Summary of practical skills for high frequency PCB design

The goal of PCB design is to be smaller, faster, and less costly. Since the interconnection point is the weakest link in the circuit chain, in the RF design, the electromagnetic properties at the interconnection point are the main problems faced by the engineering design. It is necessary to examine each interconnection point and solve the existing problems. 

For high-frequency applications, the techniques for interconnecting PCB boards for high-frequency PCB design are: 

1. The corner of the transmission line should adopt a 45° angle to reduce the return loss. 

2. It is necessary to use a high performance insulated circuit board whose insulation constant value is strictly controlled according to the level. This method facilitates efficient management of the electromagnetic field between the insulating material and adjacent wiring. 

3. Improve PCB design specifications for high-precision etching. Consider the total line width error of +/- 0.0007 inches, manage the undercut and cross-section of the wiring shape, and specify the wiring sidewall plating conditions. Overall management of the wiring geometry and coating surface is important to solve the skin effect issues associated with microwave frequencies and to implement these specifications. 

4. There is a tapped inductor in the protruding lead, and should avoid use leaded components. In high frequency environments, it is best to use surface mount components. 

5. For signal vias, should avoid use the PTH process on sensitive boards, because this process can cause lead inductance at the vias. If a via on a 20-layer board is used to connect layers 1 to 3, the lead inductance can affect 4 to 19 layers. 

6. Provide a rich grounding layer. These grounding layer are connected using molded holes to prevent the effects of 3D electromagnetic fields on the board.
 
7. Choose non electrolytic nickel plating or immersion gold plating, do not use HASL method for electroplating. This plated surface provides a better skin effect for high frequency currents. In addition, this high solderable coating requires fewer leads and helps reduce environmental pollution. 

8. The solder mask prevents the flow of solder paste. However, due to the uncertainty of thickness and the unknown nature of the insulation properties, covering the entire surface of the board with the solder resist material will result in a large change in the electromagnetic energy in the micro strip design. Generally use solder dam as a solder mask.