Surface Clearance
Shortest distance between two conductive parts measured along the surface of an insulating material defines the safe separation required to prevent tracking. The creepage path must be long enough to account for the gradual degradation of the surface caused by dust and moisture. In high-voltage PCB design, this distance is always equal to or greater than the air clearance because current travels more easily across a solid surface than through clean air.
Failure to maintain this path results in carbon tracks that eventually cause short circuits.
Barrier Implementation
Designers often incorporate physical features such as slots or V-grooves to extend the distance between high-potential traces. Cutting a slot through the board forces the energy to follow the perimeter of the opening, effectively increasing the length without increasing the footprint of the components. This technique is common in power supply layouts where board space is at a premium but safety standards require high isolation.
Surface coatings like conformal mapping provide some protection but do not allow for a reduction in the required distance under most international safety standards. Precise routing of these barriers ensures that even if the surface becomes contaminated, the creepage path remains high enough to prevent failure.
Material Resistance
Comparative Tracking Index ratings determine how a specific substrate handles the formation of conductive paths. A material with a high index allows for a shorter creepage path because it resists the carbonization that leads to failure. Pollution degrees in the operating environment further dictate the minimum required distance for a given voltage.
Indoor equipment in clean rooms requires less separation than industrial machinery exposed to metallic dust or high humidity.
