Optical circuit board and optical component mounting structure

Abstract

An optical circuit board according to the present disclosure includes a wiring board having an upper surface including a mounting region of an optical component, and an optical waveguide located on the wiring board. The optical waveguide is located adjacent to the mounting region, and includes a lower cladding, a core, and an upper cladding from the upper surface side of the wiring board. The optical waveguide has a first end surface facing the mounting region, and a second end surface including an end surface of the lower cladding, an end surface of the core, and an end surface of the upper cladding within the same plane, and located on the opposite side to the first end surface. In the second end surface, at least a portion of the end surface of the lower cladding and the end surface of the upper cladding has a protrusion protruding beyond the end surface of the core.

Description

[Technical Field]

[0001] The present disclosure relates to an optical circuit board and an optical component mounting structure using the same. [Background technology]

[0002] In recent years, optical fibers capable of transmitting large volumes of data at high speeds have come to be used in information communications. Optical signals are transmitted and received between the optical fibers and optical components (silicon photonics devices). The optical fibers and optical components are connected via optical waveguides, as described in Patent Documents 1 and 2, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-330762 [Patent Document 2] Patent No. 4678155 Summary of the Invention [Means for solving the problem]

[0004] The optical circuit board according to the present disclosure includes a wiring substrate having an upper surface including a mounting area for optical components, and an optical waveguide located on the wiring substrate. The optical waveguide is located adjacent to the mounting area and includes, from the upper surface side of the wiring substrate, a lower cladding, a core, and an upper cladding. The optical waveguide has a first end face facing the mounting area and a second end face located opposite the first end face, the second end face including the end face of the lower cladding, the end face of the core, and the end face of the upper cladding all in the same plane. At least a portion of the end face of the lower cladding and the end face of the upper cladding in the second end face has a protrusion that protrudes beyond the end face of the core.

[0005] The optical component mounting structure according to the present disclosure includes the optical circuit board described above and an optical component located in the mounting area and having an optical transmission path, with the end face of the core at the first end face facing the end face of the optical transmission path. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a plan view showing an optical component mounting structure in which optical components and electronic components are mounted on an optical circuit board according to an embodiment of the present disclosure. [Figure 2] 2 is an enlarged explanatory view for explaining a cross section of a region X shown in FIG. 1. FIG. [Figure 3] 3 is an enlarged explanatory view for explaining an example of a cross section of a region Y shown in FIG. 2. FIG. [Figure 4] 3 is an enlarged explanatory view for explaining another example of the cross section of region Y shown in FIG. 2. FIG. [Figure 5] 3 is an enlarged explanatory view for explaining an example in which the second end face of the optical waveguide has a curved shape in the cross section of region Y shown in FIG. 2. FIG. [Figure 6] 3 is an enlarged explanatory view for explaining that the conductor layer has the greatest thickness at the second end face of the optical waveguide in the cross section of region Y shown in FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0007] As mentioned above, conventional optical waveguides are prone to scratches on the end face of the connector that connects to optical fibers, etc., during product inspection or transportation. In particular, scratches on the core, which is involved in the transmission of optical signals, increase the transmission loss of the optical signals. Therefore, there is a demand for optical circuit boards that reduce the risk of scratches on the end face of optical waveguides and reduce the transmission loss of optical signals.

[0008] As described above, in the optical circuit board according to the present disclosure, at least a portion of the end face of the lower cladding and the end face of the upper cladding at the second end face has a protrusion that protrudes beyond the end face of the core. As a result, the optical circuit board according to the present disclosure can reduce the risk of scratching the end face of the optical waveguide, and can reduce the transmission loss of the optical signal.

[0009] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Figures 1 to 3. Figure 1 is a plan view showing an optical component mounting structure 10 in which an optical component 4 is mounted on an optical circuit board 1 according to an embodiment of the present disclosure.

[0010] An optical circuit board 1 according to an embodiment of the present disclosure includes a wiring board 2 and an optical waveguide 3. Examples of the wiring board 2 included in the optical circuit board 1 according to an embodiment include wiring boards that are generally used for optical circuit boards.

[0011] Although not specifically shown, such a wiring board 2 includes, for example, a core substrate and build-up layers laminated on both sides of the core substrate. The core substrate 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 and used. The core substrate usually has through-hole conductors to electrically connect the top and bottom surfaces of the core substrate.

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

[0013] The build-up layer has a structure in which insulating layers and conductor layers are alternately laminated. A part of the conductor layer located on the outermost surface (the conductor layer located on the upper surface of the wiring board 2) includes a conductor layer 21a where the optical waveguide 3 is located. The conductor layer 21a is formed of a metal such as copper. Like the core substrate, the insulating layer included in the build-up layer 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 and used.

[0014] When two or more insulating layers are present in the build-up layer, the insulating layers may be made of the same resin or different resins. The insulating layers included in the build-up layer and the core substrate may be made of the same resin or different resins. The build-up layer usually has via-hole conductors for electrically connecting the layers.

[0015] Furthermore, the insulating layer included in the build-up layer may have inorganic fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide dispersed therein.

[0016] As shown in Fig. 2, an optical waveguide 3 included in an optical circuit board 1 according to one embodiment is located on the surface of a conductor layer 21a that is present on the surface of a wiring board 2. Fig. 2 is an enlarged explanatory view illustrating a cross section of region X shown in Fig. 1. The optical waveguide 3 has a structure in which a lower clad 31, an optical waveguide core 32, and an upper clad 33 are laminated in this order from the conductor layer 21a side.

[0017] The lower cladding 31 included in the optical waveguide 3 is located on the surface of the wiring board 2, specifically on the surface of the conductor layer 21a present on the surface of the optical waveguide forming region of the wiring board 2. The material forming the lower cladding 31 is not limited, and examples thereof include resins such as epoxy resin and silicone resin.

[0018] Like the lower clad 31, the upper clad 33 included in the optical waveguide 3 is also formed of a resin such as an epoxy resin or a silicone resin. The lower clad 31 and the upper clad 33 may be made of the same material or different materials. Furthermore, the lower clad 31 and the upper clad 33 may have the same thickness or different thicknesses. The lower clad 31 and the upper clad 33 each have a thickness of, for example, about 5 μm or more and 150 μm or less.

[0019] The optical waveguide core 32 included in the optical waveguide 3 is a portion through which light that has entered the optical waveguide 3 propagates. Specifically, the side of the optical transmission line 41 included in the optical component 4 mounted in the mounting area of ​​the wiring board 2 is positioned to face the side of the optical waveguide core 32 of the optical waveguide 3. As shown in FIG. 2, the side of the optical waveguide 3 including the side of the optical waveguide core 32 facing the mounting area (optical component 4) of the wiring board 2 is defined as a first end face 3a.

[0020] Optical signals are transmitted and received between the optical waveguide core 32 and the optical transmission line 41 at this first end face 3a. The material forming the optical waveguide core 32 is not limited and is appropriately selected taking into consideration, for example, the light transmittance and the wavelength characteristics of the propagating light. Examples of the material include resins such as epoxy resin and silicone resin. The optical waveguide core 32 has a thickness of, for example, approximately 3 μm or more and 50 μm or less.

[0021] In the optical waveguide 3, the side opposite the first end face 3a is the second end face 3b, which includes the end faces of the lower cladding 31, the optical waveguide core 32, and the upper cladding 33 in the same plane. Specifically, as shown in FIG. 2, the side of the optical waveguide 3 facing the optical connector 5a is the second end face 3b. Furthermore, as shown in FIG. 5, the second end face 3b may have a curved surface portion 11 that includes the end faces of the lower cladding 31, the optical waveguide core 32, and the upper cladding 33 in the same plane. The curved surface portion 11 refers to, for example, an arch shape in which the end faces of the lower cladding 31, the optical waveguide core 32, and the upper cladding 33 are in continuous contact with each other without any steps in cross section. In this case, the apex of the arch shape is located opposite the optical connector 5a. Having such a curved surface portion 11 is advantageous in that it reduces damage to the end face of the optical waveguide core 32.

[0022] In the optical circuit board 1 according to one embodiment, the second end face 3b of the optical waveguide 3 has a protrusion 34 that protrudes beyond the end face of the optical waveguide core 32 at a portion of the end face of the lower cladding 31, as shown in FIG. 3. FIG. 3 is an enlarged explanatory view illustrating an example of a cross section of region Y shown in FIG. 2. By having such a protrusion 34, the optical circuit board 1 according to one embodiment can reduce the risk of scratching the end face of the optical waveguide 3 (the second end face 3b, particularly the end face of the optical waveguide core 32), thereby reducing the transmission loss of the optical signal. As shown in FIG. 3, the protrusion 34 located at the end face of the lower cladding 31 may be referred to as a first protrusion 341.

[0023] The protrusion 34 (first protrusion 341) may be formed of, for example, the same material as the lower clad 31 and may be molded integrally with the lower clad 31. The first protrusion 341 may be located below the intermediate portion (closer to the wiring board 2) in the thickness direction of the lower clad 31, or directly above the conductor layer 21a (at the bottom of the lower clad 31). By locating the first protrusion 341 in such a location, the first protrusion 341 is supported and reinforced by the relatively strong conductor layer 21a. When the first protrusion 341 is located directly above the conductor layer 21a (at the bottom of the lower clad 31), the support effect of the conductor layer 21a is enhanced. Furthermore, by forming the first protrusion 341 at a position away from the optical waveguide core 32, transmission of an optical signal is less likely to be hindered and the second end face of the optical waveguide 3 (particularly the end face of the optical waveguide core 32) can be protected.

[0024] The length of the protrusion 34, i.e., the length L1 from the end face of the optical waveguide core 32 to the tip of the protrusion 34, may be, for example, 1 μm or more and 3.5 μm or less, and particularly, when the protrusion 34 is the first protrusion 341, it may be, for example, 1.2 μm or more and 3.3 μm or less. When the protrusion 34 (first protrusion 341) has such a length, it is possible to sufficiently protect the second end face of the optical waveguide 3 (particularly, the end face of the optical waveguide core 32), and also to sufficiently exhibit the transmission efficiency of the optical signal.

[0025] The end face of the conductor layer 21a (conductor layer end face) may be located directly below the second end face 3b of the optical waveguide 3. Furthermore, for example, as shown in FIG. 3, the conductor layer end face may be located between the end face of the optical waveguide core 32 and the tip of the protrusion 34 in the protruding direction S of the protrusion 34 shown in FIG. 3. These may be set appropriately taking into consideration the connectivity with the optical connector 5a. When there are multiple protrusions 34, the "tip of the protrusion 34" means the tip of the protrusion 34 that is the longest from the end face of the optical waveguide core 32 to the tip of the protrusion 34.

[0026] When the end face of the conductor layer is located between the end face of the optical waveguide core 32 and the tip of the protruding portion 34 in the protruding direction S of the protruding portion 34, the relatively soft lower clad 31 can absorb the impact, and the relatively strong conductor layer 21a can protect the optical waveguide 3 from the impact. 4 As shown in Fig. 1, the thickness L3 of the conductor layer 21a may be greatest at the end face of the conductor layer. The length from the end face of the optical waveguide core 32 to the end face of the conductor layer may be, for example, 0.7 µm or more and 2 µm or less.

[0027] The protrusion 34 does not have to be located only on the end face of the lower cladding 31 as shown in Fig. 3, but may be located only on the end face of the upper cladding 33, or may be located on both the end faces of the lower cladding 31 and the upper cladding 33 as shown in Fig. 4. Fig. 4 is an enlarged explanatory view for explaining another example of the cross section of region Y shown in Fig. 2. As shown in Fig. 4, the protrusion 34 located on the end face of the upper cladding 33 is referred to as a second protrusion 342.

[0028] The second protrusion 342 is preferably located at the upper part of the end face of the upper cladding 33. For example, the second protrusion 342 may be located contiguous with the upper face of the upper cladding 33. "The second protrusion is located contiguous with the upper face of the upper cladding" means that the upper part of the base of the second protrusion 342 is substantially flush with the upper face of the upper cladding 33. By forming the second protrusion 342 at a position away from the optical waveguide core 32, the transmission of the optical signal is less likely to be impeded and the second end face of the optical waveguide 3 (particularly the end face of the optical waveguide core 32) can be protected. The protrusion 34 (second protrusion 342) may be formed, for example, from the same material as the upper cladding 33 and may be molded integrally with the upper cladding 33.

[0029] When the protrusion 34 is the second protrusion 342, the length L2 from the end face of the optical waveguide core 32 to the tip of the second protrusion 342 may be, for example, 1 μm or more and 3.5 μm or less. When the second protrusion 342 has such a length, the second end face of the optical waveguide 3 (particularly the end face of the optical waveguide core 32) can be sufficiently protected, and the transmission efficiency of the optical signal can also be sufficiently exhibited.

[0030] 4, when the protrusion 34 is located in both the lower cladding 31 and the upper cladding 33, the length L2 of the second protrusion 342 (the length from the end face of the optical waveguide core 32 to the tip of the second protrusion 342) may be longer than the length L1 of the first protrusion 341 (the length from the end face of the optical waveguide core 32 to the tip of the second protrusion 342). With this configuration, the possibility of the end face of the optical waveguide 3 being scratched can be further reduced.

[0031] Although not shown, a solder resist may be partially positioned on the surface of the wiring board 2. The solder resist is made of a resin, such as an acrylic-modified epoxy resin.

[0032] Furthermore, the end face (substrate end face) of the wiring substrate 2 may be located between the second end face 3b of the optical waveguide core 32 and the tip of the protruding portion 34 in the protruding direction of the protruding portion 34. When there are multiple protruding portions 34, the "tip of the protruding portion 34" means the tip of the protruding portion 34 that is the longest from the end face of the optical waveguide core 32 to the tip of the protruding portion 34, as described above.

[0033] Next, an embodiment of a method for forming the protrusion 34 on at least one of the lower cladding 31 and the upper cladding 33 at the second end face 3b of the optical waveguide 3 will be described.

[0034] First, the wiring board 2 is prepared. The wiring board 2 has, on its upper surface, a mounting region for the optical component 4 and an optical waveguide forming region, which are adjacent to each other. The optical waveguide forming region of the wiring board 2 includes a conductor layer 21a, which is part of the conductor layer located on the outermost surface (the conductor layer located on the upper surface of the wiring board 2). The mounting region of the wiring board 2 includes pads 21b, which are part of the conductor layer located on the outermost surface. The conductor layer 21a and the pads 21b are formed of a metal such as copper.

[0035] Next, the lower clad 31 is formed in the optical waveguide formation region. Specifically, a resin layer made of a resin such as epoxy resin or silicone resin is laminated so as to cover the optical waveguide formation region. Next, exposure and development are performed to form the lower clad 31.

[0036] Next, the optical waveguide core 32 is formed along the upper surface of the lower clad 31. The optical waveguide core 32 is formed into a predetermined shape by applying or attaching epoxy resin, silicone resin, or the like to the lower clad 31 as described above, and then performing exposure and development processes.

[0037] Next, an upper clad 33 is formed to cover the upper surface of the lower clad 31 and the optical waveguide core 32. Like the lower clad 31, the upper clad 33 is also formed by exposing and developing a resin such as an epoxy resin or a silicone resin. The lower clad 31 and the upper clad 33 may be made of the same material or different materials. Furthermore, the lower clad 31 and the upper clad 33 may have the same thickness or different thicknesses.

[0038] Next, both end faces of the lower cladding 31, the optical waveguide core 32, and the upper cladding 33 are cut, for example, with a dicer to form the first end face 3a and the second end face 3b. When cutting with the dicer, compressive stress is applied at the position where the protrusion 34 is to be formed. When the first protrusion 341 is formed on the lower cladding 31, for example, a dicing blade may be used to roll up the conductor layer 21a and apply compressive stress. When the second protrusion 342 is formed on the upper cladding 33, for example, compressive stress may be applied when the dicing blade is brought into contact.

[0039] Next, heat treatment is performed to release the accumulated compressive stress, causing a portion of at least one of the lower cladding 31 and the upper cladding 33 to protrude, thereby forming a protrusion 34 (at least one of the first protrusion 341 and the second protrusion 341). The heat treatment may be performed, for example, at a temperature of 120°C to 160°C for 30 minutes to 60 minutes.

[0040] Next, an optical component mounting structure according to the present disclosure will be described. As shown in FIG. 1 , an optical component mounting structure 10 according to an embodiment of the present disclosure has a structure in which an optical component 4 and an electronic component 6 are mounted on an optical circuit board 1 according to an embodiment. The optical component 4 mounted on the optical component mounting structure 10 according to an embodiment includes an optical transmission line 41. Examples of optical components 4 that include such optical transmission lines 41 include silicon photonics devices. Examples of electronic components 6 include ASICs (Application Specific Integrated Circuits) and driver ICs.

[0041] 2, the optical component 4 is electrically connected to a pad 21b located in the mounting region of the wiring board 2 for the optical component 4 via solder 7. The pad 21b is part of a conductor layer located on the upper surface of the wiring board 2.

[0042] A silicon photonics device will be described as an example of the optical component 4. A silicon photonics device is a type of optical component having an optical transmission line 41 with, for example, a silicon (Si) core and silicon dioxide (SiO2) cladding. The silicon photonics device includes a Si waveguide as the optical transmission line 41, and further includes a passivation film, a light source unit, a photodetector unit, and the like, although not shown. As described above, the optical transmission line 41 (Si waveguide 41) is located at one end of the optical waveguide 3 so as to face the optical waveguide core 32 included in the optical waveguide 3.

[0043] For example, an electrical signal from the wiring board 2 is transmitted to a light source unit included in the optical component 4 (silicon photonics device) via the solder 7. The light source unit receives the transmitted electrical signal and emits light. The emitted optical signal is transmitted via the optical transmission path 41 (Si waveguide 41) and the optical waveguide core 32 to the optical fiber 5 connected via the optical connector 5a.

[0044] In an optical component mounting structure 10 according to one embodiment, at least a portion of the end face of the lower cladding 31 and the end face of the upper cladding 33 on the second end face 3b of the optical waveguide 3 included in the optical circuit board 1 has a protrusion 34 that protrudes beyond the end face of the optical waveguide core 32. This reduces the risk of scratching the second end face 3b of the optical waveguide 3 (particularly the end face of the optical waveguide core 32). As a result, the optical component mounting structure 10 according to one embodiment can reduce transmission loss of optical signals. [Explanation of symbols]

[0045] 1 Optical circuit board 2. Wiring board 21a Conductor layer 21b pad 3 Optical waveguide 31 Lower Cladding 32 Optical waveguide core 33 Upper Cladding 34 Protrusion 341 1st protrusion 342 Second protrusion 4. Optical Components 41 Optical transmission line (silicon waveguide (Si waveguide)) 5. Optical Fiber 5a optical connector 6. Electronic Components 7. Solder 10 Optical component mounting structure 11 Curved part R1 Optical waveguide formation area R2 Implementation Area

Claims

1. a wiring substrate having an upper surface including an area for mounting an optical component; and an optical waveguide located on the wiring substrate; the optical waveguide is located adjacent to the mounting area and includes, from the upper surface side of the wiring substrate, a lower clad, a core, and an upper clad; the optical waveguide has a first end surface facing the mounting area; a second end face located opposite to the first end face and including an end face of the lower cladding, an end face of the core, and an end face of the upper cladding in the same plane; At least a part of the end face of the lower cladding and the end face of the upper cladding has a protrusion that protrudes beyond the end face of the core, the optical waveguide is located on a conductor layer located on an upper surface of the wiring substrate, the conductor layer includes a conductor layer end surface located directly below the second end surface, and the conductor layer end surface is located between the end surface of the core and the tip of the protruding portion in a protruding direction of the protruding portion. Optical circuit board.

2. The optical circuit board according to claim 1 , wherein the protrusions include at least a first protrusion located in the lower clad, the first protrusion located directly above the conductor layer.

3. The optical circuit board according to claim 2 , wherein the protrusions include at least a second protrusion located on the upper clad, the second protrusion being located continuously on the upper surface of the upper clad.

4. 2. The optical circuit board according to claim 1, wherein the wiring board has a board end face located between an end face of the core and a tip of the protruding portion in a direction in which the protruding portion protrudes.

5. The optical circuit board according to claim 2 , wherein the first protrusion protrudes from the end face of the core at the second end face by a length of 1.2 μm to 3.3 μm.

6. The optical circuit board according to claim 3 , wherein the second protrusion protrudes from the end face of the core at the second end face by a length of 1 μm to 3.5 μm.

7. 4. The optical circuit board according to claim 3, wherein in a direction in which the protrusion protrudes, a length from an end face of the core at the second end face to a tip of the second protrusion is longer than a length from the end face of the core at the second end face to a tip of the first protrusion.

8. 2. The optical circuit board according to claim 1, wherein the second end face has a curved surface portion that includes the end face of the lower cladding, the end face of the core, and the end face of the upper cladding in the same plane.

9. The optical circuit board according to claim 1 , wherein the conductor layer has a thickness greatest at an end face.

10. An optical circuit board according to any one of claims 1 to 9; an optical component located in the mounting area and having an optical transmission path; and an end face of the core at the first end face and an end face of the optical transmission line are opposed to each other; Optical component mounting structure.

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