Electronic Design - PCB interconnection high frequency PCB design skills

The goal of PCB design is smaller, faster and lower cost. And because 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. Each interconnection point must be investigated and the existing problems must be solved.

The interconnection of the circuit board system includes three types of interconnection: the chip to the circuit board, the interconnection within the PCB board, and the signal input/output between the PCB and external devices. This article mainly introduces a summary of practical techniques for high-frequency PCB design with interconnections in the PCB board. I believe that understanding this article will bring convenience to your future PCB design.

In PCB design, the chip-PCB interconnection is important to the design. However, the main problem of the chip-PCB interconnection is that the interconnection density is too high, which will cause the basic structure of the PCB material to become a factor limiting the growth of interconnection density. Let's share the practical skills of high-frequency PCB design for everyone.

As far as high-frequency applications are concerned, the techniques for high-frequency PCB design with interconnections within the PCB are as follows:

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

2. Use high-performance insulated circuit boards whose insulation constant values are strictly controlled by level. This method is conducive to effective management of the electromagnetic field between the insulating material and the adjacent wiring.

3. To improve the PCB design specifications related to high-precision etching. It is necessary to consider that the total error of the specified line width is +/-0.0007 inches, the undercut and cross-section of the wiring shape should be managed, and the plating conditions of the wiring side wall should be 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.

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

5. For signal vias, avoid using via processing (pth) processes on sensitive boards. Because this process will lead to lead inductance at the via. For example, when a via on a 20-layer board is used to connect layers 1 to 3, the lead inductance can affect layers 4 to 19.

6. Provide abundant ground planes. Use molded holes to connect these ground planes to prevent the 3D electromagnetic field from affecting the PCB circuit board.

7. To choose electroless 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.

8. The PCB 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.