Several layers of PCB is the best?
A designer according to the complexity of the circuit to determine the number of PCB layers.
Single-layer PCB
Sometimes, we will create a simple single-layer PCB, consumer electronic products, is fictional, in order to keep a thin layer of copper (copper cladding) of the original negatives of cheap materials. These designs typically include many jumper ("jumper", jumper wires), in the dual panel analog circuit lines. This technique is suitable only for low-frequency circuits. For these reasons, this design is quite sensitive to radiation of noise. Design of such a bottom plate is difficult, because a considerable portion will fail. Many complex designs through the use of this technology has been successfully implemented, but this requires a lot of work to anticipate. Put on the box at the bottom of all analog single-panel TV is an example, it uses a metal processed CRT, CRT will these independent digital TV modulation harmonics upper shielding. If this design requires high volume, low-cost printed circuit board requires some improvement. If you need a single layer PCB, please do not forget to trace resistance!
Layer PCB
The next step is to design complex deep layer PCB. Layer board is easy to arrange program because it has two layers of metal foil in different directions at intersections to signals on the line is possible. Nevertheless, the intersection of the line is not used in analog circuits. Whenever possible, the bottom must be dedicated to the ground plane, the other signal is used in the upper line. Ground has the following advantages:
Ground in the circuit connection method is often used. Ground at the bottom makes the circuit very sensitive.
He enhanced the bottom plate of the mechanical endurance.
In the circuit, so that all ground impedance decreases, also reduces the transmission of undesired noise.
It is like a shield, the shield plate following up radiated noise.
It increases the circuit in each of the distributed capacitance - conducive to delete radiated noise.
Multilayer PCB
Despite the two-layer board has some advantages, but it is not the best construction method, especially for sensitive or high-speed designs. The most common bottom plate thickness of 1.5mm, in order to achieve this separation was a great advantage of the above mentioned. For example: distributed capacitance, the presence of the partitions, and its capacitance is very low. Critical design needs multilayer backplanes, for obvious reasons:
Provide better ground for the power lines. If the power supply is also plane, by increasing the path can use the circuit in the connection point.
Other layers may be exploited by the signal line, so that the line is very simple.
Power and ground to produce a distributed capacitance between the plates, thus reducing the high frequency noise. There are other reasons, but not very obvious.
Better resist electromagnetic interference and radio frequency interference. As we all know, from Marconi (Marcomni) there since the days of the image plane effect. When a conductor is placed near the surface of parallel conductors, most high-frequency current to flow directly back to the lower conductor, the reverse flow in the conductor, the conductor plane of the mirror creates a transmission line. At this time the current in the transmission line is equal in the reverse direction, so it has a relative radiated noise immunity. It can also be effectively coupled signal, to the image plane and the ground, the effective operation of the power plane, the signal must be continuous. Any interval and can cause discontinuities interest effects disappear soon.
Reduce the small-scale production of integrated project costs, although it is very expensive to produce plywood, from the United States Federal Communications Commission or some other agency requires high false test design EMI / RFI demand. If you have a problem, you must re-designed PCB, so that the auxiliary quiz. A multilayer PCB has a 20dB (EMI / RFI) running better than two layers of the PCB.
