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    Summary of Practical Skills in High Frequency PCB Design

    Author:xiaozhi-zhan Views:27 Release time:2019-05-30 10:30:56

    The goal of PCB design is to be smaller, faster and cheaper. Because the interconnection point is the weakest link in the circuit chain, the electromagnetic property of the interconnection point is the main problem in RF design. It is necessary to investigate each interconnection point and solve the existing problems.


    The interconnection of PCB system includes chip to circuit board, PCB intra-board interconnection and signal input/output between PCB and external devices. This paper mainly introduces the practical skills of high frequency PCB design for PCB intraboard interconnection. It is believed that the understanding of this paper will bring convenience to PCB design in the future.


    In PCB design, the interconnection between chip and PCB is very important for design. However, the main problem of interconnection between chip and PCB is that the high interconnection density will lead to the basic structure of PCB material becoming a limiting factor for the growth of interconnection density. This paper shares the practical skills of high frequency PCB design.


    In terms of high-frequency applications, the techniques for designing high-frequency PCB for PCB intraboard interconnection are as follows:


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


    2. High performance insulated circuit boards with strictly controlled insulation constants should be adopted. This method is conducive to the effective management of electromagnetic field between insulating materials and adjacent wiring.


    3. To improve the PCB design specifications for high precision etching. Consider setting the total line width error of +/-0.0007 inches, managing the undercut and cross section of the wiring shape, and specifying the plating conditions for the side wall of the wiring. Overall management of wiring (conductor) geometry and coating surface is very important for solving skin effect problems related to microwave frequency and realizing these specifications.


    4. The tap inductance exists in the prominent lead, so the components with lead should be avoided. In high frequency environment, it is best to use surface mounting components.


    5. For signal through-hole, it is necessary to avoid the use of through-hole processing (pth) technology on the sensitive plate. Because this process will lead to lead inductance at the through hole. If a hole in a 20-layer board is used to connect layers 1 to 3, the lead inductance can affect layers 4 to 19.


    6. Provide abundant grounding layer. The grounding layers should be connected by moulding holes to prevent the influence of 3-D electromagnetic field on the circuit board.


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


    8. The solder paste flow can be prevented by the solder barrier layer. However, due to the thickness uncertainty and the unknown insulation performance, covering the whole plate surface with solder-resistant materials will lead to great changes in electromagnetic energy in microstrip design. Solderdam is usually used as the welding resistance layer.


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