Composite substrate

Abstract

This invention provides a technology that facilitates optical coupling and electrical connection in the mounting of functional devices onto a composite substrate including a conductor pattern and an optical waveguide. [Solution] The composite substrate 10A includes a wiring substrate 11A and a substrate with optical waveguides 12A. The wiring substrate 11A includes an insulating layer and a conductor pattern, and one side thereof includes a first region R1 and a second region R2 recessed thereto, the height of the second region R2 being lower than the lower surface of the conductor pattern 113 located in the first region R1. The substrate with optical waveguides 12A includes a substrate 121 and an optical waveguide layer 122, the optical waveguide layer 122 includes a first cladding layer 122A, a second cladding layer 122C, and a core 122B provided between them. The substrate with optical waveguides 12A is placed on the second region R2 such that the optical waveguide layer 122 is located above the substrate 121, and the height of the lower surface of the core 122B is higher than the first region R1.

Description

Technical Field

[0001] The present invention relates to a composite substrate.

Background Art

[0002] In recent years, in order to achieve high-speed and high-capacity communication with low power consumption, introducing photonics-based technology into all components from the network to the terminal has attracted attention.

[0003] In particular, the optoelectronic integration technology that replaces a part of the electric circuit in a terminal with a circuit that handles optical signals is one of the important technologies. In the optoelectronic integration technology, for example, an optical waveguide is provided on a circuit board, and a device that performs photoelectric conversion and a device that processes an electric signal are mounted thereon. The optical waveguide and the former device are optically coupled, and an optoelectronic integration device in which these devices are electrically connected by a circuit provided on the circuit board is used (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a technology that can facilitate optical coupling and electrical connection in mounting a functional device on a composite substrate including a conductor pattern and an optical waveguide.

Means for Solving the Problems

[0006] According to one aspect of the present invention, a wiring substrate comprising one or more insulating layers and one or more conductor patterns, having a first surface and a second surface which is its back surface, wherein the first surface comprises one or more first regions and one or more second regions which are recessed relative to the one or more first regions, one of the one or more conductor patterns is located in the one or more first regions, and the height of the one or more second regions is lower than the lower surface of one of the one or more conductor patterns located in the one or more first regions, and the substrate and an optical waveguide layer provided thereon A composite substrate is provided, comprising one or more optical waveguide substrates, each of which includes, and each of the optical waveguide layers comprises a first cladding layer provided on the substrate, a second cladding layer provided on the first cladding layer, and one or more cores provided between the first cladding layer and the second cladding layer, each of which is installed on the one or more second regions such that the optical waveguide layers are located above the substrate, and the height of the lower surface of the one or more cores is higher than that of the one or more first regions.

[0007] According to another aspect of the present invention, a composite substrate is provided in which the height of the upper surface of the substrate is lower than that of the one or more first regions.

[0008] According to yet another aspect of the present invention, a composite substrate is provided in which the lower surface of the one or more cores relates to any of the above-mentioned sides, wherein the height of the one or more first regions is 100 μm or less.

[0009] According to yet another aspect of the present invention, a composite substrate according to any of the above aspects is provided, further comprising one or more stress-relaxing layers interposed between the one or more optical waveguide substrates and the one or more second regions.

[0010] According to yet another aspect of the present invention, a composite substrate is provided in which each of the one or more stress relaxation layers has an elastic modulus in the range of 0.1 MPa to 3 GPa.

[0011] According to yet another aspect of the present invention, a composite substrate is provided in which each of the one or more stress relaxation layers has a thickness in the range of 5 μm to 50 μm, relating to any of the above aspects.

[0012] According to yet another aspect of the present invention, a composite substrate is provided which comprises one or more insulating layers including insulating resin layers and the substrate including a glass substrate, according to any of the above aspects.

[0013] In yet another aspect of the present invention, a composite substrate relating to any of the above aspects, which is an interposer, is provided.

[0014] According to yet another aspect of the present invention, a photoelectric fusion device is provided comprising a composite substrate according to any of the above aspects, a first functional device mounted on the composite substrate and optically coupled to at least one of the one or more optical waveguide substrates, and a second functional device mounted on the composite substrate and electrically connected to the first functional device. [Effects of the Invention]

[0015] According to the present invention, a technique is provided that facilitates optical coupling and electrical connection in the mounting of a functional device on a composite substrate including a conductor pattern and an optical waveguide. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a top view of a composite substrate according to a first embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view of the composite substrate shown in Figure 1 along the line II-II. [Figure 3] Figure 3 is a top view of the optical waveguide substrate included in the composite substrate shown in Figures 1 and 2. [Figure 4] Figure 4 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 3. [Figure 5] Figure 5 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figures 1 and 2. [Figure 6] Figure 6 is a cross-sectional view along the line VI-VI of the photoelectric fusion apparatus shown in Figure 5. [Figure 7] Figure 7 is a top view of the optoelectronic fusion device with a connector including the optoelectronic fusion device shown in FIGS. 5 and 6. [Figure 8] Figure 8 is a cross-sectional view showing a modified example of the optoelectronic fusion device shown in FIGS. 5 and 6. [Figure 9] Figure 9 is a top view of the composite substrate according to the second embodiment of the present invention. [Figure 10] Figure 10 is a cross-sectional view taken along the line X-X of the composite substrate shown in FIG. 9. [Figure 11] Figure 11 is a top view of the substrate with an optical waveguide included in the composite substrate shown in FIGS. 9 and 10. [Figure 12] Figure 12 is a cross-sectional view of the substrate with an optical waveguide shown in FIG. 11. [Figure 13] Figure 13 is a top view of the optoelectronic fusion device including the composite substrate shown in FIGS. 9 and 10. [Figure 14] Figure 14 is a cross-sectional view taken along the line XIV-XIV of the optoelectronic fusion device shown in FIG. 13. [Figure 15] Figure 15 is a top view of the optoelectronic fusion device with a connector including the optoelectronic fusion device shown in FIGS. 13 and 14. [Figure 16] Figure 16 is a cross-sectional view showing a modified example of the optoelectronic fusion device shown in FIGS. 13 and 14. [Figure 17] Figure 17 is a top view of the composite substrate according to the third embodiment of the present invention. [Figure 18] Figure 18 is a top view of the optoelectronic fusion device with a connector including the composite substrate shown in FIG. 17. [Figure 19] Figure 19 is a top view of the composite substrate according to the fourth embodiment of the present invention. [Figure 20] Figure 20 is a cross-sectional view taken along the line XX-XX of the composite substrate shown in FIG. 19. [Figure 21] Figure 21 is a top view of the optoelectronic fusion device including the composite substrate shown in FIGS. 19 and 20. [Figure 22] Figure 22 is a cross-sectional view taken along the line XXII-XXII of the optoelectronic fusion device shown in FIG. 21. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific to any of the above aspects. The matters described below can be incorporated into each of the above aspects, individually or in combination.

[0018] The embodiments described below illustrate examples that embody the technical concept of the present invention, and the technical concept of the present invention is not limited to the materials, shapes, structures, and arrangements of the components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims described in the patent claims.

[0019] In the drawings referenced in the following description, components with similar or identical functions are given the same reference numerals. It should be noted that the drawings are schematic, and the relationships between dimensions in the thickness direction and dimensions perpendicular to the thickness direction (i.e., in-plane direction), as well as the relationships between dimensions in the thickness direction of multiple layers, may differ from reality. Therefore, specific dimensions should be determined by referring to the following description. It should also be noted that the dimensional relationships between two or more components may differ across multiple drawings.

[0020] In this disclosure, "upper surface" and "lower surface" refer to the two main surfaces of the plate-like member or the layer contained therein, namely the surface perpendicular to the thickness direction and having the largest area, and the back surface thereof, which are shown at the top and bottom in the drawings, respectively. Furthermore, "end surface" refers to the surface of the plate-like member or the layer contained therein that is located on the outer periphery when viewed from a direction parallel to the thickness direction. And "side surface" refers to a surface that is perpendicular to or inclined with respect to the in-plane direction.

[0021] Furthermore, in this disclosure, the phrase "AA on BB" is used independently of the direction of gravity. The state specified by the phrase "AA on BB" includes the state in which AA is in contact with BB. The phrase "AA on BB" does not exclude the presence of one or more other components between AA and BB.

[0022] <1> First Embodiment <1.1> Composite substrate Figure 1 is a top view of a composite substrate according to a first embodiment of the present invention. Figure 2 is a cross-sectional view of the composite substrate shown in Figure 1 along the line II-II. Figure 3 is a top view of a substrate with an optical waveguide included in the composite substrates shown in Figures 1 and 2. Figure 4 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 3.

[0023] In these and other figures, the X and Y directions are perpendicular to the thickness direction of the composite substrate and are also orthogonal to each other. In these figures, the Z direction is perpendicular to the X and Y directions, i.e., the thickness direction of the composite substrate.

[0024] The composite substrate 10A shown in Figures 1 and 2 is an interposer. The composite substrate 10A includes a wiring board 11A, a substrate with an optical waveguide 12A, and an adhesive layer 13 that bonds them together.

[0025] The wiring board 11A includes a core insulating layer 111, an insulating layer 112, a conductor pattern 113, and an insulating layer 114.

[0026] The core insulating layer 111 is, in this case, an insulating resin layer. For example, the core insulating layer 111 is a composite material containing glass fibers and a cured resin. The core insulating layer 111 may also be a glass plate. The core insulating layer 111 may have a single-layer structure or a multi-layer structure. The core insulating layer 111 is provided with a plurality of through holes, each extending in the thickness direction.

[0027] The insulating layer 112 is laminated on each of the main surfaces of the core insulating layer 111. The insulating layer 112 is, in this case, an insulating resin layer. The insulating layer 112 is made of, for example, a cured resin. Each of the insulating layers 112 may have a single-layer structure or a multi-layer structure. Each of the insulating layers 112 is provided with a plurality of through holes, each extending in the thickness direction.

[0028] Here, two insulating layers 112 are laminated on each main surface of the core insulating layer 111. The number of insulating layers 112 provided on each main surface of the core insulating layer 111 may be one or three or more. Also, an insulating layer 112 may not be provided on at least one main surface of the core insulating layer 111.

[0029] The conductor pattern 113 is a wiring layer that includes a lead layer. The conductor pattern 113 may have a single-layer structure or a multi-layer structure. Here, the "lead layer" is the thickest layer among the conductive layers included in the wiring layer. The lead layer is made of a metallic material such as copper. Each of the conductor patterns 113 may further include one or more other layers such as an adhesion layer and a seed layer.

[0030] The conductor pattern 113 includes a first conductor pattern (not shown) which includes a portion interposed between the core insulating layer 111 and an adjacent insulating layer 112, a second conductor pattern which includes a portion interposed between adjacent insulating layers 112, and a third conductor pattern which includes a portion interposed between insulating layer 112 and insulating layer 114.

[0031] The portion of the first conductor pattern interposed between the core insulating layer 111 and the adjacent insulating layer 112 includes land portions, pad portions, and wiring portions. Each of the wiring portions has one end connected to a land portion and the other end connected to a pad portion. The first conductor pattern further includes through electrodes, which are portions that cover the side walls of through holes provided in the core insulating layer 111. Each of the through electrodes is connected to the land portions on both sides of the core insulating layer 111. The first conductor pattern may also embed the through holes provided in the core insulating layer 111.

[0032] Each of the second and third conductor patterns includes pad portions, wiring portions, and via portions. In each of the second and third conductor patterns, the pad portions include those positioned to cover or surround one opening of a through-hole provided in the insulating layer 112 adjacent to the core insulating layer 111 side, and those positioned away from the through-hole. The wiring portions connect the former pad portions to the latter pad portions. The via portions fill the through-holes provided in the insulating layer 112 adjacent to the core insulating layer 111 side of the pad portions of the second or third conductor pattern, and connect the pad portions facing each other with the insulating layer 112 in between. The third conductor pattern located below has a greater distance between pad portions compared to the third conductor pattern located above.

[0033] The insulating layer 114 is an organic insulating layer. The insulating layer 114 is made of, for example, solder resist. Each insulating layer 114 covers one of the insulating layers 112 and one of the conductor patterns 113. Each insulating layer 114 has through holes at the positions of the pads of the conductor pattern 113 that it covers.

[0034] The wiring board 11A has a first surface S1 and a second surface S2 which is its back surface. Here, the first surface S1 is the top surface of the wiring board 11A, and the second surface S2 is the bottom surface of the wiring board 11A.

[0035] The first surface S1 includes a first region R1 and a second region R2 that is recessed relative to the first region R1. That is, the first surface S1 has a recess at the location of the second region R2.

[0036] Here, the wiring board 11A has a shape that, when orthogonally projected onto a plane perpendicular to the Z direction, is a square or rectangle with sides parallel to the X direction and sides parallel to the Y direction. The dimensions of the wiring board 11A in the X and Y directions are, in one example, within the range of 30 mm to 150 mm, and in another example, within the range of 50 mm to 100 mm.

[0037] The shape of the second region R2 is, in this case, a rectangle extending from the edge of the first surface S1, which is parallel to the Y direction, in a direction parallel to the X direction. The dimensions of the second region R2 in the X direction, i.e., the length direction, are preferably within the range of 5 mm to 50 mm, and more preferably within the range of 10 mm to 30 mm. The dimensions of the second region R2 in the Y direction, i.e., the width direction, are preferably within the range of 1 mm to 10 mm, and more preferably within the range of 2 mm to 5 mm.

[0038] The uppermost conductor pattern 113 is located in the first region R1. A portion of the through-holes in the insulating layer 114 located above it is located near the second region R2.

[0039] The height of the second region R2 is lower than the lower surface of the conductor pattern 113 located in the first region R1, i.e., the uppermost conductor pattern 113. The difference between the height of the lower surface of the uppermost conductor pattern 113 and the height of the second region R2 is preferably in the range of 70 μm to 250 μm, and more preferably in the range of 100 μm to 200 μm.

[0040] The optical waveguide substrate 12A includes a substrate 121 and an optical waveguide layer 122 provided thereon.

[0041] The substrate 121 is made of, for example, glass, ceramic, plastic, metal, or a combination of two or more of these materials. The substrate 121 only needs to have a smooth surface. Here, as an example, the substrate 121 is assumed to be a glass plate.

[0042] The shape of the orthogonal projection of the substrate 121 onto a plane perpendicular to its thickness is approximately equal to the shape of the second region R2. Here, the shape of the orthogonal projection of the substrate 121 is a rectangle corresponding to the shape of the second region R2. Furthermore, the dimensions of the orthogonal projection of the substrate 121 are slightly smaller than those of the second region R2.

[0043] The difference between the lengthwise dimension of the second region R2 and the lengthwise dimension of the orthogonal projection of the substrate 121 is, in one example, within the range of 5 μm to 300 μm, and in another example, within the range of 10 μm to 200 μm. The difference between the widthwise dimension of the second region R2 and the widthwise dimension of the orthogonal projection of the substrate 121 is, in one example, within the range of 5 μm to 300 μm, and in another example, within the range of 10 μm to 200 μm.

[0044] The thickness of the substrate 121 is preferably in the range of 50 μm to 150 μm, and more preferably in the range of 80 μm to 100 μm.

[0045] The optical waveguide layer 122 includes a first cladding layer 122A, a core 122B, and a second cladding layer 122C.

[0046] The first cladding layer 122A is provided on one main surface of the substrate 121. The first cladding layer 122A is made of a first low refractive index material. For example, the first low refractive index material is a cured resin. The first low refractive index material preferably has a refractive index for light with a wavelength of 1300 nm in the range of 1.4 to 1.7, and more preferably in the range of 1.5 to 1.6.

[0047] The first cladding layer 122A includes a first portion with greater thickness and a second portion with less thickness. The first and second portions are arranged in the longitudinal direction of the substrate 121.

[0048] The thickness of the first portion is preferably in the range of 120 μm to 170 μm, and more preferably in the range of 130 μm to 160 μm. The difference between the thickness of the first portion and the thickness of the second portion is preferably in the range of 60 μm to 140 μm, and more preferably in the range of 80 μm to 120 μm.

[0049] The second cladding layer 122C is provided on the first portion of the first cladding layer 122A. The second cladding layer 122C covers the first portion of the first cladding layer 122A without covering the second portion of the first cladding layer 122A.

[0050] The second cladding layer 122C consists of a second low refractive index material. For example, the second low refractive index material is a cured resin. Preferably, the second low refractive index material has the refractive index described above for the first low refractive index material. Preferably, the second low refractive index material is the same as the first low refractive index material.

[0051] Core 122B is provided between the first cladding layer 122A and the second cladding layer 122C. Here, the number of cores 122B included in the optical waveguide substrate 12A is 2, but the number of cores 122B included in the optical waveguide substrate 12A may be 1 or 3 or more.

[0052] Each of the cores 122B has a shape that extends in the longitudinal direction of the substrate 121. These cores 122B are arranged in the width direction. Each of the cores 122B preferably has a diameter in the range of 6 μm to 60 μm, and more preferably in the range of 8 μm to 50 μm.

[0053] Core 122B is made of a high refractive index material. For example, the high refractive index material is a cured resin. The high refractive index material preferably has a refractive index for light of the above wavelength in the range of 1.4 to 1.7, and more preferably in the range of 1.5 to 1.6.

[0054] The difference between the refractive index of the high refractive index material for the above wavelength and the refractive index of the first low refractive index material for the above wavelength is preferably within the range of 0.5% to 5.0%, and more preferably within the range of 1.0% to 3.0%, when the refractive index of the high refractive index material is set to 100%. The difference between the refractive index of the high refractive index material for the above wavelength and the refractive index of the second low refractive index material for the above wavelength is also preferably within these ranges.

[0055] The optical waveguide substrate 12A is installed on the second region R2 such that the optical waveguide layer 122 is located above the substrate 121. As described above, the wiring board 11A has a recess at the location of the second region R2. The optical waveguide substrate 12A is installed within this recess.

[0056] The height of the lower surface of core 122B is higher than that of the first region R1. The height of the lower surface of core 122B relative to the first region R1, in this case, relative to the upper surface of the insulating layer 114 located above it, is preferably 100 μm or less, and more preferably 80 μm or less. Furthermore, the height of the lower surface of core 122B relative to the first region R1 is preferably 50 μm or more, and more preferably 60 μm or more.

[0057] The height of the upper surface of the substrate 121 is preferably lower than that of the first region R1. The difference between the height of the first region R1 and the height of the upper surface of the substrate 121 is preferably in the range of 10 μm to 30 μm, and more preferably in the range of 15 μm to 25 μm.

[0058] The adhesive layer 13 is interposed between the wiring board 11A and the optical waveguide substrate 12A. The adhesive layer 13 fixes the optical waveguide substrate 12A to the wiring board 11A. The adhesive layer 13 includes a layer made of adhesive. The adhesive layer 13 may have a single-layer structure or a multi-layer structure.

[0059] <1.2>Optoelectronic fusion device Figure 5 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figures 1 and 2. Figure 6 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 5 along the line VI-VI.

[0060] The photoelectric integration apparatus 1A shown in Figures 5 and 6 includes the composite substrate 10A, the bonding conductor 14, the first functional device 20A, and the second functional device 30.

[0061] The joining conductor 14 covers the pad portion of the conductor pattern 113 covered by the insulating layer 114 at the location of the through-hole provided in the insulating layer 114. Each of the joining conductors 14 includes a portion located within the through-hole provided in the insulating layer 114 and a portion protruding from the insulating layer 114. The joining conductor 14 is, for example, a solder bump.

[0062] The first functional device 20A is a device that includes an optical integrated circuit and an optical waveguide. The optical integrated circuit includes a photoelectric conversion element and performs conversion of optical signals to electrical signals, conversion of electrical signals to optical signals, or both. Here, as an example, the optical integrated circuit is assumed to perform both conversion of optical signals to electrical signals and conversion of electrical signals to optical signals. Each optical waveguide has one end face exposed to the end face of the first functional device 20A and is optically coupled to the photoelectric conversion element at the other end. Here, the number of optical waveguides included in the first functional device 20A is 2. The number of optical waveguides included in the first functional device 20A may be 1 or 3 or more.

[0063] The first functional device 20A is flip-chip mounted on the wiring board 11A via a bonding conductor 14 in the vicinity of the optical waveguide substrate 12A. Furthermore, the first functional device 20A is positioned so that the end face of the core 21 of its optical waveguide faces the end face of the core 122B of the optical waveguide layer 122. In other words, the optical waveguide of the first functional device 20A is optically coupled to the optical waveguide layer 122 by butt coupling.

[0064] The second functional device 30 is, for example, a device that operates when at least one of power and / or an electrical signal is supplied, a device that outputs at least one of power and / or an electrical signal in response to an external stimulus, or a device that operates when at least one of power and / or an electrical signal is supplied and also outputs at least one of power and / or an electrical signal in response to an external stimulus. The second functional device 30 is in the form of a chip, for example, a semiconductor chip or a chip on which circuits and elements are formed on a substrate made of a material other than a semiconductor, such as a glass substrate. The second functional device 30 can include, for example, one or more of a large-scale integrated circuit (LSI), memory, image sensor, light-emitting element, and MEMS (Micro Electro Mechanical Systems). MEMS are, for example, one or more of a pressure sensor, acceleration sensor, gyroscope, tilt sensor, microphone, and acoustic sensor. In one example, the second functional device 30 is a semiconductor chip including an LSI.

[0065] The second functional device 30 is flip-chip mounted on the wiring board 11A via a bonding conductor 14. The second functional device 30 is electrically connected to the first functional device 20A via a conductor pattern 113 and the bonding conductor 14.

[0066] Here, the number of second functional devices 30 included in the photoelectric fusion device 1A is 1. The number of second functional devices 30 included in the photoelectric fusion device 1A may be 2 or more.

[0067] <1.3> Method for manufacturing a photoelectric fusion device The above-described photoelectric fusion apparatus 1A can be manufactured, for example, by the following method. <1.3.1> Manufacturing method of a wiring board The wiring board 11A is manufactured, for example, by the following method. Specifically, first, a composite material is prepared that includes a core insulating layer 111 and first conductor layers provided on both sides thereof. Here, as will be described later, a composite substrate is first manufactured, and this composite substrate is then divided into multiple wiring boards 11A. Therefore, the dimensions of the composite material prepared here are slightly larger than the dimensions of the assembly formed by arranging multiple wiring boards 11A. The first conductor layer is, for example, copper foil attached to the core insulating layer 111.

[0068] Next, through-holes are formed in this composite material to electrically connect its front and back surfaces. These through-holes are formed, for example, using a drill.

[0069] Next, a second conductor layer is formed on the side walls of the through-holes and on the surface of the first conductor layer. The second conductor layer may be formed so that the through-holes in the core insulating layer 111 are not completely filled, or it may be formed so that these through-holes are completely filled.

[0070] The second conductive layer can be obtained, for example, by forming a seed layer by electroless plating and then forming a plating layer by electroplating, in that order. For the seed layer, metallic materials such as Cu, Pd, Al, Sn, Ni, and Cr can be used. For the plating layer, metallic materials such as Cu, Cu alloys, Ag, Ag alloys, Sn, Pd, Au, Ni, Cr, Pt, Fe, and combinations of two or more of these can be used.

[0071] Next, the through-holes in the core insulating layer 111 are filled with a hole-filling resin. For example, the through-holes are filled with resin, allowed to harden, and then any excess hardened resin that has protruded from the through-holes is removed by buffing or the like. If the through-holes in the core insulating layer 111 are completely filled with the conductive layer, this step and the following step can be omitted.

[0072] Next, a third conductive layer is formed on both sides of the composite material obtained as described above. The third conductive layer is, for example, a laminate of a seed layer and a plating layer provided thereon. These seed layer and plating layer can be formed, for example, using the method and materials described above for the second conductive layer.

[0073] The seed layer of the third conductive layer can also be formed by sputtering. When forming the seed layer by sputtering, the material can be, for example, Cu, Ni, Al, Ti, Cr, Mo, W, Ta, Au, Ir, Ru, Pd, Pt, AlSi, AlSiCu, AlCu, NiFe, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminum-doped Zinc Oxide), ZnO, PZT (Lead Zirconate Titanate), TiN, Cu3N4, Cu alloy, or a combination of two or more of these.

[0074] Next, a resist resin is applied to both sides of the composite material obtained as described above, or a dry film resist is laminated onto it. Then, pattern exposure and development are sequentially performed on these resist layers to obtain a resist pattern.

[0075] Next, etching is performed using the resist pattern as an etching mask to remove portions of the first to third conductor layers corresponding to the openings in the resist pattern. In this way, a conductor pattern including the portion covering the upper surface of the core insulating layer 111 and a conductor pattern including the portion covering the lower surface of the core insulating layer 111 are obtained.

[0076] Next, an insulating layer 112 having through holes is formed on both sides of the composite material obtained as described above. The insulating layer 112 is formed using, for example, a thermosetting resin or a photosensitive resin. When using a thermosetting resin, a coating film made of the thermosetting resin is cured, and the cured film is subjected to laser processing such as CO2 laser processing and UV laser processing to obtain an insulating layer 112 having through holes. When using a photosensitive resin, a coating film made of the photosensitive resin is subjected to pattern exposure and development to obtain an insulating layer 112 having through holes. These through holes are formed at the positions of the pad portions of the conductor pattern covered by the insulating layer 112.

[0077] Next, the seed layer is formed to cover the main surface of the insulating layer 112, the side walls of the through holes in the insulating layer 112, and the area of ​​the pad portion of the conductor pattern covered by the insulating layer 112 that is adjacent to the internal space of the through holes in the insulating layer 112. The seed layer can be formed for the seed layers of the second and third conductor layers using the method and materials described above.

[0078] Next, a resist resin is applied to both sides of the composite material obtained as described above, or a dry film resist is laminated onto it. Then, pattern exposure and development are sequentially performed on these resist layers to obtain a resist pattern.

[0079] Next, a plating layer is formed by an electroplating method using the seed layer as a power supply layer. The metal materials mentioned above can be used for these plating layers.

[0080] Next, the resist pattern is removed, and then the portion of the seed layer not covered by the plating layer is removed by etching. This yields a conductive pattern 113 consisting of the seed layer and the plating layer, respectively.

[0081] Subsequently, an insulating layer 112 and a conductor pattern 113 are formed on the upper and lower surfaces of the composite material obtained as described above.

[0082] Next, insulating layers are provided as continuous films on both sides of the composite material obtained as described above. These insulating layers are solder resist layers. The solder resist layers can be provided on the composite material by applying liquid solder resist or by laminating a dry film type solder resist. The solder resist is, for example, a photosensitive epoxy resin or a non-photosensitive thermosetting resin. The solder resist may further contain inorganic fillers.

[0083] Next, through-holes are formed in the solder resist layer to obtain an insulating layer 114. These through-holes are formed at the positions of the pads of the conductor pattern 113 covered by the solder resist layer. When using a solder resist containing a photosensitive resin, through-holes can be formed by pattern exposure and development of the solder resist layer. When using a solder resist containing a thermosetting resin, through-holes can be formed by laser processing such as CO2 laser processing and UV laser processing of the solder resist layer.

[0084] Next, a surface treatment layer is formed on the surface of the pad portion of the conductor pattern 113 so as to cover the area adjacent to the internal space of the through-hole of the insulating layer 114. The surface treatment layer is provided for the purpose of preventing oxidation of the surface of the conductor pattern 113 and improving its wettability to solder.

[0085] The surface treatment layer is, for example, an electroless Ni / Pd / Au plating layer. Alternatively, an OSP (Organic Solderability Preservative) film, i.e., a surface treatment layer using a water-soluble preflux, may be formed as the surface treatment layer. Alternatively, an electroless tin plating or electroless Ni / Au plating layer may be formed as the surface treatment layer.

[0086] Next, a bonding conductor 14 is formed on the surface treatment layer. The bonding conductor 14 is, for example, a metal bump such as a solder bump. The bonding conductor 14 can be formed, for example, by printing a metal paste such as solder paste onto the surface treatment layer using a screen printing method. Alternatively, the bonding conductor 14 can be formed by printing flux onto the surface treatment layer using a screen printing method, placing metal balls such as solder balls into the through-holes of the insulating layer 114 using a ball-filling method or the like, melting them, and then cooling them.

[0087] Subsequently, a recess corresponding to the second region R2 is formed on one surface of the composite material obtained as described above to obtain a composite substrate. These recesses are formed, for example, by cutting or laser ablation. When recesses are formed by laser ablation, it is preferable that the composite material includes a stopper film that defines the position of the bottom of the recess. The stopper film is preferably a metal layer that exhibits high reflectivity at the wavelength of the laser beam. This metal layer may also be part of the conductor pattern described above.

[0088] Next, the assembled substrate is divided into multiple individual wiring boards. Specifically, dicing is performed along the dicing lines. In this way, wiring board 11A is obtained.

[0089] <1.3.2> Method for manufacturing a substrate with optical waveguides The optical waveguide substrate 12A is manufactured, for example, by the following method. Specifically, first, a substrate 121 is prepared. Here, as will be described later, a composite substrate is first manufactured, and this composite substrate is then divided into multiple optical waveguide substrates 12A. Therefore, the dimensions of the substrate 121 prepared here are slightly larger than the dimensions of the composite formed by arranging multiple optical waveguide substrates 12A. To facilitate handling, the substrate 121 may be supported by a support that can be removed from the substrate 121.

[0090] Next, an optical waveguide layer 122 is formed on the substrate 121. Specifically, a first cladding layer 122A, a core 122B, and a second cladding layer 122C are formed on the substrate 121 in this order.

[0091] The first cladding layer 122A can be obtained, for example, by coating an ionizing radiation-curable resin onto the substrate 121 and curing it by irradiating the entire surface of the coating with ionizing radiation, thereby obtaining a continuous film with substantially uniform thickness. Alternatively, the first cladding layer 122A can be obtained by coating a thermosetting resin onto the substrate 121 and curing it by heating the entire coating. The core 122B can be obtained, for example, by coating an ionizing radiation-curable resin onto the first cladding layer 122A, irradiating the portion of the coating where the core 122B is to be formed with ionizing radiation to cure these portions, and then subjecting the coating to a developing process. The second cladding layer 122C can be obtained, for example, by the same method as described above for the first cladding layer 122A.

[0092] Subsequently, the portion of the optical waveguide layer 122 obtained as described above that is located directly above the second portion of the first cladding layer 122A is removed to obtain a composite substrate. For example, laser ablation, dry etching, or cutting can be used for this removal. This creates a first portion with a greater thickness and a second portion with a smaller thickness in the first cladding layer 122A, and exposes the end face of the core 122B at the boundary between the first and second portions.

[0093] The first cladding layer 122A may be a multilayer structure including a continuous film and a patterned film provided thereon. In this case, if the core 122B and the second cladding layer 122C are formed only on the patterned film, the removal process described above is unnecessary.

[0094] Next, the assembled substrate is divided into multiple individual substrates with optical waveguides. Specifically, dicing is performed along the dicing lines. In this way, the substrate 12A with optical waveguides is obtained.

[0095] <1.3.3> Manufacturing method of composite substrates The composite substrate 10A is manufactured, for example, by the following method. Specifically, first, adhesive is applied to the second region R2 of the wiring board 11A. Next, the substrate 12A with optical waveguides is placed on the adhesive layer. Subsequently, the adhesive is cured. This results in a composite substrate 10A in which the substrate 12A with optical waveguides is fixed to the wiring board 11A via the adhesive layer 13.

[0096] <1.3.4> Method for manufacturing a photoelectric fusion device The photoelectric fusion device 1A is manufactured, for example, by the following method. Specifically, first, the first functional device 20A and the second functional device 30 are flip-chip mounted onto the composite substrate 10A. Next, preferably, their joints are sealed. For example, an underfill agent is injected between the composite substrate 10A and the first functional device 20A, and between the composite substrate 10A and the second functional device 30, and cured to form an underfill layer. For example, a thermosetting epoxy resin is used as the underfill agent. The underfill agent is injected in a manner that prevents it from flowing between the end face of the core 122B and the first functional device 20A. In this way, the photoelectric fusion apparatus 1A is obtained.

[0097] <1.4> Effect In the above-described photoelectric integration apparatus 1A, a composite substrate 10A is formed by a wiring board 11A and a substrate with an optical waveguide 12A. Therefore, for example, by employing a low-cost manufacturing configuration for the wiring board 11A and using a substrate 121 with a smooth surface for the substrate with an optical waveguide 12A, an optical waveguide with excellent optical performance can be obtained.

[0098] This effect can be obtained even when the surface on which the optical waveguide substrate 12A is mounted on the wiring board 11A is substantially flat. However, in this case, in order to optically couple the first functional device 20A and the core 122B, the height of the bonding conductor 14 that connects the first functional device 20A and the wiring board 11A must be extremely large. It is difficult to form a bonding conductor 14 with such a large height with high dimensional accuracy. Furthermore, a photoelectric fusion device 1A in which the bonding conductor 14 has a large height has poor connection reliability between the first functional device 20A and the wiring board 11A.

[0099] In the composite substrate 10A, as described above, the height of the second region R2 is lower than the underside of the conductor pattern 113 located in the first region R1, i.e., the uppermost conductor pattern 113. When this configuration is adopted, the position of the core 122B can be lowered compared to the case where the surface on which the optical waveguide substrate 12A is mounted on the wiring substrate 11A is substantially flat. Therefore, the first functional device 20A and the core 122B can be optically coupled without increasing the height of the bonding conductor 14 that connects the first functional device 20A and the wiring substrate 11A to each other. In other words, by adopting the above configuration, optical coupling and electrical connection can be easily performed when mounting a functional device on a composite substrate including a conductor pattern and an optical waveguide.

[0100] Furthermore, by adopting the above-described configuration, the joining conductor 14 can be formed with high dimensional accuracy. In addition, the photoelectric integration device 1A employing the above-described configuration exhibits excellent connection reliability between the first functional device 20A and the wiring board 11A.

[0101] <1.5> Variation The above-described photoelectric fusion device 1A is capable of various modifications.

[0102] Figure 7 is a top view of a photoelectric fusion apparatus with connectors, including the photoelectric fusion apparatus shown in Figures 5 and 6. The photoelectric fusion apparatus 1AC with connector shown in Figure 7 is the same as the photoelectric fusion apparatus 1A described above, except for the following: the photoelectric fusion apparatus 1AC with connector further includes a connector 15. The composite substrate 10A and the connector 15 constitute the composite substrate 10AC with connector. The connector 15 is configured to allow the optical wiring 40 to be detachably connected, facilitating optical coupling between the optical wiring 40 and the core 122B.

[0103] Figure 8 is a cross-sectional view showing a modified example of the photoelectric fusion device shown in Figures 5 and 6. The photoelectric fusion apparatus 1A2 shown in Figure 8 is the same as the photoelectric fusion apparatus 1A described above, except for the following point. That is, in the photoelectric fusion apparatus 1A2, the adhesive layer 13 of the composite substrate 10A is a stress relaxation layer.

[0104] In the photoelectric integration device 1A, most of the conductor pattern 113 is located in the portion of the wiring board 11A corresponding to the first region R1, and the first functional device 20A and the second functional device 30 are mounted in this portion. Furthermore, the portion of the wiring board 11A corresponding to the first region R1 is thicker than the portion corresponding to the second region R2. Therefore, for example, in a situation where the wiring board 11A warps due to the heat generated by the operation of the second functional device 30, the amount of deformation in the portion of the wiring board 11A corresponding to the second region R2 is greater than the amount of deformation in the portion of the wiring board 11A corresponding to the first region R1.

[0105] In the photoelectric integration device 1A, the first functional device 20A is fixed to the portion of the wiring board 11A corresponding to the first region R1 via a bonding conductor 14, and the electrical connection between the first functional device 20A and the wiring board 11A is not impaired by the aforementioned warping. However, if an adhesive layer 13 with a small stress relaxation effect is used, the aforementioned warping will also cause warping in the substrate 12A with the optical waveguide, and as a result, the optical axis between the first functional device 20A and the core 122B may be misaligned.

[0106] If the adhesive layer 13 is a stress relaxation layer, even if the wiring substrate 11A warps, the substrate 12A with the optical waveguide will not warp significantly as a result. Therefore, the photoelectric fusion device 1A2 is less likely to experience optical axis misalignment due to the warping of the wiring substrate 11A, and consequently, is less likely to experience increased optical coupling loss or loss of optical coupling due to this optical axis misalignment.

[0107] In this configuration, the stress relaxation layer is provided between the second region R2 and the end of the optical waveguide substrate 12A that is closer to the center of the wiring substrate 11A, but not between the second region R2 and the end of the optical waveguide substrate 12A that is further from the center of the wiring substrate 11A. This structure is advantageous in reducing the warping of the optical waveguide substrate 12A.

[0108] The stress relaxation layer may be provided over the entire area between the second region R2 and the optical waveguide substrate 12A. This structure is advantageous for securely fixing the optical waveguide substrate 12A to the wiring board 11A.

[0109] The elastic modulus of the stress relaxation layer is preferably in the range of 0.1 MPa to 3 GPa, and more preferably in the range of 0.3 MPa to 1 GPa. Here, "elastic modulus" is the dynamic storage modulus at 25°C. Materials with a low elastic modulus often have a significantly different coefficient of thermal expansion from the wiring board 11A, etc., and therefore, if such materials are used for the stress relaxation layer, the warping of the optical waveguide substrate 12A may not be sufficiently suppressed. If materials with a high elastic modulus are used for the stress relaxation layer, the deformation of the stress relaxation layer in response to stress will be insufficient, and therefore, the warping of the optical waveguide substrate 12A may not be sufficiently suppressed.

[0110] The thickness of the stress relaxation layer is preferably in the range of 5 μm to 50 μm, and more preferably in the range of 10 μm to 40 μm. If the stress relaxation layer is made thinner, it may become difficult to securely fix the substrate 12A with the optical waveguide to the wiring substrate 11A. If the stress relaxation layer is made thicker, the thickness of the composite substrate 10A increases.

[0111] <2> Second Embodiment <2.1> Composite substrate Figure 9 is a top view of a composite substrate according to a second embodiment of the present invention. Figure 10 is a cross-sectional view of the composite substrate shown in Figure 9 along line XX. Figure 11 is a top view of a substrate with an optical waveguide included in the composite substrates shown in Figures 9 and 10. Figure 12 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 11.

[0112] The composite substrate 10B shown in Figures 9 and 10 is the same as the composite substrate 10A described above, except that it includes the optical waveguide substrate 12B instead of the optical waveguide substrate 12A. Furthermore, the optical waveguide substrate 12B is the same as the optical waveguide substrate 12A, except for the following points.

[0113] In other words, in the optical waveguide substrate 12B, the first cladding layer 122A has a uniform thickness throughout. The core 122B includes the portion sandwiched between the first cladding layer 122A and the second cladding layer 122C, as well as the portion not covered by the second cladding layer 122C. In the composite substrate 10B, as in the composite substrate 10A, the height of the lower surface of the core 122B is higher than that of the first region R1.

[0114] <2.2>Optoelectronic fusion device Figure 13 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figures 9 and 10. Figure 14 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 13 along line XIV-XIV.

[0115] The photoelectric fusion apparatus 1B shown in Figures 13 and 14 is the same as the photoelectric fusion apparatus 1A described above, except that it includes a composite substrate 10B instead of composite substrate 10A, and a first functional device 20B instead of first functional device 20A. Furthermore, the first functional device 20B is the same as the first functional device 20A, except that a core 21 is provided so as to be exposed on its main surface.

[0116] In the photoelectric fusion apparatus 1B, the first functional device 20B is mounted on the composite substrate 10B such that the region of the core 21's surface located on the main surface of the first functional device 20B is in contact with the upper surface of the core 122B. In other words, in the photoelectric fusion apparatus 1B, the optical waveguide of the first functional device 20B is optically coupled with the optical waveguide layer 122 by adiaptic coupling.

[0117] <2.3> Effects In the second embodiment, the same effects as in the first embodiment can be obtained. Furthermore, as shown in the first and second embodiments, the optical waveguide of the first functional device and the optical waveguide layer 122 may be optically coupled in any way.

[0118] <2.4> Modified Examples The above-described photoelectric fusion device 1B is capable of various modifications.

[0119] Figure 15 is a top view of a photoelectric fusion apparatus with connectors, including the photoelectric fusion apparatus shown in Figures 13 and 14. The photoelectric fusion apparatus 1BC with connector shown in Figure 15 is the same as the photoelectric fusion apparatus 1B described above, except for the following: The photoelectric fusion apparatus 1BC with connector further includes a connector 15 connected to the optical waveguide substrate 12B. The composite substrate 10B and the connector 15 constitute the composite substrate 10BC with connector. The connector 15 is the same as that described above for the photoelectric fusion apparatus 1AC with connector.

[0120] Figure 16 is a cross-sectional view showing a modified example of the photoelectric fusion device shown in Figures 13 and 14.

[0121] The photoelectric fusion apparatus 1B2 shown in Figure 16 is the same as the photoelectric fusion apparatus 1B described above, except for the following point. That is, in the photoelectric fusion apparatus 1B2, the adhesive layer 13 of the composite substrate 10B is the stress relaxation layer described above for the photoelectric fusion apparatus 1A2.

[0122] If the wiring board 11A of the photoelectric fusion device 1B experiences the same warping as described above, at least a portion of the surface of the core 21 that was in contact with the core 122B may separate from the core 122B. Adiabattic coupling is optical coupling that utilizes evanescent waves. Therefore, if the contact area between the core 21 and the core 122B decreases, the optical coupling loss will increase, and in some cases, the optical coupling between the optical waveguide of the first functional device 20B and the optical waveguide layer 122 may be lost.

[0123] If the adhesive layer 13 is a stress relaxation layer, even if the wiring substrate 11A warps, the substrate 12B with the optical waveguide will not warp significantly as a result. Therefore, the photoelectric fusion device 1B2 is less likely to experience a decrease in the contact area between the core 21 and the core 122B due to the warping of the wiring substrate 11A, and consequently, is less likely to experience an increase in optical coupling loss or loss of optical coupling due to this decrease in contact area.

[0124] <3> Third Embodiment Figure 17 is a top view of a composite substrate according to a third embodiment of the present invention.

[0125] The composite substrate 10C shown in Figure 17 is the same as the composite substrate 10A described above, except for the following: The composite substrate 10C includes a wiring board 11B instead of a wiring board 11A. The wiring board 11B is the same as the wiring board 11A described above, except for the following: The first surface S1 has four second regions R2. These second regions R2 are arranged so as to be adjacent to each of the four edges of the first surface S1. And, four optical waveguide substrates 12A are arranged in each of these four second regions R2.

[0126] Figure 18 is a top view of the photoelectric fusion apparatus with connectors, including the composite substrate shown in Figure 17. The photoelectric fusion apparatus with connectors 1CC shown in Figure 18 is the same as the photoelectric fusion apparatus with connectors 1AC, except for the following: The photoelectric fusion apparatus with connectors 1CC includes a composite substrate 10C instead of a composite substrate 10A. Four first functional devices 20A are mounted on the composite substrate 10C. Each of these first functional devices 20A is electrically connected to a second functional device 30 via a wiring board 11B. Four connectors 15 are also attached to the composite substrate 10C. The composite substrate 10C and the connectors 15 constitute the composite substrate with connectors 10CC.

[0127] In the third embodiment, the same effects as in the first embodiment can be obtained. Furthermore, as shown in the third embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more.

[0128] <4> Fourth Embodiment Figure 19 is a top view of a composite substrate according to a fourth embodiment of the present invention. Figure 20 is a cross-sectional view of the composite substrate shown in Figure 19 along the line XX-XX.

[0129] The composite substrate 10D shown in Figures 19 and 20 is the same as the composite substrate 10A, except for the following: the composite substrate 10D includes a wiring substrate 11C and an optical waveguide substrate 12C instead of the wiring substrate 11A and the optical waveguide substrate 12A.

[0130] The wiring board 11C is the same as the wiring board 11A, except for the following: the wiring board 11C is configured to mount two first functional devices 20A and two second functional devices 30. The second region R2 is provided between the region on which one second functional device 30 is to be mounted and the region on which the other second functional device 30 is to be mounted.

[0131] The optical waveguide substrate 12C is the same as the optical waveguide substrate 12A, except as follows: In the optical waveguide substrate 12C, the first cladding layer 122A has two smaller second portions. The thicker first portion of the first cladding layer 122A is interposed between the two second portions. The second cladding layer 122C covers the first portion of the first cladding layer 122A without covering the second portion of the first cladding layer 122A. Each of the cores 122B is interposed between the first portion of the first cladding layer 122A and the second cladding layer 122C and extends in the direction of the arrangement of the second portions. The optical waveguide substrate 12C is placed in the second region R2 such that the length direction of the cores 122B coincides with the arrangement direction of the area on which the two second functional devices 30 are to be mounted.

[0132] Figure 21 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figures 19 and 20. Figure 22 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 21 along the line XXII-XXII.

[0133] The photoelectric fusion apparatus 1D shown in Figures 21 and 22 is the same as the photoelectric fusion apparatus 1A, except for the following: the photoelectric fusion apparatus 1D includes a composite substrate 10D instead of a composite substrate 10A. Also, in the photoelectric fusion apparatus 1D, the number of first functional devices 20A is 2, and the number of second functional devices 30 is also 2.

[0134] In the fourth embodiment, the same effects as in the first embodiment can be obtained. Furthermore, as shown in the fourth embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more, and the number of second functional devices included in the photoelectric fusion device may also be two or more. Also, as shown in the fourth embodiment, instead of optically coupling the optical waveguide layer 122 to the first functional device and the optical wiring, it may optically couple to a plurality of first functional devices.

[0135] <5> Variation The composite substrates and photoelectric integration devices described above can be modified in various ways. For example, in the composite substrate 10C, composite substrate 10D, photoelectric fusion device 1D, and photoelectric fusion device 1CC with connector, instead of employing a configuration in which the optical coupling between the optical waveguide of the first functional device 20A and the optical waveguide layer 122 is performed by butt coupling, a configuration in which this optical coupling is performed by adiabatic coupling may be adopted. Also, in the composite substrate 10C, composite substrate 10D, photoelectric fusion device 1D, and photoelectric fusion device 1CC with connector, the adhesive layer 13 may be used as a stress relaxation layer. [Explanation of Symbols]

[0136] 1A...Photoelectric fusion device, 1A2...Photoelectric fusion device, 1AC...Photoelectric fusion device with connector, 1B...Photoelectric fusion device, 1B2...Photoelectric fusion device, 1BC...Photoelectric fusion device with connector, 1CC...Photoelectric fusion device with connector, 1D...Photoelectric fusion device, 10A...Composite substrate, 10AC...Composite substrate with connector, 10B...Composite substrate, 10BC...Composite substrate with connector, 10C...Composite substrate, 10CC...Composite substrate with connector, 10D...Composite substrate, 11A...Wiring board, 11B...Wiring board, 11C...Wiring board, 12A...With optical waveguide Substrate, 12B...Substrate with optical waveguide, 12C...Substrate with optical waveguide, 13...Adhesive layer, 14...Bonding conductor, 15...Connector, 20A...First functional device, 20B...First functional device, 21...Core, 30...Second functional device, 40...Optical wiring, 111...Core insulating layer, 112...Insulating layer, 113...Conductor pattern, 114...Insulating layer, 121...Substrate, 122...Optical waveguide layer, 122A...First cladding layer, 122B...Core, 122C...Second cladding layer, R1...First region, R2...Second region, S1...First surface, S2...Second surface.

Claims

1. A wiring board comprising one or more insulating layers and one or more conductor patterns, having a first surface and a second surface which is its back surface, wherein the first surface comprises one or more first regions and one or more second regions which are recessed relative to the one or more first regions, one of the one or more conductor patterns is located in the one or more first regions, and the height of the one or more second regions is lower than the lower surface of one of the one or more conductor patterns located in the one or more first regions, A substrate comprising a substrate and an optical waveguide layer provided thereon, wherein each optical waveguide layer comprises a first cladding layer provided on the substrate, a second cladding layer provided on the first cladding layer, and one or more cores provided between the first cladding layer and the second cladding layer, wherein the optical waveguide layers are each placed on the one or more second regions such that they are located above the substrate, and the height of the lower surface of the one or more cores is higher than that of the one or more first regions, and A composite substrate equipped with [specific features / features].

2. The composite substrate according to claim 1, wherein the height of the upper surface of the substrate is lower than the height of the one or more first regions.

3. The composite substrate according to claim 1, wherein the lower surface of the one or more cores has a height of 100 μm or less with respect to the one or more first regions.

4. The composite substrate according to claim 1, further comprising one or more stress relaxation layers interposed between the one or more optical waveguide substrates and the one or more second regions.

5. The composite substrate according to claim 4, wherein each of the one or more stress relaxation layers has an elastic modulus in the range of 0.1 MPa to 3 GPa.

6. The composite substrate according to claim 4, wherein each of the one or more stress relaxation layers has a thickness within the range of 5 μm to 50 μm.

7. The composite substrate according to claim 1, wherein the one or more insulating layers include an insulating resin layer, and the substrate includes a glass substrate.

8. The composite substrate according to claim 1, which is an interposer.

9. A composite substrate according to any one of claims 1 to 8, A first functional device mounted on the composite substrate and optically coupled to at least one of the one or more substrates with optical waveguides, A second functional device mounted on the composite substrate and electrically connected to the first functional device, A photoelectric fusion device equipped with [a specific feature].

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