Inspecting Parylene Coating

Parylene conformal coating (XY) offers insulative protection for intricate electronic circuit assemblies that need to perform under demanding conditions – facing potential chemical, electrical, moisture and vapor exposure. Applied using chemical vapor deposition (CVD), Parylene wicks deep into substrate surfaces, providing a level of protection that exceeds what liquid coatings like acrylic, epoxy, silicone and urethane can offer. Even though Parylene is applied in a vacuum, its exceptional qualities don’t come from that alone; the protective benefits of Parylene heavily rely on film adhesion, a critical aspect that requires constant and meticulous inspection throughout the production process.

Incoming Inspection

The incoming inspection process commences right after unpacking customer parts. Received assemblies are counted to confirm that quantities align with the client’s packing slip and purchase order. How detailed an incoming inspection is varies based on what is required by the customer and is usually based on the type of parts.

Cleanliness Testing

Each application follows specific procedures, which may include board cleaning and/or cleanliness testing per IPC-J-STD-001 standards. Ensuring cleanliness is crucial as contaminants may have built up on the substrate during manufacturing, handling and transportation. Surface cleanliness is paramount for proper Parylene adhesion and overall coating quality; contaminated surfaces can result in poor adhesion and delamination, undermining the effectiveness of the Parylene application.

Coating Thickness and Adhesion Testing

For quality assurance, Parylene inspection can provide a comprehensive assessment of coating thickness required to meet assignment specifications, PCB coverage, visual inspection and adhesion testing. Microscopically thin XY films undergo measurement through intensive evaluation, including using spectral reflectance directly on components or comparing film application with witness coupons.

Final Inspection

Before packaging coated assemblies, a final inspection is often performed.  This process covers many aspects of the coating process, ensuring the successful execution of steps for the XY coating application and adherence to the client’s drawings and specifications. Upon successful completion of the final inspection, the assemblies are returned to the customer.