PCB clearance is the shortest distance through air between two uninsulated conductive parts at different electrical potentials. It is a critical design parameter to prevent electrical breakdown, arcing, or short circuits. While "clearance" itself is a distance, not a voltage, the concept of minimum clearance applies even to the lowest voltage differences found on a PCB. Specifically, minimum clearance specifications are required for voltage differences starting from 0V, with the lowest defined range being 0-15V.
Understanding PCB Clearance
Clearance is crucial for ensuring the reliability and safety of electronic circuits. Its primary purpose is to:
- Prevent short circuits: Ensure conductors at different potentials do not inadvertently touch or arc across the air gap.
- Avoid electrical breakdown: Maintain sufficient insulation distance to prevent the air from ionizing and conducting electricity under high voltage fields.
- Meet safety standards: Comply with international and industry-specific regulations designed to protect users and equipment.
The required clearance distance is directly dependent on the voltage difference between conductors. Higher voltages necessitate larger clearance distances to maintain safety and functionality.
Minimum Clearance Specifications by Voltage
The minimum clearance distances vary based on the voltage between conductors and the state of the PCB (bare board or assembled). The following table outlines typical minimum spacing requirements for different voltage ranges:
| Voltage Between Conductors (DC or AC Peaks) | Minimum Spacing (Bare Board) | Minimum Spacing (Assembly) |
|---|---|---|
| 0-15V | 0.05 mm [0.00197 in] | 0.13 mm [0.00512 in] |
| 16-30V | 0.05 mm [0.00197 in] | 0.13 mm [0.00512 in] |
| 31-50V | 0.1 mm [0.0039 in] | 0.13 mm [0.00512 in] |
As shown, even for the lowest voltage range of 0-15V, specific clearance distances are mandated. This indicates that clearance is a fundamental consideration for any operational voltage in a PCB design.
Practical Implications for PCB Design
PCB designers must meticulously adhere to clearance rules to ensure the reliability and safety of their products. Practical considerations include:
- Design Tools: Modern PCB design software includes rules engines that allow designers to set clearance constraints based on voltage levels.
- Manufacturing Tolerances: Designers must account for manufacturing variations that could reduce actual clearances, often by adding a safety margin above the minimum requirements.
- Environmental Factors: Factors such as humidity, contamination, and altitude can affect the dielectric strength of air, potentially requiring larger clearances in certain operating environments.
- Component Placement: Careful placement of components and routing of traces is essential to maintain adequate clearance, especially around high-voltage areas. For example, keeping power traces separated from sensitive signal traces.
Understanding and implementing proper clearance is paramount for designing robust and safe printed circuit boards, starting from the very lowest voltage levels.
