How to Set Up Design Rules in KiCad
In this tutorial, we will show you how to set up design rules in KiCad. Before starting the layout, it is very important to determine a set of rules you will follow.
Go to Preferences and choose Preferences. Fill out the Auto Save information. We like to auto save the layout every minute but you can choose whatever you want. Same for File History Size. Here, it is nine. It means the nine latest files will be saved.
In Hotkeys, you can choose shortcuts. This is an efficient way to do your layout. You have pre-saved commands but you can also add new ones.
Feel free to browse the display options as well. You can choose among many options, such as the grid style, thickness, spacing, etc.
KiCad Layer Set Up
Click Board Setup at the top. In Layers, you can custom your layer set.
By default, you will have two copper layers. You can see the top copper layer and the bottom copper layer. These are signal layers.
You can change the number of layers. Let’s say you need a 4-layer PCB, you will now have two inside layers between your top and bottom layers. You can keep them as signal layers and make them power planes, as per your stack-up requirements.
At the top again, you can choose the PCB thickness, also defined by your stack-up.
Now suppose you are using a differential track on the first layer, the reference layer to Layer 1 should be a ground layer, because on the differential pair , the ground layer should always be below the differential pairs without breaks. This is to ensure the impedance matching of the differential pair is constant over the entire length.
This is your stack-up. Here, we have a 4-layer stack-up. You can now go to Text & Graphics. This is where you can edit the text that will appear on your board. Choose the height, width, line thickness, etc.
KiCad Net Classes
Let’s discuss net classes. It is important to go over these design rules in KiCad.
You can see over here, there are different nets. And you can see there is a default class available. This defines a particular clearance. Clearance is the minimum distance which needs to be maintained between the two tracks. KiCad will handle that part once you define this minimum clearance.
You can also define the minimum track width for a particular net. A net class is a group of nets. So all these nets will be assigned to this net class. And this net class will follow these design rules in KiCad based on the minimum values you define for clearance, track width, via size, via drill, differential pair width, etc.
If you want to create a new net class, click the + sign. For this demo, let’s create a net class for a 90-ohm differential pair used for a USB.
We have created a new net class. The width of your differential pair will be defined in your stack-up along with the spacing. And normally, for...