PCB Blog - PCB board design layout rate and design efficiency skills

In the PCB design, there is a complete set of methods for improving the deployment rate. Here, we provide you with effective techniques to improve the design deployment rate and design efficiency, which not only saves the project development cycle for customers, but also guarantees the design to the limit. The quality of the finished product.

1. The number of layers determined by the PCB board
The size and number of layers of the printed circuit board need to be determined at the initial stage of the design. If the design requires the use of high-density ball grid array (BGA)components, the fewer wiring layers required by 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 to 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. At the beginning of the design, use more circuit layers and evenly distribute the copper, 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 trouble in wiring.

2. PCB board 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 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. Layout of PCB board components
To streamline the assembly process, design for manufacturability (DFM) rules impose restrictions on 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. By setting the routing constraints and setting the layer where the signal line can be routed, the routing tool can be as the designer imagined Complete the wiring.

4. PCB board fan-out design
In the fan-out design stage, in order 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 make the automatic wiring tool efficient, it is necessary to use the via size and printed lines as much as possible, and the interval is ideally set to 50mil. Use the via type that makes the number of routing paths available. When carrying out fan-out design, it is necessary to consider the problem of circuit online testing. Test fixtures can be expensive and 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 testing can be carried out at the initial stage of the design and realized in the later production process. The type of via fan-out is determined according to the wiring path and circuit online testing. 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. Manual wiring can be used if necessary. This may affect the originally planned wiring path, and may even cause you to re-consider which type of 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 of PCB board and processing of key signals
Although this article focuses on automatic wiring, manual wiring is an important process in 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 automatic wiring of the remaining signals.

6. PCB board automatic wiring
The wiring of key signals needs to consider controlling some electrical parameters during the wiring, such as reducing distributed inductance and EMC, etc. The wiring of other signals is similar. All EDA vendors provide a way to control these parameters. After understanding the input parameters of the automatic wiring tool and the influence of the input parameters on the wiring, the quality of the automatic wiring can be guaranteed to a certain extent. General rules should be used to automatically route signals. By setting restrictions and prohibiting wiring areas to limit the layers used by a given signal and the number of vias used, the wiring tool can automatically route according to the engineer's design ideas. If the number of layers used by the automatic routing tool and the number of vias are not limited, each layer will be used during automatic routing, and many vias will be generated. After setting the constraints and applying the created rules, the automatic routing will achieve results similar to expectations. Of course, some sorting work may be required, and space for other signals and network wiring needs to be ensured. After a part of the design is completed, fix it to prevent it from being affected by the subsequent wiring process. Use the same steps to route the remaining signals. The number of wiring depends on the complexity of the circuit and the number of general rules you define. After each type of signal is completed, the constraints of the remaining network wiring will be reduced. But what comes with it is that a lot of signal wiring requires manual intervention. Today's automatic wiring tools are very powerful and can usually complete 100% of the wiring. However, when the automatic wiring tool has not completed all signal wiring, it is necessary to manually route the remaining signals.

7. The design points of PCB board automatic wiring include:

7.1 Slightly change the settings, try a variety of route wiring;

7.2 Keep the basic rules unchanged, try different wiring layers, different printed lines and spacing widths, different line widths, and different types of vias such as blind holes, buried holes, etc., and observe how these factors affect the design results;

7.3 Let the wiring tool process those default networks as needed;

7.4 The less important the signal is, the more freedom the automatic routing tool has to route to it.

8. Arrangement of PCB board wiring
If the EDA tool software you are using can list the wiring length of the signal, check the data, you may find that the length of some signal wiring with few constraints is very long. This problem is relatively easy to deal with, and the signal wiring length can be shortened and the number of vias can be reduced by manual editing. In the finishing process, you need to determine which wiring is reasonable and which wiring is unreasonable. Like manual routing design, PCB board automatic routing design can also be sorted and edited during the inspection process.