Abstract:
A method for inspecting composite tape including cover tape bonded to carrier tape comprises capturing a digital image of the composite tape, dividing the seal tracks within the image into a plurality of fragments or segments. The method also provides for analyzing each segment of the seal track for the presence or absence of the seal and for the width of the seal, and assigning a failing grade to the segment if the seal is not continuous within the segment or if the seal has a width less than a minimum width within the segment. The method further provides for notifying a machine operator of a defective seal if the number consecutively-failed segments in the seal track exceeds a defect tolerance. The method also provides for measuring the spacings of the carrier tape edge, cover tape edge, and seal tracks from each other and comparing those spacings to acceptable values.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/297,853, filed Jun 13, 2001. 
     
    
     
       BACKGROUND  
         [0002]    The invention relates to an electronic part inspection and packaging apparatus, and more specifically to a system for inspecting the seal between the cover tape and carrier tape used to package the electronic parts.  
         SUMMARY  
         [0003]    The invention provides a method and apparatus for capturing a digital image of a seal track for a carrier tape and cover tape assembly, and for analyzing the seal track for defects. The invention use gradient-based edge tools to find the edges of the carrier tape, cover tape, and seal tracks, and calculates robust line equations for the edges. The invention also divides the seal tracks into segments and inspects each segment to determine whether the seal is continuous within the segment and whether the width of the seal is greater than a minimum width. If the seal is not continuous, is too narrow, or is too wide within the segment, the segment is labeled as failing. The invention then assesses whether the entire seal is acceptable based on the number of consecutive failing segments in the seal.  
           [0004]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a side view of an electronic part inspection and packaging machine embodying the present invention.  
         [0006]    [0006]FIG. 2 is a top view of the machine.  
         [0007]    [0007]FIG. 3 is a perspective view of a length of carrier tape for use with the invention.  
         [0008]    [0008]FIG. 4 is a top view of composite tape containing electronic parts as the composite tape passes under the camera after seal inspection (“CASI”) module.  
         [0009]    [0009]FIG. 5 is a cross-section view taken along line  5 - 5  in FIG. 4.  
         [0010]    [0010]FIG. 6 is a top view of an example image captured by the CASI module.  
         [0011]    [0011]FIG. 7 is an example image of a portion of a seal track being analyzed by the CASI module.  
         [0012]    [0012]FIG. 8, consisting of FIGS.  8 A- 8 C, is a flow chart of the CASI software logic. 
     
    
       [0013]    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 arrangements of the components 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 ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order.  
       DETAILED DESCRIPTION  
       [0014]    [0014]FIGS. 1 and 2 illustrate an inspection, handling, and packaging apparatus  20  that includes a support stand  24 , an infeed carrier tape drive wheel  26 , a pick-and-place head or transport  28 , a carrier tape infeed reel  32  dispensing carrier tape  34 , a camera-over-tape or “COT” inspection module  36 , a cover tape reel  40  dispensing cover tape  41 , a cover tape flattening, smoothing, or combing mechanism  42 , a sealing shoe  44 , a resilient drive roller  48 , a backup wheel  50 , a camera-after-sealing inspection module or “CASI” module  52 , and an output reel packaging module  56 . A controller or CPU  58  (illustrated schematically) controls all aspects of the apparatus  20 , and executes the software associated with the CASI module  52 . The support stand  24  supports a plurality of part input trays  60  that contain parts  64  to be inspected and packaged. The transport  28  picks the parts  64  off the input trays  60 , and transfers the parts  64  to the carrier tape  34 . The transport  28  is preferably a pick-and-place type transport utilizing a vacuum head.  
         [0015]    The carrier tape  34  is best illustrated in FIG. 3, and includes a pair of flanges  72  running along its length, and compartments  76  formed between the flanges  72 . One or both of the flanges  72  may include sprocket holes  80  to facilitate advancing the carrier tape  34  through the apparatus  20  and/or other machinery. For example, the infeed carrier tape drive wheel  26  may be a pinwheel having sprocket pins that engage the sprocket holes  80  of the carrier tape  34 . The drive wheel  26  may be driven under power by a motor (not illustrated) to pull the carrier tape  34  off the infeed reel  32 . Alternatively, the drive wheel  26  may have a smooth or flat surface and/or be passive or not driven by a motor.  
         [0016]    The resilient drive roller  48  rotates under the power of a motor (not illustrated) to pull the carrier tape  34  through the apparatus  20  in a downstream direction  82  (an upstream direction being opposite the downstream direction  82 ). The flanges  72  of the carrier tape  34  are pinched between the drive roller  48  and the backup wheel  50  to facilitate the advancement of the carrier tape  34  under the influence of the rotating drive roller  48 . Alternatively, the drive roller  48  may include pins that engage the sprocket holes  80  in the tape flanges  72  to facilitate advancing the carrier tape  34  through the apparatus  20 . The carrier tape  34  is supported at its flanges  72  by guide rails  84  (FIGS. 4 and 6) that extend substantially the entire length of the apparatus  20 . The rails  84  are preferably made of nickel or some other light-reflective material.  
         [0017]    Referring again to FIGS. 1 and 2, the transport  28  places a single part  64  into each compartment  76  of the carrier tape  34 . The COT inspection module  36  is downstream of the transport  28 , and includes a camera, which inspects the parts  64  in the carrier tape compartments  76  as the carrier tape  34  is advanced through the apparatus  20 .  
         [0018]    The cover tape  41  is laid on top of the carrier tape  34  downstream of the COT inspection module  36 , and is pulled through the apparatus  20  along with the carrier tape  34 . The cover tape  41  is guided from the cover tape reel  40  to the carrier tape  34  by a plurality of tensioning rollers  92 . The cover tape  41  extends between the flanges  72  and completely covers the compartments  76 . The smoothing mechanism  42  smoothes wrinkles out of the cover tape  41  just before the cover tape  41  and carrier tape pass under the sealing shoe  44 . The smoothing mechanism  42  and sealing shoe  44  may be collectively referred to as a cover tape application module.  
         [0019]    Adhesive is used to seal the cover tape  41  to the flanges  72  of the carrier tape  34  and thereby create a composite tape including the carrier/cover tape combination. The adhesive is on the cover tape  41  surface and faces the carrier tape  34 , or may alternatively be provided on the carrier tape  34  flanges  72  and face the cover tape  41 . The adhesive is preferably heat activated or pressure sensitive adhesive. Heat activated cover tape  41  has adhesive across the complete cover tape surface. Pressure sensitive activated cover tape  41  has only two strips of adhesive that are located over the flanges  72  of the carrier tape  34 . The adhesive is activated by pressure and/or heat applied through the sealing shoe  44 .  
         [0020]    [0020]FIG. 4 illustrates the carrier tape  34  with the cover tape  41  adhered thereto as viewed by the CASI module  52 . The adhesive bonds the cover tape  41  to the carrier tape flanges  72  along two generally parallel and continuous lines or strips  94 , which are also referred to as seal tracks herein. The CASI module  52  inspects the quality of the seal created by the adhesive and identifies potentially flawed segments of the adhesive seal, as will be described in more detail below.  
         [0021]    The following is a description of some of the system requirements in the preferred commercial embodiment of the invention. Once the preferred system requirements are discussed, the operation of the CASI module  52  will be discussed. The CASI module  52  is currently commercially available on the following machines sold by RVSI Systemation: ST60, ST585, ST595, and CST-90. The CASI module  52  uses a fixed or zoom lens camera  100  (FIG. 5) to optimize the field-of-view (“FOV”). The FOV is optimized when the inspection area for the CASI module  52  is unobstructed for just over one full composite tape pitch, so that there is some overlap between adjacent lengths of composite tape as it advances incrementally one pitch-length at a time under the CASI module  52 . In the preferred commercial embodiment, the overlap is set to 50% of the pitch on either side of the length of composite tape being inspected, but more or less overlap may be used.  
         [0022]    The seal track  94  edges should be sufficiently isolated and thick to facilitate inspection by the CASI module  52 . In the preferred embodiment, the outer seal track  94  edges are considered isolated when they are the greater of two pixel rows or 0.005″ (0.127 mm) away from the edge of the cover tape  41 . The seal track widths are considered thick in the preferred embodiment when they are the greater of two pixel rows or 0.010″ (0.254 mm) wide.  
         [0023]    A cloudy-day illuminator (“CDI”)  104  (FIG. 5) provides cloudy-day illumination within the CASI module  52 . A preferred and commercially-available CDI is RVSI Northeast Robotics model no. NER SCDI-75. The height from the bottom of the CDI  104  to the carrier tape  41  is preferably no greater than 0.3″ (7.6 mm).  
         [0024]    The CASI module  52  works best when the cover tape  41  is laid flat over the carrier tape  34 , which is why it is preferred to have the cover tape smoother  42  up stream of the heat sealer  44 . If the cover tape  41  is not smoothly applied to the carrier tape  34 , the CDI  104  lighting may be affected, and this may result in the CASI module  52  identifying false seal defects and flagging a false rejection. A wire frame  108  (FIG. 4) around the FOV may be employed to lightly tension the cover tape  41  and further reduce such false rejections.  
         [0025]    To further reduce false rejections, a contrast should be maintained between the seal track  94  edges and the areas on either side of the seal track  94 , so that the seal track  94  edges are clearly visible. This may be accomplished by using carrier tape  34  having a light-absorptive color (e.g., black in the preferred embodiment), and cover tape  41  that is light-diffusive (e.g., semi-transparent cover tape in the preferred embodiment). The CDI  104  lighting is largely absorbed by the carrier tape  34 , and is diffused by the cover tape  41  such that the cover tape  41  appears to be a light color against the dark-color background of the carrier tape flanges  72  when viewed with the CASI module camera  100 . When the cover tape  41  is bonded to the carrier tape  34 , the cover tape  41  becomes substantially transparent to light in the seal tracks  94 , and the seal tracks  94  appear as dark lines in the light-colored cover tape  41  because the dark carrier tape  34  material shows through.  
         [0026]    To further reduce false rejections, the plane of the camera lens should be maintained substantially parallel (e.g., within 1° of parallel in the preferred embodiment) to the longitudinal extent of both seal track  94  edges. Stated another way, the cover tape  41  defines a plane of inspection for the CASI module  52 , and the optical axis  112  (FIG. 5) of the camera  100  should be maintained substantially perpendicular to the plane of inspection.  
         [0027]    One goal of the CASI module  52 , as will be explained below, is to determine various parameters of the composite tape. With reference to FIG. 5, these parameters include: the distance  132  from the carrier tape edge to the cover tape edge; the distance  136  from the carrier tape edge to the first seal track  94 ; the distance  140  between the centers of the seal tracks  94 ; and the width  144  of each seal  94 .  
         [0028]    The CASI module  52  includes several different software modules or tools that are executable by the CPU  58 . As schematically shown in FIG. 1, the CPU  58  includes a processor  150  and a memory  154 . The memory  154  stores the software modules, and the processor  150  retrieves, interprets, and executes the software modules to perform the operations of the CASI module  52 . For the embodiment described herein, the CPU  58  is a Pentium PC. However, other CPUs or controllers (e.g., programmable controllers) can be used. Additionally, as should be apparent to those of ordinary skill in the art, some software may be implemented in hardware using mechanisms such as hardware descriptor language (“HDL”) to create application specific or special purpose circuits. Accordingly, elements described herein should not necessarily or inevitably be limited to a software or hardware embodiment simply because examples given are set forth in hardware or software specific terms. The terms CPU and controller are used interchangeably herein and, unless specifically limited, encompass CPUs, controllers, application specific or special purpose circuits, and similar devices.  
         [0029]    While only a processor  150  and memory  154  are shown, the CPU  58  can include other devices or other circuitry (e.g., drivers, A/D converters, conditioners, etc.). Further, the CPU  58  can be connected to other CPUs via a network and the software modules stored and executed by the CPU  58  are not limited to the modules described below. The apparatus  20  also includes input and output devices that provide an interface between the CPU and an operator. Example input devices include, but not limited to, a keyboard, a keypad, a pointing device, and a touch screen. Example output devices include, but not limited to, a display, a printer, a magnetic storage device, and an optical storage device.  
         [0030]    These include: a carrier tape edge (CTE) tool; a cover tape location (CTL) tool; and a seal track location (STL) tool. The operation of these software modules will be discussed with reference to FIG. 8 primarily, and also with reference to FIGS. 5 and 6.  
         [0031]    As seen in FIG. 8A, at  200  the machine advances the composite tape one pitch length. At  210  the CASI module camera  100  captures a digital image (FIG. 6) of the length of composite tape within the FOV.  
         [0032]    The CTE tool includes boxes  220 - 240  in FIG. 8A. At  220 , the CTE tool positions a CTE box  222  (FIG. 6) around a portion of the carrier tape  34  edge (abbreviated “CTE”). The CTE box  222  defines a search region for the CTE tool. The length of the CTE box  222  preferably spans at least two sprocket holes  80 .  
         [0033]    At  230 , the CTE tool analyzes segments within the CTE box  222 . This includes dividing the CTE box  222  into a selected number of segments or sample regions, and using the CTE box  222  as a gradient-based edge tool. The CTE tool is programmable, and a machine operator may input the number of segments into which the CTE box  222  is divided in order to select the number of samples desired. The CTE box  222  is preferably fixed where the edge of the carrier tape  34  is predicted to be within the digital image (i.e., the nominal position of the CTE). The CTE box  222  is wide enough to accommodate normal variations in the position of the CTE. The nickel rail  84  provides a silver background for the edge of the carrier tape  34 , and therefore creates a large contrast to assist the CTE tool identify the CTE.  
         [0034]    The CTE tool analyzes each segment within the CTE box  222  to find a light-to-dark edge transition corresponding to the edge of the carrier tape  34  with the nickel rail  84  behind it. The allowable range for the grayscale threshold level to detect the upper edge of the carrier tape  34  is 0 to 255, with the default setting preferably being 40. At  240 , the CTE tool calculates a robust equation for the carrier tape edge CTE. This calculation includes uses the edge data from each segment within the CTE box  222  to construct the robust line equation. The CTE equation is used as a datum by the CTL and STL tools, as will be described below.  
         [0035]    The CTL tool includes steps  250 - 270  in FIG. 8A. At  250 , the CTL tool positions a CTL box  252  (FIG. 6) within the digital image. The CTL box  252  is located a fixed distance from the CTE datum, around the nominal position of the cover tape edge or location (abbreviated “CTL”), and defines the search region for the CTL tool. The upper edge of the CTL box  252  is aligned with the a sprocket hole  80  and lower edge of the box  252  is over the cover tape  41  near the upper edge of the carrier tape compartment  76 .  
         [0036]    At  260 , the CTL tool analyzes segments within the CTL box  252 . This includes dividing the CTL box  252  into a selected number of segments or sample regions, and using the CTL box  252  as a gradient-based edge tool. The CTL tool is programmable, and a machine operator may input the number of segments into which the CTL box  252  is divided in order to select the number of samples desired. The CTL box  252  is preferably fixed where the edge of the cover tape  41  is predicted to be within the digital image (i.e., the nominal position of the CTL), based on the position of the CTE as calculated by the CTE tool. The CTL box  252  is wide enough to accommodate normal variations in the position of the CTL. The carrier tape  34  provides a black background for the edge of the cover tape  41 , and therefore creates a large contrast to assist the CTL tool identify the cover tape edge.  
         [0037]    The CTL tool analyzes each segment within the CTL box  252  to find a dark-to-light edge transition corresponding to the edge of the cover tape  41  with the carrier tape  34  behind it. The allowable range for the grayscale threshold level to detect the upper edge of the cover tape  41  is 0 to 255, with the default setting preferably being 40. At  270 , the CTL tool calculates a robust equation for the CTL by using the edge data from each segment within the CTL box  252 .  
         [0038]    The STL tool includes steps  280 - 390  in FIGS. 8A and 8B. At  280 , the STL tool positions ST 1  and ST 2  boxes  282 ,  284  (FIG. 6) within the digital image. The STL boxes  282 ,  284  are located a fixed distance from the CTE datum, around the nominal positions of the first and second seal tracks (abbreviated “ST1” and “ST2”), and define the search regions for the STL tool. The length of the STL boxes  282 ,  284  is about equal to the pitch length of the composite tape, and is preferably slightly longer than the pitch length so there is some overlap at both ends of the STL boxes  282 ,  284  with the previous and next pitch lengths inspected by the CASI module  52 .  
         [0039]    At  290 , the STL tool analyzes segments within the STL boxes  282 ,  284 . This includes dividing the STL boxes  282 ,  284  into a selected number of segments or sample regions, and using the STL boxes  282 ,  284  as gradient-based edge tools. The STL tool is programmable, and a machine operator may input the number of segments into which the STL boxes  282 ,  284  are divided in order to select the number of samples desired. The STL boxes  282 ,  284  are preferably fixed where the STI and ST 2   94  are predicted to be within the digital image (i.e., the nominal position of the seal tracks), based on the position of the CTE as calculated by the CTE tool. The STL boxes  282 ,  284  are wide enough to accommodate normal variations in the position of the seal tracks  94 . The cover tape  41  provides a light-colored background for the edges of the seal tracks  94 , and therefore creates a large contrast to assist the STL tool identify the seal track edges.  
         [0040]    [0040]FIG. 7 illustrates an example of a portion of the image captured in one of the ST 1  and ST 2  boxes  282 ,  284 . In this figure, the segments of the box are illustrated with broken lines, and are identified with letters A-O for the sake of convenience in this written description. The seal track  94  illustrated in FIG. 7 is greatly enlarged to illustrate the non-uniformity that is sometimes encountered in the seal  94  at the micro-level. It should be noted that the STL tool must perform the following steps for each of the two seal boxes  282 ,  284 . Because the steps are identical for the two seal track boxes  282 ,  284 , they are described only once below.  
         [0041]    At  300  in FIG. 8B, the STL tool takes in all data from segment A. At  310 , the STL tool determines if there are any gaps in the portion of the seal track within segment A. If the seal track is determined to be continuous within segment A, the STL tool goes to  320 , where the STL tool finds the seal track edges and stores the data for the position of the seal track edges in segment A. The STL finds the seal track edges by first finding a light-to-dark edge transition corresponding to the top edge of the seal, and then finding a dark-to-light edge transition corresponding to the lower edge of the seal. The allowable range for the grayscale threshold level to detect the edges of the seals  94  is 0 to 255, with the default setting preferably being 30. The machine operator may customize the grayscale threshold level, however.  
         [0042]    At  330 , the STL tool calculates the center of the portion of the seal  94  within segment A, and stores the data corresponding to the center point. At  340 , the STL tool calculates the seal width by comparing the coordinates of the edges of the seal  94  found and stored at  320 . At  350 , the STL tool determines whether the seal width is greater than a minimum width. The minimum width is a variable that the machine operator may set. If the seal width within segment A is greater than the minimum width, the STL tool advances to  360 , where it determines whether the current segment is the last segment of the STL box  282 ,  284  being analyzed. If it is not the last segment, then the STL tool goes to  370 , where it advances to the next segment (e.g., segment B) and starts again at  310  for that segment. Additionally and in some constructions, the tool also determines whether the seal width within segment A is less than a maximum width, which is a variable that the machine operator may set.  
         [0043]    If at either  310  or  350  the STL tool returns a “no,” the STL tool skips to  380 , where it marks the current segment as failing in the STL tool&#39;s memory. After marking the segment as failing, the STL tool continues to  360 , where it determines whether the current segment is the last segment of the STL box  282 ,  284 . If the STL tool returns a “yes” at  360 , the STL tool has completed analysis of the STL box  282 ,  284 , and moves on to  382 .  
         [0044]    At  382 , the STL tool compares the strings of consecutively-failed segments within the STL boxes  282 ,  284  to a defect tolerance. The defect tolerance is the maximum number of consecutive segments that may receive failing grades without declaring the seal track  94  defective. The defect tolerance may be set by the machine operator. At  384 , the STL tool queries whether the defect tolerance has been exceeded. If the answer is “yes,” then the STL tool generates a fault condition, but if the answer is “no,” then the STL tool moves on to  390 . If the STL tool generates a fault condition, the CPU can notify the machine operator at  386  of the defective seal  94  and/or can perform some other action (e.g., perform further processing on the seal) as a result of the fault condition. At  390 , the STL tool calculates the center line equations for ST 1  and ST 2  based on the center point data stored in the STL tool memory for each segment. The CASI software then advances to FIG. 8C.  
         [0045]    At  400  in FIG. 8C, the CASI software calculates the distance between the CTE and the CTL by calculating the distance between the robust CTE and CTL equations calculated above at  240  and  270 . At  410 , this distance is compared to a nominal CTE-to-CTL distance, which may be set by the machine operator. The CASI software then queries at  420  whether the deviation of the CTE-to-CTL distance from the nominal distance is acceptable. The tolerable deviation may be set by the machine operator. If the deviation is not acceptable, the CASI software moves to  430 , where it generates a fault condition and notifies the machine operator of an unacceptable deviation. Such a deviation may indicate, for example, that the cover tape  41  is not being properly applied to the carrier tape  34 , and that the cover tape dispenser  40  may have to be adjusted.  
         [0046]    At  440 , the CASI software calculates the distance between the CTE and ST 1  by calculating the distance between the robust CTE and STI equations calculated above at  240  and  390 . At  450 , this distance is compared to a nominal CTE-to-ST 1  distance, which may be set by the machine operator. The CASI software then queries at  460  whether the deviation of the CTE-to-ST 1  distance from the nominal distance is acceptable. The tolerable deviation may be set by the machine operator. If the deviation is not acceptable, the CASI software moves to  470  where it generates a fault condition and notifies the machine operator of an unacceptable deviation. Such a deviation may indicate, for example, that the cover tape  41  is misaligned with the carrier tape  34 , or that there is a problem with the sealing shoe  44 .  
         [0047]    At  480 , the CASI software calculates the distance between the ST 1  and ST 2  by calculating the distance between the robust ST 1  and ST 2  equations calculated above at  390 . At  490 , this distance is compared to a nominal ST 1 -to-ST 2  distance, which may be set by the machine operator. The CASI software then queries at  500  whether the deviation of the ST 1 -to-ST 2  distance from the nominal distance is acceptable. The tolerable deviation may be set by the machine operator. If the deviation is not acceptable, the CASI software moves to  510 , where it generates a fault condition and notifies the machine operator of an unacceptable deviation. Such a deviation may indicate, for example, that one of sealing elements of the sealing shoe  44  is wandering away from the other element or that the sealing elements are not parallel to each other.  
         [0048]    After the distances between the various parts of the composite tape have been checked as set forth above, the CASI software has completed its analysis of one pitch length of composite tape, and is ready to analyze the next length. The machine advances the composite tape another pitch length, as at  200 , and begins the process over for that portion of the composite tape under the CASI module  52 .