4 layer PCB: copper and dielectric order4 layer PCB: copper and dielectric orderL1 — copperPP bonding gapL2 — copperCured core dielectricL3 — copperPP bonding gapL4 — copperWHAT THE COUNT MEANS4 copper layers1 inner core2 prepreg bonding gapsConventional foil-build concept.Actual materials to confirm.Then define:signal / ground / power rolesand each dielectric thickness.Engineering illustration, not to scale. Reference geometry is not a released manufacturing stackup.