Composition and Structure
4-layer PCB means that the printed circuit board is made of 4 layers of fiberglass. There are four routing layers: top, bottom, VCC, and GND. Generally, through holes, buried holes, and blind holes are used to connect the layers. There are more buried and blind vias than double-sided.
Design Considerations
In addition, try not to run signal traces on the VCC and GND layers.
Advantages Over Double-sided Rogers PCB Boards
Compact Design
4-layer PCB boards have many advantages over double-sided Rogers PCB boards. They can be designed to be more compact.
Improved Noise Immunity
They have significantly improved noise immunity.
Easier Layout
And are easier to lay out.