Patent Publication Number: US-6334784-B1

Title: Z-axis pressure mount connector fixture

Description:
BACKGROUND OF THE INVENTION 
     Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several printed circuit boards that are then joined together with electrical connectors. A traditional arrangement for joining several printed circuit boards is to have one printed circuit board serve as a backplane. Other printed circuit boards, called daughter boards, are connected through the backplane. 
     A traditional backplane is a printed circuit board with many connectors. Conducting traces in the printed circuit board connect to signal pins in the connectors so signals may be routed between the connectors. Daughter boards also contain connectors that are plugged into the connectors on the backplane. In this way, signals are routed among the daughter boards through the backplane. The daughter cards often plug into the backplane at a right angle. The connectors used for these applications contain a right angle bend and are often called “right angle connectors.” 
     Connectors are also used in other configurations for interconnecting printed circuit boards, and even for connecting cables to printed circuit boards. Sometimes, one or more small printed circuit boards are connected to another larger printed circuit board. The larger printed circuit board is called a “mother board” and the printed circuit boards plugged into it are called daughter boards. Also, boards of the same size are sometimes aligned in parallel. Connectors used in these applications are sometimes called “stacking connectors” or “mezzanine connectors.” 
     Regardless of the exact application, electrical connector designs have generally needed to mirror trends in the electronics industry. Electronic systems generally have gotten smaller and faster. They also handle much more data than systems built just a few years ago. These trends mean that electrical connectors must carry more and faster data signals in a smaller space without degrading the signal. Constraints imposed by the geometries of backplanes designed for certain applications however, reduce the options available for possible connector solutions. 
     For example, thick, large backplanes make some surface mount connectors impractical as the number of layers in the board hinders raising the board to a temperature necessary to solder the leads to the board. Press fit connectors require larger vias. As via diameters increase, the capacitance of the via also increases thus making an impedance match between the connector and the characteristic impedance of a transmission line on the backplane more difficult. 
     Connectors which make contact through pressure are sometimes referred to as “pressure mounted” or z-axis pressure mount connectors as the pressure applied to the connector to provide the desired contact is typically exerted in the z-axis direction. These pressure mount connectors provide the low electrical parasitics desired by current industry trends. 
     Connectors that join optical fibers to create a low loss, separable optical interface have been available and in use for a number of years. 
     These connectors use a variety of ferrule types, alignment schemes and latching mechanisms for joining solitary strands of single-mode and multi-mode optical fiber as well as a multiplicity of fibers in a ribbon form. An example of the second is typified by the “MT” style array ferrules. Each of these connectors join the fibers end to end using a variety of alignment techniques. For single fiber joints, an alignment ferrule generally surrounds and guides the fiber-ends together. 
     One application of optical connector technology is to provide an optical path for signals from board to board, or shelf to shelf within equipment chassis. This optical path is provided by passing optical fibers perpendicularly through a backplane, using so-called “pass through” optical connectors. A right angle mounting of connectors join the optical fibers from an optical module on the daughtercard to optical fibers in cables running out of a card rack. This right angle mounting relies upon a blind mating of the fibers and must conform to standard cable management conventions such as minimum bend radius that contribute to box volume requirements behind the backplane. 
     As the need for bandwidth capacity increases, “Optical Backplanes” usually in the form of laminated fiber matrices that overlay the backplane or that supplement the backplane are also being used. These optical backplanes, likewise have their fibers terminated to standard “pass through” optical connectors as previously described. 
     SUMMARY OF THE INVENTION 
     Current means for actuating z-axis pressure mount connectors typically involved bolting the circuit board, connector, and second circuit board together with screws and a form of reinforcing plate. Due to the nature of the fixturing used, these types of interfaces do not typically lend themselves to traditional, right angle daughtercard/backplane interfaces. 
     The current implementations of “optical backplane” or intra-box optical connections suffer as a result of the nature of the “pass through” optical interface onto the equipment backplane. A 90 degree turn by the optical fiber on the backplane is required. Current optical fiber technology requires the design to maintain a bend radius of greater than one inch to avoid optical loss and mechanical fatigue that can cause breakage. Fixtures that control the fiber bend radius are typically used. These fixtures gradually turn the fiber parallel to the backplane in order to plug to an overlay. Alternatively, fibers may be looped from one perpendicular “pass through” to another to effect slot to slot connectivity. Both of these options, however, consume considerable space behind the traditional electrical backplane while radius fixtures add additional cost to the system. 
     One solution described in the following disclosure provides a connector fixture for enabling a z-axis, pressure mount connection. The connector fixture includes a slot, an actuator, responsive to engagement by a circuit board inserted into the slot and a loading spring, responsive to rotation of the actuator, for compressing against a surface of a z-axis, pressure mount connector. With such an arrangement, a pressure mount connector can be used in a right angle mounting configuration. 
     Another solution described in the following disclosure provides a connector fixture for enabling an electro-optical connection. The connector fixture includes a slot, an actuator, responsive to engagement by a circuit board inserted into the slot, a channel for accepting an optical fiber and a loading spring, responsive to rotation of said actuator, for compressing against a surface of the electro-optical connector. With such an arrangement, a means for launching into an optical fiber positioned perpendicular to the circuit board is facilitated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of an Electro-Optic Connector Module, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. For clarity and ease of description, the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 is a block diagram of an electro-optical connection according to an embodiment of the invention. 
     FIG. 2 is a pictorial representation of one embodiment of an electro-optical module. 
     FIG. 3 is a pictorial representation of an alternate embodiment of the electro-optical module. 
     FIG. 4 is a pictorial representation of an electro-optical connection system. 
     FIG. 5 is an exploded view of a general purpose z-axis pressure mount connector fixture. 
     FIG. 6 is a cross-sectional view of the connector fixture of FIG. 5 
     FIG. 7 is a cut-away view of the connector fixture of FIG.  6 . 
     FIG. 8 is a pictorial representation of an alternate embodiment of a connector fixture used to mate the electro-optical module with a circuit board. 
     FIG. 9 is a cross-sectional view of the connector fixture of FIG.  7 . 
     FIG. 10 is an exploded view of the connector fixture of FIG. 7 when used in conjunction with the electro-optical module of FIG.  2 . 
     FIG. 11 is an exploded view of the connector fixture of FIG. 7 when used in conjunction with the electro-optical module of FIG.  3 . 
     FIG. 12 is a pictorial representation of an alternate embodiment for routing the optical fibers. 
     FIG. 13 is a pictorial representation of a connector fixture used in combination with the electro-optical module of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The electro-optical connection  10  of FIG. 1 includes a circuit board  12 , an electro-optical module  24  and an optical fiber or an array of optical fibers  22 . The circuit board  12  and the electro-optical module  24  are connected through a separable, electrical connection  18 . The electro-optical module  24  and the optical fiber  22  are connected through a semipermanent optical connection  26 . 
     The electro-optical module  24  is shown to include a routing substrate  14  and an optical interface  16 . The routing substrate is connected to the optical interface  16  through a fixed connection  20 . 
     In the configuration of FIG. 1, an electrical signal passes from a signal trace (not shown) within the circuit board  12  through the separable, electrical interface  18  to the electro-optical module  24 . Within the electro-optical module  24 , the electrical signal is passed from the routing substrate  14 , through the fixed connection  20  to an optical interface  16 . The optical interface  16  converts the electrical signal to an optical signal which is transferred to the optical fiber  22  through the semi-permanent optical connection  26 . The electro-optical connection system  10  also operates in reverse wherein an optical signal traveling through the optical fiber  22  to the optical interface  16  is converted to an electrical signal. The electrical signal passes through the fixed connection  20  to the routing substrate  14  and through the separable, electrical interface  18  to a signal trace on the circuit board  12 . 
     Generally, in an electro-optical connection system, the separable interface in the system is a mating between two optical fiber ends. Here, however, the separable interface is provided by an electrical connection, thus avoiding the problems encountered with fiber to fiber connections such as alignment issues and dust contamination. The semi-permanent connection between the optical fiber and the electro-optical module can be provided in a controlled factory setting allowing for better alignment and, when done in a dust free environment, minimal risks of contamination. The semi-permanent nature of the connection is generally provided to enable future servicing and repairs to the connection and/or components. 
     Referring now to FIG. 2, a pictorial representation of an electro-optical connection  30  between a circuit board  12  and an optical fiber  22   a ,  22   b  is shown to include one embodiment of the electro-optical module  24 . 
     Here, the circuit board  12  is functionally shown as a daughtercard. Here, the optical fiber is shown as an input/output fiber pair  22   a ,  22   b  however an optical fiber array can be substituted as well as any other desirable configuration of the optical fibers. Also shown is a backplane  29 . The electro-optical module  24  is shown spaced from the daughtercard in a unmated position. 
     The electro-optical module  24  is shown to include a routing substrate  14  and an optical interface mounted on a front surface of the routing substrate  14 . The optical fiber pair  22   a ,  22   b  is connected to the optical interface  16  by a semi-permanent optical connection  26 . In this way, the electro-optical module  24  provides a means for launching into an optical fiber positioned perpendicular to the circuit board  12 . 
     Referring also to FIG. 2A, the separable, electrical connection  18  is provided on a back surface of the routing substrate  14 . The separable, electrical connection  18  is preferably provided by a z-axis, pressure mount connector. Here, the separable, electrical connection  18  is shown as an array of self-retained pressure connectors  34  located on the back surface of the routing substrate  14 . These pressure connectors  34 , an exemplary one shown in FIG. 2B, are small metallic structures which are pressed into plated through holes (not shown) in the routing substrate  14 . Surface contacts  36   a ,  36   b  (FIG. 2B) contact pads (not shown) on the surface of circuit board  12 . These multiple contact surfaces  36   a ,  36   b  provide multiple points of contact with the circuit board  12  surface pads thus providing a reliable electrical contact. 
     One benefit of using these small pressure connectors  34  is that small contact pads can be used on the circuit board surface and further, small plated through holes or vias can be used on the routing substrate  14 . The small dimensions of these features allow for the separable, electrical connection  18  between the circuit board  12  and the routing substrate  14  to be optimized for low electrical parasitics. 
     In an alternate embodiment, a so-called mezzanine or stacking connector configured to provide the desired electrical signal properties can be used as the separable, electrical connection  18  between the circuit board  12  and the routing substrate  14 . These connectors typically provide an electrical connection between two parallel circuit board surfaces. 
     Referring back to FIG. 2, the optical interface  16  includes an optical transceiver (not shown) and an optical/mechanical connection between the optical transceiver and optical fiber pair  22   a ,  22   b . Typically, the optical transceiver responds to an analog signal rather than a digital signal as is typically communicated through a circuit board. Here, to provide and/or interpret the analog signal, driver electronics  28  for the optical transceiver are mounted on the circuit board  12 . Typically, these driver electronics  28  are digital to analog converters packaged in an Application Specific Integrated Circuit (ASIC). The driver electronics  28  convert a digital signal being passed through the signal trace on the circuit board  12  to an analog current which drives the optical transceiver and vice versa. 
     The mechanical connection between the optical fibers and the optical transceiver can generally be done in a controlled factory setting. Alignment of the fibers to the optical transceiver performed in a dust free environment eliminates contamination at the end of the fiber, thus minimizing optical losses. A permanent connection can be provided between the optical fibers and the optical transceiver or a semi-permanent optical connection  26  as described in conjunction with FIG.  1 . 
     In a preferred embodiment, the optical transceiver is an array of VCSEL elements. A VCSEL converts between an analog electrical signal and an optical signal. In an alternate embodiment, other opto-electrical (O/E) sources may be used in conjunction with photo detectors to provide the optical transceiver component of the optical interface  16 . 
     Referring now to FIG. 3, a pictorial representation of an electro-optical connection  40  between a circuit board  12  and an optical fiber is shown to include an alternate embodiment of the electro-optical module  24 ′. 
     The electro-optical module  24 ′ includes a routing substrate  14 . Mounted on a back surface of the routing substrate is a separable, electrical connection  18 . An optical interface  16  is mounted on the front surface of the routing substrate with the optical fiber pair  22   a ,  22   b  being connected to the optical interface  16  by a semi-permanent optical connection  26 . 
     Here, further included in the electro-optical module  24 ′ are the driver electronics  28  for the optical source/driver which are mounted on the routing substrate  14 . Mounting the driver electronics  28  on the routing substrate  14  frees up additional space on the daughtercard. In addition, it eases the transmission of the analog signals from the driver electronics to the optical source/driver. 
     In an alternate embodiment (not shown) the optical interface  16  can be mounted on the driver electronics  28  rather than on the routing substrate  14 . 
     Referring now to FIG. 4, a pictorial representation of an electro-optical connection system  45  that provides an electro-optical connection between a first circuit board  12   a  and a second circuit board  12   b  is shown. Here, the electro-optical connection system  45  is shown to include two electro-optical modules  24   a ,  24   b.    
     Included in the first electro-optical module  24   a  is a first routing substrate  14   a . Mounted on the routing substrate  14   a  is a first optical interface  16   a  located on a front surface and a second optical interface  16   c  located on a lower back surface. Optical interfaces  16   a ,  16   c  are provided on either side of the routing substrate  14   a  to enable the first circuit board  12  to communicate with circuit boards located on either side of the first circuit board  12  without requiring a bend in the optical fiber. 
     The first routing substrate  14   a  also includes a separable, electrical connection  18   a  provided on an upper back surface of the routing substrate  14   a . Here, the separable, electrical connection  18   a  is shown as an array of self retained pressure connectors. The separable, electrical connection  18   a  provides electrical contact between the electro-optical module  24   a  and the first circuit board  12   a . The optical fiber pair  22   a ,  22   b  is connected to the optical interface  16   a  by a semi-permanent optical connection  26   a . Mounted on the circuit board  12   a  are the driver electronics  28   a  for an optical transceiver included in the optical interface  16   a.    
     The second optical interface  16   b  is connected at a distal end of the optical fiber pair  22   a ,  22   b  by a second semi-permanent optical connection  26   b . A third optical interface  16   b  is mounted on a front surface of a second routing substrate  14   b . A fourth optical interface  16   d  is mounted on a lower back surface of the second routing substrate  14   b  to enable the second circuit board  12   b  to communicate with another circuit board located on its other side. The second routing substrate  14   b  connects to the second circuit board  12   b  through a separable, electrical interface  18   b , also shown as an array of self retained pressure connectors, provided on an upper back surface of the routing substrate  14   b . Mounted on the surface of the second circuit board  12   b  are the driver electronics  28   b  for an optical transceiver included in the optical interface  16   b.    
     In an alternate embodiment, the driver electronics  28   a ,  28   b  are mounted on their respective routing substrates  14   a ,  14   b  rather than on the circuit boards  12   a ,  12   b.    
     The electro-optical connection system  45  described above provides a solution to many of the problems faced by current electro-optical connection systems. Multiple mating cycles of traditional optical connectors degrade the performance of the connection and introduce, over time, additional signal losses into the system as guidance features aiding in the alignment between the two mating surfaces become worn. In addition, dirt and dust can become an increased contamination problem unless strict cleaning procedures are adhered to and even then, may still compound over time. Here, the wear and tear of multiple mate cycles are born by a separable, electrical connection  18  less susceptible to alignment issues and dirt and dust contamination. This system further eliminates the need to bend optical fibers perpendicularly to route them between daughtercards or adjacent backplanes thus eliminating significant volume associated with bend radius. 
     Referring now to FIG,  5 , an exploded view of a general purpose, z-axis pressure mount connector fixture  75  is shown to include a circuit board receiving slot  51 , an actuator  56 , and a loading spring  54 . The circuit board  12  engages an activation surface  62  when inserted into the receiving slot  51 , causing the actuator to pivot around a pivot pin  52  included on the actuator  56 . The pivoting action presses a face  53  against the loading spring  54 , compressing the spring  54  thus, applying a perpendicular force against a first surface of a mezzanine board or daughtercard  70 . 
     The perpendicular force applied by the loading spring  54  presses an opposing face of the mezzanine board  70  against a surface of the circuit board  12  thus engaging a z-axis pressure connector  71  with a corresponding mating surface. 
     For example, in one embodiment, the z-axis pressure connector  71  is an array of self-retained pressure connectors  34  (FIG.  2 A). The corresponding mating surface is an array of pads located on the surface of the circuit board  12 . The perpendicular force flattens the contact surfaces  36   a ,  36   b  (FIG. 2A) of each self-retained pressure connector  34  against a corresponding pad on the circuit board  12  thus providing an electrical connection between the mezzanine board  70  and the circuit board  12 . 
     Referring now to FIG. 6, a cross-sectional view of the connector fixture  75  illustrates a preloaded position  58   a  of the actuator  56 . Prior to insertion of the circuit board  12 , the actuator  56  is in the preloaded position  58   a . When the circuit board  12  is inserted into the slot  51  in the connector fixture, the circuit board  12  engages the actuator  56  causing the actuator  56  to rotate. The actuator  56  rotates around the pivot pin  52  until it locks into its loaded position  58   b . In the loaded position  58   b , a face  53  of the actuator  56  compresses the loading spring  54 , thus applying a perpendicular force against the mezzanine board  70 . The perpendicular force caused by the loading spring  54  causes the array of z-axis pressure connectors  71  to mate with a corresponding mating surface (not shown) on the circuit board  12 . 
     Referring now to FIG. 7, a cut-away view of the connector fixture  50  exposes an actuator retract spring  60 . The actuator retract spring  60  aids in rotating the actuator  56  back to its preloaded position  58   a  when the circuit board  12  is removed. Specifically, when the circuit board  12  is removed from the slot  51 , the actuator retract spring  60  exerts a force against the actuator  56  causing it to rotate in a clockwise direction until it comes to rest in its preloaded position  58   a  (FIG.  6 ). 
     Referring now to FIG. 8, a pictorial representation of an alternate embodiment of a connector fixture  50 ′ used to mate the electro-optical module  24  with the circuit board  12  is shown. The connector fixture  50 ′ is shown to include a channel  67  through which the optical fiber pair  22   a ,  22   b  passes. The circuit board  12  is inserted into slot  51  in the connector fixture  50 ′. Once inserted, the actuator  56  (FIG. 5) within the body of the connector fixture pivots around the pivot pin  52  causing the loading spring to exert a force against the routing substrate  14  which, in turn, presses the routing substrate  14  against the circuit board  12 . 
     Referring now to FIG. 9, a cross-sectional view of the connector fixture  50 ′ illustrates both a preloaded position  58   a  and a loaded position  58   b  of the actuator  56 . Prior to insertion of the circuit board  12 , the actuator  56  is in the preloaded position  58   a . As the circuit board  12  is inserted into the slot  51  in the connector fixture, the circuit board  12  presses against an activation surface  62  on the actuator  56 . The force against the activation surface  62  causes the actuator  56  to rotate, here, counter-clockwise around the pivot pin  52  until it locks into its loaded position  58   b . In the loaded position  58   b , a face  53  of the actuator  56  compresses the loading spring  54 , thus applying a perpendicular force against the routing substrate  14 . The perpendicular force caused by the loading spring  54  causes the array of self-retained pressure connectors  18  to mate with surface pads (not shown) on the circuit board  12 . 
     Referring now to FIGS. 10 and 11 exploded views of the connector fixture are shown when used in conjunction with the electro-optical module  24  of FIG. 2 (FIG. 10) and with the electro-optical module  24 ′ of FIG. 3 (FIG.  11 ). In both FIGS. 10 and 11, the pivot pin  52  can be seen to extend across the length of the actuator  56  extending beyond each side face  55   a ,  55   b  of the actuator  56 . These extended portions of the pivot pin  52  rest within grooves  64   a ,  64   b  in a bottom portion of the connector fixture body  49   a . The top portion of the connector fixture body  49   b  includes a similar groove  65   a , ( 65   b  is not visible). The actuator  56  then rotates within these grooves  64   a ,  64   b    65   a ,  65   b  around the pivot pin  52 . Also provided are wells  66  on each side of the bottom portion  49   a  of the connector fixture body to provide clearance for the actuator  56  as it rotates. 
     In the configuration of FIG. 10, the loading spring  54  presses against the routing substrate  14  when the actuator  56  is in the loaded position  58   b  (FIG.  8 ). In the configuration of FIG. 11 however, the loading spring  54  presses against the driver electronics package  28  when the actuator  56  is in the loaded position  58   b  (FIG.  8 ). An optional reinforcement plate (not shown) can also be used in conjunction with the loading spring  54  to protect the driver electronics package  28  from being damaged by the spring  54 . 
     Referring now to FIG. 12 a pictorial representation of an alternate embodiment for routing the optical fiber pair  22   a ,  22   b  is shown. Here, the backplane  29  includes a backplane cutout  72  through which a routing substrate  74  extends. The optical interface  16  is mounted on the substrate  74  however here, the optical fibers are routed on a back side of the backplane  29 . This embodiment enables easy maintenance from the back side of the backplane  29  and greater flexibility in routing the optical fibers. 
     For example, using the backplane cutout  72  configuration, routing of optical fibers need not be limited between adjacent daughtercards but rather may be extended between daughtercards that are not adjacent as intermediate daughtercards would not be an obstacle to the routing. Typically, a “daughtercard connector void” is provided where the optical fibers pass by the daughtercard. A “daughtercard connector void” is a location on the daughtercard where no connector is located providing a space between the edge of the daughtercard and the surface of the backplane. It is through this space that the optical fiber passes. 
     Referring now to FIG. 13, a pictorial representation of a connector fixture  50 ″ used in combination with the electro-optical module  24   a  (FIG. 4) is shown. The connector fixture  50 ″ is shown to include a second channel  76  through which a second optical fiber pair  22   c ,  22   d  pass. The second optical fiber pair  22   c ,  22   d  are semi-permanently connected to a second optical interface  16   c  (FIG. 4) located on a lower back surface of the first routing substrate  14   a  (FIG.  4 ). 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.