Enhance Conformal Coating Accuracy at Higher Velocities with Offset Calibration
Offset calibrations are critical to accurate fluid placement in non-contact dispensing as well as conformal coating. A droplet's curved fluid path follows projectile motion from a vertical drop after leaving the applicator tip and results from a combination of forces in the Z direction and the initial X-Y motion when the drop was dispensed (i.e. the linear path of the applicator when the drop was released). The momentum from the applicator's travel causes the droplet to continue moving in an X or Y direction while the downward force from the applicator and gravity moves the droplet to the board. Ultimately, this means the droplet contacts the board at a different X-Y coordinate from where it was released.
Offset calibration in precision dispensing is a well-established method to compensate for the X-Y coordinate change by calculating when to dispense the fluid for correct placement. Conformal coating dispensing follows the same projectile motion principles. The faster the applicator moves, the further the droplet will travel before contacting the board, as illustrated in Figure 1. Conformal coating applicators on Nordson ASYMTEK equipment can travel 500-750 mm/sec for film coating and 50-150 mm/sec for spray coating. At such rapid speeds, offset calibration is a requirement for accurate fluid placement and Nordson ASYMTEK's use of offset calibration for conformal coating is unique to the industry.
Applications Corner 2014-12 Newsletter Story - Offset Calibration and Conformal Coating Accuracy
Figure 1: The applicator’s velocity affects fluid placement.
The faster the horizontal velocity of the applicator, the further
the fluid will travel (V3 versus V1).
The offset calibration routine customizes the coating system for each specific application. Coating programs use different line velocities and dispense heights; therefore, maintaining accurate start and stop positions is critical. Additionally, if there are changes due to wear, fluid properties, or air supply affecting fluid pressure and flow rates, the offset calibration routine compensates for changes in response time. Ultimately, offset calibration enhances conformal coating accuracy, particularly at higher speeds.
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