I'm currently designing a power supply with high isolation between primary and secondary sides and have to comply to standard distances on clearance and creepage.

My question is regarding creepage, I understand how it works on the same surface, and that the distance can be increased by adding slots or barriers. But I have been looking (without success) for information about what happens between layers, as in, if I have components on the top and on the bottom that need a certain creepage distance.

Do I need to consider the distance towards the board outline, up/down to the other layer and to the component, like path 2? Or only path 1 should be considered? Same thing with internal layers.


Hope I explained correctly but if not feel free to ask questions. I'd appreciate any references on the issue or experiences regarding this.

  • 1
    \$\begingroup\$ creepage is along the dirty surface of the board. Path 2 is through the dielectric strength of the board thickness. The board manufacturer will give you the exact figure for the material used, but it's many, many times more voltage per distance than the creepage allowance. \$\endgroup\$
    – Neil_UK
    Jul 5, 2022 at 18:34
  • \$\begingroup\$ The applicable norm should tell you something about distance through solid insulation. \$\endgroup\$ Jul 5, 2022 at 18:59
  • \$\begingroup\$ Absolutely, I actually made a mistake on the diagram (and the wording), as I didn't intend on asking creepage through the prepreg itself, as we had already accounted for that with its dielectric strength, as you say. But rather border of the board serving as a potential path for creepage between two tracks in different layers \$\endgroup\$
    – anzorein
    Jul 6, 2022 at 19:10

1 Answer 1


Do I need to consider the distance towards the board outline, up/down to the other layer and to the component

Yes you do but, path 2 in your diagram doesn't represent this; it appears to show the distance plotted passing through the PCB from one side to the other side directly and that doesn't count for creepage because the PCB base material can be regarded as an insulator.

For internal layers there can be no external "pollution" settling on the PCB so that creepage distance is not valid unless you are considering that your PCB might delaminate and allow "pollution" to gain access.

enter image description here

Image from here.

  • \$\begingroup\$ I see what you mean, so supposing that path 2 goes along the PCB border and not through the PCB itself, then it would be a path to consider for creepage if I understood correctly, thank you \$\endgroup\$
    – anzorein
    Jul 5, 2022 at 17:04

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