From Valve:

When we first started designing hardware at Valve, we decided we wanted to try and do the manufacturing as well. To achieve our goal of a flexible controller, we felt it was important to have a similar amount of flexibility in our manufacturing process, and that meant looking into automated assembly lines. It turns out that most consumer hardware of this kind still has humans involved in stages throughout manufacturing, but we kind of went overboard, and built one of the largest fully automated assembly lines in the US. Our film crew recently put together a video of that assembly line, showcasing exactly why robots are awesome.