Drop Measurement
Optical analysis of a liquid volume on a solid surface provides a direct way to calculate the contact angle. Technicians use sessile drop goniometry to evaluate the cleanliness and surface energy of a board before coating or assembly. This method relies on a high resolution camera to capture the profile of a stationary droplet.
Measurement Execution
A precision syringe deposits a specific volume of liquid, such as deionized water or diiodomethane, onto the substrate. The software used in sessile drop goniometry then fits a curve to the droplet shape to find the tangent at the contact point. This procedure must be performed in a controlled environment to prevent dust or air currents from affecting the results.
Consistent droplet size and placement are necessary for obtaining repeatable data across different samples. Fabricators use this information to decide if a board needs additional plasma treatment or chemical cleaning.
Surface Characterization
High angles indicate poor wetting while low angles show that the liquid is spreading effectively over the surface. Sessile drop goniometry provides the empirical data needed to qualify new solder masks or conformal coatings. This testing ensures that the selected fluids will form a continuous and protective layer.
