Method of manufacturing an optical-electrical wiring board

Abstract: Disclosed is an optical-electrical wiring board (10), comprising an electrical wiring board (11) having a through-hole formed therein and an optical wiring layer (12) laminated on the board (11) and including a core (120) and a clad (121) surrounding the core (120). The electrical wiring board (11) includes an electrical wiring formed on one surface of the board (11) and pads (15, 17) on which optical parts are mounted. The pads (15, 17) are electrically connected to the electrical wiring and arranged on one surface of the electrical wiring board (11) in the vicinity of a through-hole. The core (120) includes a horizontal waveguide (120a) for propagating the light beam in a horizontal direction along the electrical wiring board (11) and a vertical waveguide having a part arranged inside the through-hole and crossing the horizontal waveguide (120a). The vertical waveguide propagates the light beam in a direction perpendicular to the electrical wiring board (11).

Description: Background Art In recent years, the clock frequency of a CPU tends to be more and more increased in an attempt to manufacture an electronic computer capable of achieving an arithmetic processing more rapidly. Nowadays, a CPU having a clock frequency of 1 GHz order has come to be put on the market. In general, the signal speed between elements outside an electric element is increased with increases in the clock frequency inside the electric element. Therefore, a portion in which a high frequency current flows is present in the electric wiring made of copper on the printed circuit board included in an electronic computer. As a result, a malfunction is brought about by the noise generation. Also, an electromagnetic wave is generated so as to give an adverse effect to the surrounding environment. In order to overcome the problems described above, an optical wiring utilizing an optical fiber or an optical waveguide is substituted for a part of the electric wiring made of copper on the printed circuit board so as to utilize the optical signal in place of the electric signal. The optical signal is utilized because, in the case of the optical signal, it is possible to suppress the generation of the noise and the electromagnetic wave. However, an electric wiring is formed on the electric wiring board. What should be noted is that the electric wiring makes the surface of the electric wiring board highly rough. The optical wiring tends to be greatly affected by the surface roughness, with the result that the propagation loss of the optical signal is considered to be increased. On the other hand, it is desirable for the optical-electrical wiring board, in which an optical wiring is partly substituted for the electrical wiring so as to propagate both the electric signal and the optical signal, to be mounted at a high density or to be miniaturized in view of the object of the use of the optical-electrical wiring board. Document EP 1 041 410 describes an optical-electrical wiring board and a method of its manufacturing. An optical wiring layer including core and clod of a waveguide is laminated on a surface of an electrical wiring board. A hole is formed through the electrical wiring board and parts of the optical wiring layer and extends through the electrical wiring board. The hole is filled with a cladding material. A second hole is formed in the centre of the first hole and with a diameter smaller than the first hole and extends through the electrical wiring layer and through parts of the optical wiring layer up to the core and clodding of the optical wiring layer. The second hole is filled with a core material. A mirror is provided of the intersection of the cores formed in the hole and present in the optical wiring layer. Disclosure of Invention According to a first aspect of the present invention, there is provided a method of manufacturing an optical-electrical wiring board, comprising the step of forming a first through-hole in an electrical wiring board having an electrical wiring formed on a first surface; the step of filling the first through-hole with a clad; the step of bonding an optical wiring layer including a first core and a clad surrounding the first core to a second surface opposite to the first surface of the electrical wiring board; the step of forming a second through-hole having an inner diameter smaller than the inner diameter of the first through-hole and extending through the electrical wiring board, the first core, and the clad surrounding the first core in a central portion of the first through-hole; the step of filling the second through-hole with a second core so as to form a waveguide extending in a direction perpendicular to the electrical wiring board; and the step of forming a mirror reflecting the light propagated through one core toward the other core in a portion where the first core and the second core are allowed to cross each other. According to a second aspect of the present invention, there is provided a method of manufacturing an optical-electrical wiring board, comprising the step of forming a first through-hole in an electrical wiring board having an electrical wiring formed on a first surface; the step of filling the first through-hole with a clad; the step of forming an optical wiring layer including a first core and a clad surrounding the first core on a second surface opposite to the first surface of the electrical wiring board; the step of forming a second through-hole having an inner diameter smaller than the inner diameter of the first through-hole and extending through the electrical wiring board, the first core and the first clad surrounding the first core in a central portion of the first through-hole; the step of filling the second through-hole with a second core so as to form a waveguide extending in a direction perpendicular to the electrical wiring board; and the step of forming a mirror reflecting the light propagated through one core toward the other core in a potion where the first core and the second core are allowed to cross each other. Further, according to a third aspect of the present invention, there is provided a method of manufacturing an optical-electrical wiring board according to the fourteenth or fifteenth aspect of the present invention, characterized in that the method further comprises the step of forming a light-collecting lens in one edge of the second core on the side of the first surface. According to the particular construction defined above, it is possible to realize an optical-electrical wiring board and a mounted board capable of a high density mounting or miniaturization and permitting an optical signal to be propagated at a high efficiency and to realize a method of manufacturing an optical-electrical wiring board. Various stages of the inventions are included in the embodiments of the present invention, and it is possible to extract various combinations of a plurality of constituents disclosed herein. For example, where a combination is extracted by omitting several constituents from all the constituents disclosed in the embodiment of the present invention, the omitted portion is supplemented by the known technology in working the extracted combination. Brief Description of Drawings FIG. 1 shows an optical-electrical wiring board 10 as viewed from the mounted side of an optical part; FIG. 2 shows the optical-electrical wiring board 10 as viewed from the side opposite to the mounted side of an optical part; FIG. 3 is a cross sectional view along the line C-C (core pattern) shown in FIG. 1 or 2; FIG. 4 exemplifies the optical-electrical wiring board 10 that facilitates the alignment of the optical axis with a light-receiving element that is mounted; FIG. 5 exemplifies the optical-electrical wiring board 10 that facilitates the alignment of the optical axis with a light-receiving element that is mounted; FIGS. 6A to 6H are cross sectional views collectively showing the steps of a method of manufacturing the optical-electrical wiring board 10; FIGS. 7A to 7F are cross sectional views collectively showing the steps of a method of manufacturing the optical-electrical wiring board 10; FIG. 8 is a cross sectional view showing a mounted board in which a lead 501 of a light-receiving element 50 is soldered to the optical-electrical wiring board 10; FIG. 9 is a cross sectional view showing a mounted board in which a lead 501 of a light-receiving element 50 is soldered to the optical-electrical wiring board 10 provided with a light collecting lens 13; FIG. 10 is a cross sectional view showing a mounted board in which a lead 521 of a light-emitting element 52 is soldered to the optical-electrical wiring board 10 provided with a tapered optical waveguide 121c; FIG. 11 is a cross sectional view showing a modification of the optical-electrical wiring board 10. Best Mode for Carrying Out of the Invention The best mode of working the present invention will now be described with reference to the accompanying drawings. In the following description, the constituents of the invention having substantially the same function and construction are denoted by the same reference numerals, and an overlapping description is made in only the required portion. 1-1: Optical-Electrical Wiring Board An important point of the optical-electrical wiring board according to a first embodiment of the present invention resides in the technical idea that a board provided with an electrical wiring and having an optical part or an electrical part mounted thereon is laminated on an optical wiring layer having an optical waveguide for propagating the light in the direction along a layer and another optical waveguide for propagating the light in a direction perpendicular to said layer. FIG. 1 shows an optical-electrical wiring board 10 as viewed from the mounted side of an optical part. On the other hand. FIG. 2 shows the optical-electrical wiring board 10 as viewed from the side opposite the mounted side of the optical part. FIG. 3 is a cross sectional view along the line C-C shown in FIG. 1 or 2. As schematically shown in FIG. 3, the optical-electrical wiring board 10 comprises an optical wiring layer 12 and an electrical wiring board 11 laminated on the optical wiring layer 12. The optical-electrical wiring board 10 and the electrical wiring board 11 forms an electrical wiring system and the optical wiring layer 12 forms an optical wiring system. Also, as described herein later, an optical part such as a laser diode or a photodiode and an electrical part such as an IC are mounted on the electrical wiring board 11 of the optical-electrical wiring board 10 (see FIGS. 8, 9, and 10). The construction of the electrical wiring board 11 and the optical wiring layer 12 will now be described in detail in the order mentioned with reference to FIGS. 1, 2 and 3. The electrical wiring board 11 is a board having an electrical wiring (not shown) formed on one surface. It is possible for the electrical wiring board 11 to be an insulating board of a single layer structure or a multi-layered wiring board in which an electrical wiring and an insulating layer are alternately laminated one upon the other. Also, it is possible for the electrical wiring board 11 to be formed of an insulating board prepared by impregnating a glass cloth with a resin, to be formed of a polyimide film or to be formed of a ceramic board. Pads 14, 15, 16, 17 for mounting optical parts and a pad (not shown) for mounting an electrical part are formed on that surface of the electrical wiring board on which an electric wiring is formed. Each of these pads is electrically connected to the electric wiring and serves to electrically connect the electric wiring to the optical part or the electric part formed on the electric wiring board 11. The number of pads is determined by the number of terminals of the optical parts, etc. and the number of parts mounted on the electric wiring board. The number of parts need not be limited to four as shown in FIG. 1 and may be optional. Also, the clearance between the adjacent pads may be optional so as to conform with the clearance between the adjacent terminals of the optical parts, etc., mounted on the electrical wiring board 11. Further, it is possible for the pad to be shaped variously. In other words, the shape of the pad is determined based on the shape of the connecting terminal of the optical part mounted on the electric wiring board 11. Needless to say, the pad need not be shaped circular as shown in FIG. 1 and may be shaped variously. In general, it is considered reasonable to understand that the pad is shaped to conform with the shape of the solder ball or the metal lead used for the connection to the optical part. The board 11 is provided with a hole for forming a vertical waveguide 120b referred to herein later and with a hole for forming a vertical clad 121b referred to herein later. Also, where the board 11 includes an electric wiring formed of a plurality of layers, it is possible to arrange a conductive layer between the adjacent layers of the electric wiring for improving the electrical conductivity. The optical wiring layer 12 is laminated on the other surface of the electric wiring board 11, and includes a core 120 used as an optical waveguide for propagating the optical signal, a clad 121 having a refractive index lower than that of the core 120 and having the core 120 buried therein, and a mirror 123 for reflecting the light propagated within the core 120. The core 120 includes a horizontal waveguide 120a for propagating the light along the electric wiring board 11 and a vertical waveguide 120b for propagating the light in the laminating direction of the electric wiring board 11 and the optical wiring layer 12, i.e., in a direction perpendicular to the electric wiring board 11. How to form these two waveguides will be described herein later. For forming the core 120, it is possible to select a resin having a refractive index suitable for the wavelength of the light to be guided. For example, it is possible to use a fluorine-containing polyimide resin or a fluorine-containing epoxy resin for forming the core 120. The clad 121 includes a horizontal clad 121a, in which is buried the horizontal waveguide 120a of the core 120, and a vertical clad 121b, in which is buried the vertical waveguide 120b of the core 120. As described previously, the clad 121 has a refractive index lower than that of the core 120. It follows that the light incident on a part of the core 120 is repeatedly reflected at the boundary plane between the core 120 and the clad 121 so as to be propagated within the core 120. It is possible to use, for example, a fluorine-containing polyimide series resin or a fluorine-containing epoxy series resin for forming the clad 121. Incidentally, the angle  made between the horizontal clad 121a and the vertical clad 121b (i.e., the angle made between the horizontal waveguide 120a and the vertical waveguide 120b) is determined in accordance with the desired optical propagating route. In the first embodiment and second embodiment described herein later, the angle  noted above is set at 90° as an example. Also, one end of each of the vertical waveguide 120b and the vertical clad 121b is exposed to that surface of the board 11 on which is mounted the optical part, etc., as shown in FIG. 1. The mirror 123 is formed at the portion where the horizontal waveguide 120a crosses the vertical waveguide 120b and acts as a reflecting mirror for reflecting the light incident on one waveguide toward the other waveguide. It follows that the angle of the mirror 123 is dependent on the angle made between the horizontal waveguide 120a and the vertical reflecting mirror 120b and is formed at an angle suitable for the light reflection between the horizontal waveguide 120a and the vertical waveguide 120b. For example, in the optical-electrical wiring board 10 shown in FIG. 3, the horizontal waveguide 120a and the vertical waveguide 120b are formed to make an angle of 90° and, thus, the mirror 123 is formed to make an angle of 45° with the axis of each of these waveguides. The mirror 123 is formed by a dicing process having a blade of 90° or by an oblique etching achieved by a dry etching such as RIE. The specific forming method of the mirror 123 will be described herein later. It should be noted, however, that, since the mirror 123 is formed on the basis of a reference position in which is arranged an optical wiring, the positional accuracy with the core of the optical wiring is rendered very high. Incidentally, the interface of the mirror 123, i.e., the surface on the opposite side of the core 120, is brought into contact with a resin having a refractive index lower than that of the core 120 or with the air. Also, it is possible to form a metal thin film on the interface noted above. The alignment of the optical axis between the optical part mounted on the optical-electrical wiring board 10 and the optical-electrical wiring board 10 will now be described. An optical part or an electrical part is mounted on the optical-electrical wiring board 10 shown in FIG. 3. For example, FIG. 8 shows a mounted board in which a light-receiving element 50 is mounted on the optical-electrical wiring board 10. As shown in FIG. 8 the light beam L incident on one end of the horizontal waveguide 120a is reflected by the mirror 123 into the vertical waveguide 120b. Then, the light beam L propagated through the vertical waveguide 120b is incident on the light-receiving surface of the light-receiving element 50. In the mounted board in which an optical information is exchanged between the optical part and the optical-electrical wiring board 10 by the particular construction described above, it is important to align the optical axis between the optical part and the optical-electrical wiring board. In order to facilitate the alignment of the optical axis between the optical part and the optical-electrical wiring board 10, it may be desirable to employ, for example, a modification of the construction described in the following. FIG. 4 shows an example that is considered to facilitate the alignment of the optical axis between the optical-electrical wiring board 10 and the light-receiving element mounted on the optical-electrical wiring board 10. This example is featured in that a light collecting lens 13 is mounted on one end of the vertical waveguide 120b on the side of the mounting surface of the optical part. In the optical-electrical wiring board 10 shown in FIG. 4, the light propagated through the vertical waveguide 120b is collected by the lens 13 (see FIG. 9) so as to make it possible to achieve the alignment of the optical axis with a high accuracy. On the other hand, it is possible to expect the effect of the optical axis alignment also in the case where a light-emitting element is mounted on the optical-electrical wiring board 10 shown in FIG. 4. To be more specific, the laser beam emitted from the light-emitting element is collected by the light collecting lens 13 on the optical axis of the vertical waveguide 120b. It follows that the alignment of the optical axis can be achieved with a high accuracy even in the case where, for example, the laser beam deviates from the optical axis of the vertical waveguide 120b incident on the light collecting lens 13. FIG. 5 shows an example that permits facilitating the alignment of the optical axis between the optical-electrical wiring board 10 and a light-emitting element mounted on the optical-electrical wiring board 10. The optical-electrical wiring board 10 shown in FIG. 5 is featured in that the vertical waveguide 120c is tapered such that the diameter of the vertical waveguide 120c is gradually diminished from the mounting surface of the optical part toward the mirror 123. In the case of the tapered vertical waveguide 120c of the particular shape, the light propagated through the waveguide 120c is collected while running from the mounting surface of the optical part toward the mirror 123 (see FIG. 10) so as to make it possible to achieve the alignment of the optical axis with a higher accuracy. (Manufacturing Method 1 of Optical-Electrical Wiring Board) A first manufacturing method of the optical-electrical wiring board 10 according to the first embodiment of the present invention will now be described with reference to FIGS. 6A to 6H, with the emphasis placed on the core 120 (i.e., the horizontal waveguide 120a and the vertical waveguide 120b) and the clad 121 (i.e., the horizontal clad 121a and the vertical clad 121b). FIGS. 6A to 6H are cross sectional views showing successively the steps of a manufacturing method of the optical-electrical wiring board 10. In the first step, as shown in FIG. 6A, a through-hole 30 having a diameter of 100 µm is formed by a laser beam irradiation in the electric wiring board 11 formed of a polyimide film having a thickness of 125 µm. As shown in the drawing, an electric wiring and pads 14, 15, 16, 17 (pads 14, 16 being not shown in FIG. 1) are formed on the electric wiring board 11. Incidentally, FIG. 6A shows that the electric wiring board 11 is divided by the through-hole 30. However, this is simply intended to facilitate the description. Needless to say, the through-hole 30 is simply a hole formed to extend through the electrical wiring board 11 as shown in, for example, FIG. 1. This is also the case with each of FIGS. 7A and 8A referred to herein later. In the next step, the through-hole 30 made in the electrical wiring board 11 is filled with the vertical clad 121b made of a fluorine-containing epoxy resin adjusted to have a refractive index of, for example, 1.52, followed by curing the vertical clad 121b at 200°C, as shown in FIG. 6B. Then, that surface of the electrical wiring board 11 on which the pads are not formed is coated with a fluorine-containing epoxy resin adjusted to have a refractive index of 1.52, as shown in FIG. 6C, followed by curing the coated fluorine-base epoxy resin at 200°C so as to form a part of the horizontal clad 121a having a thickness of, for example, 20 µm. Then, the surface of a part of the horizontal clad 121a thus formed is coated with a fluorine-containing epoxy resin adjusted to have a refractive index of 1.53, followed by curing the coated fluorine-containing epoxy resin layer at 200°C, thereby forming the horizontal waveguide 120a having a thickness of 8 µm by the ordinary method of a dry etching, as shown in FIG. 6D. In this case; the horizontal waveguide 120a has a width of, for example, 8 µm. In the next step, the horizontal waveguide 120a is coated with a fluorine-containing epoxy resin adjusted to have a refractive index of 1.52, as shown in FIG. 6E. Then, the coated fluorine-containing epoxy resin is cured so as to set the thickness of the fluorine-containing epoxy resin layer at 20 µm, thereby forming the remaining part of the horizontal clad 121a. The optical wiring layer 12 is formed by the steps described above. In the next step, a through-hole 32 having an inner diameter smaller than that of the through-hole 30 is formed in the central portion of the through-hole 30 filled with the vertical clad 121b, as shown in FIG. 6F. As a result, the side surface of the through-hole 32 is covered with the vertical clad 121b. Incidentally, in the case of forming the tapered optical waveguide 121c shown in FIG. 5, the diameter of the laser beam is diminished in the optical system in the laser processing step shown in FIG. 6F, and the laser beam having the diminished diameter is applied from the mounting side of the optical part or the like so as to make it possible to form the through-hole 32 conforming with the shape of the vertical clad 121c shown in FIG. 5. In the next step, the through-hole 32 of the electrical wiring board 11 is filled with a fluorine-containing epoxy resin, which is equal to the material of the horizontal waveguide 120a, followed by curing the fluorine-containing epoxy resin at 200°C so as to form the vertical waveguide 120b. Then, the mirror 123 having a surface inclined by 45° relative to the surface of the electrical wiring board 11 is formed by the dicing process with a blade having an angle of 90° or by an oblique etching with a RIE at the portion in which the horizontal waveguide 120a crosses the vertical waveguide 120b, as shown in FIG. 6H. It is possible for the mirror 123 to be a mirror having a metal reflecting film formed by a sputtering method or by a vapor deposition. The mirror 123 is formed by using as a reference an alignment mark (not shown) formed at the bonding surface between the electrical wiring board 11 and the optical wiring layer 12. Incidentally, the lens 13 shown in FIG. 4 can be formed easily by forming a rectangular pattern of a photosensitive acrylic resin having a low Tg or a low melting point and having a refractive index equal to that of the vertical waveguide 120b on the exposed surface of an optical through-hole, followed by melting the rectangular pattern of the acrylic resin at 200°C. (Manufacturing Method 2 of Optical-Electrical Wiring Board) A second manufacturing method of the optical-electrical wiring board 10 according to the first embodiment of the present invention will now be described with reference to FIGS. 7A to 7F, with the emphasis placed on the core 120 and the clad 121 as in the first manufacturing method described above. The second manufacturing method widely differs from the first manufacturing method in that, in place of forming the optical wiring layer 12 directly on the electrical wiring board 11, the optical wiring layer 12 and the electrical wiring board 11, which are prepared separately, are bonded to each other in the second manufacturing method. FIGS. 7A to 7F are cross sectional views collectively showing successively the steps of a method of manufacturing the optical-electrical wiring board 10. In the second manufacturing method, a glass/polyimide multi-layered substrate having an electric wiring (not shown) and pads 14, 15, 16, 17 (pads 14 and 16 being not shown in the drawing) formed on the surface and provided with the through-hole 30 having a diameter of 300 µm as shown in FIG. 7A is used as the electrical wiring board 11. As shown in FIG. 7B, the through-hole 30 of the electrical wiring board 30 is filled with a fluorine-containing epoxy resin having the refractive index adjusted at 1.52, followed by curing the fluorine-containing epoxy resin at 200°C so as to obtain the vertical clad 121b. In the next step, the optical wiring layer 12 in the form of a film is bonded to the electrical wiring board 11 with an adhesive (not shown) interposed therebetween, as shown in FIG. 7C. The optical wiring layer 11 is formed in advance by the ordinary method on a silicon wafer prepared separately. Also, the core 120 included in the optical wiring layer 12 is formed of a fluorine-containing epoxy resin having a refractive index of 1.53. On the other hand, the clad 121 included in the optical wiring layer 12 is formed of a fluorine-containing resin having a refractive index of 1.52. A cross section of the core 120 has a size of, for example, 40 µm X 40 µm. It should also be noted that the adhesive layer used for the bonding of the optical wiring layer 12 and the electrical wiring board 11 has a refractive index equal to that of the vertical clad 121b filling the through-hole 30. In the next step, as shown in FIG. 7D, the through-hole 32 having an inner diameter smaller than that of the through-hole 30 is formed by using an excimer laser in the central portion of the through-hole 30. As a result, the side surface of the through-hole 32 is covered with the vertical clad 121b. Incidentally, in the case of forming the tapered optical waveguide 121c shown in FIG. 5, the diameter of the laser beam is diminished in the optical system in the laser processing step shown in FIG. 7D, and the laser beam having the diminished diameter is applied from the mounting side of the optical part or the like, as described previously in conjunction with the first manufacturing method, so as to make it possible to form the through-hole 32 conforming with the shape of the vertical clad 121c shown in FIG. 5. In the next step, the through-hole 32 of the electrical wiring board 11 is filled with a fluorine-containing epoxy resin, which is the same as the material of the horizontal waveguide 120a, followed by curing the fluorine-containing epoxy resin at 200°C so as to form the vertical waveguide 120b. Then, the mirror 123 having a surface inclined by 45° relative to the surface of the electrical wiring board 11 is formed by the dicing process with a blade having an angle of 90° or by an oblique etching with a RIE at the portion in which the horizontal waveguide 120a crosses the vertical waveguide 120b, as shown in FIG. 7F. It is possible for the mirror 123 to be a mirror having a metal reflecting film formed by a sputtering method or by a vapor deposition. The mirror 123 is formed by using as a reference an alignment mark (not shown) formed on the electrical wiring board 11 as in the first manufacturing method. Incidentally, the lens shown in FIG. 4 can be formed easily by forming a rectangular pattern of a photosensitive acrylic resin having a low Tg or a low melting point and having a refractive index equal to that of the vertical waveguide 120b on the exposed surface of an optical through-hole, followed by melting the rectangular pattern of the acrylic resin at 200°C. (Manufacturing Method of Mounted Board) A method of manufacturing a mounted board, in which an optical part, etc. is mounted on the optical-electrical wiring board 10, will now be described. FIG. 8 shows a mounted board, in which a lead 501 of a light-receiving element is soldered to the optical-electrical wiring board. As shown in FIG. 8, the optical part and the electrical part are electrically connected to the optical-electrical wiring board 10 by the solder bonding between the pad and the metal lead 501 of each part that is performed by a solder 55. Also, where the optical part or the like does not have a metal lead, the electrical connection is achieved by a solder ball or the like. FIG. 9 shows a mounted board, in which the lead 501 of a light-receiving element 50 is soldered to the optical-electrical wiring board 10 provided with a light-collecting lens 13. As shown in FIG. 9, the laser beam propagated through the horizontal waveguide 120a of the optical wiring layer 12 is reflected by the mirror 123. Then, the laser beam L is propagated through the vertical waveguide 120b so as to arrive at the light-receiving surface 500 efficiently through the lens 13. FIG. 10 shows a mounted board; in which a lead 521 of a light-emitting element 52 is soldered to the optical-electrical wiring board 10 provided with a tapered optical waveguide 120. As shown in FIG. 10, the laser beam L emitted from the light emitting surface 520 of the light-emitting element 52 is propagated through the vertical waveguide 120b and, then, reflected by the mirror 123 so as to be propagated through the horizontal waveguide 120a. It should be noted that the core diameter of the vertical waveguide 120b is gradually diminished from the side of the mounting surface of the electric wiring board 11 toward the mirror 123 as described previously, with the result that the optical axis of the light-emitting surface can be aligned easily with the optical axis of the vertical waveguide 120b. The particular construction described above makes it possible to obtain prominent effects as described below. First of all, since the optical wiring layer is mounted on the board having an electric wiring, it is possible to achieve a high density mounting and to achieve miniaturization. It is also possible to align easily the optical axis of the optical part with the optical axis of the vertical waveguide by forming a lens at one end of the vertical waveguide or by forming the vertical waveguide in a tapered shape. As a result, it is possible to automatically mount simultaneously both the optical part and the electric part. It should also be noted that the optical wiring layer 12 is mounted on a flat surface of the electric wiring board, i.e., to the surface on which the electric wiring is not formed. Therefore, it is possible for the optical wiring layer 12 to propagate the optical signal with a low attenuation rate without being affected by the irregularity given by, for example, the electric wiring. It should also be noted that the mirror 123 is formed after the optical wiring layer 12 is bonded to the electric wiring board 11. Also, the mirror 123 is formed with the alignment mark of the electric wiring board used as a reference. It follows that it is possible to realize the mirror formation with a high accuracy. The optical-electrical wiring board of the present invention is constructed such that the electrical wiring board is laminated on the optical wiring layer 12 and, then, the optical part or the like is mounted on the electric wiring board 11. It follows that it is possible to form all of the electric wiring, the pad, and the connecting means for connecting the electric wiring to the pad on one surface of the electric wiring board 11 so as to simplify the construction of the apparatus and to simplify the manufacturing process of the apparatus. What should also be noted is that the vertical waveguide 120b and the vertical clad 121b collectively form the optical wiring extending from one surface to the other surface of the electric wiring substrate 11. It follows that the optical signal is propagated through the core 120, i.e., the vertical waveguide 120b, to reach the surface of the electric wiring board 11, and, then, is incident on the optical part. Also, the optical signal is propagated through the core 120 immediately after the optical signal is emitted from the optical part. As a result, it is possible to lower the attenuation rate of the light so as to make it possible to perform an efficient exchange of the optical signal. In addition, each of the vertical waveguide 120b and the vertical clad 121b reflects the external light on the surface at one end, thereby performing the function of removing the noise. The construction described above permits producing prominent effects as described below. First of all, since it is possible to form the optical wiring layer on that surface of the electrical wiring board on which the electrical wiring is not formed, the optical wiring layer is rendered smooth so as to suppress the attenuation of the optical signal. It should also be noted that the electrical wiring (or pad) and the optical wiring layer are formed on different surfaces of the electrical wiring board. What should be noted is that, since the optical wiring layer is formed on the lower surface of the electrical wiring board in the mounting step (soldering step) of the optical part and the electrical part to the electrical wiring, the optical wiring layer is less affected thermally. It should also be noted that the mirror 123 is formed in the present invention after the optical wiring layer 62 is bonded to the electrical wiring board 11. Also, an alignment mark of the electrical wiring board 11 is used as a reference in forming the mirror 123. It follows that it is possible to form the mirror 123 with a high accuracy. The optical-electrical wiring board of the present invention is constructed such that the electrical wiring board 11 is laminated on the optical wiring layer 62, and the optical part, etc. are mounted on the electrical wiring board 11. It follows that it is possible to mount all of the electrical wiring, the pads, and the connecting means for connecting the electrical wiring to the pads on one surface of the electrical wiring board 11 so as to make it possible to simplify the apparatus and to simplify the manufacture of the apparatus. The present invention can be modified in various fashions within the technical scope of the present invention as exemplified in items (1) and (2) given below. (1) In FIGS. 5 and 10, the tapered vertical waveguide 120b is formed to extend from that surface of the electrical wiring board on which the optical part is mounted onward the mirror 123. The particular construction assumes that the light-emitting element 52 is mounted on the optical-electrical wiring board. On the other hand, where the light-receiving element 50 is mounted on the optical-electrical wiring board 10, it is conceivable to employ the optical-electrical wiring board 10 including the tapered vertical waveguide 120b formed to extend from that side of the electrical wiring board on which the optical wiring layer 12 is bonded toward the mounting surface of the optical part. In this case, it suffices to irradiate the tapered vertical waveguide 120b with a laser beam from the side of the optical wiring layer 12 in the step shown in, for example, FIG. 6F. (2) The mirror formed in the optical wiring layer is for suitably receiving and reflecting the light beam and, thus, it is important to pay attention to the angle and the forming position of the mirror. Therefore, the mirror formed in the optical wiring layer need not be limited to the shape of the mirror 123 included in each of the embodiments described above, as far as the mirror produces the particular function described above. For example, it is possible to employ the mirror 123 shown in FIG. 11. Industrial Applicability As described above, the present invention provides an optical-electrical wiring board and a mounted board that permit a high density mounting or miniaturization and also permit propagating the optical signal with a high efficiency, and a method of manufacturing the particular optical-electrical wiring board and the mounted board.

Claims: A method of manufacturing an optical-electrical wiring board, comprising: the step of forming a first through-hole (30) in an electrical wiring board (11) having an electrical wiring formed on a first surface; the step of filling said first through-hole with a clad (121b, 121c); the step of forming an optical wiring layer (12) including a first core (120a) and a clad (121a) surrounding said first core on a second surface opposite said first surface of said electrical wiring board; the step of forming a second through-hole in a central portion of said first through-hole so as to extend through said electrical wiring board the second through-hole having an inner diameter smaller than the inner diameter of said first through-hole; the step of filling said second through-hole with a second core (120b) so as to form a waveguide extending in a direction perpendicular to said electrical wiring board; and the step of forming a mirror (123) reflecting the light propagated through one core toward the other core in a portion where said first core and said second core are allowed to cross each other the method being characterised in that the second through-hole is formed so as for extend also through the first core and the clad surrounding the first core of the optical wiring layer. A method of manufacturing an optical-electrical wiring board according to claim 1, characterised in that the step of forming the optical wiring layer comprises bonding the optical wiring layer induding the first core and the clad surrounding the first core to the second surface of the electrical wiring board. The method of manufacturing an optical-electrical wiring board according to claim 1 or 2, characterized in that said method further comprises the step of forming a light-collecting lens (13) in one edge of said second core on the side of said first surface.

Inventors: MINATO TAKAO, TSUKAMOTO TAKEHITO, YOSHIDA MASAKICHI, MINATO, TAKAO, TSUKAMOTO, TAKEHITO, YOSHIDA, MASAKICHI, Minato, Takao, Toppan Printing Co., Ltd., Tsukamoto, Takehito, Toppan Printing Co., Ltd., Yoshida, Masakichi, Toppan Printing Co., Ltd.
Applicants: TOPPAN PRINTING CO LTD, TOPPAN PRINTING CO., LTD.
Application year: 2000
Main classification: G02B6
IPC codes: H05K1, G02B6