CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/347,153 filed June 8, 2016, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present disclosure generally relates to dispensing apparatus and methods and, in particular, to apparatus and methods for controlling the temperature of discrete amounts of viscous materials provided in a non-contact manner from a dispensing apparatus onto a workpiece or substrate.

BACKGROUND

[0003] In the manufacture of microelectronic hardware and other products, pneumatic dispensing apparatus are used to dispense small amounts or droplets of a highly viscous material in a non-contact manner onto a substrate or workpiece. Many of the materials used for dispensing are of higher viscosities that are difficult to jet. Exemplary highly viscous materials include, but are not limited to, solder flux, solder paste, adhesives, solder mask, thermal compounds, oil, encapsulants, potting compounds, inks, and silicones.

[0004] Adding heat to the material may reduce the viscosity of the material and improve the jetting action, thereby making the material easier to dispense. In addition to heating the material during the jetting function, the substrate for the material is frequently also heated. This elevated temperature enables the dispensed material to flow more easily around and under components by keeping viscosities low and improving the flow out characteristics of the material. The substrate heat is applied to the substrate by either contact heating or impingement heating, which entails blowing hot air onto the underside of the substrate. Over time, this hot air also causes the end of the jetting nozzle to be heated above desired temperatures, which in turn heats the material in the nozzle end. To cool the nozzle end and material therein, current pneumatic dispensing systems include providing a fixed temperature or uncontrolled temperature air supply to the nozzle.

[0005] Such systems, however, do not allow for the desired temperature of the nozzle end to be maintained. Therefore, there is a need for a novel cooling mechanism for maintaining the nozzle end and/or material therein at a desired temperature while the material is dispensed onto a substrate or workpiece.

SUMMARY

[0006] A system for dispensing droplets of liquid or viscous material onto a surface of a substrate is disclosed. The system includes a dispenser having a nozzle in fluid communication with a source of material, and a temperature sensor associated with the nozzle. The system also includes an adjustable temperature cooling source that provides a cooling material of an adjustable temperature to the nozzle. Finally, the system includes a controller configured to receive a temperature signal from the temperature sensor and to send a control signal to the adjustable temperature cooling source to adjust the temperature of the cooling material based on the temperature signal.

[0007] In this way, the temperature of the dispensed droplets may be actively cooled below a predetermined temperature. The controller does not merely adjust the flow of a fixed or uncontrolled temperature cooling source. Adjusting the temperature of the cooling material may increase the ability of the system to provide relatively low temperature droplets which, in turn, allows the system to compensate for relatively hot substrates and ambient temperatures.

[0008] In some implementations, the system may also include a heater associated with the nozzle. The controller may be configured to send a second control signal to the heater to adjust a temperature of the heater. The adjustable temperature cooling source may include an electromechanical device that modifies operation of the adjustable temperature cooling source in response to the control signal. The adjustable temperature cooling source may include an adjustable vortex cooling generator or an adjustable Peltier device.

[0009] In some implementations, the dispenser may be ajetting dispenser comprising a needle and a valve seat having a passageway. When the needle moves toward the valve seat, a droplet of material is forced through the passageway of the valve seat and from the jetting dispenser.

[0010] In some implementations, the controller may be configured to send the control signal to the adjustable temperature cooling source to adjust the temperature of the cooling material such that the temperature of the nozzle is cooler than an ambient temperature. The temperature of the cooling material may be adjusted such that the temperature of the nozzle is at least 10°C, 15°C, or 20°C cooler than the ambient temperature or the temperature of the cooling material may be adjusted such that the temperature of the nozzle is below 30°C. [001 1] In some implementations, the temperature sensor, the controller, and the adjustable temperature cooling source may define a feedback loop to actively maintain the temperature of the nozzle at a pre-determined temperature.

[0012] A method for dispensing droplets of liquid or viscous material onto a surface of a substrate is also disclosed. Initially, a temperature of a dispensing nozzle is sensed using a temperature sensor. Next, the temperature of a cooling material is adjusted in response to the sensed temperature of the nozzle. Finally, the adjusted temperature cooling material is provided to the nozzle.

[0013] In some implementations, the nozzle may be heated with a heater. A second control signal may be sent to the heater to adjust a temperature of the heater. The temperature of the cooling material may be adjusted using an adjustable vortex cooling generator or an adjustable Peltier device. The temperature of the cooling material may be adjusted to be below 20°C. The temperature of the cooling material may be adjusted such that the temperature of the jet dispensing nozzle is cooler than an ambient temperature, such that the temperature of the j et dispensing nozzle is at least 10°C, 15°C, or 20°C cooler than the ambient temperature, or such that the temperature of the nozzle is below 30°C.

[0014] Additional advantages will be set forth in part in the description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate implementations and together with the description, serve to explain the principles of the methods and systems.

[0016] FIG. 1 is a schematic diagram of a control system for jetting droplets of liquid or viscous material onto a surface of a substrate.

[0017] FIG. 2 is a flow chart of a control system for jetting droplets of liquid or viscous material onto a surface of a substrate.

[0018] FIG. 3 is a cross-sectional view of the dispensing apparatus taken generally along line 3-3 in FIG. 4.

[0019] FIG. 3 A is an enlarged view of a portion of FIG. 3.

[0020] FIG. 4 is a perspective view of a dispensing apparatus in accordance with an implementation. [0021] FIG. 5 is a top view of the dispensing apparatus of FIG. 4 shown with the electrical cable and pneumatic conduits absent for clarity.

[0022] FIG. 6 is a perspective view of a fluid tube heater in accordance with an implementation.

[0023] FIG. 7 is a cross-sectional view similar to FIG. 3A in accordance with an alternative implementation.

DETAILED DESCRIPTION

[0024] In dispensing a material onto a surface of a substrate, it may be necessary that the material is dispensed at a relatively low temperature (e.g., 30°C), in which case little or no nozzle heating is needed because the material is already at a suitable viscosity just prior to dispensing. Yet, the substrate upon which the material is dispensed may be held at a relatively high temperature (e.g., 80°C). The relatively high temperature of the substrate, as well as the means for heating said substrate, may add heat to the nozzle and raise the temperature of the material therein to above the desired temperature.

[0025] If the temperature at the nozzle is above the desired temperature, the dispensing action is not under thermal control and may be adversely affected, such as may be caused by an undesirable change in the viscosity of the material. The control system described herein provides a method to cool the nozzle to a temperature at or below the desired temperature and to control and maintain cooling material at a temperature that is based upon the amount of heat being received from the substrate and nozzle heaters.

[0026] FIG. 1 schematically illustrates a control system 1000 for jetting or otherwise dispensing droplets of liquid or viscous material onto a surface of a substrate at a controlled temperature. The control system 1000 includes a dispenser 1004. In one implementation, the dispenser 1004 may be embodied as a jetting dispenser, as described in detail with respect to FIGS. 3-7. In other implementations, the dispenser 1004 may be embodied as a needle-type dispenser. A needle-type dispenser is generally differentiated from the jetting dispenser described herein in that the needle-type dispenser operates by disengaging a needle tip with a valve seat to allow pressurized material to flow through an opening in the valve seat and out of the dispenser. Conversely, to stop the flow of material from the dispenser, the needle tip is engaged with the valve seat to prevent the pressurized material from passing through the opening of the valve seat. It will further be appreciated that the control system 1000 may be used with other types of dispensers and is not limited to jetting or needle-type dispensers. [0027] The dispenser 1004 has a nozzle 1006 in fluid communication with a source of material 1008. A temperature sensor 1010 is associated with the nozzle 1006 to measure the temperature of the nozzle. An adjustable temperature cooling source 1012 provides a cooling material of an adjustable temperature to the nozzle 1006.

[0028] The temperature sensor 1010 may be any type of temperature sensor, such as a resistance temperature detector. A resistance temperature detector measures temperature by correlating the electrical resistance of a resistance temperature detector element with

temperature. Alternately, other types of temperature sensor may be used, such as a thermal expansion thermometer, a gas pressure change thermometer, or an infrared (IR) thermometer.

[0029] A controller 1014 is configured to receive a temperature signal from the temperature sensor 1010 and to send a control signal to the adjustable temperature cooling source 1012 to adjust the temperature of the cooling material based on the temperature signal. Thus, the controller 1014 does not merely adjust the flow of a fixed temperature cooling source, but controls the temperature of the cooling source, such as a cooling material.

[0030] The controller 1014 may be configured to control one or more variables relating to the operation of the control system 1000 and based upon one or more inputs, such as the temperature signal from the temperature sensor 1010. A number of individual control systems may be used and these individual control systems may be integrated as, or otherwise considered to collectively constitute, a single combined controller. The controller 1014 may include one or more programmable logic control (PLC) devices having one or more human machine interfaces (HMI), as are known to persons of ordinary skill in the art. Alternately, the controller 1014 may be embodied as or include a processor configured to run a control program. The controller 1014 may also control other elements in a dispenser as described with respect to FIG. 3 below.

[0031] The adjustable temperature cooling source 1012 may include a material supply along with an electromechanical device that modifies the operation (e.g., the temperature of the cooling material supplied by the adjustable temperature cooling source 1012) of the adjustable temperature cooling source 1012 in response to the control signal from the controller 1014. The electromechanical device may be embodied as an adjustable vortex cooling generator or an adjustable Peltier device, for example. The cooling material may be a gas, such as compressed air, or may be a liquid, such as water.

[0032] A vortex cooling generator, also known as a vortex tube or Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. The air emerging from the "hot" end may reach temperatures of 200°C, and the air emerging from the "cold end" may reach -50°C. In a vortex cooling generator, pressurized gas is injected tangentially into a swirl chamber and accelerated to a high rate of rotation. Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex. A vortex cooling generator may adjust the cooling temperature using a screw that adjusts the geometry of the vortex cooling generator. An adjustable vortex cooling generator may have the screw attached to an electromechanical actuator that adjusts the screw and thus the vortex cooling device geometry based on a control signal, such as from the controller 1014.

[0033] A Peltier cooler uses the Peltier effect to create a heat flux between junctions of two different types of materials. It is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy. A Peltier cooler has two sides, and when DC current flows through the device, it brings heat from one side to the other, so that one side gets cooler while the other gets hotter. The "hot" side may be attached to a heat sink so that it remains at ambient temperature, while the cool side goes below room temperature. In some applications, multiple coolers may be cascaded together for lower temperature.

[0034] In a Peltier cooler, the amount of heat that may be absorbed is proportional to the current supplied to the Peltier cooler. By adjusting the current supplied to the Peltier cooler, the temperature of the cooling material cooled by the Peltier cooler may thus be adjusted. A control signal, such as from the controller 1014, may be sent to an adjustable DC generator that powers the Peltier cooler. In this way, the Peltier cooler will be under the active control of the controller 1014.

[0035] The temperature sensor 1010, the controller 1014, and the adjustable temperature cooling source 1012 may define a feedback loop to actively maintain the temperature of the nozzle 1006 at a pre-determined temperature. Conventional control theory techniques may be used to ensure that the feedback loop is stable. In addition to cooling material temperature, the control system 1000 may also adjust cooling material flow from the adjustable temperature cooling source 1012 and heat from a heater 1015.

[0036] The temperature of the cooling material may be adjusted by the controller 1014 to be below a nominal room temperature (e.g., a temperature in the range of 20°C to 24°C). Further, the temperature of the cooling material may be adjusted by the controller 1014 such that the temperature of the nozzle 1006 is cooler than an ambient temperature (e.g., the temperature of the air within the vicinity of, but external to, the dispenser 1004), at least 10°C, 15°C, or 20°C cooler than the ambient temperature, or below 30°C. [0037] The heater 1015 may also be associated with the nozzle 1006, such as to provide heat to the nozzle 1006 and material therein. The controller 1014 may be configured to send a second control signal to the heater 1015 to adjust a temperature of the heater 1015.

[0038] The adjustable temperature cooling source 1012 may provide a variable temperature cooling material, such as that in the 20-23°C range, to ensure that the nozzle 1006 is at or below a threshold temperature, such as a 30°C threshold temperature. The control system 1000 provides a control element and feedback so that the cooling material temperature may be increased or decreased in order to maintain the nozzle 1006 temperature, such as when the dispenser 1004 moves over a both a heated substrate and a non-heated area.

[0039] FIG. 2 illustrates a flow chart of one implementation of jetting droplets of liquid or viscous material onto a surface of a substrate. In step 1020, a temperature of a nozzle 1006 is sensed using a temperature sensor 1010. In step 1022, the temperature of a cooling material is adjusted in response to the sensed temperature of the nozzle 1006. Finally, in step 1024, the adjusted temperature cooling material is provided to the nozzle 1006 to maintain the temperature of the nozzle 1006 at a desired temperature or below a threshold.

[0040] FIGS. 3-7 describe an exemplary jetting dispenser in which the control system 1000 of FIG. 1 may be used. It is to be understood that the control system 1000 of FIG. 1 may be used with other dispensers than those shown in FIGS. 3-7.

[0041] A dispensing apparatus 10 for use with a computer-controlled non-contact dispensing system (not shown) is shown. The dispensing apparatus 10 includes a module 12 partially positioned inside of a main body 22 and partially projecting from opposite ends of the main body 22, a syringe holder 16 supporting a supply device 14, a solenoid valve 20, and a junction box 18 positioned between the syringe holder 16 and the solenoid valve 20. An electrical cable 21 and air conduits 23, 25 servicing the dispensing apparatus 10 are interfaced to dispensing apparatus 10 at the junction box 18, which acts as a centralized distribution point for power and fluid to the module 12 and the solenoid valve 20. The opposite end of the electrical cable 21 is coupled with a controller 1014 of the dispensing system that controls the operation of the dispensing apparatus 10. The air conduit 23 supplies pressurized air to a fluid manifold inside the junction box 18 coupled to the solenoid valve 20, which is energized and de-energized by electrical signals supplied from the controller 1014 over the electrical cables 21 and 29 to supply pressurized air for opening and closing the dispensing apparatus 10.

[0042] The dispensing apparatus 10 is operative for dispensing pressurized viscous material supplied from a syringe-style supply device 14. Generally, the supply device 14 is a disposable syringe or cartridge, and the viscous material filling the supply device 14 is any highly-viscous material including, but not limited to, solder flux, solder paste, adhesives, solder mask, thermal compounds, oil, encapsulants, potting compounds, inks, and silicones. The supply device 14 typically includes a wiper or plunger (not shown) movable upon application of air pressure, typically between 5 psi and 30 psi, in the head space above the plunger.

[0043] The dispensing apparatus 10, the syringe holder 16, the junction box 18 and the solenoid valve 20 are aligned with a generally planar arrangement to define a reduced overall width profile, when these components are viewed in at least one direction, that increases the overall dispense envelope. Specifically, the total length, L, of the dispensing apparatus 10, including the main body 22, the syringe holder 16, the junction box 18 and the solenoid valve 20, is conventional but the width, W, of the dispensing apparatus 10 is significantly reduced as compared with conventional dispensing apparatus. Generally, the width of the dispensing apparatus 10 is about 1.2 inches. Because of the compact width, larger workpieces may be processed by multiple dispensing apparatus 10 arranged in a side-by-side relationship (i.e., the overall dispense area is increased).

[0044] With continued reference to FIGS. 3 and 3 A, the dispensing apparatus 10 also includes a valve element, illustrated as a needle 24, axially movable within a longitudinal bore 26 of the main body 22, a fluid chamber housing 28, and a nozzle assembly 34. The nozzle assembly 34 includes a nozzle 35 (e.g., the nozzle 1006 of FIG. 1) and a heat transfer member 44 having a slip fit with an exterior portion of the fluid chamber housing 28. A retainer 32, which includes a collar 30 and a wave spring 36 secured to the retainer 32 by a spring clip, removably secures the fluid chamber housing 28 to the main body 22. The heat transfer member 44 participates with the retainer 32 for securing the nozzle 35 and a valve seat disk 62 with the fluid chamber housing 28.

[0045] A portion of the collar 30 has a threaded engagement with the main body 22. Extending axially from the retainer 32 is a pair of hooked arms 39a, 39b (FIG. 5) that engage a rim of heat transfer member 44 for capturing the heat transfer member 44 with the fluid chamber housing 28. Rotation of the retainer 32 relative to the valve body aligns the hooked arms 39a, 39b with slots in the upper rim of the heat transfer member 44, at which time a downward force may remove the heat transfer member 44 from the fluid chamber housing 28. The nozzle 35 and the valve seat disk 62 are then removable tool-free as individual parts, as shown in phantom in FIG. 3. The fluid chamber housing 28 may then be removed from the main body 22 without the assistance of tools. The ease of removing these components reduces the time required for disassembly and reassembly to clean internal wetted surfaces and to perform maintenance.

When the valve seat disk 62, the nozzle 35, and optionally the fluid chamber housing 28, are removed from main body 22, the setting of the preloading spring bias applied to the needle 24 is preserved so that the setting is reestablished when these components are reassembled.

[0046] As an alternative to cleaning the fluid chamber housing 28, an existing fluid chamber housing 28 may be removed from the main body 22 and replaced by a new or cleaned fluid chamber housing 28. In particular, the dispensing apparatus 10 may be provided with a set of fluid chamber housings 28 that are interchangeable and that may be periodically replaced. Removed fluid chamber housings 28 may be cleaned for re-use or, optionally, discarded.

[0047] With reference to FIGS. 3 and 3A, the nozzle 35 consists of a nozzle tip 46 joined with a nozzle hub or nozzle mount 48. The nozzle tip 46 is inserted into a centered axial bore 50 extending along the axial dimension of the nozzle mount 48 and secured by, for example, epoxy or brazing. A truncated conical or frustoconical surface 54 of the nozzle mount 48 contacts a corresponding truncated conical or frustoconical surface 52 of the heat transfer member 44 when the heat transfer member 44 is installed on the fluid chamber housing 28 and tightened. The frustoconical surface 52 transfers an axial load to the frustoconical surface 54 that secures the nozzle 35 to the fluid chamber housing 28 in a fluid-tight relationship. The frustoconical surfaces 52, 54 are each tapered with an included angle of about 70°.

[0048] The interface between the frustoconical surfaces 52, 54 promotes efficient heat transfer from the heat transfer member 44 to the nozzle 35 by increasing the surface area over which contact exists between the heat transfer member 44 and the nozzle mount 48.

Consequently, the frustoconical interface improves the heat transfer efficiency from the heating element 84 to viscous material flowing inside a passageway 72 in the nozzle 35. In addition, the engagement between the frustoconical surfaces 52, 54 operates to self-center the heat transfer member 44 relative to the nozzle mount 48 during installation.

[0049] A fluid tube 56 of a conventional construction couples an outlet port of the supply device 14 with an inlet port 58 of a fluid chamber 60 defined inside the fluid chamber housing 28. Viscous material is supplied under pressure from the supply device 14 through the fluid tube 56 to the inlet port 58 and ultimately to the fluid chamber 60. A fitting 134 provides an interface between the fluid tube 56 and the inlet port 58.

[0050] With continued reference to FIGS. 3 and 3A, positioned within the fluid chamber 60 is the valve seat insert or valve seat disk 62, which is captured by the axial load applied by the frustoconical surface 52 to the frustoconical surface 54 in a space defined between the nozzle mount 48 and the fluid chamber housing 28. The valve seat disk 62 is removable from the dispensing apparatus 10 by removing the heat transfer member 44 and the nozzle 35 from the fluid chamber housing 28. Removal of the valve seat disk 62 will also provide access to the fluid chamber 60 for cleaning.

[0051] The fluid chamber housing 28, the nozzle 35, and the valve seat disk 62 are modular components bearing surfaces in the dispensing apparatus 10 wetted by the viscous material and that are easily removable for cleaning. As a result, the cleaning process for the dispensing apparatus 10 is simplified and the overall cleaning time is reduced. Routine cleaning and maintenance are simplified by a dramatic reduction in the number of tools required to disassemble and re-assemble the fluid chamber housing 28, the nozzle 35, and the valve seat disk 62. The fluid chamber housing 28, the nozzle 35, and the valve seat disk 62 may be replaced by comparable clean components and then batched cleaned for further reducing the time required to clean these components. In some implementations, the fluid chamber housing 28 may be formed from an inexpensive disposable material to further simplify maintenance as cleaning is avoided.

[0052] The valve seat disk 62 comprises a fluid passageway 64 of a suitable diameter extending between an outlet 66 and an inlet 68. The inlet 68 defines and coincides with a valve seat 70. In a used condition in which the material of the valve seat disk 62 surrounding the inlet 68 has been plastically deformed by contact with the needle tip 76, the inlet 68 and valve seat 70 may differ in location. In an alternative implementation, the valve seat disk 62 may be integral with the nozzle mount 48 of the nozzle 35 and, therefore, removable from the dispensing apparatus 10 as a unit or single piece with the nozzle mount 48.

[0053] The nozzle tip 46 is tubular and surrounds a discharge passageway 72 that is coaxial with the outlet 66 from the fluid passageway 64 in the valve seat disk 62. The discharge passageway 72 has a relatively high aspect ratio, which is determined by the ratio of the length of the passageway 72 to the diameter of a discharge outlet or discharge orifice 74, so that the nozzle tip 46 is lengthy and narrow as compared with conventional nozzle tips. Preferably, ratio of the length of the discharge passageway 72 to the diameter of the discharge orifice 74 is greater than or equal to about 25 : 1. In certain implementations, the diameter of the discharge orifice 74 may be one millimeter to eight millimeter and the length of the nozzle tip 46 may be 0.375 of an inch.

[0054] This relatively large aspect ratio permits the nozzle tip 46 to access crowded dispense areas on a workpiece previously inaccessible to conventional dispensing apparatus due to contact between the nozzle tip 46 or another portion of the dispensing apparatus and the workpiece to which the viscous material is being applied. Specifically, the large aspect ratio of the permits the nozzle tip 46 to protrude from the nozzle mount 48, as compared with conventional dispensing nozzles. Increasing the aspect ratio increases the length of the nozzle tip 46 that may protrude from the nozzle mount 48. The nozzle tip 46 may be formed from any suitable material including but not limited to tungsten and ceramics that are resistant to damage if contacted by an object in the environment surrounding the dispensing apparatus 10. The nozzle tip 46 may also include a layer 46a of thermally insulating material, such as a coating, that reduces heat loss from the nozzle tip 46.

[0055] The heating element 84, which may be a flexible thermal foil resistance heater, surrounds the exterior of the heat transfer member 44. The heating element 84 has an efficient heat transfer or thermal contact relationship with the heat transfer member 44 for heating the heat transfer member 44. Heat is readily transferred from the heat transfer member 44 to the nozzle mount 48 for locally heating the nozzle tip 46 and the viscous material resident in the discharge passageway 72. In some implementations, the exterior of the heating element 84 and/or the heat transfer member 44 may be covered by a layer of thermal insulation 84a that limits heat loss from the heating element 84, which aids in temperature control.

[0056] The heat transfer member 44 further incorporates an inlet passageway 86, an outlet passageway 88, and an annular internal plenum 90 coupling the inlet and outlet passageways 86, 88 and surrounding an axial length of the nozzle mount 48. A cooling material, such as a coolant gas (e.g., air), is supplied to the inlet passageway 86 from an adjustable temperature cooling source 1012 via air conduits 25 and 83, which are coupled inside the junction box 18. The coolant gas flows from the inlet passageway 86 through the annular internal plenum 90 and is exhausted through the outlet passageway 88 to create a positive fluid flow. The dimensions of the inlet and outlet passageways 86, 88 and the annular internal plenum 90 are preferably chosen to optimize heat transfer to the flowing coolant gas. The coolant gas may be provided in a different manner or cooling may be accomplished using a different cooling material, such as a liquid. In an alternative implementation, the heat transfer member 44 may be cooled using a thermoelectric cooling device, such as a Peltier cooler.

[0057] The temperature sensor 1010 of FIG. 1 may be implemented as a temperature sensor 92 shown in FIG. 3A. The temperature sensor 92 shown in FIG. 3A may be a resistance temperature detector, disposed in a blind sensor passageway 94 defined in the heat transfer member 44. The temperature sensor 92, which is positioned in heat transfer member 44 proximate to the heating element 84, provides a temperature feedback signal over a set of leads 87, 89 to the controller 1014. The leads 87, 89 emerge from the open end of a lumen 83a of air conduit 83 from the junction box 18, and couple with the temperature sensor 92. Inside the junction box 18, the leads 87, 89 are split from the air conduit 83 and coupled by a connector 95 with the electrical cable 21. More specifically, the leads 87, 89 exit from one arm of a tee 91 that is otherwise sealed to prevent coolant air leakage. [0058] The controller 1014 operates the heating element 84 (shown as the heater 1015 in FIG. 1) and also regulates the flow and temperature of coolant gas, liquid, or other type of cooling material, from the adjustable temperature cooling source 1012 to the inlet coolant passageway 86 in order to maintain the nozzle tip 46 and the viscous material resident in passageways 64 and 72 at a targeted temperature. When the temperature is less than the targeted temperature, heat is supplied from the heating element 84 to the heat transfer member 44 and subsequently conducted to the nozzle 35 and to viscous material inside nozzle tip 46. When the temperature exceeds the targeted temperature, the heat transfer member 44 is actively cooled by a flow of coolant gas through the annular internal plenum 90, which subsequently cools the nozzle 35 and viscous material inside the nozzle tip 46. In some implementations, the controller 1014 automatically switches between heating and cooling for precision temperature regulation of the viscous material inside passageways 64 and 72 without manual intervention and using only feedback temperature information supplied by the temperature sensor 92. The active cooling, which is illustrated as an air flow through the lumen 83 a, the passageway 86, and the annular internal plenum 90, may be any cooling mechanism that reduces the temperature of the heat transfer member 44 and/or the nozzle 35 by removing heat from these structures.

[0059] The precise heating and active cooling of the nozzle 35 and, in particular, the nozzle tip 46 minimizes viscosity variations of the viscous material residing in the passageways 64 and 72 for purposes of flowability and dispensing precise and reproducible amounts of viscous materials. Further, the nozzle tip 46 is maintained below a temperature that may degrade the properties of the viscous material, such as prematurely causing either gelling or curing. Typically, the dispensability of the viscous material residing in the nozzle tip 46 is improved by maintaining its temperature in a range between about 30°C to about 65°C, although the temperature range is not so limited and may depend upon the identity of the viscous material. The viscous material should be maintained at the selected temperature range for only a brief period of time and not to exceed a temperature at which curing may occur. For this reason, only the nozzle assembly 34 is held at the temperature set point and not the remainder of the dispensing apparatus 10.

[0060] With reference to FIGS. 3, 3A, 4 and 5, the solenoid valve 20 is mounted directly against the main body 22 with an intervening thermal barrier 96 that prevents or, at the least, reduces heat transfer from the solenoid valve 20 to the main body 22. Direct attachment of the solenoid valve 20 to the main body 22 promotes a rapid air pressure change to actuate the air piston 78, which decreases the response time for filling the air cavity 80 to open and close the dispensing apparatus 10. The solenoid valve 20 typically includes a movable spool actuated by selectively energizing and de-energizing an electromagnetic coil (not shown) with an electrical signal from a driver circuit 20a. The driver circuit 20a is of a known design with a power switching circuit providing electrical signals to the solenoid valve 20. The driver circuit 20a may be incorporated into the construction of the solenoid valve 20.

[0061] In response to an electrical signal from the driver circuit 20a, the solenoid valve 20 selectively switches a flow path for pressurized air to an air supply port 101 between an air inlet port 99 and an air exhaust port 100. The supply port 101 communicates with the air cavity 80 through a passageway 98 defined in the main body 22. When a suitable electrical signal is applied to the solenoid valve 20, pressurized air is supplied from the air inlet port 99 to supply the port 101 and, subsequently, to the passageway 98. A fluid path to the exhaust port 100 is blocked inside the solenoid valve 20. When the electrical signal is discontinued, the air inlet port 99 is blocked and the exhaust port 100 is coupled with the supply port 101. The pressurized air cavity 80 is serially exhausted through the passageway 98, the supply port 101 and the exhaust port 100.

[0062] The air piston 78 defines an axially-movable confinement wall of the air cavity 80 and is pneumatically sealed with the sidewall of the air cavity 80. When the solenoid valve 20 is switched by the electrical signal to fill the air cavity 80 with pressurized air through the passageway 98, the air piston 78 and the needle 24 move axially in a direction that separates the needle tip 76 from the valve seat 70 and thereby provides the opened position. Conversely, when the solenoid valve 20 is switched to exhaust the air cavity 80 of pressurized air by removing the electrical signal, the air piston 78 and the needle 24 move axially in a direction that contacts the needle tip 76 with the valve seat 70 and thereby provides the closed position.

[0063] The exhaust port 100 of the solenoid valve 20 is fluidly coupled with an air passageway 102 in the main body 22 by a slotted channel 104 formed in the thermal barrier 96. An opening 103 is also provided in the thermal barrier 96 for coupling the supply port 101 with the passageway 98. The pressurized air exhausted from the air cavity 80 is cooled by rapid decompression of the air cavity 80 as the dispensing apparatus 10 closes and by the movement of the air piston 78 toward its closed position. This cooled exhaust air from the air cavity 80 is directed by the channel 104 between its opposite closed ends from the exhaust port 100 to the air passageway 102 and subsequently to an air plenum 106 surrounding a length of the needle 24. The exhaust air is ultimately routed to the ambient environment of the dispensing apparatus 10 through an outlet passageway 108 cross-drilled through the main body 22, which has been rotated from its actual angular orientation for clarity. The flow of cool exhaust air removes heat from the needle 24 and the main body 22. The heat is dumped into the ambient environment of the dispensing apparatus 10 for disposal. The flow of cool exhaust air participates in precision regulation of the temperature of the nozzle tip 46 by reducing conductive heat flow from the main body 22 and the needle 24 to the fluid chamber housing 28 and the nozzle 35. This prevents or reduces the incidence of premature gelling and/or curing inside the main body 22. The channel 104 in the thermal barrier 96 and the air passageway 102 in the main body 22 cooperate to further reduce noise produced by the exhausted pressurized air by altering the direction of the airflow.

[0064] The thermal barrier 96 and the active air flow of the cooled exhaust air through the passageways 102 and 108 and the air plenum 106 in the main body 22, considered either individually or collectively, assist in thermal management of the heat load within the main body 22. As a result, extraneous heat sources do not influence or, at the least have a minimal influence on, the temperature of the nozzle 35 and the viscous material resident therein during a dispensing cycle.

[0065] The solenoid valve 20 may be overdriven by energizing the electromagnetic coil (not shown) of the solenoid valve 20 in order to increase the operating speed of the dispensing apparatus 10 by causing faster acceleration of the air piston 78 from a stationary state. The total response time for opening the dispensing apparatus 10 is measured from the moment that an electrical signal is initially provided to the solenoid valve 20 until the instant that the dispensing apparatus 10 is fully open. The total response time consists of a contribution from the solenoid response time required for the solenoid valve 20 to switch and supply pressurized air at full flow to the passageway 98 and a contribution from the fill time required to fill the air cavity 80 with pressurized air that terminates when the needle 24 is in a fully open position. The solenoid response time is reduced by causing the driver circuit 20a to place an overdriving voltage on the electromagnetic coil during switching beyond a rated voltage for the solenoid valve 20, which decreases the total valve response time. For example, a solenoid valve 20 rated for five VDC (volts of direct current) may be energized with a voltage of 24 VDC by the driver circuit 20a to decrease response time and then modulated to maintain the solenoid valve 20 in an opened state without damaging the solenoid valve 20. In conjunction with the close coupling of the solenoid valve 20 to the main body 22, the overdriving of the driver circuit 20a permits the air cavity 80 to be filled and the needle 24 to be placed in an opened condition, including electrical response time of the solenoid valve 20, in less than four milliseconds. The overdriving of the solenoid valve 20 thereby reduces the total response time for opening the dispensing apparatus 10 by reducing the time contribution due to the solenoid response relative to the time required to fill the air cavity 80. The air cavity 80 is typically exhausted of air pressure and the needle 24 moved to a closed condition in three to four milliseconds. This results in a maximum operating frequency of about 200 Hz, as a portion of the time required to close the dispensing apparatus 10 may overlap with the time required to open the dispensing apparatus 10.

[0066] A sonic muffler 110 may be provided in the air passageway 102 in the main body 22 for attenuating the sound waves associated with the exhausted air, which significantly reduces the noise related to air exhaust from the air cavity 80 without significantly retarding the closing response time of the air piston 78. The sonic muffler 110 may be a porous structure formed, for example, from steel wool, polyethylene, or a metal such as bronze, steel, or aluminum, or may constitute a baffle with internal passageways that slow airflow by deflecting, checking, or otherwise regulating air flow in the air passageway 102. The backpressure created by the sonic muffler 1 10 does not affect the response time for closing the dispensing apparatus 10 at the associated air pressure within the air cavity 80. Because the exhaust port 100 of the solenoid valve 20 is fluidly coupled with the air passageway 102 in the main body 22, a conventional muffler cannot be attached to the exhaust port 100.

[0067] A stroke adjust assembly includes a sleeve 1 16, a load screw 1 12 threadingly engaged with the sleeve 116, and a spring 1 14 compressed by the load screw 112 for applying an axial load to a load button 115 proximate to an end of the needle 24 opposite to the needle tip 76. The load screw 112 is secured to the main body 22 through the sleeve 116 and is movable axially by rotation relative to the main body 22. The spring 114 is partially compressed and thereby preloaded by adjustment of the axial position of the load screw 1 12 relative to the sleeve 116. After this preloaded spring bias is set, a treadlocker is applied to permanently fix the relative positions of the load screw 112 and the sleeve 116.

[0068] A stroke adjust knob 118 is affixed to the load screw 112 and, thereafter, is used to rotate the load screw 1 12 and the sleeve 1 16 relative to the main body 22 for defining a stroke length for the needle tip 76 relative to the valve seat 70. The dispensing apparatus 10 is depicted in FIG. 3 with a zero stroke length setting and the maximum preload spring bias. Setting the stroke length modifies the magnitude of the preloaded spring bias.

[0069] When sufficient pressurized air is supplied to the air cavity 80 for overcoming the preloaded spring bias, the air piston 78 will carry the needle 24 and the load button 1 15 in a direction away from the valve seat 70. Contact between the load button 1 15 and the sleeve 116 operates as a stop. As a result, the needle tip 76 separates from the valve seat 70 and a small amount of viscous material flows into the fluid passageway 64 in the valve seat disk 62. When air pressure is exhausted from the air cavity 80, the axial load from the spring 1 14 rapidly moves the needle 24 toward the valve seat 70, which forces a small amount of viscous material resident in the passageway 72 out of the discharge orifice 74.

[0070] The preloading spring bias, as modified by the stroke adjust setting, is conserved when the heat transfer member 44, the nozzle 35, and/or the fluid chamber housing 28 are removed from the dispensing apparatus 10 and replaced, such as during cleaning and maintenance. As a result, the preloading spring bias will not normally need to be readjusted from the value set at the time of manufacture and/or before the dispensing apparatus 10 is placed into operation. The ability to preserve the preloading spring bias of the spring 1 14 eases re-assembly and installation.

[0071] The needle 24 is guided during its reciprocating axial movement within the main body 22 by a pair of axially spaced needle guides or bushings 122, 124, of which the bushing 124 is positioned in a bearing sleeve 125. The bushings 122, 124 may be formed from plastic, such as PEEK (poly ether ether ketone), containing graphite that operates as a lubricant. The axial spacing of the bushings 122, 124 is selected to be at least four times the diameter of the portion of the needle 24 therein, which advantageously provides and maintains accurate axial guidance of the needle tip 76 for repeated contact and sealing with the valve seat 70 over multiple dispensing cycles. A fluid seal 126 surrounding a portion of the needle 24 and a fluid seal 128 surrounding a different portion of the needle 24 isolate the fluid chamber 60 and the air cavity 80, respectively, from the portion of the longitudinal bore 26 between the bushings 122, 124.

[0072] With reference to FIG. 6 and in accordance with an alternative implementation, a heater 150 may be positioned about a length of the fluid tube 56 for applying heat to elevate the temperature of the viscous material being transferred through fluid tube 56 to the main body 22. The heater 150 includes a thermally-conductive block or body 152 that mounts onto the fluid tube 56 with a good thermal contact. Positioned in thermal contact with the body 152 and within corresponding blind bores are a heating element 154 and a temperature sensor 156. Electrical leads extend from the heating element 154 and the temperature sensor 156 to the controller 1014. The body 152 may have a clamshell-style construction with a groove formed in each shell half 152a, 152b into which the fluid tube 56 is received with a contact effective for heat transfer. The heat supplied by the heater 150 to the viscous material in the side fluid tube 56 supplements the heating of the viscous material in the nozzle 35 and may be particularly useful for dispensing at high flow rates in which the flow of viscous material is too fast for effective temperature control by heat transfer within the nozzle 35 alone. [0073] With reference to FIG. 7 in which like reference numerals refer to like features in FIG. 3A and in accordance with alternative implementation, the heat transfer member 44 may include an annular internal plenum 160 coupling the inlet and outlet passageways 86, 88. The annular intemal plenum 160 extends circumferentially about the heat transfer member 44 and, as a result, encircles or surrounds an axial length of the nozzle mount 48. Coolant gas supplied from the air conduit 83 to the inlet passageway 86 flows through the annular intemal plenum 160 and is exhausted through the outlet passageway 88 to create a positive fluid flow. The annular internal plenum 160 may be implemented either individually or in combination with the annular internal plenum 90.

[0074] It will be apparent to those skilled in the art that various modifications and variations may be made without departing from the scope or spirit. Other implementations will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit being indicated by the following claims.