In PCB wiring design, there is a complete set of methods for improving the routing rate. Here, we provide you with effective techniques to improve the routing rate and design efficiency of PCB design, which can not only save the project development cycle for customers, but also maximize the guarantee the quality of the finished product.
1. The size of the PCB board and the number of wiring layers need to be determined at the beginning of the design
If the design calls for the use of high-density ball grid array (BGA) components, consideration must be given to the minimum number of routing layers required to route these devices. The number of wiring layers and the stack-up method will directly affect the wiring and impedance of the traces. The size of the board helps determine the stack-up and trace width to achieve the desired design effect.
For many years, people have always believed that the lower the number of PCB layers, the lower the cost, but there are many other factors that affect the manufacturing cost of PCB boards. In recent years, the cost differential between multilayer boards has been greatly reduced. It is best to start the design with more circuit layers and evenly distribute the copper to avoid being forced to add new layers when a small number of signals do not meet the defined rules and space requirements until near the end of the design. Careful planning before design will reduce a lot of hassle in wiring.
2. The autorouting tool itself does not know what to do
To accomplish routing tasks, routing tools need to work within the correct rules and constraints. Different signal lines have different wiring requirements. It is necessary to classify all signal lines with special requirements, and different design classifications are also different. Each signal class should have a priority, and the higher the priority, the stricter the rules. Rules related to trace width, maximum number of vias, parallelism, interaction between signal lines, and layer limitations have a large impact on the performance of routing tools. Careful consideration of design requirements is an important step in successful routing.
To optimize the assembly process, design for manufacturability (DFM) rules place constraints on component placement. If the assembly department allows the components to move, the circuit can be properly optimized for easier automatic routing. The rules and constraints you define affect the layout design.
3. Consider routing channels and via areas during layout
These paths and areas are obvious to the PCB designer, but the auto-routing tool only considers one signal at a time. By setting routing constraints and setting the layers on which signal lines can be routed, the routing tool can be made as the designer envisions. to complete the wiring.
In the fan-out design phase, to enable automated routing tools to connect component pins, each pin of a surface mount device should have at least one via so that the PCB can be internally routed when more connections are required. Connection, in-circuit testing (ICT) and circuit reprocessing.
In order to maximize the efficiency of the automatic routing tool, be sure to use the largest possible via size and trace, with an ideal spacing of 50mil. Use the type of via that maximizes the number of routing paths. When designing a fan-out, consider the problem of in-circuit testing. Test fixtures can be expensive and are often ordered near full production, when it is too late to consider adding nodes for 100% testability.
After careful consideration and prediction, the design of circuit in-circuit test can be carried out in the early stage of design and realized in the later stage of the production process. The type of via fan-out is determined according to the wiring path and circuit in-circuit test. Power and grounding will also affect the wiring and fan-out design. . In order to reduce the inductive reactance generated by the connection lines of the filter capacitors, the vias should be as close as possible to the pins of the surface mount device, and manual routing can be used if necessary, which may affect the originally envisaged routing path, and may even cause you to re- Considering which via to use, the relationship between via and lead inductance must be considered and the via specification prioritized.
4. Manual wiring is helpful for automatic wiring tools to complete wiring work
Although this article focuses on automatic routing issues, manual routing is and will be an important process in PCB design now and in the future. Using manual routing helps automatic routing tools to complete routing work. Regardless of the number of critical signals, route those signals first, either manually or with automated routing tools. Critical signals often require careful circuit design to achieve the desired performance. After the wiring is completed, the relevant engineering personnel will check the signal wiring, which is much easier. Once the inspection passes, the wires are secured and the auto-routing of the remaining signals begins.
The routing of key signals needs to consider controlling some electrical parameters during routing, such as reducing distributed inductance and EMC, etc. The routing of other signals is also similar. All EDA vendors provide a way to control these parameters. After understanding the input parameters of the automatic routing tool and the influence of the input parameters on the routing, the quality of the automatic routing can be guaranteed to a certain extent.
5. General rules should be used for automatic routing of signals
By setting constraints and no-routing areas to limit the layers used for a given signal and the number of vias used, the routing tool can automatically route according to the engineer's design thinking. If there is no limit to the layers used by the autorouting tool and the number of vias routed, each layer will be used during autorouting and many vias will be created.
Once the constraints are set and the rules created are applied, auto-routing will achieve similar results as expected, although some tidying may be required, as well as ensuring room for other signal and net routing. After a portion of the design is complete, it is secured to protect it from subsequent routing processes.
6. Use the same steps to route the remaining signals
The number of traces depends on the complexity of the circuit and how many general rules you have defined. After each type of signal is completed, the constraints on the routing of the remaining nets are reduced. But with that comes a lot of signal routing that requires manual intervention. Today's auto-routing tools are very powerful and often do 100% of the routing. However, when the automatic routing tool does not complete the routing of all signals, the remaining signals need to be manually routed.
If the EDA tool you are using can list the routing lengths of the signals, check this data and you may find that some signals with few constraints have very long routing lengths. This problem is relatively easy to deal with, and manual editing can shorten the signal routing length and reduce the number of vias. During the sorting process, you need to determine which wiring is reasonable and which is not. Like manually routed designs, autorouted designs can also be organized and edited during the review process.
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