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Design Rules

Design rules encode the manufacturing and engineering constraints that an electronic design must satisfy. AP 210 provides a comprehensive framework for capturing and validating these rules.

Why Design Rules Matter

Design rules prevent:

  • Manufacturing failures - Features too small to fabricate reliably

  • Assembly defects - Components too close together for pick-and-place

  • Signal integrity issues - Crosstalk, impedance mismatches, EMI

  • Reliability problems - Thermal stress, mechanical failure

Types of Design Rules

Manufacturing Rules

  • Minimum trace width

  • Minimum trace spacing

  • Minimum drill size

  • Minimum annular ring

  • Board edge clearance

Assembly Rules

  • Component spacing

  • Keepout zones

  • Orientation constraints

  • Solder paste specifications

Signal Integrity Rules

  • Maximum trace length

  • Differential pair matching

  • Impedance targets

  • Crosstalk limits

Thermal Rules

  • Maximum component power density

  • Thermal clearance around heat sources

  • Airflow path requirements

Rule Representation in AP 210

AP 210 represents rules using:

  • constraint_definition - The rule itself

  • shape_aspect - The feature the rule applies to

  • measure_representation - The numerical value of the constraint

  • rule_action - What happens when the rule is violated

Rule Application

Rules can be applied at different levels:

  • Global - Apply to the entire design (e.g., minimum trace width)

  • Class-specific - Apply to all components of a class (e.g., BGA pitch)

  • Instance-specific - Apply to a specific component (e.g., clearance around U1)

  • Net-specific - Apply to a specific net (e.g., impedance on high-speed nets)

Validation Process

Design rule checking (DRC) in AP 210 involves:

  1. Retrieve all applicable rules

  2. Identify the features each rule applies to

  3. Measure the actual values in the design

  4. Compare against the rule’s limits

  5. Report any violations