Abstract:
Direct pin attachment is the most compact method to connect the OSA and the PCBA, due to better performance in general and allows maximum PCBA space for more functionality. However, direct pin attachment can result in concentrated stress in the OSA-PCBA joint area, which can affect the reliability and yield of the module. To overcome the problem, an integrated transceiver cage and housing is provided including a direct pin attachment with reinforcing tabs, which are fixed to the PCBA prior to the pins to transfer any stress between the OSA and PCBA, thereby reducing the amount of stress applied to the pins.

Description:
TECHNICAL FIELD 
     The present invention relates to a transceiver assembly, and in particular to a compact and universal single frame design, which includes a reinforced direct pin attachment between the OSA and PCBA assembly. 
     BACKGROUND OF THE INVENTION 
     With reference to  FIG. 1 , a conventional SFP transceiver module  1  has an electrical interface  2 , e.g. circuit board end connector, for the data path, and an optical interface  3 , e.g. LC duplex optical connector. The optical connector  3  with a duplex LC port extends from one end of a housing (not shown), and the electrical connector  2  extends from the other end of the housing, and enables the transceiver  1  to be hot plugged into a host system. 
     Transmit electrical signals Tx− and Tx+ from a host computer device (not shown) enter the transceiver module  1  via the electrical connector  2 , and are transmitted across a transmit (Tx) data path to a transmitter optical sub-assembly  11 . The Tx data path includes electrical traces in a printed circuit board (PCB)  6 , which transmit the transmit electrical signals to a laser driver  7 , and from the laser driver  7  to TOSA leads, typically in the form of a flex cable lead  8  electrically connected with stub-leads  9 . The stub-leads extend outwardly from a TOSA  11 , which includes a ferrule  12  extending into the optical connector  3 . The TOSA  11  converts the electrical signals Tx− and Tx+ to optical signals and transmits them across an optical link via an optical waveguide, e.g. optical fiber, to a matching transceiver. 
     Receiver optical signals from the optical link are received by a ferrule  13  extending from a receiver optical sub-assembly (ROSA)  14 , which converts the optical signals into differential receiver electrical signals Rx− and Rx+. The receiver electrical signals Rx− and Rx+ are transmitted across a Rx data path, which includes ROSA leads, typically in the form of stub-leads  16 , extending from the end of the ROSA  14 , and a flex cable lead  17  extending between the end of the ROSA  14  and the PCB  6 . The receiver electrical signals Rx− and Rx+ travel across the PCB  6 , through a post amplifier  18  to the electrical connector  2  for transmission to the host device. 
     As the form factor of transceiver modules continues to get smaller, and the data rate keeps increasing, a more compact method to connect the OSA and the PCBA must be employed in order to make the most use of the inner space of a transceiver module. As a result, direct pin attachment is preferred over traditional flex attachment. However, direct pin attach can cause concentrated stress in OSA-PCBA joint area which affects the reliability and yield of the module. 
     Direct pin attachment is the most compact method to connect the OSA and the PCBA, due to better performance in general and allows maximum PCB space for more functionality. Because of the small footprint in direct pin attach, the OSA package size can be reduced, which makes future, lower-cost packages achievable. 
     However, direct pin attachment can result in concentrated stress in the OSA-PCBA joint area which can affect the reliability and yield of the module. The present invention significantly reduces the stress, therefore, improves the performance and reliability of the product. 
     An object of the present invention is to overcome the shortcomings of the prior art by providing an integrated transceiver cage and housing including a direct pin attachment to a PCB, and reinforcing tabs for fixing the cage to the PCB minimizing the stress on the direct pin attachment. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a cage for at least one optical subassembly comprising: 
     a housing comprising a cover, and first and second sidewalls for covering a first optical subassembly (OSA); 
     first and second tabs extending from the first and second sidewalls, respectively, for receiving an edge of a printed circuit board assembly (PCBA), which is electrically coupled to the first OSA; and 
     spring clips extending from the housing for holding the first OSA in the housing. 
     Another aspect of the present invention relates to a transceiver comprising: 
     a transmitter optical subassembly (TOSA) for converting electrical signals into optical signals, and transmitting the optical signals to an optical network, the TOSA including electrical leads extending therefrom; 
     a receiver optical subassembly (ROSA) for converting optical signals into electrical signals, and transmitting the electrical signals to a host device, the ROSA including electrical leads extending therefrom; 
     a printed circuit board assembly (PCBA) including trace leads directly fixed to the electrical leads from the TOSA and the ROSA; and 
     a cage comprising: 
     a housing including a cover, and first and second sidewalls for protecting the TOSA and ROSA; and 
     first and second tabs, extending from the first and second sidewalls adjacent to the electrical leads from the TOSA and the ROSA, respectively, fixed to an edge of the PCBA. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein: 
         FIG. 1  is a plan view of a conventional transceiver assembly; 
         FIG. 2  is an isometric view of a transceiver assembly in accordance with the present invention; 
         FIG. 3  is an isometric view of the OSA cage of  FIG. 2 ; 
         FIG. 4  is a bottom view of a transceiver assembly in accordance with an alternative embodiment of the present invention; 
         FIG. 5  is an isometric view of the OSA cage of  FIG. 4 , from above; and 
         FIG. 6  is an isometric view of the OSA cage of  FIG. 4 , from below. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 2 and 3 , transceiver module  21 , in accordance with the present invention, includes an electrical interface  22 , e.g. a circuit board end connector, for transmitting electrical data signals to and from the host computer system (not shown), and an optical interface  23 , e.g. LC duplex optical connector, for transmitting optical signals to and from an optical network. The optical interface  23  extends from one end of an OSA cage  25 , and the electrical interface  22  extends from the outer free end of a printed circuit board (PCB)  26 , and enables the transceiver  21  to be hot plugged into the host computer system. 
     Transmit electrical signals Tx− and Tx+ from the host computer device enter the transceiver module  21  via the electrical interface  22 , and are transmitted across a transmit (Tx) data path to a transmitter optical sub-assembly (TOSA)  31 . The Tx data path includes electrical traces in the PCB  26 , which transmit the transmit electrical signals to a laser driver  27 , and from the laser driver  27  to TOSA pin leads  28 , directly connected to the traces in the PCBA  26 . The TOSA pin leads  28  extend outwardly from the TOSA  31 , which also includes a ferrule  32  extending into the optical interface  23 . The TOSA  31  converts the electrical signals Tx− and Tx+ to optical signals and transmits them across an optical link via an optical waveguide, e.g. optical fiber, to a remotely located transceiver. 
     Receiver optical signals from the optical link are received by a ferrule  33  extending from a receiver optical sub-assembly (ROSA)  34 , which converts the optical signals into differential receiver electrical signals Rx− and Rx+. The receiver electrical signals Rx− and Rx+ are transmitted across a Rx data path, which includes ROSA pin leads  36 , extending from the end of the ROSA  34  fixed directly to trace leads in the PCBA  26 . The receiver electrical signals Rx− and Rx+ travel across the PCB  26 , through various post processing and testing elements, e.g. a post amplifier  38 , to the electrical connector  22  for transmission to the host device. 
     The OSA cage  25  is designed to cover and hold the TOSA  31  and the ROSA  34  relative to each other therein, but not cover the PCBA  26 , which includes the electrical control systems, e.g. laser driver  27  and post amplifier  38 . The OSA cage  25  also enables attachment of the PCBA  26  via soldering tabs  41 , which comprise a material, which is stronger than the OSA pins  28  and  36 , e.g. metal or polymer. To reduce the cost, the OSA cage  25  is preferably formed from sheet metal. 
     With particular reference to  FIGS. 4 to 6 , in the illustrated embodiments the OSA cage  25  comprises a substantially rectangular upper cover  42 , and first and second rectangular side walls  43  and  44 , respectively, extending parallel to each other and perpendicular to the upper cover  42 . In the illustrated embodiments, the first side wall  43  is longer than the second side wall  44  due to the disparity in lengths between the TOSA  31  and the ROSA  34 , i.e. the TOSA  31  is longer than the ROSA  34 . Accordingly, the upper cover  42  can include an additional rectangular section extending from one end of the main section, and a short dividing wall  45  extending parallel to the first and second side walls  43  and  44 , perpendicular to the upper cover  42 , and along the side of the portion of the TOSA  31 , which extends beyond the ROSA  34 . Furthermore, the PCBA  26  also includes an additional rectangular section extending from one end of a main section for making up the difference between the lengths of the TOSA  31  and the ROSA  34 . 
     The soldering tabs  41  extend outwardly from the side of each side wall  43  and  44 , i.e. from the rear end of the OSA cage  25 , preferably integral therewith, and include upper and lower fingers  46  and  47 , respectively, separated by a notch  48 . Each notch  48  has a width substantially the same or slightly wider than the thickness of the PCB  26 , thereby enabling the PCB  26  to be fitted and received within the notches  48  before permanently fixing the two together, e.g. by soldering or some other fixing method or material. Since the first and second sidewalls  43  and  44 , respectively, are of different lengths, the first soldering tab  41 , extending from the first side wall  43 , extends to the main section of the PCBA  26 , while the second soldering tab  41 , extending from the second side wall  44 , extends to the additional rectangular section of the PCBA  26 . 
     In the center of the upper cover  42 , a large opening  49  is provided for aligning and adjusting the TOSA  31  and the ROSA  34 . Through the opening  49 , a simple tool can be used to align the OSAs inside the OSA cage  25 , if necessary. The opening  49  has a length and width typically ⅓ to ¼ of the width and length, respectively, of the upper cover  42 . The upper cover  42  can also include a plurality of holes  51  extending therethrough, e.g. in an at least 4×4 array pattern as shown in  FIGS. 2 and 3 , to provide adequate thermal dissipation. Alternatively, the opening  49  can be sufficiently large, as illustrated in the alternative embodiment of a transceiver  61  with an OSA cage  65  in  FIGS. 5 and 6 , to provide for sufficient cooling without the need for extra holes  51 . 
     Ideally, the OSA cage  25  or  65  include clips, extending from the upper cover  42  or the side walls  43  and  44 , for engaging both ends of the TOSA  31  and ROSA  34 , and holding them in OSA cage  25 . With reference to  FIGS. 2 and 3 , the clips comprise a pair spring clips  55 , integrally formed with the upper cover  42 , extending downwardly into contact with the electrical end of each of the TOSA  31  and ROSA  34 , and a single spring clip  55 , integrally formed with the upper cover  42 , extending downwardly into contact with the opposite, optical end of both the TOSA  31  and ROSA  34 . Providing a plurality of additional spring clips  55  is also within the scope of the invention. The spring clips  55 , illustrated in  FIGS. 2 and 3 , are formed by bending an extension of the upper cover  42  downwardly at approximately 90°±10° and then folding an end section of the extension back upon itself forming an abutment surface free of sharp edges. 
     With reference to  FIGS. 4 and 5 , for the OSA cage  65 , the clips comprise a leaf spring  66  extending across each opening at the electrical end of the OSA cage  25  for engaging the ends of the TOSA  31  and the ROSA  34  below the soldering tabs  41  and electrical leads  28  and  36 . Ideally, one end of each leaf spring  66  is integral with the corresponding side  43  and  44  of the OSA cage  25 , while the other end is fixed to the dividing wall  45 . Typically, the leaf springs  66  are formed to include an arcuate section, with the midpoint of the arcuate section extending into the OSA cage  25  for engaging the TOSA  31  and the ROSA  34 . 
     A curved clip  67 , extending from each of the first and second side walls  43  and  44 , is provided at the optical end of the OSA cage  25  for engaging the opposite ends of the TOSA  31  and the ROSA  34 . Ideally the curved clip  67  are integral with the corresponding first and second side wall  43  and  44 , with the outer free ends thereof bent back around for engaging the corresponding OSA  31  and  34 . 
     A fixture that matches transceiver module design is used to assemble the OSA&#39;s  31  and  34 , the cage  25  or  65  and the PCBA  26  together. The assembling sequence for the OSA cage assembly will be as following: 
     First, assemble the cage  25 / 65  with the OSAs  31  and  34  using the clips, i.e. spring clips  55  or leaf springs  65 , to hold the OSA&#39;s  31  and  34  within the cage  25 / 65 . Align and adjust the OSA&#39;s  31  and  34  using tools extending through the opening  49 ; 
     Second, align the OSA—cage assembly with PCBA  26  in the fixture by sliding the edge of the PCBA  26  into the notches  48  of the soldering tabs  41  with the OSA leads  28  and  36  aligned with corresponding trace leads on the PCBA  26 ; 
     Third, solder the soldering tabs  41  to the PCBA  26 ; 
     Finally, fix, e.g. solder, the OSA leads  28  and  36  of OSAs  31  and  34  to the PCBA  26 . 
     By fixing the soldering tabs  41  prior to OSA leads  28  and  36 , the cage  25 / 65  restricts the relative movement between the OSAs  31  and  34  and the PCBA  26  along the X, Y and Z directions. The force resulted from relative movement between the OSAs  31  and  34  and the PCBA  26  will be taken by the cage  25 / 65  first and then transferred to the OSA leads  28  and  36 . Therefore, the connection between the OSAs  31  and  34  and the PCBA  26  is reinforced by the cage  25 / 65 , i.e. the cage  25 / 65  acts as a stress relief for OSA leads. As such, the potential problem associated with OSA-PCBA connection area, such as PCBA solder joint fracture, PCBA pad lifting and OSA pin fracture etc, will be significantly reduced. 
     Ideally, the cage  25 / 65  are formed from a single piece of sheet metal with the first and second side walls  43  and  44  bent downwardly from the cover  42 , perpendicular thereto. The material around the spring fingers  55  can be punched out from the cover  42 , and then the spring fingers  55  can be folded over into position. The openings  49  and the holes  52  are simply punched out of the cover  42 . The material around the soldering tabs  41  and spring fingers  66  and  67  are punched out at each end of the first and second sidewalls  43  and  44 , and the spring fingers  66  are bent into position. The dividing wall  45  can be formed by cutting a section of the cover  42 , and folding it downwardly parallel to the first and second side walls  43  and  44 , thereby revealing the opening for the electrical contacts for the shorter ROSA  34 , and defining the extended section of the cover  42 , which covers the end of the TOSA  31   
     The present invention is ideally suited for use in a transceiver module with both the TOSA  31  and ROSA  34 ; however, the cages  25  and  65  can be used with any electro-optical module with one or more OSAs.