2
\$\begingroup\$

Both 60950 (Table 2N – Minimum creepage distances) and 60335 (Table 18 – Minimum creepage distances for functional insulation) seem to specify a minimum creepage distance of 0.4mm (~16mil) with a IIIa / IIIb material group and pollution degree of 2 at <=10V.

This seems crazy big, and I know that many boards are in production with significantly smaller spacing between low voltage traces. With the pad spacing between common microcontroller pins, for example, this is impossible to achieve. Am I understanding this requirement correctly?

\$\endgroup\$
8
  • \$\begingroup\$ I only have access to IEC 61010, which doesn't specify any creepage requirement for voltages below 48 V. But it does have this note on the creepage table: "Coatings that meet the requirements of Annex H when applied to the outer surfaces of printed wiring boards reduce the POLLUTION DEGREE of the coated area to POLLUTION DEGREE 1." Perhaps oridinary soldermask can be used to meet this requirement in some situations, making the requirement s for pollution degree 2 moot? \$\endgroup\$ – The Photon Nov 21 '16 at 16:57
  • \$\begingroup\$ Also, not all traces need to be isolated from each other for safety purposes, so the creepage requirement doesn't apply to every pair of wires in your circuit. \$\endgroup\$ – The Photon Nov 21 '16 at 16:58
  • \$\begingroup\$ Hi Photon, I believe this typically refers to conformal coatings. The soldermask, for example, will not cover component pads, which for many smaller components will violate the above creepage requirements. \$\endgroup\$ – bt2 Nov 21 '16 at 17:01
  • \$\begingroup\$ Is there a way to determine what traces this doesn't apply to then? Since this is focused on electrical safety, I don't understand why the standards even specify creepage requirements for any voltage lower than SELV. \$\endgroup\$ – bt2 Nov 21 '16 at 17:03
  • \$\begingroup\$ I imagine (but I'm not an expert) that it doesn't apply to any trace that is otherwise isolated from the user. Like I said, I only have access to 61010, and that one in fact doesn't provide creepage requirements for anything below 48 V (actually the top line on the table is for voltages less than 150 V). \$\endgroup\$ – The Photon Nov 21 '16 at 17:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.