Abstract:
An optical transceiver that provides a plug board independent of a circuit board is disclosed. The optical transceiver further includes a holder to hold both of the plug board and the circuit board in respective positions. The holder provides a first support to support the plug board in a side thereof, and a second support to support the circuit board in a side thereof. Because the holder supports the plug board and the circuit board in respective sides thereof, the holder does not reduce a space for mounting electronic circuit on the circuit board and not interfere with the function of the plug board.

Description:
BACKGROUND 
     Field 
     The present application relates to an optical transceiver, in particular, the application relates to an optical transceiver implementing with a circuit board mounting electronic circuits and a plug board electrically coupling the electronic circuits on the circuit board with a host system, where the plug board is physically independent of the circuit board. 
     Related Background Art 
     One type of multi-source-agreements (MSA) has defined that the circuit board for mounting electronic circuits is independent of a plug board having an electronic plug to couple with a connector prepared in the host system to communicate with the host system, because, as functions requested for the optical transceiver becomes complex and power consumption of the transceiver increases, the count of lead pins provide in the plug and the connector increases, and sometimes exceeds one hundred. The accuracy of the physical dimension required for such a plug and a connector enhances. When an optical transceiver installs such a precisely formed plug board integrated with a circuit board unnecessary for such fine dimensions, the cost of the optical transceiver becomes high. In another application, an optical transceiver is requested that a plug board thereof is made of resin to secure high frequency performance thereof. In such an application, the plug board is inevitable to be independent of the circuit board. Accordingly, advanced optical tranceivers usable in applications where a huge capacity of information is transmitted in extremely high speed often provide the plug board independent of the circuit board. 
     However, when two boards have respective thicknesses, that is, the plug board is necessary to have a thickness fit to the optical connector in the host system, the dimensions of the plug board are strictly and precisely determined in the MSA to secure the coupling between the plug in the optical transceiver and the connector in the host system, while, the circuit board is likely to be formed thinner because of the material cost, and the assembly of the plug board with the circuit board becomes complex. In particular, when two boards are assembled by the reflow soldering, two boards are necessary to be held in a level. When two boards are assembled in imbalance, namely, assembled in a tilted angle, the process to install two boards within the housing may cause stresses to the boards. 
     SUMMARY 
     One aspect of the present application relates to an optical transceiver plugged in an optical connector provided in a host system. The optical transceiver comprises a circuit board, a plug board, a holder, and housing. The circuit board mounts an electronic circuit thereon. The plug board, which is to be mated with the optical connector of the host system, is assembled with the circuit board by soldering. The holder holds the circuit board on a level with the plug board. The housing installs the circuit board and the plug board therein. A feature of the optical transceiver of the present application is that the plug board is made of resin, and the holder provides a first support for supporting the plug board and a second support for supporting the circuit board. The first support provides a top cramp and a bottom cramp putting a side of the plug board therebetween, while, the second support provides a top cramp and a bottom cramp putting a side of the circuit board therebetween. 
     Another aspect of the preset application relates to a method to assemble an optical transceiver that provides a circuit board and a plug board independent of the circuit board but assembled with the circuit board by soldering a plurality of lead pins with pads provided in the circuit board. The method comprises steps of holding the plug board by a first support of a holder and the circuit board by a second support of the holder; setting the circuit board on a level with the plug board; and fixing the lead pins to the pads by the reflux soldering. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the invention may be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows an outer appearance of an optical transceiver according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of a bottom housing of the optical transceiver shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing an inside of the optical transceiver shown in  FIG. 1 ; 
         FIG. 4  is a perspective view of a circuit board and a plug board installed within the optical transceiver shown in  FIG. 1 ; 
         FIG. 5A  and  FIG. 5B  show a holder to hold the circuit board and the plug board; 
         FIGS. 6A to 6C  show processes to hold the circuit board and the plug board by the holder shown in  FIGS. 5A and 5B ; 
         FIGS. 7A and 7B  magnify arrangements around the holder; 
         FIG. 8  explains a process or the soldering of the circuit board and the plug board; 
         FIG. 9  describes the shielding mechanism around the holder; 
         FIGS. 10A and 10B  are cross sections around the holder taken along the longitudinal axis of the transceiver and a direction perpendicular to the longitudinal axis; and 
         FIG. 11  is a perspective view of an example of the plug board. 
     
    
    
     DETAILED DESCRIPTION 
     Next, some embodiments of the optical transceiver according to the present application will be described as referring to drawings. In the explanation of the drawings, numerals or symbols same with or similar to each other will refer to elements same with or similar to each other without duplicated explanations. 
       FIG. 1  shows an outer appearance of an optical transceiver according to an embodiment of the present invention. The optical transceiver  1 , which is installed on a mother board of the host system, may transmit and/or receive optical signals. The optical transceiver  1  shown in  FIG. 1  is a type of, what is called, the hot pluggable optical transceiver where the optical transceiver  1  is plugged within a cage prepared in the host system without power down the system. 
     As shown in  FIG. 1 , the optical transceiver  1  has a housing  3  made of metal, typically zinc and/or aluminum, including a top housing  4  and a bottom housing  5 . Both housings,  4  and  5 , form a space within which optical components, electrical components, a circuit board, and a plug board are installed. Two boards will be described later in detail. 
       FIG. 2  is a perspective view of the bottom housing  5 , where  FIG. 2  removes the optical receptacle  8 , the pull-tab  10 , the top housing  4  and so on. The bottom housing  5  includes a from portion  5   a  and a rear portion  5   c , where the front portion  5   a  installs transducers, such as a transmitter optical sub-assembly (TOSA) and/or a receiver optical sub-assembly (ROSA), to convert signals between an electrical from and an optical form. The rear portion  5   c  installs electronic circuits on the circuit board. The explanation below assumes that the direction “front” or “forward” corresponds to a side where the optical receptacle is provided, while, the direction “back” or “rear” corresponds to another side where the plug board is provided. However, these directions of “front” and “rear” are only for the explanation sake and not influence the scope of claims at all. A shield gasket  5   b  surrounds the front and rear portions,  5   a  and  5   c , to electro-statistically shield the portions,  5   a  and  5   c . The bottom housing  5  further provides a cut or a rear opening  5   d  behind the rear portion  5   c . The opening  5   d  exposes the plug board  12  therethrough. The opening  5   d  accompanies with a recess  5   e.    
       FIG. 3  is a perspective view showing an inside of the optical transceiver  1  in upside down, which removes the bottom housing  5  from a status shown in  FIG. 1 . The optical transceiver  1 , as shown in  FIG. 4 , installs the TOSA  6  and the ROSA  7  in the front portion  5   a . The TOSA  6  encloses a light-emitting device, typically a semiconductor laser diode (LD) therein, and the ROSA  7  encloses a light-receiving device such as a semiconductor photodiode (PD). The TOSA  6  and the ROSA  7  are electrically connected with circuits mounted on the circuit board  2  through respective flexible printed circuit (FPC) boards,  6   a  and  7   a.    
     The circuit board  2 , which has dimensions of 20×60 mm 2 , mounts the electronic circuits on top and back surfaces thereof. The electronic circuits include a driver to driver the LD in the TOSA  6  and a pre-amplifier to amplify a faint signal provided from the ROSA  7 . An end of the circuit board continues to the plug board  12  by the holder  30 . Setting the circuit board  2  in the holder  30 , the solder reflow fixes the lead pins  15   a  provided in the holder to respective electrodes provided in the surfaces of the circuit board  2 . 
     Respective ends of the TOSA  6  and the ROSA  7  receive external optical connectors through the optical receptacle  8 . The top housing  4  arranges a slider  9  and a pull-tab  10  in both sides of the optical receptacle  8 . These mechanisms of the slider  9  and the pull-tab  10  are provided for engaging the optical transceiver  1  with the cage of the host system, or releasing the optical transceiver  1  therefrom. Specifically, pulling the pull-tab  10  of the optical transceiver  1  plugged within the cage, the slider  9  co-works with the pull motion of the pull-tab  10  to release the engagement of the optical transceiver  1  with the cage. Thus, the optical transceiver  1  may be released from the cage. 
       FIG. 4  is a perspective view of the circuit board  2  assembled with the plug board  12 .  FIG. 4  removes the thermal sheet illustrated in  FIG. 3  to show the top surface of the circuit board  2 . The plug board  12 , which is arranged in the rear end of the circuit board  2 , is assembled with the circuit board  2  by soldering lead pins  15   a  with pads on the circuit board  2  after receiving the circuit board  2  in a receptacle  15  of a socket  14  of the plug card  12 . The plug board  12  provides beams  16  in respective sides or the receptacle  15 , where the beams  16  themselves support the circuit board  2 . The holders  30  supports the circuit board  2  such that the circuit board  2  is in parallel to the plug board  12 . 
       FIGS. 5A and 5B  show the holder  30  to hold the circuit board  2  attached to the plug board, where  FIGS. 5A and 5B  illustrate the holder  30  in upside down. The optical transceiver  1  of the present embodiment provides two holders  30  putting the circuit board therebetween. The holder  30  illustrated in  FIGS. 5A and 5B  corresponds to that illustrated in the front side in  FIG. 4 . The holder  30 , which may be formed by cutting and bending a metal slab without any welding and so on, comprises a first support  31 , a second support  32 , a stopper  33 , and an arm  34 , where these portions arranged from the side of the plug board  12  to the circuit board  2  in this order. 
     The second support  32  fits the circuit board  2  and provides a center plate  32   a  and top and bottom cramps,  32   b  and  32   c , respectively. The second support  32  receives the circuit board  2  in a space surrounded by the center plate  32   a  and two cramps,  32   b  and  32   c . The second support  32  continues to the first support  31  by an extension  32   d  with an L-shaped cross section. 
     The first support  31  also comprises a center plate  31   a  and two cramps,  31   b  and  31   c , namely, the top cramp  31   b  and the bottom cram  31   c . The first support  31  receives the side of the plug board  12 . Because the plug board  12  has a thickness far greater than that of the circuit board  2 , a space surrounded by the center plate  31   a  and two cramps,  31   b  and  31   c , are wider than the space formed in the second support  32 . The first support  31  further provides a stopper  33  in a site opposite to a side where the extension  32   d  extends toward the second support  32 . Thus, the center plate  31   a , two cramps,  31   b  and  31   c , the stopper  33 , and the extension  32   d  surround and support the beam  16  of the receptacle  15  of the plug board  12 . 
     The holder  30  further comprises an arm  34  extending from an end of the stopper  33  by the extension  34   a  bent rearward by a right angle from the stopper  33 . The arm  34  includes a root arm  34   b  continuous to the extension  34   a  and a top arm  34   c . The former arm  34   b , the root arm  34 , shuts against the plug board  12  in a portion in the rear of the bottom rib  17 . The top arm is elastically in contact to the bottom housing  5  in a portion between the rear opening  5   d  and the recess  5   e.    
     The other holder  30  has a structure having the plane symmetry to those illustrated in  FIGS. 5A and 5B . Supporting the plug board  12  by the pocket surrounded by the center plate  31   a , two cramps,  31   b  and  31   c , of the first support  31  and the stopper  33 ; the holder  30  may hold the circuit board  2  by the pocket surrounded by the center plate  32   a  and two cramps,  32   b  and  32   c , in the second support  32 . Thus, the circuit board  2  is assembled with the plug board  12 . 
       FIGS. 6A to 6C  show processes to hold the circuit board and the plug board by the holder shown in  FIGS. 5A and 5B , where  FIG. 6C  is a cross section of the circuit board  2  assembled with the plug board  12  taken along the line VI-VI appearing in  FIG. 4 . As shown in  FIG. 6A , preparing the plug board  12 , which assembles the holder  30 , and the circuit board  2 , and inserting the circuit board  2  into the receptacle  15  of the plug board  12 , not only the second support  32  of the holder  30  receives the circuit board  2  but the pocket  16   a  of the beam  16 , which is indicated in  FIG. 11 , may receive the edge of the circuit board  2 , as shown in  FIG. 6B . Referring to  FIG. 11 , the plug board  12 , which may be is made of resin, has a plug  13 , a receptacle  15  and a beam  16 . The plug  13  provides a plurality of pads  13   a  electrically connected with the host connector. The receptacle  15  provides a plurality of lead pins  15   a  and receives the edge of the circuit board  2 . The lead pins  15   a  in the receptacle are soldered with pads provided in the circuit board  2  after the reception thereof by the receptacle  15 . The beam  16  provides a pocket  16   a  in an inner side thereof to receive the side of the circuit board  2 . During the process of the reflow soldering of the lead pins  15   a  with the pads on the circuit board  2 , the circuit board  2  in respective sides thereof may be supported by the beam  16 . However, the dimensions of the beam  16 , in particular, those of the pocket  16   a  are defined in an MSA. When the circuit board  2  has a thickness less than a width of the pocket  16   a , the circuit board  2  is unable to be tightly supported by the beam  16 , or, the circuit board  2  is hard to be set on a level with the plug board  12 . Referring back to  FIG. 6C , further inserting the circuit board  2  between the lead pins  15   a  of the plug board  12  until the end of the circuit board abuts against the receptacle; the circuit board  2  may be securely held by not only the pocket  16   a  of the plug board  12  but the holder  30  to hold the circuit board on a level with the plug board  12 . 
       FIGS. 7A and 7B  magnify arrangements around the holder  30 . As shown in  FIG. 7A , the first support  31  receives the beam  16  in the pocket formed by the center plate  31   a , the top and bottom cramps,  31   b  and  31   c , the stopper  33 , and the extension  32   d  for the second support  32 . Also, the second support  32  supports the circuit board  2  by cramping the edge thereof by the top and bottom cramps,  32   b  and  32   c . Moreover, the stopper  33  may control the slide of the holder  30  in forward by abutting against the rear wall of the receptacle  16 , which may secure the parallelism between the plug board  12  and the circuit board  2  until the position of the circuit board  2  against the plug board  2  is permanently determined, that is, until the lead pins  15   a  are soldered with the pads on the circuit board  2 . 
       FIG. 8  explains a process of the soldering of the circuit board and the plug board shown in  FIG. 4 . Specifically, an assembly subject to the reflow soldering includes fourteen (14) circuit boards mounting electronic components in advance to the soldering an tied by the tie bar  20 . As described, after the holders  30  assemble the plug boards  12  with the circuit boards  2 , the assembly shown in  FIG. 8  is conveyed within the reflow furnace as being carried on a conveyor  22 . Because the holder  30  supports the circuit board  2  to secure the level between two boards,  2  and  12 , the soldering process may prevent two boards,  2  and  12 , from deviating in the levels thereof. 
     Also, the holder  30  may not cause unnecessary stress to the soldered lead pins  15   a , which may effectively prevent the lead pins  15   a  from breaking, or causing failures in electrical connections. Because solder pastes are applied only to the pads on the circuit board  2  and the lead pins  15   a  but not to the holder  30  at all, the holder  30 , even when it is made of metal, may be not electrically conducted to the circuit board  2  and the plug board  12 , which means that the holder  30  may be disassembled with the circuit board  2  and the plug board  12  after the reflow soldering. 
       FIG. 9  describes the shielding mechanism around the holder, and  FIGS. 10A and 10B  are cross sections around the holder taken along the longitudinal axis of the transceiver and a direction perpendicular to the longitudinal axis. As shown in  FIG. 9  the plug board  12  and the circuit board  2  are set within the top housing  4  as being assembled with the holder  30 . As shown in the cross section shown in  FIG. 10A , the top rib  18  is set within the recess  4   e  provided in the top housing  4  and a front wall of the top rib  18  comes in contact with the front wall of the recess  4   e , which determines the position of the plug board  12  against the top housing  4 , and may absorb the stress caused in the insertion of the plug board  12  into the host device. 
     After setting two boards,  2  and  12 , within the top housing  4 , the bottom housing  5  is assembled with the top housing  4  to enclose the circuit hoard  2  therein. As shown in  FIG. 10A , the bottom rib  17  is set within the bottom recess  5   e  such that the rear wall of the bottom rib  17  is in contact with the rear wall of the bottom recess  5   e , which also determines the position of the plug board  12  against the bottom housing  5 . However, the top of the bottom rib  17  makes a gap against the bottom of the bottom recess  5   e . This relation may be also reflected in the top rib  18  and the top recess  4   e , but, the top rib  18  may be in contact with the bottom of the top recess  4   e.    
     That is, dimensions of the top housing  4 , the bottom housing  5 , and the plug board  12 , in particular, the top rib  18  and the bottom rib  17  thereof are designed such that the plug board  12  forms a gap against the bottom housing  5  even after the plug board  12  is assembled between the top and bottom housings,  4  and  5 . However, as shown in  FIG. 10B , the root arm  34   b  of the holder  30  is in contact with the plug board  12  and the top arm  34   c  is forced to be in contact with the bottom housing  5  between the plug board  12  and the bottom housing  5 , which may effectively suppress or prevent the plug board  12  from rattling. 
     In the foregoing detailed description, the method and the apparatus of the present invention have been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present invention. The present specification and figures are accordingly to be regarded as illustrative rather than restrictive.