I have seen on various mains powersupply PCBs that they have a lot of silkscreen lines near the high voltage areas. So my question is that does the silkscreen helps rise the voltage rating of that section or is it just to mark that area as the high voltage one.

I am designing this PCB and was wondering if I should put silkscreen or not.MCPCB LED design

In terms of voltage creepage rating is there a difference between Left and Right?


This is an image from smps.us and this table shows the creepage distance for 100Vdc for 1. External, 2. Internal, 3. Coated.

Does the coated here means only coated with soldermask? Or does adding silkscreen to the mix also helps somewhat?

  • \$\begingroup\$ Silk screen and solder mask are not classed as insulation in any standard I am aware of. Coated refers to a suitably approved conformal coating applied after all components have been soldered. \$\endgroup\$ Commented Jun 17, 2020 at 9:51
  • 1
    \$\begingroup\$ The right looks like a guide for a layout person to keep the trace in the middle, and not accidentally screw up creepage and clearance distance. \$\endgroup\$ Commented Jun 17, 2020 at 12:58
  • \$\begingroup\$ Is the element indicated to by the red arrow a capacitor? \$\endgroup\$ Commented Jun 17, 2020 at 13:21

2 Answers 2


"Coated" means conformal coating, which is a thin polymeric film to protect the board's components. Often used on high voltage PCB or for harsh enviroment.


Silkscreen is not considered in IPC or IEC standards, coated means a conformal coating. The reason is dust, dirt, moisture can significantly reduce the distance needed to produce an arc and coating ensures that these 'pollutants' can't come into contact with conductors and make the potential shorting pathway conductive.

As to why they are using silkscreen I don't know, I have not seen anything written in any of the IEC requirements that says silkscreen will change the creepage

In addition you may want to check the IEC standards if you are putting the design through and ETL.
How to define working voltage class net to calculte the creepage?


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