JP5225490B2 - Optical transmission board and manufacturing method thereof, composite optical transmission board and optical module - Google Patents

Description

  The present invention relates to an optical transmission board having an optical path conversion surface for reflecting light, a method for manufacturing the same, and a composite optical transmission board.

  In recent years, with the improvement of information processing capability of computers, in an integrated circuit (IC) such as a semiconductor large scale integrated circuit element (LSI, VLSI) used as a microprocessor, the degree of integration of transistors has been increased. The operating speed of the IC has reached the GHz level at the clock frequency. Along with this, there has been a demand for higher density and finer electrical wiring for electrically connecting electrical elements.

  However, increasing the density and miniaturization of electrical wiring tends to cause crosstalk and propagation loss of electrical signals. Therefore, electrical signals input to and output from semiconductor devices are converted to optical signals, and the optical signals are mounted. An optical transmission technique in which an optical wiring such as an optical waveguide formed on a substrate is transmitted has been studied.

  For example, Patent Document 1 discloses an optical transmission substrate including an optical waveguide including an optical path conversion surface. Specifically, an optical path conversion surface obtained by forming a groove by cutting an optical waveguide with a dicing blade with a flat tip and forming a deflection mirror (light reflecting film) on the inner surface of the groove with a metal material or the like. An optical transmission board having the same is disclosed.

JP 2006-235126 A

  However, as shown in FIG. 1 of Patent Document 1, when the optical transmission board described in Patent Document 1 performs optical path conversion between the horizontal direction and the upper side of the deflection mirror, light that becomes stray light around the lower end of the optical path conversion surface. Since many occur, an extra signal component is transmitted, and it is difficult to transmit an optical signal having high purity.

  Therefore, an object of the present invention is to provide an optical transmission board that can be manufactured by a simpler method and that suppresses the generation of stray light, a manufacturing method thereof, and a composite optical transmission board.

  An optical transmission substrate according to an embodiment of the present invention includes a substrate, and an optical waveguide made of a resin material having a core portion and a groove portion that divides the core portion in the middle of the optical axis direction. An optical transmission board provided with an end surface in which the core portion is exposed in the groove portion of the optical waveguide and a position away from the end surface and inclined with respect to the optical axis direction of the optical waveguide. An optical path conversion surface; and a concave portion recessed in a downward direction and having an inclined surface connected to a lower end of the optical path conversion surface and inclined more greatly than the optical path conversion surface with respect to the substrate.

  The composite optical transmission board according to the embodiment of the present invention is a second light that is optically coupled to the core part via the optical transmission board and the optical path conversion surface, and light is transmitted between the main surfaces. A transmission board; and mounting means for mounting a second optical transmission board on the optical transmission board.

  An optical module according to an embodiment of the present invention is optically coupled to the core portion via the composite optical transmission board, the optical path conversion surface, and the second optical transmission board, and the second light. An optical semiconductor element mounted on a main surface opposite to the main surface on which the mounting means is provided, of the main surface of the transmission board.

  Furthermore, the method for manufacturing an optical transmission board according to the present invention includes a step (1) of forming an optical waveguide made of a resin material having a core part and a clad part on the board, and a first tilted with respect to the board. A step (2) of forming a groove having an inner surface and a second inner surface facing the first inner surface so as to divide the core portion of the optical waveguide; and a light reflecting film inside the groove. A step (3) of providing and a part of the light reflecting film on the first inner surface, the light reflecting film on the second inner surface, and a part of the optical waveguide formed in the step (3). Removed with a blade to form a groove in the optical waveguide having a recessed surface that is inclined downward with respect to the substrate from the first inner surface, and a groove having an end surface from which the core portion is exposed. Step (4).

  Since the optical transmission board according to an embodiment of the present invention includes a recess between the end surface and the optical path conversion surface, the optical transmission substrate does not include the periphery of the lower end portion of the optical path conversion surface that easily generates stray light. , Can minimize stray light.

  Moreover, when the recessed part exists between the said end surface and the said optical path conversion surface, the waste on the said optical path conversion surface slides down to the said recessed part from the inclined said optical path conversion surface, and accumulates in the said recessed part. Even if the dust accumulated in the concave portion is not removed by cleaning, the optical path conversion has little influence on the optical path conversion, so that the optical transmission substrate can obtain highly efficient optical coupling without being adversely affected by scattering due to the dust.

  The concave portion is continuously connected to the lower end of the optical path conversion surface, and preferably includes an inclined surface that is inclined more than the optical path conversion surface with respect to the substrate. Since the concave portion includes the inclined surface, the capacity of the concave portion is increased, so that a larger amount of the waste can be stored in the concave portion.

  In addition, since the concave portion is provided between the inclined surface and the end surface and has a bottom surface continuously connected to the inclined surface, the vicinity of the optical path changing surface is seen from above the optical transmission board. When aligning with the member, the bottom surface forms a mark, so that the alignment can be performed easily.

  A composite optical transmission board according to an embodiment of the present invention includes the optical transmission board, a second optical transmission board, and mounting means. The second optical transmission board is optically coupled to the core portion through the optical path conversion surface, and transmits light between the main surfaces. The mounting means mounts a second optical transmission board on the optical transmission board. The composite optical transmission board having such a configuration is easily contaminated by the flux that has flowed out of the mounting means during mounting, but the side edges of the recesses are continuously connected to the optical path conversion surface. The flux on the optical path conversion surface slides down from the inclined surface of the optical path conversion surface into the recess and accumulates in the recess. Since the flux accumulated in the recess has little influence on the optical path conversion, the optical transmission substrate can obtain highly efficient optical coupling.

The method of manufacturing an optical transmission board according to an embodiment of the present invention includes providing a light reflecting film inside a groove formed so as to divide the core portion of the optical waveguide, and providing the light reflecting film on the second inner surface. By removing, the end face of the optical waveguide can be exposed without going through complicated steps such as lift-off and etching. Furthermore, the manufacturing method has little influence on the transparency and adhesion of the optical waveguide. Since the core portion is exposed at the location where the second inner surface is removed by the manufacturing method, the optical transmission board can obtain highly efficient optical coupling.

  Further, in the manufacturing method, since the groove is formed in the optical waveguide so as to divide the core portion of the optical waveguide, the light reflecting film can be provided while directly confirming the core portion exposed on the inner surface of the groove. Therefore, as compared with the case where an optical waveguide and an optical path conversion surface are separately formed, positional deviation can be suppressed, and the obtained optical transmission substrate can obtain highly efficient optical coupling.

  The manufacturing method forms the recess by removing a region below the lower end of the first inner surface and a region including the second inner surface in the step of removing the light reflecting film on the second inner surface. be able to.

It is sectional drawing which shows typically an example of embodiment of an optical transmission board | substrate. It is sectional drawing which shows typically an example of embodiment of a composite-light transmission board | substrate. (A)-(d) is principal part sectional drawing for every process which shows an example of the embodiment of the manufacturing method of an optical transmission board | substrate (FIG. 1) typically.

  The optical transmission board according to the embodiments of the present invention will be described with reference to the drawings. However, these drawings are only examples of the embodiments of the present invention, and the present invention is not limited thereto.

  FIG. 1 is a cross-sectional view schematically showing an example of an embodiment of an optical transmission board. In FIG. 1, 1 is a substrate, 2 is an optical waveguide, 3 is an optical path conversion surface, 4 is a recess, A is an optical axis of the optical waveguide 2, and B is an optical axis of light input to and output from the optical path conversion surface 3.

  In FIG. 1, the optical waveguide 2 includes an upper clad portion 2a, a core portion 2b, and a lower clad portion 2c, and has an end face 2d of the optical waveguide 2 with the core portion 2b exposed.

  The optical transmission board of FIG. 1 reflects light B from the outside by the optical path conversion surface 3 and introduces it into the core part 2b of the optical waveguide 2, or transmits the light A propagated from the core part 2b of the optical waveguide 2 to the optical path. Reflected by the conversion surface 3 and emitted to the outside. That is, the optical path conversion surface 3 transmits and receives light between the outside and the optical waveguide through itself.

  The optical transmission substrate of FIG. 1 includes a substrate 1, an optical waveguide 2, and an optical path conversion surface 3, and further includes a recess 4.

  The recess 4 is provided on the substrate 1, is interposed between the end surface 2 d of the optical waveguide 2 and the optical path conversion surface 3, and has a structure that is recessed in the direction of the substrate 1. For example, in FIG. 1, the concave portion 4 refers to a region surrounded by the bottom surface 4b, the inclined surface 4c, and the end surface 2d.

  Since the recess 4 is interposed between the end surface 2d and the optical path conversion surface 3, the area of the optical path conversion surface 3 that is normally provided up to the lower end of the end surface 2d can be reduced. Therefore, stray light generated at the time of optical path conversion can be minimized.

The side edge 4 a of the recess 4 is continuously connected to the lower end of the optical path conversion surface 3. Thus, since the recessed part 4 and the inclined surface 4c are connected continuously, for example, in the manufacture, when waste (for example, cutting waste of an optical waveguide by a dicing saw) exists on the optical path conversion surface 3 Alternatively, when a flux generated from mounting means such as solder is present on the optical path conversion surface 3 in a mounting process with another substrate, the scrap or flux on the inclined optical path conversion surface 3 is dropped to the concave portion 4 and the concave portion Waste or flux can be stored in 3. And since the waste or flux in the recessed part 3 has little influence on optical path conversion, a highly efficient optical coupling is obtained in the optical transmission board.

  The optical path conversion surface 3 is inclined with respect to the optical axis direction A of the optical waveguide 2. This inclination angle differs depending on the angle at which the optical path is to be changed. For example, when the optical path is to be converted by 90 degrees, the inclination angle of the optical path conversion surface 3 with respect to the optical axis direction A of the optical waveguide 2 is set to 45 degrees. Is preferred.

  The recess 4 preferably has an inclined surface 4 c that is inclined more than the optical path conversion surface 3 with respect to the substrate 1. The inclined surface 4 c is continuously connected to the lower end of the optical path conversion surface 3. Since the concave portion 4 has the inclined surface 4 c, the inclination angle of the inclined surface 4 is larger than the inclination angle of the optical path conversion surface 3, and the capacity of the concave portion 4 increases, so that more waste or flux is stored in the concave portion 4. Is possible. In FIG. 1, the inclined surface 4c with respect to the substrate 1 has a substantially right angle.

  The angle formed by the surfaces of the optical path conversion surface 3 and the inclined surface 4c is preferably less than 180 degrees. It is most preferable that the angle is 135 degrees in FIG. By being less than 180 degrees, waste or the like easily falls from the optical path conversion surface 3 into the recess 4.

  Moreover, it is preferable that the recessed part 4 has the bottom face 4b further. Here, the bottom surface 4b refers to a portion that is provided between the inclined surface 4c and the end surface 2d and is continuously connected to the inclined surface 4c. Since the bottom surface 4b is provided, when the positioning is performed by looking at the vicinity of the optical path conversion surface from above the optical transmission board, the bottom surface becomes a mark smaller than the optical path conversion surface, so that it is possible to perform exact alignment. . As described above, the bottom surface only needs to be confirmed as a mark when viewed from above the optical transmission substrate, and may be flat or curved.

  Below, the material of the board | substrate 1, the optical waveguide 2, the optical path conversion surface 3, etc. are shown concretely.

(Substrate 1)
As the substrate 1, for example, a printed wiring board made of generally used epoxy resin or ceramic is used. Among them, a printed wiring board having a symmetrical layer structure in which a resin insulating layer having the same thickness is formed on both sides is preferable because the mechanical strength is large and it is possible to effectively prevent the warpage of the board due to heat. It is more preferable that the resin insulating layers on both sides have the same thickness. The thickness of the substrate 1 can be set to 0.5 to 1.6 mm.

  Further, a multilayer wiring board may be used as the substrate 1. Here, the multilayer wiring substrate may be any substrate in which a plurality of electrical wiring layers and insulating layers are alternately laminated, for example, a substrate composed of a core substrate and a buildup layer formed on the wiring substrate surface side. Is also included.

(Optical waveguide 2)
The optical waveguide 2 is formed on the surface of the substrate 1 from which the solder resist and the electric wiring layer of the substrate 1 are removed. The method of forming directly on the surface of the substrate 1 can determine the position of the core 2b while confirming the position of the marker on the electrical wiring layer that can be confirmed from the opening of the solder resist by photolithography.

  As a method for producing the optical waveguide 2, a generally used method may be used, and there are a direct exposure method, a refractive index change method (photo bleaching method), a reactive ion etching method, and the like. Examples of the material of the optical waveguide 2 include photosensitive epoxy resin, acrylic resin, and polyimide resin.

(Optical path conversion surface 3)
As a method of forming the optical path conversion surface 3, generally, a part of the optical waveguide 2 is cut obliquely by grooving with a dicing saw using a diamond blade whose tip is processed at 45 degrees or 90 degrees. Formed. In addition, there are a method of forming a slope by patterning the optical waveguide 2 using a gray mask, oblique exposure, or the like, or a method of using a marking machine used when cutting a printed circuit board.

  The surface of the optical path conversion surface 3 has a high reflectance with respect to light transmitted through the optical waveguide 2 such as gold (Au), silver (Ag), platinum (Pt), aluminum (Al), copper (Cu), and the like. A film is formed on the surface as a reflective film. When the wavelength of light is 600 to 1500 nm, a metal film such as gold (Au), silver (Ag), and aluminum (Al) is preferable.

  Examples of a method for forming the optical path conversion surface 3 include commonly used methods (evaporation method, sputtering method, plating method, etc.).

  Since the optical path conversion surface 3 is required to be a flat film with few voids in order to increase the reflectivity, film formation by vapor deposition is most suitable. Since there are elements and substrate mounting portions (not shown) on which the optical path conversion surface 3 cannot be provided on the substrate 1, a mask is required to open only necessary portions while hiding unnecessary portions during film formation. From the viewpoint of size and position accuracy, vapor deposition using a metal mask is the simplest method for production.

<Composite optical transmission board>
A composite optical transmission board according to an embodiment of the present invention includes the optical transmission board, a second optical transmission board 5, and mounting means 6 for mounting the second optical transmission board 5 on the optical transmission board. .

(Second optical transmission board)
FIG. 2 is a sectional view schematically showing an example of the embodiment of the composite optical transmission board.

  In FIG. 2, an optical transmission unit 7 for transmitting light between main surfaces is provided in the second optical transmission substrate. Further, the optical transmission unit 7 is optically coupled to the core unit 2 b through the optical path conversion surface 3. In FIG. 2, the optical transmission unit 7 indicates a transparent resin filled in a through hole between both main surfaces of the second optical transmission substrate 5.

  The optical transmission part 7 has a core part 7a having a high refractive index at the center part and a clad part 7b provided around the core part 7a and having a refractive index lower than that of the core part 7a. The core 7a is a region of the transparent resin that is provided along the central axis of the through hole and has a higher refractive index in the radial direction than the surroundings. The clad portion 7b is a region located around the core portion 7a and having a refractive index higher than that of the core portion 7a. By adopting such a structure, the second optical transmission board 5 can transmit an optical signal between the boards with high efficiency.

  The light transmission unit 7 is formed using polysilane which causes a photobleaching phenomenon in which the refractive index decreases when irradiated with light, or a photosensitive acrylic resin or epoxy resin that can be removed by developing the irradiated portion. be able to. For example, when the photo bleaching phenomenon is used, polysilane is filled in a through hole provided in the second optical transmission substrate 5 and cured by heating, and then a photomask (a light shielding of a circular pattern having a diameter smaller than that of the through hole). The refractive index distribution is formed in the transparent resin in the through hole by irradiating the ultraviolet light through a lower portion to reduce the refractive index of the ultraviolet light irradiated portion and finally performing the post baking.

When using an ultraviolet curable acrylic resin or epoxy resin, the photosensitive polymer material is filled in the through hole of the second optical transmission substrate 5 and cured by heating, and then drilled with a drill or the like. By filling the part (light transmission hole center) with a material having a higher refractive index than the material initially filled, irradiating with UV light without using a photomask, and finally post-baking to penetrate. A refractive index distribution is formed in the optical transmission part 7 in the hole.

  In addition, the drill and laser which are used for the punching process of the normal printed circuit board are used suitably for formation of the above-mentioned through-hole. And a through-hole is formed by letting the 2nd optical transmission board | substrate 5 penetrate from one main surface to the other main surface. The through hole preferably has a circular cross section and a diameter of 35 to 200 μm.

  The second optical transmission board 5 has an electric wiring layer 11 that is electrically connected from one main surface to the other main surface. For example, in FIG. 2, the second optical transmission board 5 is electrically connected to the optical transmission board via the mounting means 6.

(Mounting means)
By using a spherical conductive member (for example, a ball grid array (registered trademark), hereinafter referred to as BGA) arranged in a grid pattern with respect to the optical transmission board as the mounting means 6, Position alignment between the transmission board and the second optical transmission board 5 is performed.

  Other examples of the mounting means 6 include a pin grid array (registered trademark), but BGA is particularly preferable because it is not necessary to perform mechanical alignment.

(Optical semiconductor device)
The composite optical transmission board in FIG. 2 is used by mounting the optical semiconductor element 8 on the second optical transmission board 5. Specifically, the optical semiconductor element 8 is mounted on the electric wiring layer 11 on the main surface opposite to the main surface on which the mounting means 6 is provided, among the main surfaces of the second optical transmission board 5. . The optical semiconductor element 8 is optically coupled to the core unit 2 via the optical path conversion surface 3 and the optical transmission unit 7 of the second optical transmission substrate 5.

  Examples of the optical semiconductor element 8 include a light emitting element such as a surface emitting laser (VCSEL), a surface light receiving type semiconductor light receiving element (PD: Photo Diode), and the like.

  In the optical transmission board of one embodiment of the present invention, the optical semiconductor element 8 may be directly mounted. However, it is not necessary to provide a through electrode on the optical waveguide 2 or an electrical wiring on the optical waveguide 2, and the optical waveguide As shown in FIG. 2, between the optical transmission substrate and the optical semiconductor element 8 according to one embodiment of the present invention, the electrical wiring having a bad influence such as cracks and shape defects and disconnection of the electric wiring having a step is low. It is preferable that the second optical transmission board 5 be used.

  The optical semiconductor element 8 is mounted on the main surface of the second optical transmission board 5 opposite to the main surface on which the mounting means is provided.

  In FIG. 2, light is transmitted on the composite optical transmission board as follows.

  When the optical semiconductor element 8 is a light emitting element such as a surface emitting laser (VCSEL), an optical signal emitted from the light emitting point propagates into the core part 7 a of the optical transmission part 7. Then, the optical path is changed at a substantially right angle on the optical path conversion surface 3 and reaches the core portion 2 b of the optical waveguide 2.

FIGS. 3A to 3D are cross-sectional views of relevant parts for each process schematically showing an example of an embodiment of a method for manufacturing an optical transmission board (FIG. 1). A specific manufacturing process of the optical transmission board according to the embodiment of the present invention will be described with reference to FIGS. In addition, the manufacturing method of the optical transmission board | substrate which is this embodiment is not limited to the following aspects.

(A) Formation of optical waveguide 2 As the substrate 1, a multilayer printed wiring board having a thickness of 0.8 mm was used. The outermost surface of the substrate 1 is provided with a portion where the solder resist layer and the electrical wiring layer are removed in order to form the solder resist layer and the optical waveguide 2 (not shown).

  By applying a photosensitive epoxy resin to the outermost surface of the substrate 1, performing exposure and development, an optical waveguide 2 in which the lower clad part 2c, the core part 2b, and the upper clad 2a were laminated in this order was produced. In addition, the thickness of the lower clad part 2c, the core part 2b, and the upper clad part 2a was 25 micrometers, 50 micrometers, and 25 micrometers, respectively. The thickness of the electric wiring layer 11 of the substrate 1 was about 15 μm.

(B) Formation of Groove 9 Using a dicing saw having a dicing blade with a tip angle of 45 degrees for the optical waveguide 2, from the upper clad 2a to a part of the lower clad 2c so as not to scrape the electric wiring layer of the substrate Grooving was performed to form a groove 9 having a depth of 85 μm and a surface perpendicular to the substrate 1 (second inner surface 9b) and a surface inclined by 45 degrees (first inner surface 9a). At that time, the alignment marker of the opening of the solder resist and the core portion 2b of the optical waveguide 2 were observed to align the dicing saw.

  The core portion 2b was divided by the manufactured groove 9. Further, the groove 9 was provided substantially perpendicular to the optical axis direction of the core portion 2b.

(C) Formation of Light Reflecting Film 10 A light reflecting film 10 (thickness of about 1000 mm) was formed inside the groove 9 by depositing gold (Au) from the groove 9. The vapor deposition was performed in a state where a metal mask having an opening was aligned and fixed with the substrate 1 and only the groove 9 was exposed.

(D) Step of removing the light reflecting film 10 on the second inner surface 9b First, the gold deposited on the second inner surface 9b of the groove 9 is removed using a dicing saw having a dicing blade having a thickness of 20 μm. 2 and the lower clad portion 2c are grooved into the region of the optical waveguide 2 interposed between the core portion 2b and the substrate 1, and the end surface 2d of the optical waveguide 2 where the core portion 2b is exposed is formed. Exposed (width 20 μm).

  Specifically, by using the dicing saw, the region of the optical waveguide 2 including the second inner surface 9b and the lower clad portion 2c is removed to remove the light reflecting film on the second inner surface 9b, and The region including the lower end of the inner surface 9a of 1 was removed to form the recess 4 shown in FIG.

  In the step (d), by aligning the lower cladding portion 2c and the second inner surface 9b with a 10 μm cut, the shortest distance from the end surface 2d of the optical waveguide 2 to the optical path conversion surface 3 is finally obtained. The thickness was set to 20 μm. Thereby, it was possible to suppress as much as possible the increase in the distance between the end surface 2d of the optical waveguide 2 and the optical path conversion surface 3. Further, the influence on the electric wiring could be avoided by setting the grooving depth to 85 μm.

  Thus, an optical transmission board according to an embodiment of the present invention was obtained.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 2a Upper clad part 2b Core part 2c Lower clad part 2d End face 3 Optical path conversion surface 4 Recess 4a Recess side edge 4b Bottom face 4c Inclined surface 5 Second optical transmission board 6 Mounting means 7 Optical transmission part 7a Core Portion 7b Cladding portion 9 Groove 9a First inner surface 9b Second inner surface 10 Light reflecting film 11 Electrical wiring layer A Optical axis B of optical waveguide 2 Optical axis of light input to and output from optical path conversion surface

Claims (6)

A substrate,
An optical transmission board provided on the substrate, including a core portion and a groove portion that divides the core portion in the middle of the optical axis direction, and an optical waveguide made of a resin material,
In the groove portion of the optical waveguide, an end surface where the core portion is exposed, an optical path conversion surface which is located away from the end surface and is inclined with respect to the optical axis direction of the optical waveguide, and the optical path conversion surface An optical transmission board having a recessed part recessed downward, having an inclined surface connected to the lower end of the substrate and having an inclined surface that is larger than the optical path conversion surface with respect to the substrate.   The optical transmission board according to claim 1, wherein a metal film made of a metal material is formed on a surface of the optical path conversion surface, and a resin material is exposed on the inclined surface.   3. The optical transmission board according to claim 1, wherein an angle formed between the inclined surface and the optical path conversion surface is less than 180 degrees. The optical transmission board according to any one of claims 1 to 3,
A second optical transmission board optically coupled to the core portion via the optical path conversion surface and transmitting light between the main surfaces;
Mounting means for mounting a second optical transmission board on the optical transmission board;
A composite optical transmission board comprising: A composite optical transmission board according to claim 4,
Optically coupled to the core portion via the optical path conversion surface and the second optical transmission board, and the main surface of the second optical transmission board is opposite to the main surface provided with the mounting means An optical module comprising: an optical semiconductor element mounted on the main surface on the side. A step (1) of forming an optical waveguide made of a resin material having a core portion and a cladding portion on a substrate;
Forming a groove having a first inner surface inclined with respect to the substrate and a second inner surface facing the first inner surface so as to divide the core portion of the optical waveguide (2); When,
Providing a light reflecting film inside the groove (3);
A part of the light reflecting film on the first inner surface, the light reflecting film on the second inner surface and a part of the optical waveguide formed in the step (3) are removed with a dicing blade, A step (4) of forming, in the optical waveguide, a groove having an inclined surface inclined relative to the substrate relative to the first inner surface and having a recessed portion recessed downward and an end surface from which the core portion is exposed. Manufacturing method of optical transmission board.

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