JP7501165B2 - Optical module mounting substrate, optical module, method for manufacturing optical module mounting substrate, and method for manufacturing optical module - Google Patents

Description

The present invention relates to an optical module mounting board, an optical module, a method for manufacturing an optical module mounting board, and a method for manufacturing an optical module.

In recent years, there has been an increasing demand for high-speed, large-volume data transmission not only in core equipment used in base stations and data centers, but also in consumer devices such as 4K and 8K televisions and digital signage. Optical communication technology is one technology that can achieve this. Optical communication technology requires optical modules that can be miniaturized and manufactured at low cost. One known example of such an optical module is one in which light-emitting elements and light-receiving elements are mounted face-down on a substrate. Furthermore, there are studies being conducted on miniaturizing the entire optical module, including optical elements such as lenses.

For example, Patent Document 1 discloses an invention for an optical module in which a through hole is provided in a substrate for inserting an optical fiber, a support part that supports the optical fiber in the through hole, and a small diameter part that is smaller in diameter than the support part are provided, and a ball lens is held at the boundary between the support part and the small diameter part. In this invention, the optical module can be made smaller by housing the ball lens within the substrate.

JP 2004-309925 A

However, in the structure disclosed in Patent Document 1, it was necessary to form an even thinner small-diameter section in the thin through-hole into which the optical fiber is inserted to create a step. This made it difficult to perform precise processing, and there was a problem in that it was difficult to achieve reproducibility.

The present invention was made in consideration of the above problems, and aims to provide an optical module mounting substrate that can easily and accurately form a cavity structure.

In order to solve the above problems, the optical module mounting substrate of the present invention has an insulating light-transmitting substrate, a first wiring layer provided on a first main surface of the light-transmitting substrate, a second wiring layer provided on a second main surface of the light-transmitting substrate, and a cavity wall provided around the second wiring layer. A first opening is formed inside the first wiring layer. A first optical element is mounted on the upper surface of the first wiring layer. A second opening is formed in the second wiring layer at a position corresponding to the first opening. The cavity wall is provided to form a cavity structure with the surface of the second wiring layer as a first bottom surface, the second main surface of the light-transmitting substrate exposed from the second opening as a second bottom surface, and the cavity wall itself as a side wall of a predetermined height. A second optical element is mounted on the upper surface of the cavity wall.

The manufacturing method of the optical module mounting substrate of the present invention also includes the optical module mounting substrate described above, and an optical component housed in the cavity structure of the optical module mounting substrate.

The manufacturing method of the optical module mounting substrate of the present invention further comprises forming a first wiring layer on a first main surface of a light-transmitting substrate, the first wiring layer having a first opening formed inside and a first optical element mounted on the top surface. Then, forming a second wiring layer on a second main surface of the light-transmitting substrate, the second wiring layer having a second opening formed at a position corresponding to the first opening. Furthermore, forming a cavity wall of a predetermined height on the top surface of which the second optical element is mounted, with the surface of the second wiring layer as the first bottom surface and the second main surface of the light-transmitting substrate exposed from the second opening as the second bottom surface, to form a cavity structure with the second wiring layer as the side wall.

The optical module manufacturing method of the present invention also involves manufacturing an optical module mounting substrate using the above-mentioned optical module mounting substrate manufacturing method, and mounting optical components to be housed in the cavity structure.

The advantage of the present invention is that it is possible to provide an optical module mounting substrate that allows a cavity structure to be formed easily and accurately.

1 is a cross-sectional view showing an optical module mounting board according to a first embodiment. 2 is a plan view showing a first main surface of the optical module mounting substrate of the first embodiment. FIG. 4 is a plan view showing a second main surface of the optical module mounting substrate according to the first embodiment. FIG. FIG. 11 is a cross-sectional view showing an optical module mounting board according to a second embodiment. 13 is a plan view showing a first main surface of an optical module mounting substrate according to a second embodiment. FIG. 13 is a plan view showing a second main surface of the optical module mounting board of the second embodiment. FIG. 10A to 10C are cross-sectional views showing a first part of a method for manufacturing an optical module mounting board according to the 10A to 10C are cross-sectional views showing a first part of a method for manufacturing an optical module mounting board according to the second embodiment. 10A to 10C are cross-sectional views showing a first part of a method for manufacturing an optical module mounting board according to the 10A to 10C are cross-sectional views showing a first part of a method for manufacturing an optical module mounting board according to the second embodiment. 10A to 10C are cross-sectional views showing a first part of a method for manufacturing an optical module mounting board according to the second embodiment. FIG. 11 is a cross-sectional view showing an optical module according to a third embodiment. FIG. 13 is a cross-sectional view showing an optical module according to a fourth embodiment.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. However, the embodiment described below has limitations that are technically preferable for implementing the present invention, but does not limit the scope of the invention to the following. Note that similar components in each drawing are given the same numbers, and descriptions may be omitted.

First Embodiment
1 is a cross-sectional view showing an optical module mounting substrate 10 of this embodiment. The optical module mounting substrate 10 has an insulating light-transmitting substrate 1, a first wiring layer 2 provided on a first main surface of the light-transmitting substrate 1, a second wiring layer 3 provided on a second main surface of the light-transmitting substrate 1, and a cavity wall 4 provided around the second wiring layer 3. Note that the light-transmitting property of the light-transmitting substrate 1 means that it has light-transmitting property for light of a predetermined wavelength, and does not necessarily have to be transparent to visible light.

A first opening 2a is formed inside the first wiring layer 2, and the first main surface of the light-transmitting substrate 1 is exposed through the first opening 2a. A first optical element d is mounted on the upper surface of the first wiring layer 2.

A second opening 3a is formed in the second wiring layer 3 at a position corresponding to the first opening 2a, and the second main surface of the light-transmitting substrate 1 is exposed in the second opening 3a.

The cavity wall 4 is provided to form a cavity structure 5 having a first bottom surface, the surface of the second wiring layer 3, and a second bottom surface, which is the second main surface of the light-transmitting substrate 1 exposed from the second opening 3a, and having a side wall of a predetermined height. A second optical element e is mounted on the upper surface of the cavity wall 4.

Figure 2 is a plan view of the optical module mounting substrate 10 as viewed from the first main surface side of the light-transmitting substrate 1. A first wiring layer 2 is provided on the first main surface of the light-transmitting substrate 1, and a first opening 2a is formed inside the first wiring layer 2. In the first opening 2a, the first main surface of the light-transmitting substrate 1 is exposed.

Figure 3 is a plan view of the optical module mounting substrate 10 as viewed from the second main surface side of the light-transmitting substrate 1. A second wiring layer 3 is provided on the second main surface of the light-transmitting substrate 1, and a second opening 3a is formed inside the second wiring layer 3 at a position corresponding to the first opening 2a. The second main surface of the light-transmitting substrate 1 is exposed at the second opening 3a.

In the above configuration, the first bottom surface that contacts the cavity wall 4 of the cavity structure 5 is formed of the second wiring layer 3. With this configuration, for example, the cavity wall 4 is formed of a resin and the second wiring layer 3 is formed of a metal film, thereby increasing the etching selectivity ratio. Therefore, the cavity wall 4 can be patterned easily and accurately. As a result, the cavity structure 5 can be formed easily and accurately. In the above description, an example was used in which the first opening, the second opening, and the upper surface of the cavity wall are rectangular patterns, but the pattern can be any shape that satisfies the desired optical performance.

In addition, although not shown, electrodes and wiring can be arranged on the first wiring layer 2 to give it a shape that satisfies the desired electrical and optical characteristics.

Second Embodiment
In this embodiment, a specific configuration example of the optical module mounting board of the first embodiment will be described. Fig. 4 is a cross-sectional view showing a configuration example of the optical module mounting board 1000 of this embodiment.

The optical module mounting substrate 1000 is a multi-layer substrate in which a wiring layer and an insulating layer are provided on both sides of an insulating light-transmitting substrate 100. A first wiring layer 200 and a first insulating layer 210 covering a part of the first wiring layer 200 are provided on the first main surface of the light-transmitting substrate 100. A first opening 201 is formed inside the first wiring layer 200, and the first main surface of the light-transmitting substrate 100 is exposed in the first opening 201. For example, an optical element 400 is mounted on the upper surface of the first wiring layer 200. Note that the light-transmitting property of the light-transmitting substrate 1 means that it has light-transmitting property for light of a predetermined wavelength, and does not necessarily have to be transparent to visible light.

On the second main surface of the light-transmitting substrate 100, a second wiring layer 300, a substrate adhesive layer 310, a second insulating layer 320, a third wiring layer 330, and a third insulating layer 340 are provided in this order from the side closest to the light-transmitting substrate 100. A second opening 301 is formed in the second wiring layer 300 at a position corresponding to the first opening 201, and the second main surface of the light-transmitting substrate 1 is exposed in the second opening 301.

The substrate adhesive layer 310, the second insulating layer 320, the third wiring layer 330, and the third insulating layer 340 have openings with a diameter larger than that of the second opening 301. This forms a cavity structure 350. In the example of FIG. 4, the bottom surface of the cavity structure 350 is formed by a first bottom surface made of the second wiring layer 300 and a second bottom surface made of the second main surface of the translucent substrate 100 exposed from the second opening 301. In addition, the side wall 351 of the cavity structure 350 is formed by the opening side surface of the substrate adhesive layer 310, the second insulating layer 320, and the third insulating layer 340. By providing the cavity structure 350, for example, an optical element such as an optical component 500 having a convex portion can be compactly mounted. In the example of FIG. 4, the number of wiring layers is three layers, but this is not limited to three layers, and a structure in which more layers are stacked may be applied.

Figure 5 is a plan view of the optical module mounting substrate 1000 as viewed from the first main surface side of the light-transmitting substrate 100. A first wiring layer 200 is provided on the first main surface of the light-transmitting substrate 100, a first opening 201 is formed inside the first wiring layer 200, and the periphery of the first wiring layer is covered with a first insulating layer 210. In the first opening 201, the first main surface of the light-transmitting substrate 100 is exposed.

Figure 6 is a plan view of the optical module mounting substrate 1000 as viewed from the second main surface side of the light-transmitting substrate 100. A second wiring layer 300 is provided on the second main surface of the light-transmitting substrate 100, and a second opening 301 is formed inside the second wiring layer 300 at a position corresponding to the first opening 201. In the second opening 301, the second main surface of the light-transmitting substrate 100 is exposed. The outside of the second wiring layer 300 is surrounded by a second insulating layer 320, and the outside of the second insulating layer 320 is surrounded by a third insulating layer 340.

Next, a method for manufacturing the optical module mounting substrate 1000 will be described. First, as shown in the cross-sectional view of FIG. 7, a light-transmitting substrate 100 having metal foil formed on both sides is prepared, and each metal foil is patterned. This forms a first wiring layer 200 and a second wiring layer 300. For example, polyimide can be used as the light-transmitting substrate 100. The first wiring layer 200 and the second wiring layer 300 can be patterned, for example, by applying a photoresist to the metal foil surface, exposing and developing the metal foil in a predetermined pattern, etching the exposed metal foil, and then removing the photoresist. For example, copper, nickel, gold, tin, chromium, or an alloy containing any of these can be used as the metal foil.

Next, a substrate adhesive layer 310 is applied to the surface on which the second wiring layer 300 is formed, so as to surround the opening 301 and form a predetermined opening wider than the opening 301. Then, a second insulating layer 320 on which a metal foil that will become the third wiring layer 330 is formed is attached (FIG. 8). The substrate adhesive layer 310 can be applied, for example, by laminating a semi-cured sheet-like film, printing, dispensing, etc.

Next, as shown in FIG. 9, the metal foil is patterned to form the third wiring layer 330. Here, the patterning is performed so that the third wiring layer 330 is not placed at least in the area where the cavity structure will be formed later.

Next, the first insulating layer 210 is formed so as to cover a portion of the first wiring layer 200 that does not include the opening 201. Also, the third insulating layer 340 is formed so as to cover a portion of the third wiring layer 330 (FIG. 10). The first insulating layer 210 and the third insulating layer 340 can be formed, for example, by using a screen printing method. Alternatively, a method of laminating a coverlay film having an opening at a predetermined position may be used.

In addition, when copper foil is used as the metal foil, a thin film of nickel and gold may be formed in this order on the surface of the first wiring layer 200 exposed from the first insulating layer 210 and on the surface of the third wiring layer 340 exposed from the third insulating layer 340. The thin film may be formed, for example, by electroless plating. Nickel functions as a diffusion prevention film, and gold contributes to preventing oxidation of the surface. In addition, after forming a thin film of nickel, a thin film of palladium and gold may be formed in this order. Although not shown, through holes may be formed to connect each wiring layer. The connection using the through holes may be performed, for example, by forming a through hole penetrating each layer by laser processing or the like at a predetermined position, and forming a copper film on the side of the through hole by plating. In addition, after forming the copper film, the center of the hole may be filled with an organic material.

Next, as shown in FIG. 11, the second insulating layer 320 is cut out in the area where the cavity structure 350 is to be formed. This process can be performed, for example, by laser processing. At this time, the end of the area to be cut out is positioned on the second wiring layer 300. In this way, the second wiring layer 300 functions as a stopper layer for the laser processing, so that the position of the bottom surface of the cavity structure 350 can be precisely controlled without any special ingenuity. With the above, the optical module mounting substrate 1000 is completed.

As described above, according to this embodiment, a cavity structure can be easily formed on an optical module mounting substrate with high processing accuracy. In addition, by making the number of wiring layers three or more, the wiring density per unit area is increased, and driver ICs for controlling light-emitting elements such as VCSELs and light-receiving elements such as PDs, and other adjustment components can be densely arranged on the multi-layer wiring. Therefore, the optical module can be further miniaturized. Here, VCSEL stands for Vertical Cavity Surface Emitting Laser, PD stands for Photodiode, and IC stands for Integrated Circuit. In addition, at the bottom of the cavity structure, a second wiring layer made of metal foil is arranged at the bottom that connects to the sidewall of the cavity structure, so that the strength of the cavity structure can be improved compared to the case where the sidewall is arranged at a position where there is no wiring.
Third Embodiment
In this embodiment, a specific example of an optical module using the optical module mounting substrate of the second embodiment will be described. Fig. 12 is a cross-sectional view showing an optical module 2000. In the optical module 2000, an optical element 400 is mounted on a first main surface side of an optical module mounting substrate 1000, and a lens plate 510 is mounted on a second main surface side.

As shown in FIG. 12, the optical element 400 is mounted face-down on the first wiring layer 200 of the optical module mounting substrate 1000. The optical function section 410 of the optical element 400 is positioned in the opening 201 of the first wiring layer 200. The first wiring layer 200 and the optical element 400 are connected via bumps 420 formed of a solder material mainly composed of Au, Cu, and Sn. In addition, the optical element 400 and the light-transmitting substrate 100 are protected by a sealing resin layer 430.

The optical element 400 can be, for example, a VCSEL, which is a surface-emitting element, or a PD, which is a light-receiving element. When the optical element 400 is a light-emitting element, the optical function unit 410 is a light-emitting unit, and when the optical element 400 is a light-receiving element, the optical function unit 410 is a light-receiving unit.

The sealing resin layer 430 contributes to protecting the connection part by the bump 420 and preventing the intrusion of foreign matter. Here, the sealing resin layer 430 may be a material that transmits a predetermined wavelength, and may be a photocurable resin that undergoes a curing reaction with light of a wavelength such as visible light or ultraviolet light, or a thermosetting resin or a thermoplastic resin. When the optical element 400 is a light receiving element, an optical signal incident from the cavity structure 350 side can be transmitted through the light-transmitting substrate 100 and the sealing resin layer 430 and enter the optical function part 410. When the optical element 400 is a light-emitting element, an optical signal emitted from the optical function part 410 is transmitted through the sealing resin layer 430 and the light-transmitting substrate 100 and is emitted to the cavity structure 350 side.

The lens plate 510 is mounted on the second main surface side of the light-transmitting substrate 100. The lens plate 510 may be made of a material such as glass or a polymer-based transparent material, and may be formed by a molding method or the like. The lens portion 511 formed on the lens plate 510 contributes to the collection of light during transmission. The lens portion 511 of the lens plate 510 is accommodated in the cavity structure 350, and a first adhesive layer 520 is filled between the light-transmitting substrate 100 and the lens plate 17. The lens plate 510 is positioned so that the optical axis of the lens portion 511 passes through the opening 301 of the second wiring layer 300 and coincides with the optical axis of the optical function portion 410. The first adhesive layer 520 may be made of a material that transmits a predetermined wavelength, and for example, a refractive index matching agent or the like may be applied. Specifically, for example, a photocurable resin may be applied as the first adhesive layer 520. In this case, light of a predetermined wavelength may be applied from the back side of the lens plate 510 to harden it.

In the above description, a structure in which one optical element 400 is mounted on the first wiring layer is shown, but this is not limited to this, and multiple optical elements 400 may be mounted. In this case, the lens plate 510 may have a structure having lens portions 511 at positions opposite each of the optical elements 400.

As described above, according to this embodiment, an optical element having a three-dimensional shape, such as a lens plate, can be housed in the cavity structure, so that the optical module can be made compact. Furthermore, by disposing a lens portion in the cavity structure, the loss of the transmitted optical signal can be reduced, and high transmission characteristics can be ensured.
Fourth Embodiment
In this embodiment, a modified example of the optical module of the third embodiment will be described. FIG. 13 is a cross-sectional view showing an optical module 2100 of this embodiment. The optical module 2100 has a structure in which an optical waveguide 600 is arranged on the back surface of the lens plate 510 of the optical module 2000 of the second embodiment. The optical waveguide 600 is bonded and fixed by a second adhesive layer 530 to the surface of the lens plate 510 opposite to the surface on which the lens portion 511 is arranged. The optical waveguide 600 is composed of a core layer 610 and a clad layer 620 surrounding the periphery thereof. In addition, a mirror portion 630 that bends the optical axis of the optical waveguide is arranged in the optical waveguide 600 at a position opposite to the lens portion 511. The mirror portion 630 is formed to have an angle of 45° with respect to the optical axis of the optical waveguide 600. The mirror portion 630 bends the optical signal transmitted from the core layer 610 by 90° and transmits it to the light receiving portion (optical function portion 410) of the optical element 400. Moreover, the optical signal transmitted from the light emitting section (optical function section 410 ) is bent by 90° and transmitted to the core layer 610 of the optical waveguide 600 .

The second adhesive layer 530 may be made of any material that transmits a specific wavelength, and may be made of a refractive index matching material, as in the case of the first adhesive layer 520.

The above configuration allows the optical module to be made smaller than a configuration in which the optical waveguide is connected perpendicularly to the second main surface of the light-transmitting substrate.

The present invention has been described above using the first to fourth embodiments as exemplary examples. However, the present invention is not limited to the above-mentioned embodiments. In other words, the present invention can be applied in various aspects that can be understood by a person skilled in the art within the scope of the present invention.

A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes.
(Appendix 1)
an insulating light-transmitting substrate;
a first wiring layer provided on the first main surface of the light-transmitting substrate, the first wiring layer having a first opening formed therein and a first optical element mounted on an upper surface thereof;
a second wiring layer provided on a second main surface of the light-transmitting substrate, the second wiring layer having a second opening formed at a position corresponding to the first opening;
a cavity wall having a predetermined height and a second optical element mounted on an upper surface thereof, the cavity wall being provided so as to form a cavity structure having a first bottom surface, the second main surface of the light-transmitting substrate exposed from the second opening as a second bottom surface, and the cavity wall being provided so as to form a cavity structure having a side wall thereof;
An optical module mounting substrate comprising:
(Appendix 2)
2. The optical module mounting board according to claim 1, wherein the second wiring layer is a metal foil.
(Appendix 3)
3. The optical module mounting board according to claim 1, wherein at least one of the first wiring layer and the second wiring layer has a multi-layer structure having a wiring layer thereon.
(Appendix 4)
An optical module mounting substrate according to any one of claims 1 to 3;
an optical component housed in the cavity structure;
An optical module comprising:
(Appendix 5)
The optical module according to claim 4, wherein the optical component is a lens plate.
(Appendix 6)
6. The optical module according to claim 5, wherein an optical waveguide having a mirror portion that directs an optical axis toward the lens plate is connected and fixed to the lens plate.
(Appendix 7)
7. The optical module according to claim 4, wherein the optical element is mounted on the first wiring layer.
(Appendix 8)
forming a first wiring layer on a first main surface of a light-transmitting substrate, the first wiring layer having a first opening formed inside and a first optical element mounted on an upper surface thereof;
forming a second wiring layer on a second main surface of the light-transmitting substrate, the second wiring layer having a second opening formed therein at a position corresponding to the first opening;
a surface of the second wiring layer is defined as a first bottom surface, a second main surface of the light-transmitting substrate exposed from the second opening is defined as a second bottom surface, and a cavity wall having a predetermined height and a second optical element mounted on an upper surface thereof is formed to form a cavity structure having the cavity wall as a side wall.
4. A method for manufacturing an optical module mounting substrate comprising the steps of:
(Appendix 9)
Manufacturing an optical module mounting board by the manufacturing method of the optical module mounting board described in Appendix 8,
and mounting an optical component to be housed in the cavity structure.
(Appendix 10)
The method for manufacturing an optical module according to claim 8 or 9, further comprising mounting the optical element on the first wiring layer.

REFERENCE SIGNS LIST 1, 100 Light-transmitting substrate 2, 200 First wiring layer 2a, 201 First opening 3, 300 Second wiring layer 3a, 301 Second opening 4 Cavity wall 5, 350 Cavity structure 10, 1000 Optical module mounting substrate 210 First insulating layer 310 Substrate adhesive layer 320 Second insulating layer 330 Third wiring layer 340 Third insulating layer 400 Optical element 500 Optical component 510 Lens plate 600 Optical waveguide

Claims (10)

an insulating light-transmitting substrate;
a first wiring layer provided on the first main surface of the light-transmitting substrate, the first wiring layer having a first opening formed therein and a first optical element mounted on an upper surface thereof;
a second wiring layer provided on a second main surface of the light-transmitting substrate, the second wiring layer having a second opening formed at a position corresponding to the first opening;
an insulating layer provided on an upper surface side of the second wiring layer, the insulating layer having a third opening larger than the second opening formed at a position corresponding to the second opening;
a third wiring layer provided on an upper surface side of the insulating layer, in which a fourth opening larger than the third opening is formed at a position corresponding to the third opening;
a cavity wall having a predetermined height and a second optical element mounted on an upper surface thereof, the cavity wall being provided so as to form a cavity structure having a first bottom surface, a second main surface of the light-transmitting substrate exposed from the second opening as a second bottom surface, and the third opening and the fourth opening as side walls;
An optical module mounting substrate comprising: The optical module mounting board according to claim 1 , wherein the second wiring layer is a metal foil. 3. The optical module mounting board according to claim 1, wherein at least one of the first wiring layer and the second wiring layer has a multi-layer structure having a wiring layer thereon. An optical module mounting substrate according to claim 1 ,
an optical component housed in the cavity structure;
An optical module comprising: The optical module according to claim 4 , wherein the optical component is a lens plate. 6. The optical module according to claim 5, wherein an optical waveguide having a mirror portion whose optical axis faces the lens plate is connected and fixed to the lens plate. 7. The optical module according to claim 4, wherein an optical element is mounted on the first wiring layer. a first wiring layer is formed on a first main surface of a light-transmitting substrate, the first wiring layer having a first opening formed inside and a first optical element mounted on an upper surface thereof;
forming a second wiring layer on a second main surface of the light-transmitting substrate, the second wiring layer having a second opening formed therein at a position corresponding to the first opening;
forming an insulating layer on an upper surface side of the second wiring layer, the insulating layer having a third opening larger than the second opening at a position corresponding to the second opening;
forming a third wiring layer on the upper surface side of the insulating layer, the third wiring layer having a fourth opening formed in a position corresponding to the third opening and larger than the third opening;
forming a cavity wall of a predetermined height on an upper surface of which a second optical element is mounted, so as to form a cavity structure having a surface of the second wiring layer as a first bottom surface, a second main surface of the light-transmitting substrate exposed from the second opening as a second bottom surface, and the third opening and the fourth opening as side walls;
4. A method for manufacturing an optical module mounting substrate comprising the steps of: An optical module mounting board is manufactured by the method for manufacturing an optical module mounting board according to claim 8,
and mounting an optical component to be housed in the cavity structure. The method for manufacturing an optical module according to claim 9 , further comprising the step of mounting an optical element on the first wiring layer.

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