PCB Tech - Sharing practical skills about designing high frequency PCB

Sharing practical skills about designing high frequency PCB
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 within the PCB board. The editor of Shenzhen PCBA processing believes that understanding this article will bring convenience to future PCB design.

The interconnection between chip and PCB in PCB design is important to the design. However, the main problem of chip and 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. This article Shenzhen PCBA processing editor shared practical skills of high-frequency PCB design. 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. High-performance dielectric circuit boards whose dielectric constant values are strictly controlled according to the number of layers shall be used. This method is conducive to effective simulation calculation of the electromagnetic field between the insulating material and the adjacent wiring.

3. PCB design specifications related to high-precision etching should be specified. 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 pin leads have tap inductance and parasitic effects, so avoid using components with leads. In high frequency environments, it is best to use surface mount SMD components.

5. For signal vias, avoid using the via processing (pth) process on the sensitive board, because this process will cause lead inductance at the via. For example, when a through hole on a 20-layer board is used to connect layers 1 to 3, there are 4 to 19 layers of lead inductance, and buried blind holes or back drills should be used.

6. To provide a rich ground layer. Use molded holes to connect these ground planes to prevent the 3D electromagnetic field from affecting the 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 solder mask can prevent the flow of solder paste. However, due to the uncertainty of thickness and the unknown of dielectric constant performance, covering the entire board surface with solder mask material will cause changes in circuit performance in the microstrip design. Generally, a solder dam (solderdam) is used as the solder mask.

The above is the technique of high frequency PCB design for the interconnection of the PCB board shared by the editor today. The editor of ShenzhenPCBA processing hopes to be helpful to everyone.