Core thickness is the thickness of the core material used in a printed circuit board. The core material, also known as the dielectric, is an insulating material that separates the conductor or copper foil layers in the PCB. It is typically made of a non-conductive material such as fiberglass or epoxy. The core thickness is a critical parameter in PCB fabrication as it determines the overall thickness and mechanical stability of the board. Buy iy can vary depending on the specific requirements of the PCB design. As the number of layers in a PCB increases, the overall thickness of the board also increases due to the minimum thickness requirement of each layer. The core thickness can be varied based on the desired functionality and design considerations of the PCB. For example, designs that require specific characteristic impedance or have mechanical requirements may call for a thicker or thinner core.