FR4, often written as FR-4, is a widely recognized and high-performing substrate material used in PCB manufacturing. Its affordability, insulation properties, and structural integrity make it the foundation for most PCB designs. FR4 boards are coated with copper foil using adhesive to create conductive layers, either single or double-sided, depending on the design. This flexibility allows for the development of complex multilayer PCBs, making FR4 the default choice for many applications.