Electronic Design - How to design PCB manual layout and routing?

In PCB design, the manual layout of flying leads and the detailed use of wiring are mainly determined by whether the printed circuit board wiring can be successfully completed. The higher the wiring density, the more important the layout.

Almost every PCB designer has encountered this situation. There are only a few connections left, but they have to delete a large number or all of them anyway, and then re-adjust the layout! A reasonable layout is a prerequisite to ensure smooth wiring.

Whether the layout is reasonable and there is no absolute criterion, you can use some relatively simple criteria to judge the advantages and disadvantages of the layout.

The most common criterion is to keep the total length of the flight line as short as possible. Generally speaking, the shorter the total length of the flying line, the shorter the total length of the wiring (note: this is only correct for most cases, not absolutely correct); the shorter the line, the line occupied by the printed circuit board The smaller the area, the higher the Bouton rate.

Although the wiring is as short as possible, the problem of wiring density must also be considered. How to lay out the shortest total length of the flight line and ensure that the layout density is not too high to be realized is a very complicated problem. Because, to adjust the layout is to adjust the location of the package, the package pad is usually associated with several or even dozens of networks at the same time, and reducing the length of a network route may increase the length of the route. Another network.

How to adjust the position of the packaging to the best point really cannot give a too practical standard. In actual operation, the designer mainly depends on the experience of the designer to check whether the screen display of the flying line is simple, orderly and what is the shortest total length of the calculation. Flying line is the main reference standard for manual layout and routing. Manually adjust the layout to make the shortest path as much as possible. Manual PCB routing is often to connect the pads according to the path indicated by the flying line.

The flight line mode page in the connection parameter setting can set the route connection strategy, and the shortest tree strategy should be selected.

The dynamic flight line is mentioned in the flight line display and control section: execute display network flight line, display encapsulated flight line, and display all flight line commands after the flight line display switch is turned on, and execute all implied flight line flight line display switches to turn off After the order. When the flight line display switch is turned on, not only the designated network route will automatically appear on the screen, but also whenever you manually adjust the layout to move the package position, the flight line connected to the package will also be automatically displayed. In addition, when the connection package is automatically displayed, all remaining flying leads will be automatically closed except for the flying lead display connected to the package.

Execute the "Edit/Move/Move Package" command, if the current route display switch is turned on, all the remaining flying lines will be automatically closed except for automatically displaying the flying lines connected to the package. When the flight route strategy is "shortest tree", the start and end points of the flight line change. We know that the shortest tree flying line does not display the flying line according to the connection order of the pins in the network table, but determines the connection order of the package pins in the network according to the shortest tree after the actual position.

When the package position changes, the PCB package pins and the connection sequence calculated according to the shortest tree theory will change. In other words, the start and end points of the flying line will change, so when the package moves under the "shortest tree" strategy, the flying line connected to the package pin changes with the package position, which is called a dynamic flying line. The dynamic flight line uses the closest point to find the connection network and ensure the shortest length of the entire network, so that the dynamic flight line and the total length of the flight line of the shortest tree provide a relatively optimal judgment standard for the PCB layout.