Abstract:
A tool and method for the alignment and placement of optoelectronic devices with attached fiber optic connectors onto the electronic interface substrate of a parallel optical transceiver package. The optoelectronic devices are connected to the substrate through a flexible circuit. The tool is comprised of a mounting frame, which includes a recess for the parallel optical transceiver package, and a rotatable clamp assembly for positioning a pair of optoelectronic devices with attached fiber optic connector and flexible circuit. Rotation of the rotatable clamp assembly properly places the flexible circuit onto the attachment point of the substrate. The rotating clamp assembly is then fixed in place by securing the actuator arm to the mounting frame. Once the clamp is secured, the flexible circuit is bonded to the substrate.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method for the integration of a parallel optical transceiver package and more particularly to positioning an array of optoelectronic devices onto the electronic interface substrate of the package and maintaining relative position of the two components for application of adhesive and subsequent curing. The invention further relates to an assembly tool for the above described method utilizing a multi-piece fixture which aligns the optoelectronic device and guides it through the necessary rotation for connection to the electronic interface substrate and then is locked so as to maintain relative position of the components thereafter until bonding is complete. 
   BACKGROUND OF THE INVENTION 
   There is a need for high-speed cost effective optical transmitters which can operate as parallel optical communications data links. The preferred method of transmission for voice and data information across a network is by optical fiber due to bandwidth capacity and lower signal attenuation as compared to traditional copper networks. The light emitting and light receiving devices are referred to as optoelectronic devices and they are generally coupled at a first end to one or more fiber cables. The optical fibers provide the path for photons created by an optoelectronic device, such as a semiconductor LED or laser. An opposing end of the fiber cable is connected to a light-receiving device such as a photo detector. 
   The primary function of the optical transmitter is to translate electrical signals into optical signals. The optical transmitter interfaces with an electric interface circuit for driving the light transmitting device. A parallel optoelectronic module or package may include both receiver and transmitter functions. 
   The coupling of an optoelectronic device with an array of optical fibers at a first end and an interconnecting substrate at the opposing end is a difficult task for every time a coupling is made the quality of the signal transmission is affected. In a typical coupling, an optical connector is employed for efficiently managing the transfer of photons from the light-emitting device to the fiber optic cable. The optical connector must be aligned and connected with the optoelectronic device. The coupling of such systems generally require precise alignment for signal quality decreases with increased distances from an optical port to an optical connector unless the photons are properly directed into the fiber cable. The alignment techniques necessary to achieve such precise alignment are typically performed manually which is both time consuming and expensive. 
   Optical connections are only half the battle of effective coupling. Connection of the optoelectronic device with the electronic interface substrate of the package is complicated due to geometric constraints. The optoelectronic transmitter commonly used in fiber optic networks is the vertical cavity surface emitting laser (VCSEL). Unfortunately, the VCSEL emits light in a generally perpendicular direction to the plane of the fibers and substrate therefore making stacking of such components difficult. To solve the packaging problem the VCSEL is either mounted parallel to the substrate and the output photons directed 90° through mirrors or the VCSEL is mounted perpendicular to the substrate and the electrical interface connectors bent 90°. The optical bending solution is less than optimal due to the difficult optical design and alignment required. Conversely, the bending of electrical conductors is well known in the art through implementation of flexible circuits. Therefore, flexible electrical circuits capable of achieving the necessary 90° bend are the generally accepted solution. 
   In order to reduce electrical parasitics, short electronic interconnects are needed between the optoelectronic device and the electronic interface circuitry. The problem alignment and bending of the flexible circuit are exacerbated as data rates of the optoelectronic devices increase, closer connections must be established in order to maintain electrical performance levels. The placement and bending of the flexible circuit on the substrate is typically performed manually by a skilled technician just prior tot application of an adhesive. Unfortunately, the existing techniques employed in connection with this process are time consuming, expensive and prone to failure due to misalignment. If the placement of the flexible circuit fails to align with the substrate connectors, the entire component may need to be scrapped. While manual bending and aligning techniques exist for mounting an optoelectronic device to the substrate, it would be desirable to improve the efficiency and reduce the cost of the coupling. 
   SUMMARY OF THE INVENTION 
   The present invention is a method and integration tool for the dual alignment and placement of optoelectronic devices on the electronic interface substrate of a parallel optical transceiver package. The tool is comprised of a rotatable clamp assembly disposed on a mounting platform. The optoelectronic devices are connected to the substrate through a flexible circuit disposed adjacent to optical connector and light-emitting device. The rotatable clamp assembly positions the optoelectronic devices with the flexible circuit suspended above the appropriate recess in the package substrate. Rotation of an actuator arm connected to the rotatable clamp assembly places the flexible circuit onto the substrate. The rotating clamp assembly is then fixed in place by securing the actuator arm to the mounting frame. Properly aligned systems are fixed by applying adhesive. The completed unit is preferably constructed of a metal such as aluminum to facilitate the curing process, which may require elevated temperatures. 
   The present invention provides a cost efficient method of aligning and connecting optoelectronic devices to the electronic interface circuitry of the package. It is essential that the exact alignment of the light source or laser diode portion and light-receiving portion be maintained throughout the assembly process. The present invention enables repeatable and consistent rotation of a flexible circuit 90° so as to connect with a substrate for the parallel packaging of the electronic interface circuitry with the light source. The method maintains the integrity of the optical connection while reducing the time intensive manual component of assembly. Furthermore, the mechanical aspect of the process provides a reliable means of duplicating successful placement thus increasing the output of properly aligned assemblies. 
   In a preferred embodiment, the optoelectronic devices are VCSEL arrays to which a flexible circuit is attached. The flexible circuit contains electrical traces on one side which provide current pathways to the VCSEL from the integrated circuits of the package. A passive alignment guide in the form of a spacer block is mounted distally from the VCSEL on the opposing side of the flexible circuit. A recess disposed in the substrate is sized to accept the mating of the spacer block. Upon rotation, the electrical traces of the flexible circuit are disposed at the same level as the substrate traces so as to minimize lead distances. 
   The rotating base of the clamp assembly is initially disposed transverse to the package. The optical connector with VCSEL array positioned on the top is disposed within the appropriate cavity in the rotating base unit. The laser clamp mates with the rotating base over the VCSEL so that VCSEL and optical connector are disposed generally transverse to the package. The distal end of the flexible circuit freely extends parallel to the package. Preferably, the rotating clamp assembly pivots by manually raising the actuator arm from a resting position until contact is made with the upper mounting frame. The rotation places the spacer block in the recess of the substrate as the flexible circuit bends approximately 90°. Adhesive can then be applied to form a permanent bond between spacer block and the electronic interface substrate. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of a laser package integration tool with a parallel optical package in place. 
       FIG. 2  is an exploded perspective view of a laser insertion assembly of the present invention in which a VCSEL and MT connector are included. 
       FIG. 3A  is a rear perspective view of the laser support of the present invention. 
       FIG. 3B  is a front perspective view of the laser support of the present invention. 
       FIG. 4A  is a perspective view of the mating face of the laser clamp of the present invention. 
       FIG. 4B  is a top perspective view of the laser clamp of the present invention. 
       FIG. 5  is a perspective view of the package mount of the package support frame of the present invention. 
       FIG. 6  is a top perspective view of the laser package integration tool with VCSEL installed prior to integration. 
       FIG. 7  is a perspective view of the laser clamp assembly during rotation. 
       FIG. 8  is a perspective view of the laser package integration tool after rotation with laser clamp removed. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as to not to unnecessarily obscure aspects of the present invention. 
   The present invention is a tool and method for the integration of an optoelectronic device with a fiber optic connector to a parallel optical transceiver package. Fiber optic transmitter and receiver electrical elements are implemented on two separate substantially parallel boards. The boards are disposed substantially perpendicular to the base of the optoelectronic device. A flexible circuit is bent 90° in order to join the optoelectronic device to the electrical circuitry of the parallel optical package. 
   In the preferred embodiment, the present invention is used for the integration of a vertical cavity surface emitting laser (VCSEL) within a parallel optical package. In this geometric configuration, light emitted from the surface of the VCSEL laser is oriented nominally along a plane parallel to the substrate. This is the preferred direction for the optical portion of the package because the optical cable can then extend parallel to the substrate thus allowing multiple packages to be stacked. 
   A flexible circuit, bent at a right angle is used to electrically connect pads on the substrate to pads on the optoelectronic dyes, which are oriented perpendicular to the substrate. The flexible circuit has leads defined in one single layer protected by a sheet of insulating material. At one end of the flexible circuit, bonds are used for the connection to the optoelectronic dyes. At the other end an array of large pads provides landing sites for testing. After the flexible circuit is secured in its aligned position in the cavity of the substrate, each of its leads are electrically connected to corresponding pads on the substrate by a series of wire bonds. 
   Accurately aligning the bonding sites on the substrate to the flexible circuit is a challenging step. Too great an offset between bonding sites can effect wire bond yields and process time and create a high inductance electrical sub system, due to the longer wires and higher wire loops required to accommodate a large lateral offset. The offset of the flexible circuit and the substrate bonding site is a result of cumulative placement errors between flexible circuit and optoelectronic device, optoelectronic device and optical coupler, optical coupler to fiber optics. These attachment steps along with the right angle bending of the flexible circuit when the optical assembly is mounted onto the substrate could result in unacceptably large angular and position placement errors. However, these placement errors can be kept to a minimum through the careful design and assembly of component parts. It should be noted that placement errors can impact the amount of noise introduced into the system, possibly making the system not functional. 
   A laser package integration tool  10 , in accordance with the present invention, is constructed as shown in  FIGS. 1-5 .  FIG. 1  is a perspective view of the laser package integration tool  10  which provides for alignment of the optoelectronic device with a parallel optical transceiver package  12 . The optoelectronic device  10  is comprised of a vertical cavity surface emitting laser (VCSEL)  14 , the active face of which is mounted on a flexible circuit  16  and then aligned with an optical connector  15 . Fiber optic cables  18  mated to the connecter  15  complete the circuit. The laser package integration tool  10  is comprised of a package support frame  20  and a laser insertion assembly  40 . 
   The package support frame  20  provides a work stand for placement of the parallel optical package  12  and allows for the rotation and clamping of the laser insertion assembly  40 . Package support frame  20  is comprised of package mount  24  which is supported at one end by front support  22  and at opposing end by actuator support  26  which is disposed generally parallel to front support  22 . The top edge of front support  22  mates with front support recess  32  on the mating side of package mount  24 . 
   Front support screws  30 A and  30 B are inserted through front support holes  96 A and  96 B of a first end of package mount  24 . (See FIG.  5 ). As illustrated in  FIG. 1 , the opposing end of the package mount  24  slides into actuator support recess  34 A and  34 B which is disposed approximately midway along the length of actuator support  26 . Relative position of package mount  24  is maintained by inserting screws (not shown) through actuator support  26  into actuator holes  92 A and  92 B. (See FIG.  5 ). 
   The top face of package mount  24  includes parallel optical package recess  37  and electrical connector recess  38 . Hinge recesses  29 A and  29 B are disposed on opposing sides of package mount  24 . Hinge block  28 A and  28 B are installed in recess  29 A and  29 B, respectively, for axial insertion of hinge pins  31 A and  31 B. 
   As illustrated in  FIG. 2 , laser insertion assembly  40  is comprised of actuator arm  42 , laser support  44  and laser clamp  46 . Actuator arm  42  is mounted to the upper face of laser support  44  by inserting actuator screws  60  through respective arm holes  54  which threadably engage laser support holes  72 . Handle  50  of actuator arm  42  is disposed perpendicular to actuator mount  52 . At the distal end of handle  50  is clamp hole  56  through which clamp screw  58  is axially inserted and to engage a matching actuator hole  98  within actuator recess  97  in actuator support  26 . 
   Laser support  44 , as illustrated in  FIGS. 3A and 3B , provides the receptacle for the optoelectronic device, which in a preferred embodiment is a VCSEL. VCSEL  14  with attached flexible circuit  16  and MT connector  15  is inserted into MT connector cavity  66  on the mating face of laser support  44 . Fiber optic cable  18  will extend distally within cable cavity  64 . MT connector  15  rests on connector support  68  with VCSEL  14  and flexible circuit  16  freely extending toward laser clamp  46 . Hinge knuckles  62 A and  62 B are disposed on opposing sides of laser support  44  so that upon alignment with hinge blocks  28 A and  28 B and insertion of pins  31 A and  31 B, the axis of rotation runs through MT connector  15 . 
   As illustrated by  FIG. 2 , laser clamp  46  mates with laser support  44  to hold the VCSEL  14  in place. Laser clamp  46  is positioned by way of inserting clamp guides  77 A and  77 B through laser clamp guide holes  76 A and  76 B which align with laser support guide holes  70 A and  70 B. Position is maintained by inserting clamp screw  75  through clamp screw hole  74  in the laser clamp  46  which threadably engages support clamp hole  69 . 
     FIGS. 4   a  and  4   b  illustrate the two faces of laser clamp  46 . VCSEL  14  fits within VCSEL cavity  78  located on VCSEL support  79 . Flexible circuit  16  initially extends parallel to the package mount  24 . As VCSEL support  79  contains a flex rotation face  80  which guides rotation of flexible circuit  16  when laser support  44  is rotated. This acts as a mandrel in forming the VCSEL. The rotation face  84  of laser clamp  46  is rounded to match flex rotation face  80 , and allow free rotation of the laser clamp  86 . 
   Operation of the present invention is illustrated in  FIGS. 6-8 . Laser support  44  is connected by pins  31 A and  31 B to package mount  24 . Actuator arm  42  is then mounted on to the distal face of laser support  44 . As illustrated in  FIG. 6 , laser support  44  is initially disposed with clamping face  73  extending parallel to package mount  24 . MT connector  15  with VCSEL  14  and flexible circuit  16  attached are inserted into MT connector cavity  66  from the bottom of package mount  24  through recess  90 A and  90 B. (see FIG.  5 ). At this point in the integration, the flexible circuit  16  and distally mounted spacer  17  extend over the parallel optical package recess  37  on the package mount  24 . 
   As illustrated by  FIG. 7 , laser clamp  46  is installed over VCSEL  14  by insertion of clamp guides  77 A and  77   b  and engagement of clamp screw  75 . Parallel optical transceiver package  12  is next disposed within recess  37  of package mount  24 . As illustrated in  FIG. 5 , multiple package restraints  91  form a barrier for spacing parallel optical transceiver package  12  relative to laser support  44  for rotation. 
   To integrate the flexible circuit  16  with the parallel optical transceiver package  12 , the user rotates handle  50  of actuator arm  42  approximately ninety degrees until clamp hole  56  at the distal end of handle  50  engages actuator recess  97  in actuator support  26 .  FIG. 7  illustrates partial rotation of laser insertion assembly  40  in which flexible circuit  16  is brought to engage the parallel optical transceiver package  12  without lateral movement. Note that  FIG. 7  only includes a single flexible circuit  16  for illustrative purposes. It is envisioned that the integration would involve the simultaneous placement of two flexible circuits. 
   As illustrated in  FIG. 1 , clamp screw  58  is axially inserted and threadably engages actuator hole  98  to secure actuator arm  42  in place once the laser assembly  40  has rotated 90 degrees. As illustrated in  FIG. 8 , following rotation and clamping of actuator arm  42 , the spacer block  17  is disposed within the appropriate recess of parallel optical transceiver package  12 . Adhesive may now be applied to the integrated unit, or applied before rotation is completed. 
   It is to be understood that the embodiments described herein are only illustrative and modifications of the various dimensions and materials can be made still within the spirit and scope of this invention.