Is conformal coating necessary?

Whether or not conformal coating is required depends on the environment the electronic device will operate in, the reliability requirement of the device, and the cost of failure, whether in dollars or human lives. Typical consumer devices are generally not coated because cost is one of the top driving factors, and a coating step certainly adds to that. Devices operating in harsh environments may require coating, and the type of stresses and contamination will point to the best option, whether that is acrylic resin (AR), silicone resin (SR), urethane resin (UR), or some other type of protection. Aviation, aerospace, and medical devices often require coating because of the mission critical nature of these applications.