A multilayer PCB will, by definition, have 3 or more conductive copper layers, each separated from the others using either fully cured core material, or partially cured prepreg material. A multilayer PCB is more complex and dense than either single sided or double sided PCBs and can be used for higher technology applications. Using alternate core and prepreg materials, the required multilayer stack is created and copper foils used to form what will become the top and bottom layers of the PCB. The application of heat and pressure in the bonding press fully cures the prepreg material to create the finished multilayer. PTHs take connections from layer to layer in the same manner as a double sided PCB.

Advantages of a multilayer PCB over both single sided and double sided include:

• Increased circuit density and complexity
• More complex designs can be adopted, potentially allowing different single sided and/or double sided designs to be incorporated into one multilayer design
• Reduction in size due to extra routing space from additional layers
• Improved distribution of power, better ground shielding and good return paths for signals
• Segregation of critical design aspects e.g. digital and analogue or high speed/high frequency.
• Better EMC compliance from use of ground or power plane layers