Single Sided Board
The simplest of PCBs, because there is only one layer of substrate/circuitry. All electrical parts and components are generally fixed on one side with leads thru. the board holes to the copper traces/electrical connections on the other side. Single sided boards are most often thru. hole, rather than surface mount technology (SMT). Used when low level of technology is required.
Double Sided Board
The most common type of board, where parts and components are attached to either side of the substrate. In such cases, double-sided PCBs have connecting traces on both the sides of the board, connected thru. plated holes. Double-sided PCBs use through-hole and/or SMT components.
Multi Layered Board
Multi-layer PCBs consists of several layers of circuitry/substrate separated by insulation/dielectrics. Most common multilayer boards are: 4 layers, 6 layers, 8 layers, and 10 layers. However, the total number of layers that can be manufactured can exceed over 42 layers. These types of boards are used in extremely complex electronic circuits.