What is the requirement for coating in relation to dewetting?

The requirement for coating in relation to dewetting specifies that the coating must be free of dewetting. Dewetting refers to the phenomenon where a liquid coating fails to form a continuous layer on the surface of a substrate, leading to spots where the liquid retracts or pulls away. This can compromise the protective qualities of the coating, which is critical for preventing corrosion, adhering to the substrate properly, and ensuring the functional reliability of electronic assemblies.

In the context of IPC standards, ensuring coatings are free from dewetting is vital because any dewetting may lead to reduced performance and durability of the electrical and electronic assemblies. A continuous and uniform coating maximizes coverage and effectiveness, providing optimal protection.

The other options suggest varying degrees of acceptability of dewetting, which contradicts the strict requirements laid out in the standard. Therefore, the necessity for coatings to be entirely free from dewetting aligns with best practices in electronics assembly, ensuring reliability and longevity of the product.