Can I place 220V Live traces on top and bottom of PCB?
Typical FR-4 PCB will have a Dielectric Strength (or Dielectric Breakdown voltage) in the order of 10s of kilovolts per millimeter. Ask your PCB manufacturer to provide the datasheet of the material they use, so you can check the value yourself.

Therefore, running Line traces on the top layer and Neutral traces on the bottom is fine.

However, you need to be careful when the Line voltage appears on the bottom layer, such as the areas circled in red. In such cases, you need to ensure that the proper clearance and creepage distances are maintained.

The safe distances will depend greatly on the environment your PCB will be used in, but the typical rule of thumb is to leave a 2mm gap between mains and any low-voltage trace. The strictest requirement for voltages with peaks up to 420V is 6mm.

You can refer to UL 60950-1 Section 2.10.3 for full details.




  Why would the manufacturer leave such a narrow space between pins?


There are several considerations:


TO-220 is probably cheaper than a larger package, such as TO-247.
The manufacturer thinks that TO-220 is sufficient for the power dissipation of the device.
Not every customer is going to use the device at high voltage.


By making these tradeoffs, they can cater for a larger market, than would otherwise be possible.

And for those customers who do use high voltage, there are several ways to go about using such a device:


Interleave the pads and form the legs of the device manually.
Use conformal coating or potting.




See this app note from infineon for some ideas: https://www.infineon.com/dgdl/Infineon-ApplicationNote_MOSFET_CoolMOS_Electrical_safety_and_Isolation-AN-v01_00-EN.pdf?fileId=db3a30433d1d0bbe013d20e0cbf017fe