Multilayer PCBs are printed circuit boards with more than two layers. Double-sided PCBs have two conductive layers on both sides of the PCB substrate. Multilayer PCBs should contain at least three layers of conductive material or copper layers. These layers are connected by plated-through holes. These layers can consist of 4, 6, 8, or even up to 60 layers. 

Due to their design, multilayer PCBs become complex. The top and bottom may look similar to double-sided PCBs, but they have fixed layers on each side of the center layer. All these layers are compressed into a single PCB, which is multilayered and connected by plated-through holes. Advantages of Multilayer PCBs: 01. Enhanced Functionality and Capability By using multilayer boards, the functionality and capability of the printed circuit board can be effectively increased. With more layers, you can install more circuits and traces on the board. 02. Greater Flexibility Can be made rigid or flexible – These multilayer PCBs can be configured as either rigid or flexible, depending on your requirements. However, the more layers you add to the board, the less flexible it becomes. 03. Smaller Size When you stack layers on top of each other, this can save space. Multilayers allow you to have higher capacity in a smaller footprint, which can benefit smaller devices. 04. Lighter Weight Due to the layered configuration of these PCBs, separate PCB connectors are not required. This simplifies the manufacturing process, not only saving space but also reducing the overall weight of the board.