JP5312311B2 - Optical transmission board and optical module - Google Patents

Description

  The present invention relates to an optical transmission board that transmits light on a board and an optical module including the same.

  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 circuit has reached the GHz level at the clock frequency. Along with this, there is a demand for higher density and finer electrical wiring for connecting elements.

  However, with the increase in density and miniaturization of electrical wiring, crosstalk and propagation loss of electrical signals are likely to occur. For this reason, an optical transmission technique in which an electrical signal inputted to and outputted from a semiconductor element is converted into an optical signal, and the optical signal is transmitted through an optical wiring such as an optical waveguide formed on a mounting substrate has been studied.

  In optical transmission technology using optical wiring, not only light is transmitted substantially parallel to the substrate, such as an optical waveguide formed on the surface of a circuit board, but for example, light is substantially transmitted to the substrate. An optical transmission technique that performs three-dimensional transmission of an optical signal in the same manner as an electrical signal by transmitting the signal vertically has been studied.

  For example, Patent Document 1 discloses a technique in which light from a light emitting element is converted into an optical path by a light reflecting surface and incident on an optical waveguide.

JP 2006-235126 A

  However, among the light reflected by the light reflecting surface and incident on the optical waveguide, there is light that does not enter the core but enters the cladding. The upper surface of the cladding is usually in contact with air. Since air has a lower refractive index than that of the clad, light incident on the clad tends to be reflected at the interface with the air and becomes stray light, and there is room for improvement.

  The objective of this invention is providing the optical transmission board | substrate and optical module which reduce the stray light by the light which injected into the clad.

An optical transmission substrate according to an embodiment of the present invention includes a substrate, a clad, and a core, and has an optical receiving surface with the clad and the core exposed at an end, and the optical waveguide provided on the substrate A translucent resin layer provided on the optical waveguide and having a refractive index larger than that of the clad and leading out light incident on the exposed surface of the clad of the light receiving surface; and reflecting the light is not having a light reflecting surface to be incident on the light receiving surface, provided with a light path converting part provided on the substrate, the contact surface on the optical waveguide in contact with the transparent resin layer is perforated irregularities .

  The translucent resin layer is preferably provided so as to fill a space between the light reflecting surface and the light receiving surface.

  The translucent resin layer preferably has a covering portion that covers the upper surface of the light absorption layer.

  It is preferable to further include a light absorption layer provided on the optical waveguide adjacent to the light transmissive resin layer and positioned farther than the light transmissive resin layer with respect to the light reflecting surface.

  The light absorption layer is preferably a solder resist layer.

  An optical module according to an embodiment of the present invention includes an optical transmission board and a light emitting element that emits the light to the optical path conversion surface.

  According to this embodiment, by providing a translucent resin layer having a refractive index higher than that of the clad on the upper surface of the clad, it is possible to suppress stray light because light incident on the clad is emitted to the translucent resin layer. it can.

It is sectional drawing of the optical transmission board | substrate of embodiment of this invention. It is a figure which shows the light-receiving surface 41 of the optical waveguide 4 of the optical transmission board | substrate of embodiment of this invention. It is sectional drawing of the optical module of embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an optical transmission board according to an embodiment of the present invention will be described in detail with reference to the drawings. However, these drawings are only examples of the embodiments, and the present invention is not limited to them.

  The optical transmission substrate in FIG. 1 includes an optical waveguide 4 composed of a core 4a and a clad 4b, a substrate 1, a translucent resin layer 2, and an optical path conversion unit 3.

  In FIG. 1, when light from above the optical transmission board is reflected by the light reflecting surface 31 in the optical path conversion unit 3, all the light is not incident on the core 4 a in the light receiving surface 41 of the optical waveguide 4, and is indicated by a dotted arrow. As shown, there is light that enters the cladding 4b.

  The light receiving surface 41 indicates an end portion of the optical waveguide 4. As shown in FIG. 2, the light receiving surface 41 has the core 4a and the clad 4b exposed. In FIG. 2, a plurality of cores 4a are provided, but the number of cores 4a is not limited.

  An optical transmission substrate according to an embodiment of the present invention includes a translucent resin layer 2 having a refractive index higher than that of the clad 4b on the clad 4b. Thereby, in the clad 4b, when light incident on the clad 4b on the upper side of the core 4a is led to the translucent resin layer 2, the light is emitted to the translucent resin layer 2, The return of light is suppressed, and as a result, the effect of suppressing stray light to the core 4a is achieved.

  In addition, although not the translucent resin layer 2 but only a layer that absorbs light is provided on the clad 4b, a method of absorbing the light that has entered the clad 4b and suppressing stray light to the core 4a can be considered. When the refractive index of the layer that absorbs light is lower than that of the clad 4b, it is difficult to suppress the reflected light. Therefore, the transparent resin layer 2 having a higher refractive index than the clad 4b is formed on the clad 4b as in the present invention. Is preferably provided.

  As for the refractive index of the translucent resin layer 2, it is preferable that a relative refractive index difference is 1-3% with respect to the refractive index of the clad 4b, for example, so that light can be confined.

  The translucent resin layer 2 preferably has irregularities 42 on the contact surface with the optical waveguide 4. Thereby, it is easy to lead the light incident on the clad 4 b to the translucent resin layer 2. Furthermore, the presence of the concavo-convex portion 42 increases the ground contact area between the translucent resin layer 2 and the optical waveguide 4 and improves the adhesion between the translucent resin layer 2 and the optical waveguide 4. In addition, as for the surface roughness (ten-point average roughness) Rz of the uneven | corrugated | grooved part 42, 1-15 micrometers is preferable.

  The translucent resin layer 2 protrudes from the upper surface of the optical waveguide 4 by about 1 to 200 μm.

  The translucent resin layer 2 in FIG. 1 is provided not only on the optical waveguide 4 but also between the light reflecting surface 31 and the light receiving surface 41. As a result, light from above the light transmission substrate reaches the light reflecting surface 31 with little loss, and light that has undergone an optical path conversion at the light reflecting surface 31 reaches the light receiving surface 41 with little loss.

  When the translucent resin layer 2 is provided not only on the optical waveguide 4 but also so as to fill the space between the light reflecting surface 31 and the light receiving surface 41, the optical waveguide 4 of the translucent resin layer 2 is provided. The site | part which contact | connects an upper surface shows the function which suppresses peeling of the translucent resin layer 2 with the adhesiveness. In particular, the above-described function becomes more remarkable by having the above-described unevenness 42.

  Examples of the translucent resin layer 2 include an epoxy resin, an acrylic resin, a polyimide resin, and polysilane.

  The optical transmission substrate preferably has a light absorption layer 5 on the optical waveguide 4 so as to be adjacent to the translucent resin layer 2. The light absorption layer 5 is located farther than the translucent resin layer 2 with respect to the light reflection surface 31, and the light absorption layer 5 absorbs light transmitted through the translucent resin layer 2. The intensity of stray light can be attenuated.

  The light absorption layer 5 only needs to have a function of absorbing signal light transmitted through the optical waveguide. As the light absorption layer 5, for example, a pigment may be included in a resin such as an epoxy resin, an acrylic resin, a polyimide resin, or polysilane to absorb light transmitted through the core 4a. For example, a solder resist layer can be used.

  The light absorption layer 5 is produced on the upper surface of the optical waveguide 4 by using a laminating method, a spin coating, or a coating method represented by a doctor blade.

  The translucent resin layer 2 preferably has a covering portion 21 that covers the upper surface of the light absorption layer 5 as shown in FIG. Thereby, since the translucent resin layer 2 comes into contact with not only the side surface of the light absorbing layer 5 but also the upper surface of the light absorbing layer 5, the light transmitted from the translucent resin layer 2 is sufficiently absorbed. It can be absorbed by layer 5.

  Below, it shows about structures other than the translucent resin layer 2 and the light absorption layer 5. FIG.

(Optical path conversion unit 3)
The optical path conversion unit 3 has a light reflecting surface 31 on its slope. The light reflecting surface 31 is provided on the inclined surface by, for example, thinly coating or applying a metal such as gold, silver, copper, aluminum, or nickel.

  As shown in FIG. 1, the light reflecting surface 31 is inclined so that the angle formed between the light reflecting surface 31 and the light receiving surface 41 is about 45 °.

(Substrate 1)
The substrate 1 has a thickness of 0.2 to 2.0 mm, and a glass epoxy substrate, a BT resin substrate, a polyimide substrate, or the like is used. The substrate 1 may be a single layer or a laminate, and electrical wiring may be formed on both sides and inside of the substrate 1 with a through conductor or the like.

  Examples of the substrate 1 include a build-up substrate composed of a base substrate and a build-up layer. The buildup layer is composed of a resin insulating layer and a conductive layer. The resin insulating layer is made of a thermosetting epoxy resin or the like and has a thickness of 10 to 50 μm. Since the thickness is small, it is possible to make fine holes with a laser, and it can be laminated to route a complicated electric wiring pattern or to be integrated in a narrow range. The conductive layer in the build-up layer is electrically connected to a through electrode formed on the substrate.

(Optical waveguide 4)
As a material for the core 4a and the clad 4b forming the optical waveguide 4, a resin that can be directly exposed such as a photosensitive epoxy resin, acrylic resin, polyimide resin, or a refractive index change method such as polysilane can be used. Resin. In the direct exposure method, after the lower part of the clad 4b is formed, the material of the core 4a is applied, the core 4a is formed by mask exposure, and the upper part of the clad 4b is further applied and formed on the upper surface and side surfaces thereof. This is a method for producing the optical waveguide 4. The refractive index change method is a portion that becomes a core portion 4a by performing UV irradiation in addition to the portion that becomes the core 4a by utilizing the characteristics of a polysilane polymer material or the like whose refractive index is lowered by UV (ultraviolet) irradiation. This is a method for producing an optical waveguide by lowering the refractive index other than the above.

  The core 4a and the clad 4b are manufactured by a general optical waveguide manufacturing method. The cross-sectional size of the core 4a is, for example, 35 to 100 μm square.

  The core 4a has a higher refractive index than the cladding 4b (preferably a relative refractive index difference of 1 to 3% with respect to the refractive index of the cladding), and can confine an optical signal.

  Specific dimensions of the optical waveguide 4 include, for example, a lower thickness of the clad 4b of 15 to 25 μm, a cross-sectional size of the core 4a of 35 to 100 μm square, and an upper thickness of the clad 4b of 15 to 25 μm.

  It is preferable to have the conductor layer 6 under the clad 4b. For example, the conductor layer 6 is made of copper or the like generally used as electric wiring. The conductor layer 6 is preferably blackened on the surface in order to absorb light of a specific wavelength transmitted through the core 4a. This blackening treatment means oxidizing the surface with sodium chlorite or the like (treatment temperature 60 to 90 ° C.). By the blackening treatment, the surface of the conductor layer 3a is blackened and can absorb light of a specific wavelength. Further, this blackening treatment can form irregularities on the surface as shown in FIG. The uneven surface roughness Rz is preferably 1 to 15 μm.

  An example of a method for manufacturing an optical transmission board according to an embodiment of the present invention will be described below.

  First, the optical waveguide 4 having the clad 4b and the core 4a is produced on the conductor layer 6 whose surface is roughened.

  Next, the upper surface of the optical waveguide 4 is roughened by a method such as a chromic acid method, a concentrated sulfuric acid method, an alkaline permanganate method, or a plasma method.

  A groove for forming a 45 ° light reflecting surface 31 is formed on the optical waveguide 4 by stamping, etching, dicing, laser processing, or the like.

  Furthermore, the light reflecting surface 31 is produced by providing a metal or a low refractive index body on the inclined surface of the produced groove. The metal formed on the light reflecting surface 31 is refracted more than a highly reflective material such as gold (Au), silver (Ag), platinum (Pt), aluminum (Al), copper (Cu), or the core 4a. A low refractive index material having a low refractive index is desirable. Specifically, the light reflecting surface 31 is obtained by depositing a metal.

  Next, a solder resist layer is formed on the upper surface of the clad 4b as the light absorption layer 5 by a lamination method or the like, and the light absorption layer 5 is formed at a desired position by patterning.

  Further, a photosensitive polymer material having a high refractive index is applied from above the optical waveguide 4 and is cured by heating to form the translucent resin layer 2.

  The light emitting element 7 is mounted above the light reflecting surface 31 of the optical transmission board in FIG. 1 (see FIG. 3). The light emitting element 7 is mounted by metal bumps or solder.

  As shown in FIG. 3, the translucent resin layer 2 and the light emitting element 7 are preferably in close contact with each other. Thereby, in mounting of the light emitting element 7, it is possible to suppress adhesion of the light emitting element 7 onto the light emitting portion due to the flux from the solder used.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

1: Substrate 2: Translucent resin layer 21: Covering portion 3: Optical path changing portion 31: Light reflecting surface 4: Optical waveguide 4a: Core 4b: Cladding 41: Light receiving surface 42: Concavity and convexity 5: Solder resist layer 6: Conductor Layer 7: Light emitting device

Claims (6)

A substrate,
An optical waveguide including a clad and a core, having a light receiving surface where the clad and the core are exposed at an end, and provided on the substrate;
A translucent resin layer provided on the optical waveguide, having a refractive index greater than that of the cladding, and leading out light incident on the exposed surface of the cladding of the light receiving surface;
A light reflecting surface that reflects light to be incident on the light receiving surface, and includes an optical path changing unit provided on the substrate ,
Optical transmission substrate contact surface to have a concavo-convex on the optical waveguide in contact with the transparent resin layer. The transparent resin layer, the light transmission substrate according to claim 1 Symbol placement is provided to fill between the light reflecting surface and the light receiving surface. Wherein adjacent to the light-transmitting resin layer is provided on the optical waveguide, according to claim 1 or 2, wherein further comprising a light absorbing layer located farther than the transparent resin layer to the light reflecting surface Optical transmission board. The optical transmission substrate according to claim 3 , wherein the translucent resin layer has a covering portion that covers an upper surface of the light absorption layer. The optical transmission board according to claim 3 or 4, wherein said light-absorbing layer is a solder resist layer. An optical transmission board according to any one of claims 1 to 5 ,
A light emitting element that emits the light to the optical path conversion surface;
An optical module comprising:

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