What Should You Pay Attention To When Designing PCB?

Nov. 19, 2019

PCB design is very important throughout the board, which determines the basis of the entire PCB board. Flexible PCB Circuit Board Supplier have summarized some points that need attention in PCB design, and hope to help everyone.

Multilayer Flexible PCB

Multilayer Flexible PCB 

1, choose PCB board

Choosing PCB boards must strike a balance between meeting design requirements and mass production and cost. Design requirements include both electrical and institutional components. This material problem is usually more important when designing very high speed PCB boards (greater than GHz). For example, the commonly used FR-4 material, the dielectric loss at a frequency of several GHz has a great impact on signal attenuation, and may not be useful. In the case of electrical, it is important to note whether the dielectric constant and the dielectric loss are combined at the designed frequency. There are many Double-sided PCB Wholesale on the market, and we can find this phenomenon.

2, avoid high frequency interference

The basic idea of avoiding high-frequency interference is to minimize the interference of high-frequency signal electromagnetic fields, which is called crosstalk. You can use the distance between the high-speed signal and the analog signal, or add ground guard/shunt traces next to the analog signal, and pay attention to the digital ground noise interference to the analog ground.

3, solve the problem of signal integrity

Signal integrity is basically a matter of impedance matching. The factors affecting the impedance matching are the signal source architecture and output impedance, the characteristic impedance of the trace, the characteristics of the load end, and the topology of the trace. The solution is to terminate and adjust the topology of the trace.

4, to achieve differential wiring

There are two points to note about the wiring of the differential pair. One is that the length of the two lines should be as long as possible, and the other is that the spacing between the two lines (which is determined by the differential impedance) should remain the same, that is, to be parallel. There are two ways of paralleling. One is that the two lines are on the same layer, and the other is two lines that are on the upper and lower layers. In general, the former has implemented more methods.

5. Implement differential wiring in the case of a clock signal line with only one output

To use differential routing, it must be meaningful that both the source and the receiver are differential signals. Therefore, differential wiring cannot be used for a clock signal with only one output.

6. Matching resistance between the differential pair of the receiving end

The matching resistance between the differential pair of the receiving end is usually added, and its value should be equal to the value of the differential impedance. This signal quality will be better.

7. The wiring of the differential pair should be close and parallel

The wiring of the differential pairs should be properly close and parallel. The proper proximity is because this spacing affects the value of the differential impedance, which is an important parameter for designing differential pairs. Parallelism is also required because the consistency of the differential impedance is maintained. If the two lines are too close, the differential impedance will be inconsistent, which will affect signal integrity and time delay.

8, dealing with some theoretical conflicts in the actual wiring

a. Basically, it is correct to isolate the analog/digital partitions. It should be noted that the signal trace should not cross the divided area as much as possible, and the return current path of the power supply and signal should not be too large.

b. The crystal oscillator is an analog positive feedback oscillator circuit. To have a stable oscillation signal, the loop gain and phase specifications must be met. The oscillation specifications of the analog signal are easily interfered, and even if it is added, the interference cannot be completely isolated. And too far away, the noise on the plane will also affect the positive feedback oscillator circuit. Therefore, the distance between the crystal and the chip must be close.

The above is the problem that the Multilayer Flexible PCB Manufacturer should pay attention to when designing the PCB circuit board. Have you learned it?