Why are multilayer PCBs so popular?
Multilayer PCBs offer more complexity and capacity on a smaller footprint, thus saving space and weight whilst offering increased functionality. This is what makes them so popular in modern electronics.
The PCBs are multiple double-side boards that are bound together with alternating insulating materials to separate them. Drill holes between layers must be executed with great care and precision. Conductors on different layers are connected using vias which mean that the PCBs can accommodate a higher component density.