Give you some tips on how to achieve efficient automatic PCB routing!

Although the current EDA tools are very powerful, but as the PCB size requirements are getting smaller and smaller, 1oz vs 2oz the device density is getting higher and higher, the difficulty of PCB design is not small. How to achieve high PCB pass rate and shorten design time? This paper introduces the design skills and key points of PCB planning, layout and routing.

1. determine the number of PCB layers

The board size and number of wiring layers need to be determined early in the development of instructional design. If we design technology that requires students to use high-density ball grid array (BGA) components, we must fully consider the minimum number of wiring layers required to route through these electronics. how to test a circuit board with a multimeter The number of wiring layers and the stack-up mode will directly affect the wiring and impedance of the printed line. The size of the board helps to analyze and determine the stacking mode and the width of the printed line to achieve the desired design learning effect of the society.

For years, it was thought that reducing the number of layers on a board would reduce costs, but there are many other factors that affect manufacturing costs. In recent years, the cost difference between multilayer panels has narrowed considerably. It is best to start with more circuit layers and evenly distribute the copper deposit layers to avoid adding new layers at the end of the design when a small amount of signal does not meet the specified rules and space requirements. Careful planning before design will reduce many problems in wiring.

2. Design rules and restrictions

The automatic wiring tool itself does not know what to do. In order to complete the wiring task, the wiring tool needs to work within the correct rules and restrictions. Different signal lines have different wiring requirements, and 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. The rules involve the width of the printed line, the maximum number of holes, parallelism, the interaction between the signal lines, and the limit of the number of layers, which have a great impact on the performance of the wiring tool. Careful consideration of design requirements is an important step in successful wiring.

3. Layout of components

To optimize the assembly process, design for Manufacturability (dFM) rules impose restrictions on component layout. If the assembly department allows components to move, the circuit can be optimized for more automatic routing. Defined rules and constraints affect layout design.

Wiring channels and through-hole areas should be considered in the layout. These paths and areas are obvious to the designer, but automatic routing tools only consider one signal at a time. By setting the wiring constraints and setting the signal line layer, the wiring tool can complete the wiring according to the designer's imagination.

4. Fan out the design

In the fan-out design development phase, to enable the student auto routing tool to network the component pins, each pin of the surface mount device should serve as at least one through-hole so that the board can effectively perform inner connections, online analytical testing (ICT) and circuit reprocessing when the enterprise needs to learn more connections.

In order to maximize the efficiency of the automatic routing tool, be sure to use the largest possible through-hole size and printed line, with an interval setting of 50 ml is ideal. Channel type that maximizes the number of routing paths to be used. Online testing of the circuit should be considered when designing the fan outlet. Test units can be expensive and are often ordered shortly before full production, and it's too late to think about adding nodes to achieve 100% testability.

After careful consideration and prediction, the designer of the circuit can be tested online system can be carried out in the early stage of the development of the teaching design, in the production management process and later technical implementation, according to the wiring path and circuit through online analysis and testing to determine the through-hole fanout type, power supply and grounding will also affect the wiring and fanout design. In order to reduce the inductive reactance generated by the filter capacitor connection line, the pass hole should be as close as possible to the pin of the surface mount device, and manual wiring can be used if necessary, which may have an important impact on the wiring path problem originally envisioned by students, and may even directly cause you to reconsider how to use which pass hole. Therefore, they must fully consider the relationship between the hole and the pin reactance and set the priority of the hole specification.

5. Manual wiring and key signal processing

Although this article mainly discusses the problem of automatic wiring, manual wiring is an important process in the design of printed circuit boards now and in the future. Manual wiring helps the automatic wiring tool complete the wiring work. As shown in Figures 2a and 2b, the selected network (net) can be wired and fixed manually so that a path can be formed for automatic routing.

Regardless of the number of key signals, first of all, these data signals can be integrated wiring, manual wiring or combined with automatic wiring tools. Usually we must be able to design the circuit structure carefully by ourselves in order to truly achieve the desired performance. After the wiring is completed, the relevant project management personnel will analyze and check these signal wiring, and this development process is relatively easy to study. After the inspection is passed, these lines are fixed and the rest of the signal is automatically routed.

6. automatic wiring

When routing critical signals, some electrical parameters need to be controlled, such as reducing distributed inductance and electromagnetic compatibility, as well as other signals. All EDA vendors provide ways to control these parameters. Understanding the input parameters of the automatic routing tool and their effects on routing can ensure the quality of automatic routing to a certain extent.

Common rules should be used to automatically route signals. By setting restricted and unrouted areas to limit the layers used and the number of through-holes used for a given signal, the wiring tool can automatically route according to the engineer's design ideas. If there is no limit to the number of layers and through-holes used by the auto routing tool, each layer will be used in auto routing, and many through-holes will be generated.

After the constraints have been set and the rules created have been applied, auto-routing will produce similar results as expected, although it may take some finishing work, but you will also need to secure space for other signals and network wiring. After the part of the design is completed, it is fixed to prevent the impact of the subsequent wiring process.

Use the same steps to route the remaining signals. The amount 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 on other network cabling are reduced. But with it, a lot of signal wiring requires human intervention. Today's automatic wiring tools are very powerful and can usually complete 100% of the wiring. However, when the automatic routing tool does not complete all signal routing, the remaining signals need to be routed manually.

PCB planning design technology

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