Definition of multilayer printed circuit board

A multilayer printed circuit board is a circuit board with more than two layers. Multilayer printed circuit board is defined as a PCB made of three or more conductive copper foil layers. They are represented by several layers of double-sided circuit boards, laminated and bonded together, and there is an insulating layer between them. The entire structure is arranged so that two layers are placed on the surface side of the PCB to connect to the environment.

All electrical connections between the layers are made through through holes, such as plated through holes, blind holes and buried holes. Then, the application of this method leads to the generation of highly complex PCB of various sizes. Unlike a double-sided PCB with only two layers of conductive material, all multilayer PCBs must have at least three layers of conductive material buried in the center of the material.

The emergence of Multilayer PCB is due to the development and change of electronic industry. With the passage of time, electronic functions become more and more complex, requiring more complex PCB. Unfortunately, PCB is limited by noise, stray capacitance and crosstalk, so some design constraints need to be followed. These design considerations make it difficult to achieve a satisfactory level of performance for single or double sided PCBs – hence the birth of multilayer PCBs.

How to make multilayer printed circuit board?

Alternate layers of prepreg and core are laminated together at high temperature and high pressure to produce multilayer PCB. This process ensures that air is not trapped between the layers, the conductor is completely encapsulated in resin, and the adhesive that holds the layers together is properly melted and cured. Material combinations range from basic epoxy glass to special ceramic or Teflon materials.

The prepreg and core are essentially the same material, but the prepreg is not fully cured and therefore more malleable than the core, and the alternate layers are then placed in a laminating press. The application of extremely high temperature and pressure to the stack causes the prepreg to “melt” and bond the layers together. After cooling, the final result is a very hard and robust multilayer.

Advantages of Multilayer PCB (compared with single or double sided PCB)

• Higher assembly density
• Smaller size (saves a lot of space)
• Increase flexibility
• The controlled impedance function is easy to merge.
• Shield EMI by carefully placing the power and ground plane.
• Reduces the need for interconnect wiring harness (reduces overall weight)