Parylene coatings are completely conformal, have a uniform thickness and are pinhole free. This is achieved by a unique vapor deposition polymerization process in which the coating is formed from a gaseous monomer without an intermediate liquid stage. As a result, component configurations with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids, as shown below:
Here the orange layer is parylene, with completely uniform coverage of the substrate (illustrated in green), leads (in grey), and component (in black). This all encompassing coverage is one of parylene’s greatest competitive advantages against other liquid conformal coatings. Let’s look at what a liquid coating’s coverage may look like:
Despite the poor editing, it is easy to see that on the sharp edges the coating is substantially thinner than at other areas. There is also pooling on the sides where the leads meet the connector. Factors like this are inherent with liquid coatings, simply because they are a liquid.