PCB, what we normal call as "printed circuit Board", is the basic for all electronics products. 

If we classify the PCB by layers, there will be single sided PCB, double sided PCB, and multilayer PCB Board.

Multilayer PCB Instructions by Linked Electronics

Multilayer PCB Board is made up of more than 2 copper layers, and those copper layers are boned by prepeg.  Conductor on different layers are connected with vias.

Compared with doubled sided layers, multilayer circuit board is smaller with higher capacity, faster speed, better durability and greater functionality. For BGA and QNF packages, electronic design engineer will use HDI multilayer PCB. 

By category in Linked Electronics, there are multilayer FR4 PCB, multilayer Rogers PCB, multilayer rigid flex PCBs, heavy copper multilayer PCB and HDI multilayer PCB board. 

Applications of Multilayer PCBs

Mulilayer PCB is used more and more in electronics industries becuse of its unique advantages.

Multilayer PCB boards is much more precise and has better performance than double sided PCBs, which is widely used in industrial, medical and communication industries.