a 7 layer PCB is a type of multilayer board that comprises seven copper layers. These layers are stacked together with insulating material in between them to create a sandwich-like structure. In addition to power planes, ground planes, and routing layers, a 7 layer PCB may also include signal layers and other specialized layers, such as shielding or impedance-controlled layers.
The use of a 7 layer PCB can provide several benefits, particularly in high-speed applications. The additional routing layers allow for more complex and dense circuit designs, which can improve signal integrity and reduce electromagnetic interference (EMI). The power and ground planes also help to provide a stable power supply and reduce noise in the circuit.