Abstract:
An apparatus for manipulating a work piece in connection with a wire bonding machine including at least one magazine handler is provided. The apparatus includes a first conveyor system configured to receive work pieces from the at least one magazine handler, and a second conveyor system configured to receive work pieces from the at least one magazine handler. The apparatus is adapted such that the second conveyor system prepares a work piece for a wire bonding operation by a wire bonding tool concurrent with the first conveyor system supporting another work piece during a wire bonding operation of the another work piece using the wire bonding tool.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of priority to U.S. Provisional Patent Application No. 60/579,806, filed on Jun. 15, 2004, the contents of which are incorporated in this application by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to wire bonding equipment. More specifically, the present invention relates to an apparatus and process for indexing and bonding electronic components with increased throughput.  
       BACKGROUND OF THE INVENTION  
       [0003]     Modern electronic equipment relies heavily on printed circuit boards on which semiconductor chips, or integrated circuits (ICs), are mounted. The mechanical and electrical connections between the chip and the substrate have posed challenges for chip designers.  
         [0004]     The most common of these processes is wire bonding. In wire bonding, a plurality of bonding pads are located in a pattern on the top surface of the substrate, with the chip mounted in the center of the pattern of bonding pads, with the top surface of the chip facing away from the top surface of the substrate. Fine wires (e.g., aluminum, copper, or gold wires) are connected between the contacts on the top surface of the chip and the contacts on the top surface of the substrate.  
         [0005]     Chip scale packages (CSPs) offer a solution to the challenge of shrinking the size of semiconductor devices relative to the size of the chip (die) contained in the package. Typically, the CSP size is between 1 and 1.2 times the perimeter size of the die, or 1.5 times the area of the die. The CSP offers a compact size near that of a bare die or flip chip technology, and offers greater reliability, because the CSP need not suffer from the same thermal expansion incompatibility problems which are known in flip chips.  
         [0006]     Most CSPs use a flexible, sheetlike interposer (e.g., a polyimide film or tape), having fine, flexible wiring embedded therein. The fine wirings in the interposer end at peripheral terminals near the periphery of the chip when the chip is mounted on the interposer. An example is the Micro Ball Grid Array (Micro BGA) design. The wirings redistribute the peripheral terminals of the interposer to a grid array of solder ball lands that cover the interior area of the chip. The chip is mounted on the interposer, and the plurality of terminals in the interposer are bonded to the plurality of contacts on the periphery of the chip using a conventional bonding technique, such as ultrasonic bonding. Once bonded, the terminals may be encapsulated for protection using an elastomeric encapsulant that permits flexible movement of the terminals during thermal cycling due to differential expansion between the chip and the substrate. The solder balls are then formed on lands on the top surface of the interposer, and the individual chip packages are cut from the tape. The ball grid array can be evenly spaced at the minimum required pitch for solder connections to the substrate (which may be of the order of 0.5 mm between balls), achieving a high density of contacts. Because the interposer has a ball grid array covering most of the surface area of the chip, the BGA design results in a package size that is nearly as small as the chip itself.  
         [0007]     There is a drawback, however, in using BGA or Micro BGA devices with respect to the wire bonding process. Specifically, BGA devices typically require longer heat up time to bonding temperature, ultimately affecting throughput when using conventional work-holder designs. Further, BGA devices do not have “downsets”, and there are no “lead-fingers” available for clamping. These aspects of the BGA material are considered in the simplified approach in this innovation. Mechanisms built into existing work-holder designs to address “downsets” and clamping of “lead-fingers” not only add to the complexity of the design but also constrain the throughput due to their effects on the system dynamics. Accordingly, there is a need for a work-holder design that ensures adequate and uniform heating of BGA devices, affords significant simplification of automatic work-holder designs, and therefore reduced cost of goods, while enhancing throughput through having a heated strip as a buffer in the material flow.  
       SUMMARY OF THE INVENTION  
       [0008]     According to an exemplary embodiment of the present invention, an apparatus for manipulating a work piece in connection with a wire bonding machine including at least one magazine handler is provided. The apparatus includes a first conveyor system configured to receive work pieces from the at least one magazine handler, and a second conveyor system configured to receive work pieces from the at least one magazine handler. The apparatus is adapted such that the second conveyor system prepares a work piece for a wire bonding operation by a wire bonding tool concurrent with the first conveyor system supporting another work piece during a wire bonding operation of the another work piece using the wire bonding tool.  
         [0009]     According to another exemplary embodiment of the present invention, an apparatus for supplying work pieces to a wire bonding machine for use with at least one magazine handler is provided. The apparatus includes an indexer having a portion that couples to the at least one magazine handler. The indexer includes a first conveyor portion, a second conveyor portion adjacent the first conveyor portion, at least one heater disposed below the first and second conveyor portions, and at least one vacuum disposed below the first and second conveyor portions to maintain work pieces against an upper surface of the conveyor portions. The first and second conveyor portions are configured to receive work pieces from the at least one magazine handler. The apparatus is configured to load a second work piece onto the second conveyor portion while a first work piece is being at least one of (1) heated by the at least one heater or (2) wire bonded by the wire bonder.  
         [0010]     According to yet another exemplary embodiment of the present invention, a method of wire bonding work pieces is provided. The method includes (1) wire bonding a work piece supported by a first conveyor portion using a wire bonding tool of a wire bonding machine, (2) heating another work piece supported by a second conveyor portion during step (1), (3) moving the second conveyor portion to a position where the another work piece supported by the second conveyor portion is adjacent the wire bonding tool while moving the first conveyor portion to a position away from the wire bonding tool, and (4) wire bonding the another work piece supported by the second conveyor portion using the wire bonding tool.  
         [0011]     According to yet another exemplary embodiment of the present invention, a method for supplying work pieces to a wire bonding machine is provided including the steps of initializing a magazine handler and an indexer into respective first positions; loading a first work piece from the magazine handler onto a first conveyor portion of the indexer; repositioning the magazine handler to a second position; repositioning the indexer so as to locate the first work piece within a bonding portion of the wire bonding machine; loading a second work piece onto a second conveyor of the indexer substantially simultaneously with the first work piece being wire bonded by the wire bonding machine; repositioning the magazine handler to the first position; repositioning the indexer so as to locate the second work piece within the bonding portion of the wire bonding machine and locate the first work piece to an unload position; unloading the first work piece onto the magazine handler from the first conveyor substantially simultaneously with the second work piece being wire bonded by the wire bonding machine; loading a further work piece from the magazine handler onto the first conveyor; repositioning the magazine handler to the second position; repositioning the indexer so as to locate the further work piece within the bonding portion of the wire bonding machine; and unloading the second work piece from the second conveyor onto the magazine handler substantially simultaneously with the further work piece being wire bonded by the wire bonding machine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, various features of the drawings are not to scale. On the contrary, the dimensions of various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following Figures:  
         [0013]      FIG. 1  is a perspective view of an exemplary embodiment of the present invention;  
         [0014]      FIG. 2  is a left side elevation view of the exemplary embodiment of  FIG. 1 ;  
         [0015]      FIG. 3  is front elevation view of the exemplary embodiment of  FIG. 1 ;  
         [0016]      FIG. 4A  is a perspective view of a first exemplary conveyor according to the present invention;  
         [0017]      FIG. 4B  is a perspective view of an alternate exemplary embodiment for a gripper of the present invention;  
         [0018]      FIG. 5  is a perspective view of a conveyor according to an exemplary embodiment of the present invention;  
         [0019]      FIG. 6  is a front view of the conveyor of  FIG. 5 ;  
         [0020]      FIG. 7A  is a perspective view of a first exemplary gripper according to an embodiment of the present invention;  
         [0021]      FIG. 7B  is a perspective view of a second exemplary gripper according to an embodiment of the present invention;  
         [0022]      FIG. 8  is an exploded view of a heat block portion of the conveyor of  FIG. 5 ; and  
         [0023]      FIGS. 9-16  are illustrations of a process cycle flow according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     As used herein, the term “work piece” is intended to refer to any device that is configured to undergo a wire bonding operation, including but not limited to substrates (e.g., including substrates with a plurality of semiconductor devices thereon or integrated therein), leadframes, semiconductor devices (e.g., dies, chips), interposers, and combinations thereof.  
         [0025]     As used herein, the term “wire bonding a work piece” refers to the application of at least one wire bond or wire loop to the work piece, even if the work piece ultimately will include a plurality of wire bonds or wire loops. According to certain exemplary embodiments of the present invention, a wire bond may be applied to a work piece (using a wire bonding tool) on a first conveyor (or conveyor portion), and then, before the remaining wire bonds are applied to the work piece, a wire bond may be applied to another work piece on a second conveyor using the wire bonding tool. Of course, the present invention also contemplates applying all of the desired wire bonds to a first work piece (using a wire bonding tool) on a first conveyor and then applying all of the desired wire bonds to another work piece on a second conveyor using the wire bonding tool.  
         [0026]     As used herein, the term “magazine handler” is intended to refer to any system through which work pieces are presented to an indexer (e.g., an indexer including a conveyor system). The term is not intended to be limited to systems that present the work pieces in any particular arrangement or configuration.  
         [0027]      FIG. 1  illustrates a perspective view of an exemplary embodiment of the present invention. For clarity, the magazine handler system that stores and presents/receives work pieces before and after processing is not shown in this figure. As shown in  FIG. 1 , bonding system  100  comprises a bonding head structure  102  which includes a bonding head  104  disposed on a front portion thereof. Below bonding head  104  is the inventive shuttling dual workholder  106  mounted on support block  108 . Workholder  106  and support block  108  move in a Y direction along rail  110  with respect to support base  112 . Bonding head  104  remains stationary with respect to the X and Y axes while dual workholder  106  shuttles back and forth in the direction of arrow Y. Dual workholder  106  includes a first conveyor system  116  and a second conveyor system  118  disposed along side one another. The details of conveyor system  116  and  118  are described below.  
         [0028]      FIG. 2  illustrates a left side view of bonding system  100 . As shown in  FIG. 2 , conveyor systems  116  and  118  are spaced apart from one another such that the center lines of respective conveyor systems  116  and  118  are desirably about 4.5 inches apart. The invention is not so limited as this distance may be adjusted as necessary to meet design considerations. Adjacent each conveyor system  116  and  118  is a fixed front rail  120 . As shown in  FIG. 2 , and for purposes of explanation, the dual workholder assembly is in a rearward position such that conveyor system  118  is positioned below bonding tool  114 . As can be appreciated, as linear slide  122  of support block  108  moves forward along rail  110 , conveyor  118  will move away from bonding tool  114  while conveyor  116  moves toward bonding tool  114 . In this way, work pieces (not shown in this figure), which are detachably mounted to conveyors  118  and  116 , may be bonded.  
         [0029]      FIG. 3  illustrates a front elevation view of bonding system  100 ,  FIG. 4A  is a front perspective view of one of conveyors  116 ,  118 ,  FIG. 5  is a rear perspective view of one of conveyors  116 ,  118 , and  FIG. 6  is a front view of one of conveyors  116 ,  118 . As shown in  FIGS. 3, 4A ,  5  and  6 , puller/gripper/tucker  132  (for conveyor  118 , also shown in  FIG. 1 ) and  134  (for conveyor  116 ) are disposed along a front portion of the respective conveyors  116 ,  118 . For purposes of the following discussion, only puller/gripper/tucker  132  and its associated parts (e.g., lead screw  128 , jaw assembly  148 , and stepper motor  124 ) will be referred to for simplicity, but it is recognized that the explanation is equally applicable for puller/gripper/tucker  134  and its associated components (e.g., lead screw  130 , jaw assembly  150 , and stepper motor  126 ).  
         [0030]     Puller/gripper/tucker  132  travels along lead screw  128  in a direction orthogonal to that of workholder  106  and support block  108 . Jaw assembly  148  is coupled to the housing of puller/gripper/tucker  132  and, in one exemplary embodiment, is disposed between front rail  120  and the side of platen heat block  152 . Stepper motor  124  is coupled to one end of lead screw  128  by coupler  156 . In operation, when stepper motor  124  is activated, lead screw  128 , which is supported at one end by bearing support  140 , rotates in turn moving puller/gripper/tucker  132  along lead screw  128  toward the right side of the figure (See, e.g.,  FIGS. 4A and 6 ). As will be described further below, jaw assembly  148  is used to grasp onto a portion of a work piece from a supply of work pieces. Thus, as puller/gripper/tucker  132  moves along lead screw  128 , the work piece will move along the surface of platen heat block  152  ultimately for bonding by bonding tool  104 . Conversely, to eject a work piece, stepper motor  124  is operated in a reverse direction to move the work piece back toward the supply magazine (not shown). Referring again to  FIG. 5 , rear rail  144  may be adjustable in a Y direction to accommodate work pieces of varying widths. A detailed description of platen heat block  152 ,  154  will be addressed below with respect to  FIG. 8 .  
         [0031]     Although a stepper motor and lead screw are illustrated in  FIGS. 4A and 6 , the invention is not so limited as it is contemplated that a pulley and belt assembly, for example, may be used to move puller/gripper/tucker  132  as desired. Such an approach is illustrated in  FIG. 4B . As shown in  FIG. 4B , puller/gripper/tucker  132  is coupled to stepper motor  124  with timing belt  182  via belt clamp  180 . In operation, when stepper motor  124  is activated, pulley  186  turns which moves timing belt  182  (and pulley  184 ), in turn directing puller/gripper/tucker  132  along slide rail  188 . To return puller/gripper/tucker  132  to its initial position, stepper motor  124  is reversed.  
         [0032]      FIG. 7A  is a perspective view of a first exemplary embodiment of puller/gripper/tucker  132 ,  134 . As shown in  FIG. 7A , puller/gripper/tucker  132 ,  134  comprises fixed upper jaw  402  and movable lower jaw  404  disposed against one another. Fixed upper jaw  402  has grip points or teeth  420  disposed along a portion of the length of fixed upper jaw  402 . These grip points or teeth  420  and the surface of movable lower jaw  404  contact a work piece, such as a ball grid array (BGA) assembly or lead frame, as desired to move the work piece along the conveyor. Fixed upper jaw  402  is coupled to fixed support  418  at a top portion thereof. Movable support arm  410  is spaced apart from and coupled to fixed support  418  with upper leaf spring  406  and lower leaf spring  408 . Leaf springs  406  and  408  permit movable support  410  to articulate in the Z direction (as indicated by the double headed arrow) with respect to fixed support  418 . As such, movable lower jaw  404 , which is coupled to movable support arm  410 , will likewise move in the Z direction with respect to fixed upper jaw  402 , thereby permitting a BGA or lead frame to be gripped by upper and lower jaws  402 ,  404  as desired.  
         [0033]     In one exemplary embodiment, to effect the movement of movable support arm  410  and movable lower jaw  404 , an actuator  416 , such as a solenoid or a voice coil motor is used. In the exemplary embodiment, actuator  416  is disposed on an upper service of lower leaf spring  408  and coupled to beam  412 , which is in turn is coupled to movable support arm  410 . Upon activation of actuator  416 , beam  412  is drawn closer to the frame of actuator  416  in turn moving support arm  410  downward in the Z direction, which in turn moves lower jaw  404  away from fixed upper jaw  402  opening a space between movable lower jaw  404  and grip points  420  so that an article, such as a BGA assembly or lead frame, may be positioned between the opening of upper and lower jaws  402 ,  404 . Once the lead frame or BGA assembly (not shown) is in place, actuator  416  is de-energized, thereby moving jaw  404  closer to fixed upper jaw  402  such that the BGA or lead frame is grabbed between fixed upper jaw  402  and movable lower jaw  404 .  
         [0034]     Referring now to  FIG. 7B  a second exemplary puller/gripper/tucker  132  is illustrated. As shown in  FIG. 7B , this exemplary puller/gripper/tucker is for use with the belt drive system illustrated in  FIG. 4B  and comprises fixed gripper jaws  402  coupled to upper bracket  424 , moveable lower jaws  404  coupled to lower bracket  422 , leaf springs  406 ,  408  coupled between lower bracket  422  and upper bracket  424 , belt clamp  180  coupled to upper bracket  424 , slide block  426  coupled to upper bracket  424  and actuator  416  disposed between upper bracket  424  and lower bracket  422 . In operation slide block  426  is coupled to and moves along slide rail  188  (shown in  FIG. 4B ). Operation of the jaw assemblies  402 ,  404  is similar to the embodiment described above with respect to  FIG. 7A  and is not repeated here.  
         [0035]     Referring now to  FIG. 8 , a exploded perspective view of platen heat block  152  is illustrated. As shown in  FIG. 8 , heat block  152  comprises top heat plate  200 , preferably made of a light weight metal, such as aluminum, lower heat plate  206 , also formed from a lightweight metal, such as aluminum, heaters  202  disposed between top heat plate  200  and lower heat plate  206 , and insulator plate  208 , desirably formed from a ceramic material, disposed below lower heat plate  206 . In one exemplary embodiment, heaters  202  are desirably formed in a flat configuration from a foil type resistive heating element. In addition, to accomplish a desirable temperature ramp up and ramp down as the work piece moves along the heat block  152 , heaters  202  are configured into stages, such as a preheat stage  202   a , bond site heat stage  202   b , and post bond stage  202   c . Although three heaters  202   a ,  202   b ,  202   c  are illustrated, it is contemplated that a single heater may be used to accomplish these functions.  
         [0036]     As the work piece is draw along the surface of platen heat block  152  by puller/gripper/tucker  132 , the first stage of platen heat block  152  will preheat the work piece in preparation for bonding. As the work piece moves further along the surface of platen heat block  152 , the work piece will be subject to a higher temperature in preparation for bonding by bond head  104  (see  FIG. 1 ). In order to maintain the work piece in position during bonding, the surface of platen heat block  152  includes vacuum zones  210 ,  212 ,  214 , which receive a source of vacuum (not shown). In one exemplary embodiment, vacuum zone  210 ,  212 ,  214  extend partially into the preheat zone and post heat zone. In one exemplary embodiment, the vacuum source is coupled to a central portion of bottom heat plate  206  via inlet tubes  204 . Each inlet tube is coupled in fluid tight relationship with a respective one of vacuum zones  210 ,  212 ,  214 .  
         [0037]     In operation, when a work piece is put into place for bonding, vacuum is applied to a lower portion of the work piece to hold it in place against the surface of top heat plate  200 . This serves two purposes. One is to ensure adequate heat transfer to the work piece during bonding and the second is to prevent the work piece from moving during bonding. Once bonding is completed on the work piece, the vacuum is removed and the work piece is moved toward the post bond portion of the platen heat block  152  to allow for the work piece to gradually cool down prior to further processing.  
         [0038]     As can be appreciated, for work pieces that are coupled to one another using a substrate or other type of coupling, as the first work piece is being bonded, subsequent work piece(s) are being preheated. Once bonding of the first work piece is completed, a subsequent work piece is moved into place as the first work piece is moved away from the bonding site and vacuum is applied for bonding this subsequent work piece. This process desirably continues until all work pieces are bonded or the process is otherwise terminated. This process is best illustrated in  FIGS. 9-16  and described below.  
         [0039]     Referring now to  FIG. 9 , in an initial configuration magazine handler  300  presents a work piece  302  having a plurality of devices to be pulled into front conveyor  118  of dual workholder  106 . Work piece  302  will then be moved along the surface of front conveyor  118  with puller/gripper/tucker  132  (not shown in this figure). As device  302  is being moved along front conveyor  118 , it is being preheated prior to bonding. For simplicity, it will be assumed for this description that rear conveyor  116  is initially empty.  
         [0040]     As shown in  FIG. 10 , both magazine handler  300  and dual workholder  106  are repositioning rearward to a second position so that front conveyor  118  is positioned under bond head  104 . As work piece  302  is being processed, a second work piece  304  is loaded onto rear conveyor  116  with puller/gripper/tucker  134  (not shown in this figure) for preheating prior to bonding.  
         [0041]     As shown in  FIGS. 11 and 12 , once the last device of work piece  302  is bonded dual workholder  106  is moved forward so as to position conveyor  116  under bond head  104 . As shown in  FIG. 12 , as work piece  304  is being processed (moving from left to right), work piece  302  is being unloaded into magazine handler  300  by puller/gripper/tucker  132  for further processing. These two processes occur substantially, if not completely, simultaneous with one another. Further, and as discussed above, as work piece  302  is being unloaded it goes through a controlled cool down while passing over post-heat zone and preheat zone of heat platen  152 .  
         [0042]     As shown in  FIG. 13 , as work piece  304  is being processed a third work piece  306  is loaded onto front conveyor  118  with puller/gripper/tucker  132  for preheating prior to bonding.  
         [0043]     As shown in  FIGS. 14-16 , once the last device of work piece  304  is bonded, dual workholder  106  is moved rearward so as to position conveyor  118  under bond head  104 . As shown in  FIG. 15 , as work piece  306  is being processed (moving from left to right), work piece  304  is being unloaded into magazine handler  300  by puller/gripper/tucker  134  for further processing. These two processes occur substantially, if not completely, simultaneous with one another. Further, and as discussed above, as work piece  304  is being unloaded it goes through a controlled cool down while passing over post-heat zone and preheat zone of heat platen  152 . Next, and as illustrated in  FIG. 16 , as processing continues on work piece  306  yet another work piece  308  is being loaded onto rear conveyor  116  for processing.  
         [0044]     This process may be repeated as desired until all work pieces contained in magazine handler  300  are bonded. Thus, as can be appreciated, the exemplary system and process increase throughput of BGA and/or leadframe devices.  
         [0045]     Although the present invention has been illustrated primarily with respect to two parallel conveyor systems (e.g., conveyors  116  and  118 ) it is not limited thereto. Alternative arrangements of conveyor systems (e.g., non-parallel) are within the scope of the present invention. Further, the present invention is not limited to two conveyors. For example, in certain arrangements three or more conveyors arranged with respect to a wire bonding system may be practical and efficient.  
         [0046]     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.