Unused connections on Arduino board

Since I couldn't find any info about this through a forums search alone, I'll ask it here: what is the purpose of these undocumented through-holes?

Since they're most easily seen from the back, here's what I'm referring to:

I'm not, however, referring to the 4 connections labeled "X3".

Any ideas? I don't have software installed currently to view the board files, so I'm not sure exactly what they do.

They aren't unused if you have a voltage regulator. They are vias to provide the regulator with ground connectivity and a heat transfer path from the top ground plane to the bottom ground plane (probably more for the latter, since there are so many).


As stated above, these are thermal transfer vias.

This allows the copper on the bottom to act as a heatsink for the voltage regulator on top.

This is a fairly standard method in PCB design. (Actually we usually use a grid of vias, as the holes get soldered in the wave machine, which helps it work like a heatsink)

Ah, that makes sense. I mean, I've heard of thermal vias, but never actually seen them in use.