JP7153509B2 - Optical module, optical transmission device, and wiring board - Google Patents

Description

The present invention relates to an optical module, an optical transmission device, and a wiring board, and more particularly to technology for suppressing impedance mismatch.

A connection board that connects an optical subassembly (OSA) and a printed circuit board (PCB) is used in an optical module. Here, the connection board is, for example, a flexible board (FPC: Flexible Printed Circuits). A high-frequency transmission line is arranged on the connection board, and a high-frequency electric signal is transmitted to the high-frequency transmission line. The width of the signal line and the distance between the signal line and the ground conductor layer are set so that the signal line and the ground conductor layer forming the high-frequency transmission line of the connection board have a desired characteristic impedance (for example, 50Ω).

For example, the connection between the optical subassembly and the connection board is connected to each other by soldering, etc. In order to secure the strength of the connection, the width of the terminals (pads) of the connection is set to the line width of the signal line. may be set wider than In this case, an impedance mismatch occurs at the connecting portion, which may degrade the optical waveform quality of the optical module. Patent Literatures 1 and 2 disclose techniques for reducing impedance mismatching at connection portions.

JP 2016-72514 A JP 2010-212617 A

In the technique disclosed in Patent Document 1, the ground conductor terminals arranged at the connecting portion of the substrate are arranged so as to surround the signal terminals. Patent Literature 2 discloses a flexible wiring board in which the line width of a signal terminal is wider than the line width of a signal line (to be a transmission line). Along with the recent miniaturization of optical modules, reduction in the size of each component is desired. For this purpose, it is desirable that the area to be the connecting portion (the area where the terminals are arranged) be narrow. In the techniques disclosed in Patent Documents 1 and 2, the area that serves as the connection portion becomes large, making it difficult to reduce the impedance mismatch and achieve miniaturization.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical module, an optical transmission device, and a wiring board that can achieve both suppression of impedance mismatch and miniaturization.

(1) In order to solve the above-mentioned problems, an optical module according to the present invention includes a metal upper layer arranged on a surface on which a first connecting portion is formed, and a metal lower layer arranged inside along the stacking direction. an optical module comprising: a first substrate having a multilayer structure; and a second substrate having a second connection portion electrically connected to the first connection portion of the first substrate formed on the back surface thereof, the optical module comprising: , the first connection portion of the first substrate faces the second connection portion of the second substrate, and is physically connected to the second connection portion in a plan view so as to overlap the first signal; a line conductor strip; a first signal terminal physically connected to said first signal line conductor strip and extending in a first direction and formed at said first connection; a first signal terminal and a pair of first ground terminals respectively extending in the first direction and formed in the first connection portion are arranged on the upper metal layer of the first substrate and are located on the lower side of the first substrate; A ground layer is disposed on the metal lower layer of the first substrate, is physically connected to the first signal terminal while overlapping with the first signal terminal in a plan view, extends in the first direction, and is formed in the second connection portion. a back signal terminal; and a pair of back ground terminals that overlap and are physically connected to the pair of first connection terminals in plan view, extend in the first direction, and are formed in the second connection portion. are arranged on the rear surface of the second substrate, and the lower ground layer of the first substrate overlaps with the pair of first ground terminals in plan view and extends in the first direction while extending in the first direction. a pair of second ground terminals electrically connected to the pair of first ground terminals; a lower connection ground portion that is physically and electrically connected to the lower connection ground portion, the lower connection ground portion including the inner edges of each of the pair of second ground terminals and the inner edge of the lower connection ground portion, on the inner side of which no metal layer is formed; forming a side opening.

(2) The optical module according to (1) above, wherein the multilayer structure of the first substrate includes one or more metal intermediate layers disposed between the metal upper layer and the metal lower layer. , an intermediate ground layer is disposed on each of the one or more metal intermediate layers, and the intermediate ground layer overlaps with the pair of first ground terminals and the pair of second ground terminals in plan view to form the a pair of third ground terminals extending in a first direction and electrically connected to the pair of first ground terminals and the pair of second ground terminals; An intermediate layer opening having no metal layer formed therein may be formed including inner edges of each of the terminals, and the intermediate layer opening may extend to the distal ends of the pair of third ground terminals.

(3) In the optical module described in (1) or (2) above, the tip portion of the first signal terminal is part of the lower connection ground portion of the lower ground layer in plan view. May be superimposed.

(4) The optical module according to any one of (1) to (3) above, wherein the multilayer structure of the first substrate is arranged on the side opposite to the metal upper layer from the metal lower layer. or a plurality of first metal inner layers, wherein a first inner ground layer is disposed on each of said one or more first metal inner layers, said first inner ground layers extending from said pair of first metal inner layers in plan view; a pair of fourth ground terminals overlapping the one ground terminal and the pair of second ground terminals, extending in the first direction, and electrically connected to the pair of second ground terminals; and an inner connection ground portion extending in two directions and physically connecting the tip portions of the pair of fourth ground terminals, wherein the inner edge of each of the pair of fourth ground terminals and the inner connection ground portion. An inner opening may be formed, including an inner edge, without a metal layer formed therein.

(5) The optical module according to any one of the above (1) to (4), wherein the multilayer structure of the first substrate is arranged on the opposite side of the metal lower layer to the metal upper layer. or a plurality of second metal inner layers, wherein a second inner ground layer is disposed on each of said one or more second metal inner layers, said second inner ground layer extending into said lower opening in plan view A metal layer may also be formed in a region overlapping with the inside of the .

(6) The optical module according to any one of (1) to (5) above, further comprising one or more optical elements, wherein the first substrate is electrically connected to the one or more optical elements. It may be a wiring board connected to the .

(7) In the optical module described in (6) above, the second substrate may be a flexible substrate.

(8) In the optical module according to any one of (1) to (6) above, the first substrate may be a ceramic circuit substrate.

(9) The optical module according to any one of (1) to (8) above, further comprising an optical subassembly on which the first substrate is mounted and another optical subassembly, wherein the optical subassembly Either the assembly or the other optical subassembly may be an optical transmitter and the other may be an optical receiver.

(10) An optical transmission device according to the present invention may be equipped with the optical module according to any one of (1) to (9) above.

(11) A wiring board according to the present invention is a wiring board electrically connected to one or a plurality of optical elements, wherein the wiring board includes a metal upper layer having a first connection portion formed on the surface thereof, and a laminated and a metal lower layer positioned inside along a direction, the first connecting portion is electrically connected to a second connecting portion of another substrate, and the first connecting portion of the wiring board is , a first signal line conductor strip facing the second connection portion of the other substrate and physically connected to the second connection portion in plan view, and the first signal line conductor strip; a first signal terminal physically connected to the terminal and extending in a first direction and formed on the first connection portion; a pair of first ground terminals extending in the respective directions and formed on the first connection portion are arranged on the upper metal layer of the wiring substrate, and a lower ground layer is arranged on the lower metal layer of the wiring substrate. , the lower ground layer overlaps the pair of first ground terminals in plan view, extends in the first direction, and is electrically connected to the pair of first ground terminals. a second ground terminal; and a lower connection ground portion extending in a second direction intersecting the first direction and physically connecting tip portions of the pair of second ground terminals; A lower opening having no metal layer formed therein may be formed including the inner edges of each of the pair of second ground terminals and the inner edge of the lower connection ground portion.

The present invention provides an optical module, an optical transmission device, and a wiring board that achieve both suppression of impedance mismatch and miniaturization.

1 is a schematic diagram showing the configuration of an optical transmission device and an optical transceiver module according to a first embodiment of the present invention; FIG. It is a figure which shows the structure of the optical module main part which concerns on the 1st Embodiment of this invention. 1 is a schematic diagram showing the structure of an optical subassembly according to a first embodiment of the present invention; FIG. 1 is a cross-sectional view showing a general structure of a feedthrough according to the present invention; FIG. FIG. 3 is a schematic diagram showing the structure of the metal upper layer of the feedthrough according to the first embodiment of the present invention; FIG. 2 is a schematic diagram showing the structure of the metal intermediate layer of the feedthrough according to the first embodiment of the present invention; FIG. 3 is a schematic diagram showing the structure of the metal lower layer of the feedthrough according to the first embodiment of the present invention; FIG. 4 is a schematic diagram showing the structure of the second metal inner layer of the feedthrough according to the present invention; FIG. 3 is a schematic diagram showing the structure of the metal upper layer of the feedthrough according to the first embodiment of the present invention; FIG. 2 is a schematic diagram showing the structure of the metal intermediate layer of the feedthrough according to the first embodiment of the present invention; FIG. 3 is a schematic diagram showing the structure of the metal lower layer of the feedthrough according to the first embodiment of the present invention; It is a schematic diagram showing the structure of the flexible substrate according to the first embodiment of the present invention. It is a schematic diagram showing the structure of the flexible substrate according to the first embodiment of the present invention. FIG. 4 is a diagram showing characteristics of the optical module according to the first embodiment of the present invention; FIG. 5 is a schematic diagram showing the structure of the metal upper layer of the feedthrough according to the second embodiment of the present invention; FIG. 5 is a schematic diagram showing the structure of the second metal inner layer of the feedthrough according to the second embodiment of the present invention; FIG. 5 is a diagram showing characteristics of an optical module according to a second embodiment of the present invention; FIG. 10 is a diagram showing characteristics of an optical module according to a third embodiment of the present invention; FIG. 5 is a diagram showing characteristics of an optical module according to a comparative example;

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described specifically and in detail based on the drawings. In addition, in all the drawings for describing the embodiments, members having the same functions are denoted by the same reference numerals, and repeated description thereof will be omitted. It should be noted that the drawings shown below are only for explaining examples of the embodiments, and the sizes of the drawings and the reduced scales described in this example do not necessarily match.

[First Embodiment]
FIG. 1 is a schematic diagram showing the configuration of an optical transmission device 1 and an optical transceiver module 2 according to the first embodiment of the present invention. The optical transmission device 1 has a printed circuit board 11 and an IC 12 . The optical transmission device 1 is, for example, a large-capacity router or switch. The optical transmission device 1 has, for example, a switching function, and is arranged in a base station or the like. A plurality of optical transmission/reception modules 2 are mounted in the optical transmission device 1. Data for reception (electric signals for reception) are acquired from the optical transmission/reception modules 2, and the IC 12 or the like is used to transmit what data to where. It determines whether or not to transmit, generates data for transmission (electrical signal for transmission), and transmits the data to the corresponding optical transmission/reception module 2 via the printed circuit board 11 .

The optical transceiver module 2 is a transceiver having a transmission function and a reception function. The optical transceiver module 2 includes a printed circuit board 21, an optical receiver module 23A that converts an optical signal received via the optical fiber 3A into an electrical signal, and an optical receiver module 23A that converts the electrical signal into an optical signal and transmits the optical signal to the optical fiber 3B. and a transmission module 23B. The optical module 4 (not shown) herein is either the optical receiver module 23A or the optical transmitter module 23B. The printed circuit board 21, the optical receiver module 23A and the optical transmitter module 23B are connected via flexible boards 22A and 22B (FPC), respectively. An electrical signal is transmitted from the optical receiving module 23A to the printed circuit board 21 via the flexible board 22A, and an electrical signal is transmitted from the printed circuit board 21 to the optical transmitting module 23B via the flexible board 22B. The optical transceiver module 2 and the optical transmission device 1 are connected via an electrical connector 5 . The optical receiver module 23A and the optical transmitter module 23B are electrically connected to the printed circuit board 21 and convert optical/electrical signals into electric/optical signals, respectively. The printed circuit board 21 includes a control circuit (eg, IC) for controlling electrical signals transmitted from the optical receiver module 23A and a control circuit (eg, IC) for controlling electrical signals transmitted to the optical transmitter module 23B.

The transmission system according to this embodiment includes two or more optical transmission devices 1, two or more optical transceiver modules 2, and one or more optical fibers 3 (not shown: optical fibers 3A and 3B, for example). One or more optical transceiver modules 2 are connected to each optical transmission device 1 . An optical fiber 3 connects between the optical transceiver modules 2 connected to the two optical transmission devices 1 respectively. Data for transmission generated by one of the optical transmission devices 1 is converted into an optical signal by the connected optical transmission/reception module 2 , and the optical signal is transmitted to the optical fiber 3 . An optical signal transmitted on the optical fiber 3 is received by the optical transmission/reception module 2 connected to the other optical transmission device 1, and the optical transmission/reception module 2 converts the optical signal into an electrical signal, and converts the optical signal into an electrical signal as data for reception. is transmitted to the optical transmission device 1.

An optical receiving module 23A provided in the optical transmitting/receiving module 2 includes one or more optical subassemblies. Here, each of the one or more optical subassemblies is a ROSA (Receiver Optical Subassembly) including one or more light receiving elements. If the optical receiver module 23A includes multiple ROSAs, the flexible substrate 22A includes multiple sub-flexible substrates. The optical transmitter module 23B also includes one or more optical subassemblies. Here, each of the one or more optical subassemblies is a TOSA (Transmitter Optical SubAssembly) including one or more light emitting elements. If the optical transmission module 23B has multiple TOSAs, the flexible substrate 22B has multiple sub-flexible substrates. The optical transmission module 23B according to this embodiment includes one TOSA for transmitting 100 Gbit/s class optical signals, and the TOSA is a box-type TOSA including four light emitting elements.

An optical module according to the present invention comprises an optical subassembly including one or more optical elements, a printed circuit board including a control circuit for controlling the one or more optical elements, and connecting the optical subassembly and the printed circuit board. and a connection board. Here, the optical subassembly according to this embodiment is a TOSA provided in the optical transmission module 23B, and a control circuit (eg, IC) provided in the printed circuit board controls one or more light emitting elements provided in the TOSA. do. The connection board according to this embodiment is a flexible board. In this specification, an optical element is a light-receiving element or a light-emitting element, a light-receiving element is an optical element that converts an optical signal into an electric signal, and a light-emitting element is an optical element that converts an electric signal into an optical signal.

FIG. 2 is a diagram showing the structure of the main part of the optical module 4 according to this embodiment. The optical module 4 shown in the figure is the optical transceiver module 2 shown in FIG. It comprises an optical subassembly 31, a flexible substrate 32 (second substrate), and a printed circuit board 33. The optical subassembly 31 is a box-type TOSA provided in the optical transmission module 23B, and is connected to the flexible substrate 32. A feedthrough 36 (first substrate) is mounted for this purpose. Here, the feedthrough 36 is a wiring board provided in the optical subassembly 31, and is made of a ceramic substrate. A feedthrough 36 is a wiring board that connects the inside and outside of the housing of the optical subassembly 31 . The flexible board 32 is the flexible board 22B shown in FIG. 1, and the printed circuit board 33 is the printed circuit board 21 shown in FIG. The optical module according to the present invention is not limited to an optical transceiver module, but an optical module in which only an optical transmitter optical subassembly (TOSA) or an optical receiver optical subassembly (ROSA) is mounted. ) module, or an optical subassembly (BOSA: Bidirectional Optical Subassembly) that is an optical transceiver. In the optical subassembly 31, the optical transmission module 23B is a TOSA and the optical element provided in the optical subassembly 31 is a light emitting element. In this case, the optical element provided in the optical subassembly 31 is a light receiving element such as a photodiode. Also, the optical subassembly 31 may be a BOSA, in which case the optical elements provided in the optical subassembly 31 are a light emitting element and a light receiving element.

FIG. 3 is a schematic diagram showing the structure of an optical subassembly 31 according to this embodiment. As described above, the optical subassembly 31 is a box-type TOSA having four (4ch) light emitting elements. FIG. 3 is a plan view of the optical subassembly 31, but the lid portion of the housing is omitted in order to explain the internal structure. Note that the x-axis and y-axis are shown in FIG. 3 for ease of explanation. The optical subassembly 31 includes four light emitting elements 34 (LD: Laser Diode), a submount 35 on which the four light emitting elements 34 are mounted, a feedthrough 36, an optical component 37, and a sleeve 38. Prepare. A metal pattern is formed on the surface of the submount 35 and electrically connected to the four light emitting elements 34 . The submount 35 and feedthrough 36 are connected by connecting wires 39 . The optical component 37 collimates the optical signals emitted by the four light emitting elements 34 , multiplexes them, and causes them to enter the sleeve 38 . The light emitting element 34 may be a directly modulated DFB (Distributed FeedBack) laser, an EA (Electro-Absorption) modulator integrated DFB laser, or another laser element. may

The feedthrough 36 has a multi-layer structure including multiple metal layers. As shown in FIG. 3, the feedthrough 36 is formed with four (4ch) coplanar lines. Such a coplanar line is a so-called coplanar line with a ground (ground conductor layer). Five first ground pad portions 81A, 81B, 81C, 81D, 81E are arranged in order along the x-axis direction (second direction) on the first connection portion 36A (surface) of the feedthrough 36 . Of the five first ground pad portions 81A, 81B, 81C, 81D and 81E, two adjacent first ground pad portions are connected to four first signal pad portions 82A, 82B, 82C and 82D, respectively. They are arranged in order along the axial direction. The five first ground pad portions 81A, 81B, 81C, 81D and 81E are physically in contact with the five first ground conductor films 83A, 83B, 83C, 83D and 83E, respectively. The four first signal pad portions 82A, 82B, 82C, 82D are in physical contact with the four first signal line conductor strips 84A, 84B, 84C, 84D, respectively. Four (4ch) coplanar lines are formed in the feedthrough 36 . For example, one coplanar line is configured including the first signal line conductor strip 84A and the first ground conductor films 83A and 83B. Each of the first signal pad portions 82A, 82B, 82C and 82D and each of the first ground pad portions 81A, 81B, 81C, 81D and 81E has a rectangular shape extending in the y-axis direction (first direction). there is Each of the first signal line conductor strips 84A, 84B, 84C, 84D extends along the y-axis direction with a constant line width, but may be bent or extended obliquely in the y-axis direction as necessary. ing. The line width (the length in the lateral direction of the rectangular shape) of the first signal pad portions 82A, 82B, 82C, and 82D is set to the first signal line conductor strips 84A, 84B, 84C, A line width larger (broader) than 84D is desirable. Therefore, the first signal line conductor strip 84 has a transition region where the line width gradually widens at the end on the first signal pad portion 82 side. Further, the tip portions (ends in the +y-axis direction) of the first signal pad portions 82A, 82B, 82C, and 82D are located in front of the tip portions of the first ground pad portions 81A, 81B, 81C, 81D, and 81E (-y axial direction). The tip portions of the first ground pad portions 81A, 81B, 81C, 81D and 81E protrude in the extending direction from the tip portions of the first signal pad portions 82A, 82B, 82C and 82D.

FIG. 4A is a cross-sectional view showing the general construction of a feedthrough 36 according to the invention. For ease of explanation, the y-axis and z-axis are shown in FIG. 4A corresponding to the x-axis and y-axis shown in FIG. As described above, the feedthrough 36 has a multi-layered structure including a plurality of metal layers, and the multi-layered structure has the first connection portion 36A formed on the surface in order along the stacking direction (z-axis direction). It includes a metal top layer UL, one or more metal middle layers ML, a metal bottom layer LL, one or more first metal inner layers IL1, and one or more second inner layers IL2. A metal upper layer UL is disposed on the surface of the feedthrough 36 and a first connection portion 36A is formed in the metal upper layer UL. The metal lower layer LL is arranged inside along the stacking direction (z-axis direction). The metal intermediate layer ML is arranged between the metal top layer UL and the metallization layer LL. The first metal inner layer IL1 is arranged on the opposite side of the metal upper layer UL from the metal lower layer LL. The second inner metal layer IL2 is similarly arranged on the opposite side of the lower metal layer LL to the upper metal layer UL. When the multi-layer structure includes the first metal inner layer IL1, the second metal inner layer IL2 is arranged inside (below) the first metal inner layer IL1. Note that one or more metal intermediate layers ML, one or more first metal inner layers IL1, and one or more second inner layers IL2 are not essential metal layers, and may be arranged as necessary. It does not have to be. The multilayer structure of the feedthrough 36 in this embodiment consists of a metal upper layer UL, one metal middle layer ML and a metal lower layer LL.

FIG. 4B is a schematic diagram showing the structure of the metal upper layer UL of the feedthrough 36 according to the embodiment. FIG. 4C is a schematic diagram showing the structure of the metal intermediate layer ML of the feedthrough 36 according to the embodiment. FIG. 4D is a schematic diagram showing the structure of the metal lower layer LL of the feedthrough 36 according to this embodiment. For ease of explanation, the x-axis, y-axis, and z-axis are shown in FIGS. 4A, 4B, and 4C, respectively, corresponding to the x-axis and y-axis shown in FIG. As shown in FIGS. 3 and 4B, five first ground pad portions 81A, 81B, 81C, 81D, 81E and four first signal pad portions 82A, 82A, 82A, 81E, 82A, 82A, 82A, 82A, 82A, 82A, 82A, 82A, 82A, 82A, 82A, 82A, 82B, 82C and 82D are arranged. As shown in FIGS. 4C and 4D, an intermediate ground layer 90 is disposed on the metal intermediate layer ML, and a lower ground layer 95 is disposed on the metal lower layer LL.

4D, the lower ground layer 95 includes five second ground pad portions 96A, 96B, 96C, 96D, 96E and four lower connection ground portions 97. As shown in FIG. The five second ground pad portions 96A, 96B, 96C, 96D, and 96E overlap the five first ground pad portions 81A, 81B, 81C, 81D, and 81E in plan view, respectively, and extend in the y-axis direction (first 1 direction) and electrically connected to the five first ground pad portions 81A, 81B, 81C, 81D and 81E, respectively. The four lower connection ground portions 97 extend in the x-axis direction (second direction) and are adjacent second ground pad portions among the five second ground pad portions 96A, 96B, 96C, 96D, and 96E. Physically and electrically connect each of the 96 tips. Inner edges of two adjacent second ground pad portions 96 among the five second ground pad portions 96A, 96B, 96C, 96D, and 96E and a lower connection connecting the two second ground pad portions 96 A lower opening 98 is formed including the inner edge of the ground portion 97 and having no metal layer formed therein. Here, four lower openings 98A, 98B, 98C and 98D are formed respectively. Here, the inner edge of each of the two adjacent second ground pad portions 96 is the side facing the adjacent second ground pad portion 96 among the edges on both sides of the second ground pad portion 96 extending in the x-axis direction. It is the edge of The inner edge of the lower connection/ground portion 97 is the edge on the opposite side (−y-axis direction) to the end portion side of the feedthrough 36 among the edges on both sides of the lower connection/ground portion 97 extending in the y-axis direction. . As described above, the tip portions of the first signal pad portions 82A, 82B, 82C and 82D remain in front of the tip portions of the first ground pad portions 81A, 81B, 81C, 81D and 81E. Therefore, the first signal pad portions 82A, 82B, 82C, 82D do not overlap the lower ground layer 95 in plan view. In other words, the lower opening 98 of the lower ground layer 95 extends outside the first signal pad section 82 in plan view. The lower opening 98 is surrounded by the second ground pad portions 96 on both sides (±x-axis direction) and the lower connection ground portion 97 (+y-axis direction). There is also an edge of the ground conductor layer on the side opposite to the lower connection ground portion 97 (in the -y-axis direction), but this arrangement can be freely determined by the designer. The edge of the ground conductor layer may extend outside (-y-axis direction) of the first signal pad portion 82 in plan view. From an impedance matching point of view, the lower opening 98 of the lower ground conductor layer 95, in plan view, may include the transition region of the first signal line conductor strip 84, and furthermore, the first signal line conductor It may also include a portion of strip 84 that extends at a constant line width. Also, the lower opening 98 need not be formed by a completely closed loop, and may be open at the end on the submount 35 side (may be formed by a part of the loop). In this embodiment, the second direction is a direction intersecting the first direction, and the angle formed by the second direction and the first direction is preferably 85° or more and 90° or less, and substantially A right angle is even more desirable. Ideally it should be a right angle.

As shown in FIG. 4C, intermediate ground layer 90 includes five third ground pad portions 91A, 91B, 91C, 91D and 91E. The five third ground pad portions 91A, 91B, 91C, 91D and 91E are, in plan view, five first ground pad portions 81A, 81B, 81C, 81D and 81E and second ground pad portions 96A, 96B, 96C, 96D, 96E, respectively, and extend in the y-axis direction (first direction), and five first ground pad portions 81A, 81B, 81C, 81D, 81E and second ground pad portions 96A, 96B , 96C, 96D and 96E, respectively. An intermediate opening 93 having no metal layer formed therein is formed including inner edges of two adjacent third ground pad portions 91 among the five third ground pad portions 91A, 91B, 91C, 91D, and 91E. be done. Here, four intermediate openings 93A, 93B, 93C and 93D are formed respectively. Each of the four intermediate openings 93A, 93B, 93C, 93D extends to the tip of the adjacent third ground pad portion 91. As shown in FIG. Here, unlike the lower ground layer 95, the intermediate ground layer 90 does not have a connection ground portion. Therefore, the expression that the intermediate opening 93 extends to the tip of the adjacent third ground pad 91 means that the inner edge of the intermediate opening 93 extends to the tip of the third ground pad 91 . It is not constituted by closed loops, meaning open.

As described above, the feedthrough 36 according to the implementation system has a three-layer structure of the metal upper layer UL, the metal intermediate layer ML, and the metal lower layer LL, but is not limited to this. It may further include a first metal inner layer IL1, in which a first inner ground layer having the same structure as the lower ground layer 95 shown in FIG. 4D is arranged under the metal lower layer LL. Underneath the metal lower layer LL may further include a second inner metal layer IL2, on which a second inner ground layer 99 shown in FIG. 4E is disposed. As mentioned above, if the multilayer structure includes a first metal inner layer IL1, the second metal inner layer IL2 is arranged further below the first metal inner layer IL1.

FIG. 4E is a schematic diagram showing the structure of the second metal inner layer IL2 of the feedthrough 36 according to the present invention. As shown in FIG. 4E, a second inner ground layer 99 is disposed on the second metal inner layer IL2, and the second inner ground layer 99 is arranged on the metal upper layer UL in plan view to form four first signal pad portions. 82A, 82B, 82C, and 82D are superimposed. It also overlaps with the lower ground layer 95 arranged in the metal lower layer LL in plan view. The second inner ground layer 99 is a ground conductor layer that spreads uniformly, and metal layers are also formed in areas overlapping with the four lower openings 98A, 98B, 98C, and 98D in plan view. .

Details of the structure of the feedthrough 36 according to this embodiment will be described below. For simplicity of explanation, the explanation will be limited to the first signal pad portion 82B and the pair of first ground pad portions 81B and 81C formed in the first connection portion 36A, and the pad portions associated therewith.

FIG. 5A is a schematic diagram showing the structure of the metal upper layer UL of the feedthrough 36 according to this embodiment. FIG. 5B is a schematic diagram showing the structure of the metal intermediate layer ML of the feedthrough 36 according to the embodiment. FIG. 5C is a schematic diagram showing the structure of the metal lower layer LL of the feedthrough 36 according to this embodiment. The x-axis and y-axis are shown in FIGS. 5A, 5B, and 5C, respectively. The first signal pad portion 82B and the pair of first ground pad portions 81B and 81C are arranged in the metal upper layer UL. The first signal pad portion 82B is physically connected to the first signal line conductor strip 84B, extends in the y-axis direction (first direction), and is formed at the first connection portion 36A. A pair of first ground pad portions 81B and 81C are formed on both sides of the first signal pad portion 82B, are spaced apart from the first signal pad portion 82B, extend in the y-axis direction, and are formed in the first connection portion 36A. be done. As described above, the tip of the first signal pad portion 82B stays short of the tips of the first ground pad portions 81B and 81C.

As shown in FIG. 5C, a lower ground layer 95 is disposed on the metal lower layer LL. The lower ground layer 95 includes a pair of second ground pad portions 96B, 96C and a lower connection ground portion 97. As shown in FIG. The pair of second ground pad portions 96B, 96C overlaps the pair of first ground pad portions 81B, 81C in plan view, extends in the y-axis direction, and extends along the pair of first ground pad portions 81B, 81C. 81C is electrically connected. The pair of second ground pad portions 96B, 96C are electrically connected to the pair of first ground pad portions 81B, 81C through via holes 85, respectively. Here, the pair of first ground pad portions 81B, 81C and the pair of second ground pad portions 96B, 96C are electrically connected via the pair of third ground pad portions 91B, 91C, respectively. A pair of first ground pad portions 82B, 82C and a pair of third ground pad portions 92B, 92C are electrically connected through via holes 85, and a pair of third ground pad portions 92B, 92C are electrically connected. and a pair of second ground pad portions 97B and 92C are electrically connected through via holes 85 in the same manner. The line width of the lower connection ground portion 97 of the lower ground layer 95 is smaller (narrower) than the line width of the second ground pad portion 96 . No via hole 85 is formed in the lower connection ground portion 97 .

As shown in FIG. 5B, an intermediate ground layer 90 is disposed on the metal intermediate layer ML. Intermediate ground layer 90 includes a pair of third ground pad portions 91B and 91C. The pair of third ground pad portions 91B and 91C overlap the pair of first ground pad portions 81B and 81C and the pair of second ground pad portions 96B and 96C in plan view and extend in the y-axis direction. Also, it is electrically connected to the pair of first ground pad portions 81B, 81C and the pair of second ground pad portions 96B, 96C.

6A and 6B are schematic diagrams showing the structure of the flexible substrate 32 according to this embodiment. Although four (4ch) grounded coplanar lines are formed on the flexible substrate 32, only one grounded coplanar line is shown here for the sake of simplicity. The flexible substrate 32 is based on a flexible dielectric layer 40 . For ease of explanation, the x-axis and y-axis are shown in FIGS. 6A and 6B corresponding to the x-axis and y-axis shown in FIG. As shown in FIG. 6A, a pair of ground conductor films 41 and a second signal line conductor strip 42 are formed on the surface of (the dielectric layer 40 of) the flexible substrate 32 according to this embodiment. Although the second signal line conductor strip 42 extends along the y-axis direction with a constant line width, it may be bent or extended obliquely in the y-axis direction as necessary. A pair of ground conductor films 41 are arranged on both sides of the second signal line conductor strip 42 . A pair of surface ground pad portions 43 and surface signal pad portions 44 are further formed on the surface of (the dielectric layer 40 of) the flexible substrate 32 . A pair of surface ground pad portions 43 and surface signal pad portions 44 both have a rectangular shape extending in the y-axis direction. The surface signal pad portion 44 is physically connected to the second signal line conductor strip 42 . The line width of the surface signal pad portion 44 is preferably larger than the line width of the second signal line conductor strip 42 , and the line width of the second signal line conductor strip 42 gradually increases at the end on the surface signal pad portion 44 side. It has a wider transition area. The pair of ground conductor films 41 are in physical contact with the pair of surface ground pad portions 43, respectively.

As shown in FIG. 6B, a rear ground conductor layer 45 and a rear signal pad portion 46 are formed on the rear surface of (the dielectric layer 40 of) the flexible substrate 32 according to this embodiment. The back ground conductor layer 45 includes a pair of back ground pad portions 47 . The back surface signal pad portion 46 and the pair of back surface ground pad portions 47 are formed on the second connection portion 32A on the back surface of the flexible substrate 32 . The first connecting portion 36A of the feedthrough 36 faces the second connecting portion 32A of the flexible substrate 32, and is physically connected to the second connecting portion 32A by overlapping with the second connecting portion 32A in plan view. That is, the back signal pad portion 46 faces the first signal pad portion 82, and the pair of back ground pad portions 47 and the pair of first ground pad portions 81 face each other and overlap each other when viewed from above. Connected. A pair of back ground pad portion 47 and back signal pad portion 46 both have a rectangular shape extending in the y-axis direction. A pair of surface grounding pad portion 43 and a surface signal pad portion 44 overlap a pair of back surface grounding pad portion 47 and back surface signal pad portion 46 in plan view, respectively, and are electrically connected through via holes 49 . be done. Preferably, the rectangular shape of the front signal pad portion 44 substantially matches the rectangular shape of the back signal pad portion 47 . Similarly, the rectangular shape of the pair of front ground pad portions 43 preferably substantially matches the rectangular shape of the pair of back ground pad portions 47 . Also, unlike the positional relationship between the first signal pad portion 82 and the pair of first ground pad portions 81, the end portion of the surface signal pad portion 44 on the side of the second signal line conductor strip 42 (lower end in FIG. 6A) is It is located at the same position in the y-axis direction as the ends of the pair of surface grounding pad portions 43 . Similarly, the end of the back signal pad portion 46 (bottom end in FIG. 6B) is at the same position as the end of the pair of back ground pad portions 47 in the y-axis direction. The main portion of the back ground conductor layer 45 is physically connected to the pair of back ground pad portions 47 , and the back ground conductor layer 45 is spaced apart from the back signal pad portion 46 . Since the tip portion of the first signal pad portion 82B stays short of the tip portions of the first ground pad portions 81B and 81C, a portion of the rear signal pad portion 46 (a portion including the lower end in FIG. 6B) is the first ground pad portion. Although it does not overlap with the signal pad portion 82B, there is substantially no problem in terms of characteristics. A ground conductor layer may be formed on the front surface of the flexible substrate 32, signal wiring may be formed on the rear surface, and the surface on which the signal wiring is formed may be connected to the first connecting portion 36A.

FIG. 7 is a diagram showing characteristics of the optical module 4 according to the embodiment. FIG. 7 shows the S21 transmission characteristic (dB) in the region M from the end of the first connection portion 36A on the light emitting element 34 side (the end of the flexible substrate 32) to the light emitting element 34 in the optical subassembly 31, and the frequency (GHz). ) as a function of As shown in FIG. 7, a dip (DIP) in the S21 transmission characteristic that may occur periodically is suppressed. The lower opening 98 of the lower ground layer 95 compensates for the impedance reduction due to the line width of the first signal pad portion 82 being wider than the line width of the first signal line conductor strip 84 . The effect is further enhanced by the lower connection/earth portion 97 as compared with the conventional art. Thus, in the optical module 4 according to this embodiment, both impedance matching and miniaturization are achieved.

[Second embodiment]
FIG. 8A is a schematic diagram showing the structure of the metal upper layer UL of the feedthrough 36 according to the second embodiment of the present invention, and FIG. 8B shows the structure of the second metal inner layer IL2 of the feedthrough 36 according to the embodiment. It is a schematic diagram showing. The multilayer structure of the feedthrough 36 according to this embodiment is a four-layer structure consisting of a metal upper layer UL, a metal intermediate layer ML, a metal lower layer LL, and a second metal inner layer IL2. The upper metal layer UL according to the embodiment shown in FIG. 8A has the same structure as the upper metal layer UL according to the first embodiment shown in FIG. 5A, except that the structure of the first signal pad portion 82B is different. there is The tip portion of the first signal pad portion 82B according to the first embodiment remains short of the tip portions of the first ground pad portions 81B and 81C. The tip portion of 82B is at the same position in the y-axis direction as the tip portions of the first ground pad portions 81B and 81C. The structures of the metal intermediate layer ML (intermediate ground layer 90) and the metal lower layer LL (lower ground layer 95) according to this embodiment are the same as in the first embodiment. The multi-layer structure of the feedthrough 36 according to this embodiment further includes a second metal inner layer IL2, unlike the first embodiment, in which the second inner ground layer 99 is arranged. . The second inner ground layer 99 overlaps the first signal pad portion 82B arranged in the metal upper layer UL in plan view. It also overlaps with the lower ground layer 95 arranged in the metal lower layer LL in plan view. The second inner ground layer 99 is a ground conductor layer that spreads uniformly, and a metal layer is also formed in a region that overlaps with the lower opening 98B in plan view.

The flexible substrate 32 according to this embodiment has the same structure as the flexible substrate 32 according to the first embodiment shown in FIGS. 6A and 6B. The tip of the first signal pad portion 82B is located at the same position in the y-axis direction as the tip of the first ground pad portions 81A and 82B. The pad portion 46 (and the surface signal pad portion 44) have the same shape and are preferably arranged so as to match when viewed from above.

In the feedthrough 36 according to this embodiment, the tip of the first signal pad portion 82B arranged in the metal upper layer UL is located at the same position in the y-axis direction as the tips of the first ground pad portions 81B and 81C. As a result, it overlaps with a part of the lower connection ground portion 97 of the lower ground layer 95 arranged in the metal lower layer LL in plan view. By positively overlapping the first signal pad portion 82B with a portion of the lower ground layer 95 in a plan view, a remarkable effect can be obtained for impedance matching.

Here, a feedthrough according to a comparative example for comparing the effects of the feedthrough 36 according to the embodiment will be described. The multilayer structure of the feedthrough according to the comparative example includes two metal intermediate layers ML and a second inner contact layer ML shown in FIG. and a second metal inner layer IL2 in which the formation 99 is arranged. The feedthrough 36 according to the embodiment and the feedthrough according to the comparative example both have a four-layer structure, but differ in the structure of the metal layer, which is the third layer downward from the surface. In the feedthrough 36 according to this embodiment, the first signal pad portion 82 overlaps with a portion of the lower ground layer 95 (a portion of the lower connection ground portion 97) arranged in the third layer in plan view. is doing. On the other hand, in the feedthrough according to the comparative example, unlike the embodiment, the first signal pad portion includes an intermediate ground layer 90 (a ground conductor layer having the same structure) as the third layer in the metal intermediate layer ML. Since there is no connection ground portion in the intermediate ground layer 90, it does not overlap with the intermediate ground layer 90 in a plan view.

FIG. 9 is a diagram showing characteristics of the optical module 4 according to this embodiment. FIG. 11 is a diagram showing characteristics of an optical module according to a comparative example. 9 and 11, like FIG. 7, show S21 transmission characteristics (dB) in the optical subassembly 31 as a function of frequency (GHz). As shown in FIG. 9, compared to FIG. 11, dips (DIP) in the S21 transmission characteristic that can occur periodically are suppressed in the high frequency region.

[Third Embodiment]
The multi-layer structure of the feedthrough 36 according to the third embodiment of the present invention includes a metal upper layer UL shown in FIG. 8A, a metal lower layer LL shown in FIG. 5C, and a lower ground layer 95 shown in FIG. It is a four-layer structure consisting of a first metal inner layer IL1 with one inner ground layer and a second metal inner layer IL2 shown in FIG. 8B. The flexible substrate 32 according to this embodiment has the same structure as the first and second embodiments.

FIG. 10 is a diagram showing characteristics of the optical module 4 according to this embodiment. As shown in FIG. 10, dips (DIP) in the S21 transmission characteristic that may occur periodically are suppressed in the high frequency region.

The optical module 4 (optical transceiver module 2), the optical transmission device 1, and the optical transmission system according to the embodiment of the present invention have been described above. The present invention is not limited to the above embodiments, and various modifications are possible, and the present invention can be widely applied. The configurations described in the above embodiments can be replaced with configurations that are substantially the same, configurations that produce the same effects, or configurations that can achieve the same purpose.

In the above embodiment, the first substrate according to the present invention is the wiring substrate (feedthrough 36) provided in the optical subassembly 31, but it is not limited to this. The printed circuit board 21 may have a multilayer structure, with the printed circuit board 32 as the first board and the flexible board 33 as the second board. In the above embodiment, both the shape of the first signal pad portion 82 and the shape of the first ground pad portion 81 are rectangular. Terminals of other shapes may be used. The same applies to other pad portions.

In the above embodiment, the transmission line formed in the feedthrough 36 is a coplanar line with a ground, but is not limited to this, and may be another transmission line such as a microstrip line. The same applies to the flexible substrate 32 and the printed circuit board 33 . In addition, although the second connecting portion 32A of the flexible substrate 33 physically connected to face the first connecting portion 36A of the feedthrough 36 is composed of the rear signal pad portion 46 and the rear grounding pad portion 47, Without limitation, the surface of flexible substrate 32 may overlap feedthrough 36 (or printed circuit board 33). The first and second substrates according to the present invention are not limited to feedthrough 36 (or printed circuit board 33) and printed circuit board 32, but may be other board combinations.

1 optical transmission device 2 optical transceiver module 3, 3A, 3B optical fiber 4 optical module 11, 21, 33 printed circuit board 12 IC, 22A, 22B, 32 flexible substrate 23A optical receiver module 23B, light Transmission module, 31 optical subassembly, 32A second connection, 34 light emitting element, 35 submount, 36 feedthrough, 36A first connection, 37 optical component, 38 sleeve, 39 connection wire, 40 dielectric layer, 41 surface ground conductor film 42 second signal line conductor strip 43 front ground pad portion 44 front signal pad portion 45 back ground conductor layer 46 back signal pad portion 47 back ground pad portion 49, 85 via hole 81A, 81B, 81C, 81D, 81E first ground pad portion 82A, 82B, 82C, 82D first signal pad portion 83A, 83B, 83C, 83D, 83E ground conductor film, 84A, 84B, 84C, 84D first signal line conductor strips 90 intermediate ground layers 91, 91A, 91B, 91C, 91D, 91E intermediate ground pads 93A, 93B, 93C, 93D intermediate openings 95 lower ground layers 96, 96A, 96B, 96C, 96D , 96E, lower ground pad portion, 97 lower ground connection portion, 98, 98A, 98B, 98C, 98D lower opening, IL1 first metal inner layer, IL2 second metal inner layer, ML metal intermediate layer, LL Metal Lower Layer, UL Metal Upper Layer.

Claims (11)

a first substrate having a multi-layer structure including a metal upper layer arranged on the surface and forming the first connecting part, and a metal lower layer arranged inside along the stacking direction;
a second substrate having a second connection portion electrically connected to the first connection portion of the first substrate formed on the back surface;
An optical module comprising
the first connection portion of the first substrate faces the second connection portion of the second substrate and is physically connected to the second connection portion in a plan view, and
a first signal line conductor strip including a portion extending with a constant line width; and a first signal physically connected to the first signal line conductor strip and extending in a first direction and formed at the first connection portion. a terminal, and a pair of first ground terminals formed on the first connection portion on both sides of the first signal terminal and extending in the first direction while being spaced apart from the first signal terminal. disposed on the metal top layer of the first substrate;
a lower ground layer disposed on the metal underlayer of the first substrate;
a rear surface signal terminal that overlaps and is physically connected to the first signal terminal in a plan view, extends in the first direction, and is formed in the second connection portion; and the pair of first ground terminals. a pair of rear surface ground terminals that overlap and are physically connected in a plan view, extend in the first direction, and are formed in the second connection portion are arranged on the rear surface of the second substrate;
The lower ground layer of the first substrate overlaps the pair of first ground terminals in plan view, extends in the first direction, and is electrically connected to the pair of first ground terminals. and a lower connection ground extending in a second direction intersecting the first direction and physically and electrically connecting the tips of the pair of second ground terminals. including the part and
a lower opening having no metal layer formed therein is formed including inner edges of each of the pair of second ground terminals and inner edges of the lower connection ground part ;
The lower opening overlaps, in plan view, the portion of the first signal line conductor strip that extends with the constant line width.
An optical module characterized by: The optical module according to claim 1,
said multilayer structure of said first substrate comprising one or more metal intermediate layers disposed between said metal top layer and said metal bottom layer;
an intermediate ground layer disposed on each of the one or more metal intermediate layers;
The intermediate ground layer overlaps the pair of first ground terminals and the pair of second ground terminals in plan view, extends in the first direction, and extends in the first direction. a pair of third ground terminals electrically connected to the pair of second ground terminals;
An intermediate layer opening having no metal layer formed therein is formed including inner edges of each of the pair of third ground terminals, and the intermediate layer opening extends to tip portions of the pair of third ground terminals. ,
An optical module characterized by: The optical module according to claim 1 or 2,
a tip portion of the first signal terminal overlaps a part of the lower connection ground portion of the lower ground layer in plan view;
An optical module characterized by: The optical module according to any one of claims 1 to 3,
the multi-layered structure of the first substrate comprising one or more first metal inner layers disposed opposite the metal top layer from the metal bottom layer;
a first inner ground layer disposed on each of the one or more first metal inner layers;
The first inner ground layer overlaps with the pair of first ground terminals and the pair of second ground terminals in plan view, extends in the first direction, and overlaps with the pair of second ground terminals. a pair of electrically connected fourth ground terminals, and an inner connection ground portion extending in the second direction and physically connecting tip portions of the pair of fourth ground terminals;
forming an inner opening in which no metal layer is formed, including inner edges of each of the pair of fourth ground terminals and inner edges of the inner connection ground part;
An optical module characterized by: The optical module according to any one of claims 1 to 4,
the multi-layered structure of the first substrate comprising one or more second metal inner layers disposed opposite the metal top layer from the metal bottom layer;
a second inner ground layer disposed on each of the one or more second metal inner layers;
In the second inner ground layer, a metal layer is also formed in a region overlapping with the inner side of the lower opening in plan view.
An optical module characterized by: The optical module according to any one of claims 1 to 5,
further comprising one or more optical elements,
The first substrate is a wiring substrate electrically connected to the one or more optical elements,
An optical module characterized by: The optical module according to claim 6,
The second substrate is a flexible substrate,
An optical module characterized by: The optical module according to any one of claims 1 to 6,
The first substrate is a ceramic circuit substrate,
An optical module characterized by: The optical module according to any one of claims 1 to 8,
an optical subassembly on which the first substrate is mounted;
other optical subassemblies and
further comprising
Either one of the optical subassembly and the other optical subassembly is an optical transmitter and the other is an optical receiver,
An optical module characterized by: An optical transmission device mounted with the optical module according to any one of claims 1 to 9. A wiring board electrically connected to one or more optical elements,
The wiring board has a multi-layered structure including a metal upper layer on the surface of which the first connection part is formed, and a metal lower layer positioned inside along the stacking direction, and the first connection part is the first metal layer of another substrate. 2 electrically connected to the connecting portion,
the first connection portion of the wiring substrate faces the second connection portion of the other substrate and is physically connected to the second connection portion in a plan view, and
a first signal line conductor strip including a portion extending with a constant line width; and a first signal physically connected to the first signal line conductor strip and extending in a first direction and formed at the first connection portion. a terminal, and a pair of first ground terminals formed on the first connection portion on both sides of the first signal terminal and extending in the first direction while being spaced apart from the first signal terminal. disposed on the metal upper layer of the wiring board,
a lower ground layer disposed on the metal underlayer of the wiring substrate;
The lower ground layer overlaps the pair of first ground terminals in plan view, extends in the first direction, and is electrically connected to the pair of first ground terminals. 2 ground terminals, and a lower connection ground portion extending in a second direction intersecting the first direction and physically connecting tip portions of the pair of second ground terminals,
a lower opening having no metal layer formed therein is formed including the inner edges of the pair of second ground terminals and the inner edge of the lower connection ground part ;
The lower opening overlaps, in plan view, the portion of the first signal line conductor strip that extends with the constant line width.
A wiring board characterized by:

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