---
title: PCB Design Review
created_date: 2025-02-12
updated_date: 2025-02-12
aliases:
tags:
---
# PCB Design Review

## Rise Time vs Length
The rule of thumb is that a track length shall be shorter than 1/6th of the rise time. According to [this comment](https://electronics.stackexchange.com/a/258992) the rule of thumb can be applied like this (example with 100MHz signal):
First lets calculate the wave length in free space:
$$\lambda = \frac{c}{f} = \frac{3*10^{8}}{100*10^6} = 3m$$
In a PCB you can take roughly $\frac{\lambda}{2}$ as the wavelength, which would be $1.5m$. 
One sixth of this results in roughly $25cm$.