Backdrilling also needs a radial clearance planThe secondary drill must remove the unwanted barrel while avoiding adjacent copper. The depth worksheet does not calculate this independent radial requirement.Backdrilling also needs a radial clearance planPlan view · Oversized removal drill is conceptualLarger secondary drill envelopeOriginal plated hole centreRegistration allowanceNearby copper keepoutReference return pathUse actual drill diameters and registration bounds; a centre point is not a keepout.³Ô¹Ïtv · Engineering illustration · Conceptual, not to scale