Patent Publication Number: US-9429726-B2

Title: Optical module

Description:
The present application is a divisional application of U.S. Ser. No. 13/722,062 filed on Dec. 20, 2012, now U.S. Pat. No. 9,229,182 granted on Jan. 5, 2016 and claims the benefit of priority from Japanese patent application No. 2011-278123 filed on Dec. 20, 2011, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an optical module which transmits signals through an optical fiber. 
     2. Description of the Related Art 
     A conventional optical module is known, which is provided with a photoelectric conversion element for converting electrical energy into optical energy or vise versa and in which signals are transmitted or received through an optical fiber (see JP-A-2002-243990). 
     The optical module described in JP-A-2002-243990 is configured such that a preamplifier IC, a PD (photodiode) element and a lens are housed inside a ceramic package having a one-side opened box shape of which opening is hermetically sealed with a metal lid. A ferrule having an optical fiber internally fixed thereto is inserted into the ceramic package and light emitted from the optical fiber is incident on the PD element through the lens. The PD element converts light intensity into an electrical signal and outputs the electrical signal to the preamplifier IC. 
     In addition, JP-A-2002-243990 also describes an optical module in which VCSEL (Vertical Cavity Surface Emitting Laser) device and a laser driver IC are housed in the ceramic package in place of the PD element and the preamplifier IC. 
     SUMMARY OF THE INVENTION 
     A semiconductor circuit element such as preamplifier IC or laser driver IC which is connected to a photoelectric conversion element such as PD element or VCSEL device generates heat during use. In the optical module described in JP-A-2002-243990, since a space for housing the preamplifier IC or the laser driver IC is hermetically sealed, temperature inside the housing space easily becomes high and may go beyond the operating temperature limit of the preamplifier IC or the laser driver IC, etc., depending on usage conditions. Therefore, usage is restricted or it may be necessary to, e.g., provide an air-cooling fan in the vicinity of the optical module. In addition, the problem of heat generation in the semiconductor circuit element is remarkable in a multichannel optical module which performs multi-channel communications using plural optical fibers. 
     Accordingly, it is an object of the invention to provide an optical module that can suppress a temperature rise of a semiconductor circuit element which is electrically connected to a photoelectric conversion element. 
     (1) According to one embodiment of the invention, an optical module comprises: 
     a circuit board; 
     a photoelectric conversion element mounted on the circuit board; 
     an optical connector for optically connecting the photoelectric conversion element and an optical fiber; 
     a semiconductor circuit element mounted on the circuit board and electrically connected to the photoelectric conversion element; 
     a pressing member for pressing and fixing the optical connector to the circuit board; and 
     a supporting member for supporting the pressing member, 
     wherein the supporting member comprises a heat-absorbing surface and a heat-dissipating surface, 
     wherein the heat-absorbing surface is thermally connected to the semiconductor circuit element, and 
     wherein the heat-dissipating surface dissipates heat of the semiconductor circuit element to be absorbed through the heat-absorbing surface. 
     In the above embodiment (1) of the invention, the following modifications and changes can be made. 
     (i) The heat-absorbing surface is formed parallel to the circuit board while sandwiching the semiconductor circuit element in between, 
     wherein a gap between the heat-absorbing surface and the circuit board corresponds to a thickness of the semiconductor circuit element, and 
     wherein a heat transfer member for conducting heat from the semiconductor circuit element to the heat-absorbing surface is disposed between the heat-absorbing surface and the semiconductor circuit element. 
     (ii) The supporting member integrally comprises a main body extending in a first direction and a pair of arm portions extending in a second direction from both ends of the main body in the first direction so as to sandwich the optical connector, and 
     wherein the first direction intersects with an extending direction of the optical fiber held by the optical connector and the second direction is orthogonal to the first direction. 
     (iii) The circuit board comprises a plurality of electrodes on a non-mounting surface that is opposite to a mounting surface with the semiconductor circuit element mounted thereon, and 
     wherein the supporting member comprises an attaching portion to be fixed to a counterpart board that has a plurality of counterpart electrodes electrically connected to the plurality of electrodes. 
     (iv) The pair of arm portions each comprise a fitting portion for fitting the circuit board thereto. 
     (v) The pressing member comprises a supported portion to be engaged with the supporting member so as to pivot about the supported portion, and 
     wherein the supporting member comprises a fixing portion for fixing the pressing member in a state that the optical connector is pressed by the pressing member. 
     (vi) The optical connector is restricted from moving in a direction parallel to the circuit board by fitting a protrusion provided upright on the circuit board. 
     Effects of the Invention 
     According to one embodiment of the invention, an optical module is constructed such that a heat-dissipating block thereof has both a function as a heat-dissipating member for dissipating heat generated by a driver IC and a preamplifier IC and a function as a supporting member for supporting a lever member for pressing an optical connector against a circuit board. This eliminates the necessity of separately providing the supporting member and the heat-dissipating member, and it is thus possible to reduce the number of components and assembly steps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein: 
         FIG. 1A  is a perspective view showing a non-locked state of an optical module in a first embodiment; 
         FIG. 1B  is a perspective view showing a locked state of the optical module in the first embodiment; 
         FIG. 2  is a plan view showing a back side of the optical module; 
         FIG. 3A  is an exploded perspective view showing the optical module and  FIG. 3B  is a partial enlarged view of  FIG. 3A ; 
         FIG. 4  is a perspective view showing a heat-dissipating block; 
         FIG. 5  is a perspective view showing the heat-dissipating block as viewed from a different direction; 
         FIG. 6  is a perspective view showing a lever member; 
         FIG. 7  is a cross sectional view showing the optical module in the first embodiment when cutting between first and second arms; 
         FIG. 8  is a cross sectional view showing an optical module in a second embodiment; 
         FIGS. 9A to 9D  show a heat-dissipating block of an optical module in a third embodiment, wherein  FIG. 9A  is a top view,  FIG. 9B  is a front view,  FIG. 9C  is a bottom view and  FIG. 9D  is a perspective view; 
         FIG. 10A  is an exploded perspective view of an optical module, showing with an electronic circuit board, an LGA socket and an attaching member; 
         FIG. 10B  is perspective view showing a state in which the optical module is attached to the electronic circuit board; 
         FIG. 11A  is perspective view showing a heat-dissipating block and a keep plate of an optical module in a fourth embodiment and  FIG. 11B  is perspective view showing the heat-dissipating block and the keep plate as viewed from a different angle; 
         FIG. 12  is perspective view showing a state in which the optical module is attached to the electronic circuit board; 
         FIG. 13  is perspective view showing a heat-dissipating block and a keep plate of an optical module in a fifth embodiment; and 
         FIG. 14  is perspective view showing a state in which the optical module is attached to the electronic circuit board. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A structural example of an optical module in a first embodiment of the invention will be described below in reference to  FIGS. 1A to 7 . This optical module is mounted on, e.g., an electronic circuit board having a CPU (Central Processing Unit), etc., mounted thereon and is used for communication with another electronic circuit board which is housed together with the aforementioned electronic circuit board in a common rack. 
       FIGS. 1A and 1B  are perspective views of an optical module in the first embodiment, showing with an optical cable composed of plural optical fibers.  FIG. 2  is a plan view showing a back side of the optical module.  FIG. 3A  is an exploded perspective view showing the optical module and  FIG. 3B  is a partial enlarged view thereof. 
     An optical module  1  has a plate-like circuit board  2  on which plural LD (Laser Diode) elements  31 , plural PD (Photo Diode) elements  32 , a driver IC (Integrated Circuit)  41  and a preamplifier IC  42  are mounted, an optical connector  5 , a heat-dissipating block  6  as a supporting member, and a lever member  7  as a pressing member supported by the heat-dissipating block  6 . 
     The LD elements  31  and the PD elements  32  are mounted on a second mounting surface  2   c  (shown in  FIG. 3B ) of the circuit board  2  while the driver IC  41  and the preamplifier IC  42  are mounted on a first mounting surface  2   a  of the circuit board  2 . The LD element  31  and the PD element  32  are examples of a photoelectric conversion element of the invention. Meanwhile, the driver IC  41  and the preamplifier IC  42  are examples of a semiconductor circuit element of the invention. 
     As shown in  FIGS. 1A and 1B , the lever member  7  is pivotally supported by the heat-dissipating block  6 . In a non-locked state of the lever member  7  as shown in  FIG. 1A , the optical connector  5  is attachable and detachable to and from the circuit board  2  and the heat-dissipating block  6 . On the other hand, in a locked state of the lever member  7  as shown in  FIG. 1B , the lever member  7  presses the optical connector  5  against the circuit board  2 , thereby fixing the optical connector  5  to the circuit board  2  and the heat-dissipating block  6 . 
     As shown in  FIG. 2 , plural electrodes  21  are arranged in a grid-like pattern on a rear surface  2   d  which is a non-mounting surface of the circuit board  2 . The electrodes  21  are electrically connected to terminals of the driver IC  41  and the preamplifier IC  42 . 
     As shown in  FIG. 3A , the optical connector  5  has a lens block  50  formed of a translucent resin such as acrylic and a keep plate  51  formed of a plate-like non-translucent resin. A pair of recessed portions  501  which are depressed inwardly from an outer edge of the lens block  50  is formed on the lens block  50 . 
     An end portion of an optical cable  8  which is composed of plural optical fibers  81  and  82  is sandwiched and held between the lens block  50  and the keep plate  51 . The lens block  50  and the keep plate  51  are fixed to each other by, e.g., an adhesive. 
     As shown in  FIG. 3B , a thickness of the circuit board  2  in a region of the first mounting surface  2   a  (a distance from the first mounting surface  2   a  to the rear surface  2   d ) is larger than a thickness of the circuit board  2  in a region of the second mounting surface  2   c  (a distance from the second mounting surface  2   c  to the rear surface  2   d ). A step surface  2   b  which is parallel to a thickness direction of the circuit board  2  is formed between the first mounting surface  2   a  and the second mounting surface  2   c . The first mounting surface  2   a , the second mounting surface  2   c  and the rear surface  2   d  are parallel to each other. 
     In the first embodiment, four LD elements  31  and four PD elements  32  are mounted on the second mounting surface  2   c  in the vicinity of the step surface  2   b  so as to be arranged in a row along the step surface  2   b . Non-illustrated bonding wires are used for electrical connections between the four LD elements  31  and the driver IC  41  and between the four PD elements  32  and the preamplifier IC  42 . 
     In addition, a pair of columnar protrusions  20  is provided on the second mounting surface  2   c  of the circuit board  2 . The pair of protrusions  20  is provided upright so that a central axis thereof is perpendicular to the second mounting surface  2   c  of the circuit board  2 . A space between the pair of protrusions  20  corresponds to a space between the pair of recessed portions  501  of the lens block  50 , and the optical connector  5  is restricted from moving in a direction parallel to the circuit board  2  by respectively fitting the pair of protrusions  20  to the pair of recessed portions  501 . 
       FIG. 4  is a perspective view showing the heat-dissipating block  6 .  FIG. 5  is a perspective view showing the heat-dissipating block  6  as viewed from a different direction from that of  FIG. 4 . 
     The heat-dissipating block  6  is formed of a metal, e.g., aluminum, etc., and integrally has a rectangular parallelepiped main body  60 , and first and second arms  61  and  62  as a pair of arm portions which are formed to protrude parallel to each other from both end portions of the main body  60 . 
     The main body  60  is formed to extend in a first direction (indicated by an arrow-A in  FIG. 4 ) intersecting an extending direction of the optical fibers  81  and  82  which are held by the optical connector  5 . The first arm  61  and the second arm  62  are formed to extend in a second direction (indicated by an arrow-B in  FIG. 4 ) orthogonal to the first direction from the both end portions in the first direction of the main body  60  so as to sandwich the optical connector  5 . In the first embodiment, an extending direction of the first arm  61  and the second arm  62  (the second direction) is parallel to the extending direction of the optical fibers  81  and  82  supported by the optical connector  5  and is also orthogonal to an extending direction of the main body  60  (the first direction). 
     A first slit S 1  and a second slit S 2  are formed on the main body  60 . The first slit S 1  is formed on the first arm  61  side and the second slit S 2  is formed on the second arm  62  side. The first slit S 1  and the second slit S 2  penetrate the main body  60  in a direction parallel to the first arm  61  and the second arm  62 . In addition, a pair of retaining holes  601  is formed on the main body  60 . One of the retaining holes  601  has an opening at an end portion thereof in the first slit S 1  and the other retaining hole  601  has an opening at an end portion thereof in the second slit S 2 . 
     In the first slit S 1  and the second slit S 2 , a bottom portion on the circuit board  2  side is formed as a wide-width portion which is wider than other portion (narrow-width portion). The bottom portion of the first slit S 1  is formed to broaden toward the first arm  61  and the bottom portion of the second slit S 2  is formed to broaden toward the second arm  62 . 
     A fixing portion  602  for fixing the lever member  7  in the locked state shown in  FIG. 1B  is formed on the narrow-width portion of the first slit S 1  on the first arm  61  side and also on the narrow-width portion of the second slit S 2  on the second arm  62  side. In the first slit S 1  and the second slit S 2 , a step between the wide-width portion and the narrow-width portion is formed by the fixing portion  602 . 
     The optical connector  5  is arranged between the first arm  61  and the second arm  62 , as shown in  FIG. 1A . In addition, notches  610  and  620  for fitting the circuit board  2  are respectively formed on the first arm  61  and the second arm  62 . The notch  610  is formed on a portion of a bottom surface of the first arm  61  (a surface which can be seen from the rear surface  2   d  of the circuit board  2 ) on the second arm  62  side, and the notch  620  is formed on a portion of a bottom surface of the second arm  62  (the same definition as the above) on the first arm  61  side. The notches  610  and  620  are examples of a fitting portion to which the circuit board  2  is fitted. The heat-dissipating block  6  and the circuit board  2  are fixed to each other by, e.g., bonding at the notches  610  and  620 . 
     Meanwhile, the heat-dissipating block  6  has a heat-absorbing surface  60   b  thermally connected to the driver IC  41  as well as to the preamplifier IC  42  and a heat-dissipating surface  60   a  for dissipating heat of the driver IC  41  and the preamplifier IC  42  which is absorbed by the heat-absorbing surface  60   b . The heat-absorbing surface  60   b  is formed on a surface of the main body  60  which faces the circuit board  2 . The heat-dissipating surface  60   a  is formed on a surface of the main body  60  excluding the heat-absorbing surface  60   b.    
       FIG. 6  is a perspective view showing the lever member  7 . The lever member  7  is formed by bending a rod-like elastic metal member and has a pair of supported portions  70 , a pair of coupling portions  71 , a pair of pressing portions  72  and a handling portion  73 . The pair of supported portions  70  and the pair of coupling portions  71  are orthogonal to each other, and the pair of supported portions  70  is formed to extend in directions opposite to each other from one end of the pair of coupling portions  71 . In addition, the pair of pressing portions  72  is formed to approach to each other from another end of the pair of coupling portions  71 . The handling portion  73  is formed between the pair of pressing portions  72 . 
     The pair of supported portions  70  is respectively housed in the pair of retaining holes  601  of the heat-dissipating block  6  and the lever member  7  can thereby pivot about the pair of supported portions  70 . In the locked state shown in  FIG. 1B , the pair of pressing portions  72  is in contact with the keep plate  51  of the optical connector  5  and applies a force to the optical connector  5  toward the circuit board  2 . In order to facilitate pivotal operation of the lever member  7  by a finger of an operator, the handling portion  73  is bent so that a space is formed between the handling portion  73  and the optical connector  5  in a locked state. 
     The pair of coupling portions  71  is located in the narrow-width portions of the first slit S 1  and the second slit S 2  when the lever member  7  is in the non-locked state shown in  FIG. 1A , and the pair of coupling portions  71  is located in the wide-width portions of the first slit S 1  and the second slit S 2  in the locked state shown in  FIG. 1B . A force is applied to the lever member  7  by elasticity thereof so as to separate the pair of coupling portions  71  from each other, and the pivot of the lever member  7  is restricted in the locked state by engagement of the pair of coupling portions  71  with the fixing portions  602  of the heat-dissipating block  6 . In other words, the state that the lever member  7  presses the optical connector  5  is maintained unless, e.g., a worker pivotally operates the lever member  7  by applying an external force. 
       FIG. 7  is a cross sectional view showing the optical module  1  when cutting between the first arm  61  and the second arm and  62 . 
     The driver IC  41  has plural electrodes  410  on a rear surface thereof. The electrodes  410  are electrically connected by a non-illustrated solder to electrodes  22  formed on the first mounting surface  2   a  of the circuit board  2 . The electrodes  22  are connected to the electrodes  21  formed on the rear surface  2   d  of the circuit board  2  by wirings  23  provided in the circuit board  2 . 
     The driver IC  41  receives an electrical signal transmitted through the electrodes  22  and the wirings  23 , and outputs a drive current to the LD element  31 . The LD element  31  emits laser light when receiving the drive current, and the laser light is reflected at a reflecting surface  50   a  formed on the lens block  50  and enters optical fiber  81 . 
     Meanwhile, the light emitted from the optical fiber  82  is reflected at the reflecting surface  50   a  of the lens block  50  and enters the PD element  32 . In the PD element  32 , variation in incident light intensity is converted into an electrical signal and is then output to the preamplifier IC  42 . In the preamplifier IC  42 , the electrical signal is amplified and is then output from electrodes  420  on the back side. The electrodes  420  are electrically connected to the electrodes  22  of the circuit board  2 . 
     As described above, the LD element  31  and the PD element  32  are optically connected to the optical fibers  81  and  82  by the lens block  50  of the optical connector  5 , and the driver IC  41  and the preamplifier IC  42  optically communicate by the LD element  31  and the PD element  32  using the optical fibers  81  and  82  as transmission media. 
     Surfaces of the driver IC  41  and the preamplifier IC  42  (surfaces opposite to the circuit board  2 ) face the heat-dissipating surface  60   a  of the heat-dissipating block  6  and a heat transfer member  9  is arranged therebetween. As the heat transfer member  9 , it is possible to use, e.g., a heat-transfer sheet, etc., formed of thermally-conductive grease or silicone. In the first embodiment, the surfaces of the driver IC  41  and the preamplifier IC  42  are thermally connected to the heat-absorbing surface  60   b  of the heat-dissipating block  6  by the heat transfer member  9 . 
     The heat-absorbing surface  60   b  is formed parallel to the first mounting surface  2   a  of the circuit board  2  so that the driver IC  41  and the preamplifier IC  42  are sandwiched between the heat-absorbing surface  60   b  and the circuit board  2 . In addition, a gap g 1  between the heat-absorbing surface  60   b  and the first mounting surface  2   a  of the circuit board  2  has a size corresponding to a thickness t 1  of the driver IC  41  and the preamplifier IC  42 . In more detail, the gap g 1  has such a size that the a slight space S is formed between the heat-absorbing surface  60   b  and the surfaces of the driver IC  41  and the preamplifier IC  42 , and a size g 2  of the space S is, e.g., not more than half of the thickness t 1  of the driver IC  41  and the preamplifier IC  42 . 
     Functions and Effects of the First Embodiment 
     The following functions and effects are obtained in the first embodiment. 
     (1) The heat-dissipating block  6  has both a function as a heat-dissipating member for dissipating heat generated by the driver IC  41  and the preamplifier IC  42  and a function as a supporting member for supporting the lever member  7  which presses the optical connector  5  against the circuit board  2 . This eliminates the necessity of separately providing the supporting member and the heat-dissipating member and it is thus possible to reduce the number of components and assembly steps. 
     (2) The heat generated by the driver IC  41  and the preamplifier IC  42  is transferred to the heat-dissipating block  6  through the heat-absorbing surface  60   b  via the heat transfer member  9 , and is dissipated to the air from the heat-dissipating surface  60   a  of the heat-dissipating block  6 . This suppresses overheating of the driver IC  41  and the preamplifier IC  42 . 
     (3) Since the heat transfer member  9  is interposed between the driver IC  41 , the preamplifier IC  42  and the heat-absorbing surface  60   b , it is possible to efficiently conduct heat of the driver IC  41  and the preamplifier IC  42  to the heat-absorbing surface  60   b.    
     (4) Since the optical connector  5  is restricted from moving in a direction parallel to the first and second arms  61  and  62  by the protrusions  20 , it is possible to securely hold the optical connector  5 . In addition, the heat-dissipating block  6  is formed so that the main body  60  and the first and second arms  61  and  62  surround the rectangular optical connector  5  from three directions. Therefore, when the optical module  1  is pressed against an electronic circuit board mounting a CPU, etc., by pressing the heat-dissipating block  6 , a pressing force is transmitted to the entire circuit board  2  by the main body  60  and the first and second arms  61  and  62 , and pressure acting on the circuit board  2  is equalized. 
     (5) Since the circuit board  2  is fitted to the notches  610  and  620 , it is easy to adjust the positions of the heat-dissipating block  6  and the circuit board  2  and the surfaces of the driver IC  41  and the preamplifier IC  42  can adequately face the heat-absorbing surface  60   b.    
     Second Embodiment 
     Next, the second embodiment of the invention will be described in reference to  FIG. 8 .  FIG. 8  is a cross sectional view showing the optical module  1  in the second embodiment. 
     While the driver IC  41  and the preamplifier IC  42  described in the first embodiment have the same thickness t 1 , the thickness of the driver IC  41  is different from that of the preamplifier IC  42  in the second embodiment such that a thickness t 1  of the driver IC  41  is thinner than a thickness t 2  of the preamplifier IC  42 . Accordingly, the heat-absorbing surface  60   b  of the heat-dissipating block  6  is composed of a first step surface  60   b   1  corresponding to the driver IC  41  and a second step surface  60   b   2  corresponding to the preamplifier IC  42 . A step surface  60   b   3  is formed between the first step surface  60   b   1  and the second step surface  60   b   2 . Other configurations are the same as the optical module  1  of the first embodiment. 
     A size g 41  of a space S 41  between the first step surface  60   b   1  and the driver IC  41  is equivalent to a size g 42  of a space S 42  between the second step surface  60   b   2  and the preamplifier IC  42 . In other words, it is configured that a size of a step from the first step surface  60   b   1  to the second step surface  60   b   2  is equal to a difference between the thickness t 1  of the driver IC  41  and the thickness t 2  of the preamplifier IC  42 . The heat transfer member  9  is arranged between the first step surface  60   b   1  and the driver IC  41  and also between the second step surface  60   b   2  and the preamplifier IC  42 . 
     In the second embodiment, although the thickness of the driver IC  41  and that of the preamplifier IC  42  are different, it is possible to efficiently conduct the heat of the driver IC  41  and the preamplifier IC  42  to the heat-absorbing surface  60   b  (the first step surface  60   b   1  and the second step surface  60   b   2 ). 
     Third Embodiment 
     Next, the third embodiment of the invention will be described in reference to  FIGS. 9, 10A and 10B . In  FIGS. 9, 10A and 10B , constituent elements common to the first embodiment are denoted by the same reference numerals and the overlapped explanation will be omitted. 
       FIGS. 9A to 9D  show a heat-dissipating block  6 A of an optical module  1 A in the third embodiment, wherein  FIG. 9A  is a top view,  FIG. 9B  is a front view,  FIG. 9C  is a bottom view and  FIG. 9D  is a perspective view.  FIG. 10A  is an exploded perspective view of the optical module  1 A, showing with an electronic circuit board  90 , an LGA (Land Grid Array) socket  91  and an attaching member  92 .  FIG. 10B  is perspective view showing a state in which the optical module  1 A is attached to the electronic circuit board  90 . 
     The heat-dissipating block  6 A integrally has a first attaching portion  611  and a second attaching portion  621  in addition to the main body  60 , the first arm  61  and the second arm  62 . The first attaching portion  611  is formed continuously with the first arm  61 . The second attaching portion  621  is formed continuously with the second arm  62 . 
     Two bolt insertion holes  611   a  and a through-hole  611   b  are formed on the first attaching portion  611 . Two bolt insertion holes  621   a  and a through-hole  621   b  are formed on the second attaching portion  621 . A bottom surface  611   c  of the first attaching portion  611  and a bottom surface  621   c  of the second attaching portion  621  are formed to be a flat surface. 
     The LGA socket  91  has plural pins  911  which are arranged in a grid-like pattern. The pin  911  incorporates a spring and has elasticity so as to be stretchable in a thickness direction of the LGA socket  91 . 
     The electronic circuit board  90  is a printed-circuit board mounting non-illustrated plural electronic circuit components, such as CPU, and plural pad electrodes  900  are formed on a mounting surface  90   a  of the electronic circuit board  90 . In addition, four bolt insertion holes  90   c  (only three bolt insertion holes  90   c  are shown in  FIG. 10A ) and two through-holes  90   d  (only one through-hole  90   d  is shown in  FIG. 10A ) are formed on the electronic circuit board  90 . The electronic circuit board  90  is an example of a counterpart board of the invention and the pad electrode  900  is an example of a counterpart electrode of the invention. 
     The electrodes  21  of the circuit board  2  (see  FIG. 7 ) are electrically connected to the pad electrodes  900  via the plural pins  911  of the LGA socket  91  which is interposed between the circuit board  2  and the electronic circuit board  90 . 
     The first and second attaching portions  611  and  621  of the heat-dissipating block  6 A are fixed to the electronic circuit board  90  by the attaching member  92  which is arranged on a non-mounting surface  90   b  side (a surface on the reverse side of the mounting surface  90   a ) of the electronic circuit board  90 . The attaching member  92  has a plate-like main body  920  and two columnar protrusions  921  provided upright on the main body  920 . Four threaded holes  920   a  are formed on the main body  920  so as to correspond to the respective four bolt insertion holes  90   c  of the electronic circuit board  90 . 
     After positioning the optical module  1 A and the attaching member  92  so that the two protrusions  921  penetrate the two through-holes  90   d  of the electronic circuit board  90  as well as the through-holes  611   b  and  621   b  of the first and second attaching portions  611  and  621 , four bolts  63  are tightened, thereby attaching the optical module  1 A to the electronic circuit board  90 . The four bolts  63  are inserted into the bolt insertion holes  611   a  and  621   a  of the first and second attaching portions  611  and  621  and the bolt insertion holes  90   c  of the electronic circuit board  90 , and are screwed into the threaded holes  920   a  of the attaching member  92 . When the optical module  1 A is attached to the electronic circuit board  90 , the bottom surfaces  611   c  and  621   c  of the first and second attaching portions  611  and  621  are in contact with the mounting surface  90   a  of the electronic circuit board  90 . 
     In the third embodiment, in addition to the functions and effects described in the first embodiment, overheating of the driver IC  41  and the preamplifier IC  42  is further suppressed since the heat of the driver IC  41  and the preamplifier IC  42  absorbed by the heat-absorbing surface  60   b  of the heat-dissipating block  6 A is partially dissipated to the electronic circuit board  90  and the attaching member  92  via the first and second attaching portions  611  and  621 . 
     In addition, since it is possible to press the entire circuit board  2  against the LGA socket  91  by the main body  60  and the first and second arms  61  and  62 , it is possible to elastically deform the plural pins  911  of the LGA socket  91  by the electrodes  21  and thereby to securely electrically connect the electrodes  21  to the pad electrodes  900  via the pins  911 . 
     Fourth Embodiment 
     Next, the fourth embodiment of the invention which is a modification of the optical module  1 A of the third embodiment will be described in reference to  FIGS. 11 and 12 . An optical module  1 B in the fourth embodiment has the same configuration as the optical module  1 A in the third embodiment except that a keep plate  7 A is used as a pressing member in place of the lever member  7 . 
       FIG. 11A  is perspective view showing a heat-dissipating block  6 B and the keep plate  7 A of the optical module  1 B.  FIG. 11B  is perspective view showing the heat-dissipating block  6 B and the keep plate  7 A as viewed from a different angle from that of  FIG. 11A .  FIG. 12  is perspective view showing a state in which the optical module  1 B is attached to the electronic circuit board  90 . 
     The keep plate  7 A is formed by bending an elastic metal, e.g., stainless, etc., and integrally has a plate-like pressing-down portion  74  and a pair of locked portions  75  which are formed on both ends of the keep plate  7 A so as to sandwich the pressing-down portion  74 . A rectangular through-hole  75   a  is formed on the locked portion  75 . 
     A locking portion  612  which has a protrusion  612   a  to be fitted to the through-hole  75   a  of one of the locked portions  75  is formed on the first arm  61  of the heat-dissipating block  6 B. Meanwhile, a locking portion  622  which has a protrusion  622   a  to be fitted to the through-hole  75   a  of the other locked portion  75  is formed on the second arm  62 . 
     As shown in  FIG. 12 , when one of the locked portions  75  of the pressing-down portion  74  is locked with the locking portion  612  and the other locked portion  75  is locked with the locking portion  622 , the pressing-down portion  74  elastically presses the optical connector  5  and the optical connector  5  is thereby fixed. 
     The functions and effects described in the third embodiment are also obtained in the fourth embodiment. 
     Fifth Embodiment 
     Next, the fifth embodiment of the invention which is a further modification of the optical module  1 A of the third embodiment will be described in reference to  FIGS. 13 and 14 . An optical module  1 C in the fifth embodiment has the same configuration as the optical module  1 A in the third embodiment except that a keep plate  7 B is used as a pressing member in place of the lever member  7 . 
       FIG. 13  is perspective view showing a heat-dissipating block  6 C and the keep plate  7 B of the optical module  1 C.  FIG. 14  is perspective view showing a state in which the optical module  1 C is attached to the electronic circuit board  90 . 
     The keep plate  7 B is formed by bending an elastic metal, e.g., stainless, etc., and integrally has a plate-like pressing-down portion  76 , a fixed portion  77  fixed to the main body  60  of the heat-dissipating block  6 C and a connecting portion  78  elastically connecting the pressing-down portion  76  to the fixed portion  77 . The fixed portion  77  is fixed by a bolt  64  screwed into the main body  60 . 
     As shown in  FIG. 14 , the keep plate  7 B elastically presses the optical connector  5  by the pressing-down portion  76 , and the optical connector  5  is thereby fixed. 
     The functions and effects described in the third embodiment are also obtained in the fifth embodiment. 
     Although the embodiments of the invention have been described, the invention according to claims is not to be limited to the above-mentioned embodiments. Further, please note that all combinations of the features described in the embodiments are not necessary to solve the problem of the invention. 
     In addition, the invention can be appropriately modified without departing from the gist thereof. For example, although the case where the optical module has the LD element  31  as a light-emitting element and the PD element  32  as a light-receiving element has been described in the embodiments, it is not limited thereto and the optical module may have only the LD element  31  or the PD element  32 . 
     Alternatively, the surfaces of the driver IC  41  and the preamplifier IC  42  may be directly brought into contact with the heat-absorbing surface  60   b  of the heat-dissipating block  6  for thermal connection without using the heat transfer member  9 . Also in this case, the same functions and effects as the case of using the heat transfer member  9  can be obtained. 
     In addition, the configuration for fixing the lever member  7  at the locking position and the shape of the heat-dissipating block  6  are not limited those of the embodiment. A member for further heat dissipation may be provided in addition to the heat-dissipating block  6 .