Is there any estimation regarding the relation between PCB pad to pad distance and isolation strength?

If the board is covered with the mask and the minimum distance is 2,9 mm which isolation voltage I can expect?

enter image description here

The red region is the isolated nets.

The age effects (like surface dust) can be skipped in my case as the device will be packed and protected from such particles penetrations.


Actually I need 2 kV isolation. But I'd be much more happy to know the science behind the subject - not only estimation that my design will or will not keep this voltage. This is why I skipped to specify my actual requirements initially.


After I read the links I've been provided by you I could put the idea in the following form: as I need to withstand 2 kV test (as per my initial requirements) I will redesign the board (if necessary) and then after assembled put it to the test of 2 kV AC voltage applied and than test the insulation resistance which is should be more than 2MOhms @ 500VDC.

So the questions now are:

  1. Is the stated above correct? Is this any proper approach?
  2. How likely that this PCB as it designed right now on a picture above will pass the test (U2 optocoupler is rated to 3,75 kV RMS). As I stated earlier the minimum distance is 2,9 mm from primary to secondary.
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    \$\begingroup\$ What is supposed to be isolated from what here, and how much isolation is needed? \$\endgroup\$ – Matt Young Jan 19 '16 at 15:22
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    \$\begingroup\$ Got that from your edit, but that still doesn't answer how much isolation you need. \$\endgroup\$ – Matt Young Jan 19 '16 at 15:25
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    \$\begingroup\$ I think it was clearance, and clearance is clearance whether it be space between copper on a PCB or air gap. You really need to consult your standard on this. \$\endgroup\$ – Matt Young Jan 19 '16 at 15:34
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    \$\begingroup\$ No. Solder mask is just that, something to keep solder from going places you don't want it. You should NEVER rely on it from isulation. \$\endgroup\$ – Matt Young Jan 19 '16 at 15:42
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    \$\begingroup\$ IPC has standards for that sort of thing: smps.us/pcbtracespacing.html \$\endgroup\$ – DerStrom8 Jan 19 '16 at 18:09

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