# Overheated Length

### Description

**Overheated Length** determines the approximate analytic temperature rise of trace segments on a specified high current nets. A net segment is considered “overheated” if its approximated temperature rise exceeds 20C.

**Passing Criteria:** \
This check passes if less than a specified percentage of the length of traces within the high current net has a temperature rise below a given threshold.

**Reporting Units:** \
Length Percentage (Tolerance: Celsius)

### **Examples**

**Passing Message:** 

{% hint style="success" %}
Overheated length of 0% within acceptable range (0% to 10%)
{% endhint %}

**Failing Message:** 

{% hint style="danger" %}
Overheated length of 56.2% outside acceptable range (0% to 10%)
{% endhint %}

### Physics Justification

Minimizing the temperature rise of high-current nets is important for the following reasons:

* **Resistive Heating (Joule Heating)**  

  High current flowing through a trace causes **I²R losses**, where electrical resistance (**R**) converts current (**I**) into heat. Excessive heat can damage the PCB or nearby components.
* **Board Performance**  

  An increased temperature (**T)** raises the resistance of the trace (**R**∝**T**), leading to more heat in a feedback loop, which can degrade signal integrity and power delivery.
* **Thermal Expansion**  

  Heat causes the PCB material to expand, potentially resulting in mechanical stress, delamination, or cracks in the copper traces.
* **Electromigration**  

  High temperatures accelerate **electromigration**, where metal atoms move due to current flow, degrading the trace over time and potentially causing failure.

#### Helpful Definitions  

* **Electromigration**  \
  The gradual movement of metal atoms within a conductor caused by the flow of high electrical current. This occurs because the momentum transfer from moving electrons pushes atoms along the current's path. Over time, it can create voids or buildup in the conductor, leading to increased resistance or signal degradation.


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