Urethane conformal coating is becoming an increasingly popular conformal coating choice.  However, it is not suitable for all applications.  Instances where the product is going into a high vibration environment or has a high heat requirement would not ideal candidates for urethane conformal coatings.

For products going into a high vibration environment, such as on an aircraft, urethane conformal coatings are not a good choice.  Because of the mechanical strength and resistance to abrasion characteristics that urethanes typically exhibit, a high vibration environment could ultimately end up weakening the integrity of this rigid coating.  A better choice for a high vibration environment would be to go with a completely conforming, flexible coating, such as parylene conformal coating.

If an application is going to a high heat environment, urethanes will not provide the protection that is required.  Leading urethanes, such as HumiSeal 1A33, offer protection to 125ºC.  Silicone conformal coatings, on the other hand, offer protection as high as 200ºC.  This is typical with conformal coatings, as silicones typically offer the best protection, temperature wise.