I have a small (24 x 15 mm) PCB for a custom connector. It is intended for low voltage (< 48 VDC) applications, but I am interested in measuring it in order to provide customers a reasonable maximum voltage rating (de-rated of course).
It is a 1.6 mm thick two-sided FR4 board with 1 oz copper and soldermask. The smallest gap between traces is 1 mm. Using this calculator from Sierra Circuits, the maximum voltage should be about 528 V. They define this calculation as:
...the minimum spacing between the two copper features that can handle that voltage difference without any dielectric breakdown.
Using an insulation tester that produces a 1000 V test voltage, the insulation resistance is measured as ≥2 GΩ (at 25°C); which is the tester's maximum.
Lots of questions are based on faulty assumptions, and I am sure this is no exception. I'd like to know:
What is a better or more proper technique to measure various maximum voltages of a given PCB? (For example, I'd like to know its insulation resistance and at what voltage it starts to arc. I know that temperature affects the result.)
Is it common/accepted to assign a conservative (e.g. 300 V) rating even though I don't actually know its limit?
I would like to measure its insulation resistance value. With a basic (Fluke 1587 FC) insulation tester at its maximum, I'd be OK accepting a value of ">2 GΩ," however, what would the next steps be if I wanted to obtain a more precise value?