Abstract:
A system and method for performing operations on a plurality of workpieces comprises an operations portion and a load/unload portion, a plurality of independently operable work heads located in the operations portion, the work heads each being operable to perform work on the plurality of workpieces, a transfer system, the transfer system including a plurality of mounting devices, the transfer system being operable to deliver the mounting devices into and out of the operations portion of the system, the plurality of workpieces being contained in workpiece-holding structures, the workpiece-holding structures being mountable on the plurality of mounting devices, wherein one of the plurality of mounting devices is positioned in the operations portion of the system and work is performed on the plurality of workpieces by at least one of the plurality of independently operable work heads while another one of the plurality of mounting devices is positioned in the load/unload portion of the system and workpiece-holding structures are unloaded from the mounting devices.

Description:
CLAIM OF PRIORITY  
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119(e) to copending U.S. Provisional Application No. 60/432,483, filed on Dec. 11, 2002, the entire contents of which are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates generally to a system and method for performing a plurality of work operations in parallel using a plurality of work devices within one workstation. More specifically, the present invention relates to an apparatus and method for controlling a dispensing system that dispenses small amounts of liquid on a plurality of substrates such as electronic component packages within a dispensing system.  
         BACKGROUND OF THE INVENTION  
         [0003]    There are several types of prior art dispensing systems used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is the assembly of integrated circuit chips. In this application, dispensing systems are used in the process of encapsulating integrated circuits with an encapsulating material and in the process of underfilling flip-chip integrated circuits with an encapsulant. Prior art systems are also used for dispensing dots of liquid epoxy or solder paste onto circuit boards and integrated circuits. The liquid epoxy and solder is used to connect components to a circuit board or to an integrated circuit. The dispensing systems described above include those manufactured and distributed by Speedline Technologies, Inc., of Franklin, Mass. A challenge to the throughput efficiency of dispensing systems arises due to constant increase in the amount of interconnects beneath a die in today&#39;s high density packaging, as well as a decrease in the size of the gap to be filled.  
           [0004]    In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z) using servomotors controlled by a computer system or controller. To dispense a dot of liquid on a circuit board or other substrate at a desired location, the pump and dispenser assembly is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z axis until the nozzle of the pump and dispenser assembly is at an appropriate dispensing height over the substrate. The pump and dispenser assembly dispenses a dot of liquid, is then raised along the z axis, moved along the x and y axes to a new location, and is lowered along the z axis to dispense the next liquid dot. For applications such as encapsulation or underfilling as described above, the pump and dispenser assembly is typically controlled to dispense lines of material as the pump and dispenser are moved in the x and y axes along the desired path of the lines.  
           [0005]    The production rate of such dispensing systems, in some cases, may be limited by the rate at which a particular dispense pump assembly can accurately and controllably dispense dots or lines of material. In other cases, the production rate of such systems may be limited by the rate at which parts can be loaded into and out of the machine. In still other cases, the production rate of such systems may be limited by process requirements, such as the time required to heat a substrate to a particular temperature, or the time required for a dispensed material to flow, as in underfill applications. In all cases and applications, there is some limit to the throughput capability of a single dispense system.  
           [0006]    During the manufacture of integrated circuits, production requirements often exceed the throughput capabilities of a single dispensing system. To overcome the throughput problem, multiple independent dispensing systems may be utilized to achieve the desired collective throughput. This solution is often expensive since multiple machines are used, and since additional manufacturing space is required. In typical operations, manufacturing floor space is both limited and expensive. It is therefore desirable to reduce the “footprint” of each manufacturing system on the manufacturing floor.  
           [0007]    When a dispensing system is presented with a substrate or component to be dispensed upon, it is typical that an automatic vision system is used to locate and calibrate the actual position of the part and critical features within the part. This allows the system to compensate for variations in either the component itself or in the fixturing of the component relative to the coordinate system of the dispensing head positioning system.  
           [0008]    When multiple dispensing heads are utilized in parallel to achieve a high collective throughput, it is typical that the multiple dispensing heads are programmed to perform substantially the same task on substantially identical components. However, because of slight variations in either the components themselves or in the fixturing of the components relative to the positioning systems, corrections must be applied independently to each of the multiple dispense heads. Since these corrections are unique to each of the multiple dispense heads, each of the dispensing heads are typically independently positionable relative to its substrate.  
           [0009]    One prior art system achieves high throughput by utilizing multiple independent dispensing heads and is described in U.S. Pat. No. 6,007,631 entitled “Multiple Head Dispensing System and Method”, which is incorporated herein by reference, and is assigned to the assignee of the present application. This dispensing system utilizes multiple independent dispensing heads. Each of the multiple dispensing heads is mounted on a separate positioning system and operates over an independent work area. In addition, the system has two conveyor lanes to allow parts to be loaded into and out of the dispense work areas on one lane while the dispense heads continue to dispense on parts fixed in position in the other lane.  
         SUMMARY OF THE INVENTION  
         [0010]    It is desirable to achieve throughput advantages displayed in a multiple dispense head system and incorporate features of a dual-lane conveyor while further reducing the system cost and footprint of each printing machine. It is further desirable to provide continuous cycles in a batch machine that avoid downtime in a system, while maintaining the quality of resulting substrates.  
           [0011]    Embodiments of the present invention achieve the throughput advantages of the prior art discussed above while further reducing footprint and cost by providing multiple independent dispense heads to dispense onto a plurality of substrates transported on pallets through the system. Using two lanes, each lane having a track, dispensing occurs on substrates transported on pallets on a first front track, while pallets on a second rear track are loaded with substrates in preparation for a next dispensing cycle. By working in a continuum, pallets on one of the first front track or the second rear track are substantially continuously positioned for dispensing, alleviating downtime or overhead associated with the dispensing process.  
           [0012]    Further, in some embodiments of the present invention, smaller limited travel positioning systems are utilized to adjust the positions of the substrates relative to the dispensing heads. In other embodiments of the present invention, smaller limited travel positioning systems are mounted between each of the multiple dispensing heads and the common gantry positioning system.  
           [0013]    In other embodiments of the present invention, one of the smaller limited travel positioning systems may be eliminated from one of the multiple heads without loss of generality. Since the position of each of the other heads may be adjusted relative to the position of the first head, unique corrections can still be applied to each of the multiple heads.  
           [0014]    In other embodiments of the present invention, the travel range of the smaller limited travel motion systems may be made to be great enough to allow a dispensing pump to perform all necessary motion for a given component or part without requiring motion from the larger gantry positioning system. In such cases, the pattern dispensed by each of the multiple dispensing heads may be different than those of the other dispensing heads. An example of an application that would benefit from such a capability would be a dam &amp; fill application in which one head is controlled to dispense a perimeter boundary of a dam material, while the other head is controlled to dispense a fill pattern of encapsulant within the dam.  
           [0015]    In some embodiments of the present invention, aspects of the dual-lane conveyor are incorporated into multiple pallet loading fixtures. In such systems, the dispense heads continue to dispense on parts fixtured on one pallet while parts are loaded off of and then onto another pallet.  
           [0016]    Embodiments of the present invention are not limited to dispensing systems and include other devices in which multiple work-heads perform substantially identical operations in parallel on multiple substantially identical work-pieces.  
           [0017]    Implementations of the invention are directed to a system for performing operations on a plurality of workpieces. The system comprises an operations portion and a load/unload portion, a plurality of independently operable work heads located in the operations portion, the work heads each being operable to perform work on the plurality of workpieces, and a transfer system, the transfer system including a plurality of mounting devices, the transfer system being operable to deliver the mounting devices into and out of the operations portion of the system, wherein one of the plurality of mounting devices is positioned in the operations portion of the system and work is performed on the plurality of workpieces by at least one of the plurality of independently operable work heads while another one of the plurality of mounting devices is positioned in the load/unload portion of the system and workpiece-holding structures are unloaded from the mounting devices.  
           [0018]    Embodiments of the invention can include one or more of the following features. The plurality of workpieces can be contained in workpiece-holding structures, the workpiece-holding structures being mountable on the plurality of mounting devices. The load/unload portion can be operable to load the workpiece-holding structures onto one of the plurality of mounting devices prior to delivery of the mounting devices into the operations portion by the transfer system to perform work on the plurality of workpieces by the independently operable work heads. The load/unload portion can be further operable to unload the workpiece-holding structures from one of the plurality of mounting devices.  
           [0019]    Further embodiments of the invention can include one or more of the following features. The workpieces can be electronic substrates and the work heads can be dispensing heads. The workpiece-holding structures can be trays and the trays can hold electronic substrates. The trays can be AUER boats. The mounting devices can be pallets for holding the workpiece-holding structures. The work performed on the workpieces can be the dispensing of underfill onto the electronic substrates. A vision alignment apparatus can be included to align the independently operable work heads to the plurality of workpieces.  
           [0020]    Implementations of the invention further include a method for performing operations on a plurality of workpieces using an apparatus having an operations portion and a load/unload portion; a plurality of independently operable work heads located in the operations portion, the work heads each being operable to perform work on the plurality of workpieces; and a transfer system, the transfer system including first and second mounting devices, the transfer system being operable to deliver the first and second mounting devices into and out of the operations portion of the system and out of and into the load/unload portion, respectively. The method comprises mounting workpiece-holding structures onto a first mounting device prior to delivery of the mounting devices into the operations portion to perform work on the plurality of workpieces by the independently operable work heads, moving the first mounting device into the operations portion using the transfer system to have work performed on the plurality of workpieces by at least one of the plurality of independently operable work heads, simultaneously moving the second mounting device using the transfer system to the unload portion, and when the first and the second mounting devices have been positioned, respectively, at the operations portion and the load/unload portion, performing work on the workpieces on the first mounting devices while unloading workpiece-holding structures from the second mounting device.  
           [0021]    Embodiments of the invention can further include repeating prior steps such that workpiece-holding structures are unloaded from a mounting device after having had work performed on the plurality of workpieces contained in the workpiece-holding structures at approximately the same time period the workpieces which have not had work performed on them are delivered to the operations portion.  
           [0022]    The invention will be more fully understood after a review of the following figures, detailed description and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    For a better understanding of the present invention, reference is made to the figures which are incorporated herein by reference and in which:  
         [0024]    [0024]FIG. 1 is a perspective view of a dispensing system in accordance with one embodiment of the invention;  
         [0025]    [0025]FIG. 2 is a side perspective view of the dispenser of FIG. 1 showing the substrate handling system in accordance with one embodiment of the invention;  
         [0026]    [0026]FIG. 3 is a perspective view of the gantry system used in accordance with one embodiment of the invention;  
         [0027]    [0027]FIG. 3B is a perspective view of an alternative gantry system used in accordance with one embodiments of the invention;  
         [0028]    [0028]FIG. 4 is a perspective view of dispensing features in accordance with one embodiment of the invention;  
         [0029]    [0029]FIG. 5 is a perspective view of the boat loading features in accordance with one embodiment of the present invention;  
         [0030]    [0030]FIG. 6 is a perspective view of the boat loading features wherein the boat is being pulled in accordance with one embodiment of the invention;  
         [0031]    [0031]FIG. 7 is a top view of the dispensing system of FIG. 1 in accordance with one embodiment of the invention; and  
         [0032]    [0032]FIG. 8 is an alternative embodiment of the dispensing system of the present invention having multiple magazines. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0033]    Embodiments of the invention are directed to a multiple head dispensing system that performs a dispensing operation on a substrate such as a circuit board or other electronic component. As understood by those skilled in the art, embodiments of the invention are not limited to dispensing systems, but include other systems in which multiple work-heads perform substantially identical operations in parallel on multiple substantially identical substrates or workpieces. Embodiments of the invention can be directed to component placement systems, BGA placement systems, laser soldering systems, automatic optical inspection systems and machining systems. Embodiments of the invention are not limited to dispensing materials onto circuit boards or underfilling electronic components, nor are embodiments limited to use with multiple head dispensing systems, but may be used in single head applications. Other embodiments and processes are possible and envisioned.  
         [0034]    A multiple head dispensing unit in accordance with one embodiment of the invention is described with reference to FIGS.  1 - 3 . FIG. 1 shows a perspective view of a multiple head dispensing system  10 . The dispensing system  10  includes an operations system portion  11  and a substrate handling system portion  101 , both portions working together to accomplish delivery of electronic components from the substrate handling system portion, dispensing onto electronic components in the operations system portion, and removal of electronic components to the substrate handling portion.  
         [0035]    The operations system portion  11  is first described in detail. With further reference to FIG. 1 and referring to FIG. 2, the operations portion  11  includes a lower compartment  12 , a primary system controller  14 , a base frame  16 , a mounting surface  18 , a monitor or other graphical user interface  19 , and a gantry positioning system  28  for each of dispense units  54   a  and  54   b . The dispense units  54   a  and  54   b  include dispenser head housings  46   a  and  46   b . The lower compartment  12  is used to house electrical and pneumatic controllers and the primary system controller  14 . The base frame  16  provides a base for the gantry positioning systems  28  and the mounting surface  18 .  
         [0036]    A gantry positioning system  28  (FIG. 2) is employed to move each of the dispenser units over the surface of a respective substrate. The gantry systems  28  of FIG. 2 are substantially identical, but independent, providing independent motion of each of the dispensers. It will be understood that while two such gantry systems are illustrated in FIG. 2, any number of such gantry systems may be utilized. Referring to FIG. 3, one of the gantry systems  28  of FIG. 2 is shown from a lower perspective and enlarged view. Each of the gantry positioning systems includes a Y axis positioning portion and an X axis positioning portion. The Y axis positioning portion is comprised of linear bearings  20   a  and  20   b , a linear encoder tape scale  22 , and a linear motor magnet track  24 . The gantry positioning system  28  includes a gantry cross beam  48  which is slidably mounted in the Y axis to the base frame  16  using linear bearing sliders  26   a ,  26   b , and  26   c , as well as linear bearing rails  20   a  and  20   b . Linear bearing slider  26   a  is slidably mounted to linear bearing rail  20   b  and linear bearing sliders  26   b  and  26   c  are slidably mounted to linear bearing rail  20   a . Further included in the Y axis portion of the gantry positioning system  28  are encoder read head  34  and linear motor coil  36 . The encoder read head  34  is mounted in close proximity to the linear encoder tape scale  22 , from which it reads positional information. The encoder function performed with linear encoder tape scale  22  and encoder read head  34  may be implemented using a number of different encoder systems, including those manufactured by Renishaw PLC, of Gloustershire, UK.  
         [0037]    The X axis portion of the gantry positioning system  28  includes a dispense head housing or carriage  30   a , linear bearings  32   a  and  32   b , and linear bearing sliders  50   a ,  50   b , and  50   c . The dispense head housing  30   a  is slidably mounted to the gantry cross beam  48  and linear bearing  32   a  using linear bearing sliders  50   a  and  50   b , and to linear bearing  32   b  using linear bearing slider  50   c  (not visible). The dispense head housing  30   a  is driven by linear motor coil  42   a . The position of the dispense head housing  30   a  is sensed by an encoder read head (not shown) that is similar in construction and mounting to the encoder read head  34  of the Y axis. The X axis encoder read head is mounted in proximity to and reads position information from encoder tape scale  38 .  
         [0038]    Mounted within the dispense head housings  30   a  and  30   b  are machine vision cameras (not shown), dispense heads  46   a  and  46   b , and dispense units  54   a  and  54   b , respectively. Dispense heads  46   a  and  46   b  are mounted in the dispense head housings  30   a  and  30   b . The dispense heads  46   a  and  46   b  provide the Z axis of motion for dispense units/pumps  54   a  and  54   b . For example, the dispense heads  46   a  and  46   b  can be implemented a number of ways. Likewise, dispense units  54   a  and  54   b  may be implemented using a number of different dispensing heads or pumps. Dispense units and dispensing heads or pumps can include those disclosed in U.S. Pat. No. 6,395,334 entitled “Multiple Head Dispensing System and Method”, which is assigned to the assignee of the present invention and is incorporated herein by reference.  
         [0039]    In an alternative embodiment, multiple dispensing heads are mounted in a single gantry system, as shown in FIG. 3B. In FIG. 3B, rather than independent dispense heads, two partially dependent heads are mounted on a single gantry. The gantry cross beam assembly  28  is comprised of gantry cross beam  48 , X carriages  30   a  and  30   b , dispense units  54   a  and  54   b , and dispenser head housings  46   a  and  46   b . X carriage  30   a  is slidably mounted to gantry cross beam  48  and linear bearing  32   a  using linear bearing sliders  50   a  and  50   b . X carriage  30   b  is slidably mounted to gantry cross beam  48  and linear bearing  32   a  using linear bearing sliders  52   a  and  52   b . X carriage  30   a  is slidably mounted to gantry  30  cross beam  48  and linear bearing  32   b  using a linear bearing slider. X carriage  30   b  is slidably mounted to gantry cross beam  48  and linear bearing  32   b  using a linear bearing slider. Both carriages  30   a  and  30   b  share a common set of bearing rails  32   a  and  32   b , a common encoder tape scale  38  and a common linear motor magnet track  40 . X carriage  30   a  is driven by linear motor coil  42   a . X carriage  30   b  is also driven by a linear motor coil (not shown). The position of X carriage  30   a  is sensed by an encoder read head (not shown) that is similar in construction and mounting to the encoder read head  34  of the Y axis. The position of X carriage  30   b  is sensed by an encoder read head (not shown) that is similar in construction and mounting to the encoder read head  34  of the Y axis. These X axis encoder read heads are mounted in proximity to and read position information from encoder tape scale  38 . Linear bearings  31   a  and  31   b  positioned between the dispenser housings  46   a  and  46   b  and the common gantry system  28  provide a limited travel positioning system between each of the dispensing heads  54   a  and  54   b  and the common gantry system  28 . Thus, in a system comprised of a single gantry system, the dispensing heads  54   a  and  54   b  can adjust their respective positions in the Y axis direction to correspond to a position of the substrates.  
         [0040]    In still another alternative embodiment, the addition of a second dispense unit within a dispensing head housing is possible and provides the capability to dispense two different materials from a given dispensing head or to dispense the same material from differently configured dispense units, such as from two different needle sizes, a feature shown in FIG. 3B. Two dispense heads can be mounted side by side in a single, wider dispense head housing on each gantry. The dispense heads on each gantry can be fixed to each other in the X and Y axes. If use of a second dispense unit is not anticipated or desired, dispense head housing  46   a  and/or  46   b  may be constructed to eliminate the structure and features required to accommodate the presence of a second optional dispense unit.  
         [0041]    In order to achieve accurate dispensing on chips, it is useful for the dispense units to learn the location and height of the substrates onto which dispensing is to occur before beginning a respective dispensing process. For example, a vision alignment system can be used during the dispensing process so that precise locations and heights are determined. Accurate dispensing can require multiple passes of epoxy or other materials that flow in capillary fashion under a chip and around each interconnection on the chip.  
         [0042]    Each of the dispense units  54   a  and  54   b  has associated with it features used in the dispensing unit for accuracy and efficiency in the dispensing process. Referring to FIG. 4, each head of the dispensing system  10  includes a respective station having a needle calibrator  100 , weight scales  102 , pre-dispense plates  104 , and needle cleaners  106 . Each station can further include a bent needle detector (not shown). The needle calibrator  100  includes a plunger, or switch,  101 , a step block  103 , and a gauged step plate  105 . The height of the needle is determined by activation of the plunger  101  by contact from the needle. The step block  103  is used to calibrate a non-contact laser Z-height sensor, which, if present, is mounted within dispense head housing  30   a . This laser Z height sensor can include those manufactured by Micro-Epsilon of Ortenburg, Germany. The gauged step plate  105  is used to calibrate a contact Z sensor which, if present, is mounted within dispense head housing  30   a . This contact Z sensor can include those described in commonly owned U.S. Pat. No. 6,093,251, the disclosure of which is herein incorporated by reference.  
         [0043]    The frusta conical base of the weight scales  102  is shown, while the dish associated with the weight scales is removed in FIG. 4. The weight scales generally includes a dish, or cylindrical chamber, as well as a removable lid, which allows for dispensing into the chamber, but further acts as a draft shield and an electrostatic shield. The weight scale system and methods to utilize same can include those described in commonly owned U.S. patent application Ser. No. 09/705,080, now U.S. Pat. No. 6,541,063, and U.S. patent application Ser. No. 09/928,112, the disclosures of which are incorporated herein by reference.  
         [0044]    The pre-dispense plates  104  act as surrogate substrates upon which preliminary dispensing can be performed prior to dispensing on actual substrates being processed. The preliminary dispense step allows the condition of the needle and the particular formation of material at the end of the dispensing needle to more closely emulate the condition of the needle that exists after dispensing on actual workpieces. Thus, the preliminary dispense step serves to minimize variations between the first and subsequent products produced. The preliminary dispense step is typically programmed to occur subsequent to actions that could change the condition of the needle, such as dispensing into the weight scale dish or cleaning the needle. The pre-dispense plates  104  can include a ceramic insert which can be removed for cleaning and replaced for additional use. The use of more than one pre-dispense plate  104  allows for an increase in the number of preliminary dispense events possible before operator intervention is required.  
         [0045]    The needle cleaners  106  can include the needle cleaner described in commonly owned U.S. patent application Ser. No. 09/974,022, the disclosure of which is herein incorporated by reference.  
         [0046]    A bent needle detector can be included as part of the needle calibration station. The bent needle detector may have a switch similar to switch  101  associated with it. The switch can have an aperture on its top surface wherein the needle, when straight, enters. If the needle is not straight, it will activate the switch. Activation of the switch can lead to corrective measures in properly aligning the needle.  
         [0047]    Further features included in and associated with each of the multiple dispensers included in the system  10  are machine vision alignment and machine vision inspection. A vision processor can control and process signals received from cameras mounted on the gantry systems, and can provide processed vision signals to a system controller. The cameras may be used: to locate fiducial marks on workpieces loaded into the dispensing system for alignment purposes; to inspect workpieces after material has been dispensed, or some other operation has been performed; and to identify a type of workpiece loaded into the dispensing system.  
         [0048]    As mentioned, to properly transport substrates to a position in preparation for dispensing, the multiple head dispensing unit  10  includes a substrate handling system portion  101 , as shown in FIGS. 1 and 2. The substrate handling system portion  101  prepares and transports the substrates prior to and subsequent to an operation being performed on the substrates in the operations portion of the dispensing unit  10 . Referring to FIGS. 1 and 2, the substrate handling system portion includes magazines  110 , an elevator  112 , pallets  114   a ,  114   b ,  114   c , and  114   d , boats  116 , tracks  118   a  and  118   b , a pusher  120 , a boat shuttle  122  and an overhead gripper  126 . The boat shuttle includes a grabber  124 . The magazines  110  are loaded with a plurality of boats  116 , each boat holding one or a plurality of substrates, or one or a plurality of rows of substrates. These boats  116  may be of a known type, such as an AUER boat, or any other suitable carrier for chips or other substrates to be dispensed upon. The magazines  110  are positioned in a stack near a front portion of the substrate handling system portion  101 . A stack of magazines can be comprised of four magazines  110 , although more than four magazines  110  in a stack is acceptable. Alternatively, less than four magazines can be included in each stack. A plurality of boats  116  are stacked in each of the magazines. Each magazine can hold  5 ,  10 ,  12 , or more boats, for example. The magazines  110  are moveable in a Z axis direction along the height of the elevator  112 . Motion of the magazines  110  in the z axis direction allows the magazines to shift to a position such that a boat  116  is horizontally aligned for removal from a slot in the magazine  110  or for return to a slot in the magazine  110  as necessary. The elevator  112  indexes to the slot height of the boat  116  that is to be removed from the magazine  110 , and subsequent boats thereafter. The elevator  112  further performs scanning of the magazines to perform presence/absence checking of the boats. The elevator  112  can be continuously moved from an upper position to a lower position such that each boat  116  is moved past a sensor, thereby efficiently indicating which boats are present.  
         [0049]    Referring to FIG. 7, pallets  114   a ,  114   b ,  114   c , and  114   d  lie in a horizontal plane on tracks  118 . Pallets  114   a  and  114   b  lie on a common rear track  118   a , while pallets  114   c  and  114   d  lie on a common front track  118   b . The tracks  118  extend from the substrate handling section  101  and through the operations portion  11 . Pallets  114   a  and  114   b  are positioned adjacent to one another on the rear track  118   a . Pallets  114   c  and  114   d  are positioned adjacent to one another on the front track  118   b . The pallets  114  include top plates  117  that can be custom manufactured to accept any of a number of configurations of substrates that are being manufactured. The top plates  117  can be removed from the body of the pallet, such that a replacement top plate or a top plate  117  having a different configuration to receive different substrates can be used. Further, the top plates can be heated in some applications. The pallets  114  are further designed to accept one or a number of boats  116  received from the magazines  110 . In a preferred embodiment, each of pallets  114   a ,  114   b ,  114   c , and  114   d  accepts two boats  116  of substrates. In the example shown, each boat  116  includes three columns of electronic components. Thus, in this example, six columns of electronic components can rest on each pallet simultaneously.  
         [0050]    The pusher  120  is positioned at an outboard end of the magazine  110 . The pusher can be pneumatically actuated, or, in the alternative, the pusher can be actuated using a servomotor or other actuating device. The boat shuttle  122  is preferably positioned with a servo motor, but could in the alternative be actuated pneumatically. Referring to FIGS.  5  and  6 , the boat shuttle  122  is positioned at an inboard end of the magazine  110  and includes a grabber  124  positioned at a height substantially equivalent in height with a boat in the magazine such that the grabber  124  moves in an X axis of motion, indicated by arrow  75 , toward the magazine to grab a boat from the magazine  110 . Alternatively, the grabber  124  can be constructed to move in both the X axis and the Z axis, such that the grabber removes boats  116  from the magazines  110  at differing heights and positions.  
         [0051]    Referring to FIGS. 2, 5 and  6 , the overhead gripper  126  handles and transports boats  116  between the magazine  110  and the pallets  114 . The overhead gripper  126  includes parallel side plates  128 , each having a ledge running along the inside edge of the respective side plate  128 . The ledges provide a narrow shelf to support the longitudinal edges of the boats  116  when the boats are removed from the magazine  110 . The overhead gripper  126  is pneumatically actuated and can move from a position over the pallets  114  to a position to receive the boats  116 . The overhead gripper  126  need not be pneumatically actuated, but may be actuated by a servomotor or other source. In addition, the parallel side plates  128  of the overhead gripper, as shown in FIG. 2, are actuatable to an open or closed position, moving further away from or closer to each other about a centerline such that the space between the parallel side plates increases or decreases. When the overhead gripper  126  is closed, the boat can be pushed into the space between the parallel side plates and be supported on the ledges that run along the bottom edge of the parallel side plates for transport.  
         [0052]    It is desirable to move boats  116  having substrates from a position in the magazines  110  to a fixed position on a pallet  114 , such that the pallets can move through the dispensing system for performance of a dispensing operation on the substrates. Boats  116  positioned in the magazines  110  hold electronic components ready to be dispensed upon. The pusher  120  is actuated to push a boat  116  from the outboard side of the magazine  110  so that the boat is partially extended from the magazine  110 . The overhead gripper  126  is positioned at the inboard side of the magazine  110  in an open position. The boat shuttle  122 , also positioned on the inboard side of the magazine  116 , reaches through the overhead gripper  126  with the grabber  124 , which is mounted on the boat shuttle. As shown in FIG. 5, the grabber  124  grasps the boat  116  and retracts, withdrawing the boat from the magazine  110  and pulling the boat  116  into position in the overhead gripper  126 . Parallel side plates  128  each incorporate a stop feature  129  at the inboard end. When the grabber  124  has completed the X axis stroke of removing the boat  116 , the grabber keeps the boat positioned against the stop features  129  on the overhead gripper  126  such that the boat  116  is substantially snugly held in position. Clamp cylinders  131  mounted on the inside faces of the long parallel side plates  128  of the overhead gripper  126  secure the boat  116  within the overhead gripper  126 . Once the boat  116  is secured, the grabber  124  unclamps and the boat shuttle  122  retracts to a rest position. Thus, the original position of the boat  116  within the magazine  110  is not a factor, since the boats  116  are repeatably and reliably located within the overhead gripper.  
         [0053]    With the boat securely positioned in the overhead gripper, the overhead gripper  126  moves from a position adjacent to the magazine  110  to a placement position over one of the pallets  114   a ,  114   b ,  114   c , and  114   d . The overhead gripper can first transport an individual boat  116  for placement on pallet  114   a , for example. The boat  116  is positioned on the pallet  114   a  and secured into position by a vacuum system which fixedly holds the boats in position. The vacuum system can be selectively disabled and enabled to fix an entire pallet. Alternatively, the vacuum can be applied to specific boat locations within a pallet individually. A vacuum sensor which may be located on one or more of the pallets  114   a ,  114   b ,  114   c , and  114   d  provides feedback if one or more of the parts within the boats  116  is either not present or improperly seated. For example, if one or more parts is/are not properly seated on the vacuum apertures on the top plate, there will be air leakage into the vacuum holes. Because of the air flow, there is some loss of vacuum which the sensor detects as a low vacuum level. The pallet  114   a  remains in position while the overhead gripper  126  returns to a position at the inboard side of the magazine  110  to load a next boat  116 . Using the same method as that described above, a second boat  116  is removed from the magazine  110  and transported by the overhead gripper  126  to a second position on pallet  114   a . Upon securely fastening the boat to pallet  114   a , pallet  114   a  is fully loaded. In alternative configurations, for example if boats  116  each contain only one row of substrates, pallets  114  may have room for more than two boats  116 . The gripper  126  is accordingly used to load as many boats  116  onto the pallet  114  as can be accommodated by a particular configuration.  
         [0054]    Pallet  114   b  shares a track  118  with pallet  114   a , as seen in FIG. 2 and FIG. 7. For example, pallets  114   a  and  114   b  are positioned adjacent one another on a rear track  118   a  of the dispensing system  10 . The overhead gripper  126 , repeating the placement process, works to load a first and a second boat  116  onto pallet  114   b  following the same process by which boats are loaded onto pallet  114   a . Fully loaded pallets  114   a  and  114   b  traverse along the rear track  118   a  into the operations portion of the dispensing system  10  for a dispensing process. The pallets  114   a  and  114   b  are separated by an adjustable distance, as shown in FIG. 7, by a pneumatic actuator within the operations portion. While at the load station, there is substantially no dead space between the pallets  114   a  and  114   b , providing a more compact system. The pallets, however, may separate a required distance when the pallets are positioned in the dispenser in the operating portion. Thus, the dispenser heads can be appropriately positioned a distance from one another and the pallets  114   a  and  114   b  can separate to coordinate with the ability of the dispensers to dispense on respective pallets. The adjustable distance allows the loading area for the dispensing system  10  to be compact.  
         [0055]    Upon entry of the pallets  114   a  and  114   b  into the operations portion in the direction indicated by arrow  72 , the dispensing process begins. The two dispenser heads shown in FIGS. 2 and 7 move independently of one another. Thus, when pallets  114   a  and  114   b  move into a position for dispensing, the dispensers move to the side of the operations portion at which the pallets are located. For example, the dispensers move to the rear portion of the system when dispensing on pallets  114   a  and  114   b , so that dispensing can occur on pallets  114   a  and  114   b  substantially simultaneously, while pallets  114   c  and  114   d  are being removed after having been dispensed upon by the dispensing heads  28 . This allows for full throughput and maximum use of the dispensers so that at approximately the time at which dispensing is completed on one set of pallets, the other loaded pallets are moved into the dispenser. The process of dispensing, thus, continues cyclically.  
         [0056]    Typically, the process of dispensing is comprised of the steps of measuring the height of the top surface of the substrates in the Z direction using either a contact or non-contact height sensor, determining the precise position of the substrate in X and Y by means of a machine vision system, calculating any required X/Y offset corrections based on the precise position, and performing the required dispensing steps prescribed in a pattern recipe. The pattern recipe provides a programmatic means by which the dispensing system is instructed what and how to dispense on the substrates.  
         [0057]    In addition, prior to dispensing, a vision system has the ability to do a mass alignment by doing an alignment check on substrates in a pallet, allowing alignment to be checked for multiple substrates at once. A camera and other hardware can be incorporated into the materials handling system portion of the dispensing system. While a dispensing process is in progress, substrates on pallets prepared for a next dispense cycle can be aligned using the vision system in the materials handling portion. The alignment of each substrate can thus be learned relative to fiducials on the pallets themselves. This is advantageous in that it further improves throughput efficiency by checking alignment before pallets are inserted for dispensing, such that the vision system in the dispenser, having access to the pre-alignment information obtained by the material handling portion, need only check fiducials on the pallets themselves, rather than check alignment fiducials on each of the substrates on the pallet, which may be numerous. In addition, the off-line camera in the materials handling portion can perform post-dispense inspections.  
         [0058]    While the electronic substrates on pallets  114   a  and  114   b  receive material during dispensing, pallets  114   c  and  114   d  are loaded with additional boats holding substrates. Thus, a process is performed on the substrates transported along the rear track  118   a  substantially simultaneously with a loading process being conducted on the front track  118   b , as shown in FIG. 7. The loading process on pallets  114   c  and  114   d  is a repeat of the loading process on pallets  114   a  and  114   b . When loading is completed, pallets  114   c  and  114   d  traverse along the front track  118   b  into the operations portion  11  in a direction indicated by arrow  74  to a position for dispensing. Upon completion of the dispensing process, the dispensing heads move along respective gantry systems  28  to re-position over the front rail for the next dispensing process. Pallets  114   a  and  114   b  traverse the rear track along the X axis to return to a rest position in the loading/unloading area of the substrate handling system.  
         [0059]    Pallets  114   a  and  114   b  are prepared for unloading. The boats  116  on pallets  114   a  and  114   b  are returned to the magazine  110  from which they were removed. The overhead gripper  126  removes a boat  116  from pallet  114   a  and transports it to a position at the inboard end of the magazine  110 . The boat shuttle  122  is positioned to push the boat back into the magazine  110 . As shown in FIG. 6, the grabber  124  remains in a closed position to push the boat partially into the magazine. The boat shuttle  122  retracts. A second pusher  125 , mounted to the boat shuttle, extends to a position behind the boat  116 . The boat shuttle  122  advances a second time to complete pushing the boat  116  into the magazine  110 . The second pusher  125  allows use of a boat shuttle  122  with a substantially short stroke compared to that required if the grabber  124  is used to push the boat completely into the magazine  110 . Alternatively, however, the grabber  124  can be used to push the boat into the magazine  110  without use of a second pusher  125  mounted to the boat shuttle. Boats  116  are replaced in the same magazine slot from which they were taken prior to processing. The electronic components in each boat can be tracked by placing the electronic components in the same boat position, in the same slot position of the same magazine from which they are removed.  
         [0060]    In embodiments of the invention, magazines hold a plurality of boats that are prepared for dispensing, and an elevator positions the magazines at varying heights whereby boats can be received. In an alternative embodiment, continuous flow loaders and unloaders are used to insert boats into the dispensing system and remove boats from the dispensing system after dispensing has been completed. Magazines are presented at one location and retrieved from a separate location after processing. A queue of unprocessed magazines and an additional queue for processed magazines allows for time intervals between servicing.  
         [0061]    In embodiments of the invention, the overhead gripper is used to transport boats from the magazines to the pallets, and from the pallets to the magazines. In other embodiments of the invention, the overhead gripper can be fitted to automatically change the top plates of the pallets as required, thus improving change over operations in the system. Further, the top plates are heated, and if the top plates remain hot, the top plates would have to be allowed to cool before manual handling. Automatically changing the top plates with the overhead gripper saves considerable cooling time.  
         [0062]    In embodiments of the invention, a single elevator is used to move magazines to varying heights and to provide substrates for both dispensing heads. Alternative embodiments of the invention can include a second elevator positioned on an opposite side of the substrate handling system to further provide magazines to the system. The use of two elevators doubles the number of magazines available to the system, thereby substantially increasing the time interval between operator interventions, which are a time cost to production. Additionally, a plurality of stacks of magazines can be introduced into the system, such that one, two, three, four, or more stacks of magazines are positioned at respective areas around the substrate handling system. An embodiment of the present invention having two magazine stacks is depicted in FIG. 8. An increase in the number of magazines also reduces the need for operator intervention.  
         [0063]    In embodiments of the invention, the elevator can be used to preheat and/or post-heat parts outside of the machine process to increase throughput by reducing gating process time. Likewise, heating a continuous flow loader/unloader can reduce cycle time and increase throughput, while also minimizing process variations by causing all parts to experience the same thermal profile. Further, heating the elevator or continuous flow loader allows the system to monitor pre-heat and post-heat times.  
         [0064]    In figures depicting the dispensing system of the current invention, a right-handed system is shown. A modular design of the system allows the system to be built in a right-handed or a left-handed orientation. The ability to assemble systems in either of these two orientations allows users of the system to best optimize the productivity and workflow in a given facility by locating the material handler portion where loading and unloading operations can be performed most efficiently.  
         [0065]    In embodiments of the invention, some of the actuators in the substrate handling portion of the dispensing system are pneumatic. As is apparent to one skilled in the art, servo driven or stepper driven motors can be used to actuate devices in the dispensing system, such as the overhead gripper, the boat shuttle, the magazines, and the pallets.  
         [0066]    Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements are intended to be within the scope and spirit of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention&#39;s limit is defined only in the following claims and the equivalents thereto.