Abstract:
An electronic component pick and place machine is provided. The pick and place machine comprises a pick station, first and second pick heads, a component alignment detector and a controller. The pick station is connected to a component feed source. The first pick head has access to the pick station and a component transfer area and the second pick head has access to the component transfer area and a component mounting position. The component alignment detector is furthermore directed toward the component transfer area. The controller is coupled to the feed source, the first pick head, the second pick head and the detector, the controller containing instructions which, when executed, cause the controller to compare the detected component alignment with a known component alignment and control the feed source, the first pick head, and the second pick head in response to the comparison.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 08/915,862, filed Aug. 21, 1997. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to detecting the orientation of a body. More particularly, the present invention relates to alignment apparatuses and methods for determining whether leads on a semiconductor package are aligned in a predetermined alignment prior to placement on and attachment to a substrate. The invention can be generally used in conjunction with or integral to pick and place machines, such as surface mount placement machines, die attach machines, tape and reel production machines, wire bond machines, and the like, to verify proper lead alignment on components being placed by the machines. 
     Solid state electrical devices are typically produced by attaching a plurality of miniaturized electrical components to a common substrate, such as a printed circuit board. The proper performance of the device is dependent upon the precise placement of each electrical component on the substrate. 
     The placement of electrical components on a substrate is commonly performed using machines generally known as pick and place machines. Pick and place machines typically employ a number of movable heads each having a nozzle through which a negative pressure, preferably a vacuum, is applied to pick a component from a feed source, such as a continuous tape and reel assembly. The pick and place machine controls the movement of each head to precisely place the components on a substrate, after which the vacuum or suction is released. 
     Commonly, pick and place machines incorporate sensor systems that detect whether a component is properly aligned in a predetermined angular orientation prior to placing. Examples of such systems are discussed in U.S. Pat. No. 5,040,291 issued to Janisiewicz (“&#39;291 patent”) and U.S. Pat. No. 5,377,405 issued to Sakurai et al. 
     Other placement systems ensure alignment of the component by providing either a recessed surface in a substrate shaped to receive the component or mating surfaces on the component and the substrate. For example, See U.S. Pat. No. 5,034,802 issued to Liebes, et al. (the “&#39;802 patent”). The &#39;802 patent also discloses the use of an alignment jig for aligning a component prior to picking and placing the component on the substrate. The alignment jigs employ large recesses that are tapered down to the dimensions of the component. The large tapered recess allows the components to be placed less precisely in the jig. The taper on the jig then serves to essentially “funnel” the components into a precise alignment. 
     A problem exists with the aforementioned alignment methods when used with traditional rectangular shaped components having leads extending from two opposing sides. If the component is 180° out of alignment, the leads will appear to be properly aligned using the above methods. A component that has its leads attached 180° out of alignment will generally function improperly at a minimum and may result in damage to the component and/or other components connected to the component. The obvious exception is a component that is designed to employ mirror image lead connections, which is not the typical design. 
     This problem is further complicated by components that are designed to have symmetric leads on more than two sides, such as a square shaped component. A 90° rotation of a square shaped component in the plane of the leads will result in a lead misalignment that is undetectable using prior art methods. 
     The misalignment of leads on aligned components is a defective condition that is presently not detectable using general component orientation systems of the prior art. Thus, the present invention is directed to detecting the misalignment of lead components irrespective of the general orientation of the component to provide apparatuses and methods that can be used to determine the lead alignment of components prior to placement on and attachment to a substrate. 
     BRIEF SUMMARY OF THE INVENTION 
     The above objectives and others are accomplished by methods and apparatuses in accordance with the present invention. A method of the present invention contemplates placing a component having leads to a substrate by providing a fiducial marker on a component to be placed on a substrate that uniquely distinguishes the alignment of leads on the component. The alignment of the fiducial marker on the component is detected and compared to a predetermined fiducial alignment corresponding to a predetermined lead alignment. The component is placed on the substrate when the detected fiducial alignment corresponds to the predetermined fiducial alignment. In addition, a component that has misaligned leads can be discarded or the alignment of the components can be properly realigned in accordance with an alignment offset. 
     Apparatuses of the present invention can be operated in conjunction with or integral to various pick and place machines, such as surface mount placement machines, die attach machines, tape and reel production machines, and wire bond machines. Generally, the apparatus includes a nest for receiving a component and detector positioned to detect whether leads on the component in the nest are properly aligned and provide a signal indicative of the alignment. In a preferred embodiment, a physically asymmetric fiducial marker is provided on the component and a correspondingly asymmetric recess in provide in a surface of the nest. The detector is positioned to detect whether the asymmetric portions of the component and the nest mate. In another embodiment, a receiver is positioned in a pick and place machine relative to the feed source to detect the alignment of the leads on a component prior to the component being fed to a pick station for placement on a substrate. 
     Accordingly, the present invention overcomes the aforementioned problems to provide apparatuses and methods that provide the ability to determine, verify, and/or correct the alignment of leads on components prior to placing the components on a substrate. These advantages and others will become apparent from the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying Figures wherein like members bear like reference numerals and wherein: 
     FIGS.  1 ( a ) &amp;  1 ( b ) show two lead arrangements on components including fiducial markers that can be aligned using the present invention; 
     FIG. 2 is an example of a pick and place apparatus incorporating the present invention; 
     FIG. 3 shows a side view along the line  3 — 3  shown in FIG.  2  and including a misaligned component seated in the recess in the nest; 
     FIG. 4 is a cross section of the nest shown in FIG. 3 along the line  4 — 4 , but with a properly aligned component seated in the recess of the nest; 
     FIG. 5 shows an alternative embodiment of the device for detecting a physical asymmetry on the component; 
     FIG. 6 is a perspective view of an apparatus of the present invention including a component having both superficial and physically asymmetric marks: and, 
     FIG. 7 is a further example of a pick and place apparatus incorporating the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An apparatus  10  embodying the present invention will be described generally with reference to the drawings for the purpose of illustrating the present preferred embodiments of the invention only and not for purposes of limiting the same. The apparatus  10  generally includes a nest  12  and a detector  14 . The nest  12  and detector  14  are used in combination with a component  2  having leads  4  by providing a fiducial marker  6  on the component  2 , as shown in FIGS.  1 ( a )&amp;( b ), to determine or verify whether the leads  4  are properly aligned prior to placing the component  2  on a substrate  8 . The fiducial marker  6  is provided on the component  2  in such a way to uniquely distinguish the alignment of the leads  4 . Unless specifically stated, the term “fiducial marker” is meant to include any number and all types of marks that serve the distinguishing function, discussed above, either in isolation or combination. Such marks may include, but are not limited to, geometric shapes or characters that superficially and/or structurally alter the appearance of the component  2 . 
     In a preferred embodiment, the nest  12  includes a nest surface  16  containing an asymmetric recess  18  that corresponds to a component having a physically asymmetric fiducial marker  6 . Physically corresponding fiducial markers  6  and nests  12  are currently preferred due, in part, to the fact that most semiconductor components are manufactured with a physical asymmetry to facilitate post-production troubleshooting operations. Therefore, the manufacturing process for many components does not have to be modified to work with the present invention. 
     Many electrical components are currently manufactured with a physically asymmetric beveled edge that provides a convenient way for inspection and maintenance personnel to quickly ascertain the post-production configuration of a component as it is assembled in a machine. The use of beveled edges and other asymmetries in the prior art has represented an additional manufacturing step and expense that did not improve the overall quality or cost effectiveness of the manufacturing process. As such, an objective of the prior art has traditionally been to eliminate the beveled edge thereby decreasing manufacturing costs. 
     An asymmetric portion  20  is preferably incorporated in the recess  18 . The asymmetric portion  20  is sized to correspond to and mate with the physically asymmetric fiducial marker  6  on the component  2  when the leads  4  are properly aligned for placement on the substrate and the component  2  and nest  12  are brought into contact. Preferably, the component  2 , when properly seated in the recess  18 , will not extend beyond the nest surface  16 . This provides for a digital (on/off) detection scheme in that the component  2  is detected only if the leads are misaligned. Alternatively, the recess  18  can be designed so the component  2  extends beyond the surface  16  to produce a profile characteristic of a component having properly aligned leads. If the component  2  does not properly mate with the recess  18 , the component  2  will produce a profile that is not characteristic of a component with properly aligned leads. 
     The detector  14  of the present invention is positioned relative to the nest  12  to detect the alignment of the leads  4  and provide alignment signals or data indicative of the component alignment. Generally, the lead alignment is detected implicitly by detecting either the orientation of the fiducial marker or the component  2  relative to the nest surface  16 . The alignment signal provided by the detector  14  can be used to prompt an operator or as a control signal for additional operations as will be discussed in greater detail within. 
     In a preferred embodiment shown in FIGS. 2 and 3, the detector  14  includes an emitter  22  and a receiver  24 . The emitter  22  is positioned to emit radiation, preferably visible or infrared light, parallel and proximate to the nest surface  16 . The receiver  24  is positioned on a side of the recess  18  opposite the emitter  22  to receive the emitted radiation directed toward the recess  18 . The position of the receiver  24  is such that a misalignment of the components will result in a disruption of a radiation pattern received by the receiver  24 . The receiver  24 , in turn, provides the alignment signals indicative of the component alignment. 
     The receiver  24  preferably includes a reference radiation pattern for a properly aligned component. The reference pattern is compared with a radiation pattern received by the receiver  24  to determine the lead alignment of the component  2 . For example, in the preferred embodiment, the comparison is made to determine the presence or absence of a portion of the component  2  extending beyond the nest surface  16 . The absence of the component  2  blocking the emitted signal from the receiver  24  is indicative that the leads of the component in the nest  12  are properly aligned. 
     Any number of emitter/receiver combinations can be used with the present invention. In an alternative embodiment for the detector  14 , shown in FIGS. 4 and 5, a sensor  25  is positioned within the recess  18  at a location to discriminate between components with properly and improperly aligned leads when the nest  12  and the component  2  are brought into contact and provide alignment signals accordingly. The sensor  25  can be one or more of various types of sensors, such as contact, electrical, mechanical, pressure or environmental, but is preferably a vacuum sensor as shown in FIG.  4 . It can be appreciated that the sensor can also be used in such conjunction with emitter/receiver detectors  14  such as in FIG.  3 . 
     In addition, a receiver  24 , such as a camera, can be used that does not require a dedicated emitter. As shown in FIG. 6, a camera  24  can be used as the detector  14  for components having either physical or superficial asymmetric fiducial markers  6  with or without a nest  12 . The camera is used to detect both the location and orientation of the fiducial marker  6  for comparison with a properly aligned fiducial marker  6 . In this embodiment, a recess in the nest  12  may or may not be used in determining the alignment of the component  2 . As shown in FIG. 7, the apparatus  10  can be incorporated into existing machinery through the placement of the camera  24  in a position to detect a fiducial marker indicating the alignment of the leads. One skilled in the art will appreciate that other receivers  24  that do not require dedicated emitters  22  can be similarly incorporated. 
     In the arrangement of FIG. 6, the detector  14  can be used to facilitate realignment of the component  2  through the use of a movable nest  12  and a feedback system  26 . The feedback system  26  controls the movement of the nest  12  based on the comparison of the actual and proper alignment of the fiducial marker  6 . The alignment comparison provides an alignment offset for use in correcting the alignment either prior to or during placement of the component  2  on the substrate  8 . The feedback system  26  can also be used to halt or alter a process involving the apparatus  10 , if the component  2  is misaligned or the alignment of the component  2  can not be determined. 
     One skilled in the art will appreciate that a feedback system can be implemented in any of the embodiments described herein. For example, a feedback system for components having physical asymmetries may involve picking up and realigning the component  2  to properly seat the component  2  in the nest  12 . Alternatively, the nest  12  can be temporarily adjusted to properly seat the component  2  and then readjusted to its properly aligned position prior to removal of the component  2  for further processing. 
     An exemplary implementation of the apparatus  10  is to modify pick and place machines  30  of the prior art, such as shown in FIG.  2 . The machine  30  is further described in the &#39;291 patent, the disclosure of which is hereby incorporated by reference. In this particular embodiment, the machine  30  includes a pick spindle  32  and a placement spindle  34 , each of which contains a plurality of pick heads  36 . 
     The pick spindle  32  employs the pick heads  36  to remove components  2  from a pick station  38  and place them in a spindle transfer area  40 . Generally, components are continuously fed to the pick station  38  using a continuous track of trays  42  that are supplied from a feed source  44 , such as a continuous tape reel  46 . The feed source  44  may also include a plurality of serial feed tracks in addition to the single serial feed track shown in FIGS. 2 and 7. The spindle transfer area  40  is accessible by pick heads  36  from both the pick spindle  32  and the placement spindle  34 . 
     The placement spindle  34  employs the pick heads  36  to pick the components  2  from the spindle transfer area  40  and place the components  2  on the substrate  8  positioned in a component mounting position  48 . Generally, the substrate  8  will be fed to and removed from the component mounting position  48  along a track  50  in a continuous feed assembly. 
     The machine  30  generally includes a controller  52  and a number of additional components to bring about high speed movement of components. For example, the machines generally employ a variety of actuators  54  to move the pick heads  36  between pick and place locations. 
     In a first embodiment shown in FIG. 2, the apparatus  10  is positioned in the spindle transfer area  40 . Generally, the apparatus  10  will be connected to the controller  52  and operate to affect the control scheme of the controller  52  in response to alignment signals provided by the detector  14 . 
     Alternatively, the apparatus can have a controller that is independent of the machine controller  52 . For example, embodiments of the apparatus  10  employing the feedback system  26  can use the alignment signals to provide continual monitoring of the alignment verification process independent of the machine controller  52 . The feedback system  26  communicates with the controller  52  providing misalignment conditions. The controller  52  can be suitably modified to perform any number of actions as specified in response to the alignment signals received either directly from the detector  14  or from the feedback system  26 . Such actions include, but are not limited to, repicking the misaligned component using the pick head  36  and replacing it in the nest  12  after realigning the component. Also, the placement spindle can be used to place the misaligned component in a discard area (not shown) or can place the component on the substrate in accordance with an alignment offset required to properly align the leads  4 . The alignment offset is determined by comparing the detected alignment with the predetermined alignment for the component having its leads properly oriented. 
     A general description of the operation of the machine  30  employing the apparatus  10  is provided. Initially, components  2  are fed from the feed source  44  to the pick station  38  via a continuous series of trays  42 . The components  2  are picked from trays  42  at the pick station  38  using the pick heads  36  on the pick spindle  32 . The pick spindle  32  moves to the spindle transfer area  40  and places the components in the nests  12 . Alternatively, the component  2  can be placed into the transfer area  40  and the nest  12  and the component  2  can be brought into contact. 
     The detector  14  provides alignment signals or data on whether components  2  are properly placed in the nest  12 . If the leads  4  on the components  2  are properly aligned, the placement spindle  34  picks the components  2  from the nest  12 . The placement spindle moves the components to the mounting position  48  and places the components  2  on the substrate. 
     An alternative embodiment of the apparatus  10  in a different pick and place machine  130  described in the &#39;291 patent is shown in FIG.  7 . Machine elements that are comparable to those in machine  30  have the same last two digits in the reference number. In machine  130 , the spindle transfer area  40  and placement spindle  34  used in the embodiment shown in FIG. 2 have been eliminated. The components  2  are picked from trays  142  using pick heads  136  on a pick spindle  132 . The pick spindle  132  places the components  2  on the substrate  8  at the component mounting station position  148 . 
     The apparatus  10  is embodied as a receiver  24  positioned relative to the feed source  144  and connected to a machine controller  152 . The receiver  24  is used to detect the location of a fiducial marker  6  on the component  2  while the component  2  is in the tray  142 . If the leads  4  on the component  2  are not properly aligned, the pick heads can be used to correct the alignment offset of the component or discard the misaligned component. Alternatively, the controller  152  can control the pick spindle  132  to bypass the misaligned component. The misaligned component will be transported away from the pick station  138  in the tray  142 . A remote apparatus can be provided to realign or discard the misaligned component. 
     The positioning of the receiver  24  in the embodiment of FIG. 7 allows one receiver to inspect the components  2  as the components are transported to the pick station  138  on a continuous track. One receiver  24  can then provide lead alignment data for use by the controller  152  in directing pick operations. Also, as discussed above, the receiver  24  can be used to detect both physical asymmetries and superficial asymmetries on the components  2 . 
     One skilled in the art will appreciate the receiver  24  can be arranged in a stationary position relative to the feed source  144  or the receiver  24  can be coupled with the movement of the pick head  36 . Also, a plurality of receivers  24  can be used that correspond to one or more of a plurality of pick heads. In addition, components  2  can also be fed to the pick stations using parallel feed sources, which also may be either continuous or discontinuous. 
     Embodiments similar to FIG. 7 provide substantial flexibility in upgrading existing pick and place machines to incorporate the apparatuses and methods of the present invention. However, those apparatuses perform most reliably if the fiducial marker  6  is visually accessible while the component  2  is in the tray  142 . It should be noted that the tray  142  can also be modified to serve as a nest  12  for visually inaccessible physical asymmetries. 
     Those of ordinary skill in the art will appreciate that a number of modifications and variations that can be made to specific aspects of the method and apparatus of the present invention without departing from the scope of the present invention. Such modifications and variations are intended to be covered by the foregoing specification and the following claims.