Opto-electric hybrid module and method of manufacturing the same

An opto-electric hybrid module capable of achieving the reduction in distance between an optical element and a core end portion to improve the efficiency of light coupling therebetween, and a method of manufacturing the same are provided. The opto-electric hybrid module includes an optical waveguide section, an electric circuit section, and a light-emitting element (7) and a light-receiving element (8) both mounted on the electric circuit section. The optical waveguide section includes an under cladding layer (1), a linear core (2) for an optical path, the core being formed on a surface of the under cladding layer (1), and an over cladding layer (3) formed on the surface of the under cladding layer (1) and covering the core (2). An electric circuit (4) is formed on a surface portion of the under cladding layer (1) except where the core (2) is formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an opto-electric hybrid module including an optical waveguide section, an electric circuit section, and an optical element mounted on the electric circuit section, and to a method of manufacturing the same.

2. Description of the Related Art

As shown inFIG. 8, an opto-electric hybrid module is constructed, for example, using a technique to be described below. First, an electric circuit section E1in which an electric circuit14is formed on the surface of a substrate15, and an optical waveguide section W1in which an under cladding layer11, a core12and an over cladding layer13are disposed in the order named are produced individually. The back surface of the substrate15in the electric circuit section E1is bonded to the front surface of the over cladding layer13in the optical waveguide section W1with an adhesive16. A light-emitting element7and a light-receiving element8are mounted on portions of the electric circuit section E1corresponding to opposite end portions of the core12in the optical waveguide section W1. Such a technique is disclosed, for example, in Japanese Patent Application Laid-Open No. 2004-302345. The substrate15includes light-passing through holes15aand15bformed therein for propagation of light L between the end portions of the core12and the light-emitting and light-receiving elements7and8. A notch19of an inverted V shape is formed in the optical waveguide section W1near each of the opposite ends of the core12. One side surface defined by the inverted V-shaped notch19on the core12side is formed as an inclined surface inclined at 45 degrees to the axial direction of the core12. An end portion of the core12lying at the inclined surface serves as a light reflecting surface12a. InFIG. 8, the reference character7adesignates a light-emitting section in the light-emitting element7, and7band7cdesignate bumps in the light-emitting element7. The reference character8adesignates a light-receiving section in the light-receiving element8, and8band8cdesignate bumps in the light-receiving element8.

The propagation of the light L in the opto-electric hybrid module will be described. First, the light L is emitted downwardly from the light-emitting section7aof the light-emitting element7. The light L passes through the through hole15afor light propagation formed in the electric circuit section E1and then through the over cladding layer13near a first end portion (as seen inFIG. 8, the left-hand end portion) of the optical waveguide section W1, and thereafter enters a first end portion of the core12. Subsequently, the light L is reflected from one of the light reflecting surfaces12aprovided in the first end portion of the core12, and travels through the interior of the core12in the axial direction. The light L is propagated to a second end portion (as seen inFIG. 8, the right-hand end portion) of the core12. Subsequently, the light L is reflected upwardly from the other light reflecting surface12aprovided in the second end portion of the core12. Then, the light L passes through and exits from the over cladding layer13, and is received by the light-receiving section8aof the light-receiving element8.

In the course of the above-mentioned propagation of the light L, the light L emitted from the light-emitting section7aof the light-emitting element7is diffused as shown inFIG. 8. For this reason, if there is a long distance between the light-emitting element7and the light reflecting surface12aprovided in the first end portion of the core12, the light L deviates away from the light reflecting surface12aand is not guided into the core12in some cases. Similarly, the light L reflected from the light reflecting surface12aprovided in the second end portion of the core12is also diffused. For this reason, the light L deviates away from the light-receiving section8aof the light-receiving element8and is not received by the light-receiving section8ain some cases. It is therefore necessary to design the opto-electric hybrid module so as to minimize the distance between optical elements such as the light-emitting and light-receiving elements7and8and the light reflecting surfaces12aprovided in the end portions of the core12in the optical waveguide section W1.

Conventional opto-electric hybrid modules, however, are constructed such that the electric circuit section E1comprised of the substrate15and the electric circuit14is disposed between the optical elements such as the light-emitting and light-receiving elements7and8and the optical waveguide section W1. This makes the distance between the optical elements such as the light-emitting and light-receiving elements7and8and the end portions of the core12accordingly long which thereby result in the lowered efficiency of light coupling therebetween.

SUMMARY OF THE INVENTION

In view of the foregoing, it is therefore an object of the present invention to provide an opto-electric hybrid module capable of achieving the reduction in distance between an optical element and a core end portion to improve the efficiency of light coupling therebetween, and a method of manufacturing the same.

To accomplish the above-mentioned object, a first aspect of the present invention is an opto-electric hybrid module comprising: an optical waveguide section; an electric circuit section; and an optical element mounted on the electric circuit section, said optical waveguide section including an under cladding layer, a linear core for an optical path, the core being formed on a surface of the under cladding layer, and an over cladding layer formed so as to cover the core, said electric circuit section being formed on a surface portion of the under cladding layer except where the core is formed, without any substrate.

A second aspect of the present invention is a method of manufacturing an opto-electric hybrid module including an optical waveguide section, an electric circuit section, and an optical element mounted on the electric circuit section, wherein the production of the optical waveguide section comprises the steps of: forming an under cladding layer; forming a linear core for an optical path on a surface of the under cladding layer; and forming an over cladding layer on the surface of the under cladding layer so as to cover the core, and wherein the electric circuit section is produced on a surface portion of the under cladding layer except where the core is formed, without any substrate.

The present inventor has made studies of the placement of the electric circuit section in an opto-electric hybrid module to reduce the distance between the optical element and an end portion of the core. As a result, the present inventor has found that the formation of the electric circuit section on the surface of the under cladding layer where the core is formed without any substrate allows the position of the mounting of the optical element to approach the end portion of the core as compared with the prior art (with reference toFIG. 8). Thus, the present inventor has attained the present invention.

In the opto-electric hybrid module according to the present invention, the distance between the optical element and the end portion of the core is reduced because the electric circuit section is formed on the surface portion of the under cladding layer except where the core is formed, without any substrate. When the optical element is a light-emitting element, the opto-electric hybrid module enables light emitted from a light-emitting section of the light-emitting element to enter a first end portion of the core before the light is widely diffused. Similarly, when light exits from a second end portion of the core (when the optical element is a light-receiving element), the opto-electric hybrid module also enables the light exiting from the second end portion of the core to be received by a light-receiving section of the light-receiving element before the light is widely diffused. In this manner, the opto-electric hybrid module according to the present invention is significantly improved in the efficiency of light coupling between the optical element and the end portion of the core.

Preferably, bump positioning guides for positioning bumps of the optical element are formed on the surface of the under cladding layer and are placed in predetermined positions relative to the end portion of the core, and the bumps of the optical element are positioned using the bump positioning guides. In such a case, the mounting of the optical element on the end portion of the core is higher in accuracy. This further improves the efficiency of light coupling between the optical element and the end portion of the core.

In the method of manufacturing the opto-electric hybrid module according to the present invention, the electric circuit section is produced on the surface portion of the under cladding layer except where the core is formed, without any substrate. This reduces the distance between the optical element and the end portion of the core to achieve the manufacture of the opto-electric hybrid module with improved efficiency of light coupling therebetween.

Preferably, the method further comprises the step of forming bump positioning guides on the surface of the under cladding layer, and the mounting of the optical element comprises the step of positioning bumps of the optical element by using the bump positioning guides. In such a case, the high-accuracy positioning of the optical element is achieved easily. This improves the productivity of the opto-electric hybrid module.

DESCRIPTION OF THE EMBODIMENTS

Embodiments according to the present invention will now be described in detail with reference to the drawings.

FIG. 1Ais a plan view schematically showing an opto-electric hybrid module according to a first embodiment of the present invention.FIG. 1Bis a sectional view taken along the line A-A ofFIG. 1A. The opto-electric hybrid module according to the first embodiment includes an under cladding layer1, a linear core2for an optical path formed on a surface of the under cladding layer1, and an electric circuit (substrateless electric circuit section)4formed directly on a portion of the surface of the under cladding layer1other than the portion where the core2is formed, without any substrate therebetween. The term “substrateless electric circuit section” is used herein to distinguish an electric circuit formed directly on the surface of the under cladding layer without any substrate therebetween from a conventional electric circuit formed thereon with a substrate therebetween.

Part of the electric circuit4serves as mounting pads4afor connecting bumps7b,7c,8band8cof optical elements (a light-emitting element7and a light-receiving element8) thereto. The four mounting pads4aare formed around each of the opposite end portions of the core2, and are located in predetermined positions relative to each of the opposite end portions of the core2. Four bump positioning guides5and6for locating the bumps7b,7c,8band8cof the optical elements (the light-emitting element7and the light-receiving element8) are provided in a protruding condition on the surface of the under cladding layer1so as to surround the four mounting pads4a, respectively. Two bump positioning guides5out of the four bump positioning guides5and6are formed in a U shape as seen in plan view, and the two remaining bump positioning guides6are formed in the shape of a rectangular frame as seen in plan view. The bumps7b,7c,8band8care not shown inFIG. 1A.

An over cladding layer3is further formed on the surface of the under cladding layer1so as to cover the entire core2, portions of the electric circuit4other than the mounting pads4a, and portions of the bump positioning guides5and6other than hollow portions5aand6a. The over cladding layer3includes through holes3aformed in positions corresponding to over the mounting pads4a. The optical elements7and8are placed over the over cladding layer3. The optical elements7and8are flip-chip mounted using an electrically conductive paste, solder and the like as a bonding material (not shown), with the bumps7b,7c,8band8cof the optical elements7and8inserted through the through holes3aof the over cladding layer3into the hollow portions5aand6aof the bump positioning guides5and6in the U shape and in the shape of the rectangular frame as seen in plan view.

The under cladding layer1, the core2and the over cladding layer3constitute an optical waveguide section W0. A notch9of an inverted V shape is formed in a portion of the optical waveguide section W0corresponding to each of the opposite end portions of the core2. One side surface defined by the inverted V-shaped notch9on the core2side is formed as an inclined surface inclined at 45 degrees to the axial direction of the core2. An end portion of the core2lying at the inclined surface serves as a light reflecting surface2a. The light reflecting surfaces2aare formed under a light-emitting section7aprovided in the light-emitting element7and under a light-receiving section8aprovided in the light-receiving element8.

In the opto-electric hybrid module, light L is propagated in a manner to be described below. As shown inFIG. 1B, the light L emitted downwardly from the light-emitting section7aof the light-emitting element7passes through the over cladding layer3, and thereafter enters a first end portion of the core2. Then, the light L is reflected from the light reflecting surface2aprovided in the first end portion of the core2, and travels through the interior of the core2in the axial direction. The light L is propagated to the light reflecting surface2aprovided in a second end portion of the core2. Subsequently, the light L is reflected upwardly from the light reflecting surface2aprovided in the second end portion of the core2. Then, the light L passes through and exits from the over cladding layer3, and is received by the light-receiving section8aof the light-receiving element8.

In this manner, the opto-electric hybrid module is configured to form the electric circuit4directly on the surface of the under cladding layer1where the core2is formed, without a substrate as in the conventional module therebetween, to thereby shorten the distance between the optical elements7and8and the end portions of the core2. This enables the light L emitted from the light-emitting section7aof the light-emitting element7to enter the first end portion of the core2before the light L is diffused so widely in the course of the above-mentioned propagation of the light L. Similarly, this also enables the light L exiting from the second end portion of the core2to be received by the light-receiving section8aof the light-receiving element8before the light L is diffused so widely. In other words, the opto-electric hybrid module according to the first embodiment is significantly improved in the efficiency of light coupling between the optical elements7and8and the end portions of the core2, as compared with conventional modules.

The opto-electric hybrid module according to the first embodiment is manufactured, for example, in a manner to be described below.FIGS. 2A to 2C,3,4A,4B,5A,5B,6A and6B show a method of manufacturing the opto-electric hybrid module according to the first embodiment. Sectional views included among these figures are those taken along the line A-A ofFIG. 1A.

First, a base10of a flat shape (with reference toFIG. 2A) for use in the formation of the under cladding layer1is prepared. Examples of a material for the formation of the base10include glass, quartz, silicon, resin, metal and the like. The thickness of the base10is, for example, in the range of 20 μm to 5 mm.

Then, as shown inFIG. 2A, a varnish prepared by dissolving a photosensitive resin for the formation of the under cladding layer1such as a photosensitive epoxy resin and the like in a solvent is applied to a predetermined region of the surface of the base10. Thereafter, a heating treatment (at 50 to 120° C. for approximately 10 to 30 minutes) is performed, as required, to dry the varnish, thereby forming a photo sensitive resin layer1A for the formation of the under cladding layer1. Then, the photosensitive resin layer1A is exposed to irradiation light such as ultraviolet light and the like. This causes the photosensitive resin layer1A to be formed into the under cladding layer1. The thickness of the under cladding layer1is typically in the range of 1 to 50 μm.

Next, as shown inFIG. 2B, a photosensitive resin layer2A is formed on the surface of the under cladding layer1in a manner similar to the process for forming the photosensitive resin layer1A for the formation of the under cladding layer1. Then, the photosensitive resin layer2A is exposed to irradiation light through a photomask formed with an opening pattern corresponding to the pattern of the core2and the bump positioning guides5and6. Next, a heating treatment is performed. Thereafter, development is performed using a developing solution to dissolve away unexposed portions of the photosensitive resin layer2A, as shown inFIG. 2CandFIG. 3(which is a perspective view on an enlarged scale showing the left-hand end portion of the core2ofFIG. 2Cand its vicinity), thereby forming the remaining photosensitive resin layer2A into the pattern of the core2and the bump positioning guides5and6. In this manner, the single photolithographic process is performed to form the core2and the bump positioning guides5and6having a predetermined pattern at the same time, thereby locating the bump positioning guides5and6in predetermined positions relative to each end portion of the core2.

The arrangement of the bump positioning guides5and6is done in corresponding relation to the arrangement of the bumps7b,7c,8band8c(with reference toFIGS. 1A and 1B) of the optical elements7and8to be mounted. The bump positioning guides5and6are fence-like in the U shape and in the shape of the rectangular frame as seen in plan view. Application of the electrically conductive paste along these shapes allows the accurate positioning of the mounting pads4a(with reference toFIGS. 4A and 4B) made of the electrically conductive paste.

In the formation of the core2and the bump positioning guides5and6, the thickness (height) of the core2and the bump positioning guides5and6is typically in the range of 5 to 60 μm. The width of the core2is typically in the range of 5 to 60 μm. The dimensions of the bump positioning guides5and6are as follows. The bump positioning guides5in the U shape as seen in plan view are tailored to the size of the mounting pads4a. The outside dimensions of the bump positioning guides5are typically in the range of 80 to 200 μm by 80 to 200 μm, and the U-shaped line width thereof is typically in the range of 5 to 50 μm. The outside dimensions of the bump positioning guides6in the shape of the rectangular frame as seen in plan view are typically in the range of 50 to 120 μm by 50 to 120 μm, and the line width of the rectangular frame thereof is typically in the range of 5 to 20 μm.

A material for the formation of the core2and the bump positioning guides5and6includes, for example, a photosensitive resin similar to that of the under cladding layer1described above, and the material used herein has a refractive index greater than that of the material for the formation of the above-mentioned under cladding layer1and the over cladding layer3to be described below. The adjustment of such refractive indices may be made, for example, by adjusting the selection of the types of the materials for the formation of the under cladding layer1, the core2(including the bump positioning guides5and6) and the over cladding layer3, and the composition ratio thereof.

Next, as shown inFIGS. 4A and 4B, an electrically conductive paste such as a paste of copper, silver and the like is formed in a linear shape on predetermined portions of the surface of the under cladding layer1. Thereafter, a curing process (at 150 to 200° C. for approximately 30 minutes to one hour) is performed, as required, to form the electric circuit4. Part of the electric circuit4corresponding to the hollow portions5aand6aof the bump positioning guides5and6in the U shape and in the shape of the rectangular frame as seen in plan view serves as the mounting pads4afor connecting the bumps7b,7c,8band8c(with reference toFIGS. 1A and 1B) of the optical elements (the light-emitting element7and the light-receiving element8) thereto. The formation of the electrically conductive paste in the linear shape is carried out, for example, by using a screen printing method, a method employing a dispenser, an inkjet method, or the like. The thickness of the electric circuit4is typically in the range of 5 to 100 μm.

The bump positioning guides5and6function not only as positioning guides for use in the placement of the electrically conductive paste but also as a dam structure for stopping the electrically conductive paste placed in position from flowing out.

Next, as shown inFIG. 5A, a photosensitive resin layer3A for the formation of the over cladding layer3is formed on the surface of the under cladding layer1in a manner similar to the process for forming the photosensitive resin layer1A for the formation of the under cladding layer1(with reference toFIG. 2A) so as to cover the core2, the bump positioning guides5and6, and the electric circuit4. Then, the photosensitive resin layer3A is exposed to irradiation light through a photomask designed so that part of the photosensitive resin layer3A covering the mounting pads4ais not exposed to the irradiation light. Next, a heating treatment is performed. Thereafter, development is performed using a developing solution to dissolve away unexposed portions of the photosensitive resin layer3A, as shown inFIG. 5B, thereby forming the over cladding layer3in which the portions dissolved away correspond to the through holes3a. This uncovers the mounting pads4ain the through holes3aof the over cladding layer3. The thickness of the over cladding layer3is typically in the range of 10 to 2000 μm. An example of the material for the formation of the over cladding layer3used herein includes a photosensitive resin similar to that of the under cladding layer1.

Then, the base10is stripped from the back surface of the under cladding layer1. Thereafter, a dicing blade including a V-shaped edge having an included angle of 90 degrees or the like is used to cut the opposite end portions of the core2from the back surface side of the under cladding layer1, thereby forming the notches9of the inverted V shape in the positions corresponding to the opposite end portions, respectively, of the core2, as shown inFIG. 6A. This causes the portions of the core2corresponding to the inverted V shape to be formed into the respective light reflecting surfaces2ainclined at 45 degrees. The light reflecting surfaces2aare formed under the light-emitting section7aof the light-emitting element7to be mounted in the subsequent step and under the light-receiving section8aof the light-receiving element8to be mounted in the subsequent step.

Then, a mounting machine such as a flip chip bonder is used to insert the bumps7b,7c,8band8cof the light-emitting and light-receiving elements7and8through the through holes3aof the over cladding layer3into the hollow portions5aand6aof the bump positioning guides5and6in the U shape and in the shape of the rectangular frame as seen in plan view, as shown inFIG. 6B, and thereafter to connect the bumps7b,7c,8band8cto the mounting pads4a, thereby flip-chip mounting the light-emitting element7and the light-receiving element8by using the electrically conductive paste, solder and the like as a bonding material (not shown). In this manner, the intended opto-electric hybrid module (with reference toFIGS. 1A and 1B) is provided.

Examples of the light-emitting element7include a VCSEL (Vertical Cavity Surface Emitting Laser) and the like. Examples of the light-receiving element8include a PD (Photo Diode) and the like. The bumps7b,7c,8band8cof the optical elements7and8are classified into the two following types. The bumps7band8binserted in the bump positioning guides5in the U shape as seen in plan view are stud bumps for electrical connection. The bumps7cand8cinserted in the bump positioning guides6in the shape of the rectangular frame as seen in plan view are dummy bumps. It is preferable that the flip-chip mounting used herein is flip-chip mounting using ultrasonic waves from the viewpoint of preventing heat damages to the optical waveguide section W0.

For the mounting of the light-emitting element7and the light-receiving element8, the bump positioning guides5and6are formed by the single photolithographic process, as mentioned earlier. Thus, the bump positioning guides5and6are located in the predetermined positions relative to each end portion of the core2. Therefore, the high-accuracy positioning of the light-emitting element7and the light-receiving element8is achieved easily by inserting the bumps7b,7c,8band8cof the light-emitting and light-receiving elements7and8into the hollow portions5aand6aof the bump positioning guides5and6in the U shape and in the shape of the rectangular frame as seen in plan view. As a result, the productivity of the opto-electric hybrid module is improved.

FIG. 7Ais a plan view schematically showing an opto-electric hybrid module according to a second embodiment of the present invention.FIG. 7Bis a sectional view taken along the line B-B ofFIG. 7A. The opto-electric hybrid module according to the second embodiment is such that the over cladding layer3is formed so as to cover only the core2, with the electric circuit4and the bump positioning guides5and6uncovered. The optical elements7and8are placed over the under cladding layer1(although part of optical elements7and8is placed over the over cladding layer3). The optical elements7and8are flip-chip mounted, with the bumps7b,7c,8band8cof the optical elements7and8inserted in the hollow portions5aand6aof the bump positioning guides5and6in the U shape and in the shape of the rectangular frame as seen in plan view without the over cladding layer3therebetween. The remaining parts of the opto-electric hybrid module according to the second embodiment are similar to those of the opto-electric hybrid module according to the first embodiment shown inFIGS. 1A and 1B. Like reference numerals and characters are used to designate similar parts.

Like the first embodiment shown inFIGS. 1A and 1B, the second embodiment provides a short distance between the optical elements7and8and the end portions of the core2to improve the efficiency of light coupling between the optical elements7and8and the end portions of the core2. Further, the bump positioning guides5and6facilitates the high-accuracy positioning of the optical elements7and8. Thus, the second embodiment is excellent in the productivity of the opto-electric hybrid module.

In the first and second embodiments described above, the bump positioning guides5and6for the positioning of the bumps7b,7c,8band8cof the optical elements7and8are equal in number (in the first and second embodiments, four) to the bumps7b,7c,8band8cof the optical elements7and8. However, the number of bump positioning guides5and6may be less than the number of bumps7b,7c,8band8cof the optical elements7and8. Also, the bump positioning guides5and6need not be formed. It should be noted that, when the number of bump positioning guides5and6is less than the number of bumps7b,7c,8band8cof the optical elements7and8, the high-accuracy positioning of the optical elements7and8takes time, which in turn results in the poor productivity of the opto-electric hybrid module.

Next, an inventive example of the present invention will be described in conjunction with a conventional example. It should be noted that the present invention is not limited to the inventive example.

EXAMPLES

Inventive Example

Material for Formation of Under Cladding Layer and Over Cladding Layer

A material for formation of an under cladding layer and an over cladding layer was prepared by mixing 35 parts by weight of bisphenoxyethanol fluorene glycidyl ether (component A), 40 parts by weight of 3′,4′-epoxycyclohexyl methyl-3,4-epoxycyclohexane carboxylate which is an alicyclic epoxy resin (CELLOXIDE 2021P available from Daicel Chemical Industries, Ltd.) (component B), 25 parts by weight of (3′4′-epoxycyclohexane)methyl-3′,4′-epoxycyclohexyl-carboxylate (CELLOXIDE 2081 available from Daicel Chemical Industries, Ltd.) (component C), and 2 parts by weight of a 50% by weight propione carbonate solution of 4,4′-bis[di(β-hydroxyethoxy) phenylsulfinio]phenyl-sulfide-bis-hexafluoroantimonate (component D).

Material for Formation of Core and Bump Positioning Guides

A material for formation of a core and bump positioning guides was prepared by dissolving 70 parts by weight of the aforementioned component A, 30 parts by weight of 1,3,3-tris{4-[2-(3-oxetanyl)]butoxyphenyl}butane and one part by weight of the aforementioned component D in ethyl lactate.

Manufacture of Opto-Electric Hybrid Module

The material for the formation of the under cladding layer was applied to a surface of a polyethylene terephthalate (PET) film (having a thickness of 188 μm) with an applicator. Thereafter, the applied material was exposed to ultraviolet light irradiation (having a wavelength of 365 nm) at a dose of 2000 mJ/cm2. This formed the under cladding layer (having a thickness of 25 μm), with reference toFIG. 2A.

Then, the material for the formation of the core and the bump positioning guides was applied to a surface of the under cladding layer with an applicator. Thereafter, a drying process was performed at 100° C. for 15 minutes to form a photosensitive resin layer having a future core region and future bump positioning guide regions, with reference toFIG. 2B. Next, a synthetic quartz chrome mask (photomask) formed with an opening pattern identical in shape with the pattern of the core and the bump positioning guides was placed over the photosensitive resin layer. Then, the photosensitive resin layer was exposed to ultraviolet light irradiation (having a wavelength of 365 nm) directed from over the mask at a dose of 4000 mJ/cm2by a proximity exposure method. Thereafter, a heating treatment was performed at 80° C. for 15 minutes. Next, development was performed using an aqueous solution of γ-butyrolactone to dissolve away unexposed portions of the photosensitive resin layer. Thereafter, a heating treatment was performed at 120° C. for 30 minutes. This formed the core (having a thickness of 50 μm, and a width of 50 μm) and the bump positioning guides (having a thickness of 50 μm, and U-shaped and rectangular frame-shaped line width of 15 μm), with reference toFIG. 2C.

Next, an electrically conductive silver paste was formed in a linear shape on predetermined portions of the surface of the under cladding layer by screen printing. Thereafter, a curing process (at 150° C. for one hour) was performed on the electrically conductive silver paste to form an electric circuit, with reference toFIGS. 4A and 4B. Part of the electric circuit corresponding to hollow portions of the bump positioning guides in the U shape and in the shape of the rectangular frame as seen in plan view was used as mounting pads.

Next, the material for the formation of the over cladding layer was applied to the surface of the under cladding layer with an applicator so as to cover the core, the bump positioning guides and the electric circuit, thereby forming a photosensitive resin layer, with reference toFIG. 5A. Thereafter, the photosensitive resin layer was exposed to ultraviolet light irradiation (having a wavelength of 365 nm) at a dose of 2000 mJ/cm2through a photomask designed so that part of the photosensitive resin layer covering the mounting pads was not exposed to the irradiation. Thereafter, a heating treatment was performed at 120° C. for 15 minutes. Next, development was performed using an aqueous solution of γ-butyrolactone to dissolve away unexposed portions of the photosensitive resin layer. Thereafter, a heating treatment was performed at 120° C. for 30 minutes. This formed the over cladding layer in which the portions dissolved away corresponded to through holes, to uncover the mounting pads in the through holes, with reference toFIG. 5B. At this time, the total thickness of the under cladding layer, the core, and the over cladding layer was 100 μm.

Then, the PET film was stripped from the back surface of the under cladding layer. Thereafter, a dicing blade including a V-shaped edge having an included angle of 90 degrees was used to cut opposite end portions of the core from the back surface side of the under cladding layer, thereby causing the opposite end portions of the core to be formed into respective light reflecting surfaces inclined at 45 degrees. The light reflecting surfaces were formed under a light-emitting section of a light-emitting element to be mounted in the next step and under a light-receiving section of a light-receiving element to be mounted in the next step, with reference toFIG. 6A.

Then, a flip chip bonder was used to insert bumps of the light-emitting and light-receiving elements through the through holes of the over cladding layer into the hollow portions of the bump positioning guides in the U shape and in the shape of the rectangular frame as seen in plan view and thereafter to connect the bumps to the mounting pads, thereby flip-chip mounting the light-emitting and light-receiving elements by using the electrically conductive silver paste as a bonding material, with reference toFIG. 6B. A VCSEL (available from U-L-M photonics GmbH) was used as the light-emitting element, and a PD (a photodiode available from Hamamatsu Photonics K.K.) was used as the light-receiving element. In this manner, an opto-electric hybrid module was manufactured.

Conventional Example

An electric circuit section in which an electric circuit was formed on a surface of a substrate, and an optical waveguide section in which an under cladding layer, a core and an over cladding layer were disposed in the order named (and in which the opposite end portions of the core were formed into respective light reflecting surfaces inclined at 45 degrees, as in Inventive Example) were produced individually. The back surface of the substrate of the electric circuit section was bonded to the front surface of the over cladding layer with an adhesive. A light-emitting element (VCSEL) and a light-receiving element (PD) were mounted on portions of the electric circuit section corresponding to the opposite end portions, respectively, of the core. In this manner, an opto-electric hybrid module was manufactured, with reference toFIG. 8.

Light Propagation Test

Ten opto-electric hybrid modules according to Inventive Example and ten opto-electric hybrid modules according to Conventional Example were manufactured. A driving current of 5 mA was fed through the light-emitting element in each of the opto-electric hybrid modules to cause the light-emitting element to emit light. The light was received by the light-receiving element through the core in each of the opto-electric hybrid modules. Then, a voltage developed across the light-receiving element was measured with a tester. As a result, the voltage measured in the range of 1.0 to 1.3 V in the opto-electric hybrid modules according to Inventive Example. On the other hand, the voltage measured in the range of 0.5 to 0.7 V in the opto-electric hybrid modules according to Conventional Example.

This result shows that the efficiency of light coupling between the optical elements and the end portions of the core is much higher in the opto-electric hybrid modules according to Inventive Example than in the opto-electric hybrid modules according to Conventional Example.

Industrial Applicability

The opto-electric hybrid module according to the present invention may be used for information communications devices and signal processors for transmitting and processing digital signals representing sound, images and the like at high speeds.

Although a specific form of embodiment of the instant invention has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as a limitation to the scope of the instant invention. It is contemplated that various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the invention which is to be determined by the following claims.