Fluid Dynamics
Liquid motion physics governs the behaviour of fluid used during conformal coating deposition on printed circuit boards. Viscous drag and surface tension dictate how material flows across densely populated substrates. Process engineers adjust pump pressures to maintain uniform film thickness across components with varying heights.
Boundary layers form along component edges where fluid velocity drops to zero. Shear stress levels dictate whether the applied coating sags before thermal curing sets the polymer matrix. Conformal coating machines rely on precise fluid control to prevent bridging between fine pitch pins.
Fluid velocity must remain below the threshold that causes splashing or droplet satellite formation.
Flow Rate
Dispense velocity determines the volume of material deposited per unit time during automated dispensing operations. Volumetric flow rates depend directly on fluid viscosity and the internal diameter of the dispensing needle. Pressure decay tests verify that delivery lines maintain steady state conditions without pressure surges.
Fluid temperatures must stay within strict limits because thermal fluctuations alter viscosity and ruin dispense accuracy. Pump wear changes the delivery volume over extended production runs, so operators perform calibration checks at scheduled intervals. Back pressure valves regulate material delivery to prevent drooling when the dispenser stops moving.
Needle height above the circuit board surface influences the spreading behaviour of the dispensed dot.
Viscous Shear
Fluid resistance against deformation dictates how well adhesive materials level out after stencil printing. Shear thinning behaviour allows solder paste to flow easily through aperture openings during the squeegee stroke. High shear rates during rapid squeegee movement temporarily lower the apparent viscosity of the paste.
Recovery times depend on thixotropic index values which measure how fast the material regains its structure after printing. Slump testing evaluates whether deposited paste maintains its shape without spreading into adjacent pads before component placement. Paste deposition quality relies on fluid properties remaining stable under mechanical stress.
