There are single-sided, double-sided and multi-layer PCB boards. The number of multi-layer boards is not limited. Common ones are four-layer boards, six-layer boards, eight-layer boards, and 10-layer boards. Why is the multilayer board an even number of layers?
1. Lower cost
Because of the lack of a layer of dielectric and foil, the raw material cost of odd-numbered PCB boards is slightly lower than that of even-numbered PCBs. However, the processing cost of odd-layer PCBs is significantly higher than that of even-layer PCBs. The odd-numbered PCB requires a non-standard laminated core layer bonding process on the basis of the core structure process. Compared with the nuclear structure, the production efficiency of the factory where the foil is added outside the nuclear structure will decrease, and it is easy to increase the risk of scratches and etching errors on the outer layer.
2. Balance structure to avoid bending
Odd-numbered circuit boards are easy to bend. The key to eliminating circuit board bending is to use a balanced stack. Although a PCB with a certain degree of bending meets the specification requirements, special equipment and processes are required for subsequent assembly, which reduces the accuracy of component placement, reduces quality, and increases cost. In terms of symmetry, four-layer boards are better controlled than three-layer boards.
Therefore, designers genernally do not design odd-numbered laminates. Even if the odd-numbered layer can achieve the corresponding function, the designer will design it as a pseudo-even-numbered layer, such as designing 5 layers into 6 layers and 7 layers into 8-layer boards.
