High-voltage printed circuit boards (PCBs) require careful insulation design to maintain electrical reliability and protect connected components. One important part of this process is understanding the difference between surface tracking and air breakdown. Although both phenomena can affect insulation performance, they occur through different mechanisms and involve different parts of the PCB structure.
Surface tracking develops along the surface of an insulating material, while air breakdown occurs through the air separating conductive components. Understanding these differences helps engineers evaluate creepage and clearance distances, select appropriate PCB materials, and develop layouts that meet relevant electrical safety requirements.
1. Understanding Surface Tracking
Surface tracking is an electrical degradation process that develops along the surface of an insulating material. On a PCB, this can involve the laminate surface between conductive features such as copper tracks, pads, and component terminals.
Moisture, dust, chemical residues, and other contaminants can influence the electrical behavior of an insulating surface. Under electrical stress, these conditions may contribute to the formation of conductive paths.
Once a tracking path develops, the insulating surface may lose some of its ability to separate conductive regions reliably. This can eventually result in insulation failure.
Surface tracking is particularly relevant in equipment exposed to humidity, pollution, or changing environmental conditions. It is therefore important to consider the intended operating environment when selecting PCB materials and determining creepage requirements.
2. What Is Air Breakdown?
Air breakdown occurs when the electrical stress across an air gap becomes sufficient to cause the air to lose its insulating properties.
In a PCB assembly, this can happen between conductive parts separated by air, such as adjacent terminals, exposed copper areas, connectors, or component leads.
Unlike surface tracking, air breakdown does not require an insulating surface to become contaminated or degraded. The main concern is whether the air gap provides sufficient electrical separation under the expected operating conditions.
Factors such as voltage, electrode geometry, air pressure, and altitude can influence air insulation performance.
For this reason, clearance distances must be evaluated carefully, particularly in high-voltage equipment and assemblies operating at elevated altitudes.
3. Creepage and Clearance: Two Different Design Requirements
Creepage and clearance are essential concepts in PCB insulation coordination.
Creepage distance is the shortest distance along the surface of an insulating material between two conductive parts. It is closely associated with the prevention of surface tracking. Understanding PCB surface tracking versus dielectric breakdown helps engineers distinguish between different insulation failure mechanisms.
Clearance distance is the shortest distance through air between conductive parts. It is important for reducing the risk of air breakdown.
These distances must be evaluated independently. A PCB layout may provide sufficient creepage but insufficient clearance, or the opposite.
Designers should therefore avoid treating the two measurements as interchangeable. Both must satisfy the applicable electrical safety requirements.
4. Environmental Conditions and Their Influence
Environmental conditions can significantly affect PCB insulation performance.
Moisture can change the electrical behavior of an insulating surface, particularly when combined with dust or conductive contamination. Industrial environments may also expose PCBs to chemical residues and other pollutants.
These conditions are especially relevant to surface tracking because contamination can create more favorable conditions for conductive paths to develop.
Air breakdown is influenced by different environmental factors. Changes in air pressure and altitude can affect the insulation properties of the air gap.
Consequently, PCB designs should reflect the actual operating environmen t rather than relying only on nominal voltage values. Engineers can use the comparative tracking index of PCB materials to assess relevant insulation characteristics when specifying laminates.
5. Selecting PCB Materials for Tracking Resistance
Material selection plays an important role in controlling surface tracking risk.
The Comparative Tracking Index (CTI) is used to evaluate the resistance of insulating materials to electrical tracking under a specified test method. Higher CTI values generally indicate greater resistance to tracking.
PCB laminate classifications can influence creepage requirements under applicable insulation coordination standards.
However, CTI does not measure air breakdown strength and should not be treated as a complete indicator of PCB insulation performance.
Engineers should review manufacturer datasheets and consider the laminate's relevant electrical, thermal, and environmental properties before selecting a material.
6. PCB Layout Features That Support Insulation
PCB geometry can help manage both creepage and clearance requirements.
Designers should pay attention to the spacing between high-voltage and low-voltage circuits, connector terminals, component pads, and exposed conductive hardware.
Slots and insulating barriers may be used to extend surface paths where appropriate. However, their effectiveness must be verified according to the relevant standards and design conditions.
Protective coatings may also support insulation performance in qualified applications, but they should not automatically be assumed to replace required creepage or clearance distances.
A complete layout review should consider the shortest relevant electrical paths throughout the assembled product. For information about manufacturing and electronics production, visit https://wellerpcb.com/ and explore the available services.
7. Testing and Standards for Insulation Evaluation
Different testing methods are used to evaluate material properties and insulation performance.
IEC 60112 is relevant to determining the Comparative Tracking Index of insulating materials. It provides a standardized method for evaluating resistance to tracking under specified test conditions.
IEC 60664-1 provides important principles for insulation coordination in low-voltage systems, including considerations related to clearance, creepage, and environmental conditions.
Product-specific safety standards may introduce additional requirements, so engineers should identify the correct standard for the equipment being developed.
Material testing, design verification, and appropriate electrical testing should be considered together when evaluating high-voltage PCB insulation.
8. Practical Design Review Considerations
Before finalizing a high-voltage PCB, engineers should verify several important details:
- Confirm the working voltage and insulation category.
- Calculate creepage and clearance independently.
- Identify the expected pollution degree.
- Review the laminate's CTI classification.
- Consider altitude and environmental conditions.
- Check component placement and conductive hardware.
- Evaluate slots, barriers, and protective coatings where applicable.
- Confirm manufacturing tolerances and assembly requirements.
- Document the standards used for insulation calculations.
These checks help ensure that the PCB layout supports the intended insulation performance.
Conclusion
Surface tracking and air breakdown are two different insulation concerns in high-voltage PCB design. Surface tracking develops along insulating surfaces and is influenced by material properties and contamination, while air breakdown occurs through the air separating conductive parts.
By understanding the distinction between creepage and clearance, selecting suitable PCB materials, and considering environmental conditions, engineers can make more informed insulation design decisions. A standards-based approach helps support electrical safety, manufacturing consistency, and long-term PCB reliability.
