PCB Copper Layer Spacing & Voltage Rating
One standard used for spacing conductors based on voltage is the IPC-2221. This standard differentiates spacing requirements for inner and outer conductors. Does the IPC minimum separation between conductors on an inner copper layer apply to the minimum dielectric thickness between copper layers? In other words, when sizing the dielectric thickness between a supply and return plane does the IPC standard for minimum distance between conductors on an inner layer apply? If it does not apply, what differentiates the two scenarios (because the same dielectric material is between the conductors)? If it does apply, why is the IPC requirement so severe compared to the dielectric voltage ratings provided by the manufacturers?
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I am not familiar with that standard specifically. However, usually standards will have some multiple for effective separation distance inside a PCB versus across air. One standard I remember specifically states that PCB material is worth 6x the distance relative to air.
This method gets around judging how thick a layer there needs to be to qualify as "inside" the PCB. In the 6x example, if you've got 10 mils of PCB dielectric between two layers (for example), then that's worth the same as 60 mils of air separation. The rest of the standard then tells you what you're allowed to do with that air separation, and whether that's enough for various purposes.
Read your standard carefully. There is likely some wording in there like that.
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