There are four key reasons why Parylene masking and de-masking is more difficult compared to liquid conformal coatings.
- Parylene is a vapour. When you are masking against a gas rather than a liquid then there is more of a challenge. So you need to provide a much better barrier with the masking process compared to the liquid coatings.
- Parylene is immersion. Most liquid conformal coatings are sprayed and so the capillary is less compared to immersion in a limitless supply of material.
- Stripping Parylene is hard. It is much harder to remove unwanted Parylene material on components that should not have been coated. Parylene is chemically inert (therefore harder to strip off or remove) and more difficult to see (no UV trace in most Parylene coatings). Mistakes can be more costly.
- The Parylene can bond more to the masking materials. When the Parylene is deposited on the masking materials and circuit board it can bind the two together and it can take significant effort and care to remove the masking materials without damaging the board or the Parylene coating integrity.
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Parylene Coating Process
Parylene Coating Process – Phase 1 – Prior to Parts Arrival
Once we obtain a purchase order from a client, all of the relevant data such as drawings, specifications, and special instructions are given to the quality department from our marketing team to create custom work instructions for that individual assembly.
Parylene Coating Process – Phase 2 – Coating Processes
After the work traveler and other back-end tasks have been finished, the parylene coating production process truly begins in our shipping department. Once all of the items have been unpacked, they are then routed to incoming inspection. Here, parts are counted to verify quantity against the customer purchase order and packing slip, as well as inspected to verify that no damage occurred to the assemblies prior to arrival at Diamond-MT. After incoming inspection, assemblies are then ready for processes unique to that assembly. For example, if cleaning or cleanliness testing were needed, it would be performed at this time. Once any unique processes have been finished, the products are then given to our maskers. Masking is performed per the customer’s drawings and/or written requests for coating keep-out areas. Once completed, the parts go into masking inspection to verify compliance with the customer’s masking drawing. After parts pass masking inspection, a proprietary parylene adhesion promotion is administered. At last, the parylene deposition process is carried out. Once coating has been deposited, the coated materials have the masking material removed with great care not to damage the thin layer of parylene applied. The parts are nearing completion, but before they can be packaged up and sent back to the customer, they need to go through a final QA inspection. The final inspection ensures that all required process stages were successfully completed and that the final product completely meets the terms of the customer’s drawing and specifications. Final inspections are done on 100% of the customer’s product. Once the parts pass the final inspection, they are returned to the shipping department to be packed back into the customer supplied boxes and returned. The parylene coating process is normally a ten business day evolution, but can be completed quicker on a negotiated basis.
Parylene Coating Process – Phase 3 – Post Coating Follow-up
Our sales team is in very close contact with our clients after the coating process to make sure the parylene coating is exactly as the customer requires. If any changes are necessary to our process, our quality department will diligently with the customer to make sure that the end product is exactly what is expected.
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.