Optical / electrical hybrid board

Abstract

An optoelectric hybrid substrate (30) wherein an electric circuit part (E) which comprises a pad (34a) for mounting thereon an optical element, a pad (34b) for a drive device therefor, and electric wiring (Y) including a wiring part (A) that connects the pad (34a) and the pad (34b) is provided on a first surface of an insulating layer (31). On a second surface of the insulating layer (31), a metal reinforcement layer (37) and an optical waveguide (W) which partially overlaps the metal reinforcement layer are provided. An opening (60) is formed by removing a part of the metal reinforcement layer (37) which faces the wiring part (A) located on the opposite side of the insulating layer (31).　In the optoelectric hybrid substrate, since electric characteristics are prevented from being affected by the metal reinforcement layer, it is possible to transmit an electric signal having a higher frequency.

Description

[Technical field]

[0001] The present invention relates to an optical / electrical hybrid board used in an optical communication module, and more particularly to an optical / electrical hybrid board having excellent reliability for high-frequency signals. [Background technology]

[0002] In recent electronic devices, optical wiring has been adopted in addition to electrical wiring due to the increase in the amount of information transmitted, and optoelectronic hybrid boards in which electrical wiring and optical wiring are arranged compactly are being used. In addition, the optoelectronic hybrid boards are being further connected to wiring boards equipped with a signal transmission function for various electronic devices, and are being used in optical communication modules and the like for high-speed signal transmission.

[0003] An example of such an optical communications module is shown typically in Fig. 10. This optical communications module is configured by integrally connecting an optical / electrical hybrid substrate 2 to a wiring board 1. To explain in more detail, first, on the surface of the wiring board 1, electrical wiring X is provided, in which multiple pairs of wiring for differential signal transmission are arranged side by side.

[0004] The optical / electrical hybrid board 2 also includes an insulating layer 3 (shown by rough diagonal lines in the drawing) with a wide portion and a narrow portion, and an electric circuit section 6 including electric wiring Y, in which a plurality of pairs of wires for differential signal transmission are arranged, optical elements (VCSELs, photodiodes, etc.) 4, and optical element driving devices (ICs, etc.) 5 are provided on the rear surface of the wide portion of the insulating layer 3, i.e., the surface overlapping the surface of the wiring board 1. The electric circuit section 6 has portions requiring insulation covered by a coverlay (not shown).

[0005] On the other hand, a metal reinforcing layer 7 for reinforcing the electric circuit section 6 is provided on the surface of the insulating layer 3 opposite to the surface on which the electric circuit section 6 is provided, and a band-shaped optical waveguide 8 is provided so as to partially overlap this metal reinforcing layer 7.

[0006] The electric circuit section 6 of the optical / electrical hybrid board 2 will be described in more detail with reference to Fig. 11 which shows an enlarged schematic view of this portion (illustration of the coverlay is omitted). That is, in the electric circuit section 6 provided on one side of the insulating layer 3, a pad 10 for mounting an optical element 4 (such as a VCSEL or a photodiode, shown by a dashed line) and a pad 11 for mounting a driving device 5 (such as an IC, shown by a dashed line) for driving the optical element 4 are formed, and an electric wiring Y including a wiring portion A connecting the pads 10 and 11 extends to the edge opposite to the side where the optical waveguide 8 extends.

[0007] The electrical wiring Y includes an electrical wiring section that connects the optical element 4 and a driving device 5 for driving the optical element 4, and an electrical wiring section that connects the driving device 5 and the electrical wiring X of the wiring board 1 (see FIG. 10) by a differential electrical signal. A terminal 13 that serves as a connection point with the electrical wiring X is provided at the tip of the electrical wiring Y.

[0008] In addition, a metal reinforcing layer 7 is provided on the opposite surface of the insulating layer 3 on which the electrical circuit section 6 is provided, in order to reinforce the electrical circuit section 6, and an optical waveguide 8 is provided on the surface of the insulating layer 3 on which the metal reinforcing layer 7 is provided, partially overlapping the metal reinforcing layer 7.

[0009] A reflective surface (not shown) for changing the path of light is formed in the optical waveguide 8 at a portion facing the optical element 4 with the insulating layer 3 in between, so that the light reflected from the reflective surface is optically coupled with the optical element 4. A through hole 14 is formed in the metal reinforcing layer 7 at a portion sandwiched between the reflective surface of the optical waveguide 8 and the light receiving and emitting portion of the optical element 4, so that the metal reinforcing layer 7 does not obstruct the path of light.

[0010] In such optical communications modules, there is an increasing demand for faster and more accurate transmission of huge amounts of information, including image and audio information. This has led to a demand for even denser electrical and optical wiring, as well as more stable transmission technologies for electrical and optical signals.

[0011] For example, in a structure for connecting a circuit-equipped suspension board and a wired circuit board, a technology has been proposed in which a portion of a metal reinforcing layer provided on the wired circuit board that overlaps with a terminal portion that serves as a connection point between the boards is partially opened in advance, thereby preventing this portion from adversely affecting the electrical characteristics of the connection point (see Patent Document 1). [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2004-363205 A Summary of the Invention [Problem to be solved by the invention]

[0013] As the electrical characteristics at the connection points between the substrates are affected by the metal reinforcing layer, research is being conducted into whether the metal reinforcing layer affects the electrical characteristics of the optical-electrical hybrid substrate at points other than the above-mentioned connection points, and, if so, what kind of improvements can be made.

[0014] The present invention has been made in consideration of the above circumstances, and provides an optical / electrical hybrid board in which the influence of a metal reinforcing layer on electrical characteristics is suppressed and which is capable of transmitting higher frequency electrical signals. [Means for solving the problem]

[0015] That is, the present invention provides the following [1] to [3]. [1] An optical / electrical hybrid board for use in an optical communication module, an insulating layer; an electric circuit section provided on a first surface side of the insulating layer, the electric circuit section having a pad for mounting an optical element, a pad for an optical element driving device, and an electric wiring Y including a wiring portion A connecting the pads; a metal reinforcing layer provided on a second surface side of the insulating layer; and an optical waveguide provided on the second surface side of the insulating layer in such a manner that a part of the optical waveguide overlaps with the metal reinforcing layer; The optical / electrical hybrid board has an opening formed by removing a portion of the metal reinforcing layer that faces the wiring portion A provided on the opposite side of the insulating layer. [2] The optical / electrical hybrid board according to [1], wherein the optical element is a photodiode (PD). [3] The optical-electrical hybrid board according to [1] or [2] above, wherein the opening dimension of the opening of the metal reinforcing layer along the longitudinal direction of the wiring portion A is set to 0.8 to 1 when the longitudinal dimension of the wiring portion A is 1.

[0016] As a result of extensive research into the effect of the metal reinforcement layer on the electrical characteristics of an opto-electrical hybrid board, the inventors have discovered that the effective capacitance of an optical element mounted on an opto-electrical hybrid board is larger than that before mounting due to the addition of the capacitance generated between the metal reinforcement layer and wiring portion A in addition to the capacitance of the optical element itself.

[0017] And, since the larger the effective capacitance of the optical element mounted on the opto-electrical hybrid board, the more the frequency band shifts to the lower frequency side than the high frequency band that the optical element had before mounting, the idea was reached that if the effect of the metal reinforcing layer on the effective capacitance value of the optical element mounted on the opto-electrical hybrid board is eliminated, the frequency band of the optical element before mounting can be maintained and a higher frequency signal can be transmitted. And, as a result of further research, it was found that in wiring portion A connecting the pad for mounting the optical element and the pad for the optical element driving device, if the portion of the metal reinforcing layer facing this portion across the insulating layer is removed, the capacitance between wiring portion A and the metal reinforcing layer is eliminated, and the effective capacitance of the optical element returns to the low capacitance that is the original characteristic of the optical element itself. Effect of the Invention

[0018] According to the opto-electrical hybrid board of the present invention, the portion of the metal reinforcing layer facing the wiring portion A connecting the pad for mounting the optical element and the pad for the optical element driving device is removed to form an opening, so that the capacitance between the wiring portion A through which electricity flows near the mounted optical element and the metal reinforcing layer on the opposite side of the insulating layer is removed. Therefore, while the effective capacitance of the optical element mounted on the opto-electrical hybrid board is conventionally increased by the amount of the capacitance between the wiring portion A and the metal reinforcing layer, there is no such influence, and the effective capacitance of the optical element does not increase by mounting. Therefore, the frequency band of the optical element after mounting on the opto-electrical hybrid board can maintain the frequency band shown before mounting the optical element, and the amount of signal information that can be transmitted can be increased without slowing down the speed. [Brief description of the drawings]

[0019] [Figure 1] 1 is an explanatory diagram showing a schematic vertical cross section of a main part of an opto-electrical hybrid board according to an embodiment of the present invention; [Diagram 2] 1A is a schematic explanatory diagram of an electrical circuit section formed on the above-mentioned optical-electrical hybrid substrate, viewed from the side on which the electrical circuit section is formed, and FIG. 1B is a schematic explanatory diagram of a metal reinforcement layer formed on the above-mentioned optical-electrical hybrid substrate, viewed from the side on which the metal reinforcement layer is formed. [Diagram 3] 3A to 3C are explanatory diagrams of a manufacturing process of the optical-electrical hybrid board. [Figure 4] 3A to 3C are explanatory diagrams of a manufacturing process of the optical-electrical hybrid board. [Diagram 5] 3A to 3C are explanatory diagrams of a manufacturing process of the optical-electrical hybrid board. [Figure 6] 10A to 10C are explanatory diagrams illustrating a manufacturing process of an optical communication module using the above-mentioned optical / electrical hybrid board. [Figure 7] 10A to 10C are explanatory diagrams showing modified examples of openings in the metal reinforcing layer in the optical-electrical hybrid board. [Figure 8] FIG. 2 is an explanatory diagram of a method for evaluating electrical characteristics of an example of the present invention and a comparative example. [Figure 9]FIG. 2 is a characteristic curve showing insertion loss of S parameters in the example sample and the comparative sample obtained by the above evaluation method. [Figure 10] FIG. 1 is a schematic and partial explanatory diagram showing an example of a general optical communication module. [Figure 11] 3 is a schematic explanatory diagram illustrating an electric circuit section in an optical / electrical hybrid board used in the optical communication module. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment.

[0021] FIG. 1 is an explanatory diagram showing a schematic cross-section of a main part of an opto-electrical hybrid board according to an embodiment of the present invention along the extending direction of an optical waveguide.

[0022] This opto-electrical hybrid board 30 is used in an optical communication module, and its basic configuration is the same as that of a general opto-electrical hybrid board. That is, a sheet of a substantially strip-shaped insulating layer 31 is used as the substrate, and on one side (first side) of the substrate, an electric wiring Y in which a plurality of pairs of electric wiring for transmitting differential signals are arranged, a pad 34a for mounting an optical element (PD, VCSEL, etc.) 32, a pad 34b for mounting a driving device (IC, etc.) 33, etc. are provided [see FIG. 2(a)]. The parts of the electric circuit part E that require insulation protection are covered with a coverlay 36. Note that the optical element 32 and the driving device 33 may not be attached at the substrate stage, and are indicated by dashed lines.

[0023] Meanwhile, on the other surface (second surface) of the insulating layer 31, i.e., the surface opposite to the side where the electric circuit portion E is provided, a metal reinforcing layer 37 for reinforcing the strength of the insulating layer 31 is partially provided in an area requiring reinforcement. Also, on the other surface of the insulating layer 31, an undercladding layer 40, a core 41, and an overcladding layer 42 are laminated in this order in an arrangement partially overlapping with the metal reinforcing layer 37, and these three layers form an optical waveguide W [see FIG. 2(b)]. A part of the optical waveguide W is cut into an inclined surface, and the inclined surface serves as an optical reflecting portion 43 for changing the traveling direction of an optical signal transmitted through the core 41 by 90 degrees.

[0024] The electric circuit section E of the opto-electrical hybrid board 30 will be described in more detail. That is, as shown in Fig. 2(a) in which the opto-electrical hybrid board 30 is viewed from the side on which the electric circuit section E is formed, the electric circuit section E is provided with pads 34a for mounting the optical elements 32, indicated by diagonal lines slanting downward to the right, and pads 34b for mounting the driving devices 33, indicated by diagonal lines slanting downward to the right (a coverlay 36 is not shown). In addition, a connection terminal 35 for connecting the opto-electrical hybrid board 30 to a wiring board having a signal transmission function to various electronic devices is provided at an end of the electric circuit section E.

[0025] The electrical wiring Y of the electrical circuit section E includes a wiring portion A that connects the pads 34a for the optical elements 32 and the pads 34b for the driving device, and a wiring portion B that connects the pads 34b and the connection terminals 35 for other wiring boards. Of course, other wiring may be formed as necessary, but is not shown in the drawings.

[0026] 2(a), the region where the metal reinforcing layer 37 is formed on the surface of the insulating layer 31 opposite to the surface on which the electric circuit portion E is formed is indicated by a diagonal line going up to the right. FIG. 2(b) shows the metal reinforcing layer 37 as viewed from the side on which the metal reinforcing layer 37 is formed. In this figure, the optical waveguide W that partially overlaps with the metal reinforcing layer 37 is indicated by a dashed line.

[0027] As can be seen from these figures, the metal reinforcing layer 37 has a through hole 50 for optical coupling formed therein as in the conventional case, but in addition, a portion facing the wiring portion A connecting the pad 34a for the optical element 32 and the pad 34b for the driving device, which is provided on the opposite side of the insulating layer 31, is removed in a substantially rectangular shape to form an opening 60. This is the greatest feature of the present invention. The metal reinforcing layer 37 has other appropriate openings formed therein as necessary, but these are not shown in the drawings.

[0028] <Opto-electrical hybrid board manufacturing process> Next, an example of a process for obtaining the above-mentioned opto-electric hybrid board 30 will be briefly described while giving specific examples of materials. (1) Formation of electrical circuit section E First, as shown in FIG. 3, a metal plate 100 that will become the metal reinforcing layer 37 is prepared, and a photosensitive insulating resin such as polyimide is applied to the surface of the metal plate 100 to form an insulating resin layer 101 that will become the insulating layer 31.

[0029] Examples of materials for the metal plate 100 include stainless steel, copper, silver, aluminum, nickel, chromium, titanium, platinum, gold, etc., with stainless steel being preferred from the viewpoints of strength, flexibility, etc. The thickness of the metal reinforcing layer 37 is preferably set within the range of, for example, 10 to 70 μm (more preferably, 10 to 30 μm).

[0030] Then, the insulating resin layer 101 is subjected to a photolithography method (exposure, pre-baking, development, curing) to form an insulating layer 31 having a predetermined pattern shape. The thickness of the insulating layer 31 is preferably set within a range of, for example, 3 to 50 μm (more preferably, 3 to 25 μm) (this step is not shown).

[0031] Next, a conductive layer made of a conductive material such as copper is formed on the insulating layer 31 by sputtering or electroless plating, and then a conductive pattern including electrical wiring Y including wiring portions A and B, various pads 34a and 34b, connection terminals 35, etc. is formed through necessary processes such as dry film resist lamination, exposure, and development. Then, as shown in Fig. 4, a photosensitive insulating resin such as polyimide is applied on this conductive pattern, and a coverlay 36 is formed on the parts requiring insulating protection in the same manner as in the formation of the insulating layer 31.

[0032] As the conductive material for forming the conductive pattern, metal materials having excellent conductivity and malleability, such as copper, chromium, aluminum, gold, tantalum, etc., are preferably used. In addition, alloys using at least one of these metals are also preferably used. The thickness of the conductive pattern of the electric wiring Y, etc. is preferably set in the range of 3 to 30 μm (more preferably 3 to 18 μm). In addition, the thickness of the coverlay 36 formed thereon is preferably set in the range of, for example, 1 to 50 μm (more preferably 1 to 25 μm) in consideration of insulation, protection, and reinforcement of the electric wiring Y, etc.

[0033] Then, an electrolytic plating layer of nickel, gold, or the like is formed on the portions that are to become the various pads 34a, 34b and the connection terminals 35, which are exposed from the coverlay 36, thereby obtaining the electric circuit section E (see FIG. 4).

[0034] (2) Patterning of the metal reinforcing layer 37 Next, the metal reinforcing layer 37 on the opposite side of the electrical circuit portion E across the insulating layer 31 is subjected to an etching process (dry film resist lamination, exposure, development, etching, dry film resist peeling, etc.) to remove unnecessary portions and form a predetermined pattern shape. As a result, as shown in Fig. 5, a through hole 50 for optical coupling with the optical element 32 (see Fig. 1), an opening 60 in a portion facing the wiring portion A, etc. are formed.

[0035] (3) Formation of optical waveguide W Next, the insulating layer 31 provided with the electric circuit portion E and the metal reinforcing layer 37 is turned upside down so that the metal reinforcing layer 37 faces upward. Then, on the surface of the insulating layer 31 on which the metal reinforcing layer 37 is formed, an undercladding layer 40, a core 41, and an overcladding layer 42 are laminated by a known method, with each layer being patterned into a predetermined pattern as necessary, to obtain an optical waveguide W (see FIG. 1).

[0036] Then, assuming optical coupling with the optical element 32 provided on the electrical circuit unit E side of the insulating layer 31, a predetermined portion of the optical waveguide W is formed into an inclined surface inclined at 45° with respect to the longitudinal direction of the core 41 by dicing, laser processing, cutting processing, or the like to form an optical reflecting surface 43. In this manner, the optical-electrical hybrid board 30 shown in Fig. 1 can be obtained. Note that, in the longitudinal direction of the optical waveguide W, the tip side (not shown) opposite the side facing the electrical circuit unit E may be configured to have an optical connector attached for connection to another optical wiring member, or a similar electrical circuit unit E' may be formed on the tip side across the optical waveguide W.

[0037] The photoelectric hybrid board 30 thus obtained is connected to a wiring board 20 used in various electric and electronic devices to become an optical communications module board, as shown in Fig. 6, for example, and necessary devices are mounted on this board to obtain an optical communications module. The wiring board 20 includes an insulating board 21, electrical wiring X, a connection terminal 22, and a coverlay 23. The wiring board 20 and the photoelectric hybrid board 30 are usually connected by arranging the connection terminals 35, 22 so as to face each other so as to overlap each other vertically, and electrically connecting the facing connection terminals 35, 22 by solder bumps or the like.

[0038] According to the above-mentioned opto-electrical hybrid board 30, in the metal reinforcing layer 37 provided on one side of the insulating layer 31, a portion facing the wiring portion A connecting the pad 34a for mounting an optical element and the pad 34b for a driving device thereof is removed to form an opening 60, so that it is possible to eliminate the electrostatic capacitance generated between the wiring portion A through which electricity flows and the metal reinforcing layer 37 near the optical element 32 to be mounted. Therefore, the effective electrostatic capacitance of the optical element 32 does not increase even after mounting on this opto-electrical hybrid board 30, and the frequency band of the optical element 32 can be maintained as it was before mounting. In other words, it is possible to increase the amount of signal information that can be transmitted without reducing the speed.

[0039] Furthermore, in the above-mentioned optical-electrical hybrid board 30, if an opening is provided in the coverlay 36 covering the wiring portion A to expose the wiring portion A connecting the optical element 32 and its driving device 33, the effective capacitance of the optical element 32 can be made smaller than when no opening is provided.

[0040] In addition, since the inherent capacitance of the optical element 32 is smaller in a PD than in a VCSEL, the effect of the additional capacitance between the wiring portion A and the metal reinforcement layer 37 is more pronounced in the PD. Therefore, it is particularly effective to apply the present invention when a PD is used as the optical element 32.

[0041] In the above example, the opening 60 of the metal reinforcing layer 37 is preferably set so that, when the dimension [shown by H in FIG. 2(a)] in the longitudinal direction (direction in which the wiring extends) of the wiring portion A provided on the opposite side of the insulating layer 31 is 1, the opening dimension [shown by J in FIG. 2(b)] of the opening 60 of the metal reinforcing layer 37 along the longitudinal direction of the wiring portion A is 0.8 to 1. That is, if the opening dimension J of the opening 60 along the longitudinal direction of the wiring portion A is longer than the dimension H of the longitudinal direction of the wiring portion A, the metal reinforcing layer 37 in the portion overlapping the pads 34a and 34b is partially removed, and the function as a reinforcing plate is reduced when the optical element 32 and the optical element driving device 33 are mounted. For this reason, sufficient connection strength is not obtained at the mounting portion, and the reliability of the connection strength of this portion is reduced during subsequent handling, which is not preferable. In addition, since the capacitance between the wiring portion A and the metal reinforcing layer 37 is proportional to the area of ​​the portion where the wiring portion A and the metal reinforcing layer 37 face each other, if the opening dimension J is smaller than the above range, a non-negligible capacitance occurs in this portion. Therefore, the effective capacitance of the optical element 32 increases, and the frequency band tends to shift to the lower frequency side, which is not preferable.

[0042] Furthermore, in the above example, the opening 60 of the metal reinforcing layer 37 is formed as a single elongated opening facing the wiring portion A consisting of four pairs of wires corresponding to the multiple channels arranged in parallel [see FIG. 2(a), corresponding to four channels in this example], but the opening 60 may be a plurality of individual openings 60a (four in this example) that are opened individually for each channel, as shown in, for example, FIG. 7. According to this configuration, since the metal reinforcing layer 37 remains as a partition between each channel, it is inferior to the above example in terms of the effect of removing electrostatic capacitance, but has the advantage that the reinforcing effect when mounting the optical element 32 and the optical element driving device 33 near the opening 60 is improved compared to the above example.

[0043] In the above example, the opening 60 is provided in the portion of the metal reinforcing layer 37 facing the wiring portion A of the electric circuit portion E as a removal portion for improving the electrical characteristics, but the metal reinforcing layer 37 may be provided with an appropriate removal portion in addition to the opening 60, as long as the reinforcing function is not impaired. For example, in the portion facing the wiring portion B [see FIG. 2(a)] extending toward the connection terminal 35, the metal reinforcing layer 37 may be removed in a strip shape along the wiring. With this configuration, the frequency band of the wiring portion B, which is a differential electrical wiring, can be made higher.

[0044] In the above example, the types of signals flowing through the wiring parts A and B are not particularly limited, and appropriate ones are selected depending on the types of optical elements 32 and various devices to be connected. Examples of the types of signals include single-ended signals, differential signals, and coplanar signals.

[0045] Next, examples will be described together with comparative examples, but the present invention is not limited to the following examples. EXAMPLES

[0046] A test was conducted to verify the difference in capacitance of the optical element mounted on the optical-electrical hybrid board when an opening is formed in the part of the metal reinforcing layer in the optical-electrical hybrid board facing wiring portion A on the electric circuit side [see Figure 2(a)] and when no opening is formed.

[0047] <Verification of electrostatic capacitance of optical elements> [Measurement of Example Sample 1] That is, first, according to the procedure described in the above embodiment, an opto-electrical hybrid board shown in Fig. 8 was fabricated similar to the opto-electrical hybrid board 30 shown in Fig. 1, Fig. 2(a) and (b). In the figures, the same parts are given the same reference numerals and their explanations are omitted. Then, in the electric circuit section E of the opto-electrical hybrid board 30, a 25 Gbps photodiode (product number APA1201040000, manufactured by II-VI Laser Enterprises) was mounted as the optical element 32 on the pad 34a for mounting the optical element.

[0048] Then, the capacitance of the optical element 32 at 1 MHz was measured using an impedance analyzer (model number 4294A, Keysight Technologies) while applying a reverse bias voltage of 2 V to the optical element 32 from the pads 34b arranged at the end of the wiring portion A extending from the optical element 32. The result was 0.09 pF.

[0049] [Measurement of Comparative Example Sample 1] 8, a conventional product was prepared in which the metal reinforcing layer 37 was not provided with the opening 60, and the capacitance of the optical element 32 (the same photodiode as in Example Sample 1) at 1 MHz was measured in the same manner as above. The result was 0.14 pF.

[0050] From the above results, it is understood that Example Sample 1 has a smaller capacitance than Comparative Example Sample 1.

[0051] Next, we conducted a test to verify the difference in the frequency band of the optical elements mounted on the optical-electrical hybrid board when an opening was formed in the part of the metal reinforcing layer in the optical-electrical hybrid board facing wiring portion A on the electrical circuit side [see Figure 2(a)] and when no opening was formed.

[0052] <Verification of frequency band of optical elements> [S-parameter measurement] A high-frequency optical signal output from a high-frequency light source with known S-parameters was input to the above-mentioned Example Sample 1 or Comparative Example Sample 1, and the S-parameters were obtained using a two-port vector network analyzer (N5227A, Keysight Technologies). Since the obtained S-parameters are a combination of the characteristics of the light source and Example Sample 1 or Comparative Example Sample 1, the S-parameters of Example Sample 1 or Comparative Example Sample 1 were obtained from the value of this combination of S-parameters and the value of the S-parameters of the known light source.

[0053] 1, 2(a) and 2(b) was prepared as the high-frequency light source, and a 25 Gbps VCSEL (product number: APA4501040001, manufactured by II-VI Laser Enterprises) was mounted as an optical element for the light source. A connector for optical transmission was formed at the other end of the optical waveguide W extending from the above-mentioned opto-electrical hybrid board, and a high-frequency electrical signal was superimposed on a direct current of 6 mA and input from pads 34b arranged at the end of the wiring portion A extending from the VCSEL (for light source), and this electrical signal was converted into an optical signal by the above-mentioned VCSEL (for light source), which was used as the light source.

[0054] [Evaluation of Example Sample 1] A connector portion for optical transmission was formed at the other end of the optical waveguide W of Example Sample 1, and the above connector portion was connected to a connector portion of the optical-electrical hybrid board used as the light source, so that an optical signal input from the light source through the optical waveguide W could be converted into an electrical signal by the photodiode (optical element 32) of Example Sample 1.

[0055] Then, the S parameters were obtained by a network analyzer while applying a DC reverse bias voltage of 2V from the pads 34b arranged at the ends of the wiring portions A extending from the photodiodes (optical elements 32) of the above-mentioned embodiment sample 1.

[0056] Using the obtained S-parameter insertion loss and the known S-parameter insertion loss of the light source, the S-parameter insertion loss of the example sample 1 was obtained. The normalized S-parameter insertion loss [response (dB)] of the example sample 1 is shown in FIG.

[0057] [Evaluation of Comparative Example Sample 1] The insertion loss of the S parameters of Comparative Sample 1 was obtained using the same procedure as above. The insertion loss of the normalized S parameters of Comparative Sample 1 is also shown in FIG.

[0058] In FIG. 9, when comparing the frequency bands up to which the insertion loss of the S parameters decreases by 3 dB, Example Sample 1 shows a higher frequency band exceeding 5 GHz than Comparative Example Sample 1.

[0059] Therefore, when an optical / electrical hybrid board having the structure of Example Sample 1 is used in an actual optical communications module, it has excellent characteristics that can handle an increase in communication information and faster speeds.

[0060] In the above embodiment, specific embodiments of the present invention are shown, but the above embodiment is merely illustrative and should not be interpreted as being limiting. All of the various modifications that are obvious to those skilled in the art are intended to be within the scope of the present invention. [Industrial Applicability]

[0061] In the optical / electrical hybrid board of the present invention, the optical elements mounted on the board are not affected by the presence of the metal reinforcing layer on the back side, and the optical elements can maintain their inherent low capacitance. This allows the transmission signal to be at a higher frequency than before, and the board can be widely used in high-speed signal transmission technology. [Explanation of symbols]

[0062] 30 Optical / electrical hybrid board 31 Insulating layer 32 Optical elements 33 Driving Device 34a, 34b pads 37 Metal Reinforcement Layer 60 Opening A wiring part E Electrical Circuit Section W optical waveguide Y Electrical Wiring

Claims

1. An optical / electrical hybrid board for use in an optical communication module, an insulating layer; an electric circuit section provided on a first surface side of the insulating layer, the electric circuit section having a pad for mounting an optical element, a pad for an optical element driving device, and an electric wiring Y including a wiring portion A connecting the pads; a metal reinforcing layer provided on a second surface side of the insulating layer; and an optical waveguide provided on the second surface side of the insulating layer in such a manner that a part of the optical waveguide overlaps with the metal reinforcing layer; a portion of the metal reinforcing layer facing the wiring portion A provided on the opposite side of the insulating layer is removed to form an opening; An optical / electrical hybrid board in which the opening dimension of the opening of the metal reinforcing layer along the longitudinal direction of the wiring portion A is set to 0.8 to 1 when the longitudinal dimension of the wiring portion A is 1.

2. 2. The optical / electrical hybrid board according to claim 1, wherein said optical element is a photodiode.

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