Microwave Tech - Design skills of high-frequency circuit boards

Design skills of high-frequency circuit boards

1. Improve the PCB design specifications for high-precision etching. Considering that the total error of the specified line width is +/-0.0007 inches, the undercut and cross section of the wiring shape are managed, and the plating conditions of the wiring sidewall are specified. The overall management of wiring (wire) geometry and coating surface is very important to solve the skin effect problem related to microwave frequency and realize these specifications.

2. The protruding leads have tap inductance, so avoid using components with leads. In high frequency environments, it is best to use surface mount components.

3. The corner of the transmission line should be 45° to reduce the return loss.

4. The use of high-performance insulated circuit boards whose insulation constant values are strictly controlled in accordance with levels is conducive to effective management of the electromagnetic field between the insulating material and the adjacent wiring.

5. Choose non-electrolytic nickel plating or immersion gold plating process, do not use HASL method for electroplating. This kind of electroplated surface can provide better skin effect for high frequency current. In addition, this highly solderable coating requires fewer leads, which helps reduce environmental pollution.

6. The solder mask can prevent the flow of solder paste. However, due to the uncertainty of the thickness and the unknown of the insulation performance, the entire surface of the board is covered with solder mask material, which will cause a large change in the electromagnetic energy in the microstrip design. Generally, a solder dam is used as the solder mask. The electromagnetic field. In this case, we manage the conversion from microstrip to coaxial cable. In the coaxial cable, the ground layer is interwoven ring-shaped and evenly spaced. In microstrip, the ground plane is below the active line. This introduces certain edge effects, which need to be understood, predicted and considered during design. Of course, this mismatch will also cause return loss, and this mismatch must be minimized to avoid noise and signal interference.

7. For signal vias, avoid using a via processing (pth) process on sensitive boards, because this process will cause lead inductance at the vias.

8. Provide abundant grounding layers, and use molded holes to connect these grounding layers to prevent the influence of the three-dimensional electromagnetic field on the circuit board.

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