PCB News - The first consideration in PCB design

The first consideration in PCB design

1. How to choose PCB board?
   The choice of PCB board must strike a balance between meeting design requirements and mass production and cost. The design requirements include both electrical and mechanical parts. This material issue is usually more important when designing very high-speed PCB boards(frequency greater than GHz). For example, the commonly used FR-4 material, the dielectric loss at a frequency of several GHz will have a great influence on the signal attenuation, and may not be suitable. As far as electricity is concerned, pay attention to whether the dielectric constant and dielectric loss are suitable for the designed frequency.

   

   
   2. How to avoid high frequency interference?
   The basic idea of avoiding high-frequency interference is to minimize the interference of the electromagnetic field of high-frequency signals, which is the so-called crosstalk (Crosstalk). Can increase the distance between high-speed signal and analog signal, or add ground guard/shunt traces beside the analog signal. Also pay attention to the noise interference from the digital ground to the analog ground.
   3. How to solve the problem of signal integrity in high-speed design?
   Signal integrity is basically a problem of impedance matching. The factors that affect impedance matching include the structure and output impedance of the signal source, the characteristic impedance of the trace, the characteristics of the load end, and the topology of the trace. The solution is to *termination (termination) and adjust the topology of the wiring.
   4. How is the differential wiring method realized?
   There are two points to pay attention to in the layout of the differential pair. One is that the length of the two wires should be as long as possible, and the other is that the distance between the two wires (this distance is determined by the differential impedance) has to be kept constant, that is, to keep parallel. There are two parallel ways, one is that the two wires run on the same side-by-side, and the other is that the two wires run on two adjacent layers above and below (over-under). Generally, the former has more side-by-side implementations.
   5. How to implement differential wiring for a clock signal line with only one output terminal?
   To use differential wiring, it makes sense that both the signal source and the receiving end are differential signals. Therefore, it is impossible to use differential wiring for a clock signal with only one output terminal.