Due to the lack of a layer of media and foil, the cost of raw materials odd PCB plate is slightly lower than even layer PCB. But the processing cost of odd layer PCB is obviously higher than even layer PCB. The processing cost of the inner layer is the same, but the foil / nuclear structure significantly increases the processing cost of the outer layer.
Odd layers of PCB need to be added on the basis of the nuclear structure process to increase the non-standard lamination of the core layer bonding process. Compared with the nuclear structure, the production efficiency will be decreased when the foil is added outside the nuclear structure. In the case of laminated bonding, the outer core requires additional processing, which increases the risk of the outer layer being scratched and etched.
Balanced structure avoid bending
The best reason for designing PCB without odd layers is that the odd layer circuit board is easy to bend. When the PCB is cooled after the multilayer circuit bonding process, the different lamination tension of the core structure and the foil structure will cause PCB bending. With the increase in the thickness of the circuit board, the risk of PCBA OEM foundry material with two different structures of composite PCB bending is greater. The key to eliminate the bending of the circuit board is to adopt a balanced stack. Although a certain degree of curvature of the PCB meet the specification requirements, but subsequent processing efficiency will be reduced, resulting in increased costs. Because assembly requires special equipment and technology, component placement accuracy is reduced, it will damage the quality.
Use even layer PCB
When the odd layer PCB in the design, the following methods can be used to achieve a balanced stack, reduce the cost of PCB production, to avoid PCB bending. The following methods are arranged according to the preferred order.
1.layer signal layer and use. If the power layer of PCB is even and the signal layer is odd, this method can be used. The increase of the layer does not increase the cost, but can shorten the lead time, improve the quality of PCB.
2.add an additional power layer. This method can be used if the power layer of PCB is odd and the signal layer is even. A simple way is to add a layer in the middle of the stack without changing the other settings. First, according to the odd layer PCB kinds of wiring, and then duplicate the layer in the middle, marking the remaining layer. This is the same as the electrical properties of the foil in the thickened formation.
3.add a blank signal layer to the center of the PCB stack. This method minimizes stack imbalance and improves the quality of PCB. First, the odd layer wiring, and then add a layer of blank signal layer, marking the remaining layers. In microwave circuits and mixed media (media with different dielectric constant).