Optical circuit board

Abstract

To solve the problem that an optical waveguide plate mounted on a wiring board tends to be affected by thermal expansion and contraction of the wiring board and is at risk of being cracked.SOLUTION: An optical circuit board disclosed herein comprises: an optical waveguide plate 4 including a base material 41, an optical waveguide 42 provided on an upper surface of the base material, and legs 43 provided on a lower surface of the base material; and a wiring board 3 including an insulating plate 31, leg-fitting portions provided on an upper surface of the insulating plate, and electrodes 32 located on the upper surface of the insulating plate and electrically connected to optical components. The legs of the optical waveguide plate are fitted into the leg-fitting portions of the wiring board in such a way that a gap is created between the lower surface of the optical waveguide plate and the upper surface of the wiring board.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical circuit board. [Background technology]

[0002] In recent years, optical communication networks capable of transmitting large volumes of data at high speeds have expanded, and various optical communication devices that utilize such optical communication networks exist. Such devices are equipped with optical circuit boards in which optical waveguides are connected to a wiring substrate, as described in Patent Document 1, for example. Such optical circuit boards are generally obtained by mounting optical waveguides on an organic substrate (base substrate) that is a wiring substrate.

[0003] However, because organic substrates have warping and undulations, it is difficult to mount optical waveguides on such substrates without adversely affecting flatness and positional accuracy. As a result, it becomes difficult to align the mounted optical waveguide with the optical components mounted on the wiring board (aligning the optical axis), which may result in a deterioration of the optical transmission characteristics between the optical components and the optical waveguide.

[0004] Furthermore, to improve flatness, a substrate-attached optical waveguide (optical waveguide plate), in which an optical waveguide is formed on glass, may be mounted on the organic substrate of a wiring board. However, optical waveguide plates mounted on wiring boards are susceptible to the effects of thermal expansion and contraction of the wiring board, which can lead to cracks in the optical waveguide plate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-53579 Summary of the Invention [Means for solving the problem]

[0006] The optical circuit board according to the present disclosure includes an optical waveguide plate having a substrate, an optical waveguide located on the upper surface of the substrate, and legs located on the lower surface of the substrate, and a wiring board having an insulating plate, fitting portions for the legs located on the upper surface of the insulating plate, and electrodes located on the upper surface of the insulating plate and electrically connected to an optical component. The legs of the optical waveguide plate are fitted into the fitting portions of the wiring board, and a gap exists between the lower surface of the optical waveguide plate and the upper surface of the wiring board. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1A is an explanatory diagram showing a mounting structure including an optical circuit board according to one embodiment of the present disclosure; FIG. 1B is a schematic diagram showing an optical waveguide plate included in FIG. 1A, viewed from above; and FIG. 1C is a schematic diagram showing a wiring board included in FIG. 1A, viewed from above. [Figure 2] 10A and 10B are explanatory diagrams showing a mounting structure including an optical circuit board according to another embodiment of the present disclosure. [Figure 3] (A) is an explanatory diagram showing a modified example of a leg body provided on an optical waveguide plate, (B) is an explanatory diagram showing a modified example of a first opening, and (C) is an explanatory diagram showing a modified example of a third opening. [Figure 4] FIG. 1 is an explanatory diagram showing an optical waveguide plate equipped with a connector. DETAILED DESCRIPTION OF THE INVENTION

[0008] As described above, conventional optical circuit boards have difficulty in aligning the mounted optical waveguide with the optical components mounted on the wiring board (aligning the optical axes), which may result in a deterioration in the optical transmission characteristics between the optical components and the optical waveguide. Furthermore, the optical waveguide plate mounted on the wiring board is susceptible to the effects of thermal expansion and contraction of the wiring board, which may cause cracks in the optical waveguide plate. Therefore, there is a need for an optical circuit board that can suppress cracks in the mounted optical waveguide plate and has excellent positional accuracy between the mounted optical waveguide plate and the mounted optical components.

[0009] In the wiring board according to the present disclosure, the legs of the optical waveguide plate are fitted into fitting portions of the wiring board, and a gap exists between the lower surface of the optical waveguide plate and the upper surface of the wiring board. Therefore, according to the present disclosure, it is possible to provide an optical circuit board that can suppress cracks from occurring in the mounted optical waveguide plate and has excellent positional accuracy between the mounted optical waveguide plate and the mounted optical components.

[0010] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1(A) is an explanatory diagram showing a mounting structure 1 including an optical circuit board 2 according to an embodiment of the present disclosure. The optical circuit board 2 according to the embodiment shown in Fig. 1(A) includes a wiring board 3 and an optical waveguide plate 4.

[0011] First, the wiring board 3 will be described. The wiring board 3 includes an insulating plate 31, electrodes 32, a support member 33, and a solder resist 34. The insulating plate 31 is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. Two or more of these resins may be mixed together.

[0012] The insulating plate 31 may contain a reinforcing material. Examples of the reinforcing material include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Two or more types of reinforcing materials may be used in combination. Furthermore, the insulating plate 31 may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, or titanium oxide.

[0013] The insulating plate 31 shown in Fig. 1(A) has a single-layer structure consisting of only a core layer. However, it may have a build-up structure in which insulating layers and conductor layers are alternately stacked on at least one surface of the insulating core layer. Although not shown in Fig. 1(A), through-hole conductors are usually formed to electrically connect the top and bottom surfaces of the insulating plate 31, and via-hole conductors are usually formed to electrically connect between layers in a build-up structure.

[0014] An electrode 32 and a support member 33 are positioned on the surface of the insulating plate 31. The electrode 32 is made of a metal such as copper, and is used for electrical connection with an optical component 5, which will be described later. The support member 33 is used to support legs 43 provided on the optical waveguide plate 4, which will be described later. Like the electrode 32, the legs 43 are also made of a metal such as copper. The support member 33 is not necessarily required for the wiring board 3. The support member 33 may be appropriately positioned when it is desired to reduce the length of the legs 43, for example, by raising the position where the bottoms of the legs 43, which will be described later, abut.

[0015] In the wiring board 3 shown in FIG. 1(A), a solder resist 34 is positioned so as to cover the surface of the insulating plate 31. The solder resist 34 is formed of, for example, an acrylic-modified epoxy resin. As shown in FIG. 1(C), the solder resist 34 has a first opening 341 for exposing the support member 33 and a second opening 342 for exposing the electrode 32. The first opening 341 functions as a fitting portion 35 into which the leg 43 of the optical waveguide plate 4 is inserted. The second opening 342 functions as a connection portion 36 that connects the electrode 32 and the electrode 52 of the optical component 5 with solder 6. FIG. 1(C) is a schematic diagram showing the wiring board 3 as viewed from above.

[0016] Next, the optical waveguide plate 4 will be described. The optical waveguide plate 4 includes a substrate 41, an optical waveguide 42, and legs 43. The substrate 41 is preferably formed of a light-transmitting material such as glass or resin. The size of the substrate 41 is not limited as long as it is large enough to form the optical waveguide 42 on its upper surface. For example, as shown in FIG. 1(B), when the optical waveguide plate 4 is viewed from above, at least a portion of the periphery of the substrate 41 is exposed and not covered by the optical waveguide 42. This exposure facilitates the formation of the legs 43, which will be described later. The width of the periphery is appropriately set depending on the diameter of the legs 43, and is, for example, approximately 0.5 mm to 10 mm from the end.

[0017] In particular, it is preferable that the peripheral portion on the side where the optical component 5 (described later) is mounted is exposed and not covered with the optical waveguide 42. With this configuration, a part of the optical component 5 can be placed on the peripheral portion of the base material 41. This makes it easy to position the light transmitting and receiving portion 51 of the optical component 5 and the core 42b in the height direction.

[0018] The optical waveguide 42 is located on the upper surface of the substrate 41. A lower clad layer 41a is located on the upper surface side of the substrate 41, and a core 42b is located on the upper surface of the lower clad layer 41a. An upper clad layer 42c covers the upper surface of the lower clad layer 41a and the core 42b.

[0019] The core 42b included in the optical waveguide 42 acts as an optical path, and light that enters the optical waveguide 42 is transmitted while repeatedly refracted at the side, top, and bottom surfaces of the core 42b. The material forming the core 42b is not limited and is appropriately selected taking into consideration, for example, the light transmittance and the wavelength characteristics of the light passing through. Examples of such materials include epoxy resin and polyimide resin. The core 42b may have a thickness of 1 μm or more and 100 μm or less and a width of 1 μm or more and 100 μm or less.

[0020] The materials forming the lower cladding layer 42a and the upper cladding layer 42c are not limited, and examples thereof include epoxy resin and polyimide resin. The lower cladding layer 42a and the upper cladding layer 42c may have a thickness of, for example, 1 μm or more and 100 μm or less. The lower cladding layer 42a and the upper cladding layer 42c may have the same thickness or different thicknesses.

[0021] Light that enters the core 42b is transmitted while repeatedly refracting at the boundaries between the core 42b and the lower cladding layer 42a and the upper cladding layer 42c. Therefore, the resin forming the core 42b has a higher refractive index than the resins forming the lower cladding layer 42a and the upper cladding layer 42c.

[0022] Legs 43 are located on the underside of substrate 41. Legs 43 are used to secure a gap between optical waveguide board 4 and wiring board 3 and to fix optical waveguide board 4. Specifically, legs 43 are inserted into first openings 341 formed in solder resist 34 included in wiring board 3, and optical waveguide board 4 is mounted on the upper surface of wiring board 3. Legs 43 are formed of, for example, resin, and may be formed of the same resin as core 42b.

[0023] The diameter of the leg 43 is not limited as long as it is large enough to be inserted into the first opening 341. From the viewpoint of ease of insertion and positioning accuracy, the diameter of the leg 43 is preferably 1 μm to 3 μm smaller than the diameter of the first opening 341. The length of the leg 43 is not limited as long as it allows a gap to exist between the upper surface of the wiring board 3 and the lower surface of the optical waveguide plate 4, and allows the core 42b included in the optical waveguide 42 to be mounted on the wiring board 3 so that its height is aligned with that of the light transmitting and receiving unit 51 of the optical component 5 (described below). The gap between the upper surface of the wiring board 3 and the lower surface of the optical waveguide plate 4 prevents contact between the upper surface of the wiring board 3 and the lower surface of the base 41 of the optical waveguide plate 4. This makes the base 41 less susceptible to deformation due to thermal expansion and contraction, such as warping and undulation, that occurs in the wiring board 3. As a result, cracks occurring in the optical waveguide plate 4 can be suppressed. In order to reduce the influence of such deformation, the gap may be, for example, 10 μm or more per 10 mm of the length of the optical waveguide 42, although this depends on the length of the optical waveguide 42. The leg 43 and the fitting portion 35 may be reinforced with an adhesive. The gap may be filled with an elastic adhesive, the tensile modulus of which is 1 N / mm. 2 Over 100N / mm 2 It may be the following:

[0024] In a mounting structure 1 according to an embodiment of the present disclosure shown in FIG. 1(A), an optical component 5 is mounted on an optical circuit board 2 including a wiring board 3 and an optical waveguide plate 4. The optical component 5 includes a light transmitting and receiving unit 51 on at least one side surface. The light transmitting and receiving unit 51 is a component that transmits an optical signal from the optical component 5, or a component that causes the optical component 5 to receive an optical signal. Since the light transmitting and receiving unit is either a transmitting component or a receiving component depending on the optical component 5, the term "light transmitting and receiving unit" is used for convenience as a term that indicates both transmission and reception.

[0025] In the optical component 5, the lower surface of the portion where the light transmitting and receiving unit 51 is located rests on the peripheral edge of the substrate 41 of the optical waveguide plate 4, as described above. That is, the lower surface of the portion where the light transmitting and receiving unit 51 is located abuts against the upper surface of the substrate 41 of the optical waveguide plate 4. With this configuration, as described above, the heightwise positions of the core 42b of the optical waveguide 42 and the light transmitting and receiving unit 51 of the optical component 5 can be determined with high precision.

[0026] Furthermore, the optical component 5 is electrically connected to the wiring board 3. Specifically, the electrodes 52 included in the optical component 5 and the electrodes 32 included in the wiring board 3 are electrically connected via the solder 6.

[0027] Next, a method for manufacturing the optical circuit board 2 according to one embodiment will be described. The manufacturing method for the optical circuit board 2 according to one embodiment includes the steps of forming an optical waveguide plate 4, forming a wiring board 3, and mounting the optical waveguide plate 4 on the wiring board 3.

[0028] The process for forming the optical waveguide plate 4 will now be described. First, a light-transmitting substrate 41 made of glass, resin, or the like is prepared. Next, an optical waveguide 42 is formed on the upper surface of the substrate 41. Specifically, a material for the lower clad layer 42a is applied to the upper surface of the substrate 41. Examples of materials for the lower clad layer 42a include resin films and resin pastes such as epoxy resin and polyimide resin. After applying such a material, masking, exposure, and development are performed as necessary to form the lower clad layer 42a.

[0029] Next, a photosensitive material for the core 42b is applied to the upper surface of the lower cladding layer 42a. Examples of photosensitive materials for the core 42b include resin films and resin pastes such as epoxy resin and polyimide resin. When applying the photosensitive material for the core 42b, care is taken to avoid applying the material for the core 42b to positions that overlap with the areas where the legs 43 will be formed in a planar perspective view. Next, a photosensitive material for the legs 43 is applied to the lower surface of the substrate 41. The material for the legs 43 is preferably a photosensitive and developable material that can be exposed to the same amount of light and developed with the same developer as the material for the core 42b, and may be the same material as the material for the core 42b.

[0030] After the material for the core 42b and the material for the legs 43 are applied, masking, exposure, and development are performed. Specifically, first, a mask having openings corresponding to the patterns of the core 42b and the legs 43 is prepared. The mask is placed above the material for the core 42b. Light is then irradiated from above the mask. At this time, the light that passes through the openings irradiates the material for the core 42b on the upper surface of the substrate 41 and the material for the legs 43 on the lower surface of the substrate 41. The irradiated portions are hardened. The upper and lower surfaces of the substrate 41 are developed. As a result, the core 42b and the legs 43 are simultaneously formed in the portions irradiated with light. By simultaneously forming the core 42b and the legs 43, the relative positional accuracy of the core 42b and the legs 43 can be further improved.

[0031] Next, a material for the upper cladding layer 42c is applied so as to cover the lower cladding layer 42a and the core 42b. Examples of materials for the upper cladding layer 42c include resin films and resin pastes such as epoxy resin and polyimide resin. After applying such a material, masking, exposure, and development are performed as necessary to form the upper cladding layer 42c.

[0032] Next, the process of forming the wiring board 3 will be described. First, an insulating plate 31 is prepared. As described above, the insulating plate 31 is not particularly limited as long as it is made of an insulating material such as an epoxy resin or a bismaleimide-triazine resin. As described above, the insulating plate 31 may have a single-layer structure consisting of only a core layer, or may have a build-up structure in which insulating layers and conductor layers are alternately laminated on at least one surface of an insulating core layer. Furthermore, through-hole conductors may be formed to electrically connect the top and bottom surfaces of the insulating plate 31, or via-hole conductors may be formed to electrically connect between layers in a build-up structure.

[0033] Next, support members 33 for supporting legs 43 included in optical waveguide plate 4 and electrodes 32 for mounting optical components 5 are formed on the upper surface of insulating plate 31. Electrodes 32 and support members 33 are formed of a metal such as copper, specifically, a metal foil such as copper foil or a metal plating such as copper plating. As mentioned above, support members 33 are not necessarily required, and may be provided as appropriate when it is desired to shorten the length of legs 43, for example.

[0034] Next, a photosensitive material for solder resist 34 is applied to the upper surface of insulating plate 31 so as to cover support member 33 and electrodes 32. Examples of materials for solder resist 34 include resin films and resin pastes such as acrylic-modified epoxy resin. After applying such material, masks are applied to prevent light from reaching the first openings 341 exposing support member 33 and the second openings 342 exposing electrodes 32. Exposure and development are then performed to form solder resist 34. First opening 341 functions as a fitting portion 35 into which legs 43 of optical waveguide plate 4 are inserted. Second opening 342 functions as a connecting portion 36 that connects electrodes 32 and electrodes 52 of optical component 5 with solder 6. Simultaneous formation of first opening 341 and second opening 342 enhances the relative positional accuracy of the first opening 341 and second opening 342. In other words, it is possible to form an optical circuit board 2 with high relative positional accuracy between the fitting portion 35 on which the optical waveguide plate 4 is mounted and the connection portion 36 on which the optical component 5 is mounted.

[0035] Next, the optical waveguide plate 4 is mounted on the wiring board 3 by inserting the legs 43 included in the optical waveguide plate 4 into the fitting portions 35 and abutting them against the support members 33. To strengthen the connection between the optical waveguide plate 4 and the wiring board 3, the legs 43 and the fitting portions 35 may be reinforced with an adhesive. In this manner, an optical circuit board 2 according to one embodiment is obtained. By mounting an optical component 5 on such an optical circuit board 2, a mounting structure 1 can be provided that has excellent relative positional accuracy between the optical waveguide plate 4 and the optical component 5.

[0036] Next, an optical circuit board according to another embodiment of the present disclosure will be described with reference to Fig. 2. Fig. 2 is an explanatory diagram showing a mounting structure 1' including an optical circuit board 2' according to another embodiment of the present disclosure. The optical circuit board 2' according to another embodiment shown in Fig. 2 includes a wiring board 3' and an optical waveguide plate 4. With regard to the components used in the mounting structure 1' shown in Fig. 2, the same components as those in the mounting structure 1 shown in Fig. 1(A) are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0037] 1A, a wiring board 3 included in a mounting structure 1 according to one embodiment has a solder resist formed on the upper surface of an insulating plate 31. On the other hand, a wiring board 3' included in a mounting structure 1' according to another embodiment shown in FIG. 2 differs from the wiring board 3 in that a solder resist is not formed on the upper surface of an insulating plate 31'.

[0038] A fitting portion 35' having a third opening 331' for fitting the leg body 43 of the optical waveguide plate 4 is located on the upper surface of the insulating plate 31'. By inserting the leg body 43 into the third opening 331' of the fitting portion 35', it becomes easy to mount the optical waveguide plate 4 at a predetermined position on the wiring board 3'. Furthermore, by fitting the leg body 43 into the third opening 331', the optical waveguide board 4 is less likely to come off the wiring board 3'.

[0039] The mating portion 35' and the electrode 32 are simultaneously formed by, for example, plating. Specifically, for example, electroless copper plating is performed on the surface of the insulating plate 31'. Next, a plating resist having openings corresponding to the patterns of the mating portion 35' and the electrode 32 in a plan view is applied to the electroless copper-plated surface. Next, electrolytic copper plating is performed to deposit copper plating within the openings. Finally, the plating resist is removed to remove the electroless copper plating underneath the plating resist, thereby simultaneously forming the mating portion 35' and the electrode 32 that will become the joint portion 36'. By simultaneously forming the mating portion 35' and the joint portion 36' (electrode 32), the relative positional accuracy between the mating portion 35' and the joint portion 36' (electrode 32) can be further improved. In other words, an optical circuit board 2 can be formed with high relative positional accuracy between the mating portion 35' on which the optical waveguide plate 4 is mounted and the joint portion 36' on which the optical component 5 is mounted. By mounting the optical component 5 on such an optical circuit board 2, it is possible to provide a mounting structure 1' in which the relative positional accuracy between the optical waveguide plate 4 and the optical component 5 is excellent.

[0040] The optical circuit board and mounting structure of the present disclosure are not limited to the above-described embodiment. In the above-described embodiment, the leg 43 included in the optical waveguide plate 4 has a cylindrical shape with a certain diameter, as shown in Figures 1(A), 1(B), and 2.

[0041] However, the optical waveguide plate may include, for example, legs 43' as shown in FIG. 3(A). The legs 43' have a shape that continuously narrows with increasing distance from the base 41. When the optical waveguide plate includes the legs 43' as shown in FIG. 3(A), the first opening formed in the solder resist included in the wiring board has a shape that continuously widens with increasing distance from the insulating plate, in accordance with the shape of the legs 43', as shown in FIG. 3(B). Furthermore, when a wiring board that does not include a solder resist is used, the third opening formed in the support member has a shape that continuously widens with increasing distance from the insulating plate, in accordance with the shape of the legs 43', as shown in FIG. 3(C).

[0042] The shape of the leg is not limited to a circle when viewed from above in cross section. For example, the shape of the leg may be a polygonal shape such as a triangle or a square, an oval, or an L-shape when viewed from above in cross section. For example, if the leg has an L-shape when viewed from above in cross section, the leg will not easily slip out of the first opening and the third opening. The first opening and the third opening are also appropriately formed to match the shape of the leg.

[0043] Furthermore, the optical waveguide plate may be provided with a connector 7 for connecting to an optical fiber 8, as shown in Fig. 4. Providing the optical waveguide plate with the connector 7 makes it possible to perform a transmission and reception test of an optical signal including the connector 7 and the optical waveguide 42 before mounting the optical waveguide plate on a wiring board. This makes it possible to reduce the occurrence of defects in the optical circuit board and reduce waste of wiring boards due to defects. [Explanation of symbols]

[0044] 1, 1' Mounting structure 2, 2' Optical circuit board 3, 3' wiring board 31 Insulating plate 32 electrodes 33, 33' support members 35, 35' fitting part 331' Third opening 34 Solder resist 341 First Opening 342 Second Opening 4 Optical waveguide plate 41 Base material 42 Optical waveguide 42a Lower cladding layer 42b Core 42c Upper cladding layer 43, 43' leg body 5 Optical Components 51 Light transmitting and receiving unit 52 electrodes 6 Solder 7 Connector 8. Optical Fiber

Claims

1. a substrate, an optical waveguide located on an upper surface of the substrate, and legs located on a lower surface of the substrate; The substrate has optical transparency, the optical waveguide has a lower clad layer located on the upper surface of the substrate, a core made of a photosensitive material located on the lower clad layer, and an upper clad layer located on the lower clad layer and on the core, The legs are made of a photosensitive material and are positioned so that they do not overlap with the core in a plan view. Optical waveguide plate.

2. The optical waveguide plate according to claim 1 , wherein at least a part of a peripheral edge of the substrate is exposed without being covered with the optical waveguide when viewed from above.

3. 3. The optical waveguide plate according to claim 1, wherein the core and the legs are made of the same photosensitive material.

4. the optical waveguide has a first end face and a second end face in a direction in which the core extends, a connector positioned opposite the first end face and adapted to connect to an optical fiber; an optical component positioned opposite the second end surface and having a first electrode; The optical waveguide plate according to any one of claims 1 to 3, comprising:

5. 5. The optical waveguide plate according to claim 4, wherein the optical component has a light transmitting and receiving section on a side surface opposite the second end face, and a lower surface below the light transmitting and receiving section abuts against an upper surface of the substrate.

6. The optical waveguide plate according to claim 4 or 5; a wiring board having a fitting portion and a second electrode located on an upper surface of an insulating plate; Including, the legs of the optical waveguide plate are positioned in the fitting portions, the first electrode of the optical component is connected to the second electrode; Optical circuit board.

7. 7. The optical circuit board according to claim 6, wherein a gap exists between the lower surface of said optical waveguide plate and the upper surface of said wiring board.

8. 8. The optical circuit board according to claim 6, wherein a solder resist having a first opening that serves as the fitting portion and a second opening that exposes the second electrode is located on the upper surface of the insulating plate.

9. 9. The optical circuit board according to claim 8, wherein the leg has a shape that continuously narrows with increasing distance from the base material, and the first opening has a shape that continuously widens with increasing distance from the insulating plate.

10. 10. The optical circuit board according to claim 6, wherein a conductor having a third opening serving as the fitting portion is located on the upper surface of the insulating plate.

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