WO2023063313A1

WO2023063313A1 - Photoelectric composite substrate and method for manufacturing same

Info

Publication number: WO2023063313A1
Application number: PCT/JP2022/037877
Authority: WO
Inventors: 徹中芝; 潤子栗副; 彩吉田; 直幸近藤
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2021-10-14
Filing date: 2022-10-11
Publication date: 2023-04-20
Also published as: TW202316156A

Abstract

The purpose of the present invention is to provide a photoelectric composite substrate capable of reducing light loss at the time of input and output.　One aspect of the present invention relates to a photoelectric composite substrate comprising: a substrate (1) having an insulating layer and an electrode pad (4) formed on one surface of the insulating layer; and an optical waveguide stacked on the one surface of the insulating layer, the optical waveguide having a cladding (3), a core (2) surrounded by the cladding (3), an input micromirror (5) and an output micromirror (5'), and a hole (9) leading to a surface on the reverse side from a surface abutting on the insulating layer of the electrode pad (4).

Description

Optoelectric composite substrate and manufacturing method thereof

The present invention relates to an opto-electric composite substrate and a manufacturing method thereof.

Conventionally, optical fiber has been the mainstream transmission medium in the field of FTTH (Fiber to the Home) and long-distance and medium-distance communication in the in-vehicle field. In recent years, there has been a need for high-speed transmission using light over a short distance of 1 m or less. In this area, high-density wiring (narrow pitch, branching, crossing, multi-layering, etc.), surface mountability, integration with electric substrates, and optical waveguide type optical wiring boards that can be bent at small diameters, which cannot be done with optical fibers. is suitable.

In order to utilize the light input and output from the optical waveguide, such an optical wiring board includes a light emitting device such as a vertical cavity surface emitting laser (VCSEL), a light receiving device such as a photodiode (PD), and the like. It is preferable that a semiconductor element such as an integrated circuit (IC) is mounted. In order to drive these elements, an electric circuit must be provided on the optical wiring board or the like. For this reason, the opto-electrical composite wiring board is preferably provided with not only an optical waveguide but also an electric circuit. Such an opto-electric composite wiring board includes, for example, a bendable opto-electric composite flexible wiring board (for example, Patent Documents 1 and 2). This opto-electric composite flexible wiring board can be flexibly mounted, for example, by arranging it over the hinge of a small terminal device or by changing its shape according to the space.

Conventional opto-electrical composite substrates usually have an electric circuit layer (electrode pad A substrate 1) containing 4 was placed on top, and an optical waveguide with a core 2 and a cladding 3 was formed as a second layer, and a coverlay layer 6 was formed for protection purposes. Further, in the conventional composite substrate, when the electrode pads 4 for mounting the components are on the back side (optical waveguide side) of the surface electrical circuit layer, in order to obtain electrical connection from the front side, the electrode pads 4 shown in FIG. 2, a through-hole was provided in the upper portion of the electrode pad 4 by laser processing or the like.

In such a conventional opto-electric composite substrate, since the electrode pads 4 are on the surface side of the optical waveguide, when an optical element (laser chip 7, etc.) is mounted, the cross-sectional view shown on the right side of FIG. , the distance from the light receiving/emitting unit to the input/output unit (mirror 5) tends to increase. If the distance from the laser chip 7 to the mirror 5 is long, the light spreads, so there is a problem that the light cannot be received by a light receiving element such as an optical waveguide or a photodiode (PD), resulting in a large loss. Polyimide (PI) resin, which is commonly used as a base material for flexible substrates, is opaque. There is also the problem that if physical or chemical processing is applied for removal, the adjacent optical waveguides are likely to be damaged.

Therefore, an object of the present invention is to provide an opto-electric composite substrate that can improve the above problems and reduce the loss of light during input and output.

JP 2013-137469 A WO2012/093462

As a result of intensive studies aimed at solving the above problems, the inventors found that the above problems can be solved with the following configuration.

That is, an opto-electrical composite substrate according to one aspect of the present invention includes a substrate having an insulating layer and an electrode pad formed on one surface of the insulating layer, and an optical waveguide laminated on the one surface of the insulating layer. and the optical waveguide leads to a clad, a core surrounded by the clad, an input micromirror, an output micromirror, and a surface of the electrode pad opposite to the surface in contact with the insulating layer. It is characterized by having holes.

According to another aspect of the present invention, there is provided a method of manufacturing an opto-electrical composite substrate, comprising the steps of preparing a substrate having an insulating layer and electrode pads formed on one surface of the insulating layer, and forming an optical waveguide on the substrate. and at least the step of
The step of forming the optical waveguide includes laminating a lower clad material on the substrate, forming through holes on the electrode pads by photolithography, and forming a lower clad having through holes; laminating a core material on the lower clad to form a core by photolithography; laminating an upper clad material on the lower clad on which the core is formed; a step of forming a through hole in the substrate to form an upper clad; and a step of forming a micromirror.

FIG. 1 is a schematic cross-sectional view showing a general configuration of a conventional optoelectric composite substrate. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the optoelectric composite substrate according to this embodiment. FIG. 3 is a schematic top view of the opto-electric composite substrate shown in FIG. 2 as viewed from above. FIG. 4 is a schematic cross-sectional view (upper) and a schematic top view (lower) showing steps related to the formation of through-holes in the method for manufacturing an opto-electrical composite substrate of the present embodiment. FIG. 5 is a schematic cross-sectional view showing a step related to mirror formation in the method for manufacturing an optoelectric composite substrate according to this embodiment. FIG. 6 is a schematic cross-sectional view showing a state in which an optical signal is transmitted using the opto-electric composite substrate of this embodiment.

Embodiments for carrying out the present invention will be specifically described below with reference to the drawings and the like, but the present invention is not limited to these. In the opto-electrical composite substrate according to the present embodiment, the vertical and horizontal directions are not particularly defined in actual use. are identified. In addition, in each drawing and the following description, each reference sign indicates the following: 1 substrate, 2 core, 3 clad, 4 electrode pad, 5 mirror, 6 coverlay layer, 7 laser chip, 8 bump, 9 through hole, 10 Photomask, 11 blade, 12 diluted varnish, 13 deposition mask, 14 gold (metal layer).

(Optical-electrical composite substrate)
As shown in FIG. 2, the opto-electrical composite substrate according to the present embodiment includes a substrate 1 having an insulating layer and an electrode pad 4 formed on one surface of the insulating layer, and a laminated optical waveguide comprising a clad 3, a core 2 surrounded by the clad, an input micromirror 5 and an output micromirror 5', and the insulating layer of the electrode pad 4. It is characterized by having a through hole 9 leading to the surface opposite to the surface in contact with the .

With such a configuration, the distance between the optical component and the mirror can be shortened, and the optical loss can be reduced. In addition, since the base material of the wiring board is not present in the input/output optical path, the attenuation of light can be suppressed, and the loss of light during input/output can be further reduced. Therefore, according to the present invention, it is possible to provide an opto-electric composite substrate capable of reducing light loss and having high light input/output efficiency. Furthermore, a method for manufacturing the optoelectric composite substrate can also be provided.

For the insulating layer that constitutes the substrate 1, any material can be used without particular limitation as long as it is a material used for ordinary substrates for electrical materials, and examples thereof include materials for general printed wiring boards.

When the substrate is a rigid substrate, examples of materials for forming the insulating layer include epoxy resin, acrylic resin, phenol resin, silicone resin, bismaleimide resin, polyimide resin, liquid crystal polymer (LCP), benzoxazine, PPE (polyphenylene ether). ), vinyl-based resins, fluorine-based resins such as Teflon (registered trademark), and various modified products thereof.

When the substrate is a flexible substrate or a stretchable substrate, the substrate 1 is preferably composed of a flexible insulating layer.

In this embodiment, the insulating layer "has flexibility" means that it does not break even if it is deformed by bending the substrate. Specifically, it means that the tensile modulus at 20°C is 10 GPa or less. In this embodiment, the tensile modulus is measured by attaching a sample cut to a size of 90 mm * 5.5 mm to a universal testing machine (AGS-X manufactured by Shimadzu Corporation) and testing at a tensile speed of 500 mm / min. and the tensile modulus is calculated from the stress at elongation from 1.0% to 5.0%.

As a material for such an insulating layer, it is particularly preferable to use a material having durability against mechanical stress such as bending. It can be used as one insulating layer.

An electrode pad 4 made of a conductive material such as metal is formed on one surface (for example, the upper surface) of the insulating layer. When mounting an optical component 7 such as a laser chip, the electrode pad 4 is electrically connected to the optical component via bumps 8, as shown in the right diagram of FIG.

The conductive material that constitutes the electrode pad 4 is not particularly limited, but examples thereof include copper, gold, silver, aluminum, and alloys thereof.

Further, on the upper surface of the insulating layer, not only the electrode pad 4 but also an electric circuit (wiring) made of the same conductive material as the electrode pad 4 may be provided.

The positions of the electrode pads 4 and the electric circuit are not limited to the left and right positions of the substrate 1, and can be patterned according to the purpose of use.

Although the thickness of the insulating layer in the substrate 1 is not particularly limited, it is preferably 20 μm or more and 80 μm or less. With such a thickness, there is an advantage that both high flexibility (ease of bending) and ease of processing can be achieved at the same time.

The thickness of the substrate 1 is preferably 20 µm or more and 50 µm or less, more preferably 30 µm or more and 40 µm or less.

An optical waveguide is laminated on the surface of the insulating layer on which the electrode pads 4 are formed. The optical waveguide includes a core 2, a clad 3 surrounding it, micromirrors 5 and 5' capable of inputting and outputting light, and a through hole leading to the surface of the electrode pad 4 opposite to the surface in contact with the insulating layer. and holes 9 .

FIG. 3 is a schematic top view of the opto-electric composite substrate of this embodiment (actually, the core 2 is not visible in the top view, but the core 2 is also shown for convenience). Since the electrode pads 4 of the substrate 1 are exposed by having the through holes 9, optical components such as the laser chip 7 can be mounted there. The size of the through hole 9 is not particularly limited as long as it can accommodate the bump 8 for mounting the optical component.

Optical components that can be mounted on the opto-electric composite substrate of this embodiment include laser chips, photodiodes, and the like.

When mounting an optical component, it is preferable that the optical component and the optical waveguide are not completely in close contact with each other and are slightly separated from each other. This is because it is possible to prevent physical interference with optical components when the optical waveguide material expands and contracts according to temperature changes during use.

The optical waveguide of the present embodiment is not particularly limited as long as it has the through hole 9 as described above and can be provided in the opto-electrical composite wiring board. Specifically, as described above, it is an optical waveguide that includes the core 2 and the clad 3 surrounding the core 2, reflects light at the interface between the core 2 and the clad 3, and propagates the light into the core 2. .

In addition, the optical waveguide of this embodiment includes an input micromirror (inclined surface) 5 for reflecting light so as to guide light incident from the outside of the opto-electrical composite wiring board into the core 2, It has an output micromirror 5' for reflecting light so as to guide the emitted light to the outside of the opto-electrical composite wiring board. As the input micromirror 5 and the output micromirror 5', for example, an inclined surface forming an angle of 45° with the planar direction of the opto-electrical composite wiring board can be used. By making the inclined surface the interface between the core for the optical waveguide and the air, it is possible to realize a mirror with high reflection efficiency using the property of total reflection of light. These micromirrors may be provided with a metal layer of gold, silver, copper, aluminum, etc. on the slanted surfaces. These micromirrors 5 and 5' are formed in the mounting area of the optical elements (parts), and the micromirrors 5 and 5' pass light when introducing light from the outside or leading it to the outside. The electrode pad 4 and the through hole 9 are not formed in the region where the .

As a clad material for forming the clad 3, a resin material having a lower refractive index at the transmission wavelength of guided light than the material of the core 2, which will be described later, is used. Specifically, a resin material having a refractive index at the transmission wavelength of, for example, about 1.5 to 1.55 can be used. Examples of such resin materials include curable resins that are cured by energy rays such as light or heat. For example, it is preferable to use photosensitive materials.

In this specification, a photosensitive material is a material whose solubility in a liquid used in development, which will be described later, changes in a portion irradiated with energy rays. Specifically, for example, there is a material that is difficult to dissolve in a liquid used in development, which will be described later, before being irradiated with energy rays, but is easily dissolved after being irradiated with energy rays. Another example is a material that dissolves easily in a liquid used in development, which will be described later, before being irradiated with energy rays, but becomes less soluble after being irradiated with energy rays. The photosensitive material specifically includes, for example, a photosensitive polymer material. Also, the energy ray is not particularly limited as long as it can change the solubility. Specifically, ultraviolet rays are preferably used because of ease of handling and the like. As the photosensitive material, generally, a photosensitive polymeric material is preferably used in which the solubility of the portion irradiated with ultraviolet rays changes. More specifically, it is preferable to use a photosensitive polymer material whose portion irradiated with ultraviolet rays is cured and becomes difficult to dissolve in the liquid used in the development described below.

More specifically, examples of the photosensitive polymer forming the clad 3 include epoxy-based resins, acrylic-based resins, polycarbonate-based resins, polyimide-based resins, and the like, which have refractive indices as described above. Among these, bisphenol type epoxy resins are particularly preferred.

For the clad, it is preferable to use a dry film made of a resin composition containing the above resin and a curing agent (for example, a photocationic curing agent). The resin composition may further contain additives such as leveling agents and antioxidants.

The thickness of the clad 3 of the present embodiment is not particularly limited, but among the clads surrounding the core, when the clad on the substrate side is the lower clad and the clad on the opposite side to the substrate is the upper clad, the lower clad Preferably, the clad is thinner than the upper clad. As a result, the distance between the optical component 7 and the core 2 mounted on the opto-electric composite substrate of the present embodiment is shortened, and the loss of light can be further reduced. expected to improve.

As for the specific thickness of the clad, it is preferable that the thickness of the lower clad is 2 μm or more thicker than the thickness of the electrode pad described above. As a result, there is an advantage that variations in thickness when the electrode pads are buried can be suppressed. Specifically, the thickness of the lower clad is preferably 20 μm or more and 50 μm or less. On the other hand, the thickness of the upper clad is preferably about 5 μm or more and 10 μm or less.

Next, as a core material for forming the core 2, a material having a higher refractive index at the transmission wavelength of guided light than the material of the clad 3 is used. Specifically, a resin material having a refractive index at the transmission wavelength of, for example, about 1.55 to 1.6 can be used.

More specifically, similarly to the cladding material, it is preferable to use a photosensitive polymer material. For example, epoxy resin, acrylic resin, polycarbonate resin, polyimide resin having a refractive index as described above and the like as a resin component. Among these, bisphenol type epoxy resins are particularly preferred.

For the core, it is preferable to use a dry film made of a resin composition containing the resin as described above and a curing agent (for example, a photocationic curing agent). The resin composition may further contain additives such as leveling agents and antioxidants.

From the viewpoint of adhesion between the core 2 and the clad 3, the core material for forming the core is preferably of the same type as the clad material for forming the clad.

Although the thickness of the core 2 is not particularly limited, it is preferably about 20 μm or more and 50 μm or less. That is, the thickness of the entire optical waveguide is preferably 45 μm or more and 110 μm or less, including the thicknesses of the upper clad and the lower clad. As a result, there is an advantage that both high flexibility (ease of bending) and ease of processing can be achieved at the same time. A more preferable thickness of the optical waveguide is 50 μm or more and 100 μm or less.

The optical waveguide of this embodiment may have a coverlay layer 6 laminated on the surface opposite to the surface in contact with the substrate 1 . As shown in FIGS. 2 and 3, it is preferable that the coverlay layer 6 is mainly provided on the portion where the optical components are not mounted. In the opto-electrical composite substrate of the present embodiment, the portion where the optical component is not mounted can be a bending portion, and the presence of the coverlay layer 6 at that portion improves the bending resistance of the opto-electrical composite substrate, Furthermore, there is an advantage that the waveguide can be prevented from being damaged.

The coverlay layer 6 is preferably an insulating resin film, and for example, a resin film made of polyimide resin, PET resin, liquid crystal polymer (LCP) or the like can be used. Although the thickness of the coverlay layer 6 is not particularly limited, it is preferably equal to the thickness of the insulating layer of the substrate 1 described above from the viewpoint of symmetry. More specifically, it is usually about 20 μm or more and 80 μm or less.

The coverlay layer 6 is preferably laminated via an adhesive layer (not shown) made of epoxy resin, acrylic resin, or the like, and the thickness of the adhesive layer is usually about 5 μm or more and 20 μm or less.

(Method for manufacturing optoelectric composite substrate)
Next, a method for manufacturing an opto-electric composite substrate will be described. Here, a method for manufacturing the opto-electric composite substrate shown in FIGS. 2 and 3 will be described as an example.

The method for manufacturing an opto-electrical composite substrate of this embodiment includes the steps of preparing a substrate having an insulating layer and electrode pads formed on one surface of the insulating layer, and forming an optical waveguide on the substrate. with at least
The step of forming the optical waveguide includes laminating a lower clad material on the substrate, forming through holes on the electrode pads by photolithography, and forming a lower clad having through holes; laminating a core material on the lower clad to form a core by photolithography; laminating an upper clad material on the lower clad on which the core is formed; a step of forming a through hole in the substrate to form an upper clad; and a step of forming a micromirror.

Each step will be explained in more detail below.

First, prepare a substrate 1, that is, an electric wiring board, which includes an insulating layer, electrode pads 4 laminated on the insulating layer, and, if necessary, an electric circuit. The substrate 1 is a portion corresponding to the substrate portion of the opto-electric composite substrate as the final product.

The means for preparing the substrate 1 is not particularly limited, and can be carried out by appropriately using means for manufacturing a normal flexible circuit board.

Specifically, for example, a copper-clad laminate is used in which a copper foil having a desired thickness is laminated on one side of an insulating layer made of polyimide film or the like, and electrode pads 4 are formed at sites where optical components are desired to be mounted. Thus, the substrate 1 having the insulating layer and the electrode pads can be prepared by removing the copper foil from the other portions.

Next, the process of forming an optical waveguide on the substrate 1 will be described mainly with reference to FIG. 4, but the present embodiment is not limited thereto. In FIGS. 4A to 4F, the upper diagrams are schematic cross-sectional views seen from the cut planes indicated by dotted lines A to F in the lower diagrams.

First, a clad 3 (lower clad) is formed on the substrate 1 as shown in FIG. 4(A). The method of forming the clad 3 is not limited, but the clad 3 (lower cladding) is obtained.

A first specific example is a method in which a resin film made of a lower clad material having a predetermined refractive index for forming the clad 3 is attached to the surface of the substrate 1 and then cured. As a second example, there is a method of applying a liquid lower clad material for forming the clad 3 and then curing the material. As a third example, there is a method of applying a varnish of a lower clad material for forming the clad 3 and then curing the varnish. In addition, when forming the clad 3, it is preferable to subject the surface of the substrate 1 to a plasma treatment or the like in advance in order to improve adhesion.

As a more specific method of the first example, for example, the following method is used. First, a resin film made of the material for the lower clad is placed on the surface of the substrate 1 so as to be superimposed and then laminated by a hot press or the like. Stick together with an agent. Then, the bonded resin film is cured by irradiating energy rays such as light.

Also, as a specific method of the second and third examples, for example, the following method is used. First, a liquid lower clad material or varnish of the lower clad material is applied to the surface of the substrate 1 by spin coating, bar coating, dip coating, or the like. Then, the applied liquid lower clad material or varnish of the lower clad material is cured by irradiation with energy rays such as light.

In this embodiment, as shown in FIG. 4A, after bonding a clad resin film to the substrate 1 or applying a clad material to the substrate 1, through holes 9 are formed by photolithography. do. Specifically, a photomask 10 is placed only on the electrode pads 4, the cladding material is subjected to exposure processing from thereon, and then the through holes 9 are formed by developing processing.

The exposure treatment here can be used without any particular limitation, as long as it is a method of exposing the curable resin material (photosensitive material) with a necessary amount of light having a wavelength that can cause the curable resin material (photosensitive material) to be altered (cured, etc.) by light. Specifically, for example, a method using energy rays such as ultraviolet rays and X-rays as the exposure light used here can be used. Ultraviolet rays are preferably used because of ease of handling and the like.

The exposure conditions can be appropriately selected according to the type of the photosensitive material. For example, the conditions are selected such that an ultra-high pressure mercury lamp is used and the exposure is performed at 500 to 3500 mJ/cm ² .

Note that the clad resin layer may be heat-treated before being cured by exposure. By doing so, irregularities, air bubbles, voids, etc. on the clad surface can be eliminated to make the clad surface smoother. The heat treatment temperature is preferably a temperature at which the clad surface becomes smooth without irregularities, bubbles, voids, etc., and is appropriately selected according to the type of the curable resin material forming the clad. Further, the heat treatment time is preferably about 20 to 40 minutes, since the effect of eliminating irregularities, bubbles, voids, etc. on the surface of the clad and making it smooth can be sufficiently obtained. The means of heat treatment is not particularly limited, and a method of treating in an oven set at a predetermined temperature, a method of heating with a hot plate, or the like is used.

After the exposure process, through-holes 9 are formed in the clad 3 (lower clad) by performing a development process, as shown in FIG. 4(B). After the exposure process, the clad 3 may be subjected to heat treatment (post-curing) before the development process. It is believed that this makes it possible to more reliably cure the resin forming the clad. The post-curing conditions are preferably a temperature of about 120 to 150° C. and a time of about 10 to 30 minutes. However, it is not particularly limited to this range, and may be optimized according to the resin material used.

In the embodiment shown in FIG. 4B, since the resin layer made of the clad material is a positive type, the developing process for forming the through holes 9 is performed by washing away the unexposed areas with a developing solution. , to remove unnecessary parts. That is, in the embodiment shown in FIG. 4(B), the clad 3 in the portion of the through hole 9 is removed. If the resin layer is of a negative type, the exposed portion will be removed with a developer.

Examples of the developer used here include acetone, isopropyl alcohol, toluene, ethylene glycol, MEK, or a mixture thereof at a predetermined ratio. Furthermore, for example, a water-based developer as disclosed in JP-A-2007-292964 can also be preferably used. Examples of the developing method include a method of injecting a developer by spraying, a method of using ultrasonic cleaning, and the like.

Through the above steps, the clad 3 (lower clad) having the through holes 9 is formed on the substrate 1 .

Next, as shown in FIG. 4(C), a core 2 is formed on the clad 3 by photolithography.

Specifically, first, a core resin layer made of a core material having a predetermined refractive index for forming the core 2 is formed on the outer surface of the clad 3 (lower clad) formed above. The method is not particularly limited, and can be formed by bonding a resin film to the lower clad or applying a liquid resin (or resin varnish) to the surface of the lower clad in the same manner as the clad described above. Also when forming the core resin layer, a plasma treatment or the like may be performed in advance in order to activate the outer surface of the lower clad and improve adhesion.

After that, the core resin layer is irradiated with exposure light through a photomask 10 to perform pattern exposure of a predetermined shape on the core resin layer. The exposure is not particularly limited as long as it is a method of exposing the photosensitive material to light having a wavelength that can cause deterioration (curing, etc.) of the photosensitive material with the necessary amount of light, and can be performed under the same conditions as for the cladding described above. can.

The heat treatment before exposure, the heat treatment after exposure (post-cure), and the development treatment can be performed in the same manner as for the lower clad described above. As for development processing, in the embodiment shown in FIG. 4D, since the core resin layer is of a positive type, processing is performed to remove unnecessary portions by washing away unexposed portions with a developer. That is, in the embodiment shown in FIG. 4D, the core 2 is formed by removing the exposed resin layer other than the core 2, and the through hole 9 is also maintained.

Next, as shown in FIGS. 4(E) to 4(F), an optical waveguide is formed by forming a clad 3 (upper clad) so as to bury the core 2 formed above. .

The method of forming the clad 3 (upper clad) is not particularly limited. A clad 3 (upper clad) is obtained.

Specifically, first, an upper clad material having a predetermined refractive index for forming the clad 3 (upper clad) is applied to the outer surface of the clad 3 (lower clad) on which the core formed above is laminated. A cladding resin layer is formed. The material for the upper clad is not particularly limited as long as it is a material having a lower refractive index at the transmission wavelength of the guided light than the material for the core. Use resin material.

The method of forming the resin layer for the upper clad is not particularly limited, and in the same manner as the formation of the lower clad described above, a resin film is attached to the lower clad, or a liquid resin (or resin varnish) is applied to the surface of the lower clad. It can be formed by coating.

After that, as shown in FIG. 4(E), through holes 9 are formed by photolithography. Specifically, a photomask 10 is placed only on the electrode pad 4, the material for the upper clad is exposed from thereon, and then the through hole 9 is formed by developing.

The exposure treatment, heat treatment before exposure, heat treatment after exposure (post-cure), and development treatment can be performed in the same manner as for the lower clad described above.

Through the above steps, an optical waveguide having a through hole 9 is formed on the substrate 1 (FIG. 4(F)).

Furthermore, although not shown, the manufacturing method of this embodiment includes a step of forming a micromirror on the optical waveguide.

A micromirror is a core with an inclined surface for reflecting light. The method is not particularly limited as long as it can form an inclined surface as described above on the optical waveguide.

Specifically, examples of the method of forming the inclined surface include a method of cutting with a dicing blade and a method of laser ablation. More specifically, for example, one surface of the cutting edge is a surface parallel to the plane direction of the blade, and the other surface is a surface having a predetermined angle, for example, 45°, with respect to the plane direction of the blade. For example, a blade is used to cut into the optical waveguide. As the blade to be used, a disk-shaped rotary blade having a cutting edge on the circumference, such as a dicing blade, is used.

When cutting the optical waveguide with a blade, the cutting may be performed while softening the optical waveguide by heating the substrate, the blade, etc., if necessary. Since the micromirror is an inclined surface for reflecting light on the core, it may be formed from the outer surface of the opto-electrical composite substrate to the core. may have reached

Furthermore, a metal layer may be formed on the inclined surface formed as described above. As a result, there is an advantage that even if dust or the like enters the space created by the cut, the reflectance is not affected. The metal constituting the metal layer is not particularly limited, and gold, silver, copper, aluminum, etc. can be used, for example. Also, the method for forming the metal layer is not particularly limited, and a known method can be used. Specifically, for example, a vapor deposition method such as a vacuum vapor deposition method, a sputtering method, a nano-paste method, and the like can be used. The thickness of the metal layer is not particularly limited as long as it can reflect light, and examples include a thickness of about 1000 Å.

Furthermore, the manufacturing method of this embodiment may include a step of providing a coverlay layer on the optical waveguide.

The means for providing the coverlay layer is not particularly limited. Lay layers. The resin film is preferably laminated on the optical waveguide via an adhesive layer such as epoxy resin and/or acrylic resin.

In the opto-electric composite substrate of the present embodiment obtained in this way, since the distance between the optical component and the mirror is short, the incident light does not spread so much, and the optical loss can be reduced. In addition, since the base material of the wiring board is not present in the input/output optical path, the attenuation of light can be suppressed, and the loss of light during input/output can be further reduced.

As described above, this specification discloses various aspects of the technology, of which the main technologies are summarized below.

An opto-electric composite substrate according to a first aspect of the present invention comprises a substrate having an insulating layer and electrode pads laminated on the insulating layer, and an optical waveguide formed on one surface of the insulating layer,
The optical waveguide has a clad, a core surrounded by the clad, an input micromirror, an output micromirror, and a through hole leading to a surface of the electrode pad opposite to the surface in contact with the insulating layer. .

An opto-electric composite substrate according to a second aspect is the opto-electric composite substrate according to the first aspect, wherein, of the clads surrounding the core in the optical waveguide, the clad on the substrate side is the lower clad and is opposite to the substrate. When the clad on the side is defined as the upper clad, the lower clad is thinner than the upper clad.

An opto-electric composite substrate according to a third aspect is the opto-electric composite substrate according to the first or second aspect, wherein the substrate has a thickness of 20 μm or more and 50 μm or less, and the optical waveguide has a thickness of 50 μm or more and 100 μm or less. .

An opto-electric composite substrate according to a fourth aspect is the opto-electric composite substrate according to any one of the first to third aspects, wherein an optical component is arranged on the optical waveguide, the optical component and the electrode pad are electrically connected through the through holes.

An opto-electric composite substrate according to a fifth aspect is the opto-electric composite substrate according to any one of the first to fourth aspects, wherein the insulating layer has flexibility.

In the opto-electric composite substrate according to the sixth aspect, a coverlay is laminated on the surface opposite to the surface in contact with the substrate in the optical waveguide of the opto-electric composite substrate according to the fifth aspect.

A method for manufacturing an opto-electrical composite substrate according to a seventh aspect includes the steps of preparing a substrate having an insulating layer and electrode pads formed on one surface of the insulating layer, and forming an optical waveguide on the substrate. comprising at least a step and
The step of forming the optical waveguide includes:
a step of laminating a lower clad material on the substrate, forming through holes on the electrode pads by photolithography, and forming a lower clad having through holes;
A step of laminating a core material on the lower clad and forming a core by a photolithographic method;
a step of laminating an upper clad material on the lower clad on which the core is formed, forming through holes on the electrode pads by photolithography, and forming an upper clad;
and forming a micromirror.

(Production example 1)
A flexible printed wiring board was prepared in which electrode pads and electric circuits were formed on an insulating layer made of polyimide resin with a thickness of 25 μm and a copper foil with a thickness of 18 μm.

A lower clad material (a dry film made of UV-curing epoxy resin, with a release film, 20 μm thick) is laminated on the substrate so as to cover the electrode pads and electric circuit, and a pressurized vacuum laminator (Nikko Materials Co., Ltd.) is applied. V-130 manufactured by Nichigo-Morton Co., Ltd., hereinafter simply referred to as "vacuum laminator V-130"), by applying pressure at 80 ° C. and 0.2 MPa, the substrate A dry film for the lower clad was laminated thereon.

Then, through a photomask as shown in FIG. 4A, the lower clad dry film was exposed to ultraviolet light from an ultra-high pressure mercury lamp under the condition of 2 J/cm ² . Specifically, a mask having four circular slits with a diameter of 50 μm was positioned above the lower clad dry film, and the lower clad dry film was exposed through the mask. By doing so, the portion corresponding to the lower clad was cured.

Next, after peeling off the release film from the cured lower clad dry film, heat treatment was performed at 140°C for 30 minutes. Then, development processing was performed using an aqueous flux cleaning solution (Pine Alpha ST-100SX manufactured by Arakawa Chemical Industries, Ltd.) adjusted to 55° C. as a developer. By doing so, the unexposed portion of the lower clad dry film was dissolved away to form through holes. Further, after finishing washing with water, air blowing was performed. After that, it was dried at 100° C. for 10 minutes. Thus, a lower clad was formed on the substrate.

Next, on the surface of the substrate on which the lower clad is formed, a core material (dry film made of UV curable epoxy resin, with release film, thickness 25 μm) is placed, and vacuum laminator V-130 is applied. The core dry film was laminated on the lower clad by applying pressure at 80° C. and 0.2 MPa.

Then, using a photomask as shown in FIG. 4(C), the core dry film was exposed to ultraviolet light under the conditions of 3 J/cm ² with an ultra-high pressure mercury lamp so as to obtain a core of a predetermined shape. was exposed by irradiating the Specifically, a mask having a linear pattern of slits with a width of 25 μm and a length of 50 mm was used, and the mask was positioned so that the slits were at appropriate positions above the core dry film. exposed. By doing so, the portion corresponding to the core was cured.

Next, after peeling off the release film from the cured core dry film, heat treatment was performed at 100°C for 30 minutes. Then, development processing was performed using an aqueous flux cleaning solution (Pine Alpha ST-100SX manufactured by Arakawa Chemical Industries, Ltd.) adjusted to 55° C. as a developer. By doing so, the unexposed portions of the core dry film were dissolved away. Further, after finishing washing with water, air blowing was performed. After that, it was dried at 100° C. for 10 minutes. As a result, a core having a cross-sectional shape of 25 μm in length×25 μm in width was formed on the lower clad. Moreover, the clad thickness between the core and the insulating layer surface of the substrate is 20 μm.

Next, on the surface of the substrate on which the lower clad and core are formed, an upper clad material (a dry film made of UV-cured epoxy resin, with a release film, thickness of 30 μm) is placed, and vacuum laminator V is applied. The upper clad dry film was laminated on the entire surface of the substrate by applying pressure at 100° C. and 0.3 MPa using −130.

Then, through a photomask as shown in FIG. 4(E), the upper clad dry film was exposed to ultraviolet light from an ultra-high pressure mercury lamp under the condition of 2 J/cm ² . Specifically, a mask having four circular slits with a diameter of 50 μm was positioned above the upper clad dry film, and the upper clad dry film was exposed through the mask. By doing so, the portion corresponding to the upper clad was cured.

After that, after peeling off the release film from the cured upper clad dry film, heat treatment was performed at 120°C for 30 minutes. Then, development processing was performed using an aqueous flux cleaning solution (Pine Alpha ST-100SX manufactured by Arakawa Chemical Industries, Ltd.) adjusted to 55° C. as a developer. By doing so, the unexposed portion of the dry film for the upper clad was removed by dissolving to form through-holes. Further, after finishing washing with water, air blowing was performed. After that, it was dried at 100° C. for 10 minutes. Thus, an upper clad having through holes was formed. The clad thickness between the core and the later-described coverlay layer is 5 μm.

Next, as shown in FIG. 5A, a blade 11 (a blade manufactured by Disco Co., Ltd. (particle size: No. 5000) (model number: B1E863SD5000L100MT38)) having an angle of 45° with respect to the surface direction of the blade on only one side in the plane of the cutting edge. was used to make two cuts at both end portions of the core under conditions of a rotation speed of 10000 rpm and a moving speed of 0.1 mm/sec. By doing so, the core was formed with a 45° inclined surface as shown in FIG. 5(B). At that time, a cut of 40 μm was made from the surface of the optical waveguide.

After that, as shown in FIG. 5(C), a solution 12 obtained by diluting a resin varnish made of the same material as the lower clad material 50 times with a mixed solvent of toluene and MEK at a mass ratio of 3:7. was thinly applied to the 45° inclined surface and the 90° surface with a brush. Then, after drying at 100° C. for 30 minutes, exposure was performed by irradiating ultraviolet light under the condition of 1 J/cm 2 with an extra-high pressure mercury lamp. After that, heat treatment was further performed at 120° C. for 10 minutes. By doing so, the 45° inclined plane and the 90° plane were smoothed.

Then, as shown in FIG. 5(D), a vapor deposition mask (metal mask) 13 having an opening only in the region where the 45° inclined surface is formed is used to mask the surface of the 45° inclined surface with gold 14 having a thickness of 1000 Å. A micromirror having a metal layer 14 on the optical waveguide was formed by vacuum deposition (FIG. 5(E)).

After that, the surface of the upper clad is treated with oxygen plasma, and a coverlay film (coverlay film “CISV-1215 manufactured by Nikkan Kogyo Co., Ltd. ”, Laminated film having an adhesive layer with a thickness of 12.5 μm on one side of a polyimide film with a thickness of 15 μm), and using a vacuum laminator V-130 at 120 ° C. and 0.3 MPa. , laminated. After that, it was heated at 160° C. for 1 hour. By doing so, the adhesive layer of the coverlay film was cured to form a coverlay layer.

A substrate having an insulating layer and electrode pads stacked on the insulating layer and an optical waveguide stacked on a surface of the substrate on which the electrode pads are stacked are provided by the above steps, and the optical waveguide comprises a clad and a , an opto-electric composite substrate having a core surrounded by the clad, an input micromirror, an output micromirror, and a through hole provided on the electrode pad.

According to the opto-electric composite substrate of the present embodiment, as shown in FIG. 6, optical signals can be efficiently transmitted with high reliability.

This application is based on Japanese Patent Application No. 2021-168549 filed on October 14, 2021, the contents of which are included in this application.

In order to express the present invention, the present invention has been properly and fully described above through the embodiments with reference to specific examples, drawings, etc., but those skilled in the art may modify and/or improve the above-described embodiments. should be recognized as something that can be done easily. Therefore, to the extent that modifications or improvements made by those skilled in the art do not deviate from the scope of the claims set forth in the claims, such modifications or modifications do not fall within the scope of the claims. is interpreted to be subsumed by

The opto-electric composite substrate of the present invention has flexibility and can reduce optical loss. Therefore, the present invention is preferably used as a flexible printed wiring board for optical transmission, and is very applicable to various electronic devices such as mobile phones, personal digital assistants, communication devices such as routers and servers, and base station equipment. useful for

Claims

a substrate having an insulating layer and an electrode pad formed on one surface of the insulating layer;
an optical waveguide laminated on the one surface of the insulating layer,
The optical waveguide has a clad, a core surrounded by the clad, an input micromirror, an output micromirror, and a hole leading to a surface of the electrode pad opposite to the surface in contact with the insulating layer.
Optoelectric composite substrate.
In the optical waveguide, when the clad on the substrate side of the clad surrounding the core is defined as a lower clad and the clad on the opposite side of the substrate is defined as an upper clad, the lower clad is thicker than the upper clad. The opto-electric composite substrate according to claim 1, which is thin.
The opto-electric composite substrate according to claim 1, wherein the substrate has a thickness of 20 µm or more and 50 µm or less, and the optical waveguide has a thickness of 50 µm or more and 100 µm or less.
The photoelectric composite substrate according to claim 1, wherein an optical component is arranged on the optical waveguide, and the optical component and the electrode pad are electrically connected through the through hole.
The optoelectric composite substrate according to claim 1, wherein the insulating layer has flexibility.
The optoelectric composite substrate according to claim 5, wherein a coverlay is laminated on the surface of the optical waveguide opposite to the surface in contact with the substrate.
at least comprising the steps of: preparing a substrate having an insulating layer and an electrode pad formed on one surface of the insulating layer; and forming an optical waveguide on the substrate;
The step of forming the optical waveguide includes:
a step of laminating a lower clad material on the substrate, forming through holes on the electrode pads by photolithography, and forming a lower clad having through holes;
A step of laminating a core material on the lower clad and forming a core by a photolithographic method;
a step of laminating an upper clad material on the lower clad on which the core is formed, forming through holes on the electrode pads by photolithography, and forming an upper clad;
forming a micromirror;
A method for manufacturing an optoelectric composite substrate.