JP2009111170A - Optical communication module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce the impact of radiation noise on a frame ground in a wide frequency band. <P>SOLUTION: This optical tranceiver module 2 includes: a package 8a, a TOSA 4a having a plurality of lead pins 12a, 12b, 12c and 12d that are electrically connected to the package 8a, a main circuit substrate 5a having conductive portions 20a, 20b, and 20c for electrically connecting the lead pins 12a, 12b and 12c to an electronic circuit 24 used for driving the TOSA and an SG electrode, and a secondary circuit substrate 5b mounted on the main circuit substrate 5a so that a conductive portion 28 electrically connects to the conductive portion 20a of the main circuit substrate 5a under a condition that both portions face each other, while a capacitance component is formed between a conductive portion 30 arranged on a main surface M3 and the conductive portion 28 arranged on a main surface M2. The lead pin 12a is electrically connected to the conductive portion 30 through an FPC 38. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical communication module that transmits an optical transmission signal via an optical transmission medium.

2. Description of the Related Art Conventionally, there is known a radiation noise reduction device for reducing the influence of radiation noise generated from a cable connected to a printed board on a frame ground (FG) (see Patent Document 1 below). This radiation noise reduction device includes an FG electrode provided on a printed circuit board and connected to a shielded cable, an SG electrode (SG: signal ground), and a capacitor element provided between the FG electrode and the SG electrode. The noise current generated by radiation noise and flowing to the frame ground is shunted to the signal ground.
JP 2003-283177 A

  In general, an optical communication module such as an optical transceiver module operates at a high speed on the order of GHz. Therefore, in order to reduce the influence of the radiation noise on the frame ground (generation of noise current), between the FG electrode and the SG electrode. It is desirable to set the capacitance of the capacitor to be inserted into several pF or more. However, chip-type capacitors used in optical communication modules do not have the above-described capacitance, and it is difficult to develop such capacitors.

  In addition, when connecting the case pin connected to the package (FG) of the optical transceiver module and the printed circuit board, there are cases where the positional relationship between the case pin and the printed circuit board is restricted from the viewpoint of standards and manufacturing efficiency. When the case pin needs to have a certain length due to such a restriction, the case pin has an inductance component, and as a result, a configuration close to an LC series resonance circuit due to the capacitance component between FG and SG and the case pin. May occur. At this time, in order to make the stem constituting the package sufficiently low in the operating frequency band of the optical transceiver module, the time constant of the LC circuit constituted by the capacitance component and the case pin is set to a frequency near or higher than the transmission rate. It is necessary to set to. However, crosstalk and EMI radiation in the optical transceiver module are not only problems with the frequency component of the maximum transmission rate specified by each optical transceiver, but also with a frequency component lower than the maximum transmission rate. It is necessary to reduce the impedance of the stem even in a low frequency region than the time constant of the LC circuit.

  In order to reduce the impedance of the stem in the low frequency region and not to reduce the time constant of the LC circuit, it is necessary to increase the capacitance between FG and SG and decrease the inductance of the case pin. In order to increase the capacity, it is conceivable to increase the area of the capacity. However, there is a pad for soldering to the transmission signal lead pin on the printed circuit board side of the optical transceiver module. There is a limit. Therefore, a large number of capacitor layers on the surface of the printed circuit board must be taken. However, when the number of capacitor layers is increased, the distance between the base of the case pin and the upper surface of the printed circuit board also increases. As a result, the case pin needs to be extended and connected to the upper surface of the printed circuit board, and the inductance component of the case pin tends to increase.

  Therefore, the present invention has been made in view of such problems, and an object thereof is to provide an optical communication module that can effectively reduce the influence of radiation noise on the frame ground in a wide frequency band.

  In order to solve the above-described problems, an optical communication module of the present invention is an optical communication module that transmits an optical transmission signal via an optical transmission medium, and is used for a metal package and a ground electrically connected to the package. An optical transmission module having a plurality of lead pins including a lead pin and generating an optical transmission signal in response to an electric signal applied through the plurality of lead pins, and a circuit unit for driving the optical transmission module and a ground. A main circuit board having a conductive portion for electrically connecting to a potential; a first conductive portion provided on the first main surface; and a second conductive portion provided on the second main surface; A sub-circuit board mounted on the main circuit board so that the second conductive part and the conductive part of the main circuit board are electrically connected to each other. Equipped with ground lee Pins are electrically connected to the first conductive portion of the sub-circuit board via a flexible printed board provided between the first main surface.

  According to such an optical communication module, the ground lead pin of the optical transmission module connected to the FG is connected to the first conductive portion formed on the first main surface of the sub circuit board, and the sub circuit. The sub circuit board is placed on the main circuit board in a state where the second conductive part formed on the second main surface of the board faces and is connected to the conductive part of the main circuit board. As a result, the capacitance component formed by the sub circuit board is connected between the ground lead pin and the conductive portion of the main circuit board, and it becomes easy to secure the capacitance component of the noise filter. Even if the thickness of the sub circuit board must be increased in order to restrict the arrangement on the main circuit board and secure the capacity, the conductive part of the main circuit board and the ground lead pin are routed through the sub circuit board. Thus, when connecting, the wiring part on the flexible substrate can be widened. Thereby, in a wide operating frequency band, the inductance of the ground lead pin is reduced, and radiation noise can be effectively released from FG to SG. As a result, the influence of radiation noise such as crosstalk in the package can be sufficiently suppressed.

  The sub circuit board is a multi-layer board having a plurality of unit layers, and the first conductive part and the second conductive part are provided on the first surface and the second surface of the unit layer, respectively. Is preferred. In this case, even if it is necessary to reduce the size of the sub circuit board due to restrictions on the arrangement on the main circuit board, the capacitance component connected to the ground lead pin can be increased, so that even when used at a high transmission rate, radiation is possible. Noise can surely escape from FG to SG.

  According to the optical communication module of the present invention, it is possible to effectively reduce the influence of radiation noise on the frame ground in a wide frequency band.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an optical communication module according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a partially broken perspective view showing a configuration of an optical transceiver module 2 according to a preferred embodiment of the present invention. FIG. 2 shows a TOSA 4a (TOSA: Transmitter Optical Sub-) which is an optical transmission module of FIG. It is the top view seen from the axial direction before the attachment to the optical transceiver module 2 of Assembly). The optical transceiver module 2 is a small optical transceiver including a TOSA 4 a, a ROSA 4 b (ROSA: Receiver Optical Sub-Assembly), a circuit board 5, and a case 6. The TOSA 4 a and the ROSA 4 b are fixed to the side wall 6 a of the case 6, and the circuit board 5 is accommodated in the case 6. The case 6 is made of a metal material and has a role as an FG. The circuit board 5 is formed using an insulating prepreg as a main material, and a circuit pattern is formed on the surface thereof.

  The TOSA 4a is an optical transmission module having a laser diode 7 and a metal package 8a that houses the laser diode 7. The laser diode 7 has an anode terminal and a cathode terminal (not shown), and a laser beam (optical transmission signal) according to a bias current and a modulation current (electric signal) supplied / applied from outside the package 8a. Is generated. The package 8a is a coaxial package made of a metal material, and a flange 16a and a flange 16b are formed on the side surfaces thereof, and a groove 18 is provided between the flange 16a and the flange 16b. The package 8a is electrically insulated from all electric elements (for example, the laser diode 7) included in the TOSA 4a. The laser diode 7 is housed in the end 10a of the package 8a, and the laser light emitted from the laser diode 7 is transmitted to the outside from the end 14 via an optical transmission medium such as an optical fiber.

  The TOSA 4a further includes a stem 10a provided at the other end 10 of the package 8a, and four lead pins 12a, 12b, 12c, and 12d extending from the stem 10a (FIG. 2). The lead pins 12a are FG terminals electrically connected to the package 8a, and are insulated from any of the electric elements of the TOSA 4a housed in the package 8a. The lead pins 12b and 12c are light emission drive terminals connected to the anode terminal and the cathode terminal of the laser diode 7, respectively. The lead pin 12d is a monitor output terminal for monitoring the light output of the laser diode 7. is there.

  The TOSA 4 a having the above configuration is fixed to the side wall 6 a by fitting the side wall 6 a of the case 6 into the groove 18. In this way, the case 6 of the optical transceiver module 2 and the package 8a of the TOSA 4a are electrically connected.

  The ROSA 4b is an optical receiver subassembly having a photodiode (not shown) and a package 8b made of a metal material that accommodates the photodiode (the portion excluding the sleeve from the optical receiver subassembly corresponds to the optical receiver module). .) The package 8b is covered with a sleeve made of a resin material. The package 8b is electrically insulated from any of the electric elements accommodated by the ROSA 4b. The ROSA 4b is provided with a groove 18a similarly to the TOSA 4a, and the side wall 6a of the case 6 is fitted into the groove 18a. Thereby, ROSA4b is fixed to the side wall 6a. The ROSA 4b package 8b is insulated from the side wall 6a by a sleeve made of a resin material covering the package. Further, the ROSA 4b has a plurality of lead pins 12e, and each lead pin 12e is connected to a plurality of electrodes made of a metal material provided on the main surface M1 of the circuit board 5.

  The circuit board 5 is a circuit board for electrically connecting the TOSA 4a and the ROSA 4b to an electronic circuit (circuit unit) 24 described later, and includes a main circuit board 5a and a sub circuit board 5b. On the main surface M1 of the main circuit board 5a, a plurality of electrode patterns such as conductive portions 20a to 20c made of a metal material are formed. The conductive portions 20b and 20c are electrically connected to the electronic circuit 24, and the conductive portion 20a is electrically connected to the SG electrode provided in the main circuit board 5a. The lead pins 12b and 12c of the TOSA 4a are electrically connected to the conductive portions 20b and 20c by solder bonding, respectively.

  The electronic circuit 24 has a signal ground potential (SG potential) and is provided on the main surface M1 of the circuit board 5 on which the conductive portions 20a to 20c are provided. The electronic circuit 24 is equipped with an amplifier circuit for amplifying the received signal from the ROSA 4b, a drive circuit for driving the laser diode 7 of the TOSA 4a, and the like.

  Next, the configuration of the sub circuit board 5b will be described. FIG. 3 is a longitudinal sectional view along the direction of the central axis of the TOSA 4a of the sub circuit board 5b of FIG.

  The sub circuit board 5b is placed on the main surface M1 of the main circuit board 5a, and is a multilayer board formed by laminating ten unit boards 26 made of an insulating material such as a sheet-like prepreg. On one main surface M2 of the sub circuit board 5b on the main circuit board 5a side, that is, on the surface of the lowermost unit substrate 26, a conductive layer 28a that is an electrode pattern made of a metal material is formed. A conductive layer 30a that is an electrode pattern is formed on the other main surface M3 of the circuit board 5b, that is, on the surface of the uppermost unit substrate 26. The conductive layer 30a is an electrode for connecting the lead pin 12a of the TOSA 4a, and the conductive layer 28a is an electrode for connecting to the conductive portion 20a of the main circuit board 5a.

  Further, the sub circuit board 5b includes a metal conductive layer 28b and two conductive layers 28b formed on the boundary surface of the adjacent unit boards 26 so as to face each other with the two unit boards 26 interposed therebetween. A metal conductive layer 30b formed to face the conductive layer 28b with the two unit substrates 26 interposed therebetween is further formed on the boundary surface of the unit substrate 26 located in the middle. The conductive layer 28b is connected to the conductive layer 28a through through holes 32 and 34 formed so as to penetrate the plurality of unit substrates 26, and the conductive layer 30b penetrates the plurality of unit substrates 26. The conductive layer 30a is electrically connected through the formed through hole 36. The through holes 32, 34, and 36 may be filled with a metal material or may be coated with a metal material only on the inner surface. Therefore, the conductive layers 28a and 28b constitute one conductive part 28 electrically connected to each other, and the conductive layers 30b and 30a constitute one conductive part 30 electrically connected to each other.

  Thus, the conductive layer 28b of the conductive portion 28 and the conductive layers 30a and 30b of the conductive portion 30 are formed on the sub circuit board 5b so as to face each other. Furthermore, by disposing the insulating unit substrate 26 between the conductive layer 28b and the conductive layers 30a and 30b adjacent to the conductive layer 28b, a capacitance component is provided between the conductive layer 28b and the conductive layers 30a and 30b. Will be formed.

  FIG. 4 is a longitudinal sectional view along the central axis of the TOSA 4a showing the connection form of the sub circuit board 5b, the TOSA 4a and the main circuit board 5a. As shown in the figure, the sub circuit board 5b is placed on the main surface M1 of the main circuit board 5a with the conductive part 20a and the conductive layer 28a of the sub circuit board 5b facing each other. The layer 28a is electrically connected by solder bonding. The conductive portion 20a of the main circuit board 5a is connected to an SG electrode formed inside the main circuit board 5a through a through hole. Here, the sub circuit board 5b is arranged so that the end of the main surface M2 protrudes from the main surface M1 of the main circuit board 5a toward the TOSA 4a.

  Furthermore, the lead pins 12a of the TOSA 4a are electrically connected to the conductive layer 30a on the main surface M3 of the sub circuit board 5b through a flexible printed circuit board (hereinafter referred to as FPC) 38. The FPC 38 has a structure in which a wide metal conductor film 42 covered with a resin is formed on the surface of the insulator flat plate 40 using a flexible long insulator flat plate 40 as a base member. At both ends, holes 44a and 44b for connecting the conductor film 42 to the lead pin 12a of the TOSA 4a and the conductive layer 30a of the sub circuit board 5b are formed (FIG. 2). The conductive film 42 is provided with exposed portions 46a and 46b exposed around the holes 44a and 44b. The exposed portions 46a and 46b can be electrically connected to the lead pin 12a or the conductor layer 30a. . That is, with the lead pin 12a penetrating through the hole 44a, the lead pin 12a and the exposed portion 46a of the FPC 38 are connected by solder joint. Further, the FPC 38 is bent so that the other end on the hole 44b side is in contact with the main surface M3 with one end on the hole 44a side held on the lead pin 12a side, and the exposed portion 46b of the conductor layer 30a and the hole 44b Are connected by solder joints.

  According to the optical transceiver module 2 described above, the FG lead pin 12a of the TOSA 4a connected to the FG is connected to the conductive layer 30a formed on the main surface M3 of the sub circuit board 5b and the sub circuit board 5b. The sub circuit board 5b is placed on the main circuit board 5a with the conductive layer 28a formed on the main surface M2 facing and connected to the conductive portion 20a of the main circuit board 5a. As a result, the capacitance component formed by the sub circuit board 5b is connected between the FG lead pin 12a and the conductive portion 20a of the main circuit board 5a, and the capacitance component of the noise filter can be easily secured. Further, the area of the sub circuit board 5b is limited due to various metal patterns, circuit components, and the like on the main circuit board 5a, and the thickness of the sub circuit board 5b is ensured to ensure the capacity of the sub circuit board 5b with respect to the operating frequency. In such a case, the lead pin for FG tends to be long and its inductance component tends to increase. In the present embodiment, when the conductive portion 20a of the main circuit board 5a and the FG lead pin 12a are connected via the sub circuit board 5b, the root of the lead pin 12a and the conductive portion 30a are connected by the FPC 38. The wiring part for connecting both can be efficiently and widely taken. As a result, in a wide operating frequency band including a low frequency region, the inductance of the ground lead pin is reduced, and radiation noise can be effectively released from FG to SG. As a result, the influence of radiation noise such as crosstalk in the TOSA 4a package can be sufficiently suppressed.

  In addition, since the capacitance component is formed by disposing the unit substrate 26 between the conductive layers 30a and 30b and the conductive layer 28b in the sub circuit board 5b, the capacitance component is increased even if the sub circuit board 5b is downsized. Capacitance is facilitated, and even if the sub circuit board 5b interposed between the FG lead pin 12a and the main circuit board 5a is small, the influence of radiation noise such as crosstalk in the TOSA package can be sufficiently suppressed. In addition, the thickness and area of the sub circuit board 5b can be variously changed, and the degree of freedom in arrangement of the TOSA 4a and the main circuit board 5a is increased.

  Further, since each of the conductive portion 28 and the conductive portion 30 is electrically connected to each other through a through hole penetrating the unit substrate 26, even if the thickness of the sub circuit board 5b or the number of stacked layers is changed. Processing when connecting the conductive layers is facilitated.

  Here, FIG. 8 shows a connection form of a conventional optical transceiver module. Here, according to SFP-MSA (Small Form Factor Pluggable Multi-Source Agreement) which is an industry standard for small optical transceivers, the thickness of the connector portion of the circuit board of the optical communication module is defined as 1 mm. Therefore, in order to produce a circuit board at low cost, it is desirable to unify the thickness of the circuit board to 1 mm. In SFP-MSA, the total height of the transceiver (the total height of the main body, excluding structures protruding from the main body for engagement with the cage) is 8.6 mm to 8.5 mm, and the total width (the total width of the main body) is It is specified as 13.7 mm, and the LC connector used is also specified as 2.29 mm from the bottom of the receptacle to the optical axis. Therefore, assuming that the outer diameter of the TOSA is about 5.5 mm and the lead pin for FG is arranged on the circumference having a diameter of 4.0 mm, the lead pin is positioned at a height of about 4.5 mm at the maximum from the bottom of the transceiver. .

  In the conventional connection form shown in FIG. 8, when following the above-described standard, the thickness D1 of the circuit board 905 is set to 1 mm, and the distance D2 from the transceiver bottom surface to the optical axis of the TOSA 904a is set to 2.29 mm. In this case, the height from the base end portion of the lead pin 912a of the TOSA 904a to the surface of the circuit board 905 is about several millimeters. Accordingly, the lead pin 912a becomes longer and the inductance of the FG lead pin 912a becomes larger. As a result, noise in the TOSA 904a package cannot be sufficiently released above a certain frequency.

  On the other hand, in order to shorten the lead pin, a method of designing the distance in the optical axis direction of the TOSA 904a between the stem of the TOSA 904a and the circuit board 905 in FIG. However, in this case, it is necessary to bend the lead pin 912a toward the circuit board 905 at 90 degrees or more, which increases EMI (electromagnetic noise), which is not preferable. Although it is conceivable to arrange pins on the stem so that the forming of the lead pins 912a is not necessary, the circuit arrangement on the circuit board and the arrangement of the electrode patterns may be modified at any time to improve the characteristics. Therefore, it is not practical in cost to correct the pin arrangement of the TOSA each time the correction is made. In addition, from the viewpoint of component arrangement inside the TOSA, it may be impossible to correct the pin arrangement of the TOSA following the board correction. On the other hand, in the optical transceiver module 2, the EMI is reduced without causing an increase in manufacturing cost by connecting the pins of the TOSA and the sub circuit board through a flexible FPC with a wide conductor portion. be able to.

  In addition, this invention is not limited to embodiment mentioned above. For example, a plurality of sub circuit boards may be provided in parallel on the main circuit board, and the lead pins of the TOSA and the conductive portions on the main circuit board may be connected via the plurality of sub circuit boards. More specifically, a plurality of conductive portions 20a connected to the SG electrodes in the main circuit substrate 105a are formed on the main surface M1 of the main circuit substrate 105a, and the respective conductive portions 20a on the main surface M1 are formed on the main surface M1. A plurality of sub circuit boards 105b are placed on (FIG. 5). The conductive layer 30a provided on the main surface M3 of each sub circuit board 105b and the lead pin 12a of the TOSA 4a are connected by one FPC 138 (FIG. 6). This FPC 138 has a structure in which a wide conductor film 142 is formed on the surface of an insulating flat plate 140. One end of the FPC 138 is provided with a hole 144a for connecting the conductor film 142 and the lead pin 12a of the TOSA 4a. At the end, three holes 144b for connecting to the conductive layers 30a of the three sub circuit boards 105b are formed side by side (FIG. 7). The conductor film 142 is provided with exposed portions 146a and 146b exposed to the outside around the holes 144a and 144b. The lead pin 12a is electrically connected to the conductor film 142 of the FPC 138 while penetrating through the hole 144a. At the same time, the end portions of the FPC 138 on the hole 144b side are bent so as to extend in contact with the main surface M3 of the three sub circuit boards 105b, whereby the three conductor layers 30a and the conductor film 142 are electrically connected. With such a configuration, even when the installation area of the sub circuit board 105b on the main circuit board 105a is largely limited, the capacitance component connected to the ground lead pin can be increased, so that it is used at a high transmission rate. But radiation noise can be surely escaped from FG to SG.

1 is a partially broken perspective view showing a configuration of an optical transceiver module according to a preferred embodiment of the present invention. It is the figure seen from the central axis direction of TOSA of FIG. It is a longitudinal cross-sectional view along the central axis direction of TOSA of the sub circuit board of FIG. FIG. 2 is a longitudinal sectional view taken along the central axis of TOSA of the optical transceiver module of FIG. 1. It is a top view of the main circuit board in the modification of the present invention. It is a longitudinal cross-sectional view along the central axis line of TOSA of the optical transceiver module of the modification of this invention. It is the figure seen from the central axis direction of TOSA of FIG. It is a figure which shows the connection form of the conventional optical transceiver module.

Explanation of symbols

2 ... Optical transceiver module, 5a ... Main circuit board, 5b ... Sub circuit board, 8a ... Package, 12a ... Lead pin for FG, 12b, 12c, 12d ... Lead pin, 20a, 20b, 20c ... Conductive part, 24 ... Electronic circuit ( Circuit portion), 28, 30 ... conductive portion, M2, M3 ... main surface, 38, 138 ... FPC (flexible printed circuit board).

Claims (2)

An optical communication module for transmitting an optical transmission signal via an optical transmission medium,
An optical transmission having a metal package and a plurality of lead pins including a ground lead pin electrically connected to the package, and generating an optical transmission signal according to an electric signal applied through the plurality of lead pins Modules,
A main circuit board having a conductive portion for electrically connecting the plurality of lead pins to the circuit portion for driving the optical transmission module and a ground potential;
A capacitive component is formed between the first conductive portion provided on the first main surface and the second conductive portion provided on the second main surface, and the second conductive portion and A sub circuit board mounted on the main circuit board so as to be electrically connected in a state of facing the conductive portion of the main circuit board,
The ground lead pin is electrically connected to the first conductive portion of the sub circuit board via a flexible printed board provided between the first main surface and the ground lead pin.
An optical communication module. The sub circuit board is a multilayer board having a plurality of unit layers, and each of the first conductive portion and the second conductive portion is provided on the first surface and the second surface of the unit layer. ,
The optical communication module according to claim 1.

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