Thin line conformal coating apparatus and method

Abstract

A coating system with an applicator that has an air cylinder with a needle valve. A control has a timer that provides a string of electrical pulses to a solenoid. With each pulse, the solenoid applies pressurized air to a cylinder piston, thereby opening the needle valve and permitting coating material to flow past the needle valve. The needle valve is closed for durations of time between pulses, and the coating material is ejected from a dispensing needle in response to closings of the needle valve.

1 . A coating system for dispensing a coating material onto a substrate, the coating system comprising:
 an applicator comprising
 a cylinder and piston configuration adapted to be in fluid communication with a pressurized fluid and the coating material, 
 a needle valve being operable by the piston to open the needle valve, and 
 a dispensing needle in fluid communication with the needle valve; 
   a solenoid fluidly connected between the pressurized fluid and the cylinder; and   a control comprising a timer connected to the solenoid, the timer being operable to provide a string of electrical pulses to the solenoid, each pulse in the string of pulses causing the solenoid to apply the pressurized fluid to the piston, thereby opening the needle valve and permitting a flow of coating material past the needle valve, the needle valve being closed for durations of time between pulses, and the coating material being ejected from the dispensing needle in response to closings of the needle valve.   
   
   
       2 . The coating system of  claim 1  wherein the timer further comprises a pulse width modulator. 
   
   
       3 . The coating system of  claim 2  wherein the control further comprises a memory for storing at least one modulator operating parameter selected from an On time, an Off time, a Cycle time or any combination thereof. 
   
   
       4 . The coating system of  claim 1  wherein the needle valve further comprises a return spring for closing the needle valve for the durations between pulses. 
   
   
       5 . The coating system of  claim 1  further comprising an adjustable pressure regulator for providing the pressurized fluid. 
   
   
       6 . The coating system of  claim 1  further comprising a second pressure regulator providing a second pressurized fluid for supplying the coating material under pressure. 
   
   
       7 . The coating system of  claim 1  wherein the coating material is a conformal coating material and the substrate is a PC board. 
   
   
       8 . A coating system for dispensing a coating material onto a substrate, the coating system comprising:
 an applicator comprising
 a cylinder adapted to be in fluid communication with the coating material and a pressurized fluid, 
 a piston sealingly located in the cylinder and separating a coating material chamber from a pressurized fluid chamber, 
 a seat mounted on the cylinder adjacent the coating material chamber and having a flow channel extending therethrough, 
 a needle locatable against the seat to form a needle valve with the seat, the needle being mechanically connected to the piston and movable by the piston to a first, open position away from the seat, thereby allowing a coating material to pass through the flow channel, 
 a return spring operable to move the needle to a second, closed position in contact with by the seat, thereby blocking a flow of coating material through the flow channel, and 
 a dispensing needle in fluid communication with the flow channel for receiving and dispensing the coating material; 
   a solenoid fluidly connected between the source of pressurized fluid and the cylinder;   a control comprising a timer connected to the solenoid, the timer providing a string of pulses to the solenoid, each pulse in the string of pulses causing the solenoid to apply the pressurized fluid against the piston and cause the piston to move the needle to the open position thereby allowing a quantity of coating material to pass through the flow channel, and the return spring moving the needle into contact with the seat for a duration of time between pulses, and the coating material being ejected from the dispensing needle in response to the return spring moving the needle into contact with the seat.   
   
   
       9 . The coating system of  claim 8  wherein the timer further comprises a pulse width modulator. 
   
   
       10 . The coating system of  claim 9  wherein the control further comprises a memory for storing at least one modulator operating parameter selected from an On time, an Off time, a Cycle time or any combination thereof. 
   
   
       11 . The coating system of  claim 8  wherein the source of pressurized fluid is a source supplying air at a regulated pressure and the source of pressurized coating material is a source supplying the coating material at a regulated pressure 
   
   
       12 . The coating system of  claim 8  wherein the coating material is a conformal coating material and the substrate is a PC board. 
   
   
       13 . A method of automatically dispensing a coating material onto a substrate with an applicator being movable by a programmable control operating a positioner supporting the applicator, the applicator having a flow channel conducting a coating material from a needle valve to a dispensing needle, the needle valve being movable by a cylinder piston to an open position in response to a pressurized fluid received from a solenoid, and the needle valve then being movable to a closed position, the method comprising:
 applying a string of electrical pulses to the solenoid;   moving coating material past the needle valve by repeatedly opening the needle valve in response to each pulse in the string of electrical pulses being applied to the solenoid; and   ejecting the coating material from the dispensing needle by repeatedly closing the needle valve in response to periods of time between pulses in the string of electrical pulses.   
   
   
       14 . The method of  claim 13  further comprising generating the string of pulses with a timing device. 
   
   
       15 . The method of  claim 13  further comprising generating the string of pulses with a pulse width modulator. 
   
   
       16 . The method of  claim 15  further comprising operating the pulse width modulator with an On time stored in a computer, wherein the On time determines a duration of each pulse in the string of pulses. 
   
   
       17 . The method of  claim 16  further comprising closing the needle valve for a duration of time between the pulses in the string of pulses. 
   
   
       18 . A method of automatically dispensing a coating material onto a substrate with an applicator being movable by a programmable control operating a positioner supporting the applicator, the applicator having a flow channel conducting a coating material from a needle valve to a dispensing needle, the needle valve being movable by an air cylinder piston to an open position in response to a pressurized fluid received from a solenoid, and the needle valve then being moved to a closed position, the method comprising:
 generating a string of electrical pulses, each pulse having a duration defined by an On time and a duration between pulses being defined by an Off time;   opening the needle valve in response to a pulse being applied to the solenoid and permit coating material to flow past the needle valve toward the dispensing needle;   closing the needle valve for a duration of an Off time, the closing of the needle valve ejecting coating material from the dispensing needle; and   repeating the opening and closing of the needle valve in response to the string of electrical pulses being applied to the solenoid to repeatedly eject coating material from the dispensing needle.   
   
   
       19 . The method of  claim 18  further comprising operating a timing device to generate the string of electrical pulses. 
   
   
       20 . The method of  claim 18  further comprising operating a pulse width modulator to generate the string of electrical pulses. 
   
   
       21 . The coating system of  claim 18  wherein the coating material is a conformal coating material and the substrate is a PC board.