Definition

Design rules are manufacturing constraints that CAD tools check during layout: minimum trace width, spacing, annular ring, drill sizes, etc. Rules vary by manufacturer capability - standard PCB shops might require 0.15mm trace/space while HDI specialists achieve 0.075mm. Design Rule Check (DRC) flags violations before fabrication. Rules also encode electrical requirements: controlled impedance traces, differential pair spacing, high-voltage clearance. Getting design rules from your fabricator early prevents redesigns. Violating design rules increases cost, reduces yield, or makes the design unfabricable.