What is Contact Angle

What is Contact Angle

The contact angle refers to the angle formed between a stationary drop of liquid and a solid surface. It provides insights into the wetting behavior and adhesion of liquids on solid surfaces. The contact angle is measured at the three-phase contact point, where the liquid drop, the liquid-solid interface, and the solid surface intersect.

The contact angle is influenced by various factors, including the surface tension of the liquid, the surface energy of the solid, and the intermolecular forces between the liquid and the solid. It is commonly measured using techniques such as the sessile drop method, where a drop of liquid is placed on a solid surface and the contact angle is determined by analyzing the shape of the drop.

There are two important equilibrium contact angles associated with the contact angle: the advancing angle and the receding angle. The advancing angle refers to the angle at which the liquid drop spreads on the surface, while the receding angle refers to the angle at which the liquid drop contracts or retracts from the surface. These angles represent a thermodynamic equilibrium between the liquid and the surface.

Contact angle affects the adhesion and spreading of liquid materials used in the manufacturing processes. For example, in the application of solder paste onto PCBs, the contact angle determines the wetting ability of the solder paste on the surface of the PCB pads. A proper contact angle ensures good wetting and reliable solder joints.