Different types of single board, its routing strategy is naturally not the same, this paper mainly introduces two types of PCB routing strategy.
Type I PCB routing strategy
1) The main characteristics of type 1 are as follows: strict length rule, strict crosstalk rule, topology rule, differential rule, power ground rule, etc.
2) Key network processing: Bus
Some constraints of topology, stub and its length (time domain) are required;
The diagram of balanced daisy chain and intermediate drive daisy chain
Virtual pins are set to control the topology;
Virtual T-point diagram
Limit stub. The maximum stub length should be set and the delay / length should be within a given range; outgoing from the long side of the pad is prohibited; junction is allowed at the terminal.
3) Key network processing: clock line
Define class and set enough line spacing or spacing between classes;
The clock line is set in a specific layer and area.
4) Key network processing: difference line
Generally, the wiring layer should be specified;
Parallel mode is adopted instead of standard mode;
The length matching of two difference lines and the length matching of difference pairs are defined;
The usual way to set the spacing between differential line pairs is to define the differential pair as class, and then define the class to class spacing.
5) Crosstalk control
There should be enough clearance between network groups; for example, there should be space constraints between data lines, address lines and control lines. Set these networks as corresponding classes, and then set crosstalk control rules between data lines and address lines, between data lines and control lines, and between address lines and control lines.
Shielding mode: parallel, coaxial and tandem;
After the rules are set, manual or automatic routing can be used.
Type 2 PCB routing strategy
1) Type 2 PCB design has the challenge of both physical implementation and electrical rule implementation.
2) In the process of routing, we need to “guide”, such as fanout, layer segmentation, automatic routing process control, forbidden area definition, routing order and so on.
3) Test and analyze the feasibility of wiring;
4) Firstly, the realization of physical rules is considered, followed by the realization of electrical rules;
5) For the conflicts or errors, it is necessary to comprehensively analyze the causes and adjust the routing strategy.
For PCB engineers, PCB routing strategy is a necessary knowledge, we should be proficient.