Why is the board size and number of wiring layers to be determined at the beginning of the design?

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[Introduction]

Board size and number of wiring layers need to be determined early in the design process. If the design requires the use of high-density ball grid array (BGA) components, the minimum number of routing layers required for wiring these devices must be considered. The number of wiring layers and the stack-up method directly affect the wiring and impedance of the printed wiring.

In the PCB layout design, there is a complete method for improving the routing rate. Here, we provide effective techniques for improving PCB layout and design efficiency, which not only saves the project development cycle for customers, but also maximizes The limit guarantees the quality of the finished product.

Board size and number of wiring layers need to be determined early in the design process. If the design requires the use of high-density ball grid array (BGA) components, the minimum number of routing layers required for wiring these devices must be considered. The number of wiring layers and the stack-up method directly affect the wiring and impedance of the printed wiring. The size of the board helps determine the stacking and line width to achieve the desired design.

To optimize the assembly process, the Manufacturability Design (DFM) rules place restrictions on the component layout. If the assembly department allows the components to move, the circuit can be properly optimized for easier automatic routing. The defined rules and constraints affect the layout design.

In the fan-out design phase, for the auto-wiring tool to connect the component pins, each pin of the surface mount device should have at least one via so that the board can perform the inner layer when more connections are needed. Connectivity, online testing (ICT) and circuit reprocessing.

In order to maximize the efficiency of the automatic routing tool, it is important to use the largest via size and trace as much as possible, with an interval of 50 mils. Use a via type that maximizes the number of routing paths. When performing fan-out design, consider the online test of the circuit. Test fixtures can be expensive and are usually ordered when they are ready for full production. It is too late to consider adding nodes to achieve 100% testability.

Wiring of critical signals requires consideration of controlling some electrical parameters during routing, such as reducing distributed inductance and EMC, and wiring for other signals. All EDA vendors offer 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 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 constraints and disabling the routing area to define the layers used for a given signal and the number of vias used, the routing tool can be automatically routed according to the engineer's design philosophy. If there are no restrictions on the number of layers and the number of vias used in the automatic routing tool, each layer will be used for automatic routing and many vias will be created.

After setting the constraints and the rules created by the application, the automatic routing will achieve similar results as expected. Of course, some finishing work may be required, and other signals and network wiring space need to be ensured. After a part of the design is completed, fix it to prevent it from being affected by the rear wiring process.

7.1 slightly change the settings, try a variety of path wiring;

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

7.3 Let the routing tools handle the default networks as needed;