Abstract:
A drive for a carrier tape used in conjunction with a pick and place module of a machine for inspecting and handling advances the carrier tape to its desired position in two steps. Using the number of sprocket holes between compartments in the tape (n holes), the first step is n−1 sprocket holes. The second step takes the carrier tape the remaining distance to complete the advance to the distance equal to n sprocket holes. The tape is driven by friction rollers not by the use of the sprocket holes. The presence of a device in a compartment and its proper positioning in the compartment is also inspected.

Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/462,555 filed on Apr. 7, 2000 (now U.S. Pat. No. 6,481,187), which is a national stage filing under 35 U.S.C. §371 of international application PCT/US98/14618, filed Jul. 15, 1998, which claims the benefit under 35 U.S.C. §119 of co-pending provisional patent applications 60/052,698, filed Jul. 16, 1997 and 60/076,702, filed Mar. 4, 1998. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a position sensing system, and more particularly, to a position sensing system for use in a taper module of an inspection and handling system for devices such as semiconductors. 
     BACKGROUND OF THE INVENTION 
     Some devices, such as integrated circuit chips, need to be precisely fabricated. Accordingly, inspection of such devices is necessary to ascertain whether the devices meet exacting acceptance standards. The devices to be inspected are often provided in compartmented trays which have multiple rows and columns of pockets in which the devices are transported. 
     An inspection and handling system is utilized to inspect such devices. Trays of devices are transported through various stages of the inspection and handling system including laser scanning, inversion, camera scanning and individual placement at a final destination so that devices meeting the exacting acceptance standards are separated from those devices which do not meet such standards. 
     One final destination of devices that meet the acceptance standards is carrier tape. Typically, carrier tape is an elongate tape which includes pockets that are arranged in series. The pockets are typically shaped to be complementary to the dimensions of the devices that are to be housed therein. An instrument such as a vacuum operated precisor of a pick-and place system can transport a device from a tray into a pocket of the carrier tape. Once devices are individually placed into the pockets of the carrier tape, a cover tape is often applied and the carrier tape with devices housed in the sealed pockets can be wound onto a reel and conveniently transported to another destination, such as where the devices will be put into final use. 
     Pick and place systems are generally capable of motion in one direction (transverse to the direction of movement of trays through the inspection and handling system) and have limited, if any, movement in a direction perpendicular to that motion (parallel to the direction of movement of the trays). Therefore, the carrier tape needs to be incrementally moved by a drive system so that the pick and place system can place devices into successive pockets of the carrier tape. It is therefore necessary to determine the location of individual pockets of the carrier tape with respect to the pick and place system. Typically, the carrier tape includes sprocket holes that run the length of the carrier tape on one or both sides of the pockets. The sprocket holes are utilized to determine the position of a pocket relative to the pick and place system. 
     In some inspection and handling systems, problems may occur if the carrier tape is not consistently advanced by the proper distance equivalent to the length of one pocket. Traditionally, the beginning of a pocket is determined by forwarding the carrier tape by a fixed distance, and assuming that the carrier tape moved forward the distance programmed. Use of a sensor may also be employed to detect the number of sprocket holes passed as the carrier tape is advanced. In such systems, the drive system assumes that the point to which the carrier tape is forwarded is the correct starting point of the pocket. 
     Specifically, in some systems, simply advancing the carrier tape by a set distance, or counting the number of sprocket holes passed, may not be sufficiently accurate in determining the position of a pocket. Jitter or slipping of the carrier tape can occur. In the case of slipping, the carrier tape may not be advanced the amount the drive system is programmed to advance. In the case of jitter, the carrier tape may move backward, thereby counting a sprocket hole twice. Accordingly, errors may incur in determining the location of a pocket. 
     An object of this invention is to achieve accurate and reliable placement of a carrier tape, or the like, relative to a pick and place assembly or the like. 
     SUMMARY OF THE INVENTION 
     For the achievement of those and other objects, this invention proposes to achieve the desired placement of the carrier tape in two steps. A first step positions one of the compartments in the tape in the vicinity of but not at the final placement position, and the second subsequent step moves the compartment into placement position. 
     More specifically, the carrier tape has a plurality of compartments of a size to receive one semiconductor device. The compartments are serially spaced along the longitudinal axis of the tape and the tape also includes a plurality of sprocket holes serially spaced along a line which is parallel to said longitudinal axis. The distance between compartments corresponds to a predetermined number of sprocket holes and, in the first step, the tape is advanced a distance corresponding to less than that predetermined number of sprocket holes. In the second step, the tape is advanced the remaining number of said sprocket holes. Preferably, the first step is equal to one less than the distance between the predetermined number of sprocket holes and the second step is equal to the distance to the last sprocket hole. 
     Preferably, this invention also contemplates transporting the tape by engaging the tape surfaces and not the sprocket holes, and it includes the capability of inspecting for the presence of a device in the tape compartment and proper positioning of the device in the compartment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of a tape positioning system embodying this invention; 
     FIG. 2 is a plan view, in schematic form, of a carrier tape with the positioning sensor; 
     FIG. 3 is a side view of the drive roller assembly; 
     FIG. 4 is an end view, partly in section of the drive roller assembly of FIG. 3; 
     FIG. 5 is a plan view of the tape positioning system of FIG. 1; 
     FIG. 6 is a side view of the device sensing mechanism; 
     FIG. 7 is a plan view of the mechanism of FIG. 6; 
     FIG. 8 is a plan view of a sensor assembly; 
     FIG. 9 is a side view of a sensor assembly; 
     FIG. 10 is a schematic diagram of the tape positioning sensing system; and 
     FIG. 11 is a timing diagram of the tape position sensing system. 
    
    
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components or steps set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various other ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before describing the tape positioning system, a type of carrier tape packaging system will be described. 
     With reference to the drawings, the tape positioning system  100  is shown in association with a precisor  200  of a typical pick and place (PNP) system. The PNP system will only be shown schematically to illustrate its relationship with the tape positioning system. 
     The relationship of the PNP system to the overall inspection and handling system and a taper system or module can be as set forth in U.S. application Ser. No. 09/142,338, filed Sep. 27, 1999 (now U.S. Pat. No. 6,293,408) and entitled “Inspection Handler Apparatus and Method” and assigned to the assignee of this application. If details of those relationships are necessary, reliance is placed on that application. 
     The tape system includes a carrier tape drive  102  that draws carrier tape from a supply reel assembly  104  and conveys the carrier tape through a device placement station  106 , several inspection stations, a cover tape placement station  108 , and a heat seal station  110  to an outfeed reel assembly  112 . Further, it includes a frame  114  whereon the major assemblies are mounted and a control system  116  for coordinating the various operations of the tape positioning system. 
     In general terms, carrier tape  120  is drawn from reel  104  by the combination of friction roller  122 , driven by drive  102 , and friction roller  124 , driven by drive  126 . The carrier tape travels through placement station  106 , is engaged with covering tape  128  from reel  130 , then passes through heat seal station  110  where the cover tape is sealed to the carrier tape, and goes to its destination on reel  112 . 
     FIG. 2 depicts one of several types of carrier tape  12  used in the semiconductor industry and adaptable for use in this system. Rectangular shaped device pockets  20  are spaced uniformly along the longitudinal axis of the carrier tape  12 . The pockets are dimensioned to fit with a particular semiconductor device and each pocket includes a central test hole  22 . The distance between test holes  22  is commonly referred to as the pitch  24  of the carrier tape. 
     The carrier tape also has a series of uniformly spaced sprocket holes  14  provided along one or both edges  16  and  18  of the carrier tape. The sprocket holes are a means for driving the carrier tape. Typically, the sealed carrier tape provided by the tape system is unwound by the semiconductor device user using the sprocket holes  14 . To reduce the risk of damage to the sprocket holes, this taper positioning system does not use the sprocket holes  14  to drive the tape  102  through the taper module. 
     In lieu of sprockets, this tape system utilizes soft friction rollers at both the main drive, roller  122 , and the take-up drive, roller  124 , to drive and guide the carrier tape through the various stations to the carrier tape  102  as the carrier tape is driven by the soft roller. 
     Referring to FIG. 3, a main drive roller  122  is mounted between a pair of mounting blocks  132  near the left ends of the guide rails  146 ,  148 . The main drive roller comprises a core  134  mounted onto a drive shaft  136  and has an outer layer  138  of urethane material. 
     A pinch roller  139  is supported beneath roller  122  and preferably is of the same general construction as roller  122 . A pneumatic assembly  140  is connected to the mount for roller  139  and is operative to move the roller  139  up or down to vary the pressure exerted on the carrier tape as it passes between the rollers. 
     Drive shaft  136  is driven by stepper motor  102  through a pulley system  142 . 
     Elongated guide rails  146 ,  148  (See FIG. 5) extend from the drive roller  122  through roller  124 . The carrier tape  120  is shown entering the roller  122  and exiting roller  124  but not between for clarity of illustration of the intervening parts. The edges of the carrier tape are caused to travel snugly over the guide rails  146 ,  148  as it is conveyed through the device placement and inspection stations. The center hole  22  of the individual pockets of the carrier tape is maintained positioned directly above the centerline of the rail gap  144 . 
     The precisor  200  (shown in dotted lines in FIG. 5) from the PNP module is positionable overhead of the guide rails to the right of the main drive roller  122  and over the rail gap  144 . The precisor places devices into individual pockets  20  to the carrier tape. The precisor, except for the device which actually engages the circuit devices by moving vertically, is capable of movement in only one direction. That direction is illustrated by arrow  201  in FIG.  5 . 
     A tape position sensor assembly  32  is mounted adjacent the front guide rail  146  and will be described more completely hereafter. 
     Referring again to FIGS. 5 and 6, a part hold down assembly  150  is disposed to the right of the tape position sensor assembly  32  and the device placement station  106 . Referring to FIGS. 6 and 7, the hold down assembly  150  includes a left pivot arm  152  and a right pivot arm  154 , and a hold down bar  156  that is fastened across both pivot arms  152 ,  154 . The pivot arms  152 ,  154  extend over the rear guide rail  148  and support the hold down bar  156  directly over the rail gap  144 . 
     The pivot arms  152 ,  154  are pivotably connected to a mounting block  158  by a bushing  160 . The part hold down assembly is biased such that the arms  152 ,  154  pivot downward and the hold down bar  156  rests down onto the carrier tape. A leading or left end of the hold down bar  156  may be beveled so as to guard against the hold down bar catching on the passing carrier tape. The hold down bar  156  typically rides over the carrier tape pockets as the carrier tape is conveyed forward. Pressure applied by the hold down bar on the carrier tape helps to keep devices in the carrier pockets. 
     Further, a proximiter probe  162  is vertically mounted to the left pivot arm  152  at a location directly above the rear guide rail  148 . The probe end extends downwardly through the left pivot arm  152  and is set to face the top surface of the front guide rail  148 . The proximiter probe senses vertical displacement of the left pivot arm  152 . When an unseated device protrudes outward of a pocket  20 , the hold down bar  156  and the left pivot arm  152  are displaced upwardly as the carrier tape passes underneath, thereby alarming the probe. In this event, the carrier tape drive may be prompted to reverse index the carrier pocket so that the unseated device is returned to the device placement station. At that point, the precisor may pick and discard the unseated device, and replenish the carrier pocket with another device. 
     A missing part photo sensor assembly  165  of conventional construction is preferably the through-beam type is disposed to the right of the hold down bar assembly  150  and directly overhead of the rail gap  144  and includes a photo sensor  163  located above rail gap  144  and emitter cone assembly (not shown) supported below the rail gap  144 . 
     When a carrier tape pocket  20  is moved past the photo sensor without a device therein, the exposed center hole allows the through beam to be picked up by the emitter cone. Accordingly, the carrier tape drive is prompted to move the carrier tape in the reverse direction until the empty pocket is vertically aligned with the device placement station. At this point, the precisor is prompted to place a device in the empty carrier pocket. 
     After passing through those testing stations, the carrier tape pocket is ready to be sealed. In the cover tape placement station  108 , cover tape is directed over the pockets. The cover tape placement station  108  includes a supply reel  130  that is mounted overhead of the guide rails  146 ,  148 . 
     Below the supply reel shaft, an idler roller  167  and a conventional vacuum manifold  164  are separately mounted to the support place. The cover tape travels from the supply reel  130 , underneath the idler roller  167  and over the vacuum manifold  164  before engaging the cover tape roller  166 . The vacuum manifold applies a constant drag on the cover tape between the vacuum manifold  164  and the cover tape roller  166 . The cover tape is brought into engagement with the carrier tape under roller  166  and covers the pockets  20  in the carrier tape. 
     After the cover tape is applied over the carrier tape, the carrier tape is conveyed to the heat seal station  110 . The heat seal mechanism is conventional and thus will not be described in detail. 
     The roller  124  is a take up roller. In the preferred embodiment of the invention, the main drive roller assembly  102  has the primary responsibility for pushing the carrier tape, while the take-up drive roller assembly  124  maintains tension on the carrier tape. The take-up drive roller assembly is disposed across the guide rails  146 ,  148  to near to the right end of the module frame, feeding sealed carrier tape to the outfeed reel assembly  112 . 
     The construction and arrangement of the take up roller  124  and its associated parts is the same as that at main drive roller  122 , including the pressure roller and pneumatic assembly to vary pressure between the main roller and the pressure roller, and a stepper motor to drive roller  124 . For that reason, it will not be described in detail. The relative speeds of rotation of the rollers  122  and  124  are controlled in a conventional manner to maintain the proper tension on the carrier tape as it passes through the various operations. 
     Referring to the drawings, FIG. 2 illustrates a tape position sensing system  10  which operates to determine the position of carrier tape  102 . 
     The carrier tape  12  has a series of uniformly spaced sprocket holes  14  provided along one or both edges  16  and  18  of the carrier tape  12 . The sprocket holes  14  can be used as a means for driving the carrier tape  12 . A plurality of pockets, such as pocket  20 , are positioned sequentially along the carrier tape  12 , and are dimensioned to be complementary to devices that are to be housed therein. 
     After devices have been housed in the pockets  20  of the carrier tape  12 , the ultimate user of the devices typically will utilize the sprocket holes  14  as a means by which to move the carrier tape  12 . To reduce or eliminate the risk of damage to the sprocket holes  14 , it is preferable that the inspection and handling system does not utilize the sprocket holes  14  as part of the drive system. Preferably, a friction drive is utilized to move the carrier tape  12  through the taper module of the inspection and handling system. The friction drive will be described hereinafter. 
     In the present invention, to determine the beginning of a pocket  20  of the carrier tape  12  and thus the proper position of the tape and compartment, a known fixed distance to advance the carrier tape  12  (corresponding to a set number of sprocket holes) is preprogrammed such as in an encoder. This fixed distance lies between the last sprocket hole (n) and the second to last sprocket hole (n−1) adjacent to the end of pocket  20 , where n is the number of sprocket holes corresponding to the spacing between pockets  20 . 
     A pair of conventional photo sensors P 1  and P 2  detect the passing of the serial sprocket holes  14  as the carrier tape  12  is advanced by the drive system. In the embodiment shown in FIG. 1, P 1  and P 2  are 2 mm apart and a pocket length is the distance between four of the sprocket holes  14 . The number of sprocket holes  14  passed by the photo sensors P 1  and P 2  is counted by the encoder. Preferably, the carrier tape  12  is advanced rapidly (“jumped”) by the drive system the distance of the jump zone, n−1 sprocket holes. The carrier tape  12  is then slowly advanced (“crept”) by the drive system until the edge of the last sprocket hole  14  (n) is reached. The photo sensors P 1  and P 2  are used to determine when the edge of the n th  sprocket hole  14  is reached to determine the end of the current pocket  20 , and accordingly, the beginning of the next pocket  20 . 
     With reference to FIG. 2, the sprocket holes are spaced on centers  2 , in the preferred embodiment 4 mm. There is a distance  4  between the leading and trailing edges of adjacent sprockets, that is leading and trailing relative to the direction of travel of the tape illustrated by arrow  6 . In the preferred embodiment, the spacing between is equal to or less than the distance  4 . Specifically in this embodiment the spacing  4  equals 2 mm. 
     With reference to FIG. 10, a circuit schematic of the tape position sensing system  10  is illustrated. The circuit processes the information received from the photo sensors P 1  and P 2  resulting from the detection of the passing of sprocket holes  14 . Specifically, the photo sensors P 1  and P 2  are electrically connected to transistors Q 1  and Q 2 . Each source of transistors Q 1  and Q 2  is electrically connected to a conventional SR flip-flop  30 , through Schottky diodes D 1  and D 2 . The source of transistor Q 1  is electrically connected to the “S” input of SR flip-flop  30 , and the source of transistor Q 2  is electrically connected to the “R” input of SR flip-flop  30 . Each drain of transistors Q 1  and Q 2  is grounded. 
     When the first or leading photo sensors P 1  detects a sprocket hole  14 , a signal is sent to transistor Q 1  and to flip-flop  30 , setting the flip-flop  30 . When the second or trailing photo sensors P 2  detects a sprocket hole  14 , a signal is sent to transistor Q 2  and to flip-flop  30 , resetting the flip-flop. As flip flop  30  is set and reset, the “Q” output of the flip flop is fed to the encoder which increments a sprocket hole counter. The sprocket holes being advanced are counted in this manner. 
     Turning now to FIG. 8, the photo sensors P 1  and P 2  are shown. A sensor assembly  32  is mounted adjacent to a front guide rail  146  of the taper module. The sensor assembly  32  supports the photo sensors P 1  and P 2 . Each photo sensor P 1  and P 2  typically includes a beam element  36  and  38 , and pick-up elements  40  and  42  opposed to elements  36  and  38 , respectively. One of the pick up elements  42  is visible in FIG.  8 . When the carrier tape  12  is caused to move linearly along the rail guide  146 , the series of sprocket holes  14  pass directly between the beam elements  36  and  38  and the pick-up elements  40  and  42 . 
     The sensor assembly  32  is mounted horizontally on an elongated support block  44  that extends substantially into a slot on the front guide rail  146 . As illustrated, both photo sensors P 1  and P 2  are mounted on the same support block  44 . However, it is contemplated that each sensor P 1  and P 2  may be supported separately and accordingly, the position of each photo sensor P 1  and P 2  may be adjusted separately. The support block  44  is mounted to a bracket via a ball slide  46 . By operating a rotatable dial  48 , the support block  44  may be secured to or loosened from the bracket. A micrometer  50  is mounted on the left of the support block  44  and engages the support block  44  with a ball tip  46 . Through adjustment of the micrometer  50 , the lateral position of the sensor assembly  32  in the slot of the front guide rail  34  may be fine tuned. 
     With reference to FIG. 11, a timing diagram of photocell detection and its relationship with the flip-flop  30  is illustrated. “Q” is ON (set) every time S is ON. S is triggered or ON when the leading photo sensor P 1  sensors a sprocket hole  14 . “Q” is OFF (reset) every time R is ON. R is triggered or ON when the lagging photocell P 2  detects a sprocket hole  14 . As illustrated in FIG. 11, the leading photo sensor P 1  is turned ON at time t 1  when the second to last (n−1) sprocket hole  14  is reached. This sets “Q” in the ON position. “Q” is not reset until time t 2  when the lagging photo sensor P 2  is turned ON. “Q” remains in the OFF position until time t 4 , when the photo sensor PI is once again activated. This occurs when the beginning of each sprocket hole is reached. Accordingly, the pair of photo sensors P 1  and P 2  consistently detect each serial sprocket hole  14  up to the nth sprocket hole for a given pocket size. That is, it counts the sprocket holes passing the sensor. 
     Utilizing photo sensors P 1  and P 2  in this manner eliminates any potential jitter problems that may occur. 
     As the carrier tape  12  is advanced the distance between sprocket holes n−1 and n, the carrier tape  12  can move (i.e. jitter) backwards slightly, as opposed to always moving forward. In such a case, if the carrier tape  12  is advanced to just beyond the n−1 sprocket hole  14 , and jitter forces the carrier tape  12  slightly backward, either photo sensor P 1  or P 2  may count the n−1 sprocket twice. 
     However, by using the pair of photo sensors P 1  and P 2  in tandem as disclosed in this invention, both the leading edge and trailing edge of each sprocket hole  14  must be encountered before allowing the encoder to increment or decrement the sprocket hole  14  count. Jitter does not move the carrier tape  12  so far back such that both photo sensors P 1  and P 2  are activated. Accordingly, slight jitter will not increment the counter, and therefore, the sprocket hole  14  count of the encoder remains accurate.