fig1 is a schematic representation of a computer controlled noncontact viscous material jetting system 10 , for example , an “ axiom ” x - 1020 series commercially available from asymtek of carlsbad , calif . a droplet generator 12 is mounted on a z axis drive that is suspended from an x , y positioner 14 in a known manner . the x , y position 14 is mounted on a frame 11 and defines first and second nonparallel axes of motion . the x , y positioner includes a cable drive coupled to a pair of independently controllable stepper motors ( not shown ) in a known manner . a video camera and led light ring assembly 16 are connected to the droplet generator 12 for motion along the x , y and z axes to inspect dots and locate reference fiducial points . the video camera and light ring assembly 16 may be of the type described in u . s . pat . no . 5 , 052 , 338 entitled “ apparatus for dispensing viscous materials a constant height above a workpiece surface ”, the entire disclosure of which is incorporated be reference herein . a computer 18 provides overall system control and 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 the computer 18 via a keyboard ( not shown ) and a video monitor 20 . the computer 18 is provided with standard rs - 232 and smema cim communications busses 50 which are compatible with most types of other automated equipment utilized in substrate production assembly lines . a substrate ( not shown ) with devices mounted thereon onto which conformal coating material , such as a silicone , acrylic or polyurethane resin , is to be applied is located directly beneath a droplet generator 12 . the substrate can be manually loaded or transported by an automatic conveyor 22 . the conveyor 22 is of conventional design and has a width which can be adjusted to accept pc boards of different dimensions . the conveyor 22 also includes pneumatically operated lift and lock mechanisms . this embodiment further includes a nozzle priming station 24 and a nozzle calibration set - up station 26 . a control panel 28 is mounted on the frame 11 just below the level of the conveyor 22 and includes a plurality of push buttons for manual initiation of certain functions during set - up , calibration and viscous material loading . referring to fig2 , the droplet generator 12 is shown ejecting droplets 37 of conformal coating material onto a substrate 36 , for example , a pc board , that supports an electrical component 39 , for example , a semiconductor chip or die , etc . the pc board 36 is of the type designed to have components surface mounted thereon . the pc board is moved to a desired position by the conveyor 22 . the axes drives 38 often include the x , y positioner 14 ( fig1 ) and a z axis drive system , which are capable of rapidly moving a jetting dispenser 40 along x , y and z axes 77 , 78 , 79 , respectively , with respect to the pc board 36 . the droplet generator 12 can eject droplets of conformal coating material from one fixed z height , or the droplet generator 12 can be raised under program control during a cycle of operation to dispense at other z heights or to clear other components mounted on the board . the droplet generator 12 includes an on / off dispenser 40 which is a non - contact dispenser specifically designed for jetting minute amounts of viscous materials , such as conformal coating material . the dispenser 40 has a jetting valve 44 with a piston 41 disposed in a cylinder 43 . the piston 41 has a lower rod 45 extending therefrom through a material chamber 47 . a distal lower end of the lower rod 45 is biased against a seat 49 by a return spring 46 . the piston 41 further has an upper rod 51 extending therefrom with a distal upper end that is disposed adjacent a stop surface on the end of a screw 53 of a micrometer 55 . adjusting the micrometer screw 53 changes the upper limit of the stroke of the piston 41 . the dispenser 40 may include a syringe - style supply device 42 that is fluidly connected to a supply of conformal coating material 35 in a known manner . a droplet generator controller 70 provides an output signal to a voltage - to - pressure transducer 72 , for example , a pneumatic solenoid connected to a pressurized source of fluid , that , in turn , ports pressurized air to the supply device 42 . thus , the supply device 42 is able to supply pressurized conformal coating material to the chamber 47 . a jetting operation is initiated by the computer 18 providing a command signal to the droplet generator controller 70 , which causes the controller 70 to provide an output pulse to a voltage - to - pressure transducer 76 , for example , a pneumatic solenoid connected to a pressurized source of fluid . the pulsed operation of the transducer 76 ports a pulse of pressurized air into the cylinder 43 and produces a rapid lifting of the piston 41 . lifting the piston lower rod 45 from the seat 49 draws conformal coating material in the chamber 47 to a location between the piston lower rod 45 and the seat 49 . at the end of the output pulse , the transducer 76 returns to its original state , thereby releasing the pressurized air in the cylinder 43 , and a return spring 46 rapidly lowers the piston lower rod 45 back against the seat 49 . in that process a droplet 37 of conformal coating material is rapidly extruded or jetted through an opening or dispensing orifice 49 of a nozzle 48 . as schematically shown in exaggerated form in fig2 , a very small conformal coating material droplet 37 breaks away as a result of its own forward momentum and is deposited as a dot of conformal coating material on the substrate 36 . successive operations of the cylinder 43 provide respective droplets of material 37 . as used herein , the terms “ jetting ” refers to the above - described process for forming the conformal coating material droplets 37 . the dispenser 40 is capable of jetting droplets from the nozzle 48 at very high rates , for example , up to 100 or more droplets per second . a line pattern of conformal coating material dots is formed on the substrate by the positioner 14 linearly moving the dispenser 40 while the dispenser 40 jets a plurality of droplets in rapid succession . a motor 61 controllable by the droplet generator controller 70 is mechanically coupled to the micrometer screw 53 , thereby allowing the stroke of the piston 41 to be automatically adjusted , which varies the volume of conformal coating material forming each droplet . the motion of the droplet generator 12 and the camera and light ring assembly 16 connected thereto , are governed by a motion controller 62 . the motion controller 62 provides command signals to separate drive circuits for the x , y and z axis motors . a conveyor controller 66 is connected to the substrate conveyor 22 . the conveyor controller 66 interfaces between the motion controller 62 and the conveyor 22 for controlling the width adjustment and lift and lock mechanisms of the conveyor 22 . the conveyor controller 66 also controls the entry of the substrate 36 into the system and the departure therefrom upon completion of the dot deposition . in some applications , a substrate heating system 68 and / or a nozzle heating / cooling system 56 are operative in a known manner to heat the substrate and / or nozzle to maintain a desired temperature profile of the conformal coating material dots as the substrate is conveyed through the system . the nozzle setup station 26 is used for calibration purposes to provide a dot size calibration for accurately controlling the weight or size of the dispensed droplets 37 and a dot placement calibration for accurately locating conformal coating material dots that are dispensed on - the - fly , that is , while the droplet generator 12 is moving relative to the substrate 36 . in addition , the nozzle setup station is used to provide a material volume calibration for accurately controlling the velocity of the droplet generator 12 as a function of current material dispensing characteristics , the rate at which the droplets are to be deposited and a desired total volume of conformal coating material to be dispensed in a pattern of dots . the nozzle setup station 26 includes a stationary work surface 74 and a measuring device 52 , for example , a weigh scale that provides a feedback signal to the computer 18 representing the weight of material weighed by the scale 52 . weigh scale 52 is operatively connected to the computer 18 , which is capable of comparing the weight of the conformal coating material with a previously determined specified value , for example , a conformal coating material weight setpoint value stored in a computer memory 54 . other types of devices may be substituted for the weigh scale 24 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 . 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 . such a dispensing system is more fully described in pending provisional application ser . no . 60 / 473 , 1616 , entitled “ viscous material noncontact dispensing system ”, filed may 23 , 2003 , which is hereby incorporated by reference in its entirety herein . in operation , cad data from a disk or a computer integrated manufacturing (“ cim ”) controller are utilized by the computer 18 to automatically assign dot sizes to specific components based on the user specifications or component library . computer 18 then commands the motion controller 62 to move the droplet generator 12 . this ensures that the minute dots of conformal coating material are accurately placed on the substrate 36 at the desired locations . in applications where cad data is not available , the software utilized by the computer 18 allows for the locations of the dots to be directly programmed . in a known manner , the computer 18 utilizes the x and y locations , the component types and the component orientations to determine where and how many conformal coating material dots to deposit onto the upper surface 80 of the substrate 36 . referring to fig3 , a pc board 36 is shown having electrical devices 39 a - 39 d mounted thereon for selective conformal coating . the computer 18 sends signals to motion controller 62 based on the board / device configuration as determined by computer 18 . the motion controller 62 sends signals to the x , y positioner 14 to move the jetting dispenser 40 along a path parallel to a first axis of motion , such as the x direction 77 . while the dispenser 40 is being moved , the droplet generator controller 70 operates the jetting valve 44 to jet droplets 37 of conformal coating material in a linear pattern on one of the devices , for example , device 39 b . after jetting a conformal coating along the first path , the motion controller 62 increments the dispenser 40 in a second axis of motion , such as the y direction 78 , and then , initiates motion back along the y axis . simultaneously , the motion controller 62 operates the jetting valve to apply a second linear pattern of conformal coating material adjacent to and contiguous with the first linear pattern . this process of applying linear patterns of conformal coating material is then repeated to provide a coated area 100 over the device 39 b . the above process is further repeated to jet a conformal coating on the remaining devices 39 a , 39 c , 39 d on the substrate 36 . the axes drives 38 often have x , y and z drives ; however , as will be appreciated , in another embodiment , the dispenser 40 can be mounted on the z axis positioner to be pivotable in a c axis 96 , that is , a rotation about the z axis 79 . in a still further embodiment , the jetting dispenser can be mounted to be pivotable about either an a axis , that is , a rotation about the x axis 77 or , a b axis , that is , a rotation about the y axis 78 . thus , the jetting dispenser can be manually set at an angle . alternatively , in other embodiments , electric or fluid motors can be used to power one or more of the angles of rotation . further , the electric and fluid motors can be placed under program control of the computer 16 or the motion controller 26 . examples dispensing systems having programmable axes of angular motion are shown and described in u . s . pat . nos . 6 , 447 , 847 and 5 , 141 , 165 , which are hereby incorporated by reference in their entireties herein . jetting of conformal coating material onto a substrate has several advantages over existing conformal coating methods . one advantage , for example , is that jetting provides a small wetted area through the precise control of the volume of ejected droplets . the small wetted area of conformal coating dots allows for precise coating of small areas thus enhancing the selectivity of conformal coating systems . by precisely and selectively placing the conformal coating on a substrate without overspray , edge definition between coated and uncoated areas is enhanced . further , by eliminating overspray , only the desired areas of the substrate are coated ; and undesirable machine contamination is substantially reduced . therefore , the need for masking is essentially eliminated , thereby reducing production and maintenance costs . further , jetting the conformal coating material permits only the reverse of the solder mask , that is , the solder joints to be coated . the net result is a substantial savings in the conformal coating material used and thus , providing additional cost savings . while the present invention has been illustrated by the description of one embodiment and while the embodiment has been described in considerable detail , it is not intended 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 skilled in the art . for example , in the described embodiment , only a single dispenser 40 is illustrated ; however , as will be appreciated , in other embodiments , multiple dispensers on one or more positioners may be used to jet common or different conformal coating materials either sequentially or simultaneously . the invention in its broader aspects is therefore not limited to the specific details shown and described . accordingly , departures may be made from such details without departing from the scope or spirit of applicant &# 39 ; s claims which follow .