Patent Publication Number: US-2016231516-A1

Title: Communication Module and Signal Transmission Device Including the Same

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a communication module which is used in signal transmission between boards inside electronic devices and also used in signal transmission between such electronic devices, and a signal transmission device including the same. 
     BACKGROUND OF THE INVENTION 
     A general signal transmission device includes a board on which a semiconductor element (IC chip) and a communication module are mounted. In the following descriptions, such aboard on which an IC chip and a communication module are mounted may be called as a “motherboard”. 
     An existing communication module includes a module frame. The module frame contains therein, a module board on which an IC, optical element, etc. are mounted. In addition, at the bottom surface of the module frame, a plurality of terminal pads are provided in a reticular pattern and electrically connected to the module board. Here, the bottom surface of the module frame means a surface that faces a mounting surface of a motherboard when the communication module is mounted onto the motherboard. 
     Upon mounting the communication module having such a structure on a motherboard, an interposer is disposed between the bottom surface of the module frame and the mounting surface of the motherboard. That is, the communication module and the motherboard are electrically connected via the interposer. Normally, the communication module stacked onto the interposer is pressed against the interposer by a spring. 
     SUMMARY OF THE INVENTION 
     In the existing communication module, the terminal pads are provided in substantially the whole area of the bottom surface of the module frame. In addition, the communication module and the motherboard are electrically connected via the interposer disposed between the bottom surface of the module frame and the mounting surface of the motherboard. That is, there is almost no gap between the communication module and the motherboard. More specifically, there is almost no gap between the bottom surface of the module frame and the mounting surface of the motherboard. 
     Accordingly, the connection of the communication module and an optical fiber needs to be made at an upper surface (a surface opposite to the bottom surface) of the module frame. More specifically, an optical connector is needed to connect the communication module and the optical fiber and the optical connector is needed to be disposed on the upper surface of the module frame. 
     Meanwhile, the amount of heat generation of the communication modules is on the increase along with an increase of speed of signals inputted to and outputted from the communication modules. Thus, improvements of heat-dissipation efficiency and cooling efficiency of the communication modules are required. 
     However, when the existing communication module is mounted on the motherboard, there is almost no gap between the bottom surface of the module frame and the mounting surface of the motherboard and the optical connector is disposed on the upper surface of the module frame. Thus, an effective heat-dissipating surface in the surface of the module frame is small and the surface of the module frame is also difficult to receive cooling wind. That is, the heat-dissipation efficiency and cooling efficiency of the existing communication module are far from good. 
     Further, when a heatsink is disposed on the communication module, the heatsink is needed to be disposed clear of the optical connector that is disposed on the upper surface of the module frame. That is, in the upper surface of the module frame, an area to be thermally connected to the heatsink is limited to an area not covered with the optical connector. 
     An aim of the present invention is to ensure space between a board and a communication module mounted on the board, the space being usable in various usages such as heat dissipation, cooling, and cable connection. 
     A communication module according to the present invention is a communication module mounted on a board inside a signal transmission device, the communication module includes: a module frame having a lower plate and an upper plate facing each other and containing a module board between the lower plate and the upper plate; and a second connector that is protruded from the lower plate and connected to a first connector and provided in the board. In the communication module, when the second connector is connected to the first connector, a gap is formed between the lower plate of the module frame and the board. 
     According to an aspect of the present invention, a communication cable is led out from the lower plate of the module frame. 
     According to another aspect of the present invention, a light-emitting element provided in the module board, an optical fiber as the communication cable, and a connecting portion for changing a running direction of light emitted from the light-emitting element and letting the light enter the optical fiber are provided. 
     According to another aspect of the present invention, a light-receiving element provided in the module board, an optical fiber as the communication cable, and a connecting portion for changing the running direction of light emitted from the optical fiber and letting the light enter the light-receiving element are provided. 
     According to another aspect of the present invention, there is provided a metal plate disposed between the upper plate of the module frame and the module board, so that the light-emitting element is thermally connected to the module frame via the metal plate. 
     According to another aspect of the present invention, there is provided a metal plate disposed between the upper plate of the module frame and the module board, so that the light-receiving element is thermally connected to the module frame via the metal plate. 
     According to another aspect of the present invention, the optical fiber is connected to a part of the connection portion protruded from the lower plate. 
     According to another aspect of the present invention, the second connector has a protruding portion protruded from the lower plate and linearly extending along a side of the lower plate; and an electrode line, which is composed of a plurality of electrodes formed at a constant interval along a longitudinal direction of the protruding portion, is provided in each of a first side surface and a second side surface of the protruding portion, the second side surface facing the first side surface. 
     A signal transmission device of the present invention is a signal transmission device having a board on which a semiconductor element and a communication module are mounted, the communication module includes: a module frame having a lower plate and an upper plate facing each other and containing a module board between the lower plate and the upper plate; and a second connector that is protruded from the lower plate and connected to a first connector and provided in the board, and a gap is formed between the lower plate of the module frame and the board. 
     In an aspect of the present invention, a heatsink is mounted on the upper plate of the module frame of the communication module. 
     According to the present invention, between the board and the communication module mounted on the board, space usable in various usages such as heat dissipation, cooling, and cable connection is ensured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating an example of a signal transmission device to which the present invention is applied; 
         FIG. 2A  is a plan view of the signal transmission device illustrated in  FIG. 1 ; 
         FIG. 2B  is a side view of the signal transmission device illustrated in  FIG. 1 ; 
         FIG. 3A  is an enlarged plan view of a communication module illustrated in  FIG. 1 ; 
         FIG. 3B  is an enlarged side view of the communication module illustrated in  FIG. 1 ; 
         FIG. 3C  is an enlarged bottom view of the communication module illustrated in  FIG. 1 ; 
         FIG. 4  is an enlarged cross-sectional view of the communication module illustrated in  FIG. 1 ; 
         FIG. 5  is an enlarged perspective view of a male connector and a female connector illustrated in  FIG. 1 ; 
         FIG. 6A  is a cross-sectional view of the male connector taken along the line A-A illustrated in  FIG. 5 ; 
         FIG. 6B  is a cross-sectional view of the female connector taken the line B-B illustrated in  FIG. 5 ; and 
         FIG. 6C  is a cross-sectional view illustrating a fitting state of the male connector and the female connector. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an example of an embodiment of the present invention will be described with reference to the accompanying drawings. A signal transmission device  1  illustrated in  FIGS. 1 to 2B  includes a board (motherboard  3 ) for mounting a semiconductor element (IC chip  2 ) and a plurality of connection modules  10 , and a heatsink  20  composing a cooling mechanism for cooling the communication modules  10 . The heatsink  20  includes a heat-absorbing plate  21  having a substantially-rectangular shape in a plan view and a plurality of heat-dissipating fins  22  provided on the heat-absorbing plate  21 . The heat-absorbing plate  21  and the heat-dissipating fins  22  are integrally formed using a metal (aluminum or copper) having a good heat conductivity. 
     In the present embodiment, near a side (longitudinal side) of the IC chip  2 , four of the communication modules  10  are arranged in a line parallel to the side. Upon such a plurality of communication modules  10 , the heatsink  20  is mounted such that a side (longitudinal side) of the heat-absorbing plate  21  is in parallel with the side of the IC chip  2 . 
     As illustrated in  FIGS. 3A to 3C , each of the communication modules  10  has a module frame  11 . The module frame  11  has two pairs of sides (sides  11   a  and lib and sides  11   c  and  11   d ) facing each other and its exterior appearance is substantially square in a plan view and a bottom view. Each length of the sides of the module frame  11  is 10 to 30 mm. However, the lengths of the module frame  11  can be optionally set and are not limited to the numeral range mentioned above. In addition, the shapes of the module frame  11  in a plan view and a bottom view are not limited to a square or a substantial square. 
     As illustrated in  FIG. 4 , the module frame  11  is composed of a first frame  31  and a second frame  32 . The lower half of the module frame  11  is formed of the first frame  31  and the upper half of the module frame  11  is formed of the second frame  32 . 
     The first frame  31  includes a lower plate  31   a  forming a bottom surface of the module frame  11 , a sideplate  31   b  extended from an edge of the lower plate  31   a  to be substantially orthogonal to the lower plate  31   a,  and a supporting leg  31   c  extended from an external surface of the lower plate  31   a  in an opposite direction to the direction in which the side plate  31   b  is extended. That is, an inner surface of the lower plate  31   a  is surrounded by the side plate  31   b.  In addition, as illustrated in  FIG. 3C , the supporting leg  31   c  is provided at each of two corners of an external surface of the lower plate  31   a.  In other words, the supporting leg  31   c  is provided at each of two corners of a bottom surface of the module fame  11 . More specifically, one of the supporting legs  31   c  is provided near a cross section of the side lib and the side  11   c  of the module frame  11 , and the other of the supporting legs  31   c  is provided near a cross section of the side  11   b  and the side  11   d.    
     As illustrated in  FIG. 4 , the second frame  32  includes an upper plate  32   a  forming the upper surface of the module frame  11 , and a side plate  32   b  extended from an edge of the upper plate  32   a  to be substantially orthogonal to the upper plate  32   a.  That is, an inner surface of the upper plate  32   a  is surrounded by the side plate  32   b.    
     The first frame  31  and the second frame  32  are assembled such that both edge surfaces of the side plates  31   b  and  32   b  of the first and second frames  31  and  32  abut each other. A containing space  33  is formed between the first frame  31  and the second frame  32  facing each other. A module board  34  is contained in the containing space  33  of the module frame  11 . The module board  34  is disposed to be parallel to the lower plate  31   a  of the first frame  31  and the upper plate  32   a  of the second frame  32 . An edge of the module board  34  is sandwiched and supported between edge surfaces of the facing side plates of the first frame  31  and the second frame  32 . The module board  34 , which is in parallel with both of the lower plate  31   a  and the upper plate  32   a,  has a first surface facing the inner surface of the lower plate and a second surface facing the inner surface of the upper plate. That is, the module board  34  is contained between the lower plate  31   a  and the upper plate  32   a  of the module frame  11 . In the following description, the first surface of the module board  34  will be called as a “back surface  34   a ” and the second surface of the module board  34  will be called as a “front surface  34   b”.    
     At the substantially center of the module board  34 , a rectangular opening portion  35  is formed. In addition, a metal plate  36  is attached to the front surface  34   b  of the module board  34 , so that the opening portion  35  is closed by the metal plate  36 . Inside the opening portion  35 , a plurality of elements (light-emitting elements  37  in the present embodiment) and a plurality of driver ICs  38  for driving the light-emitting elements  37  are disposed. That is, the light-emitting elements  37  and the driver ICs  38  are mounted on the metal plate  36 , and thermally connected to the metal plate  36 . In other words, the light-emitting elements  37  and the driver ICs  38  are mounted on one of main surfaces of the metal plate  36 . The entire of the other main surface of the metal plate  36  is in contact with the inner surface of the upper plate of the second frame  32  via a heat-conductive rubber  39  functioning as a heat conductive member. More specifically, the light-emitting elements  37  and the driver ICs  38  provided in the module boards  34  are thermally connected to the module frame  11 , particularly to the upper plate  32   a  of the second frame  32 , via the metal plate  36  and the heat conductive rubber  39 . 
     Around the opening portion  35  of the module board  34 , a plurality of electrode pads are formed. Each of the electrode pads is connected to a predetermined one of the driver ICs  38  via a bonding wire  40 . In addition, each of the driver ICs  38  is connected to a predetermined one of the light-emitting elements  37  via a bonding wire  41 . Here, by making a depth (thickness of the module board  34 ) of the opening  35  and heights of the driver IC  38  and the light element  37  substantially the same, lengths of the bonding wires  40  and  41  are made as short as possible. 
     At the back surface  34   a  of the module board  34 , there is provided a second connector to be connected to a first connector that is provided in a mounting surface  3   a  of the motherboard  3 . In the following description, the first connector provided in the motherboard  3  will be called as a “female connector  50 ”, and the second connector provided in the communication module  10  will be called as “a male connector  60 ”. 
     As illustrated in  FIG. 5 , the male connector  60  includes a base portion  61  fixed to the module board  34  ( FIG. 4 ), and a protruding portion  62  extended from the base portion  61 . The base portion  61  and the protruding portion  62  are integrally formed using a synthetic resin. At both ends in a longitudinal direction of the base portion  61 , a positioning protrusion  61   a  is formed. An end portion of the module board  34  ( FIG. 4 ) is fitted between the positioning protrusions  61   a  and  61   a  facing each other. The protruding portion  62  is extended from a lower surface of the base portion  61  to be orthogonal to the lower surface of the base portion  61 . As illustrated in  FIGS. 3C and 4 , the protruding portion  62  of the male connector  60  is protruded to the outside from an opening portion provided in the lower plate  31   a  of the first frame  31 . As illustrated in  FIG. 3C , the protruding portion  62  protruded to the outside from the lower plate  31   a  of the first frame  31  is linearly extended along one side of the lower plate  31   a.  That is, the protruding portion  62  of the male connector  60  is protruded from the bottom surface of the module frame  11  and linearly extended along the side  11   a  of the module frame  11 . 
     As illustrated in  FIGS. 5 and 6A , the plurality of electrodes  63  are formed at a constant interval in the first side surface  62   a  of the protruding portion  62  and the second side surface  62   b  facing the first side surface  62   a.  In other words, in each of the first side surface  62   a  and the second side surface  62   b,  the electrode line formed of the plurality of electrodes  63  formed at a constant interval is provided. An end of each of the electrodes  63  penetrates the base portion  61  and protrudes from the upper surface of the base portion  61 . The protruding end portion of each of the electrodes  63  is connected to the driver IC  38  via a printed wiring, which is not illustrated, formed in the module board  34  illustrated in  FIG. 4 . 
     Note that, to avoid crosstalk, some of the electrodes  63  formed in the protruding portion  62  are used as terminals for grounding. That is, not all of the electrodes  63  formed in the protruding portion  62  can be used as terminals for signal input/output. Thus, for not only avoiding crosstalk but also for inputting and outputting a large number of signals, it is needed to increase the total number of the electrodes  63 . Meanwhile, the area of an electrode forming surface (first side surface  62   a,  second side surface  62   b ) of the protruding portion  62  is limited. Accordingly, it is needed to make the interval between the electrodes as narrow as possible. That is, it is needed to form the electrodes  63  at a narrow pitch. In the present embodiment, an interval (P 1 ) between the electrodes illustrated in  FIG. 5  is 0.5 mm and an interval (P 2 ) between electrode lines illustrated in  FIG. 6A  is 1.5 mm. 
     As illustrated in  FIG. 4 , the male connector  60  having the above-described structure is fitted into the female connector  50  provided in the mounting surface  3   a  of the motherboard  3 . As illustrated in  FIGS. 5 and 6B , in the female connector  50 , a fitting groove  51  is formed linearly along the longitudinal direction, the fitting groove  51  opening upwards and being capable of inserting thereto and removing therefrom the protruding portion  62  of the male connector  60 . The plurality of electrodes  52  are provided inside the fitting groove  51 . An end of each of the electrodes  52  penetrates a bottom portion of the fitting groove  51  and protrudes outside the fitting groove  51 . A protruding end of each of the electrodes  52  is connected to the IC chip  2  via a printed wiring, which is not illustrated, formed in the motherboard  3  illustrated in  FIG. 1 . 
     As illustrated in  FIG. 4 , the communication module  10  is mounted on the motherboard  3  by fitting the male connector  60  into the female connector  50 . In addition, as illustrated in  FIG. 6C , when the male connector  60  is fitted into the female connector  50 , the electrodes  63  and  52  provided in the respective connectors  60  and  50  are in contact with each other and electrically conducted. In this manner, the IC chip  2  and each of the communication modules  10  illustrated in  FIG. 1  are electrically connected, so that transmission and reception of signals are enabled. 
     As illustrated in  FIG. 4 , when the male connector  60  is fitted into the female connector  50 , the supporting leg  31   c , which is extended from the bottom surface of the module frame  11 , abuts the mounting surface  3   a  of the motherboard  3 . In other words, the length of the supporting leg  31   c  is set to be the length that makes the supporting leg  31   c  abut the mounting surface of the motherboard  3  when the male connector  60  is fitted into the female connector  50 . That is, the communication module  10  mounted on the motherboard  3  is supported by the supporting leg  31   c  and the male connector  60  that is protruded from the bottom surface (lower plate  31   a  of the first plate  31 ) of the module frame  11 . In other words, the bottom surface of the module frame  11  has an area in which the male connector  60  protruded from the bottom surface is present, and an area in which the male connector  60  is not present. Thus, when the communication module  10  is mounted on the motherboard  3 , that is, when the male connector  60  is fitted into the female connector  50 , a gap  70  corresponding to the height of both the connectors  50  and  60  fitted together is formed between the mounting surface  3   a  of the motherboard  3  and the area in which the male connector  60  is not present in the bottom surface of the module frame  11 . Thus, in comparison to the embodiment in which there is no gap between the bottom surface of the module frame  11  and the mounting surface  3   a  of the motherboard  3 , the amount of heat dissipation from the bottom surface of the module frame  11  is increased. In addition, the bottom surface of the module frame  11  is easy to receive cooling wind. That is, the gap  70  is used as space for heat dissipation and cooling. 
     In addition, as illustrated in  FIG. 3C , since the male connector  60  is provided near the side  11   a  of the module frame  11  and the supporting leg  31   c  is provided near both ends of the side  11   b  facing the side  11   a,  the communication module  10  is supported in a balanced manner. 
     Note that, between the female connector  50  and the male connector  60  which are connected as illustrated in  FIG. 6C , there are a fitting length and an effective fitting length. The effective fitting length means a length included in the fitting length and also a length in a range capable of maintaining the electrical conduction between the female connector  50  and the male connector  60 . That is, upon inserting the protruding portion  62  of the male connector  60  into the fitting groove  51  of the female connector  50 , although the connectors  50  and  60  are physically fitted with each other in the beginning, they are not electrically conducted. Thereafter, when the protruding portion  62  of the male connector  60  is further inserted into the fitting groove  51  of the female connector  50 , the connectors  50  and  60  are electrically conducted to each other. Further, since the effective length defines a length (e.g., 0.5 to 1.0 mm) to some extent, the electric conduction of the connectors  50  and  60  is maintained within that range even when the male connector  60  is inserted to and removed from the female connector  60 . In other words, the male connector  60  fitted into the female connector  50  can be shifted to some extend in an upward and downward direction in the plane of the paper of  FIG. 6  while maintaining the electric conduction with the female connector  60 . 
       FIG. 4  is referred again. At the back surface  34   a  of the module board  34 , an optical connector  80  as a connecting portion is provided in addition to the male connector  60 . A part of the optical connector  80  is protruded to the outside of the lower plate  31   a  through the opening portion provided in the lower plate  31   a  of the first frame  31 . In other words, a part of the optical connector  80  is exposed to the outside of the module frame  11 . Accordingly, in the following description, the part of the optical connector  80  exposed to the outside of the lower plate  31   a  will be called as an “exposed portion  80   a ”. That is, the exposed portion  80   a  of the optical connector  80  is protruded to the gap  70  formed between the bottom surface (the lower plate  31   a  of the first frame  31 ) of the module frame  11  and the mounting surface  3   a  of the motherboard  3 , and a plurality of communication cables (optical fibers  81 ) are connected to the exposed portion  80   a.  In other words, the optical fibers  81  connected to the module frame  11  via the optical connector  80  are led out around the module frame  11  through the gap  70 . 
     However, there is an embodiment of disposing the whole optical connector inside a module frame. In such an embodiment, the optical fibers connected to the optical connector inside the module frame are led to the outside of the module frame from a side surface (for example, from the side plate  31   b  or the side plate  32   b  illustrated in  FIG. 4 ) of the module frame. In this case, the portion from which the optical fibers are led out is covered by boots so as to protect the optical fibers. On the contrary, in the communication module  10  of the present embodiment in which the optical fibers  81  are connected to a part (exposed portion  80   a ) of the optical connector  80  protruded to the gap  70  that is formed between the motherboard  3  and the module frame  11 , the boots is not needed and thus the cost can be reduced. In addition, in the communication module of the present embodiment, as compared to the embodiment in which the optical fibers are led out from the side surface of the module frame, the starting point of bending of the optical fibers  81 , which are led out from the module frame  11 , can be set near the module frame  11 . Thus, the space necessary for handling the optical fibers  81  is reduced. 
     The optical connector  80  illustrated in  FIG. 4  changes the running direction of light emitted from the light-emitting element  37  and letting the light enter an end surface of the optical fiber  81 . That is, the light-emitting element  37  and the optical fiber  81  are optically coupled. More specifically, the optical connector  80  has a lens array and a mirror, so that the light emitted from the light-emitting element  37  and entered to the lens array is reflected on the mirror, and the light enters the end surface of the optical fiber  81 . In the present embodiment, the running direction of the light, which is emitted from the light-emitting element  37  illustrated in  FIG. 4  in a downward direction in the plane of the paper of  FIG. 4 , is converted by 90 degrees by the optical connector  80 , and the light enters the end surface of the optical fiber  81 . 
     As described above, in the present embodiment, the gap  70  is formed between the bottom surface of the module frame  11  and the mounting surface  3   a  of the motherboard  3 . The gap  70  is used also as space for connecting the optical fibers  81  as communication cable. 
     As illustrated in  FIGS. 1 and 4 , on the communication module  10 , the heatsink  20  is disposed. Particularly, as illustrated in  FIG. 4 , the heat-absorbing plate  21  of the heatsink  20  is stacked on the upper surface (the upper plate  32   a  of the second frame  32 ) of the module frame  11  interposing the heat-conductive rubber  90  as a heat conductive member. In the embodiment of connecting the module frame  11  and the optical fibers  81  using the gap  70  formed between the bottom surface of the module frame  11  and the mounting surface  3   a  of the motherboard  3 , there is no convex or concave in an external surface of the upper plate of the second frame  32  forming the upper surface of the module frame  11 . Thus, in the whole area, the external surface of the upper plate of the second frame  32  is thermally connected to the heat-absorbing plate  21  of the heatsink  20 . Here, it has been already described that the light-emitting element  37  and the driver IC  38  are thermally connected to the upper plate  32   a  of the second frame  32  via the metal plate  36  and the heat-conductive rubber  39 . That is, heat generated from the light-emitting element  37  and the driver IC  38  is efficiently transmitted to the heatsink  20  via the upper plate  32   a  of the second frame  32 . 
     Note that, as illustrated in  FIG. 1 , the heatsink  20  mounted on the communication module  10  is fixed to the motherboard  3  by bolts  91  at four corners. More specifically, a cylindrical spacer  92  is disposed in each of between the heat-absorbing plate  21  of the heatsink  20  and the motherboard  3 . A female screw is formed in each of the upper end surface and lower end surface of the spacers  92 . The bolt  91 , which penetrates the heat-absorbing plate  21  from above to below of the heat-absorbing plate  21 , is coupled to the female screw formed in the upper end surface of the spacer  92 . A bolt  93 , which penetrates the motherboard  3  from below to above of the motherboard  3 , is coupled to the female screw formed in the lower end of the spacer  92 . 
     In addition, as illustrated in  FIG. 2 , each of the communication modules  10  is disposed across two heat-dissipating fin groups in a plan view. More specifically, the communication module  10   a  is disposed across the heat-dissipating fin group  22 A and heat-dissipating fin group  22 B. The communication module  10   b  is disposed across the heat-dissipating fin group  22 B and heat-dissipating fin group  22 C. The communication module  10   c  is disposed across the heat-dissipating fin group  22 C and heat-dissipating fin group  22 D. The communication module  10   d  is disposed across the heat-dissipating fin group  22 D and heat-dissipating fin group  22 E. That is, two heat-dissipating fin groups are allocated to one communication module  10 . 
     Further, between adjacent ones of the heat-dissipating fin groups, each of gaps  23  is provided. Each of the gaps  23  plays a role of increasing cooling effect by generating turbulence between adjacent heat-dissipating fin groups. 
     The present invention is not limited to the above-described embodiment and various modifications and alterations can be made within the scope of the present invention. For example, although the male connector has been provided in the connection module and the female connector has been provided in the board in the above-described embodiment, the female connector can be provided in the communication module and the male connector can be provided in the board. The supporting leg for supporting the communication module can be integrally formed with the board. Moreover, a member being independent with respect to the communication module and the board can be disposed as a supporting leg, between the communication module and the board. 
     In the above-described embodiment, the light-emitting element and the driver IC are mounted on the module board. That is, the communication module according to the above-described embodiment is used for transmission. However, a light-receiving element and an amplifying IC maybe mounted on the module board. That is, a communication module for reception and a signal transmission device including the same are included in the present invention. In addition, on the module board, a light-emitting element and a driver IC, and a light-receiving element and an amplifying IC may be mounted. That is, the communication module for transmission and reception and a signal transmission device including the same are included in the present invention. Moreover, the present invention may include such a case that a semiconductor element (IC) is mounted on the module board and the semiconductor element and a metal wire are connected via a connection portion. In this case, as the connection portion, an electrical connector having a predetermined function (e.g., waveform rectifying function) is used. That is, an active transmission module having an IC is included in the present invention. 
     While the heatsink in the above-described embodiment is an air-cooling type heatsink having a heat-absorbing plate and a heat-dissipating fin, the heatsink may be replaced by a water-cooling heatsink having a heat-absorbing plate and a coolant path. 
     The heat-conductive rubber in the above-described embodiment may be replaced by a heat-conductive sheet and grease having a good heat conductivity, etc. 
     A plurality of communication modules may be disposed so as to surround the four sides of a semiconductor element (IC chip) mounted on the board. Moreover, a plurality of communication modules may be disposed along two or three sides of the semiconductor element (IC chip).