23, a wiring layer 24, and a solder resist layer 25 are sequentially stacked on the other surface (lower surface) of the core substrate 10C.

[0013] As the core substrate 10C, for example, a so-called glass epoxy substrate obtained by impregnating a glass cloth with an insulating resin such as an epoxy resin can be used. As the core substrate 10C, a substrate obtained by impregnating a woven fabric or non-woven fabric of glass fiber, carbon fiber, aramid fiber, etc. with an epoxy resin or a polyimide resin may also be used. The thickness of the core substrate 10C can be, for example, about 60 μm to 400 μm. The core substrate 10C is provided with through holes 10x penetrating in the thickness direction of the core substrate 10C. The planar shape of the through holes 10x is, for example, circular.

[0014] The wiring layer 12 is formed on one surface of the core substrate 10C. Also, the wiring layer 22 is formed on the other surface of the core substrate 10C. The wiring layer 12 and the wiring layer 22 are electrically connected by a through wiring 11 formed in the through holes 10x. The wiring layers 12 and 22 are each patterned into a predetermined planar shape. As the material of the wiring layers 12 and 22 and the through wiring 11, for example, copper (Cu) or the like can be used. The thickness of the wiring layers 12 and 22 can be, for example, about 10 μm to 30 μm. Note that the wiring layer 12, the wiring layer 22, and the through wiring 11 may be integrally formed.

[0015] The insulating layer 13 is formed so as to cover the wiring layer 12 on one surface of the core substrate 10C. As the material of the insulating layer 13, for example, an insulating resin mainly composed of an epoxy resin or a polyimide resin can be used. The thickness of the insulating layer 13 can be, for example, about 30 μm to 40 μm. The insulating layer 13 can contain a filler such as silica (SiO2).

[0016] The wiring layer 14 is formed on one side of the insulating layer 13. The wiring layer 14 includes via wirings filled in via holes 13x that penetrate the insulating layer 13 and expose one surface of the wiring layer 12, and wiring patterns formed on one surface of the insulating layer 13. The wiring layer 14 is electrically connected to the wiring layer 12. The via hole 13x can be a frustum-shaped concave portion with a diameter of the opening on the solder resist layer 15 side larger than the diameter of the bottom surface of the opening formed by one surface of the wiring layer 12. The material of the wiring layer 14 and the thickness of the wiring patterns constituting the wiring layer 14 can be, for example, the same as those of the wiring layer 12.

[0017] The solder resist layer 15 is the outermost layer on one side of the wiring substrate 10 and is formed on one surface of the insulating layer 13 so as to cover the wiring layer 14. The solder resist layer 15 can be formed from, for example, a photosensitive resin such as an epoxy resin or an acrylic resin. The thickness of the solder resist layer 15 can be, for example, about 15 μm to 35 μm.

[0018] The solder resist layer 15 has an opening 15x, and a portion of one side of the wiring layer 14 is exposed at the bottom of the opening 15x. The planar shape of the opening 15x can be, for example, circular. If necessary, a metal film may be formed on one side of the wiring layer 14 exposed within the opening 15x, or an anti-oxidation treatment such as OSP (Organic Solderability Preservative) treatment may be applied. Examples of metal films include an Au layer, a Ni / Au layer (a metal film formed by stacking a Ni layer and an Au layer in that order), and a Ni / Pd / Au layer (a metal film formed by stacking a Ni layer, a Pd layer, and an Au layer in that order).

[0019] External connection terminals 19 are formed on the wiring layer 14 exposed within the opening 15x. The external connection terminals 19 are, for example, solder bumps. As the material for the solder bumps, for example, alloys containing Pb, alloys of Sn and Cu, alloys of Sn and Ag, alloys of Sn, Ag and Cu, etc. can be used. The external connection terminals 19 are terminals that are electrically connected to light-emitting elements and light-receiving elements.

[0020] The insulating layer 23 is formed on the other side of the core substrate 10C so as to cover the wiring layer 22. The material and thickness of the insulating layer 23 can be the same as, for example, the insulating layer 13. The insulating layer 23 may contain a filler such as silica (SiO2). The wiring layer 24 is formed on the other side of the insulating layer 23. The wiring layer 24 consists of via wiring filled in via holes 23x that penetrate the insulating layer 23 and expose the other side of the wiring layer 22, and a wiring pattern formed on the other side of the insulating layer 23. The wiring layer 24 is electrically connected to the wiring layer 22. The via holes 23x can be frustoconical recesses in which the diameter of the opening that opens towards the solder resist layer 25 is larger than the diameter of the bottom surface of the opening formed by the other side of the wiring layer 22. The material and thickness of the wiring layer 24 can be the same as, for example, the wiring layer 12.

[0021] The solder resist layer 25 is the outermost layer on the other side of the wiring substrate 10 and is formed to cover the wiring layer 24 on the other side of the insulating layer 23. The material and thickness of the solder resist layer 25 can be the same as, for example, the solder resist layer 15. The solder resist layer 25 has an opening 25x, and a portion of the other side of the wiring layer 24 is exposed within the opening 25x. The planar shape of the opening 25x can be, for example, circular. The wiring layer 24 exposed within the opening 25x can be used as a pad for electrically connecting to a mounting substrate (not shown), such as a motherboard. If necessary, the aforementioned metal film may be formed on the other side of the wiring layer 24 exposed within the opening 25x, or an anti-oxidation treatment such as OSP treatment may be applied.

[0022] [Optical waveguide] The optical waveguide 30 is formed on the solder resist layer 15 of the wiring substrate 10. The optical waveguide 30 comprises a first cladding layer 31, a core layer 32, a second cladding layer 33, a first metal film forming projection 35, a second metal film forming projection 36, a first metal film 351, and a second metal film 361.

[0023] The first cladding layer 31 is formed of, for example, a photosensitive material. Specifically, the first cladding layer 31 can be formed of a polymer such as a polyimide resin, acrylic resin, epoxy resin, polyolefin resin, or polynorbornene resin. The thickness of the first cladding layer 31 can be, for example, about 10 μm to 30 μm. The first cladding layer 31 is arranged on the wiring substrate 10, substantially parallel to the wiring substrate 10.

[0024] The core layer 32 is selectively formed on the upper surface of the first cladding layer 31. The core layer 32 covers a portion of the first metal film 351 and a portion of the second metal film 361. In the example shown in Figure 1, two elongated core layers 32, with the X direction as the longitudinal direction, are placed side by side on the upper surface of the first cladding layer 31. However, this is just an example, and one core layer 32 may be formed, or three or more may be formed. The pitch of the side by side core layers 32 can be, for example, about 200 μm to 300 μm. The core layer 32 can be formed from the same material as the first cladding layer 31. The thickness of the core layer 32 can be, for example, about 15 μm to 35 μm. The cross-sectional shape of the core layer 32 in the short direction can be, for example, a square.

[0025] The second cladding layer 33 is formed on the upper surface of the first cladding layer 31 so as to cover at least the upper surface and both sides of the core layer 32. The second cladding layer 33 can be formed from the same material as the first cladding layer 31. The thickness of the second cladding layer 33 can be, for example, about 10 μm to 30 μm.

[0026] As described above, the first cladding layer 31, the core layer 32, and the second cladding layer 33 can be formed from the same material, but the refractive index of the core layer 32 is higher than that of the first cladding layer 31 and the second cladding layer 33. By including a refractive index control additive such as Ge in the core layer 32, the refractive index of the core layer 32 can be made higher than that of the first cladding layer 31 and the second cladding layer 33. For example, the refractive index of the first cladding layer 31 and the second cladding layer 33 can be 1.5, and the refractive index of the core layer 32 can be 1.6.

[0027] The first metal film forming projection 35 is formed on the upper surface of the first cladding layer 31. The first metal film forming projection 35 has an upper surface 35a and an inclined surface 35b that is connected to the upper surface 35a and inclined with respect to the upper surface 35a. The upper surface 35a of the first metal film forming projection 35 is, for example, parallel to the upper surface of the first cladding layer 31. The angle between the upper surface of the first cladding layer 31 and the inclined surface 35b is, for example, 45 degrees. In addition to the upper surface 35a and the inclined surface 35b, the first metal film forming projection 35 may also have surfaces that are parallel to or perpendicular to the upper surface of the first cladding layer 31.

[0028] As shown in Figure 2, in a plan view, the first region 35c, which includes the upper surface 35a and the inclined surface 35b of the first metal film forming projection 35, does not have a bend where two line segments intersect, except for the side of the inclined surface 35b that is in contact with the upper surface of the first cladding layer 31. Note that in the first region 35c, the two locations enclosed by dashed lines are bends where two line segments intersect.

[0029] The upper surface 35a of the first metal film forming projection 35 is formed, for example, by a line segment L1 that forms a boundary with the inclined surface 35b and a curve L2 directly connected to both ends of the line segment L1. The upper surface 35a of the first metal film forming projection 35 is, for example, semicircular. The upper surface 35a of the first metal film forming projection 35 may also be semielliptical. The upper surface 35a of the first metal film forming projection 35 may also be a shape other than semicircular and semielliptical, formed by the line segment L1 and the curve L2.

[0030] Returning to Figure 1, the second metal film forming projection 36 is formed on the upper surface of the first cladding layer 31. The second metal film forming projection 36 has an upper surface 36a and an inclined surface 36b that is connected to the upper surface 36a and inclined with respect to the upper surface 36a. The upper surface 36a of the second metal film forming projection 36 is, for example, parallel to the upper surface of the first cladding layer 31. The angle between the upper surface of the first cladding layer 31 and the inclined surface 36b is, for example, 45 degrees. In addition to the upper surface 36a and the inclined surface 36b, the second metal film forming projection 36 may also have surfaces that are parallel to or perpendicular to the upper surface of the first cladding layer 31.

[0031] As shown in Figure 2, in a plan view, the second region 36c, which includes the upper surface 36a and the inclined surface 36b of the second metal film forming projection 36, does not have a bend where two line segments intersect, except for the side of the inclined surface 36b that is in contact with the upper surface of the first cladding layer 31. Note that in the second region 36c, the two locations enclosed by dashed lines are bends where two line segments intersect.

[0032] The upper surface 36a of the second metal film forming projection 36 is formed, for example, by a line segment L3 that forms a boundary with the inclined surface 36b and a curve L4 directly connected to both ends of the line segment L3. The upper surface 36a of the second metal film forming projection 36 is, for example, semicircular. The upper surface 36a of the second metal film forming projection 36 may also be semielliptical. The upper surface 36a of the second metal film forming projection 36 may also be a shape other than semicircular and semielliptical, formed by the line segment L3 and the curve L4. The upper surface 36a of the second metal film forming projection 36 may or may not be the same shape as the upper surface 35a of the first metal film forming projection 35. Here, the same shape includes a shape that coincides with the other when one is rotated by a predetermined angle.

[0033] Returning to Figure 1, the first metal film 351 is formed on at least the inclined surface 35b of the first metal film forming projection 35. The first metal film 351 is formed in the central part of the inclined surface 35b that is covered by the core layer 32, and is exposed from the core layer 32 and widens on both sides in the Y direction. The second metal film 361 is formed on at least the inclined surface 36b of the second metal film forming projection 36. The second metal film 361 is formed in the central part of the inclined surface 36b that is covered by the core layer 32, and is exposed from the core layer 32 and widens on both sides in the Y direction.

[0034] The second metal film 361 formed on the inclined surface 36b is generally opposite the first metal film 351 formed on the inclined surface 35b. The interface between the core layer 32 and the first metal film 351, and the interface between the core layer 32 and the second metal film 361, become reflective surfaces that change the propagation direction of incident light. The first metal film 351 and the second metal film 361 are, for example, gold (Au) films with a thickness of 0.2 μm to 0.5 μm.

[0035] [Manufacturing method for optical waveguide mounted substrate] Next, the manufacturing method of the optical waveguide mounting substrate 1 will be described. Figures 3 to 9 illustrate the manufacturing process of the optical waveguide mounting substrate according to the first embodiment. In Figures 4, 5, 6, and 8, (a) is a cross-sectional view and (b) is a plan view.

[0036] First, in the process shown in Figure 3(a), the wiring board 10 is prepared. The wiring board 10 can be manufactured, for example, by a well-known build-up method. The wiring board 10 may also be prepared by purchasing a commercially available product.

[0037] Next, in the process shown in Figure 3(b), a first cladding layer 31 is formed on the upper surface of the solder resist layer 15 of the wiring board 10. The thickness of the first cladding layer 31 is, for example, about 10 μm. Next, in the process shown in Figure 3(c), an ultraviolet-curable resin 300 is laminated on the upper surface of the solder resist layer 15 of the wiring board 10 to cover the first cladding layer 31. The thickness of the ultraviolet-curable resin 300 is, for example, about 35 μm.

[0038] Next, in the process shown in Figures 4(a) to 6(b), the ultraviolet-curable resin 300 is patterned so that only the portions that will become the first metal film forming protrusion 35 and the second metal film forming protrusion 36 remain, thereby forming the resin protrusions 350 and 360.

[0039] First, as shown in Figures 4(a) and 4(b), a mask 400 having openings 400x is placed on the ultraviolet-curable resin 300, for example, at positions corresponding to the first metal film forming projection 35 and the second metal film forming projection 36. In plan view, the openings 400x have shapes corresponding to the first metal film forming projection 35 and the second metal film forming projection 36 shown in Figure 1.

[0040] Next, as shown in Figures 5(a) and 5(b), ultraviolet light is irradiated onto the UV-curable resin 300 through the mask 400 to pattern it by exposure. This cures the portion of the UV-curable resin 300 exposed within the opening 400x, forming resin protrusions 350 and 360. Next, as shown in Figures 6(a) and 6(b), the unnecessary portions of the UV-curable resin 300 are removed by development to form the resin protrusions 350 and 360.

[0041] Next, in the process shown in Figure 7(a), the resin protrusions 350 and 360 are cut at an angle of approximately 45 degrees, such that their inclined surfaces are generally opposite each other. Cutting can be performed, for example, by dicing with a dicing blade 410 or by polishing with an abrasive plate. If scratches or dents occur on the inclined surfaces 35b and 36b, which are the cut surfaces, it is preferable to smooth the inclined surfaces 35b and 36b by irradiating the cut surfaces with laser light or applying resin liquid. This process forms a first metal film forming protrusion 35 having an inclined surface 35b that is inclined with respect to the upper surface of the first cladding layer 31, and a second metal film forming protrusion 36 having an inclined surface 36b that is inclined with respect to the upper surface of the first cladding layer 31.

[0042] Next, in the steps shown in Figures 7(b) to 8(b), a first metal film 351 is formed on at least the inclined surface 35b of the first metal film forming projection 35, and a second metal film 361 is formed on at least the inclined surface 36b of the second metal film forming projection 36.

[0043] First, as shown in Figure 7(b), a mask 500 having an opening 500x at the position where the first metal film 351 and the second metal film 361 are to be formed is placed above the first metal film forming projection 35 and the second metal film forming projection 36. The mask 500 is, for example, made of metal. In a plan view, the opening 500x can be any shape, such as a circle or rectangle, as long as it exposes the position where the first metal film 351 and the second metal film 361 are to be formed.

[0044] Next, as shown in Figure 7(c), a first metal film 351 and a second metal film 361 are formed on at least the inclined surfaces 35b and 36b exposed within the opening 500x by sputtering or deposition through the mask 500. The first metal film 351 and the second metal film 361 are, for example, gold films. Parts of the first metal film 351 and the second metal film 361 may be formed on the upper surfaces of the first metal film forming projection 35 and the second metal film forming projection 36 or on the upper surface of the first cladding layer 31.

[0045] Next, the mask 500 is removed as shown in Figures 8(a) and 8(b). Note that while this example shows the formation of two sets of first metal film forming protrusions 35 and second metal film forming protrusions 36, this is merely an example; one set of first metal film forming protrusions 35 and second metal film forming protrusions 36 may be formed, or three or more sets may be formed.

[0046] Next, in the process shown in Figure 9(a), a core layer 32 is formed on the upper surface of the first cladding layer 31 using a photosensitive resin so as to cover a portion of the first metal film 351 and a portion of the second metal film 361. The core layer 32 is formed, for example, by placing an uncured photosensitive resin film on the first cladding layer 31 and exposing and developing it using the same mask. The upper surface of the core layer 32 is flush with the upper surfaces of the first metal film 351 and the second metal film 361, for example. The upper surfaces of the first metal film 351 and the second metal film 361 may be exposed from the core layer 32. Here, two elongated core layers 32 are formed on the upper surface of the first cladding layer 31, with the X direction being the longitudinal direction. The core layers 32 are formed to correspond to the number of sets of the first metal film forming projections 35 and the second metal film forming projections 36.

[0047] Next, in the process shown in Figure 9(b), a second cladding layer 33 is laminated on the core layer 32. The second cladding layer 33 can be formed into a predetermined pattern by, for example, placing an uncured photosensitive resin film on the upper surface of the first cladding layer 31 so as to cover at least the upper surface and both sides of the core layer 32, and then exposing and developing it. With these steps, the optical waveguide mounting substrate 1, on which the optical waveguide 30 is mounted on the wiring substrate 10, is completed.

[0048] Thus, in the optical waveguide-mounted substrate 1, in a plan view, the first region 35c, which includes the upper surface 35a and the inclined surface 35b of the first metal film-forming projection 35, does not have a bend where two line segments intersect, except for the side of the inclined surface 35b that is in contact with the upper surface of the first cladding layer 31. Also, in a plan view, the second region 36c, which includes the upper surface 36a and the inclined surface 36b of the second metal film-forming projection 36, does not have a bend where two line segments intersect, except for the side of the inclined surface 36b that is in contact with the upper surface of the first cladding layer 31.

[0049] If, in a plan view, the first metal film forming projection 35 and the second metal film forming projection 36 are rectangular in shape, then the first metal film forming projection 35 and the second metal film forming projection 36 will have a roughly right-angle bend on the opposite side of each inclined surface where two line segments intersect in a plan view. In this case, when the mask 500 is placed above the first metal film forming projection 35 and the second metal film forming projection 36 in the process shown in Figure 7(b), if the mask 500 comes into contact with the first metal film forming projection 35 and the second metal film forming projection 36, the area near the bend is likely to be damaged. However, in the optical waveguide mounting substrate 1, the first metal film forming projection 35 and the second metal film forming projection 36 do not have a bend where two line segments intersect in a plan view on the opposite side of each inclined surface, so even if the mask 500 comes into contact with them, the risk of damage can be greatly reduced. In other words, the curved portions L2 and L4 of the first metal film forming projection 35 and the second metal film forming projection 36 are shaped to be less likely to be damaged even if the mask 500 comes into contact with them.

[0050] In this embodiment, a first metal film forming projection 35 and a second metal film forming projection 36 are provided, but either the first metal film forming projection 35 or the second metal film forming projection 36 may be provided.

[0051] <Variations of the first embodiment> A modification of the first embodiment shows other examples of the planar shapes of the first and second regions. In the modification of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0052] Figure 10 is a partially enlarged plan view (part 1) of the first and second metal film forming protrusions according to a modified example of the first embodiment. The first region 35c and the second region 36c may have the shapes shown in Figure 10.

[0053] In the case of Figure 10, in a plan view, the first region 35c, which includes the upper surface 35a and the inclined surface 35b of the first metal film forming projection 35, does not have a bend where two line segments intersect, except for the side of the inclined surface 35b that is in contact with the upper surface of the first cladding layer 31. Also, in a plan view, the second region 36c, which includes the upper surface 36a and the inclined surface 36b of the second metal film forming projection 36, does not have a bend where two line segments intersect, except for the side of the inclined surface 36b that is in contact with the upper surface of the first cladding layer 31.

[0054] In Figure 10, the upper surface 35a of the first metal film forming projection 35 is formed by, for example, a line segment M1 that forms a boundary with the inclined surface 35b, a line segment M2 connected to one end of line segment M1, a line segment M3 connected to the other end of line segment M1, and a curve M4 that connects the ends of line segments M2 and M3.

[0055] Furthermore, the upper surface 36a of the second metal film forming projection 36 is formed, for example, by a line segment M5 that forms a boundary with the inclined surface 36b, a line segment M6 connected to one end of line segment M5, a line segment M7 connected to the other end of line segment M5, and a curve M8 that connects the ends of line segment M6 and line segment M7.

[0056] Thus, the upper surface 35a of the first metal film forming projection 35 may be formed by a line segment M1 that forms a boundary with the inclined surface 35b and a curve M4 connected to both ends of the line segment M1 via other line segments. Similarly, the upper surface 36a of the second metal film forming projection 36 may be formed by a line segment M5 that forms a boundary with the inclined surface 36b and a curve M8 connected to both ends of the line segment M5 via other line segments. The upper surfaces 35a of the first metal film forming projection 35 and the upper surface 36a of the second metal film forming projection 36 may include a semicircular portion or a semielliptical portion.

[0057] Figure 11 is a partially enlarged plan view (part 2) of the first and second metal film forming protrusions according to a modified example of the first embodiment. The first region 35c and the second region 36c may have the shapes shown in Figure 11.

[0058] In the case of Figure 11, in a plan view, the first region 35c, which includes the upper surface 35a and the inclined surface 35b of the first metal film forming projection 35, does not have a bend where two line segments intersect, except for the side of the inclined surface 35b that is in contact with the upper surface of the first cladding layer 31. Also, in a plan view, the second region 36c, which includes the upper surface 36a and the inclined surface 36b of the second metal film forming projection 36, does not have a bend where two line segments intersect, except for the side of the inclined surface 36b that is in contact with the upper surface of the first cladding layer 31.

[0059] In Figure 11, the upper surface 35a of the first metal film forming projection 35 is formed by a line segment N1 that forms a boundary with the inclined surface 35b, a curve N4 connected to one end of line segment N1 via line segment N2, a curve N5 connected to the other end of line segment N1 via line segment N3, and a line segment N6 connecting the ends of curves N4 and N5. Line segments N1 and N6 may or may not be parallel. Curves N4 and N5 may or may not be arc-shaped. Furthermore, curve N4 may be directly connected to one end of line segment N1 and curve N5 may be directly connected to the other end of line segment N1 without using line segments N2 and N3.

[0060] Furthermore, the upper surface 36a of the second metal film forming projection 36 is formed by a line segment N7 that forms a boundary with the inclined surface 36b, a curve N10 connected to one end of line segment N7 via line segment N8, a curve N11 connected to the other end of line segment N7 via line segment N9, and a line segment N12 connecting the ends of curve N10 and curve N11. Line segments N7 and N12 may or may not be parallel. Curves N10 and N11 may or may not be arc-shaped. Also, without using line segments N8 and N9, curve N10 may be directly connected to one end of line segment N7, and curve N11 may be directly connected to the other end of line segment N7.

[0061] In the structures shown in Figures 10 and 11, as with the structure in Figure 2, the first metal film forming projection 35 and the second metal film forming projection 36 do not have a bent portion where two line segments intersect in a plan view on the opposite side of each inclined surface. Therefore, even if the mask 500 comes into contact with them, the risk of damage can be greatly reduced. Furthermore, it is preferable that the upper surfaces of the first metal film forming projection 35 and the second metal film forming projection 36 do not have a straight portion in a plan view, as shown in Figure 2, for example, because this maximizes strength.

[0062] <Second Embodiment> In the second embodiment, an example of an optical communication device is shown that includes an optical waveguide mounting substrate according to the first embodiment, and a light-emitting element that emits light into the optical waveguide mounted on the optical waveguide mounting substrate, or a light-receiving element that receives light emitted from the optical waveguide, or both. In the second embodiment, descriptions of components that are the same as those described in the previously described embodiments may be omitted.

[0063] Figure 12 is a cross-sectional view illustrating an optical transceiver according to the second embodiment. Referring to Figure 12, the optical transceiver 5 includes an optical waveguide mounting substrate 1, a light-emitting element 110, a light-receiving element 120, and underfill resins 150 and 160.

[0064] The light-emitting element 110 comprises a main body 111, a bump 112, and a light-emitting section 113, and emits light into the optical waveguide 30. The bump 112 and the light-emitting section 113 are provided on the wiring board 10 side of the main body 111. The bump 112 is, for example, an Au bump and is electrically connected to the external connection terminal 19 of the wiring board 10. The light-emitting section 113 is positioned to irradiate the first metal film 351 with light. As the light-emitting element 110, for example, a surface-emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser), a light-emitting diode (LED: Light Emitting Diode), etc., can be used.

[0065] The underfill resin 150 is provided between the light-emitting element 110 and a portion of the solder resist layer 15 and a portion of the optical waveguide 30. As the underfill resin 150, for example, a light-transmitting resin that can transmit light emitted from the light-emitting element 110 can be used.

[0066] The light-receiving element 120 has a main body 121, a bump 122, and a light-receiving section 123, and receives light emitted from the optical waveguide 30. The bump 122 and the light-receiving section 123 are provided on the wiring board 10 side of the main body 121. The bump 122 is, for example, an Au bump and is electrically connected to the external connection terminal 19 of the wiring board 10. The light-receiving section 123 is positioned to receive light reflected by the second metal film 361. As the light-receiving element 120, for example, a photodiode or an avalanche photodiode (APD) can be used.

[0067] The underfill resin 160 is provided between the light-receiving element 120 and a portion of the solder resist layer 15 and a portion of the optical waveguide 30. As the underfill resin 160, for example, a light-transmitting resin that can transmit light received by the light-receiving element 120 can be used.

[0068] In Figure 12, the light L emitted from the light-emitting part 113 of the light-emitting element 110 passes through the underfill resin 150 and the second cladding layer 33 and enters the core layer 32, where it reaches the first metal film 351, where it undergoes total internal reflection and its light propagation direction is changed by approximately 90 degrees. Then it propagates within the core layer 32, reaches the second metal film 361, where it undergoes total internal reflection and its light propagation direction is changed by approximately 90 degrees. Finally, it exits the core layer 32, passes through the second cladding layer 33 and the underfill resin 160, and is received by the light-receiving part 123 of the light-receiving element 120.

[0069] The optical transceiver 5 has an optical waveguide 30 equipped with metal film-forming protrusions that are less prone to damage, thus enabling a highly reliable device.

[0070] Figure 13 is a cross-sectional view illustrating an optical transceiver according to a modified example of the second embodiment. Referring to Figure 13, the optical transceiver 6 differs from the optical transceiver 5 (see Figure 12) in that the optical waveguide 30 is replaced with an optical waveguide 30A, and an optical fiber 130 for signal transmission is added in place of the photodetector 120.

[0071] Optical waveguide 30A differs from optical waveguide 30 in that it does not have a second metal film forming projection 36 and a second metal film 361. Optical fiber 130 is placed on the solder resist layer 15 of the wiring substrate 10 such that the incident surface of optical fiber 130 faces the end face of optical waveguide 30A on the side farther from the first metal film 351 with a small gap between them. The optical axis of optical fiber 130 coincides with the optical axis of optical waveguide 30A.

[0072] Light L incident perpendicularly from the light-emitting portion 113 of the light-emitting element 110 to the optical waveguide 30A is reflected at a 90-degree angle by the first metal film 351, passes through the core layer 32 of the optical waveguide 30A, and is incident into the optical fiber 130 from the end face of the optical waveguide 30A, thereby transmitting the optical signal. It is also possible to replace the light-emitting element 110 with a photodetector, and configure the light incident from the optical fiber 130 to the optical waveguide 30A to be reflected at a 90-degree angle by the first metal film 351 and received by the photodetector.

[0073] The optical transceiver 6 has an optical waveguide 30A equipped with metal film-forming protrusions that are less prone to damage, thus enabling a highly reliable device.

[0074] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of Symbols]

[0075] 1. Optical waveguide mounting substrate 5,6 Optical transceiver 10 Wiring board 10C Core Board 10x through holes 11. Through-wiring 12,14,22,24 wiring layer 13,23 Insulating layer 13x, 23x Beer Hall 15,25 Solder Resist Layer 15x,25x opening 19 External connection terminals 30,30A optical waveguide 31. First cladding layer 32 core layers 33. Second Cladding Layer 35 First metal film forming protrusion 35a,36a top surface 35b,36b Slope 35c 1st area 36 Protrusion for forming second metal film 36c 2nd area 110 light-emitting elements 111,121 Main unit 112,122 Bump 113 Light-emitting part 120 light-receiving elements 123 Light receiving part 130 optical fibers 150,160 Underfill resin 300 UV curable resin 350,360 Resin protrusion 351 First metal film 361 Second metal film 400,500 masks 400x,500x opening

Claims

1. Wiring board and The circuit board has an optical waveguide formed on it, The optical waveguide is, The first cladding layer, The first cladding layer has an upper surface and an inclined surface connected to the upper surface and inclined with respect to the upper surface, and a first metal film forming projection formed on the upper surface of the first cladding layer, The first metal film formed on at least the inclined surface of the first metal film forming projection, A core layer formed on the upper surface of the first cladding layer so as to cover a portion of the first metal film, The first cladding layer has a second cladding layer formed on its upper surface so as to cover at least the upper surface and both sides of the core layer, In a plan view, the first region including the upper surface and the inclined surface of the first metal film forming projection does not have a bent portion where two line segments intersect, except for the side of the inclined surface that is in contact with the upper surface of the first cladding layer, in an optical waveguide mounting substrate.

2. The optical waveguide mounting substrate according to claim 1, wherein the upper surface of the first metal film forming projection is formed by a line segment forming a boundary with the inclined surface and curves connected directly or via other line segments to both ends of the line segment.

3. The optical waveguide mounting substrate according to claim 2, wherein the upper surface of the first metal film forming projection includes a semicircular portion.

4. The optical waveguide mounting substrate according to claim 2, wherein the upper surface of the first metal film forming projection includes a semi-elliptical portion.

5. The optical waveguide mounting substrate according to claim 1, wherein the upper surface of the first metal film forming projection is formed by a first line segment forming a boundary with the inclined surface, a first curve connected directly or via another line segment to one end of the first line segment, a second curve connected directly or via another line segment to the other end of the first line segment, and a second line segment connecting the ends of the first curve and the second curve.

6. The first cladding layer has an upper surface and an inclined surface connected to the upper surface and inclined with respect to the upper surface, and a projection for forming a second metal film is formed on the upper surface of the first cladding layer, The second metal film is formed on at least the inclined surface of the second metal film forming projection, In a plan view, the second region including the upper surface and the inclined surface of the second metal film forming projection does not have a bent portion where two line segments intersect, except for the side of the inclined surface that is in contact with the upper surface of the first cladding layer, as described in claim 1.

7. The optical waveguide mounting substrate according to claim 6, wherein the upper surface of the second metal film forming projection has the same shape as the upper surface of the first metal film forming projection.

8. A substrate for mounting an optical waveguide according to any one of claims 1 to 7, An optical communication device having a light-emitting element that emits light into the optical waveguide, or a light-receiving element that receives light emitted from the optical waveguide, or both thereof.

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