# Invalid Width Span

### 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:** 

{% hint style="success" %}
Invalid width span of 1.05% within acceptable range (0% to 10%)
{% endhint %}

{% hint style="success" %}
Invalid width span of 0.17cm within acceptable range (0cm to 1cm)
{% endhint %}

**Failing Message:** 

{% hint style="danger" %}
Invalid width span of 87.06% outside acceptable range (0% to 10%)
{% endhint %}

### 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.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.quilter.ai/physics-rule-checks-prcs/invalid-width-span.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.