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I think this is not a duplicate of this question. My design has the following constraints:

  • type and position of connectors
  • pinout assignments
  • 260 VDC / 2A for high-voltage tracks
  • 12V / 200 mA for low-voltage tracks

Here a part of my layout. It's repeated identically for every sector of the circular PCB:

PCB

Let's call the square pad of the connector pin 1:

  • Pin 1 and 2: high-voltage tracks (260 VDC / 2A)
  • Pin 3 and 4: low-voltage tracks (12V / 200 mA)
  • pin 5 and 6: low-voltage (signals) tracks (5V / 1 mA)

The connector pitch is 3,5 mm in X and 3 mm in Y. They are Molex 172316-1206 and can withstand 400V / 11A. For pins 3..6 I have no problems.

My concerns are about pins 1..2, in particular how to properly route the tracks between pin 2 and the middle pad above. I'm afraid about the isolation between bottom track (blue) and the nearby pads.

The track is 32 mil width (to maximise isolation) and the distance to the left and right pads (one is the capacitor, the other pin 1 of the connector) is 2.2 mm from center-to-center. The real creepage between the track and the outer ring of the pad is about 1 mm.

I checked here the needed spacing for 300 VDC isolation:

IPC-2221B:   
    external   1.25 mm
    internal   0.2 mm
    coated     0.4 mm

I'm not sure (even reading the description in the page) what does "coated" actually mean.

I'm working on a standard PCB with 2-layers and solder mask on both sides. I have to consider my tracks as "external" or "coated"?

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  • \$\begingroup\$ Depends. Do you do conformal coating over the pins? \$\endgroup\$ – winny Feb 25 '18 at 14:56
  • \$\begingroup\$ As said, it's a common PCB with solder mask but without any other treatment on pins. \$\endgroup\$ – Mark Feb 25 '18 at 15:42
  • \$\begingroup\$ Then you need to measure the creepage from pin to pin on top of your solar mask. What CTI does your soldermask have? \$\endgroup\$ – winny Feb 25 '18 at 16:00
  • \$\begingroup\$ @winny why pin-to-pin? Aren't we talking about track-to-pin isolation? \$\endgroup\$ – Mark Feb 25 '18 at 16:02
  • \$\begingroup\$ About soldermask CTI: I cannot find this information on the website of my supplier (Eurocircuits). I'm going to ask them tomorrow if it's an important value to know. \$\endgroup\$ – Mark Feb 25 '18 at 16:04
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If you can't modify the PCB layout to provide the necessary clearance, you could coat the PCB after assembly with something like Corona Dope which has a high dielectric strength.

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  • \$\begingroup\$ Most board manufactures use Polyurethane spray on both sides of the board. This covers most creapage issues. In cases where high-voltage (>400VAC) isolation is needed only slot cuts work. \$\endgroup\$ – Sparky256 Jun 8 '18 at 22:50

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