A Multilayer products PCB exist out of at least three or more conductive layers(copper foil layer). A Multilayer products has for the different layers 1 type of material, but sometimes a mix with another material is possible. These layers are pressed together and form a multilayer PCB. Copper foil layer is bonded together with prepreg.
The complexity in the manufacturing process makes the price higher. It depends on the number of layers and the density. (HDI or VHDI) A Multilayer can have different types of vias such as through holes, blind and burried vias, stacked and staggered Micro vias and filled vias in pad.
Multilayer products has full copper layers for power and ground and that is a benefit. In case of design problems, such as noise, crosstalk and so on, it is important to make the length of the signal wires as short as possible and avoid parallel circuits. This is easier to realize it on a multilayer then on a single- or double PCB.
Multilayer products PCBs are used all over the world.