PCB Technical - How to improve wiring efficiency in PCB design process

How to improve wiring efficiency in PCB design process
There are many popular EDA tool software on the market, but these PCB design software are similar in terms of terms and function key positions. How to use these tools to better realize PCB design? Careful analysis of the design and careful settings of the tool software before starting the wiring will make the design more in line with the requirements. The following is the general design process and steps.
1, determine the number of layers of the PCB
The size of the circuit board and the number of wiring layers need to be determined at the beginning of the design. If the design requires the use of high-density ball grid array (BGA) components, the minimum number of wiring layers required for wiring these devices must be considered. The number of wiring layers and the stack-up method will directly affect the wiring and impedance of the printed lines. The size of the board helps determine the stacking method and the width of the printed line to achieve the desired design effect.
For many years, people have always believed that the lower the number of layers of the circuit board, the lower the cost, but there are many other factors that affect the manufacturing cost of the circuit board. In recent years, the cost difference between multilayer boards has been greatly reduced. It is best to use more circuit layers and evenly distribute the copper at the beginning of the design, so as to avoid discovering that a small number of signals do not meet the defined rules and space requirements until the end of the design, so that new layers are forced to be added. Careful planning before designing will reduce a lot of troubles in wiring.

2, design rules and restrictions
The automatic routing tool itself does not know what to do. In order to complete the wiring task, the wiring tool needs to work under the correct rules and restrictions. Different signal lines have different wiring requirements. All signal lines with special requirements must be classified, and different design classifications are different. Each signal class should have a priority, the higher the priority, the stricter the rules. The rules involve the width of the printed lines, the maximum number of vias, the degree of parallelism, the mutual influence between the signal lines, and the limitation of layers. These rules have a great influence on the performance of the wiring tool. Careful consideration of design requirements is an important step for successful wiring.
3, the layout of components
In order to optimize the assembly process, design for manufacturability (DFM) rules will restrict component layout. If the assembly department allows the components to move, the circuit can be appropriately optimized, which is more convenient for automatic wiring. The defined rules and constraints will affect the layout design.
The routing channel and via area need to be considered during layout. These paths and areas are obvious to the designer, but the automatic routing tool will only consider one signal at a time. By setting routing constraints and setting the layer of the signal line, the routing tool can be as the designer imagined Complete the wiring like that.
4. Fan-out design
In the fan-out design stage, to enable automatic routing tools to connect component pins, each pin of the surface mount device should have at least one via, so that when more connections are needed, the circuit board can be internally layered Connection, online testing (ICT) and circuit reprocessing.
In order to maximize the efficiency of the automatic routing tool, the largest via size and printed line must be used as much as possible, and the interval is ideally set to 50mil. Use the via type that maximizes the number of routing paths. When carrying out fan-out design, it is necessary to consider the problem of circuit online testing. Test fixtures can be expensive, and they are usually ordered when they are about to go into full production. If only then consider adding nodes to achieve 100% testability, it would be too late.
After careful consideration and prediction, the design of circuit online test can be carried out at the early stage of the 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 online test. The power supply and grounding will also affect the wiring and fan-out design. . In order to reduce the inductive reactance generated by the connection line of the filter capacitor, the vias should be as close as possible to the pins of the surface mount device, and manual wiring can be used if necessary. This may affect the originally envisaged wiring path, and may even cause you to re- Consider which via to use, so the relationship between via and pin inductance must be considered and the priority of via specifications must be set.
5. Manual wiring and processing of key signals
Although this article mainly discusses automatic wiring problems, manual wiring is an important process of printed circuit board design now and in the future. The use of manual wiring helps automatic wiring tools to complete the wiring work. Regardless of the number of key signals, these signals should be routed first, either manually or in combination with automatic routing tools. Critical signals usually have to pass careful circuit design to achieve the desired performance. After the wiring is completed, the relevant engineering personnel will check the signal wiring. This process is relatively easy. After passing the inspection, fix these lines, and then start to automatically route the remaining signals.