Standardized wiring rules for rigid circuit boards are established to ensure the reliability, manufacturability, and performance of the PCBs in various electronic applications. These rules, often defined by international standards organizations such as IPC, cover aspects such as trace width and spacing, via design, component placement, and signal integrity considerations.

Trace width and spacing are fundamental aspects of wiring rules. The width of the copper traces is determined based on the current-carrying capacity required. For example, a trace carrying a high current (such as in power supply circuits) needs to be wider to prevent overheating. IPC-2221 provides guidelines for calculating the appropriate trace width based on current, ambient temperature, and allowable temperature rise. Typically, a trace width of 0.1mm can carry around 0.5A of current in a 1oz copper layer, but this increases with wider traces. The spacing between traces is determined by the voltage difference between them to prevent arcing and crosstalk. For high-voltage circuits, the spacing must be larger; for example, a voltage difference of 500V may require a spacing of at least 0.5mm. In high-frequency circuits, smaller spacing can lead to increased capacitive coupling, so larger spacing is often used to minimize crosstalk.

Via design is another important aspect. Vias are used to connect different layers of a rigid PCB, and their size and placement are governed by standardized rules. The diameter of the via (both the drill size and the pad size) must be compatible with the manufacturing capabilities. For example, a standard via may have a drill diameter of 0.3mm and a pad diameter of 0.6mm. The spacing between vias and between vias and traces must also be sufficient to avoid short circuits and ensure proper routing. Additionally, via-in-pad technology, where vias are placed within the pads of surface-mount components, is subject to specific rules to ensure solderability and prevent solder wicking into the via.

Component placement and orientation are also regulated by standardized rules. Components should be placed in a way that facilitates efficient routing, heat dissipation, and assembly. For example, high-power components that generate a lot of heat should be placed near heat sinks or in areas with good airflow. Passive components such as resistors and capacitors should be oriented to minimize the length of connecting traces, reducing signal delay and crosstalk. Polarized components (like diodes and capacitors) must be placed with the correct orientation to avoid circuit failures.

Signal integrity rules are crucial for high-speed circuits. These include maintaining consistent impedance along the signal traces, avoiding sharp corners (which can cause signal reflections), and using ground planes to provide a return path for the signals. Impedance control is achieved by adjusting the trace width, the thickness of the dielectric material, and the distance from the ground plane. For example, a microstrip line (a trace on the surface layer with a ground plane below) may have a characteristic impedance of 50Ω, which is standard for many high-frequency applications. Sharp corners in traces are replaced with 45-degree angles or rounded corners to minimize signal reflections and EMI.

Manufacturability rules are also part of the standardized wiring guidelines. These rules ensure that the PCB can be fabricated efficiently and with high yield. For example, the minimum trace width and spacing must be compatible with the manufacturing process (such as etching capabilities) of the PCB fabricator. The minimum drill size for vias must be within the range that the drilling equipment can handle. Additionally, the placement of components must allow for automated assembly processes, such as pick-and-place machines, with sufficient clearance between components for the machine's nozzles.