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Introduction to Creepage and Clearance rules in Electrical Constraints

PCBTech

With the Enterprise PCB Designer and Allegro X Venture licenses, two new high-voltage Constraint Sets, Creepage and Clearance, have been introduced. These rules can be set in the Electrical Constraint Set worksheet.

Creepage DRCs shown below demonstrate the new path renderings for this new DRC class. Creepage DRCs graphically show the shortest path across the surface of the PCB between the exposed metal surfaces. A new powerful feature considers any non-plated slots and cutouts and calculates the total creepage distance accordingly.

Creepage DRCs will also consider pads on the opposite side of the board, regardless of PCB cutouts and board outline. Creepage will consider the board thickness in the DRC path calculation.

Clearance DRCs calculate the minimum path through the air, giving a straight-line path between the metal surfaces.

This rule can be applied at net level, netclass level, NetGroup level, or bus level. The additional functionality of intra-group DRC checks can also be set.

applications you think will make the best use of this feature? Leave your comments below.

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  • in reply to Byron365

    Hi Byron365, the truthful answer is that there is no default clearance set into the tool. There are several differing standards which can be applied depending on the industry you are in. Designers need the versatility to change their clearance requirements from design to design and this can be accomplished by the tool. You can decide to apply IPC clearance values for example according to the spark gap between conductors for the maximum height and voltages for which your electronic will operate. This is typically specified in a lookup table within the standard you are adhering to, and these or any values can be entered into the Constraint Editor accordingly.

    Please let me know if we have understood your question and if there is anything further that needs to be clarified. 

  • in reply to John T

    Thanks John T. You are correct that the question is regulatory based on various safety standards. I was simply trying to understand if elevation was factored in or not in any way, but understandable that will vary depending on what standard you ware trying to meet. The spacing requirement to be set in the electrical constraint will still be driven by the appropriate safety standard and the only thing the CAD tool is helping with is measuring what the actual creepage and clearance spacing is along the appropriate path.

    Thanks.

  • in reply to Byron365

    No problem - and good luck with your projects!

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