The design of the printed circuit board is based on the circuit schematic diagram to achieve the functions required by the circuit designer. PCB design mainly refers to layout design, which needs to consider the layout of external connections. Optimized layout of internal electronic components. Optimized layout of metal wiring and vias. Electromagnetic protection. Various factors such as heat dissipation. Excellent layout design can save production costs and achieve good circuit performance and heat dissipation. Simple layout designs can be implemented manually, and complex layout designs need to be implemented with computer-aided design (CAD).

In high-speed PCB design, the characteristic impedance of the controllable impedance plates and lines is one of the most important and common problems. First, let's look at the definition of a transmission line: a transmission line consists of two conductors of a certain length, one for transmitting signals and the other for receiving signals (remember that the "loop" replaces the concept of "ground"). In a multi-layer board, each line is part of the transmission line and the adjacent reference plane can be used as a second line or loop. The key to a line becoming a "perfect" transmission line is to keep its characteristic impedance constant throughout the line.

The key to making a board a "controllable impedance board" is to make the characteristic impedance of all lines meet a specified value, typically between 25 ohms and 70 ohms. In a multilayer circuit board, the key to good transmission line performance is to keep its characteristic impedance constant throughout the line.