PCB board single-sided, double-sided and multilayer, wherein the layers of the multilayer is not limited, there are already more than 100 layers of the PCB, and the PCB is a multilayer common four and six boards. So why have we, "Why are even layer multilayer PCB?" This question it? Relatively speaking, indeed even layer PCB to PCB than the odd-layer, but also an advantage.
1, since lower cost and less plating a dielectric foil, costs of raw materials slightly below the PCB odd even-layer PCB. However, the processing cost is significantly higher than the odd-layer PCB even-layer PCB. Processing costs the same as the inner layer, the foil cladding / core structure significantly increases the cost of processing the outer layer. Odd-layer PCB need to increase the nucleation layer laminated bonding process on the basis of non-standard process on the core structure. Compared with the core structure, adding an outer cladding foil core structure plant efficiency will drop. Before laminating adhesive, the outer core requires additional treatment process, which increases the risk of being scratched layer and etching errors.
2, the best balance structure to avoid bending without reason odd-layer PCB design are: odd number of layers of the circuit board is easily bent. When the multilayer circuit PCB cooled after the bonding process, and a different core structure of the cooling structure when deposited foil laminate will cause tension bend PCB. With increasing circuit board thickness, the risk of having a composite structure of two different curved PCB greater. Key to eliminating the circuit board is bent is balanced laminate. Although a certain degree of bending PCB to specifications, but processing efficiency will decrease, resulting in increased costs. Because the process requires special equipment and the assembly, component placement accuracy is reduced, it will compromise the quality.
Another argument is easier to understand: the process in the PCB process, the four-layer board better control than three sheets, mainly in terms of symmetry, four-layer board warpage can be controlled to 0.7% or less (the standard IPC600), but three times larger board size, warpage exceed this standard, this will affect the reliability SMT placement and the entire product, it is generally the designer, not an odd design shelves, even the odd layer to achieve functional, will designed to be false even layer, layer design is about 5 to 6 layers, 7 layers is designed to 8 layers. For the above reasons, PCB layer multilayer often designed into even less odd layers.
How odd-layer PCB stack balance, reduce cost? If, when the odd-layer PCB designs appear, how to do it? Equilibrium can be reached with the following lamination methods, to reduce the manufacturing cost PCB, PCB to avoid bending.
1) one signal layer and use. If the power supply layer PCB design layer is an even number and an odd signal of this method may be employed. Layer is increased without increasing the cost, but it is possible to shorten delivery times, quality improvement PCB.
2) increasing an additional power supply layer. If the power supply layer PCB design is an odd number and an even number of signal layers can be used this way. A simple method is applied without changing the formation in a laminate disposed intermediate the other cases. Press PCB wiring odd seed layer, and then copy the intermediate formation, marking the remaining layers. This foil cladding and electrical characteristics as the formation thickened.
3) adding a blanking the laminated layer close to the central PCB. This approach minimizes the laminated imbalance, to improve the quality of the PCB. Press the odd-layer wiring, and then add one signal layer blank, marking the remaining layers. In microwave circuits, and mixed media (media have different dielectric constants) circuit species employed.