To make the Printed circuit board alternating layers of epoxy-infused fiberglass sheets becomes used; these are called prepreg core materials, which are laminated together. This process becomes happened at a high temperature only. At the time of making 4 layers or multilayer PCB to make it thicker, inner layer imaging becomes used, along with this process prepreg and outer copper layers become used.
At the time of the PCB drilling process, it needs to drill with wholes, which helps to attach the components. Besides that, it needs linking copper; layers together, or for the purpose of mounting the PCB in its housing.