Definition

Creepage is the shortest path between two conductive parts measured along the surface of the insulating material, as opposed to clearance which is the straight-line distance through air. If two pads are separated by a slot, the clearance might be 2 mm across the gap, but the creepage follows down one side and up the other - potentially much longer. This distinction matters because contamination, humidity, and dust can create leakage paths along surfaces that wouldn't arc through air. Dirty or damp insulator surfaces become slightly conductive, allowing tracking currents. IPC-2221 and safety standards (IEC 60950/62368) specify minimum creepage distances based on working voltage, pollution degree (environmental contamination level), and material group (tracking resistance of the laminate). Conformal coating can effectively increase creepage by providing a clean, hydrophobic barrier over the PCB surface.