Optical circuit board and mounting structure

Abstract

An optical circuit board according to the present disclosure includes a wiring board having a first surface, a first cladding positioned on the first surface and having a first area and a second area, an optical waveguide positioned in the first area, and a guide structure positioned in the second area. The optical waveguide includes a core and a second cladding positioned to cover the core. The guide structure is positioned along the core. A third cladding is positioned between the second cladding and the surface of the core on the side opposite to the surface on the first cladding side, and on the surface of the guide structure on the side opposite to the surface on the first cladding side.

Description

Optical circuit board and mounting structure

[0001] The present invention relates to an optical circuit board and a mounting structure using the optical circuit board.

[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. As described in Patent Document 1, the optical fibers are mounted on an optical circuit board equipped with an optical waveguide via an optical connector.

[0003] Optical circuit boards are provided with optical connector mounting alignment marks to clearly indicate the mounting position of optical connectors. These mounting alignment marks are formed simultaneously with the optical waveguide cores, and therefore have approximately the same height as the optical waveguide cores. Mode field diameter (MFD) is an index used to evaluate the connectivity between optical components such as silicon photonics devices and optical fibers. MFD refers to the diameter of the portion of the optical signal that has a predetermined intensity or greater, passing through the optical component and optical fiber. Small MFD values ​​are generally required.

[0004] Patent No. 6623332

[0005] The optical circuit board according to the present disclosure includes a wiring substrate having a first surface, a first cladding located on the first surface and having a first region and a second region, an optical waveguide located in the first region, and a guide structure located in the second region. The optical waveguide includes a core and a second cladding located to cover the core. The guide structure is located along the core. A third cladding is located between the second cladding and the surface of the core opposite to the surface on the first cladding side, and on the surface of the guide structure opposite to the surface on the first cladding side.

[0006] A mounting structure according to the present disclosure includes the above-described optical circuit board, an optical component mounted on the optical circuit board, and an optical connector connected to the optical circuit board.

[0007] 1 is a plan view showing a mounting structure in which optical components and electronic components are mounted on an optical circuit board according to an embodiment of the present disclosure. FIG. 1 is an enlarged explanatory diagram illustrating a cross section of region X shown in FIG. 1. FIG. 2 is an enlarged explanatory diagram illustrating a state in which region Y shown in FIG. 2 is viewed from above. FIG. 3 is an explanatory diagram illustrating a cross section taken along line A-A shown in FIG. 4. FIG. 4 is an enlarged explanatory diagram illustrating another embodiment of region Z shown in FIG. 4. FIG. 7A to FIG. 7E are explanatory diagrams illustrating an embodiment of a method for forming an optical waveguide.

[0008] In conventional optical circuit boards, thickening the core of the optical waveguide increases the MFD, making it impossible to meet the transmission characteristics between the core and optical components. On the other hand, thinning the core of the optical waveguide satisfies the required MFD, but the mounting alignment mark formed at the same time also becomes thin. If the mounting alignment mark is thin, the optical connector will ride up on the mounting alignment mark, causing misalignment. In other words, adjusting the thickness of the optical waveguide core and mounting alignment mark to meet one purpose will not achieve the other purpose.

[0009] Therefore, there is a demand for an optical circuit board that reduces misalignment of optical connectors and has excellent optical signal transmission characteristics between the core of the optical waveguide and the optical component.

[0010] The optical circuit board according to the present disclosure has a configuration as described in the section on means for solving the above problems, thereby reducing misalignment of optical connectors and making it difficult for the MFD to increase in the core of the optical waveguide. Therefore, the optical circuit board according to the present disclosure has excellent optical signal transmission characteristics between the core of the optical waveguide and optical components.

[0011] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Figures 1 to 6. Figure 1 is a plan view showing a mounting structure 10 in which an optical component 4 and an electronic component 6 are mounted on an optical circuit board 1 according to an embodiment of the present disclosure.

[0012] 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.

[0013] Although not specifically illustrated, such a wiring board 2 includes, for example, a core layer and build-up layers laminated on both sides of the core layer. The core layer includes a core insulating layer and a core conductor layer. The core insulating 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. These resins may be used alone or in combination of two or more.

[0014] The core insulating layer 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. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the core insulating layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0015] The core conductor layer is located on the surface of the core insulating layer. The core conductor layer is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper.

[0016] A through-hole conductor is located in the core insulating layer to electrically connect the upper and lower surfaces of the core insulating layer. The through-hole conductor is located in a through-hole that penetrates the upper and lower surfaces of the core insulating layer. The through-hole conductor is formed of a metal such as copper. The through-hole conductor may be formed only on the inner wall surface, or may fill the through-hole. The through-hole conductor is connected to the core conductor layer on the surface of the core insulating layer.

[0017] The build-up layer is located on one or both sides of the core layer, and has a structure in which at least one build-up insulating layer and at least one build-up conductor layer are laminated.

[0018] The build-up insulating 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. These resins may be used alone or in combination of two or more.

[0019] The build-up insulation layers may be made of the same resin or different resins. The build-up insulation layers and the core insulation layers may be made of the same resin or different resins. Furthermore, the build-up insulation layers may have the same thickness or different thicknesses.

[0020] The build-up insulating layer 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. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the build-up insulating layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0021] The conductor layer for build-up is not limited as long as it is a conductor such as a metal, etc. Specifically, the conductor layer for build-up is formed of a metal foil such as a copper foil, or a metal plating such as copper plating.

[0022] Via-hole conductors are located in the build-up insulating layer to electrically connect the upper and lower surfaces of the build-up insulating layer. The via-hole conductors are located in via holes that penetrate the upper and lower surfaces of the build-up insulating layer. The via-hole conductors are formed, for example, by metal plating such as copper plating. The via-hole conductors are connected to build-up conductor layers located on both sides of the build-up insulating layer. The via-hole conductors may fill the via holes, or may be located only on the inner surfaces of the via holes.

[0023] As shown in Fig. 2, the optical waveguide 3 included in the optical circuit board 1 according to one embodiment is located on the surface of a metal layer 21a present on the surface of the wiring board 2. Fig. 2 is an enlarged explanatory view for illustrating a cross section of region X shown in Fig. 1. The optical waveguide 3 has a structure in which a first cladding 31, a core 32, and a second cladding 33 are laminated in this order from the metal layer 21a side.

[0024] The first cladding 31 included in the optical waveguide 3 is located on the first surface 21 of the wiring board 2, specifically on the surface of the metal layer 21a present on the surface of the optical waveguide forming region of the wiring board 2. The material forming the first cladding 31 is not limited, and examples thereof include resins such as epoxy resin and silicone resin. The metal layer 21a is an optional component and may or may not be used. In other words, the wiring board 2 does not need to include the metal layer 21a.

[0025] As shown in Fig. 2, the first clad 31 has a surface located on the first surface 21 side of the wiring substrate 2 and a second surface located on the opposite side of this surface. As shown in Figs. 3 and 4, the second surface of the first clad 31 has a first region 311 and a second region 312. Fig. 3 is an enlarged explanatory view for explaining the state of region Y shown in Fig. 2 as viewed from above. Fig. 4 is an explanatory view for explaining a cross section when cut along line A-A shown in Fig. 3.

[0026] The core 32 included in the optical waveguide 3 is a portion through which light that has entered the optical waveguide 3 propagates. The core 32 extends in the first region 311 of the first cladding 31, and has a first end face and a second end face positioned opposite each other in the extending direction of the core 32. In the optical circuit board 1 according to the embodiment, for convenience, the first end face of the core 32 is the end face on the optical connector 5a side, and the second end face of the core 32 is the end face on the optical component 4 side.

[0027] Specifically, an end face of an optical transmission path (Si waveguide) 41 included in an optical component 4 mounted in a mounting area of ​​the wiring board 2 is positioned to face a second end face of the core 32 of the optical waveguide 3. With this configuration, optical signals are transmitted and received between the core 32 and the optical transmission path 41. The material forming the 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 core 32 has a thickness of, for example, 3 μm or more and 12 μm or less.

[0028] The second cladding 33 included in the optical waveguide 3 is located on the second surface of the first cladding 31 and covers the core 32 so that the first end face and the second end face of the core 32 are exposed. The second cladding 33 is also formed of a resin such as epoxy resin or silicone resin. The first cladding 31 and the second cladding 33 may be formed of the same material or different materials. Furthermore, the first cladding 31 and the second cladding 33 may have the same thickness or different thicknesses. The first cladding 31 and the second cladding 33 each have a thickness of, for example, 5 μm or more and 100 μm or less.

[0029] The optical waveguide 3 has a first side surface 3a including a first end face of the core 32 and a second side surface 3b including a second end face of the core 32. In other words, the first side surface 3a refers to a surface including an end face of the first cladding 31 and an end face of the second cladding 33 adjacent to the first end face of the core 32. The second side surface 3b refers to a surface including an end face of the first cladding 31 and an end face of the second cladding 33 adjacent to the second end face of the core 32.

[0030] 3 and 4, the guide structure 34 is located in the second region 312 of the first cladding 31 so as to be aligned with the core 32. The guide structure 34 may be formed simultaneously with the core 32, or may be formed separately.

[0031] As shown in FIG. 3 , the guide structure 34 functions as a connection guide when mounting the optical connector 5a. For example, by fitting the guide structure 34 into a groove provided in the optical connector 5a, the optical connector 5a can be connected to the optical circuit board 1 so that the core 32 and the transmitter / receiver of the optical connector 5a are not misaligned. To further improve positional accuracy, it is preferable to increase the height of the guide structure 34 so that the guide structure 34 is less likely to come off the groove of the optical connector 5a. When the guide structure 34 and the core 32 are formed simultaneously, the guide structure 34 and the core 32 are formed from the same material and have the same thickness. In this case, the positional accuracy between the guide structure 34 and the core 32 can be improved. The guide structure 34 does not necessarily have to extend from the first side surface 3a to the second side surface 3b like the core 32, but only needs to have a length from the first side surface 3a to function as an alignment mark.

[0032] As shown in Fig. 5, the third cladding 35 is located in the core 32 and the guide structure 34. Specifically, the third cladding 35 is located between the surface of the core 32 opposite to the surface on the first cladding 31 side and the second cladding 33, and on the surface of the guide structure 34 opposite to the surface on the first cladding 31 side. Fig. 5 is an enlarged explanatory view for explaining one embodiment of region Z shown in Fig. 4.

[0033] The third cladding 35 is located in the guide structure 34, which increases the thickness of the connection guide. Therefore, when mounting the optical connector 5a on the optical circuit board 1, the optical connector 5a is less likely to come off the guide structure 34 including the third cladding 35, reducing misalignment. As a result, the transmission efficiency of the optical signal between the core 32 and the optical connector 5a is improved. The third cladding 35 is located in the core 32 and is formed simultaneously, which improves the adhesion between the third cladding 35 and the core 32. Furthermore, a structure in which the third cladding 35 is located in the core 32 reduces the occurrence of cracks above the core 32 during a temperature cycle test compared to a structure in which the core 32 and the second cladding 33 are in contact with each other.

[0034] The third cladding 35 may be formed of a material different from that of the core 32 and the guide structure 34. The material forming the third cladding 35 is not limited, and examples thereof include resins such as epoxy resin and silicone resin. By forming the third cladding 35 with a different composition from that of the core 32, the thickness of the core 32 itself does not change, the MFD is less likely to increase, and the desired MFD can be easily maintained.

[0035] Furthermore, a mixed layer of the material of the core 32 and the material of the third cladding 35, or a mixed layer of the material of the guide structure 34 and the material of the third cladding 35, may be located at least one between the core 32 and the third cladding 35 and between the guide structure 34 and the third cladding 35. The presence of such a mixed layer reduces delamination between the core 32 and the third cladding 35, or between the guide structure 34 and the third cladding 35. Furthermore, the presence of a mixed layer of the material of the core 32 and the material of the third cladding 35 reduces stress concentration between the core 32 and the second cladding 33. Specifically, when the core 32 and the second cladding 33 are formed of different materials, stress concentration between the different materials is reduced. As a result, cracking is reduced.

[0036] The shape of the third cladding 35 is not limited. For example, in a cross section taken along line A-A in FIG. 3 (a cross section in the width direction of the third cladding 35), the surface of the third cladding 35 may be flat, or as shown in FIG. 6, at least a portion of the third cladding 35 may have a convex surface. FIG. 6 is an enlarged explanatory view illustrating another embodiment of region Z shown in FIG. 4. When the surface of the third cladding 35 located on the upper surface of the core 32 is convex, stress generated between the third cladding 35 and the second cladding 33 is easily dispersed, reducing delamination between them. When the surface of the third cladding 35 located on the upper surface of the guide structure 34 is convex, dust generation is reduced when the corners of the guide come into contact with grooves provided in the optical connector 5a.

[0037] 3 and 4 , in the optical circuit board 1 according to one embodiment, a plurality of cores 32 are positioned side by side, and guide structures 34 are positioned on both sides of the plurality of cores 32. However, the optical circuit board according to the present disclosure may have only one core, and the guide structure may also be positioned on only one side of the core along the core, as long as it is positioned in the second region of the first cladding.

[0038] There are no limitations on the method for forming the optical waveguide 3 on the first surface 21 of the wiring substrate 2. One embodiment of a method for forming the optical waveguide 3 will be described with reference to Figures 7A to 7E. Figures 7A to 7E are explanatory diagrams for explaining one embodiment of a method for forming the optical waveguide 3.

[0039] First, as shown in Fig. 7A, a first clad 31 is formed on the first surface 21 of the wiring substrate 2. Next, as shown in Fig. 7B, a core material 32a that will become the material for the core 32 is disposed on the second surface of the first clad 31. The materials that form the first clad 31 and the core 32 are as described above, and detailed description thereof will be omitted.

[0040] 7C, a third cladding material 35a is disposed so as to cover the upper surface of the core material 32a. The material forming the third cladding 35 is as described above, and a detailed description thereof will be omitted.

[0041] 7D , the core material 32a and the third cladding material 35a are simultaneously exposed to light, followed by heat treatment and development, to form the core 32 including the third cladding 35 and the guide structure 34 including the third cladding 35. By performing the heat treatment, a mixed layer of the core material 32a and the third cladding material 35a is formed at least between the core 32 and the third cladding 35 and between the guide structure 34 and the third cladding 35. The guide structure 34 is also made of the core material 32a.

[0042] 7E , a second cladding material is disposed so as to cover the second surface of the first cladding 31 and the core 32 including the third cladding 35. The material forming the second cladding 33 is as described above, and a detailed description thereof will be omitted. After disposing the second cladding material, the second cladding 33 is formed by exposure and development. Through this procedure, the optical waveguide 3 is formed on the first surface 21 of the wiring substrate 2.

[0043] Next, a mounting structure according to the present disclosure will be described. As shown in FIG. 1 , a 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 mounting structure 10 according to an embodiment includes an optical transmission path 41. Examples of the optical component 4 including such an optical transmission path 41 include a silicon photonics device. Examples of the electronic component 6 include an ASIC (Application Specific Integrated Circuit) and a driver IC.

[0044] 2 , the optical component 4 is electrically connected to the wiring board 2. Specifically, the optical component 4 is electrically connected to a pad 21b located in a mounting area (an area for mounting the optical component 4) of the wiring board 2 via solder 7. The pad 21b is part of a conductor layer located on the upper surface of the wiring board 2.

[0045] A silicon photonics device will be described as an example of the optical component 4. The silicon photonics device has, for example, a silicon (Si) core and silicon dioxide (SiO２ The silicon photonics device is a type of optical component having an optical transmission line 41 with a cladding of silicon carbide (Si) 32. 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, which are not shown. As described above, the optical transmission line 41 (Si waveguide 41) is located on the second side surface 3b of the optical waveguide 3 so as to face the second end face of the core 32 included in the optical waveguide 3.

[0046] 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 core 32 to the optical fiber 5 connected via the optical connector 5a.

[0047] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (6) below.

[0048] (1) An optical circuit board according to the present disclosure includes a wiring board having a first surface, a first cladding located on the first surface and having a first region and a second region, an optical waveguide located in the first region, and a guide structure located in the second region. The optical waveguide includes a core and a second cladding located to cover the core. The guide structure is located along the core. A third cladding is located between the second cladding and the surface of the core opposite to the surface facing the first cladding, and on the surface of the guide structure opposite to the surface facing the first cladding. (2) In the optical circuit board described in (1) above, the wiring board further includes a metal layer on the first surface, and the first cladding is located on an upper surface of the metal layer. (3) In the optical circuit board described in (1) or (2) above, the core and the guide structure are made of the same material. (4) In the optical circuit board according to any one of (1) to (3) above, a mixed layer of the core material and the third cladding material, or a mixed layer of the guide structure material and the third cladding material, is located at least either between the core and the third cladding or between the guide structure and the third cladding. (5) In the optical circuit board according to any one of (1) to (4) above, a plurality of cores are located side by side, and the guide structures are located on both sides of the plurality of cores to sandwich them. (6) A mounting structure according to the present disclosure includes the optical circuit board according to any one of (1) to (5) above, an optical component mounted on the optical circuit board, and an optical connector connected to the optical circuit board.

[0049] REFERENCE SIGNS LIST 1 Optical circuit board 2 Wiring board 21 First surface 21a Metal layer 21b Pad 3 Optical waveguide 31 First clad 311 First region 312 Second region 32 Core 32a Core material 33 Second clad 34 Guide structure 35 Third clad 35a Third clad material 3a First side surface 3b Second side surface 4 Optical component 41 Optical transmission path (silicon waveguide (Si waveguide)) 5 Optical fiber 5a Optical connector 6 Electronic component 7 Solder 10 Mounting structure

Claims

1. An optical circuit board comprising: a wiring board having a first surface; a first clad located on said first surface and having a first region and a second region; an optical waveguide located in said first region; and a guide structure located in said second region, wherein said optical waveguide includes a core and a second clad located so as to cover said core, said guide structure being located so as to follow said core, and a third clad being located between said second clad and the surface of said core opposite to the surface on said first clad side, and on the surface of said guide structure opposite to the surface on said first clad side.

2. The optical circuit board according to claim 1, wherein said wiring substrate further includes a metal layer on said first surface, and said first clad is located on an upper surface of said metal layer.

3. The optical circuit board according to claim 1 or 2, wherein the core and the guide structure are made of the same material.

4. An optical circuit board according to any one of claims 1 to 3, wherein a mixed layer of the material of the core and the material of the third clad, or a mixed layer of the material of the guide structure and the material of the third clad, is located at least either between the core and the third clad or between the guide structure and the third clad.

5. An optical circuit board according to any one of claims 1 to 4, wherein a plurality of the cores are positioned side by side, and the guide structures are positioned on both sides of the plurality of cores so as to sandwich them.

6. A mounting structure comprising: an optical circuit board according to any one of claims 1 to 5; an optical component mounted on said optical circuit board; and an optical connector connected to said optical circuit board.

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