JP2010085438A - Optical transmission substrate, optical module, and method of manufacturing optical transmission substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission substrate which is usable over a long period of time, and also capable of achieving optical transmission with low loss, and to provide an optical module. <P>SOLUTION: The optical transmission substrate includes: a substrate 1 including a first main surface 11 and a second main surface 12; and an optical transmission path. The optical transmission path includes: an optical transmission part 2 disposed extending from the first main surface to the second main surface so that it may open in the first main surface of the substrate 1; and a protrusion part 3 disposed protrusively on the second main surface 12 of the substrate 1, having an optical path 31 optically coupled with the optical transmission part 2 and an edge portion 33 tightly coming in contact with the upper surface of the substrate 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical transmission board for performing optical signals 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 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. 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 an optical transmission unit in the substrate thickness direction embedded in an optical waveguide between the optical waveguide and the optical semiconductor element.
JP 2004-333922 A

  However, since the technique disclosed in Patent Document 1 is formed by laminating a number of layers, there is a tendency that the optical transmission unit is easily peeled off from the photoconductive waveguide when used for a long period of time. Moreover, since it is applied by spin coating, there is a problem that the thickness direction is severely restricted and the thickness cannot be increased freely.

  The present invention has been devised to solve the above-described problems in the prior art, and its purpose is to enable long-term use and to enable low-loss optical transmission with a free thickness. An optical transmission board and an optical module are provided.

  The present invention provides a substrate having a first main surface and a second main surface, and the first main surface to the second main surface so as to open at the first main surface of the substrate. And an optical path optically coupled to the optical transmission unit and an edge that can be in close contact with the upper surface of the substrate. The present invention relates to an optical transmission board having an optical transmission line having a protrusion.

  It is preferable that both the substrate and the optical transmission line are made of an epoxy material.

  It is preferable that the protrusion is further provided with a clad portion of a protrusion provided around the optical path and having a refractive index lower than that of the optical path.

  The optical transmission part includes a core part and a cladding part of the optical transmission part provided around the core part and having a refractive index lower than that of the core part, and the refractive index of the core part of the optical transmission part And the refractive index of the optical path are preferably the same.

  The present invention provides an optical module comprising: the optical transmission board; and an optical semiconductor element mounted on the second main surface and positioned above the protrusion and optically coupled to the optical transmission path. About.

  The present invention includes a step A of forming a first through hole in a substrate, and filling the through hole with a first photosensitive resin so as to overflow on one main surface of the substrate, and then the first photosensitive resin. A step B of forming a clad portion of the optical transmission portion and a clad portion of the protruding portion by curing the resin, and forming a second through hole in the cladding portion of the optical transmission portion and the clad portion of the protruding portion And a step C of filling the second through hole with the second photosensitive resin, then curing the second photosensitive resin, and an optical path having a refractive index higher than that of the clad portion of the protrusion And a step D of forming a core part of the optical transmission part having a refractive index higher than that of the clad part of the optical transmission part.

  According to the present invention, the optical transmission path is provided on the substrate, and the edge portion is in close contact with the main surface of the substrate, so that the optical transmission path is prevented from being peeled, and even when used for a long time, the loss is stable. An optical transmission board that enables optical transmission can be provided.

  Since the substrate and the optical transmission path are both made of an epoxy resin, the substrate and the optical transmission path are firmly adhered to each other by hydrogen bonding between the epoxy groups, and peeling of the optical transmission path can be suppressed.

  A sufficient light confinement effect can be obtained because the optical transmission part and the projecting part have the core part and the clad part, respectively.

  Since the refractive index of the core part and the optical path of the optical transmission part are the same, the refractive index difference between them is small, and the light transmission between the optical transmission part and the protruding part can be made smooth.

  Since the optical semiconductor element and the protrusion are close to each other, light leakage between them can be prevented, and crosstalk and light loss can be suppressed.

  Further, according to the manufacturing method of the present invention, an optical transmission board having an optical transmission section that enables low-loss optical transmission with a free thickness by filling a photosensitive resin after forming a through hole in the board. Can be produced. Furthermore, a protrusion part can be provided by including the process of filling 1st photosensitive resin into a through-hole so that it may overflow on one main surface of a board | substrate.

  The optical transmission board of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of an optical transmission board. FIG. 2 is a cross-sectional view illustrating a configuration of an optical transmission board having a plurality of optical transmission units. 3A to 3D are cross-sectional views showing a method for manufacturing an optical transmission board. FIG. 4 is a cross-sectional view showing the configuration of an optical module having an optical transmission board.

  1-4, 1 is a board | substrate, 11 is a 1st main surface, 12 is a 2nd main surface, 2 is an optical transmission part, 21 is a core part, 22 is a clad part of an optical transmission part, 3 is a protrusion part , 31 is an optical path, 32 is a clad portion of a protruding portion, 33 is an edge portion, 4 is an optical semiconductor element, 5 is a joint portion, 6 is an optical transmission board, 7 is an optical module, 8A is a first through hole, And 8B represent the second through holes.

  The optical transmission board of the present invention is used, for example, when a plurality of semiconductor devices are connected by optical signals on a circuit board mounted in an electronic device.

  The optical transmission board 6 of the present invention is used to transmit light between the boards 1 and optically couple the optical components provided on both principal surface sides of the board 1. Any optical component may be used as long as it can transmit and receive light, and examples thereof include optical semiconductor elements such as VCSEL and PIN-PD, optical waveguides, and the like. Further, a semiconductor element can be mounted on the substrate 1, and an optical waveguide and a mirror can be formed on a large substrate (not shown) on which the substrate 1 is mounted, so that it can be used as an optical transmission substrate that bears a vertical optical path above the mirror. .

  The optical transmission board 6 includes a board 1 and an optical transmission path composed of the optical transmission part 2 and the protruding part 3. Each configuration will be described below.

(Substrate 1)
As the substrate 1, for example, a printed substrate made of a resin material such as ceramics or glass epoxy resin is used. Among these, from the aspect of compatibility with the resin that forms the optical transmission part 2 and the protruding part 3, it is preferable to use the same resin substrate as the resin that forms the optical transmission part 2 and the protruding part 3, and the mechanical strength is large. A substrate having a symmetrical layer structure in which a resin insulating layer having the same thickness is formed on both sides is desirable because it can effectively prevent the substrate from being warped by heat. The thickness of the substrate 1 can be 0.4 to 2 mm.

  Further, a multilayer wiring board may be used as the substrate 1. Here, the multilayer wiring board may be any one in which a plurality of electrical wiring layers and insulating layers are alternately laminated, and includes, for example, a core board and a buildup layer formed on the front and back sides of the wiring board. A substrate is also included. The substrate 1 preferably has a connection portion (for example, an element mounting pad, a solder resist layer, etc.) for electrical connection with the outside. In addition, in the board | substrate 1, the 2nd main surface 12 of the board | substrate 1 is the side in which the protrusion part 3 is provided, and the 1st main surface 11 of the board | substrate 1 is the main surface on the opposite side to the side in which the protrusion part 3 is provided. Say.

(Optical transmission line)
The optical transmission path plays a role of optically coupling optical components provided on the first main surface 11 and the second main surface 12 of the substrate 1 by transmitting light between the substrates 1. The optical transmission path is composed of an optical transmission part 2 and a protruding part 3.

(Optical transmission unit 2)
The light transmission unit 2 is a part that is provided inside the substrate 1 and transmits light from the first main surface 11 to the second main surface 12. The optical transmission unit 2 has a circular cross section with respect to the optical transmission direction. In that case, the diameter of the optical transmission part 2 is about 50-200 micrometers.

  The optical transmission unit 2 preferably includes a core part 21 having a high refractive index at the center and a clad part 22 provided around the core part 21 and having a refractive index lower than that of the core part 21. By adopting such a structure, a sufficient light confinement effect can be obtained in the optical transmission unit 2.

  In addition, the diameter of the core part 21 is about 35-100 micrometers.

  The light transmission unit 2 is formed using polysilane that causes a photo bleaching phenomenon in which the refractive index decreases when irradiated with light, or a photosensitive acrylic resin, epoxy resin, or the like that can be removed by developing the irradiated portion. be able to. For example, when the photo bleaching phenomenon is used, a through hole is provided in the substrate 1, and after filling the through hole with polysilane and heat-curing, a photomask (light shielding of a circular pattern having a smaller diameter than the light transmission hole) is performed. The optical transmission part 2 having the core part 21 and the clad part 22 is formed by lowering the refractive index of the ultraviolet light irradiation part and finally performing post-baking. . In this method, in order to obtain the refractive index difference between the core and the clad, it is necessary to divide into an exposed part and an unexposed part. It becomes difficult.

  In the case of using a photosensitive material such as an ultraviolet curable acrylic resin or epoxy resin, a through hole is provided in the substrate 1, and then the photosensitive polymer material that becomes the cladding is formed from the second main surface 12 side of the substrate 1. Fill. An optical semiconductor element can be mounted on the substrate 1 above the optical transmission unit 2 as shown in FIG. 4. At this time, a solder resist opening (not shown) of the element mounting unit is filled with a material. By using it as a flow-out prevention dam, it is possible to prevent the filled resin from spreading on the substrate in a wide range. Thereafter, a necessary area as the edge 3 is exposed using a photomask, and cured by performing pre-baking / developing / post-baking. Thereafter, a core material having a higher refractive index than that of the initially filled material is filled from the second main surface 12 side of the substrate 1 into the portion drilled by a drill or a laser (center portion of the light transmission hole). Also in this case, by using a solder resist opening (not shown) of the element mounting portion as a flow-out prevention dam at the time of material filling, it is possible to prevent the filling resin from spreading on the substrate in a wide range. Thereafter, a necessary area is exposed using a photomask and cured by pre-baking / developing / post-baking. If the core material can be filled only in the core 21 and the center of the optical transmission hole to be the optical path 31, the above-described mask exposure is not necessary, but it is necessary to fill a very small hole. There is an advantage that it is easy to produce by exposing only. Finally, the surface is polished so as to have a thickness necessary for the protruding portion. By the above, the optical transmission part 2 having the core part 21 and the clad part 22 and the protruding part 3 having the optical path 31 and the protruding part clad 32 can be formed at a time.

  When the optical transmission path is made of an epoxy resin and a glass epoxy substrate is used as the substrate 1 and both are made of an epoxy material (referred to as a polymer material having an epoxy group), the substrate 1 and the optical transmission path are made of epoxy. Since hydrogen bonding is performed between groups, adhesion is good and defects such as peeling are suppressed.

  For the formation of the above-described through holes, a drill, a laser, or the like used in a normal printed circuit board drilling process is preferably used. And a through-hole is formed by letting the board | substrate 1 penetrate from one main surface to the other main surface. The through hole provided in the substrate 1 preferably has a circular cross section, and the diameter is preferably 50 to 200 μm.

(Protrusion 3)
As shown in FIGS. 1 and 2, the protrusion 3 is provided so as to protrude on the substrate 1. The thickness of the protrusion part 3 is 10-100 micrometers.

  Since the protruding portion 3 protrudes from the substrate 1, it has good visibility and serves as a marker when mounting external components. The protruding portion 3 can be formed with high accuracy by a photo process. In this case, the protruding portion 3 also serves as a fitting part and can perform mounting positioning so that highly efficient optical transmission can be performed without alignment. Make it possible. Further, the distance between the optical paths can be shortened at the time of mounting, and the optical loss can be reduced. If the height of the convex part is sufficient, it is possible to connect the optical parts, and even if there is a gap, the thickness when the underfill is performed after mounting the element is thin, so bubbles are involved or foreign matter is mixed in. Can also be prevented.

  The protrusion 3 has an optical path 31. The optical path 31 optically couples the outside of the optical transmission board 6 and the optical transmission unit 2. The optical path 31 is made of a transparent resin capable of transmitting light in the same manner as the optical transmission unit 2. The material is the same as that of the optical transmission unit 2. The optical path 31 refers to a portion having a high refractive index (so-called core portion) in the refractive index distribution of the protruding portion 3. A portion of the protruding portion 3 other than the optical path 31 is a clad portion 32 having a refractive index lower than the refractive index of the optical path 31. In FIGS. 1 and 2, the part other than the optical path 31 is a clad portion 32.

  The diameter of the optical path 31 is about 35 to 100 μm.

  The optical path 31 is provided so as to correspond to the core unit 21 of the optical transmission unit 2. Specifically, when the optical transmission board 6 is seen through from above, the optical path 31 and the core part 21 of the optical transmission part 2 are provided so as to overlap each other. Moreover, it is preferable that the diameter of the optical path 31 and the diameter of the core part 21 are equal.

  The protrusion 3 has an edge 33. The edge portion 33 refers to a portion in contact with the second main surface 12 of the substrate 1 in the protruding portion 3. The edge portion 33 is provided on the substrate 1 by, for example, photolithography. In particular, when an epoxy material (referred to as a polymer material having an epoxy group) is used, such as an epoxy resin as the edge 33 and a glass epoxy substrate as the substrate 1, the substrate 1 and the edge 32 are made of epoxy. Since hydrogen bonding is performed between groups, adhesion is good and defects such as peeling are suppressed. As described above, since the edge 33 is in close contact with the substrate 1, the edge 33 is used over a long period of time in order to hold the optical transmission path composed of the optical transmission part 2 and the protruding part 3. However, the optical transmission line is not easily peeled off from the substrate 1, and low-loss optical transmission can be performed over a long period of time.

  The length of the edge 33 is about 1-1000 μm. In addition, the length of the edge part 33 means the length from the boundary of the outer periphery part of the optical path 2 and the 2nd main surface 12 to the edge of the edge part 33 (length of a of FIG. 1).

  FIG. 2 shows an optical transmission board 6 when a plurality of optical transmission units 2 are provided on the board 1. Thus, the optical transmission board 6 of the present invention preferably has a plurality of optical transmission units 2. Thus, the edge 33 is provided not only on the edge 33 in the case of one optical transmission unit 2 but also on the second main surface 12 on the substrate 1 between the optical transmission unit 2 and the optical transmission unit 2. In addition, since a large number of edge portions 33 are provided, peeling of the optical transmission path from the substrate 1 can be sufficiently suppressed.

  A specific example of a method for producing an optical transmission line composed of the optical transmission part 2 and the protruding part 3 is shown in FIG.

  The substrate 1 is provided with a first through hole 8A by a drill, a laser, or the like (step A, see FIG. 3A). The first through hole 8A is uniformly filled with a transparent epoxy resin as the first photosensitive resin, and the transparent epoxy resin spreads on the second main surface 12 of the substrate 1 overflowing from the through hole. Then, apply a transparent epoxy resin. At that time, in order to reduce the amount of material used, if a solder resist is provided around the through hole, the solder resist is used as a resin flow prevention dam, and transparent epoxy resin is stored in the opening of the solder resist. The epoxy resin may be spread on the second main surface 12. In addition, as a method of spreading the transparent epoxy resin on the second main surface 12, spin coating, die coating, and the like can be mentioned. By using a solder resist as a dam, filling and partial application can be performed with a dispenser. It is effective from the viewpoint of material efficiency and workability.

  Thereafter, pre-baking, mask exposure, development, and post-baking are performed in order, and unnecessary portions are removed to form the clad portion 22 of the optical transmission portion 2 and the clad portion 32 of the protruding portion 3 (step B, see FIG. 3B). ).

  Next, the 2nd through-hole 8B is produced in the center part of both clad parts using a precision drill or a laser (refer process C and FIG.3 (c)). After that, the second through-hole 8B is filled with a material such as a transparent epoxy resin having a relative refractive index difference of 1 to 3% higher than that of the previously used transparent epoxy resin as a second photosensitive resin, and prebaked. Mask exposure, development, and post-baking are performed in this order to remove unnecessary portions, thereby forming the core portion 21 and the optical path 31 of the optical transmission portion 2 (step D, see FIG. 3D).

  Both the core part and the clad part may be made of a transparent epoxy resin. In this case, the core part and the clad part have very good adhesion because the resin skeleton is the same. More efficient coupling can be obtained by setting the diameter of the through hole so as to couple well with the size of the light incident / exit portion of the optical semiconductor element and the core size of the optical waveguide.

  As described above, the optical transmission unit 2 and the protrusion 3 are integrally formed. In this case, since the height of the protrusion 3 is determined by the coating thickness, the height of the protrusion 3 can be set more accurately by polishing if necessary. In order to obtain a sufficient optical path confinement effect, it is preferable to polish all of the core material on the protruding cladding 32 so that the protruding cladding 32 is formed of only the cladding material. There is no problem even if it remains on the clad 32. Note that the flow-out prevention dam at the opening of the solder resist can store the resin inside the solder resist more than the thickness of the solder resist due to the surface tension of the resin.

  FIG. 4 shows an optical module 7 having an optical transmission board 6 and an optical semiconductor element 4. An optical semiconductor element 4 is provided on the second main surface 12 of the optical transmission substrate 6, and a light emitting / receiving unit 4 A that receives and emits light is provided below the optical semiconductor element 4. The light emitting / receiving unit 4A, the optical transmission unit 2 and the protrusion 3 of the optical semiconductor element 4 are optically coupled.

  The optical transmission board 6 and the optical semiconductor element 4 are electrically connected by a joint 5 such as a gold bump. When gold bumps are used as the joints 5, gold bumps are interposed between electrode pads (not shown) provided on the optical transmission substrate 6 and the optical semiconductor element 4, and the electrode pads are connected by ultrasonic pressure bonding. be able to.

  An interval of about 20 to 100 μm exists between the optical transmission substrate 6 and the optical semiconductor element 4 due to the junction 5.

  In the present invention, as shown in FIG. 4, the gap between the optical transmission substrate 6 and the optical semiconductor element 4 is reduced by the protrusion 3, thereby preventing light leakage between them and suppressing crosstalk and optical loss. can do.

  Further, when a solder ball or the like is used as the bonding portion 5, for example, the solder mainly contains a flux due to an organic solvent and tends to diffuse by heating. As a result, the flux enters the gap between the optical transmission board 6 and the optical semiconductor element 4, and the flux tends to adhere to the mutually facing surfaces of the gap between the optical transmission board 6 and the optical semiconductor element 4. In general, the flux is colorless and transparent, but it becomes cloudy by reaction or turns brown with time. Therefore, adhering to the exposed surface of the optical transmission line of the optical semiconductor element 4 and the optical transmission board 6 causes light loss. There was a tendency to cause. However, in the present embodiment, the protrusion 3 can reduce the gap between the optical transmission substrate 6 and the optical semiconductor element 4 so that foreign matters such as flux can be prevented from interposing.

It is sectional drawing which shows the structure of an optical transmission board | substrate. It is sectional drawing which shows the structure of the optical transmission board | substrate which has a some optical transmission part. (A)-(d) is sectional drawing which shows the manufacturing method of an optical transmission board | substrate. It is sectional drawing which shows the structure of an optical module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 11 1st main surface 12 2nd main surface 2 Optical transmission part 21 Core part 22 Clad part 3 of optical transmission part Protrusion part 31 Optical path 32 Clad part 33 of protrusion part Edge part 4 Optical semiconductor element 4A Optical semiconductor Light receiving / emitting part 5 of element 5 Junction part 6 Optical transmission board 7 Optical module 8A 1st through-hole 8B 2nd through-hole

Claims (6)

A substrate having a first main surface and a second main surface;
An optical transmission portion provided from the first main surface to the second main surface so as to open at the first main surface of the substrate, and so as to protrude on the second main surface of the substrate. An optical transmission path provided with an optical path optically coupled to the optical transmission section and a protrusion having an edge that can be in close contact with the upper surface of the substrate;
An optical transmission board comprising:   The optical transmission board according to claim 1, wherein both the board and the optical transmission path are made of an epoxy-based material.   3. The optical transmission board according to claim 1, wherein the projecting portion is further provided with a clad portion of a projecting portion provided around the optical path and having a lower refractive index than the optical path. The optical transmission part includes a core part, and a cladding part of an optical transmission part provided around the core part and having a lower refractive index than the core part,
The optical transmission board according to any one of claims 1 to 3, wherein a refractive index of a core part of the optical transmission part and a refractive index of the optical path are the same. An optical transmission board according to any one of claims 1 to 4,
An optical semiconductor element mounted on the second main surface, located above the protrusion, and optically coupled to the optical transmission path;
An optical module comprising: Forming a first through hole in the substrate;
After filling the through hole with the first photosensitive resin so as to overflow on one main surface of the substrate, the first photosensitive resin is cured, and the clad part of the light transmission part and the clad of the protrusion part A step B of forming a portion;
Forming a second through hole in the clad portion of the optical transmission portion and the clad portion of the protruding portion; and
An optical path having a refractive index higher than that of the clad portion of the projecting portion by filling the second through hole with the second photosensitive resin and then curing the second photosensitive resin; Forming a core part of the optical transmission part having a higher refractive index than that of the cladding part,
A method of manufacturing an optical transmission board comprising:

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