Optical communication module substrate

Abstract

Provided is an optical communication module substrate comprising a wiring substrate (20) and an optoelectronic hybrid substrate (30) connected together. A connection terminal (22) of the wiring substrate (20) and a connection terminal (35) of the optoelectronic hybrid substrate (30) form an electric connection point. The optoelectronic hybrid substrate (30) includes a metal reinforcement layer (37) partly opposing the connection terminal (35) with an insulating layer (31) therebetween. With respect to each connection terminal, the opposing part is removed around the terminal, forming a frame-like removed portion (60). The configuration ensures sufficient connection strength at the connection point between the wiring substrate and the optoelectronic hybrid substrate, and provides excellent electric characteristics for handling high-speed signal transmission.

Description

Technical Field

[0001] The present invention relates to an optical communication module substrate formed by connecting a wiring substrate (including a wiring circuit substrate) and an optoelectronic hybrid substrate, and more particularly to an optical communication module substrate having excellent reliability for high-frequency signals.

Background Art

[0002] In recent electronic devices, with the increase in the amount of transmitted information, in addition to electrical wiring, optical wiring is adopted, and an optoelectronic hybrid substrate in which electrical wiring and optical wiring are compactly arranged is widely used. Further, the use of an optical communication module or the like that further connects the optoelectronic hybrid substrate to a wiring substrate or the like having a signal transmission function to various electronic devices for high-speed signal transmission is also expanding.

[0003] An example of such an optical communication module is schematically shown in FIG. 13. This optical communication module is formed by integrally connecting an optoelectronic hybrid substrate 2 to a wiring substrate 1. More specifically, first, on the surface of the wiring substrate 1, an electrical wiring X in which a plurality of pairs of two differential signal transmission wirings are arranged is provided.

[0004] Further, the optoelectronic hybrid substrate 2 includes an insulating layer 3 (shown by thick oblique lines in the figure) having a wide portion and a narrow portion. On the back surface of the wide portion of the insulating layer 3, that is, the surface overlapping the surface of the wiring substrate 1, an electrical circuit portion 6 having an electrical wiring Y in which a plurality of pairs of two differential signal transmission wirings are arranged, an optical element 4, an IC 5 for driving the optical element 4, etc. is provided. And on the front surface of the insulating layer 3, a metal reinforcing layer 7 for reinforcing the electrical circuit portion 6 is provided. In a form partially overlapping with this metal reinforcing layer 7, a strip-shaped optical waveguide 8 is also provided on the front surface of the insulating layer 3.

[0005] In the above optical communication module, the electrical connection between the wiring board 1 and the optoelectronic hybrid mounting board 2 is made by arranging the connection terminals provided at the ends of the respective electrical wirings X and Y so as to overlap each other as shown in Fig. 14 which schematically shows an enlarged view of this connection portion, and connecting the two using solder bumps or the like. In the figure, the connection point is indicated by P.

[0006] When electrically connecting a substrate to another substrate as in the above optical communication module, it becomes an important issue to control the impedance at the connection point P. In particular, in the case where the wiring has a fine pitch or the signal has a high frequency such that the differential signal is transmitted, since the transmitted signal becomes very delicate, if there is an impedance mismatch at the connection point P, there is a risk that the signal transmission efficiency will be greatly reduced due to the influence.

[0007] By the way, in a structure for connecting a circuit-mounted suspension board and a wiring circuit board, a technique has been proposed in which a portion of the metal reinforcing layer provided on the wiring circuit board that overlaps the terminal portion which becomes the connection point between the substrates is partially opened in advance to remove the capacitance component generated between the metal reinforcing layer and the terminal portion, so as to avoid a large reduction in the impedance of the connection point with respect to the differential impedance of the differential signal wiring (see Patent Document 1).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, based on the same concept as this technology, in an optical communication module as well, it has been proposed to use a substrate in which, among the metal reinforcement layers on the back side of the insulating layer in the optoelectronic hybrid substrate, the connection terminals of the electrical wiring Y that becomes the connection point P and the portions facing the opposite side across the insulating layer are removed to form openings. For example, as shown in FIG. 15(a), in the metal reinforcement layer 7 of the optoelectronic hybrid substrate 2 that is part of the optical communication module, the portions facing each terminal at the tip of the electrical wiring Y (see FIG. 13) are removed to form an opening 10 having a contour larger than the terminals, and this has been under consideration. In the figure, the through-hole 50 is generally provided in the metal reinforcement layer 7 and is for optical coupling between the optical element and the optical waveguide.

[0010] Also, based on the same concept, as shown in FIG. 15(b), in the metal reinforcement layer 7, not only the portions facing each terminal but also strip-shaped openings 11 are formed along each wiring of the electrical wiring Y, and this has also been under consideration.

[0011] However, in the above configuration, although the electrical characteristics at the connection point P are improved, when crimping the terminals to connect the terminals on the optoelectronic hybrid substrate 2 side and the terminals on the other wiring substrate side, on the optoelectronic hybrid substrate 2 side, since the metal reinforcement layer 7 forms an opening and comes off, there is a problem that the function as a reinforcing plate is lost and the connection strength at the connection point P becomes insufficient.

[0012] For this reason, giving priority to ensuring mechanical strength, for example, as shown in FIG. 16(a), openings are not provided in the portion of the metal reinforcement layer 7 that becomes the connection point P or the portions facing the electrical wiring Y, or as shown in FIG. 16(b), openings 11 are provided only in the portions facing the electrical wiring Y except for the portion that becomes the connection point P, and these are still being used. However, as described above, due to the requirements for higher signal frequencies and finer wiring pitches, there is a strong demand for the development of a technology to enhance the electrical characteristics at the connection point P while ensuring mechanical strength.

[0013] The present invention has been made in view of such circumstances, and provides an optical communication module substrate in which the connection strength at the connection point P is sufficiently ensured and which has excellent electrical characteristics capable of supporting high-speed signal transmission.

Means for Solving the Problems

[0014] That is, the present invention provides the following [1] to [5]. [1] An optical communication module substrate formed by connecting a wiring substrate and an optoelectronic hybrid substrate, wherein the wiring substrate includes an electrical wiring X and its connection terminal, the optoelectronic hybrid substrate includes an insulating layer, an electrical circuit portion provided on the first surface side of the insulating layer and having pads for mounting optical elements, an electrical wiring Y, and its connection terminal, a metal reinforcing layer provided on the second surface side of the insulating layer, and an optical waveguide provided on the second surface side of the insulating layer and arranged such that a part thereof overlaps with the metal reinforcing layer, the connection terminal of the wiring substrate and the connection terminal of the optoelectronic hybrid substrate form an electrical connection point, and in a portion of the metal reinforcing layer of the optoelectronic hybrid substrate that faces the connection terminal of the electrical wiring Y provided on the opposite side with the insulating layer interposed therebetween, the metal reinforcing layer is removed so as to surround each terminal, and a frame-shaped removal portion is formed, an optical communication module substrate. [2] The optical communication module substrate according to [1], wherein the portions of the metal reinforcing layer surrounded by the frame-shaped removal portion are each electrically connected to the connection terminal of the electrical wiring Y. [3] The optical communication module substrate according to [1] or [2], wherein a portion of the metal reinforcing layer that faces the electrical wiring Y provided on the opposite side with the insulating layer interposed therebetween is removed in a strip shape along the electrical wiring Y. [4] The connection terminals of the wiring board and the connection terminals of the optoelectronic hybrid board are arranged so as to overlap each other, and the overlapping connection terminals are electrically connected to each other directly or via a conductive member. The optical communication module substrate according to any one of [1] to [3] above. [5] The connection terminals of the wiring board and the connection terminals of the optoelectronic hybrid board are electrically connected via an electrical connector disposed between the wiring board and the optoelectronic hybrid board. The optical communication module substrate according to any one of [1] to [3] above.

[0015] That is, as a result of intensive studies to solve the above problems, the inventors have found that in the metal reinforcing layer of the optoelectronic hybrid board constituting the optical communication module substrate, at the portion facing the connection terminal of the electrical wiring, for each terminal, a frame-shaped removal portion is formed so as to surround the terminal. In this way, the mechanical strength of the terminal portion is ensured by the portion remaining within the frame of the metal reinforcing layer, and moreover, the periphery of the portion facing the terminal is disconnected from the large-area metal reinforcing layer, suppressing the influence on the electrical characteristics.

Effect of the Invention

[0016] According to the optical communication module substrate of the present invention, at the connection point P between the wiring board and the optoelectronic hybrid board, sufficient connection strength is ensured, and no impedance drop or the like occurs, and it has excellent electrical characteristics. And since its performance can fully cope with the high-frequencyization of signals and the fine-pitchization of wirings, it is possible to provide an optical communication module for high-speed signal transmission with excellent reliability.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

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Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Embodiments for Carrying out the Invention

[0018] Next, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0019] FIG. 1 is a partial longitudinal sectional view schematically showing an embodiment of an optical communication module substrate of the present invention (cut along the extending direction of the optical waveguide).

[0020] This optical communication module substrate is formed by electrically connecting and integrating a wiring substrate 20 and an optoelectronic hybrid substrate 30 in the same manner as the substrate used in the general optical communication module shown in FIG. 13 described above.

[0021] The wiring substrate 20 is a wiring substrate for differential signal transmission, and on the surface of the insulating layer 21, an electrical wiring X in which a plurality of pairs of two electrical wirings for transmitting differential signals are arranged is formed. And at the end of each wiring of the electrical wiring X, a connection terminal 22 for electrically connecting to the electrical wiring Y on the optoelectronic hybrid substrate 30 side is provided, and in a state where each terminal 22 is exposed, the other parts are covered with a coverlay 23.

[0022] Note that various wiring patterns, pads, etc. for mounting or connecting appropriate electronic and electrical components according to the use can be provided on the wiring substrate 20. And the wiring substrate 20 may be rigid or flexible, but usually, considering the connection strength with the optoelectronic hybrid substrate 30, it is preferably rigid.

[0023] On one hand, the optoelectronic hybrid substrate 30 connected to the wiring substrate 20 is for differential signal transmission, similar to the wiring substrate 20, and its basic configuration is the same as that of a general optoelectronic hybrid substrate. That is, using a single substantially strip-shaped insulating layer 31 as the substrate, on one side (the first side) thereof, a plurality of pairs of two electrical wirings Y for transmitting differential signals are arranged side by side, and an electrical circuit portion E provided with pads 34 and the like for mounting optoelectronic elements 32 and their driving ICs 33 and the like is provided. And the tip of each wiring of the electrical wiring Y serves as a connection terminal 35 for electrically connecting to the connection terminal 22 of the wiring substrate 20, and the portions that need insulation protection, excluding these terminal portions and the like, are covered with a coverlay 36. Note that the optoelectronic element 32 and the driving IC 33 may not be mounted at the substrate stage and are shown by dashed-dotted lines.

[0024] Also, on the other side (the second side) of the insulating layer 31, that is, the side opposite to the side where the electrical circuit portion E is provided, a metal reinforcing layer 37 for reinforcing the strength of the insulating layer 31 is partially provided in the region that requires reinforcement. Also, on the other side of the insulating layer 31 in the same way, an underclad layer 40, a core 41, and an overclad layer 42 are laminated in this order in an arrangement that partially overlaps with the metal reinforcing layer 37, and an optical waveguide W is formed by these three layers. Note that a part of the optical waveguide W is cut at an inclined surface, and the inclined surface serves as an optical reflection portion 43 for changing the traveling direction of the optical signal transmitted through the core 41 by 90 degrees.

[0025] In the metal reinforcing layer 37 provided on the other side of the insulating layer 31, as shown in FIG. 2, through holes 50 and the like for optical coupling are formed in the same manner as in the prior art. Further, in the portion facing the connection terminal 35 of the electrical wiring Y provided on the opposite side across the insulating layer 31, for each terminal, the metal reinforcing layer 37 is removed in a frame shape so as to surround the terminal, and a frame-shaped removal portion 60 is formed. This is the greatest feature of the present invention.

[0026] When the portion of the metal reinforcing layer 37 where the frame-shaped removal portion 60 is formed is enlarged as viewed from the side where the electric circuit portion E is formed, which is the opposite side sandwiching the insulating layer 31, as shown in Fig. 3(a), the connection terminals 35 are individually surrounded by the frame-shaped removal portion 60 one by one.

[0027] Note that, since the portion of the metal reinforcing layer 37 where the frame-shaped removal portion 60 is formed becomes a small piece independent from the surroundings, in order to avoid this portion being in an electrically independent state from the surrounding metal, through holes 31a are formed in advance in the portion of the insulating layer 31 where the connection terminals 35 are formed, and the inside of these through holes 31a is filled with a conductive material for electrical wiring during electrical wiring formation, so as to conduct and fix the connection terminals 35 and the small piece portion of the metal reinforcing layer 37. Thereby, it is possible to avoid having a capacitance between the small piece portion and the connection terminals 35. Also, the small piece portion does not peel off from the insulating layer 31, and sufficient mechanical strength is ensured in this portion.

[0028] The through holes 31a may be holes of any shape in plan view. For example, when they are circular, their diameter is preferably 5 to 200 μm, more preferably 5 to 100 μm. Also, when the shape in plan view is, for example, square, one side thereof is preferably 5 to 200 μm, more preferably 5 to 100 μm. And, as shown in Fig. 3(a), the through holes 31a are not only provided one by one for each connection terminal 35, but may also be provided two by two at both ends of each connection terminal 35 as shown in Fig. 3(b), for example. Of course, three or more may be provided.

[0029] However, when providing the above through-hole 31a, depending on the manufacturing process, the surface of the connection terminal 35 in which the through-hole 31a is formed may be recessed more than other portions, and there is a problem that such a recessed portion tends to cause connection failure during connection between substrates. Therefore, when forming the above through-hole 31a, assuming that the area of the portion where the connection terminal 35 is recessed due to the formation thereof is S1 and the area of the flat portion that is not recessed is S, it is desirable to consider the size and arrangement of the through-hole 31a so that (S) / (S1) is 1 or more. Among these, it is more preferable that it is 3 or more, and particularly 7 or more (refer to Fig. 3(a) for S and S1). Of course, if the through-hole 31a can be formed without causing such a recess by examining the manufacturing conditions, since the entire area of the connection terminal 35 contributes to substrate connection, it is most preferable.

[0030] <Formation Process of Optoelectronic Hybrid Substrate> Next, an example of the process for obtaining the above optoelectronic hybrid substrate 30 will be briefly described while exemplifying specific materials. (1) Formation of Electrical Circuit Portion E First, as shown in Fig. 4, a metal plate 100 to be the metal reinforcing layer 37 is prepared, and a photosensitive insulating resin such as polyimide is applied to the surface thereof to form an insulating resin layer 101 to be the insulating layer 31.

[0031] Examples of the material of the above metal plate 100 include stainless steel, copper, silver, aluminum, nickel, chromium, titanium, platinum, gold, etc. From the viewpoints of strength, flexibility, etc., stainless steel is preferable. Further, the thickness of the above metal reinforcing layer 37 is preferably set within a range of, for example, 10 to 70 μm (more preferably 10 to 30 μm).

[0032] Then, the insulating resin layer 101 is subjected to photolithography (exposure, pre-baking, development, curing) to form an insulating layer 31 having a predetermined pattern shape including through-holes 31a for conduction with independent pieces of the metal reinforcing layer 37. The thickness of the above insulating layer 31 is preferably set within a range of, for example, 3 to 50 μm (more preferably 3 to 25 μm) (not shown).

[0033] Next, after forming a conductive layer made of a conductive material such as copper on the insulating layer 31 by sputtering or electroless plating, etc., necessary processes such as dry film resist lamination, exposure, and development are carried out to form conductive patterns such as the electrical wiring Y, various pads 34, and connection terminals 35. Then, as shown in FIG. 5, a photosensitive insulating resin such as polyimide is applied on this conductive pattern, and a coverlay 36 is formed in portions that require insulation protection in the same manner as the formation of the insulating layer 31.

[0034] In addition, as the above-mentioned conductive material, in addition to copper, metal materials excellent in conductivity and malleability such as chromium, aluminum, gold, and tantalum are preferably used. Also, alloys using at least one of these metals are preferably used. And the thickness of the conductive pattern such as the electrical wiring Y, etc. is preferably set in the range of 3 to 30 μm (more preferably 3 to 18 μm). Also, 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 and protection of the electrical wiring Y, etc., and further reinforcement.

[0035] And, an electrolytic plating layer such as Ni, Au, etc. is formed on the portions that become various pads 34 and connection terminals 35 and are exposed from the coverlay 36, whereby the electrical circuit portion E can be obtained (see FIG. 5).

[0036] (2) Pattern formation of the metal reinforcement layer Next, an etching process (dry film resist lamination, exposure, development, etching, dry film resist peeling, etc.) is performed on the metal reinforcement layer 37 on the opposite side of the electrical circuit portion E with the insulating layer 31 interposed therebetween to remove unnecessary portions and form a predetermined pattern shape. Thereby, as shown in FIG. 6, a through hole 50 for optical coupling with the optical element 32 (see FIG. 1) and a frame-shaped removal portion 60, etc. in the portion facing the connection terminal 35 are formed.

[0037] (3) Formation of the optical waveguide W Next, turn the insulating layer 31 provided with the electric circuit portion E and the metal reinforcing layer 37 upside down so that the metal reinforcing layer 37 faces upward. Then, on the surface of the insulating layer 31 on the side where the metal reinforcing layer 37 is formed, an underclad layer 40, a core 41, and an overclad layer 42 are laminated and formed by a known method, with each layer patterned into a predetermined pattern as necessary, thereby obtaining an optical waveguide W.

[0038] Then, as shown in FIG. 7, assuming optical coupling with the optical element 32 provided on the electric circuit portion 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, etc., to form a light reflecting surface 43. Thereby, an optoelectronic hybrid substrate 30 used for an optical communication module substrate can be obtained. Note that the tip side (not shown) of the optical waveguide W on the side opposite to the side facing the electric circuit portion E may be configured with an optical connector attached for connection to other optical wiring members, or a similar electric circuit portion E' may be formed on the tip side with the optical waveguide W interposed therebetween. This may also be the case.

[0039] <Formation process of optical communication module substrate> The optoelectronic hybrid substrate 30 thus obtained and the wiring substrate 20 are arranged such that the connection terminals 35 and 22 thereof overlap with each other as shown in FIG. 1, and the joint portions thereof are electrically connected by solder bumps or the like. Then, the wiring substrate 20 and the optoelectronic hybrid substrate 30 are stably assembled. Thereby, the target optical communication module substrate can be obtained.

[0040] According to the above optical communication module substrate, since the frame-shaped removal portions 60 corresponding to the respective connection terminals 35 are individually formed in the metal reinforcing layer 37 of the optoelectronic hybrid substrate 30, the mechanical strength of each terminal portion is ensured by the small piece portions remaining within the frames of the frame-shaped removal portions 60 of the metal reinforcing layer 37. Moreover, the periphery of the small piece portion facing each connection terminal 35 is insulated from the large-area metal reinforcing layer and is electrically connected to each connection terminal 35, so that the influence on the electrical characteristics is greatly suppressed.

[0041] Therefore, the optical communication module substrate of the present invention has excellent connection strength and electrical characteristics at the connection point P (see FIG. 14) between the wiring substrate 20 and the optoelectronic hybrid substrate 30, and can fully cope with the high-frequencyization of signals and the fine pitch of wirings. By using the optical communication module substrate of the present invention, an optical communication module for high-speed signal transmission with excellent reliability can be provided.

[0042] In the above example, the removed portion of the metal reinforcing layer 37 is only the frame-shaped removed portion 60 surrounding each connection terminal 35, apart from the generally provided through holes 50 and the like shown in FIG. 2. However, for example, as shown in FIG. 8, in order to improve the insertion loss in the high-frequency band of the differential signal wiring portion, a strip-shaped removed portion 61 extending along the wiring can also be formed for the portion facing the wiring of the electrical wiring Y (not shown) together with the above frame-shaped removed portion 60.

[0043] Also, in the above example, in order not to have a capacitance between the independent small piece portion inside the frame-shaped removed portion 60 of the metal reinforcing layer 37 and the connection terminal 35, through holes 31a were provided in the insulating layer 31 in advance to integrate and conduct the above small piece portion with the connection terminal 35. However, in some cases, such a conductive structure is not necessarily required.

[0044] Furthermore, in the above example, when forming the optical communication module substrate, the connection terminal 22 of the wiring substrate 20 and the connection terminal 35 of the optoelectronic hybrid substrate 30 are arranged to overlap each other, and the joint portion of the connection terminals 22 and 35 is electrically connected by solder bumps (see FIG. 1). However, the electrical connection of the connection terminals 22 and 35 is not limited to solder bumps, and can also be performed by other metal bumps such as gold bumps. It can also be performed by interposing a conductive film such as an ACF (anisotropic conductive film). That is, the type of the conductive member for electrically connecting the overlapping connection terminals 22 and 35 is not particularly limited. Also, depending on the structure of the connection terminals 22 and 35, they can be directly joined.

[0045] In addition, in order to electrically connect the connection terminals 22 and 35, not limited to the conductive members as described above, an electrical connector may be used. For example, as shown in FIG. 9, an electrical connector (e.g., a ZIF connector or the like) 70 is attached to one end portion of the optoelectronic hybrid substrate 30 where the connection terminals 35 are arranged, and the connection terminal 71 of this electrical connector 70 is interposed between the connection terminal 35 on the optoelectronic hybrid substrate 30 side and the connection terminal 22 on the wiring substrate 20 side, whereby the two can be electrically connected.

[0046] In this way, for the optoelectronic communication module substrate incorporating the electrical connector 70 as well, since the frame-shaped removal portion 60 is provided in the metal reinforcing layer 37, excellent effects similar to those of the optoelectronic communication module substrate shown in FIG. 1 can be obtained.

[0047] Note that depending on the structure of the electrical connector 70, the optoelectronic hybrid substrate 30 can be arranged upside down, and in an arrangement where the surface of the optoelectronic hybrid substrate 30 on the side where the metal reinforcing layer 37 is provided faces the wiring substrate 20, the two can be electrically connected. That is, by connecting the first connection terminal of the electrical connector 70 to the connection terminal 35 on the optoelectronic hybrid substrate 30 side and connecting the second connection terminal of the electrical connector 70 to the connection terminal 22 on the wiring substrate 20 side, the two can be electrically connected (illustration is omitted). Also in this case, since the frame-shaped removal portion 60 is provided in the metal reinforcing layer 37, excellent effects similar to those of the optoelectronic communication module substrate shown in FIG. 1 can be obtained.

[0048] Also, of course, depending on the structure 70 of the electrical connector used, the arrangement of the connection terminal 35 on the optoelectronic hybrid substrate 30 side, and the arrangement of the connection terminal 22 on the wiring substrate 20 side, the respective terminals may not overlap vertically and may be displaced from each other. Even in such a case, since the frame-shaped removal portion 60 is provided in the metal reinforcing layer 37 of the optoelectronic hybrid substrate 30, excellent effects similar to those of the optoelectronic hybrid substrate shown in FIG. 1 can be obtained.

[0049] The above example is an example of applying the present invention to an optical communication module substrate for differential signal transmission. However, the optical communication module substrate does not necessarily have to be for differential signal transmission. For example, it may be a substrate for single-ended transmission. However, as described above, in high-frequency signal transmission or high-speed signal transmission assuming fine pitch wiring, the advantages of the present invention are utilized, so it is preferably used for high-speed signal transmission applications such as differential signal transmission.

[0050] Next, examples will be described together with comparative examples. However, the present invention is not necessarily limited to the following examples.

Examples

[0051] Two types of tests were conducted to verify the difference in electrical characteristics between the case where a frame-shaped removal portion was formed and the case where no frame-shaped removal portion was formed in the portion of the metal reinforcement layer in the optoelectronic hybrid substrate constituting the optical communication module substrate that faces the connection terminals on the electrical circuit portion side.

[0052] <Verification Test 1> First, a strip-shaped wiring substrate with a width of 10 mm and a length of 60 mm as shown in Fig. 10(a) was fabricated. The substrate has a metal reinforcement layer 121 formed on the back surface with an insulating layer 120 interposed therebetween, and a pair of two electrical wirings Y1 for differential transmission formed on the surface. Connection terminals 122 are provided at both ends of the electrical wiring Y1.

[0053] The materials and thicknesses of the respective layers of the above wiring substrate are as follows. Insulating layer 120: Polyimide, thickness 10 μm Metal reinforcement layer 121: Stainless steel, thickness 20 μm Electrical wiring Y1: Copper, thickness 6 μm (connection terminal 122 has gold plating)

[0054] [Example Sample 1] Then, as shown in FIG. 10(b), on the wiring board, at the portion of the metal reinforcing layer 121 facing the connection terminal 122, a frame-shaped removal portion 123 that individually surrounds each terminal 122 and a strip-shaped removal portion 124 along the electrical wiring Y1 were formed to obtain Example Sample 1. A through-hole was formed at the position of the insulating layer 120 corresponding to the connection terminal 122, and copper, which is the forming material of the electrical wiring Y1, was filled into this through-hole to conduct the small piece portion of the metal reinforcing layer 121 that is independent by the frame-shaped removal portion 123 (see FIG. 3).

[0055] [Comparative Example Sample 2] Also, as shown in FIG. 10(c), on the metal reinforcing layer 121 of the wiring board, no frame-shaped removal portion 123 as in the Example Sample was formed, and only a strip-shaped removal portion 124 along the electrical wiring Y1 was formed to obtain Comparative Example Sample 1.

[0056] Then, for these Example Sample 1 and Comparative Example Sample 1, the following two measurements were performed to evaluate their electrical characteristics. These measurement results are shown in FIGS. 11(a) and (b).

[0057] [Evaluation of Impedance Matching of the Connection Port] For each sample, the differential impedance (Ω) was measured by the time-domain reflectometry (TDR) method using a device (manufactured by Tektronix) consisting of a sampling oscilloscope DSA8200 and a TDR module 80E04. The TDR method inputs a pulse wave with a fast rise time into the sample and measures the impedance using the reflection phenomenon that occurs at the impedance mismatch portion. Thereby, the impedance matching at the connection portion can be evaluated.

[0058] [Evaluation of High-Frequency Signal Quality by Measuring Insertion Loss (Sdd21)] For each sample, the insertion loss (Sdd21) at the time of differential signal input was measured using a 4-port vector network analyzer N5232A device (manufactured by Keysight Technologies). The above insertion loss is the ratio of the transmitted signal energy to the input signal energy to the sample, expressed in dB. Thus, the high-frequency signal quality can be evaluated.

[0059] From the above results, it can be seen that Example Sample 1 has very excellent electrical characteristics compared to Comparative Example Sample 1. That is, as shown in Fig. 11(a), in Comparative Example Sample 1, the impedance decreases at the connection terminal portion, resulting in a large impedance discontinuity, while in Example Sample 1, it can be seen that such a discontinuity does not occur.

[0060] Also, as shown in Fig. 11(b), in the frequency region exceeding 1 GHz, it can be seen that Example Sample 1 has no deterioration in insertion loss due to impedance discontinuity at the connection terminal portion compared to Comparative Example Sample 1, and the signal quality degradation is suppressed.

[0061] And since an independent small piece of the metal reinforcement layer 121 remains also in the portion facing the connection terminal 122 in Example Sample 1, it is considered that Example Sample 1 has mechanical strength comparable to the case where the metal reinforcement layer 121 is not removed.

[0062] Therefore, when the structure of the above Example Sample 1 is applied to the optical communication module substrate of the present invention, it can be seen that an optical communication module substrate of excellent quality having both excellent electrical characteristics and mechanical strength is obtained.

[0063] <Verification Test 2> [Example Sample 2] According to the above description, an optical communication module substrate (Example Sample 2) with the configuration shown in FIG. 9 was fabricated. The structure of each layer and the like conforms to that of a general optical communication module substrate, and the details thereof are omitted. In this Example Sample 2, on the optoelectronic hybrid substrate 30 side, there are eight connection terminals 35 for high-speed differential signals in a row, and eight frame-shaped removal portions 60 are formed (see FIG. 2). Then, as an electrical connector 70 for connecting the connection terminals 35 to the connection terminals 22 on the wiring substrate 20 side, a ZIF connector (FH43B-21S-0.2SHW, manufactured by Hirose Electric Co., Ltd.) was used.

[0064] [Comparative Example Sample 2] An optical communication module substrate (Comparative Example Sample 2) was fabricated in the same manner as Example Sample 2, except that the frame-shaped removal portions 60 were not formed.

[0065] Then, from the optoelectronic hybrid substrate 30 side of each sample (optical communication module substrate), digital signals of 6 Gbps, 8 Gbps, and 10 Gbps were input using a pulse pattern generator M8045A (manufactured by Keysight Technologies), and the output signal waveforms taken out from the wiring substrate 20 side were observed with a sampling oscilloscope N1000A and a module 54754A (both manufactured by Keysight Technologies). For each sample, an eye pattern was obtained by superimposing 3000 observed signal waveforms. In each eye pattern, the value at which the voltage width of the eye opening is maximum was defined as the "eye height" (denoted by H in FIG. 12), and the eye heights H of the samples were compared. The larger the eye height H, the better the quality of the transmitted signal is maintained. The results are as follows.

[0066]

Table 1

[0067] From the above results, it can be seen that Example Sample 2 has suppressed deterioration in the quality of the transmitted signal compared to Comparative Example Sample 2 and has excellent optical communication performance.

[0068] In addition, in the above-described embodiments, specific forms of the present invention have been shown. However, the above embodiments are merely illustrative and should not be construed in a limiting manner. It is contemplated that various modifications obvious to those skilled in the art are all within the scope of the present invention.

Industrial Applicability

[0069] The optical communication module substrate of the present invention ensures sufficient connection strength at the connection point P between the wiring substrate and the optoelectronic hybrid substrate, and moreover has excellent electrical characteristics capable of supporting high-speed signal transmission, and is widely applicable to high-speed signal transmission technologies using differential signal transmission and the like.

Explanation of Reference Numerals

[0070] 30 Optoelectronic hybrid substrate 31 Insulating layer 35 Connection terminal 37 Metal reinforcing layer 60 Frame-shaped removal portion

Claims

1. An optical communication module substrate formed by connecting a wiring substrate and an optoelectronic hybrid substrate, wherein the wiring substrate includes an electrical wiring X and a connection terminal therefor, the optoelectronic hybrid substrate includes an insulating layer, an electrical circuit portion provided on the first surface side of the insulating layer and having pads for mounting optical elements, an electrical wiring Y, and connection terminals therefor, a metal reinforcing layer provided on the second surface side of the insulating layer, and an optical waveguide provided on the second surface side of the insulating layer and partially overlapping the metal reinforcing layer, the connection terminal of the wiring substrate and the connection terminal of the optoelectronic hybrid substrate form an electrical connection point, and in a portion where the metal reinforcing layer of the optoelectronic hybrid substrate faces the connection terminal of the electrical wiring Y provided on the opposite side across the insulating layer, the metal reinforcing layer is removed for each terminal so as to surround the terminal, forming a frame-shaped removal portion, and the inside of the frame-shaped removal portion is a small piece independent from the periphery. The optical communication module substrate is as described above.

2. The optical communication module substrate according to Claim 1, wherein portions of the metal reinforcing layer surrounded by the frame-shaped removal portion are each electrically connected to the connection terminal of the electrical wiring Y.

3. The optical communication module substrate according to Claim 1 or 2, wherein a portion of the metal reinforcing layer facing the electrical wiring Y provided on the opposite side across the insulating layer is removed in a strip shape along the electrical wiring Y.

4. The optical communication module substrate according to any one of Claims 1 to 3, wherein the connection terminal of the wiring substrate and the connection terminal of the optoelectronic hybrid substrate are arranged to overlap each other, and the overlapping connection terminals are electrically connected to each other directly or via a conductive member.

5. The optical communication module substrate according to any one of Claims 1 to 3, wherein the connection terminal of the wiring substrate and the connection terminal of the optoelectronic hybrid substrate are electrically connected via an electrical connector disposed between the wiring substrate and the optoelectronic hybrid substrate.

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