Then A potting compound, for example epoxy or silicone, is poured about it. The liquid flows all around all elements and fills empty spaces. The moment it cures, it forms a solid layer that seals The full board. Potting is really a well-established system for safeguarding PCBs in hostile environments. https://www.jiadi-newmaterials.com/news/pcb-potting-compound-selection-guide.html