Patent ID: 12216315

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, those parts that are the same are designated by the same reference numerals, and a repeated description of the same parts may be omitted.

First Embodiment

[Structure of Substrate with Optical Waveguide]

First, a structure of a substrate with an optical waveguide will be described.FIG.1AandFIG.1Bare diagrams illustrating an example of the structure of the substrate with the optical waveguide according to a first embodiment.FIG.1Ais a plan view, andFIG.1Bis a cross sectional view along a line A-A inFIG.1A. InFIG.1A, the illustration of a second cladding layer33illustrated inFIG.1Bis omitted. InFIG.1AandFIG.1B, directions are defined with reference to an XYZ coordinate system, for example. An X-direction, a Y-direction, and a Z-direction that are perpendicular to one another. InFIG.2AthroughFIG.10which follow, the directions may be defined in a similar manner, as required.

As illustrated inFIG.1AandFIG.1B, a substrate1with optical waveguide according to the first embodiment, includes a wiring substrate10, and an optical waveguide30formed on the wiring substrate10. In this example, it is assumed for the sake of convenience that the wiring substrate10has a planar shape that is rectangular, a long side of the rectangular shape is parallel to the X-direction, and a short side of the rectangular shape is parallel to the Y-direction. Various layers forming the wiring substrate10are laminated in a laminating direction that is parallel to the Z-direction.

[Wiring Substrate]

In the wiring substrate10, interconnect layers and insulating layers are laminated on both surfaces (that is, upper and lower surfaces inFIG.1B) of a core substrate10C. More particularly, in the wiring substrate10, an interconnect layer12, an insulating layer13, an interconnect layer14, and a solder resist layer15are successively laminated on one surface (upper surface) of the core substrate10C. Further, an interconnect layer22, an insulating layer23, an interconnect layer24, and a solder resist layer25are successively laminated on the other (lower surface) of the core substrate10C.

For example, a so-called glass epoxy substrate or the like, obtained by impregnating glass cloth with an insulating resin, such as an epoxy-based resin or the like, can be used as the core substrate10C. A substrate obtained by impregnating a woven or nonwoven fabric of glass fiber, carbon fiber, aramid fiber, or the like with an epoxy resin, a polyimide resin, or the like, can also be used as the core substrate10C. The core substrate10C may have a thickness in a range of approximately 60 μm to approximately 400 μm, for example. The core substrate10C is provided with through holes10xpenetrating the core substrate10C in a thickness direction thereof. The through hole10xhas a planar shape that is circular, for example.

The interconnect layer12is formed on one surface of the core substrate10C. On the other hand, the interconnect layer22is formed on the other surface of the core substrate10C. The interconnect layer12and the interconnect layer22are electrically connected to each other through via interconnects11formed in the through holes10x, respectively. Each of the interconnect layers12and22is patterned into a predetermined planar shape. A material that is used for the interconnect layers12and22and the via interconnect11may be copper (Cu) or the like, for example. The interconnect layers12and22may have a thickness in a range of approximately 10 μm to approximately 30 μm, for example. The interconnect layer12, the interconnect layer22, and the via interconnect11may be integrally formed.

The insulating layer13is formed on the one surface of the core substrate10C, so as to cover the interconnect layer12. A material that is used for the insulating layer13may be an insulating resin or the like including an epoxy-based resin or a polyimide-based resin as a main component thereof, for example. The insulating layer13may have a thickness in a range of approximately 30 μm to approximately 40 μm, for example. The insulating layer13may include a filler, such as silica (SiO2) or the like, for example.

The interconnect layer14is formed on one surface of the insulating layer13. The interconnect layer14includes via interconnects, filling an inside of via holes13xpenetrating the insulating layer13and exposing one surface of the interconnect layer12, and an interconnect pattern formed on the one surface of the insulating layer13. The interconnect layer14is electrically connected to the interconnect layer12. The via hole13xmay be a cavity having an inverted truncated cone shape, and a diameter of an opening of the cavity at one end which opens to the solder resist layer15is greater than a diameter of an opening of the cavity at the other end (that is, a bottom surface of the cavity) formed by the one surface of the interconnect layer12. A material that is used for the interconnect layer14, and a thickness of the interconnect pattern forming the interconnect layer14, may be the same as those of the interconnect layer12, for example.

The solder resist layer15is an outermost layer on one side of the wiring substrate10, and is formed on the one surface of the insulating layer13, so as to cover the interconnect layer14. The solder resist layer15may be formed of a photosensitive resin or the like, such as an epoxy-based resin, an acrylic-based resin, or the like, for example. The solder resist layer15may have a thickness in a range of approximately 15 μm to approximately 35 μm, for example.

The solder resist layer15includes openings15x, and a portion of one surface of the interconnect layer14is exposed at the bottom of the openings15x. The opening15xmay have a planar shape that is circular, for example. A metallic film may be formed on the one surface of the interconnect layer14exposed inside the opening15x, or the one surface of the interconnect layer14may be subjected to an anti-oxidation treatment, such as an organic solderability preservative (OSP) treatment or the like, as required. Examples of the metallic film include a Au layer, a Ni/Au layer (that is, a metallic film in which a Ni layer and a Au layer are laminated in this order), a Ni/Pd/Au layer (that is, a metallic film in which a Ni layer, a Pd layer, and a Au layer are laminated in this order), or the like.

External connection terminals19are formed on the interconnect layer14exposed inside the openings15x. The external connection terminals19may be solder bumps, for example. A solder material, such as an alloy containing Pb, an alloy of Sn and Cu, an alloy of Sn and Sb, an alloy of Sn and Ag, or an alloy of Sn, Ag, and Cu, or the like can be used for the solder bumps, for example. The external connection terminals19are terminals to be electrically connected to a light emitting element or a light receiving element, for example.

The insulating layer23is formed on the other surface of the core substrate10C, so as to cover the interconnect layer22. A material that is used for the insulating layer23, and a thickness of the insulating layer23, may be the same as those of the insulating layer13, for example. The insulating layer23may include a filler, such as silica (SiO2) or the like, for example. The interconnect layer24is formed on the other side of the insulating layer23. The interconnect layer24includes via interconnects, filling an inside of via holes23xpenetrating the insulating layer23and exposing one surface of the interconnect layer22, and an interconnect pattern formed on the one surface of the insulating layer23. The interconnect layer24is electrically connected to the interconnect layer22. The via hole23xmay be a cavity having an inverted truncated cone shape, and a diameter of an opening of the cavity at one end which opens to the solder resist layer25is greater than a diameter of an opening of the cavity at the other end (that is, a bottom surface of the cavity) formed by the one surface of the interconnect layer22. A material that is used for the interconnect layer24, and a thickness of the interconnect pattern forming the interconnect layer24, may be the same as those of the interconnect layer12, for example.

The solder resist layer25is an outermost layer on the other side of the wiring substrate10, and is formed on the other surface of the insulating layer23, so as to cover the interconnect layer24. A material that is used for the solder resist layer25, and a thickness of the solder resist layer25, may be the same as those of the solder resist layer15. The solder resist layer25includes openings25x, and a portion of the other surface of the interconnect layer24is exposed inside the openings25x. The opening25xmay have a planar shape that is circular, for example. The interconnect layer24exposed inside the opening25xcan be used as a pad to be electrically connected to a mounting substrate (not illustrated) or the like, such as a motherboard or the like, for example. The metallic film described above may be formed on the other surface of the interconnect layer24exposed inside the opening25x, or the other surface of the interconnect layer24may be subjected to the anti-oxidation treatment described above, such as the OSP treatment or the like, as required.

[Optical Waveguide]

FIGS.2A and2Bare partial plan views on an enlarged scale illustrating first and second metallic film forming protrusions and vicinities thereof. The optical waveguide30will be described with reference toFIG.2AandFIG.2B, in addition toFIG.1AandFIG.1B.

The optical waveguide30is formed on the solder resist layer15of the wiring substrate10. The optical waveguide30includes a first cladding layer31, a core layer32, a second cladding layer33, a first metallic film forming protrusion35, a second metallic film forming protrusion36, a pair of first protrusions38, a pair of second protrusions39, a first metallic film351, and a second metallic film361.

The first cladding layer31is formed of a photosensitive material, for example. More particularly, the first cladding layer31can be formed of a polymer, such as a polyimide-based resin, an acrylic-based resin, an epoxy-based resin, a polyolefin-based resin, a polynorbornene-based resin, or the like, for example. The first cladding layer31may have a thickness in a range of approximately 10 μm to approximately 30 μm, for example. The first cladding layer31is disposed on the wiring substrate10, so as to be approximately parallel to the wiring substrate10.

The core layer32is selectively formed on an upper surface of the first cladding layer31. The core layer32covers a portion of the first metallic film351, and a portion of the second metallic film361. In the example illustrated inFIG.1AandFIG.1B, two core layers32are elongated in a longitudinal direction, that is, the X-direction, and the two elongated core layers32are arranged side by side on the upper surface of the first cladding layer31. However, this arrangement is merely an example, and one core layer32may be formed, or three or more core layers32may be formed, as appropriate. A pitch of the core layers32arranged side by side may be in a range of approximately 200 μm to approximately 300 μm, for example. A material that is used for the core layer32may be the same as that of the first cladding layer31. The core layer32may have a thickness in a range of approximately 15 μm to approximately 35 μm, for example. A cross sectional shape of the core layer32along a short (or lateral) direction perpendicular to the longitudinal direction may be square, for example.

The second cladding layer33is formed on the upper surface of the first cladding layer31, so as to cover at least the upper surface and both side surfaces of the core layer32. A material that is used for the second cladding layer33may be the same as that of the first cladding layer31. The second cladding layer33may have a thickness in a range of approximately 10 μm to approximately 30 μm, for example.

As described above, the first cladding layer31, the core layer32, and the second cladding layer33can be formed of the same material, but a refractive index of the core layer32is higher than refractive indexes of the first cladding layer31and the second cladding layer33. The refractive index of the core layer32can be made higher than the refractive indexes of the first cladding layer31and the second cladding layer33, by including a refractive index controlling additive, such as Ge or the like, in the core layer32. The refractive indexes of the first cladding layer31and the second cladding layer33can be set to 1.5, for example, and the refractive index of the core layer32can be set to 1.6, for example.

The first metallic film forming protrusion35is formed on the upper surface of the first cladding layer31. The first metallic film forming protrusion35has an inclined surface35athat is inclined with respect to the upper surface of the first cladding layer31. An angle that is formed between the upper surface of the first cladding layer31and the inclined surface35ais 45 degrees, for example. The first metallic film forming protrusion35may include a surface parallel to or perpendicular to the upper surface of the first cladding layer31, in addition to the inclined surface35a.

As illustrated inFIG.2A, the first metallic film forming protrusion35includes, in a plan view, a first central portion35boverlapping the core layer32, a first wide portion35cextending from the first central portion35band protruding in the +Y-direction from one side surface32aof the core layer32, and a second wide portion35dextending from the first central portion35band protruding in the −Y-direction from the other side surface32bof the core layer32. The inclined surface35aspans the first central portion35b, the first wide portion35c, and the second wide portion35d.

The second metallic film forming protrusion36is formed on the upper surface of the first cladding layer31. The second metallic film forming protrusion36has an inclined surface36athat is inclined with respect to the upper surface of the first cladding layer31. An angle that is formed between the upper surface of the first cladding layer31and the inclined surface36ais 45 degrees, for example. The second metallic film forming protrusion36may include a surface parallel to or perpendicular to the upper surface of the first cladding layer31, in addition to the inclined surface36a.

As illustrated inFIG.2B, the second metallic film forming protrusion36includes a second central portion36boverlapping the core layer32, a third wide portion36cextending from the second central portion36band protruding in the +Y-direction from the one side surface32aof the core layer32, and a fourth wide portion36dextending from the second central portion36band protruding in the −Y-direction from the other side surface32bof the core layer32. The inclined surface36aspans the second central portion36b, the third wide portion36c, and the fourth wide portion36d.

The first metallic film351is formed on at least the inclined surface35aof the first metallic film forming protrusion35. At the inclined surface35a, the first metallic film351is formed on the first central portion35bcovered with the core layer32, and is exposed from the core layer32to extend to the first wide portion35cand the second wide portion35d. The second metallic film361is formed on at least the inclined surface36aof the second metallic film forming protrusion36. At the inclined surface36a, the second metallic film361is formed on the second central portion36bcovered by the core layer32, and is exposed from the core layer32to extend to the third wide portion36cand the fourth wide portion36d.

The second metallic film361formed on the inclined surface36aapproximately opposes the first metallic film351formed on the inclined surface35a. An interface between the core layer32and the first metallic film351formed on the first central portion35b, and an interface between the core layer32and the second metallic film361formed on the second central portion36b, serve as reflection surfaces that convert a propagation direction of incident light. The first metallic film351and the second metallic film361are gold (Au) films having a thickness in a range of 0.2 μm to 0.5 μm, for example.

The pair of first protrusions38is formed on the upper surface of the first cladding layer31with the core layer32interposed therebetween in the plan view, so as to be separated from the core layer32and the first metallic film forming protrusion35. The pair of first protrusions38is formed of a photosensitive resin, and protrudes from the upper surface of the first cladding layer31. Because the pair of first protrusions38is separated from the core layer32and the first metallic film forming protrusion35, light passing through the core layer32does not leak to the first protrusions38.

A distance between one of the first protrusions38and the core layer32and the first wide portion35c, and a distance between the other of the first protrusions38and the core layer32and the second wide portion35d, are preferably in a range of approximately several μm to approximately 200 μm, for example. The distance between one first protrusion38and the core layer32and the first wide portion35c, and the distance between the other first protrusion38and the core layer32and the second wide portion35d, may be constant or may not be constant. A height of the core layer32and a height of the pair of first protrusions38, with reference to the upper surface of the first cladding layer31, are the same. The term “same” as used herein includes a case where the height of the pair of first protrusions38differs by ±15% or less with respect to the height of the core layer32. The core layer32and the pair of first protrusions38may be formed of the same material.

In the pair of first protrusions38, the one first protrusion38is preferably formed along a portion of an outer edge of the first wide portion35cin the plan view, and the other first protrusion38is preferably formed along a portion of an outer edge of the second wide portion35din the plan view. In the example illustrated inFIG.1AthroughFIG.2B, the first wide portion35cand the second wide portion35dhave a rectangular shape in the plan view, the one first protrusion38has portions opposing three sides of the rectangular shape of the first wide portion35cin the plan view, and the other first protrusion38has portions opposing three sides of the rectangular shape of the second wide portion35din the plan view.

More particularly, each of the first protrusions38includes a first portion38rextending in the X-direction, a second portion38sextending in the Y-direction continuously from one end of the first portion38r, and a third portion38textending in the Y-direction continuously from the other end of the first portion38r. In this case, the first portion38r, the second portion38s, and the third portion38tof the one first protrusion38oppose the three sides of the rectangular shape of the first wide portion35cin the plan view, respectively. The first portion38r, the second portion38s, and the third portion38tof the other first protrusion38oppose the three sides of the rectangular shape of the second wide portion35din the plan view, respectively.

When the first metallic film351is viewed in a direction perpendicular to an end surface of the core layer32(a direction indicated by an arrow P1inFIG.2A), the core layer32overlaps the first metallic film351formed at the first central portion35b. In addition, when the first metallic film351is viewed in the direction perpendicular to the end surface of the core layer32, the one first protrusion38has a portion overlapping the first metallic film351formed at the first wide portion35c, and the other first protrusion38has a portion overlapping the first metallic film351formed at the second wide portion35d.

In the example illustrated inFIG.1AthroughFIG.2B, when the first metallic film351is viewed in the direction perpendicular to the end surface of the core layer32, the second portion38sof the one first protrusion38has a portion overlapping the first metallic film351formed on the inclined surface35aof the first wide portion35c. Moreover, the second portion38sof the other first protrusion38has a portion overlapping the first metallic film351formed on the inclined surface35aof the second wide portion35d. In other words, the second portion38sof the one first protrusion38has a portion opposing the first metallic film351formed on the inclined surface35aof the first wide portion35c, and the second portion38sof the other first protrusion38has a portion opposing the first metallic film351formed on the inclined surface35aof the second wide portion35d.

The pair of second protrusions39is formed on the upper surface of the first cladding layer31with the core layer32interposed therebetween in the plan view, so as to be separated from the core layer32and the second metallic film forming protrusion36. The pair of second protrusions39is formed of a photosensitive resin, and protrudes from the upper surface of the first cladding layer31. Because the pair of second protrusions39are separated from the core layer32and the second metallic film forming protrusion36, light passing through the core layer32does not leak to the second protrusions39.

A distance between one of the second protrusions39and the core layer32and the third wide portion36c, and a distance between the other of the second protrusions39and the core layer32and the fourth wide portion36d, are preferably in a range of approximately several μm to approximately 200 μm, for example. The distance between one second protrusion39and the core layer32and the third wide portion36c, and the distance between the other second protrusion39and the core layer32and the fourth wide portion36d, may be constant or may not be constant. A height of the core layer32and a height of the pair of second protrusions39, with reference to the upper surface of the first cladding layer31, are the same. The term “same” as used herein includes a case where the height of the pair of second protrusions39differs by ±15% or less with respect to the height of the core layer32. The core layer32and the pair of second protrusions39may be formed of the same material. The pair of second protrusions39may have the same shape as the pair of first protrusions38.

In the pair of second protrusions39, the one second protrusion39is preferably formed along a portion of an outer edge of the third wide portion36cin the plan view, and the other second protrusion39is preferably formed along a portion of an outer edge of the fourth wide portion36din the plan view. In the example illustrated inFIG.1AthroughFIG.2B, the third wide portion36cand the fourth wide portion36dhave a rectangular shape in the plan view, the one second protrusion39has portions opposing three sides of the rectangular shape of the third wide portion36cin the plan view, and the other second protrusion39has portions opposing three sides of the rectangular shape of the fourth wide portion36din the plan view.

More particularly, each of the second protrusions39includes a first portion39rextending in the X-direction, a second portion39sextending in the Y-direction continuously from one end of the first portion39r, and a third portion39textending in the Y-direction continuously from the other end of the first portion39r. In this case, the first portion39r, the second portion39s, and the third portion39tof the one second protrusion39oppose the three sides of the rectangular shape of the third wide portion36cin the plan view, respectively. The first portion39r, the second portion39s, and the third portion39tof the other second protrusion39oppose the three sides of the rectangular shape of the fourth wide portion36din the plan view, respectively.

When the second metallic film361is viewed in a direction perpendicular to the end surface of the core layer32(a direction indicated by an arrow P2inFIG.2B), the core layer32overlaps the second metallic film361formed at the second central portion36b. In addition, when the second metallic film361is viewed in the direction perpendicular to the end surface of the core layer32, the one second protrusion39has a portion overlapping the second metallic film361formed at the third wide portion36c, and the other second protrusion39has a portion overlapping the second metallic film361formed at the fourth wide portion36d.

In the example illustrated inFIG.1AthroughFIG.2B, when the second metallic film361is viewed in a direction perpendicular to the end surface of the core layer32, the second portion39sof the one second protrusion39has a portion overlapping with the second metallic film361formed on the inclined surface36aof the third wide portion36c. In addition, the second portion39sof the other second protrusion39has a portion overlapping the second metallic film361formed on the inclined surface36aof the fourth wide portion36d. In other words, the second portion39sof the one second protrusion39has a portion opposing the second metallic film361formed on the inclined surface36aof the third wide portion36c, and the second portion39sof the other second protrusion39has a portion opposing the second metallic film361formed on the inclined surface36aof the fourth wide portion36d.

[Method for Manufacturing Substrate with Optical Waveguide]

Next, a method for manufacturing the substrate1with optical waveguide will be described.FIG.3AthroughFIG.7are diagrams illustrating examples of manufacturing processes of the substrate with optical waveguide according to the first embodiment.

First, in a process or step illustrated inFIG.3A, the wiring substrate10is prepared. The wiring substrate10can be manufactured by a well known build-up method or the like, for example. The wiring substrate10may be prepared by purchasing or the like of a commercially available product.

Next, in a process or step illustrated inFIG.3B, the first cladding layer31is formed on the upper surface of the solder resist layer15of the wiring substrate10. The thickness of the first cladding layer31is approximately 10 μm, for example. Next, in a process or step illustrated inFIG.3C, an ultraviolet curing resin300, covering the first cladding layer31, is laminated on the upper surface of the solder resist layer15of the wiring substrate10. The thickness of the ultraviolet curing resin300is approximately 35 μm, for example.

Next, in processes or steps illustrated inFIG.4AandFIG.4B, the ultraviolet curing resin300is patterned so that only portions where the first metallic film forming protrusion35and the second metallic film forming protrusion36are to be formed remain. First, as illustrated inFIG.4A, for example, ultraviolet light is irradiated on the ultraviolet curing resin300via a mask400having openings400xat positions corresponding to the portions where the first metallic film forming protrusion35and the second metallic film forming protrusion36are to be formed, so as to expose and pattern the ultraviolet curing resin300. As a result, the ultraviolet curing resin300exposed inside the openings400xare cured. Next, in a process or step illustrated inFIG.4B, unnecessary portions of the ultraviolet curing resin300developed and removed, so as to form resin protrusions350and360.

Next, in a process or step illustrated inFIG.4C, the resin protrusions350and360are cut at an angle of 45 degrees, for example, so that the cut inclined surfaces of the resin protrusions350and360approximately oppose each other. The resin protrusions350and360may be cut by dicing using a dicer blade410, polishing using a polishing plate, or the like, for example. In a case where a scratch, a dent, or the like is generated on the cut inclined surfaces35aand36aduring the cutting, the inclined surfaces35aand36aare preferably smoothed by irradiating laser light, coating a resin liquid, or the like on the inclined surfaces35aand36a.

By the process or step described above, the first metallic film forming protrusion35having the inclined surface35athat is inclined with respect to the upper surface of the first cladding layer31, and the second metallic film forming protrusion36having the inclined surface36athat is inclined with respect to the upper surface of the first cladding layer31, are formed. As illustrated inFIG.2A, in the plan view, the first metallic film forming protrusion35has a structure including the first central portion35b, the first wide portion35cextending from the first central portion35band protruding from one side surface32aof the core layer32, and the second wide portion35dextending from the first central portion35band protruding from the other side surface32bof the core layer32. As illustrated inFIG.2B, in the plan view, the second metallic film forming protrusion36has a structure including the second central portion36b, the third wide portion36cextending from the second central portion36band protruding from one side surface32aof the core layer32, and the fourth wide portion36dextending from the second central portion36band protruding from the other side surface32bof the core layer32.

Next, in processes or steps illustrated inFIG.5AandFIG.5B, the first metallic film351is formed on at least the inclined surface35aof the first metallic film forming protrusion35, and the second metallic film361is formed on at least the inclined surface36aof the second metallic film forming protrusion36. The first metallic film351and the second metallic film361can be formed by sputtering or depositing gold, for example. Portions of the first metallic film351and the second metallic film361may be formed on the upper surfaces of the first metallic film forming protrusion35and the second metallic film forming protrusion36, and the upper surface of the first cladding layer31. Although two pairs of the first metallic film forming protrusion35and the second metallic film forming protrusion36are formed in this example (that is, an upper pair of the first and second metallic film forming protrusions35and36inFIG.5B, and a lower pair of the first and second metallic film forming protrusions35and36inFIG.5B), only one pair, or three or more pairs of the first metallic film forming protrusion35and the second metallic film forming protrusion36may be formed.

Next, in processes or steps illustrated inFIG.6AandFIG.6B, the core layer32is formed of a photosensitive resin on the upper surface of the first cladding layer31, so as to cover a portion of the first metallic film351and a portion of the second metallic film361. In addition, the pair of first protrusions38, protruding from the upper surface of the first cladding layer31, is formed of a photosensitive resin on the upper surface of the first cladding layer31, so as to be separated from the core layer32and the first metallic film forming protrusions35, with the core layer32sandwiched between the pair of first protrusions38in the plan view. Further, the pair of second protrusions39, protruding from the upper surface of the first cladding layer31, is formed of a photosensitive resin on the upper surface of the first cladding layer31, so as to be separated from the core layer32and the second metallic film forming protrusions36, with the core layer32sandwiched between the pair of second protrusions39in the plan view.

The core layer32, the first protrusion38, and the second protrusion39are formed by disposing an uncured photosensitive resin film on the first cladding layer31, and performing exposing and developing processes using the same mask, for example. The upper surface of the core layer32coincides with the upper surfaces of the first metallic film351and the second metallic film361, for example. The upper surfaces of the first metallic film351and the second metallic film361may be exposed from the core layer32. In this example, the two core layers32are elongated in the longitudinal direction, that is, the X-direction, and the two elongated core layers32are arranged on the upper surface of the first cladding layer31. However, the arrangement of the core layer32is not limited to such, and the core layer32may be formed in correspondence with the number of pairs of the first metallic film forming protrusions35and the second metallic film forming protrusions36, for example.

Next, a case where the first protrusion38and the second protrusion39are not formed, will be considered. The developer is used when developing the core layer32. Although the developer flows in various directions, the developer, mainly flowing in directions of arrows inFIG.6Btoward the first metallic film351and the second metallic film361, reaches the first metallic film351and the second metallic film361exposed from the core layer32. In this case, the first metallic film351and the second metallic film361exposed from the core layer32may become stripped or detached due to erosion caused by the developer. In the case where the first metallic film351and the second metallic film361exposed from the core layer32become stripped, the stripping may also affect the first metallic film351and the second metallic film361covered with the core layer32, to thereby generate an optical loss.

On the other hand, in the substrate1with optical waveguide, because the first protrusion38and the second protrusion39are formed, it is possible to reduce the problem described above. That is, because the first protrusion38and the second protrusion39function as dams with respect to the developer flowing in the directions of arrows or the like inFIG.6B, the amount of the developer reaching the first metallic film351and the second metallic film361can be significantly reduced. Accordingly, the first metallic film351and the second metallic film361exposed from the core layer32are less likely affected by the erosion caused by the developer, and it is thus possible to reduce stripping of the first metallic film351and the second metallic film361. As a result, it is possible to prevent the stripping of the first metallic film351and the second metallic film361exposed from the core layer32from affecting the first metallic film351and the second metallic film361covered with the core layer32, and causing the optical loss. The effect of the dam with respect to the developer is greatly dependent on the second portion38sof the first protrusion38and the second portion39sof the second protrusion39.

Next, in a process or step illustrated inFIG.7, the second cladding layer33is laminated on the core layer32. The second cladding layer33can be formed in a predetermined pattern, by disposing an uncured photosensitive resin film on the upper surface of the first cladding layer31, so as to cover at least the upper surface and both side surfaces of the core layer32, and exposing and developing the resin film. By the processes or steps described above, the substrate1with optical waveguide, having the optical waveguide30provided on the wiring substrate10, is completed.

As described above, in the substrate1with optical waveguide, because the first protrusion38and the second protrusion39are formed in the same process or step as the core layer32, it is possible to reduce the stripping of the first metallic film351or the second metallic film361caused by the developer. As a result, it is possible to reduce the optical loss caused by the stripping of the first metallic film351or the second metallic film361.

In each protrusion, the first portion, the second portion, and the third portion do not necessarily have to be parallel to the X-direction or the Y-direction in the plan view. In addition, in the plan view, the first portion, the second portion, and the third portion do not necessarily have to be linear, and some or all of the first, second, and third portions may be bent or curved.

Although the first metallic film forming protrusion35and the second metallic film forming protrusion36are provided in the present embodiment, only one of the first metallic film forming protrusion35and the second metallic film forming protrusion36may be provided.

Modifications of First Embodiment

In modifications of the first embodiment, other examples of the planar shape of the protrusion are illustrated. In the modifications of the first embodiment, a description of the parts that are the same as those of the embodiment described above may be omitted.

FIG.8AandFIG.8Bare plan views illustrating examples of the structure of the substrate with optical waveguide according to the modifications of the first embodiment. InFIG.8AandFIG.8B, the illustration of the second cladding layer33is omitted. A substrate1A with optical waveguide illustrated inFIG.8Adiffers from the substrate1with optical waveguide (refer toFIG.1A,FIG.1Bor the like) in that the first protrusion38and the second protrusion39are replaced with a first protrusion38A and a second protrusion39A, respectively.

The first protrusion38A includes the first portion38rand the second portion38s, but unlike the first protrusion38, does not include the third portion38t. The second protrusion39A includes the first portion39rand the second portion39s, but unlike the second protrusion39, does not include the third portion39t.

In the example illustrated inFIG.8A, the first wide portion35cand the second wide portion35dhave a rectangular shape in the plan view, one of the first protrusions38A has portions opposing two sides of the rectangular shape of the first wide portion35cin the plan view, and the other of the first protrusions38A has portions opposing two sides of the rectangular shape of the second wide portion35din the plan view. The second protrusion39A has the same shape as the first protrusion38A.

A substrate1B with optical waveguide illustrated inFIG.8Bdiffers from the substrate1with optical waveguide (refer toFIG.1A,FIG.1Bor the like) in that the first protrusion38and the second protrusion39are replaced with a first protrusion38B and a second protrusion39B, respectively.

The first protrusion38B only has a portion corresponding to the second portion38sof the first protrusion38. Further, the second protrusion39B only has a portion corresponding to the second portion39sof the second protrusion39.

In the example illustrated inFIG.8B, the first wide portion35cand the second wide portion35dhave a rectangular shape in the plan view, one of the first protrusions38B has a portion opposing one side of the rectangular shape of the first wide portion35cin the plan view, and the other of the first protrusions38B has a portion opposing one side of the rectangular shape of the second wide portion35din the plan view. The second protrusion39B has the same shape as the first protrusion38B.

In the substrates1,1A, and1B with optical waveguide, when the first metallic film351is viewed in the direction perpendicular to the end surface of the core layer32, one first protrusion at least has a portion corresponding to the second portion overlapping the first metallic film351formed in the first wide portion, and the other first protrusion at least has a portion corresponding to the second portion overlapping the first metallic film351formed in the second wide portion. In addition, when the second metallic film361is viewed in the direction perpendicular to the end surface of the core layer32, one second protrusions at least has a portion corresponding to the second portion overlapping the second metallic film361formed in the third wide portion, and the other second protrusion at least has a portion corresponding to the second portion overlapping the second metallic film361formed in the fourth wide portion.

According to this structure, it is possible to effectively reduce the stripping of the first metallic film351or the second metallic film361caused by the developer flowing in the directions of the arrows inFIG.6B. As a result, it is possible to reduce the optical loss caused by the stripping of the first metallic film351or the second metallic film361. In a case where the erosion caused by the developer flowing in directions other than the directions of the arrows inFIG.6Bbecomes a problem, it is preferable to further provide the first portion and the third portion in addition to the second portion. In this case, it becomes possible to effectively reduce the stripping of the first metallic film351or the second metallic film361caused by the developer flowing in various directions.

Second Embodiment

In a second embodiment, an example of an optical communication device including the substrate with optical waveguide according to the first embodiment, and a light emitting element that emits light to the optical waveguide of the substrate with optical waveguide, or a light receiving element that receives light emitted from the optical waveguide of the substrate with optical waveguide, or both the light emitting element and the light receiving element, will be described. In the second embodiment, a description of the parts that are the same as those corresponding parts of the embodiment described above may be omitted.

FIG.9is a cross sectional view illustrating an example of an optical transceiver according to a second embodiment. As illustrated inFIG.9, an optical transceiver5includes the substrate1with optical waveguide, a light emitting element110, a light receiving element120, and underfill resins150and160.

The light emitting element110includes a main body111, bumps112, and a light emitting portion113, and emits light to the optical waveguide30. The bumps112and the light emitting portion113are provided on a surface (bottom surface inFIG.9) of the main body111closer to the wiring substrate10. The bumps112are Au bumps, for example, and are electrically connected to the external connection terminals19of the wiring substrate10. The light emitting portion113is disposed at a position capable of irradiating light on the first metallic film351. A vertical cavity surface emitting laser (VCSEL), a light emitting diode (LED), or the like can be used for the light emitting element110, for example.

The underfill resin150is provided between the light emitting element110and each of a portion of the solder resist layer15and a portion of the optical waveguide30. An optically transparent resin (or light-transmitting resin), that can transmit light emitted from the light emitting element110, can be used for the underfill resin150, for example.

The light receiving element120includes a main body121, bumps122, and a light receiving portion123, and receives light emitted from the optical waveguide30. The bumps122and the light receiving portion123are provided on the surface (bottom surface inFIG.9) of the main body121closer to the wiring substrate10. The bumps122are Au bumps, for example, and are electrically connected to the external connection terminals19of the wiring substrate10. The light receiving portion123is disposed at a position capable of receiving the light reflected by the second metallic film361. A photodiode, an avalanche photodiode (APD), or the like can be used for the light receiving element120, for example.

The underfill resin160is provided between the light receiving element120and each of a portion of the solder resist layer15and a portion of the optical waveguide30. An optically transparent resin (or light-transmitting resin), that can transmit light received by the light receiving element120, can be used for the underfill resin160, for example.

InFIG.9, light L emitted from the light emitting portion113of the light emitting element110is transmitted through the underfill resin150and the second cladding layer33and into the core layer32, reaches the first metallic film351to be totally reflected by the first metallic film351, and a light propagation direction thereof is converted by approximately 90 degrees. Then, the light propagates through the core layer32, reaches the second metallic film361to be totally reflected by the second metallic film361, and a light propagation direction thereof is converted by approximately 90 degrees. Further, the light exits the core layer32, passes through the second cladding layer33and the underfill resin160, and is received by the light receiving portion123of the light receiving element120.

Because the optical transceiver5includes the optical waveguide30, the optical transceiver5can have a small optical loss.

FIG.10is a cross sectional view illustrating an example of the optical transceiver according to a modification of the second embodiment. As illustrated inFIG.10, an optical transceiver6differs from the optical transceiver5illustrated inFIG.9, in that the optical waveguide30are replaced with an optical waveguide30A and an optical fiber130for signal transmission is provided in place of the light receiving element120.

The optical waveguide30A differs from the optical waveguide30, in that the optical waveguide30A does not include the second metallic film forming protrusion36and the second metallic film361. The optical fiber130is disposed on the solder resist layer15of the wiring substrate10, so that an incident surface of the optical fiber130opposes an end surface of the optical waveguide30A on the side farther away from the first metallic film351with a slight gap formed therebetween. An optical axis of the optical fiber130coincides with an optical axis of the optical waveguide30A.

The light L from the light emitting portion113of the light emitting element110, vertically incident to the optical waveguide30A, is reflected by the first metallic film351at a 90 degree angle, passes through the core layer32of the optical waveguide30A, and becomes incident to the optical fiber130from the end surface of the optical waveguide30A, to thereby transmit an optical signal. The light emitting element110may be replaced with a light receiving element, so that the light incident to the optical waveguide30A from the optical fiber130is reflected by the first metallic film351at a 90 degree angle, and is received by the light receiving element.

Because the optical transceiver6includes the optical waveguide30A, the optical transceiver6can have a small optical loss.

Accordingly to each of the embodiments described above, it is possible to provide a substrate with an optical waveguide having a structure capable of preventing a metallic film from easily becoming stripped or detached.

Various aspects of the subject-matter described herein may be set out non-exhaustively in the following numbered clauses:

1. A method for manufacturing a substrate with optical waveguide, comprising:forming a first cladding layer on a wiring substrate;forming, on an upper surface of the first cladding layer, a first metallic film forming protrusion including an inclined surface that is inclined with respect to the upper surface of the first cladding layer;forming a first metallic film on at least the inclined surface of the first metallic film forming protrusion;forming a core layer made of a photosensitive resin on the upper surface of the first cladding layer, so as to cover a portion of the first metallic film; andforming a pair of first protrusions made of a photosensitive resin, on the upper surface of the first cladding layer with the core layer interposed therebetween in a plan view, and protruding from the upper surface of the first cladding layer, so as to be separated from the core layer and the first metallic film forming protrusion, whereinthe first metallic film forming protrusion includes a first central portion overlapping the core layer in the plan view, a first wide portion extending from the first central portion and protruding from one side surface of the core layer, and a second wide portion extending from the first central portion and protruding from the other side surface of the core layer,when the first metallic film is viewed in a direction perpendicular to an end surface of the core layer, the core layer overlaps the first metallic film formed at the first central portion, and one of the pair of first protrusions includes a portion overlapping the first metallic film formed at the first wide portion, and the other of the pair of first protrusions includes a portion overlapping the first metallic film formed at the second wide portion, andthe core layer and the pair of first protrusions are formed by performing exposure and development using the same mask.

2. The method for manufacturing the substrate with optical waveguide according to clause1, further comprising:forming on the upper surface of the first cladding layer a second metallic film forming protrusion including an inclined surface that is inclined with respect to the upper surface of the first cladding layer;forming a second metallic film on at least the inclined surface of the second metallic film forming protrusion; andforming a pair of second protrusions on the upper surface of the first cladding layer with the core layer interposed therebetween in the plan view, and protruding from the upper surface of the first cladding layer, so as to be separated from the core layer and the second metallic film forming protrusion, whereinthe pair of second protrusions is formed of a photosensitive resin,the second metallic film forming protrusion includes a second central portion overlapping the core layer in the plan view, a third wide portion extending from the second central portion and protruding from the one side surface of the core layer, and a fourth wide portion extending from the second central portion and protruding from the other side surface of the core layer,when the second metallic film is viewed in the direction perpendicular to the end surface of the core layer, the core layer overlaps the second metallic film formed at the second central portion, one of the pair of second protrusions includes a portion overlapping the second metallic film formed at the third wide portion, and the other of the pair of second protrusions includes a portion overlapping the second metallic film formed at the fourth wide portion.

Although the embodiments are numbered with, for example, “first,” or “second,” the ordinal numbers do not imply priorities of the embodiments. Many other variations and modifications will be apparent to those skilled in the art.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.