I noticed when I was looking at my Arduino Uno, there are a bunch of small vias all around the board that seem to lead to nowhere. What is the purpose of these small vias in regard to PCB layouts? I was thinking of some sort of thermal relief, but I am not sure.
They probably connect the copper fills between the top and bottom of the board. Most likely the ground planes, but sometimes they do this on power planes as well.
They often do this on 4+ layer boards when connecting internal traces that you can’t see from the top or bottom. I believe the Arduino Uno is a two layer board, however, so this doesn’t apply here.
They are probably being used to provide electrical and/or thermal connections between two copper layers. Placing several vias in close proximity reduces both the electrical- and thermal-resistance of the connection. This technique is used where a large amount of current must be carried between layers, or where a component requires more heat sinking than can be obtained on the layer where it is mounted. They are commonly called “stitching vias”.
In a high frequency design(not the case with Arduino though) it also helps to reduce the capacitive effect between copper planes if I’m not mistaken.