Layer count: PCB layer count refers to the number of copper layers in a printed circuit board. A PCB that has multiple layers of copper separated by non-conductive insulating material is known as a multi-layer PCB. Although multi-layer printed circuit boards have higher component density, it is usually difficult to perform field repairs or modification on them. The number of layers in a PCB not only determines the density of components that the board can support but also the cost of fabricating it.