Eight-Layer PCB is a stack-up PCB design that has 8 copper layers. One of the major reasons to design an eight-Layer PCB is to reduce the electromagnetic interference and improve on signal integrity. For this reason, eight-Layer PCB can be approximated to be equivalent to a 6-layer PCB which has better signal integrity. There are different configurations that could be used to make eight-Layer PCB. Whichever configuration used, the PCB Designer should seek to ensure that power and ground planes should be coupled together. The high speed signals should be sandwiched between the center planes of the eight-Layer PCB. The signal layers should be adjacent to the planes. For better signal integrity, ensure that your eight-Layer PCB has multiple ground planes.
In general, to make an eight-Layer PCB, you need alternating layers of copper layer, prep reg and core. The prep reg acts as a glue that firmly combines the eight-Layer PCB stack-up into a single board. Following the rules to improve on the electromagnetic compatibility, a simple eight-Layer PCB configuration would look as shown below. It is important to note that an Eight-Layer PCB is capable of achieving high signal integrity as compared to 6-layer PCB and below.