One of the major differences with boards that have more than two layers is the ability to alter what layers are actually connected by vias. Vias are plated holes through the substrate that connect different layers of copper. In the case of a 2-layer board these just go right through and connect the top to the bottom. But as you can see above, there are additional choices when it comes to multi-layer boards. #1 is a through via connecting all of the layers. #2 is a blind via; it stops part way through the board. And #3 is a buried via; it connects internal layers but cannot be seen from either side.

The guide is aimed at Eagle CAD. To use more than two layers you’ll have to purchase a license. But we think the concepts can easily be translated to other PCB layout software like Kicad.