Some chips with high input voltages have a very tiny package.

For instance, power gauge INA226 has a maximum convert voltage of 36V, but it's in MSOP8 package, the distance between two pins in its recommended layout is only 0.22mm, can such a short distance be safe for 36V?

In another way, how much voltage can a clearance of 0.2mm deal with?



Arcing voltage thru air varies a lot since air varies a lot. However, about 1 kV/mm is a rough guide. Of course you want to be well below the arcing voltage on a circuit board. At half that, 220 µm would mean 110 V, so 36 V sounds safe enough.

Usually the PCB pads extend a little past the device pins, so the clearance between pads is the limiting factor.


A comment by W5VO reminded me of something I should have mentioned.

What I said above is a very rough guide that you want to derate heavily. That may be good enough for personal projects. However, for real commercial products, there are likely regulatory requirements that apply. Some of these apply by law, while others are standards you have to meet in order to get third part approvals. Most of the time there is little practical distinction. They are simply rules you have to follow.

There are different requirements depending on what the device is intended for, where it will be used, and what third party certification the buyer or a reseller insists on. For example, patient-touching medical devices in use in the United States must meet certain creapage and clearance distances by law. These tend to be much more conservative that other rules. Intrinsic Safety (standard for electrical equipment in hazardous locations) also uses much more conservative rules than for something like office equipment.

W5VO mentioned IPC rules, but there are also rules from the IEC, local electrical codes, private certifying agencies like UL and FM, etc. Sometimes the hardest part of the design is figuring out what standards actually apply.

  • \$\begingroup\$ Would you say that part designs like this are poor practice? Seems to me that you'd want to keep creepage distances significantly (e.g. 10x) higher than the rated limits. \$\endgroup\$ – Polynomial Nov 27 '16 at 18:07
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    \$\begingroup\$ Also, off topic, but your website link in your profile is reported as a potential attack page by Google SafeSite. Might want to look into that. \$\endgroup\$ – Polynomial Nov 27 '16 at 18:10
  • \$\begingroup\$ If you look at IPC requirements, at 30 V the minimum recommended separation is 0.1mm. The next bump up is 0.6mm, but you can keep it below 0.2mm if you add an insulating coating \$\endgroup\$ – W5VO Nov 27 '16 at 18:48
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    \$\begingroup\$ @Poly: Yes, Google's virus scanners get a false positive on some of our executables. There seems to be no way to explain that to Google, though. "We don't care, we don't have to. We're Google." \$\endgroup\$ – Olin Lathrop Nov 27 '16 at 20:09
  • \$\begingroup\$ There is a distinction between insulation that is part of a safety barrier and insulation that is merely functional. AIUI standards are typically very strict on the former but much less strict on the latter. \$\endgroup\$ – Peter Green Nov 27 '16 at 20:37

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