JP2019008269A - Optical guide and optical circuit board - Google Patents

Abstract

To provide a highly functional optical waveguide and an optical circuit board.SOLUTION: An optical waveguide comprises: a stack 4 including a lower clad 1, a core 2 located on the lower clad 1, and an upper clad 3 located on the lower clad 1 to cover the core 2; via holes 5 in the stack 4 opposite each other; a cavity 6 located from an upper surface of the upper clad 3 to the lower clad 1 and having a parting surface 8 parting the core 2 obliquely to the upper surface of the upper clad 3; and a reflecting surface 7 located at the core 2 and formed of a part of the parting surface 8. The cavity 6 is located from inside to outside a region where the via holes 5 face each other, and an aperture diameter of the cavity 6 in a region in a direction where the via holes 5 face each other is smaller than an aperture diameter of the cavity 6 outside the region.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to an optical waveguide and an optical circuit board including the optical waveguide.

  Development of high-performance optical waveguides that can transmit a large amount of information at high speed and high-performance optical circuit boards equipped with such optical waveguides as electronic devices such as servers and supercomputers become more sophisticated. Is underway. The optical waveguide is a laminate having a lower clad, a core having a reflecting surface, and an upper clad, and the laminate in a state of facing each other across the core in plan view in order to mount the optical element on the optical waveguide. And located via holes.

Japanese Patent No. 2985791

  As electronic devices become more sophisticated, a plurality of optical elements are mounted on an optical waveguide, so that the optical elements are being downsized. Correspondingly, the arrangement interval between via holes is becoming smaller. By the way, the above-mentioned reflecting surface is located immediately below the optical element, and is constituted by a part of a partial section of a cavity located from the inside of the region between the opposing via holes to the outside of the region. However, if the arrangement interval between the via holes is reduced, it becomes difficult to secure a region where the cavity is positioned, so that it is difficult to cope with the downsizing of the optical element, and it may be difficult to increase the functionality of the optical waveguide. is there.

  An optical waveguide according to the present disclosure is positioned so as to face each other, a laminated body including a lower cladding, a core positioned on the lower cladding, and an upper cladding positioned so as to cover the core on the lower cladding. A via hole that is located between the upper surface of the upper clad and the lower clad, and has a cross section that divides the core in an oblique direction with respect to the upper surface of the upper clad, The cavity is located from the region where the via holes face each other to the outside of the region, and the opening diameter of the cavity in the region where the via holes face each other Is smaller than the opening diameter of the cavity outside the region.

  An optical circuit board in the present disclosure includes the optical waveguide having the above-described configuration and a wiring board having pads arranged on the surface with a space therebetween, and the pad is positioned immediately below the opening below the via hole. Is located on the wiring board.

  According to the optical waveguide of the present disclosure, it is possible to position the cavity while reducing the arrangement interval between the via holes, and thus it is possible to provide a highly functional optical waveguide.

  According to the optical circuit board of the present disclosure, since the high-performance optical waveguide having the above-described configuration is included, a high-performance optical circuit board can be provided.

FIG. 1 is a schematic cross-sectional view illustrating an embodiment of an optical waveguide according to the present disclosure. FIG. 2 is a schematic top view illustrating an exemplary embodiment of the optical waveguide according to the present disclosure. FIG. 3 is a schematic cross-sectional view illustrating an embodiment of the optical circuit board according to the present disclosure. FIG. 4 is a schematic top view illustrating another example of the optical waveguide according to the present disclosure. FIG. 5 is a schematic top view illustrating still another embodiment of the optical waveguide according to the present disclosure. FIG. 6 is a schematic top view illustrating still another embodiment of the optical waveguide according to the present disclosure. FIG. 7 is a schematic top view illustrating still another embodiment of the optical waveguide according to the present disclosure. FIG. 8 is a schematic cross-sectional view showing still another embodiment of the optical waveguide according to the present disclosure.

  An exemplary embodiment of the optical waveguide 20 of the present disclosure will be described based on FIGS. 1 and 2. 1 is a cross-sectional view taken along the line XX shown in FIG. The optical waveguide 20 includes a laminated body 4 including a lower cladding 1, a core 2, and an upper cladding 3, a via hole 5, a cavity 6, and a reflecting surface 7.

  The lower clad 1 has a flat shape having a thickness of 10 to 20 μm, for example. The lower clad 1 is formed by, for example, applying or coating a photosensitive sheet or photosensitive paste containing an epoxy resin or a polyimide resin on a substrate or the like, and then shaping and thermosetting it into a predetermined shape by exposure and development. It is formed by.

  The core 2 has a quadrangular cross section, and is a thin strip having a thickness of 20 to 40 μm, for example. The core 2 is formed, for example, by depositing a photosensitive sheet containing an epoxy resin or a polyimide resin on the lower clad 1 in a vacuum state, shaping it into a strip shape by exposure and development, and then thermosetting it. The refractive index of the resin constituting the photosensitive sheet for the core 2 is higher than the refractive index of the resin constituting the photosensitive sheet or paste for the lower cladding 1 and the upper cladding 3.

  The upper clad 3 is located on the lower clad 1 and covers the core 2. The upper clad 3 has a thickness of, for example, 10 to 20 μm above the core 2 and has a flat upper surface. If the arithmetic mean roughness Ra is 10 nm or less, the surface roughness of the area facing the light emitting part D1 or the light receiving part D2 of the optical element D to be described later on the upper surface of the upper clad 3 is diffused by irregular reflection of the optical signal. It is advantageous to reduce the production. Further, the surface roughness of the other region is such that, when the arithmetic average roughness Ra is 30 to 100 nm, for example, when the resin is integrally sealed with the resin from the optical element D to the upper surface of the upper clad 3, It is advantageous to improve the adhesion strength by increasing the contact area with the upper surface of the upper clad 3. The upper clad 3 is thermally cured after a photosensitive sheet or a photosensitive paste made of, for example, an epoxy resin or a polyimide resin is applied or applied to the lower clad 1 so as to cover the core 2, exposed and developed. Is formed.

The via holes 5 are located in the stacked body 4 so as to face each other in a direction perpendicular to the extending direction of the core 2 in a top view. In the example of FIG. 2, two via holes 5 face each other across the core 2, and the reflecting surface 7 a is located on the core 2. This corresponds to the arrangement of the two electrodes D3 of the optical element D and the light emitting part D1 or the light receiving part D2 of the optical element D. That is, the optical element D is arranged such that each electrode D3 and each via hole 5 overlap each other and the light emitting part D1 or the light receiving part D2 and the reflecting surface 7a overlap when viewed from above. The distances from the core 2 to the respective via holes 5 are approximately the same. The via hole 5 penetrates the upper surface and the lower surface of the stacked body 4. In other words, the via hole 5 is located from the upper surface of the upper cladding 3 to the lower surface of the lower cladding 1.

  The via hole 5 is formed by, for example, laser processing or blast processing. The via hole 5 may be formed by exposure and development when the lower clad 1 and the upper clad 3 are formed. The opening diameter of the via hole 5 is set to 50 to 80 μm, for example. The interval between the opening centers of the opposing via holes 5 is set to 80 to 110 μm, for example.

  The cavity 6 is located from the inside of the region between the mutually opposing via holes 5 to the outside of the region when viewed from above. In addition, the cavity 6 is located from the upper surface of the upper cladding 3 to the lower cladding 1 in a cross-sectional view, and has a dividing surface 8 that divides the core 2 in an oblique direction with respect to the upper surface of the upper cladding 3.

  The cavity 6 has an opening 9 located on the upper surface of the upper cladding 3. The opening diameter L1 in the region between the opposing via holes 5 is smaller than the opening diameter L2 outside the region. For this reason, even if the arrangement interval between the via holes 5 is reduced, the cavity 6 can be positioned in the region between the via holes 5. The opening diameter L1 is set to 10 to 40 μm, for example. The opening diameter L2 is set to 70 to 110 μm, for example. The cavity 6 is formed by, for example, laser processing. The dividing surface 8 may be subjected to a surface treatment such as plasma treatment or blast treatment.

  The reflection surface 7 is located on the core 2. The reflective surface 7 includes, for example, a first reflective surface 7 a located immediately below the optical element D connected to the optical waveguide 20 and a second reflective surface 7 b located directly below the connector C connected to the optical waveguide 20. Yes. The first reflecting surface 7 a is configured by a part of the dividing surface 8 of the cavity 6. The reflecting surface 7 has a function of changing the direction of the optical signal emitted from the optical element D and transmitting the optical signal to the connector C. Alternatively, the optical element D has a function of changing the direction of the optical signal transmitted from the connector C and receiving the optical signal.

  The central axis of the core 2 and the central position of the reflecting surface 7 coincide with each other, and an optical signal is transmitted with reference to the central axis and the central position. Here, the central axis refers to a position where a pair of diagonal lines in the cross section of the quadrangular core 2 intersect. The center position refers to a position where a pair of diagonal lines of the quadrangular reflecting surface 7 intersect.

  As described above, the optical waveguide 20 of the present disclosure has the cavity 6 having the opening 9 on the upper surface of the upper clad 3. The opening diameter L1 in the region between the opposing via holes 5 is smaller than the opening diameter L2 outside the region. Thereby, even when the arrangement interval between the opposed via holes 5 is small, the cavity 6 can be positioned, so that a highly functional optical waveguide 20 can be provided. Further, since the opening diameter L2 outside the region is relatively large, it is advantageous with respect to positioning the reflecting surface 7 over the entire width direction of the core 2. In this case, the difference between the opening diameter L1 in the region and the opening diameter L2 outside the region is set to be about 30 to 100 μm.

  Next, an exemplary embodiment of the optical circuit board 40 having the optical waveguide 20 of the present disclosure will be described based on FIG. A detailed description of the above-described optical waveguide 20 is omitted.

  The optical circuit board 40 includes a wiring board 30 and an optical waveguide 20. The wiring board 30 has a function of positioning and fixing the optical waveguide 20, the optical element D, and the connector C, and electrically connecting the optical element D and the outside (motherboard or the like). Further, an optical signal is transmitted between the optical element D and the outside (such as an optical device) via the optical waveguide 20. Examples of the optical element D include a vertical cavity surface emitting laser, a photodiode, and the like, which convert an optical signal and an electric signal.

  The wiring substrate 30 includes an insulating substrate 31 and a wiring conductor 32. The insulating substrate 31 includes a core insulating layer 31a and a build-up insulating layer 31b. The core insulating layer 31 a has a plurality of through holes 33.

  The core insulating layer 31a has a function of, for example, ensuring the rigidity of the insulating substrate 31 and maintaining flatness. The core insulating layer 31a is formed, for example, by pressing a semi-cured prepreg in which a glass cloth is impregnated with an epoxy resin, a bismaleimide triazine resin, or the like, while pressing it flatly while heating.

  The buildup insulating layer 31 b includes a plurality of via holes 34. The build-up insulating layer 31b has a function of, for example, securing a routing space for the wiring conductor 32 and the like described later in detail. The build-up insulating layer 31b is formed, for example, by sticking a resin film containing an epoxy resin, a polyimide resin, or the like to the insulating layer 31a for the core under vacuum and thermosetting it.

  The wiring conductor 32 is located on the surface of the core insulating layer 31 a, the surface of the build-up insulating layer 31 b, the inside of the through hole 33, and the inside of the via hole 34. The wiring conductor 32 positioned inside the through hole 33 is electrically connected between the wiring conductors 32 positioned on the upper and lower surfaces of the core insulating layer 31a. The wiring conductor 32 positioned inside the via hole 34 is electrically connected between the wiring conductor 32 positioned on the surface of the build-up insulating layer 31b and the wiring conductor 32 positioned on the surface of the core insulating layer 31a. The wiring conductor 32 is formed of a highly conductive metal such as copper plating by, for example, a semi-additive method or a subtractive method.

  The wiring board 30 has a plurality of first pads 35 on the upper surface. The first pad 35 is connected to the pad D3 of the optical element D via a conductive material such as solder. Further, the wiring board 30 has a plurality of second pads 36 on the upper surface and a plurality of third pads 37 on the lower surface. The second pad 36 is connected to an electronic component S such as a semiconductor element, for example. For example, a motherboard is connected to the third pad 37. The first pad 35, the second pad 36, and the third pad 37 are formed of a part of the wiring conductor 32 and are formed at the same time when the wiring conductor 32 is formed.

  The optical waveguide 20 is located on the upper surface of the wiring substrate 30 including the region where the first pad 35 is located. The via hole 5 located in the optical waveguide 20 has the first pad 35 as a bottom surface. The optical waveguide 20 has a cavity 6 having an opening 9 on the upper surface of the upper cladding 3. The opening diameter L1 in the region between the opposing via holes 5 is smaller than the opening diameter L2 outside the region. As a result, the cavity 6 can be positioned while reducing the interval between the opposing via holes 5, so that the optical waveguide 20 can be highly functionalized.

  As described above, the optical circuit board 40 according to the present disclosure allows the optical circuit board to have high functionality because the high-performance optical waveguide 20 is positioned on the upper surface of the wiring board 30.

  Note that the present disclosure is not limited to the above-described exemplary embodiment, and various modifications can be made without departing from the gist of the present disclosure. For example, FIG. 2 shows a case where the opening 9 of the cavity 6 has a trapezoidal shape, but as shown in FIG. 4, a triangle in which one of the vertices is located in a region between the opposing via holes 5. It may be a shape. In this case, it is advantageous in that the width of the opening diameter L1 is further reduced compared to the trapezoidal shape and the arrangement interval of the via holes 5 is reduced.

  Moreover, as shown in FIG. 5, about sides other than the opening side 9a which is one side of the dividing surface 8, you may be curvilinear. According to this, for example, it is possible to suppress the formation of a narrow region near the corner of the opening 9, which is advantageous in terms of improving workability.

  Moreover, although the case where one core 2 is located in one optical waveguide 20 is shown in this example, a plurality of cores 2 may be located as shown in FIG. In this case, more optical signals can be transmitted, which is advantageous for further enhancement of the functions of the optical waveguide 20 and the optical circuit board 40.

  Further, in this example, the wiring board 30 has an example in which the solder resist layer is not provided. However, the wiring board 30 is provided on the upper surface and / or the lower surface of the insulating substrate 31 on the second pad 36. Alternatively, a solder resist layer having an opening exposing the third pad 37 may be provided. Thereby, the damage which the wiring conductor 32 receives by the heat processing at the time of mounting the electronic component S can be reduced, for example. The plurality of openings may have different shapes. The openings having different shapes can also be used as alignment marks when the electronic component S is mounted, for example.

  In addition, as shown in FIG. 7, the cavity 6 may have a curved corner portion 10 of the opening 9 in plan view. The radius of curvature of the corner portion 10 is set to 5 to 10 μm, for example. In such a case, when the optical waveguide 20 receives external pressure or heat, the stress generated in the corner portion 10 can be reduced to 40 to 60%. Thereby, it can suppress that the laminated body 4 produces a crack in the corner part 10, and can provide the highly functional optical waveguide 20 excellent in reliability.

  As shown in FIG. 8, the cavity 6 is located from the upper surface of the upper cladding 3 to the dividing surface 8 having the reflecting surface 7, and intersects the dividing surface 8 at an angle that intersects the upper surface of the upper cladding 3 in a sectional view. You may have the side surface 11 in which all the angles are 90 degree | times or more. In such a case, the laminated body 4 is chipped by removing a portion where the upper surface of the upper clad 3 and the divided section 8 having the reflecting surface 7 intersect at an acute angle, or cracks due to the chipping up to the reflecting surface 7. Propagation can be suppressed. Accordingly, it is possible to provide the optical waveguide 20 having excellent transmission characteristics that can change the direction of the optical signal with high accuracy.

  Note that the upper limit value of the angle at which the side surface 11 and the upper surface of the upper clad 3 intersect and the upper limit value of the angle at which the side surface 11 and the dividing plane 8 having the reflective surface 7 intersect have the upper surface of the upper clad 3 and the reflective surface 7. It depends on the angle at which the dividing surface 8 intersects. When the angle at which the upper surface of the upper clad 3 and the dividing surface 8 having the reflecting surface 7 intersect is, for example, 45 degrees, the aforementioned upper limit value is 135 degrees.

  As described above, the corner portion 10 and the side surface 11 having a curved shape are formed by irradiating a region where the upper surface of the upper clad 3 and the divided section 8 having the reflecting surface 7 intersect with each other after forming the cavity 6. It is formed.

  The cavity 6 has a structure in which the corner portion 10 of the opening 9 has a curved shape, and a side surface 11 in which each of an angle that intersects the upper surface of the upper cladding 3 and an angle that intersects the dividing surface 8 is 90 degrees or more in a sectional view. The structure can be formed by the above processing. The optical waveguide 20 may have both of these shapes.

DESCRIPTION OF SYMBOLS 1 Lower clad 2 Core 3 Upper clad 4 Laminate body 5 Via hole 6 Cavity 7 Reflecting surface 8 Divided section 10 Corner portion 11 Side surface 35 (First) pad 40 Optical circuit board

Claims (5)

A laminate including a lower cladding, a core positioned on the lower cladding, and an upper cladding positioned so as to cover the core on the lower cladding;
Via holes positioned so as to face each other on the laminate;
A cavity that is located from the upper surface of the upper clad to the lower clad and has a cross section that divides the core in an oblique direction with respect to the upper surface of the upper clad;
A reflective surface located in the core and configured by a part of the dividing surface,
The cavity is located from the region where the via holes face each other to the outside of the region, and the opening diameter of the cavity in the region in the direction where the via holes face each other is equal to that of the cavity outside the region. An optical waveguide characterized by being smaller than an opening diameter.   The optical waveguide according to claim 1, wherein the opening of the cavity has a triangular shape having one vertex in the region.   3. The optical waveguide according to claim 1, wherein the cavity is curved outside the region in a corner portion of the opening in a plan view.   The cavity is located from the upper surface of the upper clad to the dividing surface having the reflecting surface, and both the angle intersecting the upper surface of the upper cladding and the angle intersecting the dividing surface in a cross-sectional view are 90 degrees or more. The optical waveguide according to claim 1, wherein the optical waveguide has a side surface. An optical waveguide according to any one of claims 1 to 4,
A wiring board having pads arranged on the surface at intervals, and
An optical circuit board, wherein the optical waveguide is located on the wiring board in a state where the pad is located immediately below the opening below the via hole.

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