What is the uniformity of parylene conformal coating?

Parylene  is often applied to substrates or materials where there is no room for any voids in the protective coating.  These materials are likely to be placed in harmful chemicals, a moisture packed environment, or even the human body.  These are often mission critical devices which can not allow any environmental factors to alter their performance.  Whenever these devices need this stringent level of protection from the elements, parylene is the only logical choice. 

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.