The purpose of PCB design is to be clear. For important signal lines, the length of the wiring and the processing of the ground loop are very strict, and for low-speed and unimportant signal lines, it can be placed at a slightly lower wiring priority. The important parts include: power supply segmentation; memory clock lines, control line and data line length requirements; high-speed differential line wiring and so on.

In the A project, the memory chip is used to realize 1G DDR memory. The wiring for this part is very important. It is necessary to consider the topological distribution of the control line and the address line, and the length difference control of the data line and the clock line. In the process, according to the data sheet of the chip and the actual working frequency, specific wiring rules can be obtained. For example, the length of the data lines in the same group cannot differ by more than mil, and the length between each path cannot differ by more than Mil and so on.

When these requirements are determined, the PCB designers can be clearly required to implement. If all the important wiring requirements in the design are clear, they can be converted into overall wiring constraints, and the PCB design can be realized by using the automatic routing tool software in CAD. It is also a trend in high-speed PCB design.