Invalid Width Span

Summary of the Invalid Width Span PRC, ensuring trace widths remain within acceptable tolerances for impedance control, current capacity, and EMI mitigation.

Description

Invalid Width Span determines the length of trace paths in a net are outside of an acceptable tolerance threshold. A trace segment has an “invalid width” if its width is outside of a 10% tolerance when compared to the nominal value.

For the Net Width comprehension, the expected width is explicitly defined, while for the Single-ended Impedance Signal comprehension, the nominal width is determined based on impedance and stackup characteristics.

Passing Criteria: This check passes if the length of trace segments that are outside the width tolerance falls below an acceptable percentage. If the acceptable percentage is not met (in the case of short nets), a fallback acceptable length tolerance is used. If neither of these criteria is met, the failed percentage is reported

Reporting Units: Length PERCENTAGE (%) or CENTIMETERS (cm)

Examples

Passing Messages:

Invalid width span of 1.05% within acceptable range (0% to 10%)

Invalid width span of 0.17cm within acceptable range (0cm to 1cm)

Failing Message:

Invalid width span of 87.06% outside acceptable range (0% to 10%)

Physics Justification

• Controlled Impedance

  The trace width, along with the dielectric material and distance to the reference plane, determines impedance. An incorrect width can cause reflections, signal distortion, and poor signal integrity.

• Current Carrying Capacity

  The trace width affects how much current the trace can safely handle without excessive heat. A too-narrow trace can lead to overheating and potential damage.

• Electromagnetic Interference (EMI)

  Proper trace width reduces EMI by maintaining consistent transmission line behavior, which cuts down on noise and radiation.

• Design Consistency

  The layer stackup defines the PCB's physical and electrical properties, so deviating from specified widths can throw off expected performance.

Helpful Definitions

• Electromagnetic Interference (EMI) Unwanted electromagnetic radiation or coupling that disrupts the operation of nearby electronic devices or circuits.