What is the application of mica in microwave oven? The mica sheet in the microwave oven is mainly used to isolate the magnetron from the oven cavity (to prevent impurities from entering and damaging the magnetron), and the microwave can pass through. It is used to protect the magnetron. If it is not used, it can be heated. However, the water vapor and oil fume generated during heating will damage the magnetron. Your problem is that the mica sheet is not cleaned for a long time, resulting in a lot of grease in the mica sheet. As soon as the temperature is higher than the ignition point of the substrate, the mica sheet will catch fire and burn. It is recommended to replace the mica sheet immediately.