Snuff back controlled coating dispensing apparatus and methods

摘要

Coating dispenser apparatus and methods which utilize a snuff back device for removing a small amount of coating material from the discharge passage of the dispenser upon shut-off thereof at the end of a coating run. A control is provided which discharges the material removed from the discharge passage back into the discharge passage upon a predetermined delay after the start of the next coating run. The disclosed methods contemplate the discharge of coating material back into the discharge passage in the middle of the next coating pattern, or depending on the application, during any segment of the next coating pattern after a defined leading edge of the pattern is created, during which segment the coating material discharged back into the discharge pattern smoothly blends into the coating pattern as it is applied to a substrate. The apparatus and methods are especially useful for applying conformal coating patterns onto circuit boards.