General Principles of Component Routing

PCB component routing is a crucial phase in circuit design, significantly influencing the performance, stability, and cost of production. A well-planned layout not only reduces trace length and signal delay but also minimizes electromagnetic interference (EMI), enhancing the board's immunity to noise. Moreover, it helps in optimizing heat distribution, preventing overheating issues that could affect the reliability of the circuit. When routing components, it’s essential to consider both electrical performance and mechanical constraints, as well as the manufacturing process.

1. The spacing between different network traces depends on several factors, including electrical insulation, manufacturing capabilities, and component size. It’s important to ensure that the spacing settings align with the manufacturer's specifications. Electrical insulation becomes especially critical when high-voltage and low-voltage circuits coexist on the same board. In such cases, sufficient clearance must be maintained to prevent short circuits and ensure safety.
2. When designing the routing for turns, the corner style should be chosen to improve manufacturability and aesthetics. Common options include 45-degree angles, 90-degree angles, and arcs, with sharp corners generally avoided. The connection between a trace and a pad should be smooth to avoid sharp edges that may cause manufacturing issues. Additionally, if a trace passes between two pads without connecting to them, it should maintain an equal and maximum distance from both. Similarly, the spacing between adjacent traces should be even and as wide as possible.
3. The width of the traces is determined by current levels and the need for interference resistance. Higher current paths require wider traces to reduce resistance and heat generation. Power lines are typically wider than signal lines, and ground lines should also be thick to stabilize the ground potential and minimize voltage fluctuations caused by current variations. Within the allowable space and density, using the widest possible traces can help reduce impedance and improve overall performance. For power and ground lines, increasing their width is recommended when space allows, usually with a minimum width of 50 mils.
4. Interference and electromagnetic shielding are key concerns in PCB design. Traces can introduce various types of interference, such as crosstalk between signals, noise from power lines, and other electromagnetic disturbances. Proper placement and grounding techniques can significantly reduce these issues, improving the board’s electromagnetic compatibility (EMC). For high-frequency or critical signals like clock lines, wider traces are preferred. Shielding can also be applied by surrounding the signal line with a ground plane, acting as a protective layer that isolates the signal from surrounding components.
5. For high-frequency or critical signal lines, such as clock signals, it's best to make the trace as wide as possible. To further reduce interference, these signals can be enclosed by a ground plane, which acts as a shield. This method helps isolate the signal from other nearby traces and improves signal integrity, especially in high-speed designs.
6. Each via on a PCB introduces approximately 10pF of parasitic capacitance, which can be problematic in high-speed circuits. Excessive vias can also weaken the mechanical strength of the board. Therefore, it's advisable to minimize the number of vias used during routing. When using through-hole vias, it's common to replace them with pads, as they are more reliably drilled during manufacturing. This ensures better connectivity and reduces the risk of manufacturing errors.

These are general guidelines for PCB routing, but in practice, the process is highly flexible and often requires adjustments based on specific project requirements. While the principles outlined here serve as a solid foundation, real-world experience and testing remain the ultimate measures of success in PCB design.