PCB layers as isolation

Question

What voltage can I expect primitive PCB (2 copper layers, one on each side), to hold between one and another layer?

I assume removing copper at edges should make the edge path longer, so I am mostly interested in through-PCB breakdown.

I’m interested in 3-30 kV.

If this is not a good option, what options do I have to make a pcb-trace-transformer, that can hold a large voltage? In all configurations I can imagine traces are too close to be safe.

Update: im interested in a long term load, high frequency, not one peak. Dielectric strength of FR4 is 20MV/m, I can assume 20kV/mm. But dielectric breakdown says >50kV. 3MHz will be ok

When you look up the dielectric strength of FR4, what do you find? — Spehro Pefhany, Feb 26 '22 at 22:41
@SpehroPefhany 20MV/m, i assume about 20kV for 1mm board. But dielectric breakdown says >50kV. I assume it is non-linear — Surprised Seagull, Feb 26 '22 at 22:44
Just out of curiosity, what frequency, exactly? High frequency may mean different things to different people. HF is sometimes defined as 3 MHz - 30 MHz. But that might not be what you mean. — user57037, Feb 26 '22 at 23:33
Typical FR4 is 1.6 mm thick. That is the most standard size (but other sizes are still pretty common). Is it possible that the dielectric breakdown of 50 kV is based on 1.6 mm FR4? — user57037, Feb 27 '22 at 00:33

Tony Stewart EE75 · Answer 1 · 2022-02-27T00:18:00.853

FR4 is often used for Rogowski coils for sensors in grid transformers and perform well with high voltage ratings. Degraded ratings depend on fabrication quality, and measling (voids) degradation stress from mechanical, thermal and moisture.

A more common FR4 dielectric breakdown spec is 20kV/mm , but this can easily be degraded lower or under pristine conditions increased as well. However surface breakdown or creapage is far worse due to contamination. Air with a smooth gap has a typical breakdown of 3kV/mm.

With Dk= 4.2 capacitance depends on the copper area/gap ratio that will affect HF impedance.

PCB layers as isolation

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