US20050001869A1 - Viscous material noncontact jetting system - Google Patents

Abstract

A viscous material noncontact jetting system has a jetting dispenser mounted for relative motion with respect to a surface. A control is operable to cause the jetting dispenser to jet a viscous material droplet that is applied to the surface as a viscous material dot. A device, such as a camera or weigh scale, is connected to the control and provides a feedback signal representing a size-related physical characteristic of the dot applied to the surface. The size-related physical characteristics of subsequently applied dots is controlled by heating and cooling, or adjusting a piston stroke in the jetting dispenser, in response to the size-related physical characteristic feedback. Dispensed material volume control and velocity offset compensation are also provided.

Description

• This application claims priority to U.S. application Ser. No. 60/473,166, filed on May 23, 2003, which is hereby expressly incorporated by reference herein.
FIELD OF THE INVENTION
• The present invention generally relates to equipment for dispensing viscous materials and more particularly, to a computer controlled, noncontact jetting system for applying dots of viscous material onto a surface.
BACKGROUND OF THE INVENTION
• In the manufacture of substrates, for example, printed circuit (“PC”) boards, it is frequently necessary to apply small amounts of viscous materials, i.e. those with a viscosity greater than fifty centipoise. Such materials include, by way of example and not by limitation, general purpose adhesives, solder paste, solder flux, solder mask, grease, oil, encapsulants, potting compounds, epoxies, die attach pastes, silicones, RTV and cyanoacrylates.
• In the quest for ever increasing miniaturization of circuitry, a fabrication process known as flip chip technology has developed, which has multiple processes that require viscous fluid dispensing. For example, a semiconductor die or flip chip is first attached to a PC board via solder balls or pads, and in this process, a viscous solder flux is applied between the flip chip and the PC board. Next, a viscous liquid epoxy is allowed to flow and completely cover the underside of the chip. This underfill operation requires that a precise amount of the liquid epoxy be deposited in a more or less continuous manner along at least one side edge of the semiconductor chip. The liquid epoxy flows under the chip as a result of capillary action due to the small gap between the underside of the chip and the upper surface of the PC board. Once the underfill operation is complete, it is desirable that enough liquid epoxy be deposited to encapsulate all of the electrical interconnections, so that a fillet is formed along the side edges of the chip. A properly formed fillet ensures that enough epoxy has been deposited to provide maximum mechanical strength of the bond between the chip and the PC board. Thus, underfilling with the epoxy serves first, as a mechanical bond to help reduce stress and limit strain on the interconnecting solder pads during thermal cycling and/or mechanical loading and second, protects the solder pads from moisture and other environmental effects. It is critical to the quality of the underfilling process that the exact amount of epoxy is deposited at exactly the right location. Too little epoxy can result in corrosion and excessive thermal stresses. Too much epoxy can flow beyond the underside of the chip and interfere with other semiconductor devices and interconnections.
• In another application, a chip is bonded to a PC board. In this application, a pattern of adhesive is deposited on the PC board; and the chip is placed over the adhesive with a downward pressure. The adhesive pattern is designed so that the adhesive flows evenly between the bottom of the chip and the PC board and does not flow out from beneath the chip. Again, in this application, it is important that the precise amount of adhesive be deposited at exact locations on the PC board.
• The PC board is often being carried by a conveyor past a viscous material dispenser that is mounted for two axes of motion above the PC board. The moving dispenser is capable of depositing dots of viscous material at desired locations on the PC board. There are several variables that are often controlled in order to provide a high quality viscous material dispensing process. First, the weight or size of each of the dots may be controlled. Known viscous material dispensers have closed loop controls that are designed to hold the dot size constant during the material dispensing process. It is known to control the dispensed weight or dot size by varying the supply pressure of the viscous material, the on-time of a dispensing valve within the dispenser and the stroke of an impact hammer in a dispensing valve. Each of those control loops may have advantages and disadvantages depending on the design of a particular dispenser and the viscous material being dispensed thereby. However, those techniques often require additional components and mechanical structure, thereby introducing additional cost and reliability issues. Further, the responsiveness of those techniques is proving less satisfactory as the rate at which dots are dispensed increases. Therefore, there is a continuing need to provide better and simpler closed loop controls for controlling dot size or weight.
• A second important variable that may be controlled in the dispensing process is the total amount or volume of viscous material to be dispensed in a particular cycle. Often the designer of a chip specifies the total amount or volume of viscous material, for example, epoxy in underfilling, or adhesive in bonding, that is to be used in order to provide a desired underfilling or bonding process. For a given dot size and dispenser velocity, it is known to program a dispenser control, so that the dispenser dispenses a proper number of dots in order to dispense a specified amount of the viscous material in a desired line or pattern at the desired location on the PC board. Such a system is reasonably effective in a world in which the parameters that effect the dispensing of the viscous material remain constant. However, such parameters are constantly changing, albeit, often only slightly over the short term; but the cumulative effect of such changes can result in a detectable change in the volume of fluid being dispensed by the dispenser. Therefore, there is a need for a control system that can detect changes in dispensed weight and automatically adjust the dispenser velocity, so that the desired total volume of viscous material is uniformly dispensed over a whole dispensing cycle.
• A third important variable relates to the timing of dispensing dots of viscous material on-the-fly. When dispensed on-the-fly, the dots of viscous material fly horizontally through the air prior to landing on the PC board. In order to accurately locate the dots on the PC board, it is known to perform a calibration cycle in which a time based compensation value is determined and used to pre-trigger the dispenser. Again, there is a need to continue to improve the process by which an on-the-fly dispenser can dispense dots of viscous material, so that they are more accurately located on the PC board.
• Therefore, there is a need for an improved computer controlled viscous fluid dispensing system that addresses the needs described above.
SUMMARY OF THE INVENTION
• The present invention provides an improved noncontact jetting system that more accurately applies, on-the-fly, viscous material dots on a substrate. First, the improved noncontact jetting system of the present invention permits dispensed weight or dot size to be adjusted by changing either the temperature of the nozzle or the stroke of a piston in the jetting valve. This provides a simpler and less expensive system with a faster response time for calibrating dispensed weight or dot size. Further, the improved noncontact jetting system of the present invention permits a relative velocity between a nozzle and the substrate to be automatically optimized as a function of a current material dispensing characteristics and a specified total volume of material to be used on the substrate. The result is a more accurate and uniform application of the dispensed viscous material on the substrate. In addition, the improved noncontact jetting system of the present invention optimizes the positions at which respective dots are to be dispensed as a function of the relative velocity between the nozzle and the substrate, so that viscous material dots dispensed on-the-fly are accurately located on the substrate. The improved noncontact jetting system of the present invention is especially useful in those applications where weight or volume of the viscous material dots and their location on the substrate require accurate and precise control.
• According to the principles of the present invention and in accordance with the described embodiments, the invention provides a viscous material noncontact jetting system with a jetting dispenser mounted for relative motion with respect to a surface. A control is connected to the jetting dispenser and has a memory for storing a desired size-related physical characteristic of a dot of viscous material. The control is operable to cause the jetting dispenser to apply dots of viscous material onto the surface. A device is connected to the control and provides a feedback signal representing a detected size-related physical characteristic of the dot applied to the surface. A temperature controller has a first device for increasing the temperature of the nozzle and a second device for decreasing the temperature of the nozzle. The control is operable to cause the temperature controller to change a temperature of the nozzle in response to a difference between the detected size-related physical characteristic and the desired size-related physical characteristic.
• In different aspects of this invention, the size-related physical characteristic is determinative of either a diameter, a weight or a volume of the dots applied to the surface. In another aspect of this invention, the device is a camera; and in a further aspect of this invention, the device is a weigh scale. Other aspects of this invention include methods of operating either a first device that increases the temperature of the nozzle or a second device that decreases the temperature of the nozzle in response to the difference between the detected size-related physical characteristic and the desired size-related physical characteristic.
• In another embodiment of the invention, control is operable to first cause a piston in the jetting dispenser to move through a stroke away from a seat and thereafter, cause the piston to move through the stroke toward the seat to jet a droplet of viscous material through the nozzle. The droplet is applied to the surface as a dot of viscous material. The control is further operable to increase or decrease the stroke of the piston in response to the feedback signal representing a size-related physical characteristic of the dot that is respectively, less than, or greater than, the desired dot size value. In another aspect of this invention, the device is a camera; and in a further aspect of this invention, the device is a weigh scale. In other aspects of this invention, methods are used to increase or decrease the stroke of the piston in response to the size-related physical characteristic of the dot applied to the surface being respectively, less than, or greater than, a desired value.
• In a still further embodiment of the invention, the control stores a total volume value representing a total volume of the viscous material to be dispensed and a length value representing a length overwhich the total volume of viscous material is to be dispensed. The control is operable to cause the jetting dispenser to apply dots of viscous material to the surface. The device provides a feedback signal to the control representing an amount of the viscous material contained in the dots applied to the surface. The control is responsive to the feedback signal, the volume value and the length value to determine a maximum velocity value for the relative motion between the jetting dispenser and the surface resulting in the total volume of material being uniformly dispensed over the length.
• In yet another embodiment of the invention, the control is operable to cause the jetting dispenser to jet a viscous material droplet through the nozzle at a first location resulting in a dot of viscous material being applied to the surface. A camera connected to the control provides a feedback signal representing a location of a physical characteristic of the dot on the surface. The control determines a location of the dot on the surface and then, determines an offset value representing a difference between the first location and the location of the dot on the surface. The offset value is stored in the control and is used to offset coordinate values representing the first location during a subsequent jetting of viscous material.
• These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic representation of a computer controlled, viscous material noncontact jetting system in accordance with the principles of the present invention.
• FIG. 2 is a schematic block diagram of the computer controlled, viscous material noncontact jetting system ofFIG. 1.
• FIG. 3 is a flowchart generally illustrating a dispensing cycle of operation of the viscous material jetting system ofFIG. 1.
• FIG. 4 is a flowchart generally illustrating a dot size calibration process using the viscous material jetting system ofFIG. 1.
• FIG. 5 is a flowchart generally illustrating a material volume calibration process using the viscous material jetting system ofFIG. 1.
• FIG. 6 is a flowchart generally illustrating a dot placement calibration process using the viscous material jetting system ofFIG. 1.
• FIG. 7 is a flowchart generally illustrating an alternative embodiment of a dot placement calibration process using the viscous material jetting system ofFIG. 1.
• FIG. 8 is a flowchart generally illustrating an alternative embodiment of a dot size calibration process using the viscous material jetting system ofFIG. 1.
• FIG. 9 is a flowchart generally illustrating a further alternative embodiment of a dot size calibration process using the viscous material jetting system ofFIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 is a schematic representation of a computer controlled viscous materialnoncontact jetting system10 of the type commercially available from Asymtek of Carlsbad, Calif. Arectangular frame11 is made of interconnected horizontal and vertical steel beams. A viscousmaterial droplet generator12 is mounted on a Z-axis drive that is suspended from anX-Y positioner14 mounted to the underside of the top beams of theframe11. TheX-Y positioner14 is operated by a pair of independently controllable motors (not shown) in a known manner. The X-Y positioner and Z-axis drive provide three substantially perpendicular axes of motion for thedroplet generator12. A video camera and LEDlight ring assembly16 may be connected to thedroplet generator12 for motion along the X, Y and Z axes to inspect dots and locate reference fiducial points. The video camera andlight ring assembly16 may be of the type described in U.S. Pat. No. 5,052,338 the entire disclosure of which is incorporated herein by reference.
• Acomputer18 is mounted in the lower portion of theframe11 for providing the overall control for the system. Thecomputer18 may be a programmable logic controller (“PLC”) or other microprocessor based controller, a hardened personal computer or other conventional control devices capable of carrying out the functions described herein as will be understood by those of ordinary skill. A user interfaces with thecomputer18 via a keyboard (not shown) and avideo monitor20. A commercially available video frame grabber in the computer causes a real time magnifiedimage21 of a cross-hair and dispensed dot to be displayed in a window on themonitor20, surrounded by the text of the control software. Thecomputer18 may be provided with standard RS-232 and SMEMA CIM communications busses50 which are compatible with most types of other automated equipment utilized in substrate production assembly lines.
• Substrates, for example, PC boards, which are to have dots of a viscous material, for example, an adhesive, epoxy, solder, etc., rapidly applied thereto by thedroplet generator12, are manually loaded or horizontally transported directly beneath thedroplet generator12 by anautomatic conveyor22. Theconveyor22 is of conventional design and has a width which can be adjusted to accept PC boards of different dimensions. Theconveyor22 also includes pneumatically operated lift and lock mechanisms. This embodiment further includes anozzle priming station24 and acalibration station26. Acontrol panel28 is mounted on theframe11 just below the level of theconveyor22 and includes a plurality of push buttons for manual initiation of certain functions during set-up, calibration and viscous material loading.
• Referring toFIG. 2, thedroplet generator12 is shown jettingdroplets34 of viscous material downwardly onto theupper surface81 of asubstrate36, for example, a PC board. ThePC board36 is of the type designed to have components surface mounted thereon utilizing minute dots35 of viscous material rapidly and accurately placed at desired locations. The PC board is moved to a desired position by theconveyor22 as indicated by the horizontal arrows inFIG. 2.
• Axes drives38 are capable of rapidly moving thedroplet generator12 over the surface of thePC board36. The axes drives38 include the electro-mechanical components of theX-Y positioner14 and a Z-axis drive mechanism to provide X, Y and Z axes ofmotion77,78,79, respectively. Often, thedroplet generator12 jets droplets of viscous material from one fixed Z height. However, thedroplet generator12 can be raised using the Z-axis drive to dispense at other Z heights or to clear other components already mounted on the board.
• Thedroplet generator12 can implemented using different designs; and the specific embodiment described herein is to be considered an example, and not a limitation, of the invention. Thedroplet generator12 includes an ON/OFF jetting dispenser40, which is a non-contact dispenser specifically designed for jetting minute amounts of viscous material. Thedispenser40 may have a jettingvalve44 with apiston41 disposed in acylinder43. Thepiston41 has alower rod45 extending therefrom through amaterial chamber47. A distal lower end of thelower rod45 is biased against aseat49 by areturn spring46. Thepiston41 further has anupper rod51 extending therefrom with a distal upper end that is disposed adjacent a stop surface on the end of a screw53 of a micrometer55. Adjusting the micrometer screw53 changes the upper limit of the stroke of thepiston41. Thedispenser40 may include a syringe-style supply device42 that is fluidly connected to a supply of viscous material (not shown) in a known manner. Adroplet generator controller70 provides an output signal to a voltage-to-pressure transducer72, for example, an air piloted fluid regulator, one or more pneumatic solenoids, etc., connected to a pressurized source of fluid, that, in turn, ports pressurized air to thesupply device42. Thus, thesupply device42 is able to supply pressurized viscous material to thechamber47.
• A jetting operation is initiated by thecomputer18 providing a command signal to thedroplet generator controller70, which causes thecontroller70 to provide an output pulse to a voltage-to-pressure transducer80, for example, an air piloted fluid regulator, one of more pneumatic solenoids, etc., connected to a pressurized source of fluid. The pulsed operation of thetransducer80 ports a pulse of pressurized air into thecylinder43 and produces a rapid lifting of thepiston41. Lifting the pistonlower rod45 from theseat49 draws viscous material in thechamber47 to a location between the pistonlower rod45 and theseat49. At the end of the output pulse, thetransducer80 returns to its original state, thereby releasing the pressurized air in thecylinder43, and areturn spring46 rapidly lowers the pistonlower rod45 back against theseat49. In that process, adroplet34 of viscous material is rapidly extruded or jetted through an opening or dispensing orifice59 of anozzle48. As schematically shown in exaggerated form inFIG. 2, theviscous material droplet34 breaks away as a result of its own forward momentum; and its forward momentum carries it to the substrateupper surface81, where it is applied as aviscous material dot37. Rapid successive operations of the jettingvalve41 provide respective jetteddroplets34 that form a line35 of viscous material dots on the substrateupper surface81. As used herein, the term “jetting” refers to the above-described process for formingviscous material droplets34 anddots37. Thedispenser40 is capable of jettingdroplets34 from thenozzle48 at very high rates, for example, up to100 or more droplets per second. Amotor61 controllable by thedroplet generator controller70 is mechanically coupled to the micrometer screw53, thereby allowing the stroke of thepiston41 to be automatically adjusted, which varies the volume of viscous material in each jetted droplet. Jetting dispensers of the type described above are more fully described in U.S. Pat. Nos. 6,253,757 and 5,747,102, the entire disclosures of which are hereby incorporated herein by reference.
• A motion controller62 governs the motion of thedroplet generator12 and the camera andlight ring assembly16 connected thereto. The motion controller62 is in electrical communication with the axes drives38 and provides command signals to separate drive circuits for respective X, Y and Z axes motors in a known manner.
• The camera andlight ring assembly16 is connected to avision circuit64. This circuit drives red LEDs of a light ring for illuminating the substrateupper surface81 and thedots37 applied thereto. A video camera in theassembly16 includes a charge coupled device (CCD) having an output that is converted to digital form and processed in determining both the location and size of a selected dot dispensed onto thesubstrate36. Avision circuit44 communicates with thecomputer18 and to provide information thereto in both set-up and run modes.
• Aconveyor controller66 is connected to thesubstrate conveyor22. Theconveyor controller66 interfaces between the motion controller62 and theconveyor22 for controlling the width adjustment and lift and lock mechanisms of theconveyor22. Theconveyor controller66 also controls the entry of thesubstrate36 into the system and the departure therefrom upon completion of the viscous material deposition process. In some applications, asubstrate heater68 is operative in a known manner to heat the substrate and maintain a desired temperature profile of the viscous material as the substrate is conveyed through the system. Thesubstrate heater68 is operated by aheater controller69 in a known manner.
• Thecalibration station26 is used for calibration purposes to provide a dot size calibration for accurately controlling the weight or size of the dispenseddots37 and a dot placement calibration for accurately locating viscous material dots that are dispensed on-the-fly, that is, while thedroplet generator12 is moving relative to thesubstrate36. In addition, thecalibration station26 is used to provide a material volume calibration for accurately controlling the velocity of thedroplet generator12 as a function of current material dispensing characteristics, the rate at which the droplets are to be dispensed and a desired total volume of viscous material to be dispensed in a pattern of dots, for example, in the line35. Thecalibration station26 includes astationary work surface74 and a measuringdevice52, for example, a weigh scale, that provides a feedback signal to thecomputer18 representing size-related physical characteristic of the dispensed material, which in this embodiment is the weight of material weighed by thescale52. Weighscale52 is operatively connected to thecomputer18; and thecomputer18 compares the weight of the material with a previously determined specified value, for example, a viscous material weight setpoint value stored in acomputer memory54. Other types of devices may be substituted for theweigh scale24 and, for example, may include other dot size measurement devices such as vision systems, including cameras, LEDs or phototransistors for measuring the diameter, area and/or volume of the dispensed material.
• In this embodiment, thenoncontact jetting system10 further includes atemperature controller86 including aheater56, a cooler57 and a temperature sensor58, for example, a thermocouple, an RTD device, etc., which are disposed immediately adjacent thenozzle48. Theheater56 may be a resistance heater that provides heat to thenozzle48 by radiance or convection. The cooler57 can be any applicable device, for example, a source of cooler air, a vortex cooling generator that is connected to a source of pressurized air, etc. In other embodiments, a Peltier device may be used. The specific commercially available devices chosen to provide heating and cooling will vary depending on the environment in which thenoncontact jetting system10 is used, the viscous material being used, the heating and cooling requirements, the cost of the heating and cooling devices, the design of the system, for example, whether heat shields are used, and other application related parameters. The thermocouple58 provides a temperature feedback signal to a heater/cooler controller60, and thecontroller60 operates theheater56 and cooler57 in order to maintain thenozzle48 at a desired temperature as represented by a temperature setpoint. Thecontroller60 is in electrical communications with thecomputer18. Thus, the temperature of thenozzle48 and the viscous material therein is accurately controlled while it is located in and being ejected from thenozzle48, thereby providing a higher quality and more consistent dispensing process.
• In operation, CAD data from a disk or a computer integrated manufacturing (“CIM”) controller are utilized by thecomputer18 to command the motion controller62 to move thedroplet generator12. This ensures that the minute dots of viscous material are accurately placed on thesubstrate36 at the desired locations. Thecomputer18 automatically assigns dot sizes to specific components based on the user specifications or a stored component library. In applications where CAD data is not available, the software utilized by thecomputer18 allows for the locations of the dots to be directly programmed. In a known manner, thecomputer18 utilizes the X and Y locations, the component types and the component orientations to determine where and how many viscous material dots to apply to theupper surface81 of thesubstrate36. The path for dispensing the minute viscous material droplets is optimized by aligning the in-line points. Prior to operation, a nozzle assembly is installed that is often of a known disposable type designed to eliminate air bubbles in the fluid flow path.
• After all of the set up procedures have been completed, a user then utilizes the control panel28 (FIG. 1) to provide a cycle start command to thecomputer18. Referring toFIG. 3, thecomputer18 then begins executing a dispensing cycle of operation. Upon detecting a cycle start command, at300, thecomputer18 then provides command signals to the motion controller62 that cause thedroplet generator12 to be moved to thenozzle priming station24, where a nozzle assembly is mated with a resilient priming boot (not shown) in a known manner. Using an air cylinder (not shown), a vacuum is then pulled on the boot to suck viscous material from thepressurized syringe42 and through the nozzle assembly.
• Thereafter, thecomputer18 determines, at304, whether a dot size calibration is required. A dot size calibration is often executed upon initially beginning a dot dispensing process or any time the viscous material is changed. As will be appreciated, the execution of a dot size calibration is application dependent and can be automatically run at set time intervals, part intervals, with every part, etc. If a dot size calibration is to be run, the computer executes, at306, a dot size calibration subroutine. Referring toFIG. 4, thecomputer18 executes a dot size calibration that is capable of changing the amount of the dispensed material volume and hence, the dot size, by changing the temperature of the viscous material within thenozzle48, thereby changing viscous material's viscosity and flow characteristics. In a first step of this calibration process, thecomputer18 commands, at400, the motion controller62 to move thedroplet generator12 to thecalibration station26 such that thenozzle48 is directly over thework surface74. Next, at402, thecomputer18 commands the motion controller62 to cause thedroplet generator controller70 to dispense dots37a,37b,37n(FIG. 2) on thework surface74. During this calibration process, the dispenser feedrate is not critical, but thedots37 are applied at a rate that is to be used in the production dispensing process. Thecomputer18 then, at404, commands the motion controller62 to move thecamera16 along the same path along which the dots37a,37b,37nwere applied. Thecomputer18 andvision circuit64 provide a feedback signal representing a size-related physical characteristic of the applied dot, which in this embodiment is a first edge82 of a first dot; and thecomputer18 stores in thecomputer memory54 position coordinates of a point on that first edge82. With continued motion of the camera along the path, another feedback signal is provided representing a diametrically oppositesecond edge84 of the first dot37a; and position coordinates of a point on thesecond edge84 of the first dot37aare also stored in thecomputer memory54. The distance between the two sets of position coordinates represents the diameter or size of the first dot37a. The above process of detecting dot edges and storing respective position coordinates continues for other dots37b,37non thesurface74. A sufficient number of dots are dispensed and measured by thecomputer18 so as to provide a statistically reliable measure of dot diameter. However, as will be appreciated, the diameter of a single applied dot may be measured and used to initiate a dot size calibration.
• After all of the dots have been deposited and measured, at406, thecomputer18 then determines the average dot diameter or size and, at408, determines whether the average dot diameter is smaller than a specified dot diameter. If so, thecomputer18 provides, at410, a command signal to the heater/cooler controller60 causing the temperature setpoint to be increased by an incremental amount. The heater/cooler controller60 then turns on theheater56 and, by monitoring temperature feedback signals from the thermocouple58, quickly increases the temperature of thenozzle48 and the viscous material therein to a temperature equal to the new temperature setpoint. When the increased temperature has been achieved, thecomputer18 provides command signals to the motion controller62 to cause thedroplet generator70 to again execute the previously described process steps402-408. The increased temperature reduces the viscosity of the viscous material, thereby resulting in more material being dispensed and hence, a larger average volume and dot diameter; and that larger average dot diameter is then compared with the specified dot diameter at408. If the diameter is still too small, thecontroller18 again provides command signals, at410, to again increase the temperature setpoint value. The process of steps402-410 is iterated until thecomputer18 determines that the current average dot diameter is equal to, or within an allowable tolerance of, the specified dot diameter.
• If thecomputer18 determines, at408, that the average dot diameter is not too small, then the computer determines, at412, whether the average dot diameter is too large. If so, it provides, at414, a command signal to the heater/cooler controller60 that results in a decrease of the temperature setpoint by an incremental amount. With a reduction in the temperature setpoint, the heater/cooler controller60 is operative to turn on the cooler56; and by monitoring the temperature feedback signals from the thermocouple58, thecontroller60 quickly reduces the temperature of thenozzle48 and the viscous material therein to the new lower temperature setpoint value. By reducing the temperature of the viscous material, its viscosity value increases. Therefore, during a subsequent jetting of a number of dots, a less material is dispensed; and thecomputer18 detects a smaller average volume or dot diameter. Again, that process of steps402-412 iterates until the average dot diameter is reduced to a value equal to, or within an allowable tolerance of, the specified dot diameter.
• In the dot size calibration process described above, thecomputer18 iterates the process by jetting and measuring successive dots until a specified dot diameter is achieved. In an alternative embodiment, a relationship between a change in temperature and a change in dot size for a particular viscous material can be determined experimentally or otherwise. That relationship can be stored in thecomputer18 either as a mathematical algorithm or a table that relates changes in dot size to changes in temperature. An algorithm or table can be created and stored for a number of different viscous materials. Therefore, instead of the iterative process described above, after determining the amount by which the dot diameter is too large or too small, thecomputer18 can, at410 and414, use a stored algorithm or table to determine a change in temperature that is required to provide the desired change in dot size. After commanding the heater/cooler controller60 to change the temperature setpoint by that amount, the process ends as indicated by the dashedlines416. In still further embodiments, the above-described calibration processes and be executed using radii or circumferences of respective dots that are determined from the edges detected by the camera.
• Referring back toFIG. 3, after the dot size calibration is complete, thecomputer18 then determines, at308, whether a material volume calibration is required. A material volume calibration is often executed upon initially beginning a dot dispensing process or any time the dispensed weight, dot diameter, dot size or viscous material changes. As will be appreciated, the execution of a material volume calibration is application dependent and can be automatically run at set time intervals, part intervals, with every part, etc. As discussed earlier, for an optimum process, for example, underfilling, bonding, soldering, etc., it is required that an accurate total volume of material be uniformly applied at precise locations. Often, the total material volume is specified by the user and is dependent on the size of the die, the viscous material, its specific gravity, the applied line thickness, the distance between the die and the substrate, the size of a fillet, if applicable, etc. For the total material volume to be uniformly dispensed, an accurate determination of dispenser velocity is required, which is the function of the material volume calibration subroutine.
• If thecomputer18 determines that a material volume calibration is to be run, thecomputer18 then executes, at310, the material volume calibration subroutine illustrated inFIG. 5. The first step of that process requires that thecomputer18 provide command signals, at500, to move thedroplet generator12 so that thenozzle48 is over the table76 of theweigh scale52. Thereafter, thecomputer18 determines, at502, the total volume of material required. This determination may be made either by reading a user entered value from thememory54 or determining a total volume using the user entered parameters identified above, for example, line thickness, die size, fillet size, etc. Thereafter, thecomputer18 dispenses, at504, a number of dots onto the table76 of theweigh scale52. As will be appreciated, a dispensed dot is normally not detectable within the resolution range of theweigh scale52. Therefore, a significant number of dots may have to be dispensed in order to provide a statistically reliable measurement of dispensed material weight by theweigh scale52. However, as will be appreciated, if the scale has a sufficiently high resolution, only a single dot of viscous material can be used to provide the dot size calibration. At the end of the dispensing process, thecomputer18 then, at506, reads or samples a weight feedback signal from theweigh scale52, which represents the weight of the dispensed dots. Knowing the number of dots dispensed, thecomputer18 is then able to determine, at508, the weight of each dot. Using the specific gravity provided by the user and stored in thecomputer memory54, thecomputer18 is then able to determine, at510, the volume of each dot. Knowing the total volume of material required fromprocess step502 and the volume of each dot, thecomputer18 is then able to determine, at512, the number of dots required to dispense the total volume.
• In an underfilling operation, the dots are dispensed along a single line that is immediately adjacent one side of the die. In a die bonding operation, droplets are dispensed in a pattern of lines of viscous material, and the total length is the cumulative length of the lines in the pattern over which the total volume of material is to be dispensed. In either event, the total length value is often provided by a user and stored in thecomputer memory54. Thus, thecomputer18 is able to determine, at513, the total length, either by reading it from memory or determining it from a selected dispensing pattern. Knowing the total length and the number of dots, thecomputer18 is then able to determine, at514, the dot pitch, that is, the distance between the centers of the dots. Dot pitch is also a measure of the volume of viscous material per unit length along the path. A maximum dot rate, which is generally a function of the viscosity of the material being dispensed and other application related factors, is determined either by the user, or experimentally, and is stored in thecomputer memory54. For optimum production efficiency, it is desirable that the maximum dot rate be used to determine a maximum relative velocity between thedot generator12 and thesubstrate36. Knowing the maximum dot rate and the distance between the dots, thecomputer18 is then able to determine and store, at516, a maximum relative velocity at which the motion controller62 can command thedroplet generator12 to move with respect to thesubstrate36.
• In an alternative embodiment of the material volume calibration process ofFIG. 5, in some applications, the maximum relative velocity between thedroplet generator12 and thesubstrate36 may be determined by the user or other factors, for example, theelectromechanical components38, etc. In that situation, given a desired maximum relative velocity and the dot pitch, thecomputer18 is able, at516, to determine a rate at which the dots are to be dispensed. Assuming that dot rate is equal to or less than the maximum dot rate, thecomputer18 can command thedroplet generator controller70 to dispense dots at that rate.
• Referring back toFIG. 3, upon completion of the material volume calibration, thecomputer18 then determines, at312, whether a dot placement calibration is required. A dot placement calibration is often executed upon initially beginning a dot dispensing process and any time the maximum velocity or viscous material changes. As will be appreciated, the execution of a dot placement calibration is application dependent and can be automatically run at set time intervals, part intervals, with every part, etc. Thedroplet generator12 is often jettingviscous material droplets34 on-the-fly, that is, while it is moving relative to thesubstrate36. Therefore, theviscous material droplets34 do not vertically drop onto thesubstrate36 but instead, have a horizontal motion component prior to landing on thesubstrate37. Consequently, the position at which thedroplet generator12 dispenses thematerial droplet34 should be offset to compensate for that horizontal displacement of theviscous material droplet34 prior to landing on thesubstrate36. To determine this offset, thecomputer18 executes, at314, a dot placement calibration subroutine illustrated further inFIG. 6.
• Thecomputer18 commands, at600, the motion controller62 to cause thedroplet generator12 to move to a location placing thenozzle48 over thework surface74 of thecalibration station26. Thecomputer18 then commands, at602, the motion controller62 to cause thedroplet generator controller70 to dispense a line of viscous material dots onto thework surface74 at the maximum velocity that was determined by the material volume compensation subroutine ofFIG. 5. Thereafter, thecomputer18 commands, at604, the motion controller62 to move thecamera16 along the same path over which the dots were dispensed. In a manner as previously described, thecomputer18 andvision circuit64 detect diametrically opposed edges of the dots; and thecomputer18 stores coordinate values of points on the edges. Based on those stored points, the computer determines position coordinates of a center of the dots. Thecomputer18 then determines, at606, a difference between a position of thenozzle48 when adroplet34 was ejected and a position of arespective dot37 on thework surface74. The difference in those two positions is stored as an offset value in thecomputer memory54.
• Referring toFIG. 3, after the various calibration subroutines have been executed, thecomputer18 then commands, at316, theconveyor controller66 to operate theconveyor22 and transport asubstrate36 to a fixed position within thenoncontact jetting system10. In a known manner, an automatic fiducial recognition system locates fiducials on the substrate and corrects for any misalignment to ensure thesubstrate36 is accurately placed within thenoncontact jetting system10.
• Thecomputer18 determines, at318, the position coordinates of the first and last dispense points of the line of viscous material to be deposited and further applies the offset values determined during the dot placement calibration. As will be appreciated, the offset value may be resolved into X and Y components depending on the orientation of the line on the substrate. Thecomputer18 then determines a distance required to accelerate thedroplet generator12 to the maximum velocity determined during the material volume calibration. Next, a prestart point is defined that is along the path between the first and last points but displaced from the first point by the acceleration distance. Thereafter, thecomputer18 commands, at320, motion controller62 to move thenozzle48.
• Motion is first commanded to the prestart point, and then motion is commanded to the first dispense point as modified by the offset value. Thus, after reaching the prestart point, the nozzle begins moving along a path between the first and last dispense points. The motion controller62 then determines, at326, when thenozzle48 has been moved to the next dispense point, for example, the first dispense point as modified by the offset value. The motion controller62 then provides, at328, a command to thedroplet generator controller70 to operate the jettingvalve40 and dispense the first dot. Thus, the first dot is jetted at a nozzle location offset from the first dispense position, but due to the relative velocity between thedroplet generator12 and thesubstrate36, the first dot lands on the substrate at the desired first dispense position.
• Thereafter, the dispensing process iterates through steps322-328 to dispense the other dots. With each iteration, thecomputer18 provides commands to the motion controller62, which cause thedroplet generator12 to move through an incremental displacement equal to the dot pitch. Each successive increment of motion equal to dot pitch represents the next dispense point and is detected by the motion controller62 at326. Upon detecting each increment of motion, the motion controller62 provides, at328, a command to thedroplet generator controller70 causing a droplet of viscous material to be dispensed. Since the first dispense point was modified by the offset values, the positions of the other incrementally determined dispensed points are also modified by the offset values. Therefore, further dots are applied to the substrate at the desired points.
• The motion controller62 determines when the last dispense point as modified by the offset value has been reached and provides a command to thedroplet generator controller70 to dispense the last dot. Thecomputer18 determines, at330, when all of the dots have been dispensed.
• Thus, the application of the offset value causes thedispenser40 to jet a droplet ofmaterial34 at a position in advance of a position at which dispensing would occur if the dispenser were stationary. However, with thedispenser40 being moved at the maximum velocity and using an offset value determined by the maximum velocity, by jetting the droplet at an advance position determined by the offset value, the jetteddroplet34 lands on thesubstrate36 as thedot37 at its desired location.
• It should be noted that in iterating through steps326-330, a difference exists depending on whether the motion controller62 is identifying successive dispense points in terms of absolute coordinate values or by the dot pitch. If the motion controller62 is tracking dot pitch, the offset value is applied to only the first and last dispense points in the line. However, if the motion controller62 is determining the absolute position values for each of the dispense points, then the offset value is subtracted from the absolute coordinate values for each of the dispense points.
• In use, the dot size, material volume and dot placement calibrations are performed at various times depending on the customer specifications, the type of viscous material used, application requirements, etc. For example, all three calibrations are performed upon initially beginning a dot dispensing process for a group of parts, for example, while parts are being loaded and unloaded from the machine. In addition, all three processes are executed any time the viscous material is changed. Further, the calibrations can be automatically run at set time intervals, part intervals or with every part. It should also be noted that if the dispensed weight, dot diameter or dot size changes, the material volume calibration should be re-executed to obtain a new maximum velocity; and further, if the maximum velocity changes, the dot placement calibration should be re-executed to obtain a new offset value.
• Dot size calibrations can also be performed to provide a calibration table83 (FIG. 2) in thememory54 of thecomputer18. The calibration table83 stores a range of dot sizes that have been calibrated to respective operating parameters, for example, temperature, the stroke of thepiston41 and/or the on-time of the pulse operating thetransducer80, etc. Thus, the calibration table83 relates a particular dot size to a temperature and/or piston stroke and/or operating pulse width. Further, based on those stored calibrations, the dot size can be changed in real time during a dot dispensing cycle to meet different application demands by appropriately adjusting the piston stroke or operating pulse width as required. Since the various material volumes are known in advance, in one embodiment, the selection of desired dot sizes from the calibration table83 can be programmed in advance.
• As an example of the above, a first portion of the substrate may require a first material volume that, in turn, requires dispensing three dots of a first dot size; and a second portion of the substrate may require a second material volume that is equal to3.5 of the first dots dispensed on the first portion. Since one-half of a first dot cannot be dispensed, after dispensing the first dots on the first portion, but before dispensing of dots on the second portion, thecomputer18 chooses a different, second dot size from the calibration table83. The second dot size is one which can be divided into the second material volume a whole number of times or without a significant fraction. Then, thecomputer18 provides commands to thedroplet generator controller70 to adjust the piston stroke or change the operating pulse width to provide the second dot size during the dispensing of dots on the second portion of the substrate, thereby dispensing the second material volume.
• Although dots of one size are most often dispensed over an area of the substrate to achieve the desired material volume, in an alternative application, the desired material volume may be more accurately achieved by dispensing dots of a first size over the area and then dispensing dots of a second size over the same area. Thus, piston strokes or operating pulse on-times corresponding to the respective first and second size dots can be read from the calibration table and appropriate adjustments made between dot dispensing cycles.
• Alternatively, in some applications, the desired material volume may change based on changes detected from one substrate to another or in the dot dispensing process. In those applications, upon detecting a change in the desired material volume, thecomputer18 can scan the calibration table83 and select a dot size that upon being dispensed, provides the changed desired material volume. As will be appreciated, the same parameter does not have to be used with the selection of each dot size. For example, some dot sizes may practically be more accurately or easily achieved with a piston stroke adjustment, and other dot sizes may be more readily achieved with an operating on-time pulse adjustment. The choice of which parameter to use will be determined by the capabilities and characteristics of the dispensing gun, the material being dispensed and other application related factors. As will further be appreciated, temperature can also be used to adjust dot sizes in a dot dispensing process, but the longer response time required to achieve a dot size change resulting from a temperature change makes the use of temperature less practical.
• Thenoncontact jetting system10 more accurately applies on-the-fly, viscous material dots on a substrate. First, thenoncontact jetting system10 has atemperature controller86 that includesseparate devices56,57 for, respectively, increasing and decreasing the temperature of thenozzle48, so that the temperature of the viscous material is accurately controlled while it is in thenozzle48. Second, the ability to actively heat or cool the nozzle permits the dispensed volume or dot size to be adjusted by changing the temperature of thenozzle48. Further, as will subsequently be described, the dispensed volume or dot size can be changed by adjusting the stroke of thepiston41 or the on-time of the pulse operating thetransducer80. This has an advantage of a simpler and less expensive system with a faster response time for calibrating dot size. Further, thenoncontact jetting system10 permits a relative velocity between thenozzle48 and thesubstrate36 to be automatically optimized as a function of the viscous material dispensing characteristics and a specified total volume of material to be used on the substrate. Further, the maximum velocity can be automatically and periodically recalibrated with the advantage of providing a more accurate dispensing a desired total amount of viscous material on the substrate. In addition, thenoncontact jetting system10 optimizes the positions at which respective dots are to be dispensed on-the-fly as a function of the relative velocity between the nozzle and the substrate. Thus, a further advantage is that viscous material dots are accurately located on the substrate.
• While the invention has been illustrated by the description of one embodiment and while the embodiment has been described in considerable detail, there is no intention to restrict nor in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those who are skilled in the art. For example, in the described embodiment, the dot size, material volume and dot placement calibrations are described as fully automatic calibration cycles. As will be appreciated, in alternative embodiments, those calibrations processes may be changed to permit of user activity depending on the application and preferences of the user.
• FIG. 6 illustrates one embodiment of a dot placement calibration subroutine. As will be appreciated, other embodiments may provide other calibration processes. For example, an alternative dot placement calibration subroutine is illustrated inFIG. 7. In this calibration process, the computer first, at700, commands the motion controller62 to move thedroplet generator12 to position thenozzle48 over thework surface74. Thereafter, the computer commands, at702, the motion controller62 to move thedroplet generator12 at a constant velocity in a first direction. Simultaneously, the computer commands, at704, thedroplet generator controller70 to operate the jettingvalve44 and apply a viscous material dot at a reference position. Next, thecomputer18 commands, at706, the motion controller62 to move thedroplet generator12 at the constant velocity in an opposite direction. Thecomputer18 simultaneously commands, at708, thedroplet generator controller70 to apply a dot of viscous material at the reference position. The result is that two dots of viscous material are applied to thework surface74. With all conditions being substantially the same during the two jetting processes, the midpoint between the dots should be located at the reference position.
• Next, thecomputer18 commands, at710, the motion controller to move the camera over the two dots, that is, along the same path used to apply the dots. During that motion, thecomputer18 andvision circuit64 are able to monitor the image from thecamera16 and determine coordinate values for diametrically opposite points on the respective edges of each of the dots. Given those points, thecomputer18 can then determine the distance between the dots and a midpoint between the dots. Thecomputer18 then determines, at712, whether the midpoint is located within a specified tolerance of the reference position. If not, thecomputer18 is then able to determine and store, at714, an offset value. The offset value should be substantially equal to one-half of the measured distance between the dots. To confirm the accuracy of the offset value, the steps702-712 can be repeated. However, atsteps704 and708, the position at which thecomputer18 commands the droplet generator controller to jet a droplet is offset by the value determined atstep714. If the computer determines, at712, that the distance is still not within the tolerance, the process of steps702-714 are repeated until an offset value providing an acceptable distance is determined. Alternatively, if there is a higher level of confidence in the dot placement calibration subroutine, after determining and storing the offset value at714, the process can simply return to the operating cycle ofFIG. 3 as indicated by the dashedline716.
• In an alternative embodiment, knowing the velocity of thedroplet generator12 and the distance between the dots, thecomputer18 can determine a time advance offset. That is, the increment of time that the ejection of theviscous material droplet34 should be advanced prior to thedroplet generator12 reaching the reference position.
• FIG. 4 illustrates one embodiment of a dot size calibration subroutine. As will be appreciated, other embodiments may provide other calibration processes, for example, an alternative dot placement calibration subroutine is illustrated inFIG. 8. As with the calibration process described inFIG. 4, thecomputer18 executes a dot size calibration that changes dot size or volume by changing the temperature of the viscous material within thenozzle48, thereby changing viscous material's viscosity and flow characteristics. However, the process ofFIG. 8 uses theweigh scale52 instead of thecamera16 as a measurement device. In a first step of this calibration process, thecomputer18 commands, at800, the motion controller62 to move thedroplet generator12 to thecalibration station52 such that thenozzle48 is directly over the table76 of thescale52. Next, at802, thecomputer18 commands thedroplet generator controller70 to dispense dots onto the table76. As will be appreciated, a dispensed dot is often not detectable within the resolution range of theweigh scale52. Therefore, a significant number of dots may have to be dispensed in order to provide a statistically reliable measurement of dispensed material weight by theweigh scale52. However, if the scale has a sufficiently high resolution, only a single applied dot of viscous material can be used for the dot size calibration.
• At the end of the dispensing process, thecomputer18 then, at804, samples a weight feedback signal from theweigh scale52, which represents the weight of the dispensed dots. Thecomputer18 then compares, at806, the dispensed weight to a specified weight stored in thecomputer memory54 and determines whether the dispensed weight is less than the specified weight. If so, thecomputer18 provides, at808, a command signal to the heater/cooler controller60 causing the temperature setpoint to be increased by an incremental amount. The heater/cooler controller60 then turns on theheater56 and, by monitoring temperature feedback signals from the thermocouple58, quickly increases the temperature of thenozzle48 and the viscous material therein to a temperature equal to the new temperature setpoint. When increased temperature has been achieved, thecomputer18 provides command signals to the motion controller62 anddroplet generator70 to again execute the previously described process steps802-806. The increased temperature reduces the viscosity of the viscous material, thereby resulting in each dot having a larger volume and weight as well as a larger dot diameter; and that larger weight is again compared with the specified dot diameter at806. If the dispensed weight is still too small, thecontroller18 again provides command signals, at808, to again increase the temperature setpoint value. The process of steps802-808 are iterated until thecomputer18 determines that the current dispensed weight is equal to, or within an allowable tolerance of, the specified weight.
• If thecomputer18 determines, at806, that the dispensed weight is not too small, it then determines, at810, whether the dispensed weight is too large. If so, thecomputer18 provides, at812, a command signal to the heater/cooler controller60 that results in a decrease of the temperature setpoint by an incremental amount. With a reduction in the temperature setpoint, the heater/cooler controller60 is operative to turn on the cooler56; and by monitoring the temperature feedback signals from the thermocouple58, the temperature of thenozzle48 and the viscous material therein is quickly reduced to a temperature equal to the new lower temperature setpoint value. By reducing the temperature of the viscous material, its viscosity increases; and therefore, during a subsequent dispensing operation, each dot will have less volume and weight as well as a smaller diameter. Again, that process of steps802-812 iterates until the dispensed weight is reduced to a value equal to, or within an allowable tolerance of, the specified weight.
• In the dot size calibration process described inFIG. 8, thecomputer18 iterates the process by dispensing and measuring dispensed weights until a specified weight is achieved. In an alternative embodiment, a relationship between a change in temperature and a change in dispensed weight for a particular viscous material can be determined experimentally or otherwise. That relationship can be stored in thecomputer18 either as a mathematical algorithm or a table that relates changes in dispensed weight to changes in temperature. An algorithm or table can be created and stored for a number of different viscous materials. Therefore, instead of the iterative process described above, after determining the amount by which the dispensed weight is too large or too small, thecomputer18 can, at808 and812, use a stored algorithm or table to determined a change in temperature that is required to provide the desired change in dispensed weight. After commanding the heater/cooler controller60 to change the temperature setpoint by that amount, the process ends as indicated by the dashedlines814. The dot size calibration process described above can also be executed on a dispensed dot weight basis. Knowing the number of dots dispensed, thecomputer18 is then able to determine, at804, an average weight of each dot dispensed.
• A further alternative embodiment of the dot placement calibration subroutine is illustrated inFIG. 9. As with the calibration process described inFIG. 8, thecomputer18 executes a dot size calibration that changes dot size or volume based on a feedback signal from theweigh scale52. However, in the process ofFIG. 9, the dot size is adjusted by adjusting the stroke of thepiston41 of thecontrol valve44 in thedispenser40. In a first step of this calibration process, thecomputer18 commands, at900, the motion controller62 to move thedroplet generator12 to thecalibration station52 such that thenozzle48 is directly over the table76 of thescale52. Next, at902, thecomputer18 commands thedroplet generator controller70 to dispense dots onto the table76. As will be appreciated, a dispensed dot is often not detectable within the resolution range of theweigh scale52. Therefore, a significant number of dots may have to be dispensed in order to provide a statistically reliable measurement of dispensed material weight by theweigh scale52. However, if the scale has a sufficiently high resolution, only a single applied dot of viscous material can be used for the dot size calibration.
• At the end of the dispensing process, thecomputer18 then, at904, samples a feedback signal from theweigh scale52, which represents the weight of the dispensed dots. Thecomputer18 then compares, at906, the dispensed weight to a specified weight stored in thecomputer memory54 and determines whether the dispensed weight is less than the specified weight. If so, thecomputer18 provides, at908, an increase piston stroke command to thedroplet generator controller70, which causes thecontroller70 to operate themotor61 in a direction to move the micrometer screw53 vertically upward as viewed inFIG. 2. Thecomputer18 then provides command signals to the motion controller62 anddroplet generator70 to again execute the previously described process steps902-906. The increased piston stroke results in each dot dispensed having a larger volume and weight as well as a larger dot diameter. The cumulative larger weight of all of the dots dispensed is again compared with the specified weight at906. If the diameter is still too small, thecontroller18 again provides an increase piston stroke command signal, at908, that results in the micrometer screw53 being moved by themotor61 further upward. The process of steps902-908 are iterated until thecomputer18 determines that the current dispensed weight is equal to, or within an allowable tolerance of, the specified weight.
• If thecomputer18 determines, at906, that the dispensed weight is not too small, it then determines, at910, whether the dispensed weight is too large. If so, thecomputer18 provides, at912, a decrease piston stroke command signal to thedroplet generator controller70 that results in themotor61 moving the micrometer screw53 vertically downward as viewed inFIG. 2. With a smaller piston stroke, during a subsequent dispensing operation, each dot dispensed will have a lesser volume and weight as well as a smaller diameter. Again, the process of steps902-912 iterates until the dispensed weight is reduced to a value equal to, or within an allowable tolerance of, the specified weight.
• In the dot size calibration process ofFIG. 9, thecomputer18 iterates the process by dispensing and measuring dispensed weights until a specified weight is achieved. In an alternative embodiment, a relationship between a change piston stroke and a change in dispensed weight for a particular viscous material can be determined experimentally or otherwise. That relationship can be stored in thecomputer18 either as a mathematical algorithm or a table that relates changes in dispensed weight to changes in piston stroke. An algorithm or table can be created and stored for a number of different viscous materials. Therefore, instead of the iterative process described above, after determining the amount by which the dispensed weight is too large or too small, thecomputer18 can, at908 and912, use a stored algorithm or table to determined a change in piston stroke that is required to provide the desired change in dispensed weight. After commanding thedroplet generator controller70 to change the piston stroke by that amount, the process ends as indicated by the dashedlines914. The dot size calibration process described above can also be executed on a dispensed dot weight basis. Knowing the number of dots dispensed, thecomputer18 is then able to determine, at904, an average weight of each dot dispensed.
• As will be appreciated, in another alternative embodiment, in a process similar to that described inFIG. 9, the dispensed weight of the viscous material can also be changed by adjusting the on-time of the pulse applied to thetransducer80 that operates the jettingvalve44. For example, atstep908, in response to detecting that the dispensed weight is too small, thecomputer18 can command thedroplet generator controller70 to increase the on-time of the signal operating thetransducer80. With the increased on-time, more material is dispensed, thereby increasing the dispensed weight and dot size. Similarly, atstep912, in response to detecting that the dispensed weight is too large, thecomputer18 can command thedroplet generator controller70 to decrease the on-time of the signal operating thetransducer80. With the decreased on-time, less material is dispensed, thereby decreasing the dispensed weight and dot size.
• While the invention has been illustrated by a description of several embodiments and while those embodiments have been described in considerable detail, there is no intention to restrict, or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those who are skilled in the art. For example, calibration routines are described as jetting dots of viscous material onto thestationary surface74; however, as will be appreciated, in alternative embodiments, the calibration cycles can be executed by jetting viscous material dots onto thesubstrate36. Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.

Claims (46)

1. A viscous material noncontact jetting system for applying a dot of viscous material onto a surface comprising:

a jetting dispenser having a nozzle adapted to be connected to a source of viscous material, the jetting dispenser being mounted for relative motion with respect to the surface;

a control operatively connected to the jetting dispenser and having a memory for storing a desired size-related physical characteristic of a dot of viscous material to be applied to the surface, the control being operable to command the jetting dispenser to apply dots of viscous material onto the surface;

a device connected to the control and providing a feedback signal to the control representing a detected size-related physical characteristic of the dots applied to the surface;

a temperature controller comprising a first device for increasing the temperature of the nozzle and a second device for decreasing the temperature of the nozzle, the control being operable to cause the temperature controller to change a temperature of the nozzle in response to a difference between the detected size-related physical characteristic and the desired size-related physical characteristic.

2. The noncontact jetting system ofclaim 1 wherein the size-related physical characteristic is determinative of a diameter of the dots applied to the surface.

3. The noncontact jetting system ofclaim 1 wherein the size-related physical characteristic is determinative of a volume of the dots applied to the surface.

4. The noncontact jetting system ofclaim 1 wherein the size-related physical characteristic is determinative of a weight of the dots applied to the surface.

5. The noncontact jetting system ofclaim 1 wherein the device is a camera.

6. The noncontact jetting system ofclaim 1 wherein the device is a weigh scale.

7. The noncontact jetting system ofclaim 1 wherein the temperature controller comprises:

a heater connected to the control, the control being operable to cause the heater to heat the nozzle in response to the detected size-related physical characteristic being less than the desired size-related physical characteristic; and

a cooler connected to the control, the control being operable to cause the cooler to cool the nozzle in response to the detected size-related physical characteristic being greater than the desired size-related physical characteristic.

8. A method of dispensing a viscous material onto a surface with a jetting dispenser having a nozzle, the method comprising:

operating the jetting dispenser to apply dots of viscous material onto the surface;

determining a size-related physical characteristic of the dots applied to the surface;

operating one of a first device that increases the temperature of the nozzle or a second device that decreases the temperature of the nozzle in response to the size-related physical characteristic of the dots applied to the surface deviating from a desired value.

9. The method ofclaim 8 wherein the size-related physical characteristic is determinative of a weight of the dot applied to the surface.

10. The method ofclaim 8 wherein the size-related physical characteristic is determinative of a volume of the dot applied to the surface.

11. The method ofclaim 8 further comprising

increasing the temperature of the nozzle of the jetting dispenser with a first device in response to the size-related physical characteristic of the dots applied to the surface being less than the desired value; and

decreasing the temperature the nozzle of the jetting dispenser with a second device in response to the size-related physical characteristic of the dots applied to the surface being greater than the desired value.

12. A method of dispensing a viscous material onto a surface comprising:

providing a desired size-related physical characteristic of a dot of viscous material to be applied to the surface;

causing relative motion between a dispenser and the surface;

operating the dispenser to apply dots of viscous material onto the surface;

generating feedback signals representing detected size-related physical characteristics of the dots on the surface;

operating one of a first device that increases the temperature of the nozzle or a second device that decreases the temperature of the nozzle in response to the detected size-related physical characteristics being different from the desired size-related physical characteristic.

13. The method ofclaim 12 wherein the size-related physical characteristics are determinative of respective diameters of the dots on the surface.

14. The method ofclaim 12 wherein the size-related physical characteristics are determinative of a volume of the dots on the surface.

15. The method ofclaim 12 wherein the size-related physical characteristics are determinative of a weight of the dots on the surface.

16. A viscous material noncontact jetting system for applying dots of viscous material onto a surface comprising:

a jetting dispenser having a nozzle adapted to be connected to a source of viscous material, the jetting dispenser being mounted for relative motion with respect to the surface;

a control operatively connected to the jetting dispenser and being operable to command the jetting dispenser to apply dots of viscous material to the surface;

a device connected to the control and providing a feedback signal to the control representing a detected weight of dots applied to the surface;

a temperature controller operable to increase or decrease a temperature of the nozzle, the control being operable to cause the temperature controller to change the temperature of the nozzle in response to the detected weight of the dots applied to the surface being different from a desired value.

17. A method of dispensing dots of viscous material onto a surface with a dispenser having a nozzle, the method comprising:

operating the dispenser to apply dots of viscous material onto the surface;

determining a weight of the dots applied to the surface;

changing the temperature of the nozzle in response to the weight of the dots applied to the surface deviating from a desired value.

18. A viscous material noncontact jetting system for applying a dot of viscous material onto a surface comprising:

a jetting dispenser having a nozzle and a piston being reciprocable with respect to a seat, the jetting dispenser adapted to be connected to a source of viscous material and mounted for relative motion with respect to the surface;

a control operatively connected to the jetting dispenser and having a memory for storing a desired dot size value representing a desired size of a dot of viscous material to be applied to the surface, the control being operable to command the piston to move through a stroke away from a seat and the piston being movable through the stroke toward the seat to jet a droplet of viscous material through the nozzle, which is applied to the surface as a dot of viscous material;

a device connected to the control and providing a feedback signal to the control representing a size-related physical characteristic of the dot applied to the surface;

the control being operable to change the stroke of the piston in response to the feedback signal representing a size-related physical characteristic of the dot applied to the surface being different from the desired dot size value.

19. The noncontact jetting system ofclaim 18 wherein the size-related physical characteristic is determinative of a diameter of the dot applied to the surface.

20. The noncontact jetting system ofclaim 18 wherein the size-related physical characteristic is determinative of a volume of the dot applied to the surface.

21. The noncontact jetting system ofclaim 18 wherein the size-related physical characteristic is determinative of a weight of the dot applied to the surface.

22. The noncontact jetting system ofclaim 18 wherein the device is a camera.

23. The noncontact jetting system ofclaim 18 wherein the device is a weigh scale.

24. A method of dispensing a viscous material onto a surface with a jetting dispenser having a piston reciprocable with respect to a seat, the method comprising:

withdrawing the piston through a stroke away from the seat;

moving the piston through the stroke toward the seat to jet a droplet of viscous material through the nozzle, which is applied to the surface as a dot of viscous material;

determining a physical characteristic of the dot applied to the surface;

increasing or decreasing the stroke of the piston in response to the physical characteristic being respectively, less than, or greater than, a desired value; and

iterating the steps of withdrawing, moving, determining and increasing or decreasing the stroke of the piston to apply a plurality of dots to the surface and maintain the physical characteristic of the plurality of dots close to the desired value.

25. A method of dispensing a viscous material onto a surface with a jetting dispenser having a piston reciprocable with respect to a seat, the method comprising:

providing a desired size-related physical characteristic value representing a desired size-related physical characteristic of a dot of viscous material to be applied to the surface;

causing relative motion between the jetting dispenser and the surface;

applying dots of viscous material to the surface by iteratively withdrawing the piston through a stroke away from the seat and then moving the piston through the stroke toward the seat to jet a droplet of viscous material through the nozzle;

generating feedback signals to the control representing size-related physical characteristics of the dots applied to the surface;

changing the stroke of the piston in response to the feedback signals representing an average size-related physical characteristic different from the desired size-related physical characteristic value.

26. The method ofclaim 25 wherein the size-related physical characteristics are determinative of a diameter of the dots applied to the surface.

27. The method ofclaim 25 wherein the size-related physical characteristics are determinative of a weight of the dots applied to the surface.

28. The method ofclaim 25 wherein the size-related physical characteristics are determinative of a volume of the dots applied to the surface.

29. A viscous material noncontact jetting system for applying dots of viscous material onto a surface comprising:

a jetting dispenser having a nozzle and a piston being reciprocable with respect to a seat, the jetting dispenser adapted to be connected to a source of viscous material and mounted for relative motion with respect to the surface; and

a control operatively connected to the jetting dispenser and having a memory for storing a table with values relating dot sizes to respective operating parameters, each operating parameter causing the jetting dispenser to dispense a respective dot size of viscous material on the surface, the control being operable to command the piston to move through a stroke away from a seat and the piston being movable through the stroke toward the seat to jet a droplet of viscous material through the nozzle, which is applied to the surface as a dot of viscous material, the control being further operable to select from the table a first operating parameter causing the jetting dispenser to dispense a number of first dots of a first dot size on the surface and thereafter, to select from the table a second operating parameter causing the jetting dispenser to dispense a number of second dots of a second dot size on the surface.

30. The noncontact jetting system ofclaim 29 wherein each operating parameter is one of temperature, stroke of the piston or operating pulse on-time.

31. A method of dispensing a viscous material onto a surface with a jetting dispenser having a piston reciprocable with respect to a seat, the method comprising:

providing a table of values relating dot sizes to respective operating parameters, each operating parameter causing a dispensing of a respective dot size of viscous material on the surface;

utilizing a first operating parameter from the table corresponding to a first dot size;

applying a first number of viscous material dots of the first dot size to the surface by iteratively withdrawing the piston through a stroke away from the seat and then moving the piston through the stroke toward the seat to jet a droplet of viscous material through the nozzle;

utilizing a second operating parameter from the table corresponding to a second dot size; and

applying a second number of viscous material dots of the second dot size to the surface by iteratively withdrawing the piston through a stroke away from the seat and then moving the piston through the stroke toward the seat to jet a droplet of viscous material through the nozzle.

32. The method ofclaim 31 wherein each operating parameter is one of temperature, stroke of the piston or operating pulse on-time.

33. The method ofclaim 31 wherein the surface is a substrate and the method further comprises applying the first number of viscous material dots to one portion of the substrate and applying the second number of viscous material dots to the one portion of the substrate.

34. The method ofclaim 31 wherein the surface is a substrate and the method further comprises applying the first number of viscous material dots to one portion of the substrate and applying the second number of viscous material dots to a second, different portion of the substrate.

35. A viscous material noncontact jetting system for applying dots of viscous material onto a surface, the jetting system comprising:

a jetting dispenser having a nozzle and adapted to be connected to a source of viscous material, the jetting dispenser being mounted for relative motion with respect to the surface;

a control operatively connected to the jetting dispenser and having a memory for storing a total volume value representing a total volume of the viscous material to be dispensed and a length value representing a length overwhich the total volume of viscous material is to be dispensed, the control being operable to execute a calibration cycle by commanding the jetting dispenser to apply a number of dots of viscous material to the surface;

a device connected to the control and providing a feedback signal to the control representing an amount of the viscous material contained in the dots applied to the surface, the control being responsive to the feedback signal, the volume value and the length value to determine a maximum velocity value for the relative motion between the jetting dispenser and the surface resulting in the total volume of material being dispensed over the length.

36. The noncontact jetting system ofclaim 35 wherein the device is a weigh scale.

37. A method of dispensing a viscous material onto a surface with a dispenser operatively connected to a control, the method comprising:

providing a total volume value representing a total volume of the viscous material to be dispensed and a length value representing a length over which the total volume of viscous material is to be dispensed;

operating the dispenser to apply a number of viscous material dots to the surface;

generating a feedback signal to the control representing an amount of the viscous material contained in the number of viscous material dots applied to the surface;

determining a maximum velocity of relative motion between the dispenser and the surface resulting in the total volume of viscous material being dispensed over the length.

38. The method ofclaim 37 wherein determining a maximum velocity further comprises:

determining a volume of viscous material dispensed in each of the number of viscous material dots;

determining a total number of dots required to substantially equal the total volume of viscous material represented by the total volume value;

determining a distance between each of the total number of dots required to substantially uniformly distribute viscous material dots over the length represented by the length value; and

determining a maximum relative velocity between the dispenser and the surface resulting in the total number of viscous material dots being substantially uniformly dispensed over the length.

39. The method ofclaim 37 wherein determining a maximum velocity further comprises:

determining a volume of viscous material dispensed in each of the number of viscous material dots;

determining a total number of dots required to substantially uniformly dispense the total volume of viscous material represented by the total volume value;

determining a distance between each of the total number of dots required to substantially uniformly distribute the viscous material dots over the length represented by the length value; and

determining a dot rate value representing a rate at which the viscous material dots are to be dispensed from the dispenser to dispense the total volume of viscous material over the length at the maximum relative velocity.

40. A viscous material noncontact jetting system for applying a dot of viscous material onto a surface comprising:

a jetting dispenser having a nozzle and adapted to be connected to a source of viscous material, the jetting dispenser being mounted for relative motion with respect to the surface;

a control operatively connected to the jetting dispenser and having a memory for storing an offset value, the control operating the jetting dispenser at a first location to apply a dot of viscous material onto the surface;

a camera connected to the control and providing a feedback signal to the control representing a location of a physical characteristic of the dot on the surface;

the control being operable to determine a location of the dot on the surface and then, to determine an offset value representing a difference between the first location and the location of the dot on the surface.

41. A method of dispensing a viscous material onto a surface with a jetting dispenser operatively connected to a control, the method comprising:

providing first coordinate values representing a position of the jetting dispenser at which the jetting dispenser is operable to apply a dot of viscous material onto the surface;

moving the jetting dispenser at a relative velocity with respect to the surface;

operating the dispenser to apply a viscous material dot onto the surface;

detecting the viscous material dot with a camera;

generating a feedback signal representing a location of a physical characteristic of the viscous material dot on the surface;

determining second coordinate values representing a position of the viscous material dot on the surface; and

determining an offset value representing a difference between the first coordinate values and the second coordinate values, the offset value being used to modify the first coordinate values during a subsequent application of a viscous material dot onto the surface.

42. A method of dispensing a viscous material onto a surface with a jetting dispenser operatively connected to a control, the method comprising:

moving the jetting dispenser at a relative velocity with respect to the surface;

operating the jetting dispenser to dispense a viscous material dot onto the surface;

storing first coordinate values representing a position of the jetting dispenser upon operating the jetting dispenser;

storing second coordinate values representing a position of the viscous material dot on the surface;

determining an offset value representing a difference between the first coordinate values and the second coordinate values, the offset value being used to modify the first coordinate values during a subsequent operation of the jetting dispenser.

43. A method of dispensing a viscous material onto a surface with a jetting dispenser operatively connected to a control, the method comprising:

(a) moving the jetting dispenser at a first velocity in a first direction with respect to the surface;

(b) operating the jetting dispenser at a first position with respect to the surface to apply a first viscous material dot onto the surface;

(c) moving the jetting dispenser at a second velocity in a second direction with respect to the surface;

(d) operating the jetting dispenser at a second position with respect to the surface to apply a second viscous material dot to the surface;

(e) determining a distance between the first viscous material dot and the second viscous material dot;

(f) determining an offset value for the first relative position.

44. The method ofclaim 43 wherein the second direction is opposite the first direction.

45. The method ofclaim 44 wherein the first relative velocity is equal to the second relative velocity.

46. The method ofclaim 43 further comprising

(a) moving the jetting dispenser at a first velocity in a first direction with respect to the surface;

(b) operating the jetting dispenser at the first position as modified by the offset value to apply another viscous material dot to the surface;

(c) moving the jetting dispenser at a second velocity in a second direction with respect to the surface;

(d) operating the jetting dispenser at the second position to apply a further viscous material dot to the surface;

(e) determining a distance between the other viscous material dot and the further viscous material dot;

(f) determining an offset value for the first relative position such that the distance between the other viscous material dot and the further viscous material dot is reduced during subsequent iteration of steps (a) through (d); and

iterating steps (a)-(f) until the distance between the other viscous material dot and the further viscous material dot is equal to a desired value.

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