Without vias, we would not be able to route multilayer PCBs. Vias are used to make transitions between layers in a design, so you will need to use them during layout and routing in a double-sided multilayer board. The challenge with vias, particularly among new designers, is they are often sized incorrectly such that they are un-manufacturable as designed. In addition, you might be too conservative and use vias that are simply too large, which can make routing more difficult than it needs to be.

If you look back at the example layouts in the previous lesson, you’ll notice that every example has some vias. Just like traces need to have the right width, vias need to have a diameter that conforms with the trace width, and to the pad size they are connected to. When vias are used to make connections back to components, the vias need to be properly located so they do not interfere with assembly. We’ll look at all these aspects of vias in this section, as well as how you can and access them during routing.