Definition

Spacing (or clearance) is the minimum distance between copper features - trace to trace, trace to pad, pad to plane edge. Manufacturing capability sets the floor: standard is 0.15mm (6 mil), advanced is 0.1mm (4 mil), HDI can achieve 0.075mm (3 mil). Voltage requirements often demand more: IPC-2221 specifies spacing based on voltage and coating. At 100V, uncoated internal layers need 0.25mm minimum. High-voltage designs (>500V) may need 2mm+ spacing or slots. Spacing violations cause shorts in manufacturing or arcing in the field. DRC catches spacing errors.