Abstract:
In automated gluing systems for semiconductor device manufacture, an automatic shutter system is provided for use with an adhesive dispenser that is configured to deposit adhesive for joining elements during final assembly processes. A shutter is configured to interpose itself between a needle tip of the dispenser and a working surface, on which devices in process are positioned, while the dispenser is in a ready position and not actually delivering adhesive, and to withdraw from the interposed position as, or immediately before the needle tip descends to a dispensing position to deposit adhesive on a device. In this way, drops of adhesive that fall from the needle tip while in the ready position are captured by the shutter and prevented from falling onto a device in process in an unintended location of the device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    This disclosure is related generally to the field of adhesive dispensing systems, and in particular to systems for dispensing adhesives in automated assembly systems where the position and volume of the dispensing are critical, including systems for assembly and packaging of semiconductor based devices, and electronic devices in general. 
         [0003]    2. Description of the Related Art 
         [0004]    A number of different types of adhesives are commonly used in the “back end” processes of semiconductor device manufacture, and in assembly of electronic devices. Examples include thermally conductive adhesives used to mechanically bond semiconductor dice to lead frames and to transmit heat to the lead frames; adhesives used to hermetically seal covers onto microelectromechanical devices formed on semiconductor wafers; adhesives used to attach lenses to semiconductor dice over optical sensors; solvent adhesives used to assemble plastic components; elastomeric adhesives to join components and dampen vibrations between the components, etc. Very often, adhesives must be deposited with great precision to avoid damaging the devices being bonded. In most cases, these adhesives are applied onto one of the surfaces to be bonded by automatic dispensers as part of an automated assembly process. Misplacement of such adhesives can often cause cosmetic or substantive damage to a device that will render the device unsalable. 
         [0005]    One example of an automated adhesive dispensing system is shown in  FIGS. 1 and 2 , which are diagrammatic representations of a known adhesive dispensing system  100  for applying adhesive around the perimeters of optical sensors. The adhesive is used to bond lenses over the sensors, for use in small cameras such as, e.g., cell phone cameras. 
         [0006]    The dispensing system  100  is part of a robotic assembly system for packaging semiconductor devices, and is carried by a first robotic arm  102  of the assembly system. The assembly system also includes a second robotic arm  120  that carries a placing fixture  124  for placing lenses  126 , which is shown in  FIG. 2  for context. The first robotic arm  102  carries a support fixture  103  to which an adhesive dispenser  104  and a fiducial camera  116  are coupled. The first arm  102  and fixture  103  cooperate to move the dispenser  104  in the X, Y, and Z axes. In some cases, the arm  102  is movable in two axes, but typically, the arm is in the form of a gantry that transports the support fixture  103  in the X axis over a working surface of the system, while the fixture is in the form of a carriage that carries the dispenser  104  and moves in the Y axis along the arm, and the dispenser moves in the Z axis relative to the fixture and the arm. 
         [0007]    The adhesive dispenser  104  comprises a dispenser body  105  and a nozzle  107  that includes a needle tip  106 . The dispenser  104  is configured, in the example shown, to deposit adhesive onto semiconductor dice  110  in which optical sensors  112  have been formed. The fiducial camera  116  is configured to detect fiducial marks on each die  110 . The dice  110  are mounted in quantities of about 50-100 on a carrier  114 , sometimes referred to as a stiffener, having a size of about 400-1000 cm 2 . The carrier  114  is moved though various stages of the assembly process by a transport system, which is not shown. 
         [0008]    The second robotic arm  120  carries a second support fixture  122  to which a component placement device  124  is coupled for placing the lenses  126 . 
         [0009]    In the stage depicted in  FIGS. 1 and 2 , the carrier  114  is brought into a fixed position under the arm  102  where it stays until completion of the stage. Once the carrier  114  is in position, the system goes into an acquisition mode, in which the first arm  102  and support fixture  103  move back and forth across the carrier  114  while the camera  116  scans the surface of each die  110  to read the fiducial marks and determine the precise location and orientation of each optical sensor  112 . During this detection and location step of the process, the adhesive dispenser  104  is held by the support fixture  103  in a ready position, as shown in  FIG. 1 , in which the needle tip  106  is retracted a short distance from the die  110 . Once all the sensors have been located, the system goes into a dispensing mode, in which the support fixture  103  moves the dispenser  104  in the Z axis to a dispensing position, bringing the needle tip  106  of the nozzle  107  into contact or near contact with a top surface of a first one of the die  110 , as shown in  FIG. 2 . The arm  102  and fixture  103  cooperate to move the dispenser  104 , which deposits a bead of adhesive or a series of adhesive dots around the perimeter of the sensor  112 . The arm  102  and support fixture  103  again move back and forth across the carrier  114 , this time moving the dispenser to deposit adhesive around the sensor  112  of each of the die  110 . As the dispenser  104  finishes with one die  110  and is moved to the next, the dispenser  104  is not returned to the ready position, but is lifted from the dispensing position only far enough to ensure that the needle tip  106  will not make contact with any die  110  or other element that it might pass over as it moves. When adhesive has been placed on every die  110 , the dispenser  104  is returned to the ready position and the second robotic arm  120  carries the second support fixture  122  and component placement device  124  to deposit a lens  126  over each of the optical sensors  112  in a pick-and-place operation, on top of the previously deposited adhesive. The carrier  114  is then transported to a curing station while a new carrier is moved into position. 
         [0010]    It is important that the deposition of the adhesive be precisely controlled both in terms of volume and location. When the lens  126  is placed over the adhesive, capillary action of the fluid adhesive between the lens and the surface of the semiconductor die  110  draws the lens into close contact with the die, with only a thin film of adhesive between the lens and the die. If too much adhesive is deposited, it will flow onto the surface of the optical sensor, which will ruin the device, while too little adhesive will not properly bond the lens to the die. If the adhesive is not positioned correctly, it will either fail to contact the lens along one or more edges, or will again flow onto the sensor. 
         [0011]    Additionally, the adhesive is preferably very thin, having a viscosity approaching that of water. If the adhesive is too viscous, it can fail to flow properly when the lens is positioned, leaving an uneven surface, so that the lens is out of plane. Furthermore, adhesive viscosity controls the thickness of the film between the lens and the surface of the die, which in turn controls the distance of the lens from the sensor. Thus, if the adhesive is too viscous, the lens will be seated farther from the sensor, and the focal length will be adversely affected. 
         [0012]    In order to adequately control the adhesive deposition, the needle tip  106  of the adhesive dispenser  104  is very fine, having a bore, typically, of around 150-250 μm. Dispensers typically employ one of two types of mechanisms to meter the adhesive. One class of dispensers employ mechanical control, such as by a screw-driven plunger, in which movement of a plunger in the body of the dispenser forces fluid out the tip  106 . Rotation of a drive screw advances the plunger within a syringe to force fluid from the needle tip. Control of fluid volume can be very precise because each rotation or fractional rotation of the screw moves the plunger a known distance, displacing a calculable volume within the syringe, and forcing an equal volume of fluid adhesive from the nozzle. 
         [0013]    The other class of dispensers uses pneumatic pressure behind the adhesive in the dispenser to force fluid through the tip  106 . Pneumatic dispensers are not as inherently precise as screw-driven dispensers because gas is compressible, so that for a given volume of gas moved into the dispenser it is not inherent that an equal volume of adhesive will be dispensed. Nevertheless, pneumatic dispensers can be precisely controlled, provided factors such as the viscosity and rheology of the adhesive, and the bore and length of the needle tip, are accounted for. Pneumatic dispensers are usually less expensive, and maintenance is easier and faster. However, in general, mechanically controlled dispensers are preferred for very low viscosity adhesives, because fluid flow can be closely and directly controlled, making it easier to maintain the flow of adhesive through the nozzle to within tolerances. 
       BRIEF SUMMARY 
       [0014]    In automated adhesive systems for semiconductor device manufacture, an automatic shutter system is provided for use with an adhesive dispenser system that is configured to deposit adhesive for joining elements during final assembly processes. According to an embodiment, an arm is coupled to the adhesive dispenser system so as to be movable relative to the adhesive dispenser. The arm carries a shutter that it moves between a closed position, in which the shutter is interposed between a nozzle of the adhesive dispenser and a working surface, and an open position, in which the shutter is not interposed between the nozzle and the working surface. 
         [0015]    Operation of the arm and shutter is controlled so that the shutter is moved to the closed position while the dispenser is in a ready position and not actually delivering adhesive, and to the open position as, or immediately before the needle tip descends to a dispensing position to deposit adhesive on a device. In this way, drops of adhesive that fall from the needle tip while in the ready position are captured by the shutter and prevented from falling onto a device in process in an unintended location of the device. 
         [0016]    A number of different structures of the shutter system are shown and described, according to respective embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]      FIGS. 1 and 2  are side views of an adhesive dispenser system according to known art, in diagrammatic form, in, respectively, a ready position and a dispensing position. 
           [0018]      FIGS. 3A and 3B  are side views of an adhesive dispenser system with a shutter system according to one embodiment, presented in diagrammatic form, in, respectively, a ready position and a dispensing position. 
           [0019]      FIGS. 4A and 4B  are side views of an adhesive dispenser system with a shutter system according to another embodiment, presented in diagrammatic form, in, respectively, a ready position and a dispensing position. 
           [0020]      FIGS. 5A and 5B  are views of an adhesive dispenser system with a shutter system according to another embodiment, presented in diagrammatic form, in which  FIG. 5A  is a side view of the adhesive dispenser system in a ready position, and  FIG. 5B  is a front view of the system of  FIG. 5A , in dispensing position. 
           [0021]      FIGS. 6A and 6B  are side views of an adhesive dispenser system with a shutter system according to another embodiment, presented in diagrammatic form, in, respectively, a ready position and a dispensing position. 
           [0022]      FIG. 6C  is a cross-sectional diagrammatic view of a portion of the shutter system of  FIG. 6A , taken along lines  6 C- 6 C. 
           [0023]      FIGS. 7A and 7B  are side views of an adhesive dispenser system with a shutter system according to another embodiment, presented in diagrammatic form, in, respectively, a ready position and a dispensing position. 
           [0024]      FIGS. 8A and 8B  are side views of an adhesive dispenser system with a shutter system according to another embodiment, presented in diagrammatic form, in, respectively, a ready position and a dispensing position. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    With regard to the screw-driven adhesive dispensing systems referred to in the background, the inventors have found that there are problems associated with such systems that can interfere with their efficient operation. In the dispenser of these systems, the screw-driven plunger is powered by an electric motor. In high-speed production environments, the motor operates at an increased duty cycle, generating increased heat, which warms the adhesive in the dispenser. While the adhesive is typically a two-part adhesive that cures by catalysis, heat accelerates this process. Thus, the adhesive can begin to cure while still in the dispenser. This results in a more viscous adhesive, which can affect the final product, as discussed with reference to example described in the background. Additionally, the more viscous adhesive requires greater force to dispense through the very small needle tip, which increases the load on the motor, requiring more power, and generating more heat, while restricting fluid flow. Ultimately, in the worst case, the needle tip can become completely blocked, so that no adhesive is dispensed. When this occurs, the system can continue in operation without depositing adhesive, so that the lenses are placed on a dry surface. In some cases, such a condition can continue for some time before being discovered, resulting in a significant amount of rework or ruined product. 
         [0026]    One solution is to use a pneumatically pressurized dispenser, which eliminates the heating problem. While such dispensers require care in controlling fluid flow during operation, the inventors believe that it is a generally viable solution. Unfortunately, the inventors have encountered another problem that can occur, most frequently in association with pneumatically pressurized systems, although mechanically pressurized systems are not immune. 
         [0027]    As noted above, to achieve precise positioning of adhesives, many adhesive dispensing systems use optical pattern recognition systems that scan the surface of each die to locate fiducials to ensure that the deposit of adhesive is correctly positioned and oriented. As the camera moves back and forth over the dice on the carrier to determine the position and orientation of each of the sensors, a drop of adhesive can drip from the needle tip of the dispenser. If it lands on one of the sensors, it will ruin that device, because, even if it were discovered immediately, it could not be wiped away without damage to the sensor. Furthermore, such drops are generally miniscule, and nearly impossible to detect by visual inspection, so they are usually not discovered until after the devices go through several additional packaging and assembly steps, when the sensors are tested. In functional tests, a drop appears to be a group of dead cells, producing a black spot on an image, resulting in rejection of the entire part, both the lens and the die. Thus, not only are the semiconductor device and lens discarded, but the additional time and materials thereafter expended to move that device toward completion were also wasted. Nevertheless, the expense of losses due to adhesive drips, which are relatively rare, is significantly less than losses arising from premature curing of adhesive caused by parasitic heat. To the extent that damage caused by adhesive drips may have been previously recognized as a problem, it appears that manufacturers have been willing to accept them as an additional production cost. However, most manufacturers continue to employ screw-driven systems for applications that require low-viscosity adhesives and a high degree of control over volume and placement. 
         [0028]    The inventors believe that damage caused by adhesive drips can be substantially reduced or eliminated using a simple and inexpensive mechanism, various embodiments of which are described below. 
         [0029]      FIGS. 3A and 3B  are diagrammatic representations of an adhesive dispenser system  200  according to a first embodiment. Many of the elements are substantially identical to corresponding elements described with reference to the prior art, and so will not be described in detail, and will be indicated by the same reference numbers. 
         [0030]    In addition to elements previously described, the dispenser system  200  includes a shutter system  210  that is configured to interpose a shutter  212  between the needle tip  106  and the working surface below except while the dispenser  104  is in the process of dispensing adhesive. The shutter system  210  comprises a pivot arm  214  that is rotatably coupled to a first support bracket  218  at a pivot point  216 , the support bracket serving to couple the pivot arm to the support fixture  103 . A bumper  220  is coupled to a first end of the pivot arm  214 , and bears against an upper surface of the dispenser body  105  while the dispenser  104  is in the ready position, as shown in  FIG. 3A . The shutter  212  is coupled to a second end of the pivot arm  214 . A second support bracket  224  is coupled to the support fixture  103  and supports a stopper pin  222  that extends across a plane of rotation of the pivot arm  214 , limiting the range of rotation of the arm. 
         [0031]    While the dispenser  104  is in the ready position, as shown in  FIG. 3A , the bumper  220  of the pivot arm  214  bears against the upper surface of the dispenser body  103 , thereby holding the pivot arm in a closed position, as shown, in which the shutter is interposed between the needle tip  106  and a working surface  115 . Thus, while the dispenser system  200  is operating in the acquisition mode, for example, traversing back and forth across the working surface to detect fiducials, the shutter  212  is positioned directly beneath the outlet of the needle tip  106 . Any adhesive that drips from the needle tip will strike the shutter  212  rather than falling to the working surface. When the dispenser system  200  switches to dispenser mode, the dispenser body  105  is lowered by the support fixture  103  to deposit adhesive on the product in process. As the dispenser body  105  drops, the bumper  220  is no longer supported by its upper surface, so the pivot arm  214  rotates outward, drawing the shutter  212  out from below the needle tip  106  as the tip drops toward the working surface. The pivot arm  214  rotates around the pivot point  216  until it is arrested by the stop pin  222  in an open position, as shown in  FIG. 3B , where it remains while the system  200  is in dispenser mode. When the dispenser  104  is returned to the ready position, the dispenser body  105  contacts the bumper  222  as the body is raised, and pushes the bumper upward, causing the pivot arm  214  to rotate back to the closed position, in which the shutter  212  is again positioned under the needle tip  106 . 
         [0032]    In dispenser systems that are used in high-speed production, movement of the dispenser body  105  from the ready position to the dispensing position can be extremely fast, and in some cases, might exceed the speed at which the pivot arm  214  can rotate the shutter  212  out of the path of the descending needle tip  106 . Responsiveness of the pivot arm  214  can be modified by adjusting the balance of the arm. If additional weight is added to the pivot arm  214  at or near the bumper  222 , the arm will more quickly rotate away from the closed position, as the added weight more quickly overcomes static friction at the pivot point, and the vector of force acting to rotate the arm becomes more vertical. However, if the dispenser moves at speeds that approach or exceed the acceleration of gravity, it can become impossible for a gravity-operated pivot arm to move with sufficient speed. In such cases, one or more springs can be employed to reduce response time. For example, a torsion spring positioned at the pivot point  216  and configured to bias the pivot arm toward the open position will increase the speed of response of the pivot arm  214 . 
         [0033]    In a dispenser system like the one described with reference to  FIGS. 1 and 2 , in which the bore of the needle tip  106  has a diameter on the order of 200 μm, the volume of individual drops is generally miniscule. Thus, even if an upper surface  213  of the shutter  212  is flat, adhesive fluid that drips onto the surface will harden long before it can run off the edge of the shutter. Nevertheless, according to some embodiments, the upper surface  213  is dished to form a depression to receive drips from the tip  106 . This provides an increased capacity, which may be beneficial in the event of a malfunction that results in a greater rate of dripping, and is also beneficial in systems that employ a larger bore in the needle tip  106 , and so will tend to produce larger drops. 
         [0034]    It can be seen, with reference to  FIGS. 3A and 3B , that the shutter system  210  is mechanically very simple, and can be adapted to operate with existing dispenser systems relatively inexpensively. Because it is entirely mechanically operated, and is controlled by movement of the dispenser body, it does not require any modification of electronic systems or software operating systems that control operation of the dispenser. In applications where an adhesive dispenser is employed in the assembly of devices like the optical sensors described above, loss of even a small percentage of the products in process can become expensive, and preventing those losses can quickly recover the cost of adding a shutter system to an existing dispenser system. 
         [0035]    In prototype tests with a conventional dispenser system, the inventors installed a shutter system that operates substantially as described with reference to the embodiment of  FIGS. 3A and 3B , which was employed in assembly of thousands of products over a period of months, during which time damage and loss due to adhesive drips was completely eliminated. 
         [0036]    Turning now to  FIGS. 4A and 4B , an adhesive dispensing system  230  is shown, according to another embodiment, and that includes a shutter system  240 . The shutter system  240  comprises a screw arm  242  to which a shutter  212  is coupled. Rotation of the screw arm  242  moves the shutter  212  between a closed position, as shown in  FIG. 4A , and an open position, as shown in  FIG. 4B . A first support bracket  244  is coupled to the support fixture  103  and a second support bracket  246  is coupled to the dispenser body  105 . The screw arm includes long-lead threads  248  along at least a portion of its length, and is coupled to the first support bracket  244  so as to be rotatable about its own longitudinal axis. A sliding nut  250  is rigidly coupled to the second support bracket  246  and is threaded onto the screw arm  242  so as to engage the threads  248  of the screw arm. Vertical movement of the sliding nut  250  relative to the screw arm  242  compels rotation of the screw arm. 
         [0037]    While the dispenser  104  is in the ready position, the screw arm  242  and shutter  212  are in the closed position, as shown in  FIG. 4A . When the dispenser  104  moves to the dispensing position, the vertical movement of the dispenser body  105  moves the sliding nut axially along the screw arm  242 . The engagement of the nut  250  with the threads  248  of the screw arm  242  causes the screw arm  242  to rotate with respect to the dispenser  104 , which rotates the shutter  206  to the open position and out from beneath the needle tip  106 , as shown in  FIG. 4B . The dispenser  104  is thus able to dispense adhesive as required for the particular process. When the dispenser body  105  returns to the ready position, movement of the nut  250  relative to the screw arm  242  again causes the screw arm to rotate, rotating the shutter  212  back into the closed position. 
         [0038]    As with the embodiment described with reference to  FIGS. 3A and 3B , the shutter system  240  of the embodiment of  FIGS. 4A and 4B  is entirely mechanically operated, and controlled by movement of the dispenser body  105  relative to the support fixture  103 . However, the shutter system  240  is not dependent upon gravity for operation, but is controlled by the position of the sliding nut  250  relative to the screw arm  242 . 
         [0039]      FIGS. 5A and 5B  are diagrammatic representations of a dispenser system  290  that includes a shutter system  300 .  FIG. 5A  is a side view of the dispenser system  290  in the ready position, with the shutter system  300  in the closed position.  FIG. 5B  is a front view of the dispenser system  290  in the dispensing position, with the shutter system  300  in the open position. The shutter system  300  includes a arm  302  that has a cam slot  304  and a shutter  212 . The swing arm  302  is rotatably coupled to the support fixture  103  via a pivot pin  306 , and constrained by a cam follower  308  that is coupled to the dispenser body  105  and that traverses the cam slot  304 . 
         [0040]    While the dispenser system  290  is in the ready position, the swing arm  302  hangs from the pivot pin  306  and supports the shutter  212  in the closed position, as shown in  FIG. 5A . When the dispenser system  290  moves to the dispensing position, the dispenser body  105 , with the cam follower  308  attached, drops toward the working surface  115 . As the cam follower  308  moves down the cam slot  304 , the shape of the cam slot cooperates with the cam follower to cause the swing arm  302  to rotate around the pivot pin  306 , moving the shutter  212  to an open position, as shown in  FIG. 5B . Conversely, when the dispenser body  105  moves back to the ready position, the cam slot  304  cooperates with the cam follower  308  to move the shutter  212  back into the closed position under the needle tip  106 . 
         [0041]    As with previously described embodiments, the embodiment of  FIGS. 5A and 5B  is mechanically driven, controlled by movement of the dispenser body  105 . The position of the swing arm  308  and shutter  212  are positively controlled at any given position of the dispenser body  105  by the intersection of the cam follower  308  and the cam slot  304  at that position. 
         [0042]      FIGS. 6A-6C  are diagrammatic representations of a dispenser system  260  that includes a shutter system  270 , according to another embodiment. The dispenser system  260  includes a support fixture  130  to which a dispenser  132  is rigidly coupled. To move the dispenser  132  from the ready position, as shown in  FIG. 6A  to the dispensing position, as shown in  FIG. 6B , the dispenser does not move relative to the support fixture  130 , but the support fixture extends downward with the dispenser. 
         [0043]    The shutter system  270  includes a screw arm  272  to which the shutter  212  is coupled, the screw arm  272  also includes long-lead threads  248  extending along a portion of its length, and splines  273  extending along a portion of the screw arm at a first end thereof. A first support bracket  274  is coupled to the support fixture  130  and to the first end of the screw arm  272 . A motor  276  is coupled to the support fixture  130 , and rotationally coupled to the screw arm  262 , as will be described in more detail below with reference to  FIG. 6C . While the screw arm  272  is rotationally coupled to the motor  272 , it is slidably coupled, relative to the motor  272  and support bracket  274 . A second bracket  278  is also coupled to the support fixture  130  and rigidly supports a sliding nut  280 , which engages the threads  248  of the screw arm  272 . 
         [0044]      FIG. 6C  is a partial cross-sectional view of the first support bracket  274  and screw arm  272 , taken along lines  6 C- 6 C of  FIG. 6A . The first support bracket  274  supports a splined gear  282  that has a splined aperture  284  through which the first end of the screw arm  272  passes, with the splines  273  of the screw arm engaging the splined aperture of the gear. The motor  276  comprises a motor shaft  286  and a helical drive gear  288 , which engages helical gear teeth on the outside of the splined gear  282 . 
         [0045]    Rotation of the motor  276  is transmitted by the motor shaft  286  and drive gear  288  to the splined gear  282  and thence to the screw arm  272 . Rotation of the screw arm  272  applies an axial force to the sliding nut  280 , which causes relative axial movement between the screw arm and the sliding nut. Because the first and second support brackets  274 ,  278  are both rigidly fixed to the support fixture  130 , the sliding nut  280 , supported by the second support bracket, cannot move relative to the splined gear  274 , which is supported by the first support bracket. Thus, when the screw arm  272  rotates, the screw arm itself is compelled to move axially. The splined engagement of the screw arm  272  and the splined gear  282  permits the screw arm to slide within the splined gear while remaining rotationally coupled thereto. 
         [0046]    The dispensing system  260  is configured to signal the motor  276  as it initiates movement from the ready position to the dispensing position. The motor  276  is controlled to rotate a preselected number of rotations, which are transmitted to the screw arm  272 . Rotation of the screw arm  272  rotates the shutter  212  from the closed position to the open position, and at the same time lifts the screw arm relative to the dispenser  232  and support fixture  130  because of the axial force applied to the sliding nut  280 . This raises the shutter  212  a distance that is sufficient to prevent the shutter from striking the working surface as the dispensing system  260  drops to the dispensing position. When the dispensing system  260  returns to the ready position, another signal is sent to the motor  276 , which is controlled to rotate in the reverse direction the same number of rotations, to return the screw arm  272  and shutter  212  to the closed position. Various methods for electronic control and timing of the embodiments of  FIGS. 6A-8B  will be discussed after the detailed description of the structure of the embodiment of  FIGS. 8A and 8B   
         [0047]      FIGS. 7A and 7B  are diagrammatic representations of a dispenser system  300  that includes a support fixture  130 , a dispenser  132 , and a shutter system  310 , according to another embodiment. The support fixture  130  and dispenser  132  of the dispenser system  300  are rigidly coupled, so that, when moving from the ready position to the dispense position, both translate in the Z axis. Thus, as with the embodiment of  FIGS. 6A-6C , the shutter  212  must be moved, relative to the dispenser  132  and support fixture  130 , in the plane defined by the X and Y axes in order to clear the needle tip  106 , and also in the Z axis so as not to strike the working surface as the support fixture  130 , to which it is coupled, drops to bring the dispenser system  132  to the dispensing position. 
         [0048]    The shutter system  310  includes a first translating arm  314  and a second translating arm  316  to which the shutter  212  is coupled. The first translating arm  314  is slidingly coupled to the support fixture  1  via a first support bracket  318  which also houses a first solenoid  320 . The second translating arm  316  is slidingly coupled to the first translating arm  314  via a second support bracket  322  which also houses a second solenoid  324 . First and second stops  326 ,  328  are coupled to the first translating arm  314 , and third and fourth stops  330 ,  332  are coupled to the second translating arm  316 . A first extension spring  334  is coupled to the first translating arm  314  between the second stop  328  and the first support bracket  318 , and a second extension spring  336  is coupled to the second translating arm  316  between the fourth stop  332  and the second support bracket  322 . 
         [0049]    The first and third stops  326 ,  330  limit extension of the first and second translating arms  314 ,  316 , respectively, and the second and fourth stops  328 ,  332  limit retraction of the first and second translating arms, respectively. The first and second extension springs  334 ,  336  bias the first and second translating arms  314 ,  316 , toward full extension, as indicated by arrows E 1  and E 2 . When energized, the first solenoid  320  applies to the first translating arm  314  a retraction bias, indicated by arrow R 1  in  FIG. 7B , and when energized, the second solenoid  324  applies to the second translating arm  316  a respective retraction bias, indicated by arrow R 2  in  FIG. 7B . 
         [0050]    While the dispenser  132  is in the ready position, the first and second solenoids  320 ,  324  are not energized, so that the first and second translating arms  314 ,  316  are maintained in their respective extended positions by the biasing forces of the first and second extension springs  334 ,  336 , and the shutter  212  is maintained in the closed position, as shown in  FIG. 7A . When the dispenser begins to move toward the dispensing position, the first and second solenoids  320 ,  324  are energized, which overcomes the bias of the respective extension springs and causes the first and second translating arms  314 ,  316  to retract to the limits permitted, respectively by the second and fourth stops  328 ,  332 , moving the shutter  212  to the open position, as shown in  FIG. 7B . While the dispenser  132  remains in the dispensing position, the first and second solenoids  320 ,  324  remain energized to hold the translating arms  314 ,  316  in their respective retracted positions and maintain the shutter  212  in the open position. When the dispenser system  130  returns to the ready position, the first and second solenoids  320 ,  324  are de-energized, whereupon the first and second translating arms  314 ,  316  return to their respective extended positions in response to the bias of the first and second extension springs  334 ,  336 , returning the shutter  212  to the closed position. 
         [0051]    Retraction and extension of the first translating arm  314  moves the second translating arm  316  and the shutter  212  in the Z axis, while retraction and extension of the second translating arm moves the shutter in the X axis. According to an embodiment, when moving the shutter  212  from the closed to the open positions, the second translating arm  316  is retracted earlier than the first translating arm  314  so that the shutter  212  is moved laterally beyond the end of the needle tip  106  before the first translating arm lifts the second translating arm and shutter. In contrast, when moving the shutter  212  from the closed to the open positions, the first translating arm  314  is extended before the second translating arm  316  so that the shutter  212  is below the end of the needle tip  106  before the second translating arm extends the shutter toward the closed position. 
         [0052]    Provision of timing of, and power for energizing of the first and second solenoids is well within the abilities of one of ordinary skill in the art. Integration of the shutter system  302  with the operation of the dispenser system  300  can be accomplished in a number of different ways, including by methods similar to those discussed with reference to the embodiment of  FIGS. 6A-6C . 
         [0053]    According to another embodiment, a shutter system is similar in many respects to that described with reference to  FIGS. 7A and 7B , but is coupled to an adhesive dispensing system like the dispensing system  200  of  FIGS. 3A and 3B  in which the support fixture  102  does not translate with the dispenser  104 . Thus, provided the shutter system is coupled to the support fixture, there is usually no requirement that the shutter move in the Z axis. In such an application, the first translating arm  314  of the embodiment of  FIGS. 7A and 7B  need not be slidably coupled to the first support bracket  318 , but can be rigidly coupled. Likewise, the first solenoid  320 , the first extension spring  334 , and the first and second stops  326 ,  328  can be eliminated. Thus, only the second translating arm  316  retracts when the dispenser of the system moves to the dispensing position. 
         [0054]    Turning now to  FIGS. 8A and 8B , an adhesive dispensing system  330  is shown, including a dispenser  132  rigidly coupled to a support fixture  130 , and a shutter system  340 . The shutter system  340  includes a translating arm  344  coupled to a support bracket  346 , which also supports a motor  348  coupled to the translating arm via a rack-and-pinion mechanism  350  to control movement of the translating arm. A shutter  212  is coupled to an end of the translating arm  344  and is movable by the arm between closed and open positions corresponding, respectively, to an extended and a retracted position of the translating arm. First and second stops  352 ,  354  are coupled to the translating arm  344  to limit, respectively, extension and retraction thereof. 
         [0055]    While the dispenser  132  is in the ready position, the translating arm  344  is maintained in its extended position with the shutter  212  in the closed position, as shown in  FIG. 8A . When the dispenser  132  begins to move to the dispensing position, the motor  348  rotates in a first rotation direction, retracting the translating arm  344  by operation of the rack-and-pinion mechanism  350 , as indicated by the arrow R 3  in  FIG. 8B , and moving the shutter  212  from the closed position to the open position. 
         [0056]    When the dispenser  132  begins to return to the ready position from the dispensing position, the motor  348  rotates in a second rotation direction, opposite the first rotation direction, extending the translating arm  344  by operation of the rack-and-pinion mechanism  350 , as indicated by the arrow E 3  In  FIG. 8A , and moving the shutter  212  from the open position to the closed position. 
         [0057]    Control of operation of the shutter systems  270 ,  310 , and  340 , described above with reference to  FIGS. 6A-8B , can be provided in a number of different ways, all of which are well within the abilities of one of ordinary skill in the art. For example, according to an embodiment, a control unit for controlling operation of the shutter system  340  of  FIGS. 6A-6C  is provided, in which first and second limit switches are coupled to the splined gear  282 , with a first limit switch configured to close when the screw arm  274  rotates to the closed position, and a second limit switch is configured to close when the screw arm rotates to the open position. A pressure switch, acting as a fixture position detector, is mounted to the robotic arm  102  and configured to close when the support fixture  130  moves to the ready position, and to open as the fixture begins to move away from the ready position. A dedicated logic circuit includes an input coupled to the pressure switch, and is configured to apply a voltage having a first polarity to the motor  276  when the pressure switch is closed unless the first limit switch is also closed, and to apply a voltage having a second polarity to the motor  276  when the pressure switch is open unless the second limit switch is closed. Thus, when the fixture  130  begins to move away from the ready position, the pressure switch opens. Assuming the screw arm  274  is in the closed position, in which the first limit switch is closed, and the second limit switch is open, a voltage will be applied to the motor  276  causing the screw arm  274  to rotate until the second limit switch closes, indicating the shutter is in the open position, at which point the logic circuit will stop the voltage signal. The opposite action will occur when the support fixture  132  returns to the ready position, causing the pressure switch to close, and the motor  276  to rotate in the opposite direction until the first limit switch again closes. 
         [0058]    It will be recognized that the simple arrangement described above can be adapted to control the motor  348  of the embodiment of  FIGS. 8A and 8B , with limit switches arranged to change states when the translating arm  344  moves, respectively, to and from the extended position, and to and from the retracted position. 
         [0059]    With regard to the embodiment of  FIGS. 7A and 7B , an embodiment is provided in which a first limit switch is configured to close when the first translating arm  314  is moved to the extended position, and a second limit switch that is configured to close when the second translating arm  616  is moved to the retracted position. The dedicated logic circuit is configured to energize the second solenoid while the pressure switch is open or while the first limit switch is open, and to energize the first solenoid while the pressure switch is open and the second limit switch is closed. Given this arrangement, when the support fixture begins to move away from the ready position and the pressure switch changes values, the logic circuit will first energize the second solenoid, which will retract the second translating arm  316 . When the second arm  316  reaches the retracted position, the second limit switch closes, at which point the first solenoid is energized, retracting the first translating arm  314 . Both solenoids will remain energized until the fixture  132  returns to the ready position, closing the pressure switch. At this point, the logic circuit will de-energize the first solenoid, permitting the first translating arm  314  to return to its extended position. When the first translating arm  314  reaches its extended position, the first limit switch will open, at which point the second solenoid  324  will be de-energized, permitting the second translating arm  316  to return the shutter to the closed position. 
         [0060]    According to other embodiments, the pressure switch is replaced with a sensor, such as, e.g., a proximity or hall-effects sensor, to function as the fixture position detector. 
         [0061]    The dispenser system will typically be controlled, perhaps along with other elements of the associated assembly system, by software instructions that are executed by a microprocessor. The microprocessor may be a dedicated processor that is integral to a component of the assembly system, or it may be a general purpose processor that is part of a stand-alone computer system that is coupled to the assembly system. In either case, an instruction to switch from the ready position to the dispensing position will include a change in a logic value at one or more terminals in a control circuit of the dispenser system. According to an embodiment, the input of the dedicated logic circuit is coupled to an appropriate terminal of the control circuit in order to detect the change in a logic value, which replaces the fixture position detector as a means for signaling a change from the ready position to the dispensing position and vice-versa. 
         [0062]    Finally, according to an embodiment, the software instructions that control operation of the dispenser system include instructions to provide a first logic value at an input terminal of the dedicated logic circuit to command a change of the shutter system from the closed to the open position, and to provide a second logic value to command a change from the open to the closed position. 
         [0063]    In describing the operation of the shutter systems described with reference to  FIGS. 6A-8B , each system is described as moving from its respective closed position to open position when the respective adhesive dispenser begins to move from the ready position to the dispensing position. It will be recognized that the actual timing of the movement of the shutter systems can be configured to begin before the dispenser begins to move, or concurrently therewith. In part this will depend on the configuration of the particular system. If movement of a shutter system is signaled by a change of state of a pressure switch coupled to some portion of a dispenser or support fixture to detect initial movement toward the dispensing position, then the shutter system can only begin to move after the dispensing system begins to move. However, if the shutter system is controlled by a signal that corresponds to or is also used as a command signal or enable signal to initiate movement of the dispensing system, then the shutter system can be configured to move concurrently with, or slightly before the dispensing system, depending upon the relative response times of the systems. Furthermore, if, in a software program configured to control operation of both systems, separate code instructs the operation of the shutter system, then the timing of operation can be programmed to meet any preference or requirement. Where the claims refer to movement of the shutter to or from the closed position as being substantially concurrent with movement of the adhesive dispenser, this is to be construed as reading on any movement of the shutter to or from the closed position that corresponds to movement of the dispenser, regardless of which is first to move or first to complete its movement. It thus includes simultaneous movement, but is also broader to include moving concurrently. 
         [0064]    The shutter systems of  FIGS. 6A-8B  have been described with reference to dispensing systems like the system  260  of  FIGS. 6A-6C , in which the entire support fixture  130  translates in the Z axis to move the dispenser  132  to the dispensing position. As noted above, such a dispensing system requires a shutter system capable of moving the shutter in the Z axis to avoid contact with the working surface. However, embodiments that have such a capability are not limited to dispensing systems like the system  260 , but can also be employed with dispensing systems like the system  200 , described with reference to  FIGS. 3A and 3B , in which the support fixture  103  does not translate to move the dispenser  104  to the dispensing position, but instead remains at substantially the same position, with respect to the Z axis, while the dispenser translates separately. Movement of the shutter in the Z axis, relative to the support fixture is not generally detrimental to overall operation of the dispenser system. Furthermore, in some applications, it may be preferable to attach a shutter system directly to the dispenser rather than to the support fixture as described in the disclosed embodiments. In that case, even though the support fixture does not translate, it would still be necessary to move the shutter in the Z axis, as described with reference to the embodiments of  FIGS. 6A-8B . 
         [0065]    While the invention has been described and illustrated primarily with reference to systems for applying adhesive to optical sensors on semiconductor dice, the principles of the invention can be applied with advantage to any system that is employed to automatically dispense adhesive, especially where drops of the adhesive in unintended locations can damage products in process. Accordingly, except where a particular system is explicitly claimed, the claims are not limited in that respect. The term working surface is used to refer broadly to any surface or structure positioned under the nozzle of an adhesive dispenser, particularly in a position where it can receive an adhesive. 
         [0066]    Because the drawings are diagrammatic, they are not intended to show details of actual dispensing systems, except where those details are specifically referred to and described. Otherwise, the drawings are intended to convey the function of the elements depicted. In particular, elements of known systems, such as robotic arms, support fixtures, cameras, adhesive dispensers, etc., are well known in the art, and can have any of a large number of shapes and structures, which vary widely according to system, manufacturer, capacity, model, etc. Even the structures that are described in detail are provided as examples of various structures that can be employed, according to the preferences of a user or the limitations imposed by a particular dispensing system. 
         [0067]    Most of the drawings are presented as side views of respective dispensing systems, and drawings that show views from other vantage points are defined accordingly. This is used to provide a common point of reference for the drawings, and does not impose any limitations. Furthermore, claim limitations that read on elements that are shown in the drawing as being, for example, positioned in front of an adhesive dispenser, or at the side, are not limited to the position shown. 
         [0068]    The unit symbol “μm” is used herein to refer to a value in microns. One micron is equal to 1×10 −6  meters. 
         [0069]    Ordinal numbers, e.g., first, second, third, etc., are used according to conventional claim practice, i.e., for the purpose of clearly distinguishing between claimed elements or features thereof. The use of such numbers does not suggest any other relationship, e.g., order of operation or relative position of such elements, nor does it exclude the possible combination of the listed elements into a single, multiple-function, structure or housing. Furthermore, ordinal numbers used in the claims have no specific correspondence to those used in the specification to refer to elements of disclosed embodiments on which those claims read. 
         [0070]    Where a claim limitation recites a structure as an object of the limitation, that structure itself is not an element of the claim, but is a modifier of the subject. For example, in a limitation that recites “a shutter system configured to be coupled to an adhesive dispenser system,” the adhesive dispenser system is not an element of the claim, but instead serves to define the scope of the subject term shutter system. Additionally, subsequent limitations or claims that recite or characterize additional elements relative to the adhesive dispenser system do not render the adhesive dispenser system an element of the claim. 
         [0071]    The term coupled, as used in the claims, includes within its scope indirect coupling, such as when two elements are coupled with one or more intervening elements even where no intervening elements are recited. 
         [0072]    The abstract of the present disclosure is provided as a brief outline of some of the principles of the invention according to one embodiment, and is not intended as a complete or definitive description of any embodiment thereof, nor should it be relied upon to define terms used in the specification or claims. The abstract does not limit the scope of the claims. 
         [0073]    Elements of the various embodiments described above can be combined, and further modifications can be made, to provide further embodiments without deviating from the spirit and scope of the invention. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
         [0074]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.