JP4231355B2 - Opto-electric composite wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric composite wiring board in which electrical wiring and optical wiring are provided on a single substrate.
[0002]
[Prior art]
Various structures have been proposed for opto-electric composite wiring boards.
[0003]
As an example, a 45-degree mirror is provided at the end of the optical wiring that forms the optical waveguide made of polymer on the substrate on which the photoelectric conversion element is provided, and the optical signal from the light emitting element is coupled to the optical waveguide. There is a technique in which high-speed data communication is performed by using light or by coupling an optical signal propagating through an optical waveguide to a light receiving element (see, for example, Patent Document 1).
[0004]
As an optical coupling method in such an opto-electric composite wiring board, a technique is disclosed in which optical coupling efficiency is improved by coupling an optical waveguide and an optical element using a microlens (for example, Patent Documents). 2).
[0005]
Here, as an example of a conventional photoelectric composite wiring board, the photoelectric composite wiring board disclosed in Patent Document 1 will be described with reference to FIG. The photoelectric composite wiring board 100 shown in FIG. 6 has a first waveguide 101 with a thick cladding layer and a second waveguide 102 with a thin cladding layer. Each waveguide 101, 102 has a core layer 103 sandwiched between cladding layers. In this photoelectric composite wiring substrate 100, the first waveguide 101 is directly provided on the substrate 104, and the second waveguide 102 is indirectly connected to the substrate via a spacer 105 provided between the substrate 104 and the substrate. 104 is provided. In the technique of Patent Document 1, in the first waveguide 101 and the second waveguide 102 having different clad layer thicknesses, the height of the core layer 103 in the thickness direction of the substrate 104 is set to the reference plane. Accordingly, the guided light of the optical element that is matched (adjacent) to the second waveguide 102 in advance can be optically coupled as the guided light of the first waveguide 101 with high optical coupling efficiency.
[0006]
As a result, the core layer 103 of the first waveguide 101 and the second waveguide 102 can be brought close to each other, so that the waveguide light of the optical element previously coupled to the second waveguide 102 can be transmitted to the first waveguide 101. As the guided light of the waveguide 101, it can be optically coupled with high optical coupling efficiency.
[0007]
[Patent Document 1]
JP 2002-48949 A
[Patent Document 2]
JP 2001-185752 A
[0008]
[Problems to be solved by the invention]
However, in the conventional photoelectric composite wiring substrate 100 as described above, the spacer 105 is not provided between the first waveguide 101 having a thick cladding layer and the substrate 104. For this reason, unevenness is caused by the electrical wiring provided on the substrate 104, foreign matter such as dust adheres to the substrate 104, or the thickness of the substrate 104 itself is uneven, and the surface of the substrate 104 is When unevenness or surface roughness of about 1 to 300 μm exists, the cladding layer in the first waveguide 101 may be deformed or disconnected. In such a case, the core layer 103 is deformed or disconnected as the cladding layer is deformed, and as a result, the shape of the core layer 103 itself changes or the shape of the entire waveguide 101 changes. There is.
[0009]
In such a photoelectric composite wiring board 100, there is a problem that light is not guided or the waveguide loss is increased even if the light is guided.
[0010]
Further, in the conventional optoelectric composite wiring substrate 100 as described above, the height of the core layer 103 in the plurality of waveguides 101 and 102 to be coupled is adjusted by the spacer 105, so that the waveguide that requires the spacer 105 is used. It is necessary to provide a spacer 105 corresponding to 102.
[0011]
For the portion where the spacer 105 is provided, for example, patterning can be used. In this case, the width of the waveguide 102 and the pitch of the waveguide 102 are limited not by the patterning accuracy of the waveguide 102 itself but by the patterning accuracy of the spacer 105. For this reason, the spacer 105 itself must be patterned with the same accuracy as the waveguide.
[0012]
Further, in the first waveguide 101 and the second waveguide 102, the core layer 103 and the cladding layer are both exposed to the air. For this reason, there is a tendency that waveguide loss or coupling loss due to adhesion of foreign matters such as dew condensation or dust to the core layer portion in the waveguides 101 and 102 is likely to increase.
[0013]
In addition, the clad layer is easily damaged by contact with other mechanical parts by a slight force. Since the clad layer has a great influence on the optical waveguide loss, when the waveguides 101 and 102 are used as an optical wiring, if the clad layer is damaged, the received light amount is lower than the required level of light reception sensitivity. The optical signal cannot be sufficiently transmitted, and as a result, the optical wiring is disconnected. For this reason, when the photoelectric composite wiring board 100 is manually inserted into the slot, the optical wiring is frequently disconnected at a place supported by the hand.
[0014]
Further, when a glass and epoxy composite material represented by FR4 is used as the substrate 104 and a through hole of the substrate 104 and a through hole of the waveguide are provided, for example, processing of a general substrate 104 such as processing with a drill is performed. When the method is used, the clad is very easily damaged by the scattering of the drill powder.
[0015]
By the way, in the board | substrate 104 formed with the glass epoxy composite material, the thermal expansion coefficient of a horizontal direction (surface direction) is about 20 ppm. On the other hand, when an epoxy resin or an acrylic resin, which is a polymer material different from the substrate 104, is used as the waveguide material, the thermal expansion coefficient in the horizontal direction is 100 ppm or more. That is, when a glass epoxy composite material is used as the substrate 104, if the substrate wiring length is 100 mm, the wiring length difference is about 1 mm with a temperature difference of 100 degrees.
[0016]
The difference in thermal expansion that causes such a wiring length difference is an optical integrated circuit substrate for optical communication using a quartz optical waveguide on a quartz substrate by a conventional flame deposition method, or 50 mm using a polyimide optical waveguide on a polyimide substrate. The difference in thermal expansion is so large that it can be said that it is completely different from the photoelectric composite wiring board for multi-chip module (MCM) below the corner.
[0017]
For this reason, in the conventional opto-electric composite wiring substrate 100, the substrate 104 and the waveguides 101 and 102 are peeled off or warped due to the thermal cycle in the manufacturing process or the heat generated from the electronic circuit, and the optical waveguide loss. Is likely to increase.
[0018]
For this reason, it is impossible to realize a reduction in optical transmission loss of the optical wiring, an improvement in mechanical strength and a long-term stability of performance.
[0019]
It is an object of the present invention to improve the mechanical strength of an opto-electric composite wiring board, suppress an increase in optical waveguide loss due to deformation of the optical wiring due to poor adhesion of the optical wiring layer to the board, and stabilize optical waveguide performance. It is to secure the property over a long period of time.
[0028]
Here, for example, in order to provide a single layer with a plurality of different functions of improving the adhesion of the optical wiring layer to the substrate and reducing the difference in thermal expansion coefficient between the substrate and the optical wiring layer, this intermediate layer There is a concern that the material for forming the film is limited or the cost is increased.
[0029]
Therefore, an intermediate layer having a plurality of functions can be easily realized.
[0031]
Therefore, the stress generated by the difference in thermal expansion between the optical wiring layer and the substrate can be absorbed by the intermediate layer.
[0032]
Claim 1 The invention described is electrically connected to a substrate provided with an electrical wiring for transmitting an electrical signal, an optical wiring layer provided on the substrate and having an optical wiring for transmitting an optical signal, and the electrical wiring. A photoelectric conversion element that photoelectrically converts an optical signal transmitted by the optical wiring, and an intermediate layer that is provided between the substrate and the optical wiring to improve adhesion between the substrate and the optical wiring layer. In the photoelectric composite wiring board provided, the intermediate layer is formed of a composite material of a glass cloth or a glass nonwoven fabric and a polymer material.
[0033]
Therefore, for example, the difference in coefficient of thermal expansion from a material normally used as a material for forming a substrate, such as a glass-epoxy composite material, a glass-polyimide composite material, or a glass-polyphenol oxide composite material, is selected as a material for forming an intermediate layer. Can be made smaller.
[0035]
Therefore, even when the thermal expansion coefficient of the substrate and the effective thermal expansion coefficient of the entire optical wiring layer cannot be matched, distortion due to the thermal expansion difference between the substrate and the optical wiring layer can be reduced.
[0037]
Therefore, even when the thermal expansion coefficient of the substrate and the effective thermal expansion coefficient of the entire optical wiring layer cannot be matched, distortion due to the thermal expansion difference between the substrate and the optical wiring layer can be reduced.
[0047]
Claim 2 The described invention is claimed. 1 In the opto-electric composite wiring board described above, the photoelectric conversion element and the optical wiring are provided on the opposite side with the substrate interposed therebetween.
[0048]
Here, when the photoelectric conversion element is mounted on the substrate, the substrate is heated to a high temperature by a solder reflow process or the like.
[0049]
Therefore, the step of mounting the photoelectric conversion element on the substrate and the step of mounting the optical wiring on the substrate are performed by different processes, and the optical wiring is mounted after mounting the photoelectric conversion element on the substrate. it can. Further, even a material having a glass transition point lower than the temperature at which the substrate is heated by the step of mounting the photoelectric conversion element on the substrate can be used as a material for forming the optical wiring layer.
[0050]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIG. This embodiment shows an application example to a photoelectric composite wiring board.
[0051]
FIG. 1 is a cross-sectional view schematically showing an optoelectric composite wiring board according to a first embodiment of the present invention. As shown in FIG. 1, the optoelectric composite wiring board 1 of the present embodiment includes a substrate 2 and a multichip module 3 in which an integrated circuit is combined.
[0052]
Electrical wiring (not shown) is provided on one surface side of the substrate 2. Examples of the material for forming the substrate 2 include an electronic substrate for general use, such as a glass-epoxy composite material represented by FR4, a glass-polyimide composite material, and a glass-polyphenol oxide composite material. . Practically, the material for forming the substrate 2 is limited from the viewpoint of low loss, ease of manufacture, material cost, and the like.
[0053]
In addition, as a material for forming the substrate 2, for example, a quartz waveguide substrate used for basic optical communication can be used.
[0054]
An optical wiring layer 4 is provided on one surface side of the substrate 2. The optical wiring layer 4 includes a core 5 made of a polymer material, and a pair of clad layers 6 (6a, 6a, 6a) formed of a polymer material sandwiching the core 5 and having a refractive index lower than that of the core 5. 6b). Of the pair of clad layers 6, the upper clad layer 6 a is provided on the opposite side of the substrate 2 with respect to the core 5, and the lower clad layer 6 b is provided between the core 5 and the substrate 2. In the present embodiment, an optical wiring (optical waveguide) is realized by the core 5 and the upper and lower cladding layers 6a and 6b constituting the optical wiring layer 4. Although the description is omitted because it is a known technique, the optical wiring functions to transmit an optical signal. The core 5 of the present embodiment generates multi-mode light propagation in a mode of several tens of thousands with respect to the propagation light in the optical communication band having a wavelength of 600 to 1600 nm when an optical wiring having a length of 50 μm is formed.
[0055]
Examples of a general material for forming such an optical wiring (optical waveguide) include an epoxy material, an acrylic material, a polyphenol oxide material, and a polyimide material. Many of these materials have a coefficient of thermal expansion of 100 ppm or more.
[0056]
A coupling element 7 is provided at one end of the optical wiring layer 4. The coupling element 7 receives the optical signal transmitted from the optical wiring layer 4 with respect to the light receiving element 8 included in the multichip module 3 with high efficiency, or receives the optical signal output from the light emitting element 9 included in the multichip module 3. This is an element for coupling to the optical wiring layer 4 with high efficiency.
[0057]
The multichip module 3 is provided on one surface side of the substrate 2. The multichip module 3 of the present embodiment is provided on the same side as the side on which the optical wiring layer 4 is provided with respect to the substrate. Although not shown in detail, the multichip module 3 includes at least one photoelectric conversion element and an electronic integrated circuit that drives the photoelectric conversion element, and is a surface on the side facing the optical wiring layer 4. A light emitting element 9 and a light receiving element 8 are provided. Although the explanation is omitted because it is a known technique, the photoelectric conversion element is formed of a semiconductor or the like to which a voltage is applied, and when irradiated with light, photons form electrons and holes, or electrons It is an electronic device that generates photons by recombination of holes with holes. The photoelectric conversion element of this embodiment is intended for an electronic element such as a photodiode or a semiconductor laser that generates current when irradiated with light or generates light when applied with current. In the present embodiment, a surface emitting laser is used as the light emitting element 9. The light emitting element 9 is not limited to a surface emitting laser, and a normal semiconductor laser diode or light emitting diode can also be used. In the present embodiment, a photodiode is used as the light receiving element 8.
[0058]
The multichip module 3 transmits an optical signal transmitted through the optical wiring layer 4 and received by the light receiving element 8 to the electric wiring or causes the light emitting element 9 to emit light by an electronic integrated circuit.
[0059]
The multichip module 3 is electrically coupled to the electrical wiring provided on the substrate 2 by solder bumps 10. As a result, power is supplied to the multichip module 3.
[0060]
In the photoelectric composite wiring board 1 of the present embodiment, an adhesion layer 11 as an intermediate layer is provided between the optical wiring layer 4 and the substrate 2. As thickness of the adhesion layer 11, 1-500 micrometers is preferable, More preferably, it is 10-250 micrometers. The thermal expansion coefficient of the adhesion layer 11 is preferably set to the same thermal expansion coefficient as that of the cladding layer 6 or between the thermal expansion coefficient of the cladding layer 6 and the thermal expansion coefficient of the substrate 2.
[0061]
The adhesion layer 11 is a layer formed of a material different from that of the upper cladding layer 6a or the lower cladding layer 6b.
[0062]
Here, the different material means that the upper clad layer 6a and the lower clad layer 6b are layers that are formed of materials that are materially different from each other, or that are made of materials that have the same properties, even if they are the same material. To do.
[0063]
The adhesion layer 11 may be provided on either the upper side or the lower side of the optical wiring layer 4 or may be provided on both sides. The adhesion layer 11 is preferably provided not over a part of the optical wiring layer 4 but over the entire region where the optical wiring layer 4 is provided in the same plane.
[0064]
The adhesion layer 11 is provided so that the plane is flattened over the entire region where the optical wiring layer 4 is provided. The surface on the optical wiring layer 4 side of the adhesion layer 11 is preferably flattened so that the unevenness or surface roughness of the surface on the optical wiring layer 4 side of the substrate 2 is ½ or less. In particular, the surface on the optical wiring layer 4 side of the adhesion layer 11 is preferably flattened so that the unevenness or surface roughness of the surface on the optical wiring layer 4 side of the substrate 2 is 1/10 or less.
[0065]
Then, by providing such an adhesion layer 11 over the entire region where the optical wiring layer 4 is provided, the substrate 2 and the optical wiring layer 4 are particularly formed with respect to the substrate 2 formed of a polymer and glass. The thermal expansion coefficient difference can be reduced over the entire region where the optical wiring layer 4 is provided.
[0066]
As a material for forming the adhesion layer 11, when the adhesion layer 11 and the cladding layer 6 are integrated, the warping stress due to expansion or heat of the layer is canceled by the thermal expansion of the substrate 2 or the warping stress due to heat. It is preferable to select the material.
[0067]
In the present embodiment, the adhesion layer 11 is provided between the optical wiring layer 4 and the substrate 2. However, the present invention is not limited to this, and the adhesion layer 11 is provided on at least one side of the optical wiring layer 4. As long as it is provided.
[0068]
By the way, when the board | substrate 2 is formed using a general glass-epoxy material, the thermal expansion coefficient of this board | substrate 2 is 15-20 ppm. The thermal expansion coefficient of the polymer material forming the optical wiring layer 4 with respect to the substrate 2 is 100 ppm or more in the surface direction of the substrate 2. In this case, when there is a temperature difference of 100 degrees, the substrate wiring having a length of 100 mm expands by about 1 mm.
[0069]
That is, if the difference in thermal expansion coefficient between the material forming the substrate 2 and the material forming the optical wiring layer 4 is inappropriate, warping occurs, and even if no warping occurs, the substrate 2 and the optical wiring The layer 4 is peeled off or a positional shift occurs between the light receiving element 8 and the light emitting element 9 mounted on the substrate 2 and the coupling element 7 of the optical wiring layer 4, and as a result, the optical wiring in the optical wiring layer 4. Disconnection may occur.
[0070]
For this reason, the substrate 2 and the optical wiring layer 4 are preferably formed using the same material or a material having the same thermal expansion coefficient.
[0071]
When the effective thermal expansion coefficients of the substrate 2 and the optical wiring layer 4 are substantially matched, if the substrate 2 and the optical wiring layer 4 do not peel and do not warp, the light receiving element 8 and the light emitting element 9 are displaced. Thus, the increase in coupling loss due to the optical coupling can be prevented, and the optical coupling efficiency can be made constant. Here, “substantially coincidence” means that the difference in thermal expansion coefficient is preferably within 10 ppm, more preferably within 5 ppm.
[0072]
However, materials that can be used for the optical wiring layer 4 are limited to materials that can actually be used in terms of low loss, ease of manufacture, material cost, and the like.
[0073]
Further, as described above, a quartz waveguide substrate is used as a material for forming the substrate 2 as a basic optical communication application. However, an electronic substrate as a general application is, for example, a glass represented by FR4. It is limited to epoxy composite materials, glass-polyimide composite materials, glass-polyphenol oxide composite materials, and the like.
[0074]
On the other hand, in the present embodiment, by providing the adhesion layer 11 in close contact with the lower cladding layer 6b separately from the lower cladding layer 6b, a member that is different from the substrate 2 provided on the substrate 2 is thickened. It is possible to increase the effective strength of the clad layer 6 and the entire optical wiring layer 4 regardless of the difference in thermal expansion coefficient between them. As a result, it is possible to reduce the deformation of the optical wiring layer 4 due to the difference in thermal expansion coefficient between the substrate 2 and the optical wiring layer 4, and to suppress an increase in light propagation loss due to the deformation of the optical wiring layer 4. Can do.
[0075]
Further, by appropriately selecting a material so that the warping stress due to expansion or heat as an integral composite layer of the adhesion layer 11 and the clad layer 6 is offset with the thermal expansion stress due to heat or heat from the substrate 2, the substrate 2 And the deformation of the cladding layer 6 can be reduced, thereby suppressing an increase in light propagation loss.
[0076]
When the effective thermal expansion coefficients of the substrate 2 and the optical wiring layer 4 are substantially matched, an increase in coupling loss due to the positional deviation of the light receiving element 8 and the light emitting element 9 is prevented, and the optical coupling efficiency is constant. Therefore, the reliability of the coupling of the mounted light emitting / receiving elements required in the order of several μm can be greatly improved.
[0077]
Here, when the difference in thermal expansion coefficient is within 20 ppm, if the wiring length is 100 mm, the difference in length between the substrate 2 and the optical wiring layer 4 is 100 μm. Therefore, the light receiving and emitting elements provided at a pitch of 250 μm It is possible to reduce crosstalk and secure optical coupling efficiency by coupling optical elements such as lenses, and in the case of 5 ppm or less, coupling efficiency even in the case of direct coupling to a multimode optical wiring of about 50 μm Can be ensured.
[0078]
In the present embodiment, since the thermal expansion coefficient of the adhesion layer 11 is the same as that of the cladding layer 6 or between the thermal expansion coefficient of the cladding layer 6 and the thermal expansion coefficient of the substrate 2, Even when the effective thermal expansion coefficient with the optical wiring layer 4 cannot be substantially matched, distortion due to the difference in thermal expansion between the substrate 2 and the optical wiring layer 4 can be reduced. Deformation can be suppressed. As a result, stress applied to the optical wiring layer 4 can be relaxed, and loss of optical waveguide efficiency in the optical wiring layer 4 can be suppressed.
[0079]
Note that the adhesion layer 11 may be formed of an adhesive. By forming the adhesion layer 11 with an adhesive, the adhesion between the substrate 2 and the optical wiring layer 4 can be improved. At this time, it is also effective to increase the hardness by using a photo-curing agent as an adhesive. Thereby, the mechanical strength of the photoelectric composite wiring board 1 can be further improved.
[0080]
By adopting such a structure, the risk of performance degradation of the cladding layer 6 can be effectively avoided.
[0081]
Further, when the optical wiring layer 4 having a core of 50 μm is directly formed on the substrate 2, multimode light propagation in a mode of several tens of thousands occurs with respect to the propagation light in the optical communication band having a wavelength of 600 to 1600 nm.
[0082]
Here, for example, when the substrate 2 formed of FR4 is used as the substrate 2 in the opto-electric composite wiring substrate 1, the thickness is caused by deformation in the through-hole portion due to copper electrical wiring or drilling or non-uniform pressing of the glass epoxy resin. Due to non-uniformity, the substrate itself has a plurality of types of uneven shapes on the surface, or the substrate surface is rough as an optical material.
[0083]
Higher-order mode propagation loss further increases due to stress strain, deformation, or damage of the cladding layer caused by unevenness.
[0084]
Furthermore, in the case where the irregularities are caused by foreign matter such as dust having a size of 50 μm or more, the core layer is extremely deformed simultaneously with the clad layer due to the dust, so that the optical wiring is also disconnected.
[0085]
On the other hand, in the present embodiment, since the surface of the adhesion layer 11 on the optical wiring layer 4 side is flattened, an increase in optical waveguide loss in the optical wiring layer 4 can be suppressed. In addition, since the surface of the adhesion layer 11 on the optical wiring layer 4 side is flattened, it is possible to eliminate the need for patterning the adhesion layer 11 with high accuracy as in the prior art.
[0086]
Next, a second embodiment of the present invention will be described. Although not particularly shown, the photoelectric composite wiring board 1 of the present embodiment has the same structure as the photoelectric composite wiring board 1 shown in FIG. 1, and the material forming the adhesion layer 11 in FIG. Different from the first embodiment. Note that the same parts as those of the first embodiment are denoted by the same reference numerals, and description thereof is also omitted. The same shall apply hereinafter.
[0087]
In the present embodiment, the adhesion layer 11 as an intermediate layer is formed of a viscoelastic material. The elastic modulus of the viscoelastic material is 10 ³ -10 ⁷ dyn / cm ² Is preferably set within the range of 10 ⁴ -10 ⁶ dyn / cm ² More preferably, it is set in the range. Further, the thickness of the adhesion layer 11 is preferably at least twice as large as the unevenness or surface roughness of the surface of the substrate 2 on the optical wiring layer 4 side, and more preferably at least 10 times. The thermal expansion coefficient in the adhesion layer 11 of the present embodiment is set in the same manner as the material forming the adhesion layer 11 of the first embodiment described above.
[0088]
As described above, in this embodiment, since the adhesion layer 11 is formed of a viscoelastic material, in addition to changing the effective thermal expansion coefficient in the optical wiring layer 4 by adjusting the thermal expansion coefficient. The stress generated by the difference in thermal expansion between the optical wiring layer 4 and the substrate 2 can be absorbed by viscoelasticity. Thereby, it is possible to prevent an increase in optical waveguide loss due to warpage or peeling of the substrate 2 or the optical wiring layer 4.
[0089]
Further, by forming the adhesion layer 11 from a viscoelastic material, even when the substrate 2 including the optical wiring layer 4 is sandwiched between hands or tools, the stress generated by the sandwiching is absorbed by the viscoelastic body portion. Therefore, even when the substrate 2 including the optical wiring layer 4 is sandwiched by a hand or a tool, optical waveguide loss due to warpage or peeling of the substrate 2 or the optical wiring layer 4 due to the stress generated by being sandwiched. An increase can be prevented.
[0090]
Furthermore, by providing the optical wiring layer 4 via the adhesion layer 11 formed of a viscoelastic material with respect to the substrate 2 having an uneven surface on the optical wiring layer 4 side, the viscoelastic material in the adhesion layer 11 becomes a substrate. 2 irregularities can be absorbed. Thereby, deformation and stress due to the unevenness of the optical wiring layer 4 can be reduced, and an increase in optical waveguide loss can be reduced.
[0091]
Next, a third embodiment of the present invention will be described with reference to FIG.
[0092]
FIG. 2 is a cross-sectional view schematically showing an optoelectric composite wiring board according to a third embodiment of the present invention. As shown in FIG. 2, in the optoelectric composite wiring board 20 of the present embodiment, the optical wiring layer 4 is directly provided on one surface side of the substrate 2. In the substrate 2 of the present embodiment, electrical wiring (not shown) is provided on the side where the optical wiring layer 4 is provided.
[0093]
An overcoat layer 21 as a protective layer is provided on the surface opposite to the substrate 2 with respect to the optical wiring layer 4. In the overcoat layer 21, a light receiving portion where light transmitted through the optical wiring layer 4 and traveling toward the light receiving element 8 passes, and a light emitting portion where light emitted from the light emitting element 9 travels toward the optical wiring layer 4 are transmitted to light. On the other hand, a window 22 formed of a material that is transparent and capable of transmitting an optical signal is provided.
[0094]
In the present embodiment, the overcoat layer 21 is provided with the window 22 formed of a material that is transparent to the light receiving and emitting portions and capable of transmitting an optical signal. For example, a window formed by securing a space without providing the overcoat layer 21 in the light receiving and emitting portions and exposing the light emitting element 9 and the light receiving element 8 to the optical wiring layer 4 is not limited. You may make it provide.
[0095]
In the present embodiment, the overcoat layer 21 is provided with the windows 22 in the light receiving and emitting portions, but the present invention is not limited to this. For example, the overcoat layer 21 itself is transparent to light. However, it may be formed of a material capable of transmitting an optical signal.
[0096]
The overcoat layer 21 does not have to be the same material as that for forming the window 22.
[0097]
The thickness of the overcoat layer 21 is preferably 1 to 500 μm. In particular, the thickness of the overcoat layer 21 is more preferably 10 to 250 μm.
[0098]
The material for forming the overcoat layer 21 is 10 ³ -10 ⁷ dyn / cm ² Preferably having an elastic modulus set to 10 ⁴ -10 ⁶ dyn / cm ² More preferably, it is set to.
[0099]
Thus, by providing the overcoat layer 21, the portion where the optical wiring layer 4 is provided can be thickened, and the mechanical strength of the portion where the optical wiring layer 4 is provided can be improved. It is possible to protect the optical wiring layer 4 from the impact of the above.
[0100]
Further, by providing the overcoat layer 21, it is possible to prevent the optical wiring layer 4 from being damaged by drilling the substrate 2 or surrounding dust. The material for forming the overcoat layer 21 is preferably a material having the same strength as that of the substrate 2 or higher than that of the substrate 2.
[0101]
In addition, by providing the overcoat layer 21, it is possible to prevent deformation and damage of the optical wiring layer 4 due to contact between the substrates 2 in an operation process of removing or attaching the photoelectric composite wiring substrate 20 to another member. Can do. In addition, since the work can be performed without requiring the carefulness required when handling the normal photoelectric composite wiring board 20, workability can be improved. Furthermore, when the opto-electric composite wiring board 20 is handled with bare hands, it is possible to prevent the optical wiring layer 4 from being contaminated by moisture or oil, or from being damaged due to an impact caused by touch. it can.
[0102]
By the way, when the optical wiring layer having a thickness of about 250 μm is directly bonded to the substrate, the extension of the upper cladding layer and the lower cladding layer in the optical wiring layer differs due to the difference in thermal expansion coefficient between the substrate and the optical wiring layer. In addition, deformation or disconnection may occur due to shear force applied to the core part.
[0103]
Even when no disconnection occurs, the vertical end face is inclined due to the difference in length between the upper cladding layer and the lower cladding layer after deformation. For example, if the thermal expansion coefficient of the optical wiring layer is 100 ppm or more with respect to the thermal expansion coefficient of the substrate of about 20 ppm, and the substrate wiring length is 100 mm, the length of heat is increased even with a temperature difference of 10 degrees. The difference is about 100 μm. Here, for example, if the thickness of the optical wiring layer is 250 μm, tan ^-1 An inclination of (100/250) = 22 degrees occurs. The inclination of the end face in the connection between the optical wiring layers and the connection between the optical wiring layer and the optical fiber (not shown) causes a large connection loss. Such inclination of the end face also increases coupling loss in optical coupling between the optical wiring layer, the light receiving element, and the light emitting element. Further, the deformation of the core and the clad layer also increases the loss of the optical wiring layer.
[0104]
On the other hand, as in the present embodiment, for example, by laminating a material having substantially the same thermal expansion coefficient as that of the substrate, such as a glass epoxy material, on the upper cladding layer 6a, the thermal expansion coefficient can be reduced. It is possible to compensate for the distortion of the substrate 2 resulting from the difference and to prevent the optical wiring layer 4 from warping up and down due to heating.
[0105]
In the present embodiment, the substrate 2 and the overcoat layer 21 are the same from above and below the optical wiring layer 4 unlike the relaxation of the thermal expansion coefficient difference by the adhesion layer 11 in the first embodiment described above. Can be compensated for distortion of the optical wiring layer 4 above and below the optical wiring layer 4.
[0106]
In this way, by suppressing asymmetry due to upper and lower strains, it is possible to compensate for an inclination shift at the end face of the optical wiring layer 4.
[0107]
In addition, the substantially identical thermal expansion coefficient in the present embodiment means that the difference in thermal expansion coefficient is preferably within 10 ppm, more preferably within 5 ppm.
[0108]
By making the thermal expansion coefficients of the substrate 2 and the overcoat layer 21 substantially the same (5 ppm), for example, if the thickness of the optical wiring layer 4 is 250 μm, tan ^-1 (5/250) = can be suppressed to a tilt deviation of 1 degree.
[0109]
The normally used substrate 2 is a limited material such as a glass-epoxy composite material, a glass-polyimide composite material, or a glass-polyphenol oxide composite material typified by FR4. 2 is preferably the same material. In this embodiment, a glass epoxy composite material is used as a material for forming the substrate 2 and a particularly preferable glass epoxy is used as a material for forming the overcoat layer 21 because of cost, versatility, and ease of processing. .
[0110]
Furthermore, by providing the overcoat layer 21, it is possible to absorb the impact applied from the outside. For example, the optical wiring layer 4 is damaged by drill powder or dust generated by processing the substrate 2 using a drill or the like. Can be prevented.
[0111]
In this embodiment, the overcoat layer 21 is laminated on the optical wiring layer 4. However, the present invention is not limited to this, and the overcoat layer 21 is sealed so as to seal the entire optical wiring layer 4. You may make it provide. As a result, it is possible to eliminate the influence of the change in the refractive index of the optical wiring layer 4 material due to moisture absorption, and to achieve long-term stability of the optical waveguide efficiency in the optical wiring layer 4.
[0112]
By the way, fluorinated polyimide has a refractive index of 10 due to the influence of humidity. ^-3 It changes in order to produce a relative refractive index difference of 0.5%. For this reason, it changes to the optical waveguide characteristic different from the optical waveguide characteristic of the design value due to the influence of humidity, and the reliability of the optical waveguide efficiency by the optical wiring layer 4 is reduced, or the optical wiring layer is absorbed by long-term moisture absorption. 4 may be deteriorated. Thus, the partial change in refractive index due to humidity causes an increase in the loss of light guided by the optical wiring layer 4.
[0113]
On the other hand, such a characteristic change can be prevented by uniformly covering the optical wiring layer 4 with the overcoat layer 21.
[0114]
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view schematically showing an optoelectric composite wiring board according to a fourth embodiment of the present invention. The photoelectric composite wiring board 30 of the present embodiment includes an adhesion layer 11 shown in FIG. 1 and an overcoat layer 21 shown in FIG. The difference in thermal expansion coefficient between the adhesion layer 11 and the overcoat layer 21 is set within 10 ppm.
[0115]
The adhesion layer 11 and the overcoat layer 21 are layers made of different materials or different processes from the optical wiring layer 4. The adhesion layer 11 and the overcoat layer 21 do not necessarily have the same configuration and materials.
[0116]
As described above, the adhesion layer 11 is provided between the substrate 2 and the optical wiring layer 4, the overcoat layer 21 is provided on the optical wiring layer 4 on the side opposite to the substrate 2, and the optical wiring layer 4 is sandwiched vertically. By doing so, distortion of the substrate 2 due to the difference in thermal expansion coefficient between the substrate 2 and the optical wiring layer 4 can be suppressed from above and below by the adhesion layer 11 and the overcoat layer 21.
[0117]
Moreover, the inclination in the optical wiring layer 4 edge part can be suppressed and the connection loss of the optical wiring layers 4 can be suppressed by making the thermal expansion coefficient difference of the adhesion layer 11 and the overcoat layer 21 within 10 ppm.
[0118]
Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a sectional view schematically showing a photoelectric composite wiring board according to the fifth embodiment of the present invention. The photoelectric composite wiring board 40 of the present embodiment is different from the photoelectric composite wiring board 30 of the third embodiment described above in that it includes an intermediate layer 41 and a protective layer 42 each composed of a plurality of layers. Different.
[0119]
As shown in FIG. 4, the intermediate layer 41 of the present embodiment is composed of a strain relaxation layer 41a and an adhesion layer 41b.
[0120]
Moreover, the protective layer 42 of this Embodiment is comprised by the overcoat layer 42a and the moisture absorption layer 42b.
[0121]
In the present embodiment, the photoelectric composite wiring board 40 including the intermediate layer 41 and the protective layer 42 each including a plurality of layers is used. However, the present invention is not limited to this, and the intermediate layer 41 or the protective layer 42 Either one may be constituted by a plurality of layers. In the present embodiment, the photoelectric composite wiring board 40 including the intermediate layer 41 and the protective layer 42 each composed of a plurality of layers is used. However, the present invention is not limited to this. It may be an opto-electric composite wiring board provided with either a layer or a protective layer.
[0122]
The material for forming the overcoat layer 42a, the moisture absorption layer 42b, the strain relaxation layer 41a and the adhesion layer 41b and the thickness of each layer are appropriately adjusted according to the performance of each layer, and the overcoat layer 42a and the moisture absorption layer 42b. The material for forming the strain relaxation layer 41a and the adhesion layer 41b is not necessarily the same, or the overcoat layer 42a, the moisture absorption resistant layer 42b, the strain relaxation layer 41a, and the adhesion layer 41b are not necessarily required to have the same thickness. Absent.
[0123]
In this way, by configuring the intermediate layer 41 and the protective layer 42 by a plurality of layers, materials optimal for each effect can be selectively used. In addition, since an optimum process can be selected for each material, a highly reliable layer can be formed.
[0124]
Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing an embodiment of the photoelectric composite wiring board according to the sixth embodiment of the present invention. As shown in FIG. 5, in the photoelectric composite wiring board 50 of the present embodiment, the multichip module 3 including the light receiving element 8 and the light emitting element 9 and the optical wiring layer 4 are mutually connected with the substrate 2 in between. It is arranged to be located on the opposite side.
[0125]
In the substrate 2, a through hole 51 through which light is transmitted is formed in order to couple an optical signal guided by the optical wiring layer 4 to the light receiving element 8 and the light emitting element 9.
[0126]
The optical wiring layer 4 is directly provided with respect to the substrate 2 on the opposite side of the substrate 2 with respect to the multichip module 3. An overcoat layer 21 as a protective layer is provided on the opposite side of the optical wiring layer 4 from the substrate 2.
[0127]
In this embodiment, the overcoat layer 21 is provided on the opposite side of the substrate 2 with respect to the optical wiring layer 4. However, the present invention is not limited to this, and the optical wiring layer 4 is in close contact with the substrate 2. You may make it provide through a layer. Further, an overcoat layer may be laminated on the optical wiring layer 4 provided on the substrate 2 via an adhesion layer.
[0128]
By the way, in the solder reflow process of mounting the multichip module 3 on the substrate 2, it is necessary to heat the substrate 2 provided with the optical wiring layer 4 to 300 ° C. and mount the multichip module 3. In this solder reflow process, the difference in the thermal expansion coefficient between the material forming the optical wiring layer 4 and the material forming the substrate 2 has been remarkably exhibited so far, and the optical wiring in the optical wiring layer 4 is broken or the optical waveguide loss is reduced. May increase.
[0129]
On the other hand, in the present embodiment, the multichip module 3 and the optical wiring layer 4 are arranged on the opposite sides with the substrate 2 in between, so that the mounting of the multichip module 3 on the substrate 2 and the substrate 2 Since the mounting of the optical wiring layer 4 can be performed in a separate process, various adverse effects generated on the optical wiring layer 4 in order to mount the multichip module 3 on the substrate 2 can be excluded. Accordingly, the optical wiring layer 4 can be mounted after the multichip module 3 is mounted on the substrate 2, and the deterioration of the optical wiring layer 4 due to the heating process for mounting the multichip module 3 on the substrate 2 is suppressed. Can do.
[0130]
Here, the epoxy material has a low optical waveguide efficiency but has a glass transition point of 300 ° C. or lower, so that there has been a concern that the epoxy material may be deformed by heat applied during the solder reflow process.
[0131]
On the other hand, in the present embodiment, the mounting of the multichip module 3 on the substrate 2 and the mounting of the optical wiring layer 4 on the substrate 2 can be performed in different processes. For example, like an epoxy material, The optical wiring layer 4 can be formed using a material having a glass transition point of 300 ° C. or lower. As a result, a material more suitable as a material for forming the optical wiring layer 4 such as low optical waveguide efficiency can be used, and a low-loss optical waveguide can be more effectively mounted.
[0132]
【The invention's effect】
Book According to the photoelectric composite wiring board of the invention, the optical wiring layer can be securely fixed to the substrate and the portion where the optical wiring layer is provided can be thickened. It is possible to improve the optical waveguide loss due to the deformation of the optical wiring due to the poor adhesion of the optical wiring layer to the substrate, and to ensure the stability of the optical waveguide performance over a long period of time.
[0138]
Claim 1 According to the described invention, for example, a difference in thermal expansion coefficient from a material normally used as a material for forming a substrate, such as a glass-epoxy composite material, a glass-polyimide composite material, or a glass-polyphenol oxide composite material, The size can be reduced by selecting the material to be formed.
[0145]
Claim 2 According to the described invention, the claims 1 In the photoelectric composite wiring board described, when the photoelectric conversion element is mounted on the substrate, the substrate is heated to a high temperature by a solder reflow process or the like. On the other hand, the process of mounting the optical wiring is performed by a separate process, and the optical wiring can be mounted after mounting the photoelectric conversion element on the substrate. Therefore, the optical wiring is mounted by mounting the photoelectric conversion element on the substrate. The layer can be prevented from deteriorating, and an optical wiring layer is formed even if the material has a glass transition point lower than the temperature at which the substrate is heated by the process of mounting the photoelectric conversion element on the substrate. Therefore, it is possible to select a material with low optical waveguide loss regardless of the glass transition point, and to reduce optical waveguide loss more reliably. It can be.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a photoelectric composite wiring board according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view schematically showing a photoelectric composite wiring board according to a third embodiment of the present invention.
FIG. 3 is a cross-sectional view schematically showing a photoelectric composite wiring board according to a fourth embodiment of the present invention.
FIG. 4 is a cross-sectional view schematically showing a photoelectric composite wiring board according to a fifth embodiment of the present invention.
FIG. 5 is a cross-sectional view schematically showing a photoelectric composite wiring board according to a sixth embodiment of the present invention.
FIG. 6 is a cross-sectional view schematically illustrating a conventional photoelectric composite wiring board.
[Explanation of symbols]
1 Photoelectric composite wiring board
2 Substrate
4 Optical wiring layer
11 Middle layer
20 Opto-electric composite wiring board
21 Protective layer
30 Photoelectric composite wiring board
40 Opto-electric composite wiring board
41 middle class
42 Protection Phase
50 Opto-electric composite wiring board

Claims (2)

A substrate provided with electrical wiring for transmitting electrical signals;
An optical wiring layer provided on the substrate and having an optical wiring for transmitting an optical signal;
A photoelectric conversion element that photoelectrically converts an optical signal that is electrically connected to the electrical wiring and transmitted by the optical wiring;
An intermediate layer provided between the substrate and the optical wiring to improve the adhesion between the substrate and the optical wiring layer;
In the photoelectric composite wiring board comprising:
The said intermediate | middle layer is formed with the composite material of a glass cloth or a glass nonwoven fabric, and a polymeric material, The photoelectric composite wiring board characterized by the above-mentioned. The photoelectric composite wiring board according to claim 1, wherein the photoelectric conversion element and the optical wiring layer are provided on opposite sides with the substrate interposed therebetween.

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