Abstract:
The enhanced folded flexible cable packaging for use in optical transceivers of the present invention provides a 90 degree transition between an optical signal input/output at a communication chassis bulkhead, and folds 180 degrees around a horizontal heat spreader to provide the capability to wire electrical components to the flexible cable while maintaining the upper surface of the electrical components in close proximity to a heat sink. This allows signals to be processed through a multi-layer flexible cable providing electrical performance without the mechanical stiffness associated with the bends that occur in the package. The multiple array transceiver makes the 90 degree transition within a narrow gap established by industry and manufacturing standards. The multiple array transceiver also provides cooling to the internal electronics through a heat sink attached to the flexible cable and the heat spreader, which concurrently mounts and locates the transceiver to a common host board.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 09/956,771 filed on Sep. 20, 2001 entitled “Fiber Optic Transceiver, Connector, And Method of Dissipating Heat” by Johnny R. Brezina, et al., the entire disclosure of which is incorporated by reference, herein. 
     This application also relates to the following applications, filed concurrently herewith: 
     “Optical Alignment In A Fiber Optic Transceiver”, by Johnny R. Brezina, et al. Ser. No. 10/007,027 filed Nov. 5, 2001, pending; 
     “External EMI Shield For Multiple Array Optoelectronic Devices”, by Johnny R. Brezina, et al. Ser. No. 10/006,644 filed Nov. 5, 2000, pending; 
     “Packaging Architecture For A Multiple Array Transceiver Using A Continuous Flexible Circuit”, by Johnny R. Brezina, et al. Ser. No. 10/007,026 filed Nov. 5, 2001, pending; 
     “Flexible Cable Stiffener for An Optical Transceiver”, by Johnny R. Brezina, et al. U.S. Pat. No. 6,614,658, issued Sep. 2, 2003. 
     “Apparatus and Method for Controlling an Optical Transceiver”, by Johnny R. Brezina, et al. Ser. No. 10/007,024 filed Nov. 5 2001, pending; 
     “Internal EMI Shield for Multiple Array Optoelectronic Devices,” by Johnny R. Brezina, et. al. Ser. No. 10/006,834 filed Nov. 5, 2001, pending; 
     “Multiple Array Optoelectronic Connector with Integrated Latch”, by Johnny R. Brezina, et al. Ser. No. 10/007,023 filed Nov. 5, 2001, pending; 
     “Mounting a Lens Array in a Fiber Optic Transceiver”, by Johnny R. Brezina, et al. Ser. No. 10/006,837 filed Nov. 5, 2001, pending; 
     “Packaging Architecture for a Multiple Array Transceiver Using a Flexible Cable”, by Johnny R. Brezina, et al. Ser. No. 10/006,835 filed Nov. 5, 2001, pending; 
     “Packaging Architecture for a Multiple Array Transceiver Using a Flexible Cable and Stiffener for Customer Attachment”, by Johnny R. Brezina, et al. Ser. No. 10/006,838 filed Nov. 5, 2001, pending; 
     “Packaging Architecture for a Multiple Array Transceiver Using a Winged Flexible Cable for Optimal Wiring”, by Johnny R. Brezina, et al. Ser. No. 10/006,839 filed Nov. 5, 2001, pending; and 
     “Horizontal Carrier Assembly for Multiple Array Optoelectronic Devices”, by Johnny R. Brezina, et al. Ser. No. 10/007,215 filed Nov. 5, 2001, pending. 
    
    
     TECHNICAL FIELD 
     The technical field of this disclosure is computer systems, particularly, enhanced folded flexible cable packaging for use in optical transceivers. 
     BACKGROUND OF THE INVENTION 
     Optical signals entering a communications chassis can be converted to electrical signals for use within the communications chassis by a multiple array transceiver. The configuration of optical signal connections entering the communications chassis and the circuit boards within the chassis require a 90-degree direction change in signal path from the optical to the electrical signal. This 90-degree configuration is required due to the right angle orientation between the customer&#39;s board and the rear bulkhead of the chassis. Existing multiple array transceiver designs use a number of small parts, such as tiny flexible interconnects with associated circuit cards and plastic stiffeners, to make the 90-degree transition. The size and number of the parts increases manufacturing complexity and expense. 
     In addition, existing multiple array transceivers are limited in the number of electrical signal paths they can provide between the optical input and the customer&#39;s board. It is desirable to provide as many electrical signal paths as possible, because optical fiber can typically provide a greater information flow rate than electrical wire. Industry and company standards further limit the space available for signal paths from the optical input to the customer&#39;s board, limiting the space to a narrow gap. 
     Thermal considerations may also limit the signal carrying capacity of current multiple array transceivers. Heat is generated by electrical resistance as the signals pass through the conductors and as the signals are processed by solid-state chips within the transceivers. Limitations on heat dissipation can limit the data processing speed and reduce transceiver reliability. 
     It would be desirable to have a packaging architecture for a multiple array transceiver using a folded flexible cable that would overcome the above disadvantages. 
     SUMMARY OF THE INVENTION 
     The enhanced folded flexible cable packaging for use in optical transceivers of the present invention provides a 90 degree transition between an optical signal input/output at a communication chassis bulkhead, and folds 180 degrees around a horizontal heat spreader to provide the capability to wire electrical components to the flexible cable while maintaining the upper surface of the electrical components in close proximity to a heat sink. This allows signals to be transmitted through a multi-layer flexible cable without the mechanical stiffness associated with the bends that occur in conventional optical transceiver packaging. The packaging architecture system for a transceiver comprises a forward vertical carrier having an optical converter; a rearward horizontal I/O block, the rearward horizontal I/O block oriented about 90 degrees from the forward vertical carrier; and a flexible cable operably connected between the forward vertical carrier and the rearward horizontal I/O block, the flexible cable being folded to provide a first signal path and a second signal path. The multiple array transceiver makes the 90 degree transition within a narrow gap established by industry and manufacturing standards. The multiple array transceiver also provides cooling to the internal electronics through a heat sink attached to the flexible cable and the heat spreader, which concurrently mounts and locates the transceiver to a common host board. 
     One aspect of the present invention provides a packaging architecture for a multiple array transceiver providing a 90-degree transition between the customer&#39;s board and the rear bulkhead of the chassis. 
     Another aspect of the present invention provides a packaging architecture for a multiple array transceiver with a reduced number of components for manufacturing ease and reduced cost. 
     Another aspect of the present invention provides a packaging architecture for a multiple array transceiver providing an interconnection containing a very large number of signal paths in a narrow horizontal gap. 
     Another aspect of the present invention provides a packaging architecture for a multiple array transceiver providing a thermally efficient design with heat flow to the heat sink split into two distinct parallel paths. 
     The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an isometric diagram of a forward vertical carrier made in accordance with the present invention. 
     FIGS. 2A &amp; 2B show isometric diagrams of a forward vertical carrier in place in an I/O assembly made in accordance with the present invention. 
     FIGS. 3A &amp; 3B show isometric diagrams of a packaging architecture for a multiple array transceiver using a folded flexible cable made in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The enhanced folded flexible cable packaging for use in optical transceivers of the present invention provides a 90-degree transition between an optical signal input at a communications chassis bulkhead and an interior board within the communications chassis. The multiple array transceiver makes the 90-degree transition within a narrow gap established by industry and manufacturer standards. The multiple array transceiver further provides parallel cooling paths through a heat sink. 
     The present invention is shown and described by the following description and figures, and is generally described in the order in which the individual components are assembled during manufacture. 
     FIG. 1 shows an isometric diagram of a forward vertical carrier made in accordance with the present invention. The forward vertical carrier  48  comprises common substrate carrier  50 , laser die  52 , photodetector die  54 , laser drive amplifier (LDA)  56 , and transimpedance amplifier (TIA)  58 . Laser die  52  and photodetector die  54  are attached to a common substrate carrier  50  by using standard die bond epoxy material and technique as will be appreciated by those skilled in the art. The LDA  56  and TIA  58  are also die bonded to the substrate carrier  50  in close proximity to the laser die  52  and photodetector die  54  to provide short critical transmission interconnection wire bond lengths. The TIA  58  acts as the photodetector interface chip. The laser die  52  and photodetector die  54  are precisely aligned to provide optimum communication with a fiber optic cable which can be attached to the laser die  52  and photodetector die  54 . 
     The laser die  52  and photodetector die  54  with their associated circuits perform as optical converters to convert a light signal coming into the transceiver to an electrical signal or convert an electrical signal from the transceiver to a light signal. In one embodiment, the optical converters can be lasers only, so that the transceiver only transmits optical signals. In another embodiment, the optical converters can be photodetectors only, so that the transceiver only receives optical signals. In other embodiments, the number of lasers and photodetectors can be predetermined to meet the number of transmit and receive channels desired. 
     FIGS. 2A &amp; 2B, in which like elements have like reference numbers, show isometric diagrams of a forward vertical carrier in place in an I/O assembly made in accordance with the present invention. A flexible cable is folded along its length to increase the data transfer capability between the forward vertical carrier and a rearward horizontal I/O block, while increasing the cooling capability by folding the flexible cable around a heat spreader. 
     A flexible cable  60  comprises a first signal path having a first electrical portion  62 , a first transfer portion  64 , and a first optical portion  66 ; and a second signal path having a second electrical portion  68 , a second transfer portion  70 , and a second optical portion  72 . The flexible cable  60  has two signal paths due to the folded design, which electrically connects the rearward horizontal I/O block  76  to the forward vertical carrier  48 , where the laser die  52  and photodetector die  54  are located. Each signal path can contain a plurality of conductors carrying a plurality of signals. The first and second signal paths can be routed on top of each other through a narrow gap. This allows the J-shaped interconnection between the rearward horizontal I/O block  76  and forward vertical carrier  48  to contain a very large number of signals in a narrow horizontal gap. 
     The first optical portion  66  can be bonded with adhesive to the forward vertical carrier  48  and the second optical portion  72  bonded to the first optical portion  66 . The first optical portion  66  and the second optical portion  72  can be terminated in a profile around the LDA  56  and TIA  58  to match the shape of the LDA  56  and TIA  58  to provide ease of connection. The second optical portion  72  can be further stepped back with respect to the first optical portion  66  to further increase the area for electrical connection. The first optical portion  66  and the second optical portion  72  have bond pads in the area around the LDA  56  and TIA  58  to allow wire bonding to the dies. Wire bond pads are exposed on both the first optical portion  66  and the second optical portion  72  and are ribbon bonded directly to the respective LDA  56  and TIA  58 . The wire bond pads can also provide interconnect capability between the conductors in the first optical portion  66  and the second optical portion  72 . 
     Referring to FIG. 2B, the flexible cable  60  has a folded shape, which provides the first electrical portion  62  above a heat spreader  74  and the second electrical portion  68  below the heat spreader  74 . The second electrical portion  68  is soldered to the I/O block  76  on the underside of the heat spreader  74 . If desired, interconnecting circuit traces can be routed through the solder ball array  82  to connect the receiver post amplifier  78 , eeprom  80 , and the I/O block  76 . Further connections can be made between the first electrical portion  62  and the second electrical portion  68  with circuits passing through the bend connecting the first electrical portion  62  and the second electrical portion  68  where the flexible cable  60  wraps around the heat spreader  74 . The receiver post amplifier  78  and eeprom  80  dissipate heat into the heat spreader  74 , which in turn is connected to a heat sink. 
     FIGS. 3A &amp; 3B, in which like elements have like reference numbers, show isometric diagrams of a packaging architecture for a multiple array transceiver using a folded flexible cable made in accordance with the present invention. 
     Referring to FIG. 3A, the optical lens assembly  84  is aligned and UV epoxy bonded to the forward vertical carrier  48 . Precise alignment provides efficient optical signal transfer. 
     Referring to FIG. 3B, heat sink  86  incorporates a vertically oriented surface  90  to which the forward vertical carrier  48  can be attached, and a horizontal surface  88  to which the heat spreader  74  can be attached. The attachment can be made with adhesive, thermally conductive epoxy, or the like, as will be appreciated by those skilled in the art. The heat sink  86  can be made of any material with high thermal conductivity, such as aluminum or copper, and can be formed by various processes, such as die casting or machining. The attachment to the vertically oriented surface  90  and the horizontal surface  88  provides the 90-degree angle between the forward vertical carrier and the I/O block  76 . The flexible cable  60  bends to provide the electrical connection between the vertical and horizontal portions. This 90-degree configuration is required due to the right angle orientation between the customer&#39;s interior circuit board and the rear bulkhead of the chassis. 
     The connection of the heat sink  86  to the heat spreader  74  provides heat transfer beyond the heat transfer from the forward vertical carrier to the heat sink  86  alone. This creates a thermally efficient design, since heat flow through the heat sink  86  is split into two distinct parallel paths: one path from the forward vertical carrier to the heat sink  86  near the forward vertical carrier and a second path from the heat spreader  74  to the portion of the heat sink  86  away from the forward vertical carrier. The receiver post amplifier and eeprom dissipate heat into the heat spreader. The heat sink  86  can have fins, pins, vanes, passive cooling, or active cooling on the open surface to assist in heat transfer. 
     The heat sink  86  further comprises an upper retainer shell  92  to house a fiberoptic connector (not shown). After the forward vertical carrier  48  has been assembled onto the heat sink  86 , a lower retainer shell  94  is attached to the upper retainer shell  92 . In one embodiment, the lower retainer shell  94  can be attached to the upper retainer shell  92  with two screws, which also pass through the customer board at specified hole locations to structurally anchor the lower retainer shell  94  to the customer board. An EMI assembly clip (not shown) can be slid over the upper retainer shell  92  and the lower retainer shell  94 . The EMI assembly clip can provide both EMI and ground connection points to the customer chassis bulkhead. 
     This completes the assembly of the multiple array transceiver module. The module can be attached to the customer&#39;s board by connecting the I/O block  76  to the mating connector on the customer&#39;s board, and securing four screws from the back side of the customer&#39;s board into mounting screw locations on the heat sink  86  and the lower retainer shell  94 . A ball grid array on the I/O block  76  normally connects to a complementary array on customer&#39;s board. 
     It is important to note that the figures and description illustrate specific applications and embodiments of the present invention, and is not intended to limit the scope of the present disclosure or claims to that which is presented therein. While the figures and description present a 2.5 gigahertz, 4 channel transmit and 4 channel receive multiple array transceiver, the present invention is not limited to that format, and is therefore applicable to other array formats including dedicated transceiver modules, dedicated receiver modules, and modules with different numbers of channels. For example, other embodiments can include multiple in-line lasers and receivers or arrays of lasers and receivers, e.g., 8×8 or 16×16 grids. Upon reading the specification and reviewing the drawings hereof, it will become immediately obvious to those skilled in the art that myriad other embodiments of the present invention are possible, and that such embodiments are contemplated and fall within the scope of the presently claimed invention. 
     While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.