JP2005077644A - Wiring board having optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-reliability wiring substrate with an optical waveguide by further improving relaxation of stresses between an insulating substrate and an optical waveguide, located upward on the surface thereof. <P>SOLUTION: The wiring board K1 with an optical waveguide, comprising an insulating substrate 1 having a flat surface 2, an optical waveguide C which is located upward on the surface 2 of this insulating board 1 and has a higher coefficient of thermal expansion than that of the insulating board 1, and a lower relaxation layer 11 and an upper relaxation layer 26, which are formed between the surface of the insulating board and the optical waveguide and upward on the optical waveguide C, and whose thermal expansion coefficients lie between those of the insulating substrate 1 and of the optical waveguide C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wiring board with an optical waveguide having an optical waveguide near the surface.

In order to increase the signal transmission speed and the signal processing speed, for example, an attempt is made to flow a high-frequency signal through the electrical wiring of the wiring board. However, when a high-frequency signal is passed through the electrical wiring, noise and electromagnetic waves are generated in the vicinity thereof, which may cause malfunctions in the surroundings. In order to solve such a problem, a wiring board with an optical waveguide in which electric wiring or a part thereof is replaced with optical wiring has been studied.
For example, in order to form an optical waveguide made of siloxane polymer with sufficient adhesion strength on the substrate, an optical waveguide substrate in which a buffer layer made of a similar polymer is disposed between the substrate and the optical waveguide has been proposed (for example, (See Patent Document 1).
In addition, in order to prevent the occurrence of cracks even when used for a long time, a polymer optical waveguide in which a lower cladding layer, a core, and an upper cladding layer are formed on a substrate via a stress relaxation layer has also been proposed (for example, (See Patent Document 2).

JP 2002-341162 A (pages 1-7, FIG. 1) JP 2001-264562 A (pages 1 to 6, FIG. 1)

According to the optical waveguide substrate or the polymer optical waveguide, when the optical waveguide is formed on the substrate, the optical waveguide substrate or the polymer optical waveguide is reliable in that stress hardly remains in the optical waveguide.
However, for example, when an optical element or an operating element is mounted on an optical waveguide formed on the surface of the substrate, stress remains between the upper clad layer forming the optical waveguide and the element. For this reason, there has been a problem that cracks may be generated in the upper clad layer, or the position where the optical element is to be mounted may be shifted, resulting in unstable transmission and reception of optical signals with the optical waveguide.

  The present invention solves the problems of the background art described above, further improves stress relaxation between the insulating substrate and the optical waveguide disposed above the surface thereof, and has a highly reliable wiring substrate with an optical waveguide. It is an issue to provide.

In order to solve the above-mentioned problems, the present invention was conceived in order to relieve stress between an insulating substrate and an optical waveguide disposed above the surface above and below the optical waveguide. is there.
That is, a wiring board with an optical waveguide according to the present invention (Claim 1) is provided with an insulating substrate having a surface, and is disposed above the surface of the insulating substrate and has a thermal expansion coefficient higher than that of the insulating substrate. A high optical waveguide, a lower relaxation layer formed between the surface of the insulating substrate and the optical waveguide and above the optical waveguide, and having a thermal expansion coefficient intermediate between the insulating substrate and the optical waveguide; And a relaxation layer.
The insulating substrate is made of, for example, ceramic or resin having a coefficient of thermal expansion of about 15 ppm / K or less. The optical waveguide is, for example, a double structure of a clad and a core built in the clad, and is made of an acrylic, epoxy, or polysilane resin having a thermal expansion coefficient of about 60 to 120 ppm / K. Further, the upper and lower relaxation layers are, for example, those obtained by spin-coating varnish and further curing, specifically, those obtained by applying a dry film and press-curing, and have a coefficient of thermal expansion of about 20 to 65 ppm / K.

In the present invention, the upper relaxation layer has a pair of through holes formed at positions above the reflecting mirror surfaces located at both ends of the optical waveguide, and the upper relaxation layer is located above the pair of through holes and the upper relaxation layer. A wiring board with an optical waveguide (claim 2) in which optical elements are respectively mounted on the surface of the layer is also included. The optical element is a light emitting element and a light receiving element of a photoelectric conversion element, and is made of, for example, Si or GaAs, and has a coefficient of thermal expansion of about 6 ppm / K or less.
In other words, the upper relaxation layer has a pair of through holes formed at positions above the reflecting mirror surfaces located at both ends of the optical waveguide, and above the pair of through holes and on the surface of the upper relaxation layer. In addition, a wiring board with an optical waveguide on which optical elements having a thermal expansion coefficient lower than that of the insulating substrate are mounted may be included.

Furthermore, the present invention provides a wiring board with an optical waveguide, wherein an operating element that is electrically connected to the optical element is mounted on the surface of the upper relaxation layer adjacent to the optical element and opposite to the optical waveguide. Item 3) is also included.
The operating element is a device that operates an optical element that is electrically connected to the optical element by issuing a conversion command from an electrical signal to a predetermined optical signal or a conversion command from an optical signal to a predetermined electrical signal. An electronic component such as an IC chip that incorporates an operation circuit for forming the command is used. Further, the operating elements and the optical elements that are electrically connected to each other are not limited to the same number of forms, and may be configured to use one operating element that can individually give different commands to a plurality of optical elements.

  According to the wiring substrate with an optical waveguide (Claim 1), the lower relaxation layer and the upper relaxation layer having a thermal expansion coefficient intermediate between the thermal expansion coefficients between the optical waveguide and the insulating substrate and above the optical waveguide. The layers are arranged individually. For this reason, the stress between the optical waveguide and the upper relaxation layer can be reduced and relaxed between the insulating substrate that is unlikely to thermally expand and the optical waveguide that is likely to be thermally expanded. Therefore, even when used for a long period of time in an environment with temperature changes, or when mounting an optical element with a low coefficient of thermal expansion above the optical waveguide, it is possible to prevent deformation and cracking of the optical waveguide, so stable light Signals can be exchanged, and a highly reliable wiring board with an optical waveguide can be obtained.

  According to the wiring substrate with an optical waveguide (claim 2), the lower relaxation layer having a thermal expansion coefficient intermediate between the thermal expansion coefficients of the insulating substrate and the optical waveguide is located, and the optical waveguide Since the upper relaxation layer, which has a thermal expansion coefficient intermediate between the thermal expansion coefficients of both, is positioned between the optical element and the optical element, a stepwise thermal expansion structure is formed in the thickness direction. Therefore, even if the optical waveguide is used for a long time in an environment with temperature changes, stress is not applied to the optical waveguide, so that deformation and cracks can be prevented, and stable transmission and reception of optical signals becomes possible.

  Furthermore, according to the wiring board with an optical waveguide (claim 3), since the operating element for operating the optical element is mounted above the optical waveguide, an optical signal can be transmitted through the optical element and the optical waveguide. It can be done reliably. Further, even if the thermal expansion coefficient of the operating element is equal to that of the insulating substrate, it is difficult to apply stress to the optical waveguide.

Hereinafter, modes for carrying out the present invention will be described.
FIG. 1 shows a cross section of a wiring board K1 with an optical waveguide according to one embodiment of the present invention.
As shown in FIG. 1, the wiring substrate K1 with an optical waveguide includes an insulating substrate 1 having a flat surface 2 and an optical waveguide C disposed above the surface 2 and having a higher thermal expansion coefficient than the insulating substrate 1. The lower relaxation layer 11 formed between the optical waveguide C and the insulating substrate 1 and the upper relaxation layer 26 formed above the optical waveguide C are provided. The thermal expansion coefficients of the lower relaxation layer 11 and the upper relaxation layer 26 are intermediate between the insulating substrate 1 and the optical waveguide C.

As shown in FIG. 1, the insulating substrate 1 is made of glass-ceramic having a thermal expansion coefficient of about 6 ppm / K, alumina having a thermal expansion coefficient of about 7 ppm / K, or nitriding having a thermal expansion coefficient of about 4.5 ppm / K. Ceramic layers S1 to S4 made of aluminum (AlN) are laminated. Between the front surface 2, the back surface 3, and the ceramic layers S1 to S4 of the insulating substrate 1, wiring layers 6 to 8 having a predetermined pattern made of Ag or the like are formed. The wiring layer 10 on the back surface 3 is a connection terminal (surface electrode).
The wiring layers 6 to 10 are connected via via conductors v made of Ag or the like penetrating the ceramic layers S1 to S4. The ceramic layers S1 to S4 have a thickness of about 0.2 mm, and the wiring layer 6 has a thickness of about 15 μm. Further, the insulating substrate 1 is formed by a known manufacturing method using four green sheets or a conductive paste formed on the surface thereof in a predetermined pattern by printing or the like.

As shown in FIG. 1, the optical waveguide C is a double structure of a clad 20 having a rectangular cross section and a plurality of cores 22 having a square cross section built in the clad 20. The reflecting mirror surfaces 24 are formed symmetrically. The clad 20 and the core 22 have an acrylic resin (for example, PMMA) having a thermal expansion coefficient of about 70 to 90 ppm / K, an epoxy resin having a thermal expansion coefficient of about 60 to 70 ppm / K, or a thermal expansion coefficient of about 100 to 100 ppm. It consists of 120 ppm / K polysilane resin, and the clad 20 is about 0.3-5% lower than the core 22 in the refractive index of light.
Note that one side of the core 22 is about 50 μm. In addition, the reflection mirror surface 24 is appropriately selected with an inclination angle of 30 to 60 degrees within a range where light can be reflected.

As shown in FIG. 1, a lower relaxation layer 11 having a thickness of about 40 μm is formed on the surface 2 of the insulating substrate 1, and the optical waveguide C is formed on the surface 12 of the lower relaxation layer 11. On the surface 12 excluding the optical waveguide C, the connection terminal wiring 4 and the connection wiring 5 are formed, and the lower relaxation layer 11 is provided between the wiring 4 and the wiring layer 6 of the insulating substrate 1. Are connected via via conductors v penetrating through. The optical waveguide C is fixed in position by directly adhering to the surface 12 of the lower relaxation layer 11 or by penetrating a plurality of metal pins (not shown) standing on the surface 12.
As shown in FIG. 1, an upper relaxation layer 26 having a thickness of about 40 μm is formed above the optical waveguide C excluding the vicinity of the reflection mirror surfaces 24 at both ends. The lower relaxation layer 11 and the upper relaxation layer 26 are, for example, those obtained by spin-coating an epoxy or epoxy acrylate resin or varnish, and their thermal expansion coefficient is intermediate between the insulating substrate 1 and the optical waveguide C. (About 20 to 65 ppm / K).

As shown in FIG. 1, the connection terminals 13 and 15 of the IC chip (operation element) 14a are connected to the left wiring 4 and one end of the connection wiring 5 via the solder h, so that the IC chip 14a is It is mounted on the surface 12 of the relaxation layer 11. Further, the light emitting element 16 is mounted on the surface 12 by connecting the connection terminal 17 of the light emitting element (optical element) 16 to the other end of the connection wiring 5 via the solder h. Note that a light emitting portion (not shown) of the light emitting element 16 is located immediately above the reflection mirror surface 24 at the left end of the optical waveguide C.
As shown in FIG. 1, the connection terminals 13 and 15 of the IC chip (operation element) 14b are connected to the right wiring 4 and one end of the connection wiring 5 through the solder h, so that the IC chip 14b is It is mounted on the surface 12 of the relaxation layer 11. Further, the light receiving element 18 is mounted on the surface 12 by connecting the connection terminal 19 of the light receiving element (optical element) 18 to the other end of the connection wiring 5 via the solder h. A light receiving portion (not shown) of the light receiving element 18 is located right above the reflection mirror surface 24 at the right end of the optical waveguide C.

  The IC chips 14a and 14b are supplied with necessary power in advance from the insulating substrate 1 through the wiring 4, via conductors v, and the like. The left IC chip 14 a in FIG. 1 transmits an electrical signal instructing a predetermined operation to the light emitting element 16 through the connection wiring 5, the solder h, and the connection terminal 17. Then, as indicated by the arrows in FIG. 1, the optical signal emitted from the light emitting element 16 is reflected by the left reflecting mirror surface 24, and the right inside the core 22 of the optical waveguide C is subjected to multiple reflections on its peripheral surface. Transmitted in the direction. Such an optical signal is reflected from the core 22 to the right reflecting mirror surface 24, transmitted to the light receiving element 18, converted into an electrical signal, and then transmitted to the right IC chip 14b through the connection wiring 5 and the like. . As a result, signal transmission between the IC chips 14a and 14b can be performed at a high speed through the above path and through the optical signal.

In FIG. 1, the IC chips 14a and 14b and the light-emitting elements 16 and the light-receiving elements 18 are arranged (mounted) opposite to each other on the left and right sides, so that the IC chips 14a and 14b via the optical signal through the opposite path. The signal transmission between them can be performed at a high speed.
Further, in FIG. 1, new IC chips 14b and 14a are arranged (mounted) in the same manner as described above adjacent to the depth direction of the IC chips 14a and 14b, and adjacent to the light emitting element 16 and the light receiving element 18 in the depth direction. New light receiving elements 18 and light emitting elements 16 may be arranged in the same manner as described above. With the plurality of sets of IC chips 14a and 14b, the light emitting element 16, the light receiving element 18, and the plurality of cores 22 of the optical waveguide C, an electric signal is transmitted from both the left and right sides in FIG. Transmission at speed is possible.

Even if high-speed signal transmission using the optical waveguide C for transmitting an optical signal as described above is performed over a long period of time in an environment with a temperature change, the lower relaxation occurs between the optical waveguide C and the insulating substrate 1. Since the layer 11 is located and the upper relaxation layer 26 is located above the optical waveguide C, the stress applied to the optical waveguide C is reliably relaxed. That is, the optical waveguide C that is easily thermally expanded is not only reduced in stress received by the lower relaxation layer 11 between the insulating substrate 1 that is less likely to thermally expand, but is also received by the upper relaxation layer 26 on the opposite side thereof. Stress is offset and reduced. For this reason, the clad 20 and the core 22 of the optical waveguide C are less likely to be deformed and cracked, and stable optical signal transmission is possible, so that the wiring substrate K1 with an optical waveguide having high reliability is obtained.
The wiring board K1 with an optical waveguide is mounted on a printed board such as a mother board (not shown) through a wiring layer 10 provided on the back surface 3 of the insulating substrate 1.

FIG. 2 shows a cross section of a wiring board K2 with an optical waveguide, which is a modification of the wiring board K1. As shown in FIG. 2, the wiring substrate K2 includes an insulating substrate 30, a lower relaxation layer 46 formed on the surface (first main surface) 42a, and an optical waveguide formed near the center of the surface 46a. C and an upper relaxation layer 26 formed above except for both ends of the optical waveguide C.
As shown in FIG. 2, the insulating substrate 30 includes a core substrate 31 made of, for example, a composite material of epoxy resin and glass cloth having a thermal expansion coefficient of about 15 ppm / K, an insulating layer 38 formed above the surface 32, 42 and a solder resist layer (insulating layer) 39 formed on the back surface 33 of the core substrate 31. The core substrate 31 has a thickness of about 0.8 mm, and a plurality of through holes 34 penetrating between the front surface 32 and the back surface 33 are individually formed with through-hole conductors 35 made of a copper plating film in a substantially cylindrical shape. A filling resin 36 is formed inside the through-hole conductor 35.

As shown in FIG. 2, a wiring layer 40 made of a copper plating film and having a predetermined pattern is formed on the surface 32 of the core substrate 31 and is electrically connected to the upper end of the through-hole conductor 35. A wiring layer 44 similar to the above is formed between the insulating layers 38 and 42, and a wiring layer 48 similar to the above is formed between the insulating layer 42 and the upper relaxation layer 46. Further, the wiring layers 40, 44 and 48 are electrically connected via a filled via conductor v (hereinafter referred to as a via conductor v) formed in the insulating layers 38 and 42. The insulating layers 38 and 42 have a thickness of about 40 μm, and the wiring layer 40 has a thickness of about 15 μm.
On the other hand, as shown in FIG. 2, a wiring layer 41 having a predetermined pattern made of a copper plating film is formed on the back surface 33 of the core substrate 31, and the wiring layer 41 is connected to the lower end of the through-hole conductor 35. Yes. A solder resist layer 39 having a thickness of about 30 μm is formed below the wiring layer 41 and the back surface 33, and the bottom surface of the opening 43 opening on the surface (second main surface) 49 is formed from the wiring layer 41. The extended wiring 45 is located. The wiring (connection terminal) 45 is coated with Ni plating and Au plating on its surface, and is used for connection to a printed board such as a mother board (not shown).

The lower relaxation layer 46 has a thickness of about 40 μm and is cured after an epoxy resin film is attached or varnish is spin-coated, and as shown in FIG. 2, the surface 46a of the lower relaxation layer 46 is formed. On both the left and right upper ends, connection terminal wiring 47 made of a copper plating film is formed, and is electrically connected to the wiring layer 48 via the filled via conductor v. On the surface 46a adjacent to the left and right wirings 47, the same connection wirings 5 made of a copper plating film are formed.
Further, as shown in FIG. 2, an optical waveguide C similar to the above is disposed near the center of the surface 46 a of the lower relaxation layer 46. An upper relaxation layer 26 similar to the above is formed above the optical waveguide C except for both ends including the reflection mirror surface 24. The lower relaxation layer 46, the wiring 47, the connection wiring 5, and the insulating substrate 30 are formed by a known semi-additive method, subtractive method, photolithography technique, or the like.

As shown in FIG. 2, the connection terminals 13 and 15 of the IC chip (operation element) 14a are connected to the left wiring 47 and one end of the connection wiring 5 via the solder h, so that the IC chip 14a is It is mounted on the surface 46 a of the relaxation layer 46. Further, the light emitting element 16 is mounted on the surface 46a by connecting the connection terminal 17 of the light emitting element (optical element) 16 to the other end of the connection wiring 5 via the solder h. Note that the light emitting portion of the light emitting element 16 is positioned directly above the reflection mirror surface 24 at the left end of the optical waveguide C.
As shown in FIG. 2, the connection terminals 13 and 15 of the IC chip (operation element) 14b are connected to the right wiring 47 and one end of the connection wiring 5 through the solder h, so that the IC chip 14b is It is mounted on the surface 46 a of the relaxation layer 46. Further, the light receiving element 18 is mounted on the surface 46a by connecting the connection terminal 19 of the light receiving element (optical element) 18 to the other end of the connection wiring 5 via the solder h. The light receiving portion of the light receiving element 18 is located immediately above the right reflecting mirror surface 24 of the optical waveguide C.
The IC chip 14 a and the light emitting element 16, the IC chip 14 b and the light receiving element 18 are adjacent to each other and arranged linearly in plan view including the optical waveguide C.

  The IC chips 14a and 14b are supplied with necessary power in advance from the insulating substrate 30 via the wiring 47, the via conductors v, and the like. The left IC chip 14 a in FIG. 2 transmits an electrical signal instructing a predetermined operation to the light emitting element 16 via the connection wiring 5, the solder h, and the connection terminal 17. Then, as indicated by the arrows in FIG. 2, the optical signal emitted from the light emitting element 16 is reflected by the left reflecting mirror surface 24, and the right side of the optical waveguide C is reflected in the core 22 by multiple reflection on its peripheral surface. Transmitted in the direction. Such an optical signal is reflected from the core 22 to the right reflecting mirror surface 24, transmitted to the light receiving element 18, converted into an electrical signal, and then transmitted to the right IC chip 14b through the connection wiring 5 and the like. . As a result, signal transmission between the IC chips 14a and 14b can be performed at high speed via the optical signal in the above-described path.

Also in FIG. 2, the IC chips 14a and 14b and the light emitting element 16 and the light receiving element 18 are disposed (mounted) in the left and right directions so that the IC chip 14a, Signal transmission between 14b can also be performed at high speed.
Also in FIG. 2, new IC chips 14b and 14a are disposed in the same manner as described above adjacent to the depth direction of the IC chips 14a and 14b, and new light is provided adjacent to the light emitting element 16 and the light receiving element 18 in the depth direction. The light receiving element 18 and the light emitting element 16 may be arranged in the same manner as described above. With the plurality of sets of IC chips 14a and 14b, the light emitting element 16, the light receiving element 18, and the plurality of cores 22 of the optical waveguide C, electrical signals are transmitted from both the left and right sides in FIG. Can be transmitted at high speed.

  Even if high-speed signal transmission using the optical waveguide C for transmitting an optical signal as described above is performed for a long time in an environment with temperature change, a lower relaxation layer is provided between the optical waveguide C and the insulating substrate 30. Since the upper relaxation layer 26 is located above the optical waveguide C, the stress applied to the optical waveguide C is reliably relaxed. That is, the optical waveguide C having a high coefficient of thermal expansion not only reduces the stress received by the lower relaxation layer 46 between the insulating substrate 30 having a lower coefficient of thermal expansion but also the upper relaxation layer 26 on the opposite side thereof. However, it is reduced by offsetting the stress received. Therefore, the clad 20 and the core 22 of the optical waveguide C are not easily deformed or cracked, and stable optical signal transmission is possible, so that the wiring substrate K2 with an optical waveguide having high reliability is obtained.

FIG. 3 shows a cross section of a wiring board K3 with an optical waveguide having a different form. As shown in FIG. 3, the wiring substrate K3 includes the same insulating substrate 1, the lower relaxation layer 50 formed on the surface 2, and the same optical waveguide disposed near the center on the surface 51. C and an upper relaxation layer 52 formed above the left and right surfaces 51 of the optical waveguide C and the lower relaxation layer 50. Above the surface 53 of the upper relaxing layer 52, IC chips (operation elements) 56 and 60, a light emitting element 64 and a light receiving element 67 are mounted.
The lower relaxation layer 50 has the same thickness and characteristics as the lower relaxation layer 11 and the like. The upper relaxation layer 52 is thicker than the lower relaxation layer 50 and covers the side surface and the upper surface of the optical waveguide C as shown in FIG. 3, and a pair of through-holes near the reflection mirror surface 24 of the optical waveguide C. 54 and 55 are formed. The upper relaxation layer 52 has the same characteristics as described above.

As shown in FIG. 3, the same wiring 4 made of Cu or the like is formed in the vicinity of both ends on the surface 53 of the upper relaxation layer 52, and the via conductors v penetrating the upper and lower relaxation layers 52 and 50 are provided. Through the wiring layer 6 of the insulating substrate 1. In the vicinity of both left and right ends on the surface 53, the same connection wiring 5 is formed adjacent to the wiring 4 and between the through holes 54 and 55, respectively.
As shown in FIG. 3, the connection terminals 57 and 58 of the IC chip (operation element) 56 are connected to the left wiring 4 and one end of the connection wiring 5 via solder (not shown), whereby the IC chip 56 is connected. It is mounted on the surface 53 of the upper relaxation layer 52. In addition, the connection terminal 65 of the light emitting element (optical element) 64 is connected to the other end of the connection wiring 5 via solder, and the tip portion is supported by the support piece 66 protruding on the surface 53, thereby the light emitting element. 64 is mounted on the surface 53.
The light emitting element 64 is made of Si (thermal expansion coefficient: about 3.6 ppm / K) or GaAs (thermal expansion coefficient: about 6.0 ppm / K), and the IC chip 56 is the same. Further, the light emitting portion (not shown) of the light emitting element 64 is located immediately above the reflection mirror surface 24 and the through hole 54 at the left end of the optical waveguide C.

As shown in FIG. 3, the connection terminals 61 and 62 of the IC chip (operation element) 60 are connected to the right wiring 4 and one end of the connection wiring 5 via solder (not shown), whereby the IC chip 60 is connected. It is mounted on the surface 53 of the upper relaxation layer 52. Further, a connection terminal 69 of a light receiving element (optical element) 67 is connected to the other end of the connection wiring 5 via solder, and the tip end portion is supported by a support piece 68 protruding on the surface 53, whereby the light receiving element. 67 is mounted on the surface 53. A light receiving portion (not shown) of the light receiving element 67 is located right above the reflection mirror surface 24 and the through hole 55 at the right end of the optical waveguide C.
The light receiving element 67 is also made of Si (thermal expansion coefficient: about 3.6 ppm / K) or GaAs (thermal expansion coefficient: about 6.0 ppm / K), and the IC chip 60 is the same. Further, when the clad 20 of the optical waveguide C has a rectangular cross section and a plurality of cores 22 are incorporated in parallel therein, the through holes 54 and 55 have a rectangular shape in a plan view orthogonal to the plurality of cores 22. In addition, a plurality of forms may be used in which each reflection mirror surface 24 of each core 22 is substantially square.

The IC chips 56 and 60 are supplied with required power in advance from the inside of the insulating substrate 1 through the wiring 4 and the via conductors v. The left IC chip 56 in FIG. 3 transmits an electrical signal instructing a predetermined operation to the light emitting element 64 through the connection wiring 5, the solder, and the connection terminal 65.
3, the optical signal emitted from the light emitting element 64 passes through the through hole 54 and is reflected by the left reflecting mirror surface 24 to pass through the core 22 of the optical waveguide C. Are transmitted in the right direction with multiple reflections. The optical signal is reflected from the core 22 to the right reflecting mirror surface 24, transmitted to the light receiving element 67 through the through hole 55, converted into an electric signal, and then connected to the right IC chip 60 through the connection wiring 5 and the like. Is transmitted. Therefore, signal transmission between the IC chips 56 and 60 can be performed at a high speed via the optical signal in the path.

In FIG. 3, the IC chips 56, 60 and the light emitting elements 64 and the light receiving elements 67 are arranged (mounted) opposite to each other on the left and right sides, so that the IC chips 56, 60 via the optical signal through the opposite path. The signal transmission between them can be performed at a high speed.
In FIG. 3, new IC chips 60 and 56 are disposed (mounted) in the same manner as described above adjacent to the depth direction of the IC chips 56 and 60, and adjacent to the light emitting element 64 and the light receiving element 67 in the depth direction. New light receiving elements 67 and light emitting elements 64 may be arranged in the same manner as described above. With the plurality of sets of IC chips 56 and 60, the light emitting element 64 and the light receiving element 67, and the plurality of cores 22 of the optical waveguide C, electric signals are transmitted from the left and right sides to the opposite side via optical signals in FIG. Transmission at high speed is possible.

  According to the wiring substrate with optical waveguide K3 as described above, the lower relaxation layer 50 and the upper relaxation layer 52 having an intermediate thermal expansion coefficient are located adjacent to the optical waveguide C having the highest thermal expansion coefficient, and these are Thus, a stepwise thermal expansion structure is formed in the thickness direction in which the insulating substrate 1, the light emitting element 64, the light receiving element 67 and the like having the lowest thermal expansion coefficient are disposed. For this reason, even if the optical waveguide C is used for a long time in an environment with a temperature change, it is difficult for stress to be applied to the optical waveguide C, and a mounting position shift occurs even when and after the light emitting element 64 and the light receiving element 67 are mounted. Become. Further, since the optical waveguide C is covered with the upper relaxation layer 52, the clad 20 and the core 22 are difficult to absorb water, and the refractive index is stabilized. Therefore, the cladding 20 and the core 22 of the optical waveguide C are less likely to be deformed or cracked, and stable optical signal transmission is possible, thereby further improving the reliability.

Here, a method for manufacturing the wiring substrate with optical waveguide K3 will be described.
A conductive paste pattern or the like is formed by printing on a plurality of green sheets and the surface thereof in advance, and these are laminated and baked. Make.
Next, as shown in FIG. 5, the thermal expansion coefficient is about 20 to 65 ppm / K by attaching an epoxy resin film on the surface 2 of the insulating substrate 1 or spin-coating and curing a varnish. And the lower relaxation layer 50 of the said thickness is formed.

Next, as shown in FIG. 6, the optical waveguide C is formed on the surface 51 of the lower relaxation layer 50. That is, a composite resin material composed of the clad 20 and the core 22 is arranged on the surface 51, and both ends thereof have an optical path conversion structure, so that the optical waveguide C (thickness of about 150 μm) having the reflection mirror surfaces 24 symmetrically at both ends is provided on the surface. 51 can be formed.
Further, as shown in FIG. 7, by spin-coating an epoxy acrylate varnish on the surface 51 of the lower relaxation layer 50 and on the optical waveguide C, the coefficient of thermal expansion is about 40 to 50 ppm / K and An upper relaxation layer 52 having a thickness is formed. The thickness of the upper relaxing layer 52 is about 200 μm on the surface 51 and about 40 μm on the optical waveguide C.

Next, as shown in FIG. 8, through holes 54 and 55 are formed in the upper relaxing layer 52 in the vicinity of the optical waveguide C just above the pair of reflecting mirror surfaces 24 by a known photolithography technique. In addition, through holes are formed by laser processing in the vicinity of both ends of the upper relaxation layer 52 and the lower relaxation layer 50, and electroless copper plating and electrolytic copper plating are applied to the inner walls thereof, as shown in FIG. A via conductor v connected to the layer 6 is formed.
Next, as shown in FIG. 9, a required number of connection wirings 5 and a required number of wirings 4 are formed adjacent to the openings of the through holes 54 and 55 by a known photolithography technique or the like. Further, support pieces 66 and 68 made of the same resin as that of the upper relaxing layer 52 are projected from the openings of the through holes 54 and 55 on the opposite side by the same technique as described above.

Then, as shown in FIG. 10, by connecting the connection terminals 61 and 62 of the IC chip (operation element) 60 to the right wiring 4 and one end of the connection wiring 5 through solder (not shown), Such an IC chip 60 is mounted on the surface 53 of the upper relaxation layer 52.
Further, the connection terminal 69 of the light receiving element (optical element) 67 is connected to the other end of the connection wiring 5 via solder, and the tip end portion is supported by the support piece 68, so that the light receiving element 67 is placed on the surface 53. Implement. At this time, the light receiving portion (not shown) of the light receiving element 67 is located immediately above the reflection mirror surface 24 and the through hole 55 at the right end of the optical waveguide C.
Further, as shown in FIG. 10, the connection terminals 57 and 58 of the IC chip (operation element) 56 are connected to the left wiring 4 and one end of the connection wiring 5 through solder, whereby the IC chip 56 is connected. It is mounted on the surface 53 of the upper relaxation layer 52. Further, the connection terminal 65 of the light emitting element (optical element) 64 is connected to the other end of the connection wiring 5 via solder, and the tip end portion is supported by the support piece 66, so that the light emitting element 64 is placed on the surface 53. Implement. At this time, the light emitting portion (not shown) of the light emitting element 64 is located immediately above the reflection mirror surface 24 and the through hole 54 at the left end of the optical waveguide C.

As a result, the wiring substrate with optical waveguide K3 shown in FIG. 3 can be obtained.
In addition, by replacing the insulating substrate 1 with the insulating substrate 30 made of the resin and passing through the above-described steps, a wiring substrate with an optical waveguide similar to the wiring substrate K3, which is substantially made entirely of resin, is obtained. It is also possible.

The present invention is not limited to the embodiments described above.
For example, the optical waveguide C may be configured by a clad 20 having a square cross section and a single core 22 having a square cross section inside thereof.
The optical waveguide may be a single mode in addition to the multimode optical waveguide C.
Further, the material of the optical waveguide C may be siloxane polymer or fluorine polyimide in addition to the acrylic resin.
Further, the optical waveguide C may have a right-angled end surface from which the reflection mirror surfaces 24 at both ends are omitted, and a reflective member having a triangular cross section having a reflection mirror surface having a mirror surface in the vicinity of the both end surfaces. .
Further, the wiring layer 6 and the via conductor v are not limited to Ag and Cu, and may be a metal or alloy such as W, Mo, Ag—Cu, or Cu—W.
In addition, resin fibers and other materials may be applied instead of the glass cloth forming the insulating substrate 30.

Sectional drawing which shows 1 form of the wiring board with an optical waveguide of this invention. Sectional drawing which shows the deformation | transformation form of the said wiring board with an optical waveguide. Sectional drawing which shows the wiring board with an optical waveguide of a different form. The fragmentary sectional view which shows the manufacturing process of the said wiring board with an optical waveguide. The fragmentary sectional view which shows the manufacturing process following FIG. FIG. 6 is a partial cross-sectional view illustrating a manufacturing process subsequent to FIG. 5. FIG. 7 is a partial cross-sectional view illustrating a manufacturing process following FIG. 6. FIG. 8 is a partial cross-sectional view illustrating a manufacturing process following FIG. 7. FIG. 9 is a partial cross-sectional view illustrating a manufacturing process following FIG. 8. FIG. 10 is a partial cross-sectional view showing the manufacturing process following FIG. 9.

Explanation of symbols

1, 30 ………………………… Insulating substrate 2, 42a ……………………… Surface 11, 46, 50 ……………… Lower relaxation layer 14a, 14b, 56, 60 ... IC chip (operating element)
16, 64 ………………………… Light emitting element (optical element)
18, 67 ………………………… Light receiving element (optical element)
24 ……………………………… Reflecting mirror surface 26, 52 ……………………… Upper relaxation layer 53 ……………………………… Upper relaxation layer surface 54 55 ……………………… Through hole C …………………………………… Optical waveguide K1 to K3 ……………………… Wiring board with optical waveguide

Claims (3)

An insulating substrate having a surface;
An optical waveguide disposed above the surface of the insulating substrate and having a coefficient of thermal expansion higher than that of the insulating substrate;
A lower relaxation layer and an upper relaxation layer formed between the surface of the insulating substrate and the optical waveguide and above the optical waveguide, and having a thermal expansion coefficient intermediate between the insulating substrate and the optical waveguide; A wiring board with an optical waveguide, comprising: The upper relaxation layer has a pair of through holes formed at positions above the reflecting mirror surfaces located at both ends of the optical waveguide, and the optical element is located above the pair of through holes and on the surface of the upper relaxation layer. Are implemented respectively.
The wiring board with an optical waveguide according to claim 1. An operating element that is electrically connected to the optical element is mounted on the surface of the upper relaxation layer adjacent to the optical element and opposite to the optical waveguide.
The wiring board with an optical waveguide according to claim 1 or 2.

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