Creepage and clearance are the physical spacing required between conductive features to ensure electrical insulation and prevent dielectric breakdown in high-voltage PCB designs.
- Creepage: The shortest distance measured along the surface of the insulating material between two conductive elements. It is influenced by operating voltage, pollution degree, and the material’s comparative tracking index (CTI).
- Clearance: The shortest distance measured through air between two conductive elements. It is primarily determined by the working voltage, transient overvoltage category, altitude, and applicable safety standards.
DFM guidelines for PCB designers
- Set up specific electrical clearance rules in your EDA tool based on the applicable standards (e.g., IPC-2221 or IEC 62368-1/IEC 60664-1) before routing begins.
- Use vertical plastic or insulating air-gap barriers between tight components if surface distance is too short to increase creepage.
- Utilize slots and V-notches to increase creepage. If tight component spacing makes it difficult to achieve required creepage distances on the surface, route a physical slot or milling cutout or V-notches between the traces.
- Keep high-voltage traces and components at least 10 mil away from board edges to prevent arcing during mechanical routing and panel separation.
- When applying ground or power pour near high-voltage traces, ensure your polygon cutout (solder mask/copper clearance) exceeds your minimum clearance rule to prevent accidental shorts during etching.
- Apply conformal coating for space-constrained designs and specify them in your fab notes. This can lower pollution degree requirements, allowing for reduced clearance gaps provided the coating process is tightly controlled.
- Select PCB materials with an appropriate CTI rating and dielectric thickness to meet creepage requirements.
- Clearly specify creepage and clearance requirements in the fabrication documentation and verify compliance through DRC before releasing the design.