Wiring method for multi-layer circuit boards

Assuming that the frequency of a digital logic circuit reaches or exceeds 45MHz~50MHz, and the circuit operating above this frequency occupies a certain proportion of the entire electronic system (such as 1/3), it is usually called a high-frequency circuit (multi-layer circuit board). High frequency circuit board planning is a very chaotic planning process, and its wiring is crucial to the entire planning!

First move, wiring of high and multi-layer circuit boards

High frequency circuits often have high integration and high wiring density. Choosing multi-layer circuit boards is not only necessary for wiring, but also a useful means to reduce interference. In the PCBLayout stage, selecting a certain number of layers of Printed Circuit Board scale reasonably can make full use of intermediate layers to set shielding, better achieve nearby grounding, effectively reduce parasitic inductance and shorten signal transmission length, and also significantly reduce signal interference. All of these methods are beneficial for the reliability of high-frequency circuits. There are materials showing that when using the same material, the noise of a four layer board (multi-layer circuit board) is 20dB lower than that of a double-sided board. However, there is also a problem together. The higher the number of half layers of a circuit board, the more chaotic the manufacturing process, and the higher the unit cost. This requires us to not only choose the appropriate number of layers of circuit boards when terminating PCBLayout, but also to stop reasonable equipment planning and choose the correct wiring rules to complete the planning.

The second trick is to minimize the bending of the leads between the pins of high-speed electronic equipment, as much as possible

It is best to choose a straight lead for high-frequency circuit wiring, which needs to be colored. A 45 degree broken line or circular arc can be used for coloring. This requirement is only used for the fixation strength of the copper foil in low-frequency circuits, but in high-frequency circuits, meeting this requirement can reduce the external emission and mutual coupling of high-frequency signals.

The third trick is to replace the lead wires between the pins of high-frequency circuit equipment as little as possible

The so-called "less interlayer replacement of leads is better" refers to the use of fewer vias (Via) in the process of component connection. According to the side, a PCB through-hole can bring about a scattered capacitance of about 0.5pF, reducing the number of through-holes can significantly increase speed and reduce the possibility of data errors.