Abstract:
Systems and methods for automatically attaching preforms to substrates. An example system includes a nest, a first component that places a substrate into the nest, a second component that places a preform on the substrate in the nest, a tacking device that tacks the preform to the substrate, a plurality of sensors that sense operational states of the components and the tacking device, and a controller that automatically controls operations of the components and the tacking device based on the sensed operational states.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Presently Leadless Chip Carriers (LCC&#39;s) are loaded into aluminum trays that hold 24 parts each. A preform is manually placed and positioned on the seal ring. The tray is placed on a heated stage 200-350° C. and the preforms are repositioned. The stage is moved below a heated soldering iron tip 250-350° C. and the tip is positioned above the preform. An operator uses a foot pedal to bring the tip in contact with the preform providing 1-2 pounds of force to tack the preform in place. Currently somewhere between 12 to 24 tacks are made on each preform. It is important to be sure that the preform is both secure and flat and has minimal stress. Any gaps between the preform and seal ring can lead to areas of non-wetting of the seal ring during vacuum seal which can cause vacuum leaks or voids. This process takes a considerable amount of time and does not guarantee product quality. 
         [0002]    Therefore, there exists a need for improved processes and systems for increasing the accuracy of preform attachment and decreasing the manufacturing time, thus costs. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides systems and methods for automatically attaching preforms to substrates. An example system includes a nest, a first component that places a substrate into the nest, a second component that places a preform on the substrate in the nest and also aligns the preform while not necessarily securing the preform, a tacking device that tacks the preform to the substrate, a plurality of sensors that sense operational states of the components and the tacking device, and a controller that automatically controls operations of the components and the tacking device based on the sensed operational states. 
         [0004]    In one aspect of the invention, the first component includes a conveyor component that transports substrates and a mechanical arm that retrieves one of the one or more substrates from the conveyor component and places the retrieved substrate in the nest. 
         [0005]    In another aspect of the invention, the conveyor component includes a heating device that heats some of the substrates prior to retrieval by the mechanical arm. 
         [0006]    In still another aspect of the invention, the mechanical arm returns the substrate with tacked preform back to the conveyor component. 
         [0007]    In yet another aspect of the invention, the nest includes a heating device configured to heat the nested substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0009]      FIG. 1  is a block diagram of an automated system for attaching preforms to substrates; 
           [0010]      FIGS. 2-5 ,  7  are perspective views of an example system formed in accordance with an embodiment of the present invention; and 
           [0011]      FIG. 6  illustrates an cross-sectional view of a solder tip formed in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]      FIG. 1  is a block diagram and  FIGS. 2-5  are perspective views of an example system  18  for automatically attaching preforms to Leadless Chip Carriers (LCC&#39;s) in accordance with an embodiment of the present invention. An example preform is a stamped metal component (e.g., Gold-Tin). The system  18  includes a hydraulically and/or pneumatically driven parts retrieval and attaching system  20  that is controlled by a controller  21 , such as a processor. The system  20  includes a preform loading section  24 , an LCC loading area  32  and an attachment section  34 . LCC&#39;s  62  are automatically retrieved from the loading area  32  and placed into the attachment section  34 . Preforms are retrieved from the preform staging section  24  and loaded onto the LCC&#39;s into the attachment section  34 . The retrieved preform is then tacked into place on the LCC  62  in the attachment section  34 , then are returned to the loading area  32  for offloading. 
         [0013]    The preform loading section  24  includes a loading bowl feeder  30  with attached off-loading ramps  50  and  52 . The bowl feeder  30  includes a spiral ledge  80  that is attached to the interior wall of the bowl feeder  30 . A mechanical vibrating device (not shown) vibrates the bowl causing preforms stored within the bowl to vibrate up the spiral ledge  80  until they reach an exit point in the bowl feeder  30 . The ledge  80  is higher in Z direction on the side of the ledge  80  closer to the center to the bowl feeder  30 . As the preforms reach the exit point of the bowl feeder  30  they travel down the first ramp  50 . At the end of the ramp  50  or at the beginning of a straight ramp  52  the preforms are sensed by a sensor  53 , such as an optical sensor. Once the sensor  53  senses that a preform has passed into the straight ramp  52 , a signal is sent to the controller  21  which instructs the vibrating device to turn off. The straight ramp  52  includes a vibration mechanism (not shown) that causes preforms within the ramp  52  to travel to a preform nest  92 . The ledge  80  is configured to filter out preforms that fail to meet design standards. 
         [0014]    The LCC loading area  32  includes a first conveyer belt  36  that includes belts  64  that are driven by one or more motor driven shafts  66 . The LCC&#39;s  62  rest in a conveyer boat  60 . The boat  60  is placed on top of the belts  64  of the conveyor  36 . The controller  21  controls operation of the conveyor  36  and instructs the conveyor  36  to move the boat  60  towards an LCC vacuum pick-up arm  110 . The conveyor  36  includes a sensor  68 , such as an optical sensor, that sends signals to the controller  21  based on the signal from the sensor  68  the controller  21  determines if an LCC  62  is located within the boat  60  as the boat  60  progresses along the conveyor  36 . Once the boat  60  passes under the arm  110  the boat  60  stops at a stop gate  102 . A plurality of position sensors are used throughout the system  20  to provide location information to the controller  21 . 
         [0015]    When the boat  60  is stopped underneath the arm  110  as sensed by a position sensor, a preheat rail  100  is mechanically moved up underneath the boat  60  to come into contact with five of the LCC&#39;s  62  (provided they are present) that are located on the boat  60 . The preheat rail  100  heats up the LCC&#39;s  62  to a temperature greater than 180° C. After a predetermined period of time has elapsed, the arm  110  picks up one of the been preheated LCC&#39;s  62  using a suction force produced by a vacuum system (shown partially by hoses). The arm  110  moves the retrieved LLC to an LLC nest  120  located in a first subsection  34   a  of the attachment section  34 . Then, a preform arm  90  retrieves the preform that is staged on the preform nest  92  and rotates it approximately 45° to the nest  120  and places the preform onto the LCC  62 . The preform is not secured to the LCC  62  until a bonding step. In another embodiment, a clamping device  122  secures the preform to the LCC  62  prior to permanently being attached by a soldering/bonding step. 
         [0016]    Once the preform has been extracted from the preform nest  92  a sensor (not shown), e.g. optical sensor, sends a signal to the controller  21  that determines that no preforms are present on the nest  92 . The controller  21  then instructs the bowl vibrating device to vibrate the bowl until another preform passes through the sensor  53 . 
         [0017]    After the preform is placed on top of the LCC  62  in the nest  120  the nest  120  is rotated in position into a section  34   b  of the attachment section  34 . In the section  34   b  a tacking device  132  applies a plurality of tacks using a heated tip  130  (e.g., solding tip) that is moved into place by an X, Y, Z motion control device. The tacking device  132  applies pressure between the tip  130  and the preform and the LCC  62  for a thermal compression bond. The tip  130  is heated to greater than 200° C. The nest  120  includes a heating element for heating the LLC to greater than 200° C., thereby keeping the LCC  62  near an optimal temperature for preform attachment. If other materials are used that melt/solder at lower temperatures, then the tip  130  and other components bring the LCC  62  to temps lower than 200° C. 
         [0018]    After the preform is tacked to the LCC  62  at the section  34   b , the nest  120  rotates back to the position identified in section  34   a . The arm  110  is instructed by the controller  21  to retrieve the LCC  62  with the tacked preform from the nest  120  after the clamping device  122  has released pressure on the LCC  62 . The arm  110  returns the preform tacked LCC back to the position on the boat  60  that is presently empty. The boat  60  then continues on to a second conveyer  38  and the process repeats itself. 
         [0019]    The controller  21  controls the operation of the system  20  based on more than one program sequence. A program sequence that is selected is chosen or altered based on information received from the position sensors. 
         [0020]      FIG. 6  illustrates a cross-section view of an example tip  130 . The tip  130  includes a base section  200  having a Copper core that is plated with Nickel  206 . A Tungsten Carbide tip  208  is pressure fitted into a cavity within a first end of the Copper core/base section  200 . The other end of the Copper core/base section  200  receives a heating element  210  that is connected to a heating circuit being controlled by the controller  21 . A cavity  212  in the side of the base section  200  receives a thermo coupler/sensor that sends temperature signals to the controller  21 . The base section  200  includes an annular ridge  216  that is received by opposing support mechanism (e.g., set screw) within the tacking device  132 . When the base section  200  is properly placed within the tacking device  132 , the heating element  210  is properly connected to circuit leads (not shown) with the tacking device  132 . 
         [0021]      FIG. 7  illustrates the section  34   b  with the tacking device  132  and the tip  130  positioned above the LCC  26  and preform resting in the nest  120 . The clamping device  122  holds the LCC  26  in place. An oxygen evacuation system  300  is positioned on an axis orthogonal to the axis of the two clamping devices  122 . The oxygen evacuation system  300  includes gas feed tubes  306  that is connected to a gas supply device (not shown). The gas feed tubes  306  are directed toward the nest  120  by tube clamps  304  that are attached to outer surfaces of the nest  120 . The gas feed tubes  306  supply a non-oxidizing gas, such as Nitrogen or Argon, onto the pieces that are to be attached in the nest  120 . 
         [0022]    All or parts of the system  20  may be included in a vacuum chamber or air content control chamber for reducing contamination of the process. 
         [0023]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, the standards for delivering and attaching the preforms complies with Surface Mount Equipment Manufacturers Association (SMEMA) technology. Also, a tape and reel feeder may be used in place of the bowl feeder. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.