Multilayer PCB

Multilayer PCB is a circuit board that has more than two layers.

Unlike a Double-Sided PCB which only has two conductive layers of material, all multilayer PCBs must have at least three layers of conductive material which are buried in the center of the material.

How Are Multilayer PCBs Made?

Alternating layers of prepeg and core materials are laminated together under high temperature and pressure to produce Multilayer PCBs. This process ensures that air isn't trapped between layers, conductors are completely encapsulated by resin, and the adhesive that holds the layers together are properly melted and cured. The range of material combinations is extensive from basic epoxy glass to exotic ceramic or Teflon materials.

The figure above illustrates the stackup of a 4-Layer/ multilayer PCB. Prepeg and core are essentially the same material, but prepeg is not fully cured, making it more maltable than the core.The alternating layers are then placed into a lamination press. Extremely high temperatures and pressures are applied to the stackup, causing the prepeg to "melt" and join the layers together. After cooling off, the end result is a very hard and solid multilayer board.

Benefits of Multilayer PCBs (compared to single or double-sided PCBs)

Higher assembly density
Smaller size (considerable savings on space)
Increased flexibility
Easier incorporation controlled impedance features.
EMI shielding through careful placement of power and ground layers.
Reduces the need for interconnection wiring harnesses (reduces overall weight)

Applications of Multilayer PCBs

While the weight and space benefits of multilayer PCBs are especially valuable, Multilayer PCBs are also beneficial to applications where "cross-talk" levels are critical. These are a few main applications using multilayer printed circuit boards:

Computers
File servers
Data storage
Signal transmission
Cell phone transmission
Cell phone repeaters
GPS technology
Industrial controls
Satellite systems
Hand held devices
Test equipment
X-ray equipment
Heart monitors
Cat scan technology
Atomic accelerators
Central fire alarm systems
Fiber optic receptors
Nuclear detection systems
Space probe equipment
Weather analysis