Abstract:
A wire dereeler for an ultrasonic wire bonder with a bond head has a support for rotatably supporting a reel of wire driven by a stepper motor in incremental steps. Two rollers receive the wire therebetween and are driven by a motor drive for rotating or torquing the rollers and tensioning the wire placed between the rollers. A linkage generally aligns the rollers in parallel with the wire therebetween. A photoelectric sensor determines a given amount of wire at a position between the bond head and the rollers and provides a signal for controlling the stepper motor driving the reel of wire.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The field of this invention resides within the industrial wire bonding art. More specifically, it relates to ultrasonically bonding a wire to a component such as an electrical, electronic, or semi-conductor part by an ultrasonic wire bonder. The ultrasonic wire bonder has wire fed to it from a reel which is then bonded by an ultrasonically vibratory transducer connected to a bonding tool. The invention specifically relates to providing an appropriate amount of wire to a bonder while at the same time maintaining control over the feed system to the bonder.  
           [0003]    2. Prior Art  
           [0004]    The prior art of wire bonding constitutes a number of wire bonders which receive large and small thickness wire to be ultrasonically bonded to a component. Such components can be electrical, electronic, or other types of components including many semi-conductor devices and processors in which a wire bonded connection must be undertaken. In such cases, wire is moved into proximity under a bonding tool with a transducer connected to it. This is done through a bonding head which moves in X, Y and Z directions.  
           [0005]    Generally, the bonding head moves the bonding tool with the wire in proximity thereto into juxtaposition against an electrical device to be bonded. In doing so, the bonding head usually pays out a certain amount of wire from a reel.  
           [0006]    The wire should be carefully and reliably removed from the reel or spool and then fed to the bonder as required. In some prior cases, the wire has been over fed or under fed. Such prior art dereelers created bonding problems with regard to the interaction of the bonding head, bonding tool, and movements of the bonding head.  
           [0007]    In order to allow for a given amount of play in the wire as the bonding head moved, the prior art used a dancer-arm. This was used to tension the wire as it came off of the spool or reel as it was fed to the bonder. Because of the fact the dancer-arm provided tension through the use of a spring force it was subject to bonder induced vibrations. This created not only resistance problems but increased wear.  
           [0008]    The system using the dancer-arm and other means for handling wire to place it in a properly fed tension mode caused the wire to break. Further to this extent, the tension required of the upstream tension on the wire provided by a spring force or dancer-arm created problems with regard to the movement of the wire on the downstream movement into the proximity of the bonding head. This led to wear problems downstream from the spring tensioners or dancer-arm. Further to this extent, the feeding of the wire to the bonding head through a tube or other feed system was such that it either could over feed or under feed the wire creating downstream problems of greater magnitude. The fundamental problems are such where the wire fed to the bonding head complicated the entire bonding operation and oftentimes was fouled, jammed, or improperly fed for a proper bond by the bonding tool.  
           [0009]    This invention overcomes many of the drawbacks of the prior art in providing wire to a bonding head. In particular, this invention provides for proper torque and tension of the wire. It also provides for a buffer so that a proper amount of wire is always in readiness to be fed to the bonding head.  
           [0010]    The foregoing features of the torque tension mechanism are provided by drawing the wire with a sufficient amount of tension from the wire spool. In this manner there will be a degree of pulling torque between the reel and the tensioner mechanism. This enhances the feed as well as the maintenance of the alignment of the wire coming from the reel or spool.  
           [0011]    The buffer sensor of this invention creates a sufficient amount of wire within the entire feed system so that there is wire that can be fed without over amounts of slack. The wire to be fed is constantly monitored as to the amount of the necessary slack in the system for proper feeding to the bonding head. This constant monitoring through the buffer sensor of the invention allows for improved feeding, monitoring, and delivery of wire to the downstream end of the process namely to the bonder head.  
           [0012]    For these reasons, the invention is a significant step over the prior art of bonding head wire dereelers for creating a wire bonding spool system and wire bonder of an improved type and capacity.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    In summation, this invention comprises a wire bonding spool system having a torque and tension mechanism for tensioning the wire from a spool or reel in conjunction with a buffer sensor which senses and causes the wire to be fed with a proper amount of feed length between an over slack condition and a tightened over tensioned condition.  
           [0014]    More specifically, the invention comprises a dereeler and control system for dereeling or unreeling wire from a spool or reel of wire that is to be bonded by a bonding head. The spool of wire is driven by an incremental movement of a motor which releases the wire on a basis of the required amount of wire.  
           [0015]    In order to maintain tension between the spool and the feed system, a positive torque or tension mechanism is utilized comprising a pair of rollers that are driven by a motor. The rollers maintain positive tension on the wire being fed from the reel. At the same time, the roller axes are maintained in generally parallel relationship to each other. This allows for variously sized wire to be fed therethrough across a broad spectrum of thickness and width across the dimensions of the reel or spool from which the wire is fed.  
           [0016]    The buffer sensor senses a certain amount of wire that is being fed. The buffer sensor incorporates a light responsive output reflected from the wire which is being fed. The wire being fed is passed through an opening, throat, or monitoring passage. As the wire passes with either undo slack or undo tension, the sensor puts out a signal that appropriately controls the feed of the wire from the reel.  
           [0017]    The dereeler in combination with the bonding head also incorporates pinch rollers to properly feed the wire while at the same time monitoring the amount of wire that is being fed. This helps to assure the fact as to whether or not a proper bond has been undertaken downstream while at the same time monitoring the length of wire. 
       
    
    
       [0018]    As will be seen from the following specification, this invention is a significant step over the art of providing wire to a wire bonder.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 shows a perspective view of a wire bonding head with wire bonding elements at the lower end and an attachment collar for attachment to the support tube of the bonder for use with the dereeler or wire bonding spool system of this invention.  
         [0020]    [0020]FIG. 2 shows a perspective view opposite from that of FIG. 1.  
         [0021]    [0021]FIG. 3 shows a perspective view of the front and side of the dereeler of the wire bonding spool system incorporating numerous components of the system.  
         [0022]    [0022]FIG. 4 shows a sectional view in the direction of lines  4 - 4  of FIG. 3.  
         [0023]    [0023]FIG. 5 shows a plan view of the sensor as shown in FIG. 4.  
         [0024]    [0024]FIG. 6 shows a graphic representation of the analogous positions along the sensor for the respective sensing of tight, feed and tensioning positions of the wire along the sensor.  
         [0025]    [0025]FIG. 7 shows a diagram of the logic of the system for controlling the movement of the feed system.  
         [0026]    [0026]FIG. 8 shows a side perspective view of the system as broken away from the entire system as seen in FIG. 3.  
         [0027]    [0027]FIG. 9 shows a fragmented sectional view of the tensioning rollers of this invention as sectioned through a portion thereof namely in the direction of lines  9 - 9  of FIG. 8.  
         [0028]    [0028]FIG. 10 shows a view of the pivotal movement linkages and force members to maintain the rollers of FIG. 9 in relative parallel relationship to each other.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Looking more particularly at FIGS. 1 and 2, it can be seen that the large wire bonder or bonding head that is used with the bonding spool system of this invention has been shown. The bonding head is attached to the bonder equipment and moves by means of a Z direction support tube to move in a vertical upright direction or rotationally. The Z tube control connection moves the bonding head with respect to its location over an ultrasonic bond that is to take place. The bond head also moves in X &amp; Y directions. The work is stationary during bonding.  
         [0030]    In particular, the bonding head  10  has been shown having a casting, collar, or upper cylinder  12  that specifically has tapped openings  14 . The tapped openings  14  secure the bonding head to the Z tube (i.e. upright connection) of a bonder in order for it to move over the surface of the area on which an ultrasonic bond is to take place. Fundamentally, the casting  12  is a mounting bracket or mounting member. It can be configured in any particular manner so long as it attaches to the Z tube which moves the bonding head upwardly and downwardly, rotationally, and in other modes. The bonding head Z tube connection can also move in an X-Y direction in this case.  
         [0031]    An opening  16  is shown within the bonding head which receives a cable guide  18  having cables  20  which serve the electronic and control functions of the bonding head. A second cable guide  22  is shown in which cables  24  which are the same as cables  20  emanate from.  
         [0032]    The cable guide can be mounted by a mounting screw  28  and the cables can be interconnected to a circuit board generally dotted in as circuit board  30 . The circuit board  30  provides for the controls through various integrated circuits and other control functions in concert with the signals and power provided through the cables including cables  20  and  24 . The circuit board  30  can be a printed circuit board and junction board, and have various electronic functions provided thereon for the bonding head.  
         [0033]    In order to drive the bonding tool and other elements with sufficient force against the work to be bonded, a forcer assembly  34  is shown. The forcer assembly  34  includes mounting screws such as screws  36  to secure it to the bonder head. The forcer magnetically drives the bonding tool into forced relationship on the work at a pre-established or desired level of force. This is provided by a magnet seen as magnet  40 . Coils  41  and  43  on either side are also shown that provide the force to the magnet  40  to drive it downwardly.  
         [0034]    In order to provide for active pushing or lateral movement of the cutter against the bonding tool, a pusher assembly, arm, or active pusher  46  is shown which has a piezoelectric stack  48  for providing the pushing force. This is done at a flexure or spring member  50  that is shown connected to the fixed portion of the pusher assembly  46  namely upper portion  52  to which the flexure is connected by screw  56  to the moving part by screw  54 . The piezoelectric stack  48  expands and then movement is returned by forced spring movement.  
         [0035]    The bonder head incorporates a moving clamp arm  60  for clamping the wire with a fixed clamp arm  62 . A wire guide  64  for guiding the wire is shown.  
         [0036]    Looking more particularly at FIGS. 1 and 2, it can be seen that a permanent magnet  66  with a coil  68  has been shown. The permanent magnet  66  and the coil  68  articulate the movement of the clamp arm  60  by means of an arm and lever function.  
         [0037]    In order to provide for bonding, a transducer  72  is shown connected to a bonding tool. The transducer  72  is of a standard type which converts electrical energy to ultrasonic vibrations for purposes of driving the bonding tool for an ultrasonic bond.  
         [0038]    [0038]FIG. 2 shows the forcer assembly in slightly greater detail with coils  41  and  43  providing for the electrical field to drive the magnet  40  with regard to the bonding tool. The magnetic orientation of the magnets is a pair of magnets which are fundamentally south, north looking at the top and north, south looking at the bottom.  
         [0039]    In order to provide for pattern recognition and the format of the way a bond is to be made, an optical system through the Z tube at the upper end is utilized. In particular, a bracket  78  mounts an optical lens which provides for pattern recognition. In order to guide the movement of the light correctly, a light box  80  is mounted by depending brackets  81  and  83 . This provides a wide angle coaxial light source through its opening and then to the optics for pattern recognition and movement of the bonding head over the work to be bonded.  
         [0040]    A lower tubular member  84  analogous to tubular member  12  is shown which interconnects the respective flexures and other components.  
         [0041]    In order to accommodate the movement of the bonding tool with respect to the transducer, a linear encoder  92  is provided. The linear encoder  92  is such where it encodes the movement of a depending member connected to a transducer bracket.  
         [0042]    Looking more specifically at the bond head  10  it can be seen that a tube  98  is leading therefrom having wire  99  extending therefrom. The tube  98  with the wire  99  is connected to the end of the bond head  10  while specifically at the transducer and operating end in the form of assembly  60 ,  62  and  64 .  
         [0043]    The wire  99  has been fed from a reel by a continuation of the tube  98  as seen in FIG. 3.  
         [0044]    [0044]FIG. 3 in particular shows a perspective view of the dereeler or wire bonding spool system. The wire bonding spool system is generally designated as wire bonding spool system  100  within a box, cabinet, or container  102 . The box, cabinet, or container  102  houses a stepper motor  104  connected to a spool or reel  106 . Spool or reel  106  has wire  99  wound thereon which is paid out from the reel or spool as shown.  
         [0045]    When the wire  99  is paid out from the spool, it can become crosswise, overlaid, kinked, or bound up within the general winding on the spool  106 .  
         [0046]    Spool  106  is driven by the motor  104  in an incremental manner. In particular, spool  106  is connected to the motor  104  which is a stepper motor. The motor  104  can be a two phase bi-polar load motor or any other stepper motor which does not spin freely. Also to prevent free spinning of other types of drives, electromotive movement motors, servos or coils, a brake or drag system with the electromotive drive can be utilized.  
         [0047]    Fundamentally, what the motor  104  does is it drives the spool  106  on its axial support  114  through the hub  116  thereof connected to spokes  118  in a stepped manner. In this manner, the wire  99  as it is paid off from the spool  106  is stepped out incrementally depending upon usage. The stepping provides for incremental movement so that free running of the spool  106  is avoided. The spool moves in an incremental manner. For every movement, it is then braked by the stepper motor  104  and the increments which are provided in the form of stepped current input.  
         [0048]    In order to operate the wire bonding spool system, a mode switch  120  which can be in any form of switch is shown. The switch  120  can operate the mode from a feed output, auto output, and off output. When in auto mode the respective lights tight  122 , auto  124 , and loose  126  indicate the state. This controls the system within the cabinet  102  with respect to the wire  99  as it is fed.  
         [0049]    In order to maintain tension on the wire  99 , a pair of rollers  128  and  130  are utilized. These respective rollers  128  and  130  are connected to a brushless D.C. motor by a shaft for one of the rollers. Both rollers are geared together by gears that are seen in the other views namely in FIG. 8 and FIG. 9. In order to provide tension on the wire  99  between the spool  106  and the rollers  128  and  130  the rollers are under a constant turning mode, torque, or load when wire is in the sensor. The constant current in the motor provides for a constant torque on the rollers  128  and  130  so that they nip and pull the wire  99  downwardly against the detent action of the stepper motor  104 , or braking which holds the spool  106  in its incremental movement phases.  
         [0050]    A buffer sensor unit  134  described hereinafter allows the wire  99  to pass therethrough and be oriented within a slot  136  as to its amount of slack or tightness.  
         [0051]    The wire  99  is fed after the sensor through a pair of pinch rollers  138  and  140 . Pinch roller  140  is connected to a spring biased lever arm  142 . The rollers  138  and  140  are both journaled on ball bearings or any other kind of bearing connections. A pair of alignment prongs  146  are shown which align the wire passing through the rollers  138  and  140  that are made of nylon or delrin. Roller  140  is spring biased by a coil spring against roller  138 . This allows the rollers  138  and  140  to securely hold the wire passing therethrough and provide guidance.  
         [0052]    Roller  138  is connected to an optical or other encoder to determine the length of wire paid out. In this manner, if a bond is not made with the wire, the low inertia optical encoder will sense it. In effect, if the bond head  10  when moving upwardly and downwardly does not pay out wire due to a lack of a bond, this is recorded by the optical encoder connected to the roller  138 . Also, the optical encoder determines the amount of wire being used that is fed to the main controls of the system which drives and controls the bond head  10 .  
         [0053]    In order to guide the wire  99  and maintain it relatively nipped within the length of the rollers  128  and  130  across the width of the spool  106 , a pair of rollers, guides, rods, projections, or sleeves  152  and  154  are utilized. These rollers or guides can be made of delrin plastic or other plastic and secured to a bracket  156 . The guides  152  and  154  permit the wire  99  to traverse backwardly and forwardly across the spool  106  as the wire  99  is paid off and at the same time keep it within the confines of the nip between the rollers, spools, cylinders, or tubes  128  and  130 . Any other suitable guide can be utilized in the form of a fence, arms, guide surfaces, traveling eyelet, and other systems to maintain the feed so that the wire  99  can be tensioned between the rollers  128  and  130 .  
         [0054]    Looking more particularly at the roller system comprising rollers  128  and  130  they can be seen in FIGS. 8, 9 and  10 . FIGS. 8, 9 and  10  show the features of the rollers as they function and as they are driven and supported.  
         [0055]    [0055]FIG. 8 showing the perspective and fragmented view shows a wall  160  of the cabinet  102 . The wall mounts a constant current brushless D.C. motor namely motor  162  that is secured to the wall. Any other stepped electromotive force can also be used to provide torque or tension on the rollers  128  and  130 . The brushless D.C. motor  162  has a shaft  164  extending therefrom on which the spool  128  is held. The motor  162  by means of its shaft  164  is also geared by a gear  166  to a second gear  168 . These gears  166 , and  168  are interconnected so that when the motor  162  turns, it turns the gear train and rollers respectively  128  and  130 .  
         [0056]    Rollers  128  and  130  are mounted on hubs  170  and  172  having extended shafts therefrom. The hubs  170  and  172  are part of the shafts extending outwardly in the form of shafts  174  and  176 . Shafts  174  and  176  serve to hold the mounting cylinders, rods, or connectors  180  and  182  so that a urethane cylindrical foam, sleeve or tubular exterior  186  and  188  can be mounted thereon. The round cylindrical foam, sleeve, or tube  186  and  188  is formed of a foam material that can be a urethane foam having a shore 90A softness. Any other relatively soft material having resilience or limited depression capability can also be used to provide a conformable grip on the wire  99 . The foam or resilient material can be any where of approximately 70A to 90A shore. If the material is too soft or too hard the effect of holding the wire  99  in tension can not be accomplished. As can be seen, the wire  99  has been shown interiorly of the foam  186  and  188  in a slightly pinched configuration.  
         [0057]    In order to mount the connectors  180  and  182  with the interior hubbed shafts  174  and  176 , threaded screws  194  and  196  are utilized. These threaded screws  194  and  196  can be secured with a knurled configuration, a slot screw opening or an allen head type of securement.  
         [0058]    The shaft  164  from the motor  162  is in a relatively fixed position. In order to maintain parallelism between the respective rollers  128  and  130 , the shaft  165  on which roller  130  is maintained is placed in a virtual load condition to allow for the alignment of the shaft  165  with regard to shaft  164 . This is accomplished by a linkage and virtual load system that can be seen in FIGS. 8, 9, and  10 . FIG. 10 shows an exploded view of the linkage and virtual load system and the loading elements. These are shown in different orientations with regard to FIGS. 8 and 9 and will be oriented with respect thereto.  
         [0059]    Looking more particularly at FIG. 10 it can be seen that a ground block or secure mounting  200  has been shown. The ground block, bearing support, or mounting  200  helps to support the shaft  165  which is virtually loaded for imparting a parallel relationship with the shaft  164 . The ground block  200  supports a bearing within an opening  202  so that a pivot shaft, pivot member, or rotatable connector  204  is supported therein. It is fixed from sliding out from the bearing and the opening  202  by a C clamp  206 . The C clamp or ring secures the pivot shaft  204  by a notch  208  therein.  
         [0060]    The shaft  204  rotates in the block  200  in the circular or arcuate direction of arrow A. As it rotates, it creates in combination with the connected linkage a virtual load on the rollers  128  and  130 . This is by way of a cross pivot link, pivotal linkage, pivotal arm, swinging or rotating linkage  212 . The pivot link  212  is such where it also supports a second pivot shaft  214  having a groove  216  to receive a spring connection on the opposite side of a moveable block, drive link, support, balance beam, load beam, or load linkage  220 . Moveable block  220  load beam or balance beam has an opening  222  through which the shaft  214  passes. Shaft  214  is journaled therein by way of a bearing.  
         [0061]    Shaft  165  which supports the roller  130  is seated in the block  220  and held in place by screws  226  securing the shaft  165  therein. Screws  226  drive into a groove  228  in the shaft and securing it in place within the opening  230 .  
         [0062]    In order to place a load on the load beam  220  forming a virtual load arm a first spring tension load by way of a coil spring  234  is provided. In order to provide movement on the counterbalance side, a spring  236  in the way of a coil tensioning spring is also provided. Spring  234  is attached to a rod, appendage, connection point, or depending member  238  so that the linkage  220  can pivot in the arcuate direction of arrow B. Thus, linkage  220  can rotate around a pivotal basis by virtue of a load provided by the springs  234  and  236 . The shaft  214  passing within the bearing  222  is secured to the spring  236  by means of a loop  240  of the spring engaging the groove, notch or opening  216 .  
         [0063]    The ground block  200  is held by the wall or bracket  160  which is part of the cabinet  102 . The ground block  200  is mounted on the wall or bracket  160  by screws  260 . These serve to hold the rotating linkage  212  in a manner to allow for the movement in the arcuate direction of arrow A. At the same time this allows the balance beam or balance linkage  220  creating the virtual load to rotate in the arcuate direction of arrow B.  
         [0064]    In order to adjust the tension on spring  236 , an adjustment plate  266  can be moved by a screw adjustment in the form of a screw  268  that adjusts the tension of the spring  236  inwardly and outwardly. The screw  268  adjusts the movement of the adjustment plate  266  so that it can place greater or lesser tension on the spring  236 .  
         [0065]    A second screw  270  is also utilized to move a like plate that is hidden, inwardly and outwardly, for adjustment of the spring  234 . Thus, tension can be adjusted in the direction of arrows T for the two respective springs  234  and  236 .  
         [0066]    The foregoing configuration utilizing the arms, linkages, or virtual load beams allows for a pivoting on the ground block  200  as evidenced by the direction of arrows A and B. This allows for parallelism of the two respective shafts  164  and  165 . The load provided is such where it maintains the shaft  165  generally in a parallel relationship with shaft  164  along its length. Thus, as the wire  99  moves across the nip between the rollers  128  and  130 , the parallel relationship of shaft  164  and  165  keeps a constant tensioning force. The net result of the parallelism is to maintain a uniform gap between the rollers  128  and  130  so as the wire  99  traverses along their length it is maintained smugly between the rollers.  
         [0067]    If shafts  164  and  165  were not maintained in parallel, the opening could spread from one end to the other between the rollers  128  and  130 . This would create a situation where the wire  99  would not be nipped sufficiently to provide a tensioning load on the wire as it is taken off the spool  106 .  
         [0068]    It should be understood that as the wire is paid off the spool or reel  106 , it traverses across the width of the spool. Accordingly it moves across the length of the rollers  164  and  165  which should be maintained in parallel relationship. Based upon the linkage provided by the pivot linkage  212  and virtual load balance beam  220 , a load is maintained provided by springs  234  and  236  against the rollers so that a tensioning and parallelism takes place.  
         [0069]    The foregoing parallel loading in concert with the torque provided by motor  162  turning shaft  164  creates a tensioning on the wire  99  that is wound on the spool  106  and coming off the spool. This is based upon the fact that the stepper motor  162  driving the spool is held in a detented or braked position until it is driven to the next step thus maintaining the tension on the wire  99 .  
         [0070]    The virtual load provided on the rollers  128  and  130  can be created by other linkages. For instance, a linkage for holding shaft  165  in the way of an external balance beam singularly oriented so that a center of moments drives it in a manner to provide the parallel axial orientation of shafts  164  and  165  can also be effected. Also, pressure can be exerted against the shaft  165  by direct spring loading at either end, or other driving means.  
         [0071]    It should be born in mind that when such spring loading or external loads takes place, it can create a situation which is cumbersome and clumsy from the standpoint of keeping the shafts  164  and  165  in parallel alignment. With the specific embodiment of this particular invention the aspects of maintaining parallelism are created in a more compact and unencumbered position. As can be understood, a balance point can be achieved by driving through leaf springs, compression springs, or other means against the shaft  165  directly through journaling the shaft on bearings attached to the springs for pushing it. Thus, spring forces of any type can be utilized in a particular configuration for holding the shafts  164  and  165  in parallelism.  
         [0072]    The rollers  128  and  130  can be substituted by other tensioning devices for the wire  99  as it is paid off of the spool  106 . For instance pinching nips, levers, tongs, arms, or other devices can incrementally pull down the wire  99  from the spool  106  and hold it and then be released for movement of the wire. They can then move along the wire to take up another increment and hold the wire  99  under tension from the spool  106  until further release and paying out of the wire takes place.  
         [0073]    Looking more specifically at FIGS. 4, 5, and  6 , the construction and nature of the buffer sensor  134  can be determined. Specifically, the buffer sensor  134  shown in FIG. 3 is shown sectioned in FIG. 4 along lines  4 - 4  of FIG. 3. The buffer sensor routes the wire  99  so that it passes through a slot, channel, opening, or aperture  136  that is relatively elongate but can be in other forms as long as the wire is allowed to traverse and be sensed in a certain area.  
         [0074]    The buffer sensor  134  allows for the right amount of wire  99  to be placed into the system so that there is sufficient slack and at the same time diminishing a tightened feed of the wire as it passes down to the bonding head  10 . With a constant movement of the bonding head  10  paying out the wire  99  at the working end thereof underneath the bonding tool, more wire needs to be fed out. When various speeds of bonding or various orientations of bonding take place, feed of the wire  99  must be adjusted thereto. To provide the feed of the wire  99 , the buffer sensor  134  senses the placement of the wire in its overall slack or tightened relationship.  
         [0075]    In order for the system to provide wire  99  to the bonder head  10  quickly enough, the buffer loop region is used. For the correct amount of wire  99  in the buffer  134 , the system needs to sense how much wire is in the buffer loop region.  
         [0076]    The buffer  134  comprises the passage groove or slot  136  for the wire  99  to pass through so that it can be sensed as to its relative position. In order to accomplish this, a series of light emitting diodes (LED&#39;s) are utilized. These are seen in FIG. 5 as LED&#39;s  300 ,  302 ,  304 ,  306 ,  308 ,  310 ,  312 , and  314 .  
         [0077]    It can be seen in FIG. 4 that LED  312  has been shown with its connection and mounted on a bracket or board  316 . The LED&#39;s  300  through  314  cast their light through a slot  320 . The light is reflected off of the wire  99  through a second slot  322  to a photo sensitive silicon sensor  326 . The sensor  326  can be any type of photo electric sensor to sense the position of a wire at a certain location and then provide a reading as to such location. The sensing is along the length of the photo diode silicon sensor  326  so that a determination of where the wire lies along the slot  136  can be determined.  
         [0078]    In order to avoid ambient light from affecting the reading of the position of the wire  99 , a defuser  340  is utilized. The defuser  340  defuses the light so that the reflection off of the wire  99  is the peak portion of light that is reflected back into the slot  322  and the silicon sensor  326 . The defuser  340  is such where it permits only a limited amount of light to be returned. The defuser  340  is made of an anti-static conductive material of long chain polymers which absorb light. Any other type of defuser can be used for defuser  340  in order to effect the same light absorption. The goal is that light from the LED&#39;s  300  through  314  is mainly reflected from the wire  99  so that its position along the length of the sensor  326  can be determined.  
         [0079]    When looking at FIG. 5 it can be seen that the wire  99  whenever it is crossing a particular area of sensor  134  is read along the silicon sensor  326 . The particular position of the wire  99  shown in FIG. 5 as it relates to the other showings is such where there is tension provided by the tensioner torque reeler rollers  128  and  130  with sufficient slack to be able to draw wire  99  in sufficient amounts to the bond head  10 . The positioning of wire  99  along slot  136  is such where there is a position wherein the wire is being pulled in the feed region. When it is drawn out significantly, it passes into the tension area where tension is maintained by rollers  128  and  130 . The wire  99  when fed by the reel  106  turning and the rollers  128  and  130  continuing to turn allows the wire  99  to be fed and provide for slack in the lower portion of slot  136 . The speed of feed is along the slope as seen in FIG. 6. This enables the wire  99  to be brought to a point where it is of sufficient length. Of course, when the wire is in the tight region, it signals the controller to stop the spool motor, and indicate to the user with light  122 , the tight condition. Since the stepper motor  104  feeding the wire  99  initially is stepped, there is a slight pause which is shown before the slope of feed starts to rise. When referring to the tension region reference is to the rollers  128  and  130  tensioning the wire from the spool  106  which is braked by its stepper motor  104 .  
         [0080]    In order to maintain the connection of the buffer  134 , connection points  360  and  362  are utilized. In order to hold the entire assembly together, a screw  364  secures the assembly into position.  
         [0081]    Looking more specifically at FIG. 7, it can be seen how the controls for the entire system are utilized. As previously stated there is a mode switch  120  where feed and auto control as well as an off position are selected. A status readout  122 ,  124 , and  126  is provided showing the tight position, the auto position, and the loose position respectively corresponding to the position of the wire  99  in the sensor  134  as well as the switch  120  state.  
         [0082]    The output of the buffer sensor  134  is sent to an analog to digital converter (ADC)  384  which converts the signal of the position of the wire along the buffer sensor  134 . It is then sent to the digital signal processor (DSP)  386  for processing and driving the motor  104  for further feed. The DSP  386  state has its status indicated by status LED&#39;s  122 ,  124 , and  126 .  
         [0083]    The serial network  390  is part of the entire system for allowing the programmable logic device  392  in conjunction with the DSP  386  to drive the spool motor  104  as well as maintain the tensioner in its proper position all in light of the wire  99  position as read through the buffer sensor  134 .  
         [0084]    Alternative sensors, locations, and orientations can be utilized to show the position of the wire  99  along the length of the buffer sensor  134  or in relation to any sensor. Such items as optical encoders, position indicators, sensors, in the way of contactors, or electrical bridge elements can be utilized for an output to an analog to digital converter or other output devices to provide information to the digital signal processor  386  for overall control of the wire  99  being fed.