I am interested in parylene, but how thick should I have it applied? This is a question that is often brought up by customers who are new to conformal coating, especially parylene.
The first thing that we do is explain the parylene coating process and how it differs from conventional conformal coatings. Typically conformal coatings are applied anywhere from 2 to 8 mils. Most people are shocked, but pleased to learn that parylene can be successfully and consistently applied to as little as one micron!
Something that is not often taken into account when trying to determine the proper parylene thickness is the amount of clearance needed. If it is a printed circuit board that is an enclosure, there usually will not be too many clearance issues. However, in some cases, even an extra mil of coating can cause extra mechanical abrasion to the parylene which can result in damaged parylene.
Another factor to consider is the dielectric strength required. For applications that require a higher dielectric strength, a thicker coat of parylene has better dielectric properties than a thinner coat. Trying to balance the dielectric strength concern with clearance concerns is a tight rope to walk and often requires some testing to determine the proper balance.
In the simplest of cases, an end item customer, who is familiar with parylene, has specified the coating thickness to be applied and made this requirement a part of their drawing or specification. After our review the drawing and comparison of the drawing to the assembly, we will be able to determine if any potential issues with the parylene thickness are present and make suggestions accordingly.
This was a guest post from Sean Horn, Vice President of Diamond-MT. Diamond-MT is a leading conformal coating service provider located in Johnstown, Pa.