Abstract:
The present invention provides a method and apparatus for dispensing materials onto a substrate. In one embodiment, a dispensing system includes a controller, a vacuum source in electrical communication with the controller, the vacuum source applying a vacuum to at least a portion of the substrate in response to an instruction from the controller, an injector in electrical communication with the controller, the injector comprising a valve in communication with a pressure source and a material port in communication with a material source, the valve permitting material from the material source to be dispensed onto a substrate in accordance with an instruction from the controller. In one embodiment, the dispensing system also includes a trap in communication with the vacuum source, where the trap substantially prevents excessive material dispensed by the injector from contacting the vacuum source.

Description:
RELATED APPLICATION 
     This application is related to U.S. Utility Application Ser. No. 09/168,536, filed Oct. 10, 1998, which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus, process, and system for encapsulating electronic parts, and more specifically to an apparatus and process which uses changes in air pressure to force material under and around an electronic integrated circuit chip. 
     BACKGROUND OF THE INVENTION 
     The need for denser, larger and more durable chip assemblies has broadened the use of Direct Chip Attach (DCA) technology to include flip chip integrated circuits. A typical flip chip integrated circuit utilizes a solder ball grid array to provide electrical connections between a die of the flip chip and a substrate. During manufacturing of a typical flip chip, after the flip chip is assembled on a substrate, a liquid dispensing system is used to apply an underfill encapsulant material between the die and the substrate. The flip chip underfill material is used to reduce mechanical and thermal stress on the electrical connections and to protect the electrical connections against atmospheric conditions. The underfill material provides stability and rigidity to the assembled flip chip and may also be used as a heat conductor to improve thermal performance of the flip chip. 
     In typical prior art flip chip underfilling processes, a dispenser system is used to dispense underfill material around the sides of the flip chip and the underfill material spreads under the flip chip and around the solder balls of the grid array via capillary action or “wicking”. During the assembly process, the substrate is typically heated prior to, during, and after dispensing of the underfill material to a temperature ranging from ambient conditions to approximately 120° C. The heating of the substrate increases the capillary action causing the underfill material to flow further under the die of the flip chip. A final fillet of underfill material is applied around the sides of the flip chip after the wicking action has occurred. A drawback associated with such underfilling processes is that the underfill material may not completely fill all voids between a die and a substrate in a flip chip. For example, the underfill material can fail to fill spaces between the contacts of a die. 
     To overcome the problem of voids or air gaps, one prior art dispensing system developed by Tessera of San Jose, Calif. utilizes a vacuum approach to completely underfill flip chips. In this prior art system, the dispensing system, including one or more flip chips that are to receive underfill material, is enclosed within an air tight chamber, and prior to the dispensing of underfill material, a vacuum pump is used to purge all air from the chamber to create a vacuum. The underfill material is then dispensed around all sides of the flip chips, and the chamber is returned to ambient pressure. When the chamber is returned to ambient air pressure, the underfill material is forced under the flip chips by the difference in air pressure outside the flip chips and under the flip chips. 
     While the above described prior art system is effective in preventing voids in underfill material in flip chips, the system is relatively large and the time required to purge air from the air tight chamber is rather long. Further, because the airtight chamber is so large, it is difficult to effectively purge air from the chamber. In addition, the air tight chamber of the prior art accommodates only manual loading of the flip chips into the chamber, preventing the dispensing system contained within the chamber from being effectively used in an automated assembly line. Moreover, the large size of the airtight chamber often precludes it from easy integration into automated manufacturing processes. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes disadvantages of the prior art by providing a system, apparatus and process for encapsulating flip chips using dispensing systems having fixtures operating cooperatively with injection and vacuum valves to overcome drawbacks of the prior art systems. 
     In one embodiment, a dispensing system includes a controller, a vacuum source in electrical communication with the controller, the vacuum source applying a vacuum to at least a portion of the substrate in response to an instruction from the controller, and an injector in electrical communication with the controller and having a vacuum port in communication with the vacuum source, the injector comprising a valve in communication with a pressure source and a material source, the valve permitting material to be dispensed from the material source onto a substrate in accordance with an instruction from the controller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the drawings, which are incorporated herein by reference, and in which: 
     FIG. 1 illustrates a workpiece usable in accordance with the invention and shows the flow of encapsulating material at the workpiece in accordance with an embodiment of the invention. 
     FIG. 2 is a block diagram illustration of a vacuum injection system, in accordance with one embodiment of the invention. 
     FIG. 3 is flow chart representation of a vacuum injection process, in accordance with one embodiment of the present invention. 
     FIG. 4 is a perspective view of a vacuum injection system, in accordance with one embodiment of the invention. 
     FIG. 5 is a perspective view of the conveyorized portion of the vacuum injection system of FIG.  4 . 
     FIG. 6 is a side view of the conveyorized portion of FIG. 5, viewed along the AA axis. 
     FIG. 7 is a side view of the conveyorized portion of FIG. 5, viewed along the BB axis. 
     FIG. 8 is another side view of the conveyorized portion of FIG. 5, viewed along the BB axis, illustrating the conveyorized portion in more detail. 
     FIGS. 9A-9B are front and exploded views, respectively, of the injection valve of FIGS. 18, in accordance with one embodiment of the invention. 
     FIG. 10 is an exploded view of the vacuum nozzle FIGS. 1-8, in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     For purposes of illustration, embodiments of the present invention will now be described with reference to a dispensing system used to dispense underfill material beneath and around electronic components such as flip chip integrated circuits. One skilled in the art will appreciate, however, that embodiments of the present invention are not limited to dispensing underfill materials for flip chip integrated circuits, but may be used in other applications. 
     As used in this description, the term “vacuum” does not necessarily refer only to producing a space entirely devoid of matter, but rather is intended also to encompass producing a space from which matter, especially air, has been partially or substantially removed. 
     One technique for encapsulating electronic components is described in an application filed under the Patent Cooperation Treaty (PCT) having Publication Number WO 99/53616, the contents of which are incorporated herein by reference. In the described method, electronic components are disposed in an assembly having top and bottom sealing layers defining an enclosed space containing the components. The assembly is engaged in a test fixture, and the enclosed space is evacuated by applying a vacuum to a hole in one of the sealing layers. Then, the vacuum is removed from the hole, a needle is advanced into that hole, and a liquid encapsulant is injected through the needle into the enclosed space around the electronic components. The encapsulant flows into the enclosed space, where it is free to flow around the components. 
     One disadvantage of this method, however, is that the vacuum and encapsulant flowing through the needle must be precisely controlled to ensure proper flow. Another disadvantage is that the injected liquid encapsulant may not flow sufficiently around and under all of the components to properly encapsulate each component. Still another disadvantage is that excess encapsulant can flow back out of the hole and contaminate the assembly, text fixture, vacuum, or other elements. Yet another disadvantage is that waiting for the liquid encapsulant to flow around each component increases the process time for encapsulating the components. 
     FIG. 1 illustrates a workpiece  27 , such as a substrate, having components  28  that may receive encapsulant material  24  using processes and apparatuses of the present invention. In FIG. 1, material  24  is shown flowing through the workpiece during an encapsulation process. The workpiece  27  includes a hollow area  26 , in which several components to be encapsulated, namely electronic components  28  having leads  30 , are disposed. The hollow area  26  of workpiece  27  in FIG. 1 can be formed between a top coverlay tape  34  disposed on the “die side” (i.e., the top of the components  28 ) and a bottom coverlay tape  32  disposed on the “contact side” (i.e., the bottom of the components  28 ). An injection hole  33  is formed in the top coverlay tape  34  at a first side of the hollow area  26  to permit encapsulation material  24  to be injected. Similarly, a vacuum hole  35  is formed in the top coverlay tape  34  to permit a vacuum to be drawn on the hollow area  26 . Having the injection hole  33  and vacuum hole  35  as separate holes, disposed on opposite sides of the hollow area  26 , is advantageous because the vacuum being pulled at the vacuum hole  35  helps to rapidly draw the material  24  through the hollow area  26  and around the components  28  and also helps to ensure that the material  24  flows around, over, and under all of the components  28 . 
     It should be understood that illustration of three electronic components  28  is not intended to be limiting; any number of components can be disposed in the hollow area  26 . Further, the articles disposed in the hollow area  26  need not be electronic or other types of components, but rather can include any articles to be encapsulated. As FIG. 1 illustrates, the material  24  not only flows around the components  24  but also flows around the leads  30  of the components  28 , thereby helping to prevent voids in the encapsulant. 
     FIG. 2 shows a block diagram of one embodiment of a vacuum injection system  10  in accordance with the invention, for dispensing media such as underfill material along the sides, underneath, and between components such as flip chip integrated circuits (not shown) disposed on a workpiece  27  or carrier (not shown). The vacuum injection system  10  includes a controller  12 , a vacuum source  14  having a nozzle  16 , an injector  18  having an injector valve  20 , and a trap  22 . The injector  18  injects underfill material  24  receiving force from a pressure source  23 . During operation of the vacuum injection system  10 , the vacuum nozzle  16  connects to the vacuum hole  35  on one side of the hollow area  26  in the workpiece  37  so that the vacuum source  14  can draw a vacuum on the hollow area  26 , while the injector valve  20  permits the injector  18  to inject encapsulating material  24  into the injection hole  33 . The vacuum applied by vacuum source  14  draws the encapsulating material  24  from the injection hole  33  towards the vacuum source  14 , so that the encapsulating material  24  can encapsulate and underfill all of the components in the hollow area  26  while substantially eliminating voids. This is explained more fully below. 
     The controller  12  can be any system or processor capable of controlling the vacuum injection processes described herein. For example, the controller  12  can be a programmable logic controller (PLC), a general purpose digital computer running one or more programs relating to control of the vacuum injection processes, or a proprietary processor system board. In one embodiment, the controller  12  is a proprietary processor system board having a plurality of input/output (I/O) control points. In another embodiment, the controller  12  can further include or access one or more daughter boards that can provide other circuit functions, such as analog I/O, high power switching, communications to peripherals, video display, and the like. In still another embodiment, the controller  12  is a computer having a PENTIUM microprocessor (manufactured by Intel Corporation of Santa Clara, Calif.) and storing and running a plurality of process instructions and associated software relating to control of the system  10 . The controller  12  can be a stand-alone computer, such as a personal computer, or can be networked to one or more other computers. 
     In one embodiment, the controller  12  stores a plurality of process “recipes” relating to encapsulating components and/or assemblies on the workpiece  27 . For example, a process recipe may include all instructions and control programs necessary to encapsulate a predetermined quantity of a predetermined component disposed on a fixture having a predetermined size. Because the controller  12  is in communication with the injector  18  and the vacuum source  14 , it can program either or both of these elements to operate in accordance with a particular process for a particular component or material. In another embodiment, the controller  12  can monitor the vacuum level at the vacuum source  14  and adjust it as necessary. In another example, the controller  12  can control the injector  18  to inject material  24  for a predetermined time by enabling and disabling the injector valve  20 . 
     For example, the controller  12  can instruct the vacuum source  14  to apply a predetermined vacuum level (e.g., 5 inches of mercury (in./Hg)) to the workpiece  27  and to maintain this vacuum level for a predetermined time. While the vacuum level is maintained, the controller  12  directs the injector  18  to configure the injector valve  20  to inject a specific quantity (e.g., 1 cubic centimeter (cc)) of a material  24 , for example silicone encapsulant, from a particular source of material  24 , such as a particular cartridge or syringe of material  24 . 
     Vacuum source  14  can be a pump, such as an oil-free vacuum pump, capable of reaching a predetermined vacuum level within a predetermined time. In one embodiment, the vacuum pump is a diaphragm-style pump manufactured by Varian Associates of Lexington Mass. For example, in one embodiment, the vacuum source  14  can reach a maximum vacuum of 28 in./Hg within 5 seconds. The vacuum level and time during which vacuum is applied can be set; for example, they can be programmed by controller  12  or set manually using one or more switches. Depending on how it is programmed, the vacuum source  14  can apply a vacuum at its nozzle  16  to the hollow area  26  before, during, and/or after injection of the material  24 . This permits the vacuum source  24  to “draw” injected material  24  through the hollow area  26  after the material  24  has been injected, thereby encapsulating components therein without voids. In addition, by continuing to apply a vacuum to the hollow area  26  after injection of the material  24 , the material  24  can be drawn through the hollow area  26  faster than the material  24  flows without the vacuum being applied. 
     The trap  22  is disposed between the vacuum source  14  and the vacuum nozzle  16  to trap possible excess material  24  injected into the hollow area  26  of the workpiece  27 , to prevent contamination of the vacuum source  14 . For example, the trap  22  can be a jar having a removable reservoir, so that material  24  in the trap  22  can be removed easily. In one embodiment, the trap  22  includes a disposable and easily removed reservoir. Many different types and styles of reservoir-type devices are usable in accordance with this aspect of the invention, as those skilled in the art will recognize. 
     In one embodiment, the trap  22  can include a level sensor (not shown) capable of detecting the level of material  24  in the trap  22 . Those skilled in the art will recognize that many different types of sensing devices are usable to detect the level of material  24  in the trap  22 . The level sensor can stop the injection process if the material  24  in the trap  22  reaches a predetermined level, such as if the trap  22  becomes three quarters full. Alternately, the controller  12  can monitor the level of material  24  and stop the injection process if the material  24  in the trap  22  reaches a predetermined level. The vacuum source  14  is coupled to a vacuum nozzle  16  adapted to fit tightly to the vacuum hole  35  on the workpiece  27 . 
     The injector  18  can accommodate workpieces  27  and/or hollow areas having differing sizes. The injector  18  can include an injection port  21  that fits tightly to (or within) the injection hole  33  on the workpiece  27  to inject material  24  into the hollow area  26  after the vacuum source  14  has evacuated air from the hollow area  26 . In another embodiment, the injector  18  can begin injecting material  24  into the hollow area  26  while the vacuum source  14  is evacuating air from the hollow area  26 . A pressure source  23 , such as a cartridge assembly manufactured by EFD Inc. of Providence, R.I., uses pressure to force the material  24  out of the injection port  21  and into the hollow area  26 . In one example, the material  24  is stored in a cartridge or syringe and pressure is applied to the cartridge to force material  24  from the cartridge out through the injection port  21 . In one embodiment, the pressure source  23  can be an air-driven or mechanical ram. 
     The injector  18  provides a positive shut-off, which can help to prevent material  24  from dripping out of the injection port  21  after pressure on the material  24  is released or after injection of a predetermined quantity of material  24  is complete. In one embodiment, the positive shut-off is provided using a valve  20  that is precisely controlled by controller  12 . This aspect is described more fully below. In another embodiment, the injector  18  can include one or more ports (not shown) accepting syringes and/or cartridges containing material  24  to be injected. In still another embodiment, the injector  18  can be supplied with material  24  from a bulk feeding device such as a ram pail pump, such as the DynaMite 190 manufactured by Graco, Inc. of Minneapolis Minn. The controller  12  can communicate with the injector valve  20  to control operation of the injector  18 , when injection occurs, to control the level of pressure applied at the pressure source  23 , to release the pressure on the pressure source  23 , to select the source of material  24 , and to control the flow of material  24  into the injector  18 . 
     The material  24  can be any material used for encapsulating articles. For example, some materials, such as silicone chip encapsulant material, can be used as a compliant layer to decouple the mismatched thermal expansion rates of silicon and common printed circuit board (PCB) laminates (to which a silicon electronic component being encapsulated may later be attached). Silicone chip encapsulant material can also increase the solvent resistance of the article being encapsulated. 
     The workpiece  27 , integrated circuits or other substrates that are to receive dispensing material in the system  10  can be transported as individual units on conveyors, multiple units in a common carrier, or using a continuous tape feeder system. The workpiece  27  can, in one embodiment, include such individual units, multiple units on a common carrier, or a continuous tape feeder system. The system  10  may include a conveyor (not shown in FIG. 1, but illustrated in FIGS. 4-8) for loading and unloading integrated circuits or multiple unit common carriers into the dispensing system. Alternatively, the system  10  may be configured as known in the art for receiving a continuous tape having integrated circuits that are to receive encapsulant material bonded to the top surface of the tape. 
     FIG. 3 illustrates a flow chart of a process for encapsulating components using the system of FIG. 1, in accordance with an embodiment of the invention. In a first step of the process, the chip or component  28  is aligned on the workpiece  27  or carrier and is sealed, such as by the top and bottom coverlay tapes  34 ,  32  of FIG. 2 (step  40 ). The carrier or workpiece  27  at an injection point in the system  10  is positioned on a conveyor (step  42 ). The vacuum and encapsulation holes  35 ,  33  (also referred to as vacuum input and injection input, respectively) are contacted by the vacuum and injection ports (step  44 ). The vacuum source  14  draws a vacuum at a first side of the workpiece  27  (step  46 ) to evacuate air from the hollow area  26  containing the components  28  to be encapsulated while simultaneously drawing encapsulant material  24  through the hollow area  26 . In one embodiment, prior to step  44  the workpiece  27  may be lifted off of the conveyor to place the vacuum and injection ports  35 ,  33  in contact with the vacuum nozzle  16  and a nozzle at the injector  18 . 
     After the vacuum source  14  begins applying the vacuum, the injector valve  20  opens to begin dispensing material  24  into the hollow area  26  (step  48 ). Because the material  24  is at a pressure higher than that in the hollow area  26 , the material  24 , after being injected from the injector valve  20  is drawn through the hollow area  26 , towards the vacuum hole  35 . In addition, because the vacuum source  14  is applying a vacuum to the hollow area  26 , the material  24  will flow through the hollow area  26  faster than if the hollow area  26  were evacuated then the vacuum was removed. The controller  12  determines how long the vacuum source  14  applies the vacuum and how long the injector  18  can inject material based on a number of factors, which can include the size of the hollow area  26 , the number of components  28 , the type of material  24 , the level of the vacuum being applied, and the amount of material in the trap  22 . Those skilled in the art will recognize that other factors may affect the time for encapsulation. Based on information from the controller  12 , the injection valve  20  is closed at a predetermined time to stop the injection of material  24  into the hollow area  26  (step  50 ), and the vacuum is released at a predetermined time. Any excess material  24  that flows out of the vacuum hole  35  flows into the trap  22  and is contained in the trap  22 , instead of contaminating the vacuum source  14  (step  52 ). Then, the injector  18  and vacuum source  14  are be removed from the injection and vacuum holes  33 ,  35  (step  54 ), and the next encapsulation step (such as curing of the encapsulant) can proceed. 
     Note, however, that other events can cause the injection valve  20  (and/or the vacuum valve  16 ) to stop the encapsulation process from continuing. For example, if a sensor in the trap  22  indicates that the material  24  in the trap  22  reaches a predetermined level, the sensor in the trap  22  can either disable the vacuum source  14 , or close the injector valve  20 , to stop the vacuum from drawing material  24  through the hollow area  26 . It should also be understood that the order of steps  50  and  52  can be reversed; that is, the vacuum can be released before the injection valve  20  is shut. 
     An embodiment of an automated vacuum encapsulation system  100  in accordance with the present invention will now be described with reference to FIGS.  1  and  4 - 9 . The automated system  100  includes encapsulation assemblies  102 , a conveyor  104 , and a display and control panel  106 . The panel  106  includes various indicators and switches permitting operators to monitor or control at least a portion of the encapsulation process being run at the system  100 . For example, if the encapsulation system  100  included a trap  22  (FIG.  1 ), the panel  106  can include indicators informing an operator the status of the trap  22  (e.g., empty, quarter-full, three quarters full, etc.) or that the trap  22  must be emptied to avoid a shutdown of the system  100 . 
     Also contained within the system  100  are control electronics for the vacuum encapsulation process, such as a controller  12 , power circuitry (not shown), air sources (not shown), control pneumatics for the injectors  18  and other devices, cooling fans, and the like. In one embodiment, the control electronics includes a controller  12  having a microprocessor such as a PENTIUM processor, which can be programmed to control the dispensing system, to control the flow of workpieces  27  such as integrated circuits into and out of the dispensing system, and to operate some or all of the other control electronics. 
     The conveyor  104  of the encapsulation system  100  flows from left to right and is manually adjustable to accommodate parts of varying widths. For example, in this embodiment, the conveyor  104  can be adjusted from  50  mm to  180  mm between its rails  104 ′,  104 ″. A plurality of sensors (not shown) are operable with the conveyor  104  to sense when a workpiece  27  (FIG. 1) has been placed at the entrance end (left side) of the conveyor  104  and to sense when a workpiece  27  has reached an injector assembly  102 . The conveyor  104  is made from materials that are safe from electrostatic discharge (ESD). 
     Referring to FIG. 5, the injector assemblies  102  are illustrated in greater detail. Each injector assembly  102  includes a material assembly  108  dispensing material  24  used for encapsulation. For example, the material assembly  108  accepts 80 cc syringes and 150 cc cartridges as reservoirs for material  24 . The locations of the material assemblies  108  ensure that they can be easily accessed and maintained by operators of the system. If the system  100  is running in a continuous high volume environment, however, the materials assembly  108  can be coupled to a bulk material feeding device to avoid frequent replenishment of material  24  while running. 
     As workpieces  27  move along the conveyor  104 , when the workpiece  27  reaches the injector assembly  102 , a pneumatic assembly  109  helps to lifts the workpiece  27  off of the conveyor  104  and towards the injector assembly  102  (this is shown in greater detail in FIG.  8 ). When lifted, the workpiece  27  is disposed to contact its injection hole  33  and vacuum hole  35  with a nozzle of the injector valve  20  (not shown in FIG. 5) of the injector  18 , and the vacuum nozzle  16  coupled to the vacuum source  14  (not shown in FIG.  5 ), respectively. 
     FIG. 6 illustrates a side view of an injector assembly  102  of FIG. 5 taken along the A—A line. This view illustrates the relative physical locations of the injector valve  20  and the pneumatic assembly  109  to the conveyor  104 . 
     FIG. 7 illustrates another side view of the injector assemblies  102  of FIG. 5 taken along the B—B line. In this view, alignment pins are  110 ,  112  are shown projecting from a top fixture element  114  in the injector assembly  102 . The alignment pins  110 ,  112  mate with corresponding alignment holes in the workpiece  27 , to ensure that the vacuum nozzle  16  and the injector  18  can make proper contact with the injection hole  35  and the vacuum hole  33 . Although the alignment holes in the workpiece  27  are not illustrated, those skilled in the art will recognize that conventional alignment pins and alignment holes can be used to align the workpiece  27 . 
     FIG. 8 illustrates still another side view of the injector assemblies  102  of FIG. 5 taken along the B—B line. In this view, the injector nozzle  20  and the vacuum nozzle  16  pass through the top fixture element  114 , from which alignment pins  110 ,  112  project. The workpiece  27  is disposed on a movable bottom fixture element  116 , which has been raised a predetermined distance above the conveyor  104 , to bring the workpiece  27  towards the injector nozzle  20  and vacuum nozzle  16  at the top fixture element  114 . The alignment pins  110 ,  112  are engageable with corresponding alignment holes in the workpiece  27  and in the bottom fixture element  112 , to hold the workpiece  27  and the top and bottom fixture elements  114 ,  116  at a predetermined alignment. 
     As the alignment pins  110 ,  112  are engaged with the workpiece alignment holes and the bottom fixture element alignment holes, the top face of the bottom fixture element  116  is urged towards the bottom face of the top fixture element  114 , until the injector nozzle  20  and vacuum nozzle  16  engage the injection hole  33  and vacuum hole  35  of the workpiece  27 . Depending on the depth of the alignment holes, the length of the alignment pins  110 ,  112  and the thickness of the top fixture element  114  where the vacuum nozzle  16  and injector nozzle  20  pass through it, the top fixture element  114  may be in contact with the bottom fixture element  116  when the vacuum nozzle  16  and injector nozzle  20  are in proper engagement with the vacuum hole  35  and injector hole  33 . 
     Although FIGS. 6-8 illustrate that the bottom fixture element  116  has alignment holes and the top fixture element  113  has alignment pins  110 ,  112 , those skilled in the art will recognize that the top fixture element  114  could instead have the alignment holes and the bottom fixture element  116  could have the alignment pins. Similarly, although FIGS. 6-8 illustrate that the bottom fixture element  116  is lifted vertically above the conveyor  104  towards the top fixture element  114 , it is possible to instead move the top fixture element  114  towards the bottom fixture element  116 , or to move both the top fixture element  114  and the bottom fixture element  116  towards each other. In addition, the fixture element that contacts that contacts the workpiece  27  surface (or the die surface of a component on a carrier) can be adjustable to compensate for variations in the thickness of the workpiece  27  or die thickness. This compensation allows proper clamping and fixturing of the components being processed due to lot variations. 
     FIGS. 9A-9B illustrate an example of an injector valve  20  usable in accordance with an embodiment of the invention. The injector valve  20  includes a stroke cylinder  66 , stopper rod assembly  60 , and nozzle assembly  82 , along with various fitting and hardware components, which operate together to provide a positive shut-off function that the controller  12  (FIG. 2) can control with precision. Each of these elements is described more fully below. 
     The nozzle assembly  82  includes a flexible nozzle tip  83  that forms a tight seal to the injection hole  33  of a workpiece  27  (FIGS.  1  and  2 ). The nozzle tip  83  is “doughnut” shaped and has an opening in the center therein through which material  24  to be injected can flow and which can receive the rod tip  61  of a stopper rod assembly  60  (described more fully below) to block the hole in the nozzle tip  83  and prevent material  24  from escaping. The nozzle assembly  82  is coupled to a first end of an upper body assembly  78  to which a nipple assembly  76  attaches. The nipple assembly  76  couples to a source of material  24 , such as the material assembly  108  (FIGS.  4 - 7 ), for receiving material to be injected. An  0 -ring  80  helps to form a tight seal between the nozzle assembly  82  and the upper body assembly  78 . 
     A piston seal  74  couples the second end of the upper body  78  to a first side of a bushing assembly  70  via a first retainer nut  72 . A second retainer nut  68  couples the second side of the bushing assembly  70  to a stroke cylinder  66  and a stopper rod assembly  60 . The stroke cylinder  66  is coupled via a length of tubing  62  and first, second, and third fittings  56 ,  58 ,  64 , to a pressure source  23  (FIG.  2 ). In one embodiment, the stroke cylinder  66  can be an SMC Cylinder manufactured by Kinequip Inc., Buffalo, N.Y., such as Model. No. NCJ2B16-050T. This model can operate with a maximum pressure of  100  pounds per square inch (PSI), and those skilled in the art will recognize that other stroke cylinders having comparable specifications can be used in accordance with the invention. 
     The stopper rod assembly  60  is movably coupled to the stroke cylinder  66 , such as by spring loading. During operation of the injector valve  20 , pressure from a pressure source  23  (FIG. 1) can be applied and removed from the stroke cylinder  66 . When pressure is applied, the pressure compresses the spring biasing within the stroke cylinder  66 , thereby holding the stopper rod assembly  60  back from the nozzle tip  83 . Thus, when pressure is applied, the stopper rod assembly  60  is disposed within the upper body  78  and nozzle assembly  82  to permit material  24  to flow through the nozzle tip  83  of the nozzle assembly  82 , through an injection hole  33  (FIG. 1) and into the hollow area  26  of a workpiece  27  (FIG.  1 ). 
     When pressure is released, the spring biasing within the stroke cylinder releases and the stroke cylinder  66  can move the stopper rod assembly  60  through the bushing  70  and upper body  78  so that the rod tip  61  of the stopper rod assembly  60  is disposed at the opening in the nozzle tip  83  of the nozzle assembly  82 , to prevent material  24  entering through the nipple  76  from escaping through the nozzle tip  83 . Because the controller  12  (FIG. 2) can precisely control when and how pressure from pressure source  23  (FIG. 2) is applied, the flow of material  24  out of the injector valve  20  can be precisely controlled. 
     FIG. 10 illustrates an example of a vacuum nozzle  16  usable in accordance with an embodiment of the invention. A nozzle body  88  has a seal  86  at one end and a fitting  90  at the other end. The fitting  90  and seal  86  are structured and arranged to be operable with the vacuum source  14  (FIG. 1) and to be coupled closely to the vacuum hole  35 . Those skilled in the art will recognize the types of vacuum nozzles that may be usable in accordance with the invention. 
     As described herein, the present invention provides improved systems, methods, and apparatuses for encapsulation of articles such as electronic components. The controller and injector valve precisely control the flow of encapsulant into the workpiece, which ensures that a proper quantity of encapsulant is applied to the articles, improves the yield of the encapsulation process, and decreases waste of encapsulant. Having the controller control operation of the vacuum source provides precise control of the vacuum being applied to the workpiece. This permits the time and magnitude of the applied vacuum to vary based on the encapsulant used and the number and size of articles to be encapsulated. 
     In addition, use of a vacuum source applying a vacuum directly to the area containing articles to be encapsulated, as described herein, provides advantages over the prior art. First, applying a vacuum only to that area helps to reduce the size of the vacuum source required, thereby reducing the size of the dispensing system overall. Second, applying a vacuum to the area in which encapsulant is being injected at the same time that the encapsulant is being injected speeds the flow of encapsulant through the workpiece and helps ensure that the encapsulant thoroughly contacts all the articles to be encapsulated. In addition, use of a trap in connection with the vacuum source helps prevent encapsulant being drawn through the workpiece from contaminating the vacuum source or other areas outside of the workpiece. 
     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.